Thickness measurement of gold plating

A. The other methods, as I understand, are Beta backscatter and magnetic/electromagnetic induction. "Beta" is not likely to be cheap either, but less expensive than x-ray. Magnetic methods are not that accurate for very thin films, but ok for approximation. I would suggest checking around for Eddy Current method. This method has been improved lately to measure new coatings.

A. Besides x-ray fluorescence (best for speed and accuracy on thin gold, especially if you want to do a nickel underplate at the same time), you might look into beta-backscatter. A number of distributors carry this technology. The oldest, but tried and true method is cross section, but it is heavily dependent upon the skill of the operator, is destructive of your sample, and takes a relatively long time (an hour or more per sample preparation).

A. A very common method for accurate measurement for thickness of electroplated metals is by microscopic measurement of metallographic prepared cross sections. This is a destructive test, but can be performed on almost any shape for almost any type of coating.

There are many commercial laboratories that perform this type of analysis. Measurement of gold plating, especially thin plating layers, is subject to errors from poor preparation, so make sure that any laboratory that you use has a proven track record with thin plating and soft metals.

If you are looking to do this work in house, equipment that you need is probably a little cheaper than XRF. You will need a trained technician - polishing technique is a little more difficult to master than XRF.

A. I have had some experience with cross-sectioning for thickness measurements. The problem with soft metals is smearing during cutting and polishing. A diamond saw (expensive!) probably would work better for cross-sectioning. But a layer of harder metal such as nickel on top will reduce smearing. Again, potting will help too. So it all depends on how accurate you want to get. For really good accuracy in thickness, I would recommend electron microscope (SEM) if cross-sectioning is used.

I personally prefer a straight measurement method that does not depend so much on people skills. I became tired of all the set up, training, maintenance, etc. These eventually come to the same cost as x-ray. If you do not have the set up, just send it out to a lab.

A. You can measure the thickness of gold with Beta Backscatter, Coulometic, Gravimetric and Microscopic. The X-Ray Fluorescence method which you mention is probably the most common and easy to use. I am sure there are other methods that I am not thinking of.

A. There are 2 common gravimetric methods.
1) Weighing before and after plating. Use additional samples to determine the weight change of pretreatments prior to gold plating.
2) Dissolution. For gold: weigh the plated sample, dissolve the substrate in 50 vol% nitric acid, then weigh the gold.

For further details, see ASTM B767-88 "Standard Guide for Determining Mass Per Unit Area of Electrodeposited and Related Coatings by Gravimetric and Other Chemical Analysis Procedures," and/or
ISO 4524-1 "Metallic coatings - Test methods for electrodeposited gold and gold alloy coatings - Part 1 : Determination of coating thickness."

A. Hello Ibrahim,
Just a note on gravimetric thickness testing. There are too many variables using this method for part thickness measurements. Many of the variables are plating related such as gold concentration, temp, pH, current density, time, alloy or brightener concentration (if using hard gold), buffer and make-up salt concentrations, and more importantly the configuration of the part. Thickness distribution on the part can vary from 5-15% depending on the variables mentioned here. The method is also time consuming and labor intensive. UPA Technology has gold thickness measurement devices if you don't currently have one. Using one will save you a lot of time and money, and help you keep your gold thickness distribution in check. Good Luck!

A. Gold and nickel thickness on copper can be easily measured by XRF. Gold and nickel standard calibration foils are available.This can be used for creating measurement applications.

If gold thickness is less than 50 nanometer then it may be difficult to measure using XRF.
Otherwise XRF is the easy and fastest way to measure the thickness of coated layers.

A. Hi Thao,

XRF is the supreme to determine the thickness (ASTM B568) of multi layer coatings with different substrates.

Initially Do NORMALISATION with substrate (base metal) which is to be plated for thickness test after plating.

Then calibrate using nearer (thickness) standards. Then go ahead and thickness test.

I hope your problem will solved.

Regards,