Thermocompression flip chip bonding optimization for pre-applied underfill

Thermocompression (TC) flip chip (FC) bonding enables packaging of the most advanced semiconductor devices by allowing finer pitch and higher I/O interconnect while minimizing warpage and stress on low-K dielectrics [1, 2] Adoption of thermocompression bonding is accelerating, especially in the high-end memory devices such as Hybrid Memory Cube (HMC), High Bandwidth Memory (HBM) and Wide I/O 2. In these Through-Silicon-Via (TSV) stacked die devices, thermocompression bonding is the only option that allows exceptionally short die-to-die interconnects and the associated device performance improvements. Interest in die-to-substrate bonding is also increasing for high-end applications processors and graphics processors. Especially for thin die stacks, i.e. memory stacks, the use of a pre-applied Non-Conducting underfill Film (NCF) to provide stress relief and package reliability is very attractive. One of the challenges has been somewhat low throughput, in particular because of large bondhead temperature excursions forced by a requirement for sub 100°C temperatures during the transfer of the die to the bondhead. This paper focusses on the method of optimizing NCF processes and introduces a novel method for avoiding the low handover temperature. The results show the ability to reach very high UPH and attractive cost-of-ownership for an NCF process.