29.1 INTRODUCTION

The reality in printed circuit evolution is that the parts are continuing to increase in degree of difficulty and complexity. A new genre of high-density interconnect (HDI) boards is making the transition from leading edge to mainstream. These boards are characterized by combining a series of complexity features that include buried and blind vias, high-aspect ratio plating, small-hole plating (as low as 6-mil-diameter holes), and fine lines and spaces side by side with ground plane areas of different sizes.

The industry still has a need to produce simpler product, single-sided, and double-sided boards; these are still in demand. Lower-layer-count (4 to 6), multilayer boards fall in this category also.

This chapter will focus on all aspects of electroplating. Emphasis will be on acid copper plating as the main process for providing interconnection. Tin, tin/lead, nickel, and gold electroplating will also be covered as important plated materials. In addition, the latest innovations in technology for meeting the challenges of product complexity, such as pulse plating and horizontal conveyorized plating, are discussed in detail.

29.2 ELECTROPLATING BASICS

Electroplating is the production of adherent deposition of conductive surfaces by the passage of electric current through a conductive metal-bearing solution. The rate of plating depends on current and time and is expressed by Faraday s law:

(29.1)

where<i class="emphasis">W</i> = metal, g<i class="emphasis">I</i> = current, A<i class="emphasis">t</i> = time, s<i class="emphasis">A</i> = atomic weight of the metal<i class="emphasis">n</i> = number of electrons involved in metal...