CHALLENGES OF BALL-ATTACH PROCESS USING FLUX FOR FAN-OUT WAFER/PANEL LEVEL (FOWLP/PLP) PACKAGING

摘要

In recent years, fan-out wafer level packaging (FOWLP) or panel level packaging (FOPLP) has become a popular packaging technology used in the semiconductor industry due to its many potential advantages (such as cost reduction) when compared to conventional flip-chip packages and alternative forms of heterogeneous device integration, such as system-in-package. The industry is using 300mm wafers, or even larger panels or glass, as reconstituted carriers. One of the key challenges of using these substrates is warpage of the reconstituted carrier. Typically, the last stage of the FOWLP manufacturing flow is the ball-attach or bumping process before package singulation. For the ball-attach process, flux is usually printed on the reconstituted carrier, and spheres are dropped onto the flux, then reflowed and cleaned. Due to the warpage of the reconstituted carrier, choosing a flux with appropriate properties is important for improved yields. Different aspects of flux properties will be explored in this paper.New materials are being investigated for different types of FOWLP, with different redistribution layer materials, low K dielectrics, passivation layers, solder resists, etc. The compatibility of fluxes with these materials is being studied in order to eliminate delamination caused by flux interaction during the ball-attach process or subsequent cleaning or reflow processes. Pad surface finishes and conditions are also being investigated to determine how they affect the wetting (solderability) of the solder spheres.