Heat transfer analysis in the thermal compression bonding for CoW process

We report the results of heat transfer analysis of CoW (chip on wafer) process in which IC chips are bonded on a Si wafer by using thermal compression bonding (TCB). The throughput can be remarkably improved because a lot of chips can be pre bonded on a wafer by using non-conductive film (NCF) which is pre-applied adhesive and can be thermally pressed at a time. However, to realize this process, it is necessary to reduce the heat influence on adjacent chips and to suppress the heat conducting to a substrate from the bonding head. In this research, we analyzed the temperature distribution in NCF layer, and the behavior of heat conduction from the bonding head to the adjacent chips. As a result, it was found that thermal influence on the adjacent chips was small in the case of thin substrate but the bonding temperature also decreased, especially in peripheral part of NCF layer. In addition, we proved that it is possible to prevent the reduction of the bonding temperature with heat insulation stage, and to decrease the thermal influence to adjacent chips by using air cooling system.