I look at it from a different perspective, reliability. If you populate (and reflow) warped boards, what happens to the solder joints when the boards are flattened when installed in the next higher assembly? Now that I think about it, probably nothing, since the solder will eventually relax. Right? But why else would there be a more stringent flatness requirement for SMT boards than TH since most P&P systems hold SMT boards down by the edges? Jim Marsico Senior Engineer Production Engineering EDO Electronics Systems Group [log in to unmask] <mailto:[log in to unmask]> 631-595-5879 -----Original Message----- From: Franklin D Asbell [SMTP:[log in to unmask]] Sent: Thursday, March 14, 2002 8:25 AM To: TechNet E-Mail Forum.; Marsico, James Subject: Re: [TN] Board Bow and Twist James, An afterthought, the bow and twist requirement is there to provide ease of board population as well as end use fit. If the board is warped prior to assembly, this indeed would affect population thus potentially making the boards unsuitable for end use...just something to think about, or pass along to your supplier. Franklin ----- Original Message ----- From: "Marsico, James" <[log in to unmask]> To: <[log in to unmask]> Sent: Thursday, March 14, 2002 6:48 AM Subject: [TN] Board Bow and Twist > I think this is a no-brainer, but here goes... We were delivered boards in > panel form from one of our suppliers. At Incoming Inspection, the panel was > rejected for excessive bow (>75% for SMT) and returned the supplier. The > supplier called me and said that even though the panel exceeded the bow > requirement, the individual boards were acceptable. When I quoted the bow > and twist requirement from IPC-6012, "Panels which contain multiple printed > boards which are assembled on the panel and later separated shall be > assessed in panel form." , he said yes, you measure the individual boards in > the panel. I need clarification. > Thanks, > Jim Marsico > Senior Engineer > Production Engineering > EDO Electronics Systems Group > [log in to unmask] <mailto:[log in to unmask]> > 631-595-5879 > > -------------------------------------------------------------------------- ------- > 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 e-mail to [log in to unmask]: SET Technet NOMAIL > To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest > 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 e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest 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 ---------------------------------------------------------------------------------