LAUSR

The mechanical/optical configuration of moiré interferometry for real-time observation of thermal deformations is advanced to quantify the thermomechanical behavior of fan-out wafer level packages (FO-WLPs). Two most notable advancements are on the: 1) mechanical front: conduction-based thermal chamber for a wide range of ramp rates with accurate temperature control, and 2) optical front: microscope objectives to observe a microscopic field of view. The advancements enable the method to document the global and local behavior of an FO-WLP while it is subjected to a controlled thermal excursion. After describing the details of two advancements, a procedure of actual testing is presented. The advanced configuration is implemented to analyze an FO-WLP in a package-on-package with and without a reworkable underfill. The results obtained from the global and local analyses are presented, and reliability implications are discussed.