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Design007-Sep2024

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36 DESIGN007 MAGAZINE I SEPTEMBER 2024 Welcome to the next step in the manufactur- ing process—the one that gets the chemical engineer in all of us excited. I am referring to outer layer imaging, or how we convert digital designs to physical products. On a recent epi- sode of I-Connect007's On the Line with… pod- cast, we explained how the outer layer imaging process maps the design's unique features onto the board. At this point, the boards have gone through the electroless copper process. ey are primed and ready for us to apply the photo image to the external layers, physically transferring the digital copper image of the design to the outer layer. Every component of the design layout—from pads to through-hole pads, trace routes, and ground fill—goes onto the manu- facturing panel. Designing for Reality: Outer Layer Imaging is transition from digital to physical is where the designer's IP meets the board. Dry Film vs. Liquid Photoimageable (LPI) Once the surface is prepped, we apply the photoresist to the board. It is the mechanism that will accept the digital design and physically create it on the panel. ere are two applica- tion methods available: dry film, and imaging using an LPI polymer that is like a solder mask. Dry film is a thin layer of polymer, usually blue or purple. It comes in rolls like Saran wrap, and it's applied with heat and pressure. When unwinding the roll, it physically lami- nates on the surface of the panel. is results in a uniform—usually a 2.3 mil—photoresist. Dry film is more forgiving and more uniform in thickness, but that thickness can limit some Connect the Dots by Matt Stevenson, ASC SUNSTONE CIRCUITS

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