Demonstration of 20 μm I/O pitch RDL using a novel, ultra-thin dry film photosensitive dielectric for panel-based glass interposers

This paper demonstrates, for the first time, a high density, low cost redistribution layer (RDL) stack-up using a novel, ultra-thin dry film photosensitive dielectric material for panel scale 2.5D glass interposers and fan-out packages. The salient features of this semi-additive process based RDL demonstrator include : (1) A two metal layer RDL structure with integration of 5 mu m microvias at 20 mu m pitch and escape routing of 2 mu m Cu traces at 4 mu m pitch. (2) 5 mu m microvias fabricated using low cost i-line 365 nm UV photolithography process in ultra-thin 5 mu m dry film photosensitive dielectric. The new photosensitive dielectrics, IF4605 (5 mu m thick) and IF4610 (10 mu m thick) in discussion, are primarily epoxy polymer based dry films. Epoxy resin is the standard polymer dielectric used in conventional package substrates today. Also, IF films have low dielectric constant and low curing temperatures as is the case with conventional epoxy dielectrics. This paper will demonstrate a multi-layer RDL stack with IF dry film for 20 mu m I/O pitch interposers or fan-out packages. The panel based sputtering approach will be used to deposit Ti and Cu as the barrier and seed layers respectively. This also ensures high yield and reliability of the fine pitch Cu traces. The reliability of fine pitch Cu photovias are currently being evaluated for thermal cycling tests (TCT). Initial results are presented in the paper.