1. Incorporate HALT in your Product Development Cycle

Highly Accelerated Life Testing (HALT) is a rigorous reliability test method that is used to expose product weaknesses. The goal of HALT is to proactively find weaknesses and fix them, thereby increasing product reliability. Because of its accelerated nature, HALT is typically faster and less expensive than traditional testing techniques. 

During product development, HALT can find design weakness when changes are much less costly to fix. 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 HALT is performed after a product has been introduced into the market, it 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.

More information about HALT can be found in the following blog articles:

Circuit Board HALT Testing Case Study

Rapid HALT – A Cost Effective Alternative to HALT

What Is HALT And Why Perform HALT?

What Is A Typical HALT Procedure?

What Equipment Is Used For HALT?

What Kind Of Failures Occur During HALT?

2. Perform Accelerated Life Testing (ALT)

Accelerated Life Testing (ALT) is a method used to simulate the life of a product in a short period of time.  The stresses are higher than normal to compress time.  The higher the stresses used in the ALT, the shorter the test time.  ALT is best applied to components or less complicated products to focus on specific failure modes.  Typical ALT models are the Arrhenius Model, the Arrhenius-Peck Model and the Coffin-Manson Model. 

Some benefits of ALT include:

• Determining if a product will have wear-out failures
• Estimating a product’s field life using testing.  The life determined through ALT can be compared to desired product life goals and analytical predictions and simulations. 
• Finding additional weaknesses not found in HALT

Some key differences between HALT and ALT are:

• HALT will not estimate product life whereas ALT will. 
• ALT Tests will use one or two different stresses and typically run longer than HALT tests.  Therefore, ALT typically produces wear out failures.   An example would be an ALT for a product that sees thousands of temperature cycles in its lifetime, but not much vibration other than from shipping.  The ALT would be focused on temperature cycling only and would likely expose it to a few hundred cycles or more.  The HALT would expose the product to much fewer temperature cycles, but also incorporates vibration stresses.   Thus, different types of failures could result from each test.  In HALT perhaps a weakness caused by vibration will occur that could show up during shipping and handling in the field.  In ALT, perhaps a failure caused solely by thermal fatigue would occur.  So if you only perform only one type of test, perhaps a potential field failure mode could be missed. 

More information about ALT can be found in the following blog articles:

Accelerated Temperature Humidity Testing Using the Arrhenius-Peck Relationship

Constant Temperature Accelerated Life Testing using the Arrhenius Relationship

Door Open/Close Accelerated Life Test Case Study

Accelerated Life Product Reliability Testing of a Carrying Handle

Accelerated Life Cycle Testing of a Case Handle

3. Perform Design Verification Testing (DVT)

Design Verification Testing is a comprehensive process to verify a product will meet all if its design requirements.  DVT is also referred to as verification or validation testing.  Obviously, this is done in the design phase before final production.  Examples of some of the parameters that are checked during DVT are:

• All product functions such as Electrical and Mechanical functions
• Product performance
• Climatic or environmental testing
• Electromagnetic compatibility (EMC)
• Safety testing
• Software validation

For example, a product could be exposed to specific types of climatic stresses such as salt corrosion, solar (UV), temperature-altitude stresses or water ingress.  These types of stresses would not commonly be used in a HALT or ALT.  Therefore, unique failure modes could be exposed in DVT. 

4. Perform Reliability Demonstration Testing (RDT)

The purpose of an RDT is to demonstrate the Mean Time Between Failure (MTBF) of a product.  Reliability Demonstration Tests are usually performed at a system level.  For example, a computer server that contains many components such as hard drives, fans, etc. is an example of a system level test.  RDTs are commonly performed on repairable systems.

RDTs incorporate a reliability percentage R and a confidence level C.  They are limited in using only the stresses the product will see in the field.  RDTs are focused on demonstrating the MTBF in the steady state portion of the bathtub reliability curve, where ALT’s are focused on wear-out.  Some manufacturers are required to show a minimum MTBF on their products before they can sell them to their customers. 

5. Incorporate a HASS or ESS Program

HASS stands for Highly Accelerated Stress Screening.  ESS stands for Environmental Stress Screening. Both are screening methods used to expose manufacturing defects that would cause a failure in normal field environments including shipping, handling and use.  Both HASS and ESS are performed during manufacturing on production products or components. 

The types of stresses used for HASS are similar to those used in HALT. HASS uses combined temperature cycling, random vibration and electrical loading/monitoring. HASS screens are performed in the same type of chamber that is used for HALT. The vibration in HASS is randomly applied over a broad frequency range producing energy to 10,000 Hz in 6 degrees of freedom.

ESS originated out of the military to improve the reliability of their complex products.  ESS typically uses temperature cycling and random vibration applied separately.  Products are normally electrically powered and functional tested during ESS.  Random vibration is usually preformed on and electro dynamic shaker.  “Environmental Stress Screening of Electronic Equipment”, DOD-HDBK-344, is a military handbook that provides guidelines for developing ESS programs. 

Both HASS and ESS are effective screening programs that yield more rugged/reliable products with less field failures and warranty expenses .  More information about HASS and ESS can be found in the following pages:

What is HASS Testing?

How to Implement a HASS Program

An Informational Guide to HALT and HASS

Environmental Stress Screening (ESS Test)

All of these test methods provide different benefits.  Not all of them have to be performed to produce a reliable product.  Contact DES to help determine what makes sense for your product. 

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• What is HALT (Highly Accelerated Life Testing) and Why Perform HALT?
• What Kind of Failures Occur During HALT?
• What Equipment is Used for HALT?
• What is a Typical HALT Procedure?

Number of Samples

It is recommended to HASS as many samples as possible per batch.  This will keep the screening cost per part to a minimum.  The number of samples will depend on the fixtures needed to attach the units to the chamber table, monitoring requirements, and power requirements.  The HASS setup should be optimized to work efficiently in a production environment.

Fixtures

The HASS fixtures should be manufactured for fast and efficient loading and removal of product.  They should hold as many products as possible.  The fixtures must be designed to support both vibration and thermal loading.  They must be durable in order to withstand the fatigue damage caused by the repeated stresses that will occur over the fixture’s lifetime.  The fixture needs to be lightweight, rigid, and have low thermal mass.

Functional Test Protocol

A Functional Test Protocol (FTP) must be performed on each sample undergoing HASS.  The FTP must check that the product functions within predetermined specifications.  The FTP coverage should be as comprehensive as possible for each sample under test.  The FTP equipment will be located outside of the chamber.

Proof of Screen

Before starting a HASS program, a Proof of Screen must be performed first to demonstrate that the product has sufficient life after the HASS and to demonstrate that the screen does find product defects.  After the Proof of Screen has been validated, production screening can begin.

It may be possible to determine the effectiveness of the HASS by seeding samples of the product with known defects.  The seeded defects could include solder defects or typical manufacturing process issues based upon past history of similar products.  Since, it is often very difficult to create a realistic seeded defect, mixed results may be obtained and judgment may need to be exercised as to whether the seeded defects are realistic.  Field returned units may be good candidates for seeded samples.

The main objective of the Proof of Screen is to prove that the screen has not removed significant life from the products during HASS.  The HASS profile should be repeated a minimum of 20 times, without failure occurrences. This shows that production units exposed to only one pass of the HASS profile, will still have at least 95% of their useful life remaining, or a maximum of 5% of their life was removed during one HASS screen.

Removing 5% of the life sounds like a lot, but in reality, the units would probably be able to withstand many more than 20 HASS cycles if a good job was done ruggedizing the product during HALT.  Also, ‘life” is an accelerated life.  The stresses in HASS are usually higher than normal use.  To prove that they still have sufficient life remaining after HASS, it is recommended to run the same Proof of Screen units through qual testing or reliability demonstration testing after the Proof of Screen.  If no failures show up, then it is not likely that the HASS would cause some long-term failure mode.

The Proof of Screen should be performed using the production HASS fixtures and the FTP equipment.  During the Proof of Screen, the products should be instrumented with thermocouples and accelerometers to check that a sufficient temperature rate of change/uniformity has been achieved and that sufficient vibration levels are being transmitted to the product.

Production HASS

A specific production HASS procedure should be developed for each product.  This is because the results from each HALT on dissimilar products may be different.  Typical general requirements are listed below.

General Requirements

The HASS should be conducted by qualified engineers or technicians who are familiar with how to use the HALT/HASS chambers and the support equipment.  All gauges, instruments, test equipment and measuring tools should have a current calibration status.

ESD Protection

Good ESD precautions should be used on any electronic product.  At a minimum, an ESD gown and wrist strap should be worn when handling any product with exposed circuit boards.  FTP test Fixtures shall be on a grounded stand.  Connections to product shall be carried out using ESD precautions.

Report

The reporting depends upon each product and upon each customer’s requirements.  Typically, a Pass/Fail report or certificate would be issued with each product or batch of products.  The pass/fail report or certificate should list the product serial number, a pass or fail status, and a summary of the failure mode if applicable at a minimum.

Disposition

The disposition depends upon each product and upon each customer’s requirements.  DES’s typical disposition procedure is as follows:

• All products are tagged with a Green Passed HASS label or a Red Failed HASS label as appropriate.  This may be stuck on the product or the outside of its packing.
• A HASS certificate will be inserted with each unit inside of its packing.

Corrective Action

Finally, a system to determine root cause of problems, develop corrective actions and verify corrective actions should be instituted.  Typically, a formal system such as FRACAS is implemented.  FRACAS stands for Failure Reporting, Analysis and Corrective Action System.  FRACAS is sometimes implemented using computer software and provides a process for reporting, classifying, analyzing failures, and planning corrective actions in response to those failures.

DES has over 20 years of experience performing HALT/HASS testing on a variety of medical, commercial, industrial and military products.  For more information on HASS, HALT or other testing services, contact DES or call 610.253.6637.

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The goal of this article was to teach product developers how to get the most bang for their testing buck; a goal that aligns perfectly with DES’s philosophy. No matter what your testing needs are, be they HALT, HASS, or other environmental or stress tests, DES is able to help you design and implement the most comprehensive and accurate test possible. As always, our client’s success is the source of our satisfaction.

Showing Our Advanced Testing Capabilities

The article highlighted DES’s advanced capabilities when it comes to designing complex testing equipment. In this instance, the devices being tested were a series of proposed new sensors for car engines. For this test series, the testing fixture was incredibly complicated and the testing included combined temperature, vibration, and electrical loads, a perfect fit for DES’s vibration shaker chamber.

When you need a HALT or HASS test, or any other testing services, DES has you covered. Our engineers have more than 60 years of combined successful engineering experience. We specialize in stress, reliability, durability, vibration, shock, highly accelerated life testing (HALT), highly accelerated stress screening (HASS), accelerated life testing, and environmental testing. When done correctly, these tests can help you save money, cut production time, and increase product reliability.

Helping Save on Production Costs

The article closed with a few tips from DES and other testing engineers on how they can form the best working relationship with a reliability testing facility. Appropriate communication was the top recommendation. However, there are a host of tips in the full article on getting the most out of your product test.

To read the full article, visit Desktop Engineering. If you’re interested in running a test, contact Delserro Engineering Solutions.

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HALT and HASS can accelerate a product’s aging process from actual months into test minutes much faster than traditional testing!

What is HALT?

HALT – Highly Accelerated Life Testing

HALT is used to find product design weaknesses making the product more rugged.

• HALT is typically done during Design.  It is destructive!
• Stresses are applied in steps to find a product’s weaknesses, operational design margins, and destruct limits.
• Stresses are higher than normal to obtain time compression and accelerate aging.
• HALT is not a pass/fail test.  It is pro-active!  The stresses are increased until the product fails, rather than testing to predefined limits.
• All HALT failures represent an opportunity for improvement and may show up in the field.
• Many failures are easy and inexpensive to fix.
• HALT typically takes 3 to 5 days.

What is HASS?

HASS – Highly Accelerated Stress Screening

HASS is used to find defects and flaws in production to monitor the quality and consistency of your manufacturing processes.

• HASS is done during Manufacturing.
• HASS is a screening method used to expose manufacturing process problems that would cause a failure in normal field environments including shipping, storage and use.
• Stresses may be higher than normal operation to precipitate defects in a short amount of time.  HASS stresses are typically higher than traditional Environmental Stress Screening (ESS).
• Types of stresses used are similar to those used in HALT.
• HASS screens take typically from an hour to a few hours.
• HALT must be performed before HASS.
• Safety of Screen (SOS) is used to validate the screen proving that sufficient life is left for a normal use lifetime.

Reasons to Use HALT/HASS

• To produce a rugged, reliable product.
• Products have many electronic parts subjected to combined high/low temperature and vibration loads.  Many parts are not tested for these combined loads.
• With thousands of electronic components present, a failure of a single component could cause the entire system to fail.  This will lead to warranty and engineering redesign costs, and unhappy customers.
• To find and understand the operating limits of your products.
• To find and understand the destruct limits of your products.
• To compare different electronic components and suppliers (Evaluation of Competing Vendors).
• To regularly audit or screen your production components to check for and improve manufacturing quality.

Typical Stresses Used in HALT and HASS Testing

• Vibration applied over a broad frequency range (6 DOF, 60 Grms, Random vibration energy to 10,000 Hz)
• Temperatures (-100°C to +200°C)
• High temperature rate of change (60°C / minute)
• Electrical loads
• More stresses (fluid pressure and viscosity, pH, unbalance, geometry, etc.)
• Combination of all loads

Typical HALT Profile

Why Products Fail

Every product has a statistical strength distribution. Failures will occur where the Product Strength and Field Stress Curves overlap shown in red.  HALT/HASS will force the weaker components to fail in the chamber.  HALT and HASS will shift the Product Strength curve to the right.  The goal of HALT/HASS is to produce a large design margin or gap between the 2 curves, resulting in less field failures and a more reliable product!

Benefits of HALT

• Shorter design cycle = Quicker Time to Market.
• Reduced design cost.
• Usually less expensive, faster, and more effective than traditional pass/fail testing.
• Find and improve design margins.
• Produce a more rugged/reliable product with less field failures and warranty expenses.
• Reliable products lead to happy customers.
• Happy customers lead to increased profits/market share.
• ROI’s in the thousands or greater are being reported.

Benefits of HASS

• HASS screens are shorter than traditional methods (ESS).
• Reduced time and cost to screen production.
• Finds defects sooner and correct problems faster.
• Fewer defects reach the customers hands.
• Improved product quality and manufacturing process control.

DES reliability testing can help you in all phases of your project.

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How many times have your customers returned products or circuit boards with reported defects that you can’t find?  Every manufacturer experiences this situation at some time.  Your customer reports a problem in your product and sends it back to you.  You test the faulty product in your lab and the problem doesn’t occur. Sometimes you try to bend it or tap it against the table.  You may even try heating it in a chamber or with a heat gun or using a freeze spray.  Still the problem does not expose itself.

After spending much time trouble shooting and not finding it, the problem may go unresolved, allowing a design or manufacturing deficiency to exist in the field.  It probably is not a large deficiency that will prompt a high rate of return but one that will likely cause your company some warrantee and engineering costs.  Perhaps it will annoy a brand new customer that has just purchased your product.

A returned product that contains a hard-to-find defect is valuable because it contains the flaw.  You have a product with a flaw that is seeded somewhere in it.  If you grab another sample, it will probably not contain the defect that you are looking for.  So testing more samples may waste time and money since the defect occurs in a low percentage of the products.

A highly accelerated life test (HALT) chamber can be used to find these hard-to-find defects.  The product, operating and continuously monitored during the entire test, immediately is exposed to combined temperatures, vibrations, and power or other applicable stresses (Figure 1).  The temperature is held constant while the vibration and power loads are stepped up and down.

Figure 1

Once the vibration and power load stepping is complete, the temperature is changed rapidly from cold to hot or hot to cold.  The test is started using moderate environmental stresses.  The stress range is expanded until the problem is found, the range becomes too large, other failures happen, or melting occurs.

Near the end of the test, the vibration levels can be increased if the problem is not found, or cycling can be continued at the highest stress levels.  The entire process typically takes one day from setup to finish.

Why is this method effective?  The simultaneous application of temperature, vibration, and power loads exposes your product to a multitude of stresses.  A hard-to-find defect is a weakness.  This weakness will reveal itself when certain combinations of stresses are applied.

Depending on the defect, the combination could be hot temperatures with vibration or cold temperatures with vibration.  Even though the product may never see these stresses in the field, the stresses can expose the defect quickly.

Also, the stresses are modulated between high and low levels, which is more effective in finding intermittent flaws [1].  This will expose your product to all combined stress levels where some intermediate combination of stress may expose the flaw.

For example, think of a cracked solder joint or a weak lead supporting a large component.  By applying a stress of –40ºC and 20 Grms, the temperature will cause materials to contract, opening up the crack or bending the weak lead.  The effect of vibration along with temperature may cause the crack to grow or cause the lead to break.

Sometimes problems only are exposed with rapid temperature changes because the problem only may occur during transient conditions.  As the temperatures in the product stabilize, so will the differential expansion and contraction of the components, which may cause the problem to hide itself.

A HALT chamber is the perfect tool to apply the required stresses.  The high-performance chamber can apply temperature and vibration simultaneously.  The typical HALT chamber temperature range is -100°C to +200°C.  Temperatures can be raised or lowered at 60°C per minute.

Simultaneously, the chamber can apply vibration input levels up to 60 Grms with six degrees of freedom.

If you need humidity effects or corrosion, the products can be preconditioned in other environmental chambers such as a humidity chamber or salt-fog chamber for a couple of days prior to testing in the HALT chamber.  This extends the overall test time; however these chambers are programmable and less expensive to operate.

In one situation, a manufacturer tried to find problems in different circuit boards for weeks in its lab.  Using a HALT chamber, four out of four hard-to-find field problems in different circuit boards were exposed in one day.

Some soldering process problems and a poorly mounted component were found.  A large component had week leads and was mounted in the center of a circuit board where it is most flexible.  When vibration was applied, the leads were stressed enough to affect the performance of this component.

In this example, the products did not undergo HALT.  A correctly implemented HALT and Highly Accelerated Stress Screen (HASS) program normally would find these problems.  However, it is possible that the HALT test samples will not contain a hard-to-find defect or an infrequent process problem because they occur in a very low percentage of the products.

A HASS program that is performed on 100% production should find these faults.  But if HASS is not performed on 100% production, these infrequent faults may slip through the screening process.

Conclusion

This technique is not meant to replace initial HALT/HASS testing or accelerated life reliability testing.  It is just an abbreviated technique that uses the tools of HALT to expose hard-to-find defects that somehow made it to your customers.  Don’t throw away those customer returns.  Stick them in a HALT chamber.

References

1. Hobbs, G. “Accelerated Reliability Engineering: HALT and HASS”, Wiley 2000

About The Author

Gary Delserro P.E., is president of Delserro Engineering Solutions (DES). He has more than 20 years of experience working in the field of stress optimization and reliability working for the Naval Air Warfare Center as an aerospace reliability engineer, Cooper Industries as a new product/R&D manager, and Mack Trucks as a senior durability/reliability test engineer. Mr. Delserro holds a B.S.M.E. degree from Villanova University and an M.S.M.E. degree from Lehigh University.

Reprinted with permission from Evaluation Engineering, June 2004 © 2004 by Nelson Publishing Inc * http://www.evaluationengineering.com/

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