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I can't post a picture, since I don't have a good camera.

I've noticed white powder on leads of some components. What could it be?

I'm sure that it isn't just dust, because there isn't any on the component bodies and was on some components which were stored in their own sealed bags.

I've seen it on all types of components, but not all components have it. I was unable to find any mention of it in any datasheets. I've seen in on for example Fairchild DB237 transistors, Piher potentiometers, various no name resistors and so on.

I did notice that most components which have the powder have flat leads.

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When tin, a common plating on components, is left exposed to the air, it will oxidize over time, forming tin oxide, a white powder that is insoluble in water. I believe that if your components are bright tin, the oxide layer will be fairly smooth and not "powdery", which may be the case if you have components plated with matte tin.

The flux in your solder (paste or rosin-core wire) should be able to remove a fair bit of the oxides, but if they are extremely oxidized you may have to add additional flux, or clean the parts somehow.

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    \$\begingroup\$ Would tin oxide be removable by hand? I can just wipe this stuff with my finger. It doesn't seem to stick at all to the leads. \$\endgroup\$ – AndrejaKo Mar 29 '11 at 15:44
  • \$\begingroup\$ If there's enough, sure, you could wipe off some of it. It's going to be on any tin surface in air at some level. \$\endgroup\$ – Nick T Mar 29 '11 at 15:49

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