Yep. Especially if this is a Plastic BGA. I've had rework problems
where my ramp was too fast causing the substrate  to warp slightly
which caused my shorts.The overmold is more thermally stable. That's
why it was occuring only on the corners. A more conservative profile
particularly during the soak stage fixed the problem.

-Dave

-----Original Message-----
From: MChan
Sent: Thursday, December 10, 1998 9:35 AM
To: TechNet
Cc: MChan
Subject: Re: [TN] BGA short

check the warping of the BGA PWB carrier pre and post reflow.... as the
PWB
warps, it may be pushing the solder...another check point may be your
stencil
design/process....

Marcelo

        -----Original Message-----
        From:   Poh Kong Hui [SMTP:[log in to unmask]]
        Sent:   Thursday, December 10, 1998 10:07 AM
        To:     [log in to unmask]
        Subject:        [TN] BGA short

        Hi Technetters,

        I am facing a weird problem.

        One of the board that we make, is having short underneath the
BGA.
        However, every single short is always at one of the 4 corners of
        the BGA.

        Is there anyone facing such an issue ? Could someone advise me
how
        to solve.

        Poh

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