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

--- Quote from: keitheevblog on November 15, 2019, 08:33:40 pm ---...
My question was whether the pro-active approach to runner removal is a good idea or not. In boards where there are no visible signs of corrosion that are otherwise self-testing fine?

It occurred to me while I was removing them that you could possibly damage a board that worked fine.

Do you guys have an opinion on that?

--- End quote ---
In general, I'm strong a believer in "if ain't broke, don't fix it,", which includes things like re-capping for no demonstrated reason.  I've seen too many people damage perfectly working equipment.

However, in this case my opinion is to remove the runners proactively.  I have somewhere around 25 cards, and ALL of them had corrosion on them, some severe and some only in a few spots.  For several years I was in the the "not proactive" camp until two cards I had received working and had been using were suddenly dead one day.  I took the runners off and several traces had been eaten clean through.  Fortunately, repairing the traces brought them both back.  Not wanting to repeat this fate, I removed all the runners on all my cards and scrubbed the areas with isopropyl.

No additional failures yet, but this was fairly recent within the last year or so.

I was careful but not overly paranoid about scraping off SMD components.  I have at least two of each card type so I could measure the value on the other card for replacement.  (And, yes, there were a couple of accidents involving MLCCs.)


--- Quote ---I've been using a heatgun setting on low and trying to evenly heat just the runner. While the heat helps the adhesive release, I worry about these super tiny 0201's (or whatever) accidentally re-flowing. I'm guessing the surface tension would keep it in place.....but who knows?

My technique has been to use a plastic pry tool to get under an edge, and then wand the heatgun back and forth over the runner, all the while applying a lifting force. The runner does sometimes "pop" violently off the board.

I have noticed that the adhesive tape is both still sticky and flexible.....not hard.... and that I've been able to, in 95% of the cases lift the adhesive tape AND the plastic runner off fully intact.

Am I doing this right?

--- End quote ---

Sounds like your cards are newer if the foam tape was still pliable.  Most of mine were hard as a rock and crumbled when I tried to remove them.

I think if you're heating them enough to reflow the solder, you're applying too much heat!  The plastic runners would probably melt first.

A soft nylon tool works well if you have to do scraping.  I read that some people cut up an old credit card.

keitheevblog:
Mark,

Of your 25 cards, what cards and years of manufacture are you dealing with?

I have about 10-12 cards, and I've inspected about half of them. The serial numbers are US39xxxx, US40xxxx, and US42xxxx indicating 1999-2002. 16715As, 16717As, 16752A.

I also have MY45's -- Malaysia 2005, 16951s and 16910As.

Is the corrosion you're talking about very visible? I've seen your images posted, and the god-awful ones from Alexandre, but the majority of what I've seen with real problems look like really dirty, dingy, and I'm not surprised by the fact that there's corrosion on these boards.

But mine look nothing like that. They are clean. Now I use my 3M/SDS 497AJN ESD-safe vacuum on things, and IPA to keep them clean. I use a grounded wrist-strap at all times.

I'm not judging or humblebragging about the state of the boards here, I'm truly worried that I'm missing some obvious signs. Now I did see a tiny bit of corrosion on my stacking connector pins which I used deoxit and IPA to clean up.

I'm using 10x magnification to look at the traces underneath the runners and I'm looking very carefully. I just don't see anything.

So I'm trying to figure out why you're seeing it about 100% of the time, and I'm seeing it, well, very little. The most I've seen (and I'm not discounting this) is perhaps a light green surface-level tinge on the vias. And maybe that's worse than the traces!

Thanks,
Keith
MarkL:
Hi Keith,

The vast majority of my cards are US made.

16740A, 16741A, 16750A, 16751A cards are from 2000 to 2002, all US.

16534A cards are from 1995 to 1999, all US.

16753A, 16754A, 16755A are all from 2002, all Malaysia.

I recently acquired a 16712A card from 1999 (US made) and it is extremely clean, apart from a few dots of green corrosion on some vias.  It tested good and, to be honest, I'm not rushing to remove the runners on this one.

Generally speaking, my cards are all around 20 years old and 100% of them have (or had) corrosion to some level.  The rate of whatever is leaching out of the adhesive is probably related to their environment.  The boards I had go bad on me were in a clean, cool, dry area and were not powered on continuously.  The dust had been cleaned off, but runners not removed at that point.

The only card I have without corrosion is a 16720A pattern generator.  It doesn't have runners on the bottom because it doesn't have any components on the bottom.

I don't have any 169xx cards to compare.

I know that the corrosion has wicked into some of the vias on some boards because it has shown up on the other side in a couple of cases.  And those boards don't work, no surprise.  With no schematics, they are likely scrap at this point.  It's a shame that a 10 cent strip of foam tape is systematically destroying this impressive technology.
keitheevblog:
Thank you for the detailed reply.


--- Quote ---It's a shame that a 10 cent strip of foam tape is systematically destroying this impressive technology.
--- End quote ---

I couldn't agree more. It is a shame. Of course it's the weakest link in the fence idea. Even if they did a superb job in PCB layout, most of the component choices, good SQA on the software, etc etc --- After 20 years+, which is well passed the original window of support, anything is likely to break down.

I keep checking out my various modules. The 16715A which was misbehaving as a master in some cases, I removed the runners. All the areas underneath the runners were clear.

HOWEVER, I think I finally spotted my first piece of corrosion.

Is this it? Note this wasn't under a runner but bottom right(looking at module right-side up) edge.

I've made a couple passes with deoxit and IPA. I admit having a hard time capturing this image, depth of field, light, etc.

Thanks,
Keith
NickAmes:
That looks more like delamination on an internal layer rather than corrosion.
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