Die Attach for High Temperature Applications

Abstract

The energy sector is seeing dynamic growth with advanced oil and gas recovery methods being deployed. Measure-while-drilling (MWD) and downhole production instrumentation is important to maximize production and safety. Well temperatures are moving past 175oC therefore 200oC instrumentation is increasingly in demand. Power electronics are required as part of the downhole measurement tools, geothermal and aerospace exploration instruments. Die attach materials and technology for high-temperature electronics that can be used in 200oC, 300oC and 500oC applications were developed and evaluated with reliability tests. Die attach using AuSn liquid phase transit (LPT) bonding for 500oC applications was investigated. Both single and double prints of the PtPdAu thick film layers were evaluated. Both of the samples show good mechanical reliability for high temperature storage. The assembly process for two test circuit boards using AuSn liquid phase transit (LPT) bonding and thick film substrates for 300oC application were developed. The dual in line package (DIP) socket board had contact stability beyond 3000 hours. An innovative die attach method using Au sintering with patterned die and Au thick film paste was developed. The patterned gold die attach technology using micro-scale gold paste has been evaluated and showed the potential for applications at 500oC. The patterns on both the thin film die backside metallization and thick film substrate has successfully created controlled voiding which allows the burnout gas to escape during the firing process. The shear strength after aging meets the MIL-STD-883 die attach requirement and this die attach method should be stable for use to 700oC.

AgBiX solder has potential for 200oC applications. This alloy has been used to assemble SiC test die to ceramic substrates with direct bond copper (DBC), reactive brazed CuMo, thick film PtPdAu, thick film PdAg and thick film Ag. Surface mount chip resistors have also been attached to thick film metallized substrates. The assembly process and initial shear strength test results are presented. Assemblies have also been subjected to thermal cycling -55oC to +195oC) and high temperature (200oC) storage. From the test results, the solder paste is compatible with all of the listed substrates above, except the thick film PtPdAu and thick film Au substrates. This solder paste is a promising lead-free solder paste for 200oC applications.