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Excessive electrical resistance of chrome plating on PC-ABS plastic part

December 2, 2009

I am producing a PC-ABS plastic chrome plated part for our customer. This part is a rectangle that measures 197mm x 104mm on the outside with a width of around 12mm.

Our customer has recently requested that the resistance of this piece be less than 3 OHMS.

We have measured some parts and found the electrical resistivity to range up to 12 OHMS.

Does anyone know what the resistivity of chrome plating is (ohms/cm).
How do you calculate resistivity for a cross area of chrome?

Thank you in advance.
Regards

Shane Piers
product designer - Zeeland, Michigan

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December 7, 2009

Shane

You can easily look up the bulk resistivity of chromium but I doubt if this will help much.

Electroplated chromium is commonly microporous or micro cracked plus the usual thickness variation across a flat plate etc.
Then there is the problem of accurately measuring resistance on a flat surface. It is usual to use a four electrode probe to correct for contact resistance.

My conclusion is that if your customer has a specific requirement then they will have a standardised method of measurement which may well be beyond the equipment available in the average plating shop.

If you need to get the resistance down, my first suggestion would be to plate some copper under the chromium. Copper is about 10x more conductive than chrome.

Geoff Smith
Hampshire, England

It's not the chrome but the nickel and mostly the copper in your underplate that counts. Chrome is too thin and neglectable. The bulk resistance of a physical body is expressed as Resistance = resistivity X length / area. Evidently you need a thicker underplate to reduce resistance.

Guillermo Marrufo
Monterrey, NL, Mexico
December 9, 2009