Robert, At this point, it sounds like you are confined to maximizing convective heat transfer, which means maximizing external surface area and maximum draft currents within the enclosure. The first order of business is to spread the heat away from the component body a fast as possible meaning large copper pad areas with as many thermal vias tying to planes as possible. You didn't mention the package type or material but a thermally conductive epoxy bonding the component case to the pwb might be helpful, otherwise heat transfer to the pwb will be through the leads. EG&G offers a heat sink which solders directly to a heat spreading pad (to which the component is mounted). This might be a good option if you have adequate clearance. Also, as you mentioned, large external copper areas serve as good convective surfaces. Try to position the hot components at the inlet air side of the pwb and refrain from placing large components, which can block airflow, in front of it. Position the inlets and exhaust openings in the enclosure to maximize the chimney effect across the hottest modules. Are there air filters on the enclosure which restrict air flow? Are items placed in the enclosure in a manner which promotes optimal system cooling? It's tough solving problems like this through an E-mail forum considering the limited information available but I hope some of this was useful. Good luck! Mike 0000000000000000000000000000000000000000000000000000 Mike McNulty Lockheed Martin GES Moorestown NJ Phone:(609)722-7323 Fax:(609)722-2207 [log in to unmask] 0000000000000000000000000000000000000000000000000000 I need some help for a colleague on thermal dissapation. A design with one mother board and three daughter boards, ALL with 10 lbs in a 5 lb container. The daughter boards are all within a half inch of motherboard. Needless to say when running inside the box after awhile things tend to get somewhat hot approx 125 degrees C. If outside in open air the temp drop is only about 15 degrees C. They do not want to use fans and conventional heatsinks seem out. A thermal plane on both outside layers is being considered realizing that although you may be able to solder the board once rework is out. Is there any suggestions out there in the board material. I suggested liquid cooling ha ha. I don,t now of any other means of bringing the temp down that much without fans. Any help would be greatly appreciated. The mechanical designer asking me this is supposed to do something with the enclosure, but no fans are being considered. He has no other ideas either. Thanks up front. I could not believe anyone would try and cram that much electronics in such a small area with no thought for heat untill after the design was done. The desity is double sided surface mount with thru hole jammed on all four boards. P.S. I could really use this help ASAP so E-Mail or Phone would be great. Robert M. Wolfe 203-882-6405