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sistency and repeatability. However, if I had to choose one process as the most critical, I would say that surface preparation is arguably the most critical process. ink of it in terms of building a house, where a good foundation is critical for success. Tim Blair: During my imaging training ses- sions, I always stress that pre-cleaning is criti- cal to the imaging process. Good pre-cleaning will Increase the latitude of the resist through the rest of the imaging process. But I always emphasize the importance of cleaning the resist-coated inner layer cores and outer layer panels at exposure. A direct image printer's forgiveness for micro debris is zero. You will not burn out this micro debris on a DI printer like you could on a flood or point light source contact printer. Collimated DI printers are super sensitive to micro debris. Clean, clean, and clean some more. What are some of the latest advancements in photoresist materials or processes that have significantly impacted PCB manufacturing? Krick: e biggest advancements in the field are focused on high resolution, high adhe- sion, thin resists 1 mil thick (25) for IC sub- strates, and various higher technology needs. ese resists will provide the capability to go less than 1:1 with resist height for high reso- lution and small feature sizes while still pro- viding enough resist height for plating applica- tions. We have customers with goals of finished product in the 12-20 μm range in terms of fea- ture sizes aer etching. That is getting pretty small. How do you determine the right type of photoresist for a specific PCB application, such as high- frequency RF or HDI boards? Krick: It depends on the application you are Josh Krick 20 PCB007 MAGAZINE I MAY 2025