Passive cooling system integrated into a printed circuit board for cooling electronic components

A passive cooling system is provided for dissipating heat from an electronic component. The system includes a printed circuit board including a first dielectric layer and a first conductive layer, an electronic component coupled to the printed circuit board via a plurality of electrical contacts, and a cooling component thermally coupled to the electronic component through the first conductive layer by a micro via thermal array.

FIELD OF THE INVENTION

The present invention relates to electronic systems, and more particularly to cooling solutions for electronic systems.

BACKGROUND

High power electronic components such as central processing units and graphics processing units generate a large amount of heat during operation. The heat needs to be dissipated to avoid overheating the component. Conventional cooling solutions include placing a heat sink or heat pipe in contact with a surface of the component, which draws heat away from the electronic component via conduction. The heat is then dissipated by convection, possibly in conjunction with one or more fans that force air over the heat sink or heat pipe. Efficient cooling solutions enable electronic components to operate at higher speeds, thereby making the overall system more efficient.

Current designs for heat sinks and heat pipes are limited in that these devices only draw heat away from a top surface of the electronic component. For example, the heat is transferred to the heat sink through conduction at the contact surface between the heat sink and the component. Increasing the size (i.e., volume) of the heat sink is not effective after a certain point because the additional material added to the heat sink is further and further away from the contact surface. The steady state conductive properties of the heat sink material limit the ability of the heat sink to draw any additional heat away from the component. Thus, there is a need for addressing this issue and/or other issues associated with the prior art.

SUMMARY

A passive cooling system is provided for dissipating heat from an electronic component. The system includes a printed circuit board including a first dielectric layer and a first conductive layer, an electronic component coupled to the printed circuit board via a plurality of electrical contacts, and a cooling component thermally coupled to the electronic component through the first conductive layer by a micro via thermal array.

DETAILED DESCRIPTION

FIGS. 1A & 1Billustrate a printed circuit board (PCB)100including one or more electronic components, in accordance with one embodiment. As shown inFIG. 1A, the PCB100includes one or more electronic components coupled thereto, such as processor101. In the context of the present description, an electronic component may include a central processing unit, a graphics processing unit, a System-on-chip (SoC), an application specific integrated circuit (ASIC), memory, memory array, or some other type of high power device. It should be noted that, while various optional features are set forth herein in connection with the PCB100, such features are set forth for illustrative purposes only and should not be construed as limiting in any manner.

For example, in the context of the exemplary embodiment illustrated inFIG. 1A, the PCB100may or may not include two memory modules104coupled to the processor101. It will be appreciated that the electronic components included on the PCB100are optional and other components may be included in addition to or in lieu of the components shown inFIG. 1A. For example, the PCB100may include a voltage regulator, a co-processor, additional memory modules, capacitors, resistors, and an interface such as a JTAG (Joint Test Action Group) interface, a USB (Universal Serial Bus) interface, or a PCIe (Peripheral Component Interconnect Express) interface.

In order to dissipate heat from the processor101or other high-power device, a heat sink120is placed on top of the processor101. The heat sink120is made of aluminum, copper, or other material with good thermal transfer properties. The heat sink120may include fins or other structures that increase the surface area of the heat sink120to allow for better thermal transfer due to convection. The heat sink120may include an integrated fan assembly (not shown) that increases the air flow over the surface of the heat sink120.

As shown inFIG. 1B, The PCB100includes a first layer140of dielectric material such as FR-4 (woven glass fiber and epoxy resin) and a second layer142of conductive material such as copper. The second layer142may be electronically coupled to a ground reference of the voltage supply and act as aground plane for the PCB100. The second layer142is electronically connected to a top surface of the first layer140through a plurality of micro vias144. As is known in the art, vias are holes drilled through a printed circuit board that are then filled or coated (e.g., via electroplating) with a conductive material such as copper or solder to create an electrical pathway between a pad located on a top surface of the PCB layer and a pad located on the bottom surface of the PCB layer. Micro vias144are similar to vias, but micro vias144are typically smaller in diameter; e.g., a few tens of μm in diameter (0.100 mm-0.040 mm). In one embodiment, micro vias144are typically drilled using a computer-controlled laser such that hundreds or thousands of micro vias144may be drilled in a PCB with high accuracy in a small amount of time. Micro vias144are implemented in HDI (High Density Interconnect) PCBs and may be manufactured as stacked micro vias (i.e., a copper filled hole through all layers of the PCB), blind micro vias (i.e., a hole through one or more layers of the PCB but not through all layers of the PCB), and buried micro vias (i.e., a hole through an intermediate layer of the PCB but not through the top layer or the bottom layer of the PCB).

In one embodiment, the processor101is connected to the second layer142of the PCB100via a ball-grid-array (BGA). In addition, the memory modules104are also connected to the second layer142of the PCB100via a BGA. Although the connections shown inFIG. 1Bare implemented as BGA packages, it will be appreciated that the electrical components connected to the PCB100may be connected using other technologies such as through-hole technology, dual-in-line packages (e.g., Small-Outline Integrated Circuits or SOIC; Thin Small-Outline Package or TSOP; etc.), quad-in-line packages (e.g., Low-profile Quad Flat Package or LQFP; Plastic Leaded Chip Carrier or PLCC; etc.), and grid arrays (e.g., Pin Grid Array or PGA; Fine-pitch Ball Grid Array or FBGA; etc.), among other package types. In one embodiment, the electrical connections between the BGA of the processor101and the second layer142of the PCB100is made using via-in-pad (VIP) technology, which makes the electrical connection using a micro via144that resides in the same location as the solder pad to which the ball is soldered. In other words, the micro vias144are drilled in locations corresponding to the locations of the balls in the ball grid array. Then, the micro vias144are electro plated with copper such that the micro vias144are completely filled and only a copper pad remains on the surface of the PCB100.

FIGS. 2A & 2Billustrate the printed circuit board100ofFIGS. 1A & 1Bwith one or more cooling components210integrated thereon, in accordance with one embodiment. In one embodiment, the cooling components210are dedicated convective or conductive thermal structures that provide additional cooling capacity for processor101. In one embodiment, the cooling components210are constructed from a metallic material that has good thermal transfer properties. The cooling components210may have structures formed therein that increase the cooling efficiency of the cooling components210, such as fins or other structures that increase the surface area of the cooling components210. The cooling components210do not directly contact a surface of the processor101but instead are thermally coupled to the processor101via the second layer142of the PCB100.

As shown inFIG. 2B, the cooling components210are coupled to the second layer142of the PCB100with micro vias. The cooling components210may be placed on the same side of the PCB100as the processor101. In one embodiment, the cooling component210is coupled to the second layer142of the PCB100with a micro via thermal array250that, when filled during electroplating, form a surface pad212on the surface of the PCB100. A micro via thermal array250is an array of tightly packed micro vias (e.g., every 200 μm) arranged in a two-dimensional grid pattern. The use of the micro via thermal array250provides a high ratio of copper to dielectric in the area under the surface pad212. The higher ratio of copper to dielectric provides better thermal conductivity for heat to transfer from the second layer142of the PCB100to the cooling component210. The vias of the micro via thermal array250may be plated in copper or copper alloys, as well as other materials typically used in electroplating of PCBs. In one embodiment, the micro via thermal array250is one dimensional and contains a single row of micro vias. In another embodiment, the micro via thermal array contains as few as a single via. It will be appreciated that the density of micro vias in the area of the micro via thermal array250affects the heat transfer efficiency between the cooling components210and the second layer142of the PCB100.

Heat from the processor101is transferred through a top surface of the processor101to the heat sink120. In addition, heat from the processor101is also transferred through the bottom surface of the processor101to the second layer142of the PCB100through one or more micro vias144that are thermally coupled to the bottom surface of the processor101through the BGA. Heat conducts laterally through the second layer142of the PCB100to the micro via thermal arrays250coupled to the cooling components210. The heat is transferred from the second layer142of the PCB100into the cooling component210, where the heat is dissipated via convection. The heat flow path230is shown inFIG. 2B. Although only one path is shown, other paths may also exist such as between processor101and the second cooling component210on the right side of the processor101.

In one embodiment, the cooling components210are EMI (electromagnetic interference) shielding structures. For example, the cooling components210may be EMI shielding gaskets made of a Beryllium Copper sheet metal having a cross sectional shape such as a rectangle, or other alternate form for greater surface area. Alternatively, the cooling components210may be EMI cages that are placed over other components such as low power integrated circuits. In yet other embodiments, the cooling components210may be additional heat sinks with or without integrated fan assemblies that force air over the additional heat sinks. Although shown inFIGS. 2A & 2Bas two separate components located on two sides of the processor101, in one embodiment, cooling component210is a rectangular shaped EMI shield that completely surrounds the processor101. It will be appreciated that the PCB100may include one or more cooling components210.

FIG. 3illustrates a printed circuit board300with multiple thermal flow paths between a processor101and the cooling components210integrated within multiple layers of the printed circuit board, in accordance with one embodiment. As shown inFIG. 3, the PCB300includes a first layer140of dielectric material and a second layer142of conductive material similar to the PCB100ofFIGS. 1A & 1B. The PCB300also includes a third layer340of dielectric material and a fourth layer342of conductive material. The second layer142and the fourth layer342are electrically and thermally coupled via additional micro vias344in the third layer340of the PCB300. The micro vias344may be buried, copper filled micro vias formed in the third layer340. Alternatively, the micro vias344and micro vias144may be formed by drilling one blind hole in the fully formed and laminated PCB300. It will be appreciated that, in some embodiments, through micro vias may also be implemented as micro vias344.

In one embodiment, the second layer142and the third layer342of the PCB300are electrically coupled to a reference voltage of the power supply and form a multi-layer ground plane. By forming a multi-layer ground plane, thermal energy has multiple flow paths laterally through the PCB300. A first flow path allows heat to move from the processor101to the second layer142of the PCB300and up into the cooling components210. In addition, a second flow path allows heat to move from the processor101to the fourth layer342of the PCB300and up into the cooling components210. Thermal energy flows from the second layer142of the PCB300to the fourth layer342of the PCB300via the micro vias344. It will be appreciated, that the additional layer of conductive material in the PCB300enables more heat to be transferred to the cooling components in a lateral direction due to the increased cross sectional area of the combination of the second layer142and the fourth layer342.

In other embodiments, more than two layers of conductive material may be included in the PCB300. For example, PCB300may include a fifth layer of dielectric below the fourth layer342of the PCB300and a sixth layer of conductive material below the fifth layer of the PCB300. Additional pairs of dielectric layers and conductive layers may be included to provide additional heat transfer capacity. It will be appreciated, that the thickness of the layers of the conductive material may also be increased (e.g., by lengthening the time of the electroplating process) in order to increase the heat transfer capacity of individual layers.

FIGS. 4A & 4Billustrate the electrical connections of a processor400, in accordance with one embodiment. As shown inFIG. 4A, the processor400is integrated within a ball grid array package having a plurality of balls412on the bottom surface of the package and electrically coupled to the integrated circuit of the processor400. The balls412may be soldered to surface pads on the top surface of the PCB100. A portion of the plurality of balls412are coupled to a reference voltage (i.e., GND) of a voltage supply used to power the processor400. The balls in the portion414, shown as black inFIG. 4A, are arranged in a manner that enables efficient thermal transfer from the bottom surface of the processor400to the second layer142of the PCB100. Given a uniform thermal profile of processor400(i.e., the heat generated on the surface of the processor during operation is uniform throughout the surface of the processor), the location of balls414are evenly distributed across the surface of the processor400such that thermal energy transfer from the processor400to the second layer142of the PCB100is efficient.

In another embodiment, as shown inFIG. 4B, the thermal profile of a different processor401may be non-uniform. In other words, the processor401may generate more heat at one location on the surface of the package than at another location within the package. When the thermal profile of the processor401is non-uniform, the balls in the portion414, shown as black inFIG. 4B, may be arranged such that the density of balls414is higher closer to locations that generate more heat. For example, as shown inFIG. 4B, the lower left quadrant of the processor401may generate more heat than the other three quadrants of the processor401. In order to more efficiently transfer thermal energy from the bottom surface of the processor401to the second layer142of the PCB100, the density of balls414is increased in the lower left quadrant of processor401. When compared to the arrangement of balls414of processor400illustrated inFIG. 4A, each processor includes 32 balls electrically coupled to the reference voltage. However, the lower quadrant of processor401includes 18 of the 32 balls414coupled to the reference voltage. In comparison, each of the quadrants of processor400includes 8 of the 32 balls414coupled to the reference voltage.

FIG. 5illustrates an exemplary system500in which the various architecture and/or functionality of the various previous embodiments may be implemented. As shown, a system500is provided including at least one central processor501that is connected to a communication bus502. The communication bus502may be implemented using any suitable protocol, such as PCI (Peripheral Component Interconnect), PCI-Express, AGP (Accelerated Graphics Port), HyperTransport, or any other bus or point-to-point communication protocol(s). The system500also includes a main memory504. Control logic (software) and data are stored in the main memory504which may take the form of random access memory (RAM).

The system500also includes input devices512, a graphics processor506, and a display508, i.e. a conventional CRT (cathode ray tube), LCD (liquid crystal display), LED (light emitting diode), plasma display or the like. User input may be received from the input devices512, e.g., keyboard, mouse, touchpad, microphone, and the like. In one embodiment, the graphics processor506may include a plurality of shader modules, a rasterization module, etc. Each of the foregoing modules may even be situated on a single semiconductor platform to form a graphics processing unit (GPU).

The system500may also include a secondary storage510. The secondary storage510includes, for example, a hard disk drive and/or a removable storage drive, representing a floppy disk drive, a magnetic tape drive, a compact disk drive, digital versatile disk (DVD) drive, recording device, universal serial bus (USB) flash memory. The removable storage drive reads from and/or writes to a removable storage unit in a well-known manner.

Computer programs, or computer control logic algorithms, may be stored in the main memory504and/or the secondary storage510. Such computer programs, when executed, enable the system500to perform various functions. The memory504, the storage510, and/or any other storage are possible examples of computer-readable media.

In one embodiment, the architecture and/or functionality of the various previous figures may be implemented in the context of the central processor501, the graphics processor506, an integrated circuit (not shown) that is capable of at least a portion of the capabilities of both the central processor501and the graphics processor506, a chipset (i.e., a group of integrated circuits designed to work and sold as a unit for performing related functions, etc.), and/or any other integrated circuit for that matter. For example, a PCB may be manufactured that includes the central processor501or the graphics processor506thermally coupled to cooling components210.

Further, while not shown, the system500may be coupled to a network (e.g., a telecommunications network, local area network (LAN), wireless network, wide area network (WAN) such as the Internet, peer-to-peer network, cable network, or the like) for communication purposes.