The diagram here shows the various paths for thermal resistance of an IC. The colors on the circuit on the left correspond to the various sections of the IC on the right. From the chip temperature T_j, the circuit network extends through the thermal resistances indicated to reach the ambient (surrounding environment) temperature T_A. The path surrounded by the dashed red line is the main path for heat dissipation in the case of surface-mounting on a printed circuit board (PCB). Specifically, heat is transmitted from the chip via the die bond to the exposed pad, and then via solder on a land of the printed circuit board to the printed circuit board. This heat is then transmitted from the printed circuit board to the atmosphere (T_A) by convection and emission or radiation. As another transmission path, heat from the chip passes through bonding wires to the lead frame and then to the printed circuit board, followed by convection and emission or radiation. In a further path, heat from the chip passes through the package and is dissipated by convection and emission or radiation. Thermal design involves reducing various thermal resistances such as those described here, such as reducing thermal resistance of heat dissipation paths from a chip to the ambient atmosphere. As a result, T_j is lowered and the chip reliability is improved.