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Sanjib.A
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contact material
Sanjib.A   1/18/2014 9:59:55 AM
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I have a question regarding the contact material. Did you ever came across cases where the contact material of the PCB connector was different from the contact material of the mating connector that the user was using unknowingly? What might happen if the PCB connector has gold plated contacts when the mating connector had tinned contacts? A poor contact resistance and faster wear & tear? If the current is in the order of 20-30 mA, even then would there be reliability issues?

antedeluvian
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Re: contact material
antedeluvian   1/18/2014 11:44:48 AM
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Sanjib

Did you ever came across cases where the contact material of the PCB connector was different from the contact material of the mating connector that the user was using unknowingly? What might happen if the PCB connector has gold plated contacts when the mating connector had tinned contacts?

That is a really interesting question. I must admit I have never come across a contact material issue other than how it relates to thermocouples. I don't believe I have ever seen terminal blocks (non-pluggable) with gold plating. Gold plating is available on pluggable connectors "for very small signals" (quote from a Weidmuller catalog).

IIRC I have seen a connector degrade as a result of oxidation during storage and as a result when installed the contact resistance was high enough to cause problems, but that has only happened once in over 20 years and was attributed to a production quality issue.

Mxing and matching terminal platings might be more a question for someone with electro-chemical or metalurgical knowledge- I certainly can only answer with "I don't know". I will see if I can find someone with an answer. I can say that with dissimilar metals you will get a thermocouple junction and there probably will be a uV source in series with the wire. This would not be that different to other metal junctions in the signal path- wire/connector or connector/solder.

 

 

antedeluvian
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Re: contact material
antedeluvian   1/18/2014 11:52:07 AM
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Sanjib

 A poor contact resistance and faster wear & tear?

This is a touchy issue with all connector manufacturers. Try and get data on the number of make/break operations and how the connector degrades.  As near as I can tell any pluggable connector is only rated to make/break in the tens of operations and then begin to degrade. (I have always been wary of this on devices like in-circuit programmers using flat cable connectors.) Obviously the most noticeable change would be an increase in the contact resistance. However from practical experience this number is much, much higher- hundreds, maybe even thousands and that is with light current.

 

David Ashton
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Re: contact material
David Ashton   1/18/2014 5:32:54 PM
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Aubrey, as always it is a pleasure to read something like this written by someone who knows his subject inside-out.    The only thing I can add is that when using connectors like this it is important to make sure they are soldered properly.  Poorly soldered connectors like these and power sockets are a prime cause of failures - ANYTHING that has any mechanical stress at all needs a good meaty solder joint.  You did allude to this in your 2nd-last paragraph.  The soldering machines never seem to get it right - and I seem to get most of the resultant failures.

Your information is otherwise so complete that I have only one question: why is Weidmuller spelled differently in the US?

antedeluvian
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Re: contact material
antedeluvian   1/18/2014 5:45:02 PM
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David

Aubrey, as always it is a pleasure to read something like this written by someone who knows his subject inside-out.  

Flattery works! Now what was it that you wanted? LOL

Poorly soldered connectors like these and power sockets are a prime cause of failures -

Excellent point and there is a knock on implication which I saw on my own air conditioning unit. The poor solder joint lead to higher resistance, which led to overheating, which ended up burning the PCB. Still under warranty, so no worries!

antedeluvian
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Re: contact material
antedeluvian   1/18/2014 5:54:17 PM
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David

Your information is otherwise so complete that I have only one question: why is Weidmuller spelled differently in the US?

The reason goes something like this. At its source Weidmuller actually has an umlaut (the double dot) above the "u". This converts the sound of the "u" from an "uh" (as in mull) to a "ue" (as in "avenue"). So the spelling was changed to reflect the correct pronunciation.

However it didn't adress some other issues. An American today typically pronounces it Weedmewler whereas in German it is Veedmueller- but not attempt has been made to address that. 

It was actually called Klippon in the UK, South Africa and Australia and Conexel in Brazil- all now changed to Weidmuller.

 

David Ashton
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Re: contact material
David Ashton   1/18/2014 6:29:21 PM
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"What's in a name? that which we call a rose
By any other name would smell as sweet!"

seaEE
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Re: contact material
seaEE   1/19/2014 2:14:05 AM
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Sanjib,

Check out the Tyco article here called "The Tin Commandments" :)

http://www.te.com/documentation/whitepapers/pdf/sncomrep.pdf

 

Commandment #7:

"Mating Of Tin Coated Contacts To Gold Coated Contacts Is Not Recommended"

antedeluvian
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Re: contact material
antedeluvian   1/19/2014 9:47:36 AM
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seaEE

Check out the Tyco article here called "The Tin Commandments"

This is GREAT!. Don't you just love this forum- pose a question and someone has the answer.

This does lead to additional issues though- if you are using gold plated terminals then you probably should not be using ferrules which are tin plated. I have also seen wire tinned with solder which includes tin and so should not be used with gold. And I have also seen components like resistors inserted into terminals- since they are also tin plated, this would also be a no-no.

 

antedeluvian
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Additional Factoid and more...
antedeluvian   1/19/2014 9:53:14 AM
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Most terminal manufacturers ship with the wire clamps fully open for customer convenience.

When you unscrew a terminal to remove a wire or add an additional one, you shopuld unscrew it completely (depending on you terminal's design). With the clamping mechanism in an intermediate position it is possible to insert the wire outside the clamp leading to much frustartion when you tighten the clamp only to discover the the wire just falls out and you have top repeat the process.

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