Thermal force has proven to be a useful concept for managing the package-level thermal placement problem. However, the previous thermal force model is based on insulated edge boundary condition; thus it is only suitable to face-cooled packages. A general thermal force model is proposed to extend the applicability of the thermal force to cover general cooling conditions by introducing the concept of the heat transparency of a boundary τ. By managing τ, the present method generates a series of thermal-force-equilibrium placements fitting to situations from face-cooled to edge-cooled packages. Experimental results indicate that for generating the reliability-best placements, the best τ's are in the range 0 ≤ τ ≤ 0.05 for face-cooled packages and in the range 0.1 ≤ τ ≤ 0.25 for the volumetric-cooled packages. For edge-cooled packages, the best τ's are the largest values of τ that can achieve convergent thermal-force-equilibrium placements.