Issue link: https://iconnect007.uberflip.com/i/1453746
FEBRUARY 2022 I PCB007 MAGAZINE 23 between each chemical processing step. Due to the number of chemical steps in a standard electroless copper line (more than seven), and the nature of the chemicals (heavy metals, che- lators, catalysts), there are typically at least seven cascade rinse tanks in a single line. Even in large double pass DM lines, which are utilized for high volume production, there are just five chemical baths and only three cascade rinses. Comparing two high output lines of around 20,000 square meters per month, a double pass DM line would use approximately 25,000 liters per day while a vertical electroless copper line would use approximately 84,000 liters per day. In August 2021, when water shortages were one of the issues seen in many areas around the globe, including the highly important island of Taiwan, the water consumption of these lines was more closely scrutinized than it had been in previous years. In Taiwan, there was a point where board manufacturers were exam- ining the possibility of having to deliver tanker water to keep operations running at package substrate and high-end PCB fabrication sites. e price difference between the industrial tap water at the time was $0.43/ton while tanker water was $14.44 per ton. Figure 4 examines what the two lines would have consumed per day should the situation have progressed to the one described above. these two processes on their merits from this perspective, provide some examples of where these would have met real world issues over the last year, and estimate the carbon footprint of the primary metallization process in PCB manufacturing. Direct metallization is a more sustainable primary metallization process than the traditional electroless copper primary met- allization route because it uses significantly less water, power, and harsh chemicals. Water Usage Depending on the equipment and process selection, water usage varies when comparing the many ways of performing primary metal- lization. Horizontal processes use significantly less water than vertical processes because of the efficiency gained through how the boards move through the equip- ment. Direct metallization processes are almost exclusively horizontal. In vertical processing, large rinse tanks require more water in contact overall with the rack and boards, and the water that is in contact with the boards needs to be exchanged at a certain rate during each rins- ing step to ensure that the process is sufficiently cleaning the boards in Figure 3: The surface area of HDI type boards going through primary metallization processes in 2021 may have been nearly equal to that of all multilayer boards. Figure 4: Comparison of potential costs for DM vs. electroless copper during the Taiwan water crisis of 2021.