Mornin' Bill -

The thru vias in pads will do two things: 1] scavenge solder from the
soldered connection on the pad.  If their size is sufficient, this will
result in a solder starved condition at the component lead; 2] Gravity and
surface tension will generally cause a solder bead of some proportions, on
the opposite side of the board.  Dependent on the design, this may produce a
risk of shorting, or simply an increase in solder starvation on the
component pad.

There would appear to be several possible solutions: plug the vias while in
the bare copper state and allow an imperfection in the soldered connection;
plug the vias and copper plate over them, prior to tin/led plate of the
board; redesign to convert to either blind or microvia, in order to
eliminate/control the solder scavenging.

Steve Mikell should have good clear recollections of a job we did about ten
years ago, where the customer had designed boards with this charactaristic,
then beat us up because we couldn't change the laws of physics to accomodate
the design.

Have a good day and a better week - tell old what's-his-name across the
hall, "Good morning".

Kelly
-----Original Message-----
From: Bill Robinson <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Monday, January 17, 2000 8:27 AM
Subject: [TN] VIAS IN PAD


>We have pruchased a PWB design for use in one of our products.  This design
>has through vias in the surface mount pads.  Has anyone had experience with
>this situation?  My first concern is losing solder through the via during
>reflow.  Is there a good way to fill the via and still have a good solder
>joint?  And what other kinds of problems can we expect?  thanks for the
help.
>
>Bill Robinson
>
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