Cure Process Impact on Cure Time and Properties of Low Temperature Polyimide for 3D Stacking Applications

In this paper, to meet the requirements of low thermal budget for 3D integration on fan-out wafer or panel level processing or on even bigger substrates such as Gen3.5 or above, thermal, mechanical, and dielectric properties were studied for a low temperature polyimide material as a function of cure parameters at a cure temperature of ~200°C under atmospheric and sub-atmospheric process conditions. These results are compared to a conventional higher temperature polyimide. Vacuum cure of low temperature polyimide appears to improve the outgassing properties and dielectric strength at lower pressure; however, the dissipation factor resulted in a higher value compared to that of conventional higher temperature polyimide. These results are consistent with the assumption that at reduced pressure, water and solvent are drawn out of the bulk polymer at much lower temperatures than an atmospheric pressure cure; however, cross-linker remains in the low temperature films during the curing process.