I agree that understanding the relationships, in your process, between the key variables is what matters most. SPC is a system designed to quantify your natural variation and provide visual tools to detect when your process is affected by some other cause of variation. The correlations between variable are usually determined under specific conditions. SPC is best used to detect changes in conditions that render the models you've developed invalid and/or inaccurate. For example, regardless of what the maintenance records say, I can tell when the schedule for pump cleaning has not been properly followed using my dwell time charts. Since the model which tells me which parameters are optimal (including pump speed) assumes this maintenance is done in a certain manner, when maintenance is late the process drifts away from optimal. The SPC charts warn me this is happening. yves > -----Original Message----- > From: Earl Moon [SMTP:[log in to unmask]] > Sent: Friday, October 05, 2001 12:08 PM > To: [log in to unmask] > Subject: Re: [TN] SPC @ WAVE SOLDER > > I still live in the glass plate and matrix world. Simple correlations > between variables as conveyor speed, temps, topside measurements, managing > fluxes and their applications, wave height, contact area parallelism and > dwell time all make solder joint attributes clearly acceptable or not. SPC > is used in a number of the variables and provides, again, correlation to > the > matrix (relative to PCB thermal mass, as an example) and the effects of > good > process management. Though wave soldering has a few more factors, compared > with hand or reflow soldering, the basics are all the same, to me, for > each. > I'm a simple fool and can't change at this point when it works. > > MoonMan > > -------------------------------------------------------------------------- > ------- > Technet Mail List provided as a free service by IPC using LISTSERV 1.8d > To unsubscribe, send a message to [log in to unmask] with following text in > the BODY (NOT the subject field): SIGNOFF Technet > To temporarily halt delivery of Technet send the following message: SET > Technet NOMAIL > Search previous postings at: www.ipc.org > On-Line Resources & Databases > > E-mail Archives > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for > additional > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 > ext.5315 > -------------------------------------------------------------------------- > ------- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------