The design of electronic packages and systems must address electrically generated heat dissipation within operating devices to ensure proper operation. For example, most electronic devices must be maintained below predetermined maximum temperatures to allow acceptable performance and reliability. With regard to microwave electronic systems (e.g. power amplifiers, phase shifters, low noise amplifiers), electronic components may also be sensitive to temperature gradients between associated electronics devices, for example monolithic microwave integrated circuits (MMICs). Such components must be maintained within predetermined maximum temperature gradients from device to device.
Accordingly, cooling systems are typically incorporated into such electronic systems. Cooling systems are configured to absorb heat and lower the temperature of the electronic system generally, and resist excessive temperature gradients between particular devices of the electronic package. A typical cooling system often includes a metal cold plate coupled with electronic devices. Oftentimes, the cold plate contains brazed-on finstock to increase the heat transfer surface area. This solution is very expensive and requires a complicated design and fabrication procedure for the cold plate.
Another approach utilizes a liquid coolant routed through channels embedded in the cold plate, in order to accommodate heat transfer from the electronic devices to the liquid coolant. This eliminates the need for expensive finstock brazing. However, the power, density and sensitivity of today's electronic packages has limited the efficiency and practicality of this approach.
One example of the foregoing type of system is a phased array antenna system. Phased array antenna systems are used in a wide variety of applications and often include electronics systems with integral cooling systems. In a phased array antenna system it is desirable that the antenna system be relatively small in volume and relatively light in weight. Antenna systems of this type often include MMICs, which generate a substantial amount of heat during operation. As the frequency of antenna operation increases, there is an increase in the amount of heat which is emitted by these circuits, which in turn can affect temperature gradients across the array.
In particular, in a phased array antenna system, the existence of temperature gradients across the array can produce phase errors, which affect the accuracy of the antenna system. The higher the frequency of antenna operation, the smaller the permissible temperature gradients across the array. For example, where the phased array is operating at a frequency of about 5 GHz, the maximum allowable temperature gradient across the array is about 20° C. In contrast, when the array is operating at a frequency of about 80 GHz, the maximum allowable temperature gradient across the array is only about 1.3° C. Thus, it is important to have an efficient cooling system, so that a substantially uniform temperature is maintained across the array.
As a further complication, many electronic systems have a limited supply of coolant available for the cooling system. For example, various different cooling systems on an aircraft often share a common cooling system, and a particular system's access to the coolant is limited. The performance of such systems often suffer from low coolant flow rates which provide limited heat transfer ability. Furthermore, low volumetric flow rates result in a significant temperature rise in the coolant as it flows from an inlet to an outlet of a cold plate. Rising coolant temperatures result in undesirably large temperature gradients between various portions of the electronic system.
In order to overcome this, complex fluid manifolds have been designed in order to allow each device to be cooled with only its proportional amount of coolant, in a completely parallel distribution. However, this approach is bulky and fundamentally less efficient from a heat transfer standpoint because of the low fluid coolant velocity.