Hey TechNetters,

I've got a couple questions for the solder paste printing gurus:

1. Can someone explain something about transfer efficiency for me? The typical chart (see below) shows a nice, clean set of points, but I know that my process has variation. So is transfer efficiency just about averages? The average volume printed for a specific aperture divided by the aperture volume? Meaning that instead of single points shown in the chart below, box plots would really be more accurate?

Transfer
Efficiency
100%     |                                                                    x             x
                |                                                    x
                |                                              x
                |                                            x
50%        |                                       x
                |                             x
                |            x
                |
0%          |_________________________________________________
                .3            .4            .5            .6            .7            .8            .9            1.0
                                                Area Ratio

2. What is the 10% rule? I've read a couple of articles that mention the 10% rule, but they don't make it clear what it is. I interpret it to mean that to have an 'acceptable' solder printing process, the standard deviation of the individual data points of paste printed (transfer efficiency) needs to be 10% or less of the average paste transferred. Am I on the right track here?

Thanks,
Ben


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