Preparation method of circuit board

Abstract

The invention discloses a preparation method of a circuit board, which comprises the following steps: interlayer positioning is carried out on a lamination layer for a substrate, the upper and lower surfaces of the lamination layer are provided with first copper foil layers, and the lamination layer is provided with an accommodating hole for installing an embedded part; removable layer-adding pieces are attached to the upper surface and the lower surface of the laminated layer, and avoiding holes are formed in the positions, corresponding to the embedded parts, of the layer-adding pieces; after embedded parts are placed in the accommodating holes of the laminated layers, pressing is carried out, so that a substrate is formed, and the embedded parts are fixed in the substrate; second copper foil layers are arranged on the upper surface and the lower surface of the embedded part, and the initial thickness of the second copper foil layers is larger than that of the first copper foil layers. And after pressing, removing the layer adding sheet and grinding the upper surface and the lower surface of the circuit board so as to remove glue on the board surface and enable the outer surfaces of the second copper foil layer and the first copper foil layer to be flush with each other. According to the preparation method, the thickness consistency of the first copper foil layer and the second copper foil layer can be improved, and manufacturing of a fine circuit is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of circuit boards; more specifically, it relates to a method for manufacturing a circuit board with embedded components. Background Art

[0002] Setting embedded components such as ceramic blocks in the substrate of a circuit board is an effective way to improve the heat dissipation performance of the circuit board. The existing manufacturing method for such circuit boards is to pre - groove the copper - clad core board and prepreg used to form the substrate. After laminating the copper - clad core board and prepreg, a copper - clad ceramic block is placed into the holes formed by the grooving for pressing, so as to form the substrate and fix the embedded component in the substrate. After pressing, the glue on the board surface is removed and a flat board surface is formed.

[0003] In the existing manufacturing method, the copper foil layers on the upper and lower surfaces of the ceramic block and the copper foil layers on the upper and lower surfaces of the substrate are set to have the same initial thickness. However, due to reasons such as the difference in material properties between the substrate and the ceramic block, a surface height difference will occur between the surface copper foil layer of the substrate and the surface copper foil layer of the ceramic block after pressing, resulting in the surface copper foil layer of the ceramic block protruding from the surface copper foil layer of the substrate. In this way, during the grinding process of removing the glue on the board surface, the protruding part of the surface copper foil layer of the ceramic block will be ground flat, and the actual thickness of the surface copper foil layer of the ceramic block after grinding will be lower than that of the surface copper foil layer of the substrate, making it difficult to produce fine circuits on the ceramic block when manufacturing surface circuits. Summary of the Invention

[0004] The main purpose of the present invention is to provide a method for manufacturing a circuit board to improve the copper thickness consistency of the surfaces of the substrate and the embedded component, and to realize the production of fine circuits.

[0005] To achieve the above - mentioned main purpose, the present invention discloses a method for manufacturing a circuit board, the circuit board includes a substrate and an embedded component disposed in the substrate; the manufacturing method includes the following steps:

[0006] S1, perform inter - layer positioning on the stack used to form the substrate; wherein, the upper and lower surfaces of the stack have a first copper foil layer, and the stack is provided with receiving holes for installing the embedded component;

[0007] S2, attach removable build - up sheets on the upper and lower surfaces of the stack, and the build - up sheets are provided with avoidance holes corresponding to the positions of the embedded components;

[0008] S3, place the embedded component into the receiving holes of the stack and then perform pressing to form the substrate and fix the embedded component in the substrate; wherein, the upper and lower surfaces of the embedded component are provided with a second copper foil layer, and the initial thickness of the second copper foil layer is greater than that of the first copper foil layer;

[0009] S4. After lamination, remove the build-up sheet and grind the upper and lower surfaces of the circuit board to remove the glue on the board surface and make the outer surfaces of the second copper foil layer and the first copper foil layer flush with each other.

[0010] Further, the manufacturing method further includes the following steps carried out after step S4:

[0011] S5. Electroplate the entire circuit board on the upper and lower surfaces, and fabricate surface circuits on at least one surface of the circuit board, with a part of the surface circuits disposed on the embedded component.

[0012] Further, the laminate includes at least two copper-clad core boards, and the first copper foil layer is provided in the form of being part of the outer copper-clad core board; or, the laminate includes at least one copper-clad core board, and the first copper foil layer is provided independently of the copper-clad core board.

[0013] Further, the initial thickness difference T1 between the second copper foil layer and the first copper foil layer is 15 μm to 30 μm; the thickness of the build-up sheet is T2, and T1 - T2 ≤ 5 μm. With such a setting, the copper thickness consistency on the surface of the substrate and the embedded component can be improved while reducing the grinding workload.

[0014] Further, the size of the avoidance hole is smaller than the size of the accommodation hole, so that the gap between the avoidance hole and the embedded component is smaller than the gap between the accommodation hole and the embedded component. Preferably, the unilateral gap between the accommodation hole and the embedded component is 0.1 mm to 0.15 mm, and the unilateral gap between the avoidance hole and the embedded component is 0.05 mm to 0.1 mm.

[0015] Further, step S1 performs interlayer positioning on the laminate by means of thermal fusion bonding.

[0016] Further, the build-up sheet is a release film to facilitate peeling it off from the substrate after lamination.

[0017] Further, when performing the lamination in step S3, a release film and a metal plate are sequentially covered on the upper and lower sides of the circuit board.

[0018] Further, the embedded component is arranged to block the electrical connection between the second copper foil layers on its upper and lower surfaces. Preferably, the embedded component is a ceramic block.

[0019] The technical solution of the present invention has at least the following beneficial effects:

[0020] In the preparation method of the present invention, the second copper foil layers on the upper and lower surfaces of the embedded parts are designed to have an initial thickness greater than that of the first copper foil layers on the upper and lower surfaces of the substrate / stacks. At the same time, removable build-up sheets are attached to the upper and lower surfaces of the stacks. The build-up sheets can make the inner surfaces of the second copper foil layers and the first copper foil layers as flush as possible after lamination, and avoid affecting the lamination effect of the stacks due to the existence of the initial thickness difference between the second copper foil layers and the first copper foil layers. During grinding, the protruding parts of the second copper foil layers that are higher than the first copper foil layers are first ground off, and the height difference between the outer surfaces of the first copper foil layers and the second copper foil layers gradually decreases until the outer surfaces of the two reach a substantially flush state (height difference less than 5 μm), thereby improving the consistency of the target copper thickness between the second copper foil layers and the first copper foil layers, which is beneficial to making fine circuits on the surface of the embedded parts.

[0021] To more clearly illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described in detail below with reference to the drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of the stack structure for forming a substrate in an embodiment of the present invention;

[0023] Figure 2 is a schematic diagram of the structure with build-up sheets attached to the upper and lower surfaces of the stack in the embodiment;

[0024] Figure 3 is a schematic diagram of the lamination structure of the stack in the embodiment;

[0025] Figure 4 is a schematic diagram of the circuit board structure after lamination in the embodiment;

[0026] Figure 5 is a schematic diagram of the structure of the circuit board surface after degumming / grinding in the embodiment;

[0027] Figure 6 is a schematic diagram of the structure of the entire circuit board after copper plating in the embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] Many specific details are set forth in the following description in order to fully understand the present invention, but the present invention can also be implemented in other variations or alternative ways based on this. Therefore, other implementable ways that can be known to those skilled in the art based on the embodiments described in this application all fall within the protection scope of the present invention.

[0029] As Figures 1 to 6 shown, the circuit board in the embodiment includes a substrate 10 and an embedded part 20 disposed in the substrate 10, and its preparation method includes the following steps:

[0030] S1, perform interlayer positioning on the laminate 10a for forming the substrate 10; wherein, the upper and lower surfaces of the laminate 10a have the first copper foil layer 111, and the laminate 10a is provided with a receiving hole 110a for installing the embedded part 20.

[0031] S2, attach removable build-up sheets 30 to the upper and lower surfaces of the laminate 10a, and the build-up sheets 30 are provided with avoidance holes 31 corresponding to the positions of the embedded parts 20.

[0032] S3, place the embedded part 20 into the receiving hole 110a of the laminate 10a and then perform lamination to form the substrate 10 and fix the embedded part 20 within the substrate 10; wherein, the upper and lower surfaces of the embedded part 20 are provided with the second copper foil layer 21, and the initial thickness of the second copper foil layer 21 is greater than that of the first copper foil layer 111.

[0033] S4, remove the build-up sheets 30 after lamination and grind the upper and lower surfaces of the circuit board to remove the glue on the board surface and make the outer surfaces of the second copper foil layer 21 and the first copper foil layer 111 flush.

[0034] S5, perform full-panel copper plating on the upper and lower surfaces of the circuit board, and fabricate surface circuits on at least one surface of the circuit board, and a part of the surface circuits is disposed on the embedded part 20.

[0035] In the embodiment, step S1 can perform interlayer positioning on the laminate 10a by means of thermal fusion, that is, perform thermal fusion (hot pressing) on a local set area at the edge of the laminate 10a to achieve connection and positioning between the layers of the laminate 10a. As a variation of the embodiment, interlayer positioning between the layers of the laminate 10a can also be performed by means of riveting / dowel pins.

[0036] Exemplarily, as Figure 1 shown, the laminate 10a includes two copper-clad core boards 11 and prepregs 12 disposed between the copper-clad core boards 11. Both of the two copper-clad core boards 11 are outer-layer copper-clad core boards, and the first copper foil layer 111 on the upper and lower surfaces of the laminate 10a is provided in the form of a part of the outer-layer copper-clad core board, that is, the first copper foil layer 111 has been pre-fabricated on the insulating core board 110 of the copper-clad core board 11. The copper-clad core boards 11 and the prepregs 12 are pre-processed with through holes corresponding to the positions of the embedded parts 20 before laminating to form receiving holes 110a for installing the embedded parts 20 in the laminate 10a after laminating. Among them, the sizes of the through holes in the copper-clad core boards 11 and the prepregs 12 may be the same or different. The size of the through holes in the prepregs 12 is usually relatively large, and the size of the receiving hole 110a is defined by the through holes in the copper-clad core boards 11.

[0037] Further, as Figure 1As shown, the copper-clad core board 11 may have an inner copper foil 112 attached to the insulating core board 110. The inner copper foil 112 may be pre-etched with inner-layer circuits before laminating, or may not be etched and is only used to enhance the connection strength with the prepreg 12. It is easy to understand that the number of copper-clad core boards 11 in the laminate 10a may be three or more, and can be specifically set according to the thickness of the circuit board and / or the number of conductive circuit layers required. At this time, the outermost copper-clad core board is the outer copper-clad core board, and the first copper foil layer 111 is also provided in the form of being part of the outer copper-clad core board.

[0038] As a variation of the embodiment, the first copper foil layer in the laminate is provided in a form independent of the copper-clad core board, for example, in the form of an RCC copper foil (resin-coated copper foil), forming a laminate structure of first copper foil layer - prepreg - copper-clad core board - prepreg - first copper foil layer. It is easy to understand that the copper-clad core board in this variation can be one layer or multiple layers, and can be specifically determined according to the thickness of the circuit board and / or the number of conductive circuit layers required. Prepregs are also provided between multiple copper-clad core boards.

[0039] In the embodiment, in step S2, the build-up sheet 30 can be riveted / pinned together with the laminate 10a to removably attach the build-up sheet 30 to the upper and lower surfaces of the laminate 10a, and the rivets / pins are drilled out from the substrate 10 after lamination and removed together with the build-up sheet 30. Preferably, the build-up sheet 30 is a release film to facilitate peeling it off the substrate 10 after lamination. The build-up sheet 30 can also be made of other materials such as metal sheets.

[0040] As Figure 2 shown, the size of the avoidance hole 31 in the build-up sheet 30 is preferably smaller than the size of the accommodation hole 110a in the laminate 10a. As Figure 3 shown, after the embedded part 20 is placed, the gap between the avoidance hole 31 and the embedded part 20 is smaller than the gap between the accommodation hole 110a and the embedded part 20, so that the build-up sheet 30 can be used to assist in positioning the embedded part 20 and inhibit the flow of the prepreg 12 to the board surface during lamination. Exemplarily, the unilateral gap between the accommodation hole 110a and the embedded part 20 is 0.1 mm to 0.15 mm, and the unilateral gap between the avoidance hole 31 and the embedded part 20 is 0.05 mm to 0.1 mm. Among them, the embedded part 20 can be circular or square, or can be other shapes such as stepped, and the present invention does not limit this.

[0041] Further, the embedded part 20 is preferably capable of blocking the electrical connection between the second copper foil layers 21 on its upper and lower surfaces and has good thermal conductivity. Among them, the second copper foil layer 21 can completely cover the upper and lower surfaces of the embedded part 20, or can have a spacing from the edge of the embedded part 20. Specifically, a ceramic block with good electrical insulation and thermal conductivity characteristics, such as an aluminum nitride, alumina, silicon nitride or silicon carbide ceramic block, can be used as the embedded part 20. In addition, a heat-conducting component connecting ceramic insulating layers above and below a metal body can also be used as the embedded part 20.

[0042] As described above, the second copper foil layer 21 has an initial thickness greater than that of the first copper foil layer 111. Exemplarily, the initial thickness difference T1 between the second copper foil layer 21 and the first copper foil layer 111 can be 15 μm to 30 μm, preferably 20 μm to 25 μm. Preferably, assuming the thickness of the build-up sheet is T2, then T1 - T2 ≤ 5 μm. In the present invention, the build-up sheet 30 is used to make up for the initial thickness difference between the second copper foil layer 21 and the first copper foil layer 111. On the one hand, it can avoid affecting the lamination effect of the laminate 10a due to the existence of the initial thickness difference between the second copper foil layer 21 and the first copper foil layer 111. On the other hand, it can make the inner surfaces of the second copper foil layer 21 and the first copper foil layer 111 as flat as possible after lamination, so that the second copper foil layer 21 and the first copper foil layer 111 have better thickness consistency (the thickness difference can be made less than 5 μm) after the panel grinding.

[0043] In the embodiment, as Figure 3 shown, when laminating in step S3, a release film 31 and a metal plate 32 can be respectively covered on the upper and lower surfaces of the substrate 10; among them, the metal plate 32 is preferably a steel sheet or an aluminum sheet. As Figure 4 shown, the resin material of the prepreg 12 will fill the gap between the substrate 10 and the embedded part 20 (and will flow to the panel surface at the same time) after lamination, so as to form a bonding part 121 that fixes the embedded part 20 in the substrate 10, that is, the bonding part 121 exists as a part of the prepreg 12; and, after lamination, the second copper foil layer 21 will protrude from the first copper foil layer 111, so it is necessary to perform panel grinding after removing the build-up sheet 30 to remove the glue on the panel surface and make the outer surfaces of the second copper foil layer 21 and the first copper foil layer 111 flush.

[0044] In the embodiment, in step S4, a ceramic brush, a non-woven brush and / or a nylon brush can be used to grind the upper and lower surfaces of the circuit board. Preferably, first use a ceramic brush for panel grinding to better thin the second copper foil layer 21; then, use a non-woven brush or a nylon brush for panel grinding to better remove the glue on the panel surface. As Figure 5As shown, the outer surfaces of the first copper foil layer 111 and the second copper foil layer 21 after grinding the plate will be in a substantially flush state. At the same time, since the inner surfaces of the second copper foil layer 21 and the first copper foil layer 111 also remain in a very good flush state after lamination, the thickness consistency of the first copper foil layer 111 and the second copper foil layer 21 can be improved.

[0045] As Figure 6 shown, after the entire board is electroplated with copper in step S5, a third copper foil layer 101 is formed on the upper and lower surfaces of the circuit board. The third copper foil layer 101 covers and connects the first copper foil layer 111 and the second copper foil layer 21. After the entire board is electroplated with copper, surface circuits can be etched on at least one surface of the circuit board. For example, the first copper foil layer 111, the second copper foil layer 21, and the third copper foil layer 101 on at least one surface are all etched. In this way, a part of the obtained surface circuit is located on the embedded part 20, and the other part is located on the substrate 10. Since the first copper foil layer 111 and the second copper foil layer 21 have very good thickness consistency, fine circuits can be fabricated on the embedded part 20.

[0046] It is easy to understand that the preparation method of the present invention may further include steps such as making a solder mask on the surface of the circuit board and making the outer shape of the circuit board. These steps can refer to the prior art in the art, so the detailed description thereof is omitted here.

[0047] Although the present invention is disclosed above with specific embodiments, these specific embodiments are not intended to limit the scope of implementation of the present invention. Any ordinary technician in the art can make some changes / replacements without departing from the scope of the invention of the present invention. That is, any equivalent changes made in accordance with the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a circuit board, the circuit board comprising a substrate and an embedded component arranged in the substrate; the preparation method comprises the following steps: S1, interlayer positioning of the stacked layers used to form the substrate; wherein, The upper and lower surfaces of the stack have a first copper foil layer, and the stack is provided with a receiving hole for installing the embedded component; S2, attaching removable build-up sheets to the upper and lower surfaces of the stack, wherein the build-up sheets are provided with avoidance holes at positions corresponding to the embedded parts; S3, placing the embedded component in the receiving hole of the stack and then pressing it to form the substrate and fix the embedded component in the substrate; wherein the upper and lower surfaces of the embedded component are provided with a second copper foil layer, and the initial thickness of the second copper foil layer is greater than that of the first copper foil layer; S4, after lamination, the build-up layer sheet is removed and the upper and lower surfaces of the circuit board are ground to remove the glue from the board surface and make the outer surface of the second copper foil layer flush with the outer surface of the first copper foil layer.

2. The preparation method according to claim 1, further comprising the following steps after step S4: S5, copper plating is performed on the upper and lower surfaces of the circuit board, and a surface circuit is made on at least one surface of the circuit board, and a part of the surface circuit is arranged on the embedded component.

3. The preparation method according to claim 1; wherein The laminate includes at least two layers of copper clad core boards, and the first copper foil layer is provided as a part of an outer copper clad core board.

4. The preparation method according to claim 1; wherein The laminate includes at least one copper clad core board, and the first copper foil layer is provided in a form independent of the copper clad core board.

5. The preparation method according to claim 1; wherein The initial thickness difference between the second copper foil layer and the first copper foil layer is T1=15 μm-30 μm; the thickness of the build-up layer is T2, T1-T2≤5 μm.

6. The preparation method according to claim 1; wherein The size of the avoidance hole is smaller than that of the accommodating hole.

7. The preparation method according to claim 1; wherein Step S1: positioning the laminated layers between layers by heat fusion.

8. The preparation method according to claim 1; wherein The build-up layer sheet is a release film.

9. The preparation method according to claim 1; wherein During the lamination step S3, the release film and the metal plate are sequentially covered on the upper and lower sides of the circuit board.

10. The preparation method according to claim 1; wherein The embedded component is configured to block the electrical connection between the second copper foil layers on the upper and lower surfaces thereof.

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