Hi Ho Steverino,

Whoops - dating myself.  Well you certainly got some good advice on this one Steve.  I
have been using some formulas I gleaned from a MPM Corp. Technical White Paper that was
written for presentation at the SMI '96 Conference.  Based on their data, I created an
Excel wooksheet that I can plug in the particulars - turn the crank - and out come the
aperture size.  There is a fudge factor in the Required Print Area calculation,  MPM
calls it an inspection factor,  that you can play around with to adjust the size of the
fillet.

I have found that leads 0.032" diameter or bigger can rob some of the volume from the
fillet.  This happens because the lead pushes out the paste that is printed into the
hole.  This solder will often end up reflowed on the end of the lead, rather than at
the fillet.

Good Luck

Gary Camac

Stephen R. Gregory wrote:

> 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-
>