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Comment by jcims | Hacker News Reader

Was curious what their treatment was going to be regarding tin whiskers. Not much there (of course this is point in time inspection so it kind of makes sense), but a quick google revealed quite a bit of study:

https://nepp.nasa.gov/whisker/

I thought they were just one of those low probability items until a Sunday morning when I was running live audio for a church service. Singer was mid verse and BOOOOM! Huge booming sound over speakers startling everyone into nervous laughter. I opened the cable up afterwards and sure enough found these alien crystalline structures growing between the conductors. It had shorted and even the little bit of current in the microphone vaporized about a mm of material.

Really really weird and I'm certain kept some folks up at night over the years.

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NASA and aviation in general are later adopters of lead-free. It definitely wouldn't have been reflected in older standards.

AFAIK, lead-free soldering is never enforced in space applications. An exemption is granted because of its extremely high reliability requirements.

On several levels. Avgas is still leaded.

Wow, that's disgusting.

It's pretty limited. Avgas doesn't mean jet fuel, as used by commercial aviation, it means the stuff you pump into piston engine light aircraft. Plus, at the risk of being obvious, the exhaust is either emitted way up in the air or, if at ground level, out in the middle of nowhere at an airport.

Whoa, that's crazy. It's going to take 50+ years to get the current engines out of operation. I wonder if new engines are able to run without.

Yes, there are light aircraft that run on diesel.

Not a pilot or aircraft owner, but my understanding is that part of the problem is because certifying a new aero engine is insanely onerous (as is certifying anything that goes on an airplane), a lot of basically obsolete designs requiring leaded fuel were produced long after auto engines switched to not requiring leaded gas.

Why would an engine require leaded gas, you ask? Because it helps keep the valve seats from degrading. We have other anti-knock additives, but nobody has figured out a replacement for the other properties that lead has.

And since aircraft are usually extremely long-lived, we'll be stuck with this problem until a substitute is found. Merely certifying new engines that don't require lead won't solve the problem because of the remainder of the fleet that does require leaded gas.

For those who want to know more about this: https://www.faa.gov/news/fact_sheets/news_story.cfm?newsId=1...

Essentially, we still don't have a viable replacement. The FAA was tasked with coming up with one by the end of 2018, but has been extended to 2021.

leaded solder is still allowed in the EU for medical equipment for instance.

Use leaded solder and either inspect the joint for complete coverage or solder dip the part beforehand. Then, conformal coat the circuit card with sufficient thickness for tin whisker mitigation.

Conformal coat really is the saving grace for tin whiskers. It's not perfect, a whisker can push through sometimes but then the whisker has to push back through the conformal coat again which is much harder.

Here is a picture that show how effective a solder dip can be https://nepp.nasa.gov/whisker/photos/pom/2004april.htm

About leaded solder and the environment: "Current alternatives are worse for the environment",page16 https://nepp.nasa.gov/whisker./reference/tech_papers/2011-ko...

I believe urethane conformal coating helps control whiskers problem.

> Was curious what their treatment was going to be regarding tin whiskers. Not much there (of course this is point in time inspection so it kind of makes sense)

Did you read their specs?

There's a small part about whiskers that already convey enough meaning:

> UNACCEPTABLE WHISKER

> A whisker is a slender needle-shaped metallic growth between a conductor and a land. Typically the result of mechanical stresses in high tin compounds, it is a reliability concern."

From the HN guidelines:

'Please don't comment on whether someone read an article. "Did you even read the article? It mentions that" can be shortened to "The article mentions that."'

It doesn't add anything to the discussion. And in this case it was very clear that the OP read the article and just missed that part.

Your comment would have been just as informative and less snarky if it was simply:

There's a small part about whiskers that already convey enough meaning:

> UNACCEPTABLE WHISKER

> A whisker is a slender needle-shaped metallic growth between a conductor and a land. Typically the result of mechanical stresses in high tin compounds, it is a reliability concern."

> > Did you read the specs?

> 'Please don't comment on whether someone read an article. "Did you even read the article? It mentions that" can be shortened to "The article mentions that."'

Not an article, but specs. You read specs carefully, you don't skim, especially to write long paragraphs about your personal experience

> And in this case it was very clear that the OP read the article

I disagree. Not read, skimmed at best.

> and just missed that part.

I agree: the most important part was indeed skipped.

>I agree: the most important part was indeed skipped.

You're factually wrong here. So the question would be where did this go off the rails?

"Whiskers" actually 'grow', they are not part of the soldering process[0]. Lead free solder is very susceptible to the phenomenon.

[0] https://en.wikipedia.org/wiki/Whisker_(metallurgy)

I did see that part, which is why I said 'not much' instead of 'nothing'.

The issue with whiskers is that they grow over time (which is why I mentioned 'point in time'). I didn't see anything in there about solder alloy selection or any other mitigation.

Oh, so you mean you're interested in whiskers over time, not after manufacturing?

Sorry for the misunderstanding then.

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