Related Topics:

Time-Dependent Stress Profiles

ALTA Single-Stress Example

ALTA Two-Stress Example

Stress Profile Example

A reliability engineer is asked to determine, with a confidence level of 90%, whether an electronic component has a B10 life of at least 350 hours under ordinary conditions.

To simplify the analysis, the engineer will assume that the ordinary stress conditions for the component consist of a constant stress level of 2 V. However, because the ordinary stress conditions are known to involve escalating stress values, the component will be subjected to a time-varying voltage stress during testing. The following table describes the stress values that will be applied during the test.

Starting Time (Hr)

Ending Time (Hr)

Stress Level (V)

0

250

2

250

350

3

350

370

4

370

380

5

380

390

6

390

400

7

 

All eleven units were tested to failure using the same stress profile. The following failure times were observed in the test.

Failure Time (Hr)

Stress Level

280

Time-varying

310

Time-varying

330

Time-varying

352

Time-varying

360

Time-varying

366

Time-varying

371

Time-varying

374

Time-varying

378

Time-varying

381

Time-varying

385

Time-varying

 

The results show that the component's estimated B10 life is 507.9438 hours. The lower one-sided 90% confidence bound is shown to be 300.4821 hours. Thus, the test's results do not show with 90% confidence that the component's B10 life is at least 350 hours.

 

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