Application and high temperature storage test on Zn-Al-Ge high temperature solder for die attach

Abstract

Zn-Al based alloys are good candidates in the proposal of alternative lead-free solder alloys for Silicon (Si) die attach in high-temperature applications because of its proper melting range and excellent thermal and electrical properties. There are limited studies on the feasibility of Zn based alloys in die attachment application and out of these studies, many did not include reliability test. In this report, the reliability of Si die attachment on Cu and Ni leadframes using Zn-Al-Ge based solder was investigated through high temperature storage (HTS) test. The die attachment process capability was verified using visual inspection, CSAM, and microscopic inspection on cross-sectioned samples. Die attached samples subsequently underwent HTS at 200 oC for up to 500 hours. SEM/EDX analysis was then carried out on cross-sectioned die attached samples being exposed to various storage durations to inspect for any failures and to identify intermetallic layers that were formed during the HTS. Results showed that good temperature tolerance at 500 hours was observed for soldering on Ni leadframe. However, several failures were seen in die attachment on Cu leadframe as early as 25 hours and up to 500 hours. This paper covers extensive analyses to understand these failure mechanisms applicable in this die attachment configuration.