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100 DESIGN007 MAGAZINE I OCTOBER 2021 • SAP: Semi-additive process, adopted from IC fabrication practices • SLP: Substrate-like PCB, a PCB using mSAP or SAP technology instead of subtractive etch technology While semi-additive processes are com- monly used in IC substrate fabrication, they are a new process to the PCB fabrication com- munity. As this technology is adapted to and integrated into PCB manufacturing, this has the potential to fill a gap between IC fabrica- tion and PCB fabrication capabilities. In an arguably overly simplistic light, IC manufac- turing processes are limited in overall panel size, and subtractive etch PCB fabrication is limited in line width and spacing capabilities. Blending these two worlds brings finer feature sizes to the PCB design community on larger panels (and lower cost) than IC fabrication allows. To add a little color to the difference between SAP and mSAP in a PCB manufac- turing environment, both SAP and mSAP processing start with the core dielectric and a thin layer of copper. A common differentiation between the two processes is the thickness of the seed copper layer. Generally, SAP process- ing begins with a thin electroless copper coat- ing (less than 1.5 mm) and mSAP begins with a thin laminated copper foil (greater than 1.5 mm). ere are multiple ways to approach this technology and decisions can be based on vol- ume requirements, costs, capital investment needed, and process knowledge. Two recent events highlighted this process: A webinar with PCEA's Orange County chapter where American Standard Circuits and Aver- atek presented on ASC's newly installed A-SAP process (Averatek's semi-additive process) and via fill options; and an SMTA-hosted session on additive electronics, which provided infor- mation from IDTechEx on the state of addi- tive electronics and an open discussion polling audience members to structure the technical program for February's Additive Electronics TechXchange being hosted in San Jose. I am inspired by the discussion at both events and extremely interested in the questions that are being asked as people familiarize themselves with these new technologies and the impacts of finer feature sizes on PCB design. It is intuitive to first look at the obvious advantages to increased circuit density: over- all size reduction, potential layer count reduc- tion, potential microvia layer reduction, and lamination cycle reduction, just to get started. Beyond this, there were some common questions bubbling up from those curious attendees: • What is the peel strength of additive copper compared to traditional laminate? • What materials are these processes compatible with? • Can these additive processes come from plated through-holes or only build-up construction? • Can additive layers and subtractive layers be combined in the same stackup? • Can additive processes and subtractive processes be used on the same layer? • Who is currently implementing these processes in their PCB manufacturing locations? • Can you use via-in-pad-plated-over technology with additive traces? As this technology is adapted to and integrated into PCB manufacturing, this has the potential to fill a gap between IC fabrication and PCB fabrication capabilities.

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