An experimental study of the under-fill effects for WLCSP components

For the most recent developed BGA components, such as flip chip BGAs and wafer level CSPs (WLCSP), all are required to have reliability tests conducted before being launched into mass production. Among the mechanical stress tests for electronic components, the most commonly seen are vibration tests, bend tests and shock tests. Rarely seen is the shear test for an electronic component with solder balls mounted on the printed circuit boards. This paper discusses the effects of various under-fills on a WLCSP through a series of shear tests and bend tests. The technique is applicable to new package designs, even for those with environmentally compatible materials.