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- Newsgroups: sci.electronics
- Path: sparky!uunet!snorkelwacker.mit.edu!bloom-picayune.mit.edu!hans.mit.edu!chuck
- From: chuck@hans.mit.edu (Chuck Parsons)
- Subject: Re: Green Layer on Circuit Boards?
- Message-ID: <23JUL199213163384@hans.mit.edu>
- News-Software: VAX/VMS VNEWS 1.4-b1
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- Nntp-Posting-Host: hans.mit.edu
- Organization: MIT Lab for Nuclear Science
- References: <BrsvB7.EzC@zoo.toronto.edu> <1992Jul22.183826.22771@csc.ti.com> <Brt82r.Kp@zoo.toronto.edu>
- Date: Thu, 23 Jul 1992 18:16:00 GMT
- Lines: 39
-
- In article <Brt82r.Kp@zoo.toronto.edu>, henry@zoo.toronto.edu (Henry Spenc writes...
- >In article <1992Jul22.183826.22771@csc.ti.com> jsykes@dadd.ti.com writes:
- >>I could buy stuff in England that you just sprayed on the board immediatly
- >>after tinning. You didn't need to mask out the solder pads - the film just
- >>evaporated around the touch of a soldering iron...
- >
- >That will be something different. The main point of the green stuff --
- >solder mask -- is that it *doesn't* go away at soldering temperature, so
- >it keeps solder off things that shouldn't be soldered.
- >--
- >There is nothing wrong with making | Henry Spencer @ U of Toronto Zoology
- >mistakes, but... make *new* ones. -D.Sim| henry@zoo.toronto.edu utzoo!henry
-
- The green solder mask I have applied before was epoxy with
- various aditives. Some brands were heat cured for an hour or two at about
- 120C. Other brands were cured using UV light.
-
- Silkscreening it was a bitch, comparred to silkscreening cloth/paper
- or metal panels which I have also done. Cloth and paper are absorbant
- and any the ink/epoxy that seeps under the edges of the masked screen
- is absorbed by the material on every pass.
-
- Compared to silkscreening metal panels it is hard because all the
- traces make the surface bumpy. It is particularly hard to get
- the mask to go between to closely spaced traces that run in the
- same direction that the silkscreening squegee is pulled.
-
- If you try it, a trick that helps is to put a piece of newspaper
- over every board and silkscreen an image on the paper first, then
- remove the paper and silkscreen the board. This keeps the underside
- of the screen clean.
-
- Somebody, (Kodak I think) makes a solder mask film that can be
- applied to the board and then photographically exposed, and developed.
- It is more expensive than silkscreening but easier to learn.
-
-
- regards, Chuck@pierre.mit.edu
-
-