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February 2012

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Subject:
From:
Karen Tellefsen <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Karen Tellefsen <[log in to unmask]>
Date:
Fri, 10 Feb 2012 15:59:11 -0500
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I've done this, and my recommendation is to get an appropriate sized piece
of copper clad FR4 and have the whole tested side HALSed, a little on the
thick side,  The pins will penetrate the solder better than bare copper or
enig or aluminum, and have lower contact resistance.

Karen Tellefsen - Electrical Testing
[log in to unmask]
908-791-3069



                                                                            
                                                                            
                                                                            
   [TN] [OT] Conductivity of Oxides and Passivation Coatings                
                                                                            
                                                                            
   Blair Hogg                                                               
              to:                                                           
                TechNet                                                     
                                                        02/10/2012 02:51 PM 
                                                                            
                                                                            
                                                                            
                                                                            
   Sent by:                                                                 
          TechNet <[log in to unmask]>                                         
   Please respond to TechNet E-Mail Forum, Blair Hogg                       
                                                                            
                                                                            
                                                                            






I've got a slightly off-topic question for Technetters, but I know there is
probably a few here that would have a good answer.

We are looking at creating shorting plates for use in a self check
application for our in-circuit test machines. The idea is that we would
test resistivity of the test probes through a shorting plate on a periodic
basis to determine when we needed to replace the probes in our fixtures.

I was thinking aluminum, and I don't believe that the small layer of oxide
that forms would add significant resistance. The oxide may cause some
problems and the plates may need to be specified to have a cleaning process
prior to use.  Chromate coatings are non-conductive, and the probe pressure
probably won't penetrate the coating in a reliable manner if any at all. A
copper clad board with ENIG plating or Au electroplating would probably be
better, but cost may be a factor. And since I would need one for every
fixture I have to match the physical characteristics of the board I need to
be cost conscious while ensuring adequate performance.

So the question is, would the Al oxides adversely affect performance? Would
Cu clad FR4 with ENIG plating last long enough as the ENIG is rather thin?
Any other ideas?

Thanks,

Blair




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