Laser Debonding Enabling Ultra-Thin Fan-Out WLP Devices

Fan-out packaging is an established technology for many mobile applications. Whereas early semiconductor packages have been single-chip packages, the continuing trend of expanding the wiring surface to support increased functionality has led to more complex packages, stacked packages, systems in package as well as high-performance packages. With this development, fan-out technology is bridging a gap between cost-competitive packaging and high performance. For all aforementioned packages, temporary bonding will be needed, either to enable the thinning of wafers to address the need for smaller form factors, to achieve cost savings on mold materials or to serve as a processing platform for redistribution-layer (RDL) first processes. Especially package thicknesses are playing a major role in consumer and hand-held applications where stacking of chips on a packaging level is becoming more and more important. In order to process thin wafers with a high yield, temporary carrier technologies are needed on a package level, where laser debonding is the most promising debonding technology for FOWLP in terms of cost, universal usage as well as performance needs.To limit the thermal input associated with debonding, a UV diode-pumped solid-state (DPSS) laser is used for debonding. The main advantage of such laser type is the high reproducibility, high pulse frequency and most importantly the high absorption rate of materials leading a photochemical-dominated debonding process. Most commercial as well as R&D adhesive materials feature efficient laser debond layers, that allow to be integrated and combined in different thicknesses and adhesive stacks. Analyzing laser debonding for FOWLP devices involves several parameters of testing. First of all the absorption of the material stack has to be optimized to guarantee no light penetration on the device layers. Another key performance parameter is the debonding mechanism, which could be photo-thermal or photo chemically dominated, defining the residue lever or carbonization of the material along with the interface strain behavior during debonding. Furthermore, delamination force as well as resulting roughness after debonding are still of interest for high device yield. A successful debond is characterized by delamination between carrier wafer and device wafer with lack of carbonization, therefore the degree of carbonization is evaluated in dependence of the specific process parameters like radiant exposure and beam overlap for different adhesive systems.