For post print sampling there are very reliable systems available on board the printer. The capability of these systems is much better than any manual microscope method. There are no reliable volume and height systems available on board a printer but there are systems, like Ekra’s 2 1/2D for instance, that do provide more than just 2D coverage.

If the system can provide pad coverage, bridge detection, and stencil inspection that typically provides more than enough sampling capability. Of course it depends if the customer is using an in-line printer.

If the customer is not using an in-line automatic printer and still wishes to get some sample data, there are microscope systems that can be used to calculate height and coverage. The process is obviously manual, slow, and subject to operator repeatability.

This article published on SMT Express by Mike Riddle from ASC International, Inc. gets to the root of his question and also instructs the reader on the methodology and reason for manual versus automatic inspection. See Solder Paste Measurement: A Yield Improvement Strategy That Helps Improve Profits.