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Through Hole Pad contamination

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MGL

#71348

Through Hole Pad contamination | 7 November, 2013

Below are a few photos of an ongoing issue we are having with 1 pwb style. Some of the pads appear to have contamination that appears after the selective solder step. The joints are extremely hard to rework - almost impossible. We had the joints analyzed by an outside lab and everything looked fine - they checked for black pad. Has anyone seen anything similar? These defects are limited to this cards and 2 connector locations. We have a sister card that is identical that does not exhibit these conditions. In addition to the poor wetting areas we also see this "moon" finish on the solder. Again only on this card.

Attachments:

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#71353

Through Hole Pad contamination | 8 November, 2013

First, it's a surprise that your failure analysis lab thought everything was OK with these boards. They look like shit.

Second, a few years ago, there was a bunch of complaints about ENIG boards with issues similar to what you're observing. There was dewet on the annular ring of the TH devices. On cross section, there was large amounts of nickel eroded away and the surface is non-wettable. No corrosion was evident, so was NOT black pad.

Third, rather than rattle on and speculate, how about if your give us some particulars about these boards and their processing and compare that with the "sister boards."

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#71354

Through Hole Pad contamination | 8 November, 2013

Dave is right, though apparently a bit grumpy today.

What he's saying is that the ring de-wetting is a bad thing, and should have been called out by your lab. You might consider a lab change in the future.

Some information about your processes, and comparison between these and the sister boards would be helpful to other members who might be able to contribute as well.

'hege

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MGL

#71362

Through Hole Pad contamination | 11 November, 2013

Thanks guys. Here are more details. The cards are essentially the same. They use the same connectors, same footprint, the traces / layers would be comparable etc. The difference between the 2 we see is that one is laminate - Rigid Metal Clad Base, Type GFN or GFG (this is the problem child) - the other board is Rogers 4350 .004" thick on all layers except the top layer which is .006" thick. Other than this difference they are the same basic board.

The cards are soldered using a Pillarhouse Jade. The boards are preheated to approx. 120c. Solder temp is 260c. The connectors are solder at 2mm per second and 1 mm per sec. The speed difference is to achieve vertical fill requirements. We have modified various parameters, hand soldered etc and always yield the same results thus pointing us to the pwb itself.

Any other details needed please let me know.

Any insight appreciated.

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#71365

Through Hole Pad contamination | 11 November, 2013

Are you using lead or lead-free solder? 260C would be good for lead solder but may be a bit low for lead-free. We run our lead-free selective solder pot at 300C although we do not have any pre-heat or top heat, just hot nitrogen blowing around the nozzle to help heat the boards.

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MGL

#71366

Through Hole Pad contamination | 11 November, 2013

We are leaded only. (Military CM)

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#71372

Through Hole Pad contamination | 11 November, 2013

Matt: What's the solderability protection on the boards? * Specification? * Actual?

Are the boards fabricated by the same supplier?

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MGL

#71374

Through Hole Pad contamination | 12 November, 2013

Dave, See attachments. Thanks.

Attachments:

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#71386

Through Hole Pad contamination | 13 November, 2013

It's too bad that SMTnet won't let us view your pdf. I asked the geeks to fix that. If someone really want to read it Matt can likely get it off to you. Is it OK to do that, Matt?

Anyhow, the Trace Labs report seems to be focused on some SMT pad discoloration that was the primary complaint about these boards by Matt's company. The ring dewetting on the PTH received little attention in Trace's report.

Matt, without better information, I as you, believe that there's something wrong with the fabrication of these boards. Consider: * Enlisting the support of your supplier * Obtain some 'seconds' from your supplier * Run some experiments on bare boards to attempt to narrow the possibilities

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