Patent Application
20080310119
As integrated circuit and similar technologies have improved, greater functionality has been incorporated into devices. Along with this expanded functionality, the size of devices has diminished, resulting in higher clocking frequencies and increased power dissipation per square area. As a consequence, today's integrated circuit devices generate more heat while possessing smaller surface areas to dissipate the heat. Therefore, it is useful to have a high rate of heat transfer from the integrated circuit package to maintain the temperature of the integrated circuit within safe operating limits. Excessive heat may adversely affect the performance of the circuit, cause permanent degradation of its components, and increase failure rates.
A heat exchange with a heat sink may be used for transferring heat away from a heat source, such as an electronic component or printed circuit board (PCB), to maintain the component within an optimum operating temperature range, so that the component can operate continuously and with maximized efficiency.
Conventional heat sinks typically contain a plurality of fins or rods that extend from a base that contacts the heat generating integrated circuit. Some heat sinks employ securing mechanisms that enlarge or exceed the heat sink envelope. This increases the footprint of the electronic component/heat sink assembly, thereby reducing the surface area of the PCB available for mounting elements and potentially imposing a limit on the height of nearby elements on the PCB.
One embodiment of a heat sink, and corresponding method for removably securing the heat sink, comprises a contact plate with a conduction side and a convection side. The conduction side is configured to be in thermal communication with a heat generating device. Extending outward from the convection side of the contact plate are a plurality of thermally conductive elements. The example heat sink includes spring clips with an elasticity to enable bending outward from the contact plate. The spring clips, due to their elasticity, self-restore inward toward the contact plate to self-couple the heat sink with the heat generating device.
The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention.
A description of example embodiments of the invention follows.
Conventional heat sinks and clips for their attachment are inefficient, expensive to produce and bulky. Conventional heat sinks typically include both a body and a fastener. That fastener may be a curved piece that applies pressure on an electronic component to which the heat sink is applied when installed. However, such fasteners reduce the available convection surface area of heat sinks, thereby reducing their efficiency. Other conventional heat sinks employ spring action for securing the body to the electronic component, but require special modification of the PCB. Further conventional heat sinks require screws, push pins, clips, anchors, or other forms of mechanical attachment that are additional parts beyond the body, itself, that take up valuable surface area on the PCB and block air flow to the convection surfaces of the heat.
Further, conventional methods of securing a heat sink to an integrated circuit or other heat generating device can weaken ball grid array (BGA) solder connections between the integrated circuit and the PCB through application of stresses. In a BGA, balls of solder are stuck to the bottom of the package, here the integrated circuit package, which is placed on a PCB that carries copper pads in a pattern corresponding to the solder ball pattern. The assembly is then heated, either in a reflow oven or by an infrared heater, causing the solder balls to melt. Surface tension causes the molten solder to hold the package in alignment with the circuit board, at the correct separation distance, while the solder cools and solidifies. Conventional clip-on heat sinks apply a bending moment to the heat generating device, which stresses the solder balls-to-PCB connections and decreases component reliability or useful life. Without a heat sink, the outer balls will generally fail over time due to heating and inherent stresses. By adding more stress through an application of a heat sink, failures will occur even quicker and more often.
According to an example embodiment of the present invention, a heat sink, and corresponding method for removably securing the heat sink, comprises a contact plate with a conduction side and a convection side. The conduction side is configured to be in thermal communication with a heat generating device. Extending outward from the convection side of the contact plate are a plurality of thermally conductive elements. The example heat sink includes spring clips with an elasticity to enable bending outward from the contact plate. The spring clips, due to their elasticity, self-restore inward toward the contact plate, via a restorative force, to self-couple the heat sink with the heat generating device.
The spring clips may be configured to bend substantially laterally outward from the contact plate. Further, the spring clips may extend outward from the convection side of the contact plate, and may so extend at respective edges of the contact plate and return toward and below the respective edges of the contact plate.
The spring clips may include tabs extending, at least, partially under the heat generating device. The tabs may apply a securing force to the underside of the heat generating device to minimize or prevent vertical movement of the heat sink on the heat generating device. The tabs may be angled relative to or substantially parallel to the conduction side of the contact plate.
The spring clips may include a central portion and legs separated by the central portion by respective slits. The legs may apply a securing force to an edge of the heat generating device to minimize or prevent horizontal movement of the heat sink on the heat generating device. The central portion may be configured to contact the heat generating device in a clamped state. The legs may be configured to be in an unclamped state while the central portion is in the clamped state.
A combination of the spring clips and the contact plate may exert forces on the heat generating device in a manner that does not affect a mechanical arrangement between the heat generating device and a member to which the heat generating device is coupled, such as a PCB. At least some of the forces exerted by the combination of the spring clips and the contact plate may be exerted laterally inward, diagonally upward, or vertically upward on the heat generating device.
The thermally conductive elements may provide more convection surface area than plate elements with flat surfaces, and may be configured to increase airflow across them.
The spring clips may also define slots to provide openings for a tool to bend the clips at a bend between the portion of the spring clips that extends outward and that portion that returns toward and below the contact plate.
The heat sink may be attached to the device without PCB modification. The heat sink may be extruded, machined, or die cast aluminum or other material to reduce part and tooling cost, and may be black anodized to be electrically non-conductive. A single-piece embodiment eliminates a need for a separate clip, thereby increasing heat transfer by as much as twenty-five percent or more over heat sinks employing clips. Further, wavy fins or other heat dissipation configurations may increase heat transfer by at least eleven percent, for a total heat transfer improvement of at least thirty-six percent over a two-part heat sink.
The heat sink 100 further includes spring clips 115 that extend outward, here upward, from the convection side 108 of the contact plate 105 at respective edges in this embodiment, and return toward and below the contact plate 105. In other embodiments, the spring clips 115 may connect to the contact plate 105 inside of edges of the contact plate 105. In this example embodiment, the spring clips 115 extend outward for a length approximately equal to the length of the thermally conductive elements 110, bend outward away from the thermally conductive elements 110 at a first bend 117, continue for a distance substantially parallel to the contact plate 105 or have a small radius, and bend back toward the contact plate 105 at a second bend 118. Although the spring clips 115 are illustrated as approximately the same height as the thermally conductive elements 110, this is not a requirement; the spring clips 115 may be taller, shorter, or substantially the same height as the thermally conductive elements 110. The spring clips 115 then continue below the contact plate 105 such that they may make contact with the heat generating device. Further, in this example embodiment, the spring clips 115 have an elasticity such that they may be bent outward from the contact plate 105 and self-restore laterally inward toward the contact plate 105 to self-couple with the heat generating device.
The heat sink 100 may be black anodized so that its surface is non-electrically conductive. The heat sink 100 may be fabricated through an extrusion process, machining process, or die casting process, for example, and is inexpensive to fabricate, in part, because it is a single piece. Moreover, because the heat sink 100 uses substantially little PCB surface area beyond the heat generating device, use of the heat sink 100 may not require modification to the PCB or any other member to which the heat generating device 150 is secured.
Moreover, as illustrated in
While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
For example, any material or combination of materials that can be used as heat sink material(s) may be employed to compose heat sinks described by way of example herein. Although the contact plate and fins are generally illustrated herein as being square or rectangular, it should be understood that any shape may be employed. Moreover, although the contact plates are illustrated as being substantially flat, it should be understood that any profile may be employed to support application to non-flat surfaces. In addition, coupling springs (not shown) that may be wavy and used to apply a force directed upward toward the contact plate and downward toward the heat generating device may be used to apply a balanced distribution of force and thermal coupling across the heat generating device while being held to the heat generating device by the tabs or other elements used to hold the heat sink in place.
In other example embodiments, the heat sink can be composed of multiple detachable subcomponents for selectable configurations. For example, flat fins may be detached and replaced by wavy or curved fins for various applications. The fins may be inserted into slots (not shown) on or in the contact plate. The spring clips may also be detachable and replaced with spring clips of higher or lower restorative forces to secure the heat sink to the heat generating device with selectable levels of force, with selectable directions of force, and selectable parameters related to physical or other properties associated with the spring clips.
