THERMAL CYCLING RELIABILITY OF LEAD-FREE SOLDERS (SAC305 AND SN3.5AG) FOR HIGH TEMPERATURE APPLICATIONS

Abstract

Eutectic tin lead was the most widely used solder interconnect in the electronics industry before the adoption of lead-free legislation. But eutectic tin lead solder has a low melting point (183<super>o</super>C) and was not suited for some high temperature applications, such as oil and gas exploration, automotive, and defense. Hence, for these applications, the electronics industry had to rely on specialized solders.

In this study, ball grid arrays (BGAs), quad flat packages (QFPs), and surface mount resistors assembled with SAC305 and Sn3.5Ag solder pastes were subjected to thermal cycling from -40<super>o</super>C to 185<super>o</super>C. Commercially available electroless nickel immersion gold (ENIG) board finish was compared to proprietary Sn-based board finish designed for high temperatures. The data analysis showed that the type of solder paste and board finish used did not have an impact on the reliability of BGAs. The failure site was on the package side of the solder joint. The morphology of intermetallic compounds (IMCs) formed after thermal cycling was analyzed.