Grahm: - The U.S. military standards (DOD-STD-2000 & Mil-Std-2000) had required that chip resistors with externally deposited elements be mounted with the resistive element facing away from the pwb. The major concerns at that time were: 1) leaving the resistive element "open" and available to precision (laser) trimming after mounting and 2) assuring that the resistive element was "open" to the action of whatever cleaning system was used (avoiding having flux or other process residue trapped between the resistive element and the pwb surface if the chip was mounted face-down). Heat dissipation was a concern too, but was considered less important than the above (if a chip needs max. convective cooling mount it on it's side [billboard] to expose the maximum surface to the environment - DISCLAIMER; other concerns apply to this type mounting.] - There was some discussion of this subject (face up/down) in the last meeting where Revision C of ANSI/IPC-J-STD-001 is being thrashed out. I believe the consensus, after all was said and done, is that there is not sufficient data to justify continuing to require that the resistive element be mounted facing away from the pwb surface (someone with a better memory may correct me on that). Anyway, I believe the new, revised, value engineered, issue of J- STD-001 will not require that the resistive element face away from the pwb. - Hope this helps some. Regards, Jim Moffitt, Moffitt Enterprises Consulting. ################################################################ TechNet E-Mail Forum 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's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################