How do I measure the thickness of a conformal coating on a circuit board for my selective robot process?
Both the old and new IPC test standard state you can measure the coating thickness on circuit boards using test coupons.
One of the best methods for measuring coating thickness repeatability is by measuring a test coupon rather than the PCB itself. The principle works that you produce a golden board on which you are happy. Then you spray the same pattern on a test coupon (metal plate is ideal). You measure this thickness in a variety of places and this is your test data. From that moment on you can then decide how much range the coating thickness can vary and measure it against future test coupons. It will only tell you if there is variation away from the golden board quality but it is a great indicator.
The test coupon shown shows the trace for a selective non atomising robot. You can see in the test pattern image there were two squares drawn and the thickness is written on the traces in microns. It’s a great indicator of process control.
The measurements were then made using a Positector 6000 coating thickness system. Measurement of the conformal coating is taken after application is complete and the coating is dry enough to handle. The test is achieved using a non contact technique using eddy currents. The Positestor 6000 is extremely quick and accurate to ±1 um at thin films of 25-50 um.
For further information on conformal coating thickness testing contact SCH to discuss your needs.
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