Measuring copper thickness in PWB plated holes
Is there a quick and non destructive method to measure copper thickness in a 0.3 mm copper plated drilled hole? The base material is glass fibers and epoxy resin and is approx. 1.6 mm thick. Destructive, time-consuming and difficult. I would appreciate any new idea or suggestion. Thank you.Jonas Stalhandske
I know of two ways to check hole wall copper buildup besides sectioning:
1. Use a set of known size pins and monitor go/no-go. This is the common in-process test used in the circuit board industry. It's cheap but not real precise, and requires knowing the hole size you started with.
2. There are instruments available that use the conductivity of the copper to measure buildup. A special pin with electrical contacts is inserted in the hole and the machine is calibrated to tell the user how much copper has been deposited. I don't remember any manufacturer's names, but Caviderm is what one instrument was called, I think. Both of these methods provide an average deposit estimate. They don't identify voids or uneven distribution. Good luck with either, but don't abandon cross-sectioning, which tells a lot more than just thickness.
microwave & cable assemblies
Mesa (what a place-a), Arizona
Also, please see Jan. 96 issue of Plating & Surface Finishing. The article 'NDT Instruments assure High Quality for PCB Manufacturer' sounds like exactly what you are looking for, and your exact question is answered in some detail. Good luck.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Another possible way of measuring copper plate thickness would be to use a 'shadowgraph'. A magnified silhouette of the component is projected onto a screen to which an engineering drawing or scale can be superimposed. Magnification is variable. The original hole could be traced beforehand and it should be possible to compare concentricity or pick up variations around the circumference.Nigel Laxton
The University of Western Australia
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