Issue link: https://iconnect007.uberflip.com/i/1381013
68 DESIGN007 MAGAZINE I JUNE 2021 cases. I can see a lot of uses for technology like this in the medical space or even in the wear- able devices market. Being able to have such small traces is going to enable not only smaller designs, but higher utilization of existing real estate, which will lead to the reduction of raw materials required to build a design. Dunn: You had a few questions early in our dis- cussions that I think are going to be common questions among PCB designers. Chester: What trace-to-trace gap distance is possible? Dunn: With the right photolithography set-up as small as 12.5 microns has been run. Most fabricators can do 20 to 25 microns. Chester: As this is an additive process, how tall of a trace can you get? Can you control this height? Dunn: Currently, for a 25-micron (.001") line, a 20 to 25 micron (.0008" to .001") thick line is standard with 50 microns (.002") possible but not tested. On a 50-micron line, a 50-micron thickness can be done. Chester: How tight is the line-width control? Dunn: is is very tight, typically ±1 micron (±.000039"). Chester: Do you need to use a special solder mask when using a very fine pitch semi-addi- tive design process? Dunn: No. Typically, the design will end up with an LDI imageable mask, but that is very common now. Consideration needs to be given to mask-defined pads over copper defined to keep the adjacent traces covered. Chester: Where in the design fabrication pro- cess does this fit? Dunn: e semi-additive process is completed early in the fabrication process. To over- simplify, where traditional subtractive etch processes start with a copper-clad laminate panel and etches away the copper that is not required, the semi-additive approach begins with the base dielectric and adds copper to the panel in only selected areas. Chester: Can you mechanically drill with SAP, or do you need to use a special drilling process? Dunn: Both mechanical drill and laser drill can be used with semi-additive processes. We are just scratching the surface on how best to apply these new fabrication capabilities to PCB design. ere are obvious benefits to overall size and weight. ere is also the potential to Tomas Chester