The latest on tin whiskers in lead-free soldering?

[Raveninghorde]

Having done a lot of reading, I think the industry has got away with
it, due to a number of factors:

1) The whiskers need an elevated temp to grow well, say +60C

2) The whiskers need a reduced pressure to grow well (aircraft and
satellite apps)

3) The whiskers won't grow on component leads unless *bright* (smooth)
tin plated, which most aren't (but some definitely ARE)

4) Ref 3) what really helps is if the surface is under compression
(concave curve e.g. the *inside* of a transistor case)

5) SAC solder doesn't seem to have a big problem with whiskers because
the surface finish is very dull

6) IC lead pitch miniaturisation stopped c. 0.65mm pitch (went to BGA
for high lead count packages)

7) Very few products are going to fail within say a 2 year warranty

8) IF SOMETHING FAILS IT GETS CHUCKED AWAY AND NOBODY LOOKS FOR
WHISKERS!

9) The vast majority of electronic mfg is consumer stuff which gets
chucked away after a few years at most

So there you are...

I *would* be concerned about elevated temps and TSOP packages, in
industrial products which are expected to work for years. Conformal
coatings can be used there, or just use leaded solder and nobody will
notice

The conformal coating I mentioned earlier is difficult to store (6
month shelf life and a crazy price) and extremely hazardous if warmed
up.

Does anybody make SMT solder paste with say 2-3% lead? I guess it must
exist because the military demand 2-3% lead.

We have used SAC solder since RoHS came in. All are stuff goes to
industry and military so any failures are chased down to the root
cause. We have not found a single failure due to whiskers. We never
conformal coat.

Possible reasons.

SAC solder.

We have only recently moved to ICs with a lead spacing of less than
0.8mm. Many new parts don't have a large body version so we now have
to use small pitch devices. I have been designing in 0.65mm pitch
parts for about 2 years and 0.5mm pitch for a few months.

Luck?

 

[Peter]

We have used SAC solder since RoHS came in. All are stuff goes to
industry and military so any failures are chased down to the root
cause. We have not found a single failure due to whiskers. We never
conformal coat.

Possible reasons.

SAC solder.

I have not found any good data suggesting that silver stabilises the
solder, one article saying it has no effect, but I suspect that it
*does*.

It certainly makes it flow much better.

However the flux used also makes a *dramatic* difference (to hand
soldering, at least). The Almit solder I mentioned earlier has 3-3.5%
of flux which is relatively high and clearly this helps too. We solder
at 360C - same as with 63/37.

We have only recently moved to ICs with a lead spacing of less than
0.8mm. Many new parts don't have a large body version so we now have
to use small pitch devices. I have been designing in 0.65mm pitch
parts for about 2 years and 0.5mm pitch for a few months.

Luck?

Possibly...

0.65mm is common enough - has been for over 20 years. 0.5mm is much
less common.

The "problem" is that if you take my hypothesised list of why
everybody has got away with it, and cross off each item which might
have "helped" you, it's easy to see how IF there was a problem it
might go undiscovered for quite a while.

Example: About 10 years ago we placed a few hundred 2.2uF 25V tants
backwards. They were biased to 5V. I found it only weeks after we
shipped the product, all over the world - by accident: I took a unit
for some +60C tests, and it failed within about an hour. Another one
did too. I quickly found the problem. We recalled the lot, giving
people DHL account numbers to return them on, and shipping new ones in
advance. Cost us a fortune. We got all but about 20 back. Those 20
never came back... Either they never failed (at say +30C they would
have lasted probably years) or they failed and got binned... So, many
little things can conceal a problem. At the extreme end of things, if
you sell a product cheap enough, say under €50, into the industrial
market, you won't get returns anyway - unless you happen to ship 100
to the same customer and they all pack up! (I replaced that tant with
a ceramic, right away Now we use tants only where we need the
specific range of ESR).

The space and military people are not taking any chances anyway...

IOW, I see no evidence that whiskers don't happen.

 

[Peter]

From my warped position, I find the higher temperatures to be more
difficult to work with, more destructive on the iron soldering iron
tips, and produce far more "cold" solder connections if moved during
cooling. It's also more difficult to inspect as a normal and "cold"
solder joint have a very similar surface finish.

We actually find we can hand solder with the Almit stuff at 360C (same
as before) and we can reflow solder with some other brand of SAC (we
use a subcontractor for SMT) with a temperature profile which is
within the specs of the old non-ROHS parts.

What one has to watch especially is miniature electrolytics. We had
hundreds of Nichicon 50uF 50V ones go "dome shaped" after the
contractor put a 1000 circuits through a very slightly higher (ROHS)
temp profile. We changed to another Nichicon P/N and it's OK now.

I presume you mean accidental lead contamination. Mixing RoHS and
leaded solder creates a dull and very brittle joint.

I think soldering non-ROHS components with SAC solder works OK,
because very few components have lead on their leads. Or is this
wrong? The Japanese went unleaded c. 2002.

Anyway, soldering ICs with 63/37 coated leads, using SAC solder, works
fine. The final product is not strictly "ROHS" compliant of course but
nobody can tell by looking at the board visually because SAC solder
joints looks crap compared to 63/37 ones anyway

I sometimes run
into the problem when repairing 2000-2005 vintage PCB's, that may user
either type of solder. I try to use the same type but sometimes get
them mixed up. When that happens, I have to clean and re-tin the
solder tip, use a vacuum desoldering station to remove as much of the
contaminated mix as possible, and then resolder with the correct type
of solder.

OK I can see that. Rework is a problem.

Not my idea of fun. Sometimes, I wish the EU had required
a warning label for users of RoHS solders. The RoHS logo on the PCB
is usually a good enough clue, but I've been fooled a few times by
counterfeits.

The ROHS logo probably means the company had their arm twisted by some
big customer, but they continue to use 63/37

Everything made in China in last 10 years has ROHS on the carton.

Same with the stupid CE mark...

In any case, intentional contamination of a solder joint, in order to
facilitate component removal, also doesn't strike me as sufficient
justification to intentionally switch to RoHS solders.


Look for something that is plated with pure tin or zinc. You will
need a microscope or preferably a USB microscope and some really good
lighting. Look for tin plated connectors from the 80's that have been
sitting on a shelf for at least 10 years. The whiskers are
sufficiently fragile that even walking across the room will blow them
away. Therefore do not move the PCB in open air very quickly, and
shield the PCB from and air flow. I ruined a good picture by simply
closing the office door. That's also why I like using a USB camera,
where I don't need to move the PCB. Lighting is important, but I find
that my pocket Maglite or LED ring on the USB camera are good enough.

I saw the DB connector pictures, with massive amounts of whiskers. But
surely if the connector is mated, the whiskers cannot short anything
out. They cannot do anything useful on a female connector; it is only
on an un-mated male that you can see them, and as soon as the male is
mated with a female they will be swept away.

A LOT of cheap DB connectors that have the earthing fingers (and thus
have a high mating force) are often tin plated. The higher quality
ones, and the milspec ones, always without the fingers, never use tin
AFAICS.

 

[Syd Rumpo]

Sorry, but I can't imagine any device that needs to have its
connections (component pins) removed before use. Specific examples
would be useful. In any case, I don't see this as a sufficient
advantage to justify a change to RoHS solders.

No, I mean that the non-ROHS part has its legs or pads double dipped in
lead free (a 'dirty' bath followed by a 'clean' bath) to remove the lead
as far as practical. It's not a matter of ROHS compliance, rather to
make joints which will be reliable at high temperatures. Nowadays,
that's rarely done as nearly everything is now lead free.

<snip>

Sn/Pb is easier to work with, I agree, but the evils of ROHS are
overstated. You get used to it, you carry on, the products work.

One side benefit of lead free solder which I've observed, is that you
can send any manual assembly staff on a soldering course without
upsetting them

Cheers

 

[Peter]

No, I mean that the non-ROHS part has its legs or pads double dipped in
lead free (a 'dirty' bath followed by a 'clean' bath) to remove the lead
as far as practical. It's not a matter of ROHS compliance, rather to
make joints which will be reliable at high temperatures. Nowadays,
that's rarely done as nearly everything is now lead free.

Wouldn't it be easier to solder that part with 63/37 solder and keep
quiet about it?

Sn/Pb is easier to work with, I agree, but the evils of ROHS are
overstated. You get used to it, you carry on, the products work.

One side benefit of lead free solder which I've observed, is that you
can send any manual assembly staff on a soldering course without
upsetting them

Very funny

The other person's comment about ROHS being a conspiracy by the EU to
make money... I think it is just what one gets from the intellectually
superior "intellectual masturbators" in Brussells. These very highly
paid and very smart people love making regs, and if big business hates
them that's a bonus. No need to have supporting data...

 

[Syd Rumpo]

Wouldn't it be easier to solder that part with 63/37 solder and keep
quiet about it?

No, it would fall off at high temperature - at 180'C ambient 60/40 is
very, very weak and a little vibration is all it takes. Fine pitch
parts leave little pad area for 'structural' solder so you need to give
it your best shot.

The issue is not ROHS compliance, we could easily be exempted from that.

<snip>

Cheers

 

[Peter]

No, it would fall off at high temperature - at 180'C ambient 60/40 is
very, very weak and a little vibration is all it takes. Fine pitch
parts leave little pad area for 'structural' solder so you need to give
it your best shot.

The issue is not ROHS compliance, we could easily be exempted from that.

You are running at +180C ambient?????

You should be brazing with silver solder

 

[Syd Rumpo]

On 28/07/2013 22:28, Peter wrote:

You are running at +180C ambient?????

You should be brazing with silver solder

The next thing up from the various lead free solders is HMP (high
melting point) solder with a melting point of about 300'C. Ironically,
this is mostly lead and it is sometimes used. I have hand soldered a
few TSSOP 48's using this as an experiment - it was very difficult and
the yield was about half. Silver braze is IIRC around 650'C, I've used
it but not on semiconductors! Lovely stuff, with the flux applied
correctly it flows like mercury.

Cheers

 

[Fred Abse]

I have never once seen a tin whisker under my 20x stereo inspection
microscope in many years of using lead free solders.

Recommended practice is up to 300x magnification, with oblique
illumination. Ring, "shadowless" illuminators are no good. The NASA site
has photographs taken both ways. The difference is pronounced.

Have you seen any real tin whiskers yourself?

Not personally, but I've seen the effects of the several hundred amp
metallic-vapor arcing that they can instigate. Whole busbars, just not
there anymore.

 

[rickman]

Thank goodness airplanes won't fall out of the sky and
nuclear reactors won't blow up if my stuff croaks. So, I
don't need traceability. Since I'm a one-man shop, I have
to do EVERYTHING here, from buying parts and designing boards,
to building, testing, shipping and customer support.
I really can't handle any more levels of paperwork.

Tell me about it. I recently was able to turn my production testing
over to the fab house that makes my boards reducing my work to
paperwork. But my customer has moved production to Mexico so I am doing
international shipping now. That is *such* a hassle if you don't know
the ropes. Even knowing the ropes it is not so much fun. I spent a
bunch of time today dealing with not having written down my password for
the government AESdirect site. Their requirements for passwords are not
only far, far beyond what any web site I've ever used includes, it isn't
even documented properly on their web site. I probably spent two hours
total just trying to get onto their site over the last few days. Of
course that was my fault for trying to *remember* the insanely complex
password. I should have known better, they make you replace it every
two months anyway and if you don't use it for a month they deactivate
your account...

Then there is tax time...

 

[rickman]

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.

What? They've changed TV standards once in some 60 years... that is
"ever more often"???

 

[rickman]

"Jeff Liebermann = lying radio ham cunthead"



** Yes it FUCKING is - you brainless, bullshitting TWAT !!

1. Whenever the evidence SHOULD be there and is NOT.

2. When there is simply no proper supporting evidence at all.

FYI:

The NUMBER ONE proof that something is 100% BULLSHIT

- is that nothing *credible* makes it fact.

Idiot.

Wow, such a breath of fresh air...

 

[Spehro Pefhany]

What? They've changed TV standards once in some 60 years... that is
"ever more often"???

The original set-top box:
http://tv-boxes.com/uhf/philcoUHF.jpg

... from that to 8K 3D TV, there have been a few changes.

Best regards,
Spehro Pefhany

 

[rickman]

The original set-top box:
http://tv-boxes.com/uhf/philcoUHF.jpg

.. from that to 8K 3D TV, there have been a few changes.

Really? From the time they introduced color and UHF I don't recall any
standards changes until we had HDTV and digital transmissions. What did
I miss?

 

[Spehro Pefhany]

Really? From the time they introduced color and UHF I don't recall any
standards changes until we had HDTV and digital transmissions. What did
I miss?

UHF and color are already two changes. cable boxes, digital cable
boxes, HD and digital HD cable boxes, VCD, DVD, Blu-Ray, 3D, 4K, 8K.
RCA->Component->HDMI, internet (with Hulu, Netflix, Slingbox,
Chromecast etc.) Lots of changes. Though they did succeed in
preventing analog HD from ever being adopted.


Best regards,
Spehro Pefhany

 

[DecadentLinuxUserNumeroUno]

UHF and color are already two changes. cable boxes, digital cable
boxes, HD and digital HD cable boxes, VCD, DVD, Blu-Ray, 3D, 4K, 8K.
RCA->Component->HDMI, internet (with Hulu, Netflix, Slingbox,
Chromecast etc.) Lots of changes. Though they did succeed in
preventing analog HD from ever being adopted.


Best regards,
Spehro Pefhany

You not read too well...

He said the window between UHF's introduction and HDTV's first
standard.

There was no hulu or any of that crap. It was just as MPEG-2 was being
formed that the HDTV standard got mapped out too.

ALL satellite transponders were still being fired with standard 4:3
SCPC and each 6MHz slot still only carried one channel.

All the cable boxes (companies) did was expand the channel fill to
include the rest of the already existing band allocation. At ONE channel
per 6mHz slot. After MPEG-2 and As HDTV was being formed, there came
MCPC
and a new compression schema which allowed those same 6MHz wide channel
slots to carry more than one channel. That was when we saw our channel
counts shoot up and satellites that were already in place multiply their
capacity overnight. But the NTSC video standard that constructs the
image... not much change there.

 

[Spehro Pefhany]

You not read too well...

He said the window between UHF's introduction and HDTV's first
standard.

Which, you say, is 60 years?

 

[josephkk]

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.

Hot dip plating has been around for a long time. For Zinc on Ferrous
metals it is called Hot Dip Galvanizing. Really common.

?-)

 

[Peter]

Hot dip plating has been around for a long time. For Zinc on Ferrous
metals it is called Hot Dip Galvanizing. Really common.

I know, but I was talking about IC lead frames, not busbars or water
tanks. IC lead frames are normally stamped out and plated.

Also, Japan went lead-free about 15 years ago and if whatever goes
onto IC lead frames was making whiskers, we would know about it by
now.

I've never seen IC lead frames plated with bright shiny tin, or bright
shiny anything. They are always grey.

Europe (and the USA being forced to follow commercially) went lead
free c. 2005 onwards.

More importantly many companies in the *industrial* marketplace (i.e.
where products are not chucked out after a few years) used the Control
& Monitoring exemption and didn't go LF till much later, and *that* is
where a problem could be lurking.