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www.us-tech.com
March, 2013
Highly Accelerated Stress Screenings C
By Alan Perkins, Vice President of Sales and Marketing, Qualmark
onsidering that electronics giants such as Apple® manage to introduce new and improved
products every year, the need for faster and more accurate reliability checking comes into sharp focus. While traditional environmental stress screenings such as “burn-in” still have their place, sole reliance on this 70-year old technology can put manufacturers in last place. Instead, quality and reliability
engineers now seek cutting-edge testing systems and methodologies to supplement or even replace burn-in with advanced, more effective tests that yield better results in less time for less cost. This requires the com- pression of time and energy, literally, that only Highly Accelerated Stress
The move toward
HASS and HASA improves reliability at less cost, allowing quality engineers to reconsider legacy-era environmental screenings that sacrifice time and money.
Screening (HASS) and Audits (HASA) permit. By fusing burn-in and acceler-
ated stress testing into one powerful system, engineers can incorporate the best of traditional and accelerat- ed production stress screening, enabling faster and more effective monitoring of high-volume produc- tion runs of electronic and electro- mechanical products. “You save time because an ESS
chamber might require 2-3 hours of testing, whereas a HASS chamber can do the test in half the time,” notes Harry McLean, author of “HALT, HASS and HASA Ex - plained/Accelerated Reliability Tech - niques.”
Considered as one of the best
experts on the real-world application of accelerated testing, McLean cur- rently works as Director of Relia - bility Engineering for Redwood Shores, California-based Enecys Limited — premier supplier of smart, highly reliable grid-connected micro inverters and monitoring systems that convert DC power generated by photo-voltaic arrays into AC power
for homes and businesses. Back-Burnering Burn-in Burn-in enjoyed widespread use
in the early 50s and 60s, when the predominant failure mode of early solid state devices resulted from chemical reactions within the then
the firmware has to perform temper- ature compensation. If the compo- nent is defective/marginal/out of tol- erance, then the software value does- n’t function properly any longer and the product shuts down, or even worse, provides erroneous data. Traditional burn-in may not detect
test, but under stress it will fail. “By relying solely on burn-in
and other environment stress screen- ings, you risk ending up with a prod- uct that will fail, and do so at the most inopportune times,” cautions McLean. The result is costly product
recalls, ongoing warranty expenses and time-consuming support pro- grams.
Using HASS & HASA HASS proves effective in
screening out failures that may have gone undetected during traditional burn-in testing processes by going beyond normal testing parameters to verify the integrity of mechanical interconnects, component tolerance compatibility and timing errors that only occur under high stress. With a HASS, a product is sub-
jected to the outer margins of temper- ature, rapid thermal cycling, and vibration testing — simultaneously — to rapidly uncover any design weak- nesses. For example, if the design calls out a maximum operating tempera- ture of up to 50°C, HASS may push that product past the specification in order to uncover any weaknesses.
Product is subjected to the outer margins of temperature, rapid thermal cycling, and vibration testing to rapidly uncover any design weaknesses.
While a HASS that screens 100 HASS proves effective in screening out failures.
new solid-state components. How - ever, the technology used to manu- facture integrated circuits has advanced to the point where chemi- cal reactions are no longer a signifi- cant source of failures. Components, such as an entire IC can still pose a pre-existing reliability risk. But increasingly, the integration of hard- ware and software is becoming the precipitating cause of failures. Take, for example, a case where
such subtleties, particularly if the error occurs because of cold tempera- tures or changes in temperature. “With burn-in alone, you still
could miss failure modes that are rate dependent, meaning change of temperature over time; and those do occur,” says McLean. Another example is when com-
ponent tolerances stack-up negative- ly to yield a marginal product. The complete product might pass a bench
percent of product runs prove invalu- able in mission and life critical appli- cations such as medical, avionics and defense, HASA (audits) save tremen- dous amounts of time for manufactur- ers who produce consumer goods such as cell phones, televisions, DVD play- ers and laptops. So effective are accel- erated audits that a sampling of just 15 percent or less may statistically validate the quality of a given product.
Joining the Old and New. New technology called QFus -
ion®—a proprietary name of Denver, Colorado-based Qualmark Corpor - ation — fuses traditional burn-in and
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