Electroplated Copper Filling of Through-holes: Influence on Hole Geometry


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Abstract

This paper discusses a through-hole copper filling process for application in high-density interconnect constructions on thin IC and LED substrates where high reliability and thermal management are essential. The process consists of a two-step acid copper plating cycle. The first step utilizes periodic pulse reverse (PPR) electroplating to form a conductive copper bridge across the middle of a through-hole and is followed by direct current electroplating to fill the resultant vias formed in the bridge cycle.

The ability of the process to fill a variety of through-hole sizes on substrates of varying thickness while minimizing the overall surface copper build-up are critical in applications requiring efficient thermal management as circuit miniaturization continues.

The through-hole fill technology and factors that affect its performance such as substrate thickness and through-hole diameter will be presented in this paper.

Introduction

Resin or paste plugging of through-holes in cores has been a part of build-up technology, especially in IC substrate construction, for many years. Technological advances encompassing increased circuit density and stacked via construction, coupled with higher power devices, have added an extra dimension of thermal management where a copper filled through-hole becomes advantageous (Figure 1).

Advantages of copper filled through-holes include:

  • Reduction in CTE mismatch of resin/paste plug
  • Stable platform for stacking microvias
  • Solid pillar structure within through-hole
  • Lower likelihood of adhesion failure on the plated-over filled via
  • High thermal conductivity of copper

New technologies were developed to completely fill through-holes and vias in build-up core layers in HDI and IC substrates with solid copper. Among the approaches for filling through-holes in a thin core board with copper was DC plating.

To read this article which appeared in the January 2017 issue of The PCB Magazine, click here.

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