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Ultrathin WLFO - How thin can you go with which processes?
Keywords: Fan-Out WLP, Thin Package, Active Interposer
NANIUM’s Fan-Out Wafer-Level Packaging technology WLFO (Wafer-Level Fan-Out)is based on the embedded Wafer-Level Ball Grid Array (eWLB) technology of Infineon Technologies/ Intel. Since it´s invention almost 10 years ago, it became the leading technology for Fan-Out Wafer-Level Packaging (FOWLP) with over 80% market share in the Embedded Packaging Market. It is well known that WLFO enables the shrink of the x-y footprint of system-in-package through flexible, very dense, heterogeneous system integration. This also comes already at a lower package height (z) compared to wirebond and FlipChip package solutions as WLFO package is a substrate-less active interposer. But WLFO allows for further reduction of the overall package height. A total package height for a Ball Grid Array (BGA) package below 500um (including solderballs) is currently achievable, and below 300um for a Land Grid Array (LGA), or BGA with semi-solderballs. NANIUM´s technology roadmap includes further reductions to even lower values. Two separate approaches to WLFO package thickness reduction will be presented in this paper. 1) Processing a thicker than final package body thickness reconstituted wafer, followed by heterogeneous wafer thinning of moldcompound and die to the desired final package thickness. The initial thinning may be performed in standard wafer backgrinding equipment with the only modification required being specialized grinding wheels. The result of this thinning process may be further enhanced by Chemical Mechanical Polishing (CMP) of the bare die backside to remove fine grind lines. The singulated components may be delivered with the bare die backside exposed, or with backside protection tape (BSP) as it is typically applied in Fan-in WLP/ WLCSP, a heat sink attached if required for enhanced heat dissipation, or a re-molded overmold backside. 2) The second approach is to mold the reconstituted wafer to the required final package body thickness already in the beginning, which requires to apply the final die thickness from the wafer reconstruction process onwards already. This required thin recon wafer handling and processing on temporary carrier through the thin-film manufacturing line. In this paper the different options will be analysed in a package force to break analysis. A full thickness (below 800um) BGA package will be included as reference. The goal of achieving the lowest possible profile for mobile end user devices is a constantly shifting one. Mobile devices in order to be successful need to have large screens, enhanced functionality, acceptable battery life, and be thin. Accompanying the evolution of one of the most popular smart phones from a large Korean cellphone manufacturer the thickness reduction has been dramatic with an overall reduction of around 35% while increasing functionality. This trend has been achieved.
Steffen Kroehnert, Director of Technology
Vila do Conde, Porto

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