Heat Sink Assembly for Solid State Devices

This invention relates generally to electronic solid state devices and more particularly, to apparatus for dissipating heat generated by such devices.

As advances are made in the electronics industry with more functions provided in smaller architecture, the efficient removal of heat becomes increasingly important. Solid state devices, such as microprocessors and the like, generate a great deal of heat during operation which must be removed to prevent adverse effects on operation of the system in which the solid state device is used and even self-destruction of the device or destruction of near-by components.

It is known to thermally couple heat sinks with such devices in order to dissipate heat generated by the devices and, consequently, lower the temperature of the devices to safe limits. One example of such a heat sink is shown and described in U.S. Pat. No. 4,745,456. In that patent, a finned heat sink comprising a central post having a plurality of spaced fins extending radially from the post is secured to an electronic device package by means of a clip which attaches to a latch mechanism on a frame in which the device package is held and which releasably grips the heat sink and urges it into engagement with the device package. This structure, while effective when the clamping force biases the heat sink into firm engagement with the electronic device package, tends to be inconsistent as the semi-conductor heats up and, at elevated temperatures, the force biasing the heat sink against the device package can decrease making the thermal path less efficient. In fact, apparently due to differences in the thermal expansion of the several parts, the thermal coupling between the heat sink and the device package can be significantly diminished caused by a slight tilting of the heat sink surface to break the plane to plane contact of the heat sink core with the top surface of the electronic device package. Even when thermal grease is placed between the heat sink and the device package, it is found that thermal coupling can be significantly reduced with the result that the device package overheats and causes deleterious operational effects.

Heat sinks have also been permanently bonded to the electronic device package to provide an efficient thermal coupling between the two components; however, over time the bond tends to break thereby adversely affecting the thermal path between the heat sink and the device package.

Another approach to preventing overheating has been to mount a small fan on the heat sink to increase thermal dissipation of the heat sink. While this can be very effective in maintaining the temperature of the device package to acceptable levels, it is not only costly if operation of the fan is interrupted due to some malfunction, but the device will be ineffective to prevent unwanted temperature rise.

It is an object of the present invention to provide a heat sink assembly for removing heat from an electronic device which is reliable yet inexpensive, one which obviates the limitations of the prior art mentioned above.

Briefly, in accordance with a first embodiment of the invention, a heat sink member is formed with a threaded base which is adapted to be received in a threaded bore formed in the top wall of an adaptor which is adapted to clamp spaced marginal edges of an electronic device package. The package is inserted into opposed grooves of the adaptor and then the heat sink, which may be of various configurations including the type having a plurality of generally circular fins spaced along a generally cylindrical core or a helical fin extending from the core, is screwed down toward the package until the flat bottom surface of the heat sink base is firmly biased against the top of the electronic device package and thermally coupled thereto. The adaptor, if desired, may be provided with a downwardly extending stop surface to limit travel of an electronic device package inserted into the grooves and locate the threaded bore at a central location of the package. In a modified embodiment, the top wall of the adaptor is formed with a thicker hub portion through which the bore extends in order to provide a longer threaded bore for the threaded base. In an alternative embodiment, the base is provided with an outwardly extending flange at its lower distal end and is provided with a tapered surface portion. The flange is adapted to snap through the bore in the top wall to lock the heat sink to the adaptor. The tapered surface portion also serves as a cam surface when an electronic device package is inserted in the grooves biasing the base upwardly so that there is a good thermal coupling therebetween. In yet another embodiment, the lower portion of the grooves are formed with lips having a tapered or cam curve surface so that the adaptor can be pushed onto an electronic device package with the lips snapping over the opposite marginal edges of the package.

Various objects and advantages of the present invention will become apparent from the following detailed description and accompanying drawings .

In the accompanying drawings in which several of the preferred embodiments of the invention are illustrated:

FIG. 1 is a broken apart perspective view of a heat sink assembly made in accordance with a first embodiment of the invention comprising a heat sink member and an adaptor shown along with an electronic device package in the form of a microprocessor having a g array;

FIG. 2 is a side elevation of the FIG. 1 apparatus with the adaptor shown in cross section;

FIG. 3 is a top plan view of the FIGS. 1, 2 adaptor;

FIG. 4 is a side elevation of a modified adaptor;

FIGS. 5 and 6 are side elevational views, the adaptor shown in cross section of an alternative embodiment of the invention before and after connecting the heat sink to the adaptor.

FIGS. 7 and 8 are top plan and cross sectional views of an adaptor of yet another embodiment of the invention;

FIG. 9 is a perspective view, partly in cross section, of a heat sink having a continuous helical fin useful with the adaptor of the invention;

FIG. 10 is a top plan view of a modified heat sink adaptor; and

FIG. 11 is a cross sectional view taken on line 11--11 of FIG. 10.

FIG. 12 is a cross sectional view of an alternative embodiment of the present invention taken along a line through the heat sink core and perpendicular to the path of insertion.

According to a first embodiment of the invention, as shown in FIGS. 1-3, a heat sink assembly 10 for an electronic device package containing a solid state device such as a microprocessor or the like, comprising an adaptor 12 formed of an electrically insulative material, such as an ABS plastic, having a top wall 14 and opposed side wall 16, 18 depending therefrom. Side walls 16, 18 are formed with laterally inwardly extending lips 20, 22 at their respective distal end portions forming a groove with top wall 14 adapted to capture the outer extremities or marginal portions of a solid state device 24. Top wall 14 is formed with a centrally disposed threaded bore 26. If desired a stop wall 19 can be provided depending downwardly from the back side of the adaptor to conveniently center the solid state device relative to bore 26. Stop wall 19 is shown with an optional inwardly extending lip 21.

Heat sink 28, formed of good thermally conductive material such as aluminum, comprises a plurality of thin members 30 extending integrally from a core 32 having a threaded base 34 adapted to be threadingly received in a threaded bore 26.

Solid state device 24, such as a microprocessor having a gate array, is inserted into adaptor 12 with the outer marginal portions of the housing of device 24, shown in FIG. 1 by dash lines 23, received between lips 20, 22 and top wall 14 and the stop wall 19 limiting the inward motion of device 24 so that threaded bore 26 is aligned with the central portion of device 24. Heat sink 28 is then screwed into threaded bore 26 until it bottoms out against the solid state device 24 in intimate thermal coupling therewith. The flat bottom surface of base 34 is adapted to be placed on the space formed by planes lying respectively in the top and bottom of the surfaces forming the grooves to ensure a good thermal coupling with a solid state device received therein. Threaded bore 34 of the heat sink extends longitudinally a distance preferably slightly longer than the distance between top wall 14 and the top surface of a device 24 placed within the adaptor so that the heat sink can be screwed in until top wall bows slightly biasing the heat sink against solid state device 12. If desired, the longitudinal length of the thread on the heat sink base can be selected to extend a certain length to limit downward travel of the heat sink in order to prevent excessive forces from being placed on the electronic device package. Generally, it is desirable to place some thermally conductive grease, such as a silican based grease or a flexible heat conductive tape, between base 34 and solid state device 24 to further enhance heat flow.

Due to the stress placed on the adaptor by screwing the heat sink against the solid state device, the FIG. 1 structure will maintain a bias of the heat sink against the solid state device, and thus an efficient heat path, even when the solid state device heats up. Although an electrically insulative material is convenient to use since shorting of the pins of the solid state device member is obviated, metal can also be used to form adaptor 12 with lips 20, 21 and 22 coating with a layer of suitable electrically insulative material.

In a modification of the FIGS. 1-3 embodiment shown in FIG. 4, a boss 40 can be formed on the top wall of adaptor 12' to form a longer axial length of threaded bore 26' to facilitate the attachment between the adaptor and the heat sink.

Another embodiment, shown in FIG. 5, provides a snap coupling of heat sink 28' to adaptor 12". Base 34' has a tapered flange 42 adapted to be forced through bore 26' until the radially extending lip 44 snaps beyond recessed surface 46. In order to optimize thermal coupling between heat sink 28' and solid state device 24, the vertical height of tapered flange 42, shown as "a" in FIG. 5, may be selected to be slightly more than the distance between recess surface 46 and the lower surface 48 of top wall 14". This will cause the lower surface 50 of heat sink 28' to be disposed in the space where the housing of solid state device 24 would occupy when inserted in the adaptor so that the tapered surface of flange 42 will cam wall 14 to bow it upwardly as solid state device 24 is pushed into the adaptor thereby insuring an efficient thermal coupling even with changes in temperature. Although heat sink 28' is shown formed with a cylindrical base it will be appreciated that it is within the purview of the invention to provide other configurations, if desired such as oblong or rectangular with a corresponding configured flange and aperture in the top wall.

FIGS. 7 and 8 show another embodiment of the invention in which adaptor 12'" is provided with lips 20', 22' which have tapered surfaces 20.1, 22.1 respectively so that the adaptor can be placed on top of a solid state device 24 and pushed down onto it with surfaces 20.1 and 22.1 acting as cam surfaces forcing side walls 16', 18' to spread apart with the side walls 16', 18' returning to their normal vertical orientation when lips 20', 22' pass beyond the lower edge of solid state device 24 to securely grasp device 24. When a heat sink, such as heat sink 28" shown in FIG. 9 is screwed into bore 26 and into engagement with a solid state device 24 held in adapter 12'", the grasping force will be increased as top wall 14'" starts to bow upwardly. As seen in FIG. 7, stop wall 14'" is provided with cut out portions 14.1 to enhance development of spring like characteristics to the wall.

Heat sink 28" of FIG. 9 is similar to heat sink 28 and 28' shown in the previous figures but instead of having a plurality of separate fin members 30, has a single helical fin 30' integrally formed with core 32.

FIGS. 10 and 11 show a modified heat sink in which spaced apart grooves are formed on two contiguous sides of the adaptor by lips 22.2 and 21.2 which are adapted to be received under spaced marginal portions of device package 24 to firmly grasp the package when a heat sink is inserted in bore 26 and screwed down into engagement with the package.

Turning now to FIG. 12, an alternative embodiment of the present invention is shown. Heat sink 28 with fins 30 is engaged with adaptor 12 which has extended legs 68. Solid state device 24 is installed in socket 60 via pins 62. Socket 60 is in turn connected, in permanent fashion, to circuit board 66 via soldered pins 64. In this embodiment, legs 68 are extended so that lips 20 and 22 may engage with the bottom surface of socket 60. The embodiment of FIG. 12 is particularly useful for successfully dissipating heat in vertically mounted solid state devices 24. When a heat sink 28 or other heat dissipating member is affixed to the surface of a solid state device which is vertically mounted, the weight of the heat sink gradually pulls the solid state device 24 out of its socket 60. This results in poor connection of the solid state device and bending of pins 62. As shown in FIG. 12, legs 68 grip onto socket 60 via lips 20 and 22 to place the weight on soldered socket 60 which provides a better mount for the heat sink assembly in a vertically mounted solid state device.

Although the invention has been described with respect to specific preferred embodiments thereof, variations and modifications will become apparent to those skilled in the art. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.