Method for preparing buried magnetic core circuit board

Abstract

The present invention discloses a method for preparing a buried magnetic core circuit board. The preparation method of the embodiment includes the following steps: making and pressing an upper laminate of the circuit board; making and pressing a lower laminate of the circuit board; roughening the surface of the magnetic core; placing an intermediate laminate with a receiving hole on the lower laminate of the circuit board, and placing the magnetic core in the receiving hole of the intermediate laminate, and finally placing the upper laminate of the circuit board on the intermediate laminate for overall hot pressing. The preparation method of the present invention is conducive to reducing the force on the magnetic core during overall hot pressing, reducing or avoiding the situation where the magnetic core is crushed during the hot pressing process, and improving the yield rate; further, for the situation where the upper and lower laminates of the circuit board have different numbers of conductive circuits, the preparation method of the present invention can also well improve the problems of warping and deformation of the circuit board.

Description

Technical Field

[0001] The present invention relates to the field of circuit boards; more specifically, to a method for preparing a circuit board with an embedded magnetic core. Background Art

[0002] When an inductor component containing a magnetic core is mounted on a circuit board in a surface mount manner, it will occupy a large surface area of ​​the circuit board, which is not conducive to the miniaturization of the product. As an improved solution, the magnetic core can be embedded inside the circuit board to reduce the required circuit board surface area.

[0003] Chinese patent document CN105451465A discloses a method for manufacturing a buried magnetic core printed circuit board, comprising the following steps: S1, a pre-process, and cutting the copper clad core board and the prepreg; S2, etching the copper foil, etching away the copper foil on the inner side of the copper clad core board where the magnetic core is located close to the circuit board; S3, controlling the depth of the copper clad core board to mill out a magnetic core groove, and the cross-sectional shape of the magnetic core groove is a circular ring; S4, opening a window on the prepreg; S5, pressing; S6, a post-process.

[0004] As disclosed in the above-mentioned prior art, the preparation method of the existing embedded magnetic core circuit board generally refers to the preparation method of the embedded metal block circuit board, and the interlayer bonding connection of the core board and the fixation of the magnetic core are achieved by performing a single hot pressing on the circuit board. However, since the magnetic core is usually very brittle, this one-time pressing process can easily cause the magnetic core to be crushed, resulting in a low product yield. Summary of the invention

[0005] In view of the deficiencies in the prior art, the main purpose of the present invention is to provide a method for preparing a buried magnetic core circuit board that can improve product yield.

[0006] In order to achieve the above main purpose, the method for preparing a buried magnetic core circuit board disclosed in the present invention comprises the following steps:

[0007] S1, making and pressing the upper stack of the circuit board;

[0008] S2, making and pressing the lower laminate of the circuit board;

[0009] S3, roughening the surface of the magnetic core;

[0010] S4, placing an intermediate laminate with a receiving hole on the lower laminate of the circuit board, placing a magnetic core in the receiving hole of the intermediate laminate, and finally placing the upper laminate of the circuit board on the intermediate laminate for overall hot pressing.

[0011] In the above technical solution, the upper and lower layers of the circuit board are pressed first, and then the circuit board is hot pressed as a whole, which is beneficial to reduce the force on the magnetic core during the hot pressing of the circuit board as a whole, reduce or avoid the situation where the magnetic core is crushed during the hot pressing process, and thus improve the product yield.

[0012] Furthermore, the upper laminate of the circuit board and the lower laminate of the circuit board have conductive circuits with different numbers of layers.

[0013] When the upper and lower layers of the circuit board have different numbers of conductive circuits, the upper and lower layers of the circuit board are pressed together separately first to release their internal stress. When the whole circuit board is hot-pressed, the internal stress of the circuit board caused by the asymmetric structure of the non-circuit layer can be reduced, which greatly improves the warping and deformation of the circuit board.

[0014] Further, step S1 includes:

[0015] S11, providing an upper core board with double-sided copper cladding, and etching the copper foil layers on both sides of the upper core board to form L2 and L3 conductive circuits;

[0016] S12, laminating an L1 copper foil layer on one side of the L2 conductive circuit of the upper core board.

[0017] Further, step S2 includes:

[0018] S21, providing a lower core board with double-sided copper cladding, and etching the copper foil layers on both sides of the lower core board to form L5 and L6 conductive circuits;

[0019] S22, pressing an L4 copper foil layer on one side of the L5 conductive circuit of the lower core board, and pressing an L7 copper foil layer on one side of the L6 conductive circuit;

[0020] S23, etching the L4 copper foil layer to obtain an L4 conductive circuit.

[0021] Further, step S3 includes:

[0022] S31, soaking the magnetic core to be roughened in a phosphoric acid solution for 10 to 15 minutes, and then washing with water;

[0023] S32, soaking the magnetic core in a mixture of chromium nitrate and nitric acid for 15 to 20 minutes, and then washing with water.

[0024] Preferably, the mass fraction of the phosphoric acid is 75%, the mass fraction of chromium nitrate in the mixed solution is 10%, and the mass fraction of nitric acid is 5%.

[0025] In the above technical solution, the magnetic core undergoes two-step roughening treatment to give it a rough surface and form chromium phosphate attachment on the surface, which is more conducive to enhancing the bonding strength between the magnetic core and the circuit board resin (semi-cured sheet), so that the magnetic core can be more reliably fixed in the circuit board, thereby improving product reliability.

[0026] Furthermore, during hot pressing in step S4, an upper cover plate, kraft paper, steel plate, elastic buffer pad and metal foil are sequentially arranged above the circuit board from top to bottom, and metal foil, elastic buffer pad, steel plate, kraft paper and lower base plate are sequentially arranged below the circuit board from top to bottom.

[0027] In the above technical solution, the provision of the elastic buffer pad can reduce the impact force on the circuit board during the initial pressing process, and further reduce the damage to the magnetic core.

[0028] Furthermore, the magnetic core is rectangular, and a distance of 0.3 mm to 0.6 mm is provided between the side wall of the magnetic core and the side wall of the accommodating hole, and a rounded corner is provided at the corner of the accommodating hole for positioning the magnetic core.

[0029] In the above technical solution, an appropriate size gap is formed between the magnetic core and the side wall of the accommodating hole, which is conducive to the semi-cured sheet flowing into the gap during overall hot pressing, ensuring that the magnetic core and the core plate have better bonding strength; the accommodating hole is provided with a positioning fillet, which can well ensure the accurate positioning of the magnetic core.

[0030] Furthermore, the magnetic core is a ferrite core.

[0031] Furthermore, the circuit board preparation method of the embodiment further includes the following steps:

[0032] S5, making a conductive via penetrating the circuit board.

[0033] In order to more clearly illustrate the purpose, technical solutions and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic structural diagram of a circuit board embodiment of the present invention;

[0035] Figure 2 It is a structural exploded view of the circuit board embodiment of the present invention before lamination. DETAILED DESCRIPTION

[0036] In the following description, many specific details are explained in conjunction with the embodiments, but it should be understood that the following embodiments and detailed descriptions are only for illustrative purposes and do not limit the scope of protection of the present invention.

[0037] like Figure 1 and 2 As shown, the embedded magnetic core circuit board of embodiment 1 includes an upper circuit board laminate 10, a lower circuit board laminate 20, and an intermediate laminate 30 disposed therebetween, wherein a magnetic core 40 is embedded in the intermediate laminate 30, and the magnetic core 40 may be a ferrite core. The shape of the magnetic core 40 may be rectangular, but is not limited thereto, and may be circular, for example.

[0038] Among them, the upper laminate 10 of the circuit board and the lower laminate 20 of the circuit board are both provided with conductive circuits, and the number of layers of the conductive circuits in the upper laminate 10 of the circuit board and the lower laminate 20 of the circuit board can be the same or different. In the embodiment, the upper laminate 10 of the circuit board has three layers of conductive circuits L1-L3, the conductive circuits L2 and L3 are respectively arranged on the two side surfaces of the upper core board 11, and the conductive circuit L1 is bonded to the side of the L2 conductive circuit of the upper core board 11 through the semi-cured sheet 12; the lower laminate 20 of the circuit board has four layers of conductive circuits L4-L7, the conductive circuits L5 and L6 are respectively arranged on the two side surfaces of the lower core board 21, the conductive circuit L4 is bonded to the side of the L5 conductive circuit of the lower core board 21 through the semi-cured sheet 22, and the conductive circuit L7 is bonded to the side of the L6 conductive circuit of the lower core board 21 through the semi-cured sheet 23. In the embodiment, some of the conductive circuit layers L1 to L7 form conductive coils that cooperate with the magnetic core 40 , for example, the L6 and L7 layers form conductive coils that cooperate with the magnetic core 40 .

[0039] The middle laminate 30 includes a plurality of middle core plates 31, and the plurality of middle core plates 31 can be bonded and connected by a prepreg 32. The magnetic core 40 is arranged in the receiving hole 33 of the middle laminate 30, and a spacing of 0.3 mm to 0.6 mm is arranged between the side wall of the magnetic core 40 and the side wall of the receiving hole 33, and the four corners of the receiving hole 33 are formed with fillets for positioning the magnetic core 40. The middle laminate 30 is bonded and connected to the upper laminate 10 of the circuit board by a prepreg 34, and is bonded and connected to the lower laminate 20 of the circuit board by a prepreg 35.

[0040] like Figure 2 As shown, the method for preparing a buried magnetic core circuit board of the present invention comprises the following steps:

[0041] S1, making and pressing the upper laminate 10 of the circuit board;

[0042] S2, making and pressing the lower laminate 20 of the circuit board;

[0043] S3, roughening the surface of the magnetic core 40;

[0044] S4, placing the middle laminate 30 with the receiving hole 31 on the lower laminate 20 of the circuit board, placing the magnetic core 40 in the receiving hole of the middle laminate 30, and finally placing the upper laminate 10 of the circuit board on the middle laminate 30 for overall hot pressing.

[0045] Specifically, step S1 includes:

[0046] S11, providing an upper core board 11 with copper cladding on both sides, and etching the copper foil layers on both sides of the upper core board 11 to form L2 and L3 conductive circuits;

[0047] S12, using the prepreg 12 to press the L1 copper foil layer onto one side of the L2 conductive line of the upper core board.

[0048] Specifically, step S2 includes:

[0049] S21, providing a lower core board 21 with copper cladding on both sides, and etching the copper foil layers on both sides of the lower core board 21 to form L5 and L6 conductive circuits;

[0050] S22, using the prepreg 22 to press the L4 copper foil layer on one side of the L5 conductive line of the lower core board, and using the prepreg 23 to press the L7 copper foil layer on one side of the L6 conductive line;

[0051] S23, etching the L4 copper foil layer to obtain an L4 conductive circuit.

[0052] Furthermore, step S2 also includes: making one or more conductive vias 24 in the lower laminate 20 of the circuit board, and the conductive vias 24 can realize the interlayer interconnection of the corresponding conductive circuit layers in L4-L7. The production of the conductive vias 24 can refer to the existing technology and will not be described in detail here.

[0053] Specifically, step S3 includes:

[0054] S31, soaking the magnetic core 40 to be roughened in a phosphoric acid solution for 10 to 15 minutes (eg, 10 minutes), and then washing with water; preferably, the mass fraction of the phosphoric acid is 75%.

[0055] S32, soaking the magnetic core 40 obtained in step S31 in a mixture of chromium nitrate and nitric acid for 15 to 20 minutes (for example, 15 minutes), and then washing with water. Preferably, the mass fraction of chromium nitrate in the mixture is 10%, and the mass fraction of nitric acid is 5%.

[0056] In the present application, the magnetic core 40 undergoes a two-step roughening treatment so that it has a rough surface and a chromium phosphate attachment is formed on the surface, which is more conducive to enhancing the bonding strength between the magnetic core 40 and the circuit board resin (semi-cured sheet), so that the magnetic core 40 can be more reliably fixed in the circuit board, thereby improving product reliability.

[0057] During hot pressing, the lower laminate 20 of the circuit board, the prepreg 35, the middle laminate 30, the prepreg 34 and the upper laminate 10 of the circuit board are stacked from bottom to top, and the magnetic core 40 is placed in the receiving hole 33 of the middle laminate 30. After hot pressing, the prepreg 35 is cured to achieve the bonding connection between the lower laminate 20 of the circuit board and the middle laminate 30, and the prepreg 34 is cured to achieve the bonding connection between the upper laminate 10 of the circuit board and the middle laminate 30; at the same time, during the hot pressing process, the prepreg enters the gap between the magnetic core 40 and the receiving hole 33 to achieve the adhesion and fixation of the magnetic core 40. In the present application, the prepreg 35 and the prepreg 34 can be used as part of the middle laminate 30 or set independently of the middle laminate 30; further, the prepreg 35 and the prepreg 34 can also be processed to have through holes for the magnetic core 40 to pass through.

[0058] In the present application, when performing the overall hot pressing of step S4, an upper cover plate, kraft paper, steel plate, elastic buffer pad and metal foil can be arranged from top to bottom above the circuit board, and metal foil, elastic buffer pad, steel plate, kraft paper and lower bottom plate can be arranged from top to bottom below the circuit board. The elastic buffer pad can be a silicone pad or a rubber pad, and the metal foil can be aluminum foil or titanium foil. Compared with the hot pressing step of conventional circuit boards, the overall hot pressing step of the present application adds elastic buffer pads and metal foil, which can reduce the impact force on the circuit board at the initial stage of pressing, and further reduce the damage to the magnetic core 40.

[0059] Furthermore, the circuit board preparation method of the embodiment further includes the following steps: S5, after the overall hot pressing of step S4, a conductive via 51 penetrating the circuit board is made. Specifically, a through hole penetrating the circuit board can be processed first, and then the entire circuit board is copper plated to form an interconnected copper foil layer on the inner wall of the through hole, thereby realizing the interlayer interconnection of the conductive circuit. After the entire board is copper plated, the L1 and L7 copper foil layers are etched to obtain the corresponding conductive circuit.

[0060] For the steps not described in detail in this application, reference can be made to the prior art and will not be repeated here.

[0061] Although the present invention is disclosed as above with specific embodiments, any person skilled in the art may make some changes or substitutions without departing from the scope of the present invention. That is, all equivalent changes made according to the present invention should be covered by the scope of the present invention.

Claims

1. A method for preparing a buried magnetic core circuit board, comprising the following steps: S1, making and pressing the upper stack of the circuit board; S2, making and pressing the lower laminate of the circuit board; S3, roughening the surface of the magnetic core; S4, placing an intermediate laminate with a receiving hole on the lower laminate of the circuit board, placing a magnetic core in the receiving hole of the intermediate laminate, and finally placing the upper laminate of the circuit board on the intermediate laminate for overall hot pressing; in, Step S3 includes: S31, soaking the magnetic core to be roughened in a phosphoric acid solution for 10 to 15 minutes; S32, soaking the magnetic core in a mixture of chromium nitrate and nitric acid for 15 to 20 minutes, and then washing with water.

2. The preparation method according to claim 1, wherein The upper laminated layer of the circuit board and the lower laminated layer of the circuit board have conductive circuits with different numbers of layers.

3. The preparation method according to claim 1, wherein step S1 comprises: S11, providing an upper core board with double-sided copper cladding, and etching the copper foil layers on both sides of the upper core board to form L2 and L3 conductive circuits; S12, laminating an L1 copper foil layer on one side of the L2 conductive circuit of the upper core board.

4. The preparation method according to claim 1, wherein step S2 comprises: S21, providing a lower core board with double-sided copper cladding, and etching the copper foil layers on both sides of the lower core board to form L5 and L6 conductive circuits; S22, pressing an L4 copper foil layer on one side of the L5 conductive circuit of the lower core board, and pressing an L7 copper foil layer on one side of the L6 conductive circuit; S23, etching the L4 copper foil layer to obtain an L4 conductive circuit.

5. The preparation method according to claim 1, wherein The mass fraction of the phosphoric acid is 75%, the mass fraction of chromium nitrate in the mixed solution is 10%, and the mass fraction of nitric acid is 5%.

6. The preparation method according to claim 1, wherein During hot pressing in step S4, an upper cover plate, kraft paper, steel plate, elastic buffer pad and metal foil are sequentially arranged above the circuit board from top to bottom, and metal foil, elastic buffer pad, steel plate, kraft paper and lower base plate are sequentially arranged below the circuit board from top to bottom.

7. The preparation method according to claim 1, wherein The magnetic core is rectangular, and a distance of 0.3 mm to 0.6 mm is arranged between the side wall of the magnetic core and the side wall of the accommodating hole. The corners of the accommodating hole are provided with rounded corners for positioning the magnetic core.

8. The preparation method according to claim 1, wherein The magnetic core is a ferrite core.

9. The preparation method according to claim 1, further comprising the steps of: S5, making a conductive via penetrating the circuit board.

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