Blair,

I believe the type of probe tip you are using would dictate the hardness required of your calibration pad.

Also, if your probes will always be coming down in the exact same spot [say within ±25µm] each time, you will ultimately be probing the base metal of your calibration pad [thinking conical or 'tulip' probes].

I would be inclined to have the internal resistance of the calibration pad as low as possible - thinking copper, copper foil, or OFHC copper

Alternatively, get some hard, edge connector gold [with cobalt, or other hardeners] and see how long it takes to poke through that coating.

Seems like the prober mfr might have some ideas for this as well.

I see a run-off in the works...

Sorry, could not be of more help

Steve C

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Blair Hogg
Sent: Friday, February 10, 2012 2:51 PM
To: [log in to unmask]
Subject: [TN] [OT] Conductivity of Oxides and Passivation Coatings

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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