Siliconix Si4998DY MOSFET

Gideon Analytical Laboratories received several dual N-channel SO-9 Vishay Siliconix MOSFETs. MOSFETs are transistors used for amplifying or switching electronic signals. The MOSFET is the most common transistor in both digital and analog circuits, used in many scenarios where voltage conversion is necessary. These dual N-channel SO-9 Vishay Siliconix Si4980DY MOSFETs were received for component evaluation and environmental testing in a variety of conditions to determine any noticeable flaws or anomalies with the package, die, or electrical parameters.

All the MOSFETs were tested on a curve tracer to ascertain electrical information and compare it to the manufacturers’ datasheet to get typical values for electrical parameters. The purpose of this test was to check for performance under humid conditions that would accentuate any passivation defects, poor metal to plastic seal, contamination level during assembly or materials compatibility and moisture ingress causing leakage current. The static parameters did not change before and after several environmental tests designed to exacerbate specific anomalies on the die. Radiography of a good device is pictured below. All the wire bonds, source metal, and gate pad appear normal.

The silicon SEM-EDS analysis was conducted on a variety of contact points.

Gideon Analytical Laboratories arrived at some important conclusions. The company having this done suspected a low percentage fall out during testing. We did not find this. EDS analysis found no contaminants leading to excessive leakage current. The device construction was excellent. The passivation was excellent. The trenches and diffusion depths were consistent as was the oxide layer, gate length, step coverage, and registration alignment. All the electrical parameters tested before and after the environmental and power testing revealed no anomalies. However, this lead us to discover a design flaw which accounted for 3.2 percent failure rate and when it was corrected, the failure rate was .02 percent.

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Si4980DY MOSFET

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Decapsulated Si4980DY

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Source contact window

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Termination ring at die corner

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Cross section of the trench with polysilicon removed.

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Radiography of the Si4980DY