Surface treatment method for avoiding residual glue of golden finger

Abstract

The invention discloses a surface treatment method for avoiding residual glue of a golden finger, which comprises the following steps of: horizontally placing a circuit board on a bearing plate in a posture that the golden finger faces upwards, and carrying out single-side polish-brush wire passing on a golden finger area by adopting a brush wheel to obtain a treated product; the bristles on the brush wheel are made of nylon materials, the mesh number of the nylon bristles is 1000-1200, brush marks are controlled to be 10 + / -2 mm, and the length of the bristles is larger than or equal to 10 mm. The method breaks through the usual thinking of cleaning the golden finger by sand blasting, cancels redundant procedures, shortens the production cycle, and reduces the procedure connection cost; through directional brush grinding and parameter control, the removal rate of the residual glue of the golden finger is increased to 99% or above, operation of a skilled worker is not needed, and quality control is simple; and compared with sand blasting operation, the defect rate of the polish-brush mode is obviously reduced, and the defect of poor plating resistance of the residual glue is effectively overcome.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board technology, and in particular to a surface treatment method for avoiding residual adhesive on gold fingers. Background Technology

[0002] Gold fingers are the external conductive plug-in interfaces of FPC (Flexible Printed Circuit) / PCB (Printed Circuit Board). They appear as many long, strip-shaped lines arranged side-by-side along the edge of the circuit board, used for circuit conduction, signal transmission, and power connection. Initially, gold fingers consist of many copper wires, which are then plated with a metal layer (nickel-gold plating) to ensure oxidation resistance, durability during plugging and unplugging, and reliable contact. Nickel-gold plating requires a thicker copper wire base layer for conductivity.

[0003] However, various residues are generated during the manufacturing process of copper wire. For example, during the lamination, exposure, development, and etching processes of the cover film / dry film, local overflow and edge run-through leave adhesive residues in the gold finger area; when removing pre-plating protective tape and electroplating-resistant tape, some adhesive layer remains on the gold finger surface, forming residues; during the process, flux, ink, and solder resist ink seep through and splatter at the edges, adhering to the gold finger area and forming organic contaminants; during the punching, cutting, and bending processes of FPC, the substrate or cover film is subjected to high temperature and pressure, causing small molecule adhesives to precipitate and adhere to the gold finger surface. These residues can cover local copper surfaces, and since these residues are non-conductive, the areas covered by them cannot properly deposit plating metal during the nickel-gold plating process, leading to plating defects.

[0004] To remove these residual adhesives, the traditional FPC gold finger processing flow uses a "bare plate - AOI sandblasting + bare plate - AOI - finger inspection" process. Sandblasting uses high-pressure gas to propel abrasive particles (alumina, glass frit, etc.) onto the gold finger surface, impacting and removing residual adhesives, oxide layers, and contaminants. However, this conventional approach has the following drawbacks: 1. Redundancy in process: In order to avoid sand jamming, it is generally necessary to rinse the surface with water and dry the water (such as CN118042737A). This method has a long process and requires two AOI (automatic optical inspection) related processes. The process connection is cumbersome and increases production time. 2. Incomplete removal of residual adhesive: Sandblasting does not have the ability to cut the copper surface, and larger pieces of residual adhesive cannot be effectively cleaned. The combination of sandblasting and inspection has poor targeted removal effect on the residual adhesive on the gold finger surface, resulting in poor anti-plating of residual adhesive in the subsequent nickel-gold plating process. 3. Low yield: According to current AVI (Automatic Visual Inspection) data, the average defect rate of gold fingers in the traditional process is 3.6%, among which residual adhesive and anti-plating are the main defect types, which seriously affect the overall product yield.

[0005] Figure 1The image shows a defective FPC gold finger that has been sandblasted and then plated with nickel and gold. In the lower right corner of the image, there is a black area that runs diagonally across the gold finger. This is a plating defect caused by incomplete removal of adhesive. Because of the lack of a nickel-gold layer, this area does not have a metallic luster.

[0006] Therefore, it is necessary to design a new surface treatment method to solve the above problems. Summary of the Invention

[0007] The main objective of this invention is to provide a surface treatment method that avoids residual adhesive on gold fingers, and to provide a precise and efficient gold finger pretreatment and plating process. The overall process is smoothly connected and the parameters are coordinated and controllable, which can not only thoroughly remove residual adhesive from the surface of gold fingers, but also protect the gold finger substrate and the quality of subsequent plating.

[0008] The present invention achieves the above-mentioned objective through the following technical solution: a surface treatment method to avoid residual adhesive on gold fingers, characterized in that: the circuit board is placed horizontally on a support plate with the gold fingers facing upwards, and a brush wheel is used to brush the gold finger area on one side to obtain the treated product; the bristles on the brush wheel are made of nylon material, the mesh number of the nylon bristles is 1000-1200, the brush marks are controlled to be 10±2mm, and the bristle length is ≥10mm.

[0009] Specifically, the circuit board is an FPC.

[0010] Specifically, the bearing plate is an FR-4 bearing plate.

[0011] Specifically, the brushing operation involves unidirectional brushing along the insertion and removal direction of the gold fingers.

[0012] Specifically, the brushing current is 2.9~3.1A.

[0013] Specifically, the brush linear speed is 2.5 ± 0.1 mm.

[0014] Specifically, the brushing is performed only on the gold finger area, without processing the non-gold finger areas.

[0015] Specifically, after the brushing and polishing is completed, the circuit board is immediately transferred to the nickel-gold plating process for plating treatment.

[0016] The beneficial effects of the technical solution of this invention are: 1. Simplified process: Breaking away from the conventional thinking of sandblasting to clean gold fingers, eliminating redundant processes in sandblasting, shortening the production cycle, and being able to be directly connected to the line process and nickel-gold plating process of continuous production line, reducing process connection costs. 2. Precision of residual adhesive removal: Although a single process is used to replace sandblasting, the integrity of the circuit is protected by directional brushing and parameter control. The residual adhesive removal rate of gold fingers is increased to more than 99%. Moreover, no skilled workers are required to operate the equipment, and quality control is simple. 3. Improved yield: Compared with sandblasting, the defect rate of brushing is significantly reduced (from about 3.6% to below 1%), greatly reducing the rework rate and effectively solving the problem of poor plating performance due to residual adhesive. Attached Figure Description

[0017] Figure 1 This is a magnified view of the gold fingers of a sandblasted FPC after nickel-gold plating. Figure 2 This is a schematic diagram illustrating the principle of the frosting process in this embodiment; Figure 3 This is a magnified view of the gold fingers of an FPC that has undergone surface treatment and is now nickel-gold plated.

[0018] The numbers in the diagram represent: 1-FPC, 11-Gold fingers; 2-Carrier plate; 3-Brush wheel. Detailed Implementation

[0019] This embodiment addresses the technical pain points of residual adhesive in the gold finger area of ​​FPC flexible circuit boards and the cumbersome traditional sandblasting cleaning process. It provides a precise and efficient gold finger pretreatment and plating process with smooth overall process flow and controllable parameters. It can thoroughly remove residual adhesive from the gold finger surface while protecting the gold finger substrate and the quality of subsequent plating. The specific implementation steps are as follows: Example

[0020] I. Preliminary Process Adjustments and Rework Preparations First, complete the normal reporting process for all routine procedures before the FPC1 AOI finger identification station, verify the workpiece batch, model, and production information, and confirm that the workpiece only has residual adhesive defects in the gold finger area and no other structural damage. Then, optimize and reorganize the original production process: eliminate the two processes of "bare plate-AOI sandblasting" and "bare plate-AOI-finger operation" in the traditional process to avoid impact damage to the thin plating layer of the gold finger caused by high-pressure sandblasting and secondary pollution caused by sand particles, while reducing intermediate transfer links. After the reporting is completed, directly transfer the FPC to be reworked to the electroplating process section, open a rework work order according to the production line rework management specifications, clarify the process requirements and quality standards, and start the dedicated brushing and cleaning process to achieve targeted rework treatment of defective workpieces.

[0021] II. Brushing Equipment Parameter Adjustment and Configuration The second station of the dedicated FPC brushing production line is activated, employing a unidirectional brushing operation mode to avoid FPC board deformation and gold finger edge scratches caused by double-sided or reciprocating brushing. Targeting the thin plating layer of the gold fingers and the characteristics of the soft substrate, precise settings are made for various core brushing parameters to ensure uniform brushing force, thorough cleaning, and no over-brushing damage. 1. Brushing current control: The brushing current is strictly set to a narrow range of 2.9~3.1A. This current range corresponds to a pressure of 1.45~1.55kg on the surface of the gold fingers 11 by the brush wheel 2, which is within the range of light pressure fine grinding. Compared with sandblasting, the range is more targeted, ensuring sufficient force to remove surface residue and slight oxide layer, while avoiding excessive pressure that could scratch the gold surface or thin the copper layer. 2. Production line speed setting: Adjust the production line speed to 2.5±0.1m / min to control the dwell time of FPC1 under brush wheel 3. Too fast a speed will result in incomplete cleaning of residual adhesive, while too slow a speed will easily cause over-grinding and excessive brush marks. This speed works in conjunction with the current parameter to balance cleaning efficiency and processing quality. 3. Brush Material and Size Control: Brush wheel 3 is made of 1000-1200 fine-grit nylon. The fine-grit brush material is soft and will not scratch the surface of the gold fingers 11, ensuring the flatness of the board surface after brushing. The width of the brush marks (the width of the marks produced by grinding) is precisely controlled at 10±2mm to ensure that the brushing area completely covers the gold finger area. If it is too wide, it will damage the circuit; if it is too narrow, it will miss the brush. Brushing beyond the range will damage the surrounding circuit and the cover film. At the same time, check and confirm that the bristle length of the nylon brush is >10mm to ensure that the bristles have sufficient elasticity and that the brushing pressure is evenly distributed without localized pressure concentration.

[0022] III. Implementation of FPC Gold Finger Polishing Operation Before the brushing operation, after verifying that the equipment parameters are correct, the FPC1 is placed in a standardized manner: the gold fingers 11 face upwards and horizontally, ensuring that the gold fingers face downwards to prevent direct contact with the brush wheel 3 and damage. Considering the flexible substrate of FPC1's tendency to bend, wrinkle, and deviate, a uniformly thick FR-4 material carrier plate 2 is placed on the back of the FPC1 throughout the entire process. FR-4 is a flame-retardant glass fiber reinforced epoxy resin copper-clad laminate material standard. The FR-4 carrier plate is a flame-retardant epoxy glass cloth board that meets the UL94 V-0 flame-retardant rating. The surface of the carrier plate 2 is flat, burr-free, and warped, fully adhering to the back of the FPC1, providing stable and rigid support for better adaptation to the flexible board and preventing uneven brush marks and localized over-brushing caused by board deformation during the brushing process.

[0023] like Figure 2As shown, the carrier plate 2 moves horizontally under the action of the conveying mechanism, passing under the brush wheel 3. The bristles on the brush wheel 3 scrape across the area where the gold fingers 11 are located under a certain pressure. During the operation, only the surface where the gold fingers 11 are located is brushed at a fixed point. The brush wheel 3 does not move back and forth while in contact with the gold fingers 11. The non-gold finger areas are not brushed. The brushing direction is unidirectional along the insertion and removal direction of the gold fingers 11 to avoid messy brush marks caused by lateral brushing, which would affect the appearance and conductivity of the gold fingers 11. When a batch of circuit boards passes through continuously, the width of the brush marks and the stability of the current are monitored in real time to promptly check for abnormalities such as board misalignment and improper bonding of the carrier plate 2.

[0024] IV. Personnel Management and Operating Procedures At the initial stage of this batch of heavy-duty operations, professional engineers will be on-site throughout the process to guide production personnel in completing operations such as parameter verification, board placement, and equipment start-up and shutdown. Specialized training will be conducted simultaneously to clarify the brushing and polishing parameter control requirements, abnormal handling procedures, and quality judgment standards. After the production personnel have mastered the complete set of operating procedures and the trial production circuit boards have passed inspection, fixed operators will be assigned to independently complete the subsequent batch brushing and polishing processes to ensure consistency of operations and avoid defects caused by human error.

[0025] V. Seamless connection of nickel-gold plating process After the FPC is cleaned and polished, it is immediately transferred to the subsequent nickel-gold plating process. This shortens the interval between the brushing and plating process and prevents the clean and activated copper surface from being exposed to air and undergoing secondary oxidation, which would affect the adhesion of the plating. The plating process is carried out according to the standard nickel-gold plating process for FPC gold fingers. First, a nickel layer is plated to form a barrier layer and a structural reinforcement layer, which improves the hardness and wear resistance of the gold fingers and prevents the diffusion of the copper substrate. Then, a surface gold layer is plated. The high stability and low resistance of gold are used to achieve anti-oxidation, ensure conductivity and plug-in resistance.

[0026] VI. Finished Product Inspection After all processes are completed, the gold finger area is visually inspected using AVI automatic visual inspection equipment to check whether residual adhesive has been completely removed, whether brush marks meet the 10±2mm standard, and whether there are any defects such as scratches, exposed copper, or uneven plating on the gold surface. Figure 3 As shown, the surfaces of all gold fingers have almost the same metallic luster, indirectly proving that the adhesive on gold fingers 11 has been completely removed. After passing the inspection, the gold fingers are transferred to the subsequent finished product process. After inspection, the adhesive removal pass rate of gold fingers under the process of this embodiment is over 99%, the coating damage rate is reduced by over 90% compared with the traditional sandblasting process, and the product's conductivity reliability and appearance quality both meet the mass production standards.

[0027] The significance of this invention lies in: 1. Simplified process: Breaking away from the conventional thinking of sandblasting to clean gold fingers, eliminating redundant processes in sandblasting, shortening the production cycle, and being able to be directly connected to the line process and nickel-gold plating process of continuous production line, reducing process connection costs. 2. Precision of residual adhesive removal: Although a single process is used to replace sandblasting, the integrity of the circuit is protected by directional brushing and parameter control. The residual adhesive removal rate of gold fingers is increased to more than 99%. Moreover, no skilled workers are required to operate the equipment, and quality control is simple. 3. Improved yield: Compared with sandblasting, the defect rate of brushing is significantly reduced (from about 3.6% to below 1%), greatly reducing the rework rate and effectively solving the problem of poor plating performance due to residual adhesive.

[0028] The above descriptions are merely some embodiments of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A surface treatment method to avoid residual adhesive on gold fingers, characterized in that: The process involves placing the circuit board horizontally on a support plate with the gold fingers facing upwards, and using a brush wheel to brush the gold finger area on one side to obtain the processed product. The brush bristles on the brush wheel are made of nylon with a mesh count of 1000-1200, controlling the brush marks to be 10±2mm and the bristle length to be ≥10mm.

2. The surface treatment method for avoiding residual adhesive on gold fingers according to claim 1, characterized in that: The circuit board is an FPC.

3. The surface treatment method for avoiding residual adhesive on gold fingers according to claim 1, characterized in that: The bearing plate is an FR-4 bearing plate.

4. The surface treatment method for avoiding residual adhesive on gold fingers according to claim 1, characterized in that: The brushing operation involves unidirectional brushing along the insertion and removal direction of the gold fingers.

5. The surface treatment method for avoiding residual adhesive on gold fingers according to claim 1, characterized in that: The current for brushing the board is 2.9~3.1A.

6. The surface treatment method for avoiding residual adhesive on gold fingers according to claim 1, characterized in that: The brush linear speed is 2.5 ± 0.1 mm.

7. The surface treatment method for avoiding residual adhesive on gold fingers according to claim 1, characterized in that: The brushing process only targets the gold finger area and does not process non-gold finger areas.

8. The surface treatment method for avoiding residual adhesive on gold fingers according to claim 1, characterized in that: After the brushing and polishing process is completed, the circuit board is immediately transferred to the nickel-gold plating process for coating treatment.

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