Can the acoustic microscopy catch a popcorn under the BGA or does the water
hide it?

        -----Original Message-----
        From:   Bev Christian [SMTP:[log in to unmask]]
        Sent:   Wednesday, August 26, 1998 6:14 AM
        To:     [log in to unmask]
        Subject:        Re: [TN] Solder Bridges under BGAs

        Nick,
        Are all the solder bridges under the middle of the BGAs?  If this is
the
        case alarm bells should be going off!

        When BGAs popcorn they do this on the bottom, not on the top, so it
is hard
        to spot or visualize without a cross-section or x-ray picture.  This
is one
        case where electrical test might not be better than these other
methods.
        What class of BGAs are they?  How were they shipped
(container-wise?)  Were
        they opened immediately upon receipt?  How are they stored?  How
long
        between opening and using them?  What was the wait between SMT and
wave
        soldering?

        Another possibility, a little more "far out" - I would presume from
what you
        said that the solder bumps are eutectic.  Is there any chance that
this is a
        REALLY heavy BGA, say with a metal insert heat dissipation slug?
This could
        smush the paste down and about.

        Is there solder mask between the pads on the boards?

        Are the BGAs clean on the bottom, no spider trails of solder between
solder
        bumps?

        How smooth running is your oven conveyor?

        Just a few things to think about.

        Good luck!

        Bev Christian
        Nortel


        > ----------
        > From:         Nick Nicolaides[SMTP:[log in to unmask]]
        > Sent:         Tuesday, August 25, 1998 5:55 PM
        > To:   [log in to unmask]
        > Subject:      [TN] Solder Bridges under BGAs
        >
        > Hi!
        > Our contract manufacturer employs HASL for the PCBs'. Previous to
this the
        > CM was using OSP (Entek). He stated he has better quality using
HASL PCBs.
        > However we are now experiencing some solder bridging under the
BGA's. He
        > is
        > using HASL,  WS 609 solder paste (6 mils), and what the solder
bumps are
        > on
        > the BGAs. This appears to be acceptable but why the solder
bridging under
        > the BGA. What are your thoughts!
        >
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