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54 DESIGN007 MAGAZINE I NOVEMBER 2024 In the previous episode of I-Connect007's On the Line with… podcast, we focused on pattern plating. At this point, we are close to completing our boards and ready for the strip- etch-strip (SES) process. By this stage of the manufacturing process, we have: 1. Laminated all the internal layers together. 2. Drilled the through-holes. 3. Applied the image to the external layers through photoresist. 4. Plated the copper in those channels to beef up the copper thickness for traces, pads, and through-holes. 5. Added a layer of electrolytic tin over the top of that copper to protect it during subsequent stages of production. Aer the tin plating, the circuit image on our panel has a matte silvery color. Areas without copper are blueish or purple in color, including channels on the board. ose blueish- purple areas mark photoresist areas. e next step in production begins with removing the photoresist. Stripping Away Photoresist Yes, we are talking about another chemi- cal process. Photoresist is acidic in nature, so we submerge/spray solution over the panels with an alkaline solution to essentially dissolve it. ere is a bit of risk to the overall finished product if the stripping process is not com- pleted correctly. During pattern plating—our previous step—it was possible to plate over the Designing for Reality: Strip-Etch-Strip Connect the Dots by Matt Stevenson, ASC SUNSTONE CIRCUITS