Parameters for Dendrite Model

The tests were conducted in temperature-humidity chambers. The iands were biased with 5, 10, and 20 volts, and in-situ voltage-drop measurements (across 10 M O limiting resistor in series with each gap) were made at intervals to generate a cumulative faii distribution as a function of time. A fail is defined as a resistance 5x10 Q. 

Failure analysis was performed on each failed unit. Leakages were first analyzed electrically to ascertain that they were caused by dendrites (and not other conductive paths), and then by an electron microprobe to determine the elements responsible for the high conductivity. Typical Ag dendrites are shown in Fig. 2. Those obtained at the iower voltage are 

The reciprocal tj values for both backseals are plotted against the applied voltage in Fig. 5 showing a linear dependence and an intercept of four volts. The results suggestthatthecurrentdensity distribution may be falling to subcritical values. 

There is a notable difference between the results obtained with the two backseals. The modules encapsulated with silicone rubber show a constant sigma ( 0.9) independent of the bias, whiie those encapsulated with epoxy have a sigma ranging from 0.7 to 2.5, increasing as the bias falls from 20 to 5 volts so that, at low fallout, the cumulative percentage of failures is practically independent on the applied voltage. 

The actual pore-size distribution should, however, be measured experimentally to provide materials characterization and direct model verification. MeanwhileTand a are just parameters. 

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