Brookfield Spiral Adapter - Manual (Page 12)

Brookfield Engineering Labs., Inc. Page 12 Manual No. M93-270-D0812
V.4 Application Example - Solder Paste
Applying solder paste is a printing operation that shears the materials as the paste “rolls” on
the stencil surface. Solder paste typically shows pseudoplastic behavior (exponential decrease
in viscosity with increasing shear rate) as shown in Figure 4.
1 10 100
LOG RPM
LOG VISCOSITY
(cP)
Slope of Line =
Shear Sensitivity Factor
10
6
10
5
7 x 10
5
6 x 10
5
5 x 10
5
4 x 10
5
0 5 10 15 20 25 30 35 40 45 50
RPM
VISCOSITY
(cP)
55
Figure 4 Figure 5
A plot of viscosity vs. RPM on a log/log scale approximates a straight line as shown in Figure 5.
The slope of the line provides information about the shear thinning of the paste. The absolute
value of the slope is called the “shear sensitivity factor”. Experimental correlations of these
slope values to actual printing properties allow the user to establish acceptable ranges of the
shear sensitivity factor.
The plots shown in Figures 4 and 5
can be generated easily when using Brookfield application
software. There is a math model (IPC Paste Analysis) included in the software which converts
viscosity vs. RPM data (Figure 4) into a log/log plot (Figure 5) and automatically computes
the “shear sensitivity factor.”
V.5 Cleaning the Spiral Adapter
Support the chamber and remove the clamp. Carefully lower the chamber off the spindle. Soak
in appropriate solvent. Remove spindle by lifting the lower shaft and holding it firm. Turn
the spindle nut to the right (counter-clockwise) to remove. Clean by wiping and soaking in
appropriate solvent. A soft brush is provided to aid in cleaning the threads. This brush should
also be cleaned in solvent.