Accelerated Demonstration Test Case Study for ALTA 7 and ALTA 7 PRO

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Case Study 2: Accelerated Demonstration Test	Software Used: ALTA 7 or ALTA 7 PRO
*[Download ALTA 7 Example File (.ralp)]**

Background
The accelerating stress for an electronic component is temperature. To meet the specified reliability requirement, the manufacturer is required to demonstrate with 90% confidence that 90% of the units will continue to operate for 1000 hours under normal use conditions of 300K. To save time and money, the manufacturer develops an accelerated life test designed to provide the desired reliability results in a shorter period of time than would be possible with a test performed under normal stress conditions.

Experiment and Data
A sample of units are put to an accelerated life test with three different stress levels: 353K, 373K and 393K. The time-to-failure and time-to-suspension data obtained during this test are presented in Table 1.

Table 1

Stress Level Observed Failures (hr) Observed Suspensions (hr)

353K 245 250, 250, 250, 250, 250

373K 110, 180, 200 250, 250, 250

393K 50, 70, 88, 112, 140, 160

This information can be used to determine the following:
a) What is the activation energy?
b) Is the B(10) life of 1000 hrs at a 90% lower 1-sided confidence for the use stress level (300K) demonstrated by the test?
c) Plot the acceleration factor vs. stress for this accelerated life test.
d) Assuming that 1,000 units will be sold each month, determine the expected number of failures over the next six months so that an appropriate stock of spare parts can be kept on hand.
Analysis
Step 1: Using ALTA 7 or ALTA 7 PRO, the analyst creates a Standard Folio for time-to-failure and time-to-suspension data with one stress column for temperature (in Kelvin, K), with a use stress level of 300K. The data set is analyzed in ALTA using a combination of the Arrhenius model and the Weibull distribution. The results are displayed in Figure 1.

Figure 1      [Enlarge]

Activation Energy: Notice that the Activation Energy (Ea) appears in the Results area. For this example, the Activation Energy = 0.4653.

Step 2: Once the parameters for the data with an underlying life distribution and a life-stress relationship are calculated, a variety of plots, results and reports can be obtained. ALTA 7 and ALTA 7 PRO provide the tools required to determine the B(10) life and acceleration factor vs. stress plot results required.

B(10) Life: The B(10) life demonstrated at the 90% lower 1-sided confidence is found to be 1161, well above the required 1000. The QCP can be used to calculate the B(10) life with the specified confidence bounds, as shown in Figure 2.

Figure 2      [Enlarge]

The B(10) life can also be determined graphically, as shown in Figure 3.

Figure 3      [Enlarge]

Acceleration Factor Plot: A plot of the acceleration factor vs stress is shown in Figure 4.

Figure 4      [Enlarge]

Expected Number of Failures: The analyst creates a Report using the data from the calculated Standard Folio and based on the Warranty Forecasts Template and makes the following inputs:

Use Stress Level (in the Analysis Information area): 300

Time Increment (in the Warranty Returns Forecasts area): 720 (24 hours/day * 30 days/month = 720 hours/month)

Future Sales values for Periods 1-5: 1000

The final report is shown in Figure 5.

Figure 5      [Enlarge]

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