Issue link: https://iconnect007.uberflip.com/i/1453746
22 PCB007 MAGAZINE I FEBRUARY 2022 HDI—Why Direct Metallization? In conventional PCB multilayer, the pri- mary metallization step is utilized once all innerlayers of the board have been laminated and drilled and the board is nearing comple- tion. e microvia structure is the central fea- ture of HDI that allows for the manufacture of high-density circuit boards today. e micro- via essentially replaces the singular through- hole that connects multiple layers and allows individual layers to be routed to their neigh- bors directly and separately from other lay- ers. To achieve this feat of engineering, how- ever, 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 scru- tiny from a reliability perspective. Yet, as we will discuss shortly, the sustainability question has not been widely examined. is is impor- tant since the volume of boards in the indus- try 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 cir- cuit density. With increasing volumes of PCBs being manufactured with HDI, there will be an even faster increase in the volume of boards passed through some form of primary metallization. For 2021, Prismark estimated that the total amount of board surface area considered to be microvia type designs (HDI PCB and package substrate) was in the range of 3 million square meters, while for all multilayer boards this was approximately 16 million square meters. Yet the amount of volume that passed through pri- mary metallization lines in 2021 for these HDI designs was likely something closer to 15 mil- lion square meters if one assumes an aver- age of five build-up steps per board design. is is because, while a 12-layer multilayer board would only need a single pass through an electroless copper line to create the plated through-hole that connects all layers at the end of construction a 12-layer, any layer HDI board would need to pass through the same electro- less copper process five-plus times by the end of the construction. is begs questions about sustainability and supply: Can we create an ever-increas- ing amount of printed circuit boards with HDI technologies such as mSAP while also meet- ing increasingly strict targets for carbon miti- gation, while also meeting profitability expec- tations? Comparing Electroless Copper and Direct Metallization From a Sustainability Viewpoint So, where do electroless copper and direct metallization stand when compared side-by- side on sustainability? We will now break down Figure 2: The resource-intensive primary metallization step is required for each additional build-up layer during HDI manufacturing.