Fabrication methods for millimeter-wave radar circuit boards and millimeter-wave radar circuit boards

Abstract

This invention discloses a method for fabricating a millimeter-wave radar circuit board, which achieves signal shielding by embedding copper wires. Compared to the traditional method of using blind vias for signal shielding, the embedded copper wires can be continuously arranged along the RF circuit pattern, thereby effectively increasing the signal shielding area and improving the signal shielding effect. Furthermore, it eliminates traditional processes such as blackening, de-blackening, plasma adhesive removal, via plating, and copper reduction during fabrication, significantly shortening the processing flow and improving the fabrication efficiency of the millimeter-wave radar circuit board. In addition, this invention also discloses a millimeter-wave radar circuit board fabricated using the above-described method.

Description

Technical Field

[0001] This invention relates to the field of circuit board processing technology, and in particular to a processing method for a millimeter-wave radar circuit board and a millimeter-wave radar circuit board. Background Technology

[0002] Currently, the main method for shielding signals on millimeter-wave radar circuit boards is to add blind vias to the radio frequency circuit layer, and then fill the blind vias through electroplating, achieving signal shielding through a copper layer. The specific process is as follows: inner layer circuit fabrication → plate pressing → blackening → laser blind via → de-blackening → mechanical drilling → high-pressure water washing → plasma desmearing → chemical desmearing → via metallization → via filling electroplating → pulse electroplating → resin plugging → copper reduction → outer layer circuit etching. Because there is a gap between adjacent blind vias, complete signal sealing cannot be achieved, easily leading to signal leakage. Secondly, since blind vias are laser-processed, blackening is required before laser blind via laser processing to facilitate the laser process. After laser blind via laser processing, de-blackening is required, and plasma desmearing is necessary to remove residual adhesive inside the blind vias; otherwise, subsequent copper plating on the inner wall of the blind vias cannot be successful. Furthermore, since circuit boards contain both blind vias and through-holes, electroplating is required for both. Due to limitations in the capacity of the through-hole plating process, it is usually impossible to achieve co-plating of blind and through-holes in one go. Therefore, it is necessary to first plate the inner walls of blind vias through through-hole plating, and then plate the inner walls of through-holes through pulse plating. Since the copper thickness on the surface of the circuit board increases significantly after two plating processes, it is also necessary to reduce the copper content on the surface of the circuit board after plating. This process is extremely cumbersome, has a long processing flow, and low production efficiency. Summary of the Invention

[0003] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a method for processing millimeter-wave radar circuit boards, which not only improves signal shielding effectiveness but also shortens the processing flow and increases production efficiency.

[0004] The present invention also proposes a millimeter-wave radar circuit board manufactured using the above-described millimeter-wave radar circuit board processing method.

[0005] The method for fabricating a millimeter-wave radar circuit board according to an embodiment of the present invention includes the following steps:

[0006] S1: Cutting materials to obtain the first PP board, the second PP board, the first copper foil, the second copper foil, the inner core board, and the copper wire;

[0007] S2: Router material, a first through slot is processed on the first copper foil according to the radio frequency circuit pattern, and a second through slot is processed on the first PP board according to the radio frequency circuit pattern;

[0008] S3: Inner layer circuit fabrication, fabricating inner layer circuit patterns on the inner core board;

[0009] S4: Stacking: The second copper foil, the second PP board, the inner core board, the first PP board, and the first copper foil are stacked sequentially from bottom to top to form a multilayer board. The side of the inner core board facing the first PP board is a metal surface. The first through groove and the second through groove are aligned and the first through groove, the second through groove, and the upper surface of the inner core board are enclosed to form an installation groove. The copper wire is embedded in the installation groove.

[0010] S5: Press plate, for pressing the stacked multilayer boards and copper wires together;

[0011] S6: Drilling, machining through holes in the multilayer board;

[0012] S7: Copper plating, forming a first copper layer on the surface of the first copper foil, the first copper layer covering the mounting groove and embedded between the copper wire and the inner wall of the mounting groove, and forming a second copper layer on the inner wall of the through hole;

[0013] S8: Subsequent process.

[0014] The millimeter-wave radar circuit board processing method according to embodiments of the present invention has at least the following beneficial effects:

[0015] In the millimeter-wave radar circuit board processing method of this invention, signal shielding can be achieved by embedding copper wires. Compared with the traditional method of using blind vias to achieve signal shielding, the embedded copper wires can be arranged continuously along the radio frequency circuit pattern, thereby effectively increasing the signal shielding area and improving the signal shielding effect. Secondly, since the blind via structure in the traditional structure is eliminated, there is no need for laser blind vias, and therefore no need for blackening, de-blackening, or plasma adhesive removal. In addition, during electroplating, only one electroplating is required to achieve through-hole metallization, eliminating the need for the through-hole filling electroplating process. Furthermore, the circuit board will not have excessively thick copper due to two electroplating processes, so there is no need for copper reduction processes. Therefore, compared with the traditional processing method, the millimeter-wave radar circuit board processing method of this invention only requires routing the board after blanking to process the first and second through slots, and then pressing the copper wires into the mounting groove formed by the connection of the first and second through slots during stacking. There is no need for blackening, de-blackening, plasma adhesive removal, through-hole filling electroplating, copper reduction, and other processes, which greatly shortens the processing flow and thus helps to improve the processing efficiency of millimeter-wave radar circuit boards.

[0016] According to some embodiments of the present invention, between step S3 and step S4, a browning process is further included, in which the copper wire and the inner core board are subjected to a browning treatment, the amount of copper biting during browning is 1.4μm-1.8μm, and the surface roughness Rz value of the copper wire and the inner core board after browning is 3±1μm, and the Ra value is 0.4±0.2μm.

[0017] According to some embodiments of the present invention, during the browning treatment of the copper wire, the copper wire is fixed on a tray and passed through a browning wire at a browning speed of 1.0 m / min. After browning, the copper wire is dried at a drying temperature of 90±5℃.

[0018] According to some embodiments of the present invention, step S5 includes:

[0019] S5.1: Pre-pressing, a first kraft paper assembly and a first steel plate are sequentially covered on the first copper foil, and the stacked copper wire, the second copper foil, the second PP board, the inner core board, the first PP board, and the first copper foil are pre-pressed by the first steel plate;

[0020] S5.2: Hot pressing, the second kraft paper assembly and the second steel plate are sequentially covered on the first copper foil, and the stacked second steel plate, the second kraft paper assembly, the copper wire, the second copper foil, the second PP board, the inner core board, the first PP board and the first copper foil are hot pressed, with a heating rate of 2.5℃ / min;

[0021] S5.3: Cold pressing, the stacked second steel plate, second kraft paper assembly, copper wire, second copper foil, second PP board, inner core board, first PP board and first copper foil are cold pressed, the cold pressing pressure is 30 bar and the cold pressing time is 45 min.

[0022] According to some embodiments of the present invention, the inner core plate includes at least two copper substrates, all of which are stacked sequentially, and a prepreg layer is sandwiched between two adjacent copper substrates.

[0023] According to some embodiments of the present invention, step S7 includes:

[0024] S7.1: Grinding plate, grinding the surfaces of the first copper foil and the second copper foil to remove burrs at the through holes and residual adhesive at the mounting groove;

[0025] S7.2: Remove adhesive residue formed on the inner wall of the through hole by the semi-cured sheet layer, and remove adhesive residue formed between the copper wire and the inner wall of the mounting groove by the first PP layer;

[0026] S7.3: Electroplating, using horizontal copper plating and pulse electroplating to form the first copper layer and the second copper layer.

[0027] According to some embodiments of the present invention, step S7.1 includes:

[0028] Abrasive belt grinding plate, wherein the abrasive belt has a mesh size of 320#;

[0029] The needle brush abrasive plate has a needle brush mesh size of 320#-540# and an abrasive plate pressure of 0.8±0.2kg / cm. 2 .

[0030] According to some embodiments of the present invention, the thickness of the first copper foil and the second copper foil is 20 μm, the thickness of the first PP board and the second PP board is 125 ± 12.5 μm, the width of the mounting groove is 200 μm, the width of the copper wire is 190 μm-200 μm, and the thickness of the copper wire is 90 μm-105 μm;

[0031] In step S7.1, the copper removal thickness of the first copper foil and the second copper foil is 5-10 μm;

[0032] In step S7.2, roughening is performed by chemical degumming;

[0033] In step S7.3, the thickness of the first copper layer on the surface of the first copper foil is not less than 30 μm.

[0034] According to some embodiments of the present invention, step S8 includes:

[0035] S8.1: Outer layer circuit fabrication, an outer layer circuit pattern is fabricated on the surface of the first copper layer, and an edge compensation amount is set on the portion of the outer layer circuit pattern located above the copper line;

[0036] S8.2: Baking plate, for baking the multilayer board at a temperature of 120°C for 1 hour.

[0037] The millimeter-wave radar circuit board according to an embodiment of the present invention is formed by the millimeter-wave radar circuit board processing method of any of the above embodiments.

[0038] The millimeter-wave radar circuit board according to embodiments of the present invention has at least the following beneficial effects:

[0039] In the millimeter-wave radar circuit board of this invention, by adopting the processing method of any of the above embodiments, signal shielding can be achieved by embedding copper wires. Compared with the traditional method of using blind vias for signal shielding, the embedded copper wires can be continuously arranged along the RF circuit pattern, thereby effectively increasing the signal shielding area and improving the signal shielding effect. Secondly, since the millimeter-wave radar circuit board of this invention does not require laser blind vias during processing, it also eliminates the need for blackening, de-blackening, plasma adhesive removal, via plating, and copper reduction processes. This significantly shortens the processing flow of the millimeter-wave radar circuit board and improves its processing efficiency.

[0040] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0041] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0042] Figure 1 This is a schematic diagram of step S2, machining, of the millimeter-wave radar circuit board processing method according to an embodiment of the present invention.

[0043] Figure 2 This is a schematic diagram of step S4, stacking, of the millimeter-wave radar circuit board processing method according to an embodiment of the present invention.

[0044] Figure 3 This is a schematic diagram of step S5, pressing plate, in the millimeter-wave radar circuit board processing method of an embodiment of the present invention.

[0045] Figure 4 This is a schematic diagram of step S6, drilling, in the millimeter-wave radar circuit board processing method according to an embodiment of the present invention.

[0046] Figure 5 This is a schematic diagram of copper plating step S7 in the processing method of the millimeter-wave radar circuit board according to an embodiment of the present invention.

[0047] Figure label:

[0048] Multilayer board 100, first copper foil 110, first through groove 111, first PP board 120, second through groove 121, inner core board 130, copper substrate 131, prepreg 132, second PP board 140, second copper foil 150, copper wire 160, mounting groove 200, through hole 300, first copper layer 400, second copper layer 500, third copper layer 600. Detailed Implementation

[0049] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0050] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0051] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0052] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0053] Reference Figures 1 to 5 One embodiment of the present invention provides a method for processing a millimeter-wave radar circuit board, comprising the following steps:

[0054] S1: Cutting materials to obtain the first PP board 120, the second PP board 140, the first copper foil 110, the second copper foil 150, the inner core board 130, and the copper wire 160;

[0055] S2: The first through slot 111 is machined on the first copper foil 110 according to the radio frequency circuit pattern, and the second through slot 121 is machined on the first PP board 120 according to the radio frequency circuit pattern.

[0056] S3: Inner layer circuit fabrication, fabricating inner layer circuit patterns on the inner core board 130;

[0057] S4: Stacking: The second copper foil 150, the second PP board 140, the inner core board 130, the first PP board 120, and the first copper foil 110 are stacked from bottom to top to form a multilayer board 100. The side of the inner core board 130 facing the first PP board 120 is a metal surface. The first through groove 111 and the second through groove 121 are aligned and the first through groove 111, the second through groove 121 and the upper surface of the inner core board 130 are enclosed to form a mounting groove 200. The copper wire 160 is embedded in the mounting groove 200.

[0058] S5: Press plate, which presses together the stacked multilayer board 100 and copper wire 160;

[0059] S6: Drilling, machining through holes 300 on multilayer board 100;

[0060] S7: Copper plating, forming a first copper layer 400 on the surface of the first copper foil 110, the first copper layer 400 covering the mounting groove 200 and embedded between the copper wire 160 and the inner wall of the mounting groove 200, and forming a second copper layer 500 on the inner wall of the through hole 300.

[0061] S8: Subsequent process.

[0062] By employing the millimeter-wave radar circuit board processing method of this invention, after material preparation, the inner layer circuit pattern is fabricated normally. Then, a first through-slot 111 is processed on the first copper foil 110 according to the radio frequency circuit pattern, and a second through-slot 121 is processed on the first PP board 120 according to the radio frequency circuit pattern. During stacking, the second copper foil 150, the second PP board 140, the inner core board 130, the first PP board 120, and the first copper foil 110 are stacked sequentially from bottom to top to form a multilayer board 100. The inner core board 130 faces the first PP board 120. The surface is metal. The first through groove 111 and the second through groove 121 are aligned and enclose the upper surface of the inner core plate 130 to form an installation groove 200. Thus, when the copper wire 160 is embedded in the installation groove 200, it will come into contact with the metal surface of the inner core plate 130. Then, the stacked multilayer board 100 and the copper wire 160 are pressed together. During the pressing process, the first PP layer can not only tightly connect the first copper foil 110 and the inner core plate 130, but also connect with the copper wire 160, so that the copper wire 160 is more stably embedded in the installation groove 200. After pressing, drilling and copper plating processes can be carried out according to normal procedures. Through holes 300 are processed on the multilayer board 100, and a second copper layer 500 is formed on the inner wall of the through hole 300 by copper plating, thereby realizing the metallization of the through hole 300. In addition, during the copper plating process, a first copper layer 400 can also be formed on the surface of the first copper foil 110. The first copper layer 400 covers the mounting groove 200 and is embedded between the copper wire 160 and the inner wall of the mounting groove 200. This allows the copper wire 160 to be embedded inside the multilayer board 100, making the structure of the copper wire 160 more stable. The inner core board 130 and the first copper foil 110 can be connected through the copper wire 160, thereby realizing the signal shielding function.

[0063] As can be seen from the above, in the millimeter-wave radar circuit board processing method of the present invention, signal shielding can be achieved by embedding copper wires 160. Compared with the traditional method of using blind vias to achieve signal shielding, the embedded copper wires 160 can be continuously arranged along the radio frequency circuit pattern, thereby effectively increasing the area of ​​signal shielding and thus improving the signal shielding effect. Secondly, in the millimeter-wave radar circuit board processing method of this invention, since the blind via structure in the traditional structure is eliminated, there is no need for laser blind vias, and therefore no need for blackening, de-blackening, and plasma adhesive removal. In addition, during electroplating, only one electroplating is required to metallize the through-hole 300, eliminating the need for the through-hole filling electroplating process. Furthermore, the circuit board will not have excessively thick copper due to two electroplating processes, so there is no need for the copper reduction process. Thus, compared with the traditional processing method, the millimeter-wave radar circuit board processing method of this invention only requires routing the board after blanking to process the first through-hole 111 and the second through-hole 121. Then, during the stacking process, the copper wire 160 is pressed into the mounting groove 200 formed by the connection of the first through-hole 111 and the second through-hole 121. There is no need for blackening, de-blackening, plasma adhesive removal, through-hole filling electroplating, copper reduction, and other processes, which greatly shortens the processing flow and thus helps to improve the processing efficiency of the millimeter-wave radar circuit board.

[0064] It is understandable that copper wire 160 can be made of pure copper, which gives it good flexibility and tensile strength. This not only helps to achieve signal shielding, but also facilitates the smooth operation of the pressure plate process.

[0065] Understandably, since copper wire 160 needs to be embedded in the second through groove 121 of the first PP board 120, in order to improve the installation stability of copper wire 160, the first PP board 120 is made of high-adhesion PP material with an adhesive content of ≥68%, and the first PP board 120 does not contain glass fiber, but is only filled with resin. The second PP board 140 can be made of common FR4 PP material.

[0066] It is understandable that during the milling process in step S2, a milling cutter can be used to process the first copper foil 110 and the first PP board 120 to form the first through groove 111 and the second through groove 121.

[0067] It is understandable that, in order to facilitate a stable connection between the copper wire 160 and the metal surface of the inner core board 130 near the first PP board 120 during the fabrication of the inner layer circuit in step S3, a large copper surface design can be made on the side of the inner core board 130 near the first PP board 120, while normal inner layer circuit design can be made on the other metal surfaces of the inner core board 130.

[0068] It is understandable that conventional drilling equipment can be used to mechanically drill the multilayer board 100 during step S6.

[0069] In some embodiments, between step S3 and step S4, a browning process is further included, in which the copper wire 160 and the inner core plate 130 are browned. The amount of copper bitten during browning is 1.4μm-1.8μm. After browning, the surface roughness Rz value of the copper wire 160 and the inner core plate 130 is 3±1μm, and the Ra value is 0.4±0.2μm.

[0070] By adopting the above processing method, the copper wire 160 and the inner core board 130 are browned before stacking. The browning treatment can effectively improve the surface roughness of the copper wire 160 and the inner core board 130, which is conducive to improving the surface bonding force between the copper wire 160 and the inner core board 130 in the subsequent pressing process. This makes the bonding between the copper wire 160 and the inner core board 130, and between the inner core board 130 and the first PP board 120 and the second PP board 140 more firm and stable, which is conducive to improving the structural stability of the millimeter-wave radar circuit board.

[0071] In some embodiments, when browning the copper wire 160, the copper wire 160 is fixed on a tray and passed through a browning line at a browning speed of 1.0 m / min. After browning, the copper wire 160 is dried at a temperature of 90 ± 5 °C.

[0072] By employing the above processing method, the copper wire 160 is fixed on the tray, facilitating its browning process via the browning line. Browning the copper wire 160 erodes the oxide layer on its surface and roughens the surface, enhancing surface adhesion during lamination. Drying the copper wire 160 after browning facilitates subsequent lamination.

[0073] In some embodiments, during the stacking process in step S4, rivet holes are also processed on the second copper foil 150, the second PP board 140, the inner core board 130, the first PP board 120, and the first copper foil 110. Rivets are then pressed into the rivet holes during the stacking process to fix the second copper foil 150, the second PP board 140, the inner core board 130, the first PP board 120, and the first copper foil 110 together. This allows for the positioning of the multilayer board 100 during the pressing process and ensures that the first through groove 111 and the second through groove 121 are accurately aligned, preventing the board from shifting or the pattern from shifting laterally during the pressing process.

[0074] It is understandable that rivet holes can be machined on the first PP board 120, the second PP board 140, the first copper foil 110, the second copper foil 150, and the inner core board 130 separately. Alternatively, the second copper foil 150, the second PP board 140, the inner core board 130, the first PP board 120, and the first copper foil 110 can be stacked sequentially from bottom to top, and then the rivet holes can be machined together. Rivets are then pressed into the rivet holes to fix the second copper foil 150, the second PP board 140, the inner core board 130, the first PP board 120, and the first copper foil 110 together. It is also understandable that, for better fixing, the rivet holes can be located at the four corners of the board and the middle of the four sides, meaning that eight rivet holes are provided on each board.

[0075] In some embodiments, step S5 includes:

[0076] S5.1: Pre-pressing, the first kraft paper assembly and the first steel plate are sequentially covered on the first copper foil 110, and the stacked copper wire 160, the second copper foil 150, the second PP board 140, the inner core board 130, the first PP board 120 and the first copper foil 110 are pre-pressed by the first steel plate.

[0077] S5.2: Hot pressing, the second kraft paper assembly and the second steel plate are sequentially covered on the first copper foil 110, and the stacked second steel plate, second kraft paper assembly, copper wire 160, second copper foil 150, second PP board 140, inner core board 130, first PP board 120 and first copper foil 110 are hot pressed, with a heating rate of 2.5℃ / min;

[0078] S5.3: Cold pressing, the stacked second steel plate, second kraft paper assembly, copper wire 160, second copper foil 150, second PP board 140, inner core board 130, first PP board 120 and first copper foil 110 are cold pressed, the cold pressing pressure is 30 bar and the cold pressing time is 45 min.

[0079] By employing the above method, the stacked copper wire 160, second copper foil 150, second PP board 140, inner core board 130, first PP board 120, and first copper foil 110 are pre-pressed by the first steel plate, making the second copper foil 150, second PP board 140, inner core board 130, first PP board 120, and first copper foil 110 more flat, facilitating subsequent hot pressing processes. During hot pressing, the first PP board 120 and second PP board 140 are melted at high temperature and pressure, and the first copper foil 110, inner core board 130, and second copper foil 150 are tightly bonded together through the first PP board 120 and second PP board 140, making the connection between the layers of the multilayer board 100 more robust and ensuring more reliable electrical connections. Finally, cold pressing is performed. Cold pressing can effectively eliminate the thermal stress generated by the multilayer board 100 during the hot pressing process, reduce the risk of warping and deformation of the multilayer board 100 in subsequent processing due to thermal stress, and ensure the flatness of the multilayer board 100 throughout the entire production and processing process. This helps to improve the dimensional stability and mechanical stability of the multilayer board 100.

[0080] In some embodiments, the thickness of the first steel plate is greater than the thickness of the second steel plate.

[0081] Since step S5.1 involves directly pre-pressing the stacked copper wire 160, second copper foil 150, second PP board 140, inner core board 130, first PP board 120, and first copper foil 110 using the first steel plate, and step S5.2 involves hot-pressing the stacked second steel plate, second kraft paper assembly, copper wire 160, second copper foil 150, second PP board 140, inner core board 130, first PP board 120, and first copper foil 110 using a hot-pressing device, setting the thickness of the first steel plate to be greater than that of the second steel plate facilitates the effective pre-pressing process. This allows for better pre-pressing of the stacked copper wire 160, second copper foil 150, second PP board 140, inner core board 130, first PP board 120, and first copper foil 110.

[0082] It is understood that in some embodiments, the thickness of the first steel plate is specifically 3.2 mm, and the thickness of the second steel plate is specifically 1.6 mm. Of course, this is merely an exemplary description of a preferred embodiment, and the specific thickness of the first and second steel plates is not specifically limited in this embodiment. Furthermore, to further improve the flatness of the stacked copper wire 160, second copper foil 150, second PP board 140, inner core board 130, first PP board 120, and first copper foil 110 during hot pressing, the warpage of the first steel plate during pre-pressing should not exceed 3 mm.

[0083] Understandably, the first kraft paper assembly specifically includes twelve sheets of first kraft paper. These sheets protect the first copper foil 110 during the pre-pressing process, preventing direct contact between the first steel plate and the first copper foil 110 and thus avoiding damage such as squeezing or scratches. Similarly, the second kraft paper assembly specifically includes eight sheets of second kraft paper. These sheets protect the first copper foil 110 during the hot-pressing process, preventing direct contact between the first steel plate and the first copper foil 110 and thus avoiding damage such as squeezing or scratches. To improve the utilization rate of the kraft paper, new kraft paper or used kraft paper can be used for the second kraft paper.

[0084] It should be noted that the first kraft paper assembly specifically includes twelve sheets of first kraft paper, which is merely an illustrative example of an embodiment of the present invention. The number of first kraft paper sheets can also be one, two, or other quantities, and the present invention does not specifically limit this. Similarly, the second kraft paper assembly specifically includes eight sheets of second kraft paper, which is merely an illustrative example of an embodiment of the present invention. The number of second kraft paper sheets can also be one, two, or other quantities, and the present invention does not specifically limit this.

[0085] In some embodiments, in step S5.2, the heating rate can be controlled at 2.5°C / min, thereby allowing the temperature to rise slowly and improving the hot pressing effect.

[0086] In some embodiments, in step S5.2, the hot pressing process can be divided into 10 sub-processes, thereby enabling separate control and adjustment of the hot plate temperature, hot plate time, pressure, and pressure time for each sub-process, making the control of the hot pressing process more flexible, and thus achieving better hot pressing results as needed.

[0087] It should be noted that the hot pressing process is divided into 10 sub-processes. The hot plate temperature, hot plate time, pressure, and pressure-time for each sub-process can be referenced in the following example:

[0088] subprocess 1 2 3 4 5 6 7 8 9 10 Hot plate temperature (°C) 140 165 190 210 230 230 230 210 180 140 Hot plate time (min) 8 5 3 2 2 95 73 27 20 20 Pressure (psi) 100 200 260 370 470 470 470 370 290 220 Pressure time (min) 7 5 5 4 3 95 71 25 20 20

[0089] In some embodiments, between steps S5.1 and S5.2, the multilayer board 100 needs to be preheated by electromagnetic heat fusion, and the preheating temperature can be set to 250°C. When preheating by electromagnetic heat fusion, multiple heat fusion heads can be used, and the temperature deviation between any two heat fusion heads can be controlled to not exceed 15°C.

[0090] Reference Figures 1 to 5 In some embodiments, the inner core board 130 includes four copper substrates 131, with a semi-cured sheet sandwiched between two adjacent copper substrates 131.

[0091] By adopting the above structure, it is beneficial to improve the electrical performance of millimeter-wave radar circuit boards.

[0092] Understandably, the inner core board 130 includes four copper substrates 131, which is only for... Figures 1 to 5 As an example, in some embodiments, the inner core board 130 may also include two, three, five or more copper substrates 131, which is not specifically limited by the present invention.

[0093] It is understandable that when the inner core board 130 includes at least two copper substrates 131, when the inner layer circuit is fabricated in step S3, the upper surface of the copper substrate 131 closest to the first PP board 120, i.e. the uppermost copper substrate 131, is designed with a large copper surface, while the lower surface is laid out with normal inner layer circuits. This makes it easier for the copper wire 160 to be effectively contacted with the uppermost copper substrate 131 after it is embedded in the mounting groove 200.

[0094] It is understandable that when the inner core board 130 includes at least two copper substrates 131, during the stacking process in step S4, each copper substrate 131 and the prepreg layer in the inner core board 130 need to be stacked sequentially between the first PP board 120 and the second PP board 140.

[0095] In some embodiments, step S7 includes:

[0096] S7.1: Grinding plate, grinding the surfaces of the first copper foil 110 and the second copper foil 150 to remove burrs at the through hole 300 and residual adhesive at the mounting groove 200;

[0097] S7.2: Remove adhesive residue formed on the inner wall of the through hole 300 by removing the semi-cured sheet layer, and remove the adhesive residue formed between the copper wire 160 and the inner wall of the mounting groove 200 by the first PP layer.

[0098] S7.3: Electroplating, using horizontal copper plating and pulse electroplating to form the first copper layer 400 and the second copper layer 500.

[0099] By employing the above processing method, since burrs are easily generated at both ends of the through hole 300 during drilling, and carbonization or residual adhesive is easily generated on the part of the semi-cured sheet located on the inner wall of the through hole 300, carbonization or residual adhesive will also occur on the first PP board 120 between the copper wire 160 and the inner wall of the mounting groove 200 during the pressing process, it is necessary to first grind the surfaces of the first copper foil 110 and the second copper foil 150 to remove the burrs on the surfaces of the first and second through holes 300 located at the through hole 300, as well as the residual adhesive on the first copper foil 110 located at the opening of the mounting groove 200. Then, the inner wall of the through hole 300 and the mounting groove 200 are cleaned through the adhesive removal process to remove the burrs on the surfaces of the first and second through holes 300. The carbonized structure and residual adhesive formed on the inner wall of the through hole 300 are removed, and the carbonized structure and residual adhesive between the copper wire 160 and the inner wall of the mounting groove 200 are also removed. This facilitates the normal progress of the subsequent electroplating process, allowing the first copper layer 400 to be formed smoothly on the inner wall of the through hole 300 during electroplating, and the second copper layer 500 to be formed on the surface of the first copper foil 110. The second copper layer 500 can cover the mounting groove 200 and be embedded in the gap between the copper wire 160 and the inner wall of the mounting groove 200, thereby burying the copper wire 160 inside the mounting groove 200 and improving the connection stability between the copper wire 160 and the inner core plate 130, and between the copper wire 160 and the first copper foil 110, which is conducive to achieving a better signal shielding effect.

[0100] Understandably, referring to Figures 1 to 5 In the electroplating process, in addition to forming the first copper layer 400 and the second copper layer 500, a third copper layer 600 can also be formed on the surface of the second copper foil 150.

[0101] Understandably, in order to achieve better electroplating results, the first copper foil 110 can be placed downwards during horizontal copper plating.

[0102] In some embodiments, step S7.1 includes:

[0103] Abrasive belt grinding plate, abrasive belt mesh size of 320#;

[0104] Needle brush abrasive plate, needle brush mesh size 320#-540#, abrasive plate pressure 0.8±0.2kg / cm 2 .

[0105] By using the above processing method, the burrs in the through hole 300 and the residual adhesive at the opening of the mounting groove 200 on the surface of the first copper foil 110 can be effectively removed by using a sanding belt and a needle brush. In particular, the needle brushing process can also effectively remove the burrs inside the through hole 300.

[0106] Reference Figures 1 to 5In some embodiments, the thickness of the first copper foil 110 and the second copper foil 150 is 20 μm, the thickness of the first PP board 120 and the second PP board 140 is 125 ± 12.5 μm, the width of the mounting groove 200 is 200 μm, the width of the copper wire 160 is 190 μm-200 μm, and the thickness of the copper wire 160 is 90 μm-105 μm.

[0107] In step S7.1, the copper removal thickness of the first copper foil 110 and the second copper foil 150 is 5-10 μm;

[0108] In step S7.2, roughening is performed by chemical degumming;

[0109] In step S7.3, the thickness of the first copper layer 400 located on the surface of the first copper foil 110 is not less than 30 μm.

[0110] In the above processing method, by setting the thickness of the first copper foil 110 and the second copper foil 150 to 20μm, the subsequent grinding process can be ensured to proceed smoothly, avoiding the situation where the thickness of the first copper foil 110 and the second copper foil 150 is too thin after grinding. The depth of the mounting groove 200 is the sum of the thickness of the first PP board 120 and the thickness of the first copper foil 110. By setting the thickness of the first PP board 120 to 125±12.5μm, the depth of the mounting groove 200 is 145±12.5μm. By setting the thickness of the copper wire 160 to 90μm-105μm, and the width of the copper wire 160 being less than or equal to the width of the mounting groove 200, the copper wire 160 can be well embedded into the mounting groove 200.

[0111] Furthermore, chemical desmearing effectively removes the carbonized structure and residual adhesive formed on the inner wall of the through-hole 300, as well as the carbonized structure and residual adhesive between the copper wire 160 and the inner wall of the mounting groove 200. In addition, chemical desmearing not only removes residual adhesive but also roughens the inner wall of the through-hole 300, the surface of the copper wire 160, and the inner wall of the mounting groove 200, thereby improving the adhesion of the copper layer during subsequent electroplating. Since the outer layer circuitry needs to be fabricated later, the first copper layer 400 needs to be etched during the outer layer circuitry fabrication process. Therefore, by controlling the thickness of the first copper layer 400 on the surface of the first copper foil 110 to be no less than 30 μm during electroplating, i.e., the thickness of the first copper layer 400 on the surface of the first copper foil 110 is 30 μm or more, this facilitates the etching process during the subsequent outer layer circuitry fabrication.

[0112] It is understood that in some embodiments, during the chemical desmearing step S7.2, the amount of desmearing needs to be controlled within 5-10 microinches, so as to remove as much residual adhesive as possible from the inner wall of the through hole 300 and between the copper wire 160 and the mounting groove 200.

[0113] In some embodiments, step S8 includes:

[0114] S8.1: Outer layer circuit fabrication: an outer layer circuit pattern is fabricated on the surface of the first copper layer 400, and edge compensation is set on the part of the outer layer circuit pattern above the copper line 160.

[0115] S8.2: Baking plate, used to bake multi-layer board 100 at a temperature of 120℃ for 1 hour.

[0116] In the above processing method, since the outer layer circuit fabrication requires exposure, development, and etching, when etching the portion of the outer layer circuit pattern above the copper line 160, the first copper layer 400 may be etched through to the copper line 160 due to side etching or other issues. Therefore, in step S8.1, when fabricating the outer layer circuit, an edge compensation amount is set on the portion of the outer layer circuit pattern above the copper line 160. This reduces the risk of the copper line 160 being etched due to side etching or other issues, thereby improving the signal shielding capability of the millimeter-wave radar circuit board. Furthermore, baking the multilayer board 100 in step S8.2 releases the internal stress of the multilayer board 100, reducing the risk of warping or deformation.

[0117] Understandably, before fabricating the outer layer circuitry in step S8.1, the surfaces of the first copper foil 110 and the second copper foil 150 can be roughened to improve the adhesion of the film during the fabrication of the outer layer circuitry. Furthermore, in step S8.1, an LDI exposure machine can be used for exposure, controlling the alignment accuracy to 25μm. Additionally, the edge compensation amount for the portion of the outer layer circuitry pattern above the copper line 160 can be set to 2-3mil, effectively reducing the risk of etching of the copper line 160 due to side etching, thereby improving the signal shielding capability of the millimeter-wave radar circuit board.

[0118] Understandably, referring to Figures 1 to 5 In step S7, during the copper plating process, in addition to forming the first copper layer 400 and the second copper layer 500, a third copper layer 600 can also be formed on the surface of the second copper foil 150. Therefore, in step S8.1, an outer layer circuit pattern can also be fabricated on the surface of the third copper foil.

[0119] It is understood that the subsequent processes in step S8 may include not only outer layer circuit fabrication and baking, but also solder resist, electrical testing, and shape processing in the normal processing flow. This invention does not specifically limit these processes.

[0120] An embodiment of the present invention also provides a millimeter-wave radar circuit board, which is formed by the processing method of the millimeter-wave radar circuit board of any of the above embodiments.

[0121] In the millimeter-wave radar circuit board of this invention, by adopting the processing method of any of the above embodiments, signal shielding can be achieved by embedding copper wires 160. Compared with the traditional method of using blind vias for signal shielding, the embedded copper wires 160 can be continuously arranged along the RF circuit pattern, thereby effectively increasing the signal shielding area and improving the signal shielding effect. Secondly, since the millimeter-wave radar circuit board of this invention does not require laser blind vias during processing, it also eliminates the need for blackening, de-blackening, plasma adhesive removal, via-filling electroplating, copper reduction, and other processes, greatly shortening the processing flow and thus improving the processing efficiency of the millimeter-wave radar circuit board.

[0122] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for fabricating a millimeter-wave radar circuit board, characterized in that, Includes the following steps: S1: Cutting materials to obtain the first PP board (120), the second PP board (140), the first copper foil (110), the second copper foil (150), the inner core board (130), and the copper wire (160). S2: The first through slot (111) is processed on the first copper foil (110) according to the radio frequency circuit pattern, and the second through slot (121) is processed on the first PP board (120) according to the radio frequency circuit pattern. S3: Inner layer circuit fabrication, fabricating inner layer circuit patterns on the inner core board (130); S4: Stacking: The second copper foil (150), the second PP board (140), the inner core board (130), the first PP board (120), and the first copper foil (110) are stacked from bottom to top to form a multilayer board (100). The side of the inner core board (130) facing the first PP board (120) is a metal surface. The first through groove (111) and the second through groove (121) are aligned, and the first through groove (111), the second through groove (121), and the upper surface of the inner core board (130) are enclosed to form an installation groove (200). The copper wire (160) is embedded in the installation groove (200). S5: Press plate, presses the stacked multilayer board (100) and the copper wire (160) together; S6: Drilling, machining through holes (300) on the multilayer board (100); S7: Copper plating, forming a first copper layer (400) on the surface of the first copper foil (110), the first copper layer (400) covering the mounting groove (200) and embedded between the copper wire (160) and the inner wall of the mounting groove (200), and forming a second copper layer (500) on the inner wall of the through hole (300). S8: Subsequent process; Step S5 includes: S5.1: Pre-pressing, a first kraft paper assembly and a first steel plate are sequentially covered on the first copper foil (110), and the first steel plate is used to pre-press the stacked copper wire (160), the second copper foil (150), the second PP board (140), the inner core board (130), the first PP board (120), and the first copper foil (110); S5.2: Hot pressing, the second kraft paper assembly and the second steel plate are sequentially covered on the first copper foil (110), and the stacked second steel plate, the second kraft paper assembly, the copper wire (160), the second copper foil (150), the second PP board (140), the inner core board (130), the first PP board (120) and the first copper foil (110) are hot pressed, with a heating rate of 2.5℃ / min; S5.3: Cold pressing, the stacked second steel plate, second kraft paper assembly, copper wire (160), second copper foil (150), second PP plate (140), inner core plate (130), first PP plate (120) and first copper foil (110) are cold pressed, the cold pressing pressure is 30 bar and the cold pressing time is 45 min; The thickness of the first copper foil (110) and the second copper foil (150) is 20 μm, the thickness of the first PP board (120) and the second PP board (140) is 125 ± 12.5 μm, the width of the mounting groove (200) is 200 μm, the width of the copper wire (160) is 190 μm-200 μm, and the thickness of the copper wire (160) is 90 μm-105 μm; Step S8 includes: S8.1: Outer layer circuit fabrication, an outer layer circuit pattern is fabricated on the surface of the first copper layer (400), and a pattern edge compensation amount is set on the part of the outer layer circuit pattern located above the copper line (160); S8.2: Baking plate, for baking the multilayer board (100) at a temperature of 120°C for 1 hour.

2. The processing method of the millimeter-wave radar circuit board according to claim 1, characterized in that, Between step S3 and step S4, a browning process is also included, in which the copper wire (160) and the inner core plate (130) are browned. The amount of copper bitten during browning is 1.4μm-1.8μm. After browning, the surface roughness Rz value of the copper wire (160) and the inner core plate (130) is 3±1μm, and the Ra value is 0.4±0.2μm.

3. The processing method of the millimeter-wave radar circuit board according to claim 2, characterized in that, When browning the copper wire (160), the copper wire (160) is fixed on a tray and passed through a browning line at a browning speed of 1.0 m / min. After browning, the copper wire (160) is dried at a temperature of 90±5℃.

4. The processing method of the millimeter-wave radar circuit board according to claim 1, characterized in that, The inner core board (130) includes at least two copper substrates (131), all of which are stacked in sequence, with a semi-cured sheet sandwiched between two adjacent copper substrates (131).

5. The processing method of the millimeter-wave radar circuit board according to claim 4, characterized in that, Step S7 includes: S7.1: Grinding plate, grinding the surfaces of the first copper foil (110) and the second copper foil (150) to remove the burrs at the through hole (300) and the residual adhesive at the mounting groove (200); S7.2: Remove adhesive residue formed on the inner wall of the through hole (300) by the semi-cured sheet layer, and remove adhesive residue formed between the copper wire (160) and the inner wall of the mounting groove (200) by the first PP layer; S7.3: Electroplating, using horizontal copper plating and pulse electroplating to form the first copper layer (400) and the second copper layer (500). In step S7.1, the copper removal thickness of the first copper foil (110) and the second copper foil (150) is 5-10 μm. In step S7.2, roughening is performed by chemical degumming; In step S7.3, the thickness of the first copper layer (400) on the surface of the first copper foil (110) is not less than 30 μm.

6. The method for processing a millimeter-wave radar circuit board according to claim 5, characterized in that, Step S7.1 includes: Abrasive belt grinding plate, wherein the abrasive belt has a mesh size of 320. ; Needle brush abrasive plate, wherein the needle brush mesh number is 320. -540 The grinding plate pressure is .

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