Solder joint fatigue life prediction in large size and low cost wafer-level chip scale packages

With the highly insatiable demands of higher performance and lower cost requirements for handheld and portable electronic devices in the semiconductor industry, the wafer level chip scale package (WLCSP) is widely used in integrated circuit (IC) fabrication today with rapidly growing demands. Recently, WLCSP without utilization of an under-bump metallization (UBM) layer has been proposed for cost reduction purposes, eliminating the process of electroplating the UBM layer as compared to conventional WLCSP processes. For applications with larger than 5×5 mm² die sizes, the die I/O can be increased to enhance the corresponding performance. With the increasing requirements of multifunctional, smaller form factor, lower cost and fine pitch package designs in WLCSPs, a number of challenges need to be overcome, especially in terms of preventing possible failures and enhancing reliability. It is well known that the empirical Coffin-Manson equation has been widely adopted to evaluate the thermal fatigue life of the solder joint in electronic packages. For the sake of understanding the thermal fatigue life of a large size and low cost WLCSP with Sn1.0Ag0.5Cu (SAC105) solder joints, the board level reliability (BLR) thermal cycling test (TCT) that follows JEDEC standards was evaluated. The solder joint characteristic life in a large size and low cost WLCSP can be obtained by Weibull analysis according to the experimental result. The three-dimensional (3D) finite element analysis (FEA) with rate dependent nonlinearity material properties was utilized to study the solder joint creep behaviors. With the correlation of experimental and simulation results, the modified Coffin-Manson equation for SAC105 solder joint fatigue life estimation in a large size and low cost WLCSP can be established. Based on the present equations, the thermal fatigue life for the utilization of SAC105 solder joints in a large size and low cost WLCSP can be effectively estimated through the numerical modeling without any experimental evaluation. This study will be useful if high reliability and cost reduction in a large size and low cost WLCSP is required.