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Vapor pressure analysis of popcorn cracking in plastic IC packages by fracture mechanics

Simulation studies of the popcorn cracking of plastic IC packages based on moisture diffusion analysis and fracture mechanics are performed. For analysis of the moisture diffusion during pre-conditioning and of the diffusion of heat and moisture during reflow soldering, the finite difference method with the one-dimensional Fick's law is applied to the epoxy molding compound (EMC) lying under the die pad. The vapor pressure generated due to the moisture concentration and corresponding accumulated moisture content during the soldering process are calculated using the ideal-gas equation and the plate theory. Finally, the reliability of the plastic packages relative to package cracking is evaluated by fracture mechanics. The result is applicable to general plastic packages, regardless of the package type and dimensions. Reliability tests are performed to verify the simulation results.