Two of the main driving forces for warpage deformation and residual stress in electronic packages are the thermal expansion mismatch between dissimilar package constituents and the crosslinking reaction of polymers during packaging thermal processes. For the purpose of quantitatively characterizing these two driving forces and assessing the process effect on warpage deformation, experimental and numerical analyses were applied to study the warpage evolution of overmolded ball grid array (BGA) package under post-mold curing (PMC) thermal histories. From in situ shadow Moiré warpage analyses on bimaterial and package specimens, it was observed that, during the isothermal curing condition, a significant increase in specimen warpage occurred as a result of molding compound shrinkage. A numerical modeling procedure that incorporates the models for the thermochemical cure kinetics, the curing- and chemical aging-induced shrinkage strains, and the cure-dependent viscoelastic relaxation modulus for the molding compound was then applied to simulate and compare to the experimentally obtained warpage evolutions. It can be seen from the analysis results that the evolution of package warpage over multiple thermal histories can be superpositioned by the thermal expansion mismatch-driven warpage change during non-isothermal stages and the chemical shrinkage-induced warpage evolution during isothermal aging at temperatures above the material glass transition point.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics
- Safety, Risk, Reliability and Quality
- Condensed Matter Physics
- Surfaces, Coatings and Films
- Electrical and Electronic Engineering