Effects of Underfill Materials and Thermal Cycling on Mechanical Reliability of Chip Scale Package

The thermomechanical reliability of chip-scale packages (CSPs) with various underfills was evaluated by measure the electrical resistance under thermal shock and four-point bending fatigue tests. The underfill containing cycloaliphatic-type epoxy resin had lower resistance than without cycloaliphatic-type epoxy resin under thermomechanical fatigue test because the cycloaliphatic-type epoxy resin was able to mechanically relax more than the other types. The lifetimes of the CSPs under thermomechanical fatigues were strongly dependent on the properties of the underfill.