Reliability assessment of high temperature lead-free device attach technologies

The demand for electronics capable of operating at temperatures above the traditional 125degC limit continues to increase. Devices based on wide band gap semiconductors have been demonstrated to operate at temperatures up to 500degC, but packaging them remains major hurdle to product development. Recent regulations, such as RoHS and WEEE, increase the complexity of the packaging task as they prohibit the use of certain materials in electronic products such as lead, which has traditionally been widely used in high temperature solder attach. In this investigation, a series of Pb-free die attach technologies have been identified as possible alternatives to Pb-based ones for high temperature applications. This paper describes the fabrication sequence for each system and assesses their long term reliability using accelerated thermal cycling and physics-of-failure modeling. The reliability of the lead rich alloy was confirmed during this investigation while early failures of the silver filled epoxy demonstrated their inability to survive high temperatures. An empirical damage model was developed for the silver nanoparticle paste based on fatigue induced failures. Encouraging reliability data has been presented for the gold-tin SLID system where bond quality was demonstrated to be a critical factor on its failure mode and mechanism.