by Jack Goho
Gideon Analytical Laboratories received two surface mount (SM) tantalum capacitors that had internal resistive shorts. Capacitors are passive, two-terminal electrical components used to store energy. They vary in construction, but all have at least two electrical conductors that are separated by an insulator, known as a dielectric. Tantalum capacitors are a type of electrolytic capacitor, which are ubiquitous in electronic circuits. Tantalum capacitors have a high capacitance per volume and weight and are more expensive than any other commonly used capacitor. The goal was to determine the causes of these internal resistive shorts.
Failure analysis ensued. The devices were checked for external packaging damage; none was noted. No marks were found by pick and place. The lead frame was normal and provided good flexibility and strain relief. Part of the package was removed from the body and inspected. If there is a lack of seal integrity, the tin-lead solder will scavenge the silver from the silver coated cathode. The tin should not be touching the silver directly, but in this case, it was.
The tantalum capacitor was cross-sectioned and inspected. No unusual anomalies occurred. There was, however, a breakdown in the manganese dioxides which lead to the short. No contamination was found in the dielectric cavities using SEM-EDS. These two devices failed because of electrical overstress (EOS) to the gate input.
Time and time again, Gideon Analytical Laboratories has come to the aid of electronics companies in need. Having a quick and accurate diagnosis of how and why a product is failing can prove invaluable. This type of information can help save companies time, money, and embarrassment. Failure analysis can give electronics companies the confidence their products are safe and reliable.