Design of copper laminate thickness measuring equipment

The copper laminate thickness measuring equipment is designed and implemented under the criteria of simple, low cost and practical equipment. In PCB manufacturing, there are three common types of copper laminate sheets, which are usually called 1/2 ounce, 1 ounce and 2 ounce type. Thus, the display of this equipment is designed to have three LEDs for each type, which are enough for practical work and easy to use for operators. The principle of measurement is to measure the conductivity of the copper surface with a non-destructive method. Four simple tapered probes are used for contacting the copper surface. Based on the parallel resistance model, we found that measuring the conductivity on the copper surface is enough to distinguish the difference of copper plane thickness, because the copper plane thickness is inversely proportional to its resistance as a specific ratio. By means of supplying an AC current source to the copper sheet sample via probes, then measuring the voltage across the sample, we can distinguish the level of voltage in order to identify the different thickness. Finally, the prototype of copper thickness measuring equipment has been tested and we obtained satisfactory results.