Patent Application
20140036451
Heat sinks are typically mounted to an outer surface of an integrated circuit package to facilitate the dissipation of heat from the integrated circuit contained within the package. Most heat sinks are thermally conductive and have a plurality of extruded fins to provide a large surface area, which allows heat to be more efficiently dissipated by natural or forced convection. Heat sinks are mounted to integrated circuit packages in a variety of ways. Many of the common methods of attachment use special tools to facilitate attachment without the heat sink becoming unstable or damaged.
Methods of attaching heat sinks to packages include common spring clamps, conventional clips which use a tool to attach the clip to the assembly, and adhesives.
In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. It is to be understood that features of the various embodiments described herein may be combined with each other, unless specifically noted otherwise.
Heat sinks are subjected to vibration during normal operation or transportation. Certain conventional clips are prone to slip relative to the heat sink and dislodge from attachment to the integrated circuit. This can seriously reduce the stability of a heat sink assembly and the efficiency of heat removal.
Embodiments provide heat sink assemblies which provide proper load pressure at the thermal connection surfaces and ground heat sinks for EMI compliance.
In one embodiment, holes 22 are a simple cylindrical shape, although other shapes are acceptable as appropriate to receive clamp 18 and clamp retainer 20. Holes 22 are sized appropriately to receive clamp retainers 20. In one embodiment, holes 22 are drilled into PCB 12. At least two holes 22 are defined by PCB 12. In this embodiment, four holes 22 are illustrated. More or less holes 22 are appropriate as corresponding to quantity of legs 46 included on clamp 18, to allow use of multiple clamps 18, or for ease of manufacturing.
Clamp 18 secures heat sink 14 to heat producing device 29 on PCB 12. Clamp 18 is a stamped spring clamp. In one embodiment, clamp 18 is a single piece of metal plate which has been stamped into the desired form to act as a spring. Clamp 18 produces sufficient force to secure heat sink 14 to heat generating device 29 and PCB 12. Clamp 18 can be stamped from an aluminum or tin material, for example. Clamp 18 is formed from a stamped metal of 0.3 to 0.5 mm thick material.
Clamp 18 includes a body 40, at least two legs 46 extending from body 40, and at least two feet 48. Body 40 includes at least one beam 42 configured to extend between adjacent fins 16 to opposing perimeter edges 34 of heat sink 14. The width of beam 42 is appropriate to extend between two adjacent fins 16. With continued reference to
In one embodiment, body 40 of clamp 18 includes edges 44 extending between and connecting multiple beams 42. In one embodiment, two parallel beams 42 are included on opposing ends of clamp 18 with edges 44 extending between. In one embodiment, edges 44 are perpendicular to beams 42. In one embodiment, clamp 18 includes multiple beams 42 which are distributed across the surface of heat sink 14 to provide an even distribution of applied loads when assembled to heat sink 14. Factors which contribute to determining the quantity, size and material characteristics of beams 42 include the load requirement of the thermal interface material of heat spreader 29 and the mass of heat sink 14, for example. Other factors can also be considered.
Clamp 18 has at least two legs 46 with each leg 46 terminating in a foot 48. Feet 48 are formed at an angle to legs 46. Feet 48 form hooks which protrude through holes 22 of PCB 12 and hold clamp 18 firmly in place using the spring force of the clamp 18 to bias feet 48 upward to contact bottom surface 26 of PCB 12 when assembled. In one embodiment, legs 46 extend from opposing corners of the clamp. In one embodiment, legs 46 are generally aligned with beams 42.
Clamp 18 can be installed manually, or with a tool to aid in compression and installation. Clamp 18 is biased with beam 42 between adjacent fins 16 of heat sink 14 to extend legs 46 and feet 48 through holes 22 of PCB 12. Pressure placed on beam 42 or legs 46 is released and feet 48 resiliently abut against back surface 26 of PCB 12. Once clamp 18 is in place, clamp retainers 20 are inserted into the same holes 22 that legs 46 occupy. Clamp retainer 20 occupies the space of hole 22 that leg 46 does not already occupy. In this manner, hole 22 is substantially filled and prevents dislocation of clamp 18. Clamp retainers 20 secure legs 46 and feet 48 in order that they do not become dislodged during a mechanical shock but are not under any load under normal conditions. In this manner, clamp 18 is configured to withstand a 30 G shock event.
Middle section 52 has a first perimeter 56 configured to extend within hole 22 of PCB 12. Middle section 52 has a length which allows it to extend within the thickness T1 of PCB 12, as illustrated in
Head 50 includes a main body 64 extending from a first end 68 to middle section 52. Head 50 includes tabs 62 joined to main body 64 at first end 68 and extending from main body 64 to terminate at second end 70. In one embodiment, tab 62 includes an extension 72 at second end 70. Tabs 62 are compressible and expandable in relation to main body 64. In an expanded state, second ends 70 of tabs 62 extend a distance from main body 64. In a compressed state, which is also a biased state, tabs 62 are compressed such that second ends 70 and extensions 72 are adjacent to main body 64. When compressed, head 50 has a perimeter which is smaller or equal to first perimeter 56 of middle section 52, and when expanded, head 50 has a perimeter which is larger than hole 22. In this manner, clamp retainer 20 is insertable into hole 22 and is prevented from being removed from PCB 12 until tabs 62 are once again compressed. Accordingly, clamp retainer 20 is removably attachable to PCB 12.
When fully assembled with PCB 12, head 50 extends above front surface 24 of PCB 12, middle section 52 extends within hole 22 and bottom section 54 abuts back surface 26 of PCB 12. In one embodiment, clamp retainer 20 is injected molded plastic of approximately 6 mm outside diameter and 12 to 15 mm tall. In one embodiment, middle section 52 is configured to fit within a 3 mm hole 22. Clamp retainer 20 can be made of low cost material such as a plastic of various kinds.
As illustrated further in
Clamp 118 includes a beam 140, edges 144 extending from opposing ends of beam 140, and legs 146 extending from each edge 144 opposite beam 140 and terminating at feet 148. Beam 140 is extendable between adjacent fins 16 of heat sink 14. When biased, legs 146 are urged downward into holes 22 until feet 148 are fully extended through hole 22 at back surface 26 of PCB 12. Feet 148 then resiliently abut against back surface 26. Clamp retainer 120 is inserted into hole 22 alongside leg 146. Clamp retainer 120 is inserted upward from back surface 26 to secure leg 146 within hole 22. Clamp retainer 120 is similar to clamp retainer 20, however, groove 160 is sized and shaped to accommodate the wire formed leg 146 and foot 148 of clamp 118. In one embodiment, the spring wire forming clamp 118 is 0.5 to 2 mm thick.
In one embodiment, PCB 12 includes only two holes 22 positioned diagonally opposite corners of heat sink 14 to correspond with the extension of legs 146. In another embodiment, additional holes 22 are provided and clamp retainers 120 can be inserted into holes 22 in which legs 146 are not inserted. Head 50 of clamp retainer 20 is assembled between perimeter edge 34 and edge 144 at holes 22. As with previous embodiments, clamp retainer 120 is configured to prevent heat sink 14 from becoming dislodged and moving across the surface of the heat spreader 28 and assist in positioning heat sink 14 on heat producing device 29 as desired. Clamp retainer 120 is unstressed by clamp 118.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.
