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One of the most common reasons for electronic failure is environmental contaminants and conditions. The list of contaminants includes fine and coarse particles of such species as chlorides, sulfates, sodium, ammonium, potassium, magnesium, and calcium. The single most important environmental condition affecting the impact of particulate matter and gases (such as sulfur dioxide and nitrogen oxides) is relative humidity. Coarse particles (2.5 to 15 microns) are typically formed as a result of human activity(10) or originate from soil. Fine particles (0.1 to 2.5 microns) come from the combustion of fossil fuels and, at times, from volcanic and geological activity.
In electronic devices, coarse particles may cause malfunctions by interrupting electrical contact between mating pairs of contacts on connectors or relays. They typically require higher relative humidity conditions than the fine particles. According to the ISA – Instrument Systems and Automation Society standard (ISA S71.04 1985), there are four classes of industrial atmospheres with respect to copper reactivity. (reference)
|
G1 (mild) |
G2 (moderate) |
G3 (harsh) |
G4 (severe) |
|
|
Copper corrosion |
< 30 nm/month |
< 100 nm/month |
< 200 nm/month |
< 300 nm/month |
Gas contaminants (ppb) (reference)
|
ISA category |
G1 |
G2 |
G3 |
Gx |
|
H2S |
< 3 |
< 10 |
<50 |
> 50 |
|
SO2, SO3 |
< 10 |
< 100 |
< 300 |
> 300 |
|
Cl2 |
< 1 |
< 2 |
< 10 |
> 100 |
|
NOx |
< 50 |
< 125 |
< 1250 |
> 1250 |
|
HF |
< 1 |
< 2 |
< 10 |
> 10 |
|
NH3 |
< 500 |
< 1000 |
< 25000 |
> 25000 |
|
O3 |
< 2 |
< 25 |
< 100 |
> 100 |
