Methods of underfill flow voids detection and minimization in flip chip package

Rheological properties of underfills were measured at dispensing temperatures. The surface energy of different substrates and wetting angles of underfills on the substrates were also measured and showed differences between different substrates. It was observed that the viscosity of an underfill and substrate wetting have a strong impact on the formation of flow voids. A video underfill flow metrology was developed for flow void observation. The correlation between underfill, substrate properties, and flow voids formation based on. the video flow metrology measurement will be discussed. We will also discuss how to optimize the underfill and substrate properties to minimize the flow voids.