Don't forget about dendrites (Electro migration)...
Any time your board goes through the dew point with moisture
condensing,
and you have the power applied, you can grow dendrites. They can grow
under BGA's, Connectors ,etc.
That's why chilling (freeze misting) below the dew point out side of a
chamber is so hazardous.
Ref: IPC - TR-476  How to Avoid Metallic Growth Problems on Electronic
Hardware.
Even on a really pure surface the water can become conductive enough to
start a little
electro-chemical plating cell. In low voltage high impedance circuits
it will grow a short (dendrite) and the short will stay there.


Paul Signorelli
Reliability Engineer
Sanmina-SCI Corporation, Plant 12
702 Bandley Dr.
Fountain, CO 80817

eMail address: [log in to unmask]
Phone: 719-382-2352,   Fax: 719-382-2520

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