How do you measure and state surface resistances of materials?

[Tunalover]

Folks-
Does anyone know how to measure and state surface resistivity of materials? We have two different classes of chemical conversion coatings used for aluminum and we need to express and measure surface resistivity for performance comparisons. The spec is MIL-C-5541 and the classes are:
-Class 1A for the best coating for corrosion resistance but the highest surface resistivity, and
-Class 3 for the worst coating for corrosion resistance but the lowest surface resistivity.

Is there a device and/or standard for carrying out the surface resisitivity measurements?

Thanks,
Tunalover

 

[mooimooi]

Hi,
We normally used 4 point probe method to measure
the surface resistivity of silicon wafers in the
semiconductor industry.
I am not sure what magnitude of resitivity you are
planning to measure.
The four point probe works by forcing current through
the two outer probes and measure the voltage drop sensed
from the two inner probes; in this manner, errors due to
contact lead resistances are cancelled and thus accurate
readings are obtained.
Joy to you.

 

[Tunalover]

mooimooi-
Thanks for the data. You hit the mark!

 

[gleaf]

We use a keithley 2400 source meter
and a Keithley 2182 nanovolt meter to
provide an agile low resistance
measurement system.
You might want to contact Keithley and get a copy
of their low level measurements book.

 

[donsolo]

If you use a 4 point probe, the current sourse probes go INSIDE the sensing one. Also you measure surface resistance by "squares". If you measure along opposite edges of a square the resistance is always the same for a uniform surface, no matter how large the square is.
Have a great new year!
donsolo

 

[IRstuff]

Current probes are on the outside, you are trying to measure the IR drop of the material without the impact of any contact resistance effects.

Sheet resistance is typified by ohms/sq, but that assumes that you already know the thickness of the material and that the thickness is uniform. When using a 4-point probe measurement, you wind up with ohm-cm as resistivity, until you find out the effective thickness of the material.

The sheet resistance comes from rho*L/A, where A is the cross-sectional area perpendicular to the current flow, which is parallel to the surface. The thickness is pulled out from the A and divided into rho, which is the resistivity, resulting in ohms*L/W, and the L/W term gives you "squares".

TTFN

 

[nickbo]

Tunalover
I don't know if this is what your looking for, or if it will help. In our electronics and electrical departments we have ESD safe work stations.
Check out the Desco-charleswater website at

http://www.charleswater.com.

Click on technical bulletins and select the TB 2404 digital surface resistivity tester.
nickbo

 

[nbucska]

The unit of surface resistance is Ohms per square <nbucska@pcperipherals.com>

 

[BrianR]

tunalover,
Have you checked MIL-C-5541E which is available at

http://131.82.253.19/docimages/0000/50/74/5499.PD0

where para 6.1.1 describes the detail of what you want.