Things to Think About for Reliability Test Planning

One of the jobs of reliability engineers is to obtain reliability data for products (component/assembly/system). Such data includes failure modes and life models, which describe how and when the subject will fail. The data can be acquired through reliability testing. Whether the testing is conducted within our own lab or through third-party facilities, it is crucial that the reliability engineer prepares an initial test plan to facilitate communication and coordination among involved teams.

The following bullets are the ones I think are important to think through for reliability test planning. The first three bullets are about the test subject itself. Those bullets should be consulted and discussed with the product development team (hardware/electronic team) since they are the people who are the most familiar with the product. Bullet 4 to 7 are about the reliability objective and testing itself. The reliability engineer should confirm the test objective and discuss the testing requirement with the testing team.

1. Test Subject

• Definition: Identify what is being tested: component, assembly, or system-level.
• Function: Clarify the function of the test subject and understand how the test subject operates in real-world conditions.

2. Mission Profile

• Expected Life: Define the total operational hours or number of power cycles, with an emphasis on the importance of precise time units.
• Environmental Conditions: Specify temperature, humidity, and other relevant environmental factors during operation.
• Force Profile: For mechanical parts, detail the forces or torques experienced during normal operation.
• Electrical Profile: For electronic components, specify typical voltage and current levels.

3. Failure Definition

What is considered a failure for the test subject, which may include:

• Failure to pass functional tests (fail to perform certain functions)
• Measurement exceed a given criteria: e.g., Electrical anomalies such as overcurrent or resistance deviations

4. Test Objectives

Determine the primary purpose of the test, which may include:

• Identifying failure modes (more qualitative like HALT, HASS)
• Building a life model (will need quantitative time-to-failure data)
• Demonstrating reliability concerning specific requirements
• Measuring performance metrics

Multiple objectives can be targeted within a single testing campaign.

5. Testing Parameters

• Test Type: Life testing, accelerated life testing, HALT, etc.
• Sample Size: Most of the time this is a constraint related to cost and availability.
• Test Duration & Cycles: Calculated based on expected life and accelerated testing principles.
• Testing Environment: Nominal vs. accelerated conditions.

6. Test Bench & Equipment Capabilities

• Simulation of Mission Profile: Capable of creating the required environmental condition (temperature/humidity) and/or replicating the operation of the test subject.
• Automation Level: Manual vs. automated testing processes.
• Measurement & Monitoring: Capability to halt test and/or record the timepoint/cycles upon failure What is measured (e.g., voltage, temperature, stress levels) during / at the end of the test

7. Data Collection and Analysis

• Data Collection Format: time, performance (metric or pass/fail), other observations.
• Analysis: qualitative (failure modes identification) or quantitative (time-to-failure model)