EOS of Signal Diode

Gideon Analytical Laboratories received two integrated load switches and two small signal diodes for analysis. The integrated load switches are particularly suited for compact power management in portable electronic equipment where 2.5V to 8V input and 2.8A output current capability are needed. They have an operating voltage range 1.2V-20.V. The signal diodes are non-linear semiconductor devices generally used in electronic circuits, where small currents or high frequencies are involved such as in radio, television and digital logic circuits. The goal was to diagnose the cause of failure for all of these devices.

The signal diode showed a significant destruction to the epoxy encapsulation near pin 2, which can be viewed in the picture at the top left. This type of destruction is usually indicative of EOS (electrical over stress). It was stripped in acid to reveal the diode and possible failure mechanism. The destruction was massive and caused the epoxy to carbonize and fuse the silica. It was impossible under these circumstances to view the die. Once this destruction occurs, acid will not etch off the material. The diode was cracked in several locations, as pictured at the top right. It also had a bilateral crack directly under the spot where most of the heat occurred. This type of crack is typical when the heat generated on the top of the die cannot dissipate fast enough through the silica. Thermal stress cracks occur to relieve this internal stress.

These appear to be overvoltage failures beyond the rating of the respective devices. The failure involves the circuitry of the die and the wires alone and the die is a victim of heat stress. This happened very fast. This is evident because of the location of the failure site and destruction pattern. There was also lifted aluminum metal on the die surface indicating the die circuitry was hot before the die cracked.

Failure analysis provided by Gideon Analytical Laboratories can illuminate information of which electronics companies are in dire need. Knowing how and why a device fails can be used in planning for future business. The goal of failure analysis provided by Gideon Analytical Laboratories is to help companies solve problems and help them better prepare for the future.