A SEM and TEM Study of the Interconnect Microstructure and Reliability for a New XFLGA Package

The paper focuses on electron microscopy investigations of board assembly for a new XFLGA package with emphasis on microstructure, intermetallic compound (IMC) and defect formation in solder to package and board metallization interfaces. XFLGA packages with NiAu lead finish were assembled using a commercial SnAg_3.5Cu_0.7 solder to NiAu- or CuOSP board metallization. The interface microstructure was studied using scanning electron microscopy (SEM) before and after stress testing. Both regarding the discovered intermetallic compounds and crack formation no critical defect processes were detected in the interfaces. This result was further confirmed by focused ion beam (FIB) and transmission electron microscopy (TEM) investigations on a nanometer scale for selected samples. These results support the positive electrical reliability test results and indicate a high stability of the XFLGA component during application conditions