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Frequently Asked Questions: Field
Failures (Warranty Returns)
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Failure
Investigation Protocol
Q. How do you go about investigating
the root cause of a field failure?
A. That depends on the field failure and the apparent failure
mechanism. The first step is to determine why the unit failed.
Was it due to a solder failure, which is not our bag, or from an
electrochemical failure? Was it a one-time event or is it systematic?
Does
it occur
in one area consistently? Was it due to the environment or
the manufacturing process. We usually try to gather as much information
as we can about
the assembly process, the field data, and the observable characteristics.
We most often use ion chromatography to examine the samples.
Properly interpreted, the chemical residues can tell a great deal
about the failure
mechanism and possible remedies.
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No Trouble Found
Q. I have lots of hardware that
fails in the field but tests fine in the lab, e.g. no trouble found (NTFs).
Why?
A. In most cases, field failures will occur in situations of
high humidity. When a bench tech tests the returned hardware,
it is usually at lab ambient conditions of 25C/50% RH. This may not be
humid enough
to fuel the electrical leakage phenomena. Try increasing the
localized humidity using a vaporizer or putting the hardware in a temperature-humidity
chamber at 35C/90% RH. This should be enough humidity to drive
the electrochemical
failure mechanism. If you still have an NTF, then try temperature
cycling while monitoring the function. The expansion and contraction may
exercise
marginal solder joints and find the cracked ones.
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Environmental / Service Conditions
Q.
How clean do I need to be, or what materials do I need to have for my
end use environment or service condition?
A. That depends on the end use condition. You will have vastly
different requirements for space applications than for office
products. The office environment is the most benign and humidity is often
the most
difficult factor. Outdoor applications have a wider range of
contaminants, such as mixed flowing gasses (SOx and NOx), high heat and
humidity, and
particulates. Space applications have outgassing concerns. NASA
(Goddard Space Flight Center) is a good resource for space application
requirements.
The Society for Automotive Engineers (SAE) is a good resource
for automotive and outdoor applications. Military specifications (MIL-STD-2000A
and MIL-STD-883)
are good for outdoor high-rel applications.
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