Understanding Underfill Degradation in Reliability Testing Conditions for ADAS Package Development

Harsh advanced driver assistance systems (ADAS) user conditions lead to stringent reliability requirements for electronic packages. In order to develop packages that meet ADAS reliability target, it is necessary to not only have highly reliable packaging materials but also create quick turn monitor (QTM) materials screening processes to facilitate the development cycle. In this paper, we used underfill as an example to demonstrate that material degradation in reliability testing conditions is an important modulator for underfill performance. It was found that one of underfill materials in our study experienced significant fracture toughness degradation after temperature cycling or high temperature bake; and the toughness degradation explained the poor package level reliability performance. The root cause of fracture toughness degradation is found to be the thermal degradation of polymer resin in reliability conditions. Further fundamental study revealed that fracture toughness/thermal degradation could be attributed to the thermal stability of the raw material structures. It is demonstrated that the characterization of the properties of packaging materials post temperature cycling/high temperature bake can be used as a QTM for material screening. The QTM offers more than three times improvement in data turns and allows for faster materials screening without the need for extensive package level experiments.