Processing technology of laminated chip micro-channel heat dissipation device

Abstract

The invention relates to the technical field of chip microchannels, in particular to a processing technology of a laminated chip microchannel heat dissipation device. Comprising the following steps that a chip body is provided, a heat conduction transition layer is fixedly connected to the upper surface of the chip body, a plurality of metal sheets are provided, the metal sheets are made of high-heat-conduction aluminum alloy or copper alloy, and a plurality of micro fins are machined on each metal sheet through the laser cutting technology or the electric spark wire cutting technology or the photochemical etching technology; and the stacked metal sheets and the heat conduction transition layer are integrally placed in a vacuum furnace, so that the brazing filler metal is molten and fills micron-order gaps between contact interfaces of the layers, and the microchannel heat dissipation block with airtight sealing is formed after cooling. The multi-layer heat exchanger has the beneficial effects that the micro fins on each layer of metal sheet are arranged in a non-periodic mode and staggered layer by layer in the vertical direction, so that when cooling liquid flows through the multi-layer structure, the flowing direction is continuously changed, strong vortex and secondary flow are generated, a heat boundary layer is destroyed, and the heat exchange efficiency is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of chip microchannel technology, and in particular to a processing technology for a stacked chip microchannel heat dissipation device. Background Technology

[0002] With the rapid development of high-power-density integrated circuits and advanced semiconductor devices, chip heat dissipation has become an increasingly prominent issue. Microchannel heat dissipation technology, due to its high heat transfer efficiency and compact structure, has become an important direction for solving chip thermal management problems. However, the existing microchannel heat dissipation devices rely heavily on high-precision etching or micromachining, which, limited by the small size and complex structure of microchannels, suffers from high processing difficulty, low yield, and high cost. Especially when realizing three-dimensional complex flow channels or embedded integrated structures, traditional single-unit processing methods struggle to balance precision and manufacturability. Therefore, adopting a layered processing strategy, decomposing the overall microchannel structure into multiple independently processable thin layers, and then bonding or assembling them to form a complete heat dissipation device, has become a promising technological path. However, existing related patents still have significant shortcomings in terms of layered structure design, interlayer alignment, sealing reliability, and material compatibility for heat dissipation conditions.

[0003] The existing technology, patent CN113629024B entitled "Method for Fabricating Microfluidic Cooling Channels and Chip", was published on June 28, 2024. This patent uses MEMS sacrificial layer technology to construct microfluidic cooling channels on the substrate to be cooled, forming closed channels by patterning a sacrificial layer, depositing a capping layer, and releasing the sacrificial layer. Although this method can achieve the integration of microchannels and chip substrates and is compatible with semiconductor processes, it relies on complex thin film deposition and sacrificial layer release processes, making it difficult to apply to large aspect ratio or three-dimensional meandering channel structures. More importantly, this solution does not adopt a layered processing approach; all channel structures are constructed on a single substrate surface, which cannot effectively solve the processing difficulties of complex channel internal dead corners, multi-directional branches, or three-dimensional intersections, limiting its application in high-performance heat dissipation scenarios.

[0004] Therefore, a fabrication process for a stacked chip microchannel heat dissipation device needs to be designed to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a processing technology for a stacked chip microchannel heat dissipation device to overcome the above-mentioned shortcomings of the existing technology.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A fabrication process for a stacked chip microchannel heat dissipation device includes the following steps: A chip body is provided and a thermally conductive transition layer is fixedly connected to its upper surface. The thermally conductive transition layer is made of a metal material with a coefficient of thermal expansion that matches that of the chip body and is metallurgically bonded to the chip body by eutectic bonding or diffusion bonding. A plurality of metal sheets are provided, each sheet having a thickness of 0.1 mm to 0.5 mm and being made of high thermal conductivity aluminum alloy or copper alloy. A plurality of microfins are fabricated on each sheet of metal sheet by laser cutting, electrical discharge wire cutting or photochemical etching. The microfins are arranged in a non-periodic manner, with a cross-sectional shape of trapezoidal, rectangular or needle-like, a height of 0.2 mm to 1.0 mm, and a gap width between adjacent microfins of 50 μm to 300 μm. Positioning through holes are machined at the four corners of each metal sheet, and positioning pins made of high temperature resistant stainless steel are passed through the thermally conductive transition layer and the positioning through holes of each metal sheet from bottom to top. The fit tolerance between the outer diameter of the positioning pin and the inner diameter of the positioning through hole is controlled within ±2μm, and the pins are fixed at the top by riveting or laser spot welding. The stacked metal sheets and thermally conductive transition layer were placed in a vacuum furnace and wrapped with aluminum-silicon solder foil. The furnace was then heated to a vacuum degree of 8×10⁻⁶. -3 The solder is kept at 580°C to 620°C for 15 to 30 minutes to melt and fill the micron-level gaps between the contact interfaces of each layer. After cooling, it forms an airtight microchannel heat dissipation block.

[0007] Preferably, an inlet channel and an outlet channel are processed on one end face of the microchannel heat sink by laser drilling. The inlet channel penetrates the bottom metal plate and communicates with the gap between the bottom microfins. The outlet channel penetrates the top metal plate and communicates with the gap between the top microfins.

[0008] Preferably, stainless steel quick-connect fittings are welded to the outer ends of the inlet channel and the outlet channel, respectively.

[0009] Preferably, the microfins on two adjacent metal plates are staggered in the vertical direction, with the upper microfin located directly above the gap between two adjacent microfins in the lower layer.

[0010] Preferably, the metal sheets are subjected to surface activation treatments in sequence before stacking, including alkaline washing to remove oil, acid washing to remove oxide film, ultrasonic cleaning, and nitrogen drying.

[0011] Preferably, during the vacuum brazing process, a constant pressure of 0.1 MPa to 0.3 MPa is applied to the top and bottom sides of the stack.

[0012] Preferably, a stainless steel filter screen with a pore size of 20μm is embedded inside the liquid inlet channel and the liquid outlet channel.

[0013] Preferably, a temperature monitoring hole is machined on the outer side of the microchannel heat sink, and the temperature monitoring hole extends from the outer side inward to the position of the middle layer metal plate.

[0014] The beneficial effects of this invention are: the microfins on each layer of metal sheet are arranged non-periodically and staggered layer by layer in the vertical direction, so that the coolant continuously changes its flow direction when flowing through the multi-layer structure, generating strong eddies and secondary flows, destroying the thermal boundary layer and significantly improving heat exchange efficiency; at the same time, the microfin array structure has higher structural rigidity than the traditional straight groove channel, and can withstand higher working pressure without deformation. By setting high-precision positioning through holes at the four corners of each layer of thin metal plate and using stainless steel positioning pins with tolerance control at the micron level to penetrate the stack, the gaps between each layer of microfins are ensured to be precisely connected in the vertical direction, avoiding channel blockage or uneven flow distribution due to interlayer misalignment. The entire encapsulation is completed under controlled pressure using a vacuum brazing process, which not only achieves metallurgical bonding and airtight sealing between the interfaces of each layer, but also avoids high-temperature oxidation and impurity contamination, ensuring the cleanliness of the internal surface of the microchannel and its long-term operational reliability. Attached Figure Description

[0015] Figure 1 This is a front view of the fabrication process of a stacked chip microchannel heat dissipation device according to the present invention. Figure 2 This is a side view of the fabrication process of a stacked chip microchannel heat dissipation device according to the present invention; Figure 3 This is a top view of the fabrication process of a stacked chip microchannel heat dissipation device according to the present invention; In the diagram: 1. Chip body; 3. Metal plate; 4. Microfins; 7. Liquid inlet channel; 8. Liquid outlet channel; 9. Positioning through hole. Detailed Implementation

[0016] Reference Figures 1 to 3 A fabrication process for a stacked chip microchannel heat dissipation device includes the following steps: A chip body is provided and a thermally conductive transition layer is fixedly connected to its upper surface. The thermally conductive transition layer is made of a metal material with a coefficient of thermal expansion that matches that of the chip body and is metallurgically bonded to the chip body by eutectic bonding or diffusion bonding. A plurality of metal sheets are provided, each sheet having a thickness of 0.1 mm to 0.5 mm and being made of high thermal conductivity aluminum alloy or copper alloy. A plurality of microfins are fabricated on each sheet of metal sheet by laser cutting, electrical discharge wire cutting or photochemical etching. The microfins are arranged in a non-periodic manner, with a cross-sectional shape of trapezoidal, rectangular or needle-like, a height of 0.2 mm to 1.0 mm, and a gap width between adjacent microfins of 50 μm to 300 μm. Positioning through holes are machined at the four corners of each metal sheet, and positioning pins made of high temperature resistant stainless steel are passed through the thermally conductive transition layer and the positioning through holes of each metal sheet from bottom to top. The fit tolerance between the outer diameter of the positioning pin and the inner diameter of the positioning through hole is controlled within ±2μm, and the pins are fixed at the top by riveting or laser spot welding. The stacked metal sheets and thermally conductive transition layer were placed in a vacuum furnace and wrapped with aluminum-silicon solder foil. The furnace was then heated to a vacuum degree of 8×10⁻⁶. -3 The solder is kept at 580°C to 620°C for 15 to 30 minutes to melt and fill the micron-level gaps between the contact interfaces of each layer. After cooling, it forms an airtight microchannel heat dissipation block. An inlet channel and an outlet channel are processed on one end face of the microchannel heat sink by laser drilling. The inlet channel penetrates the bottom metal plate and communicates with the gap between the bottom microfins. The outlet channel penetrates the top metal plate and communicates with the gap between the top microfins. Stainless steel quick-connect fittings are welded to the outer ends of the inlet and outlet channels, respectively.

[0017] First, the base layer module is fabricated. The chip body 1 uses a standard silicon-based high-power-density integrated circuit chip, and its upper surface is chemically and mechanically polished to achieve a surface roughness better than 0.5 μm. The thermally conductive transition layer is made of a copper-tungsten alloy material (CTE≈6.5×10⁻⁶) with a coefficient of thermal expansion matching that of the chip body. -6 The thermally conductive transition layer has a thickness of 0.8 mm and a temperature of 320°C. The lower surface of the thermally conductive transition layer is connected to the upper surface of the chip body via a eutectic bonding process: in a nitrogen protective atmosphere, a pressure of 0.2 MPa is applied at 320°C and held for 10 minutes to melt the Au-Sn eutectic solder and form a metallurgical bond at the interface. After bonding, the upper surface of the thermally conductive transition layer is CNC milled to create several groove structures with a depth of 30 μm. The positions of these grooves correspond one-to-one with the gap regions of the microfins 4 on the subsequent bottom metal sheet, guiding the coolant to uniformly enter the bottom microchannel network from the inlet channel 7.

[0018] The microchannel layer module is then fabricated. Each metal sheet 3 is made of 0.3mm thick C10200 oxygen-free copper sheet with a surface roughness Ra≤0.4μm. Figure 2As shown, positioning through holes 9 with a diameter of 1.0 mm are machined at the four corners of each metal sheet 3, with the hole position accuracy controlled within ±1 μm. In the main body area of ​​the metal sheet 3, several microfins 4 are machined using a femtosecond laser cutting device. The microfins 4 are arranged non-periodically, meaning the spacing between adjacent microfins 4 is unequal to avoid forming a regular resonant frequency. The cross-section of the microfins 4 is trapezoidal, with a bottom width of 150 μm, a top width of 80 μm, and a height of 0.6 mm. The gap width between adjacent microfins 4 varies between 80 μm and 250 μm. After processing, all metal sheets 3 undergo surface activation treatment sequentially: first, alkaline washing in a 5wt% NaOH solution at 60℃ for 5 minutes to remove grease; then, acid washing in a 10wt% HNO3 solution for 2 minutes to remove the surface oxide film; subsequently, ultrasonic cleaning in deionized water for 10 minutes; and finally, drying with high-purity nitrogen gas to ensure a clean surface without residue.

[0019] The microchannel layer module consists of 4-8 metal sheets 3 processed as described above, depending on the requirements. During stacking, the microfins 4 on adjacent metal sheets 3 are staggered vertically: the microfins 4 on the upper metal sheet 3 are directly opposite the gap between two adjacent microfins 4 on the lower layer, forcing the coolant to change its flow direction when passing through the interlayer gap, forming a continuous three-dimensional meandering path. This staggered arrangement is achieved through a high-precision positioning system: the thermally conductive transition layer is placed on a dedicated fixture base, and then each metal sheet is sequentially fitted into four positioning pins pre-installed on the fixture. The positioning pins are made of SUS310S high-temperature resistant stainless steel with an outer diameter of 1.002mm, forming an H7 / g6 fit with the positioning through-holes 9 on the metal sheet with an inner diameter of 1.000mm, with the fit tolerance controlled within ±2μm. The positioning pins pass through the corresponding through holes on the heat-conducting transition layer and the positioning through holes 9 of all 8 layers of metal sheets 3 from bottom to top, with the top end protruding about 0.8 mm above the upper surface of the top metal sheet 3.

[0020] After stacking, the interlayer sealing and soldering module is encapsulated. A 25μm thick layer of BAlSi-5 aluminum-silicon solder foil (Al-12Si composition) is wrapped around the outside of the stack, and the entire assembly is placed in a vacuum brazing furnace. The vacuum level inside the furnace is evacuated to 8×10⁻⁶. -3 The solder was heated to 600°C at a heating rate of 5°C / min and held at this temperature for 20 minutes. Simultaneously, a constant pressure of 0.2 MPa was applied to both sides of the stack using graphite pressure plates to suppress excessive solder flow and maintain consistent spacing between the metal sheets 3. After the holding period, the solder was cooled to 200°C at a rate of 3°C / min and then allowed to cool naturally to room temperature. During this process, the solder melted and filled the micron-level gaps between the contact interfaces of each layer, forming a metallurgically bonded, airtight sealing structure, thus constituting a complete microchannel heat sink.

[0021] Next, the inlet and outlet integrated module is processed. On one end face of the microchannel heat sink, a picosecond laser drilling machine is used to process the inlet channel 7 and the outlet channel 8. In one embodiment, the inlet channel 7 extends from the side of the heat sink to the bottom metal plate 3, communicating with the gap between it and the microfins 4; the outlet channel 8 extends to the top metal plate 3, communicating with the gap between it and the microfins 4. Both channels have an inner diameter of 0.8 mm and a wall roughness Ra ≤ 1.6 μm. At the outer ends of the inlet channel 7 and the outlet channel 8, stainless steel quick-connect fittings are fixed by laser spot welding. The welding parameters are: pulse energy 15 J, pulse width 5 ms, and frequency 5 Hz, ensuring a firm connection between the fitting and the channel end face without leakage. Furthermore, a 316L stainless steel filter with a pore size of 20 μm is embedded inside the inlet channel 7. The filter is fixed to the step inside the channel by interference fit to prevent particulate impurities in the coolant from entering the microchannel and causing blockage.

[0022] To further monitor the internal temperature, in other implementations, temperature monitoring holes are machined on the outer surface of the microchannel heat sink. These holes are fabricated using micro-electro-discharge machining, extending inwards from the outer surface to a depth of half the total stack height, reaching the midpoint between the 4th and 5th metal sheets 3. The hole diameter is 0.5 mm, and the inner surface is deburred. This hole is used to embed a type K micro-thermocouple, with the thermocouple leads fixed to the opening using specialized sealant, enabling real-time acquisition of the coolant temperature in the middle of the flow channel.

[0023] During actual operation, coolant (such as deionized water or ethylene glycol aqueous solution) enters the inlet channel 7 from an external pumping system via a stainless steel quick-connect fitting, flowing into the gap area of ​​the microfins 4 in the bottom layer metal plate 3. Due to the guiding grooves on the upper surface of the thermally conductive transition layer 2, the coolant is evenly distributed throughout the entire bottom microchannel network. Subsequently, the coolant flows upward layer by layer under pressure: because the adjacent microfins 4 are vertically staggered, the liquid flow continuously changes direction as it passes through the interlayer gaps, forming a three-dimensional meandering flow path. Finally, the coolant gathers at the gap of the top layer microfins 4 and flows out through the outlet channel 8, completing one complete heat exchange cycle. Throughout the entire operation, the heat generated by the chip body 1 is conducted to the thermally conductive transition layer 2 through the eutectic bonding interface, and then transferred to the coolant flowing within the microchannels through each layer of metal plates 3, achieving efficient heat dissipation. Thermocouples in the temperature monitoring holes can provide real-time feedback on the temperature in the middle of the flow channel, providing data support for system thermal management.

[0024] In a specific implementation, the chip body 1 continuously generates a local heat flux density exceeding 500 W / cm², requiring efficient liquid cooling to maintain a junction temperature below 85°C. In this case, the stacked microchannel heat dissipation device described in this invention is integrated into the bottom of the chip package. Coolant enters the inlet channel 7 from an external circulation pump via a stainless steel quick-connect connector. Since the inlet channel 7 is directly connected to the gaps between the microfins 4 on the bottom metal plate 3, and the upper surface of the thermally conductive transition layer 2 has pre-processed guide grooves with a depth of 30 μm, which correspond one-to-one with the gap areas of the bottom microfins 4, the coolant is forced to flow across the entire transverse plane upon entering the bottom channel, avoiding concentrated impact on local areas and resulting in uneven flow distribution. This structural design ensures the uniformity of the flow field at the inlet of the bottom microchannel network, thereby suppressing the formation of local hot spots.

[0025] After the coolant flows through the bottommost metal plate 3, it rises through the interlayer gaps and enters the second layer under the back pressure of the system. The microfins 4 on the second metal plate 3 are vertically aligned with the gap between two adjacent microfins 4 in the first layer. The coolant cannot rise along a straight path but must bypass the sidewalls of the upper microfins 4, changing its flow direction from horizontal to oblique or locally swirling, thus inducing secondary flow and vortex structures in the microscale space. As the number of layers increases, each layer continues this vertically staggered arrangement, creating a continuous three-dimensional meandering flow path for the coolant within the stacked structure. This path significantly extends the effective travel distance of the fluid within the microchannels and continuously disturbs the thermal boundary layer, enhancing the convective heat transfer coefficient at the solid-liquid interface. Meanwhile, the microfins 4 adopt a trapezoidal cross section (bottom width 150μm, top width 80μm, height 0.6mm) and set non-periodic gaps ranging from 80μm to 250μm between adjacent fins. This not only avoids the flow-induced vibration resonance that may be caused by regular arrangement, but also further promotes turbulence development and enhances local heat transfer intensity through the local flow channel contraction-expansion effect.

[0026] Throughout the stacking process, four positioning pins penetrate the thermally conductive transition layer and all eight metal sheets 3, forming a precise H7 / g6 fit with the 1.002mm outer diameter and 1.000mm inner diameter of the through-holes. This fit tolerance is controlled within ±2μm, ensuring that the absolute positional deviation of each microfin 4 in the X–Y plane does not exceed 3μm. This precision guarantees the geometric continuity of the interlayer gap channels, preventing abrupt changes in local flow channel cross-sectional area or complete closure due to misalignment, thus avoiding abnormal pressure drop or localized drying. Furthermore, during the vacuum brazing encapsulation stage, a constant pressure of 0.2MPa is applied, and BAlSi-5 aluminum-silicon solder is melted and filled at 600℃ to achieve airtight sealing. This not only ensures a consistent 0.3mm thickness in the Z-direction for each metal sheet 3, maintaining the designed flow channel consistency and ensuring predictable and repeatable flow resistance characteristics.

[0027] The advantages of this invention are that the microfins on each layer of metal sheet are arranged non-periodically and staggered layer by layer in the vertical direction, so that the coolant continuously changes the flow direction when flowing through the multi-layer structure, generating strong eddies and secondary flows, destroying the thermal boundary layer and significantly improving heat exchange efficiency; at the same time, the microfin array structure has higher structural rigidity than the traditional straight groove channel, and can withstand higher working pressure without deformation. By setting high-precision positioning through holes at the four corners of each layer of thin metal plate and using stainless steel positioning pins with tolerance control at the micron level to penetrate the stack, the gaps between each layer of microfins are ensured to be precisely connected in the vertical direction, avoiding channel blockage or uneven flow distribution due to interlayer misalignment. The entire encapsulation is completed under controlled pressure using a vacuum brazing process, which not only achieves metallurgical bonding and airtight sealing between the interfaces of each layer, but also avoids high-temperature oxidation and impurity contamination, ensuring the cleanliness of the internal surface of the microchannel and its long-term operational reliability.

[0028] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A process for fabricating a stacked chip microchannel heat spreader, comprising: The method comprises the following steps: ​ A chip body is provided and a heat-conducting transition layer is fixedly connected to the upper surface of the chip body, the heat-conducting transition layer is made of a metal material matching the thermal expansion coefficient of the chip body, and the heat-conducting transition layer is formed into a metallurgical bond with the chip body through eutectic welding or diffusion welding; A plurality of metal sheets are provided, each metal sheet has a thickness of 0.1 mm to 0.5 mm, is made of high-thermal-conductivity aluminum alloy or copper alloy, and a plurality of micro fins are processed on each metal sheet through laser cutting, wire electrical discharge machining or photochemical etching process, the micro fins are arranged in a non-periodic manner, have a trapezoidal, rectangular or needle-shaped cross-sectional shape, have a height of 0.2 mm to 1.0 mm, and have a gap width of 50 μm to 300 μm between adjacent micro fins; Positioning through holes are processed at the four corner positions of each metal sheet, and positioning pin columns made of high-temperature-resistant stainless steel are sequentially inserted into the positioning through holes of the heat-conducting transition layer and the metal sheets from bottom to top, the fitting tolerance between the outer diameter of the positioning pin columns and the inner diameter of the positioning through holes is controlled to be within ±2 μm, and the top is fixed through press riveting or laser spot welding; The stacked metal sheet and the heat-conducting transition layer are placed in a vacuum furnace, wrapped with an aluminum-silicon solder foil outside, and heated at a temperature of 580-620°C for 15-30 minutes under a vacuum degree of 8x10 -3 Pa to make the solder melt and fill the micron-level gaps between the contact interfaces of the layers, and form a gas-tight sealed micro-channel heat dissipation block after cooling.

2. The process for fabricating a stacked chip microchannel heat spreader of claim 1, wherein: Liquid inlet channels and liquid outlet channels are processed on one side end surface of the micro-channel heat sink through laser drilling, the liquid inlet channels penetrate through the bottommost metal sheet and are in gap communication with the bottommost micro fins, and the liquid outlet channels penetrate through the topmost metal sheet and are in gap communication with the topmost micro fins.

3. The process of claim 2, wherein: Stainless steel quick connectors are welded to the outer ends of the liquid inlet channels and the liquid outlet channels.

4. The process of claim 1, wherein: The micro fins on the adjacent two metal sheets are arranged in a vertical direction with a positional displacement, and the upper micro fins are located directly above the gap between the two adjacent micro fins of the lower layer.

5. The process of claim 1, wherein: The metal sheets are subjected to surface activation treatment of alkali washing, oil removal, acid pickling, oxide film removal, ultrasonic cleaning and nitrogen blowing in sequence before stacking.

6. The process of claim 1, wherein: During vacuum brazing, a constant pressure of 0.1 MPa to 0.3 MPa is applied to the upper and lower sides of the stack.

7. The process of claim 3, wherein: A stainless steel filter screen with a pore size of 20 μm is embedded in the liquid inlet channel and the liquid outlet channel.

8. The process of claim 1, wherein: A temperature monitoring hole is processed on the outer side surface of the micro-channel heat sink, and the temperature monitoring hole extends inward from the outer side surface to the position of the middle layer metal sheet.

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