Effect of Pneumatic Curing on Cycle Time Reduction and Void Suppression of Polyimide Wafer Coating

In this article, the polyimide formation at high pressure for advanced assembly technology is reported for the first time. Polyimides are formed in a pneumatic oven for evaluation of voids and cycle times. For comparison and production evaluation, the polyimides were fabricated by curing photo-definable aqueous developers with different recipes and batches of wafers, respectively. For the recipes in the pneumatic oven, instead of the multistep thermal cycles, the ramp-up time and curing time could be reduced drastically to enhance the production throughput. Furthermore, as shown in optical microscope (OM) results, no void was found for the pneumatic oven samples, and lots of voids were detected for the normal oven ones. This innovation enables manufacturers to reduce 36% of process cycle time. The polyimide cyclization rate was estimated from the signal strength ratio by using Fourier-transform infrared spectroscopy (FTIR). The thermal stability by using a thermogravimetric analyzer (TGA) and the glass transition temperature by thermomechanical analysis (TMA) was analyzed to clarify the properties of the polyimides for these recipes. The results show no obvious difference is observed between pneumatic cured polyimides and normal-oven cured ones. Mechanical strength and outgassing were enhanced for the pneumatic-oven samples and no oxidation was found after pneumatic curing due to the well-controlled oxygen content of the oven.