I just tried to make a PCB on my CNC but the V-Tool (0.1mm, 60°) did not cut all the way through the copper so the tracks were not isolated. I think that is because this particular board has a thicker copper layer than I am used to.

In future I will carefully note the coppeer thickness when I am buying PCB material.

For the boards which I already have, is there a good way to measure the thickness of the copper layer?

 

Hi
I can suggest, from the top of my head, two options to measure the copper thickness on your existing boards:

1. To use an NDT (Non destructive) measuring apparatus, based on eddy currents. There are quite simple devices, used by the PCB manufacturers.
2. To cut the corner of the board, microsection it and measure copper thickness under microscope.

Good luck,
Ervin

 

I don't have the equipment to that.
Note that I only need to know whether it is 0.5oz, 1oz, 1.5oz, 2oz, etc.
How about if I make an LC oscillator using a flat coil. I place the coil on the copper and see how much the frequency changes?

 

is there a good way to measure the thickness of the copper layer?

You could pass a large current from one side of the copper plane to the other, and measure the voltage drop (using separate probes).
From that you should be able to calculate the resistance, based upon the size/shape of the plane, and from that, its thickness.

 

• 1 oz copper (~35µm thick or 1.4 mils)

 

You could pass a large current from one side of the copper plane to the other, and measure the voltage drop (using separate probes).
From that you should be able to calculate the resistance, based upon the size/shape of the plane, and from that, its thickness.

I considered that but I could not find a formula for the resistance corner to corner or side to side (unless it is the whole side connected).
That calculation is well beyond my maths/calculus abilities

 

I think I have found a solution to this problem:

" Four point probe is used to measure resistive properties of semiconductor wafers and thin films. If the thickness of a thin film is known, the sheet resistance measured by four point probe can be used to calculate the resistivity of the material; conversely, if the material's resistivity is known, the thickness of the thin film can be calculated. "

https://lnf-wiki.eecs.umich.edu/wiki/Four_point_probe

 

I use calipers but it is not real accurate but just I can see it is 1oz or 2 oz or 0.5.
I think you CNC machine is the tool to use. Increase the cut depth by 25% and rout a small area again and keep changing the number until you see fiberglass. You don't care the thickness; you just want to cut through.

 

I use calipers but it is not real accurate but just I can see it is 1oz or 2 oz or 0.5.

I am surprised that the board thickness is consistent enough to allow that.

 

Here are some suggestions regarding the measurement of PCB copper thickness: https://forum.allaboutcircuits.com/threads/determining-copper-thickness-on-pcbs.78313/ These suggestions include etching, Van der Pauw's method, using eddy current scope etc. The copper thickness on a PCB is typically measured in ounces (oz) and refers to the weight of copper per square foot. The most common copper thickness is 1oz copper thickness and 2oz copper thickness, and occasionally 0.5 oz (0.7 mils) for low-current applications. You can know more about standard PCB thickness here: https://www.nextpcb.com/blog/what-is-standard-pcb-thickness

 

I am surprised that the board thickness is consistent enough to allow that.

Do not measure the thinness of the PCB, just the thickness of the copper. Use the depth measuring end. Set the body of the calipers on the PCB where there is lots of copper. Push the post down in an area with no copper.