Preparation method of co-fired integrated heat sink for LTCC substrate

Abstract

The invention discloses a preparation method of a co-fired integrated heat sink for an LTCC substrate, and belongs to the technical field of electronic components. According to the structure of the integrated heat sink, a through or non-through cavity with the size matched with that of a chip is prefabricated in the LTCC substrate according to the position of the high-power chip; before the raw ceramic tape is laminated and sintered, high-thermal-conductivity metal slurry is used for filling to form a solid metal heat sink block; the power chip is directly installed on the filled metal heat sink block, and heat generated by the chip is quickly conducted to the bottom plate through the solid metal block. The preparation method comprises a cavity forming process, a metal slurry filling process and a laminating and co-firing process. The problems that an existing LTCC substrate is low in intrinsic thermal conductivity, a heat sink cannot be welded, and the integration technology of a heat dissipation structure and a circuit substrate is poor in feasibility, high in cost and poor in practicability are solved. The method is widely applied to the substrate manufacturing technology of power electronic components, power assemblies, power modules and complete machine circuits.

Description

Technical Field

[0001] This invention belongs to the field of electronic component technology, and more specifically to the field of integrated LTCC substrate and heat sink technology. In particular, it relates to a method for preparing a co-fired integrated heat sink for LTCC substrate. Background Technology

[0002] With the rapid development of 5G / 6G communication and high-performance computing technologies (such as GaN and SiC), electronic components are evolving towards higher frequencies, higher speeds, higher power densities, and miniaturization. The resulting "heat accumulation" effect has become a core bottleneck restricting further improvements in system reliability, lifespan, and performance. Research shows that for every 10-15°C increase in junction temperature of electronic components, their failure rate approximately doubles. Therefore, efficient thermal management solutions, especially heat dissipation technologies for high heat flux densities (>100W / cm³), have become a research frontier and a key technological challenge in the field of electronic packaging.

[0003] Among numerous substrate technologies, low-temperature co-fired ceramic (LTCC) substrates have gained widespread application in aerospace, radar, and automotive electronics due to their excellent high-frequency characteristics, multi-layer wiring capability, ease of 3D integration, and high mechanical strength. However, traditional LTCC substrates have low intrinsic thermal conductivity (typically 2-3 W / m·K), and their inherent heat dissipation capacity is insufficient to meet the demands of next-generation power devices. Furthermore, LTCC cannot be soldered with heat sinks like HTCC. Against this backdrop, an efficient LTCC heat sink fabrication solution is urgently needed. This solution requires more than just simple heat conduction; it necessitates innovative microstructure design to achieve active thermal management within the package, ensuring the stable operation of high-performance electronic systems in harsh environments.

[0004] LTCC (Low Temperature Co-fired Ceramic) heat sinks are a technology that integrates heat dissipation structures with circuit boards. Currently, the main implementation methods are as follows: 1. Embedded Microchannels: This is currently a hot research topic and mainstream technology. Through precision drilling (mechanical or laser) and filling with sacrificial materials (such as carbon paste or wax-based materials) within LTCC green ceramic wafers, a complex three-dimensional microchannel network is formed during co-firing. Forced convection of the cooling medium (such as deionized water or fluorinated liquid) within the microchannels greatly enhances heat dissipation efficiency, theoretically reaching hundreds of W / cm². However, reliability, such as service life, is currently a key performance indicator. Damage to the flow channels or leakage of the cooling medium will pose a serious threat to the substrate components and chips. Furthermore, its manufacturing cost and process difficulty are too high, preventing its widespread use at present.

[0005] 2. Thermal Vias Array: This involves densely arranging vias filled with a highly thermally conductive metal paste (such as silver paste) under hot spots or in the power device area. It is the most basic and commonly used method for enhancing lateral and longitudinal heat conduction in LTCC substrates. However, this method is limited by ceramic strength; dense thermal vias can lead to a significant decrease in ceramic strength and severe ceramic deformation.

[0006] 3. Integration with high thermal conductivity substrates: LTCC is integrated with high thermal conductivity substrates (such as AlN or metal substrates) through mounting to form a hybrid structure, combining the wiring advantages of LTCC with efficient heat dissipation. However, this approach introduces additional structural components, making it difficult to meet miniaturization requirements.

[0007] In view of this, the present invention is hereby proposed. Summary of the Invention

[0008] The technical problem to be solved by this invention is to address the issues of low intrinsic thermal conductivity of existing LTCC substrates, inability to solder heat sinks, poor technical feasibility, high cost, and poor practicality in integrating heat dissipation structures with circuit boards.

[0009] Currently, low-temperature co-fired ceramic (LTCC) technology faces two key challenges when applied in high-density packaging, especially in high-power microwave RF components: insufficient heat dissipation efficiency and difficulty in achieving hermeticity.

[0010] (1) Heat dissipation bottleneck: Traditional LTCC materials have low thermal conductivity (typically only 2-5 W / (m·K)), which is insufficient to meet the heat dissipation requirements of high-power chips. To improve heat dissipation, an array of metal thermal vias is commonly used to conduct heat to the bottom of the substrate. However, this method offers limited improvement in thermal conductivity (e.g., by optimizing the aperture and spacing, it can reach up to about 50 W / (m·K)), and high-density vias can affect the mechanical strength of the substrate, potentially leading to cracking or warping.

[0011] (2) Hermeticity challenge: Traditional vertical heat conduction hole structure is prone to micro-channels at the interface due to the shrinkage matching and bonding problem between the metal paste and LTCC ceramic body during sintering. This makes it difficult to achieve high reliability standards (such as GJB548C) in terms of hermeticity (usually requiring a leakage rate of <10⁻9 Pa·m³ / s).

[0012] The inventive concept of this invention is to employ integrated co-fired LTCC heat sink technology, using a large-size buried cavity structure to replace the traditional micro-thermal via array. This utilizes a volumetric heat dissipation source rather than a thermal via array to construct an efficient thermal management path within the LTCC substrate. This significantly increases the heat flux density of the ceramic substrate while maintaining hermeticity, enabling low thermal resistance and large-area direct connection between the chip / device and external heat dissipation paths, thereby significantly improving the heat dissipation capacity of the circuit board or package module. Simultaneously, this structural design helps optimize the soldering process, significantly improves the hermeticity and reliability of the package, and supports a higher degree of integration and miniaturization.

[0013] Therefore, the present invention provides a method for preparing a co-fired integrated heat sink for LTCC substrates, the method being as follows: I. Integrated Heat Sink Structure Design of LTCC Substrate The LTCC package structure typically includes, from top to bottom, a cover plate and a high-strength integrated LTCC substrate (including a co-fired heat sink). The improvement of this invention lies in the structure of the LTCC substrate itself.

[0014] (1) Inside the LTCC substrate, a through or cavity with a size matching the chip is prefabricated for the location of the high-power chip.

[0015] (2) Before the green ceramic belt is stacked and sintered, the cavity is filled with a metal paste with high thermal conductivity (such as copper or silver) to form a solid metal heat sink block.

[0016] (3) After the LTCC substrate is sintered, the power chip is directly mounted on the filled metal heat sink block. The heat generated during the use of the chip can be quickly conducted downward to the base plate through the solid metal block.

[0017] II. Key Process Steps (1) Cavity forming: On the LTCC green ceramic tape, a cavity window slightly larger than the chip size is formed by precision die punching or laser ablation. The cavity size of odd-numbered layers should be slightly smaller than that of even-numbered layers to ensure that the cavities after stacking present an interlocking "mortise and tenon" structure at the longitudinal interface.

[0018] (2) Metal paste filling: The prepared high thermal conductivity metal paste is filled into the cavity by printing or injection molding. The sintering shrinkage rate of the paste needs to be carefully matched with that of the LTCC green ceramic tape to reduce stress and ensure reliability and airtightness.

[0019] (3) Lamination and co-firing: The green ceramic tape filled with metal paste is aligned and laminated with other green ceramic tapes of signal layer and ground layer, and then co-fired as a whole. During the sintering process, the metal paste and the ceramic green ceramic tape shrink and densify synchronously, forming a robust integrated structure with good thermal and mechanical properties.

[0020] (4) Chip mounting and interconnection: After co-firing, the power chip is directly mounted on the heat sink block formed by the cavity by sintering or welding, and then interconnection operations such as gold wire bonding are performed.

[0021] (5) Sealing: Finally, the frame, cover plate and substrate are welded together to achieve hermetically sealed packaging.

[0022] 3. Beneficial effects: Compared with existing technologies, the cavity-filled co-fired LTCC heat sink technology provided by this invention brings the following significant advantages: (1) Revolutionary improvement in heat dissipation performance: By replacing the discrete array of thermally conductive holes with a solid high thermal conductivity metal block, the most efficient and shortest heat dissipation channel is established for the chip. This significantly reduces the total thermal resistance from the internal structure of the package to the external heat dissipation interface, enabling the LTCC package to support chips with higher power levels and improving the power density and long-term reliability of the system.

[0023] (2) Superior airtightness: In traditional technologies, numerous vertical heat conduction holes are the main weak point in airtight packaging. This invention greatly reduces these potential leakage paths. The cavity structure and the base plate can be designed as a continuous planar seal, making it easier to achieve and maintain a high level of airtightness, especially suitable for high-end fields such as aerospace and military electronics.

[0024] (3) Enhanced mechanical reliability: The solid metal filling cavity plays a supporting and reinforcing role inside the substrate, which can effectively reduce the risk of warping and cracking of multilayer substrates during sintering and service, and improve the mechanical stability of the package.

[0025] (4) Greater integration and design flexibility: This structure provides greater freedom for three-dimensional system-in-package (SiP). Chips can be directly integrated on the cavity metal block, and high-density passive components (such as filters and couplers) can be embedded and interconnected with signals using the surrounding multi-layer LTCC area, further reducing module size, weight and parasitic effects, and achieving true high-performance integrated packaging.

[0026] (5) Good process compatibility and cost potential: The main processes of this technology are compatible with standard LTCC processes and require no special equipment. Although metal paste filling may increase some material costs, lower-cost copper-based pastes can be used, and the improved heat dissipation may allow for the use of lower-cost chips or simplified system cooling designs, resulting in overall cost benefits from higher yields and reliability.

[0027] The technical solution of this invention can be widely applied to the substrate manufacturing technology of power electronic components, power modules, power components, and complete circuits. Attached Figure Description

[0028] none. Detailed Implementation

[0029] The specific implementation method for preparing a co-fired integrated heat sink for LTCC substrates is as follows: I. Preparation of Co-fired Integrated Heat Sink for LTCC Substrates (hereinafter referred to as the Product) (1) LTCC green ceramic sheets with a size of 200mm×200mm and a thickness of 130μm were prepared by tape casting process; (2) A through cavity of 3mm×3mm was processed on an odd-numbered layer of green ceramic sheet using laser technology; and a through cavity of 3.1mm×3.1mm was processed on an even-numbered layer of green ceramic sheet.

[0030] (3) Use an injection-type cavity filling device to fill the cavity with LTCC co-fired conductor slurry to form a dense cavity filling metal.

[0031] (4) Through precise alignment and lamination techniques, multiple layers of films containing conductive paste are laminated to ensure that the filler metals between each layer interlock and that the electrical connections are accurate. Pressure and temperature must be controlled during the lamination process to avoid delamination or deformation; (5) Cut out LTCC substrate blanks with dimensions of 5.3mm×5.3mm×1.2mm; (6) Perform a co-firing process, sintering the prepared LTCC substrate green blank at 920°C. Obtain an LTCC circuit board with dimensions of 5mm×5mm×1mm and a co-firing heat sink size of 3mm×3mm.

[0032] II. Product Testing Five LTCC substrate products were randomly selected and their heat transfer coefficients were tested. The test results are shown in Table 1. The heat transfer coefficient test conditions were 25-300℃ and humidity of 45% to 65%.

[0033] Table 1. Measurement results of thermal transfer coefficient of LTCC substrate

[0034] As can be seen from Table 1, the thermal conductivity of the product of this invention is much higher than that of traditional LTCC materials (usually only 2-5 W / (m·K)), which can meet the heat dissipation requirements of high-power chips and achieve the purpose of this invention.

[0035] Finally, it should be noted that the above embodiments are merely examples for clear illustration. This invention includes, but is not limited to, the above embodiments, and it is neither necessary nor possible to exhaustively describe all possible implementations. Those skilled in the art can make other variations or modifications based on the above description. All implementation schemes that meet the requirements of this invention are within the protection scope of this invention.

Claims

1. A method for preparing a co-fired integrated heat sink for LTCC substrates, characterized in that, The structural design method of the integrated heat sink is as follows: (1) Inside the LTCC substrate, a through cavity with a size matching the chip is prefabricated for the location of the high-power chip; (2) Before the green ceramic belt is stacked and sintered, the cavity is filled with a metal slurry with high thermal conductivity to form a solid metal heat sink block. (3) The power chip is directly mounted on the filled metal heat sink block, and the heat generated by the chip can be quickly conducted downward to the base plate through the solid metal block.

2. The method for preparing a co-fired integrated heat sink for LTCC substrates as described in claim 1, characterized in that... The preparation method is as follows: (1) Cavity forming: On the LTCC green ceramic tape, a cavity window slightly larger than the chip size is formed by precision die punching or laser ablation. The cavity size of odd-numbered layers should be slightly smaller than that of even-numbered layers to ensure that the cavities after stacking present an interlocking "mortise and tenon" structure at the longitudinal interface. (2) Metal paste filling: The prepared high thermal conductivity metal paste is filled into the cavity through printing or injection molding. The sintering shrinkage rate of the paste needs to be carefully matched with that of the LTCC green ceramic tape to reduce stress and ensure reliability and airtightness; (3) Lamination and co-firing: The green ceramic tape filled with metal paste is aligned and laminated with other green ceramic tapes of signal layer and ground layer, and then co-fired as a whole. During the sintering process, the metal paste and the ceramic green ceramic tape shrink and densify synchronously, forming a robust integrated structure with good thermal and mechanical properties; (4) Chip mounting and interconnection: After co-firing, the power chip is directly mounted on the heat sink block formed by the cavity by bonding or welding, and then interconnection operations such as gold wire bonding are performed; (5) Sealing: Finally, the frame, cover plate and substrate are welded together to achieve hermetically sealed packaging.

3. The method for preparing a co-fired integrated heat sink for LTCC substrates as described in claim 2, characterized in that: The metal paste is a copper metal paste or a silver metal paste.

4. The method for preparing a co-fired integrated heat sink for LTCC substrates as described in claim 2, characterized in that, The specific preparation method is as follows: (1) LTCC green ceramic sheets with a size of 200mm×200mm and a thickness of 130μm were prepared by tape casting process; (2) A through cavity of 3mm×3mm was fabricated on an odd-numbered layer of green ceramic sheet using laser technology; and a through cavity of 3.1mm×3.1mm was fabricated on an even-numbered layer of green ceramic sheet. (3) Use an injection-type cavity filling device to fill the cavity with LTCC co-fired conductor slurry to form a dense cavity filling metal; (4) Through precise alignment and lamination techniques, multiple layers of films containing conductive paste are laminated to ensure that the filler metals between each layer interlock and that the electrical connections are accurate. Pressure and temperature must be controlled during the lamination process to avoid delamination or deformation; (5) Cut out LTCC substrate blanks with dimensions of 5.3mm×5.3mm×1.2mm; (6) Perform a co-firing process, sinter the prepared LTCC substrate blank at 920°C to obtain an LTCC circuit board with dimensions of 5mm×5mm×1mm and a co-firing heat sink size of 3mm×3mm.

5. The method for preparing a co-fired integrated heat sink for LTCC substrates as described in claim 3, characterized in that: At 25°C, the heat transfer coefficient per unit area of ​​the LTCC circuit board is 99.549 W / m·K.

6. The method for preparing a co-fired integrated heat sink for LTCC substrates as described in claim 1, characterized in that: At 100°C, the heat transfer coefficient per unit area of ​​the LTCC circuit board is 89.663 W / m·K.

7. The method for preparing a co-fired integrated heat sink for LTCC substrates as described in claim 1, characterized in that: At 150°C, the heat transfer coefficient per unit area of ​​the LTCC circuit board is 85.513 W / m·K.

8. The method for preparing a co-fired integrated heat sink for LTCC substrates as described in claim 1, characterized in that: At 200°C, the heat transfer coefficient per unit area of ​​the LTCC circuit board is 82.443 W / m·K.

9. The method for preparing a co-fired integrated heat sink for LTCC substrates as described in claim 1, characterized in that: At 250°C, the thermal conductivity per unit area of ​​the LTCC circuit board is 80.859 W / m·K.

10. The method for preparing a co-fired integrated heat sink for LTCC substrates as described in claim 1, characterized in that: At 300°C, the thermal conductivity per unit area of ​​the LTCC circuit board is 78.545 W / m·K.

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