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September 1998

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From:
"Chan, Marcelo" <[log in to unmask]>
Date:
Tue, 15 Sep 1998 10:25:27 -0400
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1.0
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"TechNet E-Mail Forum." <[log in to unmask]>, "Chan, Marcelo" <[log in to unmask]>
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One very important reason for using a higher melt solder is stand-off
height..ceramic BGAs are considerably heavier than plastic ...if eutectic was
used, the chances for bridges increases, the higher the ball pitch would have to
be and the lower stand-ff would make it more difficult to clean if necessary...

marcelo

        -----Original Message-----
        From:   Ed Holton [SMTP:[log in to unmask]]
        Sent:   Tuesday, September 15, 1998 10:10 AM
        To:     [log in to unmask]
        Subject:        Re: [TN] X-ray for open joints on BGA's ?

        I am curious, why are the ceramic BGA solder balls not eutectic and made
        with the 90/10 Pb/Sn solder?




        [log in to unmask] on 09/14/98 11:30:26 AM

        Please respond to [log in to unmask]; Please respond to
              [log in to unmask]

        To:   [log in to unmask]
        cc:    (bcc: Ed Holton/Hella North America Inc.)
        Subject:  Re: [TN] X-ray for open joints on BGA's ?




        Hi Daan,

        Two comments come to mind:
        1) Remember that not all BGA solder balls are eutectic (and therefore
        collapse during reflow).  CBGA devices typically use 90/10 Pb/Sn solder
        which don't melt during reflow.  Opens are much more common with these.

        2) I've had some experiences with some large PBGA devices having opens
        around the periphery during rework, but generally with packages which
        showed a marked tendency to "potato chip".  This was much more
noticeable
        when solder paste wasn't used (some folks just use a tacky flux).

        Personally, I never found much use for X-ray on BGA devices in a
production
        mode.  Develop the process (which may or may not entail the use of
X-ray)
        and control the critical parameters, and you'll find the instances of
BGA
        solder joint defects is extremely low.

        Best regards,
        Greg Bartlett
        Teledyne Electronic Technologies
        Hudson, NH
        [log in to unmask]
        -------------------------
        Hello Technet,

        I remember a discussion  a couple of weeks ago about X-ray inspection.
It
        was stated that the nr.1 defect that one wishes to see with a X-ray
machine
        is open joints, but unluckily this type of defect  can only be seen with
        the most expensive X-ray machines on the market.
        I was thinking : if the BGA (the balls) collapses during soldering and
is
        soldered perfectly parallel to the board surface, all the balls must
have
        reflowed !  If only one of the balls didn't melt,  the component can not
be
        soldered  parallel to the  board surface !
        Since the chance that  a collapsed ball  forms a joint with the pad is
        almost 100 % ,  it can be concluded that X-ray inspection for "opens"
does
        not make much sense.  Just looking at the parallellity should tell you
        enough !!

        What do you think, is this a reasonable thought or am I overlooking some
        things ??

        Regards,


        Daan Terstegge
        Signaal Communications
        * Unclassified *

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