Circuit board preparation method

Abstract

The invention discloses a circuit board preparation method. The circuit board preparation method comprises the following steps: respectively processing through holes in positions, corresponding to copper bosses or embedded parts, in a copper-clad core plate and a prepreg; laminating and hot-pressing the copper-clad core plate, the prepreg and the metal radiating plate or the embedded part provided with the copper boss, wherein one part of the prepreg is hot-pressed to form a bonding part for connecting the side wall of the copper boss or the embedded part with the copper-clad core plate; grinding the plate to reduce the concave depth of the bonding part relative to the plate surface; plating copper on the whole board to manufacture a surface copper foil layer on the surface of the circuit board; grinding the plate so as to further improve the surface flatness of the surface copper foil layer; wherein the copper-clad core plate located on the outermost side during laminated plate hot pressing comprises an outer-layer copper foil and an inner-layer copper foil, and the thickness of the outer-layer copper foil is smaller than that of the inner-layer copper foil, so that the initial concave depth of the bonding part is reduced. According to the preparation method, the surface flatness of the copper foil layer on the surface of the circuit board can be improved, and the product yield is improved.

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 embedded parts / embedded copper bosses. Background Art

[0002] In the prior art, when manufacturing a metal-based circuit board with an embedded copper boss and a circuit board with an embedded part, a commonly used manufacturing method is to stack and hot-press a copper-clad core board, a prepreg, and a metal heat sink or embedded part with a copper boss according to the circuit board structure. When stacking, the copper boss or embedded part is inserted into the corresponding through holes on the copper-clad core board and the prepreg. After hot pressing, the copper-clad core board and the prepreg form a circuit substrate. A portion of the resin in the prepreg will flow into the gap between the copper boss / embedded part and the copper-clad core board and solidify, forming a bonding portion connecting the side wall of the copper boss or embedded part and the circuit substrate.

[0003] However, due to factors such as the overall thickness requirement of the circuit board, the thickness of the prepreg is often strictly limited, which may result in the gap between the copper boss / embedded part and the circuit substrate being difficult to be completely filled with the resin of the prepreg after hot pressing, causing at least part of the resin bonding part to have a large depth of depression relative to the board surface, which in turn leads to a series of quality problems.

[0004] For example, due to the existence of the depressed area in the bonding part, the surface copper foil layer will also have a depression at the connection between the copper boss / embedded part and the circuit substrate when the entire board is copper-plated. When etching the surface copper foil layer to make a conductive circuit, it is easy for the film to be loose at the depressed part, so that the part of the surface copper foil layer that should be covered by the covering film will also be etched during etching, resulting in a low product yield.

[0005] Therefore, it is necessary to improve the existing circuit board preparation method. Summary of the invention

[0006] In view of the deficiencies of the prior art, the main purpose of the present invention is to provide an improved method for preparing a circuit board to improve the surface flatness of the copper foil layer on the surface of the circuit board.

[0007] In order to achieve the above main purpose, the present invention discloses a method for preparing a circuit board, the circuit board comprising a circuit substrate and a copper boss or an embedded part with a copper surface arranged in the circuit substrate; the circuit board preparation method comprises the following steps:

[0008] S1, processing through holes in the copper clad core board and the prepreg used to form the circuit substrate at positions corresponding to the copper boss or the embedded part;

[0009] S2, laminating and hot-pressing the copper clad core board, the prepreg, and the metal heat sink with the copper boss or the embedded part according to the circuit board structure, and forming a bonding part connecting the side wall of the copper boss or the embedded part with the copper clad core board through hot pressing of a part of the prepreg;

[0010] S3, grinding the plate to reduce the depression depth of the bonding portion relative to the plate surface;

[0011] S4, copper plating the entire board to form an outer copper foil layer on the surface of the circuit board that connects and covers the circuit substrate and a surface copper foil layer on the copper boss or embedded part;

[0012] S5, grinding the plate to improve the surface flatness of the surface copper foil layer;

[0013] Wherein, the copper clad core laminate located on the outermost side during hot pressing of the laminate comprises an outer copper foil and an inner copper foil, and the thickness of the outer copper foil is less than the thickness of the inner copper foil.

[0014] Preferably, the thickness difference between the outer copper foil and the inner copper foil is not less than 8 μm.

[0015] Preferably, in step S3, the plate is firstly ground with a non-woven brush or a nylon needle brush to remove the adhesive resin that flows to the plate surface during hot pressing; and then the plate is ground with a ceramic brush to reduce copper and improve the flatness of the copper surface.

[0016] Preferably, in step S3, the copper thickness reduced by grinding the plate is 3 μm to 8 μm.

[0017] Preferably, the copper thickness of the surface copper foil layer in step S4 is 5 μm to 10 μm greater than the target copper thickness.

[0018] Preferably, in step S5, a ceramic brush is used to grind the plate, and the copper thickness reduced by grinding is 1 μm to 2 μm.

[0019] According to a specific embodiment of the present invention, the metal heat sink is a copper heat sink, and the circuit substrate is bonded to a side of the metal heat sink provided with the copper boss.

[0020] According to another specific embodiment of the present invention, the embedded component is configured to penetrate the circuit substrate, and after grinding in step S3, the embedded component and the outer copper foil of the circuit substrate form a flush surface.

[0021] Further, the embedded part is a copper block, or a copper-clad ceramic block including a ceramic body and a copper foil layer, and the copper foil layer is arranged on two opposite surface sides of the ceramic body.

[0022] Furthermore, the circuit board preparation method further includes step S6 performed after step S5: etching at least one side surface of the circuit board to form a conductive circuit.

[0023] The technical solution of the present invention has at least the following beneficial effects:

[0024] In the preparation method of the present invention, on the one hand, the thickness of the outer copper foil of the outermost copper-clad core board is less than the inner copper foil during hot pressing of the laminate, and the initial thickness of the circuit substrate can be made relatively thin, thereby reducing the original depression depth of the bonding part; on the other hand, grinding and copper reduction are performed after hot pressing of the laminate, which can further reduce the depression depth of the bonding part, so as to reduce the depression degree of the surface copper foil layer at the bonding part position when the whole board is copper plated, and grinding and copper reduction are performed again after the surface copper foil layer is made to eliminate the depression area of ​​the surface copper foil layer, thereby ensuring the surface flatness of the surface copper foil layer. In this way, when etching is performed to make the conductive circuit later, the reliability of the film at the bonding part position on the surface copper foil layer is guaranteed, avoiding the problem of the surface copper foil layer being incorrectly etched at the bonding part position, thereby improving the product yield.

[0025] 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

[0026] Figure 1 is an exemplary flow chart of an embodiment of the preparation method of the present invention;

[0027] Figure 2 It is a schematic structural diagram of a copper-clad core board provided with accommodating through holes in the present invention;

[0028] Figure 3 It is a schematic structural diagram of a prepreg provided with an avoidance through hole in the present invention;

[0029] Figure 4 is a schematic diagram of the heat-pressed laminate structure of the circuit board in Example 1;

[0030] Figure 5 This is a schematic diagram of the structure of the circuit board in Example 1 before copper plating on the entire board;

[0031] Figure 6 This is a schematic diagram of the structure of the circuit board after the entire board is copper plated in Example 1;

[0032] Figure 7 is a schematic diagram of the heat-pressed laminate structure of the circuit board in Example 2;

[0033] Figure 8 This is a schematic diagram of the structure of the circuit board in Example 2 before copper plating on the entire board;

[0034] Fig. 9This is a schematic diagram of the structure of the circuit board after the entire board is copper plated in Example 2;

[0035] Fig.10 It is a schematic diagram of the deformation structure of the embedded part in Example 2. DETAILED DESCRIPTION

[0036] In the following description, many specific details are explained in conjunction with specific embodiments to facilitate a full understanding of the present invention. However, 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] Figure 1 This is an exemplary flow chart of some steps in the embodiment of the circuit board manufacturing method of the present invention. It should be noted that some steps that are the same as those in the prior art except for the steps shown in the figure are omitted in this exemplary flow chart. Figure 1 As shown, the circuit board preparation method of the embodiment includes the following steps:

[0038] S1, processing through holes at positions corresponding to copper bosses or embedded parts in a copper clad core board and a prepreg for forming a circuit substrate;

[0039] S2, laminating and hot-pressing the copper clad core board, the prepreg, and the metal heat sink or embedded part with the copper boss according to the circuit board structure, and hot-pressing a part of the prepreg to form a bonding part connecting the side wall of the copper boss or embedded part and the copper clad core board;

[0040] In step S2, the outermost copper clad core laminate comprises an outer copper foil and an inner copper foil during hot pressing of the laminate, and the thickness of the outer copper foil is smaller than the thickness of the inner copper foil to reduce the original depression depth of the bonding portion.

[0041] S3, grinding the board to remove glue and copper from the board surface and reduce the depth of the depression of the bonding part relative to the board surface;

[0042] S4, copper plating of the entire board to produce a surface copper foil layer on the surface of the circuit board that connects and covers the outer copper foil of the circuit substrate and the copper boss or embedded part;

[0043] S5, grinding the plate to eliminate the concave area of ​​the surface copper foil layer and improve the surface flatness of the surface copper foil layer.

[0044] Hereinafter, the preparation method of the present invention will be described in detail with reference to specific examples.

[0045] Example 1

[0046] Combination Figures 2 to 6As shown, the circuit board involved in Embodiment 1 includes a circuit substrate 20 and a metal heat sink 11 provided with a copper boss 12, the circuit substrate 20 is bonded to the side of the metal heat sink 11 provided with the copper boss 20, and the copper boss 12 is arranged in the circuit substrate 20. Among them, the metal heat sink 11 is preferably a copper heat sink, and the copper boss 12 and the metal heat sink 11 can have an integrally formed structure (for example, the copper boss 12 is obtained by partially etching the copper heat sink), and can also be connected to the metal heat sink 11 by electroplating, welding, bonding, etc.

[0047] like Figure 2 and Figure 3 As shown, step S1 processes a receiving through hole 210 at a position corresponding to the copper boss 12 of the metal heat sink 11 in the copper clad core board 21, and processes an avoidance through hole 221 at a position corresponding to the copper boss 12 in the prepreg 22. Exemplarily, the copper clad core board 21 can be a FR-4 or FR-15 double-sided copper clad core board, and the prepreg 22 can be a glass fiber cloth prepreg or a non-woven fabric prepreg. The specific material selection of the copper clad core board 21 and the prepreg 22 can be determined according to product requirements, and the present invention does not limit this. The specific implementation of step S1 can refer to the prior art and will not be described in detail here.

[0048] like Figure 4 As shown, in step S2 of embodiment 1, the prepreg 22 and the copper clad core board 21 are stacked on the metal heat sink 11 according to the circuit board structure, and the copper boss 12 is inserted into the accommodating through hole 210 of the copper clad core board 21 and the avoidance through hole 221 of the prepreg 22. When stacking the boards, the outermost copper clad core board 21 includes an outer copper foil 213 and an inner copper foil 212, and the thickness of the outer copper foil 213 is less than the thickness of the inner copper foil 212, and the inner copper foil 212 can be made with an inner conductive circuit. Preferably, the difference in thickness between the outer copper foil 213 and the inner copper foil 212 is not less than 8μm.

[0049] like Figure 5 As shown, after hot pressing, the copper clad core board 21 and the semi-cured sheet 22 form a circuit substrate 20, and the circuit substrate 20 is bonded to the side of the metal heat sink 11 provided with the copper boss 12 through the semi-cured sheet 22, and the copper boss 12 is inserted into the circuit substrate, and a part of the semi-cured sheet 22 forms a bonding portion 222 connecting the side wall of the copper boss 12 and the copper clad core board 21, and the bonding portion 222 has a recessed area 223 relative to the board surface.

[0050] In the preparation method of the present invention, since the thickness of the outer copper foil 213 of the outermost copper clad core board 21 is smaller than the inner copper foil 212 when the laminate is hot-pressed, the initial thickness of the circuit substrate 20 can be made relatively thin, thereby reducing the original depression depth of the bonding portion 223 relative to the board surface (i.e., the initial depth of the depression area 223).

[0051] After the board surface debonding and copper reduction grinding step S3 is performed, the resin that flows to the board surface (the surface of the outer copper foil 213 and the copper boss 12) during hot pressing is removed, and the outer copper foil 213 and the copper boss 12 are simultaneously thinned to have mutually flush surfaces, and the depth of the depression of the bonding portion 222 relative to the board surface (the depth of the depression area 223) is further reduced. Specifically, the copper reduction thickness of the grinding board in step S3 can be controlled within the range of 3μm to 8μm.

[0052] Preferably, the grinding of the plate in step S3 includes first grinding the plate with a non-woven brush or a nylon needle brush, and then grinding the plate with a ceramic brush. Among them, the main function of grinding the plate with a nylon needle brush or a non-woven brush is to remove glue from the plate surface, and the main function of grinding the plate with a ceramic brush is to reduce copper. Since the ceramic brush does not have the softness of the nylon needle brush or the non-woven brush, using the ceramic brush to grind the plate to reduce copper can avoid increasing the depth of the depression due to the undesired grinding of the bonding portion 222.

[0053] In the preparation method of the present invention, step S3 uses grinding instead of etching to reduce copper, which can avoid etching solution remaining in the holes on the circuit substrate 20 used to make interlayer interconnection holes (conducting holes between different circuit layers), and avoid product quality problems caused by etching solution residue (such as copper plating defects in interlayer interconnection holes).

[0054] After the board is polished in step S3, the whole board is plated with copper in step S4 to make connections on the surface of the circuit board and cover the outer copper foil 213 and the surface copper foil layer 23 of the copper boss 12. Figure 6 As shown, the surface copper foil layer 23 simultaneously fills the depressed area 223 of the bonding portion 222. Among them, since the grinding operation in step S3 is usually difficult to completely eliminate the depressed area 223 of the bonding portion 222, the surface copper foil layer 23 may be depressed in the area corresponding to the depressed area 223 after the entire board is copper plated, but the degree of depression is relatively small. Preferably, the copper thickness of the surface copper foil layer 23 is greater than the target copper thickness by 5μm to 10μm, so as to reserve sufficient copper reduction thickness for the subsequent grinding step S5.

[0055] The main purpose of the grinding step S5 is to eliminate the concave area of ​​the surface copper foil layer 23 and improve the surface flatness of the surface copper foil layer 23. Preferably, the step S5 uses a ceramic brush to grind the plate, and the copper thickness of the grinding plate can be determined according to the depth of the concave area of ​​the surface copper foil layer 23, which is usually 1μm to 2μm.

[0056] Furthermore, the circuit board preparation method of Example 1 performs step S6 after the grinding step S5: etching the outer copper foil 213 and the surface copper foil layer 23 to form a conductive circuit on the surface of the circuit board. The specific implementation of step S6 can refer to the prior art and will not be described here.

[0057] It should be noted that the circuit substrate 20 in Example 1 may include one or more layers of copper clad core board 21. Among them, when the circuit substrate 20 has only one layer of copper clad core board 21, the copper clad core board 21 is the outermost copper clad core board. When the circuit substrate 20 includes multiple layers of copper clad core boards 21, it is only necessary to ensure that the thickness of the outer copper foil 213 of the outermost copper clad core board 21 is less than the inner copper foil 212 when the laminate is hot-pressed, and there is no restriction on the thickness of the copper foil layer on the two sides of the other copper clad core boards 21.

[0058] Example 2

[0059] Combination Figures 7 to 9 As shown, the circuit board involved in the second embodiment includes a circuit substrate 20 and an embedded component 100 disposed in the circuit substrate 20. The embedded component 100 can be an embedded component with a copper surface, such as a copper block. The outer shape of the embedded component 100 can be various shapes such as round, square, oval, stepped, etc., and the present invention is not limited to this.

[0060] like Figure 7 As shown, in Example 2, when hot pressing the laminates in step S2, the copper clad core laminates 21 and the prepregs 22 are alternately stacked in such a way that the prepregs 22 are located between the copper clad core laminates 21, and the embedded parts 100 are placed in the receiving through holes 210 and the avoiding through holes 221. Figure 8 As shown, after the laminate is hot-pressed, the copper clad core board 21 and the prepreg 22 form a circuit substrate 20, and the embedded component 100 is disposed in the circuit substrate 20 as a whole and penetrates the circuit substrate 20. Part of the adhesive resin of the prepreg 22 flows to fill the gap between the embedded component 100 and the copper clad core board 21, and forms a bonding portion 222 connecting the side wall of the embedded component 100 and the copper clad core board 21, and the bonding portion 222 has a recessed area 223.

[0061] In Example 2, the circuit substrate 20 includes two layers of copper clad core boards 21, which are both located on the outermost copper clad core boards when the laminates are hot-pressed, and the thickness of their outer copper foils 213 is less than the thickness of the inner copper foil 212. As a variation of Example 2, the circuit substrate 20 may include more than three layers of copper clad core boards 21. In this case, it is only necessary to ensure that the thickness of the outer copper foils 213 of the two outermost copper clad core boards 21 when the laminates are hot-pressed is less than the thickness of the inner copper foils 212, and there is no restriction on the thickness of the copper foil layers on both sides of the other copper clad core boards 21.

[0062] In Example 2, step S3 grinds both sides of the circuit board, and after grinding, the embedded part 100 and the outer copper foil 213 of the circuit substrate 20 form a flush surface, and the depth of the depression of the bonding portion 222 relative to the board surface (the depth of the depression area 223) is further reduced. Subsequently, the both sides of the circuit board are subjected to the whole board copper plating step S4 and the grinding step S5, so that the surface copper foil layer 23 with a flat surface can be obtained.

[0063] Furthermore, the circuit board preparation method of Example 2 includes step S6 performed after the grinding step S5: etching the outer copper foil 213 and the surface copper foil layer 23 on at least one side of the circuit board to form a conductive circuit on the surface of the circuit board. Exemplarily, one side of the circuit board in Example 2 is a device connection surface etched with circuits for mounting components, and the other side is a heat dissipation surface that does not need to be etched.

[0064] As a variation of the structure of Example 2, Fig.10 As shown, the embedded part 100 can be a copper-clad ceramic block, which includes a ceramic body 101 and a copper foil layer 102 arranged on two opposite surfaces of the ceramic body 101, and the copper foil layer 102 forms the copper surface of the embedded part 100. The ceramic body 101 can be a ceramic material such as aluminum nitride, aluminum oxide, silicon nitride or silicon carbide, and a transition metal connecting layer such as a titanium layer can be provided between the copper foil layer 102 and the ceramic body 101. The copper foil layer 102 can completely cover the surface of the ceramic body 101, or it can have a gap with the edge of the ceramic body 101. In step S6, the copper foil layer 102 on the surface of the ceramic body 101 can also be etched to form a conductive circuit on the ceramic body 101.

[0065] It is easy to understand that the circuit board preparation method of the present invention can also include other steps such as making inner layer circuits, making interlayer interconnection holes that electrically connect different circuit layers, and making a solder resist layer on the surface of the circuit board. These steps can refer to the existing technology in the field, so the detailed description thereof is omitted here.

[0066] It should be noted that for the sake of simplicity, some identical descriptions in the above different embodiments are omitted. Unless there are contradictory or exclusive situations, the different embodiments disclosed above can be referenced, referred to or combined with each other, and the technical features / components of different embodiments can also be combined and / or replaced with each other.

[0067] Although the present invention is disclosed as above with specific embodiments, these specific embodiments are not intended to limit the scope of the present invention. Any person skilled in the art can make some changes / replacements 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 protection scope of the present invention.

Claims

1. A method for preparing a circuit board, the circuit board comprising a circuit substrate and a copper boss or an embedded part with a copper surface arranged in the circuit substrate; the method for preparing the circuit board comprises the following steps: S1, processing through holes in the copper clad core board and the prepreg used to form the circuit substrate at positions corresponding to the copper boss or the embedded part; S2, laminating and hot-pressing the copper clad core board, the prepreg, and the metal heat sink with the copper boss or the embedded part according to the circuit board structure, and forming a bonding part connecting the side wall of the copper boss or the embedded part with the copper clad core board through hot pressing of a part of the prepreg; S3, grinding the plate to reduce the depression depth of the bonding portion relative to the plate surface; S4, copper plating the entire board to form an outer copper foil layer on the surface of the circuit board that connects and covers the circuit substrate and a surface copper foil layer on the copper boss or embedded part; S5, grinding the plate to improve the surface flatness of the surface copper foil layer; in, The copper clad core board located on the outermost side during hot pressing of the laminated boards comprises an outer copper foil and an inner copper foil, and the thickness of the outer copper foil is less than the thickness of the inner copper foil.

2. The method for preparing a circuit board according to claim 1, wherein: The thickness difference between the outer copper foil and the inner copper foil is not less than 8 μm.

3. The method for preparing a circuit board according to claim 1, wherein: In step S3, the plate is firstly polished with a non-woven brush or a nylon needle brush, and then polished with a ceramic brush.

4. The method for preparing a circuit board according to claim 3, wherein: Step S3: grinding the plate to reduce the copper thickness to 3 μm to 8 μm.

5. The method for preparing a circuit board according to claim 1, wherein: The copper thickness of the surface copper foil layer in step S4 is greater than the target copper thickness by 5 μm to 10 μm.

6. The method for preparing a circuit board according to claim 1, wherein: In step S5, a ceramic brush is used to grind the plate, and the copper thickness of the plate is reduced by 1 μm to 2 μm.

7. The method for preparing a circuit board according to claim 1, wherein: The metal heat sink is a copper heat sink, and the circuit substrate is bonded to a side of the metal heat sink provided with the copper boss.

8. The method for preparing a circuit board according to claim 1, wherein: The embedded component is arranged to penetrate the circuit substrate, and after the plate is polished in step S3, the embedded component and the outer copper foil of the circuit substrate form a flush surface.

9. The method for preparing a circuit board according to claim 8, wherein: The embedded part is a copper block or a copper-clad ceramic block including a ceramic body and a copper foil layer, wherein the copper foil layer is arranged on two opposite surface sides of the ceramic body.

10. The method for preparing a circuit board according to claim 1, wherein: After step S5, step S6 is performed: etching at least one side surface of the circuit board to form a conductive circuit.

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