A copper-based PCB hybrid metal substrate and a preparation process thereof

Abstract

The application discloses a copper-based PCB mixed metal substrate and a preparation process thereof, and relates to the technical field of special PCB plate processing.The application comprises the following steps: a copper plate, a first surface of the copper plate is bonded with a microwave high-frequency plate, a second surface opposite to the first surface is provided with an inlay groove, the bottom of the inlay groove is provided in a zigzag shape, and the groove wall of the inlay groove is provided with an inclination of 5°; an inlay plate is formed by laminating four FR-4 plate layers, the inlay plate is embedded in the inlay groove, and the inlay plate is arranged in a flush manner with the surface of the copper plate; the copper plate and the microwave high-frequency plate are bonded through a splicing bonding part, the splicing bonding part is composed of an insulating adhesive film and a conductive adhesive film; and the inlay plate and the inlay groove are bonded through a low-flow adhesive film; thus, the problems of insufficient heat dissipation performance, low structural integration and poor reliability of a mixed manufacturing process of a traditional PCB in a high-power microwave device are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of special PCB plate processing, and in particular to a copper-based PCB mixed metal substrate and a preparation process thereof. Background Art

[0002] In current high-power microwave communication equipment (such as satellite payload systems), traditional PCB structures have the following key bottlenecks.

[0003] Inadequate heat dissipation. The thermal conductivity of traditional FR-4 substrates (typically ≤0.3 W / m•K) cannot meet the heat dissipation requirements of high-power microwave devices (such as power amplifiers). Heat accumulation during continuous device operation leads to excessive temperature rise, causing performance degradation or even failure. While existing metal substrates (such as aluminum) can improve heat dissipation, they hinder the integration of high-frequency microwave signal layers with digital control layers.

[0004] The structure has a low level of integration. The microwave high-frequency layer, digital control layer, and heat dissipation metal substrate are typically separated and interconnected via connectors or welding. This structure increases volume and weight, making it difficult to meet the lightweight requirements of aerospace equipment. Signal integrity is degraded, and impedance mismatches are introduced at interconnect points, affecting high-frequency signal transmission. Furthermore, reliability risks exist, as the connection interface is prone to fatigue failure under thermal cycling.

[0005] As satellite communications, 5G / 6G base stations and other equipment develop towards high frequency and high power, there is an urgent need for a PCB solution that combines high heat dissipation, high integration and high reliability. At the same time, it is necessary to break through the bottleneck of hybrid structure precision manufacturing process to meet the stringent requirements of aerospace and other fields for lightweight, miniaturization and long life. Summary of the Invention

[0006] The purpose of the present invention is to provide a copper-based PCB hybrid metal substrate and its preparation process to solve the problems of insufficient heat dissipation performance, low structural integration and poor reliability of hybrid manufacturing process of traditional PCB boards in high-power microwave equipment.

[0007] In order to solve the above problems, the present invention adopts the following technical means:

[0008] A copper-based PCB hybrid metal substrate, comprising:

[0009] A copper plate, the first side of which is pressed and bonded with a microwave high-frequency board, and the second side opposite to the first side is configured with an inlay groove, the bottom of the inlay groove is configured in a serrated shape, and the groove wall of the inlay groove is set at a 5° inclination angle;

[0010] A mosaic board is formed by laminating four layers of FR-4 boards, the mosaic board is embedded in the mosaic groove, and the mosaic board is arranged flush with the surface of the copper board;

[0011] The copper plate and the microwave high-frequency board are bonded together by a splicing adhesive portion, wherein the splicing adhesive portion is composed of an insulating adhesive film and a conductive adhesive film;

[0012] The inlay plate and the inlay groove are bonded together by a low-flow adhesive film.

[0013] Among them, through the setting of the splicing bonding part, the conductive adhesive film part can be combined with the copper plate to efficiently dissipate heat for the high-power devices of the microwave high-frequency board during continuous operation, so that the microwave high-frequency board with the surface laminated can accept a greater extent of input signals.

[0014] By embedding the FR-4 board in the copper board through the inlay board method, structural integration is achieved, effectively integrating the digital control function and the microwave function, achieving miniaturization and lightweight of the structure, and eliminating the risk of connection reliability.

[0015] The microwave high-frequency layer, thick copper base, and inlaid FR-4 digital control layer are integrated into one structure and electrically interconnected.

[0016] Local grooves are dug on the copper substrate to embed the FR-4 board, and the surface must be flush. This is different from conventional full-surface lamination or simple local mounting. Combined with the mixed application of conductive and insulating films between the microwave high-frequency board and the copper board, it meets the extreme requirements of aerospace satellites and other applications for power density, heat dissipation, signal integrity, lightweight, and reliability.

[0017] Moreover, due to the difference in thermal expansion coefficients between the inlaid plate and the copper plate, the synergistic effect of the serrated inlaid groove and the low-flow adhesive film reduces the mismatch in thermal expansion coefficients between the two, thus solving the phase distortion problem caused by thermal stress in high-frequency signals.

[0018] Furthermore, the conductive adhesive film is provided at the high-power components and the grounding portion of the microwave high-frequency board, and the insulating adhesive film is provided at the connection position between the microwave high-frequency board and the FR-4 board circuit.

[0019] In this way, in addition to meeting the heat dissipation power requirements of the microwave high-frequency board for high-power devices, the partition design significantly reduces the dielectric constant fluctuation of the high-frequency signal path, reducing the insertion loss by 1.2dB in the 28GHz frequency band, and significantly reducing the ground impedance.

[0020] Furthermore, the first surface of the copper plate is coated with a barrier layer formed by epoxy resin ink, and the barrier layer forms a plurality of adhesive coating areas around the first surface, and the adhesive coating areas are used for applying the insulating adhesive film or the conductive adhesive film.

[0021] In this way, epoxy resin ink is used to form a barrier layer, which is then used to divide the first surface into several adhesive-coated areas. Conductive or insulating films are then applied to the corresponding adhesive-coated areas. This prevents the thermosetting properties of the epoxy resin ink from isolating the conductive and insulating films during the lamination process, thereby preventing contamination between the conductive and insulating films, as well as adverse conditions such as delamination due to poor bonding or short circuits caused by the conductive films. Furthermore, the isolation provided by the barrier layer prevents heat from diffusing from the high-power device area through the conductive film, affecting the operating temperature of the insulating film. It also reduces the thermal resistance gradient between the high-frequency and low-frequency regions, avoiding localized hot spots.

[0022] Furthermore, a through hole is opened on the copper plate, and the inner wall of the through hole is copper-plated for connecting the microwave high-frequency board and the circuit in the mosaic board. The side of the microwave high-frequency board away from the copper plate and the side of the mosaic board away from the copper plate are covered with solder resist ink.

[0023] In addition, in a method for preparing the aforementioned copper-based PCB mixed metal substrate, the inlay groove is formed by etching;

[0024] This effectively avoids the significant thermal stress that can be left in the copper plate during machining when conventional copper plates are used to form large-area inlay grooves. Etching the inlay grooves for mounting the inlay board also meets the precision requirements for mounting FR-4 boards in this application, ensuring a depth accuracy of within 50 μm.

[0025] After the inlay plate is laminated and formed, it is then installed into the inlay groove;

[0026] Before laminating the microwave high-frequency board, a barrier layer is coated on the first side of the copper plate. The barrier layer is used to divide the copper plate into several glue-coating areas. Insulating adhesive film or conductive adhesive film is coated on different glue-coating areas respectively. After the glue coating is completed, the microwave high-frequency board is laminated on the copper plate.

[0027] Furthermore, the conductive adhesive film is arranged corresponding to the position of the high-power device of the microwave high-frequency board, and the insulating adhesive film is arranged corresponding to the connection area between the microwave high-frequency board and the FR-4 board circuit.

[0028] Furthermore, after the inlay groove is formed by etching, a mechanical grinder is used to locally grind and reshape the inner cavity edge of the inlay groove.

[0029] Thus, even if the etched groove does not meet the shape requirements for inserting the inlay plate after the groove is formed by etching, the inner wall of the groove can be trimmed by mechanical grinding. Because the groove is formed by etching, a small amount of mechanical grinding does not cause significant thermal stress inside the copper plate. Therefore, the combination of mechanical grinding and etching can ensure machining accuracy while ensuring the proper insertion of the inlay plate.

[0030] The substrate and the corresponding preparation process involved in this application have the following beneficial effects:

[0031] The copper plate is partially grooved to accommodate the FR-4 board, ensuring flush bonding. Furthermore, conductive adhesive film is applied locally between the microwave layer and the copper plate to dissipate heat from high-power devices, while insulating adhesive film is used in other areas. This "dual adhesive strategy" achieves different functions within the same adhesive layer. Furthermore, the microwave high-frequency layer (for high-power devices), the copper plate (for heat dissipation), and the embedded FR-4 digital control layer are integrated into a single structure and electrically interconnected, meeting the extreme power density, heat dissipation, signal integrity, lightweight, and reliability requirements of applications such as space satellites.

[0032] The heat dissipation efficiency of high-power devices is improved by combining copper plates and conductive adhesive films. The integrated structure of copper plates inlaid with FR-4 boards eliminates the connection interface, achieving lightweight and high reliability. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with 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.

[0034] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0035] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. Example 1

[0036] Step A

[0037] He took a 2mm copper plate and used photolithography and etching to create a 1.2mm deep sawtooth groove on the second side. The groove bottom had a sawtooth structure with a tooth height of 100μm, a pitch of 200μm, and a 5° inclination on the groove wall.

[0038] After etching, use a diamond grinding needle with a diameter of less than 0.3mm to trim the groove wall of the inlay groove to ensure that the matching accuracy of the inlay plate is ≤50μm.

[0039] Step B

[0040] An epoxy resin ink barrier layer with a thickness of 30 μm was screen-printed on the first side of the copper plate. This barrier layer was then used to separate the first side of the copper plate into different adhesive zones. The areas corresponding to high-power devices were coated with a conductive film containing silver particles, while the signal connection areas were coated with a PP insulating film.

[0041] Step C

[0042] Four layers of FR-4 board, totaling 1.18mm thick, were laminated and embedded in the mounting groove. Prior to embedding, the mounting groove was filled with a low-flow adhesive film with a flow index of less than 5%. The panels were then vacuum-pressed at 180°C for 40 minutes to level the mounting plate with the copper plate surface. The height difference between the two was less than 20μm.

[0043] Step D

[0044] The microwave high-frequency board is pressed onto the first side of the copper board through the splicing adhesive. Make sure the conductive adhesive film is aligned with the high-power components of the microwave high-frequency board, and the insulating adhesive film is aligned with the signal output position.

[0045] Step E

[0046] Through holes are constructed on the copper plate, and copper is deposited on the through holes to achieve electrical interconnection between the microwave layer and the digital layer. Finally, solder mask ink is applied on the surface.

[0047] Comparative Example 1

[0048] It uses an integral aluminum substrate, the entire surface is covered with an insulating layer, and the surface is laminated with a microwave board and an FR-4 board, which are interconnected through solder balls.

[0049] Comparative Example 2

[0050] In this comparative example, a copper substrate is used, and a single insulating adhesive film is used to bond the microwave high-frequency board to the entire surface.

[0051] The panels of Example 1, Comparative Example 1 and Comparative Example 2 were operated under the conditions of a high-power device with a frequency of 28 GHz, a continuous output power of 50 W and an ambient temperature of 85°C.

[0052] Comparing Example 1 with Comparative Example 1, the thermal resistance of Example 1 is reduced from 2.5°C / W to 0.8°C / W, the insertion loss at 2.8 GHz is reduced from 1.7 dB to 0.5 dB, and the ground impedance is reduced from 45 mΩ to 12 mΩ. After thermal cycling at -55 to 125°C, there is no delamination in Example 1, while cracks appear at the aluminum substrate connection interface of Comparative Example 1.

[0053] For the plate prepared in Comparative Example 2, its thermal resistance increased to 2.2°C / W and its ground impedance increased to 60mΩ. Moreover, local hot spots caused the dielectric constant to drift by more than 0.3 in the high-frequency region.

[0054] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A copper-based PCB hybrid metal substrate, characterized in that: include: A copper plate, the first side of which is pressed and bonded with a microwave high-frequency board, and the second side opposite to the first side is configured with an inlay groove, the bottom of the inlay groove is configured in a serrated shape, and the groove wall of the inlay groove is set at a 5° inclination angle; A mosaic board is formed by laminating four layers of FR-4 boards, the mosaic board is embedded in the mosaic groove, and the mosaic board is arranged flush with the surface of the copper board; The copper plate and the microwave high-frequency board are bonded together by a splicing adhesive portion, wherein the splicing adhesive portion is composed of an insulating adhesive film and a conductive adhesive film; The inlay plate and the inlay groove are bonded together by a low-flow adhesive film.

2. The copper-based PCB hybrid metal substrate according to claim 1, characterized in that: The conductive adhesive film is arranged at the positions of the high-power components and the grounding portion of the microwave high-frequency board, and the insulating adhesive film is arranged at the position where the microwave high-frequency board is connected to the FR-4 board circuit.

3. A copper-based PCB hybrid metal substrate according to claim 1 or 2, characterized in that: The first surface of the copper plate is coated with a barrier layer formed by epoxy resin ink. The barrier layer is surrounded by the first surface to form a plurality of adhesive coating areas. The adhesive coating areas are used to apply the insulating adhesive film or the conductive adhesive film.

4. The copper-based PCB hybrid metal substrate according to claim 1, characterized in that: A through hole is provided on the copper plate, and the inner wall of the through hole is copper-plated for connecting the microwave high-frequency board and the circuit in the inlaid board. The side of the microwave high-frequency board away from the copper plate and the side of the inlaid board away from the copper plate are covered with solder resist ink.

5. A process for preparing a copper-based PCB mixed metal substrate according to any one of claims 1 to 4, characterized in that: The damascene groove is formed by etching; After the inlay plate is laminated and formed, it is then installed into the inlay groove; Before laminating the microwave high-frequency board, a barrier layer is coated on the first side of the copper plate. The barrier layer is used to divide the copper plate into several glue-coating areas. Insulating adhesive film or conductive adhesive film is coated on different glue-coating areas respectively. After the glue coating is completed, the microwave high-frequency board is laminated on the copper plate.

6. The preparation process according to claim 5, characterized in that: The conductive adhesive film is arranged corresponding to the position of the high-power device of the microwave high-frequency board, and the insulating adhesive film is arranged corresponding to the connection area between the microwave high-frequency board and the FR-4 board circuit.

7. The preparation process according to claim 5, characterized in that: After the inlay groove is formed by etching, a mechanical grinding needle is used to locally grind and reshape the inner cavity edge of the inlay groove.