Reliability lifetime predictions on long term biased humidity reliability of Cu ball bonds

This paper compares and discusses the influence of shear strength {in terms of (SPMS) shear-per mils-square} of Au and Cu ball bonds on the biased humidity reliability performance in SOIC 8LD leaded package. Biased HAST (Highly Accelerated Temperature and Humidity Stress Test, 130°C, 85%RH) has been carried out to estimate the long term reliability of Au and Cu ball bonds. Lognormal reliability plots have been plotted for the three legs (Control, leg 1 and leg 2) whereby leg 2 is identified to have better mean-time-to-failure (t50) compared to other two legs. Open failure from biased HAST 96 hours, 192 hours are subjected for SEM cross-sectioning and found typical interfacial CuAl IMC (intermetallic compound) corrosion microcracking. HAST failure rates have been analyzed and the Cu ball bond lifetime has been established by using Peck model. The obtained Cu ball bond lifetime, of leg 2 is greater than 25 years and belongs to wearout reliability data point. This proves significant influence of SPMS on biased HAST failure rate. The higher the ball bond shear strength the lower the failure rate of biased HAST test. Hence, we should implement control on the average SPMS of ≥ 7.50 g/mil2. However, the minimum SPMS should have been controlled at minimum ≥ 6.5 g/mil2.