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When speaking of solder paste, one parameter that is often
discussed is viscosity. Viscosity is important as a paste that
is too thick (high viscosity) may lead to a bad print in the
form of an insufficient filet. A paste that is too thin (low
viscosity) may lead to the filet slumping. In order to test
that a paste has the proper thickness for optimal printing,
the paste's viscosity should be checked with an accurate and
repeatable viscometer.
The Malcom PC-1TL and PCU-200: Spiral Viscometers by design
are able to measure not only the static viscosity of solder
paste at low rpm, but it can more importantly measure the
dynamic viscosity. This is due to the fact that Malcom applies
a true shear force onto the solder paste, simulating the
forces that act on the paste on a screen printer. By varying
the rpm, one can find the shear sensitivity and thixotropic
index of the solder paste, something that could not accurately
be done with most other viscometers. Thus with a Malcom
viscometer, the user can not only measure batch to batch
variation, but can also predict how the solder paste will
perform on the screen printer. |
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