What Buyers Must Know About PCB Surface Finishes

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Rich Krajewski
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Re: Immersion Tin
Rich Krajewski   7/23/2014 2:33:42 AM
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Some of the mitigation techniques are controversial, according to

http://thor.inemi.org/webdownload/newsroom/Presentations/APEX_2006/S04%20Tin%20Whiskers/iNEMI_Recommendations_Tin%20whisker%20mitigation_APEX06.pdf

 

NASA's had their share of trouble with tin. In this doc, they say, if you can't live with tin whiskers, don't use tin:

http://nepp.nasa.gov/whisker/reference/tech_papers/2006-Leidecker-Tin-Whisker-Failures.pdf

 

docdivakar
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Immersion Tin
docdivakar   7/22/2014 3:40:23 PM
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Regarding Immersion Tin, one needs to be careful about PCB floor planning. Under certain conditions, Tin Whiskers can pose a big headache via shorting. Additives to Tin as well as stress relieving can lessen the potential for Whisker growth, see:

http://www.atotech.com/data/publications/pcb/Immersion_Tin-Kinetics_of_Whisker_growth.pdf

MP Divakar

Rich Krajewski
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Re: Did you mean
Rich Krajewski   7/21/2014 2:30:46 PM
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You know, I'll bet a cheap hairspray from the dollar store would do a good job protecting PCB surfaces from tarnish, especially if the product is going to be replaced with a new model in 12 months. That's probably what they do in some places.

Rich Krajewski
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Did you mean
Rich Krajewski   7/21/2014 12:54:48 PM
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"Silver is more expensive but does not react with the copper traces so its shelf life is longer."

You can see that silver and copper form a galvanic pair, too. However, in that pair, copper is more anodic, according to the references below. With tin-copper, the tin is more anodic. At least, that is the relationship in conditions of salt and humidity (or saltwater).

The difference in anodic indexes for silver and nickel-copper alloy is rated for harsh environments, at 0.15 V.

 

http://nepp.nasa.gov/docuploads/97164203-A4FB-479A-A075C918D51DD81E/ESA%20Red%20Plague.pdf

 

http://corrosion-doctors.org/Definitions/galvanic-series.htm

 

 



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