Trends in Accelerated Testing Improve Time to Market

When it is properly selected and applied, HALT and HASS accelerated-testing equipment enables the rapid release of quality products.

By Qualmark

As the saying goes, "First to market, first to profit." In the race to debut new products, every marketing manager knows that beating the competition to the punch can provide a head start. That head start can last throughout the product's life cycle. To securely maintain that edge, however, the product must consistently deliver on its promise. In other words, quality can never be compromised. To fulfill the requirements of delivering reliable products on time, accelerated-testing techniques are quickly being adopted. At this point, the manufacturers that don't employ these techniques actually stand to fall out of the race. For this reason, both Highly Accelerated Life Testing (HALT) and Highly Accelerated Stress Screenings (HASS) are gaining acceptance as the new standards for product development and process control.

A Proactive Testing Mentality

Every manufacturer that has a product containing a microprocessor, circuit card, or electromechanical assembly can benefit from accelerated test methods. Such methods enable companies to develop products quickly, without design flaws, and within budget. This proactive approach stands in contrast to the testing procedures used in the past, which typically consumed weeks or months.

Because many conventional test procedures call out minimum specifications and nothing more, traditional DVT only tests within specification. It therefore misses design defects that could be detected by over-stress techniques. The results of this lack of detection include product failures in the field, costly product recalls, ongoing warranty expenses, and time-consuming support programs.

HALT and HASS techniques avoid these problems by quickly exposing any weak links in a product. Such weak links can therefore be fixed before they become expensive field issues. In effect, HALT and HASS ferret out any weak links in design and/or production processes in order to make great products even better.

HALT and HASS Defined

HALT is a proven method of finding design defects. Without discovery, those defects often appear in end-use applications and cause product failures after release. By pushing a product to its operating limits and beyond, HALT increases product reliability. With HALT, a product is subjected to the outer margins of temperature, rapid thermal cycling, and vibration testing to rapidly uncover any design weaknesses.

"Most traditional testing checks the product up to the spec, but HALT goes way beyond that," says Mike Silverman, Managing Partner of Ops Ala Carte LLC, a professional consulting firm based in Saratoga, Calif. "For example, let's say a cell-phone manufacturer says their product will work up to 50°C. Well, HALT will actually take that phone up to 70°, 80°, or 90°C in order to find any weaknesses before the product goes out the door. That in itself is acceleration because we are accelerating any possible failure mechanisms and bringing them back into the laboratory so the customer doesn't see them."

After HALT has revealed any product weaknesses, proper root-cause-of-failure analysis facilitates the corrective action necessary to improve the design. As a result, HALT reduces R&D costs, shortens time to market, and increases product quality and reliability. Once an approved design goes into production, HASS testing comes into play. It ensures that any weak links in the manufacturing processes do not undermine the already proven design. In essence, the goal of a HASS is to detect failure modes that can be introduced in the production of the product.

"In HASS, the product is subjected to much the same tests performed in HALT. But the goals of the test are different," says Silverman. "HASS is a manufacturing screening process that focuses on process issues, such as assembly errors, in order to remove any possible infant mortality in the product – mostly in the area of hardware – before the product is released."

HASS proves effective in screening out failures that may have gone undetected during traditional burn-in testing processes. It also goes beyond normal testing to verify the integrity of mechanical interconnects and component tolerance compatibility. HASS can even uncover "timing" errors that only occur under high stress. A product that passes HASS testing assures manufacturing-process quality and workmanship integrity. The resulting increase in out-of-box quality and field reliability yields decreased field service and warranty costs.

Maximizing the Benefits of HALT and HASS

Ultimately, the benefits of increased product reliability help push up the bottom line of any manufacturer. In the long run, the outcome is higher customer satisfaction and confidence, increased company image and reputation, and increased market share. To realize the full potential of HALT and HASS, however, the correct testing equipment and procedures must be employed.

"Certainly, combining vibration testing and thermal cycling in the same step speeds the process. But I would say that the main thing that accelerates products to market is that failures can be created much more quickly by using HALT and HASS than with standard reliability-improvement techniques," says Ed Kyser, PhD, consultant, and author of several articles on accelerated stress testing. Kyser holds seven U.S. patents. His company, Reliability Economics—based in Los Altos, Calif.—provides assessment and economic analysis of all aspects of reliability and quality-improvement programs. "The reason: We're stressing the product/component beyond its design limits. To me, that is the genius behind this kind of approach to finding faults and fixing them."

Because accelerated testing covers an extremely broad range of products, applying such "genius" requires expertise in determining which equipment and testing procedures are best for a particular application.For instance, HASS isn't intended to be a rigid process that has an endpoint. Rather, it is a dynamic process that may need modification or adjustment over the life of the product. Because HASS levels are more aggressive than conventional screening tools, a proof-of-screen (POS) procedure is needed to determine that the HASS stresses are capable of revealing production defects.

For best results, the tables used in HALT and HASS chambers should excite every part of a product—down to the component level—at its resonant frequency. This requires vibration in all three axes as well as the simultaneous rotation around those axes and across a wide frequency range. At the same time and within the same chamber, thermal tests are undertaken—testing products from ambient to the appropriate stress temperature quickly while using less electricity and liquid nitrogen. Such chambers also should provide the lowest total cost of chamber ownership for everyday operation.

"If you looked at a pie chart and it showed all possible defects, you'd have a certain percentage showing up at extreme high and low temperatures, during thermal cycling, under vibration in all axes, and during combined vibration and thermal cycling," notes Charlie Bates, Vice President of Program Development for QualMark. "To cover all the bases, you have to test both vibration and temperature simultaneously. Studies have shown that you can otherwise miss 25% to 30% of the defects."

To ensure that weak links are quickly exposed, thorough HALT and HASS testing also requires broad frequency excitation—far beyond what a product might see in the end-use environment. Bates notes that the vibration system should shift the energy in the frequency domain down to the 0-to-5000-Hz range. "With 50% of the energy below 2000 Hz and 50% above, tests should simulate the resident frequencies in various types of electronic hardware including printed-circuit boards," continues Bates. "This quickly brings out potential real-world problems, such as weak solder joints and incomplete surface-mount connections."

When it's properly selected and applied, HALT and HASS accelerated testing enable manufacturers to bring products to market more quickly with the confidence that the product is as reliable as possible. In this manner, the companies that adopt accelerated-testing procedures can enjoy a large jump on their competition to help capture a leading share of the market.

Jeffrey Hale, Vice President of Marketing for Qualmark, jhale@qualmark.com.