Copper electrochemical migration growth in an air HAST

Abstract

Abstract High performance electronics require printed circuit boards (PCBs) with an extremely narrow pitch between adjacent copper patterns. However, copper electrochemical migration in these fine-pitch PCBs is a major source of failure. This phenomenon is typically identified using a highly accelerated temperature and humidity stress test (HAST) in which the water vapor pressure inside a chamber is increased along with the temperature and humidity. However, a side effect of this is that little air remains in the chamber despite air being required when replicating actual environments. This can be overcome by using an air HAST system that includes air inputs in its chamber. In our experiments, we analyzed the copper electrochemical migration on coupon samples with a 125\u202fμm pitch at temperatures above 120\u202f°C under various air pressures. We then compared the results for the air HAST, HAST, and high temperature and high humidity (85\u202f°C/85% R.H.) tests by plotting each lifetime in the form of a Weibull distribution. Upon inspection, the cross-sectional microstructures of the copper electrochemical migration were seen to vary between the HAST and air HAST methods due to differences in the growth mechanism of the copper electrochemical migration.