I have been doing this test since 1990. 

We buy our copper mirrors from the usual source and keep them in a small
dry box with a pan of Drierite at the bottom.
For paste flux we add the material itself and a solution of the material
made using a 50/50 IPA/toluene solvent mix to the copper mirror.  The
two sample spots do not touch.
For the test conditions we use a closed dessicator with a small
crystallization dish full of a saturated solution of Mg(NO3)2 at the
bottom under the sample space.  Why?  Because at 25C the RH will be 53%
so at 21-22C, it is pretty darned close to 50%.  IPC-TM-650, test method
2.3.32 calls for +/- 5% RH.

Most materials pass.

Recently we had a material that failed.  The supplier had it pass. We
traded copper mirrors. We still had it fail and they had it pass.  We
then re-ran the test in a humidity chamber with our mirrors, under the
same conditions. It passes.

I have my suspicions, although I am not entirely sure why everything
else passes.

Has anyone else seen this?

Bev
RIM

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