Methods and apparatus for fastening a set of heatsinks to a circuit board

A circuit board module has a circuit board which includes a circuit board structure and a set of components mounted to the circuit board structure. The circuit board module further includes a set of heatsinks (i.e., one or more heatsinks) and a heatsink retaining assembly fastened to the circuit board. The heatsink retaining assembly includes (i) a set of brackets, each bracket being elongated in shape and having a first end and a second end, (ii) a frame, and (iii) a fastening mechanism configured to fasten the frame to a circuit board. The frame is configured to simultaneously hold the first and second ends of each bracket relative to the circuit board to enable that bracket to assert holding force on the set of heatsinks.

BACKGROUND

In general, a heat sink is a thermally conductive device that dissipates heat from one or more circuit board components into the surrounding air. An air stream generated by a fan assembly then carries the heat away. Such operation enables the circuit board components to operate in a lower temperature range without increasing the likelihood of operating incorrectly and/or sustaining damage. Examples of circuit board components that use heat sinks include high speed processors, Field Programmable Gate Arrays, and optical transceivers.

There are a variety of conventional approaches for mounting a heat sink to a circuit board component. One conventional approach (hereinafter referred to as the “adhesive approach”) involves the circuit board manufacturer (or supplier) affixing the heat sink to the component package using an adhesive (e.g., tape, glue, combinations thereof, etc.) having a high thermal transfer coefficient. In this approach, the manufacturer applies the adhesive between the circuit board component and the heat sink. Glue-like material within the adhesive then cures (perhaps with the addition of heat) to fasten the heat sink directly to the outer surface of the component package. Accordingly, when the component is in operation, the heat sink, which is now held in place by the adhesive, conveys heat from the component into the surrounding air.

Another conventional approach (hereinafter referred to as the “adjacent anchor approach”) involves the circuit board manufacturer providing mounting holes in circuit board locations surrounding the circuit board component. In this approach, the manufacturer then installs anchors (i.e., threaded metallic posts, nuts, U-shaped elements, etc.) on the circuit board through the mounting holes. The manufacturer secures the anchors to the circuit board using either hardware or solder joints. Next, the manufacturer places the heat sink over the top of the component, perhaps with thermal transfer material disposed between the heatsink and the top of the component package to facilitate heat transfer therebetween. Next, the manufacturer rigidly secures the heat sink to the anchors. As a result, when the component is in operation, the heatsink, which is now held rigidly in place by the anchors, conducts heat from the component and dissipates that heat into a neighboring air stream.

In yet another conventional approach (hereinafter referred to as the “clip approach”), the heatsink includes built-in clips. During installation, the manufacturer positions the clips so that the clips grab directly on to the sides of the component package to secure the heatsink to the component package.

SUMMARY

Unfortunately, there are deficiencies to the above-described conventional approaches to mounting a heat sink to a circuit board component. For example, in connection with the above-described conventional adhesive approach, vendors often do not precisely follow instructions from the manufacturer for applying the adhesive between the component packages and the heatsinks. In particular, the vendors may apply an insufficient amount of pressure for an insufficient amount of time (e.g., two minutes rather than 10 minutes) due to high volume production requirements. Additionally, conventional adhesives are prone to failure over time. That is, as the glue-like material within the adhesive ages, it tends to becomes brittle as well as lose its elasticity and holding strength. Eventually, the combination of time, vibration and high temperature cause the adhesive's holding characteristics to deteriorate to the point where the heat sink separates from the circuit board component. In some heat sink separation situations, the loss of the heat sink's cooling operation and/or uncontrolled movement of the heat sink may result in damage to circuit board components or the circuit board itself. Furthermore, even if the adhesive successfully maintains its holding characteristics, there may be situations a user would like to remove the heat sink (e.g., to inspect the area around the circuit board component in detail, to replace the circuit board component, etc.). In such situations, it is an ugly process for a technician to remove the heat sink from the component, and any adhesive remaining on the heat sink tends to hinder the heat sink's thermal transfer capabilities thus rendering the heat sink unsalvageable.

Additionally, in the above-described conventional adjacent anchor approach, the circuit board manufacturer must sacrifice space immediately around the circuit board component to enable attachment of penetrating anchors. In particular, the manufacturer must sacrifice a significant amount of circuit board real estate in order to provide mounting holes and associated keep-out regions (i.e., anti-pads). The inner layer real estate around the circuit board component is often particularly precious since the component typically has a high density of contacts (e.g., a Ball Grid Array, a Ceramic Column Grid Array, etc.) which must electrically connect to pads and traces leading to other locations of the circuit board. If the manufacturer did not need to sacrifice this inner layer real estate to accommodate the standoffs or anchors, the manufacturer could utilize such space for other purposes (e.g., signal traces leading to and from the component mounting location, etc.). Moreover, even if circuit board space is adequate, the manufacturer risks damaging the circuit board when the manufacturer installs the anchors onto the circuit board, e.g., the loose hardware can scratch or cut surface traces if dropped onto the circuit board, debris associated with the loose hardware can fall off the loose hardware and contaminate the circuit board, etc.

Furthermore, in connection with the conventional clip approach, the heatsinks which have built-in clips are relatively small and light weight due to inadequacies in the ability of the clips to secure heavier heatsinks. Accordingly, the conventional clip approach is insufficient for tasks of mounting relatively large heatsinks and for mounting heatsinks over relatively large areas such as over multiple components.

In contrast to the above-described conventional approaches to mounting a heat sink to a circuit board, embodiments of the invention are directed to techniques for fastening a set of heatsinks (i.e., one or more heatsinks) to a circuit board using a frame which is configured to hold ends of elongated brackets such that the elongated brackets apply holding force on the set of heatsinks. The frame is capable of mounting around a periphery of the circuit board so as not to encumber circuit board real estate immediately adjacent component mounting locations. Additionally, the frame is capable of supporting multiple elongated brackets for flexibility (e.g., the brackets can be positioned to accommodate a variety of heatsink shapes, sizes and heights) and robustness (e.g., the brackets can be positioned to hold multiple heatsinks in a cost effective manner).

One embodiment of the invention is directed to a circuit board module having a circuit board which includes a circuit board structure and a set of components mounted to the circuit board structure. The circuit board module further includes a set of heatsinks (i.e., one or more heatsinks) and a heatsink retaining assembly fastened to the circuit board. The heatsink retaining assembly includes (i) a set of brackets, each bracket being elongated in shape and having a first end and a second end, (ii) a frame, and (iii) a fastening mechanism configured to fasten the frame to a circuit board. The frame is configured to simultaneously hold the first and second ends of each bracket relative to the circuit board to enable that bracket to assert holding force on the set of heatsinks.

DETAILED DESCRIPTION

Embodiments of the invention are directed to techniques for fastening a set of heatsinks (i.e., one or more heatsinks) to a circuit board using a frame which is configured to hold ends of elongated brackets such that the elongated brackets apply holding force on the set of heatsinks thus keeping the set of heatsinks in place relative to the circuit board. The frame is capable of mounting around a periphery of the circuit board so as not to encumber circuit board real estate immediately adjacent component mounting locations. Additionally, the frame is capable of supporting multiple elongated brackets for flexibility (e.g., the brackets can be positioned and shaped to accommodate a variety of heatsink shapes, sizes, heights and configurations) and robustness (e.g., the brackets can be positioned to hold multiple heatsinks in a cost effective manner and/or a heatsink that cools multiple devices, etc.).

FIG. 1shows an exploded view of a circuit board module20which is suitable for use by the invention. As shown inFIG. 1, the circuit board module20includes a circuit board22, a set of heatsinks24(i.e., one or more heatsinks24), and a heatsink retaining assembly26. The circuit board22includes circuit board structure28and a set of components30mounted to the circuit board structure28. The circuit board structure28includes layers of non-conductive material (e.g., FR-4) and conductive material (e.g., copper signal layers, power and ground planes, pads, etc.) sandwiched together to form a rigid, rectangle-shaped substrate that extends along the X-Y plane. Holes32reside at corners34of the circuit board structure28for a variety of uses such as for alignment during circuit board fabrication and assembly (e.g., for proper registration by drilling equipment) and for component attachment (e.g., for securing a metallic tray to the circuit board22for EMI protection).

By way of example only, each heatsink24includes a base36and a set of fins38that extend from the base36in the Z-direction which is perpendicular to the circuit board22. It should be understood that other heatsink configurations and heat-relief structures are suitable for use as well such as disk-shaped or post-array/column-array heatsinks, baffle-shaped airflow directors, heat pipes, and the like.

The heatsink retaining assembly26includes a set of brackets40(i.e., one or more brackets40), a frame42and a fastening mechanism44. Each bracket40is elongated in shape and has a first end46(1) and a second end46(2) (collectively, ends46). The frame42includes four elongated support members48(1,48(2),48(3) and48(4) (collectively, elongated support members48) and a set of standoff portions (or simply legs)50. The elongated support members48define grooves52(e.g., holes, channels, notches, etc.) to capture the ends46of the brackets40when the circuit board module20is fully assembled. The elongated support members48further define a rectangle54and a central opening56to keep the members48out of the way from the set of components30and thus provide convenient access to the set of components30(e.g., for airflow, for heatsink access to the components30, etc.). The standoff portions50elevate the elongated support members48in a substantially parallel manner relative to the circuit board22along the X-Y plane when the frame42is properly installed on the circuit board22thus providing additional access to the set of components30(e.g., for enhanced airflow).

In one arrangement, the frame42is made of metal and is preferably grounded to a ground layer of the circuit board structure28. In another arrangement, the frame42is made of non-conductive material (e.g., plastic). In these arrangements, the grooves52run in a distributed manner along the elongated support members48to allow for a variety of positions for the brackets40, e.g., at 0.200 inch intervals.

In some arrangements and as shown inFIG. 1, the elongated support members48extend around a periphery58of the circuit board22, and the standoff portions50are distributed around the periphery58in order to minimize the intrusiveness of the frame42. Accordingly, the heatsink retaining assembly26generally does not include parts that would otherwise encumber circuit board real estate immediately around any component30as in a conventional anchor approach which uses anchors immediately adjacent a component to fasten a heatsink to that component.

Additionally, in some arrangements, the fastening mechanism44of the heatsink retaining assembly26is combinable with other structures to perform additional operations. For example, as shown inFIG. 1, the circuit board20further includes a metallic tray60which is configured to provide electromagnetic interference (EMI) shielding to the circuit board22. Here, the fastening mechanism44includes threaded hardware62which connects to the tray60. In particular, the threaded hardware62is in the form of rotatable threaded posts having standoff portions64which provide separation between the tray60and the circuit board22, and threaded portions66which pass through the circuit board holes32and engage the standoff portions50of the frame42(e.g., the threaded portions66screw into the standoff portions50of the frame42). Accordingly, the threaded hardware62concurrently holds both the tray60and the frame42in place in a substantially parallel manner along the X-Y plane. Such a configuration is particularly suitable for use in high-density situations such as when multiple circuit board modules20reside next to each other within a card cage thus preventing EMI generated by one circuit board module20from interfering with adjacent circuitry, e.g., another circuit board module20.

As an alternative example, the fastening mechanism44includes standard hardware (bolts, screws, nuts, etc.). Here, the hardware (or alternatively parts of the standoff portions50) extend through the circuit board holes32for rigid fastening on the other ends.

As shown inFIG. 1, the brackets40are configured to fasten to the frame42. In particular, the ends46engage the grooves52of the elongated support members48. In this situation, mid-portions68of the brackets40extend along gaps70between heatsink fins38to apply holding force onto the heatsink bases36in a direction toward top surfaces72of the components30, see the arrow74inFIG. 1. In some arrangements, the components30are high power devices (e.g., an area array package with a bare die of approximately 0.47 inches by 0.40 inches). Accordingly, the heatsink retaining assembly26robustly holds the set of heatsinks24in place relative to the circuit board22and the set of components30.

In some arrangements, the brackets40align in a parallel manner to each other (e.g., along the X-direction), and include resilient metallic material. For example, in one arrangement, the mid-portions68are leaf spring type metal elements that extend across the frame42to provide spring tension against the set of heatsinks24(e.g., wire form retainers which hook into the grooves52). Such arrangements alleviate the need to consume circuit board space immediately adjacent the components as in conventional anchor approaches, and enable the brackets40to take a variety of shapes and sizes in order to accommodate a multitude of different circuit board and component shapes, sizes, heights and geometries thus providing a flexible and fully accommodating design. Moreover, such arrangements do not require the heatsinks24to directly grab the component packages where situations of insufficient gripping strength may occur as in conventional adhesive or conventional clip approaches. Further details will now be provided with reference toFIGS. 2 and 3.

FIG. 2is a top view80andFIG. 3is a side view82of the frame42of the heatsink retaining assembly26. As shown inFIGS. 2 and 3, grooves52reside along each elongated support member48thus enabling the frame42to accommodate a variety of components30at different locations. That is, the same frame42can be used on different circuit boards22having different component layouts. Accordingly, the manufacture does not need to make a different frame42for each different circuit board design. Moreover, there is no restriction to the direction of the brackets40. In particular, the brackets40are shown as extending along the X-direction inFIG. 1by way of example only. Since the elongated support members along the X-direction define grooves52, the brackets40are capable of alternatively extending along the Y-direction instead of the X-direction. As a result, the heatsink retaining assembly26is capable of being utilized by virtually any PCB regardless of size or shape.

Additionally, as shown inFIGS. 2 and 3, the standoff portions50define threaded cavities84to engage with the fastening mechanism44(i.e., see the threaded portions66of the threaded hardware62inFIG. 1). The standoff portions50of the frame42reside at locations away from the central opening56defined by the elongated support members38. Accordingly, the heatsink retaining assembly26does not interfere with the circuit board structure28or the components30. Rather, the heatsink retaining assembly26attaches around the periphery58of the circuit board22thus leaving the areas immediately around the components30unencumbered and available for other circuit board structures, e.g., other components, signal traces, etc. As a result, the brackets40are essentially capable of forming a robust network of wire form retainers for reliably holding the set of heatsinks24in place. Further details of the invention will now be provided with reference toFIG. 4.

FIG. 4is a flowchart of a procedure90which is performed by a manufacturer of the circuit board module20when installing the set of heatsinks24using the heatsink retaining assembly26. In step92, the manufacturer fastens the frame42of the heatsink retaining assembly26to the circuit board22. For example, when using a metallic tray60with rotatably attached threaded hardware62as a fastening mechanism44, the manufacturer positions the frame42and the tray60relative to the circuit board structure28so that the threaded hardware62aligns with the standoff portions50through the holes32defined by the circuit board structure28. The manufacturer then screws the threaded hardware62into the standoff portions50so that both the frame42and tray60are simultaneously held in place relative to the circuit board structure28with minimal consumption of circuit board real estate. As another example, the manufacturer simply uses threaded hardware (bolts, screws, etc.) as the fastening mechanism44. This step is capable of being performed manually or by automated equipment.

In step94, the manufacturer positions the set of heatsinks24relative to the set of components30. In particular, the manufacturer places the bases36of the heatsinks24in contact with the top surfaces72of the components30. In one arrangement, the manufacturer disposes thermal transfer material (e.g., a substance with high thermal conductivity) between the heatsink bases36and the component tops72for enhanced heat transfer.

In step96, the manufacturer attaches the set of brackets40to the frame42. In particular, the manufacturer inserts the ends46of the brackets40into the grooves52of the elongated support members48. As a result, each bracket40now asserts a robust holding force on a heatsink24to hold the set of heatsinks in place relative to the circuit board22and the circuit board components30. Such a configuration provides a cost effective heatsink retaining solution, ease of layout, versatility to accommodate different packages (e.g., ICs, multi-chip modules, etc.), different package heights, etc.

As mentioned above, embodiments of the invention are directed to techniques for fastening a set of heatsinks24to a circuit board22using a frame42which is configured to hold ends46of elongated brackets48such that the elongated brackets48apply holding force on the set of heatsinks24. The frame42is capable of mounting around a periphery of the circuit board22so as not to encumber circuit board real estate immediately adjacent component mounting locations. Additionally, the frame42is capable of supporting multiple elongated brackets40for flexibility (e.g., the brackets40can be positioned and shaped to accommodate a variety of heatsink shapes, sizes, heights and configurations) and robustness (e.g., the brackets40can be positioned to hold multiple heatsinks24in a cost effective manner and/or a heatsink24that cools multiple devices, etc.).

For example, it should be understood that the set of heatsinks38includes heatsinks of a variety of different shapes and sizes. The heatsink retaining assembly26is capable of holding a single heatsink24or multiple heatsinks24(e.g., four to 20 per circuit board22). By way of example, one large heatsink24uses multiple brackets40for robust support (see the large heatsink24which uses three brackets40inFIG. 1). Alternatively, a single bracket40is capable of supporting multiple heatsinks24. Such modifications and variations are intended to be within the scope of various embodiments of the invention.

Additionally, it should be understood that the fastening mechanism44of the heatsink retaining assembly26was described above as including threaded hardware which installs from the tray side of the circuit board module20through the holes32of the circuit board structure28. Other configurations are suitable for use as well. For example,FIG. 5shows an alternative arrangement in which the fastening mechanism44includes a set of screws100which install through holes102within the frame42first (i.e., the cavities84extend completely through the frame42, also seeFIGS. 2 and 3). Each screw100then passes through a respective hole32of the circuit board structure28to attach to the tray60such as by threading into holes104within a standoff106which is integrated with the tray60(show for illustration purposes inFIG. 5), into the tray60itself, or into nuts beneath the tray60.

Furthermore, it should be understood that the set of brackets40was described above as including wire forms having ends46which insert into the frame42by way of example only. Other configurations are suitable for use as well. For example, the set of brackets40are capable of including plane-shaped rigid beam members which extend across the central frame opening56. Such beam members are capable of engaging with the frame42by inserting into the grooves52and provide further stability to the set of heat sinks24. Alternatively, such beam members are capable of securing to the frame42using hardware (e.g., screws or bolts which thread into the frame42or into corresponding nuts, etc.). Such modifications and enhancements are intended to belong to various embodiments of the invention.