Copper Filling of Blind Microvias and Through-holes Using Reverse-pulse Plating

Estimated reading time: 1 minute

Abstract

This article describes the different techniques of via filling and their characteristics. It points out the advantages of reverse pulse plating and how the technology has been modified to approach new market requirements such as thicker core substrates and laser drilling of through holes. The current capability of the system for inclusion-free filling and the areas where development is ongoing is demonstrated.

Introduction

Laser drilling of blind microvias (BMVs) and subsequent copper filling has become the standard manufacturing technique for high density interconnects. To reach the required interconnect density and to provide the necessary surface for reliable solder attachment in IC packaging, copper-filled BMVs are used. For smartphone production, the use of multiple lamination and typically 10 layers of stacked copper BMV filling is now the preferred technology. This is also known as the “any layer” filling process. To maintain the development in circuit miniaturisation together with the reduction in overall processing costs as expected by Moore’s Law and to meet the demand for ever more filled BMVs on each plated layer, advances in filling processes are required.

Via Filling Process

Copper plating and filling can be described as shown in Figure 1.

Capture pad is the connection area of a surface feature to the inner layer beneath. Recess describes the remaining non-copper filled area on top of a copper filled feature (trench, microvia, through-hole) in relation to the copper plated on the board surface. Inclusions are non-copper filled voids within PCB features.

The filling of blind microvias without additives (normal deposition) will usually lead to the formation of a void. Copper is deposited until the via is closed, but without additives less copper is deposited inside the BMV than on the surface and voids may occur. Read the full article here.Editor's Note: This article originally appeared in the May 2014 issue of The PCB Magazine.