For proper signal transmission in high-speed printed boards measuring the controlled impedance is as important as the electrical connection test. If the impedance value deviates substantially from the previously calculated impedance, this has a significant impact on the signal integrity of the whole assembly. The consequences are reflections in the transmission line and switching signals arriving at the wrong time.
In the impedance measurement we use the TDR method (Time Domain Reflectometer). We perform the measurements on a coupon, which is placed in the manufacturing panel of the printed board and simulating the circuit structures of the PCB. With the TDR we send a pulse with a short rise time along the coupon and measure the reflections of the pulse in the defined transmission line. From the reflection behavior direct conclusions can be drawn, if the calculated target impedance is met. The result of the impedance measurement flows in your shipping documentation in the form of a test log for each individual coupon.