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April 2004

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Subject:
From:
Lance Mayes <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 1 Apr 2004 16:03:53 -0700
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Carrie;
First I have a question, is this a hard mount component?  If this is the
case it may be that an air pocket is forming below the component body
between the solder and the component..  This type of problem could be
covered in J-STD-001C 6.1.4.  What could be done about it, maybe a spacer
or a different prep on the leads such as what we call a cowboy crimp where
the lead is crimped to prevent the component from going all the way into
the through hole.  That's what comes to mind as I read your problem.  Hope
this or another answer from some more experienced Technetters help.

Thanks


                        P.  Lance Mayes
                        Mfg. Trainer




"Morse, Carrie" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
03/31/04 12:11 PM
Please respond to "TechNet E-Mail Forum."; Please respond to "Morse,
Carrie"


        To:     [log in to unmask]
        cc:
        Subject:        [TN] Voids in Thru-Hole Solder Joints


We recently had circuit card assembly sent out for cross sectioning.
One of the leads for a thru-hole device has voids -- perfectly round
voids.  The component body prevents us from seeing the top of the solder
joint (which, if we could have seen, we would have seen a void).  The
bottomside of the joint has a void, but, would not have been visible
without cross sectioning.  The board was sent out for cross sectioning
to evaluate a different problem, but, cross sectioning was done on a
sample basis to evaluate the entire board.  In other words, this
specific component has not been a problem (yet).

My questions are as follows:
1.  What causes the voids over the wave?  My first guess is insufficient
preheat or dwell time.  My second guess is materials (moisture in the
board).  Are these valid root causes?  What else should I consider?
2.  Are the voids detrimental to the reliability of the board?  We use
OA flux.  I bet there is flux entrapped.  That can't be good.
3.  What is the acceptance criteria for voids in Thru-Hole parts?
IPC-A-610 sec 6 covers circumferential wetting as well as percent fill
as these are visible without cross sectioning.  Is there a spec that
covers what a thru-hole solder joint should look like cross sectioned?

TIA,
Carrie




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