Long-Term Aging Effects on Reliability Performance of Lead-Free Solder Joints
Authors: Zhou Hai, Jiawei Zhang, Chaobo Shen, John L. Evans, Ph.D. and M. J. Bozack Company: Center for Advanced Vehicle and Extreme Environment Electronics (CAVE3) Auburn University Date Published: 10/13/2013
Abstract: Lead-free solder alloy has evolved and applied in industries for many years. The reliability is of concern for lead-free solder joints of assembled circuitry, especially those exposed to high temperature in a long period of time. In order to provide a better understanding of lead-free solder joint behavior in harsh environments, the research investigates isothermal aging of Sn-Ag-Cu (SAC) alloy in elevated temperature and studied its thermal-mechanical properties by examining the microstructure. A full experiment at matrix with varying aging temperatures and solder alloys on two finish levels (ImAg and ImSn) was considered. Also, the test samples sizes ranged from 19mm, 0.8mm pitch ball grid arrays (BGAs) to 5mm, 0.4mm pitch µBGAs. Additionally, 0.65mm MLF and 2512 resistors were tested. The test specimens all subjected to aging at temperatures leveling up from 25°C, 55°C, 85°C and 125 °C with aging over time periods of 0, 6 months, 12 months and 24 months and accelerated thermally cycled from -40°C to 125°C with 15 min dwell times at the high and low peak temperature. It was found that the thermal performance of lead-free fine-pitch packages significantly degrades up to 70% after 2 year aging at high temperature.