Hi David,

I hate having a pessimistic attitude, but...  you may have already
experienced HASL boards that are relatively flat on both sides.  Then, after
you reflow the board and try to build on the other side, you occasionally
find a little bit of solder that has dripped out of a via and made a bump.
That bump then causes bridging at the screen print process because it
prevents the stencil from properly gasketing to the board.  It may only be a
3 ppm problem, but that can be enough to show up every 10 or twenty boards.

I can't imagine any reason putting more solder in the via would prevent the
solder from dripping out.  Even if it only occurs occasionally, since you
don't know when or where, you will have to watch for it.  If the via in pad
only occurs on one side, you can build that side last to solve the stencil
printing problem.  (of course it doesn't solve the solder robbing problem).

There is a PCB manufacture that does fill the vias with conductive epoxy (I
think they patented the process), so you could investigate that option.  My
concern would be solderability to the epoxy.

Kind Regards

Ryan Grant
Advanced Technology Engineer
MCMS
(208) 898-1145
[log in to unmask]


> -----Original Message-----
> From: David North [SMTP:[log in to unmask]]
> Sent: Friday, November 02, 2001 2:27 PM
> To:   [log in to unmask]
> Subject:      [TN] Process for Vias in Lands
>
> We are a contract manufacturer.  One of our OEM customers has completed a
> design which uses ~50-75 0.016" vias in ~0.038" square lands for 0603
> components, on a 0.031" board.  We have already made redesign
> recommendations, but there may be a substantial (as many as several
> thousand) quantity of boards that need to be assembled with this design.
> Does anyone have experience with a soldering process that will yield
> reliably high quality solder connections without substantial inspection
> and
> rework given such a design?
>
> Thanks for any comments.
>
> David North
> Qualitel Corporation
>
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