Circuit board assembly

Abstract

The utility model provides a circuit board assembly. The circuit board assembly comprises a flexible circuit board and a reinforcing plate. The reinforcing plate is arranged on one side of the flexible circuit board, the elastic modulus of the reinforcing plate is larger than that of the flexible circuit board, the reinforcing plate has the thickness direction, the reinforcing plate comprises a plurality of reinforcing layers and a plurality of bonding layers, and the reinforcing layers and the bonding layers are alternately stacked in the thickness direction. In every two adjacent reinforcing layers, the reinforcing layer close to the flexible circuit board is defined as a first reinforcing layer, the reinforcing layer far away from the flexible circuit board is defined as a second reinforcing layer, and the section width of the first reinforcing layer is larger than that of the second reinforcing layer in the thickness direction.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of circuit board manufacturing, and in particular to a circuit board assembly. BACKGROUND

[0002] Flexible printed circuit board (FPC) is widely used in the fields of foldable electronic devices, new energy vehicles and medical devices due to its lightweight and bendable characteristics. However, the softness of FPC leads to deformation during surface mount technology (SMT) processing, affecting the mounting accuracy. Therefore, the prior art usually adds a rigid stiffener in the punching area to improve the local rigidity, thereby inhibiting deformation during processing.

[0003] However, the introduction of the stiffener brings new technical problems: during subsequent assembly and transportation, if external force causes the FPC to bend and deform in the stiffener area, due to the significant difference in mechanical properties between the stiffener and the flexible substrate (rigid-flexible interface), the stress concentration phenomenon in the combined area of the two is intensified, which easily causes interface delamination or peripheral material cracking, ultimately affecting product reliability and yield. CONTENT OF THE UTILITY MODEL

[0004] To solve the problems in the background art, the present application provides a circuit board assembly.

[0005] A circuit board assembly includes a flexible circuit board and a reinforcing plate. The reinforcing plate is arranged on one side of the flexible circuit board, the elastic modulus of the reinforcing plate is greater than that of the flexible circuit board, the reinforcing plate has a thickness direction, and the reinforcing plate includes a plurality of reinforcing layers and a plurality of adhesive layers, which are alternately stacked along the thickness direction. In the two adjacent reinforcing layers, the one close to the flexible circuit board is defined as the first reinforcing layer, and the one away from the flexible circuit board is defined as the second reinforcing layer. The cross-sectional width of the first reinforcing layer is greater than that of the second reinforcing layer along the thickness direction.

[0006] The circuit board assembly provided by the present application effectively solves the technical problem of stress concentration in the combined area of the traditional rigid stiffener and the flexible substrate through the multi-layer stepped reinforcing structure and the interface stress buffer design. Specifically, the gradual stiffness transition design (the cross-sectional width of the first reinforcing layer is greater than that of the second reinforcing layer) makes the stress gradually release along the thickness direction, avoiding the formation of stress discontinuity point at the rigid-flexible interface; the multi-layer adhesive layer as a modulus buffer layer helps to alleviate the difference in mechanical properties between the rigid reinforcing plate and the flexible circuit board, reducing the risk of interface delamination. At the same time, the gradient stiffness distribution allows the reinforcing area to deform cooperatively with the flexible substrate when bending, reducing the crack propagation caused by local stress concentration. In addition, the multi-layer interface structure increases the bonding area, improves the interface bonding strength, and inhibits the delamination trend.

[0007] The application optimizes dynamic mechanical response through a flexible-rigid cooperative deformation mechanism while maintaining the required rigidity of the piece assembly area, balances processing reliability and long-term use performance, and provides a more stable structural solution for the field of folding electronic devices and the like. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 A cross-sectional schematic view of a circuit board assembly according to an embodiment of the application is provided.

[0009] Figure 2 A cross-sectional schematic view of a flexible circuit board of a circuit board assembly according to an embodiment of the application is provided. Figure 1

[0010] A cross-sectional schematic view of a reinforcing plate and a connecting layer of a circuit board assembly according to an embodiment of the application is provided. Figure 3 Figure 1 A cross-sectional schematic view of a reinforcing plate and a connecting layer of a circuit board assembly according to an embodiment of the application is provided.

[0011] MAIN ELEMENT SYMBOL DESCRIPTION

[0012] Circuit board assembly: 100; flexible circuit board: 10; reinforcing plate: 20; connecting layer: 30; core plate: 11; adhesive layer: 12; insulating layer: 13; window: 14; reinforcing layer: 21; first reinforcing layer: 211; second reinforcing layer: 212; adhesive layer: 22; first adhesive layer: 221; second adhesive layer: 222; slot: 25; thickness direction: A; depth: S; thickness: H; distance: D1, D2; width: W1, W2, W3, W4, W5. DETAILED DESCRIPTION

[0013] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only some of the embodiments of the application, not all the embodiments.

[0014] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element or can be present with a middle element. When an element is considered to be "provided on" another element, it can be directly provided on the other element or can be present with a middle element.

[0015] Please refer to Figure 1 An embodiment of the application provides a circuit board assembly 100 to solve the deformation problem in the process of surface mounted technology (SMT) processing and subsequent assembly, and to improve the processing precision and the reliability of the bonding interface.

[0016] ​The circuit board assembly 100 comprises a flexible circuit board 10, a reinforcing plate 20 and a connecting layer 30. The reinforcing plate 20 is arranged on one side of the flexible circuit board 10. The connecting layer 30 is connected between the flexible circuit board 10 and the reinforcing plate 20. The elastic modulus of the reinforcing plate 20 is greater than that of the flexible circuit board 10, thereby providing structural reinforcement for the flexible circuit board 10 to facilitate reducing bending of the flexible circuit board 10.

[0017] Referring to Figure 1 and Figure 2 In the embodiment, the flexible circuit board 10 comprises a core plate 11, an adhesive layer 12 and an insulating layer 13. The adhesive layer 12 is arranged on the opposite outer sides of the core plate 11, respectively. The insulating layer 13 is arranged on the side of the adhesive layer 12 away from the core plate 11. That is, the opposite sides of the core plate 11 are adhered by the adhesive layer 12 and the insulating layer 13, respectively.

[0018] The core plate 11 comprises a conductive circuit 111 for realizing transmission of electrical signals and circuit connection, and providing overall support structure. The adhesive layer 12 is arranged on the opposite outer sides of the core plate 11, respectively, for tightly adhering the core plate 11 and the insulating layer 13 to prevent interface delamination and falling off. The insulating layer 13 is arranged on the side of the adhesive layer 12 away from the core plate 11, for protecting the core plate 11 and isolating external electrical interference. The reinforcing plate 20 is arranged on the side of the insulating layer 13 of the flexible circuit board 10 away from the adhesive layer 12.

[0019] In the embodiment, the material of the adhesive layer 12 is one of epoxy resin, acrylic and polyimide glue. The insulating layer 13 comprises one of polyimide, polyester and epoxy resin. Preferably, the material of the adhesive layer 12 is epoxy resin, and the material of the insulating layer 13 is polyimide.

[0020] In the embodiment, the side of the flexible circuit board 10 away from the reinforcing plate 20 can be provided with a window 14. The window 14 penetrates the insulating layer 13 and the adhesive layer 12 along the thickness direction A, and part of the core plate 11 is exposed at the bottom of the window 14. The orthographic projection of the window 14 in the thickness direction A is located in the reinforcing plate 20. Through the design of the window 14, the degree of mechanical mismatch between the core plate 11 and the reinforcing plate 20 can be effectively reduced when the flexible circuit board 10 is bent or subjected to external force, thereby improving the bending resistance of the overall structure of the flexible circuit board 10.

[0021] Referring to Figure 1 and Figure 3In the present embodiment, the reinforcing plate 20 comprises a plurality of reinforcing layers 21 and a plurality of adhesive layers 22. Along the thickness direction A, the reinforcing layers 21 and the adhesive layers 22 are alternately stacked, and the reinforcing plate 20 has a substantially inverted trapezoidal or multi-stage stepped structure as viewed in the overall cross section.

[0022] Specifically, among the two adjacent reinforcing layers 21, the one closer to the flexible circuit board 10 is defined as the first reinforcing layer 211, and the one farther from the flexible circuit board 10 is defined as the second reinforcing layer 212. The cross-sectional width W1 of the first reinforcing layer 211 is greater than the cross-sectional width W2 of the second reinforcing layer 212. Along the thickness direction A, the second reinforcing layer 212 is orthogonally projected within the first reinforcing layer 211, so that the reinforcing plate 20 has a stepped structure with a narrow bottom and a wide top.

[0023] In the present embodiment, as viewed along the thickness direction A, the opposite ends of the first reinforcing layer 211 protrude beyond the opposite ends of the second reinforcing layer 212. Further, the second reinforcing layer 212 can be centrally positioned relative to the first reinforcing layer 211, so that the extensions of the two ends of the first reinforcing layer 211 can form wider transition zones at the edges, thereby reducing stress concentration under bending and impact loads. The adhesive layer 22 between the first reinforcing layer 211 and the second reinforcing layer 212 has opposite ends protruding beyond the opposite ends of the second reinforcing layer 212, and the opposite ends of the first reinforcing layer 211 protrude beyond the opposite ends of the adhesive layer 22, so as to provide sufficient adhesive coverage.

[0024] In the present embodiment, the distance D1 by which the opposite ends of the adhesive layer 22 protrude beyond the opposite ends of the second reinforcing layer 212 is 0.5-0.8 mm, and the distance D2 by which the opposite ends of the first reinforcing layer 211 protrude beyond the opposite ends of the adhesive layer 22 is 0.5-1.0 mm. The above quantitative parameters can take into account the actual manufacturing tolerances and the mechanical performance requirements, so as to ensure that there is sufficient adhesive area at the edges of the reinforcing plate 20, and there is no excessive glue overflow that affects the process quality.

[0025] In the present embodiment, among the adjacent adhesive layers 22, the one closer to the flexible circuit board 10 is defined as the first adhesive layer 221, and the one farther from the flexible circuit board 10 is defined as the second adhesive layer 222. Along the thickness direction A, the cross-sectional width W3 of the first adhesive layer 221 is greater than the cross-sectional width W4 of the second adhesive layer 222. Thus, the overall cross section of the reinforcing plate 20 has a stepped structure. The stepped cross section thus designed allows the reinforcing plate 20 to meet the local reinforcement requirements while effectively dispersing interlayer stress and reducing the risk of cracking at the rigid-flex interface.

[0026] In the embodiment, the first reinforcing layer 211 is provided with a slot 25 on the side facing the second reinforcing layer 212. The depth S of the slot 25 is greater than half of the thickness H of the first reinforcing layer 211 and less than two-thirds of the thickness H of the first reinforcing layer 211, and the cross-sectional width W5 of the slot 25 can be in the range of 0.3mm to 0.5mm. By filling part of the adhesive layer 22 in the slot 25 of the reinforcing plate 20, a double effect of local buffering and limiting glue overflow can be formed in the area. On the one hand, the adhesive layer 22 forms an area with a larger thickness at the slot 25, which can slightly reduce the rigidity of the area and absorb certain bending stress; on the other hand, it can also avoid too much adhesive layer 22 material (such as glue) overflowing outside the plate and affecting the process quality.

[0027] In the embodiment, the reinforcing layer 21 can be made of polyimide, which has high elastic modulus, excellent high-temperature resistance and fatigue resistance, and can effectively improve the local rigidity in the SMT processing process. At the same time, the adhesive layer 22 can be made of materials such as epoxy resin or acrylic glue, which are compatible with polyimide and flexible circuit board 10, to meet the requirements of high-temperature reflow soldering and long-term reliability. Through the design of the slot 25 and the multi-layer structure, the stress in the "rigid-soft" transition area between the reinforcing plate 20 and the flexible circuit board 10 is significantly reduced, and the stable combination can be maintained in the subsequent bending or vibration environment.

[0028] The material of the adhesive layer 22 includes epoxy resin, acrylic glue or polyurethane glue, wherein the material of the connecting layer 30 is the same as that of the adhesive layer 22 to ensure the consistency of the interface combination.

[0029] The circuit board assembly 100 provided in the embodiment uses a multi-layer stepped reinforcing plate 20 and cooperates with the adhesive layer 22, the glue limiting slot 25 and other technical means to ensure that the flexible circuit board 10 has sufficient rigidity in a specific area to meet the SMT mounting precision requirement, effectively reduces the risk of interface delamination or peripheral material cracking in the subsequent assembly and use process, and improves the overall reliability and service life of the circuit board assembly 100.

[0030] It should be understood that the present application is not limited to the details of the above-described embodiments, and for those skilled in the art, equivalent changes or substitutions can be made to the specific structures or parameters without departing from the technical idea of the present application, which should be regarded as the protection scope of the present application.

Claims

1. A circuit board assembly, characterized in that, include: Flexible circuit board A reinforcing plate is disposed on one side of the flexible circuit board. The elastic modulus of the reinforcing plate is greater than that of the flexible circuit board. The reinforcing plate has a thickness direction and includes multiple reinforcing layers and multiple adhesive layers, which are alternately stacked along the thickness direction. In two adjacent reinforcing layers, the one closer to the flexible circuit board is defined as the first reinforcing layer, and the one farther away from the flexible circuit board is defined as the second reinforcing layer. Along the thickness direction, the cross-sectional width of the first reinforcing layer is greater than the cross-sectional width of the second reinforcing layer.

2. The circuit board assembly as claimed in claim 1, characterized in that, The two ends of the first reinforcing layer protrude from the two ends of the second reinforcing layer, respectively.

3. The circuit board assembly as described in claim 2, characterized in that, An adhesive layer is provided between the first reinforcing layer and the second reinforcing layer. The two ends of the adhesive layer protrude from the two ends of the second reinforcing layer, and the two ends of the first reinforcing layer protrude from the two ends of the adhesive layer.

4. The circuit board assembly as claimed in claim 3, characterized in that, The distance between the two ends of the adhesive layer protruding from the second reinforcing layer is 0.5 mm to 0.8 mm, and the distance between the two ends of the first reinforcing layer protruding from the two ends of the adhesive layer is 0.5 mm to 1.0 mm.

5. The circuit board assembly as claimed in claim 3, characterized in that, In two adjacent adhesive layers, the one closer to the flexible circuit board is defined as the first adhesive layer, and the one farther away from the flexible circuit board is defined as the second adhesive layer. Along the thickness direction, the cross-sectional width of the first adhesive layer is greater than the cross-sectional width of the second adhesive layer.

6. The circuit board assembly as claimed in claim 5, characterized in that, The first reinforcing layer has a groove on the side facing the second reinforcing layer, and the adhesive layer connecting the first and second reinforcing layers is partially filled into the groove.

7. The circuit board assembly as claimed in claim 6, characterized in that, Along the thickness direction, the depth of the groove is greater than half of the first reinforcing layer and less than two-thirds of the reinforcing layer, and the cross-sectional width of the groove is 0.3 mm to 0.5 mm.

8. The circuit board assembly as claimed in claim 1, characterized in that, The flexible circuit board includes a core board, an adhesive layer, and an insulating layer. The adhesive layer is disposed on two opposite outer sides of the core board, and the insulating layer is disposed on two opposite outer sides of the adhesive layer away from the core board. The reinforcing plate is disposed on the side of the insulating layer away from the adhesive layer.

9. The circuit board assembly as claimed in claim 8, characterized in that, The flexible circuit board has a window on the side opposite to the reinforcing plate. The window penetrates the insulating layer and the adhesive layer, and part of the core board is exposed at the bottom of the window. The window is provided corresponding to the reinforcing plate along the thickness direction.

10. The circuit board assembly as claimed in claim 1, characterized in that, The reinforcing layer is made of polyimide, and the adhesive layer is made of epoxy resin.

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