Study of Bondable Laser Release Material Using 355 nm Energy to Facilitate RDL-first and Die-first Fan-Out Wafer-Level Packaging (FOWLP)

A thorough evaluation on selecting a bondable laser release material for RDL-first and die-first FOWLP is presented in this paper. Four laser release materials were identified based upon their absorption coefficient at 355 nm. Additionally, all four of these materials possess thermal stability above 350°C and pull-off adhesion on a Ti/Cu layer greater than 8 psi, further illustrating their compatibility in FOWLP. To further evaluate these materials, focus ion beam (FIB) inspection was used to examine the profile of a single-pulse laser ablation region, ensuring free penetration of 355 nm laser energy. With a designated die bonding test vehicle, die shift less than 1.5 μm and rotation less than 0.02° before and after molding was achieved with the material bondable at temperatures lower than 200°C. Furthermore, this same material required laser energy of less than 3 W for laser release. A bondable laser release material that eliminates the requirement for a die attach material from the traditional process flow facilitates the development of cost effective FOWLP.