Optical inspection of interfacial thermal strains in IC composite microstructures

Thermal deformation behaviors of electronic packages, stacked-MCP (multi chip package) and SOJ (small outline J-leaded package) were measured by phase-shifting moiré interferometry. This method was developed using a wedged glass plate as a phase shifter to obtain displacement fields with a sensitivity of nanometer scale. Digital image processing was also introduced to determine the strain distributions quantitatively. In stacked-MCP, thermal loading was applied from room temperature 25°C to two elevated temperatures (75 and 100°C), and thermal strains were then examined at these two elevated temperatures. The results showed that the normal strain ε _xx concentrated at the ends of two silicon chips, and the transverse strain ε_xx increased between the two silicon chips. The shear strain γ_xy increased at the end of the lower silicon chip to 0.30% from 0.17% when the temperature increased by 25°C. In SOJ, the thermal strains were investigated with the two packages before and after mounted on PWB (printed wiring board). The results showed that the strains increased by about 50% when the SOJ was mounted on the PWB.