Abstract:
A device for use in cooling a microelectronic component in a data processing system with a heat sink and a fan. The device includes means for maintaining the fan in close proximity to the heat sink and in a position relative to the fan for moving air over cooling surfaces of the heat sink and component to vibrationally isolate the fan from the heat sink and reduce the transmission of fan vibration to the heat sink. In one embodiment, the vibration isolation component is also configured to receive the fan and secure the fan in position relative to the heat sink to locate the fan in a predetermined position relative to the heat sink. In another embodiment, the vibration isolation component comprises a compliant gasket defining an opening adapted to receive an active area of the fan to allow air flow generated by the fan to reach the heat sink.

Description:
BACKGROUND 
   1. Field of the Invention 
   The present invention is in the field of computing systems and more particularly in the field of cooling microelectronic devices within a system and reducing acoustical noise generated by the system. 
   2. Background 
   In a competitive market, particularly the market for personal computing devices, customers will weigh the characteristics of products from multiple producers before a purchase is made. Different customers and geographies, have dissimilar opinions with regards to what makes a “quality” computing device. The most commonly sought after attributes of a computing device are processor speed, disk capacity, memory size, cost, graphics capability, form factor, and appearance. These attributes tend to be comparable among the various producers of computing systems. 
   The most rapidly growing area of interest for customers is acoustics or noise. Many customers now weight the acoustical characteristics of a system as highly significant in determining the quality of the system. Currently the primary elements operative in the production of system acoustical noise are the system&#39;s various electro-mechanical cooling fans the including system fans, microelectronic component fans, and power supply fans. 
   Microelectronic component fans, commonly known as fan-sinks, include a fan and heat sink assembly utilized to cool an individual microelectronic component. A fan-sink includes a heat sink, a fan, and a fan-shroud, which affixes to the heat sink and to which the fan is affixed. Conventional fan shrouds rigidly tie together the fan and the heat sink. Initially, the fan is affixed and secured to the fan shroud by screws, typically four. Next the fan/fan-shroud sub-assembly is affixed to the heat sink by tabs (typically four) that are bent around the base of the heat sink. This rigid mounting scheme can cause excitement between the fan and the fan shroud and between the fan shroud and the heat sink. This excitement creates undesired sound power and an increased sound pressure at the operator&#39;s position. It would be desirable to reduced or eliminate the transmission of vibration in a fan sink assembly and thereby reduce the sound power and pressures experienced by the end-user. 
   SUMMARY OF THE INVENTION 
   The problem identified above are addressed by a novel fan/heat sink assembly according to the present invention. The assembly incorporates a vibration isolating element into the assembly of fan and heat sink. The vibration isolating element is interposed between the fan and any other elements of the assembly affixed to it. The transmission of vibrational energy is reduced or eliminated by the use of a material, such as an elastomer, with a high damping coefficient, for the vibration-isolating element. Such a material will internally damp out vibrations from the fan and reduce or eliminate their transmission and subsequent re-radiation as acoustic noise, thus reducing the sound power transmitted by the computing device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which like reference numerals indicate like elements. 
       FIG. 1  depicts the physical mounting scheme for the attachment of a fan to a heat sink, according to the prior art; 
       FIG. 2  depicts selected elements of a fan sink assembly according to the present invention emphasizing a heat sink, a fan, and an integral fan shroud-vibration isolation component that affixes the fan to the heat sink and prevents the transmission of vibrational energy from the fan to the heat sink; 
       FIG. 3  depicts the integral fan shroud-vibration isolation component of  FIG. 2  in greater detail; 
       FIG. 4  depicts an embodiment of the integral fan shroud-vibration isolation component comprising co-molded polymer and elastomer elements; 
       FIG. 5  depicts an embodiment of the integral fan shroud-vibrational isolation component comprising metal and elastomer elements; 
       FIG. 6  depicts a fan sink assembly according to the present invention comprising a heat sink, a fan, a fan shroud, and a vibration isolation component that vibrationally isolates the fan and the fan shroud and affixes the fan to the fan shroud; 
       FIG. 7  depicts the vibration isolation component of the embodiment depicted in  FIG. 6  emphasizing an elastomer element in the form of a gasket; and 
       FIG. 8  depicts the vibration isolation component of the embodiment depicted in  FIG. 6  emphasizing an elastomer gasket and pre-applied adhesive layers. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   The following is a detailed description of example embodiments of the invention depicted in the accompanying drawings. The example embodiments are in such detail as to clearly communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations or embodiments, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. The detailed descriptions below are designed to make such embodiments obvious to a person of ordinary skill in the art. 
   Generally speaking, the present invention contemplates a fan sink assembly with desirable acoustics characteristics for reduced noise generation in a data processing system. The fan sink assembly includes a heat sink, a fan, a fan shroud, and a vibration isolation component. In use, the assembly affixes to a microelectronic device, such as a microprocessor, affixed to a printed wiring board using a thermally conductive material. The assembly functions to cool the microelectronic device. The heat generated by the microelectronic component transfers to the heat sink by conduction through the thermally conducting materially. The fan moves air through the openings in the heat sink, removing heat from the heat sink by convective cooling. The net effect is to move heat from the microelectronic device to the ambient air, thus cooling the microelectronic device. 
   In a conventional fan sink assembly, the fan is rigidly affixed using, typically, four screws to a fan shroud, which in turn rigidly affixes to the heat sink by means of legs. The fan shroud legs are capable of being slightly elastically deformed allowing the shroud and fan sub-assembly to be affixed to a heat sink. The fan shroud legs then return to their original position, thus affixing the sub-assembly to the heat sink. 
   The fan is a rotational device and as such generates a finite amount of vibrational energy as a result of the mass of the fan motor and blades being slightly out of balance around the axis of rotation. Due to the rigid mounting of the fan to the fan shroud, the vibrational energy is transferred to the fan shroud. The fan shroud—fan subassembly is then rigidly mounted to the heat sink, again allowing transmission of vibrational energy to the heat sink. The heat sink may take any of a number of conventional forms, such as a rectangular array of pins (pin-fin heat sink) or thin blades, integrated with a solid base of material to which the fan shroud legs affix. The mechanical structure of the heat sink lends itself to the re-transmission of vibrational energy as sound pressure, thus raising the acoustic noise level of the computing system. 
   It is common for such computing systems to have ventilation structures on the front face (the face closest to the operator for a personal computer system). Since the internal structure of the cooling device is designed to move air through the ventilation holes, the sound pressure developed by the vibration of the heat sink will preferentially radiate out of the front of the machine, increasing the noise level of the system relative to the operator. 
   The insertion of a vibration isolation component into the fan sink assembly as described herein reduces or prevents the transmission of vibrational energy from the fan to other components to which it is affixed. The reduction or elimination of vibrational energy from the fan reduces or eliminates the vibrational energy which can subsequently be transmitted as acoustic noise. 
   Turning now to the drawings,  FIG. 1  depicts a conventional heat sink, fan, fan shroud (fan sink) assembly  100 . The fan  102  is rigidly affixed to the fan shroud  104  by means of screws  106 , typically located on the four corners of the fan. The result is a fan-fan shroud sub assembly  108 . 
   The heat sink  110  includes an array of pins or fins  112  affixed to a solid base  120 . The fan-fan shroud subassembly  108  affixes to the base of the heat sink  120  by means of flexible legs  114  which are capable of deforming elastically a sufficient amount to allow the formed members or feet  116  at the base of the legs  114  to capture the heat sink  110  between opposing pairs of legs  114 . 
   Referring now to  FIG. 2 , one embodiment of a fan sink assembly  200  according to the present invention is depicted. The depicted assembly  200  includes a fan  202 , a heat sink  204 , and an integral vibration isolation element-fan shroud  206  that receives and locates the fan  202  relative to the heat sink  204 . In this embodiment, the vibration isolation element  206  serves the purpose of affixing the fan  202  to the heat sink  204  in place of the fan shroud  104  ( FIG. 1 ) typically used in the currently produced fan-heat sink assemblies. The vibration isolation component  206  is produced from an elastomeric material, of which rubber is an example, having sufficient rigidity to receive the fan and a damping coefficient sufficient to reduce or eliminate the transmission of vibrational energy from the fan  202  to the heat sink  204 . 
   Continuing,  FIG. 3  depicts the integral vibration isolation component-fan shroud  206  of the embodiment depicted in FIG.  2 . The vibration isolation component-fan shroud  206  includes a carrier structure  301  that defines a cavity  302  of dimensions matched to the dimensions of the fan  202 . The carrier structure  301  includes a base that defines an opening  304  whose dimension matches the active area of the fan  202 , allowing air flow through the vibration isolation component-fan shroud  206  and the heat sink  204 , legs  306  and cross-bands  308  which connect opposing pairs of legs  306 . An opening cavity  306  captures the top surfaces of the heat sink. 
   In use, the fan  202  is received into the cavity  302  of the integral vibration isolation component-fan shroud  206 . Since the vibration isolation component-fan shroud  206  is made from an elastomeric material, it has an inherent compliance that allows the cavity  302  to deform a necessary to receive the fan  202  and then return to its original shape, retaining the fan  202 . The dimensions of opening  304  in the floor of the fan cavity  302  match the dimensions of the active flow area of the fan  202 . As the fan  202  spins under power, air moved by the fan  202  is free to flow through the opening  302 . Since the fan  202  is encapsulated in the cavity  302  of the vibration isolation component-fan shroud  206 , all air flow related to the fan  202  must go through the heat sink  204 , increasing the cooling efficiency of the heat sink-fan assembly  200  by reducing air flow in non-useful directions. The fan-vibrational isolation-fan shroud subassembly is then affixed to the heat sink  204 . The legs  306  and cross-bands  308  of the vibrational isolation component-fan shroud  206  act like elastic bands due to the elastomeric properties of the material of which it is made, to receive the heat sink  204 , deforming as necessary to receive the heat sink  204  and then returning to their original dimensions, surrounding and retaining the heat sink  204  in position. The opposing cavity  310  conforms to the perimeter of the top surface of the heat sink  204 , further insuring that all air flow moves through the pins or fins of the heat sink  204 . The elastomeric material used for the integral vibrational isolation component-fan shroud may be a solid or foam elastomer, with its properties designed as required by the vibrational frequency of the energy whose transmission is to be eliminated or reduced and by the dimensional requirements of the mechanical assembly. 
     FIG. 4  depicts an alternative embodiment of the integral vibration isolation component-fan shroud  400  produced using both an elastomeric material and a rigid polymer. A co-molding process may be used to produce the integral vibration isolation component-fan shroud  400  from the two materials. In this embodiment the fan receiving cavity  302  and opposing cavity  310  are produced from an elastomeric material which will receive and retain the fan  102 . The legs  306  are made from a rigid polymer, while the cross-bands  308  are also produced from an elastomeric material. This embodiment provides increased mechanical stability before the integral vibration isolation component-fan shroud  400  is affixed to the fan  102  and the heat sink  110 . The elastomeric material used within the integral vibrational isolation component-fan shroud may be a solid elastomer, or a foam elastomer, with its properties designed as required by the vibrational frequency of the energy whose transmission is to be eliminated or reduced and by the dimensional requirements of the mechanical assembly. 
     FIG. 5  depicts an alternative embodiment of the integral vibration isolation component-fan shroud  500  produced using both an elastomeric material and a metal frame, similar to a conventional fan shroud  104 . In this embodiment the metal frame  502  includes a frame, which is over-molded by the elastomer of the cavities  302  and  310 , legs  506  and feet  508 , which serve to affix the shroud  500  to the heat sink  110 . Additional elastomer sections  504  are molded to the feet  116 , isolating the heat sink from the vibration of the fan  102 . 
     FIG. 6  depicts an alternative embodiment  600  including a fan  202 , a heat sink  204 , a fan shroud  602 , and a vibration isolation component in the form of a gasket  604  which affixes both to the fan  202  and the fan shroud  602 , producing a fan-fan shroud subassembly  606  and vibrationally isolating the fan  202  from the fan shroud  602 . The elastomeric gasket  604  prevents transmission of vibrational energy from the fan  202  to the fan shroud  602 . The fan-fan shroud subassembly  606  affixes to the base of the heat sink  204  by means of flexible legs  608  which are capable of deforming elastically a sufficient amount to allow the formed members or feet  610  at the base of the legs  608  to capture the heat sink  204  between opposing pairs of legs  608 . The material from which the gasket  604  is made is an elastomeric material, of which natural rubber is an example. It may be a solid elastomer, molded to shape; a foam elastomer, molded to shape; a solid elastomer, stamped from a sheet; or a foam elastomer, stamped from a sheet. 
     FIG. 7  depicts the vibration isolation gasket  604  of the embodiment depicted in FIG.  6 . The gasket includes a geometric flat shape  702  approximating the shape and dimensions of the fan  202  and an opening  704  whose dimensions and shape are congruent to the dimensions and shape of the active area of the fan  202 . Air moved by the fan  202  moves through the opening in the gasket  604  to reach the heat sink  204 . An adhesive material, having the required resistance to heat, mechanical strength, and adherence may be dispensed on to one side of the gasket  604  and the gasket affixed to the fan shroud  602 . Adhesive is then applied to the opposing side of the gasket  604  and the fan  202  is affixed to the fan shroud-gasket subassembly. The adhesive layers are cured, typically using a thermal process. The resulting fan-gasket-fan shroud subassembly is then affixed to the heat sink using the elasticity of the fan shroud legs  608  and the dimensions of the fan shroud feet  610  as depicted in FIG.  1 . 
     FIG. 8  depicts an alternative embodiment  800  of the gasket  604  depicted in FIG.  7 . Before being assembled with the fan  202  (see  FIG. 6 ) and the fan shroud  602  the gasket material is in the form of a flat sheet. The material may be a solid elastomer material or a foam elastomer material. Pressure sensitive adhesive  802  with a disposable release liner is laminated to opposing sides of the material from which the gasket  604  will be made, forming a composite sheet material. The geometry required by the dimensions of the fan, the outline of the flat shape  702  and the dimensions and location of the opening  704  in the gasket, is produced from the composite sheet material by a stamping process, producing the gasket-adhesive subassembly depicted in FIG.  8 . To produce a fan-fan shroud sub-assembly, the disposable release liner is removed from the precut gasket-adhesive, exposing the press-sensitive adhesive. The gasket-adhesive material is then affixed by pressure to the fan  202 . The disposable release liner is then removed from the free side of the gasket-adhesive combination, exposing the second adhesive surface. The second adhesive surface of the fan-adhesive sub assembly is then affixed to the fan shroud  602 , with pressure applied to produce the bond. 
   It will be apparent to those skilled in the art having the benefit of this disclosure that the present invention contemplates an improved fan-fan shroud-heat sink assembly which includes a vibrational isolation component to reduce or prevent the transmission of vibration from the fan to the fan shroud and heat sink. The isolation of the vibrational energy produced by the fan thus reduces or eliminates the energy that can be radiated as acoustic noise by the heat sink-fan assembly, thus producing an acoustically quieter computer system. It is understood that the form of the invention shown and described in the detailed description and the drawings are to be taken merely as presently preferred examples. It is intended that the following claims be interpreted broadly to embrace all variations of the preferred embodiments disclosed.