Chip-on-board technology

Chip bonding

To create an optimum mechanical and thermal connection, power semiconductors are normally assembled, unhoused, on the circuit carrier in chip-on-board technology (COB). In addition to conductive glues, metallic solders are also used when there are high heat dissipation requirements. The solders can be processed conventionally by means of reflow soldering or vacuum soldering almost free of air inclusions (few cavities). This guarantees a connection between semiconductor and substrate that has high thermal conductivity and low stress. Vacuum soldering guarantees a residue-free soldering process without any surface-reducing fluxing agents during soldering. In order to achieve a particularly high thermal dissipation, the semiconductors are applied to the substrate by means of silver sintering. This process also facilitates a higher operating temperature (T>300 °C) compared with metallic soft soldering, whose maximum operating temperature is limited by the solder's liquidus temperature.

AlN-DCB-based SiC power module on Al-SiC lightweight heat sink

Wire bonding

The electrical connection of the power semiconductor to the circuit is created by means of wire bonding with Au thin wires, Al thin wires or Al thick wire bonding with wire diameters D>100 µm for ultra-high current carrying capacity. Thanks to their high thermal mass and the good thermal conductivity, the wire bonds also help to cool the power semiconductor. For high-frequency applications with extremely short switching times, ribbon bonds can be used to create a low-inductance connection of the semiconductor and to minimize the high ohmic losses (skin effect) caused by the reduction in the electrical conductivity onto the wire surface.

Commutator-hybrid circuit for use in drive electronics