by Jack Goho
Gideon Analytical Laboratories received three Fairchild RFP40N10 power MOSFETs. A MOSFET is a specific type of metal oxide semiconductor field-effect transistor (MOSFET) designed to handle significant power levels. Compared to the other power semiconductor devices, for example, an insulated-gate bipolar transistor (IGBT) or a thyristor, its main advantages are high switching speed and good efficiency at low voltages. It shares with the IGBT an isolated gate that makes it easy to drive. They can be subject to low gain, sometimes to degree that the gate voltage needs to be higher than the voltage under control. The Fairchild RFP40N10 power MOSFET is an N-Channel power MOSFET manufactured using MegaFET process, which uses feature sizes approaching those of LSI integrated circuits gives optimum utilization of silicon. These MOSFETs were in TO-220AB packages. All of the terminals on the Fairchild RFP40N10 power MOSFETs were shorted.
Electronic failure analysis was conducted on the Fairchild MOSFETs. They were electrically tested which revealed all had shorted leads. They were decapsulated. Sample 1 had an EOS located near the foot of the source wire. Examination revealed no carbonization on the source wire and no vertical cracking to the silicon. However, it did reveal melted source metal, which had receded from the passivation layer, indicating that there was a lot of heat generated within this MOSFET. Sample 2 had damage near the source wire. The underside of the wedge bonds showed silicon attached to the failed area. The silicon under the wire bond was extremely hot to the point where bonding took place. There was no damage to the remainder of the die. All of the Fairchild RFP40N10 power MOSFETs had the same failure mode located in the same spot. This appears to be an application issue and not a manufacturing issue.
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