Preparation method of stepped golden finger packaging substrate

Abstract

The invention belongs to the technical field of packaging substrates, and particularly relates to a preparation method of a stepped golden finger packaging substrate. On the basis of completing a primary circuit, an SAP process is adopted, chemical copper deposition is firstly performed, pattern electroplating is realized by using a conductive layer, a gradient copper layer for preparing a stepped golden finger is obtained, then the conductive layer on a base material is removed through flash corrosion, and finally the stepped golden finger packaging substrate is obtained. According to the preparation method provided by the invention, manufacturing of the independent step golden finger can be realized, the problems that the shape of the golden finger is influenced by over-etching easily formed by removing an electroplating lead during preparation of the independent step golden finger and point discharge is caused by incomplete etching of the electroplating lead are effectively solved, and the prepared step golden finger packaging substrate is excellent in electric signal quality and high in reliability. The stability is high. Meanwhile, the preparation method provided by the invention is simple, equipment investment does not need to be increased, only conventional packaging substrate processing equipment is needed, and the preparation method is suitable for industrial application.

Description

Technical Field

[0001] The invention belongs to the technical field of packaging substrates, and in particular relates to a method for preparing a stepped gold finger packaging substrate. Background Art

[0002] The packaging substrate is a circuit board used to carry chips. It has the characteristics of high density, high precision, high performance, miniaturization and lightness. It can provide support, heat dissipation and protection for the chip. It can also provide electrical connection and physical support between the chip and the circuit board motherboard.

[0003] At present, the independent stepped gold finger design on the package substrate cannot conduct current through other layers of conductors to achieve graphic electroplating; the industry generally uses the method of pulling electroplating leads to conduct current, and removing the electroplating leads is prone to over-etching, resulting in open circuits or deformation of the circuits, as well as the tip discharge effect caused by incomplete etching, which leads to the deterioration of the electrical signal quality of the package substrate. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a stepped gold finger packaging substrate. The preparation method provided by the present invention can realize the production of independent stepped gold fingers, and the preparation method is simple. The prepared stepped gold finger packaging substrate has excellent electrical signal quality and high stability.

[0005] In order to achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for preparing a stepped gold finger packaging substrate, comprising the following steps: The double-sided copper-clad board is drilled to obtain a via hole, and the via hole penetrates the two surfaces of the double-sided copper-clad board; then copper is deposited on the hole wall of the via hole to obtain a copper-plated through hole; finally, the whole board is electroplated to obtain a through-hole copper-plated board; Prepare primary circuits on both surfaces of the through-hole copper-plated plate, wherein the primary circuits include a first circuit connected to the copper-plated through-hole and a second circuit not connected to the copper-plated through-hole, to obtain a primary circuit board; Chemically depositing copper on both surfaces of the primary circuit board to obtain a first copper conductive layer on the upper surface of the first circuit board and a second copper conductive layer on the lower surface of the first circuit board; Laminating the surfaces of the first copper conductive layer and the second copper conductive layer with a dry film, then sequentially exposing and developing the dry film on the surface of the first copper conductive layer and / or the second copper conductive layer to expose a step gold finger region, wherein the step gold finger region includes a step gold finger region located on the first circuit and a step gold finger region located on the second circuit, to obtain a first semi-finished product; Performing pattern electroplating on the surface of the first semi-finished product to obtain a gradient copper layer in the step gold finger area to obtain a second semi-finished product; The second semi-finished product is sequentially subjected to film stripping, copper stripping and palladium removal, wherein the copper stripping is to remove the exposed first copper conductive layer and second copper conductive layer by a flash etching method, to obtain a third semi-finished product; Prepare solder resist layers on both surfaces of the third semi-finished product, wherein the solder resist layers expose the gradient copper layer on the surface of the third semi-finished product and the gold finger area on the surface of the third semi-finished product, wherein the gold finger area includes the gold finger area located on the first circuit and the gold finger area located on the second circuit, to obtain a fourth semi-finished product; A Ni layer and an Au layer are sequentially prepared on the gradient copper layer and the surface of the gold finger region exposed on the surface of the fourth semi-finished product to obtain a Ni / Au layer, thereby obtaining a stepped gold finger packaging substrate.

[0006] Preferably, the thickness of the dry film used in the lamination is 30-100 μm.

[0007] Preferably, the thickness of the first copper conductive layer and the second copper conductive layer is 0.2-1 μm.

[0008] Preferably, the thickness of the primary circuit is 15-70 μm.

[0009] Preferably, the thickness of the gradient copper layer is 15-70 μm.

[0010] Preferably, the copper foil thickness of the double-sided copper clad laminate is 2-12 μm; and the thickness of the copper deposited on the hole wall of the via hole is 0.2-1 μm.

[0011] Preferably, the hole making is performed by mechanical drilling, CO2 laser drilling or UV laser drilling.

[0012] Preferably, when the hole making is carried out by CO2 laser drilling, and the copper foil thickness of the double-sided copper clad laminate is ≥12μm, before the CO2 laser drilling, the process further includes: subjecting the double-sided copper clad laminate to browning and copper reduction treatment; after the browning and copper reduction, the copper foil thickness of the double-sided copper clad laminate is 3~9μm.

[0013] Preferably, the method for preparing the primary circuit comprises sequentially performing pre-treatment, film lamination, exposure, development, etching and film stripping.

[0014] Preferably, the thickness of the Ni layer is 3-8 μm; the thickness of the Au layer is 0.02-0.4 μm.

[0015] The invention provides a preparation method of a stepped gold finger packaging substrate, comprising the following steps: making holes in a double-sided copper-clad board to obtain a via hole, wherein the via hole penetrates the two surfaces of the double-sided copper-clad board; then copper is deposited on the hole wall of the via hole to obtain a copper-plated through hole; finally, the whole board is electroplated to obtain a through-hole copper-plated board; a primary circuit is prepared on the two surfaces of the through-hole copper-plated board, wherein the primary circuit includes a first circuit connected to the copper-plated through hole and a second circuit not connected to the copper-plated through hole to obtain a primary circuit board; chemically depositing copper on the two surfaces of the primary circuit board to obtain a first copper conductive layer on the upper surface of the first circuit board, and a second copper conductive layer on the lower surface of the first circuit board; using dry film lamination on the surfaces of the first copper conductive layer and the second copper conductive layer, and then sequentially exposing and developing the dry film on the surface of the first copper conductive layer and / or the second copper conductive layer to expose a stepped gold finger area, wherein the stepped gold finger area The invention comprises a stepped gold finger region located on a first circuit and a stepped gold finger region located on a second circuit, so as to obtain a first semi-finished product; pattern electroplating is performed on the surface of the first semi-finished product, and a gradient copper layer is obtained in the stepped gold finger region, so as to obtain a second semi-finished product; the second semi-finished product is sequentially subjected to film stripping, copper stripping and palladium removal, wherein the copper stripping is to remove the exposed first copper conductive layer and the second copper conductive layer by a flash etching method, so as to obtain a third semi-finished product; solder resist layers are prepared on both surfaces of the third semi-finished product, wherein the solder resist layers expose the gradient copper layer on the surface of the third semi-finished product and the gold finger region on the surface of the third semi-finished product, wherein the gold finger region comprises the gold finger region located on the first circuit and the gold finger region located on the second circuit, so as to obtain a fourth semi-finished product; a Ni layer and an Au layer are sequentially prepared on the gradient copper layer and the gold finger region surface exposed on the surface of the fourth semi-finished product, so as to obtain a Ni / Au layer, so as to obtain a stepped gold finger packaging substrate. On the basis of completing a circuit once, the present invention adopts a semi-additive process (SAP) method, first chemically deposits copper, and then uses the copper conductive layer obtained by chemical copper deposition to realize graphic electroplating to obtain a gradient copper layer for preparing a step gold finger, and then removes the conductive layer on the substrate by flash etching, and finally obtains a step gold finger packaging substrate. The preparation method provided by the present invention can realize the production of independent step gold fingers, and effectively solves the problem that the removal of the electroplated leads during the preparation of independent step gold fingers is prone to over-etching and affects the shape of the gold fingers, and the problem of tip discharge caused by incomplete etching of the electroplated leads. The step gold finger packaging substrate prepared by the present invention has excellent electrical signal quality and high stability. At the same time, the preparation method provided by the present invention is simple, does not require additional equipment investment, and only conventional packaging substrate processing equipment is required, which is suitable for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of the structure of a through-hole copper-plated plate prepared in an embodiment of the present invention; Figure 2This is a schematic diagram of the structure of a primary circuit board prepared in an embodiment of the present invention; Figure 3 This is a schematic structural diagram of a semi-finished product obtained after chemical copper deposition in an embodiment of the present invention; Figure 4 This is a schematic structural diagram of a first semi-finished product prepared in an embodiment of the present invention; Figure 5 This is a schematic structural diagram of a second semi-finished product prepared in an embodiment of the present invention; Figure 6 This is a schematic structural diagram of a semi-finished product obtained after film stripping according to an embodiment of the present invention; Figure 7 This is a schematic structural diagram of a third semi-finished product prepared in an embodiment of the present invention; Figure 8 This is a schematic structural diagram of a fourth semi-finished product prepared in an embodiment of the present invention; Fig. 9 This is a schematic structural diagram of a stepped gold finger packaging substrate prepared in an embodiment of the present invention; In the figure: 1 is the copper layer, 2 is the copper-plated through hole, 3-1 is the first circuit, 3-2 is the second circuit, 4 is the copper conductive layer, 5 is the dry film, 6 is the gradient copper layer, 7 is the solder resist layer, 8 is the Ni / Au layer, and 9 is the dielectric layer. DETAILED DESCRIPTION

[0017] The present invention provides a method for preparing a stepped gold finger packaging substrate, comprising the following steps: The double-sided copper-clad board is drilled to obtain a via hole, and the via hole penetrates the two surfaces of the double-sided copper-clad board; then copper is deposited on the hole wall of the via hole to obtain a copper-plated through hole; finally, the whole board is electroplated to obtain a through-hole copper-plated board; Prepare primary circuits on both surfaces of the through-hole copper-plated plate, wherein the primary circuits include a first circuit connected to the copper-plated through-hole and a second circuit not connected to the copper-plated through-hole, to obtain a primary circuit board; Chemically depositing copper on both surfaces of the primary circuit board to obtain a first copper conductive layer on the upper surface of the first circuit board and a second copper conductive layer on the lower surface of the first circuit board; Laminating the surfaces of the first copper conductive layer and the second copper conductive layer with a dry film, then sequentially exposing and developing the dry film on the surface of the first copper conductive layer and / or the second copper conductive layer to expose a step gold finger region, wherein the step gold finger region includes a step gold finger region located on the first circuit and a step gold finger region located on the second circuit, to obtain a first semi-finished product; Performing pattern electroplating on the surface of the first semi-finished product to obtain a gradient copper layer in the step gold finger area to obtain a second semi-finished product; The second semi-finished product is sequentially subjected to film stripping, copper stripping and palladium removal, wherein the copper stripping is to remove the exposed first copper conductive layer and second copper conductive layer by a flash etching method, to obtain a third semi-finished product; Prepare solder resist layers on both surfaces of the third semi-finished product, wherein the solder resist layers expose the gradient copper layer on the surface of the third semi-finished product and the gold finger area on the surface of the third semi-finished product, wherein the gold finger area includes the gold finger area located on the first circuit and the gold finger area located on the second circuit, to obtain a fourth semi-finished product; A Ni layer and an Au layer are sequentially prepared on the gradient copper layer and the surface of the gold finger region exposed on the surface of the fourth semi-finished product to obtain a Ni / Au layer, thereby obtaining a stepped gold finger packaging substrate.

[0018] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0019] The present invention makes holes in a double-sided copper-clad laminate to obtain a via hole, and the via hole penetrates the two surfaces of the double-sided copper-clad laminate; then copper is deposited on the hole wall of the via hole to obtain a copper-plated through hole; finally, the whole board is electroplated to obtain a through-hole copper-plated laminate. In the present invention, the copper foil thickness of the double-sided copper-clad laminate is preferably 2~18μm, and in the embodiment, it can be 2~3μm, 12μm or 18μm. In the present invention, the hole making is preferably mechanical drilling, CO2 laser drilling or UV laser drilling. In the present invention, when the hole making is mechanical drilling, it is not necessary to pre-treat the double-sided copper-clad laminate. When the hole making is CO2 laser drilling, and the copper foil thickness of the double-sided copper-clad laminate is ≥12μm, it can be 12μm or 18μm in the embodiment; before the CO2 laser drilling, it also includes: browning and reducing copper on the double-sided copper-clad laminate; the copper foil thickness of the double-sided copper-clad laminate after browning and reducing copper is 3~9μm. The present invention facilitates the copper foil to absorb laser energy through the browning copper reduction treatment. When the holes are made by UV laser drilling, it is preferred to reduce the copper on the double-sided copper clad laminate before drilling.

[0020] In the present invention, copper is deposited on the hole wall of the via hole to obtain a copper-plated through hole, and the thickness of the copper deposited on the hole wall of the via hole is preferably 0.2-1 μm, more preferably 0.4-0.8 μm. The thickness of the whole plate electroplating is determined according to the structural requirements of the target product.

[0021] After obtaining a through-hole copper-plated board, the present invention prepares a primary circuit on both surfaces of the through-hole copper-plated board, and the primary circuit includes a first circuit connected to the copper-plated through hole and a second circuit not connected to the copper-plated through hole, so as to obtain a primary circuit board. In the present invention, the preparation method of the primary circuit preferably includes sequentially performing pre-treatment, film pasting, exposure, development, etching and film stripping. In the present invention, the second circuit is not connected to the copper-plated through hole, and is called an independent disk. Since the second circuit is not connected to the copper-plated through hole, conduction cannot be achieved through the copper-plated through hole. In the present invention, the thickness of the primary circuit is preferably 15~70μm, more preferably 15~30μm.

[0022] After obtaining a primary circuit board, the present invention performs chemical copper deposition on both surfaces of the primary circuit board, obtains a first copper conductive layer on the upper surface of the first circuit board, and obtains a second copper conductive layer on the lower surface of the first circuit board. The first copper conductive layer and the second copper conductive layer are copper conductive layers, and the function of the copper conductive layer is to realize the preparation of a gradient copper layer on the second circuit. The present invention has no special requirements for the specific implementation of the chemical copper deposition. The thickness of the first copper conductive layer and the second copper conductive layer is preferably 0.2~1μm, and more preferably 0.4~0.8μm.

[0023] After obtaining the first copper conductive layer and the second copper conductive layer, the present invention uses a dry film to laminate on the surface of the first copper conductive layer and the second copper conductive layer, and then sequentially exposes and develops the dry film on the surface of the first copper conductive layer and / or the second copper conductive layer to expose the step gold finger area, and the step gold finger area includes the step gold finger area located on the first circuit and the step gold finger area located on the second circuit, so as to obtain a first semi-finished product. In the present invention, the thickness of the dry film used in the lamination is preferably 30-100 μm, and more preferably 40-60 μm. In the present invention, due to the existence of the primary circuit, the present invention preferably controls the thickness of the dry film to 30-100 μm, so as to ensure that the dry film can be compacted on the surface of the first copper conductive layer and the second copper conductive layer. If the dry film is not compacted, the subsequent pattern electroplating will cause infiltration and short circuit, and the target product cannot be obtained. In the present invention, the thickness of the dry film changes with the thickness of the primary circuit and matches the thickness of the primary circuit.

[0024] After obtaining the first semi-finished product, the present invention performs pattern electroplating on the surface of the first semi-finished product to obtain a gradient copper layer in the step gold finger area to obtain a second semi-finished product. In the present invention, the surface of the first semi-finished product includes the upper surface and / or the lower surface of the first semi-finished product. The thickness of the gradient copper layer is preferably 15 to 70 μm, more preferably 15 to 30 μm.

[0025] After obtaining the second semi-finished product, the present invention sequentially performs film stripping, copper stripping and palladium removal on the second semi-finished product, wherein the copper stripping is to remove the exposed first copper conductive layer and the second copper conductive layer by flash etching to obtain a third semi-finished product. In the present invention, the film stripping can be performed using an inorganic film stripping liquid or an organic film stripping liquid. The present invention preferably uses an organic film stripping liquid for film stripping. In the present invention, the flash etching is preferably performed using a flash etching solution, and the present invention has no special requirements for the specific implementation of the flash etching. After the flash etching, the present invention preferably removes palladium from the exposed substrate of the product obtained after the flash etching to prevent short circuits or micro shorts. The present invention preferably removes the exposed first copper conductive layer and the second copper conductive layer by flash etching, and the method is simple and easy.

[0026] After obtaining the third semi-finished product, the present invention prepares solder resist layers on both surfaces of the third semi-finished product, wherein the solder resist layers expose the gradient copper layer on the surface of the third semi-finished product and the gold finger region on the surface of the third semi-finished product, wherein the gold finger region includes the gold finger region located on the first circuit and the gold finger region located on the second circuit, thereby obtaining a fourth semi-finished product. The present invention has no special requirements for the preparation of the solder resist layer.

[0027] After obtaining the fourth semi-finished product, the present invention sequentially prepares a Ni layer and an Au layer on the gradient copper layer and the surface of the gold finger area exposed on the surface of the fourth semi-finished product to obtain a Ni / Au layer, thereby obtaining a stepped gold finger packaging substrate. In the present invention, the surface of the fourth semi-finished product includes the upper surface and / or the lower surface of the fourth semi-finished product. The thickness of the Ni layer is preferably 3 to 8 μm; the thickness of the Au layer is preferably 0.02 to 0.4 μm. The thickness of the Ni layer and the thickness of the Au layer are determined according to the structural requirements of the target product.

[0028] In the present invention, after obtaining the Ni / Au layer, the present invention preferably further comprises molding the semi-finished product having the Ni / Au layer to obtain the stepped gold finger packaging substrate. The present invention has no special requirements for the specific implementation of the molding.

[0029] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0030] Example 1 The present invention provides a method for preparing a stepped gold finger packaging substrate, which specifically comprises the following steps: Step 1: browning and copper reduction treatment (copper foil thickness is 8-9 μm) is performed on the double-sided copper clad laminate (copper foil thickness is 12 μm), and then CO2 laser drilling is used to obtain via holes, which penetrate the two surfaces of the double-sided copper clad laminate; copper is then deposited on the hole wall of the via hole, and the thickness of the deposited copper is preferably 0.6±0.1 μm to obtain a copper-plated through hole 2, and finally the whole board is electroplated to obtain a through-hole copper-plated laminate. The structural schematic diagram of the through-hole copper-plated laminate is shown in FIG. Figure 1 shown.

[0031] Step 2: prepare a primary circuit on both surfaces of the through-hole copper-plated board. The preparation method of the primary circuit includes sequentially performing pre-treatment, film lamination, exposure, development, etching and film stripping; the primary circuit includes a first circuit 3-1 connected to the copper-plated through hole and a second circuit 3-2 not connected to the copper-plated through hole. The thickness of the primary circuit can be 20±5μm, and a primary circuit board is obtained. The structural schematic diagram of the primary circuit board is shown in FIG. Figure 2 shown.

[0032] Step 3: Electroless copper deposition is performed on both surfaces of the primary circuit board to obtain a first copper conductive layer on the upper surface of the first circuit board and a second copper conductive layer on the lower surface of the first circuit board. The thickness of the first copper conductive layer and the second copper conductive layer is 0.6±0.1 μm. The schematic diagram of the structure of the semi-finished product having the first copper conductive layer and the second copper conductive layer is as shown in FIG. Figure 3 shown.

[0033] Step 4: Laminating the first conductive copper layer and the second conductive copper layer with a dry film (thickness of 50 μm), and then sequentially exposing and developing the dry film on the surface of the first conductive copper layer to expose the step gold finger area, the step gold finger area includes the step gold finger area located on the first circuit and the step gold finger area located on the second circuit, and obtaining a first semi-finished product. The structural schematic diagram of the first semi-finished product is shown in FIG. Figure 4 shown.

[0034] Step 5: Perform pattern electroplating on the upper surface of the first semi-finished product to obtain a gradient copper layer in the step gold finger area. The thickness of the gradient copper layer is 20±5μm to obtain a second semi-finished product. The structural schematic diagram of the second semi-finished product is shown in FIG. Figure 5 shown.

[0035] Step 6: The second semi-finished product is stripped, copper is removed and palladium is removed in sequence. The stripping liquid is used for stripping. The structural schematic diagram of the semi-finished product obtained after stripping is as follows: Figure 6 The copper stripping is to remove the exposed first conductive copper layer and the second conductive copper layer by flash etching, and the flash etching is performed by flash etching solution. After the copper stripping, the palladium is removed to obtain the third semi-finished product. The structural schematic diagram of the third semi-finished product is shown in Figure 7 shown.

[0036] Step 7: Prepare solder resist layers 7 on both surfaces of the third semi-finished product, the solder resist layers expose the gradient copper layer on the upper surface of the third semi-finished product and the gold finger area on the lower surface of the third semi-finished product, the gold finger area includes the gold finger area located on the first circuit and the gold finger area located on the second circuit, and obtain a fourth semi-finished product. The structural schematic diagram of the fourth semi-finished product is shown in FIG. Figure 8 shown.

[0037] Step 8: Prepare a Ni layer and an Au layer on the exposed gradient copper layer on the upper surface and the exposed gold finger area on the lower surface of the fourth semi-finished product in sequence, with the Ni layer having a thickness of 5±1 μm and the Au layer having a thickness of 0.05±0.01 μm, to obtain a Ni / Au layer 8, and then shape the obtained semi-finished product with the Ni / Au layer to obtain a stepped gold finger packaging substrate. The structural schematic diagram of the stepped gold finger packaging substrate prepared in this embodiment is shown in FIG. Fig. 9 shown.

[0038] It can be seen from the above embodiments that the method provided by the present invention can realize the production of independent step gold fingers; and no additional equipment investment is required, and only conventional packaging substrate processing equipment is used for production.

[0039] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a stepped gold finger packaging substrate, characterized in that: The following steps are involved: The double-sided copper-clad board is drilled to obtain a via hole, and the via hole penetrates the two surfaces of the double-sided copper-clad board; then copper is deposited on the hole wall of the via hole to obtain a copper-plated through hole; finally, the whole board is electroplated to obtain a through-hole copper-plated board; Prepare primary circuits on both surfaces of the through-hole copper-plated plate, wherein the primary circuits include a first circuit connected to the copper-plated through-hole and a second circuit not connected to the copper-plated through-hole, to obtain a primary circuit board; Chemically depositing copper on both surfaces of the primary circuit board to obtain a first copper conductive layer on the upper surface of the first circuit board and a second copper conductive layer on the lower surface of the first circuit board; Laminating the surfaces of the first copper conductive layer and the second copper conductive layer with a dry film, then sequentially exposing and developing the dry film on the surface of the first copper conductive layer and / or the second copper conductive layer to expose a step gold finger region, wherein the step gold finger region includes a step gold finger region located on the first circuit and a step gold finger region located on the second circuit, to obtain a first semi-finished product; Performing pattern electroplating on the surface of the first semi-finished product to obtain a gradient copper layer in the step gold finger area to obtain a second semi-finished product; The second semi-finished product is sequentially subjected to film stripping, copper stripping and palladium removal, wherein the copper stripping is to remove the exposed first copper conductive layer and second copper conductive layer by a flash etching method, to obtain a third semi-finished product; Prepare solder resist layers on both surfaces of the third semi-finished product, wherein the solder resist layers expose the gradient copper layer on the surface of the third semi-finished product and the gold finger area on the surface of the third semi-finished product, wherein the gold finger area includes the gold finger area located on the first circuit and the gold finger area located on the second circuit, to obtain a fourth semi-finished product; A Ni layer and an Au layer are sequentially prepared on the gradient copper layer and the surface of the gold finger region exposed on the surface of the fourth semi-finished product to obtain a Ni / Au layer, thereby obtaining a stepped gold finger packaging substrate.

2. The preparation method according to claim 1, characterized in that: The thickness of the dry film used in the lamination is 30-100 μm.

3. The preparation method according to claim 1, characterized in that: The thickness of the first copper conductive layer and the second copper conductive layer is 0.2-1 μm.

4. The preparation method according to claim 1, characterized in that: The thickness of the primary circuit is 15-70 μm.

5. The preparation method according to claim 1, characterized in that: The thickness of the gradient copper layer is 15-70 μm.

6. The preparation method according to claim 1, characterized in that: The copper foil thickness of the double-sided copper-clad laminate is 2-18 μm; the thickness of the copper deposited on the hole wall of the via hole is 0.2-1 μm.

7. The preparation method according to claim 1, characterized in that: The hole making is performed by mechanical drilling, CO2 laser drilling or UV laser drilling.

8. The preparation method according to claim 1, 6 or 7, characterized in that: When the hole making is carried out by CO2 laser drilling, and the copper foil thickness of the double-sided copper clad laminate is ≥12 μm, before the CO2 laser drilling, the method further includes: subjecting the double-sided copper clad laminate to browning and copper reduction treatment; after the browning and copper reduction, the copper foil thickness of the double-sided copper clad laminate is 3-9 μm.

9. The preparation method according to claim 1 or 4, characterized in that: The method for preparing the primary circuit comprises sequentially performing pre-treatment, film lamination, exposure, development, etching and film stripping.

10. The preparation method according to claim 1, characterized in that: The thickness of the Ni layer is 3-8 μm; the thickness of the Au layer is 0.02-0.4 μm.

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