Authored By:
Evan Griffith
Indium Corporation
NY, USA
Sam Lytwynec
Indium Corporation
NY, USA
Summary
In the advanced packaging space, fan-out wafer level packaging (FOWLP) and fan-out 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 other heterogeneously integrated packages. 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, 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.
This paper will discuss advantages of advanced ball-attach materials developed to meet the challenges of advanced packaging. First, the compatibility of these ball-attach materials with passivation materials will be discussed, with advanced materials overcoming the inherent CTE mismatch causing warpage. Next, advancements in printability of ball-attach fluxes will be discussed, with long working time being a key attribute in the assembly process. Finally, the wetting of these materials will be discussed, with a particular emphasis on consistent wetting with minimal ball movement on all areas of the package.
Conclusions
In this paper, novel ball-attach fluxes were discussed with the parameters which are important to the assembly of advanced packages. Three ball-attach fluxes were tested side-by-side with each other, with each having mostly similar results. A novel no-clean ball-attach flux was also discussed and its relevant parameters were tested. The benefits of this material as an alternative ball-attach assembly solution were highlighted. Future work will be conducted on the printability of the NC ball attach flux solution to ensure applicability is not a problem.
Initially Published in the SMTA Proceedings
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