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HASS differs from HALT in that it is a screening of theactual products being produced through manufacturing using a less stressful level of stimuli. We are not trying tobreak the product in this case but verify that the designis rugged enough to meet the actual specification limitsagreed on by ourselves and our customer. In this testinga device, or several, are pulled out of production and runthrough a series of tests that simulate the highest possiblestresses that the product will see—often times exceedingthe operational limits called out on the specification. Using the concept of time compression again, these tests show in a short amount of time that the product is operating the way it should, that it has an acceptable level of ruggedness and that there are no errors being introduced into the manufacturing process. There are times the manufacturing process strays or componentsare substituted due to obsolescence that were not reviewed properly. This in-process lot testing ensures that the process is continuously intact and that the product meets and exceeds specifications. It should be noted that HALT is required initially in the development process in order for the HASS testing to be properly performed. The HASS test is well below the limits of the products’ ruggedness and design—but we first had to find and document theselimits by means of the HALT process. One is dependant onthe other.The process of design verification through accelerated lifetesting is not a recent event but has been performed sincethe early 1950’s—beginning with the US military. Through a directive issued by our government, military vendors were required to improve the reliability of their products byapplying a standard series of tests to their components.This was especially applicable to the military where compo-nents are required to withstand extreme field conditionsand a wide variety of temperature variables as standard operating procedure. These tests directed the suppliers to stress their products beyond the specified limits of most environmental extremes—to limits not seen before.This was to find out when and how their products wouldfail, but more importantly to use that information to makefuture products more robust.What used to be the requirement of an exclusive fewdealing with the military is now the standard for many in the market place; both nationally and internationally. It is now done in order to meet customer quality expectations and to remain competitive in a global sense. The extremesof temperature, vibration and stress have been pushed out even farther than those standards of the past with thepurpose of improving all designs beyond previous expec- tations thought feasible. The result has been that productscontinue to improve and the customer can expect quality at a level not found before. value over time of checking the design of our products tomake sure they perform to the satisfaction of our cus- tomers. Hence our statement, “If you don’t have time to break it in the beginning you’ll have plenty of time to fix it in the future.”

HALT + HASS Testing - 54730 Defining HALT / HASS and the Origins of These Testing Procedures

As mentioned, HALT and HASS both act as time compres- sion, stress testing—but they differ in their focus. These two processes are closely aligned and used in tandem toultimately determine if the device was designed correctlyand is still being built properly—but they are not performed at the same time with the same criteria.In HALT testing every stimulus that has potential effect toa product, whether it will be seen in the products opera- tional life or not, is used to find the weak links in the design. The purpose is to find out how rugged the design is by taking the product or device to the point where it breaks and document the failures as they occur. The stimuli used for HALT testing may include all-axis impact vibration,broad range thermal cycling over a short period of time,electronic burn in of the components, over-voltage conditions, power or voltage cycling, humidity or all of theabove being used together or in various combinations. These stresses are not necessarily meant to simulate the environment that the product will find in the field. The stimuli are stepped up to well beyond any field conditions until a flaw or multiple flaws are exposed and the design has reached its fundamental limits. Through this process the manufacturer knows the margin between the specified operational limits of the product and how far beyond that the device will actually go. Since any product will deteriorate over time, the importance of this test is also knowing how long the product life might be under normal operating conditions and how much abuse it will take in that amount of time.HALT testing is an extremely important part of the earlydevelopment and manufacturing process. Most design processes are in a state of flux in the beginning—but as the process and design develops, the product becomes more fixed and rigid. Its ability to change, and the cost of any change, becomes increasingly more difficult to make. Using the feedback generated by the HALT testing in thebeginning allows the substitution of materials, components and improved process parameters in a timely fashionbefore the design becomes rigid and before costly failuresare produced in the field.