The Microwave Microstrip Sensor Design for Noncontact Thickness Measurement of Copper Clad Laminate

A microwave nondestructive evaluation (NDE) microstrip sensor operating in C-band (from 7 to 8 GHz) to measure different thicknesses of the copper-clad laminate (CCL). The study disclosed herein was developed and designed to perform noncontact precision measurement based on the reflection of electromagnetic waves. The different electromagnetic field losses of materials under test (MUT) with varying surface copper thicknesses, the changes in electromagnetic field losses can be observed through the S11 reflection coefficient to calculate the surface copper thickness of the MUT. The microwave microstrip sensor module was designed and manufactured to receive reflected electromagnetic waves. The sensor is sensitive and can identify copper layer variations effectively. Using noncontact measurement, the sensor achieves a sensitivity and resolution of
$0.1~\mu $
m at a standoff distance of 5.5 mm between the sensor and the MUT. The experimental results demonstrate that when measuring the copper foil thickness of CCL, the measurement error rate percentage (ERP) is within a 1% deviation compared to the four-point probe method. The study integrated an algorithm for converting the real-time online measurement results of reflected electromagnetic wave signals into the thickness of a thin copper layer, achieving the same level of measurement precision as the contact-based four-point probe measurement.