Thermal interface apparatus for PCI express M.2 printed circuit assemblies

In some embodiments, an apparatus comprises an integrated circuit module comprising two layers of thermal interface material, a printed circuit assembly disposed between the two layers of thermal interface material and comprising a plurality of integrated circuits disposed on both sides of a circuit board, wherein at least one of the integrated circuits is thermally coupled with one of the layers of thermal interface material, and two heat spreaders adapted to removably retain one another, and when retaining one another to enclose and become thermally coupled with the two layers of thermal interface material; and a printed circuit board having a connector disposed thereon, wherein a connector edge of the printed circuit assembly is disposed within the connector. In other embodiments, a frame is adapted to retain the two heat spreaders.

BACKGROUND

Modern computer systems generate large quantities of heat. While some of this heat is generated by power supplies and the like, the majority of the heat is often generated by integrated circuits such as processors and memory chips. In order to function properly, these computer systems must be kept within a certain temperature range. Therefore, the heat generated by these processors and memory chips must be dissipated or otherwise removed.

DETAILED DESCRIPTION

Printed circuit assemblies generate a lot of heat, especially in high-density configurations. One of the newer printed circuit assemblies is the Peripheral Component Interconnect Express M.2 printed circuit assembly (hereinafter “PCIe M.2 PCA”). The PCIe M.2 PCA is defined by the M.2 specification, formerly known as the Next Generation Form Factor (NGFF) specification. The M.2 specification defines internally mounted computer expansion cards and associated connectors. One of the computer bus interfaces provided through the M.2 connector is the PCIe bus interface.

In some circumstances, it may be difficult to properly cool printed circuit assemblies, such as PCIe M.2 PCAs. In particular, these PCAs generate much more heat that prior PCAs, while rejecting much less heat. These PCAs feature a very high component density, and this density is increasing with new designs to support greater functionality. In addition, these PCAs feature a double-sided topology, with components mounted on both sides. Therefore the heat generated is roughly double that of a single-sided board. Additionally, the cooling provided by the unpopulated side of a single-sided board is not available with a double sided board. The result is much greater heat generation with much less heat rejection. Another difficulty with cooling these PCAs results from the thinness of the PCA board. As described below, prior attempts to cool these PCAs have resulted in bending the board, causing components to separate from the board.

Accordingly, disclosed herein are example techniques for cooling printed circuit assemblies that solve the above noted difficulties. In particular, in the examples disclosed herein, the PCA is sandwiched between two thermal interface pads that flexibly conform to the components mounted on both sides of the PCA, and that efficiently conduct heat away from those components. In addition, the sandwich is encased in a rigid metal structure that both provides additional cooling by conducting heat away from the thermal interface pads, and also provides structural rigidity, thereby preventing flexure of the PCA board.

FIG.1shows a PCIe M.2 PCA mounted on a PCI printed circuit board (hereinafter “PCI PCB”). However, while various embodiments are described in terms of the PCIe M.2 PCA and the PCI PCB, it should be understood that the disclosed technology is applicable to other PCAs and PCBs. Referring toFIG.1, a PCI PCB102includes an M.2 connector104mounted thereon. Also shown is a PCIe M.2 PCA106. The PCIe M.2 PCA106is a two-sided printed circuit assembly, having integrated circuits, shown generally at108, mounted on both sides of a thin circuit board114. An M.2 connector edge of the PCIe M.2 PCA106, shown generally at110, is disposed within the M.2 connector104of the PCI PCB102. The other end of the PCIe M.2 PCA106is secured to the PCI PCB102by a fastener112.

FIG.2depicts one approach to cooling the integrated circuits108of the PCIe M.2 PCA106ofFIG.1. According to this approach, a thermal interface pad202is disposed between the PCIe M.2 PCA106and the PCI PCB102. This approach allows heat generated by the PCIe M.2 PCA106to pass to, and be dissipated by, the PCI PCB102. However, because the circuit board114of the PCIe M.2 PCA106is very thin, and is secured only at each end, pressure applied by the flexible thermal interface pad202to the integrated circuits108mounted on the underside of the PCIe M.2 PCA106causes the PCI Express in the PCIe M.2 PCA106to bend upward. In some applications, temperature differentials in the PCA may be sufficiently great to cause or increase this bend. This bending can cause components mounted on the PCIe M.2 PCA106, such as the integrated circuits108, to pop off of the circuit board114of the PCIe M.2 PCA106. Various embodiments disclosed herein solve this problem by enclosing the PCIe M.2 PCA106in a rigid metal structure that both dissipates heat generated by the PCIe M.2 PCA106, and prevents flexure of the PCIe M.2 PCA106both through its rigidity and through rapid and even heat dissipation.

FIGS.3A and3Bshow an integrated circuit module300according to a first embodiment.FIG.3Ais a perspective view of the integrated circuit module300in its assembled state. An exploded view of integrated circuit module300is shown inFIG.3B. The integrated circuit module300includes a PCIe M.2 PCA302, for example, such as the PCIe M.2 PCA106ofFIG.1.

Referring toFIG.3B, the integrated circuit module300also includes two layers of thermal interface material304a,band two heat spreaders306a,b. One common thermal interface material is a thermal gap pad. However, other thermal interface materials may be used. The heat spreaders306a,bmay be made of aluminum. However, other materials that are sufficiently rigid and thermally conductive may be used to form the heat spreaders306a,b, for example such as stainless steel, or the like.

The PCIe M.2 PCA302is disposed between the two layers of thermal interface material304a,bsuch that the integrated circuits108are thermally coupled with one of the layers of thermal interface material304a,b. As used herein, two objects are “thermally coupled” when the two objects are either in direct contact with one another or they are in direct contact with one or more thermally conductive intermediaries that form a thermally conductive path between the two objects. As used herein, an object comprising a continuous body of the same material is considered “thermally conductive” if the material forming the object is ‘thermally conductive’. As used herein, a material is “thermally conductive” if it has thermal conductivity (often denoted k, λ, or κ) of 7 W·m−1·K−1or greater at any temperature between 0° C. and 100° C. As used herein, an object comprising multiple distinct bodies (possibly of different materials) is considered “thermally conductive” if the object as a whole has a heat transfer coefficient of 10 W·m−2·K−1or greater from one end of the object to the other end of the object at any temperature between 0° C. and 100° C. An example of a thermally conductive object that comprises multiple distinct bodies is a heat pipe. The two heat spreaders306a,bare adapted to removably retain one another, and when retaining one another to enclose and become thermally coupled with the two layers of thermal interface material304a,b.

In the embodiment ofFIG.3, one of the heat spreaders306aincludes four tabs308a,b,c,d, and the other heat spreader306bincludes four corresponding voids310a,b,c,d. In the embodiment ofFIG.3, the heat spreaders306a,bhave a shaped cross section. However, in other embodiments, other cross-sectional shapes may be employed. The heat spreaders306a,bmay be snapped together such that they retain one another when the tabs308a,b,c,dare disposed within the corresponding voids310a,b,c,d. When assembled, as shown inFIG.3A, the integrated circuit module300both dissipates heat generated by the PCIe M.2 PCA302, and provides a rigid structure that prevents flexure of the PCIe M.2 PCA302. In contrast to the solution ofFIG.2, the pressure applied by one layer of thermal interface material304ato one side of the PCIe M.2 PCA302is balanced by the pressure applied by the other layer of thermal interface material304bto the other side of the PCIe M.2 PCA302.

FIGS.4A and4Bshow an integrated circuit module400according to a second embodiment,FIG.4Ais a perspective view of the integrated circuit module400in its assembled state. An exploded view of integrated circuit module400is shown inFIG.4B. The integrated circuit module400includes a PCIe M.2 PCA302, for example, such as the PCIe M.2 PCA106ofFIG.1.

Referring toFIG.4B, the example integrated circuit module400also includes two layers of thermal interface material304a,b, two heat spreaders406a,b, and a frame412. One common thermal interface material is a thermal gap pad. However, other thermal interface materials may be used. The heat spreaders406a,bmay be made of aluminum. However, other materials may be used to form the heat spreaders406a,b, for example such as stainless steel, or the like. The frame412may be made of any suitable material, such as plastic and the like.

The PCIe PCA402is disposed between the two layers of thermal interface material304a,bsuch that the integrated circuits108are thermally coupled with one of the layers of thermal interface material304a,b.

The frame412is adapted to removably retain the two heat spreaders406a,bsuch that the two heat spreaders406a,benclose and become thermally coupled with the two layers of thermal interface material304a,b. The frame412may include a groove416to receive an edge of the PCIe M.2 PCA302. The frame412may include an opening414to receive a M.2 connector edge420of the PCIe M.2 PCA302.

In the embodiment ofFIG.4, the heat spreaders406a,btogether include eight tabs408a,b,c,d,e,f,g,hand the frame412includes eight corresponding voids410a,b,c,d,e,f,g,h. In the embodiment ofFIG.4, the heat spreaders406a,bhave a C-shaped cross section. However, in other embodiments, other cross-sectional shapes may be employed. The heat spreaders406a,band the frame412may be snapped together such that the frame412retains the heat spreaders406a,bwhen the tabs408a,b,c,d,e,f,g,hare disposed within the corresponding voids410a,b,c,d,e,f,g,h. When assembled, as shown inFIG.4A, the integrated circuit module400both dissipates heat generated by the PCIe M.2 PCA302, and provides a rigid structure that prevents flexure of the PCIe M.2 PCA302. Although this example illustrates eight tabs408a,b,c,d,e,f,g,hand eight corresponding voids410a,b,c,d,e,f,g,h, in other implementations, other quantities of tabs and corresponding voids can be used.

FIG.5shows an integrated circuit module502mounted on a PCI PCB506. The integrated circuit module502may be implemented as the integrated circuit module300ofFIGS.3A,B or the integrated circuit module400ofFIGS.4A,B. An M.2 connector504is mounted on the PCI PCB506. A M.2 connector edge420of the integrated circuit module502is disposed within the M.2 connector504. The opposite end of the integrated circuit module502may be mechanically coupled with the PCI PCB506by any fastener, for example such as a screw, bolt, or the like. For example, an extension provided on either the heat spreaders306a,bor406a,bor the frame412may be secured with a screw or locking tab with a release tab residing on the PCI PCB506.

In the embodiment depicted inFIG.5, the PCI PCB506includes a through-hole508to accommodate the thickness of the integrated circuit module502. In other embodiments, the integrated circuit module502is mounted upon, and thermally coupled to, the PCI PCB506. In such embodiments, the PCI PCB506dissipates heat generated by the integrated circuits. In some embodiments, the PCI PCB506may include a metal layer or other thermal interface material that is thermally coupled to the PCI PCB506. In such embodiments, the metal layer dissipates heat generated by the integrated circuits. The metal layer may be made of copper or the like.

Some embodiments include a heat sink.FIG.6Bshows an exploded view with the integrated circuit module502mounted on the PCI PCB506and a heat sink620. Any suitable heat sink may be used.FIG.6Ashows the heat sink620mounted on the PCI PCB506, and thermally coupled to the integrated circuit module502. Any suitable fastener may be used to mechanically attach the heat sink620to the PCI PCB506, for example such as screws612a,b,c,dshown inFIGS.6A,B. In some embodiments, a thermal interface material is disposed between the heat sink620and the integrated circuit module602. Any suitable thermal interface material may be used, for example such as thermal grease. The heat sink620not only dissipates heat generated by the integrated circuits, but also provides additional rigidity to the integrated circuit module502.

Some embodiments include a second heat sink mounted on a second side of the PCI PCB.FIG.7Bshows an exploded view with the integrated circuit module502mounted on a PCI PCB506and a heat sink720. Any suitable heat sink may be used.FIG.7Ashows the heat sink720mounted on the underside of the PCI PCB506, and thermally coupled to the integrated circuit module502. Any suitable fastener may be used to mechanically attach the heat sink722to the underside of the PCI PCB506, for example such as screws712a,b,c,dshown inFIG.7. In some embodiments, a thermal interface material is disposed between the heat sink720and the integrated circuit module702. Any suitable thermal interface material may be used, for example such as thermal grease. The heat sink720not only dissipates heat generated by the integrated circuits, but also provides additional rigidity to the integrated circuit module502.

FIG.8shows a process800according to one embodiment. Although the steps of the process are shown in a particular sequence, some or all of the steps may be performed in other sequences, in parallel, or combinations thereof. Some of the steps may be omitted. Referring toFIG.8, the process800includes providing two layers of thermal interface material, at802.

The process800includes disposing a PCIe M.2 PCA between the two layers of thermal interface material, such that at least one integrated circuit disposed upon the PCIe M.2 PCA is thermally coupled with one of the layers of thermal interface material, at804. Any thermal interface material may be used, for example, such as a thermal gap pad.

The process800includes removably enclosing the PCIe M.2 PCA and the two layers of thermal interface material within two heat spreaders, such that the heat spreaders become thermally coupled with the two layers of thermal interface material, at806. The heat spreaders may be made of aluminum. However, other materials may be used to form the heat spreaders, for example such as stainless steel, or the like.

The process800includes providing a PCI PCB having a PCI Express M.2 connector disposed thereon, at808. The process800includes disposing a connector edge of the printed circuit assembly within the connector, at810. The process800may also include thermally coupling one of the heat spreaders to the PCI PCB. The process800may also include thermally coupling a metal layer to the PCI PCB. The process800may also include thermally coupling heat sinks to one or both of the heat spreaders. The process800may also include disposing the integrated circuit module in a through-hole of the PCI PCB, mechanically attaching a first heat sink to a first side of the PCI PCB, and mechanically attaching a second heat sink to a second side of the PCI PCB.

Embodiments of the present invention provide numerous benefits. As mentioned above, the disclosed technology provides enhanced heat dissipation. And in contrast to other approaches, the disclosed embodiments provide a thermal interface surface for both sides of the M.2 PCA. These benefits allow the use of higher-power and faster M.2 modules than before.

The disclosed technology provides strength and rigidity to the PCIe M.2 PCA, which can reduce mechanical failures during shock and vibration testing. And as mentioned above, this rigidity prevents flexure of the PCIe M.2 PCA, thereby preventing separation of the PCIe M.2 circuit board and components mounted thereon.

Embodiments of the present invention are compatible with several current M.2 designs. The disclosed embodiments are tool-less because the heat spreaders may be snapped together by hand.

Currently the PCI Express design specification is loosely followed or even violated by many of the M.2 module developers in the industry. As a result, it can be difficult for a manufacturer of a computing device to cost effectively provide heat dissipation solutions for M.2 modules that are sourced from different M.2 manufacturers, since the computing device manufacturer may need to design a unique solution for each variation of the M.2 module, which increases costs and complexity of the manufacturing process. Thus, an additional benefit of the examples disclosed herein is that they are essentially universal, meaning that they can be used with pretty much any variation of the M.2 module even if it deviates from the M.2 specifications. In particular, in examples disclosed herein, the TIM on other side of the M.2 module may provide some give or tolerance that allows for variation in the height of the integrated circuits108above the board114, variation in the placement of the integrated circuits108, variation in the thickness of the board114, etc. In addition, different lengths of M.2 modules can be accommodated in the heat spreaders306a,band406a,b, and the heat spreaders306a,band406a,bmay be dimensioned to allow for some variation in the width of the M.2 modules. Such a universal mounting and thermal solution eliminates the need for unique heat sink designs for different M.2 modules, thus reducing the types of inventory and factory spares that must be stocked.

In common usage, the term “or” can have an inclusive sense or an exclusive sense. As used herein, the term “or” should always be construed in the inclusive sense unless the exclusive sense is specifically indicated or logically necessary. The exclusive sense of “or” is specifically indicated when, for example, the term “or” is paired with the term “either”, as in “either A or B”. As another example, the exclusive sense may also be specifically indicated by appending “exclusive” or “but not both” after the list of items, as in “A or B, exclusive” and “A or B but not both”. Moreover, the description of resources, operations, or structures in the singular shall not be read to exclude the plural. Conditional language, such as, among others, “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or steps.