Hello technetters, glad to be back after a few years absence from this great forum.  I have a few comments to add to what Mark, Ingemar, and others have contributed.  I come from a physics/materials science/quality engineering background, so may have some different experiences than most.  

One thing you need before using SPC is a capable measuring instrument.  I've seen people trying to control a manufacturing process with a gage that was incapable;  they might as well have tossed a coin in making machine adjustments.  You may have heard of the QS-9000 and Automotive Industry Action Group's "Measurent Systems Analysis" manual and Gage Repeatability and Reproducibility.  This manual is worth a look, although it helps a lot to have some experience with designed experiments and Analysis of Variance.  Don Wheeler of SPC Press has a book on "Evaluation the Measurement Process" which takes a different approach.  He addresses the question Can the gage discriminate among the products coming off the line, regardless of the specification requirements?  

Wheeler also has a short paper on evaluating the destructive measurement process.  I've used his ideas.

The way I put it to my PC fab colleagues in the past is "The SPC charts force us to look at the data".  We had some success, largely in getting people to stop tinkering with processes that were running OK.  


Lou Hart
Compunetix Instrumentation Systems Division

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################