Secondary breakdown
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Secondary breakdown, in reference to semiconductors, are the destructive means that a primary breakdown may introduce and they may include the following:
- Wirebond/solder or weld failures (wire bonds are used to attach the semiconductor's metalization pads like the gate and the top electrode to the device carrier pads. These small wires may fail due to CTE mismatch or mechanical stress from oscillations putting thermal and mechanical stress on the solder or weld until it fails.) If the device latched ON these may be fuseable links.
- Delamination of metalization pads often due to thermal cycling (CTE) or high heat flux.
- Delaminations may also occur within the thermal stack because of thermal cycling and warping of materials and significantly increases thermal resistance for a catastrophic failure - the semiconductor cracks.
- Dielectric breakdown - First imagine metal contacts isolated by a semiconductor about as thick as your finger nail. Surface effects will tend to carry the potential to the edge of the semiconductor and while the dielectric constant of the semiconductor is capable of withstanding the voltage; Air is not and may develop a plasma that eats away at the semiconductor until it shorts the metal. Early IGBTs used dielectric potting material to isolate corona discharge issues and sometimes the the material was sensitive to moisture others were sensitive to harmonics.
- Early diodes were slow to capture the reverse current in circulating loads like motors and this put additional thermal strain on the power device. This is where SiC Schottky diodes showed 30% less switching loss.
