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52 PCB007 MAGAZINE I FEBRUARY 2022 Additive, Semi-Additive, and Subtractive Fabrication Introduction Is seems the operative word today is additive circuit board manufacturing, or for that matter, additive for everything. It is true that the use of additive manufacturing technology has found its way into different industries. While there may be several advantages to adopting additive technology in various industries, one should take a step back and truly assess where we are today in relation to conventional and advanced printed circuit board technology. It makes sense to understand the differences between fully additive, semi-additive, modified semi- additive (mSAP) and subtractive. In the end, there are several options available to the fab- ricator and OEM to achieve high density and ultra-density circuitry to support higher end technologies, including IC substrates. Overview In my opinion, there is much confusion with respect to additive fabrication for printed cir- cuit boards. Well over 45 years ago, there was full build (or "fully additive") circuit technol- ogy. One could employ a special pre-catalyzed substrate and build up the circuity with an electroless copper process. However, the cir- cuitry would still need to be formed via sub- tractive process. Predating the full build electroless process was the CC4 technology. A microroughened substrate was coated with a metal catalyst, then plated to 25-plus microns over an approx- imately 24 hour period. With respect to advanced packaging, where designs require ultra-fine line interposers and substrates, achieving HDI designs that require Trouble in Your Tank Feature Column by Michael Carano, RBP CHEMICAL TECHNOLOGY

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