How to measure copper layer thickness - Page 1
Forum section: electronics / general

author: donavan
author_rank: Contributor
timestamp: August 12, 2017, 12:21:36 pm
content: Hello,i got some PCB´s ordered with a copper layer thickness of 105um. I had some doubt because traces kept breaking on the pcb and cut of a small piece off on one of the boards. I had to remove the solderstopmask with a knife and measuered the thickness in the attached picture.I measured a thickness of about 80um, did i make a mistake measuring the thickness like this or did the manufacturer use 70um copper?

author: Rerouter
author_rank: Super Contributor
timestamp: August 12, 2017, 12:32:40 pm
content: 2oz would be 70 micron.I am assuming your flake is both copper foil, and the adhesive layer.For normal 1 oz with vias, you begin with 0.5 oz foil and they plate on another 0.5 oz for the vias.As for adhesion strength, many things come in to play, but the common causes are way too hot / too long on the iron tip. and very cheap PCB's (a number of the cheap services that i have used have not had this issue, but i know it happens)

author: Dave
author_rank: Super Contributor
timestamp: August 12, 2017, 02:58:46 pm
content: Doing a 4-wire resistance measurement on a trace and calculating the thickness would give you a more reliable result than measuring with a micrometer, because you're likely going to stretch and scrape the copper when you're getting it off the board.Perhaps you could find a way to dissolve the fiberglass board and solder mask, leaving the copper intact. I don't know enough about chemistry to be able to suggest a suitable solvent, if one even exists.

author: donavan
author_rank: Contributor
timestamp: August 12, 2017, 04:25:28 pm
content: Quote from: Dave on August 12, 2017, 02:58:46 pmYes first thing i tried was acetone but that didnt do anything, there are soldermask remover i could order.I did the test with 2 pieces and both had similiar results, so i think i didnt remove any/much copper off of the copper sheet

author: Pseudobyte
author_rank: Frequent Contributor
timestamp: August 15, 2017, 01:09:52 pm
content: First of all you need to have a board stack up that properly defines your copper weight. Understand that this is simply the starting point in a board house's process (but only if you say so). Once the etching and drilling is completed, the PTH process adds roughly another 1/2oz (17.5um) of copper to the board. So if you spec out 1oz (35um) on your drawing you are going to end up with about 1.5oz (52.5um) finished copper weight. The key thing here is that you define the stack up up front, otherwise the board house will assume that your 105um (3oz) is a finished copper weight. I really like to design to the limit of the copper weight that i spec out, knowing that the board house will plate in the tolerance. As for measuring the copper weight, if you don't have the tools to do the resistance measurement, I suppose you could always check the trace thickness in your design, calculate the max current that will not raise the temp of the board, and then use a lab supply to pump that through it. Does the trace melt? If yes, not the right weight. If no, then I guess it is ok.