Electrical conduction connection structure between FPCs (Flexible Printed Circuit)

Abstract

The invention discloses an electrical conduction connection structure between FPCs (Flexible Printed Circuit), which comprises an FPC main body consisting of a conductor layer positioned in the center and insulating layers arranged on the two sides of the conductor layer, and two or more groups of group FPC joints, and is characterized in that the end part of the FPC main body is provided with a first connection part; an opening of the insulating layer at one side of the first connecting part is connected with the sub FPC joint to realize electrical conduction of the front and back surfaces, the surface of the first connecting part is covered with a buffer interlayer, the buffer interlayer is provided with an opening right above the conductor layer, the sub FPC joint comprises a second connecting part connected with the first connecting part and a third connecting part arranged far away from the direction of the FPC main body, and the second connecting part is connected with the first connecting part. The second connecting part is provided with a special-shaped circuit layer and a special-shaped tin block which are electrically connected with the conductor layer of the sub FPC connector, the special-shaped tin block is of a soldering tin structure and comprises a main soldering tin column and a sub soldering tin column which are arranged in a crossed mode, and the special-shaped circuit layer and the special-shaped tin block are embedded into the opening in the surface of the buffer interlayer and are electrically connected with the conductor layer of the FPC body. Through the special-shaped circuit layer and the special-shaped tin block tin soldering structure, the tin soldering shape is kept in the welding process, the situation that the tin soldering shape is dispersed and collected is avoided, the electrical conduction performance of the FPC is guaranteed, meanwhile, pseudo soldering of welding and cracks generated during dynamic bending are reduced, and the reliability of the FPC is improved. The problems of fracture and pseudo soldering are solved through the synergistic effect of the depth difference of the special-shaped circuit layer, the special-shaped tin block and the buffer interlayer.

Description

Technical Field

[0001] The present invention relates to the technical field of FPC manufacturing, and in particular to an FPC-to-FPC electrical conductive connection structure. Background Art

[0002] To ensure soldering reliability and meet production process requirements, FPCs sometimes require that the back of the solder fingers have no PI substrate support, only a layer of copper foil. This type of FPC is called a window board, a hollow board, or a suspended lead board. Due to assembly space or design requirements, some hollow boards require that the other end of the window finger have no insulation support, only copper foil as the lead. This is called a fully suspended finger. If this type of hollow board with fully suspended fingers is directly manufactured, the lead fingers will severely deform or even break during the manufacturing process due to the lack of insulation support at the other end, making production impossible.

[0003] Chinese invention patent publication number CN113747684A discloses a fully suspended finger FPC manufacturing technology. Although this structure can reduce solder joints during the production process, the traditional solder structure will melt at high temperatures, causing the shape to disperse and aggregate. There is a risk of cracking during dynamic bending, affecting the electrical connection performance. Summary of the Invention

[0004] In order to solve the above technical problems, an electrical conductive connection structure between FPCs is provided.

[0005] To achieve the above-mentioned objectives, the present invention discloses an electrical conduction connection structure between FPCs, comprising an FPC main body consisting of a conductor layer located in the center and an insulating layer arranged on both sides of the conductor layer, and two or more groups of FPC connectors, wherein a first connecting portion is provided at the end of the FPC main body, and a single-sided insulating layer opening at the first connecting portion is connected to a sub-FPC connector to achieve electrical conduction on both sides, the surface of the first connecting portion is covered with a buffer interlayer, and an opening is provided on the buffer interlayer directly above the corresponding conductor layer, the sub-FPC connector comprises a second connecting portion connected to the first connecting portion and a third connecting portion arranged away from the FPC main body, the second connecting portion is provided with an anomalous circuit layer and an anomalous tin block electrically connected to the conductor layer of the sub-FPC connector, the anomalous tin block is a solder structure, comprising a main solder column and a sub-solder column arranged crosswise, the anomalous circuit layer and the anomalous tin block are embedded in the opening on the surface of the buffer interlayer and electrically connected to the conductor layer of the FPC main body.

[0006] Furthermore, the buffer interlayer material is an epoxy resin film, which is composed of 20% to 80% polyimide and 20% to 80% epoxy resin by weight. The depth of the buffer interlayer is greater than the thickness of the irregular tin block, and the depth of the buffer interlayer is 40μm to 110μm.

[0007] Furthermore, the abnormal circuit layer is arranged on the surface of the conductor layer exposed in the second connecting part, and is used to connect the abnormal tin block, which has a thickness of 30μm to 100μm and includes a main solder column with a width of 0.2mm to 1mm and a sub-solder column with a width of 0.05mm to 0.5mm.

[0008] Furthermore, the irregular tin block is directly formed on the irregular circuit layer through an electroplating process.

[0009] Furthermore, the irregular tin block is formed into a specified shape through a solid engraving process and then adhered to the irregular circuit layer using an adhesive resin.

[0010] Furthermore, the irregular tin block is composed of 99% tin.

[0011] Furthermore, the irregular tin block is composed of 30% to 99% of tin and 1% to 70% of alloy solder containing other metal components, and the other metal components include silver, copper or indium.

[0012] Furthermore, the shape of the solder column is X-shaped, wherein the angle range of each direction is 50° to 70°. The shape of the solder column also includes but is not limited to a cross shape, a Pozigzag shape and a fishbone shape.

[0013] Compared with the prior art, the present invention has the following beneficial effects: the present invention discloses an electrical conductive connection structure between FPCs, which maintains the solder shape during the welding process through the soldering structure of the special-shaped circuit layer and the special-shaped tin block, avoiding the situation where the solder shape is dispersed and gathered. While ensuring the electrical conductivity of the FPC, it reduces the cold solder joints and the cracks caused by dynamic bending, improves the flexibility of production, realizes the electrical function of ultra-long panels, reduces the manufacturing cost, and solves the problems of fracture and cold solder joints through the synergistic effect of the special-shaped circuit layer, the special-shaped tin block and the depth difference of the buffer interlayer. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0015] Figure 1 This is a front view of the connection status of the FPC main body and the sub-FPC connector of the present invention.

[0016] Figure 2 It is a cross-sectional view of the connection state of the FPC main body and the sub-FPC connector of the present invention.

[0017] Figure 3 This is a schematic diagram of the separation state of the FPC main body and the sub-FPC connector of the present invention.

[0018] Figure 4 Schematic diagram of the irregular circuit layer and irregular tin block according to the first embodiment of the present invention.

[0019] Figure 5 Schematic diagram of the irregular circuit layer and irregular tin block according to the second embodiment of the present invention.

[0020] Figure 6 Schematic diagram of the irregular circuit layer and irregular tin block according to the third embodiment of the present invention.

[0021] Figure 7 Schematic diagram of the irregular circuit layer and irregular tin block of the fourth embodiment of the present invention In the figure: 1 is the FPC body; 2 is the sub-FPC connector; 3 is the first connection part; 4 is the second connection part; 41 is the special-shaped circuit layer; 5 is the third connection part; 6 is the special-shaped tin block; 7 is the buffer spacer; 71 is the opening. DETAILED DESCRIPTION

[0022] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0023] like Figure 1 、 Figure 2 and Figure 4 As shown, a first connecting portion 3 is provided at the end of the FPC main body 1, and the length range of the FPC main body is 100mm to 2000mm. The single-sided insulating layer opening at the first connecting portion 3 is connected to the sub-FPC connector 2 to realize electrical conduction on both sides. The surface of the first connecting portion 3 is covered with a buffer interlayer 7, and an opening 71 is provided on the buffer interlayer 7 just above the corresponding conductor layer. The sub-FPC connector 2 includes a second connecting portion 4 connected to the first connecting portion 3 and a third connecting portion 5 arranged away from the FPC main body 1. In this embodiment, the opening directions of the third connecting portions 5 of the two components of the FPC connector 2 are opposite to each other to realize double-sided electrical connection. The opening directions can also be the same for single-sided electrical connection on the same side. The second connecting portion 4 is provided with an anomalous circuit layer and an anomalous tin block 6 electrically connected to the conductor layer of the sub-FPC connector 2. The anomalous circuit layer and the anomalous tin block 6 are embedded in the opening 71 on the surface of the buffer interlayer 7 and electrically connected to the conductor layer of the FPC main body 1. Figure 1The direction shown is side A, and the other side of the main FPC is side B. The first connection part of the main FPC is the opening of the insulation layer on side A, and the second connection parts of the corresponding sub-FPC connectors are all openings in the insulation layer on side B. The surface of the exposed conductor layer on one side of the second connection part on side B is provided with an abnormal circuit layer and an abnormal tin block, and is arranged in the opening of the buffer interlayer on the surface of the first connection part of the main FPC and soldered and fixed. The third connection part of the insulation layer on side A of the sub-FPC connector on the left is connected to the external panel, and the third connection part of the insulation layer on side B of the sub-FPC connector on the right is connected to the external panel, realizing electrical conduction of the double-sided panels, and solving the problems of breakage and cold soldering through the synergistic effect of the abnormal circuit layer, abnormal tin block and the depth difference of the buffer interlayer.

[0024] The buffer interlayer 7 is made of epoxy resin film, which is composed of 20% to 80% polyimide and 20% to 80% epoxy resin by weight. It serves as an intermediate force buffer layer to prevent excessive pressure during high-temperature and high-pressure compression welding, or the solder paste melts too quickly, causing the tin material to overflow and cause a short circuit. The depth of the buffer interlayer 7 is greater than the thickness of the abnormal tin block 6. Since the thermal expansion coefficient of the solder paste is greater than the thermal expansion coefficient of the buffer interlayer after it is completely melted, the welding conduction can still be achieved when the depth of the buffer interlayer is slightly greater than the thickness of the solder paste.

[0025] The irregular circuit layer 41 is arranged on the surface of the conductor layer exposed by the second connecting portion 4, and is used to connect the irregular tin block 6 corresponding to the shape of the irregular circuit layer. The irregular tin block 6 is a solder structure, including a main solder column 61 with a width of 0.2mm to 1mm and a sub-solder column 62 with a width of 0.05mm to 0.5mm. The main solder column 61 and the sub-solder column 62 are arranged crosswise. The main solder column realizes electrical conduction. If the width is too small, it is easy to produce a cold solder joint. If the width is too large, it is easy to crack when bending. The sub-solder column reduces the risk of multi-angle tensile cracking and is conducive to exhausting the welding from the side, increasing flexibility and reducing bending cracking. The irregular tin block structure greatly reduces the thermal expansion coefficient of the joint position, reducing the fracture of the welding position caused by thermal expansion. According to the actual test results, the thermal expansion coefficient can be reduced by more than 1 times, and the thermal expansion coefficient can be reduced from 2.0×10 -6 / ℃ dropped to 1.0×10 -6 / ℃, reducing the risk of solder cracking due to thermal expansion at the welding position; and the special tin block structure greatly reduces the rebound force at the welding position. According to the tested rebound modulus data, it is reduced from 80GPa to 20GPa, reducing the risk of solder cracking due to bending rebound force at the welding position.

[0026] The electroplating process is a process of depositing metal onto the hole wall or copper surface of a PCB through an electrochemical reaction. Its core purpose is to increase the thickness of the conductive layer, achieve metal connection in the through-hole, improve the surface condition of the pad, and prevent oxidation and corrosion. The process of directly forming the solder structure on the surface of the circuit through the electroplating process is essentially a microscopic "metal migration" in an electrolyte. The solder structure generated by the electroplating process has a uniform surface, rapid solder fusion, and minimal local heating impact, making it suitable for large-scale production.

[0027] The solid engraving process is a technology that uses physical processing to shape solder materials into specific shapes. It is mainly used in the field of electronic manufacturing. It uses sticky resin to enhance the adhesion between solder and welding surface, prevent the solder joint from separating from the circuit board or the problem of cold solder joint. At the same time, it protects the FPC from re-oxidation after welding and has a repairing effect on the solder joint. The active temperature range of the resin selected is slightly lower than the melting point of the solder to ensure that it works before the solder melts. The solder structure is hot-pressed and cured to adhere to the opening of the buffer layer, forming a dual mechanical and electrical connection with the conductor layer.

[0028] 99% pure tin solder has a high melting point (232°C), low fluidity during FPC reflow soldering (usually 220°C ~ 250°C), good solder shape retention, and a diffusion rate of <5% (traditional solder >25%), avoiding the risk of short circuits caused by solder aggregation, inhibiting high-temperature diffusion, and low cost; alloy solder adds silver (2% ~ 4%), copper (0.5% ~ 10%) or indium (10% ~ 60%) to form intermetallic compounds (such as AgSnIn, CuAgSnIn), which increases tensile strength by 30% ~ 50%, and has a dynamic bending life of > 12,000 times (pure tin is about 10,000 times), improving mechanical strength, and having good creep and fatigue resistance. The welding temperature can achieve the melting point requirement of 150 degrees or lower, reducing welding difficulties and improving welding quality. After the solder structure of this application is melted, it will be adsorbed on the copper foil on the surface of the conductor layer of the second connecting part, and can maintain the soldering effect of irregular shapes.

[0029] Example 1 The FPC body is composed of a conductor layer and a double-sided insulating layer, with a first connection portion provided at the end, and an opening in the insulating layer on one side A exposing the conductor layer. Two groups of split FPC connectors are provided, and the second connection portion of the split FPC connector with the insulating layer on the B side exposing the conductor layer is press-fitted and connected to the first connection portion. The opening directions of the third connection portions of the two groups of FPC connectors are opposite, wherein the irregular tin block is formed on the irregular circuit layer on the surface of the second connection portion by an electroplating process. The irregular tin block is composed of 99% pure tin, with a thickness of 50μm, and a main solder column width of 0.5mm, extending along the long axis direction of the second connection portion, and the split FPC connector is provided with two groups of split FPC connectors. The solder column has an X-shaped cross structure with a branch angle α1 of 58°, a cross angle α2 of 64°, and a width of 0.2mm. It is staggered with the main solder column. The buffer interlayer covers the first connection part. The material is 30% polyimide-70% epoxy resin composite film with a thickness of 60μm. A rectangular opening with a size of 0.5mm×1.5mm is opened on the surface of the buffer interlayer, which penetrates the conductor layer in depth. The irregular circuit layer and the irregular tin block are embedded in the opening of the buffer interlayer and are in direct contact with the conductor layer. Pure tin solder compensates for the strength of the end plate through the geometric structure and relies on the buffer interlayer to absorb deformation.

[0030] Example 2 The difference from the first embodiment is that the sub-solder columns of the irregular circuit layer and the irregular tin block are cross-shaped and arranged perpendicularly to the main solder columns, and the opening width of the buffer layer matches the width of the irregular circuit layer and the irregular tin block.

[0031] Example 3 The difference from Example 1 is that the solder columns of the irregular circuit layer and the irregular tin block are in the shape of a cross, which is a combination of Example 1 and Example 2. The solder composition is an alloy solder consisting of 96% tin and 4% silver. It is formed through solid carving and adhesive resin bonding processes. The alloy solder enhances the body strength, and the branch structure of the solder columns improves the stress dispersion efficiency.

[0032] Example 4 The difference from the third embodiment is that the solder columns of the special-shaped circuit layer and the special-shaped tin block are fishbone-shaped, and the branch angle α1 is 45°.

[0033] The multi-level solder structure of irregular circuit layers and irregular tin blocks effectively suppresses the high-temperature flow of solder. The solder columns of different shapes enhance the resistance to bending stress through mechanical interlocking. The depth difference of the buffer interlayer provides deformation compensation space, which comprehensively solves the problems of fracture and cold solder joints.

[0034] Several points that need to be explained are: First, in the description of this application, it should be noted that, unless otherwise specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, which can be mechanical connection or electrical connection, or internal communication between two elements, or direct connection. "Up", "down", "left", "right" and the like are only used to indicate relative position relationships. When the absolute position of the described object changes, the relative position relationship may change; secondly, in this article, relational terms such as first and second are only used to distinguish one entity from another, and do not necessarily require or imply that there is any such actual relationship or order between these entities.

[0035] The above examples are merely illustrative of the present invention and do not limit the scope of protection of the present invention. Any design that is identical or similar to the present invention shall fall within the scope of protection of the present invention.

Claims

1. An FPC-to-FPC electrical connection structure, comprising an FPC body (1) consisting of a conductor layer located in the center and insulating layers arranged on both sides of the conductor layer, and two or more sets of FPC connectors (2), characterized in that: The FPC main body (1) is provided with a first connecting portion (3) at the end thereof. The opening of the single-side insulating layer at the first connecting portion (3) is connected to the sub-FPC connector (2) to realize electrical conduction on both the front and back sides. The surface of the first connecting portion (3) is covered with a buffer interlayer (7). An opening (71) is provided on the buffer interlayer (7) just above the corresponding conductor layer. The sub-FPC connector (2) includes a second connecting portion (4) connected to the first connecting portion (3) and a third connecting portion (5) arranged in a direction away from the FPC main body (1). The second connecting portion (4) is provided with an anomalous circuit layer (41) and an anomalous tin block (6) electrically connected to the conductor layer of the sub-FPC connector (2). The anomalous tin block (6) is a solder structure, including a main solder column (61) and a sub-solder column (62) arranged crosswise. The anomalous circuit layer (41) and the anomalous tin block (6) are embedded in the opening (71) on the surface of the buffer interlayer (7) and electrically connected to the conductor layer of the FPC main body (1).

2. The electrical conductive connection structure between FPCs according to claim 1, characterized in that: The buffer interlayer (7) is made of an epoxy resin film, which is composed of 20% to 80% of polyimide and 20% to 80% of epoxy resin by weight. The depth of the buffer interlayer (7) is greater than the thickness of the irregular tin block (6), and the depth of the buffer interlayer (7) is 40 μm to 110 μm.

3. The electrical conductive connection structure between FPCs according to claim 1, characterized in that: The anomalous circuit layer (41) is arranged on the surface of the conductor layer exposed by the second connecting portion (4) and is used to connect the anomalous tin block (6). The anomalous tin block (6) has a thickness of 30 μm to 100 μm and includes a main solder column (61) with a width of 0.2 mm to 1 mm and a sub-solder column (62) with a width of 0.05 mm to 0.5 mm.

4. The electrical conductive connection structure between FPCs according to claim 3, characterized in that: The irregular tin block (6) is directly formed on the irregular circuit layer (41) through an electroplating process.

5. The electrical conductive connection structure between FPCs according to claim 3, characterized in that: The irregular tin block (6) is formed into a specified shape through a solid engraving process and then adhered to the irregular circuit layer (41) using a sticky resin.

6. The electrical conductive connection structure between FPCs according to claim 3, characterized in that: The irregular tin block consists of 99% tin.

7. The electrical conductive connection structure between FPCs according to claim 3, characterized in that: The heterogeneous tin block (6) is composed of 30% to 99% of tin and 1% to 70% of alloy solder containing other metal components, and the other metal components include silver, copper or indium.

8. The electrical conductive connection structure between FPCs according to claim 3, characterized in that: The shape of the solder column (62) is X-shaped, wherein the angle range in each direction is 50° to 70°. The shape of the solder column (62) also includes but is not limited to a cross shape, a rice shape, and a fishbone shape.

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