Thickness Measurements

Q. What are the most common ways of measuring thickness of metal deposits? R.L.

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A. Thickness measurements of plated deposits are probably the most common after plating test performed. Not surprisingly, there are many different ways of performing the measurements. There are two broad categories of tests: destructive and non-destructive.

Destructive Method

• Cross Sectioning/Microscopic Examination
• Coulometric Method
• Jet Test Method (Dropping Method)
• Strip and Weigh Method

Non-Destructive Methods

• Magnetic Methods
• Beta Backscatter Method
• X-Ray Fluorescence Method
• Optical Methods
• Eddy Current Method
• Micro-Resistance Method

Selection of a method depends on the type of deposit and the base material. Other factors include cost of equipment, ease of use and required accuracy.

In the modern plating environment, the most common methods for day-to-day measurements are magnetic, eddy current, X-ray fluorescence, beta backscatter and micro resistance methods. The cross sectioning/microscopic examination method has classically been used to resolve disputes but is not as widely used because of limitations due to the very small size of components and the very thin layers of coating that have become common today.

There is not enough space to describe all of the methods listed above but there are good sources of information that are available. A good place to start is at the Products Finishing web site, www.pfonline.com. Search under thickness measurements. The URL for an article that has a good discussion is www.pfonline.com/articles/pfd0027.html. A good book that discusses these various methods is Thickness Testing of Electroplated and Related Coatings by G. P. Ray. Electrochemical Publications, www.elchempub.com. The book is out-of-print but still can be purchased at the web site listed.