Spectrum Pi Filters

Gideon Analytical Laboratories received two Spectrum Control Pi filters, a failed Pi filter, and a good Pi filter from the same vintage as the failed one, for comparison. 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 was performed. The failed Pi filter was made non-hermetic and cross-sectioned. After progressively grinding through the ceramic on the thread side, no anomalies were found; there were no cracks. On the hex side, however, there was solder voiding and massive destruction on the internal plates of the capacitor. There was a meltdown that occurred where the plates overlap. Cracking was a result of the heat produced during the meltdown. There was a burn mark in the margin region near the ferrite core. It is electrically isolated from the plates by the ceramic. There were cracks coming from this spot which transgress the lead plates, making it very likely that this was near the origin of the failure.

Examination of the good Pi filter produced some surprising results. Cross-sectioning revealed some solder voiding on the perimeter showing up as bubbles and some small cavities running parallel to the body length. There was a large solder void on the left middle section of the hex side. The solder did not wet the capacitor metal. Excessive solder voiding on the hex side of the Pi filter is indicative of a manufacturing issue. An electrical overstress (EOS) event occurred which overwhelmed the dielectric with over voltage and caused the internal meltdown of the capacitor. Other good Pi filters were examined without any manufacturing anomalies.

Failure analysis performed and provided by Gideon Analytical Laboratories can shed light on the darkest and sinister of the problems. Imagine knowing exactly why and how components fail and being able to make the necessary corrections to prepare for future business. Accurate and candid insights provided by Gideon Analytical Laboratories can be truly beneficial. Whether the problem is in the design, manufacture, or application phase, call Gideon Analytical Laboratories for all your failure analysis needs.