Process for preventing gold permeation during nickel-gold plating

Abstract

The invention discloses a process for plating nickel and gold to avoid gold permeation, which comprises the following steps of: S1, back drilling: forming a through hole in a multi-layer circuit board according to production requirements, drilling a back drilling hole in one side of the multi-layer circuit board in a back drilling manner, and during design, enabling a base layer between a bonding pad and a grounding copper layer to have an overlapping region with the back drilling hole, and then filling resin into the back drilling hole; s2, film covering is conducted, the circuit board is covered with a dry film, and the remaining dry film keeps away from the overlapping area after film removing; s3, copper and tin plating: firstly plating a copper layer on the whole circuit board, then plating a tin layer on the copper layer to protect the copper layer, and not plating copper and tin on the area covered by the remaining dry film; s4, laser ablation: ablating the tin layer on the overlapped region by using laser, then removing the remaining dry film in the step S2, and etching the copper layer which is not protected by the tin layer by using an etching liquid medicine so as to expose the base layer between the bonding pad and the grounding copper layer; and S5, nickel and gold plating: after the tin layer for protection is removed, nickel and gold plating is carried out on the copper layer of the bonding pad.

Description

Technical Field

[0001] The invention relates to the technical field of circuit board manufacturing, and in particular to a process for nickel-gold plating to avoid gold penetration. Background Art

[0002] In the manufacturing process of circuit boards, some circuit boards have back drilling process, and there is an overlapping area between the back-drilled hole and the base layer between the pad and the ground copper layer. The back-drilled hole tree has a certain degree of depression after the grease plugging. This is caused by the reduction in volume after the resin dries. In the past, the base layer between the ground copper layer and the pad was directly covered with dry film. When copper and tin were plated on the non-masked area, copper and tin would penetrate into the overlapping area from the recessed position. When the tin layer was removed and nickel-gold was plated later, the overlapping area would also penetrate gold, which eventually caused the distance between the ground copper layer and the pad to be reduced, making it easy for the ground copper layer to be conductively connected to the pad, thus causing a short circuit problem. Summary of the invention

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

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

[0005] S1, back drilling, a through hole is set on a multilayer circuit board according to production requirements. After the through hole is metallized, a back-drilled hole is drilled on one side of the multilayer board by back drilling. The back-drilled hole is coaxially arranged with the through hole. During design, there is an overlapping area between the base layer between the pad and the grounding copper layer and the back-drilled hole, and then resin is filled in the back-drilled hole;

[0006] S2, laminating, laminating a dry film on the circuit board, developing the dry film and then retreating the film, and the remaining dry film avoids the overlapping area;

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

[0008] S4, laser ablation, using 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 by 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 on the copper layer of the pad.

[0010] A nickel-gold plating process to avoid gold penetration according to an embodiment of the present invention has at least the following beneficial effects: by changing the process, the area covered by the dry film is adjusted so that the overlapping area is no longer covered, and the tin layer in the overlapping area is removed by laser burning tin. After removing the remaining dry film, it is ensured that the etching solution fully etches away the copper between the pad and the grounding copper layer to expose the base layer, and gold will not penetrate into the base layer during subsequent nickel-gold plating, thereby avoiding the defects of previous production methods and ensuring product quality.

[0011] According to some embodiments of the present invention, in the S1 step, the circuit board is cooled by spraying coolant while drilling, and after the drilling is completed, the hole is hollow-drilled for 5 to 10 seconds, and the circuit board is cooled by spraying coolant to avoid local overheating of the circuit board causing thermal stress accumulation and warping. Hollow 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 the step S2, when making the development 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 the S3 step, the surface of the circuit board is first cleaned with desalted water before copper-tin plating, and the circuit board is naturally air-dried after cleaning. The plating solution is stirred in real time during copper plating and tin plating. The use of desalted 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 avoids warping of the circuit board. The plating solution is stirred to make the electroplating layer more uniform, thereby ensuring product quality.

[0014] According to some embodiments of the present invention, in the step S4, 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 present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0018] Figure 1 A schematic diagram of providing a through hole on a circuit board according to an embodiment of the present invention;

[0019] Figure 2 A schematic diagram of setting back drilling holes on a circuit board;

[0020] Figure 3 A schematic diagram of the dry film remaining after the dry film is coated on the circuit board and developed;

[0021] Figure 4 It is a schematic diagram of copper-tin plating on the non-dry film area of ​​the circuit board;

[0022] Figure 5 Schematic diagram of removing the remaining dry film on the circuit board and laser ablating the tin layer in the overlapping area;

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

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

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

[0026] Pad 130, ground copper layer 140, overlap region 150, base layer 160;

[0027] Dry film 200 , copper layer 300 , tin layer 400 . DETAILED DESCRIPTION

[0028] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0029] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0030] In the description of the present invention, "several" means one or more, "more" means two or more, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0031] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0032] Reference Figures 1 to 7 According to an embodiment of the present invention, a process for nickel-gold plating to avoid gold penetration comprises the following steps:

[0033] S1, back drilling, a through hole 110 is set on the multilayer circuit board 100 according to the production requirements. After the through hole 110 is metallized, a back-drilled hole 120 is drilled on one side of the multilayer board by back drilling. The back-drilled hole 120 is coaxially arranged with the through hole 110. During the design, there is an overlapping area 150 between the base layer 160 between the pad 130 and the grounding copper layer 140 and the back-drilled hole 120, and then resin is filled in the back-drilled hole 120;

[0034] S2, laminating, laminating the dry film 200 on the circuit board 100, and after the dry film 200 is developed, the film is retreated, and the remaining dry film 200 avoids the overlapping area 150;

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

[0036] S4, laser ablation, using laser to ablate the tin layer on the overlapping area 150, and then remove the dry film 200 remaining in step S2, and use etching solution to etch away the copper layer 300 not protected by the tin layer 400, so as to expose 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 plating is performed 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 in the overlapping area 150 is removed by laser burning. After removing the remaining dry film, ensure that the etching solution fully etches away the copper between the pad 130 and the grounding copper layer 140, thereby exposing the base layer 160. During the subsequent nickel-gold plating, gold will not penetrate into the base layer 160, thereby avoiding the defects of the previous production method 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 boards. Not all circuit boards have the overlapping area 150. The previous method is to directly cover the entire area with dry film, so the problem of gold penetration will occur. The previous method is suitable for the situation where the distance between the back-drilled hole 120 and the pad 130 is ≥0.3mm. The multi-layer circuit board 100 in the present invention is to be provided with a through hole 110 before back drilling. The through hole 110 is also common in the circuit board manufacturing process. The through hole 110 also needs to be metallized. Since not every layer of the multi-layer board is conductive, for example, only two layers are conductive, the through hole 110 needs to remove the metal layer in the through hole 110 by back drilling, and then use resin to fill the back-drilled hole and the through hole. The so-called back drilling means drilling from the back.

[0040] In some embodiments, in step S1, the circuit board 100 is cooled by spraying coolant while drilling. After the drilling is completed, the hole is hollow-drilled for 5 to 10 seconds, and the circuit board is cooled by spraying coolant to avoid local overheating of the circuit board causing thermal stress accumulation and warping. Hollow drilling can smooth the burrs in the hole and also make the drill bit play a temporary supporting role in the hole. It can be understood that the coolant uses the circuit board coolant commonly used in the field. During the hollow drilling process, the drill bit moves up and down in the hole.

[0041] It should be noted that the dry film used in the present invention covers the copper layer that needs to be etched away, and the uncovered part is the copper layer that needs to be retained. The so-called grounding copper layer refers to the copper layer of the non-pad and circuit part of the circuit board, which plays a grounding role.

[0042] In some embodiments, in step S2, when making the development image, the overlapping area 150 is avoided, and the overlapping area 150 is not irradiated during exposure.

[0043] In some embodiments, in step S3, the surface of the circuit board 100 is first cleaned with deionized water before copper-tin plating, and the circuit board 100 is naturally air-dried after cleaning. The plating solution is stirred in real time during copper plating and tin plating. The deionized water is used to prevent 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 avoids warping of the circuit board. Stirring the plating solution makes the electroplating layer more uniform, thereby ensuring product quality. It is understandable that the so-called natural air drying can be air-dried at room temperature or blown dry with air at room temperature.

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

[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 are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A process for nickel-gold plating to avoid gold penetration, characterized in that: The following steps are involved: S1, back drilling, a through hole (110) is provided on a multilayer circuit board (100) according to production requirements, and after the through hole (110) is metallized, a back-drilled hole (120) is drilled on one side of the multilayer board by back drilling, and the back-drilled hole (120) is coaxially arranged with the through hole (110), and during design, a base layer (160) between a pad (130) and a grounding copper layer (140) and the back-drilled hole (120) have an overlapping area (150), and then resin is filled in the back-drilled hole (120); S2, laminating, laminating a dry film (200) on the circuit board (100), and after the dry film (200) is developed, the film is retreated, and the remaining dry film (200) avoids the overlapping area (150); S3, copper-tin plating, first plating the entire circuit board (100) with a copper layer (300), and then plating a tin layer (400) on the copper layer (300) to protect the copper layer (300), and the area covered by the remaining dry film (200) is not copper-plated and tin-plated; S4, laser ablation, using 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) by 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. A process for nickel-gold plating to avoid gold penetration according to claim 1, characterized in that: In the step S1, the circuit board (100) is cooled by spraying a cooling liquid when drilling the back-drilled hole (120), and after the drilling is completed, the back-drilled hole (120) is hollow-drilled for 5 to 10 seconds.

3. A process for nickel-gold plating to avoid gold penetration according to claim 1, characterized in that: In the step S2, when making the development image, the overlapping area (150) is avoided, and the overlapping area (150) is not irradiated during exposure.

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

5. A process for nickel-gold plating to avoid gold penetration according to claim 1, characterized in that: In the step S4, UV laser or a combination of UV and carbon dioxide laser is used.

6. A process for nickel-gold plating to avoid gold penetration according to claim 1, characterized in that: In the step S5, an alkaline solution is used to remove the remaining dry film (200).

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