Mechanical characterization of plastic ball grid array package flexure using Moire interferometry

Most previous studies of PBGA packaging reliability focus on the effect of thermal cycling, However, as portable electronic products such as cellular phones and laptop computers are reduced in size and become more readily ava ilable, isothermal flexural fatigue also becomes an important reliability i ssue. Solder interconnects subjected to mechanically induced deformation ma y result in failure. In the current work, Moire interferometry is used to i nvestigate the influence of PCB flexure on interconnect strains. A versatil e testing apparatus is developed to load PBGA packages in four point bendin g. Moire fringe patterns are recorded and analyzed at various bending loads to examine the variation in displacement and strain between the components . Solder balls across the entire array experience large shear strains, ofte n resulting in plastic deformation, which reduces service life of the packa ge.