DES president Gary Delserro is featured in an article published in Assembly Magazine on July 9, 2021.  Titled “Accelerated Life Testing,” the article discusses different types of manufacturing life testing and quotes Gary with reference to highly accelerated life testing (HALT):

“Companies have reported savings in the millions after using HALT,” claims Delserro. “The test can accelerate a product’s aging process from actual months into test minutes, and it can help you discover weaknesses in your product during the design stage. Combined vibration, temperature and electrical stress variables, as well as internal fluid pressure, are typically used during HALT to induce failures and uncover fault points. By using combinations of loads, we can uncover design or manufacturing process flaws before they reach your customer.”

The entire article can be found on Assembly’s website. 

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HALT Testing can be a competitive advantage for companies when performed correctly and at the right time. 

The best time to begin HALT testing during the product development process is when prototypes first become available. HALT is designed to expose product flaws and weaknesses, therefore, a successful test will produce areas for product improvement.  A lot of designers and manufacturers tend to wait until the product design is mature.  At that time, further process improvements or design changes become too costly or timely.  Ideally, HALT should be performed while the product is still fluid and moderate changes don’t become setbacks.  This allows product design to move much more rapidly and efficiently, saving the company time and money.  HALT testing can also eliminate the need for further verification if the product has proven reliable at the much more extreme conditions exposed to in HALT. 

Delserro Engineering Solutions, Inc. (DES) has the knowledge and experience to provide HALT testing services for your product.  We offer both standard and customized test solutions depending on your testing needs.  For more information on HASS, HALT or other testing services, contact DES or call 610.253.6637.

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Customer Goal

A customer approached DES looking to perform Highly Accelerated Life Testing (HALT) on a new circuit board design.  DES and the customer agreed to test the circuit boards using DES’s traditional HALT test procedure which calls for hot/cold temperature steps followed by rapid temperature ramping, vibration steps and combined temperature and vibration stresses.  HALT testing on electrical componentry is quite common across industry to expose design weaknesses; both mechanical and electrical (What is HALT and Why Perform HALT?).  Typical failures include poor solder connections, overheating, component failure, etc. (What Kind Of Failures Occur During HALT?)

Results

The hot/cold temperature steps exposed soft failures such as power resets and lack of communication for the circuit boards.  One hard failure was also exposed during this stage which proved to be a recurring problem and thus an area of weakness in the product design.  The units functioned properly during the vibration steps and rapid thermal ramping stages.  The combined temperature and vibration stage, however, revealed the same issue as seen in the first stage on two other units.

The circuit board featured potted componentry for purposes exclusive to the customer.  This potted feature cracked on multiple units throughout testing and caused all sorts of communication issues for the units.  In 3 days the customer was able to expose a product design weakness that would most likely have caused a number of warranty and reliability issues.  In the words of the customer:

“The results from this testing have identified strong and
more importantly weak areas in our design.”

– Customer

HALT testing is a necessity for products with electrical circuity in terms of preventing field failures and high product return rates.  Problems such as these can be really damaging to a company’s bottom line if not addressed early in the design process.  Fortunately this customer has had experience with HALT in the past and chose to perform HALT before finalizing the product design.  DES has over 20 years of experience performing HALT testing on a variety of medical, commercial, industrial and military products.  Schedule your next HALT test with us by contacting us or call us at 610.253.6637.

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• 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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If the product fails to operate, the temperature or vibration will be changed toward ambient room conditions followed by a short dwell period to see if the product recovers. If the product is non-operational after dwelling at ambient conditions, trouble shooting will take place to find the failed component. The failed component will then be removed, repaired or replaced with a new component (as is practical) in an effort to expand the test stresses.

Relevant Failures

All HALT failures are relevant unless it is determined that the failure was caused by a condition external to the product which is not a test requirement. Relevant failures may include, but are not limited to the following:

• Design and Workmanship Failures
• Failures caused by Poor Manufacturing
• Component Part Failures
• Multiple Failures
• Intermittent Failures
• Built-in-Test Failures

All relevant failures represent an opportunity for improvement and should be thoroughly investigated to determine their root cause. All relevant failures should be evaluated as to whether or not they can be corrected with a reasonable amount of effort and cost. However, all failures that prevent a product from functioning in its normal environment should be fixed! Figures 1 through 3 show examples of relevant HALT failures.

In Figure 1, the mounting tabs used to hold a power supply in place failed during vibration. Larger tabs with better stress relief grooves should be used in this case to better withstand the vibrations. The capacitor leads in Figure 2 failed due to repeated fatigue stresses from vibration. Improved mounting such as placing an adhesive under the capacitor could be used to prevent this type of failure which is common for large components connected by thin metal leads.

In the case of temperature related failures such as seen in Figure 3, the temperature at which failure occurred should be well outside of the expected operating range of the equipment.

Even in this case, an evaluation should be performed to determine if a component with an improved temperature rating can be economically substituted because the failing component may be a weak point in the product design.

Non-Relevant Failures

Failures listed below may be considered as non-relevant:

• Failures directly attributable to erroneous product manufacturing or operation.
• Failures resulting from improper test setup or procedure.
• Dependent failures, unless caused by degradation of items of known limited life.
• Failures occurring during test “down-time” such as during troubleshooting on the bench unrelated to the HALT Procedure.

Care should be taken when determining if a failure is non-relevant as this may result in missing an opportunity for product improvement.

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Specialized test chambers are needed to perform a HALT. Typical HALT chambers are shown in Figure 1. The specification for HALT chambers is typically the following:

Liquid nitrogen (LN2) is used to cool the air temperature in HALT chambers. This allows for very rapid temperature changes of 60°C per minute and a cold temperature extreme of -100°C.

HALT chamber heating is provided by high power resistive heating elements that can produce changes of 60°C per minute and a hot temperature limit of +200°C.

HALT chambers produce random vibration in 6 DOF simultaneously using pneumatic air hammers attached to the bottom of the chamber table. This means random vibration energy is applied simultaneous along three orthogonal translations and three rotations which is very unique to HALT chambers. Sometimes the vibration produced in HALT is called repetitive shock because pneumatic air hammers are used to produce vibration.

Random vibration accelerations up to 60 Grms and frequency content to 10,000 Hz are common. It is important to understand how the how HALT chambers compute Grms. DES’s HALT chambers calculate Grms using a 5 kHz bandwidth. Some chamber manufactures use a 10 kHz bandwidth which approximately doubles the computed Grms, but in reality the resultant vibrations are about the same! More information about random vibration can be found in our blog article Sinusoidal and Random Vibration Testing Primer

It is important that HALT chambers can be run in automatic or manual modes of operation. Temperature and vibration profiles are programmed to run automatically during parts of the HALT procedure. This allows the temperature rate of change to be accurately controlled during temperature transitions. The chamber can also be run in manual mode with the operator controlling the temperature and vibration set points. This is useful for other parts of the HALT procedure such as when operational or destruct limits are being determined.

Fixtures

DES’s has many stock channel fixtures that can be used for products with a flat top and bottom. Examples of DES’s stock channel fixtures are shown in Figure 2.

Custom-designed fixtures can be fabricated on a case by case basis. Figure 3 shows examples of custom-designed test fixtures. The fixtures must have a flat base with holes to enable them to be bolted to the chamber vibration table. Customers or DES can supply the fixtures used to attach the test units to the vibration table inside the chamber.

When performing HALT, it is desired to change the temperature of internal components as fast as possible. If products have existing vent holes or cooling fans, then air ducts can be placed to blow air through them as seen in Figure 2. Products with a sealed enclosure or case should be modified whenever possible to allow for internal airflow. This can be done by removing covers when practical or drilling holes in the enclosure. Air ducts can then be placed near these openings to direct air flow internally into the product.

Instrumentation and Monitoring

Monitoring can be accomplished with either digital recording instruments or by manually recording gauge readings or by visual observations. Monitoring sensors are usually thermocouples and vibration accelerometers. Reference thermocouples are placed at various locations on the product to measure the response temperatures on the product. Also, during the vibration step part of the HALT procedure, reference vibration accelerometers can be placed on the product to measure its vibration response. Therefore a digital temperature data recorder is needed and a vibration spectrum analyzer or Grms recorder is useful. HALT chambers will typically provide basic digital recording of the chamber temperature and table Grms. DES provides the equipment for recording all of the temperatures and vibrations. Many times the customer provides the equipment for monitoring the specific performance of their product. However, DES has the capability to provide all of the monitoring equipment and instrumentation if desired. DES has extensive experience in setting up custom monitoring to record many different parameters such as voltage, current, pressure, etc.

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Stage 1 is used to determine the HALT Operational Limits for temperature. The goal is not to cause destruction in Stage 1, but sometimes the operational and destruct limits occur simultaneously. The HALT Destruct Limits for temperature and vibration are typically found in Stages 3 to 5.

Temperature Step Stresses – Stage 1 (Figure 1)

Stage 1 is started with Cold Step Stresses. Testing is started at 10ºC and is decreased in 10 ºC increments until the lower operating limit is determined or the chamber minimum temperature of -100 ºC is reached.

The dwell time at each step is defined as the point when stabilization and saturation of the device and its components is achieved which is typically 15 to 20 minutes. Functional testing will occur during this stabilization period. The dwell time will be determined from temperature measurements obtained from thermocouples placed on the product. Thermocouple data from individual components that can be a source of heating or cooling are not used to define the dwell time.

The second part in Stage 1 is Hot Step Stresses. Testing is started at 40 ºC and increased in 10 ºC increments until either the upper operating limit is determined or the chamber maximum temperature of +200 ºC is reached. The dwell time will be established using the same procedure as for the Cold Step testing segment.

Note that the upper and lower temperatures may be reduced if material limitations, i.e., solder melting or plastic softening are exceeded. Also, it is good practice to perform a functional test of the product at room temperature or 25 ºC before starting a HALT to get baseline measurement on its performance.

Temperature Ramps – Stage 2 (Figure 2)

During this Stage, temperature cycles with rapid transition rates (ramps) will be applied to the product. The chamber air temperature will be changed at 60 ºC/minute. The hot and cold temperatures will typically range from 10 ºC above the lower operating limit to 10 ºC below the upper operating limit. These 10 ºC reductions are to allow for over shooting caused by changing the temperatures extremely fast. The dwell time, established in Stage 1, will normally be used at each hot and cold temperature. Five cycles are applied.

Vibration Step Stresses – Stage 3 (Figure 3)

A broadband vibration spectrum will be applied through the HALT chamber table. The HALT chamber table should apply random vibration energy to 10,000 Hz in 6 DOF (degrees of freedom). Vibration step stresses will start at 10 Grms and increase in 5 Grms steps until either the operating, the destruct limits, or the chamber maximum vibration level of 60 Grms is reached. At 40 Grms levels and above, the vibration step will be returned to 10 Grms for 1 minute to detect failures that could be hidden by extreme forces occurring at higher vibration levels. Dwell time at each step, will be approximately 15 minutes to accumulate fatigue damage. Grms is measured with a 5 KHz bandwidth. This test is performed at room temperature of approximately 20 to 25 ºC.

Combined Temperature & Vibration Stresses – Stage 4 (Figure 4)

Combined temperature and vibration stresses are applied in Stage 4. During this Stage, the chamber air is changed at 60 ºC/minute. The hot and cold temperatures are the same as those used in Stage 2. The dwell time at each hot and cold temperature will be the same as used in Stage 2. Vibration level is fixed during each temperature step and begins at 10 Grms and increases in 10 Grms steps until either the operating or destruct limits or the chamber maximum vibration level of 60 Grms is reached.

Temperature Destruct Limits – Stage 5 (Figure 5)

The cold temperature destruct limit is found by starting at the lower operating limit (found in Stage 1) and decreasing the temperature in 10 ºC increments until either the low temperature destruct limit or the chamber minimum temperature of -100 ºC is reached. The hot temperature destruct limit is found by starting at the upper operating limit (found in Stage 1) and increasing the temperature in 10ºC increments until either the hot temperature destruct limit or chamber maximum temperature of 200 ºC is reached. The dwell time established in Stage 1 is used typically, however dwell times may be reduced if the product stops operating or if failures occur. If the product fails to operate, the temperature will be reduced or increased towards 20 ºC to see if the product recovers. If the unit is non operational after stabilizing at 20 ºC, the product will be repaired (if practical) so that the test temperatures can be expanded. If it is not practical to repair the product, Stage 5 will be terminated.

Power On/Off Cycling

Powered on/off cycling is recommended at every temperature or vibration step to create additional electrical stresses. These power cycles will be conducted quickly but sufficient time will be allowed so as not to create artificial excessive overloads and failure modes. Powered on/off cycling may not be appropriate for every product as it may create artificial stresses and failure modes, or the product may take too long to power up.

Test Samples

The typical number of products tested simultaneously is 1 to 4 as practical based on the cost and size of the products. Additional spare parts or backup units (not under test) may be needed for spare parts to repair and continue with testing if a non-repairable failure occurs.

Test Reporting

High quality test reports written by DES will contain, at a minimum, plots similar to those shown in Figures 1 to 5. These plots will include measured chamber control temperature, vibrations and product response temperatures, vibrations along with an indication of where each failure or significant event occurred during the HALT. Additionally plots of test voltages, currents, pressures or other applicable parameters will be included as applicable. The report will also contain identification of samples, a list of test equipment and personnel, photographs of the test setup including response sensor locations, photographs of any physical failures and a summary of the test procedure and results.

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HALT can be effectively used multiple times over a product’s life time. During product development, it can find design weakness when changes are much less costly to make. By finding weaknesses and making changes early, HALT can lower product development costs and compress time to market. When HALT is used at the time a product is being introduced into the market, it can expose problems caused by new manufacturing processes. When used after a product has been introduced into the market, HALT can be used to audit product reliability caused by changes in components, manufacturing or suppliers etc. The bottom line is that HALT can reduce product development time and cost, reduce warranty costs, improve customer satisfaction, gain market share, and increase profits.

HALT is not a qualification test, thus there are no predetermined pass/fail criteria. The goal of HALT is to quickly precipitate failures and then to determine their root causes. Once the causes of failure are determined, the failed components are repaired and the stress limits of the testing program are expanded.

Important HALT Definitions

6 Degrees Of Freedom (DOF): Refers to vibration with energy along three orthogonal translations and three rotations simultaneously

Grms: Grms is used to define the overall acceleration level of random vibration. Grms (root-mean-square) is the square root of the area under the PSD curve. More information about random vibration can be found in our blog article Sinusoidal and Random Vibration Testing Primer.

HALT Operational Limit: The stress level prior to where a product does not operate properly, but will return to correct operation if the stress level is reduced. Improper operation can be an out of specification condition. HALT is performed to determine the Operational Limits for low temperature, high temperature, vibration, and combined temperature and vibration.

HALT Destruct Limit: The stress level at which the unit becomes inoperable and will not return to correct operation if the stress level is reduced. HALT Destruct Limits are determined for low temperature, high temperature, vibration, and combined temperature and vibration.

Some Facts and Misconceptions about Highly Accelerated Life Testing

• Producing failures is the goal of HALT testing. 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.
• By applying an effective HALT procedure, the HALT Operational Limit and HALT Destruct Limit of the products under test can be found.
• The stress levels in HALT are typically far beyond those experienced by the product in its normal operating environment. These higher-than-normal stresses accelerate the time to failure and precipitate defects more rapidly than under actual service conditions.
• The product under test is in operation during HALT and is continuously monitored for operational failures.
• As stress-induced failures occur, the cause shall be determined, and if possible, the component should be repaired so that the test can continue to find other weaknesses.
• Stresses shall be increased until the practical limits of the test parameters have been reached or the fundamental limit of technology has been reached. Examples of practical limits include the melting temperature of solder joints or excessive softening of plastics. The fundamental limit of technology means that the limits of present day knowledge have been reached. An example of this would be that it would cost an unreasonable amount of effort and money to improve existing battery technology.
• One common misconception is that an abundance of failures will occur during every HALT. Numerous failures may occur, but a large quantity of failures is not likely unless the product is very different than any manufactured before. Successful companies produce pretty good products; otherwise they would be out of business. However there may be a weakness or two in a new product that could create early failures resulting in large warranty costs. These weaknesses should be found in a properly run HALT test.
• HALT is a qualitative test with the goal being to expose design weaknesses. It is very difficult to demonstrate a service life or a mean time between failures (MTBF) using HALT. Other reliability methods may be a better fit to predict an MTBF or service life.

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Highly Accelerated Life Testing Procedures

Speeding up the process of device or circuit failure requires extreme inputs, those that are unlikely to occur during real-world use by customers regardless of the environment. Three common testing inputs are high and low temperatures, rapid cycling of the same and vibration along six-axes. In some cases, a highly accelerated life test (HALT) will incorporate combined temperature and vibration stresses. These inputs can result in component failure in the span of days, hours, or even minutes compared to months or years of typical usage.

Benefits of HALT Testing

While the percentages of failure based on the stress applied to a product can vary significantly, highly accelerated life testing can typically expose weaknesses faster than other means of testing. For example, of the above inputs, roughly two-thirds of failures will only come after the introduction of vibration alone or combined vibration and temperature tests. This means that during the product development process, a significant number of potential flaws would not be identified through testing that did not include these two stresses.

Just as important, many of the failures highlighted during a HALT test arise from design problems that are relatively easy to remedy. With thermal-based malfunctions, engineers may find that the issues come from materials with vastly different rates of thermal expansion, or deficient leads or crimps. Other problems can come from flaws in the design of the printed circuit boards.

Combined vibration and temperature during HALT testing can also identify issues related to poorly soldered joints and leads. However, failures during vibration may also be caused by fretting, as well as occurring from adjacent parts coming into contact. These design flaws are relatively simple to identify, such as wires rubbing against PCBs or other sharp-edged portions of the system, and arise regularly during the vibration phase of a HALT test.

As a result of the HALT test uncovering these issues early in the process, or soon after the prototype phase, there is the ability to make relatively small changes in design or production. Companies can also identify parts that may not last even during the warranty period in the fraction of the time it might take to find out during normal lifetime testing. As a result, some clients have been able to save a great deal on their product development costs by identifying part and component weaknesses long before the production process.

Some Facts and Misconceptions about Highly Accelerated Life Testing

• Producing failures is the goal of HALT testing. 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.
• By applying a sequence of stepped low-temperature soaks, high-temperature soaks, rapid temperature transitions, high G random vibrations, and combinations of these testing modes, the HALT Operational Limit and HALT Destruct Limit of the products under test can be determined.
• The stress levels in HALT are typically far beyond those experienced by the product in its normal operating environment. These higher-than-normal stresses accelerate the time to failure and precipitate defects more rapidly than under actual service conditions.
• The unit is in operation during the testing program and is continuously monitored for operational failures.
• As stress-induced failures occur, the cause shall be determined, and if possible, the component should be repaired so that the testing program can continue.
• Stresses shall be increased until the practical limits of the test parameters have been reached. Examples of practical limits include the melting temperature of solder joints or excessive softening of plastics.
• One common misconception is that an abundance of failures will occur during every HALT. Numerous failures will typically occur, but a large quantity of failures is not likely unless the product is very different than any manufactured before. Successful companies produce pretty good products; otherwise they would be out of business. However there may be a weakness or two in a new product that could create early failures resulting in large warranty costs. These weaknesses should be found in a properly run HALT test.
• HALT is a qualitative test with the goal being to expose design weaknesses. The HALT will not demonstrate a service life or a mean time between failures (MTBF). Other reliability methods may be a better fit to predict an MTBF or service life.

Contact DE Solutions

Delserro Engineering Solutions provides a variety of testing services, not the least of which is highly accelerated life testing (HALT). However, we can also test products in a variety of environments such as vibration, shock, and climatic. We can also design custom reliability test procedures.

If you are looking to find weak points in a design through testing, please contact us for a plan that best suits your needs. Fill out the short contact form at the link above or call us at (610) 253-6637 for a review of your needs. We look forward to working with you to maximize the return on your testing and design investments.

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