Methodology to evaluate pre-applied underfill materials with concurrent flux capability for ultra-fine pitch solder-based interconnects

This work describes a methodology and a test structure to evaluate next generation pre-applied underfill materials with concurrent flux capability for ultra-fine pitch solder-based interconnects. This simple test vehicle consists of Sn-solder micro-bumps with diameters less than 10 μm. The micro-bumps reflowed to form spherical balls when heated in reducing environments. The micro-bumps are used to evaluate the concurrent flux capability of two pre-applied underfill materials. Thermosetting temperatures and viscous behavior of the pre-applied underfill materials were measured by differential scanning calorimetry (DSC) to understand the flow response of the Sn-solder micro-bumps. X-ray tomography was evaluated using this test vehicle as a technique for monitoring the bump interface through a full thickness Si wafer and underfill material.