After drafting a response with a snotty tone, I took a look at the TM 2.4.22. And I find that years of my participation on the Test Methods Subcommittee unfortunately did not include consideration of the deficiencies of this TM. So, hopefully my "restructured" comments will help: You are looking for a quantification of deviation from absolute flatness. The value will be relative to the size of the subject, whether it's laminate, bare board, bare board array, or assembly. If you're testing laminate panels of 18"x24", a .045" deflection of the panel off a flat surface is not a big deal: less than .2% (.045 divided by 24" (the dimension that is out-of-flat, usually the longest) times 100). However, a 4x6" board with a .045" bow figures out to .75%, the max generally allowed for SMB's. The procedure is pretty much as per 2.4.22: - Flat surface - Feeler gauges to measure max deflection from supporting surface - Identify whether the non-flat condition is bow or twist - For twist, hold down 3 corners and measure deflection under the 4th - Calculate % deflection: Bow: Deflection/(Dimension affected) x100 Twist: Deflection/(Dimension from lifted corner to diagonal corner) x100 - Per Tom G's response, assemblies or even bare boards that have bottom-side protrusions may have to have the corners set on spacers of equal thickness. Then simply subtract the spacer thickness from the measurement of deflection before calculating %. Jim Paulus -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Tom Gervascio Sent: Wednesday, October 06, 2004 8:53 AM To: [log in to unmask] Subject: Re: [TN] Twist & Bow I would suggest taking the desired board and place three 0.125 inch high spacers at the three corners of the board on a granite table. All three spacers must be exactly the same height and the height must be known. The board should now be elevated off the table by a known height (the spacer height) . Not you can use a surface gage to run along the edges of the board and determine the variation in height. The actual calculations for warp and twist are contained in IPC-TM-650 Test Method 2.4.22.1c. It can be downloaded from http://www.ipc.org/4.0_Knowledge/4.1_Standards/test/2.4.22.1c.pdf >>> [log in to unmask] 10/06/04 09:35AM >>> I too placed an inquire to the TechNetters about this Task. I did not receive an adequate response. Good luck Victor, -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Karnwal, Pankaj Sent: Wednesday, October 06, 2004 7:14 AM To: [log in to unmask] Subject: [TN] Twist & Bow Dear Technetters hello, Any body have the procedure for measuring the twist & bow as IPC 610 B says the .75% allowed for SMD populated module. how we measure this .75 % , in respect to what ? BR Pankaj Karnwal Jr. Engineer QA Barco Electronics System (P) Ltd. mailto:[log in to unmask] www.barco.com --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 847-509-9700 ext.5315 -----------------------------------------------------