Advances in Fast Underfill of Flip Chips
Advances in Fast Underfill of Flip Chips
Alec J. Babiarz and Horatio Quinones
Asymtek, 2762 Loker Avenue West, Carlsbad, CA.
760-930-3311
Abstract：
One of the barriers to mainstream use of flip chips was the underfill process. The time required for capillary flow out of the underfill was perceived as a process bottleneck in the production line. Consequently, flip chips have been used when the performance and other cost considerations allowed no other alternative. Recently there have been advances in the underfill processes that allow faster throughput. A combination of new materials, dispensing patterns, and high capacity equipment can reduce flow out times such that the machine dispensing times completely mask flow out time thereby optimizing throughput. The correct choice of substrate temperature, material, equipment and dispense pattern can achieve flow out under a 25mm square die with 60m gap in under 35 seconds.
This paper describes the dispensing processes and equipment configurations that provide throughput optimization. Analysis confirms that capillary flow analytical models are valid for large die with small gap (LDSG). Flow out time data for LDSG with several thousand interconnections is presented. The second method of reducing flow out time being examined today is forced underfill. Forced underfill eliminates the physical flow out time constraints of capillary underfill. Over recent years there have been several patent disclosures on forced underfill processes that offer new opportunities for throughput enhancements for LDSG production. This paper provides an overview of the forced underfill process.
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