Accurate numerical simulations of capillary underfill process for flip-chip packages

Abstract

In the capillary underfill packaging process, resin with specific characteristics such as low viscosity, high flowability, fast curing, and high reliability is utilized to fill the gaps between the substrate and the die. This underfill resin serves to reinforce the connections between metal bumps and the substrate, thereby extending the lifespan and enhancing the reliability of FCBGA (Flip-Chip Ball Grid Array) packages. Despite the availability of flow simulation tools, the development of the underfill process remains a significant challenge for engineers due to the multitude of control parameters involved. The objective of this study is to identify the key factors influencing the accuracy of underfill flow simulations and explore potential solutions to these challenges. In this study, it is found that necessary ingredients for accurate underfill simulation need to include the following items: 1. Good flow simulation software 2. Accurately measured material properties 3. Good and fine mesh 4. Right amount of dispensed resin 5. Right timing for resin dispensing. The accuracy of the simulation is particularly affected by factors such as overflowing, resin climbing, non-uniform flow, and air trapping, which are influenced by the amount and timing of resin dispensing. By addressing these factors, this study demonstrates that accurate underfill simulation can be achieved, providing valuable insights into microscale flip-chip underfill physics. This research lays the groundwork for the development of validated models applicable to next-generation high-density flip-chip products.