Preparation method of buried resistor printed circuit and printed circuit board

Abstract

The invention discloses a preparation method of a buried resistor printed circuit and a printed circuit board, and the method comprises the steps: determining the length of a resistor body corresponding to a buried resistor according to the resistance value of the buried resistor to be formed and the preset sheet resistance of resistor paste, and preparing a disconnection part on a target copper foil circuit of a target PCB according to the length of the resistor body and the preset buried resistor shape, wherein the target copper foil circuit is provided with connecting parts at the two ends of the disconnected part; after pretreatment is carried out on each disconnection part and the corresponding connection part, resistance paste with a preset thickness is printed on the disconnection parts in a silk-screen mode through a preset silk-screen plate so as to form a first resistor body, and pretreatment comprises copper foil deoxidation, connection part circuit surface coarsening and disconnection part circuit surface washing and cleaning; and carrying out high-temperature curing on the first resistor body, and carrying out resistance trimming on the cured and molded second resistor body by using a laser resistance trimming instrument so as to mold a buried resistor on the target copper foil circuit, thereby obtaining a buried resistor printed circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of PCB printed circuit board processing, and particularly to a method for preparing a buried resistor printed circuit and a printed circuit board. Background Art

[0002] In the related art, the requirements for the volume of electronic devices are getting higher and higher. In the PCB printed circuit board, higher integration needs to be achieved within a limited space to meet the requirements of product multi-functions. For the electronic devices in the related art, with the reduction of the device size, the PCB printed circuit is faced with challenges such as small space, dense lines and many functions. However, when the prior art is used to process the PCB printed circuit board for high-density wiring and multi-function integration, the following technical bottlenecks are faced: First, the discrete resistors need to occupy independent pad areas, resulting in a reduction of the wiring channels, and it is difficult to meet the wiring requirements in the advanced packaging with a PCB space utilization rate exceeding 85%. Second, the pin welding structure of the surface-mounted resistors causes the generation of parasitic inductance and equivalent series resistance, which is prone to signal crosstalk.

[0003] Currently, for the problems of few wiring channels and easy signal crosstalk existing in the PCB printed circuit board for high-density wiring and multi-function integration in the related art, no effective solution has been proposed yet. Summary of the Invention

[0004] The embodiments of the present application provide a method for preparing a buried resistor printed circuit and a printed circuit board, so as to at least solve the problems of few wiring channels and easy signal crosstalk existing in the PCB printed circuit board for high-density wiring and multi-function integration in the related art.

[0005] In a first aspect, the embodiments of the present application provide a method for preparing a buried resistor printed circuit, including: determining the length of the resistor body corresponding to the buried resistor according to the resistance value of the to-be-formed buried resistor and the sheet resistance of the preset resistor paste, and preparing a disconnection part on the target copper foil circuit of the target PCB board according to the length of the resistor body and the preset shape of the buried resistor, wherein connection parts are provided at both ends of the target copper foil circuit where the disconnection part is located; after preprocessing each of the disconnection parts and the corresponding connection parts, printing the resistor paste with a preset thickness on the disconnection part through a preset screen printing stencil to form a first resistor body, wherein the preprocessing includes copper foil deoxidation, roughening of the surface of the connection part circuit, and water washing and cleaning of the surface of the disconnection part circuit; performing high-temperature curing on the first resistor body, and trimming the cured and formed second resistor body by using a laser trimming instrument to form the buried resistor on the target copper foil circuit, so as to obtain the buried resistor printed circuit.

[0006] Second aspect, an embodiment of the present application further provides a printed circuit board for a temperature sensor, including a circuit substrate, on which a plurality of copper foil lines are arranged, and at least one of the plurality of copper foil lines is a buried resistor printed line, and the buried resistor printed line is prepared by the preparation method of the buried resistor printed line described in the first aspect.

[0007] Compared with the related art, the preparation method of the buried resistor printed line and the printed circuit board provided by the embodiment of the present application determine the resistance body length corresponding to the buried resistor according to the resistance value of the to-be-formed buried resistor and the sheet resistance of the preset resistor paste, and prepare a disconnection part on the target copper foil line of the target PCB board according to the resistance body length and the preset shape of the buried resistor, wherein connection parts are arranged at both ends of the target copper foil line where the disconnection part is located; after pre-treating each of the disconnection parts and the corresponding connection parts, through a preset screen printing stencil, screen-print the resistor paste with a preset thickness on the disconnection parts to form a first resistor body, wherein the pre-treatment includes copper foil deoxidation, roughening of the surface of the connection part line, and water washing and cleaning of the surface of the disconnection part line; perform high-temperature curing on the first resistor body, and perform resistor trimming on the cured and formed second resistor body by using a laser resistor trimming instrument to form the buried resistor on the target copper foil line, so as to obtain the buried resistor printed line. By adopting steps such as accurately calculating the resistance body length, making disconnection parts on the copper foil line, performing surface pre-treatment, screen-printing resistor paste, high-temperature curing, and laser resistor trimming, directly integrating the resistor element into the copper foil line, it solves the problems of few wiring channels and easy signal crosstalk in the PCB printed circuit board with high-density wiring and multi-functional integration in the related art, eliminates the signal routing vias required for discrete resistors to improve the signal quality; there is no need for solder joints, improves the reliability of the finished board and shortens the time cycle of PCB assembly, and improves the line impedance matching, shortens the signal path, reduces the series inductance, and reduces electromagnetic interference, crosstalk, and noise.

[0008] Details of one or more embodiments of the present application are set forth in the following drawings and description to make other features, objects, and advantages of the present application more concise and understandable. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0010] Figure 1 is a flowchart of the preparation method of the embodiment of the present application. DETAILED DESCRIPTION

[0011] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0012] It should be noted that when a component is referred to as being "mounted on" another component, it can be directly mounted on the other component or there may also be an intermediate component. When a component is considered to be "disposed on" another component, it can be directly disposed on the other component or there may be an intermediate component at the same time. When a component is considered to be "fixed to" another component, it can be directly fixed to the other component or there may be an intermediate component at the same time.

[0013] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the description of the present invention in this specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "or / and" used herein includes any and all combinations of one or more of the related listed items.

[0014] This embodiment provides a method for preparing a buried resistor printed circuit. Figure 1 It is a flowchart of the method for preparing the buried resistor printed circuit according to the embodiment of the present application; as Figure 1 shown, the process includes the following steps: Step S101, determine the length of the resistor body corresponding to the buried resistor according to the resistance value of the to-be-formed buried resistor and the sheet resistance of the preset resistor paste, and prepare a disconnection part on the target copper foil circuit of the target PCB board according to the length of the resistor body and the preset shape of the buried resistor, wherein connection parts are provided at both ends of the target copper foil circuit where the disconnection part is located.

[0015] In this embodiment, the buried resistor refers to a resistor element directly integrated on the PCB copper foil circuit, and specifically can be realized by the method of resistor paste printing and curing. The buried resistor, as a part of the copper foil circuit, also meets the requirement of resistance control for the copper foil circuit; in this embodiment, the resistor paste refers to a conductive material with a preset resistivity, and different resistance value resistor bodies can be formed according to different matching silver pastes and base carbon pastes as required.

[0016] In this embodiment, the required resistor body length is calculated based on the target resistance value of the to-be-formed buried resistor and the sheet resistance of the preset resistor paste, so as to ensure the design accuracy of the buried resistor through precise mathematical calculations. Then, a disconnection part with connection parts at both ends is fabricated on the copper foil circuit of the target PCB board, providing a position reference for printing the resistor paste into a resistor body. In this embodiment, the length and shape of the disconnection part are determined according to the resistor body length calculated previously and the preset buried resistor shape, thus ensuring the precise positioning and size control of the buried resistor.

[0017] Step S102, after pre-treating each disconnection part and the corresponding connection part, print a resistor paste with a preset thickness on the disconnection part through a preset silk screen printing stencil to form a first resistor body. Herein, the pre-treatment includes copper foil deoxidation, roughening of the surface of the connection part circuit, and water washing and cleaning of the surface of the disconnection part circuit.

[0018] In this embodiment, the silk screen printing stencil refers to a tool for precisely controlling the printing of the resistor paste and is a template tool for realizing the silk screen printing of the resistor body. In this embodiment, the silk screen printing stencil is provided with a resistor printing pattern matching the preset buried resistor shape (e.g., Z-shaped, L-shaped, strip-shaped, circular arc-shaped, serpentine-shaped). When printing through the silk screen printing stencil, a buried resistor with an expected shape can be formed.

[0019] In this embodiment, before printing the resistor paste, pre-treat the disconnection part and the connection part, including deoxidizing the copper foil corresponding to the connection part (e.g., removing oil stains), roughening the surface of the connection part circuit, and water washing and cleaning the surface of the disconnection part circuit. It can be understood that roughening the circuit can improve the adhesion between the resistor paste and the copper foil, ensuring the stability and reliability of the buried resistor.

[0020] In this embodiment, print a resistor paste with a preset thickness on the disconnection part through a preset silk screen printing stencil to form a preliminary resistor body. The design and use of the silk screen printing stencil are crucial for controlling the precise distribution of the resistor paste.

[0021] Step S103, perform high-temperature curing on the first resistor body, and use a laser resistor trimming instrument to trim the cured and formed second resistor body to form a buried resistor on the target copper foil circuit, obtaining a buried resistor printed circuit.

[0022] In this embodiment, perform high-temperature curing on the printed first resistor body to convert the resistor paste into a stable resistor material. Then, use a laser resistor trimming instrument to adjust the resistance value of the cured second resistor body, and adopt fine laser cutting and real-time resistance value measurement to ensure that the final buried resistor reaches the set resistance value accuracy. In this embodiment, after the trimming is completed, the corresponding copper foil circuit, that is, the target copper foil circuit, constitutes a buried resistor printed circuit that meets the set requirements.

[0023] Through the above steps S101 to S103, the length of the resistor body corresponding to the buried resistor is determined according to the resistance value of the buried resistor to be formed and the sheet resistance of the preset resistor paste, and a disconnection part is prepared on the target copper foil line of the target PCB board according to the resistor body length and the preset shape of the buried resistor. The target copper foil line is provided with connection parts at both ends of the disconnection part; after preprocessing each disconnection part and the corresponding connection part, a resistor paste with a preset thickness is screen-printed on the disconnection part through a preset screen printing stencil to form a first resistor body. The preprocessing includes copper foil deoxidation, roughening of the surface of the connection part line, and water washing and cleaning of the surface of the disconnection part line; the first resistor body is subjected to high-temperature curing, and the cured and formed second resistor body is trimmed using a laser resistor trimmer to form a buried resistor on the target copper foil line, obtaining a buried resistor printed circuit. By precisely calculating the resistor body length, making a disconnection part on the copper foil line, performing surface preprocessing, screen-printing the resistor paste, high-temperature curing, and laser resistor trimming and other steps, the resistor element is directly integrated into the copper foil line, solving the problems of few wiring channels and easy signal crosstalk in the PCB printed circuit board with high-density wiring and multi-functional integration in the related art, eliminating the signal routing vias required for discrete resistors to improve the signal quality; without solder joints, improving the reliability of the finished board and shortening the time cycle of PCB assembly, and improving the line impedance matching, shortening the signal path, reducing the series inductance, reducing electromagnetic interference, crosstalk, and noise.

[0024] It should be noted that the embodiment of the present application designs a method for directly fabricating a buried resistor on a PCB copper foil line. Through the coordinated work of multiple steps such as precisely calculating the resistor body length, making a disconnection part on the copper foil line, performing surface preprocessing, screen-printing the resistor paste, high-temperature curing, and laser resistor trimming, the precise fabrication and integration of the buried resistor are realized; by directly fabricating the resistor on the PCB copper foil line, the need for independent pads is eliminated, thereby increasing the space available for wiring. At the same time, due to the absence of the traditional pin welding structure, the parasitic inductance and equivalent series resistance are greatly reduced, and the risk of signal crosstalk is reduced; different sheet resistance resistor pastes are configured according to the resistance control requirements; in the resistor preprocessing process, operations such as copper foil deoxidation, roughening of the surface of the connection part line, and water washing and cleaning of the surface of the disconnection part line are adopted to improve the adhesion of the resistor paste to the copper foil, ensuring good interfacial bonding and ensuring the electrical performance and stability of the copper foil line, and improving the long-term reliability of the buried resistor; in the screen-printing process, a resistor paste with a preset thickness is printed on the disconnection part through a screen printing stencil, and then the cured resistor body is trimmed using a laser resistor trimmer to achieve high-precision resistance value control; the present application successfully integrates the resistor directly into the copper foil line of the PCB, effectively solving the problems of few wiring channels and signal crosstalk.

[0025] To perform pre - treatment on the disconnection part and the connection part, in some embodiments, pre - treatment is performed on each disconnection part and the corresponding connection part, including the following steps: Step 21: Use a sulfuric acid solution with a mass fraction of 5% to 8% to remove oil stains on the surface of the connection part.

[0026] In this embodiment, use a sulfuric acid solution with a mass fraction of 5% to 8% to remove oil stains on the surface of the connection part to clean the surface of the connection part and remove oil stains that may affect subsequent processing; in this embodiment, the concentration range of the sulfuric acid solution is optimized, which can meet the requirement of effectively removing oil stains without causing excessive corrosion to the copper foil.

[0027] Step 22: After washing the connection part with water, use a preset grinding brush to roughen the connection part until a connection surface with a preset roughness is formed on the surface of the connection part, where the particle size of the grinding brush is 800 to 1000 mesh.

[0028] In this embodiment, the particle size of the grinding brush is 800 to 1000 mesh. Preferably, a grinding brush with a particle size of 800 mesh can form a microscopic uneven structure on the copper foil surface, increase the surface area and provide mechanical locking points, so as to form an appropriate surface roughness, which will neither damage the copper foil excessively nor provide insufficient adhesion. For example, a grinding brush with 800 mesh can be used to perform grinding plate treatment on the connection part at a speed of 300 rpm until the surface shows a uniform matte state; in this embodiment, after washing and roughening the connection part with a grinding plate, the surface roughness of the connection part is increased to improve the bonding strength between the subsequent resistor paste and the connection part; in this embodiment, the water washing after degreasing with the sulfuric acid solution not only cleans the surface but also creates conditions for roughening with a grinding plate.

[0029] Step 23: Wash and dry the connection surface and the surface of the disconnection part to complete the pre - treatment of the disconnection part and the connection part.

[0030] In this embodiment, wash and dry the connection surface and the surface of the disconnection part to clean the surface and remove moisture, preparing for the subsequent printing of the resistor paste. Among them, water washing can remove debris generated during the roughening process with a grinding plate, and drying ensures that there is no moisture residue on the surface, which is beneficial to the uniform adhesion of the resistor paste; in this embodiment, the water washing and drying after roughening with a grinding plate further improve the surface quality and provide an ideal basis for the adhesion of the resistor paste.

[0031] Through the above-mentioned steps 21 to 23, the pre-treatment of the resistor is realized, effectively solving the technical problems of the pre-treatment of the disconnection part and the connection part; by removing oil stains, increasing the surface roughness, and finally cleaning and drying, ideal conditions are created for the subsequent printing and curing of the resistor paste; the pre-treatment method of this embodiment not only improves the bonding strength between the resistor paste and the copper foil, but also helps to ensure the consistency and reliability of the buried resistor.

[0032] It should be noted that the pre-treatment of the embodiment of the present application not only thoroughly cleans the surface, but also optimizes the surface characteristics, laying a foundation for the subsequent process. For example, for the connection part treated by this method, its bonding strength with the resistor paste greatly reduces the risk of the buried resistor falling off or having unstable performance.

[0033] In some of these embodiments, according to the resistance value of the to-be-formed buried resistor and the preset sheet resistance of the resistor paste, determining the resistor body length corresponding to the buried resistor includes the following steps: Step 31, determining the area parameter corresponding to the buried resistor according to the ratio of the resistance value of the buried resistor to the sheet resistance of the resistor paste.

[0034] Step 32, after obtaining the line width corresponding to the target copper foil circuit, determining the ratio of the area parameter to the line width as the resistor body length.

[0035] Through the above-mentioned steps 31 to 32, the goal of accurately determining the resistor body length of the buried resistor is achieved. By considering the resistance value requirements of the buried resistor, the characteristics of the resistor paste, and the actual width of the PCB circuit, the buried resistor that meets the control requirements can be accurately determined.

[0036] It should be noted that the area parameter can be determined according to the ratio of the resistance value of the buried resistor to the sheet resistance of the resistor paste, and can be achieved in various ways. For example, the formula A = R / Rs can be used for calculation, where A is the area parameter, R is the target resistance value of the buried resistor, and Rs is the sheet resistance of the resistor paste; the look-up table method can also be used, where a correspondence table between the resistance value and the area is established in advance, and the corresponding area parameter can be quickly found according to the specific resistance value and sheet resistance; after determining the area parameter, the line width of the target copper foil line can be obtained by measuring the width of the copper foil line on the PCB (printed circuit board), or the line width parameter can be directly extracted through the PCB design software. In this embodiment, the line width of the target copper foil line includes, but is not limited to, 0.1 mm, 0.2 mm, and 0.3 mm; then, the ratio of the area parameter to the line width is determined as the resistor body length. For example, if the area parameter is 1 mm² and the line width is 0.2 mm, the resistor body length is 1 mm² / 0.2 mm = 5 mm; it should be noted that in the embodiment of the present application, the area parameter represents the printing surface area of the buried resistor to be printed. At the same time, in actual production, the area parameter can also be represented by a graphic with a set aspect ratio. For example, if the corresponding graphic is a square with a size of 0.2 mm × 0.2 mm, when the area parameter is 1 mm², it can be represented by 25 (1 mm² / 0.04 mm²) square graphics.

[0037] It can be understood that the calculation of the area parameter depends on the target resistance value of the buried resistor and the characteristics of the resistor paste, and the determination of the resistor body length needs to be combined with the actual line width; in this embodiment, the length of the required buried resistor can be accurately calculated, thus solving the problem that it is difficult to accurately control the size of the buried resistor in the traditional method. In this way, not only the manufacturing accuracy of the buried resistor is improved, but also a reliable parameter basis is provided for the subsequent PCB manufacturing process, which helps to improve the performance and reliability of the entire PCB.

[0038] In some of these embodiments, according to the resistor body length and the preset shape of the buried resistor, a disconnection portion is prepared on the target copper foil line of the target PCB board, including the following steps: Step 41, taking the preset initial position corresponding to one of the two connection portions as the starting point of the buried resistor, and dividing a track segment corresponding to the resistor body length on the line track corresponding to the shape of the buried resistor. Among them, the starting point of the buried resistor is located on the target copper foil line, and the shape of the buried resistor includes one of the following: square, snake-shaped, L-shaped, Z-shaped, and circular.

[0039] In this embodiment, by determining the starting position of the buried resistor, a reference point is provided for subsequent fabrication, and the precise connection between the buried resistor and the existing circuit is ensured, improving the reliability of the circuit. In this embodiment, according to the pre-determined resistor body length and the shape of the buried resistor, a trajectory segment corresponding to the resistor body length is divided, and the specific position and shape of the buried resistor are planned on the PCB, so that the subsequently fabricated buried resistor can precisely match the design requirements. Among them, the shape of the buried resistor can be square, serpentine, L-shaped, Z-shaped or circular, and this diverse shape selection can adapt to different PCB layout requirements.

[0040] Step 42: Determine the other intersection point of the trajectory segment and the target copper foil circuit, and use the other intersection point as the end point of the buried resistor and the other of the two connection parts.

[0041] In this embodiment, by determining the other intersection point of the trajectory segment and the target copper foil circuit, the end position of the buried resistor is determined, the positioning of the buried resistor on the PCB is completed, and the precise connection between the buried resistor and the existing copper foil circuit can also be achieved, which helps to improve the overall performance and reliability of the circuit. It can be understood that the area between the two intersection points corresponding to the target copper foil circuit is not the shape of the buried resistor. For example, when the area between the two intersection points is a long strip space, but the preset shape of the buried resistor is serpentine, at this time, the buried resistor is located within this interval and is docked with the connection parts corresponding to the two intersection points.

[0042] Step 43: Remove the copper foil of the target copper foil circuit between the starting point and the end point of the buried resistor to obtain a disconnection part, where the trajectory segment is the printing area of the buried resistor.

[0043] In this embodiment, by removing the copper foil in a specific area, space is created for subsequent printing of the resistor paste.

[0044] Through the above steps 41 to 43, first determining the starting point of the buried resistor provides a clear reference for the entire fabrication process to improve the connection reliability between the buried resistor and the existing circuit. By dividing a trajectory segment matching the resistor body length on the circuit trajectory corresponding to the preset shape of the buried resistor, precise positioning and shape control of the buried resistor are achieved, improving the space utilization rate of the PCB. When determining the end point of the buried resistor, by finding the other intersection point of the trajectory segment and the target copper foil circuit, the spatial positioning of the buried resistor is completed to ensure the precise connection between the buried resistor and the surrounding circuits, which helps to improve the overall performance and reliability of the circuit. Finally, by removing the copper foil on the target copper foil circuit between the starting point and the end point of the buried resistor, a disconnection part is fabricated, creating the necessary space for subsequent printing of the resistor paste and also ensuring the electrical isolation between the buried resistor and the surrounding circuits.

[0045] It can be understood that the embodiments of the present application can flexibly select the shape and position of the buried resistor according to different PCB design requirements. For example, in areas with extremely limited space, a serpentine or Z-shaped buried resistor shape can be selected to achieve the required resistance value within the limited space; for areas where a large current needs to pass through, a square or circular buried resistor shape can be selected to provide a larger cross-sectional area.

[0046] In some of these embodiments, a resistor paste with a preset thickness is screen-printed on the disconnection part through a preset screen printing stencil, including the following steps: Step 51, obtain a screen printing stencil provided with a preset resistor printing pattern, wherein the resistor printing pattern is adapted to the trace segment, and the mesh size of the screen printing stencil is 200 to 250 meshes.

[0047] In this embodiment, a screen printing stencil with a preset mesh size (for example: 200 to 250 meshes) is used to control the printing accuracy of the resistor paste, so as to ensure both the printing accuracy and a sufficient paste passing amount. For example, if a finer stencil (such as above 300 meshes) is selected, although the accuracy may be improved, it may cause the paste to be difficult to pass through, affecting the printing effect; if a coarser stencil (such as below 150 meshes) is selected, although the paste passing amount increases, it may affect the printing fineness; in this embodiment, the resistor printing pattern is adapted to the trace segment to ensure that the printing pattern is consistent with the shape of the resistor body actually required. In some alternative embodiments, corresponding printing patterns can be designed according to different resistor shapes (for example: straight line type, serpentine type, L type) to improve the printing accuracy and efficiency.

[0048] Step 52, after placing the screen printing stencil above the disconnection part and making the disconnection part located within the resistor printing pattern, use the screen printing stencil to print a resistor paste with a preset thickness along the wiring path corresponding to the trace segment within the disconnection area corresponding to the disconnection part, so as to form a first resistor body, wherein the preset thickness is 18 μm to 25 μm.

[0049] In this embodiment, an existing optical alignment system is used to accurately position the screen printing stencil above the disconnection part of the PCB board, and then by adjusting the position, the disconnection part is completely located within the resistor printing pattern, and the error is controlled within the preset tolerance range; in this embodiment, precise positioning of the screen printing stencil and control of the printing thickness are adopted. Specifically, the disconnection part is placed within the resistor printing pattern to ensure accurate printing position; the thickness of the resistor paste is controlled within the range of 18 - 25 μm to achieve the required resistance characteristics; in this embodiment, during printing, the blade angle is set at 60° - 70° relative to the screen printing stencil, and the printing speed is controlled at 50 - 60 mm / s to ensure that the resistor paste uniformly passes through the stencil and forms a resistor layer with a consistent thickness.

[0050] Through the above steps 51 to 52, precise screen printing of the resist paste with a preset thickness is achieved on the disconnection part. By precisely controlling various parameters of the printing process, the consistency of the shape, position, and thickness of the buried resistor is ensured, thereby achieving high-quality printing of the buried resistor.

[0051] It can be understood that since the buried resistor is directly printed on the PCB, the number of solder joints is reduced, and the influence of parasitic inductance and equivalent series resistance is reduced.

[0052] In some of these embodiments, high-temperature curing of the first resistor body includes the following steps: using a tunnel oven to cure the first resistor body. During the curing operation, the temperature of the curing chamber of the tunnel oven is 200°C to 220°C, the working time is 30 min to 60 min, and the time when the temperature in the curing chamber is set to 220°C is 10 min to 20 min.

[0053] In this embodiment, a high-temperature environment of 200°C to 220°C is provided by the tunnel oven, and the curing process is completed within a working time of 30 min to 60 min, including a peak temperature treatment at 220°C for 10 min to 20 min. In this way, it can ensure that the resist paste is fully cured to form a stable resistor body structure.

[0054] In this embodiment, the tunnel oven provides a controllable high-temperature environment for the curing of the first resistor body; the temperature of the curing chamber is set in the range of 200°C to 220°C so that various components in the resist paste can be fully activated to form a stable resistor body structure; at the same time, a peak temperature treatment stage is adopted so that various components in the resist paste can reach the best reaction state, promoting the formation and stability of the resistor body structure. By precisely controlling the temperature parameters and working time of the tunnel oven, efficient and controllable curing of the first resistor body is achieved.

[0055] In some of these embodiments, laser trimming is performed using a laser trimmer, including the following steps: Step 71, cutting the second resistor body to be adjusted with a laser trimmer, and after cleaning and drying the cut second resistor body, detecting the resistance value difference of the buried resistor of the corresponding second resistor body.

[0056] In this embodiment, the laser trimmer includes, but is not limited to, a CO2 laser or a YAG laser. Among them, the CO2 laser is applicable to thicker resistor materials, while the YAG laser is more suitable for fine trimming work; in this embodiment, the laser power is set to 1W - 10W and adjusted based on the characteristics of the resistor material and the required accuracy.

[0057] In this embodiment, ultrasonic cleaners can be used for cleaning, and the cleaning solution can be deionized water or a special cleaning solvent. The cleaning time is set between 30 seconds and 2 minutes; in this embodiment, a hot air oven can be used for drying, the temperature is set between 60°C and 80°C, and the drying time is 5 to 10 minutes; in this embodiment, the resistance value detection includes but is not limited to digital multimeters and resistance testers.

[0058] Step 72: Determine whether the resistance value difference is not less than a preset resistance tolerance threshold. When it is determined that the resistance value difference is greater than the resistance tolerance threshold, repeat the steps of cutting the resistor body by a laser resistor trimmer, cleaning, drying, and detecting the resistance value difference until the resistance value difference is not less than the resistance tolerance threshold, where the resistance tolerance threshold is ±0.01.

[0059] Through the above steps 71 to 72, through precise laser cutting, repeated measurement and adjustment processes, and tolerance control, a high-precision resistor trimming effect is achieved, and through the loop process, it is ensured that each buried resistor can reach the required precision, improving the consistency and reliability of the buried resistors.

[0060] In some of these embodiments, the resistor paste is composed of the following parts by weight of silver paste and base carbon paste: Silver paste: 44.5 to 88 parts Base carbon paste: 12 to 55.5 parts Among them, the silver paste is composed of the following component materials: silver, molybdenum trisulfide, phenol, methanol, n-butanol, and formaldehyde, and the sheet resistance of the silver paste is not greater than 20 milliohms; The base carbon paste is composed of the following component materials: carbon powder, graphite powder, phenolic resin, diethylene glycol monoethyl ether acetate carbitol, benzyl alcohol, and butanol, and the sheet resistance of the base carbon paste is one of the following: 100Ω, 500Ω, 1000Ω, 2000Ω, 10KΩ, 100KΩ.

[0061] In this embodiment, the problems of the composition and performance of the resistor paste are solved. By adjusting the ratio of the silver paste and the base carbon paste and combining their respective component characteristics, precise control of the resistance value of the resistor paste can be achieved, while ensuring good conductivity and stability.

[0062] It should be noted that the silver paste, as the main conductive component, has a sheet resistance not greater than 20 milliohms, ensuring good conductivity. Among them, silver in the silver paste is the main conductive material, molybdenum trisulfide may be used to improve the conductive performance, and organic solvents such as phenol, methanol, n-butanol, and formaldehyde are used to adjust the fluidity and viscosity of the paste.

[0063] In this embodiment, the base carbon paste provides a variety of sheet resistance options, ranging from 100 Ω to 100 KΩ, to meet different resistance requirements. The carbon powder and graphite powder in the base carbon paste are the main resistance materials, and phenolic resin may be used as a binder. Organic solvents such as diethylene glycol monoethyl ether acetate, benzyl alcohol, and butanol are used to adjust the slurry properties.

[0064] In this embodiment, by adjusting the ratio of the silver paste and the base carbon paste, precise control of the resistance value of the resistance paste can be achieved. For example, when a sheet resistance paste of 8 ohms needs to be formulated, a silver paste with a sheet resistance ≤ 20 mΩ and a carbon paste with a sheet resistance of 100 ohms can be used in combination, and the mixing ratio is 92% silver paste and 8% carbon paste; when a sheet resistance paste of 555 ohms needs to be formulated, a silver paste with a sheet resistance ≤ 20 mΩ and a carbon paste with a sheet resistance of 1 KΩ can be used in combination, and the mixing ratio is 44.5% silver paste and 55.5% carbon paste; in this embodiment, a silver paste with a sheet resistance ≤ 20 mΩ and a carbon paste with a sheet resistance of 100 ohms can be selected for combination. For example: when a sheet resistance paste of 17 ohms needs to be formulated, 83% silver paste and 17% carbon paste can be used; when a sheet resistance paste of 28 ohms needs to be formulated, 72% silver paste and 28% carbon paste can be used.

[0065] In this embodiment, the combination of the silver paste and the base carbon paste enables the resistance paste to meet the preparation requirements of buried resistor printed circuits, improving the integration and performance of printed circuit boards; by precisely controlling the resistance value, higher integration can be achieved within a limited PCB space to meet the requirements of product multifunctionality; it can be understood that the resistance paste can be directly printed on the PCB without an additional pad area, thereby improving the space utilization rate of the PCB; at the same time, the resistance formed by direct printing reduces the generation of parasitic inductance and equivalent series resistance, helping to reduce the risk of signal crosstalk.

[0066] In some of these embodiments, after forming a buried resistor on the target copper foil circuit, the following steps are further implemented: Step 81: Obtain a solder mask screen printing stencil with a preset protection pattern, wherein the outer boundary of the protection pattern is spaced 0.45 mm to 0.5 mm from the outer boundary of the buried resistor, and the mesh size of the solder mask screen printing stencil is 350 to 400 meshes.

[0067] Step 82: After placing the solder mask screen printing stencil above the buried resistor and making the buried resistor located within the protection pattern, use the solder mask screen printing stencil to print a solder resist ink with a thickness of 10 μm to 15 μm within the protection pattern.

[0068] Step 83: Cure the printed solder resist ink in a preset manner to generate a resistor protection layer.

[0069] In this embodiment, a protection process is added after the buried resistor is printed to solve the problem of insufficient protection of the buried resistor. That is, through the protection screen printing stencil, by precisely controlling the position of the protection pattern, the mesh size of the stencil, and the thickness of the printed solder resist ink, a protective layer is formed on the surface of the buried resistor, and by curing the solder resist ink, the protective layer is firmly attached to improve its durability.

[0070] The following uses a specific embodiment to illustrate the preparation method of the resistor printed circuit of the embodiment of the present application as follows: This embodiment includes the following processes: resistor pretreatment - resistor paste printing - resistor paste curing - resistor testing - resistor trimming - printing solder resist ink - solder resist ink curing, which specifically includes the following steps: Step 1, set to make a 70Ω buried resistor, and the sheet resistance of the resistor paste used is 10Ω / mm 2 .

[0071] In this embodiment, according to the formula R = s * (L / W), where R is the target resistance value, s is the sheet resistance of the resistor paste, L is the length of the resistor body, and W is the line width, the required length of the resistor body can be calculated. For example: assuming the line width is 0.6mm, then the resistor body length L = (R * W) / s = (70Ω * 0.6mm) / 10Ω = 4.2mm.

[0072] Step 2, select a copper foil line with a width of 0.6mm on the target PCB board, make a disconnection part with a length of 4.2mm on it, and reserve 0.5mm at both ends of the disconnection part as the connection part.

[0073] Step 3, perform pretreatment on the disconnection part and the connection part.

[0074] Use a 5% sulfuric acid solution to remove the surface oil, and then use an 800 - mesh abrasive brush to roughen the connection part until the surface roughness reaches Ra 0.8μm. Finally, wash the entire area with deionized water and dry it.

[0075] Step 4, prepare a 200 - mesh screen printing stencil with an opening that matches the disconnection part, 4.2mm long and 0.6mm wide. Align the screen printing stencil with the disconnection part, and use a resistor paste with a conductivity of 10Ω / mm 2 for screen printing, and control the printing thickness to be 20μm.

[0076] Step 5, put the printed PCB board into a tunnel oven, set the curing chamber temperature to 210℃ to 220℃, and the total working time is 45 minutes. Among them, the working time at the peak temperature of 220℃ is 15 minutes.

[0077] Step 6: Trim the resistor body using a laser resistor trimmer.

[0078] Set the laser power to 2W and the scanning speed to 10 mm / s. Measure the resistance value after each cut until the resistance value reaches the range of 7 ± 0.07 Ω.

[0079] Step 7: Clean and dry the trimmed buried resistor.

[0080] Step 8: Using a protective silk screen stencil, print solder resist ink within the protective pattern. During printing, control the thickness of the ink to be 12.5 μm.

[0081] Step 9: Cure the printed solder resist ink.

[0082] In this embodiment, curing is performed using a tunnel oven. The temperature of the curing chamber is set to 150 °C, and the working time is 30 minutes.

[0083] The embodiment of the present application also provides a printed circuit board for a temperature sensor, including a circuit substrate. Multiple copper foil lines are arranged on the circuit substrate, and at least one of the multiple copper foil lines is a buried resistor printed line, and the buried resistor printed line is prepared by using the preparation method of the buried resistor printed line in the above embodiment.

[0084] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0085] Those of ordinary skill in the art of this technology should recognize that the above embodiments are only used to illustrate the present invention, rather than to limit the present invention. As long as appropriate changes and variations are made within the scope of the spirit of the present invention, they fall within the scope of protection required by the present invention.

Claims

1. A method for preparing a buried resistor printed circuit, characterized in that, Including: Determine the length of the resistor body corresponding to the buried resistor according to the resistance value of the to-be-formed buried resistor and the sheet resistance of the preset resistor paste, and prepare a disconnection part on the target copper foil circuit of the target PCB board according to the resistor body length and the preset shape of the buried resistor, wherein connection parts are provided at both ends of the target copper foil circuit where the disconnection part is located; After pre-treating each of the disconnection parts and the corresponding connection parts, screen-print the resistor paste with a preset thickness on the disconnection parts through a preset screen printing stencil to form a first resistor body, wherein the pre-treatment includes copper foil deoxidation, roughening the surface of the connection part circuit, and washing and cleaning the surface of the disconnection part circuit; Perform high-temperature curing on the first resistor body, and perform resistor trimming on the cured and formed second resistor body by using a laser resistor trimming instrument to form the buried resistor on the target copper foil circuit, thereby obtaining the buried resistor printed circuit.

2. The preparation method according to claim 1, characterized in that, Pre-treating each of the disconnection parts and the corresponding connection parts includes: Use a sulfuric acid solution with a mass fraction of 5% to 8% to remove oil stains on the surface of the connection part; After washing the connection part, use a preset grinding brush to roughen the connection part until a connection surface with a preset roughness is formed on the surface of the connection part, wherein the particle size of the grinding brush is 800 mesh to 1000 mesh; Wash and dry the connection surface and the surface of the disconnection part to complete the pre-treatment of the disconnection part and the connection part.

3. The preparation method according to claim 1, wherein Determine the length of the resistor body corresponding to the buried resistor according to the resistance value of the to-be-formed buried resistor and the sheet resistance of the preset resistor paste, including: Determine the area parameter corresponding to the buried resistor according to the ratio of the resistance value of the buried resistor to the sheet resistance of the resistor paste; After obtaining the line width corresponding to the target copper foil circuit, determine the ratio of the area parameter to the line width as the resistor body length.

4. The preparation method according to claim 3, wherein Prepare a disconnection part on the target copper foil circuit of the target PCB board according to the resistor body length and the preset shape of the buried resistor, including: Take a preset initial position corresponding to one of the two connection parts as the starting point of the buried resistor, and divide a track segment corresponding to the resistor body length on the circuit track corresponding to the shape of the buried resistor, wherein the starting point of the buried resistor is located on the target copper foil circuit, and the shape of the buried resistor includes one of the following: square, serpentine, L-shaped, Z-shaped, circular; Determine the other intersection point of the track segment and the target copper foil circuit, and take the other intersection point as the end point of the buried resistor and the other of the two connection parts; Remove the copper foil of the target copper foil circuit between the starting point of the buried resistor and the end point of the buried resistor to obtain the disconnection part, wherein the track segment is the printing area of the buried resistor.

5. The preparation method according to claim 4, characterized in that, Screen-print the resistor paste with a preset thickness on the disconnection parts through a preset screen printing stencil, including: Obtain the screen printing stencil provided with a preset resistor printing pattern, wherein the resistor printing pattern is adapted to the track segment, and the particle size of the screen printing stencil is 200 mesh to 250 mesh; After placing the silk screen printing stencil above the disconnection part and making the disconnection part located within the resist printing pattern, use the silk screen printing stencil to print the resist paste with a preset thickness along the routing path corresponding to the track segment within the disconnection area corresponding to the disconnection part, so as to form the first resistor body, wherein the preset thickness is 18 μm to 25 μm.

6. The preparation method according to claim 1, characterized in that, Perform high-temperature curing on the first resistor body, including: curing the first resistor body using a tunnel oven, wherein during the curing operation, the temperature of the curing chamber of the tunnel oven is 200 °C to 220 °C, the working time is 30 min to 60 min, and the time when the temperature in the curing chamber is set to 220 °C is 10 min to 20 min.

7. The preparation method according to claim 1, wherein, Perform resistor trimming using a laser resistor trimmer, including: Cut the second resistor body to be adjusted using a laser resistor trimmer, and after cleaning and drying the cut second resistor body, detect the resistance value difference of the buried resistor of the corresponding second resistor body; Judge whether the resistance value difference is not less than a preset resistor tolerance threshold, and in the case where it is judged that the resistance value difference is greater than the resistor tolerance threshold, repeatedly execute the steps of cutting, cleaning, drying the resistor body and detecting the resistance value difference using a laser resistor trimmer until the resistance value difference is not less than the resistor tolerance threshold, wherein the resistor tolerance threshold is ±0.

01.

8. The preparation method according to claim 1, characterized in that, The resist paste is composed of the following parts by weight of silver paste and base carbon paste: Silver paste: 44.5 to 88 parts Base carbon paste: 12 to 55.5 parts Wherein, the silver paste is composed of the following component materials: silver, molybdenum trisulfide, phenol, methanol, n-butanol and formaldehyde, and the sheet resistance of the silver paste is not greater than 20 milliohms; The base carbon paste is composed of the following component materials: carbon powder, graphite powder, phenolic resin, diethylene glycol monoethyl ether acetate carbitol, benzyl alcohol and butanol, and the sheet resistance of the base carbon paste is one of the following: 100 Ω, 500 Ω, 1000 Ω, 2000 Ω, 10 KΩ, 100 KΩ.

9. The preparation method according to claim 1, wherein, After forming the buried resistor on the target copper foil circuit, the preparation method further includes: Obtain a protective silk screen printing stencil provided with a preset protective pattern, wherein the outer boundary of the protective pattern is spaced 0.45 mm to 0.5 mm from the outer boundary of the buried resistor, and the mesh size of the protective silk screen printing stencil is 350 mesh to 400 mesh; After placing the protective silk screen printing stencil above the buried resistor and making the buried resistor located within the protective pattern, use the protective silk screen printing stencil to print a solder resist ink with a thickness of 10 μm to 15 μm within the protective pattern; Cure the printed solder resist ink in a preset manner to generate a resistor protection layer.

10. A printed circuit board for a temperature sensor, characterized in that, Including a circuit board, on which a plurality of copper foil circuits are arranged, and at least one of the plurality of copper foil circuits is a buried resistor printing circuit, and the buried resistor printing circuit is prepared by the preparation method of the buried resistor printing circuit according to any one of claims 1 to 9.

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