Lee, If you are talking room temperature measurement, then a good, non-contact CMM will do nicely. At elevated temperatures Moire and Digital Image Correlation (DIC) methods can be employed. Bev ________________________________ From: Lee parker <[log in to unmask]> To: TechNet E-Mail Forum <[log in to unmask]>; Bev Christian Sent: Mon Jul 13 14:37:02 2009 Subject: Re: [TN] Maximum Allowable Bow & Twist for PWB-PCB Bev and Richard How do you suggest we measure to local bow and twist? Best regards Lee J. L. Parker Ph. D. JLP Consultants LLC 804 779 3389 ----- Original Message ----- From: Bev Christian <mailto:[log in to unmask]> To: [log in to unmask] Sent: Monday, July 13, 2009 12:53 PM Subject: Re: [TN] Maximum Allowable Bow & Twist for PWB-PCB Richard, Correct as usual, Richard. This was always a big deal at Nortel where completed circuit packs would have to be slotted into card cages. Bev On vacation ----- Original Message ----- From: Stadem, Richard D. <[log in to unmask]> To: [log in to unmask] <[log in to unmask]>; Bev Christian Sent: Mon Jul 13 11:06:30 2009 Subject: RE: [TN] Maximum Allowable Bow & Twist for PWB-PCB Bev, I totally agree with you, but the point they are getting at in IPC 2221 is that no section of the PWB should have more than .75% per inch as a rate of warpage, extending in both the X and Y directions, after reflow. This is because if you have more warpage than that you are putting a stress on the resultant solder joints that leads to a reduction in reliability, especially with a lead-free joint and also especially if you need to straighten the CCA when mounting it into a chassis or frame. I think this specification, like so many others that were based on leaded solder, should be revisited for unleaded solders. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian Sent: Friday, July 10, 2009 3:24 PM To: [log in to unmask] Subject: Re: [TN] Maximum Allowable Bow & Twist for PWB-PCB I contend this is old school and if you aren't measuring warpage at reflow temperatures how do you know you aren't suffering from head on pillow? I suggest the term head in pillow be dropped because you don't actually put your head IN a pillow. Bev RIM PS Waiting for my Dewism. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard Sent: Friday, July 10, 2009 4:20 PM To: [log in to unmask] Subject: Re: [TN] Maximum Allowable Bow & Twist for PWB-PCB IPC-2221 5.2.4 ... Unless otherwise specified by master drawing, max bow and twist shall be 0.75% for boards that use surface mount components and 1.5% for all other board technologies. ... Values are measured as per IPC-TM-650 Method 2.4.22 Genny Gibbard, P. Eng Manufacturing Engineer, Vecima PTS dept. x.4229 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez Sent: July 10, 2009 2:15 PM To: [log in to unmask] Subject: [TN] Maximum Allowable Bow & Twist for PWB-PCB What is the maximum allowable Bow & Twist value? Not able to locate in IPC-2221, 2222, & 6012A Victor, --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------------------------- This transmission (including any attachments) may contain confidential information, privileged material (including material protected by the solicitor-client or other applicable privileges), or constitute non-public information. 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