Patent Publication Number: US-2005133934-A1

Title: Thermal interface material bonding

Description:
BACKGROUND  
      An integrated circuit (IC) die includes a semiconductor substrate and various electronic devices integrated therewith. The electronic devices may generate heat during operation of the IC die. This heat may adversely affect the performance of the IC die, and in some cases may damage one or more of its integrated electronic devices.  
      Conventional systems use fans and/or temperature monitors to regulate the heat to which an IC die is subjected. Heat dissipators (e.g. heat spreaders, heat sinks, and/or heat pipes) may also be used to direct heat away from an IC die. A thermal interface material may be disposed between a heat dissipator and an IC die in order to bond the heat dissipator to the IC die and/or to assist the transmission of heat from the IC die to the heat dissipator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of an apparatus according to some embodiments.  
       FIG. 2  is a diagram of a process according to some embodiments.  
       FIG. 3  is a cross-sectional side view of a heat dissipator according to some embodiments.  
       FIG. 4  is a cross-sectional side view of a heat dissipator and a solder preform according to some embodiments.  
       FIGS. 5A through 5C  are cross-sectional side views of a heat dissipator, a solder preform, and a roller according to some embodiments.  
       FIG. 6  is a diagram of a process according to some embodiments.  
       FIGS. 7A and 7B  illustrate systems to remove oxides according to some embodiments.  
       FIGS. 8A and 8B  are cross-sectional side views of a heat dissipator, a solder preform, and a press according to some embodiments.  
       FIG. 9A  is a cross-sectional side view of a heat dissipator, a solder preform, a press, a heating device, and a heat control according to some embodiments.  
       FIG. 9B  is a cross-sectional side view of a heat dissipator, a solder preform, a press, a heating device, and a heat control according to some embodiments.  
       FIG. 9C  is a cross-sectional side view of a heat dissipator, a solder preform, a press, a vibration device, and a vibration control according to some embodiments.  
       FIGS. 10A and 10B  are side views of a heat dissipator, a solder preform, a form, an evacuator, and a dispenser according to some embodiments.  
       FIG. 11  is a side view of a system according to some embodiments. 
    
    
     DETAILED DESCRIPTION  
       FIG. 1  is a perspective view of apparatus  1  according to some embodiments. Apparatus  1  comprises heat dissipator  10  and solder preform  20 . Apparatus  1  may be used to dissipate heat from an IC die according to some embodiments. Accordingly, heat dissipator  10  may define vent hole  12  to assist in gas, moisture and/or heat dissipation from the IC die.  
      As shown, heat dissipator  10  comprises an integrated heat spreader. Heat dissipator  10  may comprise any other structure for dissipating heat according to some embodiments, including but not limited to a heat pipe and a heat sink. Heat dissipator  10  may comprise any currently- or hereafter-known thermally conductive material. Non-exhaustive examples include copper and aluminum, which may or may not be plated with a different thermally-conductive material, including but not limited to nickel and gold. In some embodiments, heat dissipator  10  comprises nickel-plated copper that is in turn plated with gold, silver, tin, palladium, and/or another material.  
      Solder preform  20  may also comprise any suitable solder preform. In some embodiments, solder preform  20  is composed of elemental indium solder, indium-based solder, tin-based solder, or another type of soft solder.  
      A first surface of solder preform  20  is coupled to first surface  14  of heat dissipator  10 . According to some embodiments, solder preform  20  is coupled to first surface  14  by placing the first surface of solder preform  20  on first surface  14  and by rolling a roller across second surface  22  of solder preform  20 . Such coupling may produce a substantially voidless interface between solder preform  20  and heat dissipator  10  in some embodiments. In comparison to other interfaces, a voidless interface may provide increased strength at the interface, increased heat transfer across the interface and/or increased resistance to the development and propagation of cracks at the interface.  
       FIG. 2  is a diagram of process  30  to fabricate apparatus  1  according to some embodiments. Process  30  may be executed by one or more devices, and all or a part of process  30  may be executed manually. Process  30  may be executed by an entity different from an entity that manufactures heat dissipator  10  and/or solder preform  20 .  
      Initially, at  31 , a first surface of a solder preform is placed on a first surface of a heat dissipator.  FIG. 3  is a cross-sectional side view of heat dissipator  10  for purposes of explaining some embodiments. Heat dissipator  10  may rest on any suitable surface prior to process  30 .  
       FIG. 4  illustrates placement of solder preform  20  at  31  according to some embodiments. Generally, pick and place device  40  picks solder preform  20  from a repository such as a tape reel or a stack using suction devices, clamping devices and/or adhesives, transports solder preform  20  to a position above heat dissipator  10 , places a first surface of solder preform  20  at an appropriate position on first surface  14  of heat dissipator  10 , and releases solder preform  20 . Pick and place device  40  thereafter moves out of the region above solder preform  20 . Any currently- or hereafter-known placement systems may be used at  31 .  
      Next, at  32 , a roller is rolled across a second surface of solder preform  20 .  FIGS. 5A through 5C  illustrate roller  50  rolling across second surface  22  according to some embodiments. Arrow  55  indicates the direction of rotation of roller  50 . Roller  50  may comprise a teflon-plated steel roller with a 0.1875 inch diameter. According to some embodiments, roller  50  applies 20 pounds of force to solder preform  20 . Other suitable roller materials, roller sizes, and pressures may be used at  32  in some embodiments.  
      According to some embodiments, roller  50  rolls across second surface  22  two or more times at  32 . Roller  50  may roll back and forth between the position shown in  FIG. 5C  and the position shown in  FIG. 5A . Roller  50  may roll across two or more axes of second surface  22  in some embodiments.  
      Some embodiments of process  30  include dispensing a substantially inert gas (e.g. nitrogen, argon) into a volume surrounding preform  20  at  31  and/or at  32 . The gas may prevent the build-up of oxides on preform  20  and/or on heat dissipator  10 .  
      Process  30  may create a mechanical bond between solder preform  20  and heat dissipator  10 . Moreover, a resulting interface between solder preform  20  and heat dissipator  10  may be substantially voidless in some embodiments. Process  30  may also or alternatively cause plastic deformation of solder preform  20 , which may assist in breaking up surface oxides located on solder preform  20 .  
       FIG. 6  is a diagram of process  60  to fabricate apparatus  1  according to some embodiments. Process  60  may be executed by one or more devices, and all or a part of process  30  may be executed manually. Process  60  may be executed by an entity different from an entity that manufactures heat dissipator  10  and/or solder preform  20 .  
      Oxides are removed from a first surface of a solder preform and from a first surface of a heat dissipator at  61 . Removal of the oxides may increase interatomic diffusion and promote the later formation of a substantially voidless interface between the two surfaces.  FIG. 7  illustrates plasma etcher  70  for removing the oxides at  61  according to some embodiments. Plasma etcher  70  may be a dedicated unit in which one or more solder preforms and/or heat dissipators and received by input tray  72 , etched using a plasma (e.g. hydrogen plasma), and output to output tray  74 . Any currently- or hereafter-known system or systems for plasma etching made by used in conjunction with some embodiments.  
       FIG. 7B  illustrates a system for removing oxides at  61  according to some embodiments. Shown are acid applicator  76  and acid applicator  78  for applying acid to a first surface of heat dissipator  10  and to a first surface of solder preform  20 , respectively. Also shown are supports  80  and  85  respectively supporting heat dissipator  10  and solder preform  20 .  
      In operation, acid applicator  76  may apply acid to the first surface of heat dissipator  10  and, after a suitable time period has passed, may rinse the acid off of the first surface using deionized and/or distilled water. Acid applicator  78  may similarly apply acid to the first surface of solder preform  20  and, after a suitable time period, may rinse the acid off of the first surface using deionized and/or distilled water. According to some embodiments, acid is dispensed onto both heat dissipator  10  and solder preform  20  by applicator  76 , simultaneously or at different times, and is rinsed off of both heat dissipator  10  and solder preform  20  by applicator  78 , also simultaneously or at different times.  
      The acid used in some embodiments may comprise hydrochloric and/or sulfuric acid, and may preferentially attack oxides of the material to which it is to be applied. Any other suitable acid application system may be employed at  61 , including an acid dip arrangement.  
      Next, at  62 , the first surface of the solder preform is placed on the first surface of the heat dissipator as described with respect to  31  of process  30 . Similarly, a roller may be rolled across a second surface of the solder preform at  63  as described with respect to  32  of process  30 . The solder preform and the heat dissipator are then pressed against each other at  64 . In some embodiments, this pressure may promote interatomic diffusion between the two surfaces.  
       FIGS. 8A and 8B  illustrate the pressing of solder preform  20  and heat dissipator  10  against each other according to some embodiments.  FIG. 8B  shows a press comprising platen  90  and ram  100 . A second surface of heat dissipator  10  rests on platen  90  and ram  100  is positioned above solder preform  20 . Platen  90  and ram  100  are configured for relative movement toward one another. That is, platen  90  may move toward stationary ram  100 , ram  100  may move toward stationary platen  90 , and/or platen  90  and ram  100  may both move toward each other.  
      In some embodiments, ram  100  contacts a second surface of solder preform  20  at  64 .  FIG. 8B  shows platen  90  and ram  100  pressing solder preform  20  and heat dissipator  10  against each other. Such pressure may cause solder preform  20  and/or heat dissipator  10  to deform.  
      According to some embodiments, a substantially inert gas (e.g. nitrogen, argon) is dispensed into a volume surrounding preform  20  at  63  and/or at  64 . The gas may prevent the build-up of oxides on preform  20  and/or on heat dissipator  10 .  
       FIGS. 9A through 9C  illustrate systems for applying energy to the preform/dissipator interface while preform  20  and dissipator  10  are pressed against each other at  64 .  FIG. 9A  shows heating element  105  disposed within ram  100  and heat control  110  coupled to heating element  105 . Heat control  110  may control an amount of heat that is generated by heating element  105  and transferred to an interface of preform  20  and dissipator  10  at  64 .  
      Heating element  115  may be disposed within platen  90  and coupled to heat control  120  as shown in  FIG. 9B . As described with respect to heat control  110 , heat control  120  may control an amount of heat that is generated by heating element  115  and transferred to the interface of preform  20  and dissipator  10  at  64 . Heating the interface may assist the diffusion of solder preform  20  into heat dissipator  10  by softening the material thereof. Some embodiments may comprise each of heating element  105 , heat control  110 , heating element  115 , and heat control  120 .  
       FIG. 9C  shows horn  130  coupled to platen  90  and to vibration control  140 . Horn  130  may comprise a vibration device to apply vibratory energy to platen  90  at  64 . In some embodiments, horn  130  is coupled to ram  100 . The vibratory energy may comprise ultrasonic and/or mechanical vibration. Vibration control  140  may control a frequency and/or amplitude of the vibratory energy applied by horn  130 . Vibratory energy may assist in plastically deforming and breaking up surface oxides on the mating surfaces of solder preform  20  and heat dissipator  10 .  
       FIGS. 10A and 10B  illustrate the pressing of solder preform  20  and heat dissipator  10  against each other according to some embodiments. Specifically,  FIG. 10A  shows heat dissipator  10  resting on base  150 , which may comprise platen  90  according to any of the above-described embodiments or another suitable support surface. A first surface of solder preform  20  has been placed on a first surface of heat dissipator  10 . Also placed on heat dissipator  10  and around a perimeter of solder preform  20  is form  160 . Form  160  may comprise any suitable material, including teflon-plated steel.  
      Prior to  64 , evacuator  170  may operate to evacuate air from a volume surrounding solder preform  20  and surrounded by form  160 . In some embodiments, dispenser  180  also or alternatively operates prior to  64  to dispense an inert gas (e.g. nitrogen, argon) into the volume. Ram  100  is then moved downward to press solder preform  20  against heat dissipator  10 .  
       FIG. 10B  shows ram  100  after having pressed solder preform  20  against heat dissipator  10  in some embodiments of  64 . Solder preform  20  has become thinner than shown in  FIG. 10A  and extends to the walls of form  160 . Form  160  may thereby allow precise control over the final dimensions of solder preform  160  and may allow the use of greater pressure at  64  than otherwise usable.  
       FIG. 11  illustrates a system according to some embodiments. System  200  includes IC die  210  coupled to solder preform  20  of apparatus  1 . IC die  210  includes integrated electrical devices and may be fabricated using any suitable material and fabrication techniques. In some embodiments, IC die  210  comprises a microprocessor chip having a silicon substrate.  
      Electrical contacts  215  are coupled to IC die  210  and may comprise Controlled Collapse Chip Connect (C4) solder bumps. Electrical contacts  215  may be electrically coupled to the electrical devices that are integrated into IC die  210 . The electrical devices may reside between a substrate of IC die  210  and electrical contacts  215  in a “flip-chip” arrangement. In some embodiments, such a substrate resides between the electrical devices and electrical contacts  215 .  
      Electrical contacts  215  are also coupled to electrical contacts (not shown) of substrate  220 . In some embodiments, die  210  is electrically coupled to substrate  220  via wirebonds in addition to or as an alternative to electrical contacts  215 . Substrate  220  may comprise any ceramic, organic, and/or other suitable material, and includes solder balls  225  for carrying power and I/O signals between IC die  210  and external devices. Alternative interconnects such as through-hole pins may be used instead of solder balls.  
      Heat dissipator  10  is coupled to heat sink  230 . As such, apparatus  1  may increase a thermal coupling between die  210  and heat sink  230 . Heat sink  230  may comprise any currently- or hereafter-known passive or active heat sink. Heat sink  230  is coupled to heat dissipator  10  by solder preform  235 . Solder preform  235  may be coupled to heat dissipator  10  using process  30  and/or process  60  described above. Process  30  and/or process  60  may be used to couple a solder preform to any structure to which solder may be bonded, including but not limited to metallized structures.  
      Motherboard  240  may electrically couple memory  250  to IC die  210 . More particularly, motherboard  240  may comprise a memory bus (not shown) that is electrically coupled to solder balls  225  and to memory  250 . Memory  250  may comprise any type of memory for storing data, such as a Single Data Rate Random Access Memory, a Double Data Rate Random Access Memory, or a Programmable Read Only Memory.  
      The several embodiments described herein are solely for the purpose of illustration. Some embodiments may include any currently or hereafter-known versions of the elements described herein. Therefore, persons skilled in the art will recognize from this description that other embodiments may be practiced with various modifications and alterations.