T / R assembly-oriented high-efficiency heat dissipation embedded liquid metal LTCC (Low Temperature Co-Fired Ceramic) substrate and process

Abstract

The invention discloses an embedded liquid metal LTCC substrate for efficient heat dissipation of a T / R assembly and a process. According to the technical scheme, the embedded liquid metal LTCC substrate comprises a top functional layer, a middle low-frequency control layer and a bottom grounding layer. The top functional layer is integrated with an A-type chip and a B-type chip, the middle low-frequency control layer is used for arranging a control circuit and a power supply circuit, and stable operation of the T / R assembly is ensured; the bottom grounding layer is connected with the back metal ground through a metalized grounding through hole, a cavity is etched in the grounding layer to form a micro-channel structure for minimizing flow resistance, and liquid metal and inert gas are poured into the micro-channel layer in proportion to form a liquid metal micro-channel layer; the high thermal conductivity of the liquid metal enables the liquid metal to rapidly absorb and take away heat generated by the top layer and the middle layer, thereby effectively reducing the working temperature of the T / R assembly. The heat dissipation performance of the T / R assembly is effectively improved, miniaturization, integration and lightweight development of an electronic system is promoted, and the T / R assembly has wide application prospects and market value.

Description

Technical Field

[0001] The invention belongs to the technical field of high-power T / R component heat dissipation and packaging, and specifically relates to an embedded liquid metal LTCC substrate and process for efficient heat dissipation of T / R components. Background Art

[0002] Low Temperature Co-fired Ceramic (LTCC) technology is a technology that uses low-temperature sintered ceramic powder to make a green ceramic tape with precise thickness and density as a circuit substrate material. On the green ceramic tape, the required circuit pattern is made through mechanical or laser drilling, micropore grouting, precision slurry printing and other processes, and multiple passive devices are buried in it. Subsequently, these layers are stacked and sintered to form a passive integrated component or circuit substrate of a three-dimensional circuit network, and ICs and active devices are mounted on its surface to make a passive / active integrated functional module. Due to its low dielectric constant and its cavity manufacturing flexibility, LTCC has a wide range of applications in microwave and millimeter wave applications; low-temperature co-fired ceramic materials have good thermal stability, a thermal expansion coefficient close to that of single crystal silicon, and the advantages of integrated integration of passive devices. In the system-in-package (SiP) application based on LTCC, high-density integrated microsystems can be realized, becoming a feasible implementation solution for ceramic monolithic integrated systems. However, the poor thermal conductivity of LTCC results in the heat generated by the operation of the power devices integrated on the LTCC substrate cannot be dissipated quickly and in a timely manner, which becomes a weak point limiting the application of LTCC in high-power microwave components and multifunctional microsystems.

[0003] Active phased array antennas contain a large number of T / R components. The active devices such as power amplifiers and low noise amplifiers in these components are very sensitive to temperature. Excessive temperature will cause the working performance of the devices to deteriorate sharply or even burn out. In addition, the uneven temperature of the antenna array formed by a large number of distributed T / R components will cause phase inconsistency, affect the spatial beam synthesis performance of the antenna, and cause deviations in electronic scanning. Therefore, it is of great practical significance to efficiently cool the active phased array antenna to ensure that the junction temperature of the devices on the T / R components is lower than the allowable value and the temperature of the antenna array surface is uniform.

[0004] There are two main heat transfer methods for LTCC substrates: one is to bury a thermal via array just below the power component mounting area and connect it to the back metallization layer of the substrate, and the back metallization layer of the substrate is connected to the metal shell by silver paste bonding or eutectic welding to export heat; the other is to make a through cavity on the substrate and directly mount the power component on the metal shell through the cavity to export heat. For the first case, by reasonably optimizing the aperture and spacing of the thermal vias, the local thermal conductivity of the LTCC substrate can be increased to about 50W / (m·K), but the structure of the thermal vias will have a significant impact on the substrate warpage and the air tightness of the package. For the latter case, although the heat generated by the power component can be exported through the high thermal conductivity metal shell, there is a serious mismatch in thermal expansion coefficients between the power component chip and the metal shell, which will significantly reduce the reliability of the SiP. Although inserting a molybdenum-copper carrier between the two can alleviate the thermal mismatch, it is not conducive to the miniaturization of SiP. Summary of the invention

[0005] The present invention proposes a liquid metal embedded LTCC substrate for efficient heat dissipation of T / R components. The liquid metal is introduced into the microchannel, and the high thermal conductivity and fluidity brought by the two-phase flow channel of liquid metal and inert gas are utilized to achieve efficient heat dissipation of the T / R components. The LTCC substrate has the characteristics of multi-layer high-density wiring and convenient interconnection of any layer, and is very suitable for making a heat dissipation substrate with embedded liquid metal microchannels. The present invention aims to achieve efficient heat dissipation and integrated design of T / R components by integrating liquid metal microchannel heat dissipation technology into the LTCC substrate.

[0006] The technical solution to realize the present invention is: a buried liquid metal LTCC substrate for efficient heat dissipation of T / R components, including: a top functional layer, a middle low-frequency control layer, and a bottom ground layer.

[0007] The top functional layer integrates integrated microwave planar circuits and chips such as Class A chips and Class B chips, transmits microwave signals and integration through microstrip lines and gold wires, and surface-mount components are integrated through bonding.

[0008] The intermediate low-frequency control layer is used to arrange the control circuit and the power supply circuit.

[0009] The bottom ground layer is connected to the back metal ground through metallized ground vias, and cavities of specific size and layout are etched inside the ground layer to form an embedded microchannel layer that minimizes flow resistance.

[0010] Furthermore, the T / R component realizes low-noise amplification of received signals, power amplification of transmitted signals and beam control functions.

[0011] Furthermore, the rectangular shallow cavity on the upper part of the substrate is used to install Class A chips, such as amplitude and phase control multifunctional chips, low noise amplifiers and single-pole switch chips.

[0012] Furthermore, the upper opening in the substrate is used to place Class B chips, such as GaN power amplifier chips and driver amplifiers.

[0013] Furthermore, surface mount components such as capacitors and resistors are mounted on the upper part of the substrate.

[0014] Furthermore, a microchannel layer is embedded directly below the chip for rapid heat dissipation.

[0015] Furthermore, the embedded microchannel layer is a cavity structure with rounded corners on all sides to improve the flow uniformity of the heat dissipation liquid and prevent the liquid from flowing poorly due to large resistance at right angles to the channel.

[0016] Furthermore, the embedded microchannels are selected with appropriate width and depth to prevent poor liquid circulation.

[0017] Furthermore, a non-contact cross-shaped reinforcing rib structure is used in the embedded microchannel to achieve a supporting effect and avoid collapse during the lamination process.

[0018] Furthermore, an optimized teardrop-shaped flow-guiding and flow-disturbing column structure is added to the embedded microchannel to effectively enhance the liquid flow.

[0019] Furthermore, the embedded microchannel layer is divided into an inert gas layer, a liquid metal channel layer and a liquid metal filling port.

[0020] Furthermore, the volume of the liquid metal encapsulated in the liquid metal channel layer accounts for 60-80% of the embedded microchannel layer, and the rest is inert gas.

[0021] Furthermore, the liquid metal is made of a material with good fluidity and good thermal conductivity, such as a gallium-based alloy, to ensure efficient heat conduction.

[0022] Furthermore, during processing, a cavity is opened in the raw porcelain sheet to form a two-dimensional microchannel, and a single layer of raw porcelain sheets is stacked and pre-pressed. Before lamination, a carbon-based sacrificial layer material that matches the size of the channel is filled in the embedded microchannel. During lamination, the sacrificial layer material provides sufficient strength to support the embedded microchannel so that it does not deform. During sintering, the sacrificial layer material is discharged through the sealing port of the microchannel, thereby obtaining an embedded microchannel with a well-maintained structure inside the substrate.

[0023] Furthermore, the carbon-based sacrificial material can provide physical support for the cavity during lamination and sintering without squeezing the cavity and causing it to deform.

[0024] Furthermore, the carbon-based sacrificial material will not burn out until 900°C, and can still support the cavity structure at 700-900°C. During the sintering process, the carbon-based sacrificial material is vaporized and discharged to form a microchannel cavity, and the remaining carbon-based sacrificial material is cleaned by a chemical corrosive agent.

[0025] Compared with the prior art, the present invention has the following significant advantages:

[0026] (1) Combined with the high thermal conductivity of liquid metal, fast and efficient heat conduction and dissipation can be achieved, effectively reducing the operating temperature of T / R components.

[0027] (2) The present invention relies on the physical properties and structural design of the material itself and does not require external power drive, which greatly simplifies the complexity of the system and improves reliability and stability.

[0028] (3) By embedding liquid metal microchannels within the internal components of the LTCC substrate, a compact heat dissipation structure is achieved, which is convenient for integration with T / R components and is conducive to the miniaturization and integration of electronic systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A cross-sectional view of an embedded liquid metal LTCC substrate for efficient heat dissipation of T / R components provided in some embodiments of the present invention.

[0030] Figure 2 Schematic diagram of the embedded liquid metal microchannel structure provided in some embodiments of the present invention.

[0031] Figure 3 Some embodiments of the present invention provide a surface temperature simulation result diagram of an embedded liquid metal microfluidic channel substrate for efficient heat dissipation of T / R components, wherein (a) is the surface temperature simulation result diagram when the heat source working time is 0.1 second, (b) is the surface temperature simulation result diagram when the heat source working time is 0.2 second, (c) is the surface temperature simulation result diagram when the heat source working time is 0.3 second, and (d) is the surface temperature simulation result diagram when the heat source working time is 0.4 second.

[0032] Figure 4 Simulation diagrams of the gas phase volume fraction of gas-liquid two-phase flow in an embedded liquid metal microfluidic substrate for efficient heat dissipation of T / R components provided in some embodiments of the present invention, (a) is the gas-liquid volume distribution diagram when the heat source working time is 0.1 second, (b) is the gas-liquid volume distribution diagram when the heat source working time is 0.2 second, (c) is the gas-liquid volume distribution diagram when the heat source working time is 0.3 second, and (d) is the gas-liquid volume distribution diagram when the heat source working time is 0.4 second.

[0033] Figure 5Simulation diagrams of gas-liquid two-phase flow velocity in an embedded liquid metal microfluidic substrate for efficient heat dissipation of T / R components provided in some embodiments of the present invention, wherein (a) is a simulation result diagram of the bubble movement velocity when the heat source working time is 0.1 second, (b) is a simulation result diagram of the bubble movement velocity when the heat source working time is 0.2 second, (c) is a simulation result diagram of the bubble movement velocity when the heat source working time is 0.3 second, and (d) is a simulation result diagram of the bubble movement velocity when the heat source working time is 0.4 second.

[0034] Figure 6 A process flow chart of preparing an embedded liquid metal microfluidic channel substrate for efficient heat dissipation of T / R components provided in some embodiments of the present invention.

[0035] In the figure, 1. Top functional layer; 2. Middle low-frequency control layer; 3. Bottom ground layer; 4. Embedded microfluidic layer; 5. Raw porcelain sheet; 6. Microstrip line; 7. Gold wire; 8. Class A chip; 9. Class B chip; 10. Surface-mount components; 11. Carrier; 12. Control circuit; 13. Metallized ground via; 14. Interlayer metal ground; 15. Power supply circuit; 16. Inert gas; 17. Liquid metal; 18. Liquid metal filling port; 19. Back metal ground; 20. Reinforcement ribs; 21. Teardrop-shaped flow guide and spoiler column. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0038] In addition, in the present invention, the descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0039] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation" and the like should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; "connection" can be a mechanical connection or an electrical connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0040] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0041] The following will further introduce the specific implementation method, as well as the technical difficulties and inventive points of this invention in combination with this design example.

[0042] In one embodiment, see Figure 1 and Figure 2 , providing an embedded liquid metal LTCC substrate for efficient heat dissipation of T / R components, including a top functional layer 1, a middle low-frequency control layer 2, and a bottom ground layer 3.

[0043] The top functional layer 1 is formed by stacking and sintering the first to seventh layers of raw ceramic sheets. The top functional layer integrates integrated microwave planar circuits and chips such as class A chips 8 and class B chips 9. Microwave signals and integration are transmitted through microstrip lines 6 and gold wires 7. Surface-mount components 10 are integrated by bonding.

[0044] The intermediate low-frequency control layer 2 is formed by stacking and sintering the eighth to twelfth layers of green ceramic sheets. The intermediate low-frequency control layer 2 is used to arrange the control circuit 12 and the power supply circuit 15 .

[0045] The bottom grounding layer 3 is formed by stacking and sintering the thirteenth to twentieth layers of raw ceramic sheets. The bottom grounding layer is connected to the back metal ground 19 through a metallized grounding via 13. A cavity of specific size and layout is etched inside the grounding layer to form an embedded microchannel layer 4 that minimizes flow resistance.

[0046] The thickness of the LTCC substrate is at least 2 mm, that is, the total number of layers must be no less than 20 layers. The number of raw ceramic layers of the top functional layer 1, the middle low-frequency control layer 2, and the bottom grounding layer 3 is not fixed, but it must be ensured that each layer accounts for about 1 / 3 of the overall thickness.

[0047] The embedded microchannel layer 4 is located on the bottom ground layer 3 , and is divided into an inert gas layer 16 and a liquid metal channel layer 17 according to the positions occupied by the encapsulated liquid metal and the inert gas.

[0048] The volume of the liquid metal filled in the liquid metal channel layer 17 through the liquid metal filling port 18 accounts for 60-80% of the embedded microchannel layer 4, and the rest is inert gas.

[0049] The liquid metal used to fill the liquid metal flow channel layer 17 is made of a material with good fluidity and high thermal conductivity, such as a gallium-based alloy, to ensure efficient heat conduction.

[0050] In one embodiment, see Figure 1 The Class A chip 8 includes an amplitude and phase control multifunctional chip, a low noise amplifier and a single-pole switch chip, etc., and the Class B chip 9 includes a GaN power amplifier chip and a driving amplifier, etc., which are existing technologies.

[0051] In one embodiment, see Figure 2 The embedded microchannel layer 4 is a cavity structure with rounded corners on all sides to improve the flow uniformity of the heat dissipation liquid and prevent the liquid from flowing poorly due to large resistance at the right angles of the channel.

[0052] The embedded liquid metal microchannel is selected with a suitable width and depth to prevent poor liquid circulation.

[0053] The embedded liquid metal microchannel adopts a non-contact cross-shaped reinforcing rib structure to achieve a supporting effect and avoid collapse during the lamination process.

[0054] An optimized teardrop-shaped flow guide and spoiler column structure is added to the embedded liquid metal microchannel to effectively enhance the liquid flow.

[0055] In one embodiment, see Figure 3 , Figure 4 and Figure 5 , which is the simulation result of the surface temperature of the embedded liquid metal LTCC substrate, the internal gas phase volume fraction and the liquid flow velocity when the ambient temperature is 25℃ and changes with the working time.

[0056] In one embodiment, see Figure 6, is a process flow chart for preparing an embedded liquid metal LTCC substrate for efficient heat dissipation of T / R components. It includes: a) Design stage: Determine the circuit layout, circuit diagram, path and size design of the microchannel according to the heat dissipation requirements and functional layout of the T / R components; b) Green ceramic sheet processing: Mechanical or laser drilling is performed on the LTCC green ceramic sheet to form a preliminary structure of interconnected through holes and microchannels; c) Sacrificial layer filling and lamination: Single-layer green ceramic sheets are stacked and pre-pressed, and a carbon-based sacrificial layer material that matches the channel size is filled in the microchannel area, and then multiple layers of green ceramic sheets are laminated; d) Sintering and sacrificial layer removal: The laminated LTC C substrate is sintered at high temperature to densify the raw ceramic sheet to form a solid ceramic substrate, and the residual sacrificial layer material is removed by chemical corrosive agent to form a microchannel; e) Liquid metal potting: liquid metal is injected into the microchannel under vacuum environment, and the potting port is sealed by ceramic glue under inert gas environment; f) Post-processing: cleaning, drying and initial performance test of the potted LTCC substrate; g) Assembly and application: assemble the qualified LTCC substrate with other parts of the T / R component to form a complete T / R component. This component can be used in high-power electronic systems.

[0057] The carbon-based sacrificial material will burn out at 900°C and can still support the cavity structure at 700-900°C. During the sintering process, the carbon-based sacrificial material is vaporized and discharged to form a microchannel cavity, and the remaining carbon-based sacrificial material is cleaned by a chemical corrosive agent.

Claims

1. An embedded liquid metal LTCC substrate for efficient heat dissipation of T / R components, characterized in that: include: A top functional layer (1), an intermediate low-frequency control layer (2), a bottom grounding layer (3), a top functional layer integrated with a class A chip (8), a class B chip (9), microwave signals are transmitted via microstrip lines (6) and gold wires (7), and surface mount components (10) are integrated via bonding; the intermediate low-frequency control layer (2) is used to arrange a control circuit (12) and a power supply circuit (15); the bottom grounding layer (3) is connected to a back metal ground (19) via a metallized grounding through hole (13), and a cavity is etched inside the grounding layer to form an embedded microchannel layer (4) that minimizes flow resistance.

2. The embedded liquid metal LTCC substrate for efficient heat dissipation of T / R components according to claim 1, characterized in that: The type A chip (8) installed in the substrate cavity includes an amplitude and phase control multifunctional chip, a low noise amplifier and a single-pole switch chip, and the type B chip (9) placed in the upper cavity of the substrate includes a GaN power amplifier chip and a driving amplifier.

3. The LTCC substrate with embedded liquid metal microchannels for efficient heat dissipation of T / R components according to claim 1, characterized in that: The embedded microchannel layer (4) is located in the bottom grounding layer (3), and the embedded microchannel layer (4) is divided into an inert gas layer (16), a liquid metal channel layer (17) and a liquid metal filling port (18).

4. The embedded liquid metal LTCC substrate for efficient heat dissipation of T / R components according to claim 3, characterized in that: The embedded microchannel layer (4) comprises a cavity structure with rounded corners on all sides, the cavity channel is provided with non-contact cross-shaped reinforcing ribs (20) to achieve a supporting effect, and an optimized teardrop-shaped flow guide spoiler column (21) is added in the channel to strengthen self-circulation heat dissipation.

5. The embedded liquid metal LTCC substrate for efficient heat dissipation of T / R components according to claim 3, characterized in that: In a vacuum environment, liquid metal is poured into the microchannel through a liquid metal pouring port (18) by pressure injection, and the volume of the poured liquid metal accounts for 60-80% of the embedded microchannel layer (4), which is called the liquid metal channel layer (17).

6. The embedded liquid metal LTCC substrate for efficient heat dissipation of T / R components according to claim 3, characterized in that: For the LTCC substrate that has been filled with liquid metal, a liquid metal filling port (18) is sealed with ceramic glue in an inert gas environment with a concentration of 95% at normal pressure to form an inert gas layer (16).

7. The embedded liquid metal LTCC substrate for efficient heat dissipation of T / R components according to claim 5, characterized in that: The liquid metal of the liquid metal flow channel layer (17) is a gallium-based alloy to ensure efficient heat conduction.

8. The embedded liquid metal LTCC substrate for efficient heat dissipation of T / R components according to claim 3, characterized in that: When the T / R component is in working state, the liquid metal and inert gas are unevenly distributed in the embedded microchannel layer, and the temperature difference drives the liquid metal-inert gas interface to produce violent two-phase flow behavior.

9. A process for preparing an embedded liquid metal LTCC substrate for efficient heat dissipation of T / R components based on any one of claims 1 to 8, characterized in that: include: a) Design stage: Determine the circuit layout, circuit diagram, path and size design of microchannels according to the heat dissipation requirements and functional layout of the T / R components; b) Green ceramic sheet processing: mechanical or laser drilling is performed on the LTCC green ceramic sheet (4) to form a preliminary structure of interconnected through holes and microchannels; c) Sacrificial layer filling and lamination: a single layer of green ceramic sheets is stacked and pre-pressed, a carbon-based sacrificial layer material that matches the channel size is filled in the microchannel area, and then multiple layers of green ceramic sheets are laminated; d) Sintering and sacrificial layer removal: The laminated LTCC substrate is sintered at high temperature to densify the green ceramic sheet to form a solid ceramic substrate, and the remaining sacrificial layer material is removed by chemical etching to form a microchannel; e) Liquid metal potting: Liquid metal is injected into the microchannel under vacuum, and the potting port is sealed with ceramic glue under inert gas environment; f) Post-processing: cleaning, drying and initial performance testing of the encapsulated LTCC substrate; g) Assembly and application: Assemble the qualified LTCC substrate with other parts of the T / R assembly to form a complete T / R assembly.

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