Patent Application
20070263352
1. Field of the Invention
The present invention generally relates to plastics and, more particularly, to plastic enclosures.
2. Background of the Invention
In general, plastic materials are fairly inexpensive, yet very versatile for use in manufacturing. Consequently, since around the middle of the twentieth century, the use of plastics in manufacturing has grown significantly. Indeed, plastic is now the most used manufacturing material in the world and products which include plastic are a common part of present day life. One of the many industries that have embraced the use of plastic is the electronics industry. Various plastic materials now are used to form a myriad of electronic device components, for example printed circuit boards, enclosures for electronic circuits and electrical insulators.
Electronic circuits tend to generate thermal energy (i.e. heat) during operation, mostly due to power losses in electronic components. In comparison to other materials, such as metal, plastic typically is not a very good thermal conductor. Thus, plastic is not very effective at conducting thermal energy away from electronic components. As a result, undesirable hot spots tend to form in regions immediately surrounding the electrical components that generate the greatest amount of thermal energy. It therefore would be desirable to reduce the temperature at those hotspots, while still using inexpensive and versatile manufacturing materials.
The present invention relates to a method of manufacturing a device housing. The method can include positioning within a mold an insert of thermally conductive film. For example, graphite film can be positioned within the mold. The graphite film can have a first thermal conductivity in an in-plane direction and a second thermal conductivity in a normal direction that is less than one-tenth the first thermal conductivity. For example, the graphite film can have a first thermal conductivity in the in-plane direction that is greater than about 150 W/m-K and a second thermal conductivity in the normal direction that is less than 15 W/m-K.
The method also can include injecting plastic within the mold such that when the plastic is set into its molded shape to form at least a first portion of the device housing, the plastic is bonded to the insert of thermally conductive film. When the plastic is set into its molded shape, the first portion of the device housing can include a surface having a first amount of surface area that is no greater than three times a second amount of surface area of a surface of the insert of thermally conductive film.
An electronic circuit including at least one thermal energy generator can be positioned into the device housing. The thermal energy generator can be positioned proximate to the insert of thermally conductive film.
The present invention also relates to a device housing that includes a first housing portion. The first housing portion can include an insert of thermally conductive film and a plastic housing member. The insert of thermally conductive film can include a graphite film. The insert of thermally conductive film can be bonded to the plastic housing member during a molding process in which the plastic housing member is set into its molded shape. The insert of thermally conductive film can include a first surface having a first amount of surface area. The plastic housing member can include a second surface having a second amount of surface area that is no greater than three times the first amount of surface area.
A first thermal conductivity of the insert of thermally conductive film in an in-plane direction can be at least ten times a second thermal conductivity of the insert of thermally conductive film in a normal direction. For example, the first thermal conductivity of the insert of thermally conductive film in an in-plane direction can be greater than about 150 W/m-K and a second thermal conductivity of the insert of thermally conductive film in a normal direction can be less than 15 W/m-K.
Preferred embodiments of the present invention will be described below in more detail, with reference to the accompanying drawings, in which:
While the specification concludes with claims defining features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the description in conjunction with the drawings. As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting but rather to provide an understandable description of the invention.
The present invention relates to a device housing that, while being molded substantially from plastic, is thermally conductive. More particularly, the device housing can include a first housing portion that is bonded to an insert of thermally conductive film during the molding process. The thermally conductive film can be, for example, a graphite film which has a thermal conductivity in an in-plane direction (i.e. parallel to the planar surface of the film) that is significantly higher than its thermal conductivity an a normal direction (i.e. normal to the planar surface of the film). Accordingly, thermal energy generated near a particular portion of the insert can be efficiently spread across the entire surface of the insert and then uniformly transferred to the environment.
Transferring the thermal energy in this manner reduces the maximum temperature of hot spots on the device housing and results in a uniform temperature distribution across the housing surface. The uniform temperature distribution improves user comfort while holding mobile devices, such as laptop computers, mobile telephones and personal digital assistants (PDAs). Moreover, reducing the maximum temperature of hot spots reduces the temperature of devices proximately located thereto, thereby extending the operating life of such devices.
In one arrangement, the thermal conductivity in the in-plane directions 215 can be greater than about 150 W/m-K while the thermal conductivity in the normal direction 220 is less than about 15 W/m-K. Thus, the thermal conductivity in the in-plane directions 215 can be greater than ten times the thermal conductivity in the normal direction 220. In another arrangement, the thermal conductivity in the in-plane directions 215 can be greater than 600 W/m-K while the thermal conductivity in the normal direction 220 is less than 6 W/m-K. This represents a ratio between the thermal conductivity in the in-plane directions 215 and the thermal conductivity in the normal direction 220 that is greater than one hundred to one. Still, greater in-plane thermal conductivities and lower thermal conductivities in the normal direction can be achieved and the invention is not limited to these examples.
The effectiveness of the insert 205 at dissipating heat from a particular hot spot can be roughly proportional to a surface area of the insert 205. Thus, in general, a larger insert 205 should provide better heat dissipation than a smaller insert. In that regard, the insert 205 can have a surface 225 which has a surface area that is at least equal to a substantial portion of a surface area of the housing surface 230. For example, the insert 205 can define at least one-third of the total area of the housing surface 230.
The insert 205 can be cut from a larger sheet of the thermally conductive film 210. The thermally conductive film 210 can be semi-rigid or pliable. In an arrangement in which the thermally conductive film 210 is semi-rigid, the insert 205 can be formed into a desired shape using known stamping techniques. In an arrangement in which the thermally conductive film 210 is pliable, the insert 205 can form to the shape of a mold to which it is inserted during the molding process.
After the insert 205 has been inserted into the mold 300 and secured into place, mold plates 315, 320 can be pressed together to substantially enclose a cavity 325 in which the insert 205 is contained. Plastic then can be injected through one or more channels 330 to fill the cavity 325 with plastic. As noted, the invention is not limited to the type of plastic that can be used. When the plastic sets into its molded shape, the plastic can be bonded to the insert 205 of thermally conductive film 210 to form the portion 110 of the device housing depicted in
The terms “a” and “an,” as used herein, are defined as one or more than one. The term “plurality,” as used herein, is defined as two or more than two. The term “another,” as used herein, is defined as at least a second or more. The terms “including” and/or “having,” as used herein, are defined as comprising (i.e., open language).
This invention can be embodied in other forms without departing from the spirit or essential attributes thereof. Accordingly, reference should be made to the following claims, rather than to the foregoing specification, as indicating the scope of the invention.
