A preparation method of a stepped gold finger packaging substrate

Abstract

The present invention belongs to the technical field of packaging substrates, and particularly relates to a preparation method of a stepped gold finger packaging substrate. On the basis of completing the first circuit, the SAP process is adopted. First, electroless copper plating is carried out, and pattern electroplating is realized by using a conductive layer to obtain a gradient copper layer for preparing the stepped gold finger. Then, the conductive layer on the substrate is removed by flash etching, and finally, the stepped gold finger packaging substrate is obtained. The preparation method provided by the present invention can realize the production of independent stepped gold fingers, effectively solving the problems that when removing the electroplating leads during the preparation of independent stepped gold fingers, over-etching is likely to occur, affecting the shape of the gold fingers, and tip discharge caused by incomplete etching of the electroplating leads. The stepped 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 uses conventional packaging substrate processing equipment, which is suitable for industrial application.

Description

Technical Field

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

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

[0003] Currently, for the independent stepped gold finger design on the packaging substrate, it is impossible to conduct current through other layer conductors to achieve pattern electroplating; generally in the industry, the way of pulling electroplating leads is used to conduct current for production, and removing the electroplating leads is likely to form over-etching, resulting in open circuits or deformation of the lines, as well as the tip discharge effect caused by incomplete etching, leading to poor electrical signal quality of the packaging substrate. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method for 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 obtained stepped gold finger packaging substrate has excellent electrical signal quality and high stability.

[0005] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method for a stepped gold finger packaging substrate, including the following steps:

[0007] Drill holes in a double-sided copper clad laminate to obtain via holes, and the via holes penetrate through the two surfaces of the double-sided copper clad laminate; then deposit copper on the hole walls of the via holes to obtain copper-plated via holes; finally, perform full-panel electroplating to obtain a via hole copper-plated board;

[0008] Prepare a first layer of circuitry on the two surfaces of the via hole copper-plated board. The first layer of circuitry includes a first circuit connected to the copper-plated via holes and a second circuit not connected to the copper-plated via holes, to obtain a first-layer circuit board;

[0009] Chemically deposit copper on the two surfaces of the first-layer circuit board to obtain a first copper conductive layer on the upper surface of the first-layer circuit board and a second copper conductive layer on the lower surface of the first-layer circuit board;

[0010] Use dry film lamination on the surfaces of the first copper conductive layer and the second copper conductive layer, and then expose and develop the dry film on the surface of the first copper conductive layer and / or the second copper conductive layer in sequence to expose the stepped gold finger area. The stepped gold finger area includes a stepped gold finger area located on the first circuit and a stepped gold finger area located on the second circuit, to obtain a first semi-finished product;

[0011] Perform pattern electroplating on the surface of the first semi-finished product to obtain a gradient copper layer in the stepped gold finger area, and obtain a second semi-finished product;

[0012] Subject the second semi-finished product to film stripping, copper stripping, and palladium removal in sequence. The copper stripping is to remove the exposed first copper conductive layer and second copper conductive layer by flash etching to obtain a third semi-finished product;

[0013] Prepare solder mask layers on both surfaces of the third semi-finished product. The solder mask 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. The gold finger area includes the gold finger area on the first circuit and the gold finger area on the second circuit, and obtain a fourth semi-finished product;

[0014] Prepare an Ni layer and an Au layer in sequence on the exposed gradient copper layer and the surface of the gold finger area on the surface of the fourth semi-finished product to obtain an Ni / Au layer, and obtain a stepped gold finger packaging substrate.

[0015] Preferably, the thickness of the dry film used during film lamination is 30 - 100 μm.

[0016] Preferably, the thickness of the first copper conductive layer and the second copper conductive layer is 0.2 - 1 μm.

[0017] Preferably, the thickness of the primary circuit is 15 - 70 μm.

[0018] Preferably, the thickness of the gradient copper layer is 15 - 70 μm.

[0019] Preferably, the copper foil thickness of the double-sided copper clad laminate is 2 - 12 μm; the thickness of the copper deposited on the hole wall of the via hole is 0.2 - 1 μm.

[0020] Preferably, the hole making is performed by mechanical drilling, CO 2 laser drilling or UV laser drilling.

[0021] Preferably, when the hole making is performed by CO 2 laser drilling and the copper foil thickness of the double-sided copper clad laminate ≥ 12 μm, before the CO 2 laser drilling, it further includes: subjecting the double-sided copper clad laminate to brownification copper reduction treatment; the copper foil thickness of the double-sided copper clad laminate after brownification copper reduction is 3 - 9 μm.

[0022] Preferably, the preparation method of the primary circuit includes performing pretreatment, film lamination, exposure, development, etching, and film stripping in sequence.

[0023] Preferably, the thickness of the Ni layer is 3 - 8 μm; the thickness of the Au layer is 0.02 - 0.4 μm.

[0024] The present invention provides a method for preparing a stepped gold finger packaging substrate, comprising the following steps: making holes in a double-sided copper clad laminate to obtain via holes that penetrate through the two surfaces of the double-sided copper clad laminate; then depositing copper on the hole walls of the via holes to obtain copper-plated via holes; finally, performing full-panel electroplating to obtain a via hole copper-plated board; preparing a first circuit on the two surfaces of the via hole copper-plated board, where the first circuit includes a first circuit connected to the copper-plated via holes and a second circuit not connected to the copper-plated via holes, to obtain a first circuit board; chemically depositing copper on the two surfaces of the first 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 a dry film 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 the stepped gold finger area, where the stepped gold finger area includes a stepped gold finger area located on the first circuit and a stepped gold finger area 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 stepped gold finger area, to obtain a second semi-finished product; sequentially performing film stripping, copper stripping, and palladium removal on the second semi-finished product, where the copper stripping is to remove the exposed first copper conductive layer and second copper conductive layer by flash etching, to obtain a third semi-finished product; preparing a solder mask layer on the two surfaces of the third semi-finished product, where the solder mask layer exposes 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, and the gold finger area includes a gold finger area located on the first circuit and a gold finger area located on the second circuit, to obtain a fourth semi-finished product; sequentially preparing a Ni layer and an Au layer on the surfaces of the exposed gradient copper layer and the gold finger area on the surface of the fourth semi-finished product to obtain a Ni / Au layer, to obtain a stepped gold finger packaging substrate. Based on the completion of the first circuit, the present invention adopts the semi-additive process (SAP) method. First, chemically deposit copper, use the copper conductive layer obtained by chemical copper deposition to achieve pattern electroplating, obtain the gradient copper layer for preparing the stepped gold finger, then remove the conductive layer on the substrate by flash etching, and finally obtain the stepped gold finger packaging substrate. The preparation method provided by the present invention can realize the production of independent stepped gold fingers, effectively solve the problems that when preparing independent stepped gold fingers, it is easy to form over-etching when removing electroplating leads, which affects the shape of the gold fingers, and tip discharge caused by incomplete etching of the electroplating leads. The stepped 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 uses conventional packaging substrate processing equipment, which is suitable for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic structural diagram of the via hole copper-plated board prepared in the embodiment of the present invention;

[0026] Figure 2Schematic diagram of the primary circuit board prepared in the embodiment of the present invention;

[0027] Figure 3 Schematic diagram of the semi-finished product obtained after electroless copper plating in the embodiment of the present invention;

[0028] Figure 4 Schematic diagram of the first semi-finished product prepared in the embodiment of the present invention;

[0029] Figure 5 Schematic diagram of the second semi-finished product prepared in the embodiment of the present invention;

[0030] Figure 6 Schematic diagram of the semi-finished product obtained after film stripping in the embodiment of the present invention;

[0031] Figure 7 Schematic diagram of the third semi-finished product prepared in the embodiment of the present invention;

[0032] Figure 8 Schematic diagram of the fourth semi-finished product prepared in the embodiment of the present invention;

[0033] Figure 9 Schematic diagram of the stepped gold finger packaging substrate prepared in the embodiment of the present invention;

[0034] 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 mask layer, 8 is the Ni / Au layer, and 9 is the dielectric layer. Detailed implementation manners

[0035] The present invention provides a method for preparing a stepped gold finger packaging substrate, comprising the following steps:

[0036] Drill holes in the double-sided copper clad laminate to obtain via holes, and the via holes penetrate through the two surfaces of the double-sided copper clad laminate; then electrolessly plate copper on the hole walls of the via holes to obtain copper-plated through holes; finally, perform full-panel electroplating to obtain a through-hole copper-plated board;

[0037] Prepare primary circuits on the two surfaces of the through-hole copper-plated board, and the primary circuits include a first circuit communicating with the copper-plated through holes and a second circuit not communicating with the copper-plated through holes, to obtain a primary circuit board;

[0038] Electrolessly plate 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;

[0039] Apply dry film lamination on the surfaces of the first copper conductive layer and the second copper conductive layer, and then expose and develop the dry film on the surface of the first copper conductive layer and / or the second copper conductive layer in sequence to expose the stepped gold finger area, where the stepped gold finger area includes the stepped gold finger area on the first circuit and the stepped gold finger area on the second circuit, so as to obtain the first semi-finished product;

[0040] Perform pattern electroplating on the surface of the first semi-finished product to obtain a gradient copper layer in the stepped gold finger area, so as to obtain the second semi-finished product;

[0041] Strip the film, strip the electroless copper, and remove palladium from the second semi-finished product in sequence. The stripping of the electroless copper is to remove the exposed first copper conductive layer and the second copper conductive layer by flash etching, so as to obtain the third semi-finished product;

[0042] Prepare a solder mask layer on the two surfaces of the third semi-finished product. The solder mask layer exposes 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. The gold finger area includes the gold finger area on the first circuit and the gold finger area on the second circuit, so as to obtain the fourth semi-finished product;

[0043] Prepare an Ni layer and an Au layer in sequence on the exposed gradient copper layer and the gold finger area on the surface of the fourth semi-finished product to obtain an Ni / Au layer, so as to obtain the stepped gold finger packaging substrate.

[0044] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well-known to those skilled in the art.

[0045] In the present invention, holes are drilled in the double-sided copper clad laminate to obtain through holes, and the through holes penetrate through the two surfaces of the double-sided copper clad laminate; then electroless copper is deposited on the hole walls of the through holes to obtain copper-plated through holes; finally, the whole board is electroplated to obtain a through-hole copper clad laminate. In the present invention, the copper foil thickness of the double-sided copper clad laminate is preferably 2-18 μm, and in the examples, it can be 2-3 μm, 12 μm or 18 μm. In the present invention, the hole drilling preferably adopts mechanical drilling, CO 2 laser drilling or UV laser drilling. In the present invention, when the hole drilling adopts mechanical drilling, no pretreatment is required for the double-sided copper clad laminate. When the hole drilling adopts CO 2 laser drilling, and when the copper foil thickness of the double-sided copper clad laminate ≥ 12 μm, in the examples, it can be 12 μm or 18 μm; before the CO 2 laser drilling, it further includes: performing brownification and copper reduction treatment on the double-sided copper clad laminate; the copper foil thickness of the double-sided copper clad laminate after brownification and copper reduction is 3-9 μm. The present invention facilitates the absorption of laser energy by the copper foil through the brownification and copper reduction treatment. When the hole drilling adopts UV laser drilling, it is preferred to reduce the copper of the double-sided copper clad laminate before drilling.

[0046] In the present invention, after copper deposition on the pore walls of the via holes, copper-plated via holes are obtained. The thickness of the copper deposited on the pore walls of the via holes is preferably 0.2 - 1 μm, more preferably 0.4 - 0.8 μm. The thickness of the panel plating is determined according to the structural requirements of the target product.

[0047] After obtaining the copper-plated via hole board, the present invention prepares a first circuit on both surfaces of the copper-plated via hole board. The first circuit includes a first circuit connected to the copper-plated via hole and a second circuit not connected to the copper-plated via hole, and a first circuit board is obtained. In the present invention, the preparation method of the first circuit preferably includes performing pretreatment, film laminating, exposure, development, etching, and film stripping in sequence. In the present invention, the second circuit is not connected to the copper-plated via hole and is called an independent pad. Since the second circuit is not connected to the copper-plated via hole, conduction cannot be achieved through the copper-plated via hole. In the present invention, the thickness of the first circuit is preferably 15 - 70 μm, more preferably 15 - 30 μm.

[0048] After obtaining the first circuit board, the present invention performs chemical copper deposition on both surfaces of the first 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 first copper conductive layer and the second copper conductive layer are the copper conductive layers, and the function of the copper conductive layer is to realize the preparation of the gradient copper layer on the second circuit. The present invention has no special requirements for the specific implementation manner of the chemical copper deposition. The thickness of the first copper conductive layer and the second copper conductive layer is preferably 0.2 - 1 μm, more preferably 0.4 - 0.8 μm.

[0049] After obtaining the first copper conductive layer and the second copper conductive layer, the present invention uses a dry film to laminate on the surfaces of the first copper conductive layer and the second copper conductive layer, and then exposes and develops the dry film on the surface of the first copper conductive layer and / or the second copper conductive layer in sequence to expose the stepped gold finger area. The stepped gold finger area includes a stepped gold finger area on the first circuit and a stepped gold finger area on the second circuit, and a first semi-finished product is obtained. In the present invention, the thickness of the dry film used for lamination is preferably 30 - 100 μm, more preferably 40 - 60 μm. In the present invention, due to the presence of the first circuit, the present invention preferably controls the thickness of the dry film to be 30 - 100 μm, which can ensure that the dry film can be compacted on the surfaces of the first copper conductive layer and the second copper conductive layer. If the dry film is not compacted, subsequent pattern plating will cause infiltration plating 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 first circuit and matches the thickness of the first circuit.

[0050] 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 stepped gold finger area, thereby obtaining 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 15-70 μm, more preferably 15-30 μm.

[0051] 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. 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 solution or an organic film stripping solution. The present invention preferably uses an organic film stripping solution 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 manner of the flash etching. After the flash etching, the present invention preferably performs palladium removal on the substrate exposed by the product obtained after the flash etching to prevent short circuit or micro-short circuit. The present invention preferably removes the exposed first copper conductive layer and the second copper conductive layer by the flash etching, and the method is simple and easy to implement.

[0052] After obtaining the third semi-finished product, the present invention prepares a solder mask layer on both surfaces of the third semi-finished product. The solder mask layer exposes 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. The gold finger area includes the gold finger area on the first circuit and the gold finger area on the second circuit, thereby obtaining a fourth semi-finished product. The present invention has no special requirements for the preparation of the solder mask layer.

[0053] After obtaining the fourth semi-finished product, the present invention sequentially prepares a Ni layer and an Au layer on the exposed gradient copper layer and the surface of the gold finger area 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 3-8 μm; the thickness of the Au layer is preferably 0.02-0.4 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.

[0054] In the present invention, after obtaining the Ni / Au layer, the present invention preferably further includes forming the semi-finished product with the Ni / Au layer to obtain the stepped gold finger packaging substrate. The present invention has no special requirements for the specific implementation manner of the forming.

[0055] In order to further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they cannot be understood as limiting the protection scope of the present invention.

[0056] Example 1

[0057] The present invention provides a method for preparing a stepped gold finger packaging substrate, which specifically includes the following steps:

[0058] Step 1: Subject a double-sided copper clad laminate (with a copper foil thickness of 12 μm) to brownification and copper reduction treatment (to a copper foil thickness of 8 - 9 μm), and then perform CO 2 laser drilling to obtain via holes that penetrate both surfaces of the double-sided copper clad laminate; then deposit copper on the inner walls of the via holes, with the deposited copper thickness preferably being 0.6 ± 0.1 μm, to obtain copper-plated via holes 2. Finally, perform full-panel electroplating to obtain a via hole copper clad board, and the structural schematic diagram of the via hole copper clad board is as Figure 1 shown.

[0059] Step 2: Prepare a first layer of circuitry on both surfaces of the via hole copper clad board. The method for preparing the first layer of circuitry includes performing pre-treatment, laminating a film, exposure, development, etching, and film stripping in sequence; the first layer of circuitry includes a first circuit 3-1 that communicates with the copper-plated via holes and a second circuit 3-2 that does not communicate with the copper-plated via holes. The thickness of the first layer of circuitry can be 20 ± 5 μm, to obtain a first-layer circuit board, and the structural schematic diagram of the first-layer circuit board is as Figure 2 shown.

[0060] Step 3: Perform electroless copper deposition on both surfaces of the first-layer 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, and the structural schematic diagram of the semi-finished product with the first copper conductive layer and the second copper conductive layer is as Figure 3 shown.

[0061] Step 4: Press a dry film (with a thickness of 50 μm) on the surfaces of the first conductive copper layer and the second conductive copper layer, and then expose and develop the dry film on the surface of the first conductive copper layer in sequence to expose the stepped gold finger area. The stepped gold finger area includes a stepped gold finger area located on the first circuit and a stepped gold finger area located on the second circuit, to obtain a first semi-finished product, and the structural schematic diagram of the first semi-finished product is as Figure 4 shown.

[0062] Step 5: Perform pattern electroplating on the upper surface of the first semi-finished product to obtain a gradient copper layer in the stepped gold finger area, with the thickness of the gradient copper layer being 20 ± 5 μm, to obtain a second semi-finished product, and the structural schematic diagram of the second semi-finished product is as Figure 5 shown.

[0063] Step 6: Subject the second semi-finished product to film stripping, electroless copper stripping, and palladium removal in sequence. Use an organic film stripping solution for film stripping, and the structural schematic diagram of the semi-finished product obtained after film stripping is as Figure 6As shown. The copper layer is removed by flash etching to remove the exposed first conductive copper layer and the second conductive copper layer. Flash etching is carried out using a flash etching solution. After removing the copper layer, palladium is removed to obtain a third semi-finished product. The structural schematic diagram of the third semi-finished product is as Figure 7 shown.

[0064] Step 7: Prepare a solder mask layer 7 on both surfaces of the third semi-finished product. The solder mask layer exposes 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 on the first circuit and the gold finger area on the second circuit, obtaining a fourth semi-finished product. The structural schematic diagram of the fourth semi-finished product is as Figure 8 shown.

[0065] Step 8: Sequentially prepare a Ni layer and an Au layer on the surface of 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. The thickness of the Ni layer is 5 ± 1 μm; the thickness of the Au layer is 0.05 ± 0.01 μm, obtaining a Ni / Au layer 8. Then, the semi-finished product with the Ni / Au layer is formed to obtain a stepped gold finger packaging substrate. The structural schematic diagram of the stepped gold finger packaging substrate prepared in this embodiment is as Figure 9 shown.

[0066] As can be seen from the above embodiments, the method provided by the present invention can realize the production of independent stepped gold fingers; and there is no need to increase equipment investment, and it can be produced only with the equipment for conventional packaging substrate processing technology.

[0067] Although the above embodiments have made a detailed description of the present invention, they are only a part of the embodiments of the present invention, rather than all embodiments. Other embodiments can also be obtained based on this embodiment without creative work, and these embodiments all belong to 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: Holes are made on a double-sided copper-clad laminate to obtain via holes, which penetrate through two surfaces of the double-sided copper-clad laminate; copper is then deposited on the hole walls of the via holes to obtain copper-plated through holes; and finally, the entire board is electroplated to obtain a through-hole copper-plated laminate; 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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