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Journal articles on the topic 'Die-bonding sintering'
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1
Ishikawa, Dai, Hideo Nakako, Yuki Kawana, Chie Sugama, Motohiro Negishi, and Yoshinori Ejiri. "Bondability Evaluation of Pressureless Sintering Copper Die-Bonding Paste." Journal of The Japan Institute of Electronics Packaging 21, no. 3 (May 1, 2018): 224–33. http://dx.doi.org/10.5104/jiep.21.224.
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Xiao, Kewei, Jesus N. Calata, Hanguang Zheng, Khai D. T. Ngo, and Guo-Quan Lu. "Large-area Nanosilver Die-attach by Hot-pressing Below 200°C and 5 MPa." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2012, HITEC (January 1, 2012): 000129–34. http://dx.doi.org/10.4071/hitec-2012-tp25.
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Sintered nanoscale silver joint is an emerging lead-free die-attach solution for high-temperature packaging because of silver's high melting temperature. For bonding small chips, the nanosilver solution can be achieved with a simple heating profile under atmospheric pressure. However, for bonding large-area chips, e.g. > 1 cm2 IGBT chips, uniaxial pressure of a few MPa has been found necessary during the sintering stage of the bonding process, which is carried out at temperatures below 275°C. Hot-pressing at high temperatures can cause significant wear and tear on the processing equipment, resulting in high maintenance cost. In this study, we ran a series of experiments aimed at lowering the hot-pressing temperature. Specifically, we examined a process involving hot-press drying, followed by sintering without any applied pressure. A fractional factorial design of experiments was used to identify the importance and interaction of various processing parameters, such as hot-pressing pressure/temperature/time and sintering temperature/time, on the final bond quality of sintered nanosilver joints. Based on the results, a simpler process, consisting of hot-press drying at 180°C under 3 MPa, followed by sintering at 275°C under atmospheric pressure was found to produce attachments with die-shear strength in excess of 30 MPa.
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Buttay, Cyril, Amandine Masson, Jianfeng Li, Mark Johnson, Mihai Lazar, Christophe Raynaud, and Hervé Morel. "Die Attach of Power Devices Using Silver Sintering – Bonding Process Optimisation and Characterization." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2011, HITEN (January 1, 2011): 000084–90. http://dx.doi.org/10.4071/hiten-paper7-cbuttay.
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Silver sintering is becoming an attractive alternative to soldering, especially for high temperature applications. Indeed, the increase in operating temperature requires new soldering alloys with even higher melting points. Silver sintering, on the contrary, is a solution which only require moderate (<300°C) process temperature. In this paper, we present the implementation of a die attach technique based on sintering of some silver paste, with a special focus on the practical considerations. A good quality bond can be achieved by paying attention to the assembly process.
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Zhang, Hongwen, and Ning-Cheng Lee. "Perspectives of High-Temperature Pb-Free Bonding Materials." International Symposium on Microelectronics 2018, no. 1 (October 1, 2018): 000088–98. http://dx.doi.org/10.4071/2380-4505-2018.1.000088.
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Abstract High lead solders have been used as die-attach and interconnect materials in discrete power packages. Due to the demand of SiC devices serving the high-power market and the harmful effects of Pb to human health and the environment, alternative Pb-free solders, novel bonding materials, as well as solutions have been studied extensively in recent years. The exemption of using high-Pb solders has been extended again to 2021, although it could be terminated at any time if a new technology or material were to be accepted by the industry. This paper presents potential materials and technologies for high-temperature Pb-free die-attachment, focusing on alternative solders. Sintering materials and transient liquid phase bonding (TLPB) materials have been briefly covered as well. AuSn, AuSi, and AuGe solders have shown to be exceptionally high in cost, which limited their application. BiAg- and BiCu-based solders—the BiAgX® family including solder paste, solder wire, and solder preform—improved wetting and exhibited remelting temperatures of 262°C and 270°C, respectively. The acceptable reliability performance on temperature cycling and thermal aging, as well as low material cost, has made them the most competitive candidates for low-power discrete die-attach devices. SnSbAgCu, with well-designed compositions in recent studies, offers a remelting temperature above 320°C. SnSbAgCu is targeted in markets for mid-to-high power devices. Reliability testing for other recently designed SnSbAgCu pastes for various die-attach vehicles is being studied. ZnAl has a remelting temperature above 380°C and an extremely low material cost (comparable to or even lower than the high-lead solders). Although the bonding process is stringent, the excellent thermomechanical behavior and the superior thermal/electrical conductivity have allowed ZnAl to be a potential candidate for high-temperature/high-power die-attach that is competitive with AuSi and AuGe solders. Sintering materials form bonds through solid state interdiffusion, while TLPB materials create a joint through solid-liquid interdiffusion, in which the remelting temperature is enhanced by forming massive IMCs. The desired high thermal/electrical/mechanical/melting performances, as well as the relatively low processing temperature (<350°C), are shining the sintering materials (especially Ag-sintering materials). The intrinsic high porosity (>20%) and the evolution of pores from pressureless sintering may overshadow the reliability. In addition, the immaturity of the processing (time/temperature/pressure/atmosphere/equipment availability, etc.) may deter the industrial adoption of sintering materials. So far, none of these materials or technologies is ideal to satisfy all the requirements of the variety of high-temperature, Pb-free die-attach applications in terms of processing, reliability, and cost. However, each material and solution has the potential to be a niche within this broader categorization.
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Jin, Howard (Hwail), Kewei Xu, Loreto Naungayan, and Jose Quinones. "High Thermal Conductive Die Attach Paste Using Polymer and Micron Size Silver for Power Semiconductor Package." International Symposium on Microelectronics 2016, no. 1 (October 1, 2016): 000326–31. http://dx.doi.org/10.4071/isom-2016-wp41.
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Abstract Power semiconductor package manufactures and electronic device suppliers have been looking for Pb-free alternative to traditional high Pb solder die attach adhesives. Lead solders have high thermal conductivity, 30–50W/mK, and known process with some difficulties in high volume mass production such as void, bond line control, and requiring reducing atmosphere such as forming gas. Lead is now categorized as hazardous substance to human body and environment and its products are scheduled to be banned within a few years. Standard silver epoxy pastes and Electrically Conductive Adhesives (ECSs) are other forms of die attach adhesives but the thermal conductivity is not adequate for Power devices. Eutectic gold-tin solder (80Au20Sn) has 57W/mK but it is high cost material. Currently Silver sintering material has become popular for electronic device because it has high thermal conductivity (150~250W/mK) by using nano silver sintering. But it requires high bonding temperature and pressure. It makes brittle bonding structure and has limitation in die size due to high stress. New silver sintering material in this paper is composed of micron size silver and organic polymer. This technology overcomes all the limitations of conventional silver epoxy, eutectic gold thin solder and silver sintering product by using the unique design of polymer composition. This new silver sintering technology using polymer and micron size silver is a cost effective solution to replace Pb solder for power device and the thermal performance is almost same as nano silver sintering products. The application process is the same as standard silver epoxy and does not require new equipment. It is a cost effective drop in solution.
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Kang, Hyejun, Ashutosh Sharma, and Jae Pil Jung. "Recent Progress in Transient Liquid Phase and Wire Bonding Technologies for Power Electronics." Metals 10, no. 7 (July 11, 2020): 934. http://dx.doi.org/10.3390/met10070934.
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Transient liquid phase (TLP) bonding is a novel bonding process for the joining of metallic and ceramic materials using an interlayer. TLP bonding is particularly crucial for the joining of the semiconductor chips with expensive die-attached materials during low-temperature sintering. Moreover, the transient TLP bonding occurs at a lower temperature, is cost-effective, and causes less joint porosity. Wire bonding is also a common process to interconnect between the power module package to direct bonded copper (DBC). In this context, we propose to review the challenges and advances in TLP and ultrasonic wire bonding technology using Sn-based solders for power electronics packaging.
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Bhogaraju, Sri Krishna, Omid Mokhtari, Jacopo Pascucci, Fosca Conti, and Gordon Elger. "Improved sinterability of particles to substrates by surface modifications on substrate metallization." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2019, HiTen (July 1, 2019): 000066–70. http://dx.doi.org/10.4071/2380-4491.2019.hiten.000066.
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Abstract Sintering under pressure has been in the forefront of the research and development over the past decade as an alternative to high temperature soldering and die-attach bonding for high temperature electronics. However, high bonding pressure is a deterrent to mass industrialization due to the high costs involved in the design of special tooling and complex process control parameters. Further, it can cause device cracking, especially while working with sensitive high power optoelectronics devices (e.g. high power light emitting diodes). Therefore, alternatives to enhance sinterability are highly requested. Substrate metallization is observed to play an important role while sintering. An innovative low cost method to have nanostructured surface modifications on the substrates is realized and presented here. The method is applied to enhance sinterability of Cu particles to substrate. Shear tests on samples with surface modified substrates are promising with results of ca. 25 MPa, which is 24% better than sintering on unmodified bare Cu substrate. Sintering was enabled by in-house developed hybrid Cu paste under pressureless sintering conditions of 300°C, for 60 min, and under N2 atmosphere.
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Fuentes-Pacheco, L., and M. Campos. "Bonding evolution with sintering temperature in low alloyed steels with chromium." Science of Sintering 41, no. 2 (2009): 161–73. http://dx.doi.org/10.2298/sos0902161f.
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At present, high performance PM steels for automotive applications follow a processing route that comprises die compaction of water-atomized powder, followed by sintering and secondary treatments, and finishing operations. This study examines Cr-alloyed sintered steels with two level of alloying. In chromium-alloyed steels, the surface oxide on the powder is of critical importance for developing the bonding between the particles during sintering. Reduction of this oxide depends mainly on three factors: temperature, dew point of the atmosphere, and carbothermic reduction provided by the added graphite. The transformation of the initial surface oxide evolves sequence as temperature increases during sintering, depending on the oxide composition. Carbothermic reduction is supposed to be the controlling mechanism, even when sintering in hydrogen-containing atmospheres. The effect of carbothermic reduction can be monitored by investigating the behavior of the specimens under tensile testing, and studying the resultant fracture surfaces.
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Gao, Yue, Hao Zhang, Wanli Li, Jinting Jiu, Shijo Nagao, Tohru Sugahara, and Katsuaki Suganuma. "Die Bonding Performance Using Bimodal Cu Particle Paste Under Different Sintering Atmospheres." Journal of Electronic Materials 46, no. 7 (March 27, 2017): 4575–81. http://dx.doi.org/10.1007/s11664-017-5464-2.
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Shen, Zhenzhen, Aleksey Reiderman, and Casey Anude. "Pressure-less AgNP Sintering for High-power MCM Assembly for Extreme Environment Applications." International Symposium on Microelectronics 2015, no. 1 (October 1, 2015): 000342–48. http://dx.doi.org/10.4071/isom-2015-wp14.
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Silver nano-particle (AgNP) sintering has been a promising bonding material for high-temperature applications. There is an increasing demand for designs implemented as multi-chip module (MCM) in the high-temperature markets, like the oil and gas industry, primarily because of MCM's smaller size, higher-performance capability, and higher overall reliability when compared to traditional high Tg printed circuit boards. In this work, pressure-less AgNP sintering paste was used in the assembly of multi-chip modules. The assemblies included die-mounted on aluminum nitride and alumina substrates that were metallized with various thin and thick films. Sintered silver nano-particle attachments were also attempted for surface-mounted technology (SMT) chip components. Different assembly parameters such as bonding line thickness and sintering profiles were evaluated to discover the optimal assembly process window that would yield acceptable reliability for 250°C and higher ambient temperature applications. The assemblies were subjected to various tests including thermal cycling, high-ramp rate thermal shocks, and high-temperature storage tests. Shear strength measurements and analysis of the cross sections and fracture surfaces were performed to understand failure mechanisms. One of the findings was a certain and unique failure mode associated with bonding of thin-film gold metallized surfaces using pressure-less silver nano-particles sintering. That failure mode begins after a short exposure to temperatures of 200°C and higher. However, silver nano-particle sintering on substrates metallized with thin-film silver and some thick-film formulations yields dramatically better results.
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Chen, Sihai, Christine LaBarbera, and Ning-Cheng Lee. "Silver Sintering Paste Rendering Low Porosity Joint for High Power Die Attach Application." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2016, HiTEC (January 1, 2016): 000134–42. http://dx.doi.org/10.4071/2016-hitec-134.
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Abstract Silver joints with ~10% porosity for die-attach have been achieved with specially engineered Ag sintering pastes, through combined pressureless sintering process plus thermal aging. The pastes developed in this work have the following advantages: 1) they can be used under pressure-less processing condition; 2) they are compatible with conventional reflow oven, resulting in a higher through-put as compared to that of stepwise heating oven; 3) they can be used under air reflow condition; 4) a highly reliable joint has been obtained as judged from the shear strength results from thermal aging and temperature cycling tests. The silver sintering pastes are versatile in bonding different metallization surface including Au, Ag and Cu. It can also be used in bonding large area (10mm × 10mm) dies. Shear test results under varied temperatures implied that the maximum service temperature of Ag sintered joints can be as high as 470 – 530 °C, depending on the shear strength pass criteria, and this is more than 250°C higher than that of high-Pb joints. Thermal aging test at 250°C for the joints generated on Ag-die/Au-DBC combination revealed that Ag continuously consolidates in the bulk phase resulting in the formation of larger pores with reduced numbers as compared to that of untreated samples. At the same time, it diffuses to sintered Ag/Au-DBC interface to form a dense Ag layer induced by alloying with Ni(Au) and Cu, which strengthened the bonding. A large bondline thickness is critical for obtaining highly reliable joints. The total porosity of the joint is found slightly decreased during the course of 3200h aging test. Temperature cycling at −55 °C to 200°C shows that the silver joints are stable for at least 1000 cycles.
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Fujino, Masahisa, Hirozumi Narusawa, Yuzuru Kuramochi, Eiji Higurashi, Tadatomo Suga, Toshiyuki Shiratori, and Masataka Mizukoshi. "Transient liquid-phase sintering using silver and tin powder mixture for die bonding." Japanese Journal of Applied Physics 55, no. 4S (March 24, 2016): 04EC14. http://dx.doi.org/10.7567/jjap.55.04ec14.
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Li, Jianfeng, Christopher Mark Johnson, Cyril Buttay, Wissam Sabbah, and Stéphane Azzopardi. "Bonding strength of multiple SiC die attachment prepared by sintering of Ag nanoparticles." Journal of Materials Processing Technology 215 (January 2015): 299–308. http://dx.doi.org/10.1016/j.jmatprotec.2014.08.002.
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Tanaka, Yasunori, Tatsumasa Wakata, Norihiro Murakawa, Tomonori Iizuka, and Kohei Tatsumi. "Study on high temperature resistant die bonding formed by Al/Ni nano-particles composite paste." International Symposium on Microelectronics 2018, no. 1 (October 1, 2018): 000442–46. http://dx.doi.org/10.4071/2380-4505-2018.1.000442.
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Abstract In power modules using SiC devices, high temperature operation is expected. Therefore, a bonding technology having high temperature resistance of 250°C or more is required. In recent years, research on low temperature sintering bonding by Ag nanoparticles, Cu nanoparticles and sub-micron particles has been conducted as a new bonding technology corresponding to SiC power devices. Nanoparticles are sintered at a temperature much lower than the sintering temperature in ordinary powder metallurgy. We focus on Ni having high melting point and excellent corrosion resistance as a new bonding material and are conducting research on high temperature resistant interconnection technology using Ni nanoparticles. We have found that bonding is possible at a bonding temperature of 400°C or less and enable to interconnect SiC devices for high temperature operation. However, there are still following problems to be improved, as follows, especially for a large chip size : Voids formed in the bonding layer and cracks generaled stress caused by a difference in thermal expansion coefficient(CTE). In this paper, we propose a bonding material of composite paste in which Ni nanoparticles and Al particles are mixed. From the results of the research, it was found that the occurrence of cracks and gas void was suppressed by mixing Al particles. Also the thermal stress analysis by FEM, the addition of Al particles shows to reduce the thermal stress during thermal cycle test (TCT).
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Nishimoto, Akio, and Katsuya Akamatsu. "Pulsed Electric Current Bonding of Tungsten to Copper with Intermediate Layer." Solid State Phenomena 127 (September 2007): 289–92. http://dx.doi.org/10.4028/www.scientific.net/ssp.127.289.
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Pulsed electric current sintering (PECS) was applied to the bonding of W (tungsten) to Cu (copper) using Nb or Ni powder as an intermediate layer. The influence of the intermediate layer on the bond strength of the joint was investigated by observation of the microstructure. The bonding process was carried out at carbon-die temperatures of 1073 and 1173 K for 1.8 ks at a bonding pressure of 130 MPa. The bond strength of the joint with an intermediate layer of Ni powder was 250 MPa. This joint fractured in the Cu base during the tensile test. SEM observations of the joint with an intermediate layer of Ni revealed that a diffusion layer formed at the joint interface.
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Bhogaraju, Sri Krishna, Omid Mokhtari, Jacopo Pascucci, Fosca Conti, Hiren R. Kotadia, and Gordon Elger. "A multi-pronged approach to low-pressure Cu sintering using surface-modified particles, substrate and chip metallization." International Symposium on Microelectronics 2019, no. 1 (October 1, 2019): 000387–92. http://dx.doi.org/10.4071/2380-4505-2019.1.000387.
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Abstract High temperature power electronics based on wide-bandgap semiconductors have prominent applications, such as automotive, aircrafts, space exploration, oil/gas extraction, electricity distribution. Die-attach bonding process is an essential process in the realization of high temperature power devices. Here Cu offers to be a promising alternative to Ag, especially because of thermal and mechanical properties on par with Ag and a cost advantage by being a factor 100 cheaper than Ag. With the aim to achieve a low-pressure Cu sintering process, a low cost wet chemical etching process is developed to selectively etch Zn from brass to create nano-porous surface modifications to enhance sinterability, enabling sintering with low bonding pressure of 1MPa and at temperatures below 300°C. However, high tendency of Cu to oxidize poses a major challenge in realizing stable interconnects. For this purpose, in this contribution, we present the use of polyethylene-glycol 600 as reducing binder in the formulation of the Cu sintering paste. Finally, we propose a multi-pronged approach based on three crucial factors: surface-modified substrates, nanostructured surface modifications on micro-scale Cu-alloy particles and use of a reducing binder in the Cu particle paste.
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Benabou, Lahouari, Quang Bang Tao, Thien An Nguyen-Van, Xu Dong Wang, and Luc Chassagne. "Mechanical and Microstructural Analysis of an Ultra-Flexible Nano-Silver Paste Sintered Joint." Key Engineering Materials 865 (September 2020): 25–30. http://dx.doi.org/10.4028/www.scientific.net/kem.865.25.
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Soldering using common lead-free solder alloys is still one of the main die attach technology, in particular for applications in power electronics where high temperatures have to be met. However, some newly developed attach technologies promise to offer more interesting features in terms of both mechanical and thermal properties. Among these new methods, sintering of nano-silver particles allows to obtain a high thermal conductivity needed in the assemblies of electronic or optical components, as well as a relatively low elastic modulus for better stress accommodation and enhanced thermo-mechanical reliability. The sintering processing parameters, mainly the bonding pressure, the sintering temperature profile, and the sintering atmosphere, are known to have a critical effect on the properties of the sintered layer, such as its mechanical strength and electrical/thermal performances.In this study, copper substrates are fabricated and assembled by sintering using a nano-silver paste. The objective is to obtain a bonding joint with high mechanical flexbility, capable of addressing the thermomechanical stresses for systems operating under high temperatures. The measured mechanical properties of the sintered material show on the one hand low elastic modulus of the joint which is appropriate for strong difference in thermal expansion between components, and on the other hand sufficient mechanical strength for the assembly. Microstructure analyses reveal a highly porous silver network structure of the joint, with submicrometric silver grains and large micrometric porosities homogeneously distributed.
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Tatsumi, Hiroaki, Hiroshi Yamaguchi, Tomoki Matsuda, Tomokazu Sano, Yoshihiro Kashiba, and Akio Hirose. "Deformation Behavior of Transient Liquid-Phase Sintered Cu-Solder-Resin Microstructure for Die-Attach." Applied Sciences 9, no. 17 (August 23, 2019): 3476. http://dx.doi.org/10.3390/app9173476.
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We have proposed a low-temperature bonding technology utilizing the sintering of Cu particles with transient liquid-phase of Sn-based solder, called transient liquid-phase sintering (TLPS), as a die-attach solution for high-temperature power modules. A copper-intermetallic compound-resin (Cu-IMC-resin) microstructure, which consists of Cu particles connected with Cu–Sn intermetallic compounds (IMCs) partially filled with polyimide resin, is obtained by the pressureless TLPS process at 250 °C for 1 min using a novel Cu-solder-resin composite as the bonding material in a nitrogen atmosphere. Macro- and micro-deformation properties of the unique microstructure of the TLPS Cu-IMC-resin are evaluated by finite element analysis using a three-dimensional image reconstruction model. The macroscopic computational uniaxial tensile tests of the Cu-IMC-resin model reveal that the utilization of the IMCs and the addition of the easily-deformable resin facilitates the temperature-stability and low-stiffness of the mechanical properties. The microstructure exhibits a significantly low homogenized Young’s modulus (11 GPa). Microscopic investigations show that the local stresses are broadly distributed on the IMC regions under uniaxial macroscopic tensile displacement, indicating highly reliable performance of the joint within a specific macroscopic strain condition. Numerical and experimental investigations demonstrate the excellent thermal cyclic reliability of die-attached joints between silicon carbide chips and directly bonded copper substrate.
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Wereszczak, A. A., Z. Liang, M. K. Ferber, and L. D. Marlino. "Uniqueness and Challenges of Sintered Silver as a Bonded Interface Material." Journal of Microelectronics and Electronic Packaging 11, no. 4 (October 1, 2014): 158–65. http://dx.doi.org/10.4071/imaps.429.
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There are numerous attributes of sintered Ag as a bonded interface between die and substrate or even between substrate and heat sink in power devices. This is attested to by the relatively large number of studies devoted to it in recent years. Sintered Ag potentially has a high temperature capability, high electrical and thermal conductivities, a microstructure in equilibrium, predictable linear elastic response during thermal cycling, and apparently minimal or even nonexistent time-dependent pore coalescence and pore growth that exists with solders. But sintered Ag bonding is a relatively new technology and solid-state sintering science and its application can be unfamiliar to solder/bonding practitioners. There are at least five different aspects of sintered Ag bonding compared with solder bonding. Those are reviewed here based on the authors' experience with Ag sintering over the last several years. Sintered-Ag interconnect bonding is a solid-state process (i.e., no melting); its bond strength is affected by the topography of the mating surfaces; concurrent pressure application during processing can improve bond strength; issues associated with the paste's organic binder burnout and exhaust can arise depending on the interconnect size; and porosity is indigenous to its bulk microstructure, requiring its consideration and possible management. Increased understanding of these unique characteristics will help advance use of sintered-Ag technology and the exploitation of its attributes for fabricating more reliable, higher-temperature-capable, and more thermally conductive power electronic modules.
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Nishikawa, Hiroshi, and Xiangdong Liu. "Bonding strength of Cu/Cu joints using sintering process of micro-sized Cu particles for high-temperature application." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2019, HiTen (July 1, 2019): 000085–90. http://dx.doi.org/10.4071/2380-4491.2019.hiten.000085.
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Abstract Recently the new SiC power device provides the possibility to develop the next-generation power conversion circuit with high efficiency and high power density. The SiC power device can operate with significant lower power loss and higher operating temperature, which contributes to miniaturization and higher performance of power modules. To assemble these power modules, the high temperature packaging technology such as die attach process is needed. As a die attach process, we have proposed a simple oxidation-reduction bonding (ORB) process to achieve good Cu-to-Cu joints using micro-sized Cu particles. In this study, the effect of the oxidation-reduction process on the surface morphology of Cu particles was evaluated by SEM observation, and the shear strength of the Cu-to-Cu joints was investigated. As a result, the bonding using micro-sized Cu particles was successfully achieved and the shear test results showed that the joints by ORB process had a shear strength of more than 20 MPa.
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Dudina, Dina, Alexander Matvienko, Anatoly Sidelnikov, Mikhail Legan, Vyacheslav Mali, Maksim Esikov, Alexander Anisimov, Pavel Gribov, and Vladimir Boldyrev. "Electric Current-Assisted Joining of Copper Plates Using Silver Formed by In-Situ Decomposition of Ag2C2O4." Metals 8, no. 7 (July 12, 2018): 538. http://dx.doi.org/10.3390/met8070538.
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Pulsed electric current can be used for the fast sintering of powders as well as joining of macroobjects. In this work, we brazed copper plates using a silver layer that was formed in situ by the decomposition of a silver oxalate Ag2C2O4 powder placed between the plates. Joining was conducted in the chamber of a Spark Plasma Sintering (SPS) facility with and without a graphite die. In the die-assisted tooling configuration, indirect heating of the assembly from the graphite die carrying electric current occurred until the brazing layer transformed into metallic silver. The passage of electric current through a Cu/Ag2C2O4/Cu stack placed between the electrodes without a die was possible because of the formation of Cu/Cu contacts in the areas free from the Ag2C2O4 particles. Joints that were formed in the die-assisted experiments showed a slightly higher shear strength (45 MPa) in comparison with joints formed without a die (41 MPa). The shear strength of the reference sample (obtained without a die), a stack of copper plates joined without any brazing layer, was only 31 MPa, which indicates a key role of the silver in producing strong bonding between the plates. This study shows that both die-assisted tooling configurations and those without a die can be used for the SPS brazing of materials by the oxalate-derived silver interlayer.
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Schneider-Ramelow, M., M. Hutter, H. Oppermann, J. M. Göhre, S. Schmitz, E. Hoene, and K. D. Lang. "Technologies and Trends to Improve Power Electronic Packaging." International Symposium on Microelectronics 2011, no. 1 (January 1, 2011): 000430–37. http://dx.doi.org/10.4071/isom-2011-tp6-paper5.
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In the realm of power modules a strong trend toward high temperature and high reliability applications can be observed, which entails new technological challenges, especially for the assembly and packaging of power semiconductors. Because of the well known failure mechanisms of established lead-free standard soldering and heavy aluminum wire bonding technologies, such as fatigue and creep of die attach material and wire bonds at thermal cycling, academic and industrial research focuses on more reliable interconnection technologies. A priority is the research of alternative top and bottom side chip interconnection materials or technologies to improve the temperature cycling capability of power chips that are typically assembled on ceramic substrates. The scientific focus is on Ag sintering as die attach and/or heavy ribbon bonding, for example with Al or bi-metal (Al-Cu). Another focus is the material behavior of ribbon bonds in combination with bonding machine improvements (higher bonding parameters, cutting tool). But there are other very promising technologies like transient liquid phase bonding, for example with Cu-Sn or Ag-Sn systems or Cu heavy wire bonding (up to 400 μm wire diameter) or Cu/Al-Bi metal ribbon bonding. Challenges posed by these technologies have to be discussed focusing on materials and process selection and reliability issues. Process temperatures and temperature profiles must be optimized, wire bonding machines and the chip surface structures as well as finish metallizations need to be adapted. This paper will give an overview of alternative power chip interconnection technologies and discuss the challenges related to processing and reliability.
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Wereszczak, A. A., Z. Liang, M. K. Ferber, and L. D. Marlino. "Uniqueness and Challenges of Sintered Silver as a Bonded Interface Material†." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2014, HITEC (January 1, 2014): 000178–87. http://dx.doi.org/10.4071/hitec-wa23.
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There are numerous attributes of sintered silver (Ag) as a bonded interface between die and substrate or even between substrate and heat sink in power devices. This is attested to by the relatively large number of studies devoted to it the last several years. Sintered silver potentially has a high temperature capability, high electrical and thermal conductivities, its microstructure is in equilibrium, it could predictably respond linearly elastically during thermal cycling, and the time-dependent pore coalescence and pore growth that exists with solders is apparently minimal or even nonexistent. But sintered silver bonding is a relatively new technology and solid-state sintering science and its application can be unfamiliar to solder/bonding practitioners. There are at least five different aspects of it compared to solder bonding and those are overviewed here based on the authors' experience with Ag-sintering over the last several years. For sintered-Ag interconnect bonding: it is a solid-state process (i.e., no melting); its bond strength is affected by the topography of the mating surfaces; concurrent pressure application during processing can improve bond strength; issues associated with the paste's organic binder burnout and exhaust can arise depending on the interconnect size; and porosity is indigenous to its bulk microstructure requiring its consideration and possible management. Increased understanding of these unique characteristics will help advance employment of sintered-Ag technology and the exploitation of its attributes for fabricating more reliable, higher-temperature- capable, and more thermally conductive power electronic modules.
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Dai, Jingru, Jianfeng Li, Pearl Agyakwa, and Christopher Mark Johnson. "Time-Efficient Sintering Processes to Attach Power Devices Using Nanosilver Dry Film." Journal of Microelectronics and Electronic Packaging 14, no. 4 (October 1, 2017): 140–49. http://dx.doi.org/10.4071/imaps.521776.
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Pressure-assisted sintering processes to attach power devices using wet nanosilver pastes with time scales of minutes to a few hours have been widely reported. This article presents our work on time-efficient sintering using nanosilver dry film and an automatic die pick and place machine, resulting in process times of just a few seconds. The combined parameters of sintering temperature 250°C, sintering pressure 10 MPa, and sintering time 5 s were selected as the benchmark process to attach 2 × 2 × 0.5-mm dummy Si devices. Then, the effects of either the sintering temperature (240–300°C), time (1–9 s), or pressure (6–25 MPa) on the porosity and shear strength of the sintered joints were investigated with three groups and a total of 13 experimental trials. The average porosities of 24.6–46.2% and shear strengths of 26.1–46.6 MPa are comparable with and/or even better than those reported for sintered joints using wet nanosilver pastes. Their dependences on the sintering temperature, time, and pressure are further fitted to equations similar to those describing the kinetics of sintering processes of powder compacts. The equations obtained can be used to not only reveal different mechanisms dominating the densification and bonding strength but also anticipate the thermal-induced evolutions of microstructures of these rapidly sintered joints during future reliability tests and/or in service.
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Dai, Jingru, Jianfeng Li, Pearl Agyakwa, and Christopher Mark Johnson. "Time-efficient sintering processes to attach power devices using nanosilver dry film." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2017, HiTEN (July 1, 2017): 000207–12. http://dx.doi.org/10.4071/2380-4491.2017.hiten.207.
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Abstract: Pressure-assisted sintering processes to attach power devices using wet nanosilver pastes with time scales of minutes to a few hours have been widely reported. This paper presents our work on time-efficient sintering, using nanosilver dry film and an automatic die pick and place machine, resulting in process times of just a few seconds. The combined parameters of sintering temperature 250 °C, sintering pressure 10 MPa and sintering time 5 s were selected as the benchmark process to attach 2 mm × 2 mm × 0.5 mm dummy Si devices. Then the effects of either the sintering temperature (240 to 300 °C), time (1 to 9 s) or pressure (6 to 25 MPa) on the porosity and shear strength of the sintered joints were investigated with 3 groups and a total of 13 experimental trials. The average porosities of 24.6 to 46.2% and shear strengths of 26.1 to 47.7 MPa are comparable with and/or even better than those reported for sintered joints using wet nanosilver pastes. Their dependences on the sintering temperature, time and pressure are further fitted to equations similar to those describing the kinetics of sintering processes of powder compacts. The equations obtained can be used to not only reveal different mechanisms dominating the densification and bonding strength, but also anticipate the thermal-induced evolutions of microstructures of these rapidly sintered joints during future reliability tests and/or in service.
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Nishimoto, Akio, Katsuya Akamatsu, and Kenji Ikeuchi. "Microstructure of SiC/Cu Interface by Pulsed Electric-Current Bonding." Materials Science Forum 539-543 (March 2007): 3883–87. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.3883.
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Pulsed electric-current sintering (PECS) was applied to the bonding of SiC (pressureless-sintered silicon carbide) to Cu (oxygen-free copper) using a mixture of Cu and Ti powders as an intermediate layer. The influences of the intermediate powders on the bond strength of the joint were investigated by observation of the microstructure. The bonding was carried out at carbon-die temperatures from 973 to 1173 K at a bonding pressure of 10 MPa for 3.6 ks. The application of intermediate layers of 100% Ti, 95% Ti + 5% Cu, and 5% Ti + 95% Cu remarkably improved the bond strength as compared with direct bonding without an intermediate powder. SEM observations of the joint with the intermediate powders revealed that a Cu solid-solution layer, a TiC layer, and a Ti5Si3 layer had covered most of the interface, similar to those observed in the friction-bonded and pulsed-electric current bonded joints of SiC to Cu in which the application of a Ti foil as an intermediate layer remarkably improved the bond strength.
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Lo, Ming, Seyed Amir Paknejad, Harry Borrill, Wan K. Kong, Addo Addo-Kwabena, Mohamed Saidoune, Chris Powley, Naim Kapadia, Yang Zuo, and Samjid H. Mannan. "Comparative study of how additives affect sintered silver microstructure in die-attach applications." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2019, HiTen (July 1, 2019): 000061–65. http://dx.doi.org/10.4071/2380-4491.2019.hiten.000061.
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Abstract Die attach materials based on silver nanoparticles which sinter at temperatures in the range 200–300 °C are a comparatively new technology. The properties of the sintered structure can be affected by a wide range of additives which can alter the physical and chemical characteristics of the joints. In this study, a commercially available Ag nanoparticle paste has been used as the base, and a range of additives have been added principally to determine the effect of each additive on the sintered microstructure immediately after sintering, and after long term thermal ageing. The additives trialled include Au, Sn, Cu, and Zn. In each case the additive powder was mixed with the original paste and the microstructure after sintering was compared to the microstructure after ageing at 250 °C for 24 h. Another method of introducing an additive into the system is adding it as a mesh, interposed between die and substrate and immersed in the silver paste. Au was added in both this form, and in the form of a powder additive. The mesh results in a thermodynamically stable microstructure up to at least 500 °C. The design takes advantage of solid–solid interdiffusion bonding which results in a die attach assembly with a continuous, non-porous gold-silver interdiffusion layer running all the way from the die to the substrate.
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Kuramot, Masafumi, Satoru Ogawa, Miki Niwa, Keun-Soo Kim, and Katsuaki Suganuma. "Die Bonding for a Nitride Light-Emitting Diode by Low-Temperature Sintering of Micrometer Size Silver Particles." IEEE Transactions on Components and Packaging Technologies 33, no. 4 (December 2010): 801–8. http://dx.doi.org/10.1109/tcapt.2010.2064313.
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Nishikawa, Hiroshi, Xiangdong Liu, and Siliang He. "Effect of isothermal aging at 250 °C on shear strength of joints using Sn-Coated Cu particle paste for high-temperature application." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2017, HiTEN (July 1, 2017): 000202–6. http://dx.doi.org/10.4071/2380-4491.2017.hiten.202.
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Abstract High-temperature joining is a key technology for electronic component assembly and other high-temperature applications. As a die attach process for power devices, we focus on a transient liquid phase (TLP) bonding, which can be operated at a low temperatures while resulting in higher re-melting temperatures of bonded joints. However, some drawbacks of this technology still remain. For example, the duration of this process is too long, up to a few hours, and multiple hours of annealing are required to achieve a thermodynamically stable joint. So we are studying on a TLP bonding using Sn-coated Cu particles to reduce the bonding process time. In this study, we evaluated the effect of isothermal aging at 250 °C on the shear strength of Cu/Cu joints using a Sn-coated Cu particle paste. As a result, a thermally stable joint fully comprising Cu3Sn phase with a dispersion of Cu particles could be obtained after sintering for 30 s at 300 °C under a formic acid atmosphere. The shear strength of the joint before isothermal aging was about 25 MPa and the shear strength after isothermal aging at 250 °C for 1000 h was more than 25 MPa.
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Nishikawa, H., K. Matsunaga, M.-S. Kim, M. Saito, and J. Mizuno. "Effect of isothermal aging at 250 °C on shear strength of joints using Au nanoporous bonding for die attach." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2016, HiTEC (January 1, 2016): 000143–47. http://dx.doi.org/10.4071/2016-hitec-143.
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Abstract High-temperature joining is a key technology for electronic component assembly and other high-temperature applications. Recently, focusing on the sintering behavior of metal particles, the joining process using a nanoparticle paste has been proposed as an alternative to establish a high-temperature joining technology. In this study, a feasibility study has been conducted to determine whether an Au nanoporous sheet can be used for joint material. We evaluated the effect of isothermal aging at 250 °C on shear strength of joints using an Au nanoporous sheet. The shear strength of the joint after isothermal storage at 250 °C for 1000 h was more than 25 MPa.
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Li, Jie, Xin Li, Lei Wang, Yun-Hui Mei, and Guo-Quan Lu. "A novel multiscale silver paste for die bonding on bare copper by low-temperature pressure-free sintering in air." Materials & Design 140 (February 2018): 64–72. http://dx.doi.org/10.1016/j.matdes.2017.11.054.
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Chen, Chuantong, Zheng Zhang, Bowen Zhang, and Katsuaki Suganuma. "Micron-sized Ag flake particles direct die bonding on electroless Ni–P-finished DBC substrate: low-temperature pressure-free sintering, bonding mechanism and high-temperature aging reliability." Journal of Materials Science: Materials in Electronics 31, no. 2 (November 29, 2019): 1247–56. http://dx.doi.org/10.1007/s10854-019-02636-8.
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Fan, Guangyu, Christine Labarbera, Ning-Cheng Lee, and Colin Clark. "Shear Strength and Thermomechanical Reliability of Sintered Ag Joints Containing low CTE Non-metal Additives for Die Attach." International Symposium on Microelectronics 2018, no. 1 (October 1, 2018): 000167–72. http://dx.doi.org/10.4071/2380-4505-2018.1.000167.
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Abstract Ag sintering has been paid attention as an alternative to soldering in die attach for decades, especially for high temperature power electronics packages because of its high melting temperature, highly thermal and electrical conductivity of the sintered silver joints, and low process temperature less than 275°C. The coefficient of thermal expansion (CTE) of silver (19.1ppm/°C), however, is much higher than the silicon die (2.6ppm/°C) and the commonly used alumina substrate (7.2ppm/°C). CTE mismatch of the different materials in the various components in a power electronics package lead to the delamination at the interface between interconnection layer and chips or substrate, and/or cracking of the interconnection layer is one of the mostly common causes of failure of power electronics device during thermal cycling or high temperature operation. In recent years we have been developing a series of silver sinter pastes containing low CTE non-metal particles to reduce or adjust CTE of the sintered joints so as to extend the lifetime and reliability of power electronics device in high temperature applications. In the present paper, we will report a new set of silver sinter pastes containing micro scale non-metal particles, a sintering process, microstructural morphologies, thermo-mechanical reliability of the sintered joint and effect of the contents of non-metal particles on shear strength of the sintered silver joints bonding an Ag silicon die on Ni/Au DBC substrates. Shear tests on the sintered joints with and/or without the low CTE non-metal additives have been conducted at room temperature, 200, 250, and 300°C. Thermo-mechanical reliability of the sintered joints was evaluated by thermal cycling, thermal shock, high temperature storage tests (HTS), respectively. X-ray inspection and scanning electronic microscopy (SEM) were used to characterize void, crack and microstructure morphologies of the sintered joints with and/or without the additives.
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Kappert, Holger, Sebastian Braun, Norbert Kordas, Andre Kosfeld, Alexander Utz, Constanze Weber, Olaf Rämer, et al. "A High Temperature SOI-CMOS Chipset Focusing Sensor Electronics for Operating Temperatures up to 300 °C." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2021, HiTEC (April 1, 2021): 000018–24. http://dx.doi.org/10.4071/2380-4491.2021.hitec.000018.
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Abstract Sensors are key elements for capturing environmental properties and are increasingly important in the industry for the intelligent control of industrial processes. While in many everyday objects highly integrated sensor systems are already state of the art, the situation in an industrial environment is clearly different. Frequently the use of sensor systems is impossible, because the extreme ambient conditions of industrial processes like high operating temperatures or strong mechanical load do not allow a reliable operation of sensitive electronic components. Fraunhofer is running the Lighthouse Project ‘eHarsh’ to overcome this hurdle. In the course of the project an integrated sensor readout electronic has been realized based on a set of three chips. A dedicated sensor frontend provides the analog sensor interface for resistive sensors typically arranged in a Wheatstone configuration. Furthermore, the chipset includes a 32-bit microcontroller for signal conditioning and sensor control. Finally, it comprises an interface chip including a bus transceiver and voltage regulators. The chipset has been realized in a high temperature 0.35 micron SOI-CMOS technology focusing operating temperatures up to 300 °C. The chipset is assembled on a multilayer ceramic LTCC-board using flip chip technology. The ceramic board consists of 4 layers with a total thickness of approx. 0.9 mm. The internal wiring is based on silver paste while external contacts were alternatively manufactured in silver (sintering/soldering) or in gold-alloys (wire bonding). As interconnection technology, silver sintering has been applied. It has already been shown that a significant increase in lifetime can be reached by using silver sintering for die attach applications. Using silver sintering for flip chip technology is a new and challenging approach. By adjusting the process parameter geared to the chipset design and the design of the ceramic board high quality flip chip interconnects can be generated.
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Vogt, Holger, Frank Altmann, Sebastian Braun, Yusuf Celik, Lothar Dietrich, Dorothee Dietz, Marius van Dijk, et al. "HOT-300 – A Multidisciplinary Technology Approach Targeting Microelectronic Systems at 300 °C Operating Temperature." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2016, HiTEC (January 1, 2016): 000001–10. http://dx.doi.org/10.4071/2016-hitec-1a.
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Abstract Several applications in the fields of industrial sensors and power electronics are creating a demand for high operating temperature of 300 °C or even higher. Due to the increased temperature range new potential defect risks and material interactions have to be considered. As a consequence, innovation in semiconductor, devices and packaging technologies has to be accompanied by dedicated research of the reliability properties. Therefore various investigations on realizing high temperature capable electronic systems have shown that a multidisciplinary approach is necessary to achieve highly reliable solutions. In the course of the multi-institute Fraunhofer internal research program HOT-300 several aspects of microelectronic systems running up to 300 °C have been investigated like SOI-CMOS technology and circuits, silicon capacitor devices, a capacitive micromachined ultrasonic transducer (CMUT), ceramic substrates and different packaging and assembly techniques. A ceramic molded package has been developed. Die attach on different leadframe alloys were investigated using silver sintering and transient liquid phase bonding (TLPB). Copper and gold wire bonding was studied and used to connect the chips with the package terminals. Investigations in flip chip technology were performed using Au/Sn and Cu/Sn solder bumps for transient liquid phase bonding. High operating temperatures result in new temperature driven mechanisms of degradation and material interactions. It is quite possible that the thermomechanical reliability is a limiting factor for the technology to be developed. Therefore investigations on material diagnostics, reliability testing and modeling have been included in the project, complementing the technology developments.
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Guyenot, M., M. Reinold, Y. Maniar, and M. Rittner. "Advanced wire bonding for high reliability and high temperature applications." International Symposium on Microelectronics 2016, no. 1 (October 1, 2016): 000214–18. http://dx.doi.org/10.4071/isom-2016-wa51.
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Abstract The next generation of switches for power electronic will be based on white band gap (WBG) semiconductor GaN or SiC. This materials supports higher switching current and high frequency. White band gap semiconductors enables higher application temperature. Certainly, high temperature capability is also to discuss in combination with high number of thermal cycles. For a frame module concept shows these paper a comparison of different joining techniques with the focus on the reliability issue on wire and ribbon bonding. Beside to the 1000 passive thermal cycles from −40°C to +125°C there are active thermals cycles for technology qualification required [3]. Depending on the application and mission profile a high thermal cycling capability is necessary. For this reason, new high temperature joining techniques for die attach, e.g. Silver sintering or diffusion soldering, were developed in the recent past [4]. All of this new joining techniques focusing on higher electrical, thermal and thermo-mechanical performance of power modules. By using an optimized metallization system for the WBG the numbers of thermal cycles can be increased and the maximum operating temperature advanced up to 300°C. In these new temperature regions silicon semiconductors will be substituted by WBG semiconductors. The present work shows an active power cycling capability of different wire and ribbon bonds and the failure mechanism will be discussed. A calculation model explained the reliability for the different wire diameter and the impact of bonding materials. This reliability calculation explain the thermo-mechanical effects and based on materials and geometry data and is not optimized for evidence. Through these physical background understanding more than 1.000.000 thermal cycles with a 150 K temperature swing from +30°C to +180°C are now possible. These is a the basic knowledge for a design for reliability based on current, mission profile and reliability optimization for future high end applications with wire or ribbon bonding technique.
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Somton, Kritkaew, Mana Rodchom, Kannigar Dateraksa, and Ryan C. McCuiston. "The Effect of Alumina/Glass Composite Composition on the Adhesion and Strength of a 96% Alumina Joint." Key Engineering Materials 659 (August 2015): 149–53. http://dx.doi.org/10.4028/www.scientific.net/kem.659.149.
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An alumina/glass composite was examined for use as a high-temperature ceramic adhesive for bonding of 96% alumina bodies. Four compositions of alumina and glass, 90:10, 80:20, 60:40, and 40:60 by wt.% were studied, referred to here as A, B, C, and D, respectively. Rectangular bend bars were produced from compositions A-D by die pressing. Two half-sized bend bars of 96% alumina were bonded together using pastes produced from compositions A-D. The sintering shrinkage, the phase analysis, the flexural strengths, and the fracture surfaces of the sintered bend bars were examined. The XRD analysis showed a decrease in the alumina and an increase in mullite as the glass content was increased. The dilatometric results found that the onset temperature for sintering shrinkage decreased as the glass content was increased. Composition C was found to have the highest flexural strength of 94 MPa, however the flexural strength of the adhesive joint sample, was only 36 MPa. Composition D had the lowest flexural strength of 43 MPa, but it had the highest flexural strength of the adhesive joint at 61 MPa. The increased adhesive strength of composition D could be due in part to penetration of the excess glass phase into the 96% alumina body. Therefore the flexural strength of the pure compositions alone could not be used to reliably predict the adhesive bond strength. The fracture surfaces of the adhesive joints showed increasing uniformity as the glass content increased, which indicated stronger adhesion.
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Pope, Jacob, and Martin Jackson. "FAST-forge of Diffusion Bonded Dissimilar Titanium Alloys: A Novel Hybrid Processing Approach for Next Generation Near-Net Shape Components." Metals 9, no. 6 (June 4, 2019): 654. http://dx.doi.org/10.3390/met9060654.
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Material reductions, weight savings, design optimisation, and a reduction in the environmental impact can be achieved by improving the performance of near-net shape (NNS) titanium alloy components. The method demonstrated in this paper is to use a solid-state approach, which includes diffusion bonding discrete layers of dissimilar titanium alloy powders (CP-Ti, Ti-6Al-4V and Ti-5Al-5Mo-5V-3Cr) using field-assisted sintering technology (FAST), followed by subsequent forging steps. This article demonstrates the hybrid process route, firstly through small-scale uni-axial compression tests and secondly through closed-die forging of dissimilar titanium alloy FAST preforms into an NNS (near-net shape) component. In order to characterise and simulate the underlying forging behaviour of dissimilar alloy combinations, uni-axial compression tests of FAST cylindrical samples provided flow stress behaviour and the effect of differing alloy volume fractions on the resistance to deformation and hot working behaviour. Despite the mismatch in the magnitude of flow stress between alloys, excellent structural bond integrity is maintained throughout. This is also reflected in the comparatively uncontrolled closed-die forging of the NNS demonstrator components. Microstructural analysis across the dissimilar diffusion bond line was undertaken in the components and finite element modelling software reliably predicts the strain distribution and bond line flow behaviour during the multi-step forging process.
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Oppermann, Hermann, Lothar Dietrich, Matthias Klein, Bernhard Wunderle, and Herbert Reichl. "Nano-Porous Gold Interconnect." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2010, DPC (January 1, 2010): 002249–90. http://dx.doi.org/10.4071/2010dpc-tha31.
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Pure metal contacts offer some advantage as high thermal and electrical conductivity, ductile deformation behavior and reduction of mechanical peak stresses. They are used in flip chip assemblies as gold bumps, in die attach as sintered silver powder or as gold layer on very smooth surfaces for wafer bonding. Analyzing the demands in most suitable material properties we were looking for a compressible metal contact, which could compensate for all implanarities, with a highly reactive surface to reduce bonding temperature. It should be a noble metal, but with good adhesion to polymers. We have developed a nanoporous metal layer processed by electroplating a silver-gold alloy with 20 to 30% gold. High plating rates could be achieved exceeding those of standard gold electrolytes. Subsequent de-alloying by etching off the silver provides a nano-porous gold layer as an open-porous sponge with 70 to 80% porosity. Pore and ligament size were measured from different samples between 20 to 100 nm. Aging experiments showed the coarsening of pore size. We have successfully plated nano-sponge layer of 10 μm height on top of gold bumps on wafer level. But we don't see a limitation yet to further increase the thickness of gold nano-sponge. Chips were bonded by thermocompression resulting in a reduction of bump height without changing the bump diameter. At lower bond force and lower bond temperature the collapse of the porous structure occurred in the bond interface mainly, leaving the porosity in most of the bump volume unchanged. This leads to a new interconnect structure of high porosity. For very high porosity stiffness should be reduced with the square of the volume ratio. We therefore expect improved reliability due to the reduction in stiffness. Due to the compressible deformation behavior of the nano-sponge it could improve the yield during wafer-to-wafer bonding and stacking as the particle will be absorbed into the sponge. This allows bonding of wafers without the need of planarization the dielectric layer, e.g. due to steps over conductor lines. Therefore we will use the nano-sponge in stacking and 3D integration. Beside compression bonding and sintering we use the nano-sponge also as a thermal interface for adhesives. Filler particles are pressed into the sponge structure leading to a larger contact area between particle and substrate surface, thereby the adhesive matrix can penetrate into the open porous film. The locking interface should also provide very high adhesion strength.
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Myśliwiec, Marcin, and Ryszard Kisiel. "Thermal and mechanical properties of sintered Ag layers for power module assembly." Microelectronics International 32, no. 1 (January 5, 2015): 37–42. http://dx.doi.org/10.1108/mi-10-2013-0050.
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Purpose – The purpose of our paper is to investigate thermal and mechanical properties of Ag sintered layers used for assembly of SiC diode to Direct Bonding Copper (DBC) interposer. How SiC devices are assembled to ceramic package defines efficiency of heat transfer and mechanical support. Design/methodology/approach – Ag microparticles, sized 2-4 μm and flake shaped, were used as joining material. The parameters of sintering process were as follows: temperature 400°C, pressure 10 MPa and time 40 min. It was found that after sintering and long-term aging in air at 350°C the adhesion is in the range of 10 MPa, which is enough from a practical point of view. The thermal properties of the SiC die assembled into a ceramic package were also investigated. In the first step, the calibration of the temperature-sensitive parameter VF (IF = 2 mA) was done and the relation between VF and temperature was found. In the next step, the thermal resistance between junction and case was determined knowing junction and case temperature. Findings – For SiC diode with Au bottom metallization joined to the DBC interposer by Ni/Au metallization by Ag microparticle layer, Rth j-c is in the range of 2-3.5°C/W, and for SiC diode with Ag bottom metallization joined to DBC interposer with Ag metallization by Ag microparticle layer, Rth j-c is in the range of 4.5-5.5°C/W. Research limitations/implications – In the future, research on thermal resistance of SiC diodes assembled onto the DBC interposer with Au and Ag metallization in the temperature range up to 350°C needs to be carried out. To do this, it necessary to find a solution for the attaches that leads to ceramic package able to work at such high temperature. Originality/value – Obtained results are comparable with results mentioned by other studies for eutectic Au/Sn or SAC solder joints; however, the solution proposed by us can properly work at significantly higher temperatures.
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Tatsumi, Hiroaki, Adrian Lis, Hiroshi Yamaguchi, Tomoki Matsuda, Tomokazu Sano, Yoshihiro Kashiba, and Akio Hirose. "Evolution of Transient Liquid-Phase Sintered Cu–Sn Skeleton Microstructure During Thermal Aging." Applied Sciences 9, no. 1 (January 4, 2019): 157. http://dx.doi.org/10.3390/app9010157.
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The evolution of the transient liquid-phase sintered (TLPS) Cu–Sn skeleton microstructure during thermal aging was evaluated to clarify the thermal reliability for die-attach applications. The Cu–Sn skeleton microstructure, which consists of Cu particles connected with Cu–Sn intermetallic compounds partially filled with polyimide resin, was obtained by the pressure-less TLP sintering process at 250 °C for 1 min using a novel Cu-solder-resin composite as a bonding material in a nitrogen atmosphere. Experimental results indicate that the TLPS joints were mainly composed of Cu, Cu6Sn5, and Cu3Sn in the as-bonded state, where submicron voids were observed at the interface between Cu3Sn and Cu particles. After thermal aging at 150, 175, and 200 °C for 1000 h, the Cu6Sn5 phase fully transformed into Cu3Sn except at the chip-side interface, where the number of the submicron voids appeared to increase. The averaged shear strengths were found to be 22.1 (reference), 22.8 (+3%), 24.0 (+9%), and 19.0 MPa (−14%) for the as-bonded state and specimens aged at 150, 175, and 200 °C for 1000 h, respectively. The TLPS joints maintained a shear strength over 19 MPa after thermal aging at 200 °C for 1000 h because of both the positive and negative impacts of the thermal aging, which include the transformation of Cu6Sn5 into Cu3Sn and the formation of submicron voids at the interface, respectively. These results indicate an excellent thermal reliability of the TLPS Cu–Sn skeleton microstructure.
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Boettcher, Lars, S. Karaszkiewicz, D. Manessis, and A. Ostmann. "Development of Embedded High Power Electronics Modules for Automotive Applications." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2013, DPC (January 1, 2013): 001717–43. http://dx.doi.org/10.4071/2013dpc-wp35.
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The automotive industry has a strong demand for highly reliable and cost-efficient electronics. Especially the upcoming generations of hybrid cars and fully electrical vehicles need compact and efficient 400 V power modules. Within the engine compartment installation space is of major concern. Therefore small size and high integration level of the modules are needed. Conventionally IGBTs and diodes are soldered to DCB (Direct Copper Bond) ceramics substrates and their top contacts are connected by heavy Al wire bonds. These ceramic modules are vacuum soldered to water-cooled base plates. Embedding of power switches, and controller into compact modules using PCB (Printed Circuit Board) technologies offers the potential to further improve the thermal management by double-sided cooling and to reduce the thickness of the module. In the recently started “HI-LEVEL” (Integration of Power Electronics in in High Current PCBs for Electric Vehicle Application) project, partners from automotive, automotive supplier, material supplier, PCB manufacturer and research teamed up to develop the technology, components and materials to realize high power modules. The following topics of the development will be addressed in detail in this paper:Assemble of power dies (IGBT and diode) using new sinter die attach materials:The deployment of new no pressure, low temperature sinter paste for the assembly of the power dies is a mayor development goal. Here the development of a reliable process to realize a defect free bonding of large IGBT dies (up to 10x14mm2) is essentially. These pastes are applied by stencil printing or dispensing and the sintering will take place after die placement at temperatures of around 200 °C.Thick copper substrate technology:To handle the high switching current, suitable copper tracks in the PCB are required. The realization of such thick copper lines (up to 1mm thickness) requires advanced processing, compared to conventional multilayer PCB production. In this paper the essential development steps towards a 10 kW inverter module with embedded components will be described. The process steps and reliability investigations of the different interconnect levels will be described in detail.
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Chew, Ly May, and Wolfgang Schmitt. "High reliable and high bonding strength of silver sintered joints on copper surfaces by pressure sintering under air atmosphere." International Symposium on Microelectronics 2018, no. 1 (October 1, 2018): 000434–41. http://dx.doi.org/10.4071/2380-4505-2018.1.000434.
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Abstract Silver sintering is a promising die attach technology for high temperature power electronics packaging. Our previous studies have revealed that highly reliable sintered joints was obtained on silver and gold surfaces by either non-pressure or pressure sintering. In this paper, we extended our study to die attachment on copper surfaces by pressure sintering under air atmosphere. We attached Ag metallized die on silicon nitride active metal braze copper substrates with Ag metallization and without metallization by silver sintering at 230°C with a pressure of 10 MPa for 3 min. We observed that the average initial die shear strength for bare Cu substrate is lower than for Ag metallized substrate. This observation is attributed to the self-diffusion of Ag is faster than the interdiffusion between Ag and Cu. However, the average die shear strength for all samples increased considerably after temperature cycling test (−40°C/+150°C) and high temperature storage at 250°C. It is highly likely that sintering process is not yet completed under the sintering conditions used in this study and consequently Ag and Cu continued to diffuse during thermal cycling and high temperature storage and as a result strengthen the sintered joints. It is believed that after a certain time of storage at 250°C the sintering process is completed as we observed the average die shear strength remained relatively constant after 250 h storage. Voids, drying channels and delamination in the sintered joints were not detected by scanning acoustic microscopy for the samples before and after 2000 thermal cycles.
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Bobzin, K., W. Wietheger, J. Hebing, and L. Gerdt. "Softening Behavior of Cold-Sprayed Aluminum-Based Coatings AA1200 and AA7075 During Annealing." Journal of Thermal Spray Technology, November 12, 2020. http://dx.doi.org/10.1007/s11666-020-01121-7.
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AbstractFor lightweight constructions, joining dissimilar metals is often indispensable to achieve exceptional properties. A common challenge is the bonding of steel and aluminum parts. The use of cold-sprayed coatings as a bonding agent is an innovative approach for high pressure die casting (HPDC) aluminum-steel hybrid components in order to achieve a metallurgical bonding, although it comes with high requirements in terms of coating adhesive and cohesive strength. Therefore, the main aim of this study is the optimization of a post-processing treatment of cold-sprayed coatings in order to improve the cohesive strength to help the introduced coatings withstand the mechanical and thermal stresses during HPDC. The effect of the heat treatment on the mechanical properties of the cold-sprayed Al99.0 and AA7075 coatings was investigated. Freestanding coatings were heat-treated at a temperature of T = 400 °C for different dwell times in order to analyze the recrystallization kinetics through hardness measurements. Two different heat treatment states along with an as-sprayed condition were chosen to investigate the evolution of the mechanical properties of the coatings by means of 3-point bending tests. Besides the softening of the coatings during the heat treatment, sintering effects at splat boundaries and their impact on fracture mechanisms were investigated using electron microscopy.
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Kisiel, Ryszard, Marek Guziewicz, Andrzej Taube, Maciej Kaminski, and Mariusz Sochacki. "Development of assembly techniques for connection of AlGaN/GaN/Si chips to DBC substrate." Circuit World ahead-of-print, ahead-of-print (July 22, 2020). http://dx.doi.org/10.1108/cw-12-2019-0186.
Full textAbstract:
Purpose This paper aims to investigate the sintering and solid liquid interdiffusion bonding (SLID) techniques to attach AlGaN/GaN-on-Si chips to direct bond copper (DBC) substrate. The influence of metal layers deposited on the backside of AlGaN/GaN-on-Si dies on the assembly process is also investigated. Design/methodology/approach The authors assumed the value of the shear strength to be a basic parameter for evaluation of mechanical properties. Additionally, the surface condition after shearing was assessed by SEM photographs and the shear surface was studied by X-ray diffraction method. The SLID requires Sn-plated DBC substrate and can be carried out at temperature slightly higher than 250°C and pressure reduced to 4 MPa, while the sintering requires process temperature of 350°C and the pressure at least 7.5 MPa. Findings Ag-, Au-backside covered high electron mobility transistor (HEMT) chips can be assembled on Sn-plated DBC substrates by SLID technology. In case of sintering technology, Cu- or Ag-backside covered HEMT chips can be assembled on Ag- or Ni/Au-plated DBC substrates. The SLID process can be realized at lower temperature and decreased pressure than sintering process. Research limitations/implications For SLID technology, the adhesion between Cu-backside covered HEMT die and DBC with Sn layer loses its operational properties after short-term ageing in air at temperature of 300°C. Originality/value In the SLID process, Sn-Cu and Sn-Ag intermetallic compounds and alloys are responsible for creation of the joint between Sn-plated DBC and micropowder Ag layer, while the sintered joint between the chip and Ag-based micropowder is formed in diffusion process.