Independent of the underfill, which factors affect the flow of underfills?
Factors that may affect underfill flow include the substrate and the flip chip configuration. The cleanliness, uniformity, or surface energy of the substrate surface may affect underfill flow. Full array and staggered full array are easier to underfill than unique/mixed and peripheral array. More bumps provide more surface for capillary action, so depopulated areas are more prone to voids.
