The biggest problem we have is trying to get customers to understand the limitations of SPC. Many of them think SPC can and should be applied to al processes and they expect to see charts everywhere when they visit. Circuit board manufacturing presents some difficulties when you are trying to implement SPC. For example, standard SPC charts require that measurements be independent (not related to each other in any way other than the simple fact that they came from the same process). In most PCB processes this is not the case since consecutive measurements of product or process ARE related (i.e., 2 consecutive circuit width measurements will be similar since they were etched when the chemicals were at the same concentration, etc.). I don't wish to discourage anyone from using SPC. It can be used effectively in most processes. My main point is - don't let customers who have a limited understanding of PCB processes and/or SPC dictate how you will use it! We've made that mistake and currently have 10 to 15 control charts that are basically worthless. Not only are they worthless, they have a negative impact on the company by convincing many operators and engineers that SPC is a waste of time. *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To subscribe/unsubscribe send a message <to: [log in to unmask]> * * with <subject: subscribe/unsubscribe> and no text in the body. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************