SMTA International Conference Proceedings


Authors: Vatsal Shah, Rita Mohanty, Ph.D., Arun Ramasubramanian, and Joe Belmonte
Company: Speedline Technologies, Inc.
Date Published: 10/11/2007   Conference: SMTA International

Abstract: Do solder paste printing defects effect the end of the line defects? After more than 25 years of operating and optimizing the SMT process, specifically the solder paste printing process, you would think that there would be consensus among process engineers on this point. To our surprise, there is not.

The difference in opinion on solder paste printing defects resulting in end of line defects is demonstrated in the dramatic difference in how folks think the performance of the solder paste printing process should be monitored and measured. You see everything from very sophisticated Automated Optical Inspection (AOI) to no inspection or monitoring at all. In one extreme end, you see manufacturers inspecting every single solder paste deposit on every single board immediately after printing, and wiping the board clean if even one print deposit does not meet the specified solder volume requirement. In the other extreme end you see no inspection at all as some manufacturers determined that no correlation between actual end of line solder defects can be related to solder paste printing defects discovered immediately after the printing process.

At this point in the development of surface mount manufacturing technology one would assume that statistically valid data exists that would clearly define the relationship between printing processes defects identified immediately after printing to defects that will occur at the end of the line after the final soldering operations. In other words if a solder short (bridge) is identified in the wet solder paste deposit you should be able to conclude that an actual solder short (bridge) will be discovered at that location by the sophisticated inspection, process evaluation, inspectors, and/or test equipment used to verify product quality.

There have been limited studies conducted to provide this data. However, the industry still has not universally accepted any of the conclusions from those studies. Each organization is still doing ‘their own thing” in regards to solder paste printing process inspection.

This study will focus on determining what solder paste printing defects will result in what end of line defects using statistically sound methods. The goal is to assist manufacturing organizations to identify what is the correct approach to solder paste printing process inspection and process verification.

Key words: Printing, SPI, AXI, Defect, End of Line, Correlation.

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