Highly Accelerated Life Testing :: HALT
The HALT process is used to identify the weak points in a system. These weak points are realised 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 action is implemented to prevent such failures occurring in the field.
The same failure mechanisms discovered during HALT are highly likely to occur under nominal stress, long duration field conditions.
Fundamentally we’re using stress (thermal, voltage, vibration) to induce temporary failure modes by changing the components capacitance, resistance, or inductance to replicate the failures modes that will occur during natural ageing.
Use HALT if you’re wanting to Identify weaknesses in the design of the product by:
Defining the upper and lower temperature operating limits.
Defining the vibration operating limit via a vibration step.
Determining the products ability to withstand combined environment testing - thermal and vibration.
Determining and documenting all failure modes.
The results of HALT can be used to:
Provide early identification of catastrophic failures that would appear in the field.
To provide data that can be used to show the effectiveness of conducting HALT during the product development phase.
Lets make it robust
Highly Accelerated Life Testing (HALT) is specifically designed to improve product reliability, it is one of the most effective and efficient ways of characterising product response to stress. In HALT we are attempting to stimulate failures through the application of stress, the points of failure indicate an opportunity to improve product reliability.
The first challenge is identifying the failure mode, next comes repeatability and the last is debugging and corrective action – then repeat.
We’re available to help you plan, setup, and run Highly Accelerated Life Testing (HALT) on your products. We get involved early in the concept and design process to ensure adequate testability is designed into the product, prior to HALT being conducted.
We’ll provide a comprehensive test report, including recommendations based on our experience, and will be available to present this report to Management if required.
We operate a Qualmark Typhoon 2.5 located in Christchurch, New Zealand, and provide testing services for some of New Zealand and Australia’s most well-known brands.
What? How? and Why?
For a better understanding of what the process of Highly Accelerated Life Testing entails take a look at our library here. We conduct HALT to identify weaknesses in our product to determine the most likely failures in the field. By doing so we get to understand what fails and how, we also get to reliably replicate the failure mode which gives us the ability to fix it.
When to conduct HALT often comes down to when samples of sufficient quality are available with high enough test coverage to justify running stress tests. Typically we recommend looking at a two-stage process:
Run HALT at a sub-assembly level – improve these first.
Run HALT at a system level
Each step will pick up different failure modes, with the system level HALT being the more critical of the two.
How Stress Vs Strength Works
Let’s take a look at a couple of relevant distribution illustrations, first off if we assume that a population of identical products (in process, BOM, and design) are manufactured and tested for a particular failure mode exposed when the product is stressed at high temperature we would find the following (ignoring for now the shape of the distribution):
If we then analysed our field environment for each of the population of units we’d equally find that the level of stress encountered by each product will vary, most likely fitting to a distribution of it’s own:
So what happens when field stress is greater than product strength? This happens – stress overcomes product strength, i.e. the weak products will fail.
Take that same scenario but fast forward in time, what has happened to product strength? It’s degraded over time, meaning more products are now under threat of early failure.
How does HALT help?
When we conduct HALT we are attempting to increase the operating margins of the product. Shown in graphical form below the operating margins (or limits) are the limits at which the product fails. In a product that is not robust it is reasonably foreseeable that the following situation may occur:
In other words – our margins are not sufficient enough to protect the weak from our predicted field stress levels.
By conducting HALT and finding these weaknesses (dominant failure modes) we are able to drive them to root cause, correct them and verify we have increased our margins. After HALT we’d hope to see something like this:
How far do we need to push? That’s a good question, and one that needs some thought - contact us, we’re open about sharing insights based on industries we test for, and have over 20 years experience running hands-on HALT.
What else can HALT be used for?
HALT as described here is practiced using a HALT chamber, these chambers provide wide thermal and vibration capabilities giving is the ability to stress to failure. A HALT chamber is a fantastic tool, it can be used for:
HALT & HASS Testing
Field failure diagnosis (NFF*)
Regression testing
Quality control
Alternate part, or design qualification
The possibilities are limited only by your thought boundaries. Any functional test you currently perform on your products can be performed whilst the product is under duress – more to the point, it should be.
*No Fault Found (NFF) rates have been found to account for as much as 68% of all consumer electronic product returns - how many of these products are intermittently faulty and therefore returned out to the field after functional testing shows no issues? HALT can help you find out for sure. Source: Accenture study: Big Trouble with "No Trouble Found" Returns
Preparing for a HALT
This stage is often the longest part of the entire process - you need to make sure you have solid functional testing available for the product. This includes exercising all functions, monitoring inputs/outputs/voltages/clocks/resets and other key signals and ensuring that each input (power in for example) can be modulated from it’s lower specification to upper.
Firmware or support software often needs to be written specifically to query the product state, activate key functions and extract information - this is imperative to a successful HALT. Without functional testing HALT is pointless.
Additionally - all thermal cut outs must be removed, we often find faults above artificially imposed limits that have occurred in the field under nominal conditions.
Our services
We have over 20 years experience designing, running and reporting on HALT - and provide the following services for our customers:
Provide pre HALT planning and recommendations in the following fields:
Testing plans and background.
Monitoring plans and background.
Vibration fixture recommendations.
Test equipment sourcing and/or design.
Operate the HALT chamber and provide assistance with the test.
Outline and apply fault isolation techniques; if feasible.
Provide recommendations for design enhancements based upon the failure modes encountered.
Deliverables
The following items will be delivered within the specified timeframe:
Preliminary raw data provided at test conclusion.
Full test report, pictures, formatted data, and recommendations. (Delivered within 7 - 10 days of test completion)
Client preparations
HHCNZ will work with the Client to ensure a sound test plan is in place prior to shipment of the product. This includes provision for the identification of monitoring points on the product.
The Client shall prepare the following necessities in order for the testing to proceed within the allotted timeframe:
Check all samples and functional test equipment are in sound operating order prior to shipment.
Ensure the samples undergoing testing, along with all specialist test and fixture equipment is delivered to the lab of choice within 3 days of the scheduled test date (for international clients).
Disable any thermally activated safety cut off’s on the samples. Or alternatively, ensure that the ability to remove such cut offs is available at the beginning of testing.
All cables used between external test equipment and the product under test must be at least 2m in length. Thought must be given to the voltage drop encountered in such cables along with the signal integrity of any monitored point.
Provide extension cables (if applicable) to isolate sub systems of a product in the event of failure.
Provide spare parts that can be used if repairs are required.
Client provided equipment
The Client will supply the following test equipment for use during the HALT:
Specialist test equipment.
Software for monitoring the units during test.
Any other specialist equipment required.
It is envisioned that at least two samples of the product can be tested simultaneously provided sufficient test equipment is available to ensure each unit is functional.
Sample requirements
We strongly recommend providing at least 4 samples for testing, and if possible a total of 8 is beneficial.
There is a possibility that the samples will be destroyed before completing the HALT; as such it’s important to have spares on hand to prevent delays in testing.
Testing two samples at once provides confirmation an operating or destruct limit has been found. If you only test one unit we first need to determine whether the failure mode is caused by a production defect or whether it is inherent to the design.
Projected outcome
When the HALT is complete, you will have successfully gathered thorough and accurate information detailing the true temperature and vibration characteristics of the product. The primary information gathered will include:
Temperature operating and destruct limits.
Vibration operating and destruct limits.
Listings of the failure modes found during HALT.
Recommendations (if applicable) in order to fix weak links.
This information can then be used to:
Fix any weak links in the design.
Provide a benchmark to show improved reliability over time.
Develop a HASS screen to monitor production quality.
Provide feedback to management regarding the effectiveness of the HALT.