Thermal design for high-speed high-density multichip module

The boundary conditions of models for finite element analysis of the thermal design of high-speed high-density multichip modules are examined, principally the thermal via and heat sink, and a model that improves the accuracy of heat transfer analysis simulation is investigated. It is found that in evaluating the effectiveness of thermal vias in heat loss, simulation can be made to yield results close to observed values by considering the substrate a compound material with a uniform thermal conductivity coefficient determined by the ratio of thermal via cross section area to substrate area. A thermal via area ratio of 10% is satisfactory both from the standpoint of manufacturing and for effectiveness in decreasing thermal resistance. Also, in the present model the heat transfer coefficient of the heat sink can be determined by using air speeds and comparison with observed results. It is concluded that the model is capable of highly accurate simulation of thermal via and heat sink conditions and can be effective in the thermal design of high-speed, high-density multichip modules