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46 PCB007 MAGAZINE I OCTOBER 2024 Overall Reaction: Cu(EDTA)2- + 2HCHO + 4OH- → Cu + H2 + H2O + 2CHOO- + EDTA4+ Second, the manufacturing cycle time to met- allize a printed circuit board through a conven- tional electroless copper process is 45–55 min- utes. CapEx requirements aside, direct metal- lization offers faster throughput and, in turn, reduces energy costs as well as greenhouse gas laminate composites. With each incremental enhancement in materials properties, such as coefficient of thermal expansion (CTE), tem- perature of decomposition (Td), signal integ- rity, and glass transition temperature (Tg), these materials become more difficult to pro- cess. ese higher-performance materials are highly cross-linked and are more chemically resistant to processes such as alkaline perman- ganate desmear. In contrast to the carbon-based systems, conventional electroless copper requires a micro-roughened resin surface to effect suf- ficient adhesion of the copper to the resin. A precious metal catalyst (most commonly pal- ladium) is required to bring about the oxida- tion of formaldehyde (the reducing agent most commonly used in electroless copper formula- tions). Essentially, electroless copper is com- posed of two half-cell reactions, with several process steps required to provide a void-free copper deposit. In addition, during the copper plating process, hydrogen gas has evolved. e production of hydrogen gas produces bubbles that can lodge in small diameter through-holes and blind vias. If the hydrogen gas bubbles are not efficiently evacuated from the vias, plating voids will result. e overall electroless copper reaction is shown below: Figure 1: Examples of stacked vias. " If the hydrogen gas bubbles are not efficiently evacuated from the vias, plating voids will result. "