Use of Wetting Angle Measurements in Reliability Evaluations of Au-Si Eutectic Die Attach

In order to assure reliable, high yield die attach on large VLSI devices, process control must be optimized. This paper presents a contact angle technique for measuring the wettability of backside surfaces for Au-Si eutectic die attach. Wettability measurements were carried out as a function of backside gold metallization thickness and aging treatment. Contact angle degradation is correlated to a decrease in die attach adherence strength and an increased susceptibility to die cracking in thermal cycling. A precision SEM/EDX Au thickness measurement method was developed as part of this work to assure the accuracy of the conclusions. For the conditions of this study, a gold thickness minimum of approximately 150 nm was found to be required for reliable die attach. In order to assure that this minimum is met routinely in the manufacturing process with a high degree or confidence, on-line measurements correlated to the SEM/EDX method are used in conjunction with a specially designed, statistically based. acceptance control chart.