Hi Jim

We found the no clean Indium NC-SMQ90 paste (flux) wicks amazingly (it's
got 85% metal in our application) ;
that is even if you bridge the paste before reflow it wicks evenly to
pins going through oven .
We dispense here ; but one of the less usual practices on paste volume
determinations involves dispensing way on to solder mask area (in order
to avoid balls and still give it sufficient fillet ).
I answered this one once already = must be in archives :
If you have room ; extend ( in or out ) the stencil openings (ovals) way
on to the solder mask and let the solder creep back to joint .
It works without fail here ; we just have it easier without stencil .
The minimal pad rings would help you too ; with teardrop shape pointing
to paste if you really feel about it .

See you

Paul Klasek
http://www.resmed.com

> ----------
> From:         Jim Gryga[SMTP:[log in to unmask]]
> Sent:         Wednesday, 16 December 1998 7:03
> To:   [log in to unmask]
> Subject:      [TN] Pin-in-paste for 50 mil part
>
> Hey Techhies,
> Is there any body out there using pin-in-paste (intrusive reflow,
> whatever
> you want to call it) on parts with a lead pitch of 50 mils?  I have a
> 38
> pin and 30 pin 50 mil pitch through hole right angle header I need to
> solder on a double reflow board.  I can't slelective wave solder
> because
> they sit on right angles to one another (I'm sure one would have
> solder
> bridges), I don't want to hand solder because of the added cost, and I
> prefer not to use a fountain solder (we've had bridging and
> insufficient
> hole fill fountain soldering other 50 mil connectors).  The pth
> diameter is
> about 0.022".  The leads are 0.015" square.  There is minimal lead
> protrusion through the board, about 0.025".  We've done some
> experimental
> p-i-p boards with a 6 mil stencil but only acheive acceptable (75%)
> hole
> fill on about 50% of the connections.  We also tried 0.025" holes with
> worse results.  I have 20 mil QFP's on the same side as the connectors
> so
> I'm hesitant to go with a thicker stencil.  Next step will be to try a
> step
> down stencil.
>
> If you have any experience or recommendations on stencil aperture
> configurations, stencil technology, paste types, etc., etc, I'm all
> ears.
>
> Jim Gryga
>
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