Key Insights on Photoresist for Defect Reduction

Estimated reading time: 2 minutes

Feature Q&A with Josh Krick and Tim Blair, IEC

In PCB manufacturing, understanding the intricacies of the photoresist process is crucial for achieving high-quality results. Industry experts Josh Krick, a technical service engineer at IEC, and Tim Blair, a PCB imaging specialist at Tim Blair LLC, share their knowledge on the essential stages of photoresist application, highlight critical advancements in materials, and discuss common defects encountered during production. They share best practices and innovative solutions to enhance the manufacturing process, reduce defects, and ensure efficiency and reliability in high-tech applications.

What are the most critical steps in the photoresist process in PCB fabrication for ensuring high-quality results?

Josh Krick: When focusing on the photoimaging process, we will always work our way from the ground up: surface preparation, lamination, exposure, and then finish with developing. Certainly, if deemed necessary, we can also focus on the additional processes of stripping the photoresist, etching, and even plating applications. Each one of these steps is just as crucial as the next. All these processes should have daily checks and protocols to ensure consistency 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. Think of it in terms of building a house, where a good foundation is critical for success.

Tim Blair: During my imaging training sessions, I always stress that pre-cleaning is critical 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: The biggest advancements in the field are focused on high resolution, high adhesion, thin resists 1 mil thick (25) for IC substrates, and various higher technology needs. These resists will provide the capability to go less than 1:1 with resist height for high resolution and small feature sizes while still providing enough resist height for plating applications. We have customers with goals of finished product in the 12-20 μm range in terms of feature sizes after etching.

To read this entire conversation, which appeared in the May 2025 issue of PCB007 Magazine, click here.