An underfill encapsulant was used to fill the gap between the chip and substrate around the solder joints to improve the long-term reliability of flip chip interconnect system. The underfill encapsulant was filled by the capillary effect. In this study, the filing time and pattern of the underfill flow in the process with different bumping pitch, bump diameter, and gap size were investigated. A modified Hele-Shaw flow model, that considered the flow resistance in both the thickness direction and the restrictions between solder bumps, was used. This model estimated the flow resistance induced by the chip and substrate as well as the solder bumps, and provided a reasonable flow front prediction. A modified model that considered the effect of fine pitch solder bumps was also proposed to estimate the capillary force in fine pitch arrangement. It was found that, on a full array solder bump pattern, the filling flow was actually faster for fine pitch bumps in some arrangement. The filling time of the underfill process depends on the parameters of bumping pitch, bump diameter, and gap size. A proposed capillary force parameter can provide the information in bump pattern design for facilitating the underfilling process.
All Science Journal Classification (ASJC) codes
- Electrical and Electronic Engineering