A multilayer circuit board and a method of manufacturing the same

Abstract

The present application relates to a multilayer circuit board and a manufacturing method thereof, wherein the corners of the edges of the inner copper foil are rounded, stress can be effectively dispersed to the outer edges, stress concentration is avoided, deformation and warping at the corners are effectively avoided, and in combination 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, the inner copper foil can better support the adhesive sheet and the outer copper foil when the inner copper foil is separated from the carrier plate, circuit board deformation and warping are effectively avoided, and the inner copper foil is easier to peel off from the carrier.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of multilayer circuit board manufacturing, in particular to a multilayer circuit board and a manufacturing method thereof. BACKGROUND

[0002] Printed Circuit Board, referred to as PCB, is one of the important components of electronic products. In recent years, electronic products are developing towards lighter, thinner and smaller, and higher requirements are put forward for the light and thin design of printed circuit boards. However, the diversification of the functions of electronic products puts forward higher requirements on printed circuit boards. In order to meet the diversified functional requirements of electronic products, more components need to be arranged on the circuit board, and the printed circuit board needs to be provided with multiple layers to meet the requirements.

[0003] For a multilayer circuit board, it is necessary to meet the light and thin design and carry more electrical components, which brings new challenges to the manufacturing process of the printed circuit board. Because the thickness of the printed circuit board is small, during the production process of the multilayer printed circuit board, the stress distribution is uneven due to the asymmetric structure, and problems such as deformation and warping of the circuit board occur. SUMMARY

[0004] Therefore, it is necessary to provide a multilayer circuit board and a manufacturing method thereof.

[0005] A manufacturing method of a multilayer circuit board comprises the following steps.

[0006] In step 110, the Nth outer copper foil, the Nth bonding sheet, the first inner copper foil, the carrier plate, the second inner copper foil, the Mth bonding sheet and the Mth outer copper foil are stacked in sequence and then hot-pressed to obtain a first composite plate. 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. 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 bonding sheet and the Mth bonding sheet on the carrier plate. N and M are positive integers greater than or equal to 1.

[0007] In step 120, holes are drilled and electroplated in the regions of the Nth outer copper foil and the Mth outer copper foil close to the rounded corners of the first inner copper foil and the second inner copper foil to form vias. The first composite plate is subjected to pattern transfer 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 forming an N+1 bonding sheet and an N+1 outer copper foil on the outer side surface of the Nth circuit pattern, and sequentially forming an M+1 bonding sheet and an M+1 outer copper foil on the outer side 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 bonding sheet and the M+1 bonding sheet on the carrier plate;

[0009] Step 140, drilling, electroplating, forming vias on the N+1 outer copper foil and the M+1 outer copper foil, and performing pattern transfer on the N+1 outer copper foil and the M+1 outer copper foil to form an N+1 circuit pattern and an M+1 circuit pattern;

[0010] Step 150, separating the two surfaces 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 of the embodiments, the corners of the Nth outer copper foil, the corners of the Mth outer copper foil, the corners of the N+1 outer copper foil, and the corners of the M+1 outer copper foil are all rounded corners.

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

[0013] In one of the embodiments, among the vias formed by drilling and electroplating on the N+1 outer copper foil and the M+1 outer copper foil, each via is more than five times the aperture of the via away from the right-angled area on the N+1 circuit pattern and the right-angled area on the M+1 circuit pattern.

[0014] In one of the embodiments, the step 110 further comprises:

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

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

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

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

[0019] laser pre-cutting the carrier plate and the first inner copper foil along two mutually perpendicular tangent directions of each of the rounded corners of the first inner copper foil, and laser pre-cutting the carrier plate and the second inner copper foil along two mutually perpendicular tangent directions of each of the rounded corners of the second inner copper foil, so that the rounded corners of the first inner copper foil and the rounded corners of the second inner copper foil form pre-cutting gaps with the carrier plate;

[0020] spraying a dissolving solution along two mutually perpendicular tangent directions of each of the rounded corners of the first inner copper foil towards the pre-cutting gaps, and spraying a dissolving solution along two mutually perpendicular tangent directions of each of the rounded corners of the second inner copper foil towards the pre-cutting gaps, to dissolve the water-soluble polymer film;

[0021] separating the multilayer circuit board from the carrier plate by using a vacuum chuck to adsorb the outer surface of the multilayer circuit board, to obtain the multilayer circuit board.

[0022] In one of the embodiments, the step of separating the two surfaces of the carrier plate from the first inner copper foil and the second inner copper foil respectively to obtain the multilayer circuit board comprises:

[0023] repeating the steps 130 and 140 until the Pth layer of adhesive sheets and the Pth layer of outer copper foils are formed on the outer side of one side of the first composite plate, and the Qth layer of adhesive sheets and the Qth layer of outer copper foils are formed on the outer side of the other side of the first composite plate, and the two surfaces 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, wherein P and Q are positive integers greater than N and M.

[0024] In one of the embodiments, the step of separating the two surfaces of the carrier plate from the first inner copper foil and the second inner copper foil respectively to obtain the multilayer circuit board further comprises:

[0025] drilling, electroplating and pattern transferring are performed on the outer copper foils of the outermost layers of the multilayer circuit board respectively to form outer circuit patterns.

[0026] In one of the embodiments, the step of separating the two surfaces of the carrier plate from the first inner copper foil and the second inner copper foil respectively to obtain the multilayer circuit board further comprises:

[0027] drilling, electroplating and pattern transferring are performed on the first inner copper foil and the second inner copper foil respectively to form first inner circuit patterns and second inner circuit patterns respectively.

[0028] A multilayer circuit board manufactured by the method for manufacturing a multilayer circuit board according to any one of the embodiments.

[0029] The multilayer circuit board and the manufacturing method thereof set the corners of the edges of the inner copper foil as round corners, can effectively disperse stress to the outer edges, avoid stress concentration, effectively avoid deformation and warping at the corners, and combine the feature that the size of the inner copper foil is larger than the size of the outer copper foil, so that the inner copper foil can effectively support the outer copper foil, the inner copper foil can better support the adhesive sheet and the outer copper foil when the inner copper foil is separated from the carrier plate, effectively avoid deformation and warping of the circuit board, and make the inner copper foil more simple when it is peeled off from the carrier. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0031] Figure 1 A flowchart of a manufacturing method of a multilayer circuit board of an embodiment;

[0032] Figure 2A A partial cross-sectional structure schematic diagram in a manufacturing process of a multilayer circuit board of an embodiment;

[0033] Figure 2B A partial cross-sectional structure schematic diagram in a manufacturing process of a multilayer circuit board of an embodiment;

[0034] Figure 2C A partial cross-sectional structure schematic diagram in a manufacturing process of a multilayer circuit board of an embodiment;

[0035] Figure 3 A laser pre-cutting direction schematic diagram of a multilayer circuit board of an embodiment.

[0036] BRIEF DESCRIPTION OF DRAWINGS

[0037] 200, carrier plate; 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, round corner; 401, via hole; 411, Nth circuit pattern; 421, Mth circuit pattern; 511, N+1th adhesive sheet; 512, N+1th outer copper foil; 611, M+1th adhesive sheet; 612, M+1th outer copper foil; DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] like Figure 1 As shown, a method for manufacturing a multilayer circuit board according to an embodiment of the present invention includes:

[0040] Step 110: Stack the Nth outer copper foil, the Nth bonding sheet, the first inner copper foil, the carrier board, the second inner copper foil, the Mth bonding sheet, and the Mth outer copper foil in sequence and then hot-press them 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 diagonals of the second inner copper foil are rounded, the projections of the Nth outer copper foil and the Mth outer copper foil on the carrier board are located within the projections of the first inner copper foil and the second inner copper foil on the carrier board, and 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 Nth bonding sheet and the Mth bonding sheet on the carrier board, 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, such as Figure 2A As shown, the Nth outer copper foil 410 and the Nth bonding sheet 310 are the first bonding sheet and outer copper foil located outside the first inner copper foil 210, and the Mth outer copper foil 420 and the Mth bonding sheet 320 are the first bonding sheet and outer copper foil located outside the second inner copper foil 220. The core boards are stacked in the order of the Nth outer copper foil 410, the Nth bonding sheet 310, the first inner copper foil 210, the carrier board 200, the second inner copper foil 220, the Mth bonding sheet 320, and the Mth outer copper foil 420, and then hot-pressed to form a first composite board. 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, which causes the inner copper foil to be unable to fully support the outer copper foil when the inner copper foil is peeled off from the carrier plate, and easily causes deformation and warping of the edge of the outer copper foil. In the embodiment, the projection of the first inner copper foil and the second inner copper foil on the carrier plate is larger than the projection of the Nth outer copper foil and the Mth outer copper foil on the carrier plate, so that the projection of the Nth outer copper foil and the Mth outer copper foil on the carrier plate is completely located in the projection of the first inner copper foil and the second inner copper foil on the carrier plate, and the projection of each adhesive sheet on the carrier plate is larger than or equal to the projection of the first inner copper foil and the second inner copper foil on the carrier plate, so that the projection of the first inner copper foil and the second inner copper foil on the carrier plate is completely located in the projection of the Nth adhesive sheet and the Mth adhesive sheet on the carrier plate. Thus, due to the large area of the adhesive sheet, the adhesive sheet can better connect the inner copper foil and the outer copper foil.

[0043] In the embodiment, the diagonal of the inner copper foil is a rounded corner, which can effectively disperse stress and avoid edge warping due to stress concentration. It is worth mentioning that the diagonal of the traditional inner copper foil is a straight corner without rounding treatment. Due to the sharp geometry, the straight corner region is prone to stress concentration during hot pressing, cutting or use, which easily causes copper foil shell, and even leads to copper foil cracking or delamination. Therefore, in the embodiment, the rounded corner shape of the diagonal of the inner copper foil can effectively disperse stress to the outer edge, avoid stress concentration, and effectively avoid deformation and warping at the diagonal, thereby effectively supporting the adhesive sheet and the outer copper foil, so that the flatness of the manufactured circuit board is better, and the product yield is improved.

[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 with the carrier plate, 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 avoid deformation and warping of the circuit board, and make it easier for the inner copper foil to be peeled off from the carrier plate.

[0045] In step 120, the Nth outer copper foil and the Mth outer copper foil are drilled, electroplated, and formed with vias at regions corresponding to the rounded corners of the first inner copper foil and the second inner copper foil, the first composite plate is subjected to pattern transfer, the Nth circuit pattern is formed on the outer surface of the Nth outer copper foil, and the Mth circuit pattern is formed on the outer surface of the Mth outer copper foil.

[0046] In this step, as shown in FIG. 6, the Nth outer copper foil and the Mth outer copper foil are drilled, electroplated, and formed with vias at regions corresponding to the rounded corners of the first inner copper foil and the second inner copper foil. Figure 2BAs shown, the first N outer copper foil 410 and the first M outer copper foil 420 are drilled, electroplated, and formed with vias 401 corresponding to the regions near the rounded corners of the first inner copper foil 210 and the second inner copper foil 220. The first N circuit pattern 411 is formed on the outer surface of the first N outer copper foil, and the first M circuit pattern 421 is formed on the outer surface of the first M outer copper foil.

[0047] Specifically, the vias 401 are formed on the first N outer copper foil 410 and the first M outer copper foil 420, and only in the regions near 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 plating and electroplating are performed in the hole to form the vias connecting the inner copper foil and the outer copper foil near the rounded corner region. In this embodiment, the vias are arranged near the rounded corner region. On the one hand, the vias connect the adjacent inner copper foil and outer copper foil, play a connecting support role, and effectively utilize the stress dispersion effect of the rounded corner of the inner copper foil to play a tensioning, supporting and fixing role on 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 inner copper foil is arranged as a rounded corner, the phenomenon of sharp electric field concentration is avoided between the via and the right-angled edge, the capacitive coupling is avoided to be enhanced, the electric field gradient changes gently along the edge of the rounded corner region of the inner copper foil, the capacitive energy density is reduced, and the parasitic capacitance of the via can be effectively reduced.

[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 first N circuit pattern and the first M circuit pattern.

[0049] In step 130, the first N+1 adhesive sheet and the first N+1 outer copper foil are sequentially formed on the outer surface of the first N circuit pattern, and the first M+1 adhesive sheet and the first M+1 outer copper foil are sequentially formed on the outer surface of the first M circuit pattern. 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 first N+1 adhesive sheet and the first M+1 adhesive sheet on the carrier plate.

[0050] In this embodiment, as shown in FIG. 1, the first N+1 adhesive sheet 430 and the first N+1 outer copper foil 440 are sequentially formed on the outer surface of the first N circuit pattern 411, and the first M+1 adhesive sheet 430 and the first M+1 outer copper foil 440 are sequentially formed on the outer surface of the first M circuit pattern 421. The projections of the first inner copper foil 210 and the second inner copper foil 220 on the carrier plate 200 are located within the projections of the first N+1 adhesive sheet 430 and the first M+1 adhesive sheet 430 on the carrier plate 200. Figure 2CAs shown, the outer side surface of the Nth circuit pattern 411 is sequentially formed with an N+1 bonding sheet 511 and an N+1 outer copper foil 512, and the outer side surface of the Mth circuit pattern 421 is sequentially formed with an M+1 bonding sheet 611 and an M+1 outer copper foil 612. The projection area of each bonding sheet on the carrier plate is greater than or equal to the projection area of the first inner copper foil and the second inner copper foil on the carrier plate, so that the bonding sheet can better connect the adjacent outer copper foils. In addition, the projection area of the N+1 outer copper foil and the M+1 outer copper foil on the carrier plate is equal to the projection area of the Nth outer copper foil and the Mth outer copper foil on the carrier plate. In this embodiment, the outer side of the first composite plate is increased in layers on both sides to form the N+1 bonding sheet and the N+1 outer copper foil, and the M+1 bonding sheet and the M+1 outer copper foil, respectively.

[0051] In step 140, the N+1 outer copper foil and the M+1 outer copper foil are drilled, electroplated to form vias, and the N+1 outer copper foil and the M+1 outer copper foil are pattern transferred to form an N+1 circuit pattern and an M+1 circuit pattern.

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

[0053] In step 150, the two sides of the carrier plate are separated from the first inner copper foil and the second inner copper foil, respectively, to obtain a multi-layer circuit board.

[0054] In this step, the first inner copper foil and the second inner copper foil are cut and separated from the carrier plate by laser cutting to obtain two independent multi-layer circuit boards.

[0055] In this embodiment, the corners of the edges of the inner copper foil are rounded, which can effectively disperse stress to the outer edges and avoid stress concentration, thereby effectively avoiding deformation and warping at the corners. In combination with the feature that the size of the inner copper foil is greater 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 bonding sheet and the outer copper foil, effectively avoiding deformation and warping of the circuit board, and making it easier to peel off the inner copper foil from the carrier.

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

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

[0058] In one embodiment, at least one via hole is arranged near the area corresponding to the rounded corner of the N+1th outer copper foil and the rounded corner of the M+1th outer copper foil in the via hole formed by drilling and electroplating the N+1th outer copper foil and the M+1th outer copper foil.

[0059] In the embodiment, the via hole is used to connect the circuit patterns of different layers and realize conduction between the circuits of different layers. In the embodiment, the via hole is arranged near the rounded corner, which can play a connection and support role in connecting the adjacent outer copper foils. The via hole can effectively utilize the stress dispersion effect of the rounded corner of the adjacent outer copper foil, so that the interaction force between the outer copper foils in the rounded corner area can keep the corresponding area of the outer copper foil flat and avoid deformation and warping. In addition, since the corners of the copper foils of the layers are set as rounded corners, the phenomenon of sharp electric field concentration formed by the via hole and the right-angle edge is avoided, the capacitive coupling is avoided to be enhanced, the electric field gradient along the edge of the rounded corner of the rounded corner area of the outer copper foil changes gently, the energy density of the capacitor is reduced, and the parasitic capacitance of the via hole can be effectively reduced.

[0060] In one embodiment, the via hole is arranged near the area corresponding to the rounded corner of each of the four corners of the first inner copper foil and the rounded corner of each of the four corners of the second inner copper foil on the N+1th outer copper foil and the M+1th outer copper foil, that is, one via hole is arranged in the rounded corner area of each corner, which can make the outer copper foil bear balanced force on the four corner areas.

[0061] In one embodiment, the distance between the via hole in the area 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 radius of the rounded corner and less than four times the radius of the rounded corner.

[0062] It should be understood that although the rounded corners can effectively reduce the parasitic capacitance of the adjacent via, the parasitic capacitance can still be generated due to the edge electric field coupling, and 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 the edge electric field coupling, and even zero. However, in the present embodiment, the via also bears the role of supporting the outer copper foil by the stress dispersion of the rounded corner of the inner copper foil, and therefore the via should not be too far away from the edge of the rounded corner. If the via is too far away from the edge of the rounded corner, the outer copper foil cannot be supported by the stress dispersion of the rounded corner. Therefore, in the present embodiment, the distance between the via close 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 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 effectively utilize the stress dispersion of the rounded corner of the inner copper foil to tension, 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.

[0063] In one embodiment, the distance between the via in the region corresponding to the rounded corner of the N+1th outer copper foil and the rounded corner of the M+1th outer copper foil and the edge of the rounded corner of the N+1th outer copper foil or the edge of the rounded corner of the M+1th 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 the present embodiment, similarly, to reduce the parasitic capacitance, the distance between the via close to the rounded corner on the outer copper foil and the edge of the rounded corner should be as large as possible, but at the same time, in order to utilize the stress dispersion of the rounded corner of each outer copper foil to 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 effectively utilize the stress dispersion of the rounded corner of the outer copper foil to tension, support and fix the outer copper foil of the adjacent layer, so that the corresponding region of the outer copper foil can remain flat and avoid deformation and warping.

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

[0066] In the embodiment, after the pattern transfer, the circuit pattern forms a right-angle region, and the distance between each via hole and the right-angle region is greater than five times the aperture of the via hole, so that the via hole is far away from the right-angle region, and the edge of the right-angle region can effectively avoid forming a sharp electric field concentration to cause the capacitive coupling of the via hole, thereby avoiding the generation of a larger parasitic capacitance. It should be understood that, after the pattern transfer, there can be multiple right-angle regions on the formed circuit pattern, and the right-angle region is not the right angle of the original outer copper foil. For the via hole, it can only try to avoid these right-angle regions as much as possible and try to be far away, but it cannot be completely far away, such as completely far away, which will affect the overall structure of the circuit pattern. Therefore, in the embodiment, the distance between each via hole and the right-angle region on the N+1th circuit pattern and the right-angle region on the M+1th circuit pattern is greater than five times the aperture of the via hole, which can effectively avoid the edge of the right-angle region from forming a sharp electric field concentration to cause the capacitive coupling of the via hole without affecting the overall structure of the circuit pattern, thereby avoiding the generation of a larger parasitic capacitance.

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

[0068] In the embodiment, the first inner copper foil and the second inner copper foil are provided in a rectangular shape, and the corners of the first copper foil and the second copper foil are laser cut to form rounded corners. In addition, in the embodiment, before the first inner copper foil and the second inner copper foil are stacked on the carrier plate, a water-soluble polymer film is first 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 be dissolved in water. In the embodiment, a water-soluble polymer solution is coated on the two opposite surfaces of the carrier plate, and after drying, a water-soluble polymer film is formed on the two opposite surfaces of the carrier plate, and the thickness of the water-soluble polymer film is 10-30 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, and then the Nth outer copper foil, the Nth bonding sheet, the first inner copper foil, the carrier plate, the second inner copper foil, the Mth bonding sheet, and the Mth outer copper foil are stacked in order and then subjected to hot pressing to obtain a first composite plate. It should be noted that the water-soluble polymer film has flexibility and higher flexibility compared to the carrier plate as a rigid body, which can provide cushioning for the inner copper foil and effectively avoid rigid contact between the carrier plate and the inner copper foil, thereby avoiding the inner copper foil being bent in the opposite direction due to the reaction force of the carrier plate during hot pressing.

[0069] 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 multilayer circuit board comprises: laser pre-cutting the carrier plate and the first inner copper foil along two mutually perpendicular tangent directions of each round corner of the first inner copper foil, and laser pre-cutting the carrier plate and the second inner copper foil along two mutually perpendicular tangent directions of each round corner of the second inner copper foil, so that the round corners of the first inner copper foil and the round corners of the second inner copper foil form pre-cutting gaps with the carrier plate; spraying a dissolving solution along the two mutually perpendicular tangent directions of each round corner of the first inner copper foil towards the pre-cutting gap, and spraying a dissolving solution along the two mutually perpendicular tangent directions of each round corner of the second inner copper foil towards the pre-cutting gap to dissolve the water-soluble polymer film; and using a vacuum chuck to adsorb the outer surface of the multilayer circuit board to separate the multilayer circuit board from the carrier plate to obtain the multilayer circuit board.

[0070] It is worth mentioning that for the round corner, the two mutually perpendicular tangent directions thereof are the directions of the two sides of the rectangle connected with the round corner, as shown in the figure, the arrow direction is the direction of laser pre-cutting, and the core plate is placed horizontally, and the laser is cut along the two mutually perpendicular tangent directions of the round corner 211 of the first inner copper foil 210. Figure 3 As shown in the figure, the arrow direction is the direction of laser pre-cutting, and the core plate is placed horizontally, and the laser is cut along the two mutually perpendicular tangent directions of the round corner 211 of the first inner copper foil 210. In this embodiment, the carrier plate and the inner copper foil are pre-cut along the tangent direction of the round corner, so that the peeling force direction of the inner copper foil is consistent with the tangent direction of the round corner, avoiding shear stress, which can effectively reduce the warping degree of the round corner. It should be understood that, if the round corner is directly cut, it is possible to cause the round corner to warp, and in this embodiment, since the tangent direction of the round corner is parallel to one side of the inner copper foil, the side of the inner copper foil can be separated from the carrier plate during pre-cutting, realizing simultaneous separation of the round corner and the side of the inner copper foil, and avoiding local warping. During the laser pre-cutting process, the cutting moves gradually to the middle part of the carrier plate and the inner copper foil, so that the pre-cutting gap is formed between the inner copper foil and the carrier plate, and the dissolving solution is sprayed into the gap.

[0071] Subsequently, a dissolving solution is sprayed along the tangent direction to the pre-cut gap, for example, using a water gun to spray the dissolving solution, for example, the dissolving solution is water, for example, the dissolving solution is warm water at 40-60°C. The water-soluble polymer film between the inner copper foil and the carrier plate is dissolved by the dissolving solution, so that the adhesion between the inner copper foil and the carrier plate is effectively reduced, and the dissolving solution penetrates along the tangent direction to the edge outside the fillet of the inner copper foil, so that the edge of the whole inner copper foil is first separated from the carrier plate, and then gradually glass from the middle to the inside of the edge. Subsequently, the outer side surface of the multilayer circuit board on both sides is pressed by the vacuum chuck, and the vacuum chuck is kept pressed on the surface of the multilayer circuit board under the action of the hydraulic device before the water-soluble polymer film is completely dissolved. The pressure of the vacuum chuck and the liquid tension between the inner copper foil and the carrier plate are used to press the multilayer circuit board on both sides, so as to keep the multilayer 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 edge of the outer side of the multilayer circuit board, so as to keep the stress of the multilayer circuit board uniform and avoid deformation. When the water-soluble polymer film is completely dissolved, the outer side surface of the multilayer circuit board is adsorbed by the vacuum chuck, and the multilayer circuit board is peeled off from the carrier plate by the adsorption force. Since the fillet area of the edge of the inner copper foil is first separated, the inner copper foil can be easily peeled off from the carrier plate, and the warping and deformation of the multilayer circuit board are effectively avoided. It is worth mentioning that the carrier plate can be reused after the water-soluble polymer film is removed.

[0072] Compared with the traditional laser cutting to separate the inner copper foil from the carrier plate, in the embodiment, the laser cutting and the dissolution of the water-soluble polymer film are combined, which can effectively avoid the deformation and warping of the multilayer circuit board caused by high temperature and stress change in the cutting process. The ratio of the pre-cutting stroke of the laser to the spraying stroke of the dissolving solution in the gap between the inner copper foil and the carrier plate is 1:2, which can make the dissolving solution quickly penetrate between the inner copper foil and the carrier plate, and keep the support of the multilayer circuit board by the tension of the solution.

[0073] In one embodiment, after the multilayer circuit board is peeled off from the carrier plate, the multilayer circuit board is subjected to drying treatment to remove the water on the surface of the multilayer circuit board.

[0074] In one embodiment, the step of separating the two surfaces of the carrier plate from the first inner copper foil and the second inner copper foil respectively to obtain the multilayer circuit board comprises:

[0075] The steps 130 and 140 are repeated until the Pth layer of adhesive sheet and the Pth layer of outer copper foil are formed on the outer side of one side of the first composite plate, and the Qth layer of adhesive sheet and the Qth layer of outer copper foil are formed on the outer side of the other side of the first composite plate, and the two surfaces 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, wherein P and Q are positive integers greater than N and M.

[0076] In the embodiment, a plurality of outer copper foils can be arranged on both sides of the carrier plate, each outer copper foil is connected to the adjacent outer copper foil by an adhesive sheet, and the P-layer outer copper foil is formed by gradually accumulating from the N-layer to the N+1-layer. It is worth mentioning 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+1th outer copper foil is the second outer copper foil outside the inner copper foil. When the steps 130 and 140 are repeated, the original N+1th outer copper foil can be regarded as the new Nth outer copper foil. At this time, N is 2, the Nth outer copper foil is the second outer copper foil outside the inner copper foil, and the N+1th outer copper foil is the third outer copper foil outside the inner copper foil. The steps 130 and 140 are repeatedly executed until the P-layer outer copper foil and the Q-layer outer copper foil are formed on both sides of the carrier plate, thereby obtaining the multi-layer core plate. It is worth mentioning that the values of P and Q in the P-layer adhesive sheet, the P-layer outer copper foil, the Q-layer adhesive sheet and the Q-layer outer copper foil can be selected according to the requirements of the multi-layer circuit board.

[0077] In an 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 further comprises:

[0078] The outer copper foil of the outermost layer of the multi-layer circuit board is respectively drilled, electroplated and pattern transferred to form an outer layer circuit pattern.

[0079] In the embodiment, before the multi-layer circuit board is peeled off from the carrier plate, the outer copper foil of the outermost layer is not drilled, electroplated or pattern transferred, so that the outer copper foil of the outermost layer remains intact and can better support the circuit board to avoid deformation during the peeling process. After the multi-layer circuit board is peeled off, the outer copper foil of the outermost layer is respectively drilled, electroplated and pattern transferred to form an outer layer circuit pattern on the outermost side of the multi-layer circuit board.

[0080] In an 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 further comprises: the first inner copper foil and the second inner copper foil are respectively drilled, electroplated and pattern transferred to form a first inner circuit pattern and a second inner circuit pattern.

[0081] In the embodiment, after the multi-layer circuit board is separated from the carrier plate, the first inner copper foil and the second inner copper foil are exposed. Then, the parts outside the rounded corner regions of the first inner copper foil and the second inner copper foil of the two multi-layer circuit boards are respectively laser drilled, chemical copper deposition and 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 to pattern transfer 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 fillet area is connected with the outer copper foil of the definition layer through the via, so that the integrity of the inner copper foil can be maintained, the circuit board can be better supported, the deformation in the peeling process can be avoided, and the fillet area via can be used to support the outer copper foil to avoid warping at the corners. By setting part of the vias in the fillet area, the parasitic capacitance can be effectively reduced. After the inner copper foil is peeled off from the carrier plate, the remaining part of the inner copper foil is made into a via, and a circuit pattern is made, to obtain a multilayer circuit board.

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

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

[0085] The technical features of the above embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above embodiments are described, but as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present disclosure.

[0086] The above embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of variations and improvements can be made, which are all within the scope of the present application. Therefore, the scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for manufacturing a multi-layer circuit board, characterized in that: include: Step 110: stacking an Nth outer copper foil, an Nth bonding sheet, a first inner copper foil, a carrier plate, a second inner copper foil, an Mth bonding sheet, and an Mth outer copper foil in sequence and then hot pressing them to obtain a first composite plate, 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 diagonals of the second inner copper foil are rounded, 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, 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 bonding sheet and the Mth bonding sheet on the carrier plate, wherein N and M are positive integers greater than or equal to 1; Step 120: Drilling and electroplating are performed on the areas of the Nth outer copper foil and the Mth outer copper foil corresponding to the rounded corners of the first inner copper foil and the rounded corners of the second inner copper foil to form vias, pattern transfer is performed on the first composite board, and an Nth circuit pattern is formed on the outer surface of the Nth outer copper foil and an Mth circuit pattern is formed on the outer surface of the Mth outer copper foil, wherein the distance between the vias in the areas corresponding to the rounded corners of the first inner copper foil and the rounded corners 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; Step 130: sequentially forming an N+1th bonding sheet and an N+1th outer copper foil on the outer surface of the Nth circuit pattern, and sequentially forming an M+1th bonding sheet and an M+1th 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 board are located within the projections of the N+1th bonding sheet and the M+1th bonding sheet on the carrier board; Step 140: Drilling and electroplating the N+1th outer copper foil and the M+1th outer copper foil to form vias, and pattern transfer of the N+1th outer copper foil and the M+1th outer copper foil to form the N+1th circuit pattern and the M+1th circuit pattern; Step 150 : Separate the first inner copper foil and the second inner copper foil from the two sides of the carrier plate to obtain a multilayer circuit board.

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

3. The method for manufacturing a multi-layer circuit board according to claim 2, wherein: Among the vias formed by drilling and electroplating the N+1th outer copper foil and the M+1th outer copper foil, at least one via is close to the area corresponding to the rounded corner of the N+1th outer copper foil and the rounded corner of the M+1th outer copper foil, wherein the distance between the via in the area corresponding to the rounded corner of the N+1th outer copper foil and the rounded corner of the M+1th outer copper foil and the edge of the rounded corner of the N+1th outer copper foil or the edge of the rounded corner of the M+1th outer copper foil is greater than three times the rounded corner radius and less than four times the rounded corner radius.

4. The method for manufacturing a multi-layer circuit board according to claim 1, wherein: In the via holes formed by drilling and electroplating the N+1th outer copper foil and the M+1th outer copper foil, the distance between each via hole and the right-angle area on the N+1th circuit pattern and the right-angle area on the M+1th circuit pattern is greater than five times the aperture of the via hole.

5. The method for manufacturing a multi-layer circuit board according to claim 1, wherein: Before step 110, the following steps are also included: providing a first inner copper foil and a second inner copper foil; Using laser cutting, cutting the diagonal corners of the first inner copper foil and the diagonal corners of the second inner copper foil respectively, so that the diagonal corners of the first inner copper foil and the diagonal corners of the second inner copper foil form rounded corners; Water-soluble polymer films are coated on two opposite surfaces of the carrier plate.

6. The method for manufacturing a multi-layer circuit board according to claim 5, wherein: The step of separating the first inner copper foil and the second inner copper foil from the two sides of the carrier plate to obtain a multilayer circuit board comprises: Pre-cutting the carrier plate and the first inner copper foil by laser along two mutually perpendicular tangent directions of each rounded corner of the first inner copper foil, and pre-cutting the carrier plate and the second inner copper foil by laser along two mutually perpendicular tangent directions of each rounded corner of the second inner copper foil, so that pre-cut gaps are formed between the rounded corners of the first inner copper foil and the second inner copper foil and the carrier plate; spraying a dissolving liquid along two mutually perpendicular tangential directions of each rounded corner of the first inner copper foil toward the pre-cut slit, and spraying a dissolving liquid along two mutually perpendicular tangential directions of each rounded corner of the second inner copper foil toward the pre-cut slit to dissolve the water-soluble polymer film; The outer surface of the multilayer circuit board is adsorbed by a vacuum suction cup to separate the multilayer circuit board from the carrier plate to obtain the multilayer circuit board.

7. The method for manufacturing a multi-layer circuit board according to any one of claims 1 to 6, characterized in that: The step of separating the first inner copper foil and the second inner copper foil from the two sides of the carrier plate to obtain a multilayer circuit board comprises: Repeat steps 130 and 140 until a P-th bonding sheet and a P-th outer copper foil are formed on the outer side of one side of the first composite board, and a Q-th bonding sheet and a Q-th outer copper foil are formed on the outer side of the other side of the first composite board. The two sides of the carrier board are separated from the first inner copper foil and the second inner copper foil, respectively, to obtain the multilayer circuit board, wherein P and Q are positive integers greater than N and M.

8. The method for manufacturing a multi-layer circuit board according to claim 7, wherein: After the step of separating the first inner copper foil and the second inner copper foil from the two sides of the carrier plate to obtain a multilayer circuit board, the step further includes: The outer copper foil of the outermost layer of the multilayer circuit board is drilled, electroplated, and pattern-transferred to form an outer layer circuit pattern.

9. The method for manufacturing a multi-layer circuit board according to claim 7, wherein: After the step of separating the first inner copper foil and the second inner copper foil from the two sides of the carrier plate to obtain a multilayer circuit board, the step further includes: The first inner copper foil and the second inner copper foil are respectively subjected to drilling, electroplating, and pattern transfer to form a first inner circuit pattern and a second inner circuit pattern, respectively.

10. A multi-layer circuit board, characterized in that: The multilayer circuit board is manufactured using the method for manufacturing the multilayer circuit board described in any one of claims 1 to 9.

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