Mounting assembly for heat sink

1. Field of the Invention

The present invention relates to a mounting assembly for mounting a heat sink to an electronic package mounted on a circuit board, and particularly to a mounting assembly which easily and securely mounts the heat sink to the electronic package.

2. The Related Art

A computer central processing unit (CPU) is the core administrator of electrical signals in most contemporary personal computers. Continued development of CPUs has enabled them to perform more and more functions. Heat generated by CPUs has increased commensurately. Measures must be taken to efficiently remove the heat from the CPU. Typically, a heat sink having great heat conductivity is mounted on the CPU to remove heat therefrom.

A conventional configuration for fastening a heat sink to a CPU comprises a plurality of barbs formed around a bottom of the heat sink. A plurality of protruding edges extends from a CPU connector that supports the CPU, for engaging with the barbs and thereby securing the heat sink to the CPU. However, this configuration necessitates unduly large force being applied to tightly press the heat sink onto the CPU. The CPU is liable to be damaged if excessively large force is applied during assembly, or if force is applied in an incorrect direction. Therefore assembly needs to be performed carefully and slowly. This is particularly inefficient in mass production facilities.

Accordingly, various clips have been developed for mounting a heat sink to a CPU. As shown in TW Patent No. 87221090, a conventional clip includes an H-shaped portion and four legs extending from four distal ends of the H-shaped portion respectively. A barb is formed at a distal end of each leg, for engaging in a corresponding hole around a CPU. However, this configuration may not apply sufficient force to securely fasten the heat sink on the surface of the CPU. In addition, the clip is prone to fatigue and deformation after prolonged use. Deformation further reduces the retaining force.

Accordingly, an object of the present invention is to provide a mounting assembly which easily and securely mounts a heat sink to an electronic package mounted on a circuit board.

To achieve the above object, a mounting assembly in accordance with a preferred embodiment of the present invention comprises a back plate, a clip and two screws. The back plate comprises a cross-shaped main body, and a pair of first positioning posts and a pair of second positioning posts extending upwardly from the main body. An annular groove is defined in a top end of each first positioning post. A threaded hole is vertically defined in each second positioning post. The clip comprises a horizontal portion, and a pair of first legs and a pair of second legs extending from the horizontal portion. A guiding hole and a positioning slot communicating with the guiding hole are defined in a distal end of each first leg. A fastening slot is defined in a distal end of each second leg. An electronic package such as a CPU is mounted on a top side of a circuit board. The back plate abuts an underside of the circuit board, and the clip and a heat sink are disposed at the top side of a circuit board. The positioning slots of the clip engagingly receive the first positioning posts of the back plate. The screws are inserted through the fastening slots of the clip into the corresponding threaded holes of the second positioning posts of the back plate. The mounting assembly thus secures the heat sink to the CPU.

Other objects, advantages and novel features of the present invention will be drawn from the following detailed description of preferred embodiments of the present invention with the attached drawings, in which:

FIG. 1 is an exploded isometric view of a mounting assembly in accordance with a preferred embodiment of the present invention, together with a heat sink, and an electronic device mounted on a circuit board; and

FIG. 2 is an assembled view of FIG. 1 .

Referring to FIG. 1, a mounting assembly in accordance with a preferred embodiment of the present invention is used to attach a heat sink 10 to an electronic package 50 that is mounted on a circuit board 40 . The mounting assembly comprises a back plate 20 , a clip 30 and two screws 70 . Four bores 42 are defined in the circuit board 40 around the electronic package 50 .

The heat sink 10 includes a chassis 12 , and a plurality of parallel fins 14 extending upwardly from the chassis 12 . The chassis 12 defines four apertures 16 , corresponding to the bores 42 of the circuit board 40 .

The back plate 20 comprises a cross-shaped main body 22 , a pair of first positioning posts 24 extending upwardly from two distal ends of the main body 22 , and a pair of second positioning posts 26 extending upwardly from two other distal ends of the main body 22 . Each first positioning post 24 is opposite from a second positioning post 26 , and vice versa. A square opening 222 is defined in a center of the main body 22 . An annular groove 242 is defined in a top end of each first positioning post 24 . A threaded hole 262 is vertically defined in each second positioning post 26 . Cushions 28 are provided on the main body 22 as follows: around the opening 222 , at a bottom of each first positioning post 24 , and at a bottom of each second positioning post 26 . The cushions 28 protect the circuit board 40 in assembly. In addition, the cushions 28 are made of insulative material to insulate the circuit board 40 from the back plate 20 .

The clip 30 comprises an H-shaped horizontal portion 32 , a pair of L-shaped first legs 34 extending generally in a first direction from the horizontal portion 32 , and a pair of L-shaped second legs 36 extending generally in a second direction from the horizontal portion 32 , the second direction being opposite to the first direction. A positioning cutout 340 is defined in each first leg 34 . Each positioning cutout 340 comprises a guiding hole 342 , and a positioning slot 344 at a distal side of and in communication with the guiding hole 342 . A diameter of the guiding hole 342 is slightly greater than a diameter of each first positioning post 24 of the back plate 20 . A width of the positioning slot 344 is less than the diameter of each first positioning post 24 , but greater than a diameter of each first positioning post 24 at the annular groove 242 thereof. A fastening slot 362 is defined in each second positioning leg 36 . A width of the fastening slot 362 is greater than a diameter of the threaded hole 262 of each second positioning post 26 , but less than a diameter of each second positioning post 26 .

Referring also to FIG. 2, in assembly, the heat sink 10 is placed on a top surface of the electronic package 50 . The first positioning posts 24 and second positioning posts 26 of the back plate 20 are sequentially inserted through the corresponding bores 42 of the circuit board 40 and the corresponding apertures 16 of the heat sink 10 . Then the clip 30 is placed on the heat sink 10 . The first positioning posts 24 are received through the guiding holes 342 . Then the back plate is slid in the second direction, so that the first positioning posts 24 at the annular grooves 242 are engaged with the first legs 34 in the positioning slots 344 . The screws 70 are inserted through the fastening slots 362 to engage in the threaded holes 262 of the second positioning posts 26 . Thus the heat sink 10 is fastened to the circuit board 40 . The H-shaped horizontal portion 32 firmly and evenly presses the heat sink 10 onto the top surface of the electronic package 50 .

In an alternative embodiment of the present invention, the threaded holes 262 may instead be replaced by corresponding externally threaded portions of the second positioning posts 26 . Accordingly, the screws 70 may be replaced by internally-threaded screw caps.

It is understood that the invention may be embodied in other forms without departing from the spirit thereof. Thus, the present examples and embodiments are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein.