A pyrolysis-based technology for recovering useful materials from IC package molding resin waste

This paper describes a pyrolysis-based technology for recovering useful materials from molding resin waste, which is the main type of thermosetting plastic waste generated in the fabrication of IC packages. In our pyrolysis of molding resin waste, the main impurities in the recovered silica were carbon (C), antimony (Sb) and phosphoric acid ion (PO₄³). The amount of carbon and phosphoric acid ion decreased with increased heating temperature and oxygen concentration. However, the antimony remained constantly between 400 and 1000°C because diantimony tetraoxide (Sb₂O₄), which is hard to volatilize, was formed by oxidation. Our experimental results suggest that the most effective way to reduce the impurities is to heat at between 1000-1100°C and to keep oxygen concentration at about 8 vol%. On the basis of these results, we used a roller kiln type furnace as a prototype practical pyrolysis system for recovering high purity silica. The purity achieved was as follows: C<100 ppm, Sb<1000 ppm, and PO₄³<20 ppm, pure enough to be used as inorganic filler for cast insulating materials. The combustion exhaust gas generated by pyrolysis of the molding resin waste was decomposed by a secondary combustion method which was found to decrease organic brominated substances to a sufficiently safe level, and also, to convert the antimony tribromide to diantimony trioxide, which can be collected by a dry recovery process at a high recovery rate and at a useful purity