Gideon Analytical Laboratories received a JanTXV1N821 Zener diode for electronic failure analysis. A diode is a two-terminal electronic component with asymmetric conductance; it has low (ideally zero) resistance to current in one direction and high (ideally infinite) resistance in the other. A semiconductor diode is the most common type of diode; it is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. A Zener diode is a diode which allows current to flow in the forward direction in the same manner as an ideal diode but also permits it to flow in the reverse direction when the voltage is above a certain value, known as the breakdown voltage. Zener diodes are semiconductor diodes which have been manufactured to have their reverse breakdown occur at a specific, well-defined voltage. The JanTXV1N821 diode is a surface mounted diode with a voltage selection range between 6.2 and 6.55 V. Its operating temperatures are between -65° C and 175º C, has tin-lead plated leads and comes in a hermetically sealed glass case. The JanTXV1N821 diode tested open. The goal was to identify the cause of the failure.
Electronic failure analysis ensued. The glass was removed and the two die were electrically tested. The diode opened by melting the solder on the mesa. Since it opened up, there was either too much current or power was being dissipated through that junction. After disassembly, the Zener chip showed a burn mark in the middle. Solder was removed and the junction closely examined. The junction showed that significant current had passed through it. This current melted the solder on the diode in series with the Zener. This was not an electrostatic discharge (ESD) event. Typically, ESD causes more than one-third of the field failures in the semiconductor industry. ESD-induced failures in semiconductors can be seen in the form of leakage, short, burnout, contact damage, gate oxide rupture, and resistor-metal interface damage. But this was not ESD because the metallurgy was melted. Typically ESD is so fast it actually blows out metallurgy as opposed to just melting it. The conclusion was that excessive power through the Zener diode melted the solder on the terminal side of the serial diode junction. This was the weakest link in the structure of thisJanTXV1N821 diode.
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