Genny,

Hopefully you will get more responses as mine won't be the most helpful,
but at
least your question gets acknowledged.

There are too many variables; the inconsistent HASL on the back side would
not
cause more solder drain (I don't think), however it might be symptomatic
of more
HASL in the hole - which means a larger volume of solder is available to
wick down
and out the bottom of the hole.

It could also be that the holes in the last set of boards are larger or
smaller than
in the prior batches ...

Or is could be variables in the assembly process which I don't have the
expertise to speak to.

Have a good weekend,

Valerie





Genny Gibbard <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>

        To:     [log in to unmask]
        cc:
        Subject:        [TN] FW: Soldered heat slug


I posted this just over a week ago, but didn't receive any responses.
Thought I'd try again

> We have a few PCB's that we use a SM IC power amp with a heat slug that
is
> reflow soldered to the board.  We have a via hole pattern under the
> device, and the opp side of the board is exposed HASL finish gnd plane
> that is mounted against a metal heatsink.  As has been discussed on this
> forum, a problem with this design idea is during reflow, solder will
tend
> to drain away from the slug through the vias, but we have generally had
> acceptable via fill by overprinting solder paste, except for a recent
> batch of boards.
> The bare boards had less consistent HASL finish leaving more solder on
the
> gnd plane side in places, and the QA person is wondering if that may be
> the cause for increased solder drain?  Or alternatively if it is just
> related to reflow temp profile?  Or some combination of both?
>
> Genny


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