Abstract:
An integrated circuit attachment implementation includes a mechanism for inserting and securely holding a replaceable component to an integrated circuit. The mechanism includes a top plate, leaf springs in contact with the top plate, a leaf spring cradle that carries the leaf springs, with the cradle including upper projections that project through corresponding slots in the top plate, a pin inserted through openings in the upper projections, and a linear slide cam located on an upper surface of the top plate between the upper projections and further located below the pin. The cam operates in a first position to transfer a load the replaceable component to securely hold the replaceable component to the integrated circuit and a second position to allow placement of the replaceable component on the integrated circuit.

Description:
TECHNICAL FIELD 
     The technical field is integrated circuits, and more particularly attachment implementations used to attach components, such as heat sinks, to printed circuit boards. 
     BACKGROUND 
     Current integrated circuit packages are assembled by attaching one or more processors to a printed circuit board or substrate. Assembly may be by soldering electrical components of the processor to the circuit board. Current soldering methods include solder balls placed between the processors and the substrate. More recently, solder columns have been used to attach the processors to the substrate. Other components, such as heat sinks, are then attached to the integrated circuit. Some of these other components are attached using mechanical means. Such mechanical attachments may over stress the solder balls and solder columns, leading to premature failure of the integrated circuit. 
     The mechanical attachment mechanisms that are used for installation of components onto the substrate may take the form of screws, bolts, or studs that arc seated in the substrate, and then turned to operate a metal plate. Turning the screw causes the metal plate to move in a direction along the axis of the screw, compressing the components onto the substrate. However, use of screws and similar devices has many drawbacks. In particular, the application of torque may be highly variable when one human operator turns the screw through more turns than would another human operator. Next, these systems for loading components are complex, require specific tools, take up valuable space in the integrated circuit, and produce metal contamination of the integrated circuit. 
     SUMMARY 
     What is disclosed is an attachment implementation for attaching a replaceable component to an integrated circuit. The integrated circuit includes a processor electrically coupled to a circuit board using solder columns. The attachment implementation includes a top plate, leaf springs in contact with the top plate, a leaf spring cradle that carries the leaf springs, with the cradle including upper projections that project through corresponding slots in the top plate, a pin inserted through openings in the upper projections, and a linear slide cam located on an upper surface of the top plate between the upper projections and further located below the pin. The cam has a flat bottom in communication with the upper surface of the top plate. The cam includes a saddle and a valley. The cam operates in a first position with the pin engaged in the valley to apply a spring force to securely hold the replaceable component to the integrated circuit. 
     Also what is disclosed is an integrated circuit attachment apparatus that includes a replaceable component and a mechanism for inserting and securely holding the replaceable component in the integrated circuit package. The mechanism includes a top plate, leaf springs in contact with the top plate, a leaf spring cradle that carries the leaf springs, with the cradle including upper projections that project through corresponding slots in the top plate, a pin inserted through openings in the upper projections, and a linear slide cam located on an upper surface of the top plate between the upper projections and further located below the pin. The cam operates in a first position to securely hold the replaceable component to the integrated circuit and a second position to allow placement of the replaceable component on the integrated circuit. 
     Finally, what is disclosed is a device to allow repeatable application of a seating force to seat a component in a circuit. The device includes a top plate having slots and holes, a leaf spring cradle that projects through the slots and that includes holes for receiving a pin, leaf springs that are carried by the cradle, with a top leaf spring contacting an underside of the top plate, and where a spring force moves the cradle away from the top plate, and a linear slide cam that contacts the pin and a top surface of the top plate. The cam includes a first surface that contacts the pin to compress the leaf springs, and a second surface that contacts the pin to decompress the leaf springs. When the leaf springs are decompressed, the spring force is transferred to the component to securely hold the component at the required load. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The detailed description will refer to the following drawings, in which like numbers refer to like items, and in which; 
     FIG. 1 is an exploded view of components of an embodiment of a leaf spring load plate with retained linear cam; 
     FIGS. 2A and 2B shows the load plate assembled; 
     FIG. 3 shows the assembled load plate used to install a heat sink on an integrated circuit; and 
     FIG. 4 shows details of the load plate and the integrated circuit of FIG.  3 . 
    
    
     DETAILED DESCRIPTION 
     As the density of elements on a processor increases, new techniques are needed to attach the processor to its underlying substrate or circuit board. In a typical application, the processor may occupy about 42 millimeters square and may have over 1,600 contact points with the underlying circuit board. Solder columns may be used to ensure proper contact between the circuit board and the processor. Solder columns have many advantages over earlier attachment techniques such as solder balls. In particular, solder columns experience less stress due to temperature changes than do solder balls. Reducing stress leads to less fatigue of the solder joint, and a longer life for the assembled circuit board and processor. However, an overload of the solder columns during assembly of the processor and circuit board can buckle the solder columns. Buckling can cause a short if two solder columns touch. Buckling can also cause the solder column to break, causing loss of functions of the processor. 
     Solder columns can become overloaded by a component under compression seated on the processor. One such component is a heat sink, which is needed to remove heat from the processor. To ensure optimum performance of the heat sink, the heat sink must be in firm contact with the underlying processor. However, as force is applied to the heat sink to ensure it is tightly seated, the solder columns, which are located between the circuit board and the processor, are subjected to a compressive force that can buckle the solder columns over time, causing shorts or opens, as noted above. 
     FIG. 1 is an exploded view of components of an embodiment of a leaf spring load plate  10  with retained linear cam that eliminates problems with prior art techniques for attaching a heat sink or similar component to a substrate. In FIG. 1, the leaf spring load plate  10  includes a top plate  1 , having slots  6  and keyed holes  7  as shown, leaf springs  2 , leaf spring cradle  3  that holds the leaf springs  2 , and that protrudes through the slots  6  in the top plate  1 , pin  4 , and linear cam slide  5 . The top plate  1  and the leaf spring cradle  3  may be made of sheet steel. The leaf springs  2  are preferably made of hardened or heat treated stainless steel. The pin  4  is made of mild steel. The linear cam slide  5  is preferably made of molded plastic. The linear cam slide  5  is formed in such a manner that lateral movement of the linear cam slide  5  compresses or decompresses the leaf springs  2 . In particular, the linear cam slide  5  includes a saddle  11 , valley  13 , and end stop  15 . The saddle  11  is shaped to accept the pin  4 . When the pin  4  is aligned over the saddle  11 , the leaf springs  2  are in a maximum compressive state, and no force is applied to hold the heat sink to its underlying processor (i.e., the load plate  10  is loosely attached). When the pin  4  is aligned over the valley  13 , the leaf springs  2  push the leaf spring cradle  3 , seating the heat sink on the processor. 
     Although FIG. 1 shows three leaf springs  2 , the number of leaf springs  2  is not limited to three. More leaf springs  2  may be added to increase the downward force holding the heat sink to the circuit board; fewer than three leaf springs  2  will result in a decreased downward force holding the heat sink to the processor. 
     FIG. 2A shows the load plate  10  assembled. As can be seen in FIG. 2A, the ears of the leaf-spring cradle  3  project through the slots  6  in the top plate  1 , and carry the pin  4 . The linear cam slide  5  is shown in a first position with the valley  13  aligned under the pin  4 . 
     FIG. 2B shows the load plate  10  assembled, but with the linear cam slide  5  in a second position. In the second position, the pin  4  engages the saddle  11 . 
     FIG. 3 shows an attachment implementation  100  using the load plate  10  installed to provide optimal thermal performance without damaging the solder columns between processor and circuit board. In FIG. 3, the attachment implementation  100  includes bolster plate  20 , insulator  30 , load studs  40 , and heat sink  50 . The heat sink  50  includes heat sink base  60 , and heat sink columns  70 . The load plate  10  is assembled to the load studs  40  using keyed holes  7 . The linear cam slide  5  is shown in position to seat the heat sink  50  onto the circuit board (not shown In FIG.  3 ). Located between the insulator  30  and the heat sink base  60  is a modular processor and the circuit board. 
     FIG. 4 shows additional details of the integrated circuit package  100  of FIG. 3. A modular processor  90  and a circuit board  95  are located between the bolster plate  20  and the heat sink  50 . The modular processor  90  may be an integrated circuit module such as, for example, a multi-chip module or a single very large scale integrated (VLSI) package. The VLSI package may be a flip chip assembly. The modular processor  90  may also be an application specific integrated circuit (ASIC). The circuit board  95  may be, for example, a printed circuit board such as a mother board. Only a section of the circuit board  95  is shown in FIG.  4 . 
     Referring to FIGS. 3 and 4, the bolster plate  20  is set on a bottom surface of the insulator  30 . The bolster plate  20  may be attached to the circuit board  95 . The bolster plate  20  includes sockets  21  located along a perimeter of the bolster plate  20  and adapted to receive the load studs  40 . In an embodiment, the sockets  21  are threaded, and the load studs  40  thread into the threaded sockets  21 . The circuit board  95  is formed with holes  96  corresponding to the locations of the sockets  21  in the bolster plate  20 . The insulator  30  is set over the bolster plate  20  in between the bolster plate  20  and the circuit board  95 . The insulator  30  insulates between input/output (I/O) pads (not shown) that are located on the bottom surface of the circuit board  95 , and the bolster plate  20 , which is conductive. The insulator  30  prevents short circuiting between the I/O pads through the bolster plate  20 . 
     The modular processor  90  sits on a top surface of the circuit board  95  over the bolster plate  20 . The modular processor  90  includes processor  91 , thermal interface material (TIM)  92 , processor lid  93 , and solder columns  94 . The TIM  92  uses a thermal interface enhancement material for enhancing thermal conduction from the processor  20  to the heat sink  50 . The TIM  92  is set on a top face of the processor  91 . The solder columns  94  provide electrical connection between the processor  91  and the circuit board  95 . To establish and maintain a reliable thermal connection between the processor  91  and the heat sink  50 , the solder columns  94  must bear the compressive load between the circuit board  95  and the processor  91  without overloading the solder columns  91 . 
     As noted above, the load studs  40  may thread into the bolster plate  20 . Alternatively, the load studs  40  may be pressed into the bolster plate  20 . Each load stud  40  includes a head  41 , a top shoulder  42  and a bottom shoulder  43 . Each load stud  40  bottoms out on the top surface of the bolster plate  20  on the shoulder  43 . 
     The heat sink  50  is set over the load studs  40  through holes  61  located along a perimeter of the heat sink base  60 . The holes  61  correspond to the location of the sockets  21  in the bolster plate  20 . The heat sink  50  is located on top of and in contact with the modular processor  90 . The heat sink  50  includes extruded, or otherwise formed, columns  70  that provide a surface area for distributing heat generated by the processor  91 . Although the columns  70  are shown as cylinders, the columns  70  are not restricted to this configuration, and may also be square in cross-section, for example. Heat that is generated in processor  91  may be thermally conducted into the heat sink  50  and further conducted into the ambient airflow by the columns  70  to dissipate the heat. The heat sink  50  may, for example, be formed from aluminum. 
     The load plate assembly  10  is set above the heat sink  50  and shuttled onto the load studs  40  through the holes  7  in the load plate assembly  10 . The load plate assembly  10  may be lowered onto the load studs  40  through the wide opening  8  of each hole  7  and then shuttled laterally so that the narrow slot  9  of each hole  7  is placed between the head  41  and the top shoulder  42  of each load stud  40 . The locations of the holes  7  correspond to the locations of the sockets  21  in the bolster plate  20 . 
     As noted above with respect to FIGS. 1 and 2A, the load plate assembly  10  may include one or more leaf springs  2  carried in the leaf spring cradle  3 . The leaf springs  2  are concave in shape and are oriented so that the concavity faces the inner top surface of the leaf spring cradle  3 . The bottom surface of the leaf spring cradle  3  contacts tops of a number of the heat sink columns  70 . With the linear cam slide  5  positioned in the valley  13  as shown, the load created by the leaf springs  2  forces the leaf spring cradle  3  onto the tops of the heat sink columns  70 . The resulting force acts through the load plate  10  and the load studs  40  onto the bolster plate  20 , drawing the heat sink  50  into firm contact with the modular processor  90 . 
     The use of the leaf spring load plate  10  provides significant advantages over prior art designs. The leaf spring load plate  10  is particularly useful in integrated circuit packages when the applied load must be kept at a low value, and must be controlled to a tight tolerance, on the order of 10 to 16 pounds of force in one implementation. However, as noted above, the actual loading will be affected by the number of leaf springs  2  used in the attachment implementation  100 . The actual loading will also be affected by the distance between the bottom of the leaf spring load plate  10  and the top of the heat sink  50 . The leaf spring load plate  10  allows components to be installed and removed from the integrated circuit. More importantly, the leaf spring load plate  10  allows a controlled application of force to a component to be mounted to the integrated circuit, and eliminates variability in applied force due to human factors. That is, by adjusting the number of leaf springs  2  in the assembled leaf spring load plate  10 , a specific, repeatable force is guaranteed to be applied. Because there are no screws to turn, bolts to torque, or other mechanical operations for a human to complete, the leaf spring load plate  10  will always apply the desired force when the linear cam slide  5  is moved from a position in which the pin  4  rests on the saddle  11  to the valley  13 , thereby allowing the leaf springs  2  to exert a downward force on the leaf spring cradle  3 . In addition, by having the force applied on the tops of the heat sink columns  70 , the heat sink  50  retains all its originally extruded heat sink columns, thereby maximizing heat rejection. Still another advantage resides in the fact that by eliminating turning screws and bolts, metal debris are not generated during installation and setting of the heat sink.