Dual Spring Clip Attachment Mechanism for Controlled Pressure Interface Thermal Solution on Processor Cartridges

1. Field of the Invention

The present invention relates to a spring clip that couples a thermal element to an integrated circuit or integrated circuit package.

2. Background Information

Integrated circuits are assembled into packages that are soldered to printed circuit boards. The integrated circuits generate heat which must be removed to insure that the junction temperatures of the circuits operate below threshold levels. The heat generated by each integrated circuit primarily flows through the package. The package is typically constructed from a dielectric material which has a relatively low coefficient of thermal conductivity. The low thermal coefficient increases the temperature drop across the package and the junction temperature of the circuit.

Some packages contain a metal lid that reduces the thermal impedance between the integrated circuit and the ambient. A heat sink may be coupled to the metal lid to further improve the thermal efficiency of the assembly.

The surface roughness and a lack of co-planarity between the metal lid and the heat sink may create air gaps within the metal lid/heat sink interface. The air gaps increase the thermal impedance between the metal lid and the heat sink. The increase in thermal impedance may raise the junction temperature of the integrated circuit.

Some assemblies utilize a fastener such as a clip or a screw that pulls the heat sink into the metal lid. The pull force of the fastener decreases the thermal impedance of the metal lid/heat sink interface. Variations in the height of the integrated circuit package due to manufacturing tolerances may change the pull force of the fastener. The tolerances may create an undesirable reduction in the pull force and an increase in the thermal impedance of the metal lid/heat sink interface. It would be desirable to provide a clamping fastener for an electronic assembly which accommodates tolerances in the assembly.

One embodiment of the present invention is an electronic cartridge that includes a spring clip which attaches a thermal element to an integrated circuit or an integrated circuit package. The integrated circuit/package is mounted to a substrate. The cartridge may have a pin that extends from the thermal element and through the substrate. The spring clip is attached to the pin of the thermal element.

FIG. 1 is an exploded view of an embodiment of an electronic cartridge of the present invention;

FIG. 2 is a top cross-sectional view of the cartridge;

FIG. 3 is a side view of a pin of the cartridge;

FIG. 4 is a side view of another pin of the cartridge;

FIG. 5 is a top view of an alternate embodiment of the cartridge.

One embodiment of the present invention is an electronic cartridge that includes a pair of spring clips which attach a thermal element to an integrated circuit or an integrated circuit package. The integrated circuit or integrated circuit package is mounted to a substrate. The substrate may be a printed circuit board. The cartridge may have a plurality of pins that extend from the thermal element and through the substrate. Each spring clip may have a pair of bent portions that are attached to the pins of the thermal element. The spring clip exerts a pull force that pulls the thermal element into the integrated circuit/package. The bent ports can be deflected so that at least a minimum pull force is always exerted onto the thermal element even with dimensional variations in the parts of the cartridge. The bent portions can therefore accommodate for tolerances in the cartridge while clamping the thermal element to the integrated circuit/package.

Referring to the drawings more particularly by reference numbers, FIGS. 1 and 2 show one embodiment of an electronic cartridge 10 of the present invention. The cartridge 10 may include an integrated circuit package 12 that is mounted to a substrate 14. The cartridge 10 may contain a number of integrated circuit packages 12 that are mounted to both sides of the substrate 14.

The substrate 14 may be a printed circuit board which contains electrical pads, visa and routing traces (not shown) as is known in the art. One edge of the substrate 14 may contain a plurality of conductive pads 16 that can be inserted into a card edge electrical connector (not shown). The card edge electrical connector is typically mounted to a motherboard (not shown) of a computer system.

The integrated circuit package 12 may contain one or more integrated circuits 18 and a metal lid 20. The integrated circuit 18 generates heat that may primarily flow into the metal lid 20. The package 12 may further have solder balls 22 that are attached to the substrate 14. Although solder balls 22 are shown and described, it is to be understood that other contacts such as pins may be employed in the present invention.

The cartridge 10 may have a thermal element 24 that is coupled to the integrated circuit package 12. The cartridge 10 may further have a plurality of first pins 26 that extend through clearance holes 28 in the substrate 14. The thermal element 24 may be a plate that is constructed from a thermally conductive material such as aluminum or copper. The pins 26 may be screwed or pressed into the plate. A finned heat sink 30 may be attached to the thermal element 24. Although a thermal plate 24 that is separate from the heat sink 30 is shown in described, it is to be understood that the thermal element 24 may include an integral finned heat sink.

The cartridge 10 may have a pair of spring clips 32 that are attached to the pins 26. The spring clips 32 secure the thermal element 24 to the substrate 14. Each spring clip 32 may have a pair of slots 34. Each pin 26 is inserted through a corresponding slot 34 of each clip 32. The pins 26 may each have a groove 36 that receives opposing edges of the clip 32. The edges reside in the grooves 36 and prevent the pins 26 from being pulled out of the slots 34.

Each slot 34 is located in a bent portion 38 of a spring 32. When assembled to the pin 26, the bent portions 38 are deflected to exert a pull force which pulls the thermal element 24 into the integrated circuit package 12. The pull force reduces the thermal impedance between the thermal element 24 and the integrated circuit package 12. A thermal grease 40 may be inserted in between the thermal element 24 and the metal lid 20 to further minimize the thermal impedance between the two components.

Variations in the dimensions of the cartridge parts may vary the deflection of the bent portions 38 and the pull force on the thermal element 24. The cartridge 10 is preferably designed so that the bent portions 38 are always deflected to provide at least a minimum pull force on the thermal element 24.

FIG. 3 shows an embodiment of a pin 26. The pin 26 may have a stud portion 42 that extends from a shoulder 44. The stud portion 42 is inserted into a corresponding hole of the thermal element 24. The pin 26 may have a plastic bushing 45 that is pressed onto the stud portion 42 and pressed into the thermal element 24. The shoulder 44 limits the insertion depth of the pin 26.

The pin 26 may also have a head portion 46 that is adjacent to a neck portion 48. The head portion 46 captures the spring clip 32. The distance D between the stud portion 42 and the head portion 48 is one of the dimensions which define the amount of deflection of the spring clip 32. The tolerance of dimension D is typically a small value to control the clip deflection and the pull force on the thermal element 24.

Referring to FIG. 1, the cartridge 10 may further have a cover 50 that is attached to the thermal element 24 by second pins 52 that extend through holes 53 in the substrate 14. The cover 50 and thermal element 24 may essentially enclose the integrated circuit packages 12.

FIG. 4 shows an embodiment of a second pin 52. The pin 52 may include a stud portion 54 that extends from a shoulder 56. A plastic bushing 58 may be pressed onto the stud portion 54 and pressed into the thermal element 24. The shoulder 56 limits the insertion depth of the pin 52.

The cartridge 10 can be assembled by merely sliding the pins 26 through the substrate 14 and snapping the spring clips 32 onto the pins 26. The thermal grease 40 can be applied to the thermal element 24 and/or metal lid 20 before the pins 26 are inserted through the substrate 14. The cover 50 can then be snapped onto the pins 52. The cartridge does not require tools and is relatively easy to assemble in a manufacturing production line.

While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art. For example, as shown in FIG. 5, the thermal element 24 may be coupled directly to the integrated circuit 18 without a metal lid. With such a configuration the integrated circuit 18 is typically attached to a package substrate 60 with a process which is known as C4.