A reworkable fixing element includes a screw having a spring fitted thereon, a screw head with two opposite cuts, and a retaining ring for stopping the screw from axially moving down any further; a sleeve disposed outside the screw and the spring, and including two opposite windows near an upper end thereof and a coupling zone located below the windows; a spring retaining ring fitted around the coupling zone and including two upward hooked arms extended through the windows to press the spring to a compressed state. The used fixing element has an elastically released spring but is reworkable using a reworking tool, which pushes the spring into the sleeve via the two cuts. Then, the hooked arms are allowed to extend through the windows to press on and hold the spring in the compressed state again, and the fixing element is ready for use a second time.

FIELD OF THE INVENTION

The present invention relates to a fixing element capable of applying an even downward force for connecting a heat dissipation device to a bare die heat source without causing damage to the bare die or forming thermal resistance between the heat dissipation device and the heat source; and more particularly, to a fixing element that is usable with a reworking tool to be reworked for use a second time,

BACKGROUND OF THE INVENTION

Nowadays, high performance and high power chips are used in electronic devices for the latter to provide highly enhanced computing power. The chip in processing data will produce a relatively high amount of heat to form a heat source. Conventionally, the chip is packaged or encapsulated to avoid the chip from being damaged. With the enhanced computing power thereof, the chip in processing data produces even more heat than ever before. However, the package of the chip adversely affects the produced heat from efficiently dissipating into outer environment. Therefore, many currently available chips are provided in the form of bare dies without any package to protect their surfaces. The non-packaged bare die has a non-smooth and convex surface and accordingly, has a relatively small and weak contact area between it and a heat dissipation device for heat exchange. Thus, the bare die is subjected to damage and breaking when the heat dissipation device is connected thereto.

Since the bare die as a heat source is not suitable for being directly connected to the heat dissipation device, the heat dissipation device is usually connected to a base, such as a motherboard or a circuit board, which has the bare die mounted thereon. In this case, internally threaded copper sleeve rods are provided on the base at four corners outside the heat source to serve as screw fastening points. Conventionally, to fix the heat dissipation device to the base carrying the heat source, screws are sequentially tightened to the screw fastening points one by one. Since the screws are not tightened synchronously, the heat dissipation device connected to the base tends to be skewed relative to the heat source to apply uneven forces to the heat source, and the bare die subjected to unevenly distributed force is easily broken and damaged.

Please refer toFIGS.1and2, which show a conventional manner of fixing a heat dissipation device C to a heat source A in the form of a bare die. As shown, the bare die A is placed on a base D. Four corners of the base D correspondingly located outside the heat source A are provided with an internally threaded copper sleeve rod B each. The heat dissipation device C also has four holes C3formed corresponding to the four copper sleeve rods B for a screw unit C1to extend through each of the holes C3. Each of the screw units C1has a spring C2fitted therearound. To lay the heat dissipation device C to the top of the heat source A, the screw units C1are sequentially threaded through the holes C3into corresponding copper sleeve rods B one by one with a power screwdriver handled manually or by a mechanical arm. To shorten the fixing time on a production line and complete the fixing operation within a limited time period, each of the screw units C1is fully tightened in one movement at a very quick speed. As soon as the screw unit C1is fully tightened, the spring C2fitted therearound is also compressed in a direction toward the heat source A. The screw units C1individually tightened at a quick speed and the springs C2quickly compressed toward the heat source A tend to result in uneven and asynchronous distribution of downward forces over four corners of the base D and accordingly the heat source A. And, the heat source A, i.e. the bare die, being fragile and breakable, is easily damaged under uneven force application thereto.

The bare die is so fragile that even downward forces must be synchronously applied by the heat dissipation device to the four corners of the base carrying the bare die to ensure successful fixing of the heat dissipation device to the top of the bare die. In the event the four corners of the base are subjected to unevenly and asynchronously applied forces from the heat dissipation device, warp of the bare die or the heat dissipation device might occur to cause incomplete contact and thermal resistance between the two parts. In some worse conditions, the warped bare die might become damaged and non-usable and the thermal resistance might lead to uneven heat distribution over or inactive heat conduction of the heat dissipation device.

There are also manufacturers who use spring loaded screws to connect the heat dissipation device to the bare die heat source, so as to solve the problem of not able to synchronously apply even downward forces to the heat dissipation device. The spring loaded screw is different from those in the prior art in that it includes a screw sleeve externally disposed around a screw main body and a spring fitted on the main body, and a spring stopper for temporarily compressing the spring in the screw sleeve. As soon as the spring stopper is disabled using a machine or a hand tool, the spring compressed in the screw sleeve is released to provide at two ends an upward and a downward elastically restoring force synchronously for evenly pressing the heat dissipation device against the heat source. In this case, while the spring loaded screw advantageously uses the spring to provide elastic spring force for adjusting or assisting the downward force applied by the screw to the heat dissipation device, the spring stopper for compressing the spring in the screw sleeve can only be used once. When the spring stopper is disabled to release the compressed spring, the released spring can not be compressed again in the screw sleeve. The old spring loaded screw with the released spring must be dismounted from the heat dissipation device and be replaces with a new one for tightening to the heat dissipation device.

It is therefore tried by the inventor to find a fixing element that enables the heat dissipation device to apply even and synchronous forces to the heat source to ensure full and close contact between them, maintains a proper binding force between the bare die and the heat dissipation device, and is repeatedly adjustable for reuse.

SUMMARY OF THE INVENTION

To effectively solve the above problems, it is a primary object of the present invention to provide a reworkable fixing element, a plurality of which can be tightened synchronously to provide even downward forces, so as to avoid broken or collapsed edges of a bare die computing chip as would occur in the prior art where a plurality of conventional fixing screws is pre-tightened to a heat dissipation device one by one.

Another object of the present invention is to provide a reworkable fixing element, which is usable with a reworking tool, so that a released spring of the fixing element can be compressed again and the fixing element can be reused for mounting.

To achieve the above and other objects, the reworkable fixing element according to the present invention includes a screw, a sleeve, and a spring retaining ring.

The screw has a spring externally fitted therearound, and includes a screw head and a plurality of male threads formed at an upper and a lower end of the screw, respectively; two cuts formed at two diametrically opposite positions on the screw head to axially cut through the screw head; and a retaining groove formed closely above the male threads for receiving a retaining ring therein. The spring having a top and a bottom end, and the bottom end of the spring is pressed against the retaining ring.

The sleeve has an open upper end, and open lower end, and a receiving space defined in the sleeve between the upper and the lower end; the sleeve includes a pair of windows correspondingly formed near the upper end at two diametrically opposite positions and radially communicable with the receiving space, and a coupling zone located on an outer surface of the sleeve. The sleeve is disposed outside the screw and the spring.

The spring retaining ring is fitted on around the coupling zone of the sleeve, and includes a hooked arm set upward extended from an upper side of the spring retaining ring. The hooked arm set includes a pair of hooked arms for extending through the windows into the receiving space in the sleeve to press against a top end of the spring and hold the spring in a compressed state. When a heat dissipation device is to be connected to a bare die heat source using the fixing elements of the present invention, a pressing tool may be used to apply a downward pressure to the spring retaining ring, and the hooked arms are brought to move downward at the same time to thereby separate from the top end of the spring, allowing the spring to release an elastic restoring force and apply a downward force to the heat dissipation device.

When the fixing element has been used to connect the heat dissipation device to the heat source, the spring thereof is in an elastically released state. However, the fixing element is reworkable for use again. To rework the fixing element, the spring thereof must be compressed again to return to its original position. For this purpose, a reworking tool including at least two pressing columns is used. The two pressing columns of the reworking tool are correspondingly extended into the two cuts on the screw head to directly push the spring downward into the receiving space again. At this point, the hooked arms of the spring retaining ring are allowed to extend through the windows into the receiving space to abut on the top end of the spring and hold the latter in the compressed state, and the fixing element is now reworked and can be used a second time to connect the heat dissipation device to the heat source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described with a preferred embodiment thereof.

Please refer toFIGS.3and4, which are assembled and exploded perspective views, respectively, of a fixing element1according to a preferred embodiment of the present invention. As shown inFIG.7, a reworking tool P can be used with the fixing element1to restore an elastically released spring on the fixing element1to a compressed spring again, so that the fixing element1is reworked and can be used again for mounting to a heat dissipation device2, as shown inFIG.5. The reworkable fixing element1of the present invention includes a screw11, a sleeve12, and a spring retaining ring13.

The screw11includes a screw head112and a plurality of male threads113located at an upper and a lower end thereof, respectively. The screw head112has two cuts114, which are located at two diametrically opposite positions of the screw head112to axially cut through the screw head112. More specifically, the screw head112has an upper end surface1121and a lower end surface1122, and the two cuts114are extended from the upper to the lower end surface1121,1122. The screw11includes a retaining groove115formed axially above the male threads113for receiving a retaining ring116therein. A spring117is fitted on around the screw11between the screw head112and the retaining ring116and has a top end1171and a bottom end1172. The bottom end1172of the spring117is pressed against the retaining ring116, so that the retaining ring116provides an axially lower limit to the bottom end1172of the spring117, preventing the spring117from moving down out of the screw11.

The sleeve12has an open upper end121, an open lower end122, and a receiving space123defined in the sleeve12between the upper and the lower end121,122. The sleeve12is provided near the upper end121with a pair of radially retreated windows125, which are located at two diametrically opposite positions to space from each other by180degrees and are radially communicable with the receiving space123. The sleeve12is externally disposed around a length of the screw11having the spring117fitted thereon.

The windows125respectively include an upper edge1251. A coupling zone124is formed on the sleeve12between a lower edge of the windows125and the lower end122of the sleeve12. The coupling zone124may have an outer diameter the same as or smaller than that of the sleeve12. In the latter case, the sleeve12has a stepped profile showing two axially different outer diameters, and a stepped section1252is formed around a joint between a lower end of the coupling zone124and the sleeve12. The stepped section1252provides an axially lower limit for the spring retaining ring13, lest the spring retaining ring13should excessively move downward to separate from the coupling zone124.

The spring retaining ring13is fitted on around the coupling zone124of the sleeve12. The spring retaining ring13includes an annular abutting section131formed on an upper side surface of the spring retaining ring13and a hooked arm set132extended upward from the upper side surface of the spring retaining ring13. The hooked arm set132includes a pair of hooked arms132A, each of which has a free end bent radially inward to form a hooked end1321having a horizontal top surface. The hooked ends1321are extended into the receiving space123of the sleeve12via the windows125. The top end1171of the spring117is elastically upward pushed against the hooked ends1321to move them upward until the horizontal top surfaces of the hooked ends1321are abutted against the upper edges1251of the windows125. At this point, the top end1171of the spring117is also limited by the upper edges1251of the windows125, stopping the spring117from elastically upward expanding any further to stay in a compressed state in the sleeve12. In the present invention, the spring retaining ring13can be loosely or tightly fitted around the coupling zone124on the sleeve12.

To assemble the fixing element1of the present invention, first put the screw11and the spring117fitted thereon into the receiving space123of the sleeve12. Since the hooked ends1321of the hooked arms132A of the spring retaining ring13are pressed against the top end1171of the spring117, the spring117is stopped from elastically expanding upward and therefore stays in a compressed state.

Please refer toFIGS.5,6and7, which show how the fixing element1of the present invention is used to connect a heat dissipation device2to a bare die heat source3and how the fixing element1is reworked for use a second time. As shown, the heat dissipation device2has a first side12, an opposite second side22, and a heat receiving zone23. The heat receiving zone23is located on the second side22of the heat dissipation device2near a central area of the second side22.

A plurality of the fixing elements1is pre-mounted to through holes24formed at four corners outside the heat receiving zone23of the heat dissipation device2. To connect the heat dissipation device2to the bare die heat source3for the purpose of heat exchange or heat transfer, first align and preliminarily screw the male threads113of the screws11of the fixing elements1into holding structures4, such as internally threaded sleeve rods, that are correspondingly provided at four corners outside the heat source3. At this point, the springs117fitted around the screws11have not yet released their elastic forces. That is, the heat dissipation device2is only located above the heat source3without applying pressure to the heat source3, and a surface of the heat receiving zone23, i.e. the second side22of the heat dissipation device2, is only in a light contact with a surface of the heat source3. For the heat dissipation device2to apply even downward forces to the heat source3, the springs117of the fixing elements1on the four corners outside the heat receiving zone23must release their elastic forces synchronously.

For the springs117on the fixing elements1to be triggered to release their elastic force synchronously, a pressing tool5connected to an apparatus (not shown) is used for all the fixing elements1to move down synchronously and accordingly, to provide a downward force each. The apparatus can be a punch or other mechanical equipment or machinery capable of providing downward pressure. The pressing tool5connected to the apparatus includes at least one extended pressing section51, which is located corresponding to the fixing elements1mounted to the four corners outside the heat receiving zone23on a main body of the heat dissipation device2and is abutted on the annular abutting section131near an outer periphery of the upper surface of the spring retaining ring13. When the pressing tool5is driven by the apparatus (not shown) to move downward, the extended pressing section51of the pressing tool5applies downward pressure to all the abutting sections131of the spring retaining rings13synchronously. A contact location between each spring retaining ring13and each sleeve12forms a rotational fulcrum A. When the pressing tool5applies the downward pressure to the abutting section131of the spring retaining ring13, the spring retaining ring13is supported at the rotational fulcrum A while the abutting section131is turned outward and downward, such that the hooked arms132A are brought to move radially outward relative to the sleeve12to move out of the windows125and stay in a radially outward expanded state. At this point, the hooked ends1321of the hooked arms132A are no longer pressed against the spring117, and the spring117is allowed to fully release its elastic restoring force, such that the top end1171of the spring117is elastically pressed against the lower end surface1122of the screw head112. Meanwhile, the bottom ends1172of all the springs117fitted on the fixing elements1mounted to four corners outside the heat receiving zone23synchronously apply even downward forces to the four corners outside the heat receiving zone23on the heat dissipation device2, enabling the heat dissipation device2to move down and contact with the heat source3evenly.

In the present invention, the screws11are used only to preliminarily mount and support the heat dissipation device2above the heat source3. It is the springs117, which are fitted on the screws11fixed to four corners outside the heat receiving zone23, that actually provide the downward pressure to the heat dissipation device2for the latter to contact with the heat source3evenly. That is, when the springs117are no longer held down by the spring retaining rings13, they would synchronously release evenly distributed downward forces to the main body of the heat dissipation device2. With the present invention, it is able to solve the problems in the prior art that the screw units C1are individually screwed one by one to result in uneven force application; or that the screw units C1are fully tightened in one single movement or excessive pressure is exerted by the springs C2to result in warped or broken and damaged bare die that is subjected to unevenly applied forces thereto.

In addition to provide even downward forces to the heat dissipation device2and the heat source3, the fixing elements1of the present invention are reworkable when the heat dissipation device2having been mounted needs to be re-mounted or adjusted. When the fixing elements1are to be reworked, i.e. to be used for fixing again, a reworking tool P is used. With the reworking tool P, the previously elastically released springs117could be set in the sleeves12again and be held in the compressed state for use a second time.

The reworking tool P includes a head portion PI and at least two independently arranged pressing columns P2downward extended from the head portion P1. The pressing columns P2can be correspondingly extended into the two cuts114on the screw head112. When the reworking tool P is driven by a downward force, the pressing columns P2are simultaneously driven downward to press against the top end1171of the spring117, so that the spring117previously pushed against the lower end surface1122of the screw head112is now pushed downward into the receiving space123of the sleeve12and be compressed. When the top end1171of the spring117is pressed into the receiving space123of the sleeve12again, forces can be applied to the lower side of the abutting section131of the spring retaining ring13to push the abutting section131upward with hands or using a tool in cooperation with an apparatus. With the spring retaining ring13being supported at the rotational fulcrum A, the hooked ends1321of the two hooked arms132A of the spring retaining ring13can be moved into the receiving space123via the windows125to press against the top end1171of the spring117again. At this point, the hooked ends1321of the hooked arms132A have their upper side surface pressed against the upper edges1251of the two windows125and are limited by the windows125from moving axially. Therefore, the spring117returned back into the sleeve12is held by the spring retaining ring13to the compressed state again and can be advantageously used a second time when the heat dissipation device2is reworked.

In brief, in addition to be used for connecting the heat dissipation device2to the heat source3in the form of a bare die, the used fixing element of the present invention can also be reworked for use a second time when the previously mounted heat dissipation device2needs to be reworked or replaced.