Detektion fehlender Bonddrähte in Leistungsbauteilen mittels magnetooptischer Bildgebung

Power electronic components are able to handle voltages and currents in the range of kV and kA. They also have to endure rough operating conditions, like short-term electrical overload and frequent changes of temperature. The electrical interconnections between the die and the output pins is crucial in this context. These interconnections are usually established via wire bonding, using thin wires with diameters ranging from 70 μm to up to 400 μm. To guarantee the current-carrying rating of the device redundant bonding is required. As a consequence, electrical tests are not able to detect the loss of single wires. However, any current-carrying wire will create a magnetic field. This paper presents a new measurement method based on magneto-optical imaging to detect missing bond wires within a power MOSFET chip. Therefor, a measurement setup based on the Faraday effect was realized, which enables us to resolve magnetic fields down to 0.10 A/m with a spatial resolution of approximately 22 μm.