Thermomechanical diagnostics of BGA packages using digital image/speckle correlation

Thermomechanical diagnostic techniques are required for the characterization and reliability engineering of electronic packaging. Digital image/speckle correlation (DISC) is attractive for large throughput testing because it eliminates the specimen grating required by moire interferometry and does not require coherent illumination. Problems of DISC include a larger sensitivity to noise and a reduction of sensitivity for large fields of view. The present work uses DISC to study thermomechanical deformations of solder-joints in a cross-sectioned ball grid array (BGA) thermal test package. An iterative algorithm is developed to calculate the in-plane deformation and strain. Frame averaging of digital images reduces the noise, while a scanning stage allows a large effective field of view with acceptable sensitivity. This work achieves a spatial resolution of 2 μm and a sensitivity of 0.01 pixels. Average strains in these solder joints are also calculated to provide data for fatigue lifetime estimation. The approach demonstrated here is promising for on-line thermomechanical diagnostics in IC manufacturing