| Hey all- | | My question is this: My stencil printer operator has said that he has to | wipe our 6-mil stencil each pass to get the paste in the 20-mill pitch | aperatures for a QFP to release well. We are using Amtech NC-559 type 3 | paste with 89.5% metal. The paste is not old. I considered using type 4 | paste, which has a much finer powder in it. I was told by Amtech that this | finer powder paste will pack more densly into the aperatures and I could get | some bridging, unless I order a new stencil with aperature reductions. Our | squeegee speed is 0.6 inches/s, or 15mm/s. Is this too slow? Amtech | suggested that at this slow speed, the paste could be rising out of the | aperature, as if someone pressed on a wet sponge and it rose back to its | original shape. What is a good squeegee speed for 20 mil pitch parts? | Thanks! | | Ryan Jennens | TelGen Corp. | |
Your print speed is not out of line. You could probably raise it to 1.0 inch/sec. (we sometimes go up to 2.0 inch/sec). If your printer is not your line bottleneck, I would keep wiping after every 20 mil print (we do). We have an automatic wiper on an MPM-SPM and the printer is never the bottleneck in our process.
I would recommend reducing your apertures for 20 mil pitch. We use a 10% reduction on 20 mil pitch (6 mil stencil). We have found band-etch stencils to deliver results similar to laser etch at chem etch prices, so we use band-etch stencils on all of our fine pitch applications (chem etch otherwise) and reduce 10% on 20 mil and 15% on 25 mil.
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