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Brd(Electroylic Gold finishing) got blisters

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#36243

Brd(Electroylic Gold finishing) got blisters | 23 August, 2005

presently, the production facing this problem. We has couple of brd which is electroylic gold finishing with plug via. The brd has blister after the PCBA (in lead free temperature, 265 degree) Some time, bare brd already has the blisters. But most of them happen after the PCBA.

The vendor claim that it was due to the brd is electroylic gold finishing and the via is plug. I don't really buy that.

Is the vendor claim is correct?

Or there is a solution.

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#36258

Brd(Electroylic Gold finishing) got blisters | 23 August, 2005

We've never heard of this [but all of our gold is electroless, not electrolytic].

If the delamination is caused by the electroylic gold finishing and the via plug process during fabrication, something is wrong. Either your supplier: * Is goofy ... OR * Needs to tell you what it is about the board specification that causes this condition and how the two of your should go about fixing it.

Tell us what you learn.

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#36272

Brd(Electroylic Gold finishing) got blisters | 23 August, 2005

My process guy told me that. Due to black spot issue, brd with BGA must use electrolytic finishing.

And when we had this finishing with plug via, the blister issue pop out.

My supplier claim that this is due to the plug via. Which I don't know how true is that.

My brd is a 4L brd with 1.6mm thickness. So far, this blister also pop out @ the brd with 1.0mm thickness, 4L brd.

The vendor is suggesting to do a solder resist of 0.4mm on the via (hole dia 0.2mm), open on both side. Instead of plug via, they do half plug via. As for the via @ BGA, they will control the solder resist at 0.3mm.

We still have not try that out yet. DOn't know what is the outcome.

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#36279

Brd(Electroylic Gold finishing) got blisters | 24 August, 2005

First, while black pad can be a problem with poorly controlled electroless gold [search SMTnet Archives for background], it is not a suffiecient reason to use electrolytic. It's the reason the supplier should fix their electroless gold process.

Second, is the blistering at the via plugs?

Third, is your supplier plugging the via from both sides? If so, this is poor practice. After the first plug is cured, the second plug will trap air between the first and second plug. This trapped air will expand when heated and could push one [or both] plug from the via.

Between not being able to control their electroless gold and this possible double plugging do not give us confidence in your supplier's abilities.

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#36300

Brd(Electroylic Gold finishing) got blisters | 24 August, 2005

The blistering is around the plugging via.

I can forward you the pic.

For the plugging process, I'm not too sure how they plug. What is the correct practise for the plugging via.

Now, what they did is. They will do a tenting process for both side. Then open a solder resist of 0.4mm dia on the masked via (dia 0.2mm).Via @ BGA area, they will do 0.3mm solder resist.

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#36312

Brd(Electroylic Gold finishing) got blisters | 25 August, 2005

Send the pic to dave5252 at hotmail.com [you can't send pic through the SMTnet email thing]

For more on via plugging, tenting, capping ... look here: http://www.merix.com/technology.php?section=processes&page=pdf/Via_Fill_Plug.pdf

Something, a void either in the plugging material or between the double plugging, is expanding during heating and pushing the solder mask away from the board in the area of the via. Your fab is trying to compensate by applying a thicker solder mask tent over the via.

Plugging and tenting are doing the same thing. What's the point of doing both?

Consider: * Eliminating the plugging and just tent your via with a thicker solder mask. * Eliminating the tenting of via with a thicker solder mask and plugging from BGA side only and solder masking normally.

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#36356

Brd(Electroylic Gold finishing) got blisters | 27 August, 2005

From the pic, we see blistering, but none so close to via that we'd attribute the blistering to via, via plugging, or anything of the sort.

When we see blisters like this, we think of a surface contaminant being present on the boards at the time of mask application. Your board fabricator will have to isolate and deal with this is issue.

Another possibility [to surface contaminant present] is that the fabricator thinned down the solder mask (to make it go farther) and didn't change the cure recipe. The thinning down can expose copper, but more likely, degrade the adhesion and thermal resistance properties.

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