Thermal evaluation of standard and power TQFP

In this paper, thermal performance of Standard and power TQFP packages is investigated. CFD simulation is performed to study the effects of board and package construction, and power package copper slug direct attach to the board. Thermal paths are analyzed by viewing the heat dissipation percentage through package surfaces. The following conclusions can be made from this study: (1) For most plastic packages at a given power dissipation and cooling condition, the temperature drop from junction to board is only dependent on package construction. The temperature drop from board to ambient is a function of board construction. Junction to ambient thermal resistance can be obtained by superimposing the two parts. (2) In general, the dominant thermal path for plastic packages is conduction through leads to PCB. (3) The thermal resistance for the Power TQFP is 13°C/W lower than that of the standard TQFP. (4) Power TQFP slug direct attach to the board reduces the thermal resistance by 45%. (5) Copper pad and thermal vias under the package will reduce the thermal resistance up to 2.7°C/W (7%) for the Power TQFP. Using smaller package stand off results in 5°C/W (13%) thermal resistance reduction