Electronics Assembly Knowledge, Vision & Wisdom
Reliability of Tin Lead Solder vs. Lead Free Solder
Reliability of Tin Lead Solder vs. Lead Free Solder
The issue of tin-lead solder versus lead-free solder reliability and whether lead in solders used for circuit board assembly impacts the reliability.
Board Talk
Board Talk is presented by ITM Consulting

Phil Zarrow
Phil Zarrow, ITM Consulting
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.


Jim Hall
Jim Hall, ITM Consulting
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.

ITM Consulting
* EMS Qualification, Evaluation and Selection
* SMT Process Consulting and Troubleshooting
* SMT Process Development and Set-up
* SMT Process Audits
* Lead-free Process Readiness Audits
* SMT Process Optimization
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Transcript
Phil
Welcome to Board Talk with Phil Zarrow and Jim Hall of ITM Consulting, the Assembly Brothers, pick and place. Coming to you from the ITM cave high above Mount Rialto.

Wherever Mount Rialto is. We are here to talk about electronic assembly, materials, equipment, components, practices and procedures, among other things. Jim, today we have a question on lead-free reliability, SAC vs. tin-lead.

The old one short of the meaning of life. This is from L.B. L.B. is saying could you please give me some further explanation of your answers regarding the tin-lead versus lead-free versus unknown leaded alloy reliability issue?

Jim
What answers were they?

Phil
I don't know. We must have said something, which was true. We must have parted some wisdom.

L.B. goes on to say from all of the reliability problems that I have read about with lead-free alloys for circuit board assembly it seems like almost any amount of lead is more reliable than none.

Jim
I know where L.B. is coming from and I can guess what I said. This idea that any amount of lead is better than none addresses one specific reliability issue and that is whiskers, tin whiskers.

The presence of lead, even in a small amount 1 or 2%, is the best way to mitigate tin whiskers. So if you are building space satellites or pacemakers or any ultra-high reliability where you are concerned about shorting due to tin whiskers adding any amount of lead will significantly reduce, if not eliminate, that reliability issue of tin whiskers.

What I am assuming I was talking about was the many more common reliability issues such as drop shock, vibration and thermal cycling where in most cases lead-free has been found to be at least as reliable as tin-lead, except for some high-rel, high-stress environments where the jury is still out and we are still trying to understand the complete issue to be certain that we can build a pacemaker or something like that, assuming we can mitigate the whisker issues, in terms of thermal cycle reliability being the biggest one.

So that was what I was concerned with. When I say unknown lead-free reliability that is for these ultra-high stress, high-reliability, long-life factors.

Again, the more typical failure modes of thermal cycling, drop shock and vibration where we just don't understand the nature of the failure mechanism to have complete confidence in the lead-free alloys in terms of the long-term reliability. But yes, if you are worried about whiskers, lead is the way to go. That is why people building satellites, all of the tin finishes on the leads come off and are replaced with tin-lead.

Phil
This is a question that persists. It started in the dark days prior to 2005 and the implementation of ROHS was still being debated and kicked around.

More and more papers are being written to the contrary of what our participant has asked here. It is all pointing in the direction that Jim mentioned.

This is the stuff we have been reading and more and more long-term data is being harvested as we go on. It is now long-term data. We are now 11 years past.

Jim
That's right. An article published by IBM referring to servicing that nobody is asking for an extension of the server exemption for lead-free because all of the problems have been solved. They are going to make even enterprise-level servers with lead-free because they have developed the knowledge to have confidence in their reliability.

Which has taken a lot of work. They have just achieved this in the last couple of years. They have been working continuously since before ROHS to understand the problems to achieve the confidence in the reliability in these different server products which are of course very critical and long-life, very high reliability.

Phil
That is very significant and telling.

Jim
Nobody is building hard pacemakers for lead-free yet.

Phil
Well you have to ask yourself, would you want one? With what we know so far and everything else? Do you feel lucky?

We hope we steered you in the right direction on that one. You have been listening to Board Talk with Phil Zarrow and Jim Hall. Remember Board Talk melts in your mind not in your ears. And whatever you do...

Jim
Don't solder like my brother.

Phil
And please don't solder like my brother.

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