Gideon Analytical Labs received Wamco Display Socket 4160001-1 for failure analysis. The device had a reported open diode on pin G.
This display socket is encapsulated in a plastic housing filled with a silicone rubber filler to stabilize movement of the diodes. The diodes are hermetically sealed in glass and position via plastic at one end and a socket located at the bifurcation line. The electrical data indicated the diode was open when initially measured but was intermittent when moved.
The glass was removed to expose the die. The die is cracked oblique to the die surface. Since this die functioned (at least intermittently), the crack (did not prior to decapsulation) break the plane of the junction, otherwise, it would have been open/short. The remainder of the glass was removed and the die was inspected. The die is indeed cracked. Leakage current always occurs with cracked die once it transverses the junction.
The cause of the diode failure is a result of mechanical lead stressing which caused the glass to crack leaving the diode as the weakest and most vulnerable electrical link in the structure. The solder bond was broken. Once the glass cracks, it is only a matter of time before the die opens up (breaking solder contact, as it did above) or cracks (producing a short).
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