Printed circuit board with microchannel and processing technology

Abstract

The invention relates to the field of printed circuit boards, in particular to a printed circuit board with a microchannel, which comprises a first solder mask layer, a second solder mask layer, a first electric copper layer arranged on the first solder mask layer, a second electric copper layer arranged on the second solder mask layer, and an insulating base layer arranged between the first electric copper layer and the second electric copper layer, according to the invention, a three-dimensional channel network is formed in the insulating base layer in a bonding state through cooperation of the main channel, the branch capillary channels and the vertical communicating holes, so that heat of the whole insulating base layer is fully dissipated, and direct mounting of a GaN power device with a heat flux of 35W / cm < 2 > can be supported; and meanwhile, the multiplexing structure of the vertical communicating holes reduces the aperture ratio of the insulating base plate body, the problem that the mechanical strength is reduced due to the fact that heat dissipation holes and electrical holes are independently formed in a traditional scheme is avoided, cooling working media generate vortexes in a main channel and branch capillary channels through particles, the convection coefficient is increased, and efficient and low-resistance heat dissipation is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of printed circuit board, in particular to a printed circuit board with micro-channels and a processing technology. BACKGROUND

[0002] With the development of 5G communication, high-power radio frequency devices and compact power electronic modules, the heat flux density of printed circuit board (PCB) has exceeded 25W / cm 2 The traditional heat dissipation scheme needs to increase the heat dissipation fin and fan, resulting in an increase of more than 30% in volume, and the heat pipe integration process is complex and cannot be embedded in the board body. Currently, the micro-channel heat dissipation plate uses laser to directly form micro-grooves on the circuit board, but the channel depth is limited and cannot meet the heat dissipation demand of internal heat sources of multi-layer boards. SUMMARY

[0003] In view of the above or the problem in the prior art that the micro-channel heat dissipation plate uses laser to directly form micro-grooves on the circuit board, but the channel depth is limited and cannot meet the heat dissipation demand of internal heat sources of multi-layer boards, the present application is proposed.

[0004] Therefore, the purpose of the present application is to provide a printed circuit board with micro-channels.

[0005] To solve the above technical problems, the present application provides the following technical scheme: including solder resist layer one and solder resist layer two, electric copper layer one arranged on the solder resist layer one, electric copper layer two arranged on the solder resist layer two, and insulating base layer arranged between the electric copper layer one and the electric copper layer two; both sides of the electric copper layer one are provided with connecting channels one, both sides of the electric copper layer two are provided with connecting channels two, and the insulating base layer is provided with cooling micro-channels for matching the connecting channels one and the connecting channels two, and the cooling micro-channels are provided with multiple groups in the insulating base layer.

[0006] As a preferred scheme of the printed circuit board with micro-channels of the present application, wherein: the cooling micro-channels include main trunk channels arranged on the insulating base layer, and branch capillary channels arranged on the main trunk channels, the branch capillary channels are provided with multiple groups on the main trunk channels, and form a tree structure in cooperation with the main trunk channels; the connecting channels one and the connecting channels two have the same size structure as the cooling micro-channels.

[0007] As a preferred scheme of the printed circuit board with micro-channels of the present application, wherein: the width of the main trunk channel is set to 0.5-1.2mm, and the depth is set to 0.2-0.4mm; the width of the branch capillary channel is set to 0.1-0.3mm, and the depth is set to 0.1-0.15mm; the aperture of the vertical communication hole is 0.05-0.15mm.

[0008] As a preferred scheme of the printed circuit board with micro-channels of the present application, the cooling micro-channels, the connecting channel one, the connecting channel two and the cooling micro-channels can be bonded to form a channel with larger flux.

[0009] As a preferred scheme of the printed circuit board with micro-channels of the present application, the main channel and the branch capillary channel are further provided with vertical communication holes.

[0010] As a preferred scheme of the printed circuit board with micro-channels of the present application, the vertical communication holes communicate the branch capillary channels on the upper and lower sides of the insulating base layer, and in the stacked state, the end portions of the branch capillary channels on the upper insulating base layer are communicated through the vertical communication holes, and the end portions of the main channel on the lower insulating base layer are communicated through the vertical communication holes.

[0011] As a preferred scheme of the printed circuit board with micro-channels of the present application, the inner wall of the branch capillary channel is covered with the solder resist layer one, the solder resist layer two, the electro-copper layer one and the electro-copper layer two.

[0012] As a preferred scheme of the printed circuit board with micro-channels of the present application, the copper inner wall of the cooling micro-channels is provided with particles.

[0013] Based on the printed circuit board with micro-channels, the present application further provides a processing technology of the printed circuit board with micro-channels, which comprises the following steps: S: laser pre-drilling a blind hole array with a diameter of 0.1-0.5 mm on the electro-copper layer one, the electro-copper layer two and the insulating base layer; S2: filling the blind hole with a temporary etchable resin containing urethane and curing; S3: performing lamination, drilling and electroplating to form an outer circuit according to the conventional PCB process; and S4: selectively etching the resin in an alkaline solution to release the channel network on the insulating base layer.

[0014] As a preferred scheme of the processing technology of the printed circuit board with micro-channels of the present application, the etchable resin comprises 30%-50% of urethane prepolymer, 20%-35% of filler and 5%-10% of catalyst by weight, and can be completely dissolved in an alkaline solution with pH>10 at 50-60°C for 30-45 minutes.

[0015] The printed circuit board with micro-channels has the following beneficial effects: the three-dimensional channel network in the insulating base layer in the bonded state is formed by the cooperation of the main channel, the branch capillary channel and the vertical communication hole, the insulating base layer is fully cooled, and the heat flux density can reach 35W / cm 2The GaN power device is directly mounted, meanwhile, the multiplex structure of the vertical communication hole reduces the opening rate of the insulating base plate body, avoids the mechanical strength reduction problem caused by the independent setting of the heat dissipation hole and the electrical hole in the traditional scheme, the cooling working medium generates vortex in the main channel and the branch capillary channel through the particles, improves the convection coefficient, realizes high-efficiency and low-resistance heat dissipation, meanwhile, the application can be compatible with the existing PCB production line, adopts the etchable material filling process, the micro-channel forming is completed synchronously with the PCB drilling and pressing process, no additional micro-processing equipment is needed, the production cycle is only slightly extended, the cost rises less than 10%, and the application is suitable for mass production. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0017] Figure 1 It is a schematic diagram of the overall structure of the printed circuit board with micro-channels.

[0018] Figure 2 It is a schematic diagram of the cross-sectional structure of the printed circuit board with micro-channels.

[0019] Figure 3 It is a schematic diagram of the structure of the insulating base layer of the printed circuit board with micro-channels.

[0020] Figure 4 It is Figure 3 It is an enlarged schematic diagram of the structure at A in the middle.

[0021] Figure 5 It is a schematic diagram of the structure of the particles in the printed circuit board with micro-channels.

[0022] In the figure: 1, solder resist layer one; 2, solder resist layer two; 3, electro-copper layer one; 31, connection channel one; 4, electro-copper layer two; 41, communication channel two; 5, insulating base layer; 51, cooling micro-channel; 511, main channel; 512, branch capillary channel; 513, particle; 52, vertical communication hole. DETAILED DESCRIPTION

[0023] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the drawings of the specification.

[0024] Example 1, refer to Figure 1 and Figure 2This is the first embodiment of the present invention, which provides a printed circuit board with microchannels, including a first solder resist layer 1 and a second solder resist layer 2, an electroplated copper layer 3 disposed on the first solder resist layer 1, an electroplated copper layer 4 disposed on the second solder resist layer 2, and an insulating base layer 5 disposed between the first electroplated copper layer 3 and the second electroplated copper layer 4. Both the first solder resist layer 1 and the second solder resist layer 2 are made of photosensitive epoxy resin solder resist ink or polyimide film, and are applied to the surface of the corresponding conductive copper layer by vacuum lamination or screen printing to form a composite protective layer with both insulating protection and fluid sealing functions. Its core function is to prevent solder short circuits and protect the copper foil. To enhance reliability, both electrolytic copper layers 3 and 4 are electrolytic copper foils used to form circuit traces, pads, and conductive layers on the walls of microvias through pattern transfer and electroplating, achieving ohmic connections between component pins and the inner layer network. In the microchannel region, the copper surfaces of the first conductive copper layer 3 and the second conductive copper layer 4 directly participate in the heat exchange process, utilizing the high thermal conductivity of copper to efficiently transfer the heat conducted by layer 5 to the cooling medium, forming an embedded heat sink effect. The microchannel insulating substrate layer 5 uses epoxy resin or glass fiber prepreg with a high glass transition temperature, i.e., a prepreg, which melts and solidifies during lamination to form the main enclosure structure of the microchannel network. This layer not only undertakes the interlayer electrical insulation function of traditional PCBs, but more importantly, it serves as a mechanical constraint boundary for fluid transport, ensuring that the cooling medium flows strictly along a preset path without cross-layer crosstalk. Connecting channels 31 are provided on both sides of the first conductive copper layer 3, and connecting channels 41 are provided on both sides of the second conductive copper layer 4. Cooling microchannels 51 are provided on the insulating base layer 5 to cooperate with the connecting channels 31 and the connecting channels 41. Multiple sets of cooling microchannels 51 are provided in the insulating base layer 5. The cross-sectional profile of the cooling microchannels 51 is preferably rectangular or trapezoidal, and its interior is hollow to form a closed three-dimensional flow channel. When the cooling medium flows through the flow channel under pressure, it can fully wet and carry away the heat generated by the first conductive copper layer 3, the second conductive copper layer 4 and the high-heat-generating element.

[0025] In summary, when the circuit board is running normally, the cooling medium forms a three-dimensional flow channel around the first copper layer 3 and the second copper layer 4 through the cooling microchannel 51, in conjunction with the connecting channel 1 31 and the connecting channel 2 41. This allows the cooling medium to flow fully through all positions of the first copper layer 3 and the second copper layer 4, cooling the heat generated by the operation of the first copper layer 3 and the second copper layer 4.

[0026] Example 2, refer to Figure 1 - Figure 5This is the second embodiment of the present invention. Unlike the previous embodiment, it provides a specific structure for the cooling microchannel 51 in a printed circuit board with microchannels. Compared to embodiment 1, the cooling microchannel 51 further includes a main channel 511 disposed on the insulating substrate 5, and branch capillary channels 512 disposed on the main channel 511. Multiple sets of branch capillary channels 512 are disposed on the main channel 511, forming a tree-like structure with the main channel 511. The main channel 511 serves as the main channel for the flow of the cooling medium, and the branch capillary channels 512 are used to disperse the cooling medium on the main channel 511 to the surrounding areas, increasing the heat dissipation area. The connecting channel 31, the connecting channel 41, and the cooling microchannel 51 have the same size and structure. With this arrangement, when the electroplated copper layer 3, the electroplated copper layer 4, and the insulating base layer 5 are bonded, the connecting channel 31, the connecting channel 41, and the cooling microchannel 51 can fully fit with the cover film to form a closed three-dimensional flow channel.

[0027] The width of the main channel 511 is set to 0.5-1.2mm, and the depth is 0.2-0.4mm. This setting prevents the insulating base layer 5 from failing to fully fill the tiny gaps during the PCB lamination process, thus preventing increased delamination and voids at the top of the channel and leading to sealing failure. This is based on the following experimental data:

[0028] Comparative example: A polyetheretherketone (PEEK) microchannel substrate was bonded to the PCB surface with epoxy adhesive, with an interfacial thermal resistance of 0.5. ; Within the 0.5–1.2mm × 0.2–0.4mm window, larger sizes result in stronger Dean vortices and better heat transfer, but it is essential to ensure adequate filling of the insulation substrate. The maximum value of 1.2 × 0.4mm provides a minimum temperature rise of 23°C and a minimum pump consumption of 9kPa, while maintaining 0% seal failure even with low-viscosity prepreg, making it the optimal heat dissipation cross-section for high-power applications. The intermediate value of 0.85 × 0.3mm strikes a balance between performance and process margin, and is recommended as the first choice for mass production. The width of the branch capillary channel 512 is set to 0.1–0.3 mm, and the depth is 0.1–0.15 mm. If the width of the branch capillary channel 512 is less than 0.1 mm, it will cause an increase in capillary flow resistance, and uneven flow distribution will lead to local hot spot temperature differences exceeding 15℃, resulting in a loss of temperature uniformity. This was demonstrated by the following experimental data:

[0029] Comparative example: Polyetheretherketone (PEEK) straight groove microchannel bonded to PCB, groove spacing 2mm, no tree-like branches; Within a window of 0.1–0.3 mm × 0.1–0.15 mm: the larger the size, the lower the proportion of capillary resistance, the significantly improved flow uniformity, and the reduction of the far-end hot spot temperature from 19°C to 3°C. The maximum size of 0.30 × 0.15 mm provides the best temperature uniformity. =3℃) and the lowest pump consumption, the optimal heat dissipation cross-section of 0.20×0.125mm for high-power scenarios strikes a balance between performance and process margin, and is recommended as the default size for mass production; The diameter of the vertical connecting via 52 is 0.05–0.15 mm, used to ensure the uniformity of copper deposition on the via wall and the reliability of electrical connections. This is determined through the following experimental data:

[0030] CV: Coefficient of variation of copper thickness on hole wall; the smaller the value, the more uniform the hole. The comparison example is a traditional through hole, which is processed by mechanical drilling and copper rivets. It does not participate in chemical release and there is no alkali solution infiltration. Within the 0.05–0.15 mm window: the larger the pore size, the faster the alkali penetrates, the higher the interlayer flow rate, and the far-end hot spot temperature drops from 19°C to 3°C. 0.15 mm provides a minimum release time of 30 min, a minimum vertical board direction resistance of 0.6 mΩ, and optimal temperature uniformity. =3℃, is the preferred aperture for high-performance heat dissipation, and 0.10mm achieves a golden balance between cycle time, electrical properties and heat dissipation, and is recommended as the default aperture for mass production.

[0031] Among them, the cooling microchannel 51, the connecting channel 31, the connecting channel 41, and the cooling microchannel 51 can be bonded together to form a channel with a larger throughput. With this setting, the flow channel height is directly superimposed in the direction perpendicular to the circuit board, but the width of the single-layer channel is not changed. Thus, the cross-sectional area of ​​the flow channel is increased by about 100% without increasing the lateral dimension. According to the Hagen-Poiseuille law, the volumetric flow rate Q of the rectangular channel is related to the cross-sectional area A and the hydraulic diameter Dh as follows: Q∝A*. When the cross-sectional area is doubled, the hydraulic diameter Dh also increases synchronously. After bonding, the cooling working fluid wets the upper and lower copper walls simultaneously in the same channel, realizing double-sided heat exchange.

[0032] The main channel 511 and the branch capillary channel 512 are also provided with vertical connecting holes 52, which are used for the flow of cooling working fluid and electrical connection.

[0033] The vertical connecting hole 52 connects the branch capillary channels 512 on both the upper and lower sides of the insulating base layer 5. When the insulating base layers 5 are stacked, the upper layer of the insulating base layer 5 connects the ends of the branch capillary channels 512 on both sides through the vertical connecting hole 52, and the lower layer of the insulating base layer 5 connects the ends of the main channel 511 through the vertical connecting hole 52. This arrangement allows multiple sets of cooling microchannels 51 in the insulating base layer 5 to be interconnected through end-to-end connections. Essentially, it upgrades the planar tree-like network to a three-dimensional braided pipe network, allowing the cooling medium to flow in a stepped manner in the direction perpendicular to the circuit board, improving heat exchange... Regarding the heat exchange area and heat exchange time, when the cooling medium is in an odd number of layers, the vertical connecting hole 52 is located at the end of the branch capillary channel 512, which vertically draws the low-temperature working medium of the branch capillary channel 512 to the upper layer. When the cooling medium is in an even number of layers, the vertical connecting hole 52 is located at the end of the main channel 511, which vertically lowers the high-temperature working medium in the center of the main channel 511 to the lower layer. The high-temperature outlet of the upper layer and the low-temperature inlet of the lower layer are directly adjacent through the vertical connecting hole 52, forming a local countercurrent heat exchange. The heat is self-equilibrium in the copper layer of the hole wall. At the same time, the flow directions of the two adjacent layers are opposite, forming a spiral stepped flow and generating secondary turbulence.

[0034] The inner wall of the branch capillary channel 512 is simultaneously covered with solder resist layer 1, solder resist layer 2, copper plating layer 3 and copper plating layer 4. With this arrangement, the cooling medium flows evenly through the solder resist layer 1, solder resist layer 2, copper plating layer 3 and copper plating layer 4 through the cooling microchannel 51 and the vertical connecting hole 52, so as to achieve uniform heat dissipation.

[0035] Among them, the inner copper wall of the cooling microchannel 51 is provided with particles 513. This arrangement prevents the cooling working fluid from creeping along the first copper layer 3 and the second copper layer 4, which could cause a short circuit.

[0036] The rest of the structure is the same as in Example 1.

[0037] In summary, when the circuit board is operating normally, the cooling medium enters the branch capillary channels 512 through the main channel 511, dispersing to various corners to absorb the heat generated by the circuit operation. Then, it enters the next layer of cooling microchannels 51 through the vertical connecting hole 52, circulating and converging and dispersing. Together with the connecting channel 1 31 and the connecting channel 2 41, a three-dimensional circulating flow channel is formed around the first copper layer 3 and the second copper layer 4 for continuous heat dissipation. Example 3, referring to Figure 1 - Figure 5 This is the third embodiment of the present invention. This embodiment provides a printed circuit board processing technology with microchannels, which includes S1: laser pre-drilling an array of blind holes with a diameter of 0.1-0.5 mm on the first copper layer 3, the second copper layer 4 and the insulating base layer 5. The blind holes are sealed by the bottom copper foil during subsequent lamination, which can prevent the etchable resin from being squeezed out from the back side at the high temperature of lamination. S2: Fill the blind holes with a temporary etchable resin containing urethane and cure it to form a removable support core to support the subsequent lamination process; S3: The outer layer circuit is formed by lamination, drilling, and electroplating according to conventional PCB processes. S4: Selectively etch away the resin in an alkaline solution to release the channel network on the insulating base layer 5. This method will not damage the solder mask layer 2, copper layer 3, and copper layer 4, achieving targeted removal. After etching, there is no need for high-pressure water rinsing, thus avoiding channel blockage.

[0038] The removable resin contains 30%–50% by weight of urethane prepolymer, 20%–35% by weight of filler, and 5%–10% by weight of catalyst. It can be completely dissolved by soaking in an alkaline solution with pH > 10 at 50–60°C for 30–45 minutes, as shown by the following experimental data:

[0039] Comparative example: Traditional hot-melt polyester resin requires 80℃ hot water for 60 minutes to soften and does not participate in chemical release; Within the window of 30–50% prepolymer, 20–35% filler, and 5–10% catalyst: the higher the proportion of prepolymer, the faster the hydrolysis rate, the lower the residual rate, and the risk of channel blockage is reduced from 25% to <0.1%. The higher the proportion of filler, the closer the CTE is to the substrate, the thermal stress is reduced by 80%, and there are no cracks after 1000 temperature cycles. The maximum value formulation 50-35-10 provides the shortest release time of 30 minutes, the lowest roughness Ra=0.3μm, and the highest heat transfer coefficient +17%, making it the preferred formulation for high-performance heat dissipation. The intermediate value 40-27.5-7.5 strikes a balance between cycle time, cost, and performance and is recommended as the default formulation for mass production.

[0040] The rest of the structure is the same as in Example 2.

[0041] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A printed circuit board with microchannels, characterized in that: It includes a first solder resist layer (1) and a second solder resist layer (2), a first electroplated copper layer (3) disposed on the first solder resist layer (1), a second electroplated copper layer (4) disposed on the second solder resist layer (2), and an insulating base layer (5) disposed between the first electroplated copper layer (3) and the second electroplated copper layer (4); Connecting channels 1 (31) are provided on both sides of the first copper layer (3), and connecting channels 2 (41) are provided on both sides of the second copper layer (4). Cooling microchannels (51) are provided on the insulating base layer (5) to cooperate with connecting channels 1 (31) and connecting channels 2 (41), and multiple sets of cooling microchannels (51) are provided in the insulating base layer (5).

2. The printed circuit board with microchannels as described in claim 1, characterized in that: The cooling microchannel (51) includes a main channel (511) disposed on the insulating base layer (5) and branch capillary channels (512) disposed on the main channel (511). Multiple sets of branch capillary channels (512) are disposed on the main channel (511) to form a tree structure in conjunction with the main channel (511). The size and structure of the connecting channel 1 (31), the connecting channel 2 (41) and the cooling microchannel (51) are the same.

3. The printed circuit board with microchannels as described in claim 2, characterized in that: The width of the main channel (511) is set to 0.5-1.2mm, and the depth is 0.2-0.4mm; The width of the branch capillary channel (512) is set to 0.1-0.3 mm, and the depth is 0.1-0.15 mm; The diameter of the vertical connecting hole (52) is 0.05-0.15 mm.

4. The printed circuit board with microchannels as described in claim 3, characterized in that: The cooling microchannel (51) can be bonded together with connecting channel one (31), connecting channel two (41) and cooling microchannel (51) to form a channel with greater throughput.

5. The printed circuit board with microchannels as described in claim 4, characterized in that: Vertical connecting holes (52) are also provided on the main channel (511) and the branch capillary channels (512).

6. The printed circuit board with microchannels as described in claim 5, characterized in that: The vertical connecting hole (52) connects the branch capillary channels (512) on the upper and lower sides of the insulating base layer (5). When the insulating base layers (5) are stacked, the upper layer of the insulating base layer (5) achieves the connection of the ends of the branch capillary channels (512) on both sides through the vertical connecting hole (52), and the lower layer of the insulating base layer (5) achieves the connection of the ends of the main channel (511) through the vertical connecting hole (52).

7. The printed circuit board with microchannels as described in claim 6, characterized in that: The inner wall of the branch capillary channel (512) is simultaneously covered with solder resist layer 1 (1), solder resist layer 2 (2), electroplated copper layer 1 (3) and electroplated copper layer 2 (4).

8. The printed circuit board with microchannels as described in claim 7, characterized in that: The copper inner wall of the cooling microchannel (51) is provided with particles (513).

9. A process for manufacturing a printed circuit board with microchannels, based on the printed circuit board with microchannels as described in claim 8. Its characteristics Includes the following steps: S1: A blind hole array with a diameter of 0.1-0.5 mm is pre-drilled by laser on the first copper layer (3), the second copper layer (4) and the insulating base layer (5); S2: Fill the blind holes with a temporary etchable resin containing urethane and cure it; S3: The outer layer circuit is formed by lamination, drilling, and electroplating according to conventional PCB processes. S4: Selectively etch the resin in an alkaline solution to release the channel network on the insulating base layer (5).

10. The printed circuit board processing technology with microchannels as described in claim 9, characterized in that: The removable resin contains 30%–50% by weight of urethane prepolymer, 20%–35% by weight of filler, and 5%–10% by weight of catalyst. It can be completely dissolved by soaking in an alkaline solution with pH > 10 at 50–60°C for 30–45 minutes.

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