Flexible circuit board, combined circuit board and circuit board welding system

Abstract

The embodiment of the utility model provides a flexible circuit board, a combined circuit board and a circuit board welding system, which are applied to the technical field of circuit board design. The flexible circuit board provided by the utility model comprises a flexible circuit board main body, a plurality of first bonding pads and a plurality of metalized via holes, the first bonding pad is arranged at the welding position of the flexible circuit board main body, the cross sectional area of the metalized via hole is smaller than that of the first bonding pad, and the metalized via hole penetrates through the first bonding pad and the flexible circuit board main body. According to the flexible circuit board and the combined circuit board provided by the utility model, the metalized via hole penetrating through the first bonding pad and the flexible circuit board main body is arranged, so that when the flexible circuit board is welded with other circuit boards, the flexible circuit board can be easily aligned, welding flux can reach a welding area through the metalized via hole, the welding difficulty of the circuit board can be reduced, and the welding quality of the circuit board is improved. In addition, the cross sectional area of the metalized via hole is smaller than that of the first bonding pad, the situation that the welding flux overflows out of the bonding pad can be reduced, and therefore welding operation is simpler and more convenient.

Description

Technical Field

[0001] The utility model relates to the technical field of circuit board design, in particular to a flexible circuit board, a combined circuit board and a circuit board welding system. Background Art

[0002] FPC (Flexible Printed Circuit Board) is a circuit board with bending and folding capabilities, suitable for applications that require bending, curves or three-dimensional shapes. With the development of multifunctional electronic devices, PCB circuit boards are welded together with other circuit boards when designing circuit boards to support the functional realization of electronic products. In related technologies, manual welding or hot pressing welding is usually used when welding PCB circuit boards with other circuit boards. This method requires taking into account the alignment of the two circuit boards and the placement of solder while welding, which places high demands on relevant technical personnel and is difficult to operate. Utility Model Content

[0003] The purpose of the embodiment of the utility model is to provide a flexible circuit board, a combined circuit board and a circuit board welding system to reduce the difficulty of circuit board welding. The specific technical solution is as follows:

[0004] In a first aspect of an embodiment of the present application, a flexible circuit board is provided, the flexible circuit board comprising:

[0005] A flexible circuit board body, and a plurality of first pads and metallized vias;

[0006] The first pad is disposed at a welding position of the flexible circuit board body, the cross-sectional area of ​​the metal via is smaller than the cross-sectional area of ​​the first pad, and the metallized via passes through the first pad and the flexible circuit board.

[0007] In a possible implementation manner, the metallized via is a circular via.

[0008] In a possible implementation manner, the first pad is a circular pad, the first pad and the metallized via hole are arranged in concentric circles, and the diameter of the metallized via hole is smaller than the diameter of the first pad.

[0009] In a possible implementation manner, a diameter of the first pad is not less than 0.35 mm, and a diameter of the first pad is not greater than 0.45 mm.

[0010] In a possible implementation manner, the diameter of the metallized via hole is not less than 0.18 mm, and the diameter of the metallized via hole is not greater than 0.25 mm.

[0011] In a possible implementation manner, a distance between centers of two adjacent first pads is not less than 0.8 mm.

[0012] In a possible implementation, the flexible circuit board further includes: a copper foil structure;

[0013] The copper foil structure is disposed on the flexible circuit board body, a first gap exists between the copper foil structure and the first pad, and the copper foil structure is electrically connected to a ground of the flexible circuit board.

[0014] In a possible implementation manner, the first interval is not less than 0.125 mm.

[0015] In a possible implementation manner, the first solder pads are distributed in multiple rows at the soldering positions of the flexible circuit board body.

[0016] In a second aspect of the embodiments of the present application, a combined circuit board is provided, the combined circuit board comprising a printed circuit board and the flexible circuit board described in any one of the first aspects of the embodiments of the present application, the printed circuit board comprising a second solder pad, the second solder pad being at a soldering position in the printed circuit board;

[0017] The printed circuit board and the flexible circuit board are welded via the first welding pad and the second welding pad.

[0018] In a possible implementation manner, the second pad has the same shape and size as the first pad.

[0019] In a third aspect of the embodiment of the present application, the circuit board welding system includes:

[0020] Laser welding equipment, printed circuit board and any flexible circuit board described in the present application;

[0021] The laser welding equipment includes a laser emitter, a nitrogen emitter, a solder ball emitter and a welding head. The welding head includes a solder ball track, a laser channel, a nitrogen channel and an injection port. The laser channel is connected to the laser emitter, the solder ball track is connected to the solder ball emitter, and the nitrogen channel is connected to the nitrogen emitter.

[0022] In a possible implementation manner, the metallized via hole of the flexible circuit board is a circular via hole, the first pad is a circular pad, the second pad is a circular pad, and the diameter of the metallized via hole is greater than the diameter of the solder ball;

[0023] When the circuit board is welded, the first welding pad of the flexible circuit board is aligned with the second welding pad of the printed circuit board, and the jet nozzle of the laser welding equipment is aligned with the metallized via hole.

[0024] The embodiment of the utility model provides a flexible circuit board, a combined circuit board and a circuit board welding system, wherein the flexible circuit board includes: a flexible circuit board body, and a plurality of first pads and metallized vias; the first pad is arranged at the welding position of the flexible circuit board body, the cross-sectional area of ​​the metallized via is smaller than the cross-sectional area of ​​the first pad, and the metallized via runs through the first pad and the flexible circuit board body. By setting the metallized via that runs through the first pad and the flexible circuit board body, the flexible circuit board can be easily aligned when welding with other circuit boards, and the solder can reach the welding area through the metallized via, which can reduce the difficulty of circuit board welding. In addition, the cross-sectional area of ​​the metallized via is smaller than the cross-sectional area of ​​the first pad, which can reduce the situation where the solder overflows the pad, thereby making the welding operation easier.

[0025] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0027] Figure 1 A schematic diagram of the first structure of a flexible circuit board provided in an embodiment of the present application;

[0028] Figure 2 A schematic diagram of the shape of the first pad in the flexible circuit board provided in an embodiment of the present application;

[0029] Figure 3 A second structural schematic diagram of a flexible circuit board provided in an embodiment of the present application;

[0030] Figure 4 A schematic diagram of the distribution of first pads in a flexible circuit board provided in an embodiment of the present application;

[0031] Figure 5 A third structural schematic diagram of a flexible circuit board provided in an embodiment of the present application;

[0032] Figure 6 A schematic diagram of the structure of a combined circuit board provided in an embodiment of the present application;

[0033] Figure 7a A schematic diagram of the first structure of a printed circuit board provided in an embodiment of the present application;

[0034] Figure 7bA second structural schematic diagram of a printed circuit board provided in an embodiment of the present application;

[0035] Figure 7c A third structural schematic diagram of a printed circuit board provided in an embodiment of the present application;

[0036] Figure 8 A schematic diagram of the structure of the laser welding equipment provided in the embodiment of the present application;

[0037] Fig. 9 A schematic diagram of a working condition of a circuit board welding system provided in an embodiment of the present application;

[0038] Fig.10 A flow chart of welding steps provided in an embodiment of the present application. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field based on this application belong to the scope of protection of the utility model.

[0040] In order to better understand this application, the following technical terms that may be involved in this application are first explained:

[0041] Printed Circuit Board: A basic device used to support and connect electronic components, commonly used in electronic equipment.

[0042] Flexible Circuit Board: A circuit board that has the ability to bend and flex, suitable for applications that require bends, curves or three-dimensional shapes.

[0043] Pad: Usually refers to the metal contact on the circuit board, which is used to connect electronic components such as processors, resistors, capacitors and other components.

[0044] Impedance continuity: The resistance matching and continuity of the signal transmission lines in the circuit to ensure stable transmission of the signal throughout the circuit.

[0045] Round Pad: A pad of a specific shape, often used to connect electronic components.

[0046] Circular metallized via: A metallized hole usually used to connect different layers of a circuit board, facilitating circuit connection and communication.

[0047] Laser solder ball welding: A soldering technique that uses lasers and liquid solder balls to connect electronic components to circuit boards.

[0048] Bond strength: refers to the strength and firmness of the connection when connecting different parts or materials.

[0049] Signal line density: refers to the number of signal lines per unit area, usually used to describe the connection density on a circuit board.

[0050] Metallized via hole diameter: refers to the diameter of the metallized via, which usually needs to be large enough to accommodate the solder ball to ensure a good connection.

[0051] Crosstalk: refers to the mutual influence between different signal lines, which may cause signal interference or distortion.

[0052] Ground wrap: A treatment method used to reduce crosstalk between signal lines, usually achieved by introducing a ground layer or metal foil.

[0053] Pad Center Spacing: The distance between the centers of adjacent pads, often used to optimize signal integrity.

[0054] Laser welding machine: A device that uses laser technology to weld, usually used in high-precision welding scenarios.

[0055] In the related art, manual welding or hot pressing welding is usually used to weld flexible circuit boards to other circuit boards. This method requires taking into account the alignment of the two circuit boards and the placement of solder while welding, which places high demands on related technicians and is difficult to operate.

[0056] In addition, in the related art, the flexible circuit board used in the circuit board welding includes a pad for welding with the printed circuit board; wherein the pad includes: a signal pad layer and a ground pad layer; the signal pad area in the signal pad layer is smaller than the ground pad area in the ground pad layer. By applying the flexible circuit board, the flexible circuit board can be used as a "transition bridge" for welding the printed circuit board with other devices, thereby improving the welding flexibility of the printed circuit board; and by setting the signal pad area smaller than the ground pad area in the ground pad layer, the signal return path can be reduced to optimize the impedance continuity, thereby improving the signal integrity of the transmission.

[0057] However, only a single row of pads can be set in the flexible circuit board in this solution, and the number of pads is limited by the width of the connection area, which cannot meet the high-density interconnection requirements. Among them, the number of effective signal transmission pads = (connection area width – 2*ground pad width – 2*distance between ground pad and signal pad) / signal pad width. Therefore, the flexible circuit board in the related art cannot be used in application scenarios with a large number of signals.

[0058] In order to solve at least one of the above technical problems, in a first aspect of an embodiment of the present application, a flexible circuit board is provided, the flexible circuit board comprising: Figure 1 The structure shown:

[0059] A flexible circuit board body 101, and a plurality of first pads 102 and metallized vias 103;

[0060] The first pad 102 is disposed at a welding position of the flexible circuit board body 101 , the cross-sectional area of ​​the metallized via 103 is smaller than that of the first pad 102 , and the metallized via 103 passes through the first pad 102 and the flexible circuit board body 101 .

[0061] The position and number of the first pads can be determined according to the conductor layout in the flexible circuit board. The shape of the first pad can be of various types, for example, the first pad can be a rectangular pad, a circular pad, an elliptical pad, a special-shaped pad, etc. Figure 2 In the flexible circuit board shown, the shape of the first pad is a rectangular pad. Similarly, the shape of the metallized via can also be of various types, for example, the metallized via is a circular metallized via, a square metallized via, an elliptical metallized via, etc. Usually, the metallized via has the same shape as the first pad, and both the metallized via and the first pad are circular.

[0062] Figure 3 Another structural diagram of a flexible circuit board is shown in FIG. 1 , in which the cross-sectional area of ​​the metallized via 103 is smaller than the cross-sectional area of ​​the first pad 102, and the metallized via 103 passes through the first pad 102 and the flexible circuit board body 101. The function of the metallized via is to allow the solder to reach the welding area through the metallized via, so the cross-sectional area of ​​the metallized via needs to pass through the first pad and the flexible circuit board body. The first pad is located on the surface of the flexible circuit board. In practical applications, the thickness of the first pad is extremely small, about 0.03 mm, and can be ignored when making connections or calculations.

[0063] When the flexible circuit board is welded together with other circuit boards, the solder can reach the welding area of ​​the flexible circuit board and other circuit boards through the metallized vias, thereby welding the flexible circuit board and other circuit boards together. The effective bonding area between the flexible circuit board and other circuit boards is the area of ​​the first pad minus the cross-sectional area of ​​the metallized vias; the area of ​​the metallized vias needs to be smaller than the cross-sectional area of ​​the first pad. If the cross-sectional area of ​​the metallized vias is too large or the area of ​​the first pad is too small, the effective bonding area between the flexible circuit board and other circuit boards becomes smaller, thereby reducing the welding bonding strength, which may cause the flexible circuit board to be disconnected from the other circuit boards during use.

[0064] When applying the flexible circuit board of the embodiment of the present application, a metallized via hole penetrating the first soldering pad and the main body of the flexible circuit board can be provided, and the cross-sectional area of ​​the metallized via hole is smaller than the cross-sectional area of ​​the first soldering pad. When the flexible circuit board is welded to other circuit boards, the solder can directly reach the welding area through the metallized via hole, thereby reducing the difficulty of welding the circuit board and making the welding operation easier.

[0065] In a possible implementation, the plurality of first solder pads in the flexible circuit board may be arranged in a single row at the soldering position of the flexible circuit board body, or may be arranged in multiple rows at the soldering position of the flexible circuit board body. In one example, the first solder pads are arranged in multiple rows at the soldering position of the flexible circuit board body, such as Figure 1 In the flexible circuit board shown in FIG. 1 , the first solder pads are arranged in three rows at the soldering positions of the flexible circuit board body. In another example, the first solder pads in the flexible circuit board are arranged in three rows. Figure 4 As shown, they are distributed in a single row at the welding position of the flexible circuit board body.

[0066] By using the flexible circuit board of the embodiment of the present application, the first solder pads can be arranged in multiple rows at the soldering positions of the flexible circuit board body, so that the number of first solder pads can be increased within the limited connection area of ​​the flexible circuit board, so that the flexible circuit board can connect more components.

[0067] In a possible implementation, the first pad is a circular pad and the metallized via is a circular via. In the flexible circuit board of the embodiment of the present application, the first pad and the metallized via can be arranged in concentric circles, and the diameter of the metallized via is smaller than the diameter of the first pad.

[0068] like Figure 1 As shown, the first pad 102 and the metallized via 103 are both circular, and the first pad and the metallized via have the same center. Setting the diameter of the metallized via smaller than the diameter of the first pad can ensure that the cross-sectional area of ​​the metallized via is smaller than the cross-sectional area of ​​the first pad.

[0069] In addition, in order to ensure that the solder can pass through the metallized via, the diameter of the metallized via can be set larger than the diameter of the solder. If the metallized via is too small, the kinetic energy of the solder passing through the metallized via will be absorbed by the metallized via, resulting in the solder not being able to reach the welding area, making it impossible for the flexible circuit board to bond with other circuit boards or the bonding strength is too low. In an example, if the solder is a liquefied solder ball, the diameter of the metallized via should be larger than the solder ball diameter and smaller than the cross-sectional area of ​​the first pad.

[0070] The bonding of the flexible circuit board to the other circuit board is achieved by soaking the solder in the gap between the first pad and the pad of the other circuit board. In one example, the solder is a liquid solder ball, and the liquid solder ball is dripped onto the pad of the other circuit board through the metallized via, and the liquid solder ball fills the gap between the first pad of the flexible circuit board and the pad of the other circuit board through the soaking effect, and then the liquid solder is cooled and formed to achieve the bonding of the flexible circuit board to the other circuit board.

[0071] In order to ensure the bonding strength between the flexible circuit board and other circuit boards, when setting the diameter of the first pad, it is necessary to consider whether the solder can completely wet and fill the gap between the first pad of the flexible circuit board and the pads of other circuit boards. Therefore, the diameter of the first pad can be set to be no less than 0.35mm and no more than 0.45mm; the diameter of the metallized via is set to be no less than 0.18mm and no more than 0.25mm. In an example, the diameter of the metallized via is set to 0.2mm, and the diameter of the first pad is 0.4mm.

[0072] By using the flexible circuit board of the embodiment of the present application, by arranging the first soldering pad and the metallized via in concentric circles, it is possible to facilitate alignment of the flexible circuit board with the other circuit boards through the center of the concentric circles during welding, and the solder can be evenly distributed in the welding area through the concentric circle arrangement, which can avoid affecting the adhesion between the flexible circuit board and the other circuit boards due to uneven solder layout in the welding area caused by the biased position of the metallized via.

[0073] In addition, in practical applications, the diameter of the first pad needs to consider not only the bonding strength between the flexible circuit board and other circuit boards, but also the signal line density and signal integrity of the flexible circuit board. The signal line density can be calculated by dividing the number of signals by the area of ​​the connection between the flexible circuit board and the printed circuit board. The larger the diameter of the first pad in the flexible circuit board, the fewer the number of signal line first pads that can be designed per unit area.

[0074] The diameter of the first pad will also affect the impedance of the signal line in the flexible circuit board. If the impedance is discontinuous, it will cause signal reflection, thus affecting signal integrity. Therefore, the larger the diameter of the first pad, the stronger the fringe field coupling between the first pad and the surrounding conductor, the larger the equivalent capacitive load of the transmission line at the first pad, and the smaller the impedance.

[0075] In the embodiment of the present application, considering the bonding strength between the flexible circuit board and other circuit boards, the signal line density of the flexible circuit board and the signal integrity, the diameter of the first pad is set to be no less than 0.35 mm and no more than 0.45 mm. This can ensure that the area of ​​the first pad is small while reducing the possibility of sudden change in impedance of the signal transmission line, thereby ensuring signal integrity.

[0076] In a possible implementation, when the distance between two adjacent first pads is too small, there is a possibility of signal crosstalk. For high-speed single-ended signals, the crosstalk between the first pad and the metallized via will cause edge jitter and noise to the signal, thereby affecting the signal quality. In order to reduce this effect, the first pad and the metallized via need to be grounded, that is, the gap between the two first pads is filled with copper foil with grounding properties.

[0077] Therefore, the flexible circuit board of the embodiment of the present application further includes a copper foil structure, which is disposed on the flexible circuit board body, a first gap exists between the copper foil structure and the first pad, and the copper foil structure is electrically connected to the ground of the flexible circuit board. Figure 5 As shown, the copper foil structure 501 is disposed on the flexible circuit board body, and a first gap 502 exists between the copper foil structure 501 and the first pad 102 .

[0078] In order to consider the integrity of the signal, there is a spacing between two adjacent first pads; in order to prevent the copper foil from affecting the circuit connection in the flexible circuit board, there is a first spacing between the copper foil structure and the first pad. The spacing between the centers of two adjacent first pads can be calculated by the following formula:

[0079] The minimum spacing between the centers of two adjacent first pads = the diameter of the first pad + the minimum processable width of the copper foil + 2 * the spacing between copper foils of different network attributes.

[0080] The spacing between copper foils with different network attributes refers to the spacing between the first pad in the circuit and the copper foil with grounding attributes, that is, the first spacing.

[0081] In one example, referring to the conventional process capabilities of various circuit board processing manufacturers, the spacing between the centers of two adjacent first pads is set to be no less than 0.8 mm; and the first spacing is set to be no less than 0.125 mm.

[0082] When using the flexible circuit board of the embodiment of the present application, the first solder pad and the metallized via can be grounded by setting a copper foil electrically connected to the ground on the flexible circuit board body, and the spacing between the centers of two adjacent first solder pads is set to be no less than 0.8 mm; the first spacing is no less than 0.125 mm, thereby reducing the possibility of signal quality being affected by crosstalk between the first solder pad and the metallized via, and improving signal integrity.

[0083] In practical applications, when a flexible circuit board is welded with other circuit boards, it is usually welded with a printed circuit board. Therefore, in a second aspect of an embodiment of the present application, a combined circuit board is provided, such as Figure 6 As shown, the combined circuit board includes a printed circuit board 601 and a flexible circuit board 602 according to the first aspect of the embodiment of the present application, the printed circuit board includes a second solder pad 6011, and the second solder pad is at a soldering position in the printed circuit board;

[0084] The printed circuit board and the flexible circuit board are welded via the first welding pad and the second welding pad.

[0085] Among them, the flexible circuit board and the printed circuit board can be welded by laser welding equipment. During welding, the first pad and the second pad can be aligned through the metallized via first. In order to facilitate the welding of the flexible circuit board and the printed circuit board and the alignment of the first pad and the second pad, the second pad can be set to have the same shape and size as the first pad; and the first pad in the flexible circuit board corresponds to the second pad in the printed circuit board one by one. For example, if the first pad is a circular pad, the second pad is a circular pad with the same cross-sectional area as the first pad, and the second pad is placed concentrically with the first pad. In one example, the first pad is a circular pad with a diameter of 0.4 mm, and the center distance between two adjacent first pads is 0.8 mm. In the printed circuit board, the second pad is also a circular pad with a diameter of 0.4 mm, and the center distance between two adjacent second pads is 0.8 mm. Among them, in order for the solder to reach the welding area, such as Figure 7a and Figure 7b In the structure shown, the printed circuit board is not provided with metallized vias, and the second pads 6011 are distributed on the surface of the printed circuit board 601, so that the solder can successfully drip on the second pads when passing through the metallized vias in the flexible circuit board, and finally fill the gap between the first pad and the second pad through the wetting effect to complete the welding of the flexible circuit board and the printed circuit board. Figure 7c As shown, there is also a grounded copper foil 701 in the printed circuit board, and there is a second interval 702 between the copper foil 701 and the second pad 6011 that is equal to the first interval.

[0086] By using the combined circuit board of the embodiment of the present application, the flexible circuit board of the first aspect of the embodiment of the present application is welded to the printed circuit board, and the solder can reach the connection area between the first pad and the second pad through the metallized via in the flexible circuit board to achieve the bonding of the flexible circuit board and the printed circuit board, making the welding operation of the circuit board easier. And when using the combined circuit board of the embodiment of the present application, when welding, for example, when welding by laser solder ball welding, it is only necessary to drip the liquid solder ball on the second pad through the metallized via to achieve the welding of the combined circuit board, making the welding operation easier, and can reduce the overflow of the liquid solder ball, so that the welding effect of the combined circuit board is better.

[0087] In a third aspect of the embodiment of the present application, a circuit board welding system is provided, the circuit board welding system comprising a laser welding device, a printed circuit board and the flexible circuit board in the first aspect of the embodiment of the present application;

[0088] The laser welding equipment includes a laser emitter, a nitrogen emitter, a solder ball emitter and a welding head. The welding head includes a solder ball track, a laser channel, a nitrogen channel and an injection port. The laser channel is connected to the laser emitter, the solder ball track is connected to the solder ball emitter, and the nitrogen channel is connected to the nitrogen emitter.

[0089] The structure of the laser welding equipment can be as follows Figure 8 As shown, the laser welding equipment is composed of various modules, including a laser emitter 801, a nitrogen emitter 802, a solder ball emitter 803 and a welding head 804. The laser channel, the solder ball track and the nitrogen channel intersect above the welding head. In order to allow the solder ball to smoothly roll down to the junction so that the laser heats and melts it, the solder ball track can be set to be tilted. In actual use, the solder ball emitter emits the solder ball, and the solder ball reaches the junction of the laser channel, the solder ball channel and the nitrogen channel along the solder ball track. The laser emitter emits a laser, and the laser reaches the junction through the laser channel to melt the solder ball into a liquid solder ball. The nitrogen emitter emits pressurized nitrogen, and the pressurized nitrogen emits the liquid solder ball from the injection port of the welding head through the nitrogen channel.

[0090] In such Fig. 9 In the working condition of the circuit board welding system shown, when the circuit board is welded, the first pad of the flexible circuit board is aligned with the second pad of the printed circuit board, and the injection port 9014 of the laser welding device is aligned with the metallized via 103. The laser welding device 901 is used to weld the combined circuit board composed of the flexible circuit board and the printed circuit board, and the second pad in the printed circuit board is first aligned with the first pad in the flexible circuit board, wherein the laser welding device is located above one side of the flexible circuit board, and the injection port 9014 of the laser welding device is aligned with the metallized via 103. The laser welding device melts the solder ball 9012 in the solder ball track 9011 by laser heating, and then ejects the melted liquid solder ball 9013 from the injection port 9014 by pressurized nitrogen. Among them, the solder ball track needs to be tilted to ensure that the solder ball can slide to the junction of the solder ball track and the laser channel, so that the laser can melt the solder ball into a liquid solder ball through the laser channel. Correspondingly, the nitrogen channel also intersects with the laser channel and the solder ball track at this junction, so as to ensure that the nitrogen can blow the liquid solder ball to the injection port.

[0091] After the liquid solder ball is ejected by high-pressure nitrogen, it passes through the metallized via of the flexible circuit board and falls on the second pad of the printed circuit board. It fills the gap between the first pad of the flexible circuit board and the second pad of the printed circuit board through the wetting effect, and then cools and sets to achieve the bonding of the flexible circuit board and the printed circuit board. In order to ensure that the liquid solder ball can pass through the metallized via, the metallized via of the flexible circuit board can be set as a circular via, the first pad is a circular pad, the second pad is a circular pad, and the diameter of the metallized via is larger than the diameter of the liquid solder ball, thereby avoiding the metallized via being too small to block the liquid solder ball, so that the liquid solder ball can completely reach the second pad, so that the welding effect is better.

[0092] In an example, you can Fig.10 The steps shown are used for welding. First, step S1001 is performed to set the pads of the flexible circuit board, wherein the pads of the flexible circuit board are set as the settings of the first aspect of the embodiment of the present application; then step S1002 is performed to set the pads of the printed circuit board; after the pads of the flexible circuit board and the printed circuit board are set, step S1003 is performed to dock the flexible circuit board with the printed circuit board, wherein, when docking the flexible circuit board with the printed circuit board, it is necessary to ensure that the first pads in the flexible circuit board correspond to the second pads in the printed circuit board one by one to achieve alignment of the connection area; finally, laser welding equipment is used to perform step S1004 to achieve laser welding and bonding.

[0093] The circuit board welding system of the embodiment of the present application adopts the laser solder ball welding method for welding, which has higher welding accuracy than reflow soldering, manual soldering and other methods, and can make the required area of ​​the pad in the circuit board smaller. And using the laser solder ball welding method to weld the combined circuit board of the second aspect of the embodiment of the present application can reduce the welding difficulty and make the welding operation easier.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A flexible circuit board, characterized in that: The flexible circuit board comprises: A flexible circuit board body, a copper foil structure, and a plurality of first pads and metallized vias; The first pad is disposed at a welding position of the flexible circuit board body, the cross-sectional area of ​​the metallized via hole is smaller than the cross-sectional area of ​​the first pad, and the metallized via hole passes through the first pad and the flexible circuit board body; The copper foil structure is disposed on the flexible circuit board body, a first gap exists between the copper foil structure and the first pad, and the copper foil structure is electrically connected to a ground of the flexible circuit board.

2. The flexible circuit board according to claim 1, characterized in that: The metallized via hole is a circular via hole.

3. The flexible circuit board according to claim 2, characterized in that: The first pad is a circular pad, the first pad and the metallized via hole are arranged in concentric circles, and the diameter of the metallized via hole is smaller than the diameter of the first pad.

4. The flexible circuit board according to claim 3, characterized in that: The diameter of the first pad is not less than 0.35 mm, and the diameter of the first pad is not more than 0.45 mm.

5. The flexible circuit board according to claim 2, characterized in that: The diameter of the metallized via hole is not less than 0.18 mm, and the diameter of the metallized via hole is not greater than 0.25 mm.

6. The flexible circuit board according to claim 1, characterized in that: The distance between the centers of two adjacent first pads is not less than 0.8 mm.

7. The flexible circuit board according to claim 1, characterized in that: The first interval is not less than 0.125 mm.

8. The flexible circuit board according to claim 1, characterized in that: The first solder pads are distributed in multiple rows at the soldering positions of the flexible circuit board body.

9. A combined circuit board, characterized in that: The combined circuit board comprises a printed circuit board and the flexible circuit board according to any one of claims 1 to 8, wherein the printed circuit board comprises a second solder pad, and the second solder pad is at a soldering position in the printed circuit board; The printed circuit board and the flexible circuit board are welded via the first welding pad and the second welding pad.

10. The combined circuit board according to claim 9, characterized in that: The second pad has the same shape and size as the first pad.

11. A circuit board welding system, characterized in that: The circuit board welding system comprises: Laser welding equipment and the combined circuit board according to claim 9; The laser welding equipment includes a laser emitter, a nitrogen emitter, a solder ball emitter and a welding head. The welding head includes a solder ball track, a laser channel, a nitrogen channel and an injection port. The laser channel is connected to the laser emitter, the solder ball track is connected to the solder ball emitter, and the nitrogen channel is connected to the nitrogen emitter.

12. The circuit board welding system according to claim 11, characterized in that: The metallized via hole of the flexible circuit board is a circular via hole, the first pad is a circular pad, the second pad is a circular pad, and the diameter of the metallized via hole is greater than the diameter of the solder ball; When the circuit board is welded, the first welding pad of the flexible circuit board is aligned with the second welding pad of the printed circuit board, and the jet nozzle of the laser welding equipment is aligned with the metallized via hole.

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