Inspection of electrical interconnections within power ICs via magneto-optical imaging

During their lifetime, power electronic components have to endure several million cycles of thermo-mechanical stress. In this context, the electrical interconnections between the die and the output pins are crucial. Usually, bond wires with diameters ranging from 400 μm to less than 50 μm are used to establish the electrical interconnections. Typically, due to the small diameters, redundant wires are necessary in order to guarantee the current-carrying rating of the device. In this particular case, commonly used electrical tests are not able to detect the loss of single wires. However, missing or not connected bond wires will result in a different magnetic field distribution surrounding the device. This paper presents a new measurement method based on a magneto-optical sensor to detect missing bond wires in a power MOSFET chip via magnetic field imaging. The Faraday effect is utilized, which enables us to resolve magnetic flux densities down to 127 nT with a spatial resolution of approximately 21.6 μm.