Versatile laser release material development for chip-first and chip-last fan-out wafer-level packaging

Fan-out wafer-level packaging (FOWLP) has evolved from chip-scale packaging to be one of the enablers of heterogenous integration through chip-first or redistribution-layer (RDL)-first processes, which draw significant momentum in packaging industries to develop newer and better materials. Among all of the essential packaging materials currently being investigated, novel laser release materials are of particular interest because they are vital to the successful separation of reconstituted wafers and glass carriers. Thus, the thermal, chemical, and mechanical stability of the laser release material play a vital role for success in FOWLP integration. In this study, four laser release materials with UV-light absorbance were evaluated through experiments divided into two phases to select a champion material for chip-first and RDL-first FOWLP integration. Phase I consisted of the collection of material properties and characteristics including light transmittance, interaction with laser energy, thermal stability, adhesion, and melt rheology to determine compatibility with RDL-first and chip-first processes, respectively. In Phase II, all candidate laser release materials were introduced to a short-loop evaluation that started with a laser release material coating on 300-mm glass carrier with a coefficient of thermal extension (CTE) of 8 ppm/°C, followed by 50-nm titanium deposition, 100-nm copper deposition, and 6-μm dielectric material coating before encapsulation with 300-μm epoxy molding compound. Multiple 355-nm laser powers that created different diameters of effective ablation region inside the crater, were used to determine the sensitivity of each candidate material. Meanwhile, chips sized 10 mm x 10 mm x 725 μm, were picked and placed on coated glass carriers with candidate laser release materials to evaluate the compatibility with the chip-first process. Finally, design of a die bonding experiment was used to summarize the optimal conditions of a laser release material, proved compatible with RDL-first in advance, for a chip-first process. Through the comprehensive material evaluation discussed in this study, optimal laser release materials for the RDL-first and chip-first processes are identified. Of particular interest are materials that possess both laser release properties and good adhesion, since their use in die bonding applications will enhance throughput and lower the cost of ownership for FOWLP.