stencil cleaning (framed) & paste applying - Page 1
Forum section: electronics / projects

author: justroll
author_rank: Newbie
timestamp: January 29, 2014, 02:12:27 pm
content: HiBy error i got shipped a framed stencil instead of a unframed one.it looks nice; but this is the first time that I'm using a stencil.I did apply paste to the stencil (Mechanic solderpaste 25-45 microns); but when lifting the stencil the paste seemed to have shifted a little bit.Problem is; i got QFP 48's on it and the paste seem to have filled the holes (maybe my apply paste (squeeguee) wasn't correct); when i look thru the mask i see that some pads are "closed" due to solder past that is still in the pads on the stencil.I tried to use some alcohol/water/degreaser but all of them result in the same failure; i can't get the pads to open up. I tried apply some tape and ripping it of to get the pads open; some open up, some don't.I don't think using a hot airgun is a good idea due to the limited steel thickness (0.13mm)* what is the correct way to apply paste on a framed stencil if you don't have a stencil printer?* how can I clean my stencil so that the pads are back open again?

author: JoeyP
author_rank: Frequent Contributor
timestamp: January 29, 2014, 04:26:17 pm
content: As far as cleaning, I find that compressed air does a good job of opening up blocked apertures (though normally, alcohol and a lint-free rag are enough to do the trick).

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 29, 2014, 04:37:38 pm
content: It is important to clean while the paste is still soft, as it can be hard to do once it dries.A method I use is to lay the stencil on several layers of paper towel, pour on some isopropyl alcohol, then scrub with a toothbrush - the alcohol soaks into the towel, taking a lot of the paste with it.Compressed air also works well for fine apertures.One day I plan to make an 'air knife' type thing to allow easy cleaning.

author: JoeyP
author_rank: Frequent Contributor
timestamp: January 29, 2014, 06:24:02 pm
content: BTW, I use methanol rather than isopropyl alcohol. Seems to work well even on paste that has dried for weeks or months. But it may also depend on the type of paste you use. I use only water-soluble types.

author: justroll
author_rank: Newbie
timestamp: January 29, 2014, 08:37:06 pm
content: guys .. thank for the tipspressured air didn't do the job .. but funny .. the toothbrush didso .. only now finding a good way to put paste on a board using a framed stencil without a stencil printer..

author: SeanB
author_rank: Super Contributor
timestamp: January 30, 2014, 09:31:46 pm
content: Credit card works well, or a plastic scraper.

author: justroll
author_rank: Newbie
timestamp: February 03, 2014, 06:24:50 pm
content: I used one of these ..but doesn't seem to be the best way ; it scrapes paste out of the bigger holes

author: JoeyP
author_rank: Frequent Contributor
timestamp: February 03, 2014, 06:38:45 pm
content: Whatever you use, the thinner the better. That will help it not drag the paste out of the apertures. The squeegees from professional machines use stainless blades which are only about 0.007" thick. If I were going to try to apply by hand, I'd buy some thin stainless sheet stock from the hobby store.

author: calexanian
author_rank: Super Contributor
timestamp: February 03, 2014, 09:02:26 pm
content: Flux off or any flux cleaner for that matter works as what holds the solder spheres together is just goopey flux. Techspray G3 flux remover is great stuff! You definitely want some ventilation though. Its expensive as well, but you use a lot less of it cause its good. It also dries very fast.