Today it is becoming increasingly difficult to locate faults in state-of-the-art electronic circuits. Apart from a greater complexity (and consequently a much higher number of potential fault sources), small mechanical dimensions make it more and more difficult for the developer to pinpoint faults. Here is an example from measurements.
The control unit of a new disturbance generator for immunity tests was the object of the examination. The circuit board comprises an LCD display (+ controller), µC (142 pin TQFP), FPGA (100 pin TQFP), interface modules, passive components (such as SMD 0603) and various control elements (rotary encoder, push-button, switch). Furthermore, the circuit board hosts USB sockets, connectors for the voltage that will subsequently be generated by the generator and power supply inputs. For cost reasons the circuit board was designed as a two-layer system with feature sizes of 200 µm. There is no continuous GND layer. The busses / lines are laid on both levels. The proximity of the control unit to the generator unit results in high immunity requirements.
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