HALT is an effective tool used during product development to stimulate design weaknesses into failure modes, where they can be diagnosed, and corrected before the product is introduced to mass manufacturing.
In addition, HALT will identify the weakest points in a system or product that requires ‘ruggedizing’ to increase the overall reliability of the product. These weak points will often lead to failures in the field some months, or even years after general product release.
Why conduct HALT?
The goal of HALT is to improve the products operating margins by discovering and correcting failures until the Fundamental Limit of Technology (FLT) is achieved. At this point the margins should be wide enough to ensure failures within the published environmental operating specification of the product do not occur in the field.
The HALT process is used to identify the weakest points in a system. These weak points are realized through the application of higher than usual stress levels, for short periods of time in a controlled environment. All failure modes are then driven to failure cause, and corrective actions are implemented to prevent such failures occurring in the field.
Weaknesses are identified by:
- Defining the upper and lower temperature operating limits.
- Defining the upper and lower temperature destruct limits.
- Defining the vibration operating and destruct limits.
- Determining and document all failure modes.
After conducting HALT, you will understand your product a lot better then before you started. You will know when the product fails, what failed, and will have an idea of how to fix the failure(s). Knowledge is power, and the more you know about your product the more ammunition you have against your competitors.
There are five stages to a traditional HALT test.
Cold Step Stress
Cold step stress consists of decrementing the ambient temperature inside the HALT chamber in approximately 10°C steps starting from an ambient temperature of approximately 10°C. The unit is functionally tested at each step before moving on.
The Unit Under Test (UUT) is positioned inside the HALT chamber where it will receive uniform airflow. The test begins at approximately room temperature with a minimum dwell time of ~15 minutes. Testing is conducted on the product to ensure full functionality is attained. After the dwell period has expired the temperature is stepped down in ~10°C decrements and the dwell time repeated.
Hot Step Stress
Hot step stress testing consists of incrementing the ambient temperature inside the HALT chamber in 10°C steps starting from an ambient temperature of ~20°C. The unit is functionally tested at each step before moving on.
The Unit Under Test (UUT) is positioned inside the HALT chamber where it will receive uniform airflow. The test begins at approximately room temperature with a minimum dwell time of 15 minutes. Testing is conducted on the product to ensure full functionality is attained. After the dwell period has expired the temperature is stepped up ~10°C and the dwell time repeated.
Rapid Thermal Transitions
Rapid Thermal Transitions consists of extreme temperature cycling between the operating limits identified during cold and hot step testing. The unit is functionally tested throughout the entire process, including dwells, and transitions.
The Unit Under Test (UUT) is positioned inside the HALT chamber where it will receive uniform airflow. Temperature limits are defined based upon the Lower and Upper Operating Limits achieved during the cold and hot step stress.
The temperature is then rapidly cycled from the lower limit to the upper at change rates of at least 60C per minute. The temperature is dwelled for at least 10 minutes at each limit before the cycle continues, and the temperature is ramped from the upper limit down to the lower limit, again with a change rate of at least 60C per minute. Functional testing is conducted on the product to ensure the functionality throughout the entire cycle.
Five temperature cycles between the upper and lower limits are conducted, with the product being continuously monitored throughout testing. When testing electronic goods Rapid Thermal Transitions predominantly discovers failures related to timing issues.
Vibration Step Stress
Vibration step stress consists of increasing the vibration level in 5 Grms steps until the Operating & Destruct Limits are found. The products functionality is checked at each step. The temperature is held at an ambient temperature of ~30°C.
The Unit Under Test (UUT) is mounted onto the vibration table using a fixture that is thermally transparent, lightweight, and rigid. Accelerometers are attached to the UUT to monitor the response of the product. The test is conducted at an ambient air temperature and begins at 5 Grms, with a minimum dwell time of 15 minutes. Testing is conducted on the product to ensure full functionality is attained. After the dwell period has expired the vibration is stepped up in 5 Grms increments, and the dwell time repeated.
Combined Environment is the last, and most destructive of the tests applied during a HALT. The temperature cycling profile used for Rapid Thermal Transitions is combined with the vibration step stress profile to make the ultimate thermal and vibration stress test.
The vibration level is traditionally set to one fifth of the operating limit attained during the vibration step stress, and the first thermal cycle is conducted. The product is continuously monitored for functionality throughout the entire process.
There are many varieties of combined environment testing, and our consultants will work with your organization to ensure the appropriate test is applied.