Colleagues, We have occasional boards (just a few from a batch of 200 or more) warp quite badly following reflow. The boards concerned are about 270mm x290mm (10.5" x 11.4") Is there any logical explanation why this happens? The boards are supplied flat, so it would appear there is a built in stress factor which gets relieved when the board is heated or there is some unequal expansion/contraction occuring across the layers. Can this be down to a mixed warp and weft of the glass in the outers during the layer build? > Thanks, > > Nigel Burtt > Production Engineering Manager > Dolby Laboratories Inc - European HQ > Email: [log in to unmask] > Tel: +44 (0)1793 842132 [direct line with voicemail] > Fax: +44 (0)1793 842101 > > --------------------------------------------------------------------------------- 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 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 ---------------------------------------------------------------------------------