Bev - Any chance that perhaps at least one set of the mirrors had not
been cleaned in the EDTA solution?  

Also, how the film from the drop of flux forms seems to effect the
results.  Does the droplet form a uniform film OR a ring that seems to
push the solids out the perimeter of the circle?  I have always
suspected that technique (ie.dropping height & size) along with room
temperature, rh% and air currents can strongly influence the formation
of the film and ultimately the final results.

Perhaps investigating these aspects could help. 

In my experience the copper mirror test is really a little more
subjective than most people think. 


Rich Kraszewski
Plexus 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Wednesday, February 11, 2009 2:57 PM
To: [log in to unmask]
Subject: [TN] Copper Mirror Test

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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