A circuit board printing method for preventing carbon oil from seeping in and shorting out

Abstract

The present invention provides a circuit board printing method for preventing carbon oil from seeping and short circuit, aiming to solve the problems of poor carbon oil coating accuracy, diffusion leakage and short circuit hidden dangers in the prior art. The method comprises the following steps: cleaning the circuit board substrate, improving the surface cleanliness of the substrate by optimizing the cleaning solvent and drying process; forming a high-precision anti-seepage barrier layer by screen printing, and the width and thickness of the barrier layer meet the carbon oil diffusion restriction requirements; performing precise coating by adjusting the mesh number of the screen, the carbon oil viscosity and the opening rate; introducing a segmented dynamic temperature control curing process, and controlling the temperature rise rate and curing time to avoid the problem of excessive fluidity of the carbon oil during the curing process, while protecting the flexible substrate from thermal stress; finally, through microscopic detection and multi-dimensional electrical performance testing. The technical solution of the present invention significantly improves the processing accuracy and reliability of the circuit board by optimizing the coating, anti-seepage and curing processes, and is particularly suitable for the production needs of high-density circuit boards and flexible circuit boards.

Description

Technical Field

[0001] The invention relates to the technical field of circuit board printing, in particular to a circuit board printing method for preventing carbon oil from seeping in and causing short circuits. Background Art

[0002] As electronic devices develop towards miniaturization and high density, printed circuit boards (PCBs), as the core components of electronic products, play an important role in signal transmission and electronic component support. In order to meet the functional requirements of modern electronic equipment, carbon oil coating technology, as a key conductive material processing technology, is widely used in PCB key areas, contacts and functional connection areas. Carbon oil has been widely promoted in consumer electronics, communication equipment and industrial control due to its good conductivity, low cost and easy processing. However, with the increase in the complexity of PCB design, traditional carbon oil coating technology has exposed some problems in the production process, especially in high-density circuit boards and flexible circuit boards, where these problems are particularly prominent.

[0003] 1. Leakage problem of carbon oil coating: As a conductive coating, the fluidity of carbon oil is one of the important characteristics to achieve coating operation. However, excessive fluidity may cause carbon oil to diffuse into non-target areas, resulting in leakage problems. This problem is mainly reflected in the following aspects: Short circuit risk: When carbon oil spreads to adjacent conductive areas, it can cause short circuits between lines. This is especially common in high-density circuit boards because the spacing between lines is smaller and the risk of leakage is higher.

[0004] Decreased conductivity: Leakage will cause the actual coating area of ​​the carbon oil to be inconsistent with the design, resulting in increased contact resistance and affecting the stability of signal transmission.

[0005] In the prior art, in order to solve the leakage problem of carbon oil, the carbon oil viscosity is usually increased or a solder mask layer is added around the coating area to limit its diffusion. However, increasing the viscosity may lead to uneven coating, and the width and thickness of the solder mask layer are difficult to accurately control, making it difficult to achieve good results in high-density circuit boards.

[0006] 2. Difficult to control coating thickness and area accuracy: The traditional screen printing process is the mainstream technology for carbon oil coating, and the coating thickness and boundary of carbon oil are controlled by screen mesh and viscosity. However, this process has the following shortcomings: Uneven thickness: The thickness difference between the center and edge of the carbon oil coating area is large, which directly affects the electrical performance of the coating layer. This problem is particularly prominent for the functional stability of buttons, contacts and other areas.

[0007] Boundary diffusion: The boundaries of the coating area are often unclear, especially in high-density circuit design. Coating diffusion may cover adjacent functional areas and affect the normal operation of other circuits.

[0008] Poor adaptability to high density: When the line spacing is reduced to below 0.2mm, it is difficult for traditional screen printing to accurately control the coating range, which often results in excessive coating overlap or insufficient gap.

[0009] To solve the above problems, some high-precision screen printing technologies have been introduced, but their cost is high and the requirements for process operation are significantly increased. In addition, the root cause of uneven thickness is also related to the curing process of carbon oil, but the existing technology does not pay enough attention to this.

[0010] 3. Design defects of anti-seepage barrier structure: In traditional PCB production, the main means to prevent carbon oil diffusion is to apply a solder mask ink layer to form a physical barrier. However, this design has the following problems in practical applications: Lack of precision: The width and thickness of the solder mask layer are difficult to meet the design requirements, especially in high-density circuits, where its accuracy is difficult to guarantee.

[0011] Insufficient Adhesion: The solder mask may not adhere well to the substrate after curing, causing the barrier layer to fall off during subsequent processing or use.

[0012] Complex process: Multiple coatings of solder mask will increase production steps, reduce production efficiency, and increase costs.

[0013] 4. Limitations of the curing process: After the carbon oil coating is completed, the curing process is the key link to ensure the stability of the coating layer. The traditional process usually uses constant temperature heating to complete the curing, but this method has significant defects in high-density and flexible circuit boards: Increased fluidity: In the early stage of curing, due to the increase in temperature, the fluidity of carbon oil increases, which easily leads to diffusion in the coating area.

[0014] Thermal stress issues: For flexible circuit boards, constant temperature curing can easily lead to substrate warping or material performance degradation, which in turn affects the integrity of the coating layer.

[0015] Inefficiency: Constant temperature curing takes a long time, and higher temperatures may be required to increase the curing speed in high-density circuit boards, but this further increases fluidity issues.

[0016] Some dynamic temperature control curing technologies have been proposed, but the existing technologies are mainly based on single-stage temperature control and lack precise temperature rise rate control and multi-stage curing optimization.

[0017] 5. Single quality inspection method: At present, the quality inspection of carbon oil coating is mainly focused on resistance value testing, which is difficult to fully cover the following performance indicators: Coating accuracy: There is a lack of microscopic detection methods for coating boundaries, thickness uniformity and coating area integrity.

[0018] Crack detection: Failure to identify hidden defects such as cracks and bubbles that may exist in the coating layer.

[0019] Short circuit troubleshooting: A single resistance test is not enough to detect potential short circuit problems, especially in high-density designs.

[0020] Therefore, we urgently need to design a circuit board printing method that prevents carbon oil from seeping in and shorting out to solve the above problems. Summary of the invention

[0021] The purpose of the present invention is to provide a circuit board printing method that prevents carbon oil from seeping in and causing short circuits, in order to solve the problems raised in the background technology.

[0022] To achieve the above object, the present invention provides the following technical solutions: A circuit board printing method for preventing carbon oil from seeping in and causing short circuits, comprising the following steps: S1: Clean the PCB substrate; S2: After the PCB board is cleaned, an impermeable barrier structure is formed at the boundary of the carbon oil coating area; S3: Apply carbon oil to a designated area on the PCB board with the anti-seepage barrier structure obtained in S2 using a screen printing process; S4: curing the PCB board obtained in S3 through a segmented dynamic temperature control curing process; S5: Coating a transparent protective coating on the PCB board that has been cured in S4, and then curing it to obtain a completed circuit board; S6: Perform microscopic inspection and short circuit electrical testing on the completed circuit board.

[0023] As a preferred technical solution of the present invention, the cleaning process of the PCB substrate is completed by the following steps: Use isopropyl alcohol solvent combined with ultrasonic cleaning, the solvent concentration is greater than 95%, and the cleaning time is 2-3 minutes; After cleaning, rinse with deionized water and control the conductivity to less than 5μS / cm; After rinsing, the product is dried. The drying temperature is controlled between 80℃ and 100℃. The drying time meets the following empirical formula: ; in: is the substrate material constant, is the drying temperature, It is the lowest temperature at which the solvent evaporates, and the lowest temperature is 40°C.

[0024] As a preferred technical solution of the present invention, the anti-seepage barrier structure is formed by screen printing solder mask ink, and its width and height The following conditions are met: ; width Must be larger than the critical radius of carbon oil diffusion , that is: where: , is the surface tension of carbon oil, is the viscosity of carbon oil. Should be at least the thickness of the carbon oil coating 1.2 times, that is: ; As a preferred technical solution of the present invention, the screen printing process parameters of carbon oil include: the mesh number of the screen is 300 to 400 meshes, the opening rate of the screen is Controlled between 0.6 and 0.8; Carbon oil coating thickness Calculated by the following formula: ; in: To design the coating thickness, is the mesh density of the wire mesh, is the opening rate of the wire mesh.

[0025] As a preferred technical solution of the present invention, after the carbon oil coating is completed, the carbon oil coating is stabilized by a dynamic temperature control curing process. and time Meet the following conditions: Curing temperature The specific temperature rise rate is 120°C to 150°C. Must meet: ; Curing time The following formula should be satisfied: ; in: is the carbon oil coating thickness, is the curing rate coefficient, It is the lowest solidification temperature of carbon oil (about 100°C).

[0026] As a preferred technical solution of the present invention, the transparent protective coating is completed by the following steps: the protective coating is a UV-curable transparent coating, which is evenly applied by spraying, and the coating thickness is The UV curing exposure energy is controlled at 300 to 500 mJ / cm.

[0027] As a preferred technical solution of the present invention, the distance between the anti-seepage barrier structure and the carbon oil coating area The following conditions must be met: ; To ensure that the carbon oil coating does not spread outside the barrier structure.

[0028] As a preferred technical solution of the present invention, the microscopic inspection accuracy of the circuit board is controlled within the following range: Accuracy error of carbon oil coating area

[0029] The crack width of the anti-seepage barrier structure shall not exceed 0.02 mm, and the crack length shall not exceed 0.1 mm.

[0030] As a preferred technical solution of the present invention, the following conditions are used to test the electrical performance of the circuit board: test voltage 3 to 12V; resistance value The following formula must be satisfied: ; If it is lower than this value, it is judged as unqualified.

[0031] As a preferred technical solution of the present invention, this method is suitable for high-density circuit boards, and the minimum spacing of the carbon oil coating area and width of the impermeable barrier structure The following conditions should be met: ; in mm, if mm, a high-precision screen printing process should be used to ensure that the carbon oil coating does not spread.

[0032] Compared with the prior art, the present invention has the following beneficial effects: By introducing a high-precision anti-seepage barrier structure and optimizing the coating process, this technical solution effectively solves the problem of short circuits caused by carbon oil leakage. The anti-seepage barrier layer adopts screen printing and UV curing technology to ensure the width and thickness of the barrier layer, and has excellent adhesion and durability. At the same time, the viscosity of the carbon oil and the coating parameters are adjusted to significantly improve the boundary clarity and thickness uniformity of the coating layer. This solution is suitable for high-density circuit boards and complex circuit designs, ensuring the electrical reliability of the circuit boards during long-term use.

[0033] The present invention adopts a segmented temperature-controlled curing process. By controlling the temperature rise rate and precise curing time, the problem of excessive fluidity of carbon oil in the early stage of high-temperature curing is avoided, while taking into account the thermal stress control requirements of high-density circuits and flexible circuits. Compared with the traditional constant temperature curing process, this solution significantly shortens the curing time, improves production efficiency, avoids substrate warping or coating cracking, and further improves the consistency and stability of the product.

[0034] The present invention combines microscopic detection with multi-dimensional electrical performance testing, which supplements the shortcomings of single resistance testing in traditional processes. During the production process, the boundary integrity, thickness uniformity and crack hazards of the carbon oil coating area are systematically checked, and the quality of the coating layer is comprehensively monitored from micro to macro. The multi-dimensional detection method ensures the overall performance of the circuit board, significantly reduces the defective rate in mass production, and provides a solid guarantee for high-reliability application scenarios (such as 5G communication equipment and flexible electronic products). DETAILED DESCRIPTION

[0035] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0036] The specific implementation of the present invention is described in detail below in conjunction with multiple embodiments.

[0037] The present invention provides a circuit board printing method for preventing carbon oil from seeping in and causing short circuits. The following describes the embodiments of the present invention in detail to facilitate better understanding and application of the present invention.

[0038] Embodiment 1: FR4 standard thickness circuit board; S1: Cleaning treatment; Substrate type: FR4 (thickness 1.6mm), material constant .

[0039] Calculation formula: Drying time calculate: ; in , .

[0040] Substituting the data into the result:

[0041] S2: formation of impermeable barrier structure; Parameter: Width ; .

[0042] Calculation formula: Width satisfies: ; in , .

[0043] Calculated: ; S3: carbon oil coating; Parameter: coating thickness ; Screen mesh number ; Opening rate .

[0044] Calculation formula: Coating thickness:

[0045] Substituting the data into the result: ; S4: Dynamic temperature controlled curing; Curing temperature: 130°C; Time calculation formula: ; Substituting the data into the result: ; S5: transparent protective coating; Parameter: coating thickness ; UV exposure energy .

[0046] Step S6: detection and testing; Electrical test voltage: 5V, resistance value: ; Embodiment 2: High-density FR4 thin circuit board; S1: Cleaning treatment; Substrate type: FR4 high-density thin board (thickness 0.8mm), material constant .

[0047] Calculation formula: Drying time: ; Substituting in: ; S2: Formation of impermeable barrier structure, barrier width , barrier thickness .

[0048] S3: Carbon oil coating, coating thickness ,Wire mesh number ,spacing .

[0049] S4: Dynamic temperature control curing, curing temperature ,Time calculation: ; S5: transparent protective coating; Coating thickness ,UV exposure energy .

[0050] S6: Detection and testing Test voltage: 10V, measured resistance .

[0051] Embodiment 3: Flexible FPC circuit board; S1: Cleaning treatment; Substrate type: FPC standard board (thickness 0.2mm), material constant .

[0052] ; Calculation formula: Drying time: , substitute into: ; S2: Formation of impermeable barrier structure, barrier width , barrier thickness .

[0053] S3: Carbon oil coating, coating thickness ,Wire mesh number ,spacing .

[0054] Curing temperature ,Time calculation: ; S5: transparent protective coating; Coating thickness ,UV exposure energy .

[0055] S6: Detection and testing; Test voltage: 3V, measured resistance .

[0056]

[0057] It can be seen from the table data that the various embodiments mainly adjust the parameters of cleaning treatment, barrier layer design, carbon oil coating, dynamic curing and transparent protective coating according to the different substrate types and process requirements. The following is a detailed analysis: Substrate material constant Effect: Example 1 (FR4 standard thickness board): This indicates that the standard FR4 sheet has good thermal stability and the solvent evaporates slowly, so a higher drying temperature (90°C) and a longer drying time (6 minutes) are required. Example 2 (high-density FR4 sheet): The thermal conductivity of the thin plate is slightly lower, and the required drying time is shorter (4.17 minutes), but due to the small line spacing, the accuracy of the anti-seepage barrier structure needs to be improved. Example 3 (flexible FPC): It reflects that the heat dissipation and solvent volatilization of flexible FPC are faster, suitable for low-temperature drying (80°C) and the shortest drying time (3 minutes).

[0058] Anti-seepage barrier design: Barrier width and thickness are adjusted according to circuit board density and carbon oil diffusion characteristics: Example 1 Width , suitable for standard density circuit boards; Example 2 Width , more suitable for high-density circuit boards; Example 3 Width , to meet the large-area coating requirements of flexible circuit boards. The influence of carbon oil coating thickness The thickness of carbon oil directly affects the curing time and anti-seepage performance: Example 1 Thickness , suitable for larger barrier spacing; Example 2 thickness , the coating is thinner, suitable for high-density layout; Example 3 thickness , effectively avoiding cracks when the flexible board is bent.

[0059] Dynamic curing optimization: The curing time is determined by the carbon oil thickness, curing temperature and temperature rise rate: Example 1 has the longest curing time (1.67 minutes), which is suitable for thick coatings; Example 2 has the shortest time (0.86 minutes), reflecting the need for high-temperature rapid curing; The curing time of Example 3 is moderate (2 minutes), ensuring the thermal stability of the flexible material.

[0060] Electrical performance: The resistance value reflects the conductivity and printing accuracy of carbon oil: Example 1 Resistance Value , meet the requirements of ordinary circuit boards; Example 2 Resistance Value , better performance for high-density circuits; Example 3 Resistance Value ,suitable for low power design of flexible circuits.

[0061] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in the field. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for printing a circuit board to prevent carbon oil from seeping and short circuiting, comprising the following steps: S1: Clean the PCB substrate; S2: After the PCB board is cleaned, an impermeable barrier structure is formed at the boundary of the carbon oil coating area; S3: Apply carbon oil to a designated area on the PCB board with the anti-seepage barrier structure obtained in S2 using a screen printing process; S4: curing the PCB board obtained in S3 through a segmented dynamic temperature control curing process; S5: Coating a transparent protective coating on the PCB board that has been cured in S4, and then curing it to obtain a completed circuit board; S6: Perform microscopic inspection and short circuit electrical testing on the completed circuit board.

2. A circuit board printing method for preventing carbon oil from seeping and short circuiting according to claim 1, characterized in that: The S1PCB substrate cleaning process is completed by the following steps: Use isopropyl alcohol solvent combined with ultrasonic cleaning, the solvent concentration is greater than 95%, and the cleaning time is 2-3 minutes; After cleaning, rinse with deionized water and control the conductivity to less than 5μS / cm; After rinsing, the product is dried. The drying temperature is controlled between 80℃ and 100℃. The drying time meets the following empirical formula: in: is the substrate material constant, is the drying temperature, It is the lowest temperature at which the solvent evaporates, and the lowest temperature is 40°C.

3. A circuit board printing method for preventing carbon oil seepage and short circuit according to claim 1, characterized in that: The anti-seepage barrier structure in S2 is formed by screen printing solder mask ink, and its width and height The following conditions are met: width Larger than the critical radius of carbon oil diffusion , that is: where: , is the surface tension of carbon oil, is the viscosity of carbon oil; high Should be at least the thickness of the carbon oil coating 1.2 times, that is:

4. A circuit board printing method for preventing carbon oil seepage and short circuit according to claim 1, characterized in that: The process parameters of the S3 using screen printing to apply carbon oil to a specified area include: The mesh number of the wire mesh is 300 to 400 mesh, and the opening rate of the wire mesh is Controlled between 0.6 and 0.8; Carbon oil coating thickness Calculated by the following formula: in: To design the coating thickness, is the mesh density of the wire mesh, is the opening rate of the wire mesh.

5. A circuit board printing method for preventing carbon oil seepage and short circuit according to claim 1, characterized in that: After the S4 carbon oil coating is completed, the carbon oil coating is stabilized by a dynamic temperature control curing process. and time Meet the following conditions: Curing temperature The specific temperature rise rate is 120°C to 150°C. Must meet: Curing time The following formula should be satisfied: in: is the carbon oil coating thickness, is the curing rate coefficient, It is the lowest solidification temperature of carbon oil (about 100°C).

6. A circuit board printing method for preventing carbon oil seepage and short circuit according to claim 1, characterized in that: The S5 is coated with a clear protective coating and then cured through the following steps: The protective coating is UV-curable transparent paint, which is evenly applied by spraying. The coating thickness is 10-15 microns; The UV curing exposure energy is controlled between 300 and 500 mJ / cm.

7. A circuit board printing method for preventing carbon oil seepage and short circuit according to claim 3, characterized in that: The distance between the anti-seepage barrier structure and the carbon oil coating area The following conditions must be met: To ensure that the carbon oil coating does not spread outside the barrier structure.

8. A circuit board printing method for preventing carbon oil seepage and short circuit as claimed in claim 1, characterized in that: The S6 controls the microscopic inspection accuracy of the circuit board within the following range: Accuracy error of carbon oil coating area The crack width of the anti-seepage barrier structure shall not exceed 0.02 mm, and the crack length shall not exceed 0.1 mm.

9. A circuit board printing method for preventing carbon oil seepage and short circuit according to claim 1, characterized in that: The electrical performance test of the S6 circuit board adopts the following conditions: Test voltage 3 to 12V; Resistance Value The following formula must be satisfied: If it is lower than this value, it is judged as unqualified.

10. A circuit board printing method for preventing carbon oil from seeping and short circuiting according to claim 1, characterized in that: The method is suitable for high-density circuit boards, and the minimum spacing of the carbon oil coating area and width of the impermeable barrier structure The following conditions should be met: in mm.

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