A nickel-gold plating process to prevent gold seepage.

Abstract

This invention discloses a process for nickel-gold plating to avoid gold seepage, comprising the following steps: S1, back drilling: multilayer circuit boards are configured with through holes according to production requirements. Back drill holes are drilled on one side of the multilayer board using a back drilling method. In the design, there is an overlapping area between the base layer between the pads and the ground copper layer and the back drill hole. Resin is then inserted into the back drill hole; S2, film coating: dry film is coated on the circuit board. After film removal, the remaining dry film avoids the overlapping area; S3, copper-tin plating: copper layer is first plated on the entire circuit board, and then tin layer is plated on the copper layer to protect the copper layer. The area covered by the remaining dry film is not plated with copper or tin; S4, laser ablation: the tin layer on the overlapping area is ablated using a laser. Then, the remaining dry film from step S2 is removed. The copper layer not protected by the tin layer is etched away using an etching solution, thereby exposing the base layer between the pads and the ground copper layer; S5, nickel-gold plating: after removing the tin layer used for protection, nickel-gold is plated on the copper layer of the pads.

Description

Technical Field

[0001] This invention relates to the field of circuit board manufacturing technology, and in particular to a process for nickel-gold plating to prevent gold seepage. Background Technology

[0002] In the manufacturing process of printed circuit boards (PCBs), some PCBs undergo back-drilling, and there is an overlapping area between the back-drilled holes and the base layer between the pads and the ground copper layer. After the back-drilled holes are plugged with resin, there is a certain degree of depression. This is caused by the volume reduction after the resin dries. In the past, the base layer between the ground copper layer and the pads was directly covered with dry film. When copper and tin were plated on the non-covered areas, copper and tin would seep into the overlapping area from the depression. When the tin layer was removed and nickel-gold was plated later, gold would also seep into the overlapping area, which would eventually reduce the distance between the ground copper layer and the pads. This would make it easy for the ground copper layer and the pads to conduct electricity and make short circuits possible. Summary of the Invention

[0003] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a process for nickel-gold plating that avoids gold seepage, which can prevent gold seepage in overlapping areas during nickel-gold plating and avoid short circuit problems.

[0004] A process for preventing gold seepage during nickel-gold plating according to an embodiment of the present invention includes the following steps:

[0005] S1, back drilling, multilayer circuit boards are provided with through holes according to production requirements. After the through holes are metallized, back drilling holes are drilled on one side of the multilayer board by back drilling. The back drilling holes are coaxial with the through holes. In the design, there is an overlapping area between the base layer between the pads and the ground copper layer and the back drilling holes. Then, resin is stuffed into the back drilling holes.

[0006] S2, Lamination: A dry film is laminated onto the circuit board. After the dry film is developed, it is removed, and the remaining dry film avoids the overlapping area.

[0007] S3, copper-tin plating, involves first plating a copper layer onto the entire circuit board, and then plating a tin layer on the copper layer to protect it. The area covered by the remaining dry film is not plated with copper or tin.

[0008] S4, laser ablation, using a laser to ablate the tin layer on the overlapping area, then removing the dry film remaining in step S2, and etching away the copper layer not protected by the tin layer using etching solution, thereby exposing the base layer between the pad and the ground copper layer.

[0009] S5, Nickel-gold plating: After removing the tin layer used for protection, nickel-gold is plated onto the copper layer of the pad.

[0010] According to an embodiment of the present invention, a process for avoiding gold seepage during nickel-gold plating has at least the following beneficial effects: by changing the process and adjusting the area covered by the dry film, the overlapping area is no longer covered, and the tin layer in the overlapping area is removed by laser tin burning. After removing the remaining dry film, it is ensured that the etching solution fully etches away the copper between the pads and the ground copper layer, thereby exposing the base layer. In subsequent nickel-gold plating, gold will not seep into the base layer, avoiding the defects of previous manufacturing methods and ensuring product quality.

[0011] According to some embodiments of the present invention, in step S1, the circuit board is cooled by spraying coolant during drilling. After drilling is completed, the circuit board is air-drilled in the hole for 5 to 10 seconds. The coolant spraying coolant cools the circuit board and prevents local overheating of the circuit board from causing thermal stress accumulation and warping. Air drilling can smooth the burrs in the hole and also allow the drill bit to play a temporary supporting role in the hole.

[0012] According to some embodiments of the present invention, in step S2, when creating the developed image, the overlapping area is avoided, and the overlapping area is not irradiated during exposure.

[0013] According to some embodiments of the present invention, in step S3, the surface of the circuit board is first cleaned with deionized water before copper and tin plating. After cleaning, the circuit board is air-dried naturally. During copper and tin plating, the plating solution is stirred in real time. The use of deionized water prevents the circuit board from being affected by the salt in the water, thereby improving the product quality of the circuit board. Natural air drying reduces the accumulation of thermal stress on the circuit board and prevents the circuit board from warping. Stirring the plating solution makes the electroplated layer more uniform and ensures product quality.

[0014] According to some embodiments of the present invention, in step S4, a UV laser or a combination of UV and carbon dioxide laser is used.

[0015] According to some embodiments of the present invention, in step S5, a strong alkaline solution is used to remove the remaining dry film.

[0016] 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

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0018] Figure 1 This is a schematic diagram of a through-hole being provided on a circuit board according to an embodiment of the present invention;

[0019] Figure 2 A schematic diagram for setting back-drilled holes on a circuit board;

[0020] Figure 3 This is a schematic diagram of the dry film remaining after development following the application of dry film on a circuit board.

[0021] Figure 4 A schematic diagram of copper-tin plating in non-dry film areas of a circuit board;

[0022] Figure 5 A schematic diagram illustrating the process of removing residual dry film from the circuit board and laser ablation of the tin layer in the overlapping areas;

[0023] Figure 6 A schematic diagram showing the copper layer under the remaining dry film after etching and the exposed base layer after etching the copper layer in the overlapping area;

[0024] Figure 7 This is a schematic diagram showing the planar distribution of each region on the circuit board.

[0025] Circuit board 100, through hole 110, back drill hole 120;

[0026] Pad 130, ground copper layer 140, overlapping area 150, base layer 160;

[0027] Dry film 200, copper layer 300, tin layer 400. Detailed Implementation

[0028] 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.

[0029] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0030] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0031] 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.

[0032] Reference Figures 1 to 7 According to an embodiment of the present invention, a process for preventing gold seepage during nickel-gold plating includes the following steps:

[0033] S1, back drilling, multilayer circuit board 100 is provided with through holes 110 according to production requirements. After the through holes 110 are metallized, back drill holes 120 are drilled on one side of the multilayer board by back drilling. The back drill holes 120 and through holes 110 are coaxially arranged. In the design, the base layer 160 between the pads 130 and the ground copper layer 140 has an overlapping area 150 with the back drill holes 120. Then, resin is filled into the back drill holes 120.

[0034] S2, Lamination: A dry film 200 is laminated onto the circuit board 100. After the dry film 200 is developed, it is removed, and the remaining dry film 200 avoids the overlapping area 150.

[0035] S3, copper-tin plating: First, a copper layer 300 is plated on the entire circuit board 100, and then a tin layer 400 is plated on the copper layer 300 to protect the copper layer 300. The area covered by the remaining dry film 200 is not plated with copper and tin.

[0036] S4, laser ablation, using a laser to ablate the tin layer on the overlapping area 150, then removing the dry film 200 remaining in step S2, and etching away the copper layer 300 not protected by the tin layer 400 using etching solution, thereby exposing the base layer 160 between the pad 130 and the ground copper layer 140.

[0037] S5, nickel-gold plating: After removing the tin layer 400 used for protection, nickel-gold is plated on the copper layer 300 of the pad 130.

[0038] It should be understood that by changing the process and adjusting the area covered by the dry film, the overlapping area 150 is no longer covered, and the tin layer 400 of the overlapping area 150 is removed by laser tin burning. After removing the remaining dry film, it is ensured that the etching solution fully etches away the copper between the pad 130 and the ground copper layer 140, thereby exposing the base layer 160. During the subsequent nickel-gold plating, gold will not seep into the base layer 160, avoiding the defects of previous manufacturing methods and ensuring product quality.

[0039] It should be noted that the overlapping area 150 is generated during the design process and is aimed at the problems that occur in this type of circuit board. Not all circuit boards have an overlapping area 150. The previous method was to directly cover the entire board with dry film, which led to the problem of gold penetration. The previous method was suitable for situations where the distance between the back drill hole 120 and the pad 130 is ≥0.3mm. In the multilayer circuit board 100 of this invention, through holes 110 are set before back drilling. Through holes 110 are also common in circuit board manufacturing processes. Through holes 110 also need to be metallized. Since not every layer of the multilayer board is conductive, for example, only two layers are conductive, the metal layer in the through hole 110 needs to be removed by back drilling, and then the back drill hole and through hole are filled with resin. The so-called back drilling means drilling from the back.

[0040] In some embodiments, during step S1, the circuit board 100 is cooled by spraying coolant during drilling. After drilling is completed, the circuit board is air-drilled in the hole for 5 to 10 seconds. The coolant spraying coolant cools the circuit board and prevents local overheating of the circuit board, which can cause thermal stress accumulation and warping. Air drilling can smooth the burrs in the hole and also allow the drill bit to provide temporary support in the hole. It is understood that the coolant used is a commonly used circuit board coolant in the field. During the air drilling process, the drill bit moves up and down in the hole.

[0041] It should be noted that the dry film used in this invention covers the copper layer that needs to be etched away, while the uncovered copper layer is the copper layer that needs to be retained. The so-called grounded copper layer refers to the copper layer of the circuit board that is not on the solder pads and circuit parts, and serves as a grounding layer.

[0042] In some embodiments, during step S2, when creating the developing image, the overlapping region 150 is avoided, and the overlapping region 150 is not exposed during exposure.

[0043] In some embodiments, in step S3, the surface of the circuit board 100 is cleaned with deionized water before copper-tin plating. After cleaning, the circuit board 100 is allowed to air dry naturally. During copper and tin plating, the plating solution is stirred in real time. The use of deionized water prevents the circuit board from being affected by salt in the water, improving the product quality of the circuit board. Natural air drying reduces the accumulation of thermal stress on the circuit board, preventing warping. Stirring the plating solution makes the electroplated layer more uniform, ensuring product quality. It is understood that "natural air drying" can mean drying at room temperature or drying with a cool air blower.

[0044] In some embodiments, step S4 is performed using a UV laser or a combination of UV and carbon dioxide laser.

[0045] In some embodiments, in step S5, a strong alkaline solution is used to remove the remaining dry film 200.

[0046] 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 process for nickel-gold plating to prevent gold seepage, characterized in that, Includes the following steps: S1, back drilling, multilayer circuit board (100) is provided with through holes (110) according to production requirements. After the through holes (110) are metallized, back drill holes (120) are drilled on one side of the multilayer board by back drilling. The back drill holes (120) are coaxially arranged with the through holes (110). In the design, the base layer (160) between the pads (130) and the ground copper layer (140) has an overlapping area (150) with the back drill holes (120). Then, resin is inserted into the back drill holes (120). S2, coating, dry film (200) is coated on the circuit board (100), after the dry film (200) is developed, the film is removed, and the remaining dry film (200) avoids the overlapping area (150). When making the developed image, the overlapping area (150) is avoided, and the overlapping area (150) is not exposed during exposure. S3, copper-tin plating: the entire circuit board (100) is first plated with a copper layer (300), and then a tin layer (400) is plated on the copper layer (300) to protect the copper layer (300). The area covered by the remaining dry film (200) is not plated with copper and tin. S4, laser ablation, using a laser to ablate the tin layer on the overlapping area (150), then removing the dry film (200) remaining in step S2, and etching away the copper layer (300) not protected by the tin layer (400) with etching solution, thereby exposing the base layer (160) between the pad (130) and the ground copper layer (140). S5, nickel-gold plating: After removing the tin layer (400) used for protection, nickel-gold is plated on the copper layer (300) of the pad (130).

2. The process for preventing gold seepage during nickel-gold plating according to claim 1, characterized in that: In step S1, the circuit board (100) is cooled by spraying coolant while drilling the back drill hole (120), and after drilling is completed, the back drill hole (120) is drilled for 5 to 10 seconds.

3. The process for preventing gold seepage during nickel-gold plating according to claim 1, characterized in that: In step S3, the surface of the circuit board (100) is cleaned with deionized water before copper and tin plating. After cleaning, the circuit board (100) is air-dried naturally. The plating solution is stirred in real time during copper and tin plating.

4. The process for preventing gold seepage during nickel-gold plating according to claim 1, characterized in that: In step S4, a UV laser or a combination of UV and carbon dioxide laser is used.

5. The process for preventing gold seepage during nickel-gold plating according to claim 1, characterized in that: In step S5, an alkaline solution is used to remove the remaining dry film (200).

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