Processing method for improving diffusion coating and diffusion corrosion phenomena of multi-layer flexible circuit board

Abstract

The invention discloses a processing method for improving diffusion coating and diffusion corrosion phenomena of a multilayer flexible circuit board, and belongs to the technical field of flexible circuit boards. According to the processing method for improving the diffusion coating and diffusion corrosion phenomena of the multilayer flexible circuit board, separated spot plating is carried out on a PTH hole and a bonding pad, so that the phenomenon that the bonding pad is excessively electroplated to guarantee the hole copper requirement can be effectively avoided; in the pattern manufacturing and film pressing process, a dry film cannot be filled into a height difference gap position, diffusion coating and diffusion corrosion occur during tin plating and acid etching, and then short circuit and open circuit are caused, so that reworking, repairing and scrapping of products can be reduced, and the process yield is improved.

Description

Technical Field

[0001] The invention relates to the technical field of flexible circuit boards, and in particular to a processing method for improving the plating and corrosion phenomena of a multi-layer flexible circuit board. Background Art

[0002] Flexible circuit boards are printed circuit interconnect structures built on ultra-thin substrate materials that can be bent. They can be bent into three-dimensional structures, which is impossible for rigid circuit boards. Due to this flexibility, flexible circuit boards have more advantages than other connection methods and are more suitable for electronic devices that achieve high-density interconnection in a small space. Multilayer flexible boards can have a via structure like rigid boards, but their microporous structure also has some other characteristics, which are derived from the flexible substrate film used in flexible circuit boards. Since the copper plating layer is much more brittle than the rolled copper foil, the flexible circuit board needs to ensure that the copper plating layer is very thin to ensure its excellent flexibility. Therefore, in the processing of flexible circuit boards, it is necessary to ensure that the vias meet their hole copper requirements and that the copper plating layer of the circuit is as thin as possible. Therefore, in the production process of flexible circuit boards with via structures, point plating is generally used for hole copper processing. When there are plug-in hole rings, gold fingers and pads with cover film openings in the flexible circuit board, these pad positions also need to be spot-plated together with copper vias. At this time, the multi-layer flexible circuit board has high requirements for hole copper, resulting in the copper thickness of the spot-plated pads being electroplated very thickly. As a result, when the graphics are made, there is a difference in copper thickness at the pad position, and the dry film cannot be filled. In the subsequent graphics production process, short circuits and open circuits caused by plating and corrosion are prone to occur. Summary of the invention

[0003] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a processing method for improving the plating and corrosion phenomena of a multi-layer flexible circuit board, which can avoid the short circuit, open circuit and gap problems in the flexible circuit, improve the yield in the product manufacturing process, reduce rework and repair, and improve processing efficiency.

[0004] The processing method for improving the plating and corrosion phenomena of a multi-layer flexible circuit board according to an embodiment of the present invention comprises:

[0005] Step 1: Laminating a multi-layer flexible substrate material with a copper foil layer to form a flexible circuit board substrate;

[0006] Step 2: Bond the layers of the flexible circuit board with an adhesive to form a multi-layer structure;

[0007] Step 3: Drill holes on the circuit board to form PTH holes. The vias are used to connect circuits between different layers.

[0008] Step 4: deposit a layer of copper on the hole wall to achieve hole wall metallization;

[0009] Step 5: Coat the photoresist on the circuit board, complete the external light imaging on the circuit board through exposure and development, and open the PTH hole;

[0010] Step 6: Perform the first spot plating on the circuit board and electroplate the PTH holes to meet the requirements of electrical connection;

[0011] Step 7: Remove the photoresist layer on the circuit board by stripping the film, and polish the bumps formed during the first spot plating process;

[0012] Step 8: Coat the photoresist on the circuit board, complete the external light imaging on the circuit board through exposure and development, and open the window of the pad;

[0013] Step 9: Perform a second spot plating on the circuit board and electroplate the pads;

[0014] Step 10: Remove the photoresist layer on the circuit board by stripping the film, and polish the bumps formed during the second spot plating process;

[0015] Step 11: Coat photoresist on the circuit board, expose and develop the circuit pattern of the circuit board to form the circuit pattern.

[0016] The processing method for improving the plating and corrosion phenomena of a multi-layer flexible circuit board according to an embodiment of the present invention has at least the following beneficial effects: by separately spot-plating the PTH hole and the pad, it is possible to effectively avoid the pad being electroplated too high to ensure the copper requirement of the hole, and during the pattern production and lamination process, the dry film cannot be filled into the height difference gap position, and plating and corrosion occur during tin plating and acid etching, thereby causing short circuits and open circuits, which can reduce product rework, repair and scrapping and improve process yield.

[0017] According to some embodiments of the present invention, in step 6, a 35 μm copper layer is electroplated on the PTH hole.

[0018] According to some embodiments of the present invention, in step 9, a 12 μm copper layer is electroplated on the pad.

[0019] According to some embodiments of the present invention, in step 11, after the external light imaging is completed, the circuit board is subjected to acid etching to remove the copper layer not protected by the photoresist, thereby producing a circuit pattern.

[0020] According to some embodiments of the present invention, the circuit board is tinned after the external light imaging is completed, and the excess tin layer is removed by alkaline etching after the tinning to produce a circuit pattern.

[0021] According to some embodiments of the present invention, after step 11, the circuit board is cleaned and dried to remove residual etching liquid on the circuit board.

[0022] According to some embodiments of the present invention, in step 11, the pH value of the acidic etching solution is controlled between 2 and 3 to ensure etching uniformity.

[0023] According to some embodiments of the present invention, in step 11, the thickness of the tin-plated layer is controlled between 0.5-2 μm.

[0024] According to some embodiments of the present invention, in step 11, the pH value of the alkaline etching solution is controlled between 11-13.

[0025] 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

[0026] The present invention is further described below in conjunction with the accompanying drawings and embodiments:

[0027] Figure 1 The present invention is a flowchart of a processing method for improving the plating and corrosion phenomena of a multi-layer flexible circuit board according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] 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.

[0029] In the description of the present invention, "several" means one or more, "more" means more than two, "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.

[0030] 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.

[0031] refer to Figure 1 A processing method for improving the plating and corrosion phenomena of a multi-layer flexible circuit board according to an embodiment of the present invention is described.

[0032] like Figure 1 As shown, the processing method for improving the plating and corrosion phenomenon of a multi-layer flexible circuit board according to an embodiment of the present invention includes:

[0033] Step 1: Laminating a multi-layer flexible substrate material with a copper foil layer to form a flexible circuit board substrate;

[0034] Step 2: Bond the layers of the flexible circuit board with an adhesive to form a multi-layer structure;

[0035] Step 3: Drill holes on the circuit board to form PTH holes. The vias are used to connect circuits between different layers.

[0036] Step 4: deposit a layer of copper on the hole wall to achieve hole wall metallization;

[0037] Step 5: Coat the photoresist on the circuit board, complete the external light imaging on the circuit board through exposure and development, and open the PTH hole;

[0038] Step 6: Perform the first spot plating on the circuit board and electroplate the PTH holes to meet the requirements of electrical connection;

[0039] Step 7: Remove the photoresist layer on the circuit board by stripping the film, and polish the bumps formed during the first spot plating process;

[0040] Step 8: Coat the photoresist on the circuit board, complete the external light imaging on the circuit board through exposure and development, and open the window of the pad;

[0041] Step 9: Perform a second spot plating on the circuit board and electroplate the pads;

[0042] Step 10: Remove the photoresist layer on the circuit board by stripping the film, and polish the bumps formed during the second spot plating process;

[0043] Step 11: Coat photoresist on the circuit board, expose and develop the circuit pattern of the circuit board to form the circuit pattern.

[0044] like Figure 1 As shown in the figure, firstly, fast pressing is performed, which is the preliminary step in the manufacture of flexible circuit boards. Its purpose is to press the multi-layer flexible substrate material and the copper foil layer together. In this step, high temperature and high pressure are used to tightly combine the multi-layer flexible substrate material and the copper foil layer to form a solid flexible circuit board substrate. The temperature and pressure parameters need to be precisely controlled during the fast pressing process to ensure good bonding between layers while avoiding excessive deformation of the material.

[0045] After the quick pressing is completed, lamination is carried out. Lamination is to bond the various layers of the flexible circuit board together through adhesives to form a multi-layer structure. During the lamination process, it is necessary to ensure that there are no bubbles and gaps between the layers to ensure the mechanical strength and electrical performance of the circuit board. After lamination is completed, the circuit board will be cut into the required size and shape.

[0046] The circuit board is then drilled to create PTH holes (i.e., through-holes) on the circuit board. These holes connect circuits on different layers to achieve electrical interconnection. During the drilling process, the position and size of the holes need to be precisely controlled to ensure the accuracy and reliability of the circuit. After drilling, copper plating is performed. Copper plating is the process of metalizing the hole wall. A layer of copper is deposited on the hole wall by chemical copper plating or electroplating to achieve electrical connection in the hole. The copper plating process requires strict control of the thickness and uniformity of the copper layer to ensure the reliability and performance of the circuit.

[0047] After the copper deposition is completed, the circuit board is imaged for the first time, and the desired pattern is formed on the circuit board using photolithography technology. In this step, only the PTH holes are opened for the subsequent spot plating process. Photoresist is coated on the circuit board, and then the desired pattern is formed through exposure and development.

[0048] The first spot welding of the circuit board is performed. Spot plating is an electroplating process for PTH holes. The purpose is to form a sufficient copper layer in the hole to meet the requirements of electrical connection. Electroplate a copper layer of about 35μm to ensure that there is enough copper thickness in the hole and avoid subsequent problems caused by over-plating. After spot welding, the film is stripped to remove the unnecessary photoresist layer on the circuit board. After stripping, since the bumps formed during the spot plating process may affect the subsequent processes, these bumps need to be polished to ensure the flatness of the circuit board surface.

[0049] Then the circuit board is imaged for the second time with external light, and only the pads that need to be spot plated are opened. This is to electroplate only these specific pads in the subsequent second spot plating step to control the copper thickness of the pads. After completion, the circuit board is spot welded for the second time, and the electroplating process is carried out on specific pads to electroplate a copper layer of about 12μm. The purpose of this step is to accurately control the copper thickness of the pad to avoid short circuit or open circuit problems caused by uneven copper thickness. After spot welding is completed, the film is stripped to remove the unnecessary photoresist layer on the circuit board. After stripping, the spot plated bumps also need to be polished to ensure the flatness of the circuit board surface.

[0050] After the two spot platings are completed, the circuit board is produced. The circuit pattern on the circuit board is formed by the third external light imaging. The circuit pattern of the entire circuit board is exposed and developed to prepare for the subsequent etching process. The copper layer not protected by the photoresist is removed by acid etching to form the required circuit pattern. Tin plating can also be performed, followed by alkaline etching to complete the circuit production. Finally, the circuit board is cleaned, dried and tested to ensure that the circuit board meets the quality and performance requirements.

[0051] The copper thickness requirement for spot-plated pads of multi-layer flexible circuit boards is generally ≥38.4μm, and the electroplated copper is about 20μm. During the first electroplating, the hole copper requirement must be guaranteed first. After the pads are electroplated, they often exceed the standard, and the copper thickness of the pads cannot be effectively controlled. After separate spot plating, the copper thickness requirements of the pads and hole copper can be accurately controlled. Separate spot plating of PTH holes and pads can effectively avoid the pads being electroplated too high to meet the hole copper requirements. During the pattern production and lamination process, the dry film cannot be filled into the height difference gap position, and infiltration and erosion occur during tin plating and acid etching, which in turn causes short circuits and open circuits, which can reduce product rework and scrap and improve process yield.

[0052] The pH value of the acidic etching solution is controlled between 2-3, and the pH value of the alkaline etching solution is controlled between 11-13. This precise pH control can ensure the uniformity and consistency of the etching process and avoid circuit performance problems caused by uneven etching. This control helps to improve the processing quality and yield rate of circuit boards. The thickness of the tin plating layer is controlled between 0.5-2μm. This precise thickness control can ensure the uniformity and protection effect of the tin plating layer, while avoiding circuit performance problems caused by too thick a tin layer. This control helps to improve the reliability and durability of circuit boards.

[0053] After step 11, the circuit board is cleaned and dried to remove the residual etching solution on the circuit board. This step helps prevent the residual chemicals from causing further corrosion or damage to the circuit board. The cleaning and drying process ensures the cleanliness of the circuit board and improves the quality and reliability of the product.

[0054] 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 technical field without departing from the purpose of the present invention.

Claims

1. A processing method for improving the plating and corrosion phenomenon of a multi-layer flexible circuit board, characterized in that: include: Step 1: Laminating a multi-layer flexible substrate material with a copper foil layer to form a flexible circuit board substrate; Step 2: Bond the layers of the flexible circuit board with an adhesive to form a multi-layer structure; Step 3: Drill holes on the circuit board to form PTH holes. The vias are used to connect circuits between different layers. Step 4: deposit a layer of copper on the hole wall to achieve hole wall metallization; Step 5: Coat the photoresist on the circuit board, complete the external light imaging on the circuit board through exposure and development, and open the PTH hole; Step 6: Perform the first spot plating on the circuit board and electroplate the PTH holes to meet the requirements of electrical connection; Step 7: Remove the photoresist layer on the circuit board by stripping the film, and polish the bumps formed during the first spot plating process; Step 8: Coat the photoresist on the circuit board, complete the external light imaging on the circuit board through exposure and development, and open the window of the pad; Step 9: Perform a second spot plating on the circuit board and electroplate the pads; Step 10: Remove the photoresist layer on the circuit board by stripping the film, and polish the bumps formed during the second spot plating process; Step 11: Coat photoresist on the circuit board, expose and develop the circuit pattern of the circuit board to form the circuit pattern.

2. The processing method for improving the plating and corrosion phenomenon of a multi-layer flexible circuit board according to claim 1, characterized in that: In step 6, a 35 μm copper layer is electroplated for the PTH holes.

3. The processing method for improving the plating and corrosion phenomenon of a multi-layer flexible circuit board according to claim 1, characterized in that: In step 9, the pads are electroplated with a 12 μm copper layer.

4. The processing method for improving the plating and corrosion phenomenon of a multi-layer flexible circuit board according to claim 1, characterized in that: In step 11, after the external light imaging is completed, the circuit board is subjected to acid etching to remove the copper layer not protected by the photoresist, thereby producing a circuit pattern.

5. The processing method for improving the plating and corrosion phenomena of a multi-layer flexible circuit board according to claim 1, characterized in that: In step 11, after the external light imaging is completed, the circuit board is tinned, and after the tinning, the excess tin layer is removed by alkaline etching to produce a circuit pattern.

6. The method for improving the plating and corrosion phenomena of a multi-layer flexible circuit board according to claim 4, characterized in that: After step 11, the circuit board is cleaned and dried to remove the residual etching solution on the circuit board.

7. The processing method for improving the plating and corrosion phenomena of a multi-layer flexible circuit board according to claim 4, characterized in that: In step 11, the pH value of the acidic etching solution is controlled between 2 and 3 to ensure etching uniformity.

8. The method for improving the plating and corrosion phenomena of a multi-layer flexible circuit board according to claim 5, characterized in that: In step 11, the thickness of the tin-plated layer is controlled between 0.5-2 μm.

9. The processing method for improving the plating and corrosion phenomena of a multi-layer flexible circuit board according to claim 5, characterized in that: In step 11, the pH value of the alkaline etching solution is controlled between 11-13.

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