Thermount is a registered trade name. A web search of Thermount will give huge blocks of info. The following is my experience. Thermount advantage is XY CTE in the 7-9 range verses FR4 of 13-15. Unlike the "fiberglass weave" or E-glass FR4 Thermount dielectric (B & C stage) uses Kevlar. The Thermount differs in the "Ole Kevlar" configuration in that it is non woven. [Non woven is an odd word, it is akin to referring to wooden particle board as "non woven."] The reason for the Kevlar "bits" is to eliminate or greatly reduce the large Z axis expansion of the woven configuration. There is the ability to have PWBs built in either Polyimide or Epoxy Thermount configurations. Two cautions from my own experience; Thermount is high in moisture absorption and being non woven the CTE is effected by copper percentage (adjacent to plane will exhibit higher CTE numbers). A lesson learned for me is increase the worst case dielectric distance between outside diameter of plated through hole barrel and clearance of plane. The small quasi spheres of Kevlar can be dislodged at or after drill and (be it ever so small) the Z axis expansion is still present albeit relative to itself. I am a Apps Eng for Coretec and we build Thermount all the time (www.coretec-inc.com) as well as other shops, it is not that exotic. Alternatives to Thermount are the good ole CIC which is a Texas Instruments Tradename for a trimetal (Copper Invar Copper) contained inside the PCB that acts as a constraining layer or layers with dual function as electrical planes (also manufactured by Coretec at our SAS facility). My favorite method to "manage" these pesky LCCC's... never use more than a 28 pin device (okay, maybe 32... but that's upper limit) AND when you do go higher than 28 attach leads (I like Penn, they do a nice job). LCCC's (especially high pin count) are usually thermally hot, make sure your thermal plan is a systems approach... Sorry for the shameless company plugs... Boston Brad 781 858 0783 --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------