Printing method of lap joint type carbon film strip capable of prolonging service life

Abstract

The invention relates to a printing method of a lap joint type carbon film strip capable of prolonging the service life, which is characterized in that a carbon film is printed twice, and a low-mesh silk screen and soft scraping glue are adopted for printing when the carbon film is printed for the first time, so that the ink feeding amount between silver layers at the two ends is increased, and the height difference between the carbon film between the silver layers at the two ends and the carbon film on the silver layers is reduced or eliminated; printing a second carbon layer for the second time, adjusting the thickness of the second carbon layer to make the surface of the final carbon film smooth, and preventing the edge of the silver layer from forming steps on the surface of the carbon film, thereby eliminating the impact friction of the electric brush on the carbon film, preventing the carbon film from being worn in advance, and prolonging the service life of the carbon film.

Description

Technical Field

[0001] The invention belongs to the technical field of circuit board processing, and in particular relates to a printing method for overlapping carbon film strips capable of increasing service life. Background Art

[0002] The speed control switch circuit board of the power tool is usually printed with a resistance-adjusting carbon film, which is used with the switch brush to adjust the resistance in the connected circuit, thereby adjusting the output power of the power tool. In order to achieve the opening and closing of the switch and the adjustment of resistance by the same brush and the resistance-adjusting carbon film, it is necessary to print a silver layer substrate at both ends of the resistance-adjusting carbon film. This design results in the formation of steps on the surface of the carbon film layer at the junction of the silver layer substrate and the carbon film layer, such as Figure 1 As shown, when the brush slides on the surface of the carbon film layer, it will continuously impact and rub the carbon film at the step, causing the carbon film at the step to wear out prematurely, and then causing the wear area to continue to expand until the resistance accuracy of the carbon film drops to a reasonable range. Therefore, the carbon film of this structure currently has a technical problem of short service life. According to actual tests, the service life of this carbon film will be reduced by about 50% compared to the design life. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a printing method for overlapping carbon film strips that can increase the service life, thereby solving the technical problem that the traditional overlapping carbon film strips have steps that make the carbon film at the steps easily worn, thereby reducing the actual service life of the entire carbon film.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a printing method of overlapping carbon film strips capable of improving service life, comprising the following specific steps: a. Print the silver layers at both ends of the circuit board using screen printing technology. When printing the silver layer, use a hard scraper with a hardness of Shore A80-A85 to make the surface of the silver layer flat. The silver layer at one end is connected to the circuit on the circuit board to solidify the silver layer. b. Printing a first carbon layer on the silver layers at both ends and between the silver layers at both ends by screen printing technology, using a low-hardness squeegee with a hardness of Shore A55-A60, and using a screen with a lower mesh count than that used in step a for printing, so that the first carbon layer fully fills the area between the silver layers at both ends, and the first carbon layer completely covers the silver layers at both ends and fills the empty area between the silver layers at both ends, forming a first carbon layer with a uniform width and continuity, and the thickness of the first carbon layer is not less than 1.5 times the thickness of the silver layer, and solidifying the first carbon layer; c. Printing the second carbon layer on the surface of the first carbon layer by screen printing technology, using a squeegee with a hardness of Shore A70-A75, and a screen mesh number between the screen mesh numbers used in step a and step b.

[0005] As a preferred solution, when performing step b, the scraper is scraped obliquely along the diagonal direction of the silver layers at both ends, and the scraper forms an angle of 70°-80° with the axial direction of the first carbon layer.

[0006] As a preferred solution, the thickness of the second carbon layer is not less than twice the height difference between the highest point and the lowest point of the first carbon layer and is not less than one third of the thickness of the first carbon layer.

[0007] The beneficial effects of the present invention are as follows: the present invention prints the carbon film twice, and adopts a low-mesh screen and a soft scraper for printing when printing the carbon film for the first time, thereby increasing the amount of ink applied between the silver layers at both ends, reducing or eliminating the height difference between the carbon film between the silver layers at both ends and the carbon film on the silver layer, and then printing the second carbon layer for the second time, adjusting the thickness of the second carbon layer so that the surface of the final carbon film is smooth, avoiding the edge of the silver layer from forming a step on the surface of the carbon film, thereby eliminating the impact friction of the brush on the carbon film, avoiding premature wear of the carbon film, and extending the service life of the carbon film. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings, wherein: Figure 1 It is a schematic diagram of the structure of a conventional lapped carbon film; Figure 2 is a flow chart of the printing method shown in the present invention; Figure 3 is a schematic diagram of the state and movement direction of the scraper when performing step b; Figure 1~Figure 3 Middle: 1. Circuit board; 2. Silver layer; 3. First carbon layer; 4. Second carbon layer; 5. Glue scraping. DETAILED DESCRIPTION

[0009] The specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0010] like Figure 2 As shown, the printing method of the overlapping carbon film strips capable of increasing the service life of the present invention comprises the following specific steps: a. Printing the silver layers 2 at both ends of the circuit board 1 by screen printing technology, the silver layers 2 at both ends are separated from each other, and when printing the silver layer 2, a hard scraper with a hardness of Shore A80-A85 is used to make the surface of the silver layer 2 flat, and the silver layer 2 at one end is connected to the circuit on the circuit board 1 to solidify the silver layer; b. Printing the first carbon layer 3 on the silver layers 2 at both ends and between the silver layers 2 at both ends by screen printing technology, using a low-hardness squeegee with a hardness of Shore A55-A60, and using a screen with a lower mesh count than that used in step a for printing, so that the first carbon layer 3 fully fills the area between the silver layers 2 at both ends, and the first carbon layer 3 completely covers the silver layers 2 at both ends and fills the empty area between the silver layers 2 at both ends, forming a first carbon layer 3 with a uniform and continuous width, and the thickness of the first carbon layer 3 is not less than 1.5 times the thickness of the silver layer 2, and solidifying the first carbon layer 3; c. Print the second carbon layer 4 on the surface of the first carbon layer 3 using screen printing technology, using a squeegee with a hardness of Shore A70-A75, and a screen mesh number between the screen mesh numbers used in step a and step b.

[0011] As a further improvement of the above technical solution, in this embodiment, when performing step b, the scraper 5 is scraped obliquely along the diagonal direction of the silver layers 2 at both ends, and the angle α formed by the scraper 5 and the axial direction of the first carbon layer is 70°-80°. In this way, the scraper can gradually reach the end of the silver layer 2, so that the end of the silver layer 2 can be filled with more ink, thereby reducing the height difference formed on the surface of the first carbon layer 3 at the end of the silver layer 2, laying a foundation for improving the surface flatness of the second carbon layer 4.

[0012] The thickness of the second carbon layer 4 is not less than twice the height difference between the highest point and the lowest point of the first carbon layer 3 and not less than one third of the thickness of the first carbon layer 3. In this way, the surface of the second carbon layer 4 can be flat.

[0013] The working principle of the present invention is as follows: the present invention prints the carbon film twice, and adopts a low-mesh screen and soft scraper glue for printing when printing the first carbon layer 3 for the first time, thereby increasing the amount of ink applied between the silver layers 2 at both ends, reducing or eliminating the height difference between the carbon film between the silver layers 2 at both ends and the carbon film on the silver layer 2, and then printing the second carbon layer 4 for the second time, adjusting the thickness of the second carbon layer 4 so that the final carbon film surface is smooth, avoiding the edge of the silver layer 2 from forming a step on the carbon film surface, thereby eliminating the impact friction of the brush on the carbon film, avoiding premature wear of the carbon film, and extending the service life of the carbon film.

[0014] The wear-resistant test shows that the carbon film printed by the method of the present invention can completely exceed the designed service life by 0~33%. The above embodiments are only illustrative of the principles and effects of the invention, as well as some embodiments of its application, and are not intended to limit the invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the invention, and all of these belong to the protection scope of the invention.

Claims

1. A method for printing overlapping carbon film strips capable of increasing service life, characterized in that: The specific steps include: a. Print the silver layers at both ends of the circuit board using screen printing technology. When printing the silver layer, use a hard scraper with a hardness of Shore A80-A85 to make the surface of the silver layer flat. The silver layer at one end is connected to the circuit on the circuit board to solidify the silver layer. b. Printing a first carbon layer on the silver layers at both ends and between the silver layers at both ends by screen printing technology, using a low-hardness squeegee with a hardness of Shore A55-A60, and using a screen with a lower mesh count than that used in step a for printing, so that the first carbon layer fully fills the area between the silver layers at both ends, and the first carbon layer completely covers the silver layers at both ends and fills the empty area between the silver layers at both ends, forming a first carbon layer with a uniform width and continuity, and the thickness of the first carbon layer is not less than 1.5 times the thickness of the silver layer, and solidifying the first carbon layer; c. Printing the second carbon layer on the surface of the first carbon layer by screen printing technology, using a squeegee with a hardness of Shore A70-A75, and a screen mesh number between the screen mesh numbers used in step a and step b.

2. The method for printing overlapping carbon film strips capable of increasing the service life according to claim 1, characterized in that: When performing step b, the scraper is scraped obliquely along the diagonal direction of the silver layers at both ends, and the scraper forms an angle of 70°-80° with the axial direction of the first carbon layer.

3. The method for printing overlapping carbon film strips capable of increasing service life according to claim 1, characterized in that: The thickness of the second carbon layer is not less than twice the height difference between the highest point and the lowest point of the first carbon layer and is not less than one third of the thickness of the first carbon layer.

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