The Expermental and Numerical Study of Electromigration in 2.5D Packaging

In this study, an electromigration (EM) experiment of a ball in a flip chip package with eutectic SnPb solder has been performed. The test vehicles had two types of ball grid array (BGA) interconnects between the traces: one with Cu via and one without. The package was stressed at 125oC and 150oC ambient temperature with 7A and 10A currents. Voltage and mean temperature of the test structures were measured in real-time. It was observed that the different micro-electrical structures of the two types causes great effects on the EM behavior. The time to failure (TTF) of BGA with via in the substrate is smaller than that without via. In the BGA with via, the EM-induced failure was detected at the solder ball near via, but, in BGA without via, it was found at the edge of the solder ball. A numerical simulation based on Atom Flux Divergence (AFD) was performed to understand the failure mechanism and predict the TTF. In all cases, the simulations were accurate within 10%. The accumulation of vacancies is faster in BGA with a via structure than the BGA without a via structure, and the vacancy concentration in BGA with via is almost 5 times greater than the BGA without via structure after 1000h. Thus, the BGA with via structure poses a greater chance of EM failure.