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WITH the continued development of high density, multi-function, and high power electronic devices, there are growing requirements for high-performance electronic packaging materials, with high thermal conductivity (TC), strength, processability, low coefficient of thermal expansion (CTE), and low cost.[1,2] There are limitations of most commonly used metal packaging materials, such as Cu, low-carbon steel, Kovar alloy, and Mo(W)-Cu alloys. For example, Cu has very high TC, but its high CTE is extremely unmatched with the CTE values of ceramic chip carriers like AlN and Al2O3.[3] This mismatch can induce high thermal stress in the electronic devices, possibly leading to fracture failure of the electronic devices. Kovar alloys have perfect processing properties and low CTE, but rather

XIN ZHANG, YINGQIU HUANG and XIANGYU LIU are with the School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China. LEI YANG and CHANGDONG SHI are with the 43 Institute, China Electronics Technology Group Corporation, Hefei 230088, China. YUCHENG WU is with the Key Laboratory of Functional Materials and Devices of Anhui Province, Hefei 230009, China. WENMING TANG is with the School of Materials Science and Engineering, Hefei University of Technology and also with the Key Laboratory of Functional Materials and Devices of Anhui Province. Contact e-mail: [email protected] Manuscript submitted August 19, 2017.

METALLURGICAL AND MATERIALS TRANSACTIONS A

low TCs. Mo(W)-Cu alloys have low CTEs, high TCs, and high strengths, but their high price and poor processing properties are unsatisfactory. Thus, advanced composite technology may be the only choice to fabricate better electronic packaging materials. One successful example is the development and use of SiC(Si)p/Al composites with high fractions of SiC(Si).[4,5] However, the processing properties of these SiC(Si)p/Al composites, such as machining, plating, and soldering, are so poor that the application of these materials has been seriously restricted. Cu/Invar composites have the potential to be excellent novel electronic packaging materials by combining the high TC of Cu with the low CTE (less than 1.8 9 106/ K) of the Fe-36Ni based Invar alloy.[6–8] The composites also have good processing properties, because they are composed of two face-centered-cubic (fcc) metals. Powder metallurgy (PM) is the most suitable approach to fabricate the Cu/Invar composites. Wu et al. used PM to prepare Cu/Invar composites in which the Cu content varied from 30 to 50 wt pct and carefully investigated the microstructures and properties of the resulting composites.[9] They found that the CTE of the Invar alloys increased and the TC of Cu decreased, apparently, due to rapid Cu/Invar interfacial diffusion during sintering of the Cu/Invar composites at high temperature. This interfacial diffusion results in the deterioration of the thermo-physical properties of the composites.[9] Therefore, a key issue to successful

development of high-performance Cu/Invar composite