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26 SMT007 MAGAZINE I JULY 2021 speaking about product life. ere are also a host of acronyms associated with this branch of faith-based prediction, most of which are so important that they have been bumped up from three- to four-letter acronyms: ESS (environ- mental stress screening), HATS (highly accel- erated thermal shock), HAST (highly acceler- ated stress testing), HALT (highly accelerated life testing), HASS (highly accelerated stress screening), MTBF (mean time between fail- ure) and burn-in (first on the scene, entrenched before someone came up with an appropri- ately long acronym). ere is a whole branch of palm readers—I mean scientists and engi- neers—whose job it is to predict the life span of a product. You remember the part in your car, TV, or cellphone that dies a short time aer the warranty expires? Well, these wizards (and witches) are the ones who predicted that for- tune. How do you think they came up with the warranty terms in the first place? How to Deal with the Stresses of Life "I can't wait years to see if my product will last. Is there any way you can speed that up?" is is a question I hear oen and is at the heart of the mystical art of life predictions. e current focus of this faith-based exploration is by using accelerated stress testing to predict product life. e basic premise of this philos- ophy is that by increasing the amount of stress a product sees, the time of the product's death can be accelerated in measurable increments. e medical profession has been preaching this about us humans for a long time. Corre- lating the accelerated stresses of life testing to actual non-accelerated life environment is the real challenge. Quantifying the stresses a prod- uct will see during its life can be accomplished by thoroughly evaluating the mechanical and environmental conditions experienced dur- ing its life and then finding a way to acceler- ate them without introducing additional fac- tors of life acceleration that do not appear in real-world use. Mechanical stresses are typically related to the dropping, vibrating, shaking, rattling, and bumping the product is expected to see in the real-world during its life. Environmen- tal stresses involve the atmospheric conditions the product will experience during its intended life (thermal, moisture, light, weather, pres- sure, etc.). In many cases, the product will generate an environment of its own during operation. To plan an effective environmental stress screening program that accelerates product life, all the mechanical and environmental con- ditions that will be present during operation, storage and use of the product must be consid- ered. It is also important to evaluate the non- operational mechanical and environmental stresses that are experienced during a prod- uct's birth (assembly, delivery, and set-up) that can be the worst stresses the product will expe- rience during its life. The GUESS Test One of the most common types of accelerated life testing I see employed today is the GUESS (grossly un-correlated and exaggerated stress) test. ere is much literature thought to exist about the GUESS test, and people recount experiences and data obtained from GUESS testing like they would a UFO abduction expe- rience. Many GUESS tests have their roots in ancient history. Various references to GUESS tests found in literature are usually based upon faith, hearsay, or anecdotal experience rather than science. ese tests are usually handed There is a whole branch of palm readers— I mean scientists and engineers—whose job it is to predict the life span of a product.