A series of designed experiments was conducted to characterize stenciling solder paste and measuring paste bricks by three-dimensional automated optical inspection (AOI). For this study, squeegee pressure, squeegee speed, and separation speed were manipulated on three levels.Detailed studies were conducted on printed area, height of the brick, volume, and X-Y offset. Brick volume was selected for the process response.Confirmation runs verified that the mathematical model could predict volume and standard deviation of printed paste volume for all package styles, and response curves revealed that not all apertures share the same optimum level settings. For instance, levels that minimize variability in stenciled paste for a BGA may induce more variability for 0603 resistor nets.Means response tables for volume standard deviation of each package type were used to make a programmed spreadsheet for determining optimal printer settings. This tool allows for quick prediction of solder paste print standard deviations for numerous package types and setting optimal process levels to minimize variability. The programmed spreadsheet can prepare a population weighted average by total pin count for different packages to set control factors at “best fit” levels.
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