Hi James and other Technetters, I've been following this subject on the forum and Just have to put in my two cents. The comments from both Earl Moon and Kelly Schriver are very pertinent. I understand the Heat pipe scenario well, but have some concerns about the open via contracting contaminates. We have built a number of boards with constrained/thermal cores and usually follow the path mentioned by Kelly. In the early '80s, we tried to fill with solder, but could never get the solder to stay in place. Two concerns with solder are: 1) during assembly the solder may wick away solder from a joint making a poor interconnection, and 2) as in the case that we tried early on in the SMT effort, is that during assembly it will errupt out of the hole and create all sorts of problems, among which are shorts. We found that our best approach was to fill the via with a thermally conductive/electrically insulating epoxy. There are several sources of these materials available in the industry. It's not much but there's my two cents worth! Regards, Les ################################################################ 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 ################################################################