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| February 10, 2012
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Circulation Over 51,000
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March 10, 2010
Plating Lead Free Parts for Tin/Lead Assembly
We work with an aerospace manufacturer on a PCB assembly that includes Pb-free components (no BGAs). The device is processed using SnPb (60-40) solder, but this does not solve the issue of Sn plating on the leads and the risk of tin whiskers.
According to information on this website http://nepp.nasa.gov/whisker/ tin whisker formation is an issue on the exposed component leads outside of the solder region.
Is there a process that can be used to re-plate component leads to add Pb?
E. B.
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Hot solder dip is the accepted process for replacing the tin termination with tin/lead. The process involves dipping the tin terminations into a sacrificial solder pot with Sn/Pb alloy to dissolve the tin into solution.
Then flux the terminations followed with a dip into a fresh Sn/Pb. The process must me machine controlled for repeatability. There are several companies that do this as a service. Follow this link to see a video . . . Hope this helps.
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Alan Cable
President
ACE Production Technologies
Alan Cable, the principle owner of ACE production technologies Inc. has over 40 years experience in the electronics manufacturing arena. Alan's expertise is high production manufacturing automation, equipment design and process engineering. For the past 25 years Alan has focused specifically on soldering issues relating to component solderability, lead tinning and selective soldering, owning several companies with this focus.
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I believe several companies exist that will redip a no lead component to give it a lead finish.
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Steven Adamson
Market Specialist
Nordson ASYMTEK
Market Specialist for Nordson ASYMTEK. Mr. Adamson worked for Kodak, Motorola and Plessey, ICL in the UK with 5 US and 2 UK patents. He was awarded a HNC in electrical engineering and was 2008 President of IMAPS. Mr. Adamson was a respected mentor in the electronics industry. He passed away October, 2011. Learn about the Steve Adamson Memorial Annual Scholarship Fund.
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As you are an aerospace manufacturer you may be conformaly coating the boards.
If so HumiSeal has just completed a study with the NPL (National Physical Laboratory) into the interaction between tin whiskers and conformal coating.
Conformal coatings will abate tin whisker growth.
Various conformal coating chemistry types perform in different ways with tin whiskers but they all abate growth.
Please contact us if you would like full information on this project.
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Chris Palin
European Manager
HumiSeal
Chris Palin is currently managing European sales and support for HumiSeal Conformal Coatings. His expertise is in test & reliability, solder technology, power die attach and conformal coating.
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The re-plate and solder dipping processes depend on the type of component. There are companies such as Corfin and Meehan that are doing this for companies today.
They reduce the surface of exposed tin only to the best of the processes ability and pay attention to the post cleaning protocols that bring the components to a very low level of contamination to allow for good electrical performance.
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Terry Munson
President/Senior Technical Consultant
Foresite
Mr. Munson, President and Founder of Foresite, has extensive electronics industry experience applying Ion Chromatography analytical techniques to a wide spectrum of manufacturing applications.
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If you want to eliminate any risk of tin whiskers occurring you really need to replace the tin finish with tin/lead. This involves solder dipping the device for the full length of the leads up to the component body to ensure all pure tin is removed.
Note that you may have to prove that this is not harmful to the specific component you are dipping. There are other possible mitigation techniques such as conformal coating however the jury is still out on whether this is really effective.
I would point you towards GEIA-STD-0005-2 for more detailed information. This is still a bit of a hot potato in the industry so good luck !
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Bryan Kerr
Principal Engineer - CMA Lab
BAE Systems
Bryan Kerr has 35 years experience in providing technical support to PEC assembly manufacturing. His experience ranges from analysis of materials and components to troubleshooting and optimizing, selecting reflow, cleaning, coating and other associated processes.
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