The Carbon Footprint of HDI: Direct Metallization vs. Electroless Copper

Estimated reading time: 2 minutes

Introduction
As the electronics supply chain contends with the struggles of moving out of the pandemic and into a new normal, it is increasingly obvious that a new normal will be one with sustainability and resource conservation as the top priority. Over the past year, we have seen printed circuit board manufacturers encounter challenges associated with environmental regulations, water and power outages, and pressures from the supply chain to reduce environmental footprints.  

From the perspective of a board fabricator, especially one that specializes in HDI, a highly resource-intensive step in the process of making a printed circuit board is the primary metallization step. All circuit boards that have multiple layers go through such a primary metallization, which is either electroless copper or direct metallization (DM). The main difference between a direct metallization process and the more traditional electroless copper plating process is that the former deposits a paint-like conductive coating through absorption onto the surface, while the latter deposits a copper coating from solution through chemical reduction. The DM coatings are most typically a carbon or graphite, and this kind of board manufacturing has been done reliably for nearly four decades.  

Electroless copper processes have a larger carbon footprint than direct metallization for several reasons. Compared to direct metallization, electroless copper is more water and energy intensive, has a higher variety and amount of chemical ingredients, and has higher process variation. When looking at the comparison from the perspective of HDI, the impact of all of this becomes even more critical. 

HDI—Why Direct Metallization?
In conventional PCB multilayer, the primary metallization step is utilized once all innerlayers of the board have been laminated and drilled and the board is nearing completion. The microvia structure is the central feature of HDI that allows for the manufacture of high-density circuit boards today. The microvia essentially replaces the singular through-hole that connects multiple layers and allows individual layers to be routed to their neighbors directly and separately from other layers. To achieve this feat of engineering, however, every single build-up operation that the board goes through requires an additional run through a primary metallization step.

It is for this reason that the electroless copper and direct metallization are under constant scrutiny from a reliability perspective. Yet, as we will discuss shortly, the sustainability question has not been widely examined. This is important since the volume of boards in the industry that use microvia designs is as high as it has ever been and will continue to grow to meet the needs of any electronic design that can economically benefit from increased circuit density.

Can we create an ever-increasing amount of printed circuit boards with HDI technologies such as mSAP while also meeting increasingly strict targets for carbon mitigation, while also meeting profitability expectations?

To read this entire article, which appeared in the February 2022 issue of PCB007 Magazine, click here.