Creep Corrosion on PCB's

[redwire]

I'm seeing this on Western Digital HDD's and Synology NAS in dry, not corrosive home environments.

It's a black fuzzy slime on PCB's mainly on via's, any exposed copper.

Thought it was just due to manufacturing crappy PCB wash, but after searching the web- it is metal-sulfide dendrites that cause semi-conducting/shorting problems.
It looks like due to RoHS - lead-free, immersion tin and organic flux.

Do people know about this? I just learned it.
I use a toothbrush and IPA, give the board a scrub and it's OK afterwards. But under a BGA?

http://thor.inemi.org/webdownload/Pr..._Corrosion.pdf
https://community.wd.com/t/wd-hdd-pc...ame-it/13414/3

[capwizard]

Re: Creep Corrosion on PCB's

Ooh...or..oh.. My home-made untested organic flux. After few years I have return customers....

"...........But under a BGA?" How about Ultrasonic Cleaner?

[llonen]

Re: Creep Corrosion on PCB's

Often referred to as tin whiskers, a well known problem that plagued not just early transistors but a range of electronics. One of the reasons for the lead component in solder I believe, with this lead free rubbish it now seems to be making a comeback. From what I read ultrasonic cleaning can get rid of some of it but it grows back.

[budm]

Re: Creep Corrosion on PCB's

Dendrite:
http://circuitsassembly.com/ca/magaz...tory-1412.html
http://www.smtmagazine.com/index.php...9729/?skin=pcb

https://www.youtube.com/watch?v=COMTYzqe_XE
https://www.youtube.com/watch?v=AoGQB3EEUyE

Tin whiskers:
https://nepp.nasa.gov/whisker/background/

[srhofmann]

Re: Creep Corrosion on PCB's

One interesting thing to note from budm's linked articles is the fact that the dendrite growth was found on solder domes where they weren't completely covered by conformal coating. Also, the test was performed on "no-clean" assemblies, I wonder what the results would be if the assemblies had been cleaned first?

[capwizard]

Re: Creep Corrosion on PCB's

The Obsolescence of TV is at fast speed, plasma TV and CCFL TV already are out of date, Tin whiskers and Creep Corrosion are not common on TV service maintenance, more often I've seen are water-damage?

[Per Hansson]

Re: Creep Corrosion on PCB's

Yes here is how the precursor looks.
All WD drives I have look like this...

https://www.badcaps.net/forum/showthread.php?t=58024

[capwizard]

Re: Creep Corrosion on PCB's

Thank you, Per Hansson, I check my not working WD 2000: 200G IDE 5". See if you're right?

pic3, 4: U1 This Disc motor drive IC is burnout, it is a common problem.

pic 5, 6, 7 : The connectors to the HD heads, are like you said, are really bad, Thank you, I really did not pay attention to it.

[redwire]

Re: Creep Corrosion on PCB's

We're talking three different PCB problems?

Tin Whiskers - metal hair/tin crystals forming shorts
Creep Corrosion - copper/silver plating dendrites (fern shaped) forming bridging growth
Oxidation - oxygen reacting with the metal, basically corrosion so high resistance connection {no shorts}

The metallurgy mechanisms are different I think.

The 2005 WD hard-drive head contacts look like PCB gold plating (ENIG finish) against a tin connector? The motor is all gold connections. Ah the good old days.

[Slow_Frank]

Re: Creep Corrosion on PCB's

I too have seen this in a Synology DS412+ and it's replacement DS415+, took approximately 2yrs from new to failure. I have also seen it in a WD hard drive enclosure, searching the internet I found this paper that takes about it in extreme situations.

https://www.researchgate.net/publica...r_Environments

Pictures of Synology and HD enclosure are below. The thing I don't get is where the sulfur is coming from, possibly the rubber mounts? Other theory is that it is in the drywall, apparently it comes from coal burning plants and mixes in with the gypsum so comes out of the drywall with moisture. We do have a lot of coal burning plants where I live (Alberta), so maybe....