Heat sink and method of making same

#The subject invention relates to the control and reduction of thermal gradients, and, in one example, to a heat sink which may be used in a phased array radar system.

#Phased array radar systems employ amplifiers and phase shifters to electronically steer radio frequency (RF) beams, in contrast to the more familiar rotating radar dish. By using phase shifts, phased array radar systems eliminate the time delay between signals that is typically associated with rotating systems as the dish rotates 360°. Thus, phased array radar systems result in improved performance.

#One key parameter governing the RF performance of a phased array radar system, however, is the temperature or thermal gradient at all levels of the system. This is due to the fact that the RF performance changes with temperature. The gain and the phase shift of an amplifier each change with a change in temperature. The gain changes approximately 0.1 dB/° C. and the phase changes approximately 0.8°/° C. Thus, controlling thermal gradients in phased array radar systems is an important and challenging requirement to meet.

#Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:

#FIG. 1 is a schematic representation of fluid temperature increase in a typical heat sink or manifold;

#FIG. 2 is a schematic cross-sectional side view of one embodiment of a heat sink in accordance with the subject invention;

#Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.

#As discussed in the Background section above, thermal gradients occur in fluid cooled heat sinks because, as the fluid travels through the heat sink, it picks up heat from the heat sources. Consequently, the coolant further downstream is at a higher temperature. This condition is shown schematically in FIG. 1. In this example, for an isothermal heat sink, it is desirable that the temperature at all points of surface 10 of heat sink wall 14 should be the same. In one example, the temperature at location 11 of surface 10, namely Tsurface-1, and the temperature at surface location 12 of surface 10, namely Tsurface-2, should each be 32° C. In such a case thermal gradients on cooling surface 10 would be eliminated.

#With typical heat sinks, however, as coolant flows in the direction of arrow X in channel 15, it picks up heat from the heat sources 16 on cooling surface 10. The temperature of the coolant or fluid Tcool-in nearer the entry point or upstream 18 of manifold or heat sink 20 is thus lower than the temperature of the coolant Tcool-out farther downstream or closer to the exit 22 of the manifold 20. In the case of a typical coolant where the specific heat remains constant, if Tcool-in is 20° C. for example, Tcool-out will be 28° C., or 8° C. warmer than Tcool-in. This results in less effective cooling downstream and a consequent thermal gradient because Tsurface-2 ends up much greater than the desired 32° C.