We had some problems with dendritic growth under BGAs when we
        first incorporated them into our assembly process.  We have
        since resolved the issue with a very tightly controlled cleaning
        process both during initial assembly and more critically, during
        rework - and let me stress this - ANY rework, no matter where it
        occurs on the board.

        The combination of flux residue, moisture, and time results in
        dendritic growth and test failure.  The flux residue required to
        start the process is microscopic - literally.  The residue does
        NOT have to be associated with BGA rework.  We found that rework
        in any area of the board could contribute to dendrites since the
        cleaning process can initially deposit flux and leave it there
        if the cycle duration isn't long enough to reclean the area out.
        This requires an intrusive cleaning process.  Hand cleaning or
        spot cleaning will not cut it.

        We use an aqueous cleaning process, so our flux is compatible
        with that.


        Jan Pelchat


______________________________ Reply Separator _________________________________
Subject: Re: [TN] BGA'S IN SPACE
Author:  Charles Barker <[log in to unmask]> at 0UTG0ING
Date:    8/20/98 3:43 PM


Hi Jim,

I'm no BGA expert, but I would think you would tend to experience dendrite
growth on anything that doesn't get cleaned properly.  Some people may have
equated this to BGA's since it may be harder to clean thoroughly under some
of them.  I would thank that if you get the cleaning down pat, the dendrite
thing would go away.

Good luck in your new role.   ; > )

Charlie B.
[log in to unmask]





Jim Marsico 516-595-5879 <[log in to unmask]> on 08/20/98 03:07:00 PM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to Jim Marsico 516-595-5879 <[log in to unmask]>

To:   [log in to unmask]
cc:    (bcc: Charles Barker/US/I-O INC)
Subject:  [TN] BGA'S IN SPACE




Dear Experts:

I've been asked to investigate this concern, so here goes:

When someone in my company mentioning using BGAs for a space application,
one
of our customers raised a concern about dendrite growth.  Unfortunately,
this
is the only information I have.  I don't know any specifics regarding the
assembly or the application (or the customer, for that matter) or where or
what
kind of dendrites.  All I know is that I'm now deemed the "company expert"
on
BGAs, so I got the task.

Has anyone heard of a dendrite growth problem associated with BGAs?

Thanks for your help.

Jim Marsico
AIL Systems Inc.
(516) 595-5879
[log in to unmask]


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