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84 PCB007 MAGAZINE I JANUARY 2022 e semi-additive processes (SAP) are not new. I first used them with a novel process back in 1978. MacDermid had a novel SAP process called PLADD II (plated additive). It was an anodized aluminum foil applied to lam- inates that we could easily etch off aer drilling and continue with a special electroless copper for thin metallization. In his Tech Talk column, Karl Dietz wrote about SAP many times from 2000 to 2010. 1-5 In a 2010 column, Karl included a table (Table 1) to show the relationship between copper thickness, resist thickness, and resolution capabilities of processes. 5 Karl devoted many Tech Talks to "fine-line imaging" and to related Semi-Additive Processes and Heterogeneous Integration topics such as photoresist adhesion, develop- ing, fine-line etching, stripping, and pattern plating. Semi-Additive Processes e older mSAP processes used thinned copper, usually to nine or five microns, from half-ounce foil or very thin copper foil (usually with a peelable protection). ey would usu- ally have a flash copper strike and may use tin plating as the etch resist. e IC substrates (for flip-chips) were always the leading edge of this technology, from 2005 onward, but quickly converted to the use of the Ajinomoto build-up film (ABF) from Japan Happy's Tech Talk by Happy Holden, I-CONNECT007 Table 1: Relationship between copper thickness, resist thickness, and resolution capability of process. 5

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