Thermal management apparatus and method for a circuit substrate

The present disclosure relates to thermal management apparatus for a circuit substrate having heat generating components mounted on one or both sides thereof. The apparatus and method includes a circuit assembly having a first thermally conductive layer disposed on each side of the circuit substrate and being thermally coupled to one or more heat generating components of the circuit substrate. The apparatus and method includes a second thermally conductive layer disposed on each side of the circuit substrate and being thermally coupled to the first thermally conductive layer. The first thermally conductive layer and the thermally conductive layer can be shaped, sized, and/or configured to provide cooling of the one or more heat generating components disposed on each side of the circuit substrate by transferring and spreading the heat to the outside of the circuit assembly.

FIELD OF THE INVENTION

The present invention generally relates to thermal management of electronic components, and more particularly, to a thermal management apparatus and method for a circuit substrate.

BACKGROUND OF THE INVENTION

Electronic components such as integrated chips generally produce heat when operating. The heat is then transferred to an object to which the electronic component is attached and/or to the surrounding air. However, cooling solutions may be necessary for certain electronic components to maintain the operational temperature thereof below a critical temperature, which if reached, the electronic component may either not operate efficiently or fail due to heat damage. Various known cooling solutions for such electronic components can be used. For example, a heat sink that is typically constructed with copper can be attached to the outer surface of the electronic component with a thermally conductive adhesive. The heat generated by the electronic component is then transferred by conduction to the copper heat sink through the adhesive. The copper heat sink then transfers the heat to the surrounding air by convection. To provide additional cooling, a fan may also be placed near or on the copper heat sink to increase the air flow near and inside the structure of the heat sink to increase the heat transfer by convention.

Air cooling, however, fails to provide adequate cooling for certain electronic devices that use heat generating components. In small electronic devices or certain electronic devices, the internal space between the various components may be limited. Accordingly, even if a copper heat sink is used with or without a fan to cool a heat generating component, the limited space in the electronic device does not provide proper air circulation for the cooling of the heat generating component. This problem is further amplified in certain electronic devices where circuit substrates having heat generating components mounted thereon may be stacked on top of each other. Furthermore, cooling electronic components mounted on stacked circuit substrates becomes yet a bigger issue when one or more of the stacked substrates are double-sided, i.e., include heat generating components on both sides thereof. Although spacers can be provided between the stacked substrates to distance the substrates from each other to provide air gaps, such air gaps may not be sufficient to provide adequate air flow to cool the components that are positioned between a pair of stacked circuit substrates.

Various solutions to the above-described problem of cooling stacked substrates exist. However, most of these solutions solve the problem of cooling only single-sided stacked substrates, which are substrates that include heat generating components mounted only on one side of the substrate. One solution for cooling a double-side stacked substrates is to provide various heat conductive paths from each circuit substrate that connect to a heat sink which is disposed on top of the stack of substrates. However, this solution does not address the problem of limited air flow between the stacked substrates to cool the heat generating components. Additionally, in certain electronic devices where space is limited the noted solution occupies a relatively large volume due to the presence of the heat sink. Therefore, none of the solutions solve the problem of having single-sided or double-sided stacked substrates with adequate cooling provided and implemented in electronic devices where space is limited.

Therefore, there is a need for a cooling solution for single-sided or double-sided stacked substrates that can be implemented in electronic devices where space is limited.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The present disclosure relates to thermal management apparatus for a circuit substrate having heat generating components mounted on one or both sides thereof. The apparatus and method includes a circuit assembly having a first thermally conductive layer disposed on each side of the circuit substrate and being thermally coupled to one or more heat generating components of the circuit substrate. The apparatus and method includes a second thermally conductive layer disposed on each side of the circuit substrate and being thermally coupled to the first thermally conductive layer. The first thermally conductive layer and the thermally conductive layer can be shaped, sized, and/or configured to provide cooling of the one or more heat generating components disposed on each side of the circuit substrate by transferring and spreading the heat to the outside of the circuit assembly.

Referring toFIG. 1, one embodiment of a circuit assembly20constructed in accordance with the teachings of the present disclosure is shown. The circuit assembly20includes a circuit substrate22having a first side24and a second side26, which are also used herein to generally refer to the first side and the second side of the circuit assembly20. The circuit assembly20includes at least one heat generating component28disposed on the first side24of the circuit substrate22and at least one heat generating component30disposed on the second side26of the circuit substrate22. The circuit assembly20also includes a first thermally conductive layer32on each of the first side24and the second side26of the circuit substrate22that is thermally coupled to the heat generating components28and30, respectively. The circuit assembly20further includes a second thermally conductive layer34that is thermally coupled to first thermally conductive layer30. Accordingly, the heat generated by the heat generating components28and30is spread and transferred through the first thermally conductive layer32to the second thermally conductive layer34. The second thermally conductive layer34spreads and transfers the heat either to an object to which it is thermally coupled, or to the air surrounding the circuit assembly20by convection.

Each heat generating component28and30is mounted on the circuit substrate22and may be an application specific integrated chip or any other electronic or optical component that produces heat when operating. The circuit substrate22may be constructed from any suitable materials that can provide an electronic or optic circuit structure and support a variety of electronic or optic components. For example, the circuit substrate22can be a printed circuit board, a ceramic circuit board, or other types of circuit substrates that are known in the art.

The heat generating component28includes a mounting surface36and an outer surface38. When mounted on the circuit substrate22, the mounting surfaces36may be near or in contact with the circuit substrate22. The entire outer surface38or any desired portion thereof may be contacting the first thermally conductive layer32. Similarly, the heat generating component30includes a mounting surface40and an outer surface42. When mounted on the circuit substrate22, the mounting surface40may be near or in contact with the circuit substrate22. The entire outer surface42or any desired portion thereof may be contacting the first thermally conductive layer32. During the operation of the heat generating components28and30, the heat generated in the heat generating components28and30transfers to the mounting surfaces36and40, and the outer surfaces38and42, respectively. The mounting surfaces36and40transfer the heat to the circuit substrate22, while each of the outer surfaces38and42transfers the heat either to the first thermally conductive layer32by conduction, and/or to the surrounding air by convection.

The first thermally conductive layer32may be in contact with all or portions of the outer surfaces38and42. One of ordinary skill in the art will readily appreciate that the larger a contact area between the outer surfaces38and42and first thermally conductive layer30, the more heat can be transferred from the outer surfaces38and42to the first thermally conductive layer32. Additionally, the first thermally conductive layer32may be more heat conductive than air. Accordingly, the amount of heat transfer from the outer surfaces38and42of each of the heat generating components28and30to the first thermally conductive layer32may be controllable based on the size of the contact area between the outer surfaces38and42and the first thermally conductive layer32.

Referring toFIG. 2, another embodiment of a circuit assembly120constructed in accordance with the teachings of the present disclosure is shown. The circuit assembly120includes a circuit substrate122having a first side124and a second side126, which are also used herein to generally refer to the first side and the second side of the circuit assembly120. The circuit assembly120includes at least one heat generating component128disposed on the first side124of the circuit substrate122and at least one heat generating component130disposed on the second side126of the circuit substrate122. The circuit assembly120also includes a first thermally conductive layer132on each of the first side124and the second side126of the circuit substrate122that is thermally coupled to the heat generating components128and130, respectively. The circuit assembly120further includes a second thermally conductive layer134that is thermally coupled to first thermally conductive layer130. Accordingly, the heat generated by the heat generating components128and130is transferred through the first thermally conductive layer130to the second thermally conductive layer134. The second thermally conductive layer134transfers the heat either to an object to which it is thermally coupled, or to the air surrounding the circuit assembly120by convection.

Although not shown inFIG. 2, the circuit substrate122may only include heat generating components on only one side thereof. For example, the circuit substrate122may only include the heat generating component128on the first side124. Accordingly, the first thermally conductive layer132on the first side124can be thermally coupled to both the heat generating component128and the first side124of the circuit substrate122. The first thermally conductive layer132on the second side126can be thermally coupled to the second side126. The heat generated by the heat generating component128is then transferred through the first thermally conductive layer132of the first side124to the second thermally conductive layer134. The heat generated by the heat generating component128is also transferred through the circuit substrate122to the first thermally conductive layer132of the second side126. The second thermally conductive layer134then transfers the heat either to an object to which it is thermally coupled, or to the air surrounding the circuit assembly120by convection. Therefore, the present disclosure is applicable to circuit substrates with heat generating components on only one side or on both sides thereof.

The heat generating component128includes a mounting surface136and an outer surface138. When mounted on the circuit substrate122, the mounting surface136may be near or in contact with the circuit substrate122. As shown inFIG. 2, the outer surface138may be fully in contact with the first thermally conductive layer132. Similarly, when mounted on the circuit substrate122, the mounting surface140may be near or in contact with the circuit substrate122. As shown inFIG. 2, the outer surface142may be fully in contact with the first thermally conductive layer132. During the operation of the heat generating components128and130, the heat generated transfers to the mounting surfaces136and140, and the outer surfaces138and142, respectively. The mounting surfaces136and140transfer the heat to the circuit substrate122, while each of the outer surfaces138and142transfers the heat to the first thermally conductive layer132by conduction.

The first thermally conductive layers132may be deformable so that when contacting the circuit substrate122, they substantially conform to the outer surfaces138and142of the heat generating components128and130. Alternatively, inner surfaces of the first thermally conductive layer132that contact the circuit substrate122may be embossed or shaped to include a negative image of the corresponding side of the circuit substrate122. Accordingly, when the first thermally conductive layer132is placed or mounted on the circuit substrate122, it may complementarily contact the outer surfaces138and142of the heat generating components and may contact the surfaces of the circuit substrate122.

As shown inFIG. 2, the first thermally conductive layer132substantially contacts the outer surfaces138and142. Additionally, the first thermally conductive layer132can be sized to contact the circuit substrate122. Accordingly, the heat from the heat generating components128and130and the heat transferred by the heat generating components128and130that is transferred to the circuit substrate, can be transferred to the first thermally conductive layer132. The heat can spread throughout the first thermally conductive layer132. The second thermally conductive layer134may be sized and shaped to contact all or substantially large portions of the first thermally conductive layer132. Accordingly, the second thermally conductive layer134can provide heat transfer from the first thermally conductive layer132to the outside of the circuit assembly120. Additionally, the larger the contact surface area between the first thermally conductive layer132and the second thermally conductive layer134, the more heat may be transferred from the first thermally conductive layer132to the second thermally conductive layer134.

Referring now toFIG. 3, a side cross sectional view of the circuit assembly120ofFIG. 2is shown. The second thermally conductive layer134surround the circuit substrate122and the first thermally conductive layer132to form an enclosure150. The enclosure150includes a first side wall152and a second side wall154, which can cover and be in contact with the sides of the thermally conductive layer132. Accordingly, the first side wall152and the second side wall154can facilitate heat transfer even from the corresponding sides of the first thermally conductive layer132to the outside of the circuit assembly120.

The size and shape of the first thermally conductive layer32,132and the second thermally conductive layer34,134may be dictated by the size of the circuit substrate22,122and the application for which the circuit substrate22,122is used, respectively. Additionally, the method of assembly of the circuit substrate22,122with the first thermally conductive layer32,132and the second thermally conductive layer34,134may also be dictated by the shapes, sizes and the materials used for the first thermally conductive layer32,132and the second thermally conductive layer34,134. For example, referring toFIG. 1, the first thermally conductive layer32may simply be a pad constructed from a thermally conductive material that can be attached to each of the heat generating components28and30with a thermally conductive adhesive (not shown). Similarly, the second thermally conductive layer34can be the same or larger sized pad to connect with and cover the first thermally conductive layer32. The second thermally conductive layer34can also be attached to the first thermally conductive layer32with a thermally conductive adhesive (not shown). Referring toFIG. 4, the enclosure150of the circuit assembly120can be constructed prior to assembling the circuit assembly120. Accordingly, after the first thermally conductive layers132are attached to the corresponding sides of the circuit substrate122, circuit substrate122and the first conductive layer132can be inserted in the enclosure150and secured thereto with a thermally conductive adhesive.

As described in the foregoing, the first thermally conductive layer132may be constructed from a deformable material so that when it is attached to the first side124or the second side126of the circuit substrate122it conforms to the outer sides138and142of the heat generating components128and130, respectively. The first thermally conductive layer132may be constructed from a material that is either heat conducting or includes heat conducting particles evenly distributed therein. An example of such a material that can be used for the first thermally conductive layer132is Therm-A-Gap™ 570 & 580, manufactured by Chomerics, a Division of Parker Hannifin Corporation, Woburn, Mass. If the first thermally conductive layer132is not deformable, then a negative image of a corresponding side of the circuit substrate122can be created by etching, embossing, or other methods in the first thermally conductive layer132. Accordingly, when the first thermally conductive layer132is attached to circuit substrate122, it substantially conforms to the surface of this circuit substrate122. The first thermally conductive layer132can be attached to the circuit substrate122with a thermally conductive adhesive. Alternatively, the enclosure150may hold the first thermally conductive layer132in a contact position with the circuit substrate122when installed over the first thermally conductive layer132.

The height of the first thermally conductive layer132may be determined so as to be able to cover all or portions of the heat generating components128and130if desired. For example, the height of the first thermally conductive layer132may be larger that the height of the tallest heat generating component on the circuit substrate122. Accordingly, such a first thermally conductive layer can cover the tallest heat generating component of the circuit substrate. In yet another example, the first thermally conductive layer132may only contact a side of a heat generating component. Accordingly, the height of such a first thermally conductive layer132may be less or equal to the corresponding heat generating component. Therefore, the first thermally conductive layer132may be vertically sized to contact any heat generating component of the circuit substrate122as desired, and/or to accommodate the surface irregularities or other components of the circuit substrate122when contacting the circuit substrate122.

The second thermally conductive layer134contacts an outer surface of the first thermally conductive layer132. The second thermally conductive layer134may have a flat inner surface for contact with the outer surface of the first thermally conductive layer132Accordingly, the second thermally conductive layer134may be in the shape of a thin flat sheet that includes the disclosed thermal conductivity and heat spreading properties. The second thermally conductive layer134may be constructed from a thin sheet of copper, which may be referred to herein as the copper core. To provide electrical insulation for the second thermally conductive layer134, the copper core is enveloped by an outer layer that is constructed with a material that is not electrically conductive but is thermally conductive. Therefore, the second thermally conductive layer134includes a thermally conductive core surrounded by an electrically insulative material. An example of such a second thermally conductive layer is a T-Wing® flexible heat spreader, manufactured by Chomerics, a Division of Parker Hannifin Corporation, Woburn, Mass.

The second thermally conductive layer134may be rigid and can be attached to the first thermally conductive layer132with a thermally conductive adhesive. However, because the above-described second thermally conductive layer134is constructed with a thin sheet of copper, it is flexible so that it can be constructed in the shape of the enclosure150, or wrapped around the first thermally conductive layer132to form an enclosure similar to the enclosure150.

The circuit assembly120can be supported by being mounted to a support surface162with a thermal filler160. The thermal filler160can provide continuous heat transfer between the second thermally conductive layer134and the support surface162. Additionally, the thermal filler160may serve as an adhesive to securely attach the circuit assembly120to the support surface162. Accordingly, in the disclosed examples, attaching the circuit assembly120to the support surface162with fasteners or other similar assembly structures may not be necessary. The support surface162may be another circuit substrate, a support plate inside an electronic device, the enclosure walls of an electronic device, or any other suitable structure. The support surface162may also provide a thermal path to transfer the heat from the circuit assembly120to other components of an electronic device or to an enclosure of an electronic device for transfer of the heat to the outside of the electronic device. The thermal filler material may be a pliable or gel-like material that is deformable to fill the gaps between the second thermally conductive layer134and the support surface162. An example of such a gap filling material is Therm-A-Gap™ T630, manufactured by Chomerics, a Division of Parker Hannifin Corporation, Woburn, Mass.

The circuit assembly120can be used in electronic devices where space is limited such that the heat generating components128and130of the circuit substrate122cannot be sufficiently cooled with air flow, heat sinks, or a combination thereof. Additionally, the circuit assembly120may be applicable in devices where the circuit substrate122is disposed between one or more additional circuit substrates such that with common cooling methods (e.g., air flow) the heat between two or more circuit substrates cannot be sufficiently dissipated to cool the components of the circuit substrate122. The circuit assembly120can be installed in a space that may have a height that is slightly larger than the height of the circuit assembly120. The second thermally conductive layer134can be attached to any component of a device, the interior walls of a device, or any other component inside the device that can absorb the heat dissipated from the second thermally conductive layer134.

FIG. 4illustrates another embodiment of a circuit assembly220constructed in accordance with the teachings of the present disclosure. The circuit assembly220is shown as an internal component of a laptop or mobile computer300, which may be referred to herein as the laptop computer300. The circuit assembly220includes a circuit substrate222having a first side224and a second side226, which are also used herein to generally refer to the first side and the second side of the circuit assembly220. The circuit assembly220includes two heat generating components228and229disposed on the first side224and one heat generating component230disposed on the second side226. The circuit assembly220also includes a first thermally conductive layer232on each of the first side224and the second side226that is thermally coupled to the heat generating components228,229and230, respectively. The circuit assembly220further includes a second thermally conductive layer234that is thermally coupled to first thermally conductive layer232. Accordingly, the heat generated by the heat generating components228,229and230is transferred through the first thermally conductive layer232to the second thermally conductive layer234.

The laptop computer300includes a bottom surface302, shown as a lower panel, and a top surface304, shown as an upper panel, that generally define a housing306for the electronic components of the laptop. Laptop computers are generally smaller in size than their desktop counterparts. Accordingly, the internal electronic components of laptop computers are positioned much closer together than a comparable desktop computer. As shown inFIG. 4, the laptop300may include a motherboard308that is attached to the bottom surface302. The circuit assembly220is shown mounted on the motherboard308and substantially occupies the space between the motherboard308and the top surface304. The top surface304may include a keyboard310, or the top surface304may itself be the keyboard310.

As shown inFIG. 4, the thermally conductive layer232that is on the first side224of the circuit substrate222is in contact with a top surface of the heat generating component228and with both the top surface and one side of the heat generating component229. Accordingly, several air gaps312are present on the first side of the circuit substrate222. As discussed above, the larger the contact surfaces are between the first thermally conductive layer232and the heat generating components228and229on the first side224of the circuit assembly220, the more heat can be transferred from the heat generating component228and229to the second thermally conductive layer234on the first side224of the circuit assembly220. However, in certain applications of the disclosed circuit assembly220, the amount of heat that is transferred to the second thermally conductive layer234may have to be restricted to maintain an object to which the second thermally conductive layer234is attached or is near below a certain temperature.

As shown inFIG. 4, the keyboard310is positioned directly above and near the outer surface of the second thermally conductive layer234of the first side224. Accordingly, to maintain the keyboard310at an acceptable temperature for use by an operator of the laptop300, the size and configuration of the first thermally conductive layer232of the first side224may be determined accordingly. Therefore, as shown inFIG. 4, the first thermally conductive layer232does not contact the entire outer surfaces of the heat generating components228and229, and provides the air gaps312on the first side224. If the first thermally conductive layer232were made larger so as to substantially cover the heat generating components228and229and/or fill the air gaps312, the keyboard310could become too warm and uncomfortable to the touch for the operator of the laptop300. In addition, the height HC of the circuit assembly220is less than the internal height HL of the housing of the laptop300to provide an air gap316between the keyboard310and the second thermally conductive layer234of the first side224. The air gap316further controls the transfer of heat from the second thermally conductive layer234on the first side224to the keyboard310. Therefore, one of ordinary skill in the art will readily appreciate that the sizes and configurations of the first thermally conductive layer232, the second conductive layer234, and the entire circuit assembly220can be tailored so that the amount of heat transferred from the circuit assembly220can be controlled as desired.

The heat from the heat generating components228and229are also transferred to the circuit substrate222, which in turn can transfer the heat to the first thermally conductive layer232of the second side226. As shown inFIG. 4, the first thermally conductive layer232is sized and configured to substantially cover the second side226of the circuit substrate222including the outer surface of the heat generating component230. Accordingly, the heat transferred to the second side226of the circuit assembly20may be greater than the heat that is transferred to the first side224of the circuit assembly220.

The second thermally conductive layer234of the second side226is thermally coupled to the motherboard308with a thermal filler260. The thermal filler160can provide continuous heat transfer between the second thermally conductive layer234and the mother board308. Additionally, the thermal filler260may serve as an adhesive to securely attach the circuit assembly220to the mother board308. Accordingly, in the disclosed examples, attaching of the circuit assembly220to the mother board308with fasteners or other similar devices may not be necessary. The thermal filler material may be a pliable or gel-like material that is deformable to fill the gaps between the second thermally conductive layer234and the motherboard308. An example of such a gap filling material is Therm-A-Gap™ T630, manufactured by Chomerics, a Division of Parker Hannifin Corporation, Woburn, Mass. The motherboard is mounted to the bottom surface302, which transfers the heat to outside the laptop300.

The second thermally conductive layer234may be a C-shaped enclosure250, as shown inFIG. 4, to also provide transfer of heat from the first thermally conductive layer232and the circuit substrate222to a first side wall252of the enclosure250. As described in the foregoing, the second thermally conductive layer234can include a thin copper core with an outer layer to provide electrical insulation of the copper core. Accordingly, the second thermally conductive layer234is flexible and may be shaped as desired. Therefore, a flat sheet of the material that forms the second thermally conductive layer234can be bent and wrapped around the first thermally conductive layer232of the first side224and the second side226to form the C-shaped enclosure250. The enclosure250can be secured to the first thermally conductive layer232on both sides224and226with a thermally conductive adhesive. Optionally, to secure the C-shaped enclosure250in contact with the first thermally conductive layer232, a thermally conductive wrapping material324(shown with dashed lines) can be wrapped around the enclosure250and secured by a thermally conductive adhesive to the enclosure250. The thermally conductive wrapping material324may be constructed from the same material as the enclosure250but also include adhesive backing to attach to the enclosure250. Accordingly, the thermally conductive wrapping material324provides transfer of heat from the first thermally conductive layer232and the circuit substrate222to a second side wall254.

The first thermally conductive layer232and the second thermally conductive layer234may also include electromagnetic insulation (EMI) properties. Accordingly when the circuit assembly120,220is constructed with the enclosures150,250(i.e., enclosures150,250forming a Farady cage), respectively, the circuit assembly20can also be electromagnetically shielded from any external interferences. Such EMI shielding may be desired or necessary when a circuit assembly120,220is installed in a device having limited internal space, such as the laptop300. Therefore the circuit assembly120,220can also provide EMI shielding in devices where the components are tightly installed inside the device such that electromagnetic interference between various internal components maybe an issue.

The invention is not limited to particular details of the apparatus and method depicted and the modifications and applications may be contemplated. Certain other changes may be made in the above-described method and apparatus without departing from the true spirit of the scope of the invention herein involved. It is intended, therefore, that the subject matter in the above depiction should be interpreted as illustrative and not in a limiting sense.