Gideon Analytical Laboratories received several failed N-channel JFET 2N4856 parts. Several good N-channel JFET 2N4856 parts were also provided for comparison. A junction gate field-effect transistor (JFET) is a simple type of field-effect transistor. JFET source, respectively. The JFET 2N4856 were taken out of the application because of a waveform distortion at elevated temperature. The suggestion was to identify an electrical parameter (one or more) by which these unstable JFETs could be eliminated by a screen.
Gideon Analytical Laboratories got to work quickly to diagnose this failure. All samples in question had their polymeric materials removed and were decapped to reveal their chips inside. One sample had bent leads that were touching the kerf area as well as the guard ring. There was some sort of debris on every sample, and this debris was not a result of decapping. The debris particles would not blow off. If contamination was the root cause, then it will cause possible electrical field distortions and will be more noticeable at higher temperatures. None of the contamination caused a direct short in the JFET, but field distortions could be observed on a curve tracer as some of the parts were heated up. The conclusion was that contamination on the die surface is causing the field distortion at elevated temperature.
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