Werner's comments are on target (as usual). As we used to say about an
avionics tech I worked with in the Navy, "He's not always right but you
have to ask yourself, 'How often is he wrong?'" :-)
Werner gave a good summary of obvious/likely causes to consider first
off. One other factor we've encountered that you may want to keep in mind
is holewall quality. Specifially, itsy bitsy pinholes in the plating as
the result of small localized plating voids -- typically at the ends
of glass fibers protruding into the hole (nodules, skip plating, plating
folds, et al). So while you're looking at cross sections and focusing on
the solder/component lead don't forget to look at the pwb hole wall/plating
as well.
cheers,
Dwight Mattix
Sr Staff Quality Engineer
Corporate Engineering, Qualcomm, Inc
At 02:11 PM 3/31/2004 -0500, Morse, Carrie wrote:
>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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