Triac Failure Analysis

SCRs are unidirectional (one-way) current devices, making them useful for controlling DC only. If two SCRs are joined in back-to-back parallel fashion just like two Shockley diodes were joined together to form a DIAC, we have a new device known as the TRIAC. The TRIAC is a three terminal semiconductor device for controlling current. It is effectively a development of the SCR or thyristor, but unlike the thyristor which is only able to conduct in one direction, the TRIAC is a bidirectional device.

Triacs are used to switch AC loads, for example in light dimmers, motor speed controllers and heating control. Common failure modes are overvoltage or overcurrent damage that destroys the junction, a fractured die that causes leakage, and a short across all terminals. Optically coupled triacs can also fail from contamination inside the package.

The case studies in this category include power triacs with an abnormal curve trace and a fractured die. They also include an optocoupler with an internal leakage path that went away after a bake.

The lab begins with curve tracing to see how the part fails. We then decapsulate it and inspect the die with optical microscopy. Scanning electron microscopy and X-ray radiography help to find cracks and contamination.

If you have failed triacs, request a quote.