Actually, my calculations indicate one of the 45 measurements should have been out, and one very nearly was. (The mean is shifted from center, so unless you knew the amount of shift, assuming a centered process, more than 2 measurements should have been out of spec.) Actually, I have the fortunate benefit of being able to compare measurements of that specific lot from two different receiving factories around the world. The tails are still there, but slightly cut off of the high end. The spread is still pretty wide. They may have screened and sorted the product, but until I know that, I can only assume the out of spec product is in there somewhere...(and I don't want to be the one looking for it!) -Ryan -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Louis Hart Sent: Wednesday, March 28, 2007 10:20 AM To: [log in to unmask] Subject: Re: [TN] Explanation of Cpk (Ppk) Ryan, to my eye, it is curious that of 45 measurements, with a Cpk of 0.65, none were out of spec. My quick and perhaps erroneous calculation suggests you could expect 2 or more of the 45 measurements to be out of spec. It looks to me like the supplier's process is not so good, and he is doing a 100% screen of product before shipping it to you. The distribution of data may be like that of a normal, with the tails truncated. Lou Louis Hart Technology Transfer Specialist National Technology Transfer Center 316 Washington Av Wheeling, WV 26003 304-243-2553 [log in to unmask] Ryan Grant <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 03/28/2007 11:39 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to [log in to unmask] To [log in to unmask] cc Subject [TN] Explanation of Cpk (Ppk) Hi all, I have a supplier that is wondering why we rejected a shipment for finding a critical dimension as having a Cpk of 0.65 (Ok, technically, we are calculating Ppk). None of the 45 measurements were actually out of spec (although one measurement just missed exceeding the upper limit by 0.002mm). Now they want to know why we are rejecting for low Cpk. Sigh... Rather than go through the tedium of carefully explaining what a distribution is, what it means, how to calculate it and what the calculation implies, etc., does anyone know of some websites I can point them to that can explain this? Any help is appreciated. Thanks, Ryan Grant --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------