Multilayer circuit board and manufacturing method thereof

Abstract

The invention relates to a multilayer circuit board and a manufacturing method thereof, in the method, the opposite angles of the edge of an inner copper foil are arranged to be fillets, stress can be effectively dispersed to the outer edge, stress concentration is avoided, deformation and warping at the opposite angles are effectively avoided, and in combination with the characteristic that the size of the inner copper foil is larger than that of the outer copper foil, the thickness of the inner copper foil is larger than that of the outer copper foil. The inner copper foil can effectively support the outer copper foil, when the inner copper foil is separated from the bearing plate, the inner copper foil can better support the bonding sheet and the outer copper foil, the circuit board is effectively prevented from deforming and warping, and the inner copper foil is easier to strip from the bearing plate.

Description

Technical Field

[0001] The present invention relates to the technical field of multi - layer circuit board manufacturing, and particularly to a multi - layer circuit board and a manufacturing method thereof. Background Art

[0002] A printed circuit board (PCB) is one of the important components of electronic products. In recent years, electronic products have been developing towards being lighter, thinner, and smaller, which puts forward higher requirements for the lightweight and thinning design of printed circuit boards. However, the diversification of the functions of electronic products has put forward higher requirements for printed circuit boards. To meet the diversified functional requirements of electronic products, more components need to be arranged on the circuit board. In order to meet the requirements, multi - layer circuit boards need to be set up.

[0003] For multi - layer circuit boards, it is necessary to meet the lightweight and thinning design and carry more electrical components, which brings new challenges to the manufacturing process of printed circuit boards. Since the thickness of the printed circuit board is small, during the production process of multi - layer printed circuit boards, uneven stress distribution will occur due to asymmetric structure, resulting in problems such as deformation and warping of the circuit board. Summary of the Invention

[0004] Based on this, it is necessary to provide a multi - layer circuit board and a manufacturing method thereof.

[0005] A manufacturing method of a multi - layer circuit board includes:

[0006] Step 110: Stack the Nth outer copper foil, the Nth adhesive sheet, the first inner copper foil, the carrier plate, the second inner copper foil, the Mth adhesive sheet, and the Mth outer copper foil in sequence and then perform hot pressing to obtain a first composite board. Wherein, the first inner copper foil and the second inner copper foil are rectangular, and the diagonals of the first inner copper foil and the second inner copper foil are rounded corners. The projections of the Nth outer copper foil and the Mth outer copper foil on the carrier plate are located within the projections of the first inner copper foil and the second inner copper foil on the carrier plate, and the projections of the first inner copper foil and the second inner copper foil on the carrier plate are located within the projections of the Nth adhesive sheet and the Mth adhesive sheet on the carrier plate. Here, N and M are positive integers greater than or equal to 1.

[0007] Step 120: Drill holes and electroplate in the areas corresponding to the rounded corners of the first inner copper foil and the second inner copper foil near the Nth outer copper foil and the Mth outer copper foil to form vias. Perform graphic transfer on the first composite board to form an Nth circuit pattern on the outer surface of the Nth outer copper foil and an Mth circuit pattern on the outer surface of the Mth outer copper foil.

[0008] Step 130: Sequentially form an (N + 1)-th adhesive sheet and an (N + 1)-th outer copper foil on the outer surface of the N-th circuit pattern, and sequentially form an (M + 1)-th adhesive sheet and an (M + 1)-th outer copper foil on the outer surface of the M-th circuit pattern, wherein the projections of the first inner copper foil and the second inner copper foil on the carrier plate are located within the projections of the (N + 1)-th adhesive sheet and the (M + 1)-th adhesive sheet on the carrier plate;

[0009] Step 140: Drill holes and perform electroplating on the (N + 1)-th outer copper foil and the (M + 1)-th outer copper foil to form vias, and perform pattern transfer on the (N + 1)-th outer copper foil and the (M + 1)-th outer copper foil to form an (N + 1)-th circuit pattern and an (M + 1)-th circuit pattern;

[0010] Step 150: Separate the two sides of the carrier plate from the first inner copper foil and the second inner copper foil respectively to obtain a multilayer circuit board.

[0011] In one embodiment, the diagonals of the N-th outer copper foil, the M-th outer copper foil, the (N + 1)-th outer copper foil, and the (M + 1)-th outer copper foil are all rounded corners.

[0012] In one embodiment, among the vias formed by drilling holes and performing electroplating on the (N + 1)-th outer copper foil and the (M + 1)-th outer copper foil, at least one via is close to the area corresponding to the rounded corners of the (N + 1)-th outer copper foil and the (M + 1)-th outer copper foil.

[0013] In one embodiment, among the vias formed by drilling holes and performing electroplating on the (N + 1)-th outer copper foil and the (M + 1)-th outer copper foil, the distances between each via and the right-angle regions on the (N + 1)-th circuit pattern and the (M + 1)-th circuit pattern are greater than five times the diameter of the via.

[0014] In one embodiment, before step 110, it further includes:

[0015] Provide a first inner copper foil and a second inner copper foil;

[0016] Use laser cutting to cut the diagonals of the first inner copper foil and the second inner copper foil respectively, so that the diagonals of the first inner copper foil and the second inner copper foil form rounded corners;

[0017] Coat water-soluble polymer films on two opposite surfaces of the carrier plate.

[0018] In one embodiment, the step of separating the two sides of the carrier plate from the first inner copper foil and the second inner copper foil respectively to obtain a multilayer circuit board includes:

[0019] Laser pre-cutting is performed on the carrier plate and the first inner copper foil along two mutually perpendicular tangent directions of each rounded corner of the first inner copper foil, and laser pre-cutting is performed on the carrier plate and the second inner copper foil along two mutually perpendicular tangent directions of each rounded corner of the second inner copper foil, so as to form pre-cutting gaps between the rounded corners of the first inner copper foil and the second inner copper foil and the carrier plate;

[0020] Dissolving liquid is sprayed towards the pre-cutting gaps along two mutually perpendicular tangent directions of each rounded corner of the first inner copper foil, and dissolving liquid is sprayed towards the pre-cutting gaps along two mutually perpendicular tangent directions of each rounded corner of the second inner copper foil to dissolve the water-soluble polymer film;

[0021] The outer surface of the multilayer circuit board is adsorbed by a vacuum chuck, and the multilayer circuit board is separated from the carrier plate to obtain the multilayer circuit board.

[0022] In one embodiment, the step of separating the two sides of the carrier plate from the first inner copper foil and the second inner copper foil respectively to obtain a multilayer circuit board includes:

[0023] Steps 130 and 140 are repeated until a Pth adhesive sheet and a Pth outer copper foil are formed on the outer side of one side of the first composite board, and a Qth adhesive sheet and a Qth outer copper foil are formed on the outer side of the other side of the first composite board. The two sides of the carrier plate are separated from the first inner copper foil and the second inner copper foil respectively to obtain the multilayer circuit board, where P and Q are positive integers greater than N and M.

[0024] In one embodiment, after the step of separating the two sides of the carrier plate from the first inner copper foil and the second inner copper foil respectively to obtain a multilayer circuit board, the following steps are further included:

[0025] Drilling, electroplating, and pattern transfer are respectively performed on the outermost outer copper foil of the multilayer circuit board to form an outer layer circuit pattern.

[0026] In one embodiment, after the step of separating the two sides of the carrier plate from the first inner copper foil and the second inner copper foil respectively to obtain a multilayer circuit board, the following steps are further included:

[0027] Drilling, electroplating, and pattern transfer are respectively performed on the first inner copper foil and the second inner copper foil to form a first inner circuit pattern and a second inner circuit pattern respectively.

[0028] A multilayer circuit board is manufactured by using the manufacturing method of the multilayer circuit board in any of the above embodiments.

[0029] In the above multi-layer circuit board and its manufacturing method, the corners at the diagonal of the inner copper foil edge are set as rounded corners, which can effectively disperse stress to the outer edge, avoid stress concentration, and thus effectively avoid deformation and warping at the diagonal. Combining with the feature that the size of the inner copper foil is larger than that of the outer copper foil, the inner copper foil can effectively support the outer copper foil. When the inner copper foil is separated from the carrier board, the inner copper foil can better support the adhesive sheet and the outer copper foil, effectively avoiding deformation and warping of the circuit board, and making it easier for the inner copper foil to be peeled off from the carrier. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0031] Figure 1 Schematic diagram of a partial cross-sectional structure of a multi-layer circuit board according to an embodiment;

[0032] Figure 2A Schematic diagram of a partial cross-sectional structure during the manufacturing process of a multi-layer circuit board according to an embodiment;

[0033] Figure 2B Schematic diagram of a partial cross-sectional structure during the manufacturing process of a multi-layer circuit board according to an embodiment;

[0034] Figure 2C Schematic diagram of a partial cross-sectional structure during the manufacturing process of a multi-layer circuit board according to an embodiment;

[0035] Figure 3 Schematic diagram of the laser pre-cutting direction of a multi-layer circuit board according to an embodiment.

[0036] Description of the Reference Numerals:

[0037] 200, carrier board; 210, first inner copper foil; 220, second inner copper foil; 310, Nth adhesive sheet; 320, Mth adhesive sheet; 410, Nth outer copper foil; 420, Mth outer copper foil; 211, rounded corner; 401, via hole; 411, Nth circuit pattern; 421, Mth circuit pattern; 511, (N + 1)th adhesive sheet; 512, (N + 1)th outer copper foil; 611, (M + 1)th adhesive sheet; 612, (M + 1)th outer copper foil; Detailed Embodiments

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] As Figure 1 shown, it is a manufacturing method of a multi-layer circuit board according to an embodiment of the present invention, including:

[0040] Step 110: Stack the Nth outer copper foil, the Nth adhesive sheet, the first inner copper foil, the carrier plate, the second inner copper foil, the Mth adhesive sheet, and the Mth outer copper foil in sequence and then perform hot pressing to obtain a first composite board. Wherein, the first inner copper foil and the second inner copper foil are rectangular, and the diagonals of the first inner copper foil and the second inner copper foil are rounded corners. The projections of the Nth outer copper foil and the Mth outer copper foil on the carrier plate are located within the projections of the first inner copper foil and the second inner copper foil on the carrier plate, and the projections of the first inner copper foil and the second inner copper foil on the carrier plate are located within the projections of the Nth adhesive sheet and the Mth adhesive sheet on the carrier plate. Wherein, N and M are positive integers greater than or equal to 1.

[0041] In this step, the first inner copper foil and the second inner copper foil are respectively located on both sides of the carrier plate, and N and M are 1. As Figure 2A shown, the Nth outer copper foil 410 and the Nth adhesive sheet 310 are the first-layer adhesive sheet and outer copper foil located outside the first inner copper foil 210, and the Mth outer copper foil 420 and the Mth adhesive sheet 320 are the first-layer adhesive sheet and outer copper foil located outside the second inner copper foil 220. Stack each core board in the order of the Nth outer copper foil 410, the Nth adhesive sheet 310, the first inner copper foil 210, the carrier plate 200, the second inner copper foil 220, the Mth adhesive sheet 320, and the Mth outer copper foil 420, and then perform hot pressing to obtain a first composite board. Wherein, the first inner copper foil 210 and the second inner copper foil 220 are symmetrically arranged, and the Nth outer copper foil 410 and the Mth outer copper foil 420 are symmetrically arranged.

[0042] In the prior art CN102186316A, the size of the inner copper foil is smaller than that of the outer copper foil, resulting in the inability of the inner copper foil to fully support the outer copper foil when peeling off from the carrier plate, which easily causes deformation and warping of the edges of the outer copper foil. In this embodiment, the areas of the projections of the first inner copper foil and the second inner copper foil on the carrier plate are larger than the areas of the projections of the Nth outer copper foil and the Mth outer copper foil on the carrier plate, such that the projections of the Nth outer copper foil and the Mth outer copper foil on the carrier plate are completely located within the projections of the first inner copper foil and the second inner copper foil on the carrier plate, and the areas of the projections of the respective bonding sheets on the carrier plate are greater than or equal to the areas of the projections of the first inner copper foil and the second inner copper foil on the carrier plate, such that the projections of the first inner copper foil and the second inner copper foil on the carrier plate are completely located within the projections of the Nth bonding sheet and the Mth bonding sheet on the carrier plate. In this way, due to the larger area of the bonding sheet, the bonding sheet can better connect the inner copper foil and the outer copper foil.

[0043] In this embodiment, the diagonals of the inner copper foil are rounded corners, which can effectively disperse stress and avoid edge warping due to stress concentration. It is worth mentioning that the diagonals of traditional inner copper foils are right angles without rounding treatment. Due to the sharp geometric shape in the right-angle area, stress concentration is likely to occur during hot pressing, cutting, or use, which easily causes the copper foil hull, and even leads to copper foil cracking or delamination. Therefore, in this embodiment, the rounded-corner shape of the diagonals of the inner copper foil can effectively disperse the stress to the outer edges, avoid stress concentration, thereby effectively avoiding deformation and warping at the diagonals, effectively supporting the bonding sheet and the outer copper foil, making the formed circuit board flatter, and improving the product yield.

[0044] It is worth mentioning that since the area of the inner copper foil is larger than that of the outer copper foil and the inner copper foil is directly connected to the carrier plate, in this way, the inner copper foil can effectively support the outer copper foil. When the inner copper foil is separated from the carrier plate, the inner copper foil can better support the bonding sheet and the outer copper foil, effectively avoiding deformation and warping of the circuit board, and making it easier for the inner copper foil to peel off from the carrier.

[0045] Step 120: Drill holes and electroplate in the areas corresponding to the rounded corners of the first inner copper foil and the second inner copper foil that are close to the Nth outer copper foil and the Mth outer copper foil to form vias, perform pattern transfer on the first composite board, form the Nth circuit pattern on the outer surface of the Nth outer copper foil, and form the Mth circuit pattern on the outer surface of the Mth outer copper foil.

[0046] In this step, as Figure 2BAs shown, drilling and electroplating are performed in the regions corresponding to the rounded corners of the Nth outer copper foil 410 and the Mth outer copper foil 420 near the first inner copper foil 210 and the second inner copper foil 220 to form vias 401. Pattern transfer is performed on the first composite board, and an Nth circuit pattern 411 is formed on the outer surface of the Nth outer copper foil, and an Mth circuit pattern 421 is formed on the outer surface of the Mth outer copper foil.

[0047] Specifically, vias 401 are made on the Nth outer copper foil 410 and the Mth outer copper foil 420, and vias 401 are made only in the regions corresponding to the rounded corners of the first inner copper foil 210 and the second inner copper foil 220. In this embodiment, laser drilling is performed on the outer copper foil, and chemical copper deposition and copper electroplating are performed in the holes to form vias connecting the inner copper foil and the outer copper foil in the region near the rounded corners. In this embodiment, the vias are arranged in the region near the rounded corners. On the one hand, the vias connect the adjacent inner copper foil and outer copper foil, playing a connecting and supporting role. The vias can effectively utilize the stress dispersion effect of the rounded corners of the inner copper foil to tighten, support and fix the outer copper foil, so that the corresponding region of the outer copper foil can remain flat and avoid deformation and warping. On the other hand, since the diagonals of the inner copper foils are rounded, the phenomenon of sharp electric field concentration formed by the vias and the right-angle edges is avoided, and the enhancement of capacitive coupling is avoided. The electric field gradient changes gently along the edges of the rounded corners in the rounded corner region of the inner copper foil, and the capacitive energy density is reduced, which can effectively reduce the parasitic capacitance of the vias.

[0048] In addition, in this embodiment, laser imaging technology is used to perform pattern transfer on the outer copper foils on both sides of the first composite board to form the Nth circuit pattern and the Mth circuit pattern.

[0049] Step 130, an (N + 1)th adhesive sheet and an (N + 1)th outer copper foil are sequentially formed on the outer surface of the Nth circuit pattern, and an (M + 1)th adhesive sheet and an (M + 1)th outer copper foil are sequentially formed on the outer surface of the Mth circuit pattern, wherein the projections of the first inner copper foil and the second inner copper foil on the carrier board are located within the projections of the (N + 1)th adhesive sheet and the (M + 1)th adhesive sheet on the carrier board.

[0050] In this embodiment, as Figure 2CAs shown, a (N + 1)th adhesive sheet 511 and a (N + 1)th outer copper foil 512 are sequentially formed on the outer surface of the Nth circuit pattern 411, and a (M + 1)th adhesive sheet 611 and a (M + 1)th outer copper foil 612 are sequentially formed on the outer surface of the Mth circuit pattern 421. The area of the projection of each adhesive sheet on the carrier plate is greater than or equal to the area of the projection of the first inner copper foil and the second inner copper foil on the carrier plate, so that the adhesive sheet can better connect adjacent outer copper foils. In addition, the area of the projection of the (N + 1)th outer copper foil and the (M + 1)th outer copper foil on the carrier plate is equal to the area of the projection of the Nth outer copper foil and the Mth outer copper foil on the carrier plate. In this embodiment, build-up layers are respectively carried out on the outer sides of both sides of the first composite board to respectively form the (N + 1)th adhesive sheet and the (N + 1)th outer copper foil, and the (M + 1)th adhesive sheet and the (M + 1)th outer copper foil.

[0051] Step 140: Drill holes and perform electroplating on the (N + 1)th outer copper foil and the (M + 1)th outer copper foil to form vias, and perform pattern transfer on the (N + 1)th outer copper foil and the (M + 1)th outer copper foil to form a (N + 1)th circuit pattern and a (M + 1)th circuit pattern.

[0052] In this embodiment, laser drilling is performed on the outer copper foil of the outer layer, chemical copper plating and electroplating copper are performed in the holes to form vias connecting the outer copper foils of adjacent layers, and laser imaging technology is used to perform pattern transfer on the outer copper foil of the outer layer to form a (N + 1)th circuit pattern and a (M + 1)th circuit pattern.

[0053] Step 150: Separate the two sides of the carrier plate from the first inner copper foil and the second inner copper foil respectively to obtain a multilayer circuit board.

[0054] In this step, laser cutting is used to cut and separate the first inner copper foil and the second inner copper foil from the carrier plate respectively to obtain two independent multilayer circuit boards.

[0055] In this embodiment, the corners of the diagonal of the inner copper foil are set as rounded corners, which can effectively disperse the stress to the outer edge, avoid stress concentration, thereby effectively avoiding deformation and warping at the diagonal corners, and combined with the feature that the size of the inner copper foil is larger than the size of the outer copper foil, the inner copper foil can effectively support the outer copper foil. When the inner copper foil is separated from the carrier plate, the inner copper foil can better support the adhesive sheet and the outer copper foil, effectively avoiding deformation and warping of the circuit board, and making it easier for the inner copper foil to be peeled off from the carrier.

[0056] In one embodiment, the diagonals of the Nth outer copper foil, the Mth outer copper foil, the (N + 1)th outer copper foil, and the (M + 1)th outer copper foil are all rounded corners.

[0057] In this embodiment, the diagonals of the outer copper foils of each layer are all set as rounded corners, which can effectively disperse the stress at the diagonals of the outer copper foils of each layer to the edges, effectively avoid the stress concentration of the outer copper foils of each layer, and further avoid the deformation and warping of the multi-layer circuit board at the diagonals.

[0058] In one embodiment, in the vias formed by drilling and electroplating on the (N + 1)-th outer copper foil and the (M + 1)-th outer copper foil, at least one via is close to the region corresponding to the rounded corners of the (N + 1)-th outer copper foil and the (M + 1)-th outer copper foil.

[0059] In this embodiment, the vias are used to connect the circuit patterns of different layers to achieve electrical conduction between the circuits of different layers. In this embodiment, the vias are arranged in the region close to the rounded corners. On the one hand, the vias connect the adjacent outer copper foils and play a role of connection and support. The vias can effectively utilize the stress dispersion effect of the rounded corners of the adjacent outer copper foils, so that the outer copper foils generate mutual forces in the rounded corner region, enabling the corresponding regions of the outer copper foils to remain flat and avoiding deformation and warping. On the other hand, since the diagonals of the copper foils of each layer are set as rounded corners, the phenomenon of sharp electric field concentration formed by the vias and the right-angle edges is avoided, and the enhancement of capacitive coupling is avoided. The electric field gradient changes gently along the edge of the rounded corner in the rounded corner region of the outer copper foil, and the capacitive energy density is reduced, which can effectively reduce the parasitic capacitance of the vias.

[0060] In one embodiment, vias are respectively arranged in the regions corresponding to the rounded corners of the four diagonals of the (N + 1)-th outer copper foil and the (M + 1)-th outer copper foil close to the first inner copper foil, that is, one via is arranged in the rounded corner region of each diagonal, which can enable the outer copper foils to be evenly stressed in the four diagonal regions.

[0061] In one embodiment, the distance between the via in the region corresponding to the rounded corner of the first inner copper foil and the rounded corner of the second inner copper foil and the edge of the rounded corner of the first inner copper foil or the edge of the rounded corner of the second inner copper foil is greater than three times the rounded corner radius and less than four times the rounded corner radius.

[0062] It should be understood that although rounded corners can effectively reduce the parasitic capacitance of the adjacent vias compared to right angles, parasitic capacitance may still be generated due to edge electric field coupling. Therefore, the distance between the via and the edge of the rounded corner should be as large as possible. The larger the distance between the via and the edge of the rounded corner, the smaller the parasitic capacitance generated by edge electric field coupling, and even zero. However, in this embodiment, the via also plays a role in supporting the outer copper foil by dispersing the stress of the rounded corner of the inner copper foil. Therefore, the via should not be too far away from the edge of the rounded corner. If the distance between the via and the edge of the rounded corner is too large, the stress dispersion effect of the rounded corner cannot be used to support the outer copper foil. Therefore, in this embodiment, the distance between the via and the edge of the rounded corner of the rounded corner close to the first inner copper foil and the rounded corner of the second inner copper foil is greater than three times the radius of the rounded corner and less than four times the radius of the rounded corner, which can effectively reduce the parasitic capacitance and can effectively utilize the stress dispersion of the rounded corner of the inner copper foil to tighten, support and fix the outer copper foil, so that the corresponding area of the outer copper foil can remain flat and avoid deformation and warping.

[0063] In one embodiment, for the vias in the area corresponding to the rounded corners of the (N + 1)-th outer copper foil and the (M + 1)-th outer copper foil, the distance between the via and the edge of the rounded corner of the (N + 1)-th outer copper foil or the edge of the rounded corner of the (M + 1)-th outer copper foil is greater than three times the radius of the rounded corner and less than four times the radius of the rounded corner.

[0064] In this embodiment, similarly, to reduce the parasitic capacitance, the distance between the via on the outer copper foil close to the rounded corner and the edge of the rounded corner should be as large as possible. However, at the same time, in order to utilize the stress dispersion of the rounded corners of each outer copper foil to make the outer copper foils support each other and avoid warping, the via should not be too far away from the edge of the rounded corner. Therefore, the distance between the via close to the rounded corner of the outer copper foil and the edge of the rounded corner is greater than three times the radius of the rounded corner and less than four times the radius of the rounded corner, which can effectively reduce the parasitic capacitance and can effectively utilize the stress dispersion of the rounded corner of the outer copper foil to tighten, support and fix the adjacent-layer outer copper foils, so that the corresponding area of the outer copper foil can remain flat and avoid deformation and warping.

[0065] In one embodiment, in the vias formed by drilling and electroplating on the (N + 1)-th outer copper foil and the (M + 1)-th outer copper foil, the distance between each via and the right-angled area on the (N + 1)-th circuit pattern and the right-angled area on the (M + 1)-th circuit pattern is greater than five times the diameter of the via.

[0066] In this embodiment, after pattern transfer, the circuit pattern forms a right-angle region, and the distance between each via and the right-angle region is greater than five times the diameter of the via. This can keep the vias away from the right-angle region and effectively avoid the formation of sharp electric field concentration at the edge of the right-angle region, which may cause via capacitance coupling and generate a large parasitic capacitance. It should be understood that after pattern transfer, there may be multiple right-angle regions on the formed circuit pattern, and these right-angle regions are not the right angles of the diagonal of the original outer copper foil. For vias, they can only try to avoid these right-angle regions as much as possible and stay away from them, but it is impossible to completely stay away. If completely staying away, it will affect the circuit structure. Therefore, in this embodiment, the distance between each of the vias and the right-angle regions on the (N + 1)-th circuit pattern and the right-angle regions on the (M + 1)-th circuit pattern is greater than five times the diameter of the via, which can effectively avoid the formation of sharp electric field concentration at the edge of the right-angle region, causing via capacitance coupling and generating a large parasitic capacitance, without affecting the overall structure of the circuit pattern.

[0067] In one embodiment, before step 110, it further includes: providing a first inner copper foil and a second inner copper foil; using laser cutting to cut the diagonals of the first inner copper foil and the second inner copper foil respectively, so that the diagonals of the first inner copper foil and the second inner copper foil form rounded corners; coating water-soluble polymer films on two opposite surfaces of the carrier plate.

[0068] In this embodiment, a rectangular first inner copper foil and a second inner copper foil are provided, and the diagonals of the rectangular first copper foil and the second copper foil are cut by laser to form rounded corners. In addition, in this embodiment, before stacking the first inner copper foil and the second inner copper foil on the carrier plate, first, water-soluble polymer films are coated on two opposite surfaces of the carrier plate. For example, the material of the water-soluble polymer film is polyvinyl alcohol, and the water-soluble polymer film has water solubility and can dissolve in water. In this embodiment, a water-soluble polymer solution is coated on two opposite surfaces of the carrier plate, and after drying, water-soluble polymer films are formed on two opposite surfaces of the carrier plate. The thickness of the water-soluble polymer film is 10 μm to 30 μm. In step 110, the first inner copper foil and the second inner copper foil are stacked on the water-soluble polymer film of the carrier plate. Subsequently, the N-th outer copper foil, the N-th adhesive sheet, the first inner copper foil, the carrier plate, the second inner copper foil, the M-th adhesive sheet, and the M-th outer copper foil are stacked in sequence and then hot-pressed to obtain a first composite board. It is worth mentioning that the water-soluble polymer film has flexibility. Compared with the rigid carrier plate, it has higher flexibility, can provide buffering for the inner copper foil, effectively avoid rigid contact between the carrier plate and the inner copper foil, and avoid the inner copper foil being bent backward by the reaction force of the carrier plate during the hot-pressing process due to rigid contact.

[0069] In one embodiment, the step of separating the two sides of the carrier board from the first inner copper foil and the second inner copper foil respectively to obtain a multilayer circuit board includes: laser pre-cutting the carrier board and the first inner copper foil along two mutually perpendicular tangent directions of each rounded corner of the first inner copper foil, and laser pre-cutting the carrier board and the second inner copper foil along two mutually perpendicular tangent directions of each rounded corner of the second inner copper foil, so as to form pre-cutting gaps between the rounded corners of the first inner copper foil and the second inner copper foil and the carrier board; spraying a dissolving liquid towards the pre-cutting gaps along two mutually perpendicular tangent directions of the respective rounded corners of the first inner copper foil, and spraying a dissolving liquid towards the pre-cutting gaps along two mutually perpendicular tangent directions of the respective rounded corners of the second inner copper foil to dissolve the water-soluble polymer film; adsorbing the outer surface of the multilayer circuit board by a vacuum chuck, and separating the multilayer circuit board from the carrier board to obtain the multilayer circuit board.

[0070] It is worth mentioning that for a rounded corner, the two mutually perpendicular tangent directions thereof are the directions of two sides of the rectangle connected to the rounded corner. As Figure 3 shown, the arrow direction in the figure is the direction of laser pre-cutting. The core board is placed horizontally, and the laser cuts along two mutually perpendicular tangent directions of the rounded corner 211 of the first inner copper foil 210. In this embodiment, pre-cutting the carrier board and the inner copper foil along the tangent direction of the rounded corner makes the peeling force direction of the inner copper foil consistent with the tangent direction of the rounded corner, avoiding shear stress and effectively reducing the warping degree of the rounded corner. It should be understood that if directly cutting at the rounded corner, it may cause warping of the rounded corner. In this embodiment, since the tangent direction of the rounded corner is parallel to one side of the inner copper foil, the side of the inner copper foil can be separated from the carrier board during pre-cutting, realizing the simultaneous separation of the rounded corner and the side of the inner copper foil and avoiding local warping. During the laser pre-cutting process, gradually cut and move towards the middle of the carrier board and the inner copper foil, so as to form a pre-cutting gap between the inner copper foil and the carrier board, facilitating the injection of the dissolving liquid.

[0071] Subsequently, a dissolving solution is sprayed along the tangential direction into the pre-cut gap. For example, the dissolving solution is sprayed using a water gun. For example, the dissolving solution is water. For example, the dissolving solution is warm water at 40°C to 60°C. The water-soluble polymer film between the inner copper foil and the carrier plate is dissolved by the dissolving solution, effectively reducing the adhesion between the inner copper foil and the carrier plate. Moreover, the dissolving solution gradually penetrates along the tangential direction towards the edge outside the rounded corner of the inner copper foil, enabling the entire edge of the inner copper foil to first separate from the carrier plate and gradually peel from the middle of the edge towards the inside. Subsequently, a vacuum chuck is pressed on the outer surfaces of the multi-layer circuit boards on both sides, and before the water-soluble polymer film is completely dissolved, the vacuum chuck is kept pressed on the surface of the multi-layer circuit board under the action of a hydraulic device. The pressure of the vacuum chuck and the tension of the liquid between the inner copper foil and the carrier plate are used to apply pressure to both sides of the multi-layer circuit board to keep the multi-layer circuit board flat. It is worth mentioning that the number of vacuum chucks is multiple, and the multiple vacuum chucks are respectively pressed on the middle and edges of the outer sides of the multi-layer circuit board, thereby keeping the force on the multi-layer circuit board uniform and avoiding deformation. When the water-soluble polymer film is completely dissolved, the outer surface of the multi-layer circuit board is adsorbed by the vacuum chuck, and the multi-layer circuit board is peeled from the carrier plate using the adsorption force. Since the rounded corner area of the edge of the inner copper foil separates first, the inner copper foil can be easily peeled from the carrier plate, effectively avoiding warping and deformation of the multi-layer circuit board. It is worth mentioning that after removing the water-soluble polymer film, the carrier plate can be reused.

[0072] Compared with the traditional method of separating the inner copper foil from the carrier plate by laser cutting, in this embodiment, by combining laser cutting and dissolving the water-soluble polymer film, it can effectively avoid deformation and warping of the multi-layer circuit board caused by high temperature and stress changes during the cutting process. Moreover, the ratio of the pre-cutting travel of the laser to the spraying travel of the dissolving solution in the gap between the inner copper foil and the carrier plate is 1:2, enabling the dissolving solution to quickly penetrate between the inner copper foil and the carrier plate and using the tension of the solution to maintain the support of the multi-layer circuit board.

[0073] In one embodiment, after the multi-layer circuit board is peeled from the carrier plate, the multi-layer circuit board is dried to remove the moisture on the surface of the multi-layer circuit board.

[0074] In one embodiment, the step of separating the two sides of the carrier plate from the first inner copper foil and the second inner copper foil respectively to obtain the multi-layer circuit board includes:

[0075] Steps 130 and 140 are repeated until a Pth bonding sheet and a Pth outer copper foil are formed on the outer side of one side of the first composite board, and a Qth bonding sheet and a Qth outer copper foil are formed on the outer side of the other side of the first composite board. The two sides of the carrier plate are separated from the first inner copper foil and the second inner copper foil respectively to obtain the multi-layer circuit board, where P and Q are positive integers greater than N and M.

[0076] In this embodiment, multiple layers of outer copper foils can be respectively arranged on both sides of the carrier board, and each outer copper foil is connected to the adjacent outer copper foil through an adhesive sheet. In this way, starting from the Nth layer to the (N + 1)th layer, they gradually accumulate to form P layers of outer copper foils. It should be noted that N and M are positive integers greater than or equal to 1. For example, when N is 1, the Nth outer copper foil is the first outer copper foil outside the inner copper foil, and the (N + 1)th outer copper foil is the second outer copper foil outside the inner copper foil. When steps 130 and 140 are repeated, the original (N + 1)th outer copper foil can be regarded as the new Nth outer copper foil. At this time, when N is 2, the Nth outer copper foil is the second outer copper foil outside the inner copper foil, and the (N + 1)th outer copper foil is the third outer copper foil outside the inner copper foil. By continuously repeating steps 130 to 140 in this way, until the Pth layer of outer copper foil and the Qth layer of outer copper foil are respectively formed on both sides of the carrier board, a multi-layer core board is obtained. It should be noted that the values of P and Q in the Pth adhesive sheet, the Pth outer copper foil, the Qth adhesive sheet, and the Qth outer copper foil can be selected according to the requirements of the multi-layer circuit board.

[0077] In one embodiment, after the step of separating the two sides of the carrier board from the first inner copper foil and the second inner copper foil respectively to obtain a multi-layer circuit board, the following steps are further included:

[0078] Drilling, electroplating, and pattern transfer are respectively performed on the outermost layer of outer copper foils of the multi-layer circuit board to form outer circuit patterns.

[0079] In this embodiment, before the multi-layer circuit board is peeled off from the carrier board, drilling, electroplating, and pattern transfer are not performed on the outermost layer of outer copper foils, so that the outermost layer of outer copper foils remains intact, which can better support the circuit board and avoid deformation during the peeling process. After the multi-layer circuit board is peeled off, drilling, electroplating, and pattern transfer are respectively performed on the outermost layer of outer copper foils to form outer circuit patterns on the outermost side of the multi-layer circuit board.

[0080] In one embodiment, after the step of separating the two sides of the carrier board from the first inner copper foil and the second inner copper foil respectively to obtain a multi-layer circuit board, the following steps are further included: Drilling, electroplating, and pattern transfer are respectively performed on the first inner copper foil and the second inner copper foil to form a first inner circuit pattern and a second inner circuit pattern.

[0081] In this embodiment, after the multi-layer circuit board is separated from the carrier board, the first inner copper foil and the second inner copper foil are exposed. Subsequently, laser drilling is respectively performed on the parts of the first inner copper foil outside the rounded corner area and the second inner copper foil outside the rounded corner area of the two multi-layer circuit boards. Chemical copper deposition and copper electroplating are performed in the holes to form vias connecting the inner copper foil and the outer copper foil, and laser imaging technology is used for pattern transfer on the inner copper foil to form a first inner circuit pattern and a second inner circuit pattern.

[0082] It is worth mentioning that before the inner copper foil is peeled off from the carrier plate, only the rounded corner area is connected to the outer copper foil of the defined layer through vias. This can maintain the integrity of the inner copper foil, better support the circuit board, avoid deformation during the peeling process, and the vias in the rounded corner area can be used to support the outer copper foil to avoid warping at the diagonal corners. And setting some vias in the rounded corner area can effectively reduce the parasitic capacitance. After the inner copper foil is peeled off from the carrier plate, vias are made in the remaining part of the inner copper foil, and circuit patterns are made to obtain a multilayer circuit board.

[0083] In one embodiment, a multilayer circuit board is provided, which is manufactured by using the manufacturing method of the multilayer circuit board described in any of the above embodiments.

[0084] In one embodiment, an electronic device is provided, and the electronic device includes the multilayer circuit board in any of the above embodiments.

[0085] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0086] The above-described embodiments only represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A method for manufacturing a multi-layer circuit board, characterized in that, Including: Step 110: Stack the Nth outer copper foil, the Nth adhesive sheet, the first inner copper foil, the carrier plate, the second inner copper foil, the Mth adhesive sheet, and the Mth outer copper foil in sequence and then perform hot pressing to obtain a first composite board. Wherein, the first inner copper foil and the second inner copper foil are rectangular, and the diagonals of the first inner copper foil and the second inner copper foil are rounded corners. The projections of the Nth outer copper foil and the Mth outer copper foil on the carrier plate are located within the projections of the first inner copper foil and the second inner copper foil on the carrier plate, and the projections of the first inner copper foil and the second inner copper foil on the carrier plate are located within the projections of the Nth adhesive sheet and the Mth adhesive sheet on the carrier plate. Here, N and M are positive integers greater than or equal to 1. Step 120: Drill holes and perform electroplating in the areas corresponding to the rounded corners of the first inner copper foil and the second inner copper foil that are close to the Nth outer copper foil and the Mth outer copper foil to form vias. Perform pattern transfer on the first composite board to form an Nth circuit pattern on the outer surface of the Nth outer copper foil and an Mth circuit pattern on the outer surface of the Mth outer copper foil. Step 130: Sequentially form an (N + 1)th adhesive sheet and an (N + 1)th outer copper foil on the outer surface of the Nth circuit pattern, and sequentially form an (M + 1)th adhesive sheet and an (M + 1)th outer copper foil on the outer surface of the Mth circuit pattern. Wherein, the projections of the first inner copper foil and the second inner copper foil on the carrier plate are located within the projections of the (N + 1)th adhesive sheet and the (M + 1)th adhesive sheet on the carrier plate. Step 140: Drill holes and perform electroplating on the (N + 1)th outer copper foil and the (M + 1)th outer copper foil to form vias, and perform pattern transfer on the (N + 1)th outer copper foil and the (M + 1)th outer copper foil to form an (N + 1)th circuit pattern and an (M + 1)th circuit pattern. Step 150: Separate the two sides of the carrier plate from the first inner copper foil and the second inner copper foil respectively to obtain a multilayer circuit board.

2. The manufacturing method of the multi-layer circuit board according to claim 1, wherein The diagonals of the Nth outer copper foil, the Mth outer copper foil, the (N + 1)th outer copper foil, and the (M + 1)th outer copper foil are all rounded corners.

3. The method for manufacturing a multilayer circuit board according to claim 2, wherein, Among the vias formed by drilling holes and performing electroplating on the (N + 1)th outer copper foil and the (M + 1)th outer copper foil, at least one via is close to the areas corresponding to the rounded corners of the (N + 1)th outer copper foil and the (M + 1)th outer copper foil.

4. The method for manufacturing a multilayer circuit board according to claim 1, wherein Among the vias formed by drilling holes and performing electroplating on the (N + 1)th outer copper foil and the (M + 1)th outer copper foil, the distances between each via and the right-angle areas on the (N + 1)th circuit pattern and the (M + 1)th circuit pattern are greater than five times the diameter of the via.

5. The method for manufacturing a multilayer circuit board according to claim 1, wherein Before the step 110, it further includes: Providing a first inner copper foil and a second inner copper foil; Using laser cutting to cut the diagonals of the first inner copper foil and the second inner copper foil respectively, so that the diagonals of the first inner copper foil and the second inner copper foil form rounded corners; Coating a water-soluble polymer film on the two opposite surfaces of the carrier plate.

6. The manufacturing method of the multilayer circuit board according to claim 5, characterized in that, The step of separating the two sides of the carrier board from the first inner copper foil and the second inner copper foil respectively to obtain a multilayer circuit board includes: Laser pre-cutting the carrier board and the first inner copper foil along two mutually perpendicular tangent directions of each rounded corner of the first inner copper foil, and laser pre-cutting the carrier board and the second inner copper foil along two mutually perpendicular tangent directions of each rounded corner of the second inner copper foil, so as to form pre-cutting gaps between the rounded corners of the first inner copper foil and the second inner copper foil and the carrier board; Spraying a dissolving solution towards the pre-cutting gaps along two mutually perpendicular tangent directions of the rounded corners of the first inner copper foil, and spraying a dissolving solution towards the pre-cutting gaps along two mutually perpendicular tangent directions of the rounded corners of the second inner copper foil to dissolve the water-soluble polymer film; Using a vacuum chuck to adsorb the outer surface of the multilayer circuit board, separating the multilayer circuit board from the carrier board to obtain the multilayer circuit board.

7. The method for manufacturing a multilayer circuit board according to any one of claims 1-6, characterized in that, The step of separating the two sides of the carrier board from the first inner copper foil and the second inner copper foil respectively to obtain a multilayer circuit board includes: Repeating step 130 and step 140 until a Pth adhesive sheet and a Pth outer copper foil are formed on the outer side of one side of the first composite board, and a Qth adhesive sheet and a Qth outer copper foil are formed on the outer side of the other side of the first composite board, separating the two sides of the carrier board from the first inner copper foil and the second inner copper foil respectively to obtain the multilayer circuit board, where P and Q are positive integers greater than N and M.

8. The method for manufacturing a multilayer circuit board according to claim 7, wherein After the step of separating the two sides of the carrier board from the first inner copper foil and the second inner copper foil respectively to obtain a multilayer circuit board, the following steps are further included: Drilling, electroplating, and pattern transfer are respectively performed on the outermost outer copper foil of the multilayer circuit board to form an outer circuit pattern.

9. The method for manufacturing a multilayer circuit board according to claim 7, characterized in that, After the step of separating the two sides of the carrier board from the first inner copper foil and the second inner copper foil respectively to obtain a multilayer circuit board, the following steps are further included: Drilling, electroplating, and pattern transfer are respectively performed on the first inner copper foil and the second inner copper foil to form a first inner circuit pattern and a second inner circuit pattern respectively.

10. A multilayer circuit board, characterized in that, Manufactured by using the multilayer circuit board manufacturing method described in any one of claims 1-9.

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