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How to Plan and Conduct Highly Accelerated Life Testing (HALT)

Posted by Chris Montgomery on Jun 17, 2016 10:00:00 AM

Planning-and-Conducting-HALT.jpgAssessing the robustness of an electronic product is integral to successful design and performance. HALT is an important testing tool for this purpose, and its effectiveness can be maximized through careful planning prior to testing and detailed execution.

1. Developing a HALT plan

Setting clear expectations and directives for conducting HALT is a multi-step process that starts with bringing the design engineers together to:

  • Develop a test plan based on Physics of Failure (PoF), clearly defining objectives, expected environments and sample availability.
  • Determine the applicable stresses, such as temperature, vibration and/or shock.
  • Decide how many devices (known as samples) are available for testing. Generally, one to five samples are used.
  • Select the functional tests to be run during development, such as what the device should be doing; which circuits should be active; and what codes/sensors should be gathering data.
  • Identify which parameters need to be monitored based upon the expected environment.
  • Define what constitutes a failure.
  • Consider using Sherlock Design Analysis™ software to simulate the vibration and thermal loads so a model can be created that may reach HALT limits. 

In conjunction with developing the foundational outline, two key areas must be addressed: 

Applicable Stresses

Select the appropriate stresses for testing:

  • Vibration
  • High temperature
  • Low temperature
  • Voltage/frequency margining
  • Power cycling
  • Combined stresses, i.e., temperature and vibration

Step Stress Approach

For each intended stress, clearly delineate:

  • The starting stress point
  • The amount by which to increment the intended stress in each step
  • The duration of each step
  • The device or equipment limit for that stress, thereby ending HALT efficacy

2. Setting Up a HALT

For accurate results, particular attention must be paid to the HALT configuration:

  • Design a vibration fixture to ensure vibrational energy is being transmitted into the product.
  • Design air ducting to ensure thermal energy is being transmitted into the product.
  • Tune chamber for the sample being tested.
  • Determine locations for thermocouples to monitor temperature.
  • Set up all functional test equipment and cabling.

3. Conducting a HALT

HALT is comprehensive and encompasses several testing phases, each with specific parameters to follow. 

Thermal Step Stress

Thermal Step Stress testing applies incremental temperature stress levels throughout the product lifecycle in order to identify product failure modes.

To do so:

  • Begin with cold step stress, followed by hot step stress.
  • Initially use 10°C increments, decreasing to 5°C increments as limits are approached.
  • Set the dwell time minimum at 10 minutes plus the time needed to run a functional test. Timing should commence once the temperature has reached its set point.
  • Continue test until technology limits are reached.
  • Apply power cycling, load variations and frequency variation during vibration stress test.

Fast Thermal Transitions

Fast Thermal Transitions are exactly as the name implies – changing temperatures as quickly as the testing equipment/chamber allows. 

To do so:

  • Keep temperature range within 5°C of the operating limits determined during step testing
  • If the sample cannot withstand maximum thermal transitions, decrease the transition rate by 10°C per minute until the limit is found.
  • Continue transitions for 10 minutes, or the time it takes to run a functional test.
  • Apply power cycling, load variations and frequency variation during vibration stress test. 

Vibration Step Stress

Vibration Step Stress testing applies incremental vibrational stress levels throughout the product lifecycle in order to identify product failure modes.

To do so:

  • Determine the Grms increments, typically ranging from 3-5 Grms on product.
  • Set the dwell time minimum at 10 minutes plus the time needed to run a functional test. Timing should commence once the temperature has reached its set point.
  • Continue test until technology limits are reached.
  • Apply power cycling, load variations and frequency variation during vibration stress test. 

Combine Testing

Merge testing results and methodologies to further test products. 

To do so:

  • Develop a thermal profile using thermal operating limits, dwell times and transitions identified in earlier testing.
  • Apply additional product stresses during vibration stress test.
  • Use a constant vibration level of ≈5 Grms in first combined runs, and stepped in the same increments as those in vibration step stress tests.
  • Add ticket vibration (≈5 Grms) at higher Grm levels (>20 Grms) to determine if failures were precipitated at high G levels, but only detectable at low G levels.

4. Post-HALT

Once HALT is completed, the design engineers’ focus becomes determining the root causes of all failures and corrective action. Essentially, a verification HALT needs to be implemented to evaluate if testing adjustments fixed the problems.

Sherlock Automated Design Analysis software shortcuts this process by creating simulations based on testing models before any physical sample modification or the verification HALT takes place – saving time and money. Sherlock can also be applied in the future, as previously tested products are evaluated for engineering changes. 

Contact us today to discuss how Sherlock can help streamline your HALT process and accurately confirm results.

Test Plan Development: How To Do It