Method for electroplating soft gold on a circuit board and circuit board

Abstract

This invention discloses a method for electroplating soft gold onto a circuit board, and also discloses the circuit board. The method includes the following steps: S1: Obtaining a circuit board with a copper layer on its surface; S2: Electroplating a nickel layer on the surface of the copper layer, wherein the surface of the nickel layer has gold bonding lines and non-gold bonding lines; S3: Forming multiple arrayed and spaced bump structures in the gold bonding lines, each bump structure including a nickel substrate and a gold surface layer disposed on the surface of the nickel substrate; S4: Electroplating the circuit board with gold to form a first gold layer on the gold bonding lines and a second gold layer on the non-gold bonding lines, wherein the thickness of the first gold layer is greater than the thickness of the second gold layer. In this way, selective thickening of the gold bonding lines is achieved during the gold plating process, ensuring that the gold bonding lines have a sufficiently thick gold layer to guarantee the reliability of the gold bonding lines, while the non-gold bonding lines maintain a relatively thin gold layer, which can reduce the amount of gold used and lower the production cost of the circuit board.

Description

Technical Field

[0001] This invention relates to the field of circuit board technology, and in particular to a method for electroplating soft gold onto a circuit board and the circuit board thereof. Background Technology

[0002] Electroplating soft gold involves coating the copper surface of a printed circuit board (PCB) with a nickel and gold layer. No impurities are added to the gold, and the gold content is above 99.9%. The main purpose of soft gold plating is to create gold wires to connect chips to the circuit board's wiring. To ensure the reliability of these gold wires, the gold layer needs to be sufficiently thick, which increases the manufacturing cost of the PCB. Summary of the Invention

[0003] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for electroplating soft gold on circuit boards, which can reduce the amount of gold used, thereby reducing the manufacturing cost of circuit boards.

[0004] The present invention also proposes a circuit board obtained by the above-described method of electroplating soft gold on a circuit board.

[0005] A method for electroplating soft gold on a circuit board according to a first aspect embodiment of the present invention includes the following steps: S1: Obtain a circuit board, the surface of which has a copper layer; S2: A nickel layer is electroplated on the surface of the copper layer, and the surface of the nickel layer is provided with a gold wire area and a non-gold wire area; S3: A plurality of arrayed and spaced bump structures are formed in the gold-plating line area. The bump structure includes a nickel substrate and a gold surface layer disposed on the surface of the nickel substrate. The nickel substrate is connected to the nickel layer. S4: The circuit board is electroplated with gold to form a first gold layer connecting the gold surface layer on the gold-plated line area and a second gold layer on the non-gold-plated line area, wherein the thickness of the first gold layer is greater than the thickness of the second gold layer.

[0006] The method for electroplating soft gold on a circuit board according to the first aspect of the present invention has at least the following beneficial effects: When electroplating soft gold on a circuit board, a nickel layer is electroplated onto the copper layer surface using an electroplating process. Then, multiple bump structures are set in the gold bonding area of ​​the nickel layer. Since the bump structure includes a nickel substrate and a gold surface layer, the metallic bonds between the surface atoms of the nickel substrate and the gold surface layer form a continuous network of metallic bonds, giving the bump structure itself strong bonding force. The nickel substrate connects to the nickel layer, increasing the bonding force between the bump structure and the nickel layer. The gold surface layer connects to the first gold layer, increasing the bonding force between the gold surface layer and the first gold layer. Furthermore, the nickel substrate reduces the amount of gold used in the first gold layer at the bump structure, ensuring a sufficiently thick gold layer in the gaps between adjacent bump structures in the gold bonding area to guarantee the reliability of the gold bonding. Simultaneously, a thinner gold layer is maintained in the non-gold bonding areas, reducing gold usage and lowering circuit board production costs.

[0007] According to some embodiments of the present invention, in step S3, before forming the bump structure, the surface of the nickel layer is subjected to plasma activation treatment to form a gold-nickel alloy transition layer between the nickel layer and the bump structure. According to some embodiments of the present invention, the gold content of the gold-nickel alloy transition layer gradually increases from the copper layer to the nickel layer.

[0008] According to some embodiments of the present invention, after the circuit board is electroplated with gold, the circuit board is subjected to post-processing, the post-processing including roughening the first gold layer to form a plurality of grooves in the first gold layer.

[0009] According to some embodiments of the present invention, the maximum diameter of the convex structure is smaller than the minimum spacing between adjacent convex structures.

[0010] According to some embodiments of the present invention, the thickness of the first gold layer is 0.05-0.07 μm, and the thickness of the second gold layer is 0.003-0.008 μm.

[0011] According to some embodiments of the present invention, the gold content of the first gold layer gradually increases from the copper layer to the nickel layer. According to some embodiments of the present invention, the thickness of the nickel substrate is greater than the thickness of the gold surface layer. According to some embodiments of the present invention, the bump structure is conical, and the diameter of the bump structure gradually decreases from the copper layer to the nickel layer.

[0012] The circuit board according to the second aspect of the present invention is obtained by the method of electroplating soft gold described in the above embodiments.

[0013] The circuit board according to the second aspect of the present invention has at least the following beneficial effects: The method for electroplating soft gold on a circuit board according to the first aspect of the present invention involves electroplating a nickel layer on the surface of a copper layer using an electroplating process. Then, multiple bump structures are formed in the gold bonding area of ​​the nickel layer. Since the bump structure includes a nickel substrate and a gold surface layer, the metallic bonds between the surface atoms of the nickel substrate and the atoms of the gold surface layer form a continuous network of metallic bonds, giving the bump structure itself strong bonding force. The nickel substrate connects to the nickel layer, increasing the bonding force between the bump structure and the nickel layer. The gold surface layer connects to the first gold layer, increasing the bonding force between the gold surface layer and the first gold layer. Furthermore, the nickel substrate reduces the amount of gold used in the first gold layer at the bump structure, ensuring that the gold bonding area has a sufficiently thick gold layer between adjacent bump structures to guarantee the reliability of the gold bonding. Simultaneously, a thinner gold layer is maintained in the non-gold bonding area, reducing the amount of gold used and lowering the circuit board production cost.

[0014] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a schematic flowchart of a method for electroplating soft gold onto a circuit board according to an embodiment of the present invention. Detailed Implementation

[0016] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0017] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, etc., are based on the orientation or positional relationship shown in the drawings and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0018] In the description of this invention, "multiple" refers to two or more. The use of "first" and "second" is for distinguishing technical features only and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features or their sequential relationship.

[0019] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0020] In related technologies, the electroplating soft gold process involves coating the copper surface of a printed circuit board with a nickel layer and a gold layer. No other impurities are added to the gold, and the gold content is above 99.9%. The main purpose of electroplating soft gold is to create gold wires to connect chips and circuit board traces. To ensure the reliability of the gold wires, the gold layer needs to be sufficiently thick, which increases the manufacturing cost of the circuit board.

[0021] Reference Figure 1 An embodiment of the present invention provides a method for electroplating soft gold on a circuit board, comprising the following steps: S1: obtaining a circuit board having a copper layer on its surface; S2: electroplating a nickel layer on the surface of the copper layer, wherein the surface of the nickel layer has a gold bonding line area and a non-gold bonding line area; S3: forming a plurality of arrayed and spaced bump structures in the gold bonding line area, the bump structure including a nickel substrate and a gold surface layer disposed on the surface of the nickel substrate, the nickel substrate being connected to the nickel layer; S4: electroplating the circuit board with gold, such that a first gold layer connecting the gold surface layer is formed on the gold bonding line area, and a second gold layer is formed on the non-gold bonding line area, the thickness of the first gold layer being greater than the thickness of the second gold layer. Thus, selective thickening of the gold bonding line area is achieved during the gold plating process, ensuring that the gold bonding line area obtains a sufficiently thick gold layer to guarantee the reliability of the gold bonding line, while the non-gold bonding line area maintains a relatively thin gold layer, which can reduce the amount of gold used and lower the production cost of the circuit board.

[0022] For example, when electroplating soft gold on a circuit board, a nickel layer is electroplated onto the copper layer surface using an electroplating process. Then, multiple bump structures are set in the gold bonding area of ​​the nickel layer. Since the bump structure includes a nickel substrate and a gold surface layer, the metallic bonds between the surface atoms of the nickel substrate and the gold surface layer form a continuous metallic bond network, giving the bump structure itself strong bonding force. The nickel substrate connects to the nickel layer, which can increase the bonding force between the bump structure and the nickel layer. The gold surface layer connects to the first gold layer, which can increase the bonding force between the gold surface layer and the first gold layer. Moreover, the nickel substrate can reduce the amount of gold used in the first gold layer at the bump structure, so that the gold bonding area has a sufficiently thick gold layer in the gap between adjacent bump structures to ensure the reliability of the gold bonding. At the same time, the non-gold bonding area maintains a thinner gold layer, which can reduce the amount of gold used and reduce the production cost of the circuit board.

[0023] It should be noted that in step S4, the gold plating process uses pulse electroplating with a current density of 0.3-1.0 A / dm³. 2 The pulse frequency is 100-300Hz and the duty cycle is 40-60%, which are not limited here.

[0024] It should be noted that in this embodiment, a nickel substrate can be formed in the gold-plating area by means of electroless nickel plating, electroplating nickel, or physical vapor deposition, and a gold surface layer can be formed on the nickel substrate by means of electroless gold plating, electroplating gold, or gold deposition, thereby forming a bump structure. No limitation is made here.

[0025] In this embodiment, in step S3, before forming the bump structure, the surface of the nickel layer is subjected to plasma activation treatment to form a gold-nickel alloy transition layer between the nickel layer and the bump structure. The formation of the gold-nickel alloy transition layer on the surface of the nickel layer through plasma activation treatment enhances the interfacial bonding force between the nickel layer and the bump structure, prevents the electroplated gold layer from peeling or delaminating during the gold wire bonding process, and improves the reliability and yield of the gold wire bonding area.

[0026] For example, plasma treatment generates active sites on the surface of the nickel layer, increases surface energy, and promotes subsequent gold deposition. The activated nickel layer and the gold surface layer undergo atomic diffusion at the interface to form a gold-nickel alloy transition layer, which can alleviate the difference in thermal expansion coefficients between nickel and gold, reduce interfacial stress, improve bonding strength, prevent the electroplated gold layer from peeling or delaminating during the gold wire bonding process, and improve the reliability and yield of the gold wire bonding area.

[0027] It should be noted that, at the microstructural level, plasma activation treatment not only forms a gold-nickel alloy transition layer, but also cleans the nickel layer surface, removes oxides and contaminants, and improves the surface activity of the nickel layer, which is beneficial to the uniform deposition of subsequent bump structures. No restrictions are imposed here.

[0028] In this embodiment, the gold content of the gold-nickel alloy transition layer gradually increases from the copper layer to the nickel layer, so that the interfacial stress between the nickel layer and the gold layer changes continuously, avoiding stress concentration, reducing the generation of interfacial cracks, optimizing the interfacial bonding performance between the nickel layer and the gold layer, effectively releasing interfacial stress, reducing interfacial cracks caused by thermal stress, and improving the long-term reliability and service life of the gold wire area.

[0029] In this embodiment, after electroplating gold on the circuit board, the circuit board undergoes post-processing, which includes roughening the first gold layer to form multiple grooves. This increases the roughness of the first gold layer, thereby increasing the contact area between the first gold layer and the bonding wires, improving the mechanical bonding force between the first gold layer and the bonding wires, and thus enhancing the bonding reliability of the gold wire area.

[0030] For example, when roughening the first gold layer, chemical etching or plasma treatment can be used. For example, chemical etching uses a specific chemical solution to selectively react with the surface of the first gold layer. By controlling the reaction conditions, the surface of the first gold layer is unevenly dissolved, resulting in multiple grooves on the surface of the first gold layer, thereby forming a rough structure. The reaction conditions include, but are not limited to, concentration, temperature and time.

[0031] In this embodiment, the maximum diameter of the bump structure is smaller than the minimum spacing between adjacent bump structures, which avoids bridging between adjacent bumps or uneven gold layer thickness during electroplating, thereby improving the stability of the electroplating process and the uniformity of the gold layer thickness in the gold line area.

[0032] For example, when the minimum spacing between adjacent bump structures is too small, the electric fields of adjacent bump structures will interfere with each other, resulting in a decrease in the electric field strength at the tip of the bump structure, a weakening of the tip effect, and a decrease in the gold deposition rate. On the other hand, when the diameter of the bump structure is too large, although the electric field concentration effect of a single bump structure is strong, the number of bump structures per unit area is reduced, resulting in poor overall selective deposition. By setting the maximum diameter of the bump structure to be smaller than the minimum spacing between adjacent bump structures, bridging of the gold surface layer of adjacent bump structures can be avoided, improving the stability of the electroplating process and the uniformity of the gold layer thickness in the gold wire area.

[0033] In this embodiment, the thickness of the first gold layer is 0.05-0.07 μm, which can improve the reliability of gold wire bonding and reduce the manufacturing cost of the circuit board. It is understood that when the thickness of the first gold layer is less than 0.05 μm, the contact area between the gold wire and the gold layer is insufficient, resulting in decreased connection strength and a higher risk of connection failure during thermal cycling or mechanical vibration testing. When the thickness of the first gold layer is greater than 0.07 μm, the amount of gold used increases, leading to an increase in the manufacturing cost of the circuit board.

[0034] In this embodiment, the thickness of the second gold layer is 0.003-0.008μm. While ensuring the anti-oxidation and solderability of the non-gold-plated areas, the amount of gold used is minimized, thereby reducing the production cost of the circuit board.

[0035] In this embodiment, the gold content of the first gold layer gradually increases from the copper layer to the nickel layer, and the gold content inside the first gold layer changes in a gradient. This can optimize the interfacial bonding performance between the first gold layer and the nickel layer, while improving the ductility and mechanical strength of the first gold layer. This is beneficial for plastic deformation during the gold wire bonding process, thereby improving the bonding reliability.

[0036] It should be noted that during the electroplating process, the plating solution, substrate, environment, etc. may introduce trace impurities into the first gold layer. Trace impurities such as nickel, copper, silver, iron, etc. When electroplating the first gold layer in the gold line area, the gold content of the first gold layer can be gradually increased from the copper layer to the nickel layer by adjusting the concentration of the plating solution or the electroplating environment. No restrictions are imposed here.

[0037] In this embodiment, the thickness of the nickel substrate is greater than the thickness of the gold surface layer, ensuring that the bump structure has sufficient mechanical strength before electroplating, preventing the bump structure from deforming or collapsing during subsequent electroplating, and ensuring the uniformity and consistency of the gold layer thickness in the gold-plating area.

[0038] In this embodiment, the bump structure is conical, and the diameter of the bump structure gradually decreases from the copper layer to the nickel layer. Compared with traditional hemispherical or cylindrical bumps, the conical structure has a sharper tip, resulting in a higher electric field intensity at the tip during electroplating. Gold ions preferentially deposit at the tip, and the tip effect is more obvious. On the one hand, it can improve the deposition rate of the first gold layer, and on the other hand, it is conducive to the uniform deposition of the gold layer during electroplating. At the same time, the conical structure can provide a larger specific surface area and mechanical interlocking effect, thereby enhancing the bonding force between the gold layer and the nickel layer and the reliability of gold wire bonding.

[0039] The circuit board of the second aspect of the present invention is obtained by the method of electroplating soft gold in the circuit board of the first aspect of the present invention. In the process of electroplating gold, selective thickening of the gold bonding area is achieved, so that the gold bonding area obtains a gold layer of sufficient thickness to ensure the reliability of the gold bonding, while the non-gold bonding area maintains a thinner gold layer, which can reduce the amount of gold used and reduce the production cost of the circuit board.

[0040] For example, when electroplating soft gold on a circuit board, a nickel layer is electroplated onto the copper layer surface using an electroplating process. Then, multiple bump structures are set in the gold bonding area of ​​the nickel layer. Since the bump structure includes a nickel substrate and a gold surface layer, the metallic bonds between the surface atoms of the nickel substrate and the gold surface layer form a continuous metallic bond network, giving the bump structure itself strong bonding force. The nickel substrate connects to the nickel layer, which can increase the bonding force between the bump structure and the nickel layer. The gold surface layer connects to the first gold layer, which can increase the bonding force between the gold surface layer and the first gold layer. Moreover, the nickel substrate can reduce the amount of gold used in the first gold layer at the bump structure, so that the gold bonding area has a sufficiently thick gold layer in the gap between adjacent bump structures to ensure the reliability of the gold bonding. At the same time, the non-gold bonding area maintains a thinner gold layer, which can reduce the amount of gold used and reduce the production cost of the circuit board.

[0041] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for electroplating soft gold onto circuit boards, characterized in that, Includes the following steps: S1: Obtain a circuit board, the surface of which has a copper layer; S2: A nickel layer is electroplated on the surface of the copper layer, and the surface of the nickel layer is provided with a gold wire area and a non-gold wire area; S3: A plurality of arrayed and spaced bump structures are formed in the gold-plating line area. The bump structure includes a nickel substrate and a gold surface layer disposed on the surface of the nickel substrate. The nickel substrate is connected to the nickel layer. S4: The circuit board is electroplated with gold to form a first gold layer connecting the gold surface layer on the gold-plated line area and a second gold layer on the non-gold-plated line area, wherein the thickness of the first gold layer is greater than the thickness of the second gold layer.

2. The method for electroplating soft gold on circuit boards according to claim 1, characterized in that: In step S3, before forming the bump structure, the surface of the nickel layer is subjected to plasma activation treatment to form a gold-nickel alloy transition layer between the nickel layer and the bump structure.

3. The method for electroplating soft gold on circuit boards according to claim 2, characterized in that: The gold content of the gold-nickel alloy transition layer gradually increases from the copper layer to the nickel layer.

4. The method for electroplating soft gold on a circuit board according to claim 1, characterized in that: After electroplating the circuit board with gold, the circuit board undergoes post-processing, which includes roughening the first gold layer to form multiple grooves in the first gold layer.

5. The method for electroplating soft gold on a circuit board according to claim 1, characterized in that: The maximum diameter of the convex structure is smaller than the minimum spacing between adjacent convex structures.

6. The method for electroplating soft gold on a circuit board according to claim 1, characterized in that: The thickness of the first gold layer is 0.05-0.07 μm, and the thickness of the second gold layer is 0.003-0.008 μm.

7. The method for electroplating soft gold on a circuit board according to claim 1, characterized in that: The gold content of the first gold layer gradually increases from the copper layer to the nickel layer.

8. The method for electroplating soft gold on a circuit board according to claim 1, characterized in that: The thickness of the nickel substrate is greater than the thickness of the gold surface layer.

9. The method for electroplating soft gold on a circuit board according to claim 1, characterized in that: The bump structure is conical, and its diameter gradually decreases from the copper layer to the nickel layer.

10. A circuit board, characterized in that, Obtained by the method of electroplating soft gold on circuit boards according to any one of claims 1 to 9.

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