"mc" wrote in message
...
At this web site

http://www.kester.com/en-us/document...de%20Line).pdf

Kester gives a test for whether solder paste is fresh enough. The test is
to melt a drop of it onto an unsolderable surface and see whether it forms
one ball or several. If it sheds a number of smaller balls (rather than
forming just one), the flux has deteriorated. The failure mode is flux
deterioration.

The funny thing is, I have some solder paste that is 10 years old and
seems to pass this test. I'm going to repeat the test more rigorously.

.... And it wasn't reproducible. Apparently, a lot of flux had gone to one
end of the tube.