Printing SPC

Peter,

QC-calc: Verifying vision accuracy of your printer with calibration stencil and hundreds of repeats. If your boards are large and specially if you have finepitch parts on them you will find usefully to use QC-calc to measure board stretch/shrink.

reply »

The most effective method is to monitor both printing results and parameters. Periodically (maybe once per month), run QCCalc or another program to measure the machine's capability to hold its set parameters. I also run control charts on the paste height or volume. The paste height/volume results are what show you set the parameters correctly. Just because a machine can hold the parameters doesn't mean they parameters are set at the right points. The control charts are quick and easy and don't require extra resources and cost. One example is when a part int the machine wore down. The control charts being plotted during the process hsowed a trend of increasing paste height. We were able to identify the problem and get it fixed before we misprinted boards or damaged the machine. QCCalc works well, but you need to check and see if it works with your screen printer. They work well with DEK, but not with MPM UP series last time I checked. You can also use some of the quality systems to enter variable data, and they can be linked to your measurement device to automatically download the measurements. This is one part of the system I have used which reduced defects in the plant to under 50ppm. Defect prevention reduces cost and increases throughput. When combined with Continuous Improvement efforts, we were able to get our defects down and get more product out. Many times boards started in the morning would ship the same day after going through SMT, Wave, Assembly Cell and Test. Our RMA rate was around .5%.

Hope this helps, Brian

reply »