The paper outlines a method for predicting the results of humidity tests applied to electronic equipments. It is based on a theory of vapor entry into parts to cause failure. Depending on the packaging, the entry mechanism and the test conditions, the rate of vapor entry can be calculated and a severity factor can be estimated for different test levels.

If a base level is set at about 25°C (77°F) and 50% RH, a base failure rate can be derived for each part from the dormant or storage failure rates, which are well established.

The expected failure rate under the test is derived from the base failure rate and the acceleration factor for each part in an equipment or unit to calculate a total failure rate. With the total failure rate and the test exposure time, the basic reliability equation can be used to calculate the probability of passing or failing the test. The method provides an estimate of the probability similar in principle and with an accuracy comparable to the reliability prediction methods of MIL-HDBKD-217. Examples of prediction and references are given.

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