Patent Description:
A mesh network is a network that includes multiple nodes that link together to improve network performance and network accessibility. As an example, a mesh network supporting a wireless local area network (WLAN) may include multiple wireless nodes linking together across an area. Each wireless node, or mesh network device, may provide wireless devices access to the WLAN and exchange network information with other mesh network devices. The aggregate functions of the multiple mesh network devices, in general, improve connectivity to the WLAN across the area and improve efficiency of data exchange.

In some instances, the mesh network device may be a range-extending mesh network device that includes a voice assistant. The mesh network device may be a small form-factor and include multiple electronic subsystems that generate heat. An example of an electronic subsystem is a printed circuit board (PCB) that is populated with a variety of integrated circuit (IC) devices. Another example of an electronic subsystem is a speaker module that may be used by the voice assistant.

To dissipate heat from the electronic subsystems and avoid degradation of the electronic subsystems, a thermal-control system may be used. However, an active thermal-control system, such as a thermal-control system that circulates a coolant or a liquid, may not be feasible due to form-factor and/or power consumption considerations.

<CIT> relates to system-in-package assemblies in portable electronic devices. <CIT> relates to a mid-spreader for stacked circuit boards in an electronic device.

Features of exemplary embodiments are defined in the dependent claims.

The details of one or more aspects of a passive thermal-control system for a mesh network device and associated mesh network devices are described below. The use of the same reference numbers in different instances in the description and the figures may indicate like elements:.

This document describes a passive thermal-control system that is integrated into a mesh network device. The passive thermal-control system, which may include a heat sink and multiple heat spreaders, is structured such that heat originating from IC devices of the mesh network device and a speaker module of the mesh network device may be transferred to other components of the mesh network device, such as a housing component. The heat may then be dissipated to an external environment to maintain a desired thermal profile of the mesh network device.

Heat transfer, in general, is energy that is in transit due to a temperature difference. If one or more temperature differences exist across components of a system, such as the mesh network device, heat (e.g., energy in Joules (J)) will transfer from higher temperature zones to lower temperature zones to reduce the temperature differences. There are several mechanisms for heat transfer across the components of the system to reduce temperature differences, including convection, radiation, and conduction.

Convection, or heat transfer from a surface due to movement of molecules within fluids such as gases and liquids, may be quantified by equation (<NUM>) below: <MAT>.

For equation (<NUM>), qconv represents a rate of heat transfer from a surface through convection (e.g., in J per second or Watts (W)), h represents a convection heat-transfer coefficient (e.g., in W per meter squared (W/m<NUM>)), Ts represents a temperature of a surface (e.g., in Kelvin (K) or degrees Celsius (°C)), and T∞ represents a temperature of a fluid (e.g., in K or °C) to which the surface is exposed. The term A represents an area of a surface (e.g., in m<NUM>).

Radiation, or heat transfer from a surface through electromagnetic radiation, may be quantified by equation (<NUM>) below: <MAT>.

For equation (<NUM>), qrad represents a rate of heat transfer through radiation (e.g., in W), ε represents emissivity (dimensionless), σ represents the Stefen-Boltzmann constant (e.g., σ = <NUM> × <NUM>-<NUM> W/(m<NUM>·K<NUM>)), Ts represents a temperature of a surface (e.g., in K or °C), and Tsurr represents a temperature of surroundings of the surface (e.g., in K or °C). The term A represents an area of the surface (e.g., in m<NUM>).

Conduction, or heat transfer through a solid body through atomic and molecular activity, may be quantified by equation (<NUM>) below: <MAT>.

For equation (<NUM>), qcond represents a rate of heat transfer in a solid material through conduction (e.g., in W), k represents a thermal conductivity of the solid material (e.g., in W/(m·K)), and dT/dx represents a temperature gradient through the solid material (e.g., in K/m or °C/m). The term A represents a cross-sectional area of the solid material (e.g., in m<NUM>).

In instances of heat transfer from one physical body to another, through one or more of a convection heat-transfer mechanism, a radiation heat-transfer mechanism, or a conduction heat-transfer mechanism, the physical bodies may be in thermal contact. In some instances, this can include direct physical contact between the bodies or a material (e.g., a TIM) located between the bodies, enabling conduction-based heat transfer between the bodies. In other instances, this can include an air gap between the bodies that enables convection-based and/or radiation-based heat transfer between the bodies.

A mesh network device includes a passive thermal-control system that, e.g., transfers heat using one or more of the heat-transfer mechanisms described above. In general, and in accordance with equations (<NUM>) and (<NUM>), rates and/or quantities of heat transfer can be varied by increasing or decreasing surface areas for convection and/or radiation within the mesh network device (e.g., increasing or decreasing surface areas of planar heat spreaders). In accordance with equation (<NUM>) and within the passive thermal-control system, rates and/or quantities of heat transfer can also be varied by introducing, between surfaces, one or more thermal interface materials (TIMs) that have a high thermal conductivity.

Through conduction, convection, and radiation heat-transfer mechanisms, as described and quantified by equations (<NUM>) - (<NUM>) above, the passive thermal-control system may transfer heat originating from heat-generating electronic devices within the mesh network device to an interior surface of a housing component of the mesh network device. An exterior surface of the housing component may then dissipate the heat to an external environment through convection and/or radiation, effective to prevent degradation of the electronic subsystems that may include the heat-generating electronic devices.

While features and concepts of the described passive thermal-control system can be implemented in any number of different environments, apparatuses, and/or various configurations, aspects are described in the context of the following examples.

<FIG> illustrates an example operating environment <NUM> including a mesh network device <NUM>. The mesh network device <NUM> includes multiple electronic devices, including a PCB <NUM> populated with one or more IC devices. The mesh network device <NUM> also includes a speaker module <NUM>.

The mesh network device <NUM> may serve as a node of a wireless mesh network (e.g., a WLAN network conforming to IEEE <NUM> communication protocols (Wi-Fi)). In general, the mesh network device <NUM> may wirelessly couple other wireless devices (e.g., a wireless phone, a laptop computer) to the wireless mesh network.

The mesh network device <NUM> may, in some instances, include a voice-assistant to receive audible inputs from a user of the mesh network device <NUM>. For example, the mesh network device <NUM> may receive, through the speaker module <NUM> and from a user of the mesh network device <NUM>, a vocal command that the mesh network device <NUM> transmits to one or more applications available through the wireless mesh network (e.g., available from a cloud-computing environment or available through another device to which the mesh network device <NUM> is wirelessly coupled). As an example, the vocal command may be transmitted to a remote application supporting a home automation or security system.

As another example, the mesh network device <NUM> may receive, through the speaker module and from the user of the mesh network device <NUM>, a vocal query. The mesh network device <NUM> may transmit the vocal query to one or more other applications available through the wireless mesh network (e.g., available from a cloud-computing environment or available through another device to which the mesh network device <NUM> is wirelessly coupled). In some instances, the vocal query may direct a search to be performed by a search engine available through the wireless mesh network. In other instances, the vocal query may direct media to be streamed through the speaker module <NUM> of the mesh network device <NUM> (e.g., play music through the mesh network device <NUM>).

In general, and while performing operations (e.g., wirelessly coupling the other devices, receiving vocal commands, receiving vocal queries, playing media), the one or more IC devices populated on the PCB <NUM> and the speaker module <NUM> may generate an internal heat load <NUM> within the mesh network device <NUM>. To manage the internal heat load <NUM> within the mesh network device <NUM> (e.g., prevent thermal runaway or damage to electronic systems of the mesh network device <NUM>), a passive thermal-control system <NUM> is used.

The passive thermal-control system <NUM> includes multiple elements, including a heat sink <NUM>, a heat-sink heat spreader <NUM>, and a speaker-module heat spreader <NUM> (not visible in <FIG>). In some instances, the passive thermal-control system <NUM> may also include multiple thermal interface materials (TIMs).

The heat sink <NUM> is generally cylindrical in shape, die-cast from a metal material (e.g., an aluminum material, a magnesium material). The heat-sink heat spreader <NUM> and the speaker-module heat spreader <NUM> each may be generally elliptical (or generally circular) in shape. The heat-sink heat spreader <NUM> and the speaker-module heat spreader <NUM> each are also generally planar, formed from respective sheets of a graphite material.

The elements of the passive thermal-control system <NUM> (e.g., the heat sink <NUM>, the heat-sink heat spreader <NUM>, the speaker-module heat spreader <NUM>) conduct, spread, and transfer the internal heat load <NUM> (e.g., a rate of heat transfer qi in Watts) to a housing component <NUM> of the mesh network device <NUM> or to a base <NUM> of the mesh network device. The housing component(s) <NUM> may then dissipate the internal heat load <NUM> (e.g., using a thermal-convection heat-transfer mechanism and/or a thermal-radiation heat-transfer mechanism) to an external environment. In some instances, and depending on configurations of the passive thermal-control system <NUM>, portions of the internal heat load <NUM> transferred to the housing component(s) <NUM> may vary.

The passive thermal-control system <NUM> further maintains a desired thermal profile of the mesh network device <NUM>. As an example, the conduction, spreading, and transfer of the internal heat load <NUM> by the passive thermal-control system <NUM> may maintain a surface temperature of the housing component(s) <NUM> at or below a temperature of approximately <NUM>° Celsius (°C) while the mesh network device <NUM> is operating in ambient conditions of <NUM>. The passive thermal-control system <NUM> may also maintain junction temperatures of the IC devices populating the PCB <NUM> at or below different respective temperature thresholds.

<FIG> illustrates a top isometric view <NUM> of an example heat sink and an example heat-sink heat spreader (e.g., the heat sink <NUM> and the heat-sink heat spreader <NUM> of <FIG>). As illustrated, the heat sink <NUM> includes a body <NUM> that is generally disk-like (e.g., middle region of the heat sink <NUM>) extending radially from a central axis <NUM> to define a perimeter. The body <NUM> includes a first generally planar surface <NUM> (located under the heat-sink heat spreader <NUM> in <FIG>) that is substantially orthogonal to the central axis <NUM>. The heat-sink heat spreader <NUM> attaches to the first generally planar surface <NUM> (e.g., using a thermally conductive epoxy). Further, the heat-sink heat spreader <NUM> may be positioned coaxially with the heat sink <NUM>, according to the central axis <NUM>.

In some instances, the heat-sink heat spreader <NUM> may spread and transfer heat to the body <NUM> using a thermal-conduction heat-transfer mechanism. In other instances, the heat-sink heat spreader <NUM> may spread and transfer heat to a surrounding environment (e.g., a cavity within the mesh network device <NUM> of <FIG>) using a thermal-convection heat-transfer mechanism and/or a thermal-radiation heat-transfer mechanism. For example, the heat-sink heat spreader <NUM> may spread and transfer heat in a generally outward direction away from the first generally planar surface <NUM> of the body <NUM> of the heat sink <NUM>.

The heat-sink heat spreader <NUM> may include one or more sheets (e.g., layers) of a thermally conductive material such as a graphite material. Furthermore, different types of materials may be selected to increase or decrease emissivity (ε) and alter thermal radiation characteristics of the heat-sink heat spreader <NUM>.

The heat sink <NUM> may include one or more fin region(s) <NUM>. Each fin region <NUM> may extend from the perimeter of the body <NUM> in one or more directions that are substantially parallel to the central axis <NUM>. Furthermore, each fin region <NUM> may include an interior surface <NUM> and an opposing exterior surface <NUM>. In some instances, each fin region <NUM> may transfer heat to a surrounding environment (e.g., to a cavity within the mesh network device <NUM> of <FIG> or to the housing component(s) <NUM> of the mesh network device of <FIG>) using one or more of a thermal conduction, a thermal convection, and/or a thermal-radiation heat-transfer mechanism. The heat sink <NUM> may also include mounts, stands, or other fixturing mechanisms for one or more antenna(s) <NUM> that support wireless communications.

<FIG> illustrates a bottom isometric view <NUM> of an example heat sink (e.g., the heat sink <NUM> of <FIG>). As illustrated, the body <NUM> of the heat sink <NUM> includes a second generally planar surface (e.g., second generally planar surface <NUM> that is opposite the first generally planar surface <NUM> of <FIG>). The second generally planar surface <NUM> may be generally orthogonal to the central axis <NUM>. Furthermore, the second generally planar surface may face a speaker module (e.g., the speaker module <NUM>).

As illustrated, the body <NUM> includes one or more pedestal(s) <NUM> that protrude from the second generally planar surface <NUM>. Each pedestal <NUM> may interface with a thermal interface material (TIM) and enable the TIM to make physical (and thermally conductive) contact with a respective, heat-generating device (e.g., an IC device that may be part of the PCB <NUM> of <FIG>). The TIM may effectuate thermal coupling between the heat-generating device and the pedestal <NUM>. The pedestal <NUM> may, in turn, and using a thermal-conduction heat-transfer mechanism, transfer heat to the body <NUM> of the heat sink <NUM>.

Examples of TIMs include gel materials and/or grease materials that may be thermally conductive. These materials may be injected with nano-particles, such as magnesium or aluminum nano-particles, to improve thermal conduction properties. Furthermore, TIMs located between the heat-generating devices and the one or more pedestal(s) <NUM> may reduce gaps and/or bond line gaps and improve thermal conduction efficiencies. Other examples of TIMs include thermally conductive foam materials and thermally conductive pad materials.

<FIG> illustrates a top isometric view <NUM> of an example speaker-module subassembly <NUM> that may be included in a mesh network device (e.g., the speaker-module subassembly <NUM> may be part of the speaker module <NUM> of the mesh network device <NUM> of <FIG>). As illustrated, the speaker-module subassembly <NUM> includes a base <NUM> and a speaker-module driver <NUM>. The base <NUM> includes an interior surface <NUM> that is generally planar and substantially orthogonal to the central axis <NUM>. The interior surface <NUM> faces a second surface of a heat sink (e.g., the second generally planar surface <NUM>).

As illustrated, a heat spreader (e.g., the speaker-module heat spreader <NUM> of <FIG>) attaches to the interior surface <NUM> of the base <NUM>. For example, the speaker-module heat spreader <NUM> may attach to the interior surface <NUM> using a thermally conductive epoxy. In some instances, the interior surface <NUM> may face a surface of a heat sink (e.g., the second generally planar surface <NUM> of <FIG>).

In some instances, the speaker-module heat spreader <NUM> may be located between the interior surface <NUM> and a magnet of the speaker-module driver <NUM>. The speaker-module heat spreader <NUM> may use a thermal-conduction heat-transfer mechanism to transfer heat from the speaker-module driver <NUM> to the base <NUM>. In some instances, the base <NUM> may use thermal conduction and/or thermal convection heat-transfer mechanisms to transfer the heat to a surrounding environment.

The speaker-module heat spreader <NUM> may include one or more sheets (e.g., layers) of a thermally conductive material such as a graphite material. Furthermore, different types of materials may be selected to increase or decrease emissivity (ε) and alter thermal radiation characteristics of the speaker-module heat spreader <NUM>.

<FIG> illustrates a top plan view <NUM> of an example PCB that may be included in a mesh network device (e.g., the PCB <NUM> of the mesh network device <NUM> of <FIG>). The PCB <NUM> may be a multi-layer PCB that includes a glass-reinforced epoxy laminate material (e.g., FR-<NUM>) and multiple layers of electrically conductive traces. The PCB <NUM> may also be a "double-sided" PCB, where different IC devices may be mounted to opposing surfaces of the PCB <NUM> using surface-mount (SMT) soldering techniques. In some instances, traces within the multiple layers of the PCB <NUM> may include a thermally conductive material. For example, traces within the multiple layers of the PCB <NUM> may include a copper material. The PCB <NUM> may also include one or more ground planes (e.g., copper ground planes) that may each absorb, spread, and transfer heat within the PCB <NUM>.

A first surface of the PCB <NUM> (e.g., a first surface <NUM>) may be populated with a first set of IC devices. The first set of IC devices include, for example, one or more memory IC devices <NUM>, such as double-data rate dynamic random access memory (DDR DRAM) devices. Alternatively or additionally, the first set of IC devices (also) includes a system-on-chip (SoC) IC device <NUM> or an embedded multimedia card (eMMC) IC device <NUM>.

Each IC device may electrically connect to the PCB <NUM> using solder connections that result from surface-mount (SMT) manufacturing techniques. In general, the first set of IC devices populating the first surface <NUM> of the PCB <NUM>, when operating, may contribute to a heat load (e.g., the internal heat load <NUM> of <FIG>) within a mesh network device (e.g., the mesh network device <NUM> of <FIG>). In some instances, an electromagnetic interference (EMI) shield <NUM> may surround one or more planar regions <NUM> of the first surface <NUM> containing one or more the first set of IC devices.

<FIG> illustrates a bottom plan view <NUM> of an example PCB that may be included in a mesh network device (e.g., the PCB <NUM> of the mesh network device <NUM> of <FIG>). A second surface of the PCB <NUM> (e.g., a second surface <NUM> that is opposite the first surface <NUM> of <FIG>) may be populated with a second set of IC devices. The second set of IC devices may include, for example, one or more front end module (FEM) IC devices <NUM> (e.g., <NUM> Gigahertz (GHz) FEM, <NUM> FEM, Thread FEM) and one or more radio frequency (RF) IC devices <NUM> (e.g., <NUM> RF, <NUM> RF) that may be associated with wireless communications of a wireless local area network (WLAN).

In general, the second set of IC devices populating the second surface <NUM> of the PCB <NUM>, when operating, may contribute to a heat load (e.g., the internal heat load <NUM> of <FIG>) within a mesh network device (e.g., the mesh network device <NUM> of <FIG>). In some instances, another electromagnetic interference (EMI) shield may surround one or more planar regions <NUM> of the second surface <NUM> containing or more of the second set of IC devices.

<FIG> illustrates a top isometric view <NUM> of an example arrangement of TIMs that may be included in a mesh network device. The TIMs, as arranged, may transfer heat from IC devices populating the PCB <NUM> to a heat sink (e.g., the heat sink <NUM> of <FIG>).

A first set of TIMs <NUM> may thermally couple a first set of IC devices populating a first surface of the PCB <NUM> (e.g., the one or more memory IC devices <NUM>, the SoC IC device <NUM>, and the eMMC IC device <NUM> populating the first surface <NUM> of <FIG>) to respective pedestals that are part of the heat sink (e.g., a subset of the one or more pedestal(s) <NUM> of <FIG>). The first set of TIMs <NUM> may be in directed thermal contact with the first set of IC devices.

In general, the first set of TIMs <NUM> may be positioned between the first set of IC devices and respective pedestals that are part of the heat sink. Furthermore, the first set of TIMs <NUM> may use a thermal-conduction heat-transfer mechanism to transfer heat from the first set of IC devices to the heat sink. In some instances, an EMI shield <NUM> may surround the first set of IC devices. In such instances, a thermally conductive foam may be located between the EMI shield <NUM> and the heat sink.

A second set of TIMs <NUM> may thermally couple, indirectly, a second set of IC devices, populating a second surface of the PCB <NUM> (e.g., the one or more FEM IC devices <NUM>, and the one or more RF IC devices <NUM>, populating the second surface <NUM> of <FIG>), to other respective pedestals that are part of the heat sink (e.g., another subset of the one or more pedestal(s) <NUM> of <FIG>). In this instance, and as opposed to being in direct physical contact with the second set of IC devices, the second set of TIMs <NUM> may be in direct physical contact with the surface of the PCB <NUM> (e.g., the first surface <NUM> of <FIG>), which is opposite from the surface to which the other IC devices are mounted (e.g., the second surface <NUM> of <FIG>) and proximate (e.g., located coaxially, respectively) to the second set of IC devices.

In general, the second set of TIMs <NUM> may be positioned between the surface of the PCB <NUM> and the other respective pedestals that are part of the heat sink, proximate to multiple other IC devices. Furthermore, the second set of TIMs <NUM> may use a thermal-conduction heat-transfer mechanism to transfer heat from the multiple other IC devices to the heat sink.

<FIG> illustrates example details <NUM> of heat-transfer paths within the example mesh network device <NUM>. The example details <NUM> include several instances of a sectional view of the mesh network device <NUM>, including instances <NUM>, <NUM>, and <NUM>. The top illustration of <FIG> illustrates a first heat-transfer path <NUM> that transfers heat (e.g., a portion of the internal heat load <NUM> originating from multiple IC devices populating the PCB <NUM> and/or the speaker module <NUM> of <FIG>) through the heat sink <NUM>. The heat sink <NUM> may then, using convection, conduction, and/or radiation heat-transfer mechanisms, transfer the heat through the one or more fin regions <NUM> to the housing component <NUM> in a direction that is generally orthogonal to the central axis <NUM> of the heat sink <NUM>. The housing component <NUM> may then, using convection and/or radiation heat-transfer mechanisms, transfer heat received through the first heat-transfer path <NUM> to the surrounding environment.

The middle illustration of <FIG> illustrates an enlarged view <NUM> of the second instance <NUM> within the example mesh network device <NUM>. As illustrated, the second instance includes a second heat transfer path <NUM>. As part of the second heat transfer path <NUM>, a TIM of the first set of TIM(s) <NUM> uses thermal conduction to transfer heat from the SoC IC device <NUM> to one of the one or more pedestal(s) <NUM> (e.g., a corresponding respective pedestal of the one or more pedestal(s) <NUM>). Heat transferred through the second heat-transfer path <NUM> may "join" with heat of the first heat-transfer path <NUM> to be transferred through the housing component <NUM> to the surrounding environment.

The bottom illustration of <FIG> illustrates a third instance <NUM>. The third instance <NUM> includes a third heat-transfer path <NUM> that may use convection and/or radiation heat-transfer mechanisms to transfer heat (e.g., another portion of the internal heat load <NUM> originating from multiple IC devices populating the PCB <NUM> and/or the speaker module <NUM> of <FIG>) to the housing component <NUM>. Then, the housing component <NUM> may, using convection and/or radiation heat-transfer mechanisms, transfer heat received through the third heat-transfer path <NUM> to the surrounding environment.

Claim 1:
An apparatus (<NUM>) comprising:
one or more integrated circuit devices (<NUM>, <NUM>, <NUM>);
a speaker module (<NUM>) comprising a base (<NUM>) and a speaker driver (<NUM>); and
a passive thermal-control system (<NUM>) to conduct heat generated by the speaker module (<NUM>) and by the one or more integrated circuit devices (<NUM>, <NUM>, <NUM>) to a housing component (<NUM>) of the apparatus (<NUM>) for external dissipation, the passive thermal-control system (<NUM>) comprising:
a heat sink (<NUM>), the heat sink generally cylindrical and centered about a central axis (<NUM>), the heat sink (<NUM>) including an interior disk-like body (<NUM>) that is substantially orthogonal to the central axis (<NUM>) and thermally coupled to at least one of the one or more integrated circuit devices (<NUM>, <NUM>, <NUM>);
a first heat spreader (<NUM>), the first heat spreader generally planar and attached to a first surface (<NUM>) of the interior disk-like body (<NUM>); and
a second heat spreader (<NUM>), the second heat spreader generally planar and attached to a surface (<NUM>) of the speaker module (<NUM>) that is substantially orthogonal to the central axis (<NUM>) and faces a second surface (<NUM>) of the interior disk-like body that is opposite the first surface (<NUM>) of the interior disk-like body (<NUM>),
wherein the second heat spreader (<NUM>) is attached to the base (<NUM>) of the speaker module (<NUM>) and is located between the surface (<NUM>) of the speaker module (<NUM>) and a magnet of the speaker driver (<NUM>).