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Comment by nrp | Hacker News Reader

Ideally, we would be building devices that don't suffer from tin whiskers in the long term. Pragmatically, the vast majority of e-waste is being generated from simpler failures than tin whiskers (degraded batteries, simple mechanical breakage, changing standards and performance requirements, etc). In that case, it is better that the supply chains for those products are lead-free, reducing harm in production and in disposal.

We need to make our consumer products longer lived and circular, and that should be a prerequisite for RoHS exemptions (as it is currently for certain classes of long lived non-consumer devices).

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Funny, the simplest thing to do there, and relatively cheap, is to lacquer the whole device after it's soldered. This is done on military grade hardware - or even tougher conformal coating.

Would that help against lead, or against tin whiskers? AFAIK tin whiskers can develop through lacquer too. But probably it helps some.

> Funny, the simplest thing to do there, and relatively cheap, is to lacquer the whole device after it's soldered. This is done on military grade hardware - or even tougher conformal coating.

That helps avoid tin whiskers, but those aren't the only problem with lead free solder. It doesn't flow as easily as tin-lead, so dry joints are more common. It's relatively brittle, so it's more susceptible to vibration and thermal fatigue. Melting point is higher so components are more likely to be damaged during soldering.

Military hardware is exempt from RoHS for good reason.

Sadly, no, this does not avoid or stop tin whiskers at all. The general technique you are referring to us called “conformal coating”. It can help a bit but it does not stop growth. Also, at that scale the whiskers are super strong and easily puncture right through the coating.

This is a deceptively complex topic (as I learned over the years). For example, a whisker that does not penetrate the coating will either buckle and curl-up under the film or grow laterally under it. With fine pitch components having pin-to-pin gaps in the range of 0.25 mm, a short between pins can happen in just a few weeks.

Conformal coating is useful for other reasons, but, ultimately, it isn’t a solution for tin whiskers.

Back in the day I even looked into using specially formulated epoxy encasement. What starts happening there is that the coefficient of thermal expansion differential between The epoxy, board and components can cause all kinds of failures...and it still does not stop tin whisker growth or buckling.

This is fascinating, I'd never heard of tin whiskers before today. From a short look at the literature, nickel-palladium-gold alloys seem to be an alternative lead-free finish that doesn't suffer from whiskers. Have you worked with that at all? Does it have other shortcomings?

Well, being that most of my work during the last few years has been in aerospace we just use conventional lead-containing solder. When you can't afford for things to fall out of the sky you go with what you know works. We've known about tin whiskers since, I think, the 1940's. In fact, if I remember the history correctly, we added lead to solder precisely for this reason way back in the prehistoric era.

I might be diving into some industrial work soon that does not benefit from RoHS exemptions in this domain. This is one of the important cards in my kanban board...likely a rabbit hole that will not be pleasant to navigate.

I took a quick look myself. Here's a note from Maxim with interesting data:

https://www.maximintegrated.com/en/design/technical-document...

I've used pretty much all the conformal coatings they list in this article. What they don't go into is buckling under the coating, which can short adjacent pins in fine pitch chips.

I truly hate this problem. I has wasted more of my time over the years than anything else. RoHS is, in my opinion, a very misguided directive. It's a perfect example of when politics gets ahead of reason and fear-mongering wins over science. If we are not careful we are on track to do something similar with climate change.

> the vast majority of e-waste is being generated from simpler failures than tin whiskers

I can't assert or challenge this conclusion because we simply do not have the data. This is yet another reality of this issue: Tin whisker failures in the consumer domain are nearly 100% unreported.

Consumers are certainly not in a position to conduct the forensic work required in order to determine failure modes. My guess is that the large majority of devices are thrown out upon failure, which means we know nothing about why they failed.

Companies, on the other hand, frankly, have little incentive to conduct that research other than to use best practices during design. If a product survives a couple of years they are good. This isn't due to some dark profit motive, it's just a reality of business. You simply can't ask every single customer to send you their failed hardware for expensive --very expensive-- forensic analysis no matter their age or condition. This would mean having to manage a process involving forensics of millions of devices per month or year, depending on scale.

When I was investigating tin whisker mitigation options I explicitly sought out data from the consumer electronics domain. I quickly discovered there was none, at least nothing useful. This is why I don't think a statement such as the one you made is neither right or wrong, it simply has virtually no supporting data in either direction.

I should rephrase. From my experience in consumer electronics, the vast majority of instances of consumers stopping using a device are not from unknown failures. They are from visible failures (including reduced battery life), software/content incompatibility or obsolescence, or the consumer just generally losing interest in the device. I should caveat though that this is in PC and mobile categories. It’s plausible that things like appliances don’t fall into those failure or obsolescence modes and could be facing unknown failures that are solder related.

Yeah, it's hard to quantify in any meaningful way. That's why I said I am not in a position to confirm or challenge what you said and all I know is that, for the most part, we can't really make scientifically supportable statement about the consumer world (by this I mean with actual published data from an authoritative source). We are blind.

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