Silver Paste Transferability During Imprinting Using PDMS Replica Mold

The minimum pitch for flip-chip bonding is limited by the difference in the thermal expansion coefficient between the chip and substrate, which is approximately 40 microns when solder is used for the bumps. This problem can be greatly alleviated by using conductive paste on the bumps and bonding the chips together at low temperatures. Bumps made of conductive paste are usually formed by screen printing. On the other hand, using the imprint method, it is possible to form bumps and wiring with a narrow pitch and high aspect ratio. In addition, replica molds can be repeatedly used to reduce processing costs. To use the replica mold repeatedly, the silver paste embedded in the recessed pattern of the replica mold during imprinting must be completely transferred to the substrate, and the initial state of the replica mold must be kept constant. It was confirmed that complete transfer of the silver paste was possible without using the UV curing function by adopting a PDMS replica mold and setting a sufficient load application time.