Flexible circuit board binding membrane switch structure

Abstract

The utility model relates to electronic component manufacturing technical field, concretely is a kind of flexible circuit board binding membrane switch structure, including flexible circuit board and membrane switch, the end binding area of flexible circuit board is equipped with multiple conductive pads of plum blossom array distribution, the corresponding electrode area of membrane switch is equipped with the contact point matched with conductive pad, segmented conductive adhesive layer is arranged between conductive pad and contact point, segmented conductive adhesive layer is made of multiple independent conductive adhesive islands, and the gap region between adjacent conductive adhesive islands is filled with elastic silica gel buffer layer, and the back of the binding area of flexible circuit board is also attached with a layer of stepped reinforcing sheet.The flexible circuit board binding membrane switch structure effectively disperses the stress concentration when bending or stressed, avoids the direct impact on membrane switch electrode, improves the reliability of connection and the durability of product.

Description

Technical Field

[0001] This utility model relates to the field of electronic component manufacturing technology, specifically to a flexible circuit board bonding membrane switch structure. Background Technology

[0002] Flexible circuit boards (PCBs), due to their thinness, flexibility, and high wiring density, have become indispensable connection components in modern electronic products. In human-machine interface units (HMIs), PCBs are often directly bonded to membrane switches to achieve stable signal transmission and compact structural integration. This integrated bonding method not only simplifies the assembly process but also improves the overall reliability and space utilization of the product.

[0003] In existing technologies, the bonding area between flexible circuit boards and membrane switches is typically achieved using a full-surface or large-area conductive adhesive layer for bonding and conduction. This design presents a significant problem in practical applications: when the flexible circuit board is bent or subjected to external force, stress is directly transmitted to the electrode area of ​​the membrane switch through the rigid adhesive layer. This can easily lead to microcracks or interlayer delamination in the conductive carbon particle layer or silver paste circuitry inside the membrane switch due to localized stress concentration, resulting in reliability issues such as poor contact and button failure. This defect is particularly pronounced under frequent operation or complex mechanical environments. At the same time, the large-area rigid bonding also limits the deformation buffering capacity of the bonding area, making the overall structure less adaptable to dynamic stress and affecting the long-term service life and environmental tolerance of the product. Utility Model Content

[0004] The purpose of this invention is to provide a flexible circuit board bonding membrane switch structure to solve the problems mentioned in the background art, which are caused by the direct transmission of stress due to the large-area rigid bonding between the flexible circuit board and the membrane switch, resulting in damage to the electrode area of ​​the membrane switch, poor contact, and reduced reliability.

[0005] To achieve the above objectives, this utility model provides the following technical solution: a flexible circuit board bonding membrane switch structure, comprising a flexible circuit board and a membrane switch. The end bonding area of ​​the flexible circuit board is provided with a plurality of conductive pads arranged in a quincunx pattern. The corresponding electrode area of ​​the membrane switch is provided with contact points that match the conductive pads. A segmented conductive adhesive layer is provided between the conductive pads and the contact points. The segmented conductive adhesive layer is composed of a plurality of independent conductive adhesive islands, and the gap area between adjacent conductive adhesive islands is filled with an elastic silicone buffer layer. Furthermore, a stepped reinforcing sheet is attached to the back of the bonding area of ​​the flexible circuit board.

[0006] Preferably, the conductive pad has a nickel-gold plating layer on its surface, the contact point is formed by screen printing and high-temperature curing of conductive silver paste, and its top has a micro-convex spherical structure. The conductive adhesive island is made of thermosetting anisotropic conductive adhesive, and its diameter is less than 90% of the minimum circumscribed circle diameter of the area where the conductive pad and the contact point overlap.

[0007] Preferably, the elastic silicone buffer layer is made of two-component room temperature vulcanizing silicone rubber, and its thickness is 1.3 times the height of the conductive rubber island. The elastic silicone buffer layer forms a closed annular dam structure between adjacent conductive rubber islands and wraps the lower half of the sidewall of the conductive rubber island.

[0008] Preferably, the stepped reinforcing sheet is made of polyimide film and copper foil composite, and the thickness of the portion near the end of the flexible circuit board is 1.8 to 2.2 times that of the portion away from the end, and the thickest part of the stepped reinforcing sheet covers the rear half of the bonding area of ​​the flexible circuit board.

[0009] Preferably, the membrane switch has an annular recessed groove around the contact point, and the depth of the annular recessed groove matches the filling depth of the elastic silicone buffer layer.

[0010] Preferably, the flexible circuit board has multiple micro-holes on the substrate in the conductive pad area, and the micro-holes penetrate the substrate and are partially embedded below the conductive pads.

[0011] Compared with existing technologies, the beneficial effects of this invention are as follows: the flexible circuit board bonding membrane switch structure effectively disperses stress concentration during bending or under stress, avoids direct impact on the membrane switch electrodes, and improves connection reliability and product durability. This structure, by setting independent conductive islands in a segmented conductive adhesive layer and an elastic silicone buffer layer filling the gaps, blocks the continuous stress transmission path and provides a buffering and energy absorption effect. Combined with the local reinforcement of the stepped reinforcing sheet on the back of the flexible circuit board, it achieves a mechanical gradient transition in the bending area. Simultaneously, the discrete connection method between the conductive pads and contact points further suppresses local stress accumulation, thereby improving the overall stability and fatigue resistance of the bonding structure under dynamic loads. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of a flexible circuit board bonding membrane switch structure according to the present invention;

[0013] Figure 2 This is a schematic diagram of the flexible circuit board bonding end structure of a flexible circuit board bonding membrane switch structure according to the present invention;

[0014] Figure 3 This is a schematic diagram of the membrane switch bonding end structure of a flexible circuit board bonding membrane switch structure according to the present invention.

[0015] In the figure: 1. Flexible circuit board; 11. Conductive pad; 12. Micro-via; 2. Membrane switch; 21. Contact point; 22. Annular groove; 3. Segmented conductive adhesive layer; 31. Conductive adhesive island; 4. Elastic silicone buffer layer; 5. Stepped reinforcing sheet. Detailed Implementation

[0016] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0017] Please see Figure 1-3This utility model provides a technical solution: a flexible circuit board bonding membrane switch structure, including a flexible circuit board 1 and a membrane switch 2. The end bonding area of ​​the flexible circuit board 1 has multiple conductive pads 11 arranged in a quincunx pattern. The corresponding electrode area of ​​the membrane switch 2 has contact points 21 that match the conductive pads 11. A segmented conductive adhesive layer 3 is provided between the conductive pads 11 and the contact points 21. The segmented conductive adhesive layer 3 is composed of multiple independent conductive adhesive islands 31, each conductive adhesive island 31 correspondingly covering a conductive pad 11 and its paired contact point 21. The gap between adjacent conductive adhesive islands 31 is filled with an elastic silicone buffer layer 4. Furthermore, a stepped reinforcing sheet 5 is attached to the back of the bonding area of ​​the flexible circuit board 1. The end of the stepped reinforcing sheet 5 extends to but does not cover the outer edge of the segmented conductive adhesive layer 3, and its stepped transition section is located inside the bending start line of the flexible circuit board 1. When the flexible circuit board 1 is bent due to assembly or operation, or subjected to external tensile force, the stress is first transmitted to the bonding area. At this time, the stepped reinforcing sheet 5, with its specific stepped transition section located inside the bending start line, provides local reinforcement and stress guidance to the substrate of the flexible circuit board 1, effectively suppressing excessive deformation during bending. When this stress is further transmitted to the bonding interface, since the segmented conductive adhesive layer 3 is composed of multiple independent conductive adhesive islands 31, rather than a traditional large-area continuous adhesive layer, each conductive adhesive island 31 is separated by an elastic silicone buffer layer 4, forming a mechanical... The "island-bridge" structure prevents stress from being continuously transmitted to the electrode area of ​​the membrane switch 2 through the rigid adhesive layer. Instead, it is absorbed and dispersed by the elastic silicone buffer layer 4. Simultaneously, the flexibility and compressibility of the elastic silicone buffer layer 4 allow the conductive islands 31 to undergo minute independent displacements or deformations under stress, preventing stress concentration in a localized area. Furthermore, each conductive island 31 covers only the connection area between a conductive pad 11 and its corresponding contact point 21. While ensuring reliable electrical conduction, this divides the mechanical connection into multiple discrete units, further blocking the lateral propagation path of stress. Combined with the support of the stepped reinforcing sheet 5 on the back of the flexible circuit board 1, a synergistic mechanical response mechanism of "front resistance, middle absorption, and rear support" is formed, thus demonstrating… This significantly reduces the risk of microcracks or interlayer delamination caused by stress concentration at the contact points 21 and their internal circuitry on the membrane switch 2. It solves the problem in existing technologies where rigid bonding across the entire surface leads to direct stress transmission, easily causing poor contact and button failure. This improves the stability and durability of the bonding structure under dynamic operating environments. Furthermore, during manufacturing, the flexible circuit board 1 and membrane switch 2 are aligned using precision alignment equipment, and a hot-pressing process is used to complete the curing and connection of the conductive adhesive islands 31 and the filling and molding of the elastic silicone buffer layer 4 in one step. This ensures a strong and precise interface bond between the functional layers. The conductive pads 11 have a nickel-gold plating, and the contact points 21 are formed by screen printing and high-temperature curing of conductive silver paste, with a slightly convex spherical structure at their top.Furthermore, the conductive adhesive island 31 uses a thermosetting anisotropic conductive adhesive, with a diameter less than 90% of the minimum circumscribed circle diameter of the overlapping area between the conductive pad 11 and the contact point 21. This structure not only enhances the oxidation resistance and welding reliability of the conductive pad 11, but also improves the interfacial bonding strength with the conductive adhesive island 31. The micro-convex spherical structure at the top of the contact point 21 can pierce the oxide film on the surface of the conductive silver paste during the pressing process, which is beneficial for forming a stable electrical contact and provides a certain deformation margin when bonded to the conductive adhesive island 31, alleviating local stress. After curing, the conductive adhesive island 31 possesses good mechanical bonding strength and vertical conductivity, while its diameter control ensures a safe gap between it and the edge of the conductive pad 11. To effectively prevent short-circuit risks caused by thermal expansion or compression misalignment of the colloid, and further enhance stress isolation through a segmented layout, the elastic silicone buffer layer 4 is made of two-component room temperature vulcanized silicone rubber. Its thickness is 1.3 times the height of the conductive island 31. The elastic silicone buffer layer 4 forms a closed annular dam structure between adjacent conductive islands 31 and wraps around the lower half of the sidewall of the conductive island 31. This structure of the elastic silicone buffer layer 4 can effectively absorb and disperse the dynamic stress generated by the flexible circuit board 1 during bending or vibration. Its thickness ensures sufficient buffer space in the vertical direction, allowing the conductive island 31 to have a certain settlement margin when compressed, preventing stress from being directly transmitted to the thinner surface. The contact point 21 of the membrane switch 2, along with the elastic silicone buffer layer 4, not only defines the distribution area of ​​each conductive island 31, preventing lateral flow or fusion during the pressing process and maintaining the independence of the electrical connection, but also enhances the bonding force between the islands and the substrate by wrapping the lower half of the sidewall of the conductive islands 31, suppressing interface peeling. This structure significantly improves the structural integrity and electrical contact stability of the bonding area under repeated deformation conditions. The stepped reinforcing sheet 5 is composed of polyimide film and copper foil. Its thickness near the end of the flexible circuit board 1 is 1.8 to 2.2 times that of the portion away from the end, and the thickest part of the stepped reinforcing sheet 5 covers the rear half of the bonding area of ​​the flexible circuit board 1. The leading edge of the stepped reinforcing sheet 5 is connected to the nearest conductive island 31. With a 0.4mm gap, the stepped reinforcing sheet 5 provides gradient mechanical support to the bonding area of ​​the flexible circuit board 1. The end portion of the stepped reinforcing sheet 5 allows bending stress to be gradually released along the thickness variation area, avoiding abrupt deformation at the bending start line. The thickest section covering the rear half of the bonding area effectively enhances the tensile and bending stiffness of this area, preventing local tearing or pad displacement of the flexible circuit board 1 under tension. At the same time, the leading edge of the stepped reinforcing sheet 5 maintains a gap with the nearest conductive adhesive island 31, ensuring that the end of the stepped reinforcing sheet 5 does not directly cover the conductive connection area, avoiding pressure or stress transmission to the conductive adhesive island 31 and contact point 21 caused by rigid extension, and preserving the stress buffer space of the segmented conductive adhesive layer 3 and the elastic silicone buffer layer 4.This enhances the overall structural strength without compromising the flexibility of the electrical connection interface, significantly improving the reliability and durability of the bonding structure under dynamic operating conditions. The membrane switch 2 has an annular groove 22 around the contact point 21, and the depth of the annular groove 22 matches the filling depth of the elastic silicone buffer layer 4. The inner wall of the annular groove 22 is a 30-degree slope, and the outer wall is a vertical surface, used to define the flow boundary of the elastic silicone buffer layer 4. This structure ensures that the elastic silicone buffer layer 4 is flush with the surface of the membrane switch 2 after curing, avoiding assembly interference caused by colloid protrusions. The inner wall structure of the annular groove 22 facilitates the smooth flow of the elastic silicone buffer layer 4 along the slope during filling, reducing air bubble retention and enhancing the interface bonding strength. Furthermore, this groove structure and the elastic silicone buffer layer 4... The mechanical interlock significantly enhances the shear resistance between the two components, preventing the buffer layer from detaching during long-term vibration or bending. The flexible circuit board 1 has multiple micro-holes 12 on the substrate in the area of ​​the conductive pad 11. These micro-holes 12 penetrate the substrate and are partially embedded below the conductive pad 11. The inner wall of each micro-hole 12 is plated with copper, and its axial direction penetrates the substrate of the flexible circuit board 1, with the opening facing the contact point 21. This structure, with its multiple micro-holes 12 and the plated copper layer on the inner wall, creates multi-point anchoring and three-dimensional conductive connections between the conductive pad 11 and the substrate of the flexible circuit board 1. This significantly improves the adhesion and peel strength of the conductive pad 11. Furthermore, the micro-holes 12 facilitate the removal of air and excess adhesive during the pressing process, ensuring sufficient contact between the conductive adhesive island 31 and the conductive pad 11, thus improving conductivity reliability.

[0018] Working principle: When using this flexible circuit board to bond the membrane switch structure, firstly, the end of the flexible circuit board 1 is fixed to the installation area by the stepped reinforcing piece 5, aligning the stepped transition section of the stepped reinforcing piece 5 with the preset bending start line. Then, the membrane switch 2 is aligned and bonded to the bonding area of ​​the flexible circuit board 1, ensuring that the contact point 21 on the membrane switch 2 is precisely aligned with the conductive pad 11 on the flexible circuit board 1. Simultaneously, the annular recess 22 around the contact point 21 corresponds to the segmented conductive adhesive layer 3 above the conductive pad 11. Then, under the action of a hot-pressing device, the conductive adhesive island 31 is heated and cured, achieving electrical connection between the conductive pad 11 and the contact point 21, while maintaining elasticity. The silicone buffer layer 4 is filled and formed in the annular recessed groove 22, forming a closed dam structure that matches the periphery of the contact point 21. During the hot pressing process, the electroplated copper layer inside the micro-hole 12 is further combined with the conductive pad 11 to complete the three-dimensional conductive anchoring, and finally form a complete bonding structure between the flexible circuit board 1 and the membrane switch 2. During the operation of the equipment, when the flexible circuit board 1 is bent or pulled by external force, the stress is transmitted through the substrate of the flexible circuit board 1 to the stepped reinforcing sheet 5, and then transmitted to the membrane switch 2 through the alternating layout of the segmented conductive adhesive layer 3 and the elastic silicone buffer layer 4. Finally, the contact point 21 receives and responds to the external button action, thereby completing a series of tasks.

[0019] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A flexible circuit board-bonded membrane switch structure, comprising a flexible circuit board (1) and a membrane switch (2), characterized in that: The end bonding area of ​​the flexible circuit board (1) is provided with a plurality of conductive pads (11) arranged in a plum blossom pattern. The corresponding electrode area of ​​the membrane switch (2) is provided with contact points (21) that match the conductive pads (11). A segmented conductive adhesive layer (3) is provided between the conductive pads (11) and the contact points (21). The segmented conductive adhesive layer (3) is composed of a plurality of independent conductive adhesive islands (31). The gap area between adjacent conductive adhesive islands (31) is filled with an elastic silicone buffer layer (4). Furthermore, a stepped reinforcing sheet (5) is attached to the back of the bonding area of ​​the flexible circuit board (1).

2. The flexible circuit board bonding membrane switch structure according to claim 1, characterized in that: The conductive pad (11) has a nickel-gold plating layer on its surface. The contact point (21) is formed by screen printing and high-temperature curing of conductive silver paste. Its top has a micro-convex spherical structure. The conductive adhesive island (31) is made of thermosetting anisotropic conductive adhesive. Its diameter is less than 90% of the minimum circumscribed circle diameter of the overlapping area between the conductive pad (11) and the contact point (21).

3. The flexible circuit board bonded membrane switch structure of claim 1, wherein: The elastic silicone buffer layer (4) is made of two-component room temperature vulcanized silicone rubber, and its thickness is 1.3 times the height of the conductive rubber island (31). The elastic silicone buffer layer (4) forms a closed annular dam structure between adjacent conductive rubber islands (31) and wraps the lower half of the sidewall of the conductive rubber island (31).

4. The flexible circuit board bonded membrane switch structure of claim 1, wherein: The membrane switch (2) has an annular recess (22) around the contact point (21), and the depth of the annular recess (22) matches the filling depth of the elastic silicone buffer layer (4).

5. The flexible circuit board bonded membrane switch structure of claim 1, wherein: The flexible circuit board (1) has multiple micro-holes (12) on the substrate in the area of ​​the conductive pad (11), and the micro-holes (12) penetrate the substrate and are partially embedded below the conductive pad (11).

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