HALT and HASS continue to be mainstay test methods among board designers

June 1, 2002
Single-board computer designers have seen a lot of improvements in processor speeds and overall board performance during the last several years

by John McHale

SANTA CLARITA, Calif. — Single-board computer designers have seen a lot of improvements in processor speeds and overall board performance during the last several years, yet their methods for testing boards for military applications, namely highly accelerated life testing (HALT) and highly accelerated stress screening (HASS), remain the same.

Engineers at Vista Controls in Santa Clarita, Calif., perform HALT and HASS, but mostly HASS as part of environmental stress screening (ESS), says Doug Patterson, director of marketing at Vista.

"We do HALT in limited amounts because it can be expensive," Patterson says. Many times a product is tested until it breaks under HALT, he adds. When HALT reaches a certain limit a HASS profile is then generated, Patterson continues. HALT simulates the lifetime of a product over several weeks through increased environmental and stress testing and HASS represents an ongoing series of tests of rugged products, he adds.

HASS and ESS cover most of the testing process for shock, vibration, and extreme temperatures, Patterson says.

Take a board specified to work under a temperature of -40 degrees Celsius, for example. Test engineers might like to see it continue to function under temperatures as cold as -48 or -50 degrees C. If it stops working at -41 degrees C, then engineers need to take another look at the product, Patterson says.

Vista also uses HALT to determine a product's mean time between failure, or MTBF, Patterson says. When designers really want to understand how a product fails HALT is the right choice, he adds. It uses actual data extrapolation and is the ideal test for any product going into a mission- or life-critical application, Patterson says.

Dy 4 engineers also perform HALT on their products "as a test of design integrity," says Duncan Young, director of marketing at Dy 4 in Kanata, Ontario. It is not useful in determining lifetime reliability, Young notes. However, it does give a view of the design margins, which enables engineers to select the right components for particular environments.

Dy 4 engineers put their products through a long testing process before they get to HALT and HASS, Young says. They debug, do other functional tests such as voltage and temperature, and then transfer HALT results into HASS and ESS, he adds.

At General Dynamics Canada in Ottawa, engineers mostly perform HALT and HASS on their rugged, military products, says Christopher Chance, manager of business development for Vetronics Systems at General Dynamics Canada.

The company General Dynamics Canada was formerly known as Computing Devices Canada.

HALT is good for determining the environmental range of a product, he adds.

Then, like the other board designers, transfers the HALT data into a HASS profile, Chance says.

The amount of HALT and HASS a company does on a particular product can also depend on the customer's requirements, Chance adds.

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