Voltage Step-Stress Example
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An electronic component is subjected to a voltage stress, starting at 2 V (use stress level) and increased to 7 V in stepwise increments. The following steps, in hours, are used to apply stress to the products under test: 0 to 250, 2 V; 250 to 350, 3 V; 350 to 370, 4 V; 370 to 380, 5 V; 380 to 390, 6 V; and 390 to 400, 7 V. This profile is represented graphically next.
The objective of the test is to determine the B10 life of the components at the normal use stress level of 2 V. In this experiment, the overall test time is 385 hours. If the test were performed at use conditions until all the units have failed, the expected test duration would be approximately 1,700 hours.
Eleven units are available for the test, and are all tested using the same stress profile. The units that failed were removed from the test and their total time on test recorded. The following times-to-failure are observed in the test, in hours: 280, 310, 330, 352, 360, 366, 371, 374, 378, 381 and 385.
Solution
The first step is to create a stress profile for this experiment. The profile is defined in segments, and the stress applied during each segment can be a constant value (as is the case in this step example) or defined as a function of a time variable (t). The following figure shows the stress profile for this analysis.
The following figure shows a plot of the stress profile.
Enter the times-to-failure data in the ALTA standard folio and assign the voltage step-stress profile to each data point, as shown next.
Analyze the data set using the following assumptions: cumulative damage power life-stress relationship and Weibull life distribution. Then use the QCP to calculate the B10 life at the 2V use stress level. The B10 is estimated to be 507.943755 hr, as shown next.
