Study on silver sintered die attach material with different metal surfaces for high temperature and high pressure (300°c/30kpsi) applications

Abstract

In this study, Silver sintering material is being evaluated on different metal surfaces for high temperature storage and high temperature plus high pressure test up to 300°C/30kpsi. Three different type of Alumina based ceramic substrates (gold, silver and copper metal finishes) are used as test vehicle in this evaluation. Die attach material and process quality has been evaluated in terms of die shear strength before and after high temperature storage for gold and silver surfaces, further study is the evaluation for the combined test with high temperature and high pressure (HTHP) for plasma treated metal surfaces (silver, gold and copper) and failure mode analysis. Silver-filled epoxy and high temperature epoxy materials are also used as references to make comparison with sintered materials at high temperature storage. After high temperature (300°C) storage test for 500 hours, shear strength of silver surface samples is increased from average shear strength of 17.96N/mm2 to 25.97N/mm2. However, shear strength of gold surface finished (ENEPIG) samples are decreased drastically from average shear strength of 14.78N/mm2 to 0.30N/mm2. A porous layer is observed at the interfaces near the dense Au/Ag alloy between Ni/Pd/Au finished surface and Ag sintering layer where the interfacial failure mode is happened. High temperature (300°C) and high pressure (30kpsi) storage test samples for 500 hours shows relatively higher shear strength for both silver surface and ENEPIG surface while degradation happened on the bare copper surface. After combined HPHT test (300°C/30kpsi/500hours), gold layer in ENEPIG surface is diffused into palladium and nickel layers without creating a porous layer near the Au/Ag alloy and the exhibits good shear strength results which is significantly different behavior from the high temperature storage without pressure. SEM and EDX are used to analyze the cross-sectioned layers after HPHT aging tests. Silver sintering on copper surface shows the lowest shear strength among Ag, Au and Cu substrates. Au substrates has an average shear strength of >20N/mm2, which is higher than Ag substrate which has an average shear strength of >10.9N/mm2.