Temperature Cycling Reliability of High-Temperature Lead-Free Die-Attach Technologies

The demand for electronics capable of operating at temperatures above the traditional 125 degrees C limit continues to increase. Devices based on wide bandgap semiconductors have been demonstrated to operate at temperatures up to 500 degrees C, but packaging remains the major hurdle to product development. Recent regulations, such as RoHS and WEEE, increase the complexity of the packaging task by prohibiting the use of certain materials, such as lead, in electronic products. Traditionally, lead has been widely used in high-temperature solder attach. In this paper, 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 have been presented for the gold-tin solid-liquid interdiffusion system where bond quality was demonstrated to be a critical factor in its failure mode and mechanism.