By now, most test engineers have recognized that both HALT (Highly Accelerated Life Testing) and HASS (Highly Accelerated Stress Screening) are the fastest and most effective new methodologies for quickly passing design verification and testing (DVT), and the most effective production screenings. Leaders across a broad range of industries have now embraced accelerated testing as a strategic move that can increase competitiveness and improve market share.

Profitability and Time to Market

Every manufacturer whose product contains an electronic or electromechanical assembly can benefit from accelerated test methods. “You can use accelerated testing for testing components, subassemblies, or finished products, so we use it at all three levels,” said Brian Dahl, environmental test engineer at Agilent Technologies. “HALT has become a culture here. We start using it as soon as we select system components like disk drives, power supplies, and motherboards in a new production design.”

Business benefits and savings are driving awareness of accelerated testing techniques such as HALT and HASS from the engineering level to the C-level.

HALT and HASS techniques shortcut and avoid the problems of slower traditional testing methods that only test to minimum specifications and nothing more. HALT and HASS quickly expose any weak links in a product by testing well beyond minimum specs so that any reliability problems can be fixed before they become expensive field issues.

The goal of HASS is to develop a screen that is effective in causing latent failures to become actual failures without removing a significant amount of the product’s life. The HASS development process typically includes fixture design, fabrication, qualification, profile development, and proof-of-screen. To accomplish accelerated testing of boards and components, HASS uses rapid thermal transitioning combined with multilevel vibration performed over a frequency bandwidth from 2 Hz to 5 kHz. In addition to these stresses, product-specific stresses, such as voltage margining, frequency margining, and power cycling, are applied.

HALT is typically the first step in the testing process, followed subsequently with a production HASS screen. Qualmark often develops, tests, and proves a HASS profile in their lab using third-generation HALT/HASS testing chambers, such as the Typhoon-2.5HP. Additional functional test equipment located outside the chamber verifies the operation of the unit under test to its performance specification. This test equipment is located outside of the chamber and cabled via the chamber access port to the units under test.

Fixtures to Profiles

The HASS fixture is designed and fabricated to support the product throughput testing, ergonomics, and to provide proper vibration transmissibility, thermal uniformity, and a balanced thermal rate of change. Functional units are secured to all of the fixture locations. Thermocouples and accelerometers are attached to each unit to perform thermal and vibration surveys.

The HASS profile is based on the HALT results, along with other product related variables such as functional test duration, thermal long-term degradation effects (long-term failure modes that may require a reduction of stress levels), product-specific stresses, and production throughput test requirements. The profile consisted of combined environment cycles performed within the product’s operating limits. The upper operating limit (UOL), lower operating limit (LOL), and destruct limit (DL) values for temperature and vibration are acquired from the HALT results.

Vibration is modulated throughout the testing phase and is slowly ramped to a percentage of the UOL level. This process is repeated in reverse. Dwell times at each temperature extreme began where the products attained the desired temperature, and are held a minimum of five minutes during which time the functional tests are run. The vibration modulation ramps are slow, with a five-minute dwell minimum requirement at the maximum vibration level. Functional test routines are performed throughout the profile.

Testing the Test Profile

Proof-of-screen is a two-step process that determines how effective the screen is in detecting manufacturing flaws and verifying that the screen does not remove significant life from the screened products.

The screen’s effectiveness is measured by its capability to precipitate latent defects, such as component weaknesses, PCB flaws, circuit timing problems, mechanical tolerance problems, solder defects, and other manufacturing assembly- related issues associated with the manufacturer’s or vendor’s process going out of control.

For this process, no trouble found (NTF) or parametrically marginal functional units are preferred; however, production units can be used when checked NTF units are not available. Functional production units are seeded with flaws representative of the manufacturing process going out of control, such as a poor solder process or damaged or incorrect component insertion. The screen should detect these flaws. If not, it should be modified (increase or decrease severity levels) until it does.

Life cycle Benefits

The benefits of HALT and HASS testing can be found throughout a product lifecycle. “Accelerated testing always shortens product development cycles because it allows for earlier detection of reliability problems: weak components, timing relationships, things like that,” noted Brian Flanagan, hardware qualification manager for McDATA, a provider of storage networking products for the enterprise.

“We recently used the [HALT] equipment to do hardware qualification testing for McDATA’s new 4Gb/s blade enhancement to the ... Intrepid 10,000 platform, a 256-port director that has 10 Gb/s capabilities,” continued Flanagan. “Without HALT testing, this likely would have taken six to nine months. Using the QualMark chambers, it only took us eight weeks.”

Accelerated testing proves effective at screening out failures that may have gone undetected during traditional burn-in testing processes by going beyond normal testing to verify the integrity of mechanical interconnects and component tolerance compatibility. This results in increased out-of-box quality and field reliability, which yields decreased field service and warranty costs.

“When I started this job, power supplies were the highest-failing items in our division, but thanks to accelerated testing it’s almost a non-issue now,” said Agilent’s Dahl. “In one particular case, HALT helped us go back to a vendor to show them where their product failed. The vendor redesigned the power supply, which subsequently passed the accelerated stress screenings. We awarded the business to that supplier. We have since fielded over two thousand of those power supplies. Guess how many have failed? Zero.”

In the case of mission-critical applications, accelerated testing becomes essential because of the nature of the application. “In our industry, ‘product maturity’ means delivering products with a very high operational reliability, from the very first delivery,” explained Daniel Goulet, test strategy and product maturity manager in the Industrial Operation Division of Thales-Avionics, a division of Thales that serves the defense, aerospace, and security markets. “Our products end up in planes manufactured by Airbus, Boeing, and others, so there is no room for failure.

“However, to get product maturity at entry into service was initially taking months, or sometimes years, due to the time required to discover any issues,” continued Goulet. “But our customers, like Airbus, do not want to wait and to have issues. So that is why we decided to introduce product maturity methodologies that included HALT to discover and fix weaknesses and HASS to catch infant failures. We now use [accelerated testing] equipment to apply a very high level of constraints on our products in order to uncover issues very quickly. I have some examples of product testing where, after two to three hours of running HALT and HASS, we discovered issues that normally required two to three weeks or months of testing with traditional equipment and procedures.”

“I once performed a back-of-the-envelope calculation that looked at the price of continuing accelerated testing with all the consumables and the investment in the chambers, versus stopping the program,” said Pat Kader, quality engineering manager at Harris RF Communications, of his experience at a company he worked for before Harris. “I was able to convince my manager in less than ten minutes to invest in additional HALT and HASS chambers during that meeting because the cost savings was that considerable.”

This article was written by Alan Perkins, vice president of sales and marketing, at QualMark, Denver, CO. For more information, contact Mr. Perkins at This email address is being protected from spambots. You need JavaScript enabled to view it., or visit http://info.hotims.com/10960-401 .