![]() Something to do with the thickness of the stencil, the size of the openings, or the viscosity of paste maybe? I had to make repeated passes from different directions with the plastic scraper before all the stencil openings were filled evenly. I’d thought I would be able to make a single pass and fill all the holes, but some holes only partially filled with paste, even when there was plenty of paste scraped over them. Scraping the paste into the stencil openings was more difficult than I’d expected. I then squirted some solder paste from a syringe onto the stencil, and used a plastic card to scrape the paste across the stencil, filling the holes. Aligning the stencil correctly with the pads underneath was easier than I expected, even for the sub-millimeter sized pads. Next, I placed a ROM-inator II PCB in the frame, and taped the stencil over it. I taped the acrylic framing pieces to my desk, along with an extra blank PCB, to create a secure frame. It required some extended futzing around in EAGLE in order to suppress the unwanted outline and pads, and generate a new paste file. It also contained openings for all the edge contact pads on the PCB, which are not meant to be soldered. The paste layer also contained my board outline, which I clearly didn’t want cut into the stencil. Ordering was easy, but I did run into a a few problems with my paste layer generated by EAGLE. I ordered a 4 mil stainless steel stencil from OSH Stencils, and paid a little over $20 for the stencil and a couple of acrylic framing pieces. For that, I’d need boards to come out of reflow with zero solder bridges at least 80-90% of the time, and I was never anywhere close to that level of success. I was able to fix up the solder bridges manually with an iron, so all the boards worked in the end, but reflow totally failed as a faster and easier replacement for drag-soldering. With the 0.5mm chips, no matter what method I tried, I ended up with numerous solder bridges between adjacent pins. If my boards only had larger components, SOICs, and the like, my attempts would probably have gone much better. The ROM-inator II PCB has two chips with 0.5mm pin spacing, which makes home reflow particularly challenging. You can read about the previous reflow attempts here: ![]() I’ll save you the suspense: it didn’t work any better than my earlier efforts. After various failures in the previous attempts, this time I used a stainless steel stencil to apply solder paste to the pads, hoping the stencil was the missing ingredient needed for success. This was my 5th attempt to assemble some ROM-inator II boards using reflow soldering, instead of my normal drag-soldering with an iron.
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