Lead-Free Alternatives for Interconnects in High-Temperature Electronics

2017 ◽  
Author(s):  
Sandeep Mallampati ◽  
Liang Yin ◽  
David Shaddock ◽  
Harry Schoeller ◽  
Junghyun Cho
Keyword(s):  
Thermal Conductivity ◽  
Plastic Deformation ◽  
Shear Strength ◽  
High Temperature ◽  
Heat Dissipation ◽  
Volume Fraction ◽  
High Volume ◽  
Die Attach ◽  
Average Shear Strength ◽  
Average Shear

Predominant high melting point solders for high temperature and harsh environment electronics (operating temperatures from 200 to 250°C) are Pb-based systems, which are being subjected to RoHS regulations because of their toxic nature. In this study, high bismuth (Bi) alloy compositions with Bi-XSb-10Cu (X from 10 wt.% to 20 wt.%) were designed and developed to evaluate their potential as high-temperature, Pb-free replacements. Reflow processes were developed to make die-attach samples made out of the cast Bi alloys. In particular, die-attach joints made out of Bi-15Sb-10Cu alloy exhibited an average shear strength of 24 MPa, which is comparable to that of commercially available high Pb solders. These alloy compositions also retained original shear strength even after thermal shock between −55°C and +200°C and high temperature storage at 200°C. Brittle interfacial fracture sometimes occurred along the interfacial NiSb layer formed between Bi(Sb) matrix and Ni metallized surface. In addition, heat dissipation capabilities, using flash diffusivity, were measured on the die-attach assembly, compared to the corresponding bulk alloys. The thermal conductivity of all the Bi-Sb alloys was higher than that of pure Bi. By creating high volume fraction of precipitates in a die-attach joint microstructure, it was feasible to further increase thermal conductivity of this joint to 24 W/m·K, which is three times higher than that of pure Bi (8 W/m·K). Bi-15Sb-10Cu alloy has so far shown the most promising performance as a die-attach material for high temperature applications (operated over 200°C). Hence, this alloy was further studied to evaluate its potential for plastic deformation. Bi-15Sb-10Cu alloy has shown limited plastic deformation in room temperature tensile testing, in which premature fracture occurred via the cracks propagated on the (111) cleavage planes of rhombohedral crystal structure of the Bi(Sb) matrix. The same alloy has, however, shown up to 7% plastic strain under tension when tested at 175°C. The cleavage planes, which became oriented at smaller angles to the tensile stress, contributed to improved plasticity in the high temperature test.

Lead-Free Alternatives for Interconnects in High-Temperature Electronics

2018 ◽  
Vol 140 (1) ◽  
Author(s):  
Sandeep Mallampati ◽  
Liang Yin ◽  
David Shaddock ◽  
Harry Schoeller ◽  
Junghyun Cho
Keyword(s):  
Thermal Conductivity ◽  
Plastic Deformation ◽  
Shear Strength ◽  
High Temperature ◽  
Heat Dissipation ◽  
Volume Fraction ◽  
High Volume ◽  
Die Attach ◽  
Average Shear Strength ◽  
Average Shear

Predominant high melting point solders for high-temperature and harsh environment electronics (operating temperatures from 200 to 250 °C) are Pb-based systems, which are being subjected to RoHS regulations because of their toxic nature. In this study, high bismuth (Bi) alloy compositions with Bi-XSb-10Cu (X from 10 wt % to 20 wt %) were designed and developed to evaluate their potential as high-temperature, Pb-free replacements. Reflow processes were developed to make die-attach samples made from the cast Bi alloys. Die-attach joints made from Bi-15Sb-10Cu alloy exhibited an average shear strength of 24 MPa, which is comparable to that of commercially available high Pb solders. These alloy compositions also retained original shear strength even after thermal shock (TS) between −55 °C and +200 °C and high-temperature storage (HTS) at 200 °C. Brittle interfacial fracture sometimes occurred along the interfacial NiSb layer formed between Bi(Sb) matrix and Ni metallized surface. In addition, heat dissipation capabilities, using flash diffusivity, were measured on the die-attach assembly and were compared to the corresponding bulk alloys. The thermal conductivity of all the Bi–Sb alloys was higher than that of pure Bi. By creating high volume fraction of precipitates in a die-attach joint microstructure, it was feasible to further increase thermal conductivity of this joint to 24 W/m·K, which is three times higher than that of pure Bi (8 W/m·K). Bi–15Sb–10Cu alloy has so far shown the most promising performance as a die-attach material for high-temperature applications (operated over 200 °C). Hence, this alloy was further studied to evaluate its potential for plastic deformation. Bi–15Sb–10Cu alloy has shown limited plastic deformation in room temperature tensile testing in which premature fracture occurred via the cracks propagated on the (111) cleavage planes of rhombohedral crystal structure of the Bi(Sb) matrix. The same alloy has, however, shown up to 7% plastic strain under tension when tested at 175 °C. The cleavage planes, which became oriented at smaller angles to the tensile stress, contributed to improved plasticity in the high-temperature test.

Cu3Sn-microporous copper composite joint for high-temperature die-attach applications

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Zhen Pan ◽  
Fenglian Sun
Keyword(s):  
Thermal Conductivity ◽  
Shear Strength ◽  
High Temperature ◽  
Transient Liquid Phase ◽  
Content Type ◽  
Composite Joint ◽  
Die Attach ◽  
Aging Property ◽  
Copper Composite ◽  
Temperature Aging

Purpose The purpose of this paper is to design a novel die-attach composite joint for high-temperature die-attach applications based on transient liquid phase bonding. Moreover, the microstructure, shear strength, electrical property, thermal conductivity and aging property of the composite joint were investigated. Design/methodology/approach The composite joint was made of microporous copper and Cu3Sn. Microporous copper was immersed into liquid Sn to achieve Sn-microporous copper composite structure for die attachment. By the thermo-compression bonding, the Cu3Sn-microporous copper composite joint with a thickness of 100 µm was successfully obtained after bonding at 350 °C for 5 min under a low pressure of 0.6 MPa. Findings After thermo-compression bonding, the resulting interconnection could withstand a high temperature of at most 676 °C, with the entire Sn transforming into Cu3Sn with high remelting temperatures. A large shear strength could be achieved with the Cu3Sn-microporous copper in the interconnections. The formed bondlines demonstrated a good electrical and thermal conductivity owing to the large existing amount of copper in the interconnections. Furthermore, the interconnection also exhibited excellent reliability under high temperature aging at 300 °C. Originality/value This die-attach composite joint was suitable for power devices operating under high temperatures or other harsh environments.

scholarly journals Test Vehicle for Studying Thermal Conductivity of Die Attach Adhesives for High Temperature Electronics

2012 ◽  
Vol 188 ◽  
pp. 238-243
Author(s):  
Conor Slater ◽  
Fabrizio Vecchio ◽  
Thomas Maeder ◽  
Peter Ryser
Keyword(s):  
Thermal Conductivity ◽  
Shear Strength ◽  
High Temperature ◽  
Thick Film ◽  
Test Vehicle ◽  
High Temperature Electronics ◽  
Temperature Decay ◽  
Die Attach ◽  
Viable Method ◽  
Degree Of Degradation

Polymer adhesives offer a viable method for mounting silicon dies for high temperature applications. Here a test vehicle for comparing the thermal conductivity of different die attach materials is presented. The setup can be used to determine the degree of degradation of polymers. It consists of a mock die that has an integrated thick film heater, which is mounted onto a substrate. In operation, the substrate is placed on a heatsink and the die is heated. When the temperature reaches equilibrium the heater is switched off and the temperature of the die is measured as it cools. The time constant of the temperature decay is calculated to give the thermal conductivity. In this paper the thermal conductivity of an epoxy die attach adhesive is compared to its shear strength.

Vacuum Brazing Incoloy 800 Using the Copper Foil

2015 ◽  
Vol 1101 ◽  
pp. 99-103
Author(s):  
Cheng Yen Wang ◽  
Ren Kae Shiue
Keyword(s):  
Shear Strength ◽  
Copper Foil ◽  
Vacuum Furnace ◽  
Vacuum Brazing ◽  
Average Shear Strength ◽  
Average Shear ◽  
Incoloy 800 ◽  
Brazed Joints ◽  
Brazed Joint ◽  
Time Average

The purpose of this research is focused on vacuum furnace brazing Incoloy 800 (IN-800) using the copper filler foil. Microstructural evolution and shear strength of brazed joints for various brazing conditions has been evaluated in the experiment. The Cu-rich matrix dominates entire brazed joint. The width of Cu-rich matrix is decreased with increasing the brazing temperature and/or time. Average shear strength of the joint is approximately 215 MPa. Dimple dominated fracture is widely observed for the specimen brazed below 1160oC. However, cleavage dominated fracture is found for the specimen brazed at 1200oC. It is advised that copper brazing IN-800 alloy should be confined below 1160oC.

Shear strength and cracking behavior of Cr coatings on zirconium alloy fuel claddings at different strain rates

2021 ◽  
pp. 2150194
Author(s):  
Xiulin Yan ◽  
Ruiqian Zhang ◽  
Yan Liu ◽  
Yunhua Zhang ◽  
Hui Chen
Keyword(s):  
Shear Strength ◽  
Interfacial Shear Strength ◽  
Strain Rates ◽  
Cracking Behavior ◽  
Shear Lag Model ◽  
Loading Direction ◽  
Average Shear Strength ◽  
Average Shear ◽  
Lag Model ◽  
Cr Coating

Cr coating on Zr-based fuel tubes is a potential approach for the development of accident tolerant fuels (ATF). To settle the cracking behavior and quantitative evaluation of shear strength of Cr coating under different loading conditions, the average shear strength between Cr coating and zircaloy substrate has been estimated using a modified shear-lag model in this paper. Its key parameters are determined experimentally, and the tensile method has been used to research the cracking behavior of Cr coating under different strain rates. The results show that with the increase of strain rate, the interfacial shear strength increases because of the decrease of cracking spacing, while the shear strength changes erratically with the coating thickness increases. Furthermore, abundant two unequal-crack-spacings and few two equal-crack-spacings are observed which are perpendicular to the loading direction.

Mobile Packaging and Interconnect Trends

2014 ◽  
Vol 2014 (DPC) ◽  
pp. 1-21
Author(s):  
Brandon Prior
Keyword(s):  
Shear Strength ◽  
High Temperature ◽  
Thick Film ◽  
Cross Sections ◽  
Shear Test ◽  
Short Review ◽  
Test Machine ◽  
Die Attach ◽  
Shear Failures ◽  
Film Substrate

This paper will focus on emerging and fast growth package solutions to meet mobile products' density and cost requirements. A short review of where package miniaturization and modularization has taken us so far, and where it will lead in the next 5 years. Teardowns of high density systems and packages will be used to illustrate key points. Low temperature Ag sintering technology provides a lead-free die attachment compatible with high temperature (300°C) applications. Previous work with Ag sintering has required some pressure during the sintering process or been limited to small area die. In this paper, a pressureless sintering of micro-scale silver paste procedure is presented for large (8mm x 8mm) area die. Experimental combinations included: Ag metallized Si die, Au metallized Si die, Ag thick film substrate metallization, Au thick film substrate metallization, PdAg thick film metallization and sintering temperature. For Au metallization (die and/or substrate), the initial shear strength results were good with 8mm x 8mm die sintered at lower temperatures (200°C). The shear strength was out range of our shear test machine (100 kg), corresponding to >15.3 MPa. However, after aging for 24 hours at 300°C, the shear strength dropped significantly to 40.38 Kg (6.183 MPa). An SEM was used to characterize cross sections of as-built and aged sample. The decrease in die shear strength with high temperature sintering (250°C and 300°C) or high temperature aging is attributed to surface diffusion of Ag along the Au surface resulting in a dense Ag layer adjacent to the Au surface and a depletion layer within the die attach on the opposite side of the the dense Ag layer. Shear failures occurred through the depleted region. For Ag metallization, no decrease in shear strength was observed with 300°C aging. Shear strength of 8x8cm2 dies was out range of our shear test machine (>100 kg, >15.3 MPa) as-built. The shear strength remained out of range (>15.3MPa) after more than 2000 hours of 300C aging.

LT-TLPS Die Attach for High Temperature Electronic Packaging

2014 ◽  
Vol 11 (1) ◽  
pp. 7-15
Author(s):  
Hannes Greve ◽  
F. Patrick McCluskey
Keyword(s):  
Shear Strength ◽  
High Temperature ◽  
Melting Point ◽  
Low Temperature ◽  
Transient Liquid Phase ◽  
Liquid Phase Sintering ◽  
Die Attach ◽  
Metallic Interfaces ◽  
Dsc Analyses ◽  
Transient Liquid Phase Sintering

Low temperature transient liquid phase sintering (LT-TLPS) can be used to form high-temperature joints between metallic interfaces at low process temperatures. In this paper, process analyses and shear strength studies of paste-based approaches to LT-TLPS are presented. The process progression studies include DSC analyses and observations of intermetallic compound (IMC) formation by cross-sectioning. It was found that the sintering process reaches completion after sintering times of 15 min for process temperatures approximately 50°C above the melting point of the low temperature constituent. For the shear studies, test samples consisting of copper dice and copper substrates joined by sintering with a variety of sinter pastes with different ratios of copper and tin have been assessed. A fixture was designed for high temperature enabled shear tests at 25°C, 125°C, 250°C, 400°C, and 600°C. The influence of the ratio of the amount of high melting-point constituent to the amount of low melting-point constituent on the maximum application temperature of the sinter paste was analyzed. Ag20Sn and Cu50Sn pastes showed no reduction in shear strength up to 400°C, and Cu40Sn pastes showed high shear strengths up to 600°C. It was shown that LT-TLPS can be used to form high temperature stable joints at low temperatures without the need to apply pressure during processing.

scholarly journals Infrared Brazing of CoCrFeMnNi Equiatomic High Entropy Alloy Using Nickel-Based Braze Alloys

Entropy ◽  
2019 ◽  
Vol 21 (3) ◽  
pp. 283 ◽  
Author(s):  
Chieh Lin ◽  
Ren-Kae Shiue ◽  
Shyi-Kaan Wu ◽  
Huai-Li Huang
Keyword(s):  
Shear Strength ◽  
Grain Boundary ◽  
High Entropy Alloy ◽  
Solidification Shrinkage ◽  
Vacuum Brazing ◽  
High Entropy ◽  
Average Shear Strength ◽  
Average Shear ◽  
Brazed Joints ◽  
Liquidus Temperatures

Infrared vacuum brazing of CoCrFeMnNi high entropy alloy (HEA) using BNi-2 and MBF601 fillers has been investigated. Both brazes show poor wettability at temperatures only 20 °C above their liquidus temperatures. However, the wettability of BNi-2 and MBF601 fillers on CoCrFeMnNi HEA is greatly improved with increasing the test temperatures, 50 °C above their liquidus temperatures. The BNi-2 brazed joints are dominated by Ni-rich matrix with huge CrB and a few tiny boride precipitates. Average shear strengths of joints increase with increasing brazing temperature and/or time, and fracture location changes from blocky CrB in the brazed zone to grain boundary boride in the substrate. The MBF601 brazed joints are composed of CoCrFeMnNi-based matrix, particles of B/Co/Cr/Fe/Mn/Ni/P compounds, and some phosphides form along the grain boundaries of the substrate. The specimen brazed with MBF601 filler foil at 1050 °C for 600 s has the highest average shear strength of 321 MPa, while that brazed at 1080 °C for 600 s has a lower average shear strength of 271 MPa due to the presence of solidification shrinkage voids.

Diffusion Barrier Effect of Carbide Layer on Bonding Characteristics of Ti/Steel Clad

1996 ◽  
Vol 458 ◽  
Author(s):  
Y. Morizono ◽  
M. Nishida ◽  
A. Chiba
Keyword(s):  
Stainless Steel ◽  
Shear Strength ◽  
Reaction Layer ◽  
Holding Time ◽  
Barrier Effect ◽  
Parent Materials ◽  
Prolonged Annealing ◽  
Average Shear Strength ◽  
Average Shear ◽  
Bonding Characteristics

ABSTRACTBonding characteristics and interfacial microstructures in explosively welded Ti/stainless steel clad of the as-welded and annealed states were investigated. In case of Ti/SUS430 ferritic stainless steel combination, the average shear strength of an as-welded clad was 555 MPa, and metastable phases such as amorphous and fine crystalline phases were observed at the interface. These were considered to be the trace of melting and subsequently rapid solidification at the contact surface of both the parent materials. By annealing below 1173 K, the strength gradually decreased with increasing holding time. The average shear strength of the clad annealed at 1073 K for 360 ks was 242 MPa, while that of the clad annealed at 1273 K abruptly decreased down to 107 MPa with increasing holding time up to 360 ks. The reaction layer formed at the interface consisted only of TiC in the former. On the other hand, the coexistence of TiC, TiFe, TiFe2 and χ was observed at the interface in the latter. The TiC in the former was considered to serve as a barrier for diffusion of Ti, Fe and Cr across the interface and to suppress the formation of intermetallic compounds. As a result, the growth of reaction layer was inhibited and high bonding strength was preserved even after prolonged annealing. The results of the Combination of Ti and SUS304 austenitic stainless steel were also discussed.

On Thermal Interface Materials With Polydisperse Fillers: Packing Algorithm and Effective Properties

2018 ◽  
Author(s):  
Piyas Chowdhury ◽  
Kamal Sikka ◽  
Anuja De Silva ◽  
Indira Seshadri
Keyword(s):  
Thermal Conductivity ◽  
Elastic Modulus ◽  
Volume Fraction ◽  
Effective Properties ◽  
Material Design ◽  
High Volume ◽  
Thermal Interface Materials ◽  
Thermal Interface ◽  
Packing Algorithm ◽  
Interface Materials

Thermal interface materials (TIMs), which transmit heat from semiconductor chips, are indispensable in today’s microelectronic devices. Designing superior TIMs for increasingly demanding integration requirements, especially for server-level hardware with high power density chips, remains a particularly coveted yet challenging objective. This is because achieving desired degrees of thermal-mechanical attributes (e.g. high thermal conductivity, low elastic modulus, low viscosity) poses contradictory challenges. For instance, embedding thermally conductive fillers (e.g. metallic particles) into a compliant yet considerably less conductive matrix (e.g. polymer) enhances heat transmission, however at the expense of overall compliance. This leads to extensive trial-and-error based empirical approaches for optimal material design. Specifically, high volume fraction filler loading, role of filler size distribution, mixing of various filler types are some outstanding issues that need further clarification. To that end, we first forward a generic packing algorithm with ability to simulate a variety of filler types and distributions. Secondly, by modeling the physics of heat/force flux, we predict effective thermal conductivity, elastic modulus and viscosity for various packing cases.

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