Tom,

I would guess that consistency of operation was more important than
traceable accuracy in this sistuation so I would want to try it on
a range of solder pastes and surface finishes. We have a (research
rather than production) system based around a Rhodestock laser
sensor which can be very sensitive to surface finish, particularly
on very steep sided features, as it relies on a few percent of the
laser energy being reflected directly back into the sensor (if the
surface is shiny and not perpendicular to the beam then most of the
energy shoots off in the wrong direction).

>We are purchasing an automated machine to do paste inspection of SMT
>solder paste prints after the printing operation.  Within the next few
>weeks we are going for an in-plant machine acceptance and are in the 
>process of outlining our acceptance criteria.
>
>The first, and obvious test is to do a series of measurements against
>a slug of known volume (NIST certified) - the vendor can supply this.
>
>We are also thinking of doing accuracy and repeatiblilty testing on a 
>custom substrate we have yet to design.  I envision this being the maximum
>board size the machine can accept (18" X 22") with known volume slugs
>positioned at various locations across the substrate.
>
>Has anyone done anything like this?  Any ideas on the most efficient
>method of designing this experimental board (one thing we thought of
>is cutting up a stencil foil to specific dimensions and gluing them
>to the 18 X 22 piece of G10)? 
>
>Any other ideas on machine acceptance criteria for solder paste inspection?

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