High-Resolution Printing of Redistribution Layers for Fan-Out Wafer-Level Packaging by using Ultra-Precise Micro-deposition Technology

Implementing Additively Manufactured Redistribution Layers (AM-RDL) for Fan-Out Wafer-Level Packaging (FOWLP) has spurred interest recently. Especially for MEMS FOWLP, where the standard fabrication of RDLs faced challenges to provide conformity to 3D topographies or protecting delicate structures, AM-RDLs can be regarded as the most promising approach. The state-of-the-art AM RDLS (e.g. inkjet printed) are lagging way behind the lithography-based ones due to inferior feature sizes (i.e. higher line/ space or high pitch interconnects). To address this bottleneck, in this study a recently-developed Ultra-Precision Deposition (UPD) technology was utilized to print high-resolution RDLs. By optimizing UPD printing parameters, such as printing pressure, nozzle size, nozzle movement and speed, ultra-fine silver (Ag) and polyimide features were extrusion printed. Here, molded daisy chain chips were used as test samples, on which ultra-fine Ag RDLs with an average width of 6.5 µm and thickness of 2.7 µm were printed successfully. Electrical test and cross-sectional analysis verified line continuity and full out-of-plane offset (Z-step) coverage at the chip/ epoxy molding compound (EMC) interface. Additionally, multilayering of printed layers for high-density FOWLP was demonstrated.