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Electronics
The Power of Population in Semiconductor Device Reliability
When we introduce a new chip, we plan and execute a comprehensive reliability qualification plan. This plan will be based on many different reliability stresses addressing infant mortality rate test, early life failure rate test, long term life test failure rate prediction based on a small population of samples pulled from early production lots . Due to the fact of limited device sample sizes, we are trying to assign a confidence level to our failure rate predictions using "industry standard" chi-square adjustment in the hope, our prediction will be closer to real field failure rates. This is a "standard" approach of the semiconductor industry because testing very large sample sizes of chips is economically not feasible, especially for small-and fabless semiconductor companies. IBM Corp.'s …
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Functional Safety: Reliability Prediction vs. Reliability Demonstration
An adaption of the Functional Safety standards IEC 61508 and IEC 26262 by the European Union brought a new life into slowly fading activity of reliability prediction. Both reliability prediction and reliability demonstration are now key parts of many product development programs, however despite phonetic similarity those two have little in common as well as the result they generate. While reliability prediction is an analytical activity often based on mathematical combination of reliabilities of parts or components comprising the system; reliability demonstration is based on product testing and is statistically driven by the test sample size. Therefore the obtained results could drastically differ. For example, a predicted system failure rate of 30 FIT (30 failures per billion (109) …
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Zener Diode Failure in a Clipper Application
This is an application where two Zener diodes were placed in series, in a back to back configuration. They were placed across the primary winding of a transformer used to apply modulation to an AM transmitter. The modulation was in the form of a single frequency, and the modulation level was not to exceed 30% by specification. The modulation level showed some variation with temperature, so that the diodes were selected to limit the voltage across the transformer primary to ensure that the 30% modulation limit would not be exceeded. The drive for the transformer/limiter combination was from a low impedance source, adjusted to provide 30% modulation peaks during final test. The pole mounted transmitter was required to operate in all weather, unsheltered conditions, at any airport in the …
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Printed Circuit Boards and Reliability
Potting compounds are often used on printed circuit boards to improve reliability. In spite of this added protection, adhesive failures, otherwise known as delamination, can occur and lead to substantial problems from moisture ingress. Root causes of adhesive failures may be surface contaminants, inherently weak bonding between solder mask and potting material or thermal stresses that develop during temperature cycling. In an adhesion analysis a combination of chemical and mechanical tests is often needed to determine the root cause. Chemical testing includes surface analyses such as XPS and SIMS; both reveal chemical groups available for bonding at the surface. Contaminants may be revealed during these tests. Basic tests such as FTIR, TGA and EDS provide information on the …
