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Title :
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REAL TIME STATISTICAL PROCESS CONTROL OF THE SCREEN PRINT PROCESS
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Author :
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Bill Beair
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Author Company :
Raytheon
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Date :
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09/30/2001
Conference :
SMTA International
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Abstract : Increased component density found on today's printed circuit boards (PCBs), coupled with faster assembly cycle time requirements and the increased cost of screen print defects, necessitate continuous process monitoring of manufacturing operations. Paste rheology, board warp, aperture size and many other assembly features drive the need for continuous monitoring of solder deposition volume. Current screen print equipment offers 2D and 3D paste inspection capability, but fails to archive the inspection data to permit continuous monitoring of solder volume. Access to historical data, trend analysis, and data set comparisons facilitates process monitoring. This paper provides an insight into continuous monitoring and the positive effects it can produce in the electronics market. Defining the Paste Deposition Process Window There are many factors that come into play when defining solder volume control limits. To determine the control limits the minimum and maximum solder volume must be determined. Factors to consider when evaluating solder volume include plating on the circuit card, plating on the component leads and the component lead and circuit card pad dimensions. The online IPC-SM-782-Land Pattern Calculator (www.ipc.org/html/fsresources.htm) is a good tool to establish initial control limits. The control limits can then be compared to the theoretical print volume calculated from the stencil apertures. Stencil apertures aspect ratios will change the mean of the volume printed.
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