Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2003-04-30
2004-04-20
Chervinsky, Boris (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S699000, C257S714000, C165S080400, C165S104210
Reexamination Certificate
active
06724626
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to portable electronic devices and, more particularly, to thermal management in such devices.
BACKGROUND OF THE INVENTION
Portable electronic devices, such as portable computers, cellular telephones, etc., are becoming more widespread as the convenience and utility of such devices become more apparent. Along with the increasingly widespread use of such devices, new capabilities and functionalities of those devices are being developed that require higher processing capacity. In order to make an electronic device more powerful (to possess greater processing capacity), additional transistors within components of those devices are usually necessary to accommodate more computational operations in a given amount of time. Alternatively, the frequency of calculations made by the transistors may be increased to produce greater computational operations. In portable electronic devices, the number of transistors may be increased by adding additional electronic components, or by increasing the number of transistors on an existing component. Adding components in such devices is usually not desired because doing so requires more circuit board space and, accordingly, a larger device. Therefore, increasing the processing power in such portable devices is typically accomplished by 1) adding transistors to existing components, 2) by increasing the computational frequency of existing transistors, or 3) by utilizing a combination of both approaches.
Heat dissipation is of paramount importance when designing increasingly powerful electronic devices. This is because increasing the frequency or increasing the number of transistors can lead to more heat generated by the electronic component. This concern is especially paramount in portable devices because, typically, the electronic components are contained within a relatively small, confined housing that makes adequate cooling difficult to achieve.
Various attempts have been made to address heat dissipation problems in portable electronic devices. For instance, in portable computers, various configurations of heat sinks, fans and other devices are traditionally used. In some applications, a heat sink is connected to a heat-generating component, such as a central processing unit (CPU) or a graphics processing unit (GPU) disposed on a circuit board within the computer. Heat sinks operate based on the principle that heat is dissipated at a lower temperature over a large surface area as compared to that dissipated over a relatively small surface area. The heat sink, therefore, has a physical geometry (e.g., heat conducting fins disposed on a heat conducting substrate), that creates a large total surface area. Thus, when heat is transferred from the CPU or GPU to the heat sink, heat is dissipated at a lower temperature due to the large fin surface area relative to the case where no heat sink is used.
Fans have also been used, either alone or in conjunction with a heat sink, to provide airflow over the heat-generating component/heat sink. Heat is transferred to the air as it flows over the component, thus cooling the component. However, as greater processing power has been introduced to components in portable electronic devices, such as the exemplary CPUs and GPUs in portable computers, fan-based and heat-sink based cooling solutions have proven undesirable in some instances, either because of insufficient cooling or because of increased noise due to an excessively high fan rotation speed needed to cool the heat-generating component. Therefore, more recently, other attempts have been made to cool these components.
In one such attempt, liquid cooling has been used to remove heat from heat-generating components. In these attempts, a reservoir of liquid (e.g., water) is used that is relatively cool compared to the heat-generating component. Hollow tubes are used with a small pump to transport the liquid to a heat spreader that is connected to the component. When the component is heated, this heat is transferred to the liquid within the heat spreader. The pump causes the water to circulate back to the reservoir where the heat is dissipated. As is obvious, the cooler the temperature of the liquid in the water reservoir, the more heat that can be dissipated. This cooling method has achieved significant reductions in the temperatures of heat-generating components in computers, especially in desktop-based systems. However, this method is less useful in portable electronic devices, such as portable computers because, while liquid cooling can achieve significant heat dissipation, such systems tend to greatly increase the size and weight of the computer if the reservoir is internal to the computer. Additionally, these active pumps may also add cost and decrease the reliability of the cooling system and, hence, the portable device itself. In the case of a portable computer, any such reservoir will be necessarily limited to a relatively small size and, therefore, will only be of limited effectiveness in cooling components within the computer. While an external reservoir could be used, portable computers generally are not manufactured with the necessary components to interface a heat-generating component with such an external reservoir. Since disassembling a portable computer can be technically challenging (compared for example to a desktop computer), such an interface would be difficult to achieve.
In another recent attempt to cool portable computers, phase-change devices have been used. Such devices take advantage of the fact that it takes a significant amount of thermal energy to change a substance from one physical state to another. These devices can utilize either a liquid-gas phase change or a solid-liquid phase change.
One example of a liquid-gas type of phase-change device is a device known as a “heat pipe.” A heat pipe typically uses one or more hollow tubes (or pipes) to transport heat from one point to another (e.g., from a heat-generating component to a cooler location). Such devices usually are connected to a heat spreader device that is connected to the heat-generating component. The hollow tubes are used to transfer the heat from the heat spreader to a heat sink located at a cooler location (e.g., near a vent in a computer). The hollow tubes are typically filled with a fluid, such as distilled water. Typically, the liquid is at a very low pressure because the tube itself contains very little fluid in order to reduce the evaporation point of the liquid. In the portion of the heat pipe that is in contact with the heat spreader, the heat from the heat-generating component causes the water to evaporate. The vaporized water transports the heat through the hollow tube(s) to the aforementioned heat sink. Once in the heat sink, the evaporated water cools, condenses and returns to the heat spreader as a liquid via the hollow tubes. The same amount of heat is removed as in previous attempts however, because of the evaporation/condensation process, far less temperature difference between the heat generation component and the heat sink is required.
However, such heat pipe devices are limited in their usefulness. Specifically, such devices cannot transfer the amount of heat generated by many kinds of components, such as state of the art CPUs. Thus, this solution may be insufficient to cool components with an extremely large number of transistors or transistors that operate at a very high frequency. Additionally, the heat sink of such heat-pipe devices must usually be in a higher position than the heat spreader. With portable computers this may be problematic as the geometric form of such computers is such that it may not be possible to place the heat sink in this position.
Another example of a liquid-gas phase change device used with computers is a compressor- or refrigerator-based device. These devices work much the same as the heat pipe type system, discussed above. Similar to a heat pipe device, refrigerator-based systems remove heat from a heat-generating component with a heat spreader connected to hol
Hodes Marc Scott
Lyons Alan Michael
Chervinsky Boris
Herring David W.
Lucent Technologies - Inc.
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