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Tin Contact Finish

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art(at)zemon.name
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Posted: Wed Jul 27, 2016 7:31 pm Post subject: Tin Contact Finish

Folks, 

This has nothing to do with airplanes. 

I was idling away my evening browsing through digikey.com (don't ask me why this is fun!) and noticed some connectors are brass colored and others, like http://www.digikey.com/product-detail/en/te-connectivity-amp-connectors/170032-5/A100888CT-ND/2259557 , are grey. By carefully reading the specs, I see that the grey one is brass with a tin "contact finish".  

Why would you choose all brass vs. brass with a tin contact finish? 

Thanks,

     -- Art Z.

 

http://CheerfulCurmudgeon.com/ 

"If I am not for myself, who is for me? And if I am only for myself, what am I? And if not now, when?" Hillel

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bob.verwey(at)gmail.com
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Posted: Wed Jul 27, 2016 10:04 pm Post subject: Tin Contact Finish

Art my guess would be that the brass wants to go back to the sea when there is a hint of moisture...it turns green with envy, which leads to other problems!



On Thursday, 28 July 2016, Art Zemon <art(at)zemon.name (art(at)zemon.name)> wrote:

 	  Quote: 	
		  

Folks, 

This has nothing to do with airplanes. 

I was idling away my evening browsing through digikey.com (don't ask me why this is fun!) and noticed some connectors are brass colored and others, like http://www.digikey.com/product-detail/en/te-connectivity-amp-connectors/170032-5/A100888CT-ND/2259557 , are grey. By carefully reading the specs, I see that the grey one is brass with a tin "contact finish".  

Why would you choose all brass vs. brass with a tin contact finish? 

Thanks,

     -- Art Z.

 

http://CheerfulCurmudgeon.com/ 

"If I am not for myself, who is for me? And if I am only for myself, what am I? And if not now, when?" Hillel 	




-- 

Best...Bob Verwey

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rampil

Joined: 04 May 2007
Posts: 870

Posted: Thu Jul 28, 2016 5:26 am Post subject: Re: Tin Contact Finish

Tin is supposed to be easier to solder to.

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_________________
Ira N224XS

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jul 29, 2016 7:53 am Post subject: Tin Contact Finish

At 10:26 PM 7/27/2016, you wrote:



  	  Quote: 	
		  Folks,



 This has nothing to do with airplanes.



 I was idling away my evening browsing through digikey.com (don't ask me why this is fun!) and noticed some connectors are brass colored and others, like  http://www.digikey.com/product-detail/en/te-connectivity-amp-connectors/170032-5/A100888CT-ND/2259557  , are grey. By carefully reading the specs, I see that the grey one is brass with a tin "contact finish". 



 Why would you choose all brass vs. brass with a tin contact finish? 	


   It's a combination of effects on performance influenced

   by environmental stresses.



   A freshly made up, bright metal joint is at that moment,

   as good as it can get. But where the conductive materials

   come together, there are usually risks for the surface

   finished of those materials to degrade. Degradation

   always raises the resistance of the joint. If the joint

   carries much current, there's a snowballing effect that

   leads to loss of integrity of the joint.



   Connectors must have openable joints . . . you want to

   plug and unplug the wires for installation and/or

   maintenance. The interface between movable cannot

   benefit from the advantages of gas-tight connections

   offered by crimping or soldering.



   Depending on criticality of the application and the

   environment, bare brass might be just fine . . . one

   example is in the fabrication of fast-on terminals

   where by design, there is a lot of PRESSURE at the

   interface.



   Pins and sockets in connectors are another matter.

   Here we generally see smooth bore female pins which

   engage equally smooth male pins. Large area, low

   pressure interface. Here you will probably never

   see bare base metal pins. At a minimum, they will

   be plated with tin or perhaps even gold.



   Gold is the plating of choice for its resistance

   to corrosion but tin is probably used in 90% of

   terrestrial, consumer and industrial applications.

   I've see some bare-metal products in fast-ons and

   ring terminals but it's rare . . . and on very

   pedestrian applications.



 

 

   Bob . . .

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alpha(at)concordnc.com
Guest

Posted: Tue Aug 02, 2016 8:16 am Post subject: Tin contact finish

To answer the question, "Why a tin contact finish."  According to Jim 

Weir, of Kitplanes Magazine, at a Oshkosh forum this week, the 

explanation was that you have "wiping contact" that will not corrode.

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