Gideon Analytical Labs received two AD73311L CMOS general purpose analog front end processors. Each device had external thermal damage to the package and solder leads. The intent was to determine whether the failures were thermally or EOS induced. The AD73311L is a front-end processor for applications such as speech and telephony. It has a 16-bit A/D conversion channel and a 16-bit D/A conversion channel. Each channel provides 70 dB signal-to-noise ratio over the voice band signal bandwidth. The AD73311L has on-chip filtering, operates from 3.0 V only, and the gains of the A/D and D/A conversion channels are programmable over 38 dB and 21 dB respectively. An on-chip reference voltage is included to allow single-supply operations. A serial port (SPORT) allows easy interfacing for single or cascaded devices to industry standard DSP engines.
The potential defective failure appears as a thermal failure for a number of reasons listed in the report. The defective failure was in close proximity to the ADD1, pin 3, rail. If the oxide (an insulator separating the trace lines from shorting) were not of sufficient thickness to prevent leakage current at elevated temperatures, then a small leakage could develop sufficient heat to break down the insulating layer and evolve into a full-blown short when the temperature remained high. Since there is evidence of extreme heat (melted ball bond and melted solder) from the lead frame, the die were both beyond the rated temperate for operation. The heat generated on the ball bond indicates the problem may be coming from an external source which induced the die to fail via heat. A close look at the circuit and the PCB eliminating contamination and design has to be performed.
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