Copper electroplating for HDI and IC substrate through hole fill

Abstract

Established methods for filling through holes in core layers of HDI and IC substrates are labor intensive, multistep processes that rely on mechanical filling with epoxy or paste after conformal through hole metallization, planarization, and a cap layer of electrodeposited copper before subsequent build-up of additional dielectric layers. Additionally, the mechanical strength and thermal conductivity properties of current epoxy or paste materials used to fill through holes are sub-optimal. With recent advances in copper electroplating technology, it is now possible to completely fill through holes in build-up core layers with planar, void-free solid copper electrodeposits, while simultaneously improving mechanical and thermal properties. The use of a single copper electroplating process eliminates the separate filling, planarization and capping steps, shortening the circuit board manufacturing process. This paper describes a novel pattern-plate, Direct Current (DC) copper electroplating process designed for filling core layer through holes in HDI and IC substrates. Copper through hole fill performance for a variety of substrate thicknesses and hole diameters as a function of chemical parameters, processing variables and electroplating equipment design is discussed.