Electronics > Repair
Series defect on agilent 167xx boards?
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MarkL:
Hi Keith,

I think Nick is right that it's not corrosion.  The corrosion is crusty green on the surface, and when it gets underneath the soldermask it turns the copper grayish brown.

Below are a few examples.

The first two are the practically untouched 16712A that I mentioned.  I had to look hard to find anything, but it's there.

The last two are a 16534A card that I recently received.  This one is in terrible condition and fails self-test, and I was going to use it for a thread on how to repair these cards.  There is severe corrosion to traces, and on this one the metal back plate for the hybrid ADC on top has also been thoroughly attacked (it's not just copper that it likes).

EDIT: Hmmm.... seems the photos came out in the opposite order I posted them.  I'm sure you get the idea.
keitheevblog:
Thanks much for the sample images.

Yeah, I've been pretty lucky --- nothing even close. It's nice to see images of the exact type here.

The key feature looks like almost neon green crusty deposits.....

I'm going to pull my 16900 modules and check those too. My 167xx modules are all clean the best I can tell.

Thanks
keitheevblog:
Ok no photos yet because I was too tired to remember to take them.

However.

The 16951A I pulled last night has a considerably different designed runner. First, the runners are easily 1/3 to 1/4 the overall width --- very narrow in comparison. So instead of 6.5mm wide, they are something like 2mm wide.

Next, instead of being about 5" long, they are closer to 3-4" long.

First impression is that they sit a touch more proud....that is, a little taller. And more skinny. And they are less long. They take up MUCH less surface area as a whole. It also seemed to be that their placement was better --- given that they are smaller, are located in more "don't care" areas crossing fewer traces.

It does appear that they might have known of an issue and/or might have just been trying to conserve board space....

This module is from 2006 and looked pretty clean to me. Some surface dust. No visible corrosion that I can see.

Just another data point to put in our caps.

Thanks
MarkL:
The 16753A/54A/55A cards that I have all have the skinny runners too.  They're 3mm wide, and as you point out on your 16951A, are less in number.

They have less corrosion than my other cards, but it's still there.

While less in number, the runners cross several areas of dense escape vias underneath a couple of the BGAs.  Maybe it's same on the 16951A.  When I took the runners off, many of the annular rings on the vias were partially or completely eaten away and corrosion was down some of the holes.  I couldn't believe the card still worked.  Year 2002 serial number.

Out of the 5 16753A/54A/55A cards I have, only 2 of them work.  The picture I posted earlier in this thread:

  https://www.eevblog.com/forum/repair/series-defect-on-agilent-167xx-boards/msg1353955/#msg1353955

was a repair attempt on a 16755A card.  Also from 2002.

With any luck maybe they figured it out by 2006.
keitheevblog:
ok fellas, I've got some new information. Been on a warpath for days trying to find the right replacement adhesive tape. I think I've got a good start:

Don't try to use VHB acrylic adhesive tapes on silicone conformal coating. 3M application engineers told me that specifically it won't bond. 3M 830 rubber adhesive 442KW should work here, though. It has a nice feature too "Provides clean removability from many surfaces"

While 3M says you should always test the tape for suitability for your specifically application, they think there's a good chance that the 5952 series, specifically the 5915, should work. You cannot, however, easily remove this tape. It's designed to be permanent, although they publish a PDF with removal instructions.

While anything is possible, the application engineer said that it likely was not the adhesive that leached or had some bad interaction with the substrate/adherend. They said they've got "decades of the various formulations in hundreds of thousands of applications" and they thought it would be common knowledge (amongst his peers) and/or covered specifically as a warning if it was a problem. Take that for what it's worth.

He also said extensive tests with this tape in electronic applications have NOT been done.

I'm inclined to think that there was something corrosive on the board that then got trapped underneath the adhesive at the time of assembly. It's also possible that poor environmental storage conditions exacerbated the problem -- perhaps the adhesive/runner attracting or trapping some bit of water on a stored on the side board.

I think this answer is good enough for me. I will say that shearing off a component is definitely going to happen, so I'm going to replace the runners soon. I'll use just enough tape strategically placed to avoid high density trace/via areas.
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