Hi Ted, What is the board thickness of your board design? You might want to increase the board thickness (2mm)...yes stiffener/ solid tray will minimise the issue. Hope things are going well for you. Regards GA Tan (Old Friend) ________________________________ From: TechNet on behalf of Ted Kong Sent: Tue 7/1/2008 4:59 AM To: [log in to unmask] Subject: Re: [TN] Bow PCAs Hi Ryan, I did run the board through with the narrower side. The interesting thing is that the board bowed upward. When I run the blank boards through twice, I don't see any bowing. I will consider the stiffeners if I can remove it the bow from other means. Thanks for everyone's reply. Ted --- On Mon, 6/30/08, Ryan Grant <[log in to unmask]> wrote: > From: Ryan Grant <[log in to unmask]> > Subject: Re: [TN] Bow PCAs > To: [log in to unmask] > Date: Monday, June 30, 2008, 12:35 PM > Hi Ted, > > The bowing is due to the weight of the heatsink/BGA combo. > > > By 175C, your boards are sure to have reached their glass > transition > temperature, which means, even though the board is still a > solid, it is > soft and malleable and can easily be distorted. The weight > of the > heatsink/BGA combo is causing the board to sag between the > oven rails. > > Rotate the board 90 degrees through reflow and the bowing > should go > away. 4 inches is usually the minimum conveyor rail width, > so you are > in luck, your board will still fit. > > If you don't think rotating the board is an option, > your other > alternative is Titanium board stiffeners that must be > attached before > reflow and removed afterwards. > > Thanks, > Ryan > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Ted > Kong > Sent: Monday, June 30, 2008 1:24 PM > To: [log in to unmask] > Subject: [TN] Bow PCAs > > Hi Technetters, > > I have a 14.5" x 4" PCB that bows after top side > reflow. I haven't > measure the actural bow amount yet, but it looks like it > will meet IPC > spec. However, I want to see what I can do to eliminate > it. > > I run a blank board through the same reflow profile and > don't see any > bowing. The production boards do not have any bowing after > bottom side > reflow. Bowing only occur after the top side reflow. I > believe the > bowing is due to the two 40mm2 BGAs on the board, which is > located 4" > from the long edge (center from the narrow width). Both > BGAs have large > heat-sinks attached to them. I reflowed three additional > boards on a 10 > zone reflow oven (instead of a 7 zone) oven, but didn't > see any > improvements. Can anyone give me any other suggestion on > how to > eliminate the bowing? Is my assumption of the cause > correct? > > Thanks all in advance. > > > Ted > > > > > --------------------------------------------------- > 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------