Tusonix Pi Filters

Gideon Analytical Laboratories received several Tusonix Pi filters that were failing in the field. Capacitor-input filters (also known as Pi filters) are a type of electronic filter used to remove unwanted frequencies from a signal. Pi filters are primarily constructed of two capacitors and an inductor and are used in situations where the ripple of a signal or the AC and DC currents within the signal are found to interfere with each other.

Failure analysis ensued. The electrical parameters were measured and recorded, the two bad devices had abnormal capacitance readings as well as inductance lower than normal. The Pi filters were had hermetically sealed silver plated brass housing with a solder coated copper lead. One of the two had a hole in the side of the casing, which is indicative of a surge or catastrophic failure because of the housing lead short through the capacitor. In both failures, cracks were emanating from the middle of the ceramic toroid where the lead makes contact with the capacitor electrode. The nature of the cracks reveals that there is something significant with the pulse or surge the device had experienced. One of the Pi filters had a hole in the side of the casing, while on the other Pi filter, the lead had been vaporized.

The failed Pi filters had similar problems. Pi filter 1 had cracks in both capacitors. The upper electrode had voiding where melting occurred. The heat developed along the lead spread to the capacitor electrodes, and finally to the ceramic. The ceramic could not accommodate such heat as metal can and, therefore, cracked to relieve the internal stress. Pi filter 2 had an oblique crack extending through the ceramic, which is related to excessive voltage. Gideon Analytical Laboratories concluded that these Tusonix Pi filters were failing due to electrical overstress (EOS) caused by voltage or current spike that exceeded their respective power ratings.

Gideon Analytical Laboratories had decades of experience in failure analysis and has helped dozens of companies in the electronics industry. Gideon Analytical Laboratories had the experience and the expertise to get the job done. We are here to consult, assist, and help your company solve its reliability and quality issues. Failure analysis performed by Gideon Analytical Laboratories can save companies time, money, public image, and provide peace of mind.