Abstract:
A heat sink structure includes a heat sink; a threaded heat sink base pocket within the heat sink; a module lid, where the module lid thermally interfaces with a die; a threaded exterior portion of the module lid; and a thread engagement between the threaded heat sink base pocket and the threaded exterior portion of the module lid, where the thread engagement mechanically couples the heat sink to the module lid.

Description:
BACKGROUND 
       [0001]    The present disclosure relates to the field of electronic circuits, and specifically to cooling devices used in electronic circuits. Still more specifically, the present invention relates to heat sinks used as cooling devices in electronic circuits. 
       SUMMARY 
       [0002]    In an embodiment of the present invention, a heat sink structure includes a heat sink; a threaded heat sink base pocket within the heat sink; a module lid, where the module lid thermally interfaces with a die; a threaded exterior portion of the module lid; and a thread engagement between the threaded heat sink base pocket and the threaded exterior portion of the module lid, where the thread engagement mechanically couples the heat sink to the module lid. 
         [0003]    In an embodiment of the present invention, a circuit board includes the heat sink structure described above. 
         [0004]    In an embodiment of the present invention, a computing device includes an air moving device and a circuit board that includes the heatsink structure described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  depicts an exemplary computing device into which a novel heat sink structure is incorporated; 
           [0006]      FIG. 2  illustrates a top view of the novel heat sink structure presented herein; and 
           [0007]      FIG. 3  depicts a cross-sectional view of the heat sink structure shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    Electronics cooling for packaged modules often uses two methods of mounting/mating their cooling solution: mounting hardware and adhesive thermal interface material (TIM). In the prior art, mounting hardware used clips, screws, springs, etc. that provided tensions between the cooling solution (e.g., a heat sink) and the device being cooled (e.g., an integrated circuit (IC), also known as a “die”, which is a small block of semiconducting material on which a functional circuit is fabricated). The adhesive TIM provides thermal conduction between the heat sink and the die. 
         [0009]    Mounting hardware poses several problems. 
         [0010]    First, mounting hardware takes up high quality board space and is sometimes impossible to use on various modules. That is, springs, clips, etc. not only take up space in a system, they are also difficult to manipulate. 
         [0011]    Second, mounting hardware is not adjustable. That is, a clip/spring simply holds the heat sink down at a certain pressure, which is fixed. This results in undue pressure on connectors (between the die and a circuit board) as well as on the die itself. 
         [0012]    Third, mounting hardware such as ball grid array (BGA) spring clips (used on modules to provide actuation to small heat sinks and used in conjunction with high performance TIMs) have the drawbacks of reduction in heat sink performance (due to poor mating between the heat sink and the die); solder ball stress/integrity issues (due to undue pressure against the die by the BGA spring clips); the inability to support high loads (due to the limited strength of the springs in the BGA spring clips); and the inability to survive shock/vibe requirements (due to the limited resilience provided by BGA spring clips). 
         [0013]    Furthermore, adhesive thermal interface materials (TIMs), when used alone to adhere a heat sink to a die are among the lowest performers for thermal conductivity since they are mainly composed of polymer adhesive. Furthermore, adhesive TIMs are also extremely difficult to rework or remove, since they are an adhesive (glue) that permanently bonds the heat sink to the die. 
         [0014]    Other actuation hardware requires board space and sometimes holes in the board in order to have retention. This is the most undesirable option since board space near modules is at a premium and any hardware in these regions takes away from the capability and/or signal integrity of the whole system. 
         [0015]    With reference now to the figures, and specifically to  FIG. 1 , an exemplary computing device  101  into which the presently-presented and novel heat sink structure  103  is incorporated is presented. Heat sink structure  103  includes a module lid  105 , which is mounted atop a die  107  (e.g., an integrated circuit), which is mounted atop a substrate  109  (e.g., a glass epoxy that supports internal wires to external connectors), which is mounted on a circuit board  111  (e.g. a glass epoxy structure that supports various integrated circuits, power supplies, fans, input/output interfaces, etc.). 
         [0016]    As shown in  FIG. 1 , in an embodiment of the present invention module lid  105  has a polygonal shape (e.g., a square) that has multiple threaded corners, such as threaded corner  113 . When a heat sink (shown in  FIGS. 2-3  but not  FIG. 1 ) is fully engaged with the module lid  105 , airflow  115  from an air moving device  117  (e.g., a cooling fan within a housing of computing device  101  and/or mounted on the circuit board  111  itself) flows parallel to (and thus unimpeded by) cooling vanes on the heat sink. Additional details of the heat sink structure  103  are shown below in  FIGS. 2-3 . 
         [0017]    With reference now to  FIG. 2 , a top view of the novel heat sink structure  103  introduced in  FIG. 1  is presented. As shown in  FIG. 2 , a heat sink  202  is mounted over the module lid  105 . Heat sink  202  has a threaded heat sink base pocket  204 , which is screwed onto the threaded corners (e.g., threaded corner  113 ) of module lid  105  to form multiple thread engagements (e.g., thread engagement  206 ). Thus, heat sink  202  is screwed down onto module lid  105  until 1) solid mechanical and thermal contact is established between heat sink  202  and module lid  105 , and 2) the airflow  115  from air moving device  117  flows unobstructed across the vanes (e.g., vane  208 ) on heat sink  202 . 
         [0018]    With reference now to  FIG. 3 , a cross-sectional view of the heat sink structure  103  shown in  FIG. 2  is presented. 
         [0019]    As shown in  FIG. 3 , a package ball grid array (BGA)  301  provides electrical connections between a planar (i.e., a printed circuit board—not shown) and the die  107  using internal wiring, such as the depicted wire  303  that connects one of the solder balls from package BGA  301  to one or more of the solder balls in the chip BGA  305 . The chip BGA  305  is connected to internal circuitry (not shown) within the die  107 , which is thermally coupled by a die thermal interface material (TIM)  307  to the underside of the module lid  105 . As depicted, module lid  105  is adhered to substrate  109  using a lid adhesive  311  (e.g., a heat resistant glue), thus providing a fixed combination of module lid  105 , die  107 , and substrate  109 . 
         [0020]    The present invention provides a novel and adjustable means for affixing the heat sink  202  to the module lid  105 . That is, the heat sink  202  has a threaded heat sink base pocket  204 , whose inner surfaces are threaded. These threaded inner surfaces from the threaded heat sink base pocket  204  screw onto the threaded corners (e.g., threaded corner  113 ) of the polygonal-shaped module lid  105  at areas such as the depicted thread engagement  206  area. 
         [0021]    As a user screws the heat sink  202  down onto the module lid  105 , the user is able to 1) selectively control the amount of pressure forced against the module lid  105 ; 2) evenly spread out the lid thermal interface material (TIM)  309  between the heat sink  202  and the module lid  105  by the rotational movement of the heat sink  202 ; and 3) align the orientation of the vanes (e.g., vane  208 ) such that airflow  115  from the air moving device  117  shown in  FIGS. 1-2  flows between the vanes, thereby providing maximum heat removal. 
         [0022]    Thus, as depicted and described herein, the corners of a lidded module are rounded and threaded such that a heat sink with a certain-depth threaded recess can be screwed on. Mounting a heat sink in this fashion prevents the need for board level mounting hardware and allows the use of a high quality thermal interface material. The threading is aligned such that at an optimal, nominal gap, the fins and heat sink orientation are properly aligned with the airflow direction. Given the planarity of lidded modules, this type of actuation has a beneficial effect on the thermal bond line directly over the hottest components, further improving thermal performance of the heat sink. 
         [0023]    An additional benefit of the mounting scheme presented and described in the present disclosure and figures includes better electromagnetic interference (EMI) protection due to the intimate contact between the heat sink base and the module lid. 
         [0024]    In an alternative embodiment of the present invention, a threaded ring is used on the previously described heat sink structure to provide a compliant surface for mounting a standard heat sink. This type of mounting allows a spring clip or other constant force mounting scheme without using board space or impacting signal integrity. 
         [0025]    Having thus described embodiments of the present invention of the present application in detail and by reference to illustrative embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the present invention defined in the appended claims.