Isothermal Aging Effects on the Mechanical Shock Performance of Lead-Free Solder Joints

Abstract

Isothermal aging effects on lead-free solders have been extensively investigated in recent studies. Researches show that aging effects significantly degrade the mechanical properties of lead-free solders. However, limited work has been done on the effects of aging on the board-level dynamic performance of lead-free solder joints, especially for large flip-chip ball grid array (FCBGA) packages. Due to the sensitivity of aging effects on lead-free solders, it is crucial to investigate the aging effects on the board-level dynamic performance of lead-free solders. In this paper, dynamic performance of lead-free solder joints has been characterized and isothermal aging effects have been investigated. It was found that the dynamic shock performance of lead-free FCBGA packages significantly degrades up to 20-35% after aging at elevated temperatures. It was also observed that aging at 100°C shows more severe degradation than aging at 75°C and 150°C. This is an important finding because many electronic products operate in the 100°C range for long periods. The unique finding of aging effects is related to the growth of Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> intermetallics after aging. Even though failure analysis shows mixed failure of pad cratering and intermetallic compound (IMC) failures, the IMC growth is the most sensitive factor contributing to the failure observed.