• What is HALT Highly Accelerated Life Testing and why perform HALT?
• What is a typical HALT procedure?

A Rapid HALT is an abbreviated HALT, typically one day of tests, making it a great cost-effective solution for those seeking faster qualitative results.  Exposing a product to a Rapid HALT early in the design process can help reduce product development time and cost by enabling manufacturers to identify flaws or areas of improvement before it’s too late.

Rapid HALT’s are a good tool for assessing the reliability of different suppliers of components but can also be used to assess the reliability of less complicated products.  For example, DES has performed Rapid HALT’s to evaluate the reliability of different suppliers of power supplies, cooling fans, and LED’s.  DES has also performed a Rapid HALT to study different fastening methods in order to determine which was more robust.

Rapid HALT profiles may vary slightly depending on the product.  Figure 1 illustrates DES’s standard Rapid HALT profile.  Vibration levels are ramped up concurrently with hot and cold temperature cycles.  The stresses are increased until the practical limits of products have been reached.  Examples of practical limits include the melting temperature of solder joints or excessive softening of plastics.  These stress levels are obviously well beyond the scope of most product designs and that is ok.  The purposes of any HALT is time compression by applying higher-than-normal stress levels.  The user should not necessarily focus on what level of stress caused the problem, but should focus on improving the weak points in their product.

Many times our customers are surprised with the Rapid HALT results because the less expensive components perform better.  Thus our customers are able to apply a significant cost reduction to their products.  This results in increased profits and reduced warranty costs.

For more information on HALT or other testing services, contact DES or call 610.253.6637.

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A customer approached DES looking to find an accelerated test solution for an AC powered cooling fan used in one of their products.  The product had been established in the marketplace and the company was now looking for ways to reduce cost by looking at different cooling fan suppliers.  Most fans, however, have a mean life rated for over 20,000 hours, so a typical accelerated life test would require a significant amount of time and money. 

DES Solution

Performing a quantitative accelerated life test on cooling fans presents challenges because they have such a long lifespan.  Reasonably speaking, the shortest quantitative solution for determining the lifespan of a fan could take as long as a couple months.  DES proposed a qualitative solution, a Rapid HALT.  A Rapid HALT (Highly Accelerated Life Test) is designed to apply a variety of stresses, concurrently, to a product in order to significantly time compress a product’s lifespan.  A typical Rapid HALT lasts only one day which is extremely convenient for companies that need results quickly.

Results

A sample size of 3 cooling fans were tested for 4 different fan suppliers.  We will refer to these suppliers as Supplier A, B, C and D.  All 12 fans were placed in the chamber together and a Rapid HALT was conducted.  None of the four suppliers survived testing without some issues but the results were still differentiating.  Supplier A had no electrical issues in any of its samples but the fan blades on all 3 samples vibrated off the armature.  Fans of Supplier B, all experienced sputtering of the fan blade and eventually saw two of its fans current levels drop to 0.  By the time testing was completed, none of the fans were functioning.  Supplier C fared slightly better than A and B.  One of Supplier C’s fans lost current at the most extreme step and never recovered.  The other two however, experienced fan blade sputtering but were functioning normally upon final inspection.  Supplier D performed the best out of the four suppliers and thus would be considered the most durable of the suppliers tested.  Only one of the fans experienced any issues, in which it lost current at the most extreme step.  Upon final inspection all of the fans were functioning normally.

There are other factors to consider such as price and accessibility but these results were able to successfully assist our customer in differentiating between the reliability of the four fan suppliers.  While a HALT is qualitative and will not produce an actual estimated fan lifetime, it is a great comparison tool to evaluate the reliability of different suppliers faster and less expensive than traditional testing techniques.

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A leading medical technology company contracted DES to perform Product Reliability Testing of a carrying handle. A sample of the test can be seen below and in our video library. The carrying handle had to be pulled, released, rotated and subjected to a sizable lifting force, approximately 20,000 times during its life time. 

DES has considerable capability to complete product reliability testing. The main challenge for this project was that each cycle consisted of complex motion. The motion included pulling/releasing the handle to unlatch/latch a pin while rotating the handle. In order to achieve this, DES had to design fixtures and mechanisms that would reposition the carrying handle into each of the designated positions. The number of cycles was automatically counted until failure or 20,000 cycles were completed. During the test, the force to pull the handle was measured at various intervals. The Accelerated Life Testing was completed successfully demonstrating a high reliability.

Please visit our video library to see more examples of DES’s capabilities.

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Real world vibrations are usually of the random type. Vibrations from automobiles, aircraft, rockets are all random. A random vibration test can be correlated to a service life if the field vibrations are known. Since random vibration contains all frequencies simultaneously, all product resonances will be excited together which could be worse than exciting them individually as in sine testing. Sometimes random vibrations are mixed with sine vibrations in Sine-on-Random Vibration Testing. Also, a low level of broad band random vibration can be mixed with additional high levels of narrow band random vibrations in Random-on-Random Vibration Testing.

Some common test standards that have specifications for Random Vibration Testing are:

• ASTM D4169 Standard Practice for Performance Testing of Shipping Containers and Systems
• ASTM D4728 Standard Test Method for Random Vibration Testing of Shipping Containers
• GMW 3172 General Motors Specification for Electrical/Electronic Components – Environmental/Durability
• IEC 60068-2-64 Environmental testing Part 2-64: Tests Fh: Vibration, Broadband Random and Guidance
• ISTA 2A and 3A Procedures for Testing Packaged Products
• MIL-STD-202 Department of Defense Test Method Standard for Electronic and Electrical Component Parts
• MIL-STD-810 Department of Defense Test Method Standard for Environmental Engineering Considerations and Laboratory Tests
• MIL-STD-883 Department of Defense Test Method Standard for Microcircuits
• RTCA DO-160 Environmental Conditions and Test Procedures for Airborne Equipment
• SAE J1455 Recommended Environmental Practices for Electronic Equipment Design in Heavy-Duty Vehicle Applications

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DES has considerable capability to complete push pull reliability testing.  The main challenge for this project was that one third of the cycles had to be completed at -7 °C and one third had to be completed at +49 °C.  This was difficult because DES did not want to expose a precision actuator to extreme hot/cold temperatures because it could be damaged.  Therefore the case was placed inside of a large temperature chamber while the actuator was located outside of the chamber.  The chamber had to be large because the case was big and the handle extended 18 inches.  DES made a special link to connect between the case handle and actuator.  The link moved through a sealed chamber access port.  A frame was built around the case to hold it in place while the handle was pulled opened and pushed closed.

The push/pull cycling motion was performed using a special actuator.  The actuator travel, velocity and acceleration were programmed into a controller.  The number of cycles was automatically counted until failure or thousands of cycles were completed.  During the test, the force to open and close the handle was measured at various intervals.

The Accelerated Life Cycle Test was completed successfully providing highly useful results to the customer.  This was a unique challenge to perform push pull reliability testing at extreme hot and cold temperatures.  Please visit our video library to see more examples of DES’s capabilities.

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The Arrhenius Equation that relates reaction rates to temperature is:

The Acceleration Factor (AF) can be obtained by the ratio of the reaction rates at two different temperatures and is given by the following equation:

As an example, consider a product with a normal operating temperature of 50 °C. Testing the product at 100 °C will result in the following acceleration factor, assuming an activation energy of 0.7 eV:

Testing the product for 1,000 hours (≈ 6 weeks) at 100 °C is therefore equivalent to 29,000 hours or 3.3 years of life at the normal operating temperature of 50 °C. Increasing the test temperature will increase the acceleration. For example, if the same sample could be tested at 130 °C, the acceleration factor (AF) would increase to 146 so that the same 1,000 hours of testing would now be equivalent to 16.7 years of life at the normal use temperature. However, care must be taken such that the test temperature is not higher than what the product can withstand. Using too high of a test temperature may result in unrealistic failures that would not occur during normal product operating temperatures. It is therefore always important to evaluate failures obtained during accelerated temperature testing to determine if they are the same type of failure that would be expected to occur at normal operating temperatures.

Using the correct value for the activation energy is also important as a small change in the activation energy will have an effect on the acceleration factor. Activation energy values for various processes have been reported and can be found in the literature or the Internet. It is also possible to experimentally determine the activation energy by performing tests at multiple temperatures and plotting the results.

What sets Delserro Engineering Solutions, Inc. (DES) apart from other labs is our knowledge on how to relate test time to time in the field. So if you do not know what test conditions that you should use, what specification to choose, or how to correlate your test to field life, then we will help you because we are reliability testing experts!

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