In-situ interfacial tensile strength measurements in microelectronic packages using a laser spallation technique

As a promising reliability testing tool for electronic packages, the basic laser spallation methodology was successfully adapted to measure the interfacial tensile strengths in three types of packages. The samples included C4 flip chip packages, freestanding (component-level) and board-mounted BGA chip-scale packages with different solder/substrate chemistries and stressed by baking for specific temperatures and times. Substantial qualitative data in terms of critical laser energies for solder joint strengths were generated for the above test matrix. The test data with a variation less than 15% indicate good producibility of the laser spallation test. These data also allowed for the evaluation of the effects of solder chemistry, pad chemistry, aging temperature and aging time on the solder joint strength. The correlation between the laser spallation results and the interfacial microstructure of the solder joint was evaluated by performing combined optical and SEM/EDX/FIB analyses on the failed pad and solder surfaces. Additionally, the effect of board chemistry on the solder joint strength was evaluated by comparing the critical laser energy data as a function of thermal aging time for the component- and board-level samples as well as comparing their failure locus using the SEM/EDX microscopy.; To determine if the laser spallation technique could replace or enhance the drop tests, the laser spallation data was also compared with those from drop tests, ball pull and ball shear tests. The ball pull and ball shear tests cannot pick up the solder joint degradation as well as the laser spallation due to mixed failure modes generated in these tests. The laser spallation tests may track well with the drop tests for strongly weakened joints while divergence exists for some other cases.; Besides measurement of the critical laser energies, quantification analysis was also performed to characterize the interfacial strengths in the package samples. The analysis involved stress wave measurements using interferometry and stress field quantification using a wave mechanics simulation.