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Tue, 6 Apr 2004 07:40:18 -0500 |
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Franklin,
Here is some wording that I wrote for one of the IPC handbooks currently
being drafted. Doing M&IR testing is more practical if you are looking for
electrochemical failure mechanisms.
Doug Pauls
Rockwell Collins
MIR vs. SIR
Many individuals who deal with solder masks and printed wiring board
materials and processes have expressed confusion over the terms “moisture
and insulation resistance (MIR or M&IR)” and “surface insulation resistance
(SIR)” when reading IPC-SM-840, the specification for solder masks.
In all practicality, they refer to the same thing, though term purists will
argue. Both of these terms refer to the exposure of material systems to
elevated levels of temperature and humidity, often under electrical bias,
to examine propensities for degradation of insulating properties by
temperature and humidity. The two terms can usually be used
interchangeable, though SIR testing has the greater acceptance as a term.
Surface insulation resistance is the measurement of a characteristic
property of a material set, such as solder mask over bare copper. The
measurement of SIR can take place at ambient conditions, where it is
sometimes called insulation resistance (IR), or at some elevated conditions
of temperature or humidity, of varying test times or conditions.. In
practice, SIR testing has generically referred to these kinds of biased
temperature humidity tests.
The term Moisture and Insulation Resistance testing is usually only found
in the SM-840 document. It is a measurement of insulation resistance at
ambient conditions prior to temperature-humidity testing, at elevated
temperature-humidity conditions during the cyclical humidity test, and
finally at ambient conditions at the end of the test.
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