Forming a Vertical Interconnect Structure Using Dry Film Processing for Fan Out Wafer Level Packaging

In this study dry film photoresist material is employed to fabricate thicker Cu pillars and solder interconnects. The development of the dry film photoresist process for forming 200 μm thick copper pillar were introduced. Several experiments were conducted to find the optimized process parameters for the dry film photoresist. A Laminator was adopted to laminate the dry film. The lamination temperature was 110°C on the top roll and 65 °C on the bottom roll are controlled. And the pressure was 20 psi. Lamination speed was about 2 FPM. For pattern with 200 μm thickness and 150 μm pitch Cu pillar, optimized exposure dose and developing time were 400 mJ/cm2 and 20 minutes respectively. Cu plating was performed on developed wafers and dry film photoresist was stripped using spray developer tool. Results show good performance for 200 μm copper pillar with flat surface and no dry film photoresist residues.