Temporary Protective Packaging for Vertical Integration of Optical-Window-Free TSV-Based Micromirror Array

Temporary protective packaging is a critical enabler to the development of micromirror array (MMA) module. Herein, aimed at the vertical integration of optical-window-free through-silicon-via-based (TSV-based) MMA and its corresponding application specific integrated circuits (ASICs), this paper proposes a temporary protective packaging method that is compatible with a series of back-end processing, including under-bumping-metallization (UBM), dicing, solder bumping and flip-chip bonding. An ultraviolet-curing (UV-curing) strippable adhesive with tolerance to water, organic solvent and high temperature is carefully selected and introduced into this temporary protective packaging method to bond caps to MMA wafer. A programmable dispenser is employed to inject the chosen adhesive into pre-fabricated trenches on MMA wafer, which enables patterning of this adhesive. In response to its contradiction between detachability and sufficient adhesion, a double-level temporary protective packaging is proposed, which is composed of wafer-level cap and die-level cap. Wafer-level cap not only focuses on adhesion to guarantee MMA wafer being sealed in UBM fabrication and to keep die-level cap free of mechanical influence before it comes into use, but also guarantees wafer profile quality in specific processing. Die-level cap focuses on its detachability, and comes into play after dicing to protect MMA in processing of solder bumping and flip-chip bonding. The effectiveness of the chosen adhesive is verified experimentally. Finally, an intact optical-window-free vertical integrated MMA module is achieved after all the back-end process and removal of die-level cap.