Benchmark of Surface Mount Autoclave Reliability Performance

Abstract

This benchmark study examined the effect of four different backmetal/ leadframe schemes on the time to failure from autoclave testing for surface mount, small signal transistors in the SC59 package configuration. The four schemes examined included die with Au backmetal bonded to a Cu plated Alloy 42 leadframe, Au backmetal bonded to a Ag striped, Ni plated, Cu plated alloy 42 leadframe, Au backmetal with a thin, permeable Ni layer bonded to a Ag striped, Ni plated Cu leadframe and V/Ni/AuGe/Au backmetal bonded to a Cu leadframe. Devices with AuSi eutectic bonded directly to the Cu plated Alloy 42 leadframe separated between the Si die and the AuSi eutectic after 240 hours of autoclave testing which produced VCESAT failures. Identical devices bonded to Ag striped, Ni plated, Cu plated Alloy 42 leadframes had the same failure mechanism after 624 hours of autoclave testing. Adding a permeable Ni layer to the AuSi eutectic structure and bonding to a Ag striped, Ni plated Cu leadframe increased the lifetime to 744 hours but still produced the same failure mechanism. Devices using a V/Ni/AuGeJAu bonded to a Cu leadframe remained electrically good and physically intact after 864 hours of autoclave testing. These results indicate the use of leadframe plating and/or backmetal barrier metals is needed in order to produce devices that can withstand extended reliability testing.