Failure analysis on interconnection fault for BGA module after board assembly

In the transition to lead-free process, one of the most prominent problems is the lead-free solder joint interconnection reliability. Interconnection failure analysis is an important tool for improving the lead-free PCBA product design as well as assembly process quality. Combining a typical fault case, this study deeply analyzed the failure phenomena and the failure mechanism as to interconnection failure for BGA module after board assembly. The failure phenomenon was manifested as that IC programming could not be finished for the main BGA device after reflow soldering. A serial of experimental analysis technologies were used, such as X-ray inspection, scanning acoustic microscope (SAM) inspection, IV testing for the IC, microsectioning and scanning electron microscope (SEM) analysis, Tg testing for PCB substrate, etc., which can obtain the information such as BGA package integrity, I/O port feature, solder joints' microstructure, PCB's thermal characteristics, etc. The results showed that the solder joints' cracking failure in BGA module was the direct cause of the IC programming fault. And the failure phenomena in this case were indicated as a thermal-induced cracking, which was related to the poor heat-resistance of the PCB substrate.