Mike, I should know better than to say such foolish things as you can't, etc. Sometimes you can, and someone will do it. I should have said 12 and 14 layer .062" thick boards offer particular challenges. When fabricating a 12 layer board .062" thick, lots of 5 core, and a little 4 core stuff, along with lots of 5 mil preg must be used. The 4 core and 4 mil preg is ideal if used throughout as it should be single ply 2113 material with a near ideal resin to glass ratio meaning it has enough glass to make the structure highly dimensionally stable and enough resin to provide lots of laminate integrity. 5 mil stuff often is composed of two plies of 1080 material with very high resin content, really juicy and sticky, making it not dimensionally stable but having very high inner laminar bond strength. This could go on forever so I'll just say if you use all 4 mil dielectrics, you will be on the low side of .062 when using .5 oz copper throughout. You will have a great board however. If you use all 5 mil stuff with the same copper weights, you will have a monster slipping and sliding in the press board with little chance of having pads line up for drilling - and on it goes. Of course, you could use all 1 oz copper foil with 4 mil dielectrics and nearly get to the desired thickness. Hell, this is too much even for me. It's just that there are too many compromises involved to effect really high yields for 12 and 14 layer 62 mil thick boards. Therefore, you pay more for the thickness and you may not get your impedance requirements, and you may wish for a thicker or thinner board to make it all go away. If you're really happy, then this is a waste of time. I think I wasted words anyway so enjoy your boards as they are. Earl --------------------------------------------------------------------------------- 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 the following message: SET Technet NOMAIL 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 ---------------------------------------------------------------------------------