Ed: Kovar and Invar are vary similar. Both are used for hermetic type applications in RF systems. But, as I said yesterday to you, the machining advice that I gave you is still valid. If you did not receive it let me know and I will resend it. Part of the reason that this material is so sensitive to machining with a good finish is that because of the Cobalt in the material. Tracy Black Design Engineer ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8d ############################################################## 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 Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ##############################################################