Aging impact on the accelerated thermal cycling performance of lead-free BGA solder joints in various stress conditions

Abstract

Isothermal aging effects on lead-free solders have been extensively investigated in recent studies for both bulk solders and package solder joints. Researches show that aging significantly degrades the mechanical properties of bulk lead-free solders and dynamic performances of lead-free solder joints. There are studies exploring the impact of aging on accelerated thermal cycling (ATC) performance of lead-free solder joints, however, the results are discrepant, some research shows minimal impact of isothermal aging on long term ATC performances since most of the failure mode are not related to intermetallic (IMC) growth which has been impacted more significantly during aging. Some others show significant degradation of the of ATC life due to evidence of weakening of solder joints after aging. This study is intended to explore the factors that may affect the aging impact on the lead-free solder joint fatigue life. The test vehicle is designed with different package types, pitch sizes, and solder alloy metallurgies to capture the impact of affecting factors. The test vehicles have been aged at 100°C and 150°C for different aging durations, ATC test were subsequently performed on the aged samples and with the non aged samples as control. The effects of aging on the fatigue life of lead-free solder joints are extensively explored in this study.