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| Mylar Stencil thickness |
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| Pack34:
I've used some mylar stencils in the past with some mixed results. The main issue that I think I found with them was that the material was too malleable. This seemed to cause the paste to push up a bit around the pads. This caused everything to smear a bit. Because of this, I try to avoid them for anything that has a real fine pitch. I was looking at some stenciling options and I noticed that PCBStencils.com has a couple different options when it comes to the material type. https://www.pcbstencils.com/index.php?option=com_k2&view=item&layout=item&id=2&Itemid=2 They have two different thickness options for the standard stencil, but I'm intrigued by their "Stabil-Flex M3-4000" stencil. It looks like a completely different material. I'm guessing it's more rigid? Does anyone here have experience with it? I'm tempted because I typicaly use iTead's framed stencil offering since it's cheap ($70 for a framed laser cut stencil). But the lead time tends to be a killer. I think I typically get them in two weeks. With a mylar stencil made locally I can get them in a day or two. A lot of the time I typically use these for one-off prototypes before I send them off to production. Mainly, I'm looking at the quickest and economical way to do quick prototyping. |
| theatrus:
That looks like a Kapton (polyamide) like material. Easy to laser cut. I've used Kapton stencils from OSHStencil for fine pitch QFN without issue, and now have some sheets I can run in my laser cutter (since I usually iterate on apertures a bit) |
| Pack34:
--- Quote from: theatrus on January 22, 2016, 04:07:20 am ---That looks like a Kapton (polyamide) like material. Easy to laser cut. I've used Kapton stencils from OSHStencil for fine pitch QFN without issue, and now have some sheets I can run in my laser cutter (since I usually iterate on apertures a bit) --- End quote --- I've been able to get the orange material from OSHStencil to work, but only after switching to a less rigid applicator. The included credit-card-like applicator just didn't work well for me. I was probably pressing too hard. |
| calexanian:
I use both the Polymide and stainless ones from StencilsUnlimited. Both work fine, but i do like the rigidity of the framed ones they make. Frame refers to perforations a little way in from the edges you bend up. Makes the paste come out sharper, but in all honesty after you flow it, no real difference is made. |
| uncle_bob:
Hi You have (at least) three variables involved: 1) Your solder paste 2) Your applicator 3) Your stencil (material, thickness, hole size ...) 4) The pitch of your parts (solder pad size) Yes, there are a few others, but these are the big ones. Change any one of these and you will impact your outcome. In general, the tighter things get, the more careful you have to be. Your stencil likely will get thinner as things get tighter. Your solder paste may be different for a fine pitch part (smaller particle size) than for something massive (like a SO-8 package). Best approach - set up a frame for printing and control the tension on the stencil (regardless of the material). Index your applicator against the frame (constant pressure etc). Come up with a hold down for the board you are working on. (might be two sided tape). There is no need to get crazy expensive with this. You can do it with junk you have lying around. Just plan on a bit of experimentation / trial and error. Once you get a formula worked out, things will repeat pretty well. Bob |
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