Ultra-Fine Pitch Interconnects using a Novel Lift-off based Process of Thick Copper Films on Organic Substrate for Advanced Packaging

The increasing requirements of bandwidth and inputs/outputs (IOs) density for high performance computing (HPC) and artificial intelligence (AI) applications are driving the need for the development of finer copper redistribution layers (RDLs). In this paper, a novel lift-off-based microfabrication process of 2.3 μm thick copper films on organic substrate for below 10 μm ultra-fine pitch interconnects (Line (L)/Space (S) < 10 μm) is presented as a simple and cost-effective alternative to standard semi-additive and modified semi-additive processes (SAPs and mSAPs) widely used in the printed wiring boards (PWB) technology. No seed layer flash etch step is required as for the SAP process and the copper lines surface finish is ultraflat which avoids any extra copper polishing as for overburden copper in the organic damascene process (ODP). As such, the developed process is suitable for both high density RDLs on package for advanced packaging as for integrated RF/mm-wave packages.