Electronics > Beginners
LED driver at -40degc ambient
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mzzj:

--- Quote from: Ian.M on August 21, 2018, 05:34:25 am ---You may find this page helpful: http://www.dbicorporation.com/tinpest.htm

--- End quote ---
I'm afraid that guy is borderline nutcase:
http://www.dbicorporation.com/rohsbib.htm
mdszy:

--- Quote from: mzzj on August 21, 2018, 01:43:38 pm ---
--- Quote from: Ian.M on August 21, 2018, 05:34:25 am ---You may find this page helpful: http://www.dbicorporation.com/tinpest.htm

--- End quote ---
I'm afraid that guy is borderline nutcase:
http://www.dbicorporation.com/rohsbib.htm

--- End quote ---


--- Quote ---For myself and my companies, in early 2005 I adopted the following version of the "Precautionary Principle", which so far has worked very well for me:

Don't buy-- or fly in-- anything manufactured in Europe.
Don't buy new electronic/electrical stuff, if you can find an older item (manufactured before 2006) that will do the job.
If you buy a new, expensive electronic/electrical item, get the longest warranty that you can for it.
If you buy a new, inexpensive electronic/electrical item, buy at least three, to give yourself a fighting chance that one of them will still work when you need it.
If you are replacing an older, working unit, HANG ON TO THE OLD ONE!
--- End quote ---

Holy shit, I'm glad I don't work for this whacko...
Ian.M:

--- Quote from: mzzj on August 21, 2018, 01:43:38 pm ---
--- Quote from: Ian.M on August 21, 2018, 05:34:25 am ---You may find this page helpful: http://www.dbicorporation.com/tinpest.htm

--- End quote ---
I'm afraid that guy is borderline nutcase:
http://www.dbicorporation.com/rohsbib.htm

--- End quote ---
Yes, he comes across as fairly obsessive, but he *has* collected a comprehensive list of technical references, including ones to books and papers that are not readily available online.
mdszy:

--- Quote from: Ian.M on August 21, 2018, 01:57:12 pm ---
--- Quote from: mzzj on August 21, 2018, 01:43:38 pm ---
--- Quote from: Ian.M on August 21, 2018, 05:34:25 am ---You may find this page helpful: http://www.dbicorporation.com/tinpest.htm

--- End quote ---
I'm afraid that guy is borderline nutcase:
http://www.dbicorporation.com/rohsbib.htm

--- End quote ---
Yes, he comes across as fairly obsessive, but he *has* collected a comprehensive list of technical references, including ones to books and papers that are not readily available online.

--- End quote ---

He seems to make it sound like lead-free solder shall be the downfall of humanity, though.
Ian.M:

--- Quote from: mzzj on August 21, 2018, 01:36:33 pm ---
--- Quote from: treez on August 21, 2018, 05:00:51 am ---
I hope the EU   have a clause in their regulations so that we can get our boards  made up with leaded solder...rant on

--- End quote ---

Nope, your led drivers are not on  exception list.  |O

Seem like Tin pest on lead-free solder joints is mostly academical problem, not too many real-world cases. I'd worry more about mechanical stresses from thermal cycling.

--- End quote ---

The problem is: Grey tin auto-catalyses the low-temperature transition from white (metallic) tin to grey tin.   As long as your equipment regularly cycles all tin in it to above +13.2°C, for long enough for the fairly rapid reverse transition to occur, you wont have any tin pest problems unless it is significantly sub-zero for a continuous extended period.  However, if some tin plated part of your device doesn't get above +13.2°C, (e.g. a shield or housing) it doesn't stop the clock on the tin pest, and at sufficiently low temperatures, a single grain of grey tin dust forced into intimate contact with the solder surface (e.g by differential expansion/contraction of parts in mechanical contact or near contact due to thermal cycling) can cause Pb free high Sn percentage alloys  to develop tin pest far more rapidly than would normally be the case.   

In Treez's application, that would mean that if the lights have to withstand Arctic winter conditions, there is a risk of tin pest related failure if they aren't used long enough to fully warm up on a daily basis.

Combined with your point about fatigue due to thermal cycling, choosing a ROHS compliant solder alloy for extended low temperature high reliability applications is *NOT* at all easy.   Even NASA don't have any good answers except:

--- Quote ---3.2.6 TIN PEST (TIN DISEASE) MITIGATION
Lead-free Tin (Sn) and Lead-free Tin (Sn) technology shall not be used in applications with exposure to
temperatures at or below -30°C -22°F), unless combined with one of the following alloys by weight
percentage:
a. Not less than 5 percent lead (Pb)
b. Not less than 0.3 percent bismuth (Bi)
c. Not less than 0.5 percent antimony (Sb)
d. Not less than 3.5 percent silver (Ag)

--- End quote ---
https://standards.nasa.gov/file/283/download?token=rMus0Zx4

I don't have the data to asses the risk in relation to the risks of other possible low temperature and thermal cycling related failures.   Maybe if you plow through the references from DBI corp's tinpest page, you'll have enough data, but its going to be highly dependent on the exact solder alloy used, and the the purity of tin plating on other parts of the device.
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