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November 2010

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From:
"Post, Scott E" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Post, Scott E
Date:
Thu, 18 Nov 2010 12:57:51 +0000
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You're right - those graphs you see of area ratio vs. transfer efficiency are averages and I don't find them very useful as area ratio shrinks.  As you mentioned, when the apertures get very small I prefer box plots and looking for outliers.  I also like to create xbar/R charts and look for stability and in control.  It's worthwhile to sub-group in various ways to understand where variation is coming from.  I typically subgroup by reference designator, by board, by squeegee direction (you'll be amazed at the difference between front-back & back-front).  With QFPs you can subgroup by aperture orientation (top/bottom vs. left/right) and see very large differences.  Sub-grouping by board can help you identify the best wipe frequency or the effect of abandon time.

I'm not sure what the "10% rule" is.

Scott Post
Staff Manufacturing Engineer
P.O.U. 0000-001E-0CTC
2151 E. Lincoln Road
Kokomo, Indiana    46904-9005
765-451-2983 (Phone)
765-451-0287 (FAX)

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gumpert, Ben
Sent: Thursday, November 18, 2010 7:45 AM
To: [log in to unmask]
Subject: [TN] Solder Paste Transfer Efficiency

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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