UV laser releasable temporary bonding materials for FO-WLP

Temporary bonding/de-bonding (TBDB) technology in a FOWLP process is required to adapt to a low temperature process because of the potential for damage in handling the thin molded compound embedding dies. We have developed laser releasable TBDB materials for low temperature bonding processes that enable UV laser release with high throughput and low thermal/mechanical stress. The developed TBDB materials consist of two layers, an adhesive layer and a release layer. The appropriate wafer bonding temperature can be controlled by the molecular weight of the polymer which is the main component of the adhesive material. Good bonding property has been seen, even at 160°C by adopting the lowest molecular weight polymer. On the other hand, the release layer material exhibits excellent stability that allows for fabrication of RDLs directly onto the layer to give a stacked structure in the Chip-last (RDL-first) method. The laser energies preferred for wafer release processes are 130 mJ/cm
²
for a 308 nm excimer laser and 190 mJ/cm
²
for a 355 nm YAG. These materials will be promising for advancements of FO-WLP applications.