Hi Guenter - Daan shouldn't have to worry about the tin pest phenomena
despite the -50 degree temperature extreme. Solders with a minimum of 40%
Pb have been shown to very seldom (although it is metallurgically possible)
undergo tin pesting. The addition of other "poisons" such as bismuth or
antimony in the solder alloy prevent the tin alpha/beta transformation.
David Hillman
Rockwell Collins
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Guenter Grossmann <[log in to unmask]> on 02/05/99 05:57:25 AM
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Subject: Re: [TN] Storage of assembled boards at - 50 degrees Celcius
Daan
I don't think the storage at -50 deg. does harm your equipment too much.
Just be sure it is sealed in dry gas or vacuum. I have one thought: Tin has
a transition temperature of +13 deg. from tetragonal ( metallic tin ) to
cubic (tinpest). This effect is very slow, but if one is storing electronic
equipment for years at low temperatures it might at least have a cosmetic
effect on the solder joints. And if the PCB's are coated ( as usual in
military applications ) this will look really ugly.
Best regards
Guenter Grossmann
Swiss Federal Institute for Materials Testing and Research
Center for Reliability
Duebendorf
Switzerland
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