Microstructure and Fracture of Pb-free Solder Interconnects in Ceramic Ball Grid Array Packages under Thermal Cycling
CBGA结构热循环条件下无铅焊点的显微组织和断裂

Microstructure and thermal fatigue behavior of Pb-free solder interconnects in ceramic ball grid array (CBGA) packages were examined by cross-sectional microscopy, thermal cycling experiments and finite element modeling. In the as-reflowed condition, Cu6Sn5 and Ag3Sn formed at the solder interfaces with Cu and Ag metallizations respectively. Following thermal cycling, the Cu6Sn5 layer grew thicker and Cu3Sn was found at the interface with Cu metallization. On the ceramic side, visible thickening of the Ag3Sn layer was also observed. The morphology of Ag3Sn in the solder near the interface changed from strip-like to spherical shape. As a result of repeatedly thermal cycling, the fatigue crack appeared first at the corner of the solder ball with the chip, where the maximum shear stress was found by the finite element analysis. The cracks preferred to propagate along the Cu6Sn5/solder interface on the side of the print circuit board and in the solder joint near the interfacial Ag3Sn layer on the ceramic side.