Gideon Analytical Laboratories received several rectifier assembly rotors for failure analysis. A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The simplest kind of rectifier circuit is the half-wave rectifier. It only allows one half of an AC waveform to pass through to the load. Rectifiers are used as components of power supplies and as detectors of radio signals. Rectifiers may be of solid state diodes, vacuum tube diodes, mercury arc valves, and more. Each rectifier assembly rotor had three DO-5 type package in a standard configuration (stud is the cathode ). At least one of the three power rectifiers had failed in the assembly. The goal was to find the cause of these failures.
Failure analysis ensued. The DO-5 package is was hermetic and had a glass to metal seal insulating the anode from the cathode. The devices were tested for seal integrity, and two out of the six devices failed. In the first failure, the connection to the anode post was suspect because it was only a few strands of crimped copper. At the bottom of a cathode wire near the base of the rectifier, a fluid was discovered, which was later analyzed using FTIR. This liquid was similar to Anderson Royco 500. The silver plated copper wire from all of the anodes had evidence of pyrolysis in varying degrees. The PTE had burned in the anaerobic atmosphere and carbon was produced on the surface. This demonstrated that wire was extremely hot to produce the combustion of the PTE. Somehow, there was conduction across the glass seal. This cannot occur unless the dielectric is contaminated. The entire device must have been immersed a fluid like Anderson Royco 500. The second failure had no fluid but was also a result of intense heat overload. There were also cracks in the glass. It appeared to be the same problem as the first failure: leakage current from possible fluid contamination cause the die to run hot.
Gideon Analytical Laboratories is one of the preeminent failure analysis laboratories in the United States. For over two decades, we have been assisting electronics companies in their time of need. Companies from around the world have used our services because they want to get the job done right. We solve problems. From ROHS compliance to relay failures and from resistors to capacitors, we do it all. If it is electronic and is not working, call Gideon Analytical Laboratories.