Roger, in hearing the many discussions on this subject at J-STD-001 and IPC-A-610 meetings, I feel pretty confident in saying that height has nothing to do with failure mechanisms. Studies done by Roger Wild, Colin Lea and others showed that PTHs that had solder fill edges near the center of the PTH experienced fractures to the barrel plating and internal layer connections when there was a high degree of thermal stress applied (rapid rather than slow ramp rate). We have a bunch of the papers that the committee reviewed in electronic format available for download from our FTP site. It's a few MB worth, and you probably wouldn't want to do it with a slow modem connection, but let me know if you would like to review them and I'll tell you how to do it. Reply to my regular e-mail [log in to unmask] rather than here to the technet. Jack ========================================== APEX - the industry's premier trade show in Electronics Manufacturing, March 12-16, 2000, Long Beach, California. More information on website www.ipc.org/html/apex.htm ----------- Jack Crawford, IPC Director of Assembly Standards and Technology 2215 Sanders Road, Northbrook IL 60062-6135 [log in to unmask] 847-790-5393 fax 847-509-9798 >>> "Deakin, Roger" <[log in to unmask]> 09/13/99 08:54AM >>> HI ALL !!!! I HAVE A BACKPLANE WITH 14 LAYERS. THE PANEL IS 6.8mm THICK. IPC CAT 3 REQUIRES 75% FILL ON PECS WHICH ARE UP TO 3.8mm THICK ? MY QUESTION IS, WHAT DICTATES THE REASON FOR 75% FILL ? I WOULD LIKE TO ACCEPT THE PANEL WITH ONLY 40% FILL. THIS WOULD STILL HAVE A FILLET OF 2.72mm. WOULD THIS FAIL IPC-610 CAT 3 ? Regards - Roger Deakin. EMAIL [log in to unmask] TEL +44 (0)1983 202632 FAX +44 (0)1983 202106 COMPANY BRITISH AEROSPACE LAND AND SEA SYSTEMS NEWPORT ROAD COWES ISLE OF WIGHT PO31 8PF ENGLAND ############################################################## 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. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################