Instructions: This page calculates the Aspect Ratio (AR) for rectangular apertures, the Area Ratio (ArR) for circular apertures, and the Area Ratio (ArR) for square apertures. The white cells are inputs, whereas the green cells are calculations or locked cells.

As an example, assume that the user wants to determine the stencil metrics and paste type for 20 mil pitch PQFPs. The first input box references the pitch and the input box directly below allows the user to enter the pad width. There is a recommendation for all rectangular apertures that the pad width be the pitch divided by 2 plus 1 to 3 mils. So a reasonable entry, into pad width, would be 12 mils. Once the pitch and width have been input, the box below tells the user that they have met the recommended criteria. The aperture should then be the pad width minus 2 to 3 mils. If the user enters 10 mils into aperture input box, StencilCoach^® tells the user they have met the recommended criteria. The next box is where the user inputs the stencil thickness. After entering the stencil thickness, StencilCoach^®; then calculates the AR and compares it to the criterion. In the final box, the solder paste type is recommended.

Metrics for circular or square apertures (cells to the left) are handled in a similar manner. Typically these cells are for chip scale packages or ball grid arrays. As a rule of thumb, the Area Ratio should be >0.66. However with some Type 4 pastes, >0.50 may be acceptable. Note: For square apertures: Diameter "D" = Width "W"