Abstract
The full field moire interferometry and the micro moire interferometry were applied to investigate the thermo-mechanical deformation induced by thermal loading in electronics packages. The packages investigated were flip chip and flip chip ball grid array (BGA) packages. The solder alloys used in the packages were eutectic solder, tin silver solder and tin silver copper solder. Thermo-mechanical deformations and shear strains generated from CTE mismatch were determined experimentally using a holographic grating. Micro-deformations within the solder joints of the flip chip packages were captured and analyzed. The results showed that micro moire interferometry was effective in micro-deformation measurement. The thermally induced shear strains in the underfilled flip chip packages increased almost linearly with distance from the neutral point. The outermost solder joints suffered the highest shear strains. For flip chip BGA packages on FR-4 boards, the solder joints under the die corners had the highest shear strains. High shear strains were also observed at the underfill fillet. The performances of the two lead-free solder alloys, tin silver solder and tin silver copper solder, were compared with that of the conventional eutectic solder. It was found that tin silver solder joints had the highest shear strains whereas the shear strains for tin silver copper solder were comparable with or lower than those of eutectic solder.
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