Dear Technetters,

My question is: how do you measure solder paste height and volume
accurately?  My situation is with using the VisionMaster Model 150A, I am
having trouble obtaining reasonably accurate measurements.  The
VisionMaster is a small bench top system that uses a template consisting
of a "region of interest" (the solder paste), and reference regions (the
areas on each side of the pad).  Because there are inconsistencies in the
PCB (HASL finish), like raised areas from traces, valleys surrounding the
pad, and irregularities in the solder mask, the readings I get cannot
possibly be true.  Many times the measured readings for weighted average
height are over 7.5 mils using a 6 mil screen and 9.5 mils using an 8 mil
screen.  The process specifics are Multicore NC-40 paste, shore 94-97
polyurethane blades, DEK 265 Infinity, and correct squeegee pressures,
print gap, etc..  I believe the bricks are good, I just can't use the
measurements for SPC as it shows the process to be out of control.

In theory, polyurethane blades should "scoop" if anything, leaving a
shorter brick than the stencil thickness.  It seems logical to me that the
best way to obtain accurate measurements would be to use the pad as a
reference region and measure the height from the pad, but the VisionMaster
system does not allow me to do this.  Does anyone have knowledge or
recommendations on what I can do here?  How do the more expensive systems
measure solder paste?  Oh yea, spending $$ on new equipment is not a real
good option at this point!

Thanks in advance for the assistance,

Howard Watson
Manufacturing Engineer
AMETEK/Dixson