This chapter discusses the use of ceramic interconnects for heat transfer and mechanical support. Thermomechanical design is a vital part of the design process and needs to be addressed early in the design of the chip and its packaging. Packaging trade-offs need to be evaluated early enough so that an optimal design is achieved. Heat sinks are used to increase the surface area exposed to the air or other cooling gas. They are the final interface between the heat generating devices and the outside world. Thermal vias in low-temperature cofired ceramic are fabricated in the same manner with the same constraints as in multilayer thick films. Multilayer thick-film substrates use screen-printed glass as the dielectric material. The glass is both an electrical insulator as well as a thermal insulator. The goal in performing a thermal simulation is to determine the temperature distribution within a medium with the given boundary conditions.