Let’s look at how to measure glass, plastic, and other non-conductive materials. Using the MTI Instruments D202 Unit and ASP 300M CTA probes, we can measure thickness values of sapphire wafer, plastics, and gorilla glass.
The four items needed are a two-channel capacitance amplifier, two sets of 180-degree probes, a fixture to hold the probes and wafer, and a computer or laptop to run the Digital Accumeasure software and to record readings.
To set the probes, the range is equal to two times the distance plus the thickness of the target. The system will be calibrated once setup using two wafers of known thicknesses based on a contact micrometer reading.
Using the software to calibrate, open the thickness calibration tab to get started. Go to User Cal and clear current factors in the tab. Now click Thickness Calibration and input the thickness from the first known-thickness sample. Then, click Calibrate Thickness. Measure the second wafer of known thickness and enter that information. Next, take the absolute delta difference by using the difference between the two probe readings: the actual wafer reading from the micrometer minus what the system is reading. Divide the difference between the known thickness by the apparent thickness to get the slope factor.
From the User Calibration window, enter in the new slope information in each section of the software in the area labeled channel 1 and channel 2. Make sure to save the new factors. The factory setting defaults to 1.0.
Before any measurements are taken, always make sure to check the thickness calibration by placing a wafer of known thickness between the probes to verify the calibration. Having a properly calibrated system will lead to a better-quality product, especially when measuring for use in applications such as LED fixtures. Cleanliness, waves, dings, dents and issues caused from shipping material can skew accurate readings.
Download this brochure to learn more about the Digital Accumeasure.
This article in AZO Sensors explains how to use MTI’s Accumeasure capacitance sensors to measure the thickness of dielectric materials.
Watch the How to Accurately Measure Dielectric Materials video and see the benefits of MTI’s capacitance-based technology.
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