Lance is very correct. In order for the solder to go into a barrel there is a need for the air to escape up the barrel as it passes through the wave. One solution for cases like this is to preheat the board. The hot air in the barrel expands and there is less of it. Another one is to raise the wave to force the solder up into the barrel. It might create icicles. A second pass might be necessary to remove the icicles.
Regards,
Ramon
> -----Original Message-----
> From: Lance Mayes [SMTP:[log in to unmask]]
> Sent: Thursday, April 01, 2004 6:04 PM
> To: [log in to unmask]
> Subject: Re: [TN] Voids in Thru-Hole Solder Joints
> Importance: High
>
> 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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