What HALT and HASS Can Do For Your Products as an EXCELLENT FA tools?

Highly accelerated life test (HALT) and highly accelerated stress screen (HASS) are two processes that very quickly uncover problems in the design and production phases of your products. Both rely on the concept of time compression.

That is, HALT and HASS use much higher stresses than exist in the field environment to force failures to occur in significantly less time than would be required in a normal environment.

In HALT, every stimulus of potential value is used during the design phase to find the weak links in the design and fabrication processes of a product. These stimuli may include all-axis impact vibration, broad-range thermal cycling, burn-in, over-voltage, voltage cycling, humidity and whatever else exposes relevant defects in the product.

The stresses aACre not meant to simulate the field environments but to find the weak links in the design and manufacturing processes using only a few units and in a very short period of time. They are stepped up to well beyond the expected field environments until the fundamental limit of the technology is reached. Reaching the fundamental limit generally requires fixing everything found, even if it is uncovered above the qualification levels.

HASS screens use the highest possible stresses, frequently well beyond the qualification level, to attain time compression in the screens. Many stimuli exhibit an exponential acceleration of flaw precipitation. Using these stimuli results in a much shorter duration of stress, if we use the correct stress, so a drastic reduction in screening equipment and manpower is realized.

The screens must be of acceptable fatigue-damage accumulation, or lifetime degradation, using proof-of-screen techniques where one or more products are screened repeatedly to show that enough product life is left after just a few screens. Generally, HASS is not possible unless a comprehensive HALT has been performed.

Without HALT, fundamental design limitations will tend to restrict the acceptable stress levels in production screens and prevent the large accelerations of flaw precipitation, or time compression, possible with a very robust product. A less than robust product probably cannot be effectively screened by the classical screens without substantial reduction in its useful field life since it will have none to spare.

 

Summary
HALT has provided substantial (five to 1,000 times) MTBF gains even when used without production screening and has reduced product time to market, warranty expenses, design and sustaining engineering, and total development costs. HALT still is an emerging technology and continues to be improved at an amazing rate.

Today, HALT and HASS are required on an ever-increasing number of commercial and military programs. Many of the leading commercial companies use HALT and HASS techniques with all-axis impact vibration and moderate to ultra-rate thermal systems successfully; however, most are being relatively quiet about it because of the phenomenal improvements in quality and reliability and vast cost savings.

The aerospace industry and the military have been slow to accept the advanced techniques because stressing the product above the expected field environment is quite foreign to them. And even if they wanted to use HALT and HASS, it is very difficult to specify or interpret in contractual language. You must want to obtain top quality for your products to adopt HALT and HASS.