Grain Orientation and Microstructure Evolution in Sn-Ag-Cu Solder Joints as a Function of Position in Ball Grid Array Packages

Thermally cycled PBGA packages with 196 full array solder joints after various pre-conditions are examined to observe the microstrcuture evolution of Sn-Ag-Cu solder joints during aging and thermal cycling, focusing on Sn grain orientation. Each PBGA package was polished to obtain plan view cross sections of every solder joint, and characterized them using both Polarized Optical microscopy and Orientation Imaging Microscopy. Based on observations using polarized optical images, a single grain solder joint distribution map shows that thermal aging has a relatively small impact on the overall single grain solder joint fraction, but with thermal cycling, many single crystal joints transform to multi grained solder joints. A combined study and observation of Polarized light images and OIM provides further understanding about deformation and microstructure evolution processes that occur during thermal cycling.