Steve,
I cranked yer numbers thru my super-duper intrusive reflow stencil
computer, and her are some assumptions:
Assumptions:
1) No lead diameter was given, so assuming .020" round lead.
2) 47% solder volume in your paste.
3) Pad annular ring diameter of .065".
4) .006" thick stencil used.
5) LPI solder mask: Not mandatory, but this has gooooooood wick-back
response.
Based on the assumptions, here are the stencil aperture size results:
(I do not know how much room you have, so I did it 3 ways):
Square opening: .145" per side.
Round opening: .164" diameter
Rectangular (with width same as annular ring dia) .324"
I have also used triangles, which fit between things nicely.
Standard "USE AT YOUR OWN RISK"...PAST SUCCESS IS NO GUARANTEE OF
FUTURE RESULTS"...THESE ARE MY PERSONAL VIEWS AND NOT NECESSARILY
THOSE OF MY EMPLOYER" disclaimer applies, of course.
Good luck.
Jeff Hempton
United Technologies Electronic Controls
______________________________ Forward Header __________________________________
Subject: [TN] Intrusive Reflow
Author: "Stephen R. Gregory" <[log in to unmask]> at Internet
Date: 11/11/1999 2:51 PM
Hi ya'll!
I'm getting ready to do some intrusive reflow on this board we got
here...(this is my first time! I'm s-o-o-o nervous...not really...well, maybe
a little...hehehe) Anyways,
the parts are going to be 2, 20-pin SIP sockets. The board is .063" thick,
the holes
are spaced .100" apart, and the hole diameter is .040". I'm trying to decide
how big I should make my apertures.
I've looked at all the archive postings (there are a 168 of them on intrusive
reflow) to see if anybody posted any recommended stencil thicknesses, and/or
aperture sizes,
but there was none. I looked on the web, but couldn't find any real
guidelines either...
(hmmmm, something I couldn't find...now THAT's a change!)
I need to keep my stencil thickness at 6-mils, 'cause I've got some 20-mil
pitch stuff on the same side. I was thinking of doing .060-.070" diameter
circles over the holes...
does that sound okie-dokie?
I did a little test with the SIP socket and a syringe full of solder paste. I
drew a bead of paste (about .030" dia.) down the row of holes and dropped the
connector in, then reflowed it. Then I got my dremel tool out and did me a
rough cross section to check the barrel fill. It actually wasn't too
bad...there were about 2-3 holes that were a little shy volume-wise but that
was because (I think) the solder wicked over to the holes next to it because
of the continuous bead of paste I had laid down. That shoudn't happen when I
have individual deposits of paste for each hole.
So how big should I make my openings? Did I guess right at .060-.070"?
-Steve Gregory-
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