Technetters I am in agreement with Dave that the greatest cause of board bow and twist is board design. Also if you look in IPC-6012 Para. 3.4.4, you will note that the flatness requirement for all Classes is 0.75% max. for surface mount and 1.5% max. for through-hole. The design specification, IPC-2221 series, has the same numbers and this spec. which replaces IPC-D-275 will be issued in the near furture Phil Hinton ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ##############################################################