Sn-Ag-Cu Solder Joint Microstructure and Orientation Evolution as a Function of Position and Thermal Cycles in Ball Grid Arrays Using Orientation Imaging Microscopy

Abstract

Thermally cycled plastic ball grid array (PBGA) packages with full arrays of 196 solder joints after various preconditions were examined to observe the microstructure evolution of Sn-Ag-Cu solder joints during aging and thermal cycling, focusing on Sn grain orientation. Each PBGA package was polished to obtain a plan-view cross-section of every solder joint, and characterized using both polarized optical microscopy and orientation imaging microscopy (OIM). By OIM observations, distribution maps were obtained based on Sn crystal c-axis orientations. Each precondition showed a characteristic distribution related to the combined thermal aging and thermal cycling history. This study on Sn grain orientation using OIM provides further understanding about deformation and microstructure evolution processes that occur during thermal cycling, and the impact of isothermal aging as a precondition.