Assembly process issues in integrating commercial reflow encapsulants into flip chip assembly

Reflow encapsulants introduce an alternative way to assemble flip chips other than the conventional use of flux spraying. Reflow encapsulants combine both the fluxing and underfilling, and are applied outside the placement machine, improving throughput and reducing manufacturing cost. During reflow soldering, some reflow encapsulants fully cure and therefore eliminate the post-curing process, thereby further reducing the manufacturing cost. Reflow encapsulants also eliminate the need for a nitrogen atmosphere during reflow. There are many reflow encapsulants that are being sold commercially today. Although there are advantages associated with the use of reflow encapsulants, these materials introduce new issues to the assembly process. This paper discusses some of these issues in evaluating current commercial reflow encapsulants. Various reflow encapsulants from several vendors were used to build flip chip assemblies. The reflow encapsulants were evaluated for the effect of various process parameters, and their compatibility with the SMT assembly process. The process parameters included the placement force and hold time, and reflow profiles with various temperature settings and durations