Substrate Embedded Heat Pipes Compatible With Ceramic Cofire Processing

A prototype miniature heat pipe has been fabricated that is compatible with MCM-C processing using post-fired alumina substrates. A heat pipe was constructed as a laminate structure using thick film dielectric (glass) paste to hermetically bond the layers together. Capillary pumping action was provided by an axially grooved wick fabricated in alumina by laser patterning. The working fluid for the heat pipe was water. The axially grooved heat pipe was found to have an effective thermal conductivity exceeding 3000 W/m-K which is over 100 times higher than the alumina it replaced within the substrate.. Heat pipe chandlers were fabricated in high temperature cofire ceramic to assess sag in the layers above and below the channel. The sag was found to be minimal and acceptable for multilayer cofire applications.