Issue link: https://iconnect007.uberflip.com/i/1535414
24 PCB007 MAGAZINE I MAY 2025 and stripped within 72 hours), surface prep- aration for outer layer processing, and main- taining cleanroom controls are the most crit- ical and common areas where defects happen. What challenges are associated with the pho- toresist process when working with complex materials like PTFE or flexible substrates? What scenarios might encourage a fabricator to change their resist product? Krick: ese types of materials will require optimal conformation. A scenario where a customer has adhesion loss or resist break- down would be the first that comes to mind. Soer resist with high adhesion promotion is ideal. Hurdles will depend on the capabil- ities of the manufacturer. Flexible substrates are more prone to handling damage, dents, and scratches. You will want a resist that can make up for any of these potential issues, as well as making up for poor material prep prior to lamination. How do you address issues with photoresist adhesion on the PCB surface, especially in multilayer boards or those with challenging materials? Blair: Anytime adhesion loss is an issue, the first thing to do is review the process con- trols and what is being done to the surface. For example, is surface preparation a chemical or mechanical pro- cess, or is nothing being done at all? Ideally, you are always doing something to the surface to pro- mote the best environment for resist adhesion and conforma- tion. Some customers, how- ever, may not have those capa- bilities, or the material may not be suitable due to handling (so flex material), or cannot have the grain or surface changed (RF work). In those worst-case situations, we would still recommend a non-etch based adhe- sion promoter for RF work or a better handling system for the soflexible materials. How has the evolution of photoresist technol- ogy addressed the challenges of producing smaller, finer PCB features? What new tech- nologies or techniques in photoresist devel- opment are being researched and developed to improve performance and reduce defects in PCB fabrication? Krick: Photoresist technology has come such a long way over the years. Today, we have mul- tiple exposure units with exposure unit heads as small as 6 μm, which is incredible when you think about it. e resists themselves are really at the forefront for fine feature and high-reso- lution work. Now, we are working with feature sizes less than 1 mil (25 μm) that customers are plating, something that is not easy to do. e resists we are testing and selling for this type of work have the capability to go much smaller than 1:1 with resist height. is means we can print, for example, a 15 μm line and space with a 25 μm resist height and still have the leeway to add plating per the design needs. But even with photoresist at the forefront of this tech- nology level, you also need to consider the technology capabilities of the newest expo- sure units available, along with vacuum lami- nation techniques and orbital vertical develop- ing for improving yields and capabilities. And again, considering the size of the fine features and the materials being used, we cannot over- stress the importance of cleanli- ness and handling. Blair: is is the fun part of the job: new resists for lines and spaces that you cannot see with the naked eye. Packaging resists have been able to do this for years. ese resists operate in the 10-50 micron range and are imaged with projection or step printers. ey use high exposure energy with zero line or space growth and have high resist adhesion. Pre-clean is chemical polishing, and vacuum lamination is the norm. ose packaging resists are expensive and have limits regarding shelf life. " ...we cannot over-stress the importance of cleanliness and handling. "