Hello everyone,

We have a Malcom PM-2A handheld viscometer here, and I'm trying to make use
of it, however I'm having difficulty
obtaining stable readings when testing solder paste.

IPC TM-650 Test Methods Manual sect 2.4.34.3 says to take a reading when
output data is stable for at least 1 minute.
When I insert the spiral cylinder into the paste, after a few minutes it
seems to just dig a hole into the paste and then begins to rotate freely and
the viscosity reading steadily drops.  The paste from the surrounding just
doesn't seem to "flow" into the void space.  However, when I rotate the
paste container, or use a spatula to push the solder to fill in the voids,
the readings seem to shoot up after a little delay, and then steadily
decrease after that.
At other times, if left alone for a while. the readings fluctuate a little
(ie between 171-177). Is this considered "stable", and if so should I just
take the middle value in that range, and how long would one recommend I wait
before taking a measurement?
Since solder paste is thixotropic, my understanding is that under constant
shear for extended period of time, the viscosity will slowly decline.  I'm
not sure how quickly this effect takes place and how that would effect the
stability of the readings.

Any comments/suggestions will be greatly appreciated,
(Thanks!)

Toby

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