Abstract:
A cooling structure for an electronic device comprises a compliant cap preloaded over the electronic device. The compliant cap comprises a horizontal top surface and at least one vertical support for the surface, the vertical support comprising a compliant portion and wherein the compliant cap comprises a thermally conducting material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not Applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED-RESEARCH OR DEVELOPMENT 
   Not Applicable. 
   INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
   Not Applicable. 
   FIELD OF THE INVENTION 
   The invention disclosed broadly relates to the field of electronic devices and more particularly relates to the field of thermal caps for electronic devices. 
   BACKGROUND OF THE INVENTION 
   During the normal operation of a computer, integrated circuit devices generate significant amounts of heat. This heat must be continuously removed, or the integrated circuit device may overheat, resulting in damage to the device and/or a reduction in operating performance. Cooling devices, such as heat sinks, have been used in conjunction with integrated circuit devices in order to avoid such overheating. Generally, a passive heat sink in combination with a system fan has provided a relatively cost-effective cooling solution. In recent years, however, the power of integrated circuit devices has increased exponentially, resulting in a significant increase in the amount of heat generated by these devices, thereby making it extremely difficult to extract heat form these devices. 
   Heat is typically extracted by coupling a heat spreader and a thermal cap to the electronic device as a heat sink. Heat sinks operate by conducting heat from a processor to the heat sink and then radiating it into the air. The better the transfer of heat between the two surfaces (the processor and the heat sink metal) the better the cooling. Some processors come with heat sinks attached to them directly, or are interfaced through a thin and soft layer of thermal paste, ensuring a good transfer of heat between the processor and the heat sink. The thermal paste serves not only to transfer heat but to provide some degree of mechanical compliance to compensate for dimensional changes driven by the high operating temperatures of the devices. However, the paste is a weak link in the thermal path. Attempts to thin this layer have resulted in failure of the layer when it is exposed to dimensional changes. There are some known mechanically complaint solutions but these solutions still rely on paste film somewhere in the path. Thus there is a need for a solution that overcomes these shortcomings. 
   SUMMARY OF THE INVENTION 
   Briefly according to an embodiment of the invention a cooling structure for an electronic device comprises a compliant cap preloaded over the electronic device. The compliant cap comprises a horizontal top surface and at least one vertical support for the surface, the vertical support comprising a compliant portion and wherein the compliant cap comprises a thermally conducting material. In another embodiment of the present invention, the horizontal top surface comprises a top plate comprising thinned edges and the compliant cap comprises a first material having high thermal conductivity and a second material comprising compliant properties. 
   In yet another embodiment of the present invention, a method for cooling an electronic device comprises placing an electronic circuit on a substrate and preloading a compliant cap over the electronic device. The compliant cap comprises compliant properties and heat conducting properties. In yet another embodiment of the present invention, the method further comprises applying a thermal interface material such as a paste between the electronic device and the thermal cap and applying a spreader over the electronic device for coupling with the thermal cap. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and also the advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings. Additionally, the left-most digit of a reference number identifies the drawing in which the reference number first appears. 
       FIG. 1  shows a compliant thermal cap according to an embodiment of the invention. 
       FIG. 1A  shows a top view of the cooling structure of  FIG. 1 . 
       FIG. 2  shows a compliant thermal cap according to an alternate embodiment of the invention. 
       FIG. 2A  shows a top view of the cooling structure of  FIG. 2 . 
       FIG. 3  shows a preload scheme for a thermal cap according to another embodiment of the invention. 
       FIG. 4  shows another preload scheme for a thermal cap according to another embodiment of the invention. 
       FIG. 5  shows another preload scheme for a thermal cap according to another embodiment of the invention. 
       FIG. 6  is a high level block diagram showing an information processing system useful for implementing one embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a cross sectional side view of a cooling structure  100  for an electronic device  108 . A compliant thermal cap  102  comprises a serpentine portion  104  for providing the resilience required to overcome the problems of the prior art. The electronic device (e.g., a semiconductor chip)  108 , situated on a circuit board  106 , is connected by a coupling layer  110  comprising a thermal paste, adhesive, or other thermal interface material. The layer  110  can also act as a heat spreader for extracting heat from the chip  108 . The cap  102  serves the function of dissipating heat generated by the electronic device  108  and has compliance in the “z” direction to conform to thermal expansion by the device  108  and its substrate materials caused by the difference in the coefficients of thermal expansions of the materials of the device  108  and its substrate materials and the cap  102 .  FIG. 1A  shows a top view of the cooling structure  100 . The device  108  is shown in broken lines. 
     FIG. 2  shows a cooling structure  200  comprising a compliant thermal cap  202  according to an alternate embodiment of the invention. The compliant thermal cap  202  comprises a top plate (a horizontal top surface)  203  having thinned edges  206  that provide the required compliance to accommodate the vertical (z direction) movement cause by thermal (temperature) variations in the operation of the device  204 . The compliant cap  202  also comprises a vertical support member  205 . A thermally-conductive layer  208  attaches the device  204  to the top plate  203 . 
     FIG. 2A  is a top view of the cooling structure  200  shown in  FIG. 2 . The thermal cap  202  is shown, as well as an outline of the thinned edges  206  and the inner section of the top plate  203 . 
     FIG. 3  shows a preload scheme for a thermal cap according to a to another embodiment of the invention. The compliant cap  300  is preloaded so that the compliance of the cap maintains contact between the device and the cap  300 , which is situated on a circuit board  304 . The preload is accomplished by inserting pins  308  and  310  into holes in the cap  300 . 
     FIG. 4  shows another preload scheme for a compliant thermal cap  400  comprising a serpentine compliant part  402  according to another embodiment of the invention. Members  404 ,  406 , and  408  are temporarily attached to the cap, via connecting members  410  and  412 , in order to provide preload while the cap is attached to the system. These members would be removed after the attachment was complete. 
     FIG. 5  shows another preload scheme for a thermal cap  502  according to a to another embodiment of the invention. The device  508  is shown within the cap with the resilience preloaded (note the position of the thinned portions  504 ). The fasteners or screws  512  and  514  are inserted through the substrate or circuit board  506  to attach it to the cap  502 . Additional compliance can be introduced by using a compliant material for the attachment layer  510 . 
   The present invention can be utilized for cooling any of a variety of electronic devices. In one embodiment of the present invention, the present invention is used to cool a microprocessor of an information processing system such as a computer.  FIG. 6  is a high level block diagram showing an information processing system useful for implementing one embodiment of the present invention. The computer system includes one or more processors, such as processor  604 . The processor  604  is connected to a communication infrastructure  602 . Various software embodiments are described in terms of this exemplary computer system. After reading this description, it will become apparent to a person of ordinary skill in the relevant art(s) how to implement the invention using other computer systems and/or computer architectures. 
   The computer system can include a display interface  608  that forwards graphics, text, and other data from the communication infrastructure  602  for display on the display unit  610 . The computer system also includes a main memory  606 , preferably random access memory (RAM), and may also include a secondary memory  612 . The secondary memory  612  may include, for example, a hard disk drive  614  and/or a removable storage drive  616 , representing a floppy disk drive, a magnetic tape drive, an optical disk drive, etc. The removable storage drive  616  reads from and/or writes to a removable storage unit  618  in a manner well known to those having ordinary skill in the art. Removable storage unit  618 , represents a floppy disk, a compact disc, magnetic tape, optical disk, etc. which is read by and written to by removable storage drive  616 . As will be appreciated, the removable storage unit  618  includes a computer readable medium having stored therein computer software and/or data. 
   In alternative embodiments, the secondary memory  612  may include other similar means for allowing computer programs or other instructions to be loaded into the computer system. Such means may include, for example, a removable storage unit  622  and an interface  620 . Examples of such may include a program cartridge and cartridge interface, a removable memory chip (such as an EPROM, or PROM) and associated socket, and other removable storage units  622  and interfaces  620  which allow software and data to be transferred from the removable storage unit  622  to the computer system. 
   The computer system may also include a communications interface  624 . Communications interface  624  allows software and data to be transferred between the computer system and external devices. Examples of communications interface  624  may include a modem, a network interface (such as an Ethernet card), a communications port, a PCMCIA slot and card, etc. Software and data transferred via communications interface  624  are in the form of signals which may be, for example, electronic, electromagnetic, optical, or other signals capable of being received by communications interface  624 . These signals are provided to communications interface  624  via a communications path (i.e., channel)  626 . This channel  626  carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, an RF link, and/or other communications channels. 
   In this document, the terms “computer program medium,” “computer usable medium,” and “computer readable medium” are used to generally refer to media such as main memory  606  and secondary memory  612 , removable storage drive  616 , a hard disk installed in hard disk drive  614 , and signals. These computer program products are means for providing software to the computer system. The computer readable medium allows the computer system to read data, instructions, messages or message packets, and other computer readable information from the computer readable medium. The computer readable medium, for example, may include non-volatile memory, such as a floppy disk, ROM, flash memory, disk drive memory, a CD-ROM, and other permanent storage. It is useful, for example, for transporting information, such as data and computer instructions, between computer systems. Furthermore, the computer readable medium may comprise computer readable information in a transitory state medium such as a network link and/or a network interface, including a wired network or a wireless network, that allow a computer to read such computer readable information. 
   Computer programs (also called computer control logic) are stored in main memory  606  and/or secondary memory  612 . Computer programs may also be received via communications interface  624 . In particular, the computer programs, when executed, enable the processor  604  to perform the features of the computer system. Accordingly, such computer programs represent controllers of the computer system. 
   What has been shown and discussed is a highly-simplified depiction of a programmable computer apparatus. Those skilled in the art will appreciate that other low-level components and connections are required in any practical application of a computer apparatus. 
   Therefore, while there has been described what is presently considered to be the preferred embodiment, it will be understood by those skilled in the art that other modifications can be made within the spirit of the invention.