Fastening assembly for heat dissipation device

A fastening assembly used for securing a heat dissipation device to a printed circuit board, comprises a sleeve, an inserting device extending through the sleeve, a spring encircling the inserting device and received in the sleeve, and a supporting device inserted in the sleeve. The inserting device engages with a back plate below the printed circuit board. The sleeve is integrally formed of plastic and comprises a hollow body, a resilient portion extending from an outer surface of the body and pressing a bottom of the heat dissipation device upwardly, and four supporting portions extending from the outer surface of the body and pressing a top of the heat dissipation device downwardly. The supporting device is inserted between the body and the resilient portion, and abuts against the resilient portion, to thereby reliably keep the resilient portion at its locked position.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a fastening assembly, and more particularly to a fastening assembly used for reliably fastening a heat dissipation device to a printed circuit board.

2. Description of Related Art

With development in computer technology, electronic devices operate at high speed. It is well known that higher speed the electronic devices operate at, more heat they generate. If the heat is not dissipated duly, the stability of the operation of the electronic devices will be impacted severely. Generally, in order to ensure the electronic device to run normally, a heat dissipation device is used to dissipate the heat generated by the electronic device. Moreover, in order to keep the heat dissipation device intimately contacting the electronic device, a fastening assembly is usually desired to secure the heat dissipation device to the electronic device.

Nowadays, numerous fastening assemblies are used to secure the heat dissipation devices to the electronic devices located on respective printed circuit boards. Typically, a fastening assembly mainly formed of plastic is used. The fastening assembly comprises a lengthwise shaft, a head formed at an end of the shaft, a spring encircling the shaft and a retaining portion formed at an opposite end of the shaft for engaging with the printed circuit board. The retaining portion comprises a left flexible portion, a right flexible portion and a longitudinal groove defined between the two portions for providing a deforming space to the two portions. In assembly, the retaining portion of the fastening assembly is inserted into a through hole defined in the heat dissipation device and an aperture defined in the printed circuit board. Due to confine of the hole and the aperture, the left flexible portion and the right flexible portion are deformed toward each other in the groove, and then pass through the hole and the aperture. Thereafter, the left flexible portion and the right flexible portion are released to their original positions where they are free. Here, the heat dissipation device and the printed circuit board are sandwiched between the retaining portion and the spring with the retaining portion pressing against the printed circuit board upwardly and the spring pressing the heat dissipation device downwardly toward the printed circuit board. Thus, the heat dissipation device is secured to the electronic device. However, due to the fastening assembly being formed of plastic, the fastening assembly is prone to aging after being used for a long time. Then the retaining portion of the fastening assembly will become loosen due to aging and thus cannot secure the fastening assembly on the heat dissipation device firmly, causing an unreliable engagement between the heat dissipation device and the electronic device.

What is needed, therefore, is a fastening assembly which can overcome the above disadvantages.

SUMMARY OF THE INVENTION

A fastening assembly used for securing a heat dissipation device to a printed circuit board, comprises a sleeve, an inserting device extending through the sleeve, a spring encircling the inserting device and received in the sleeve, and a supporting device engaged in the sleeve. The inserting device engages with a back plate below the printed circuit board to secure the heat dissipation device on the printed circuit board. The sleeve is integrally formed of plastic and comprises a hollow body, a resilient portion extending from an outer circumference of the body and pressing the heat dissipation device upwardly, and four supporting portions extending from the outer circumference of the body and pressing the heat dissipation device downwardly. The supporting device is inserted between the body and the resilient portion and abuts against the resilient portion, whereby a deformation of the resilient portion due to aging is prevented. Thus the heat dissipation device can be securely mounted on the printed circuit board.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, a fastening assembly20in accordance with an embodiment of the present invention is used for securing a heat dissipation device10to an electronic device32mounted on a printed circuit board30. The heat dissipation device10comprises a square heat absorbing plate12thermally contacting with the electronic device32, a heat sink14located above and spaced from the heat absorbing plate12, a bracket16fixed on the heat absorbing plate12and four U-shaped heat pipes18extending through the heat sink14and attached to the heat absorbing plate12.

The bracket16comprises a rectangular body160attached to a top of the heat absorbing plate12and four arms162extending outwardly from four corners of the rectangular body160. The four arms162each define an elliptical through hole1620near an outer end thereof.

Also referring toFIGS. 2,3and4, the fastening assembly20comprises a sleeve21, a first screw25extending through the sleeve21and acting as an inserting device, a spring23encircling the first screw25and received in the sleeve21, and a second screw27engaged in the sleeve21and acting as a supporting device. The first screw25comprises a circular head250and a cylindrical shaft252extending downwardly from the head250. The first screw25with the spring23encircling thereon is for threadedly engaging with a back plate34located below the printed circuit board30(seeFIG. 1). The second screw27engaged in the sleeve21is used for preventing the sleeve21from deforming.

The sleeve21is integrally formed of plastic and comprises a hollow body210defining a through hole2100therein, for receiving the first screw25and the spring23. The body210has a column-shaped circumferential outer surface with a wider, upper part and a narrower, lower part. The through hole2100shrinks inwardly from a top to a bottom thereof, whereby the through hole2100has three different inner diameters, wherein the inner diameter of the through hole2100in the top of the body210is the largest, and the inner diameter of the through hole2100in the bottom of the body210is the smallest. Two annular inner steps2102,2104(shown inFIG. 4) are formed at joints of three parts of the through hole2100with the three different inner diameters, wherein the inner step2102is located above the inner step2104and has an inner diameter smaller than an outer diameter of the head250of the first screw25, for supporting the head250thereon, and the inner step2104has an inner diameter smaller than an outer diameter of the spring23, for supporting a bottom of the spring23thereon, whereby the first screw25and the spring23are prevented from falling off from the bottom of the sleeve21. An outer step212extends outwardly and horizontally from the circumferential outer surface of the body210at a position corresponding to the inner step2102. Two lateral walls2122extend downwardly from a bottom surface of the outer step212at two opposing sides thereof. The two lateral walls2122are spaced from each other. Two pairs of supporting portions213are formed on a periphery of the sleeve21, and are located at two flanks of the two lateral walls2122for pressing a top surface of the arm162of the bracket16, thereby pressing the heat dissipation device10toward the printed circuit board30. A resilient portion214extends downwardly and slantwise from a middle portion of a periphery of the outer step212and is located between the two lateral walls2122, for being engagingly received in the elliptical through hole1620, after the sleeve21extends through the arm162of the heat dissipation device10. A bulge2106projects outwardly from the circumferential outer surface of the sleeve21and is located at a lower portion thereof. The resilient portion214is angled an acute angle with respect to the bulge2106. A gap215is formed between an inner surface of the resilient portion214and an outer surface of the bulge2106, for receiving the second screw27therein. A wedge-shaped rib216extends outwardly from the circumferential outer surface of the lower portion of the body210, opposite to the bulge2106. The rib216has a gradually increased thickness along a bottom-to-top direction thereof. The rib216is for guiding the sleeve21through the elliptical through hole1620of the arm162when assembling the sleeve21with the heat dissipation device10, and preventing the sleeve21from falling off the arm162after the sleeve21is substantially locked with the arm162. The resilient portion214includes a beam2142and a retaining block2144formed at a distal, bottom end of the beam2142. The beam2142can be flexibly deformed toward the bulge2106, guiding the sleeve21into the elliptical through hole1620of the arm162of the bracket16before the second screw27engages in the gap215and be deformed outwardly by pushing of the second screw27after the second screw27engages in the gap215. The retaining block2144includes a flat, horizontal abutting face2146and a slantwise guiding face2148slanting inwardly along a top-to-bottom direction (shown inFIG. 4). The slantwise guiding face2148can be pressed by an inner sidewall of the arm162of the bracket16defining the through hole1620, to push the beam2142to be deformed inwardly, and thereby to guide the sleeve21into the corresponding through hole1620of the arm162. The flat abutting face2146is located below bottom surfaces of the supporting portions213, for pressing a bottom surface of the arm162after the retaining block2144extends through the through hole1620of the arm162, whereby the arm162is sandwiched between the bottom surfaces of the supporting portions213and the flat abutting face2146of the retaining block2144when the fastening assembly20is mounted to the arm162.

In assembly, each fastening assembly20is brought to extend through the corresponding through hole1620in the bracket16of the heat dissipation device10. Due to confine of the through hole1620of the arm162, the beam2142is deformed inwardly to make the retaining block2144pass through the through hole1620of the arm162. After the sleeve21being substantially inserted into the arm162, the beam2142is released outwardly to its original position. Then the second screw27is inserted into the gap215formed between the inner surface of the resilient portion214and the outer surface of the bulge2106, abutting against the inner surface of the resilient portion214, thereby to hold the resilient portion214securing with the arm162reliably. At this position, the bracket16of the heat dissipation device10is sandwiched between bottoms of the supporting portions213, the flat abutting face2146of the retaining block2144of the resilient portion214and a top of the rib216, with the abutting face2146of the retaining block2144and a top surface of the rib216abutting against the bottom surface of the arm162upwardly and the supporting portions213pressing the top surface of arm162downwardly towards the printed circuit board30. Finally, the first screw25with the spring23encircling thereon is brought to extend through the through hole2100of the sleeve21and engage with the back plate34below the printed circuit board30, thereby securing the heat dissipation device10on the printed circuit board30.

In order to prevent the resilient portion214from deforming inwardly due to aging after the fastening assembly20has been used for a long time, the second screw27is provided to be inserted into the gap215of the sleeve21, keeping the resilient portion214at its original position. Therefore, the fastening assembly20can still reliably secure the heat dissipation device10on the printed circuit board30even after a long-period use.