Patterned design for thermal management of two-phase immersion cooling system for electronic devices

Abstract

Provided herein is a direct chip cooling film for two-phase cooling. The film includes a dielectric layer having a first surface for attachment to a cold plate or circuit and having a second surface. A metal layer is on the second surface of the dielectric layer having a pattern of features on the side opposite the dielectric layer. The surface pattern provides increased surface area and multiple nucleation sites for bubble formation for two-phase cooling. The features can also include metal nucleation to further enhance nucleation.

Description

BACKGROUND

[0001] High-density semiconductor chips generate high temperatures, requiring thermal management solutions to keep chip operating temperatures constant. Immersion cooling technology is being considered for use in new data centers as part of a thermal management solution. Immersion cooling technology involves a phase change in the heat transport process, whereby it reduces the interfacial resistance when it comes into contact with a heated semiconductor device. SUMMARY

[0002] Dielectric fluids such as fluorocarbons are being used in immersion two-phase cooling systems. However, due to its low surface tension and wetting properties, the fluid penetrates deeply into the cavity, which promotes the accumulation of overheating on the chip surface. This accumulation results in local hot spots on the chip surface and causes thermal stress that ultimately reduces chip performance and increases chip failure rates. Embodiments of the present invention include films that can mitigate the accumulation of local hot spots and enhance two-phase cooling of electronic devices.

[0003] A first film having features for two-phase cooling includes a dielectric layer having a first surface for attachment to a cold plate or circuit and having a second surface. A metal layer is on the second surface of the dielectric layer and has a pattern of features on a side opposite the dielectric layer.

[0004] A second film having features for two-phase cooling includes a metal layer having a first surface for attachment to a cold plate or circuit and having a second surface. Metal supports are on the first surface of the metal layer with a bonding material between the metal supports. A plurality of metal nodules are on the second surface of the metal layer. BRIEF DESCRIPTION OF DRAWINGS

[0005] Figure 1A is a side cutaway view of a chip cooling film with a micro-pattern.

[0006] Figure 1B is a side cutaway view of a chip cooling film with a micro-pattern having angled sidewalls.

[0007] Figure 2 is a side cutaway view of a chip cooling film with a micro-pattern and a plurality of cavities.

[0008] Figure 3A is a side cutaway view of a chip cooling film with a micro-pattern having angled sidewalls.

[0009] Figure 3B is a side cutaway view of a chip cooling film with a micro-pattern having angled sidewalls.

[0010] Figure 4 is a side cutaway view of a chip cooling film with a micro-pattern and an etched dielectric.

[0011] Figure 5A is a side cross-sectional view of a chip cooling film with nubs.

[0012] Figure 5B and Figure 5C is Figure 5A is a top view image of a chip cooling film of

[0013] Figure 6 is a side cross-sectional view of a chip cooling film with nubs on an angled micro pattern.

[0014] Figure 7 is a side cross-sectional view of a chip cooling film with a uniform micro structure pattern.

[0015] Figure 8 is a side cross-sectional view of a chip cooling film with a uniform feature pattern with nubs.

[0016] Figure 9 is a side cross-sectional view of a chip cooling film with nubs and multiple cavities.

[0017] Figure 10A is an illustration of a two-phase immersion cooling system.

[0018] Figure 10B is an illustration of a two-phase immersion cooling system using an internal heat sink.

[0019] Figure 10C is an illustration of a two-phase immersion cooling system using a tube for cooling fluid. DETAILED DESCRIPTION

[0020] Embodiments include flexible or rigid heat transfer nucleation films with features such as patterns and nubs to enhance two-phase immersion cooling systems for electronic devices. These films include a dielectric and a thin metal layer formed on top of the dielectric, where a uniform metal pattern is formed on the thin metal layer. The uniform metal pattern includes a three-dimensional microstructure and is formed with a specific trace width and thickness. One or more cavities extend through the bottom side of the dielectric and solder or metal paste is filled within the dielectric cavities, which facilitates the film attachment to electronic devices for cooling with thick cold plates or directly to electronic devices without the need for thick cold plates.

[0021] Figure 1A is a side cross-sectional view of a chip cooling film with a micro pattern attached to a cold plate 18 and having metal features 10, a thin metal layer 12, a dielectric 14, and solder 16 arranged as shown. Figure 1B is a side cross-sectional view of a chip cooling film with a micro pattern having angled sidewalls attached to a cold plate 28 and having angled metal micro features 20, a thin metal layer 22, a dielectric 24, and solder 26 arranged as shown.

[0022] The microstructure of metal features 10 and 20 can be formed by an additive electroplating process using a photomask or by a subtractive process using an applied photomask. The formation of micro-patterns as bubble formation creates more surface area and nucleation sites during the heating process. Also, the uniformity of the metal microstructure is critical to provide uniform heat dissipation across the surface.

[0023] These micro-patterns help nucleate bubbles to transport the heat load from the electronic device. The spacing and feature size of the micro-patterns can be tailored to the desired thermal performance.

[0024] Furthermore, as Figure 2 shown, the dielectric can be etched to create one or more cavities, which are then filled with solder 35. Figure 2 is a side cross-sectional view of a chip cooling film with micro-patterns and multiple cavities attached to a cold plate 36 and having metal features 30, thin metal layer 32, dielectric 34, and cavities containing solder 35 arranged as shown. The cavities can help provide structural integrity to the circuit attached to the cold plate when the cold plate is subjected to solder reflow. The microstructure of metal features 30 can be formed as described above.

[0025] Figure 3A and Figure 3B shows metal features with different angles. Figure 3A is a side cross-sectional view of a chip cooling film with micro-patterns having angled sidewalls attached to a cold plate 46 and having angled sidewalls 38, metal features 40, thin metal layer 42, dielectric 44, and cavities containing solder 45 arranged as shown. Figure 3B is a side cross-sectional view of a chip cooling film with micro-patterns having angled sidewalls attached to a cold plate 56 and having tapered pattern 48, metal features 50, thin metal layer 52, dielectric 54, and cavities containing solder 55 arranged as shown. The angled metal features create more surface area and promote liquid flow between the metal features. The microstructure of metal features 40 and 50 can be formed as described above. Furthermore, the space is reduced on the bottom of the sidewalls to promote a fast nucleation process. The gap and sidewall angle can be tailored to the thermal performance requirements. Figure 3B shows a uniform tapered structure that helps nucleate at a faster rate and due to the narrow nucleation sites helps form tiny bubbles, which speeds up the heat dissipation performance.

[0026] As Figure 4 shown, to provide structural integrity and to be able to easily handle thin, flexible chip cooling films, the dielectric can be further etched and filled with metal through a via electroplating technique.Figure 4 is a side cross-section of a chip cooling film with a micro-pattern and etched dielectric and with micro-features 58, vias 60 filled with metal, and solder or metal paste 62 arranged as shown. This etch fill provides rigidity and ease of handling during solder reflow or other bonding processes. The etch also enhances the thermal performance of the system.

[0027] Figure 5A Formation of nucleated features on a uniform metal layer is shown. Figure 5A is a side cross-section of a chip cooling film with nucleation attached to a cold plate 72 and with metal nucleation 64, thin metal layer 66, supporting metal standoffs 68, and vias 70 arranged as shown. Uniform nucleation features can be formed by electroplating techniques. The vias 70 extend between the metal standoffs 68 and can be formed by patterning and then chemically etching a dielectric layer. These vias can be filled with solder or metal bonding paste by screen printing or dispensing and then the solder or metal bonding paste can be attached to a thick rigid cold plate. These micro-patterns help to nucleate bubbles to transport the heat load from the electronic device. The nucleation feature size can be tailored to the required thermal performance.

[0028] Figure 5B Micrographs showing metal nucleation particles and the size of these nucleations are shown and the distance between the nucleations can be tailored to the thermal performance requirements. Figure 5C Uniform roughness on a metal surface is shown. Instead of nucleation, uniform roughness can be created to enhance the heat transfer of a boiling system. Uniform nanometer to micrometer scale roughness can help to create a large number of bubbles due to the large surface area and nucleation sites.

[0029] Figure 6 Nucleation on a tilted uniform metal pattern is shown. Figure 6 is a side cross-section of a chip cooling film with nucleation on an angled micro-pattern attached to a cold plate 80 and with nucleation 74, thin metal layer 76, dielectric 78, and vias 80 filled with metal bonding material arranged as shown. This surface pattern provides a further increase in surface area and multiple nucleation sites for bubble formation. The microstructure of the metal layer 76 can be formed as described above.

[0030] Figure 8 Formation of nucleated features on a uniform metal layer is shown. Figure 7 Another embodiment of nucleated features on top of a uniform metal pattern is shown. Figure 7 is a side cross-section of a chip cooling film with a uniform pattern of micro-structures attached to a cold plate 92 and with uniform feature pattern 84, thin metal layer 86, supporting metal standoffs 88, and vias 90 filled with metal bonding material arranged as shown. Figure 8is a side cutaway view of a chip cooling film with uniform pattern of nubs attached to a cold plate 104 and having metal nubs 94, uniform metal features 96, thin metal layer 98, supporting metal cradle 100, and through holes 102 filled with metal bonding material arranged as shown.

[0031] As shown in Figure 7 and Figure 8 Multiple cavities can be formed under a single patterned cold plate, which helps provide structural integrity of the circuit when the cold plate is subjected to solder reflow. Figure 7 and Figure 8 The uniform metal microstructure features of the chip cooling film shown in

[0032] Figure 9 Metal pillars under thin metal features are shown. These pillars can enhance thermal performance due to greater surface area and heat capacity, and can provide structural integrity when the circuit is attached to a thick metal cold plate. Figure 9 is a side cutaway view of a chip cooling film with nubs and multiple cavities attached to a cold plate 114 and having metal nubs 106, thin metal layer 108, supporting metal cradle 110, and solder or metal bonding material 112 arranged as shown. Once the metal nubs are formed as described above, the dielectric side of the film is patterned using a photomask and the dielectric is chemically etched to form cavities. After the chemical etching process, the photoresist is removed. The etched portions are filled with metal using electroplating from inside the cavities to form metal pillars. Finally, the remaining exposed dielectric is removed by a chemical etching process to form cavities adjacent to the metal pillars. These cavities can be filled with metal bonding material to bond to a thick metal cold plate or directly to an electronic device.

[0033] The features described above can also be formed using a thick metal stamping technique. Different sizes and features can be stamped at the bottom of a thick metal foil or plate, then a uniform nub is created using an electroplating technique. Finally, the stamped metal cavities are filled with a bonding material.

[0034] The following are exemplary materials, sizes, and configurations for the chip cooling films described herein.

[0035] Suitable dielectric materials include polyimide, liquid crystal polymer, PEEK polymer, polyethylene terephthalate, flexible FR4 sheet, and polyolefin. Suitable metals for creating features and layers are copper, steel, and silver. Suitable plating over materials include gold, silver, and tin. Suitable bonding materials include solder, metal paste, silver paste, and anisotropic conductive film (ACF) bonding solutions.

[0036] Suitable bonding materials include lead-free solder, copper paste, silver paste, ACF film or paste, and thermally conductive adhesive.

[0037] Suitable thicknesses of dielectric layers are in the range of 25 pm to 125 pm. Thicknesses of vias filled with metal can be in the range of 25 pm to 125 pm. Micropatterned features can have a height from the underlying metal layer of 5 pm to 100 pm. Nubs can have a diameter in the range of 0.1 pm to 5 pm.

[0038] Non-inclined metal features formed on the top metal surface can have an angle of 90 degrees within a certain tolerance with respect to the underlying metal layer.

[0039] Inclined or angled metal features formed on the top metal surface can have an angle of approximately 30 to 90 degrees with respect to the underlying metal layer.

[0040] Etched dielectric cavities can have a tilt angle of approximately 25 to 90 degrees with respect to the underlying cold plate or circuit. This trapezoidal tilt angle helps to retain metal bonding pastes such as solder or silver within the cavities.

[0041] Figure 10A to Figure 10C is an illustration showing the use of a chip cooling film in a two-phase cooling system.

[0042] Figure 10A is an illustration of a two-phase immersion cooling system with a printed circuit board (PCB) 116, an integrated circuit (IC) 118, and a chip cooling film 120. The IC 118 can be attached to the chip cooling film 120 using solder or metal bonding materials such as materials within cavities or vias without the need for a separate thick metal cold plate.

[0043] Figure 10B is an illustration of a two-phase immersion cooling system using an internal heat sink and having a PCB 122, an IC 124, an internal heat sink (IHS) 126, and a chip cooling film 128. The chip cooling film 128 can be attached to the IHS 126 using solder or metal bonding materials such as materials within cavities or vias without the need for a separate thick metal cold plate.

[0044] Figure 10Cis an illustration of a two-phase immersion cooling system using tubing for cooling fluid and having ICs 130, tubing 132 for cooling fluid, and internal baffles with chip cooling films, such as baffle 134 with chip cooling film 136. Chip cooling film 136 can be attached to baffle 134 using solder or a metallic bonding material, such as material within a cavity or through-hole, without a separate thick metallic cold plate. Each baffle can include chip cooling films attached in a similar manner.

[0045] Chip cooling films 120, 128, and 136 can be implemented with any of the chip cooling films described herein, and possibly with associated metallic cold plates. Chip cooling films can be used in two-phase cooling systems with flexible or rigid circuitry. Chip cooling films can be attached directly in physical contact to circuitry without a separate metallic cold plate, or alternatively, used with and in physical contact with a metallic cold plate between the circuitry and chip cooling film.

Claims

1. A membrane having features for two-phase cooling, comprising: A dielectric layer having a first surface for attachment to a cold plate or circuit and having a second surface; and A metal layer, located on the second surface of the dielectric layer, has a feature pattern including sidewalls on the side of the metal layer opposite to the dielectric layer, and is used for two-phase cooling when the film is attached to the cold plate or circuit. The dielectric layer includes a cavity having a trapezoidal angle relative to the cold plate or circuit, the cavity extending through the first surface and the second surface of the dielectric layer, the film further includes an adhesive material located in the cavity, and the film is attached to the cold plate or circuit by the adhesive material.

2. The membrane according to claim 1, wherein, The feature has sloping sidewalls.

3. The membrane according to claim 1, wherein, The feature includes a conical pattern.

4. The membrane according to claim 1, wherein, The pattern is uniform.

5. The membrane according to claim 1, further comprising nodules located on the feature.

6. The membrane according to claim 5, wherein, The nodules are made of copper, steel, or silver.

7. The membrane according to claim 1, wherein, The dielectric layer is etched to form the cavity.

8. The membrane according to claim 1, wherein, The metal layer is made of copper, steel or silver.

9. The membrane according to claim 1, wherein, The dielectric layer is composed of polyimide, liquid crystal polymer, PEEK polymer, polyethylene terephthalate, flexible FR4 sheet, or polyolefin.

10. A membrane having features for two-phase cooling, comprising: A metal layer having a first surface and a second surface; A metal support, the metal support being located on the first surface of the metal layer; An adhesive material is located on the first surface of the metal layer, between the metal supports, and is used to attach the membrane to a cold plate or circuit. and Multiple metal nodules are located on the second surface of the metal layer and are used for two-phase cooling when the film is attached to the cold plate or circuit. The metal support includes a cavity having a trapezoidal angle relative to the cold plate or circuit, the cavity extending through two surfaces of the metal support, and the adhesive material located in the cavity.

11. The membrane according to claim 10, wherein, The metal layer has a feature pattern including sidewalls, and the nodule is located on the feature.

12. The membrane according to claim 11, wherein, The pattern is uniform.

13. The membrane according to claim 10, wherein, The metal layer is made of copper, steel or silver.

14. The membrane according to claim 10, wherein, The nodules are made of copper, steel, or silver.

15. A two-phase cooling system for electronic devices, comprising: Printed circuit boards; Integrated circuit, the integrated circuit being located on the printed circuit board; and A chip cooling film is located on the side of the integrated circuit opposite to the printed circuit board, wherein the chip cooling film comprises the film according to any one of claims 1-14.

16. A two-phase cooling system for electronic devices, comprising: Printed circuit boards; Integrated circuit, the integrated circuit being located on the printed circuit board; An internal heat sink is located above the integrated circuit and on the printed circuit board; and A chip cooling film is located on the side of the internal heat sink opposite to the integrated circuit, wherein the chip cooling film comprises the film according to any one of claims 1-14.

17. A two-phase cooling system for electronic devices, comprising: integrated circuit; A conduit containing cooling fluid in contact with the integrated circuit; A baffle, the baffle being located inside the pipe; and A chip cooling film located on one or more of the baffles, wherein the chip cooling film comprises the film according to any one of claims 1-14.

Images