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Which PCB Connectors Are Best?

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David Ashton
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Re: Torque settings and mechanical design
David Ashton   1/19/2014 2:50:29 PM
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The modern connectors we use today are heaps better than the old "Chocolate strip" screw connector blocks we used to use (and which are still around):



Although they are very handy, the fact that the screw impinges directly on the wire usually destroys the wire if you pur any more torque on it than is absolutely necessary.  Even ferrules can get destroyed, though they help a lot.  The modern terminal blocks which bring two flat surfaces together to hold the wire are much better.  

antedeluvian
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Torque settings and mechanical design
antedeluvian   1/19/2014 10:10:13 AM
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The electrical simplicity of the connector belies the complex mechanical design needed. The contact itself is a tradeoff between mechanical strength, conductivity, clearances, corrosion resistance, gas tight,  surface area, regulatory requirements, pressure and vibration resistance. The last item is often covered by a patent. Take a look at the 13th page of this document in the section marked "The principle of vibration resistance".

Pluggable connectors have a specified retention force, required by standards authorities to be as stornog as possible, yet low enough so that the user can separate them wioth reasonable ease.

Did you know that every screw terminal has a torque rating to meet the specifications? Some manufacturers actally sell torque screwdrivers and bits sutyiable for their terminals. Here is one for instance. Page F.8 for the mechanical ones and F.4 for the electric one.

I highly reccomend using the electric screwdriver when you have a lot of connections, for obvious reasons.

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.

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.

 

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"

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!"

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.

 

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!

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 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.

 

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