Tin Whiskers: Still a thing?

[EvilLOON]

So I stumbled across the article I will post below.

Seriously, we are still dealing with tin whiskers?  After all this time I figured we would have figured a simple chemical solutions to this problem.  So uh, why are we using tin in so many products? I mean on top of it all their putting the stuff on the important sensors on vehicles.  Important meaning things like Electronic Throttle Controls.  Reading stories about ETC getting stuck in the open position  .  So what's everyone's take on this? Is this truly still something that's going to cause huge issues?

http://cartech.about.com/od/Safety/a/Electronic-Throttle-Controls.htm

[John Coloccia]

There is a simple solution.  We figured it out decades ago.  Mix some lead in with the tin.

[ignator]

100% pure Tin use in electronic became a problem when the EU wanted to stop lead contamination. So this became a ROHS compliance requirement for all electronics.
My industry was Avionics, and it is a real big deal. Component vendors don't want to manufacture any low volume component with our very small usage that uses lead.
The bigger issue is that the lead provided a soft interface between PWB and component, and was part of the reliability to temperature cycles.
In Avionics, you have to perform common mode safety analysis as part of fault propagation. When your using dual channels (or triple channels) architecture for single fault safety design techniques, and you now can grow shorts that exceed the 50 year olds design standards of 10mm segregation, the designs now need a better method of just physical separation on a PWB.
As our designs have a 35 year life, and they are certified products, (meaning you re-certify if you make all but minuscule changes, so you don't change designs) the tin whisker issue had to have methods of preventing.
The big method is the PWB products have a conformal coating, mainly used for humidity. But as it was an electrical insulator, it provided short protection from whiskers.

The avionics industry was given a pass to continue using lead in electronic production, so most of the products that were surface mount just used a lead based solder flux for reflow. This provides the pure tin  with lead contamination. And yes there still are thru hole products made that use a lead solder based wave soldering machine.
I'm glad I'm retired from this as it was getting tiresome to do tin whisker analysis every time you changed a component.

[EvilLOON]

Scary to think planes could drop out of the sky because of tin whiskers. 

So yah I'm aware that lead was the fix and then the EU, US, and other countries limited or banned the use.  What I can't understand, why they haven't found something to cure this.  My reading has even told me that their still not 100% sure what causes it.  It's just really silly that this is still a thing.

[CatalinaWOW]

You do understand that some problems are really hard?

The lead tin soldering system was developed over decades (or even centuries if you take it's antecedants in the tin-smithing business).  A system to replace it must meet a multitude of requirements.  The system has to have a chemical affinity for leads and circuit traces to allow fusion bonding.  It has to be somewhat malleable to take up the stresses that result from different temperature coefficients of the various parts of the system (circuit board, conductive traces, lead frames, packages, etc.).  It has to be non-poisonous, non-polluting and easy to clean with materials that are also non-poisonous and non-polluting.  It has to melt at a temperature that doesn't fry the components being connected and it has to cost a reasonable amount.  It would be really nice if it was compatible with the existing infrastructure for fabricating and repairing electronics, and it would be nice if it didn't require significant retraining of the workforce.  Plus a number of other factors.  Most of these factors interact in some way.  For example, if your new mix requires a somewhat higher temperature for fusion (most of them have), the mechanical requirements become harder because the thermal expansion differences are bigger.

Finally, once you have found your magic mix that meets all of the above, you need years of data and tens of thousands of samples before you are sure that it doesn't have some hidden fatal flaw.

[T3sl4co1l]

AFAIK, precise alloy formulation and temperature control during reflow have, if not conquered, then at least significantly extended, product life.  You don't hear about LCD TVs and cell phones dying from mysterious whiskers, they die from capacitors or trendy fads.  (One would still expect some "infant mortality" from bad processes, but they're probably just thrown out without analysis.)

Extreme lifetimes would seem to select against any kind of risky thing; AFAIK, even a good process will eventually whisker on the decade scale.

I suppose the metallic* lining is, aviation can afford huge prices anyway, since 90% of the BOM cost is paper trails already.  Adding a lead production line, at direct cost to the customer, isn't exactly heart breaking.

* "Silver lining" being the common turn of phrase... but silver plating is notorious for whisker formation, too. So a lead lining would be more appropriate here...

Tim

[CatalinaWOW]

Don't forget medical, military, space, industrial and to some degree automotive in the groups wanting long lifetimes.  All except the last are low volume relative to the market drivers, and all end up paying price penalties

Special alloy formulations seem to be working fairly well, but weren't fully standardized the last I checked, and don't have a long enough track record to be really solid for applications that really matter. 

[EvilLOON]

Yah some of the new alloys show promise. They are working with an alloy of gallium and tin.   From what I know it's currently only used in some soldering compounds.

What is always strange about tin whiskers is the fact there is such limited information on the subject. TV's could be dying to tin whiskers in some situation, but people just toss them to the trash.  Why bother fixing this when I can go replace the whole thing for about the same price. On top of that, since the whiskers are damn near microscopic, most people will never see them if they develop.

I would like to see more information about how much stuff is actually effected by this.  Did that power supply blow a cap or did tin whiskers short it out?

Appreciate the feedback.  Wanted this talk to be informative and fun.