Modeling of vapor chamber as heat spreading devices

As the heat density on the chip increases and heat dissipation is more localized, there are growing interests in developing alternative heat spreading devices. Vapor chambers have been used as heat spreading devices in heat sink bases. Before considering for integration into package heat spreaders or lids, the compatibility of the vapor chamber with the assembly processes would have to be assessed. However, before embarking down that path, this paper attempts to quantify the thermal benefit, if any, of vapor chamber heat spreaders compared to commonly used solid metal heat spreaders. A thermal model has been developed consisting of a heated chip integrated with a substrate, thermal interface material, vapor chamber lid and heat sink. The vapor chamber is represented by multiple block layers with effective thermal conductivities. It is revealed that the model can predict the temperature profile fairly well as compared with the results of a detailed numerical model. A sensitivity study shows that the thermal performance is sensitive to the effective thermal conductivity of the wick structure and insensitive to the effective thermal conductivity of the vapor space. A parametric study indicates that the vapor chamber heat spreader out-performs a copper block of the same dimension when the footprint size is larger than a certain value. It is concluded that vapor chamber is most effective in spreading heat over large areas. Consequently, it is suitable for applications where more surface area is desired due to reasons such as low heat transfer coefficients