The latest on tin whiskers in lead-free soldering?

You need a military product or two.

But even that may not help - it's getting hard to find non-ROHS components.

Joe Gwinn

Lead-free parts solder fine with 63/37 solder. That combination looks great but probably still has some whisker hazards.

There is debate about temperature profiles when soldering lead-free BGAs with leaded solder. Some people say you have to melt the balls, and some think that all you need to do is solder to them, which takes a lower peak temperature. We've done it both ways and both seem to work fine.

I've been using SAC 305 type solder for some time to finish assembling lead free boards, after they come off the pick and place machine. Yes, it is a lot more expensive that tin-lead. Mostly, I end up buying solder on eBay at about half list price. Some works better than others. The latest wire solder I have gotten is from Cookson, and it seems to wet and flow better than stuff I've used before. I normally run my iron at 370C (700F) but with a really heavy tip on my Weller WMP iron I can solder fine at 343C (650 F). I have excellent results with this.

Jon

• ---------- our -------------^

SAC has a higher MP than Sn96.3Ag3.7, and i understand that it has soldering problems, some of which you allude to. Those higher processing temps degrade everything..

The "plain" tin/silver alloy mentioned above seems to flow as easily as original tin/lead (aka 60/40 or thereabouts) and i have made zero adjustments to iron temp. Reflow also works like a charm.

What diff? The arts have so little solder on them that machs nicht.

Some more current info on tin and zinc whiskers.

I thought the Toyota incident was relatively recent. But looking at the NASA paper I see the car was a 2005 model. It just took five years to get the info to NASA... or maybe it took nearly five years for the whisker to form?

It was a 2003 Toyota Camry. The incident happened in 2005. The report was commission by the Dept of Transportation in 2010, and was completed in 2011. The full report is at: Looks like any potential difference over 2.6v will form whiskers. Amazing. See Pg 25.

I have to deal with tin whiskers in older GE MSTR radios, commonly used in mountain top repeaters. There are various fixes, but the one we've adopted is to wait until there are signs of sensitivity loss. Then we drive up to the mountain with an air compressor and service monitor, tear open the helical resonator assembly, blow out the tin whiskers with compressed air, and retune the cavities with the service monitor. It's been every 10 years so it's not a major problem.

Before the ban on leaded solder arrived, I decided to stock up on

Jeff Liebermann wrote

This is scary and it seems that nothing has actually changed, and all that the EU has achieved is to trash long term product life.

I do find this hard to believe...

Jeff Liebermann wrote

The 2.6V is actually the voltage needed to break down the oxide layer which forms on the whiskers and which stops them shorting things out.

The whiskers form without any power applied to the component(s).

Yes, lead free is a crime against humanity. It is designed by clueless politicians and gang-green infected whale hunter hunters.

It is a crime because industry wanted it so it can sell you a new pad every few years, and now it no longer needs to design in replaceable batteries, as the thing will last shorter than the batteries anyways. AND silver solder is poisonous to humans. And now land fill after landfill fills with pad and mobile phones and pods and whiskers basically.

All my equipment is military luckily so I am exempt.

;-)

On a sunny day (Sun, 28 Jul 2013 07:41:39 +0100) it happened Peter wrote in :

It was the PURPOSE of that rule: produce and sell more. For the same reason they change TV standards and other standards ever more often: sales.

It's a bit like the first gulf war when we saw on the TV news a laser guided bomb blow up a bunker by flying down the ventilation shaft. The same one, over and over and over again.

Every time this comes up, these same pictures come out. If whiskers really are such a problem why are there not many hundreds of pictures?

FWIW, I've been using lead-free for many years for other than ROHS reasons, and once you're used to the difference, it seems easy and reliable.

cheers

Absence of evidence is not evidence of absence. Tin whiskers is not something that the general public would find entertaining. Same with bulging electrolytic capacitors. That's a known major problem, yet few people outside of the industry even know that it's happening. It's much the same with tin whiskers. Once you're outside of the electronics community, nobody knows or cares about it.

In my personal experience, I've had to deal with tin whisker problems in 2-way radios on helical resonator cans and on square stake pin connectors. I've also seen various problems that magically disappeared after I brushed the boards, which were probably tin whiskers. It's far from epidemic, but certainly present.

However, if it's photos and horror stories that you want:

Enlighten me please. Why would you want to use RoHS solder other than for ecological reasons? I can possibly see it if you are using very dense PCB traces, because the non-wetting properties of RoHS solders will reduce bridging. What other benefits did I miss?

Syd Rumpo wrote

Googling suggests that the issue of whiskers shorting out component

What is a worry is that, immediately post the ROHS shafting of electronic manufacturing back c. 2005, a lot of chips went to tin-only plating on the leads, and this WILL grow whiskers. They grow up to 1mm per year. They grow rapidly in vacuum which is why this has been a huge issue in space and high altitude (unpressurised) applications.

But I see nothing having obviously changed on whiskers growing out of lead-free solder *joints*. There is a suggestion that SAC (silver loaded) solder suffers less from whiskers, but it's only a degree, nowhere near an elimination.

There is one conformal coating, Arathane 5750, which stops whiskers growing. It is very expensive (though probably insignificant on a per-PCB basis), very hard to get here in the UK, but most importantly conformal coatings are very expensive to apply. I have used them for many years, and they are a pain in the ****. You have to let the PCBs dry off, etc. We use CC on PCBs which have little toroidal transformers as it helps secure the windings in place. But it cannot be used on PCBs that have connectors, or mounting holes through which you are expecting earthing continuity, etc, unless you do fancy masking.

My guess is that anybody using pure-tin-plated chips ought to stick some Arathane 5750 onto the pins, at least. A quick spray through a template would do it.

Researching this leads to a really sh*t realisation that the EU has shafted all of us, and the big corporations (with the US ones behaving in the most disgusting manner when it comes to screwing suppliers) having a big play in it...

Higher softening and melting point for high temperature work. ROHS actually made things better in that regard as the Sn/Pb solder on component pins would often need to be removed before use. It doesn't take much Pb contamination to lower the melting point and weaken the solder joint, particularly with the small amount of solder used with surface mount.

Sometimes Sn/Pb solder is used to deliberately contaminate a joint to aid component removal. This solder is kept in a locked cabinet.

I've never seen a tin whisker in real life, and have spent many an hour looking at solder joints through a microscope.

Cheers

On a sunny day (Sun, 28 Jul 2013 12:17:03 +0100) it happened Syd Rumpo wrote in :

You may not have noticed them, AF118 was a common failure in TV vidicon cameras input stage:

Scares me!

Jan Panteltje wrote

I have just done hours of reading on this.

One way to guarantee getting loads of whiskers is to plate *bright* tin onto some substrate and then compress the substrate.

In that "1960s transistor" case above that is probably what happened. They started with a tin plated sheet and pressed it into the transistor casing, which compressed the tin coating inside it, causing massive whisker growth.

So that may be an extreme case.

I don't think bright tin has been plated onto IC leads. The tin I see is normally dull grey. That is just as well since the leads get bent into shape *after* plating.

Also tin plated IC leads go back decades before ROHS, with no reported problems AFAIK. So maybe the problem was known in the industry for a long time, which is what my reading does confirm.

The ROHS-related problems would be to do with the solder used, rather than component leads.

I don't think component leads were ever plated with tin-lead, were they? Can you even do that? You would have to solder bath immerse them I think, which isn't going to be done with an IC lead frame. That will always be plated, and I don't think you can plate tin-lead as such.

Maybe that's what they wanted...