A rigid-flexible circuit board structure and a manufacturing process thereof

Abstract

The application discloses a kind of hard-soft combination circuit board structure, it includes: hard circuit board and soft circuit board;The hard circuit board has several pads;The soft circuit board has conductive circuit, insulating film and several welding tabs.The both sides of the conductive circuit are covered and connected with the insulating film;The welding tab is electrically connected with the conductive circuit;And, the welding tab extends the overlapping range of the insulating film and the conductive circuit outside.Said welding tab is electrically connected with each pad respectively.In addition, the application also discloses a preparation process of the above structure, which comprises: first, processing welding tabs on the soft circuit board;Then print bonding glue on the main connection area and the auxiliary connection area;Then, soft circuit board and hard circuit board are connected by pressing;Finally, the welding tab is connected with each pad respectively.The application solves the technical problems of existing technology, such as the insulating film is easy to be damaged and the production efficiency is low.

Description

Technical Field

[0001] This invention relates to the technical field of circuit boards, and in particular to a rigid-flex circuit board structure and its manufacturing process. Background Technology

[0002] With the increasing demand for terminal application products characterized by lightness, thinness, shortness, and smallness, such as 5G mobile phones, smart wearable devices, and medical devices, and the technological development of flexible printed circuit boards (FPCs) and rigid printed circuit boards (PCBs), a new type of rigid-flex circuit board has emerged. This refers to a new type of PCB (Flexible Printed Circuit). The rigid-flex PCB refers to a circuit board formed by combining a flexible circuit board and a rigid circuit board through processes such as lamination, according to relevant technological requirements, thereby creating a circuit board with both FPC and PCB characteristics. That is, the rigid-flex PCB possesses both FPC and PCB characteristics; therefore, it can be applied to products with special requirements. The rigid-flex PCB has both flexible and rigid areas; therefore, it greatly helps to save internal space, reduce the volume of the finished product, and improve product performance. Based on this, Chinese Patent CN214315750U discloses a rigid-flex PCB, which includes: a rigid board, a flexible board, and a fixing mechanism. The rigid board and the flexible board are soldered together; the fixing mechanism is mounted on the rigid board and is used to fix the flexible board.

[0003] However, the aforementioned rigid-flex circuit boards also suffer from technical problems such as easy damage to the insulating film of the flexible circuit board and low production efficiency. For details, please refer to [link to relevant documentation]. Figures 1 to 3 ;exist Figures 1 to 3 The image illustrates the connection structure between rigid and flexible circuit boards in the prior art. For example... Figures 1 to 3 As shown, the rigid circuit board and the flexible circuit board are arranged opposite each other. The rigid circuit board has several conductive circuit areas, and the flexible circuit board has several soldering areas corresponding to the conductive circuit areas. The conductive circuit areas and the soldering areas are connected by molten solder, thereby connecting the rigid circuit board and the flexible circuit board. Due to the significant thickness difference between the rigid circuit board and the flexible circuit board, solder much thicker than the flexible circuit board must be piled up on the soldering areas of the flexible circuit board. This results in the soldering areas of the flexible circuit board being subjected to prolonged high-temperature heating to ensure that the solder covers both the soldering areas and the conductive circuit areas. Prolonged high-temperature heating can burn off the insulating film covering the surface of the flexible circuit board, leading to product defects and scrap. Furthermore, the processing time required for the soldering process also affects the production efficiency, making it unsuitable for large-scale production. Summary of the Invention

[0004] Therefore, it is necessary to provide a rigid-flex circuit board structure and its manufacturing process to address the technical problems of easy damage to the insulating film and low production efficiency in existing rigid-flex circuit boards.

[0005] A rigid-flex circuit board structure includes a rigid circuit board and a flexible circuit board, wherein the rigid circuit board and the flexible circuit board are disposed opposite to each other. The rigid circuit board has a plurality of pads; the flexible circuit board has conductive lines, an insulating film, and a plurality of solder tabs. The insulating film covers and connects to both sides of the conductive lines; the solder tabs are electrically connected to the conductive lines; and the solder tabs extend beyond the overlap area between the insulating film and the conductive lines. Each solder tab is electrically connected to each pad.

[0006] Furthermore, the flexible circuit board has a main connection area and an auxiliary connection area.

[0007] Furthermore, the main connection area is located in the middle of the flexible circuit board.

[0008] Furthermore, the auxiliary connection area is disposed around each of the welding tabs.

[0009] Furthermore, the welding tab is provided with a solder joint; the solder joint is located in the overlapping area of ​​the welding tab and the solder pad.

[0010] Furthermore, a process for fabricating the above-mentioned rigid-flex circuit board structure includes the following steps: S1: The welding tabs are fabricated on the flexible circuit board; S2: Print adhesive on the main connection area and the auxiliary connection area provided on the flexible circuit board; S3: Press and connect the flexible circuit board and the rigid circuit board together. S4: Weld each of the aforementioned welding tabs to each of the aforementioned pads.

[0011] Specifically, in step S1, the flexible circuit board is processed using a die-cutting process to obtain the welding tabs.

[0012] Specifically, in step S4, the welding tabs are connected to the welding pads using laser welding or ultrasonic welding processes.

[0013] In summary, the present invention provides a rigid-flex circuit board structure in which a plurality of solder tabs, not covered by the insulating film, are provided on the flexible circuit board, and the solder tabs are electrically connected to the conductive lines; while a plurality of pads are provided on the rigid circuit board corresponding to each solder tab; the solder tabs and the pads are connected by laser welding or ultrasonic welding. Because the solder tabs have a flexible structure and extend beyond the insulating film, they can conform to the surface of the pads for welding; that is, the solder tabs and the pads are located on the same plane. Therefore, compared with the prior art, the welding process between the solder tabs and the pads has advantages such as shorter soldering time, lower heat generation in the welding area, and faster production cycle, thus solving the technical problems of easy damage to the insulating film and low production efficiency in the prior art of rigid-flex circuit boards. Furthermore, this invention also discloses a manufacturing process for a rigid-flex PCB. First, the flexible PCB is die-cut to obtain the solder tabs without the insulating film covering both sides. Then, adhesive is uniformly printed onto the main connection area and auxiliary connection area of ​​the flexible PCB. Next, the rigid PCB and the flexible PCB are pressed together. Finally, laser welding or ultrasonic welding is used to connect the solder tabs to the pads. Therefore, this rigid-flex PCB manufacturing process avoids the technical defects of existing technologies, such as excessive molten solder buildup in the soldering area affecting connection quality. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of a rigid-flex circuit board using existing technology. Figure 2 This is a schematic diagram of the structure of a conventional rigid-software integrated circuit board from another direction. Figure 3 This is a schematic diagram of the structure of a rigid-flex circuit board using existing technology. Figure 4 This is a schematic diagram of a rigid-flex circuit board structure according to the present invention; Figure 5 This is a schematic diagram of the rigid-flex PCB structure of the present invention from another direction; Figure 6 This is a schematic diagram of a partial structure of a rigid-flex circuit board structure according to the present invention; Figure 7 This is a flowchart of a rigid-flex PCB fabrication process according to the present invention; Figure 8 This is a schematic diagram of an embodiment of step S1 in the fabrication process of a rigid-flex PCB according to the present invention. Figure 9This is a schematic diagram of an embodiment of step S2 in the fabrication process of a rigid-flex PCB according to the present invention. Figure 10 This is a schematic diagram of an embodiment of step S3 in the fabrication process of a rigid-flex PCB according to the present invention. Figure 11 This is a schematic diagram of an embodiment of step S4 in the fabrication process of a rigid-flex PCB according to the present invention.

[0015] a- Rigid circuit board, b- Conductive circuit area, c- Flexible circuit board, d- Soldering area, e- Soldering area. Detailed Implementation

[0016] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0017] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0018] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0019] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0020] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0021] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0022] Please refer to the following: Figures 4 to 6 The present invention discloses a rigid-flex circuit board structure comprising: a rigid circuit board 1 and a flexible circuit board 2; the rigid circuit board 1 and the flexible circuit board 2 are disposed opposite to each other. The rigid circuit board 1 has a plurality of pads 101; the flexible circuit board 2 has conductive lines 201, an insulating film 202, and a plurality of solder tabs 203. The insulating film 202 covers and connects to both sides of the conductive lines 201; the solder tabs 203 are electrically connected to the conductive lines 201; and the solder tabs 203 extend beyond the overlap area between the insulating film 202 and the conductive lines 201. Each solder tab 203 is electrically connected to each pad 101.

[0023] Specifically, the rigid circuit board 1 may have a solder pad 101 at each of its four corners; while the flexible circuit board 2 may have a solder tab 203 near each of the solder pads 101, and each solder tab 203 is electrically connected to its corresponding solder pad 101. More specifically, the flexible circuit board 2 may be a common flexible circuit board, which mainly includes conductive lines 201 and an insulating film 202; the conductive lines 201 are covered by the insulating film 202 on both sides; the insulating film 202 can support and protect the conductive lines 201 located therein. Further, outside the area covered by the insulating film 202 covering the conductive lines 201, the solder tab 203 is provided; the solder pad 101 is also provided nearby; and the solder tab 203 is connected to both the conductive lines 201 and the solder pad 101. Since the solder tab 203 extends beyond the coverage of the insulating film 202 and can flexibly cover the pad 101, the solder tab 203 can be electrically connected to the pad 101 by a low-heat-affected process such as laser welding or ultrasonic welding. That is, the solder tab 203 and the welding surface of the rigid circuit board 1 are on the same plane, thereby reducing the soldering time, reducing the heat generated during the connection process, accelerating the production cycle, and reducing the damage to the insulating film 202 due to high heat.

[0024] Furthermore, the flexible circuit board 2 also has a main connection area 204 and an auxiliary connection area 205; the main connection area 204 is located in the middle of the flexible circuit board 2; the auxiliary connection areas 205 are located around each of the solder tabs 203. Specifically, to further enhance the connection stability between the flexible circuit board 2 and the rigid circuit board 1, the main connection area 204 can be provided in the middle of the flexible circuit board 2; and the main connection area 204 is connected to the rigid circuit board 1 by means of adhesive or double-sided tape. The main connection area 204 plays a major structural connection role in the connection between the flexible circuit board 2 and the rigid circuit board 1. In addition, an auxiliary connection area 205 can be provided near each of the solder tabs 203; the auxiliary connection area 205 can also be connected to the rigid circuit board 1 by means of adhesive or double-sided tape. The auxiliary connection area 205 strengthens and stabilizes the connection between the welding tab 203 and the pad 101, so that the auxiliary connection area 205 can bear the sudden tensile force when the welding tab 203 is subjected to it, thereby preventing the welding tab 203 from being damaged.

[0025] Furthermore, the welding tab 203 is provided with a solder joint 203a; the solder joint 203a is located in the overlapping area of ​​the welding tab 203 and the pad 101. Specifically, the user can connect the welding tab 203 and the pad 101 in the solder joint 203a using the laser welding or ultrasonic welding process; thereby, a solder nugget 203b is formed on the side of the welding tab 203; the solder nugget 203b connects the welding tab 203 and the pad 101 respectively. Specifically, the solder nugget 203b can be formed on the side of the welding tab 203 using the laser welding or ultrasonic welding process; the solder nugget 203b helps to further enhance the connection stability between the welding tab 203 and the pad 101.

[0026] For further information, please refer to [link / reference]. Figures 7 to 11 ; Figure 7 This is a flowchart illustrating a rigid-flex PCB fabrication process according to the present invention. Figure 7 As shown, the present invention discloses a process for fabricating a rigid-flex PCB, which includes the following steps: S1: The welding tabs 203 are fabricated on the flexible circuit board 2; S2: Print adhesive on the main connection area 204 and the auxiliary connection area 205 provided on the flexible circuit board 2; S3: Press and connect the flexible circuit board 2 and the rigid circuit board 1 together. S4: Weld each of the welding tabs 203 to each of the welding pads 101.

[0027] For details, please continue reading. Figure 8 ; Figure 8 This is a schematic diagram of an embodiment of step S1 in the fabrication process of a rigid-flex PCB according to the present invention. Figure 8As shown, a solder tab 203 can be fabricated corresponding to each solder pad 101 provided on the rigid circuit board 1. The end of the solder tab 203 is connected to the flexible circuit board 2, and neither side of it is covered with an insulating film 202. Specifically, the flexible circuit board 2 includes conductive lines 201 and an insulating film 202; the material of the insulating film 202 can be a commonly used thin film material such as PP, PET, PI, or LCP. Furthermore, the conductive lines 201 and the insulating film 202 can be bonded together through a composite process; this composite process is also commonly referred to as a lamination process. The composite process specifically refers to bonding thin film materials of different properties together in a certain way, and then sealing them to protect the contents. The solder tab 203 can be obtained by separating the conductive lines 201 from the insulating film 202 through a die-cutting process. More specifically, the insulating film 202 covering both sides of the conductive line 201 can be partially peeled off using a die-cutting process. That is, the user can use the die-cutting process to cut away the area where the welding tab 203 needs to be processed, and then peel off the cut portion of the insulating film 202 to expose the welding tab 203. Since the welding tab 203 is partially removed from the conductive line 201 through the die-cutting process, that is, the end of the welding tab 203 extends from the conductive line 201, meaning the welding tab 203 is electrically conductive to the conductive line 201. More specifically, the die-cutting process refers to a forming process in which a die-cutting plate is assembled according to the product design requirements using die-cutting blades; then, under the pressure generated by the die-cutting equipment, the thin film product is cut into the required shape or cuts. The die-cutting process needs to be carried out using a die-cutting machine. The die-cutting machine can also be called a die-cutting machine, a cutting machine, or a CNC punching machine. The working principle of the die-cutting machine is to use die-cutting blades, steel blades, hardware molds, templates carved from steel wire or steel plates, etc., to apply a certain pressure to the material being processed through the printing plate, thereby cutting the material being processed into a preset shape. Figure 8 The welding tab 203 shown is an embodiment produced by die-cutting using a die-cutting machine.

[0028] For details, please continue reading. Figure 9 ; Figure 9 This is a schematic diagram of an embodiment of step S2 in the fabrication process of a rigid-flex PCB according to the present invention. Figure 9 As shown, the user can uniformly print adhesive on the main connection area 204 and the auxiliary connection area 205 provided on the flexible circuit board 2.

[0029] For details, please continue reading. Figure 10 ; Figure 10This is a schematic diagram of an embodiment of step S3 in the fabrication process of a rigid-flex PCB according to the present invention. Figure 10 As shown, the user can connect the pre-prepared rigid circuit board 1 with the required solder pads 101 to the flexible circuit board 2 by pressing. Specifically, a preset pressure can be applied to the corresponding areas of the main connection area 204 and the auxiliary connection area 205 of the flexible circuit board 2 to ensure that the adhesive pre-printed in the area fully contacts and connects with the corresponding area of ​​the rigid circuit board 1.

[0030] For details, please continue reading. Figure 11 ; Figure 11 This is a schematic diagram of an embodiment of step S4 in the fabrication process of a rigid-flex PCB according to the present invention. Figure 11 As shown, in step S4, the user can connect the welding tab 203 to the solder pad 101 using laser welding or ultrasonic welding. Specifically, laser welding can minimize the required heat input, resulting in a small range of metallographic changes in the heat-affected zone and minimal deformation due to heat conduction. Furthermore, laser welding does not require electrodes, eliminating concerns about electrode contamination or damage. Additionally, laser welding is not a contact welding process, minimizing equipment wear and deformation. Therefore, laser welding effectively avoids the damage to the insulating film 202 or other components caused by prolonged heating in traditional soldering processes. Further, ultrasonic welding utilizes high-frequency vibration waves transmitted to the surfaces of two objects to be welded, and under pressure, causes the surfaces to rub against each other, forming a fusion between molecular layers. In step S4, the welding tab 203 can also be connected to the pad 101 using an ultrasonic welding process. This ultrasonic welding process prevents melting at the connection point between the welding tab 203 and the pad 101, thus preserving the metal's properties. Furthermore, after ultrasonic welding, the welding tab 203 and the pad 101 exhibit excellent electrical conductivity with extremely low resistivity. Most importantly, the ultrasonic welding process is short and avoids generating high temperatures in the welding area.

[0031] In summary, the present invention provides a rigid-flex circuit board structure in which a plurality of solder tabs 203 without covering the insulating film 202 are provided on the flexible circuit board 2, and the solder tabs 203 are electrically connected to the conductive lines 201; while the rigid circuit board 1 has a plurality of pads 101 corresponding to each solder tab 203; the solder tabs 203 and the pads 101 are connected by laser welding or ultrasonic welding processes. Because the welding tab 203 has a flexible structure and extends beyond the insulating film 202, it can be bonded to the surface of the pad 101 for welding connection. That is, the welding tab 203 and the pad 101 are located on the same plane. Therefore, compared with the prior art, the welding process between the welding tab 203 and the pad 101 has the advantages of short soldering time, low heat generation in the welding area, and fast production cycle, thus solving the technical problems of easy damage to the insulating film and low production efficiency of rigid-flex circuit boards in the prior art. Furthermore, this invention also discloses a manufacturing process for a rigid-flex PCB. First, the flexible PCB 2 is die-cut to obtain the solder tabs without the insulating film 202 covering both sides. Then, adhesive is uniformly printed onto the main connection area 204 and auxiliary connection area 205 of the flexible PCB 2. Next, the rigid PCB 1 and the flexible PCB 2 are pressed together. Finally, laser welding or ultrasonic welding is used to connect the solder tabs 203 to the pads 101. Therefore, this rigid-flex PCB manufacturing process avoids the technical defects of existing technologies, such as excessive molten solder buildup in the soldering area affecting connection quality.

[0032] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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, they should be considered to be within the scope of this specification.

[0033] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A rigid-flex PCB structure, characterized in that, Including rigid circuit boards and flexible circuit boards; The rigid circuit board has several solder pads; The flexible circuit board has conductive lines, an insulating film, and several solder tabs; The insulating film covers both sides of the conductive line; The welding tab is a completely exposed metal tab that is integrally formed from the conductive line by a die-cutting process and extends beyond the insulating film; The end of the welding tab is in contact with the solder pad on the hard circuit board in the same plane; The welding tabs and the welding pads are electrically connected by laser welding or ultrasonic welding.

2. A process for fabricating the rigid-flex PCB structure of claim 1, characterized in that, Includes the following steps: The welding tabs and the opening structure of the insulating film are simultaneously formed on the flexible circuit board through a die-cutting process. Adhesive is printed in the main connection area and auxiliary connection area of ​​the flexible circuit board; The flexible circuit board and the rigid circuit board are pressed together; The welding tabs and the welding pads are welded together in the overlapping area by means of laser welding or ultrasonic welding after pressure bonding.

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