Mechanical characterization of plastic ball grid array package flexure using moiré 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 available, isothermal flexural fatigue also becomes an important reliability issue. Solder interconnects subjected to mechanically induced deformation may result in failure. In the current work, Moiré interferometry is used to investigate the influence of PCB flexure on interconnect strains. A versatile testing apparatus is developed to load PBGA packages in four point bending. Moiré 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, often resulting in plastic deformation, which reduces service life of the package.