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February 1998

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Subject:
From:
"Lustig, Steven K.." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 26 Feb 1998 14:34:11 -0500
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Koushik,

The crackling noise, at least when the board is in or coming out of the
reflow oven, sounds like it could be due to "popcorning" - plastic parts
that absorb moisture during storage and which expands during heating in
the reflow oven.  This results in stress which can cause cracks (the
"popcorn" noise) in the package and create other damage which may not be
caught at test.  Have you closely examined your larger plastic parts on
the board for any such damage?  Have they been handled prior to reflow
according to the appropriate JEDEC moisture sensitivity number for those
parts?

Steven Lustig
Process Engineer
EMS Technologies
Norcross, GA
(770) 263-9200 x4714
[log in to unmask]


>----------
>From:  Koushik ATD Banerjee[SMTP:[log in to unmask]]
>Sent:  Thursday, February 26, 1998 2:41 PM
>To:    [log in to unmask]
>Subject:       [TN] Question :  "Crackling" noise in boards post SMT
>
>I would like to request for input / feedback on an interesting problem
>that we are seeing sporadically in our SMT line.
>
>Some of the PCBs, post component attach, when they are either in or
>are coming out of the reflow oven are making a "crackling" noise !  We
>have not identified any defects in the boards or the components yet
>and we are unsure what is causing the noise.  Sometimes, we are also
>hearing this noise when we take a board in our hands post SMT and try
>to warp it a little !  The boards are approx 5" x 12", have components
>on both sides (passives and some actives) and is not very densely
>populated.  Any suggestions on what could be the reason would be
>greatly appreciated !
>
>Thanks,-Koushik Banerjee-
>
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