Lead free solder in system boards

[flanker]

Anyone notice the effects from any of the the major computer system board Mfgs. that are now using lead free solder as demanded by the European Union WEEE/RoHS?

There is a great deal being written about the growing of tin wiskers in pure tin solder joints.

The wiskers are fine like hairs that grow out of the soldered joints and in many cases cause shorts and complete failures in the system using the leadfree solder.

 

[PC eye]

One study on lead free solder can be seen at http://www.aimsolder.com/techarticles/A Study of Lead-Free Solder Alloys.pdf

One article that addresses the whisker problem is seen here.

ElectronicsWeekly.com

Thursday 7 September 2006

Ask Dr RoHS: problems with lead-free BGA solder balls


Thursday 20 April 2006

April 19, 2006
Dear Dr RoHS
Can unleaded BGA solder balls potentially grow tin whiskers as tin plated leads do? Annealing seems to be the standard approach for pure tin plated lead devices, but what about BGAs?
Are unleaded BGA joints as reliable as leaded? I hear all sorts of problems after n thermal cycles and that they are brittle.
David Cooke
Surrey Satellite Technology

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http://www.electronicsweekly.com/assets/getasset.aspx?ItemID=50659 Answer
Even tin-lead solder can potentially grow tin whiskers. It has, but it is extremely rare. So tin-inclusive lead-free solder balls cannot be guaranteed free from the possibility of tin whiskers.
However, I phoned around and no one I asked remembers hearing of a lead-free solder ball growing a whisker. Lead-free and lead-inclusive joints are differently reliable, neither being superior in all circumstances.
Lead-inclusive solder might have an edge with large BGAs under fast thermal cycling as it is more flexible than lead-free, and I have recently heard rumours - which I cannot substantiate and know no more of - regarding lead-free joint reliability under drop testing.
You may have to organise testing aimed at your particular environment. If you are already using that particular BGA in lead-inclusive form, do you need to change?
I would be interested in feedback from readers who have had reliability problems with lead-free BGAs on otherwise reliable assemblies. Or from anyone who knows more about drop test reliability.
Dr RoHS thanks www.twi.co.uk and www.lead-free.org
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