Folding circuit board and preparation method thereof

Abstract

The invention provides a folding circuit board. The folding circuit board comprises a substrate and an insulating protection layer, the substrate comprises a base material layer and a conductive circuit layer which are stacked. The insulating protection layer covers part of the conductive circuit layer and is provided with a window. The substrate comprises a first area, a second area and a third area connected between the first area and the second area. The first area is arranged on one side, in the first direction, of the second area in a bent mode through the third area. The conductive circuit layer comprises a first bonding pad located in the first area and a second bonding pad located in the second area. The first bonding pad comprises a first surface, the second bonding pad comprises a second surface, and the first surface and the second surface are arranged away from the substrate layer and are exposed out of the window. The second surface is welded to the first surface. According to the folding circuit board provided by the invention, the problem of stress concentration can be solved, so that the reliability of the folding circuit board can be improved. The invention also provides a preparation method of the folding circuit board.

Description

Technical Field

[0001] The present application relates to the field of foldable circuit board processing, and in particular to a foldable circuit board and a preparation method thereof. Background Art

[0002] A circuit board generally includes a substrate layer and a conductive circuit layer. When a foldable circuit board is to be prepared, an adhesive layer is generally applied to the circuit board and the circuit board is folded, and then pressed so that the adhesive layer adheres to the folded circuit board. However, the adhesive layer is prone to overflow after pressing, and stress concentration occurs at the bending part of the circuit board, thereby reducing the reliability of the foldable circuit board. Summary of the invention

[0003] In view of this, the present application provides a foldable circuit board that is beneficial for solving the stress concentration problem, so as to improve the reliability of the foldable circuit board.

[0004] In addition, the present application also provides a method for preparing the circuit board.

[0005] The present application provides a foldable circuit board, comprising a substrate and an insulating protective layer. The substrate comprises a base material layer and a conductive circuit layer stacked along a first direction. The insulating protective layer covers a portion of the conductive circuit layer, and the insulating protective layer is provided with a window. The substrate comprises a first region, a second region, and a third region connected between the first region and the second region, and the first region is bent through the third region and arranged on one side of the second region in the first direction. The conductive circuit layer comprises a first pad located in the first region and a second pad located in the second region, the first pad comprises a first surface, the second pad comprises a second surface, the first surface and the second surface are both arranged away from the base material layer and are both exposed at the window, and the second surface is welded to the first surface.

[0006] The present application also provides a method for preparing a foldable circuit board, comprising the following steps: providing a substrate, the substrate comprising a base material layer and a conductive circuit layer stacked along a first direction, the substrate comprising a first area, a second area and a third area connected between the first area and the second area, the conductive circuit layer comprising a first solder pad located in the first area and a second solder pad located in the second area, the first solder pad comprising a first surface, the second solder pad comprising a second surface, and the first surface and the second surface are both arranged away from the base material layer; forming an insulating protective layer covering a portion of the conductive circuit layer, the insulating protective layer being provided with a window, the first surface and the second surface being both exposed from the window; bending the first area around the third area and stacking it on one side of the second area in the first direction, so that the first surface and the second surface are stacked in the first direction; welding the first surface and the second surface.

[0007] In the present application, the first pad of the first area is welded to the second pad of the second area to form a foldable circuit board, and the welding site avoids the third area, the junction between the first area and the third area, and the junction between the second area and the third area. In addition, the foldable circuit board provided by the present application is shaped after the first pad and the second pad are welded, rather than being shaped by the whole surface bonding between the first area and the second area, so the rigid constraint force of the third area after the welding site is formed can be weakened (the closer the welding site is to the third area, the stronger the rigid constraint force of the third area). Thus, the foldable circuit board provided by the present application can reduce the stress concentration at the bend caused by welding. Therefore, the foldable circuit board of the present application can solve the problem of stress concentration to improve the reliability of the foldable circuit board. At the same time, the present application shapes the foldable circuit board by welding the pads, which is also beneficial to the heat conduction inside the circuit board. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 A top view of a substrate with an insulating protective layer provided in one embodiment of the present application;

[0009] Figure 2 for Figure 1 A cross-sectional view of the substrate along V-V is shown;

[0010] Figure 3 for Figure 1 A schematic diagram of a shape combination of a first surface of a first pad and a second surface of a second pad on a substrate shown;

[0011] Figure 4 For Figure 2 A cross-sectional view showing a substrate in which an anti-oxidation layer is formed on the first surface and first side surface of a first pad and the second surface and second side surface of a second pad;

[0012] Figure 5 For the general Figure 4 A cross-sectional view of the substrate after bending shown;

[0013] Figure 6 A cross-sectional view of a foldable circuit board provided in one embodiment of the present application;

[0014] Figure 7 A top view of a foldable circuit board provided in one embodiment of the present application;

[0015] Figure 8 A cross-sectional view of a substrate covered with an insulating protective layer and a welding layer provided in another embodiment of the present application;

[0016] Fig. 9 A cross-sectional view of a foldable circuit board provided in accordance with another embodiment of the present application.

[0017] Main component symbols

[0018] Folding circuit board 100, 200 substrate 10

[0019] Base material layer 11 Conductive circuit layer 12

[0020] First pad 121 First surface 1211

[0021] First side surface 1212 Second pad 122

[0022] Second side 1221 Second side 1222

[0023] First area 101 Second area 102

[0024] Third region 103 Insulation protection layer 20

[0025] Window 21 Anti-oxidation layer 30

[0026] Positioning hole 104 Welding layer 40

[0027] First direction X Second direction Y

[0028] The third direction Z

[0029] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0031] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. When an element is considered to be "set on" another element, it may be directly set on the other element or there may be a central element at the same time.

[0032] Embodiment 1:

[0033] An embodiment of the present application provides a method for preparing a foldable circuit board 100. According to different requirements, the order of the steps of the preparation method can be changed, and some steps can be omitted or combined. The preparation method includes the following steps:

[0034] Step 1: Reference Figure 1 and Figure 2, providing a substrate 10. The substrate 10 includes a substrate layer 11 and a conductive circuit layer 12 stacked along a first direction X. In some embodiments, the number of the conductive circuit layers 12 is two. The two conductive circuit layers 12 are respectively arranged on two opposite surfaces of the substrate layer 11. The conductive circuit layer 12 includes a first pad 121 and a second pad 122. In this embodiment, the two conductive circuit layers 12 each include a first pad 121 and a second pad 122. The first pad 121 includes a first surface 1211 disposed away from the substrate layer 11 and a first side surface 1212 respectively connected to the substrate layer 11 and the first surface 1211. The second pad 122 includes a second surface 1221 disposed away from the substrate layer 11 and a second side surface 1222 connected to the substrate layer 11 and the second surface 1221. Exemplarily, the number of the first pads 121 may be two, three, one or at least three. Correspondingly, the number of the second pads 122 may also be two, three, one or at least three. Exemplarily, the material of the substrate layer 11 may be one of polyimide, liquid crystal polymer, polyethylene terephthalate or epoxy resin. The material of the conductive circuit layer 12 may be copper. The substrate 10 may be a single-layer conductive plate or a multi-layer conductive plate. The substrate 10 includes a first region 101, a second region 102, and a third region 103 connected between the first region 101 and the second region 102. The first pad 121 is located in the first region 101. The second pad 122 is located in the second region 102. The third region 103 may be bent in a subsequent step, that is, the first region 101 may be bent around the third region 103 and then overlapped on one side of the second region 102 in the first direction X, so that a first pad 121 overlaps a second pad 122 in the first direction X. Exemplarily, the conductive circuit layer 12 may be prepared by an additive method, a subtractive method, or a semi-additive method.

[0035] In some embodiments, the number of the first region 101 and the number of the third region 103 are both two. Each first region 101 is connected to the second region 102 through a third region 103. A first pad 121 is provided at one end of each first region 101 connected to the third region 103. A second pad 122 is provided at both ends of the second region 102. Specifically, a third region 103 is connected to an end of a first region 101 and an end of a second region 102. The two first regions 101 are arranged at intervals along a second direction Y perpendicular to the first direction X and are both located on the same side of the second region 102. The angle between the third region 103 and the second direction Y is an acute angle. The shape of the substrate 10 is conducive to shortening the volume occupied by the substrate 10 in the second direction Y, thereby facilitating the processing of a substrate 10 with a longer extension length.

[0036] In some embodiments, further, the two first regions 101 are parallel to each other along the second direction Y. The parallel first regions 101 can further reduce the volume occupied by the substrate 10 in the second direction Y. In some embodiments, the two first regions 101 extend along the third direction Z. The third direction Z is perpendicular to the first direction X and the second direction Y. The angle between the third region 103 and the second direction Y can be 45 degrees.

[0037] In another embodiment, the substrate 10 may extend along the second direction Y in a unidirectional manner.

[0038] Reference Figure 2 , forming an insulating protective layer 20 covering part of the conductive circuit layer 12. In the present embodiment, an insulating protective layer 20 is formed on a conductive circuit layer 12, and each insulating protective layer 20 is provided with a window 21. The first side 1211 of the first pad 121 and the second side 1221 of the second pad 122 of each conductive circuit layer 12 are both exposed at the window 21. In some embodiments, the first side 1212 of the first pad 121 of each conductive circuit layer 12 and the second side 1222 of the second pad 122 of the conductive circuit layer 12 are also exposed at the window 21. Exemplarily, the insulating protective layer 20 provided with the window 21 can be formed by selectively printing solder mask ink.

[0039] Reference Figure 1 In some embodiments, a surface of the insulating protective layer 20 facing away from the substrate layer 11 may be provided with a positioning hole 104. The positioning hole 104 is located at one end of the first region 101 away from the first pad 121 and penetrates the substrate 10 along the first direction X. The positioning hole 104 is provided to facilitate the positioning and fixing of the substrate 10. When the substrate 10 is processed, the positioning block on the operating table can be inserted into the positioning hole 104 to fix the substrate 10.

[0040] Reference Figure 1 and Figure 3 In some embodiments, when viewed along the first direction X, the shapes of the first surface 1211 and the second surface 1221 are a combination of a trapezoid and an inverted trapezoid, a combination of a square and a rectangle, a combination of cross-placed quadrilaterals, or a combination of a circle and an ellipse. Figure 3 (a), the first surface 1211 can be a square, and the corresponding second surface 1221 can be a rectangle. Conversely, when the first surface 1211 is a rectangle, the second surface 1221 is a square. At this time, the shape setting of the first surface 1211 and the second surface 1221 is conducive to the first surface 1211 and the second surface 1221 having a good contact area in the subsequent welding steps, thereby improving the welding stability between the first surface 1211 and the second surface 1221. The length of the long side of the above-mentioned rectangle can be greater than the length of the square. Or, refer to Figure 3(b), the first surface 1211 may be circular, and the corresponding second surface 1221 may be elliptical. Conversely, when the first surface 1211 is elliptical, the second surface 1221 may be circular. The long diameter of the ellipse may be greater than the diameter of the circle. In this case, the shape of the first surface 1211 and the second surface 1221 is conducive to improving the stability and tensile strength of the first surface 1211 and the second surface 1221 after welding. Alternatively, refer to Figure 3 (c), both the first surface 1211 and the second surface 1221 can be inclined quadrilaterals (e.g., rectangles or parallelograms), and the first surface 1211 and the second surface 1221 can form a cross pattern with an acute angle (e.g., a 45-degree angle) after being stacked. In this case, the shape of the first surface 1211 and the second surface 1221 is conducive to improving the ability of the first surface 1211 and the second surface 1221 to resist tensile or shearing after welding. Or, refer to Figure 3 (d), the first surface 1211 may be a trapezoid (e.g., an isosceles trapezoid), and the corresponding second surface 1221 may be an inverted trapezoid (e.g., an inverted isosceles trapezoid). The side lengths and angles between the trapezoid and the inverted trapezoid may be completely equal. The shape setting of the first surface 1211 and the second surface 1221 can ensure that there is a relatively large contact area between the first surface 1211 and the second surface 1221, thereby improving the welding stability between the first surface 1211 and the second surface 1221 in subsequent steps.

[0041] In another embodiment, the first surface 1211 and the second surface 1221 may have the same shape and the same size. For example, the first surface 1211 and the second surface 1221 may be a combination of the same rectangular, square, polygonal or circular shapes.

[0042] In this embodiment, both the first surface 1211 and the second surface 1221 are continuous planes. In another embodiment, a first opening (not shown) may be provided in the first pad 121, and the first opening may pass through the first surface 1211. A second opening (not shown) may be provided in the second pad 122, and the second opening may pass through the second surface 1221.

[0043] Step 2: Reference Figure 4 , an anti-oxidation layer 30 covering the first surface 1211, the first side surface 1212, the second surface 1221 and the second side surface 1222 is formed in the window 21. Exemplarily, the anti-oxidation layer 30 (e.g., a gold layer) can be formed by chemical plating. The anti-oxidation layer 30 is formed on the first pad 121 and the second pad 122 to prevent the first pad 121 and the second pad 122 from being excessively oxidized in the air.

[0044] In another embodiment, step 2 may be omitted.

[0045] Step 3: Reference Figure 5 The first region 101 is bent around the third region 103 and then overlapped on one side of the second region 102 in the first direction X, so that the first surface 1211 and the second surface 1221 are overlapped in the first direction X.

[0046] In this embodiment, the two first regions 101 are respectively overlapped on two opposite sides of the second region 102 in the first direction X.

[0047] Step 4: Reference Figure 6 , the overlapping area of ​​the first pad 121 and the second pad 122 can be welded by a spot welder, so that the second surface 1221 is welded to the first surface 1211 by metal-metal bonding, so as to improve the connection stability between the first pad 121 and the second pad 122. The spot welder can be an ultrasonic spot welder (the sound wave frequency can be a value of 15kHz to 20kHz) or a high-frequency spot welder (the sound wave frequency can be greater than 100kHz). In this embodiment, a high-frequency spot welder is used to heat and weld the first surface 1211 and the second surface 1221.

[0048] In some embodiments, after the above welding, the first pad 121 of a first region 101 is welded to the second pad 122 on one side of the substrate layer 11, and the first pad 121 of another first region 101 is welded to the second pad 122 on the other side of the substrate layer 11, so as to obtain a foldable circuit board 100 with a three-layer stacking structure (see Figure 7 ), so that the size of the foldable circuit board 100 in the second direction Y can be reduced.

[0049] In some embodiments, after the welding, the projection of the second region 102 in the first direction X is located within the range of each first region 101 .

[0050] In another embodiment, when only one conductive circuit layer 12 is provided, two first regions 101 may be stacked on the same side of the second region 102 to obtain a circuit board with a two-layer stacked structure, thereby reducing the size of the foldable circuit board 100 in the first direction X.

[0051] In some embodiments, during the welding process of the first solder pad 121 and the second solder pad 122, the anti-oxidation layer 30 disposed on the first surface 1211 and the second surface 1221 is removed to obtain the foldable circuit board 100. The anti-oxidation layer disposed on the first surface 1211 and the second surface 1221 can be removed by melting (high frequency spot welding) or friction (ultrasonic spot welding).

[0052] Embodiment 2:

[0053] Reference Figure 6In one embodiment of the present application, a foldable circuit board 100 is provided. The foldable circuit board 100 can be prepared by the method of embodiment 1. The foldable circuit board 100 includes a substrate 10 and an insulating protective layer 20. The substrate 10 includes a base material layer 11 and a conductive circuit layer 12 stacked along a first direction X. The substrate 10 can be a single-layer conductive plate or a multi-layer conductive plate. In some embodiments, the number of the conductive circuit layers 12 is two. The two conductive circuit layers 12 are respectively arranged on two opposite surfaces of the base material layer 11. Figure 1 , the substrate 10 includes a first area 101, a second area 102, and a third area 103 connected between the first area 101 and the second area 102. Each conductive circuit layer 12 includes a first pad 121 located in the first area 101 and a second pad 122 located in the second area 102. The first pad 121 includes a first surface 1211 disposed away from the substrate layer 11 and a first side surface 1212 connected to the substrate layer 11 and the first surface 1211. The second pad 122 includes a second surface 1221 disposed away from the substrate layer 11 and a second side surface 1222 connected to the substrate layer 11 and the second surface 1221. Exemplarily, the number of the first pads 121 may be two, three, one or at least three. Correspondingly, the number of the second pads 122 may also be two, three, one or at least three. The insulating protective layer 20 covers part of the conductive circuit layer 12. The insulating protective layer 20 is provided with a window 21. The first surface 1211 and the second surface 1221 are both exposed at the window 21. In some embodiments, both the first side surface 1212 and the second side surface 1222 are also exposed in the window 21 . The first region 101 is bent around the third region 103 and overlapped on one side of the second region 102 in the first direction X. The second surface 1221 is welded to the first surface 1211 .

[0054] In the present application, the first pad 121 of the first area 101 is welded to the second pad 122 of the second area 102 to form the foldable circuit board 100, and the welding site avoids the third area 103, the junction between the first area 101 and the third area 103, and the junction between the second area 102 and the third area 103. And the foldable circuit board 100 provided in the present application is shaped after the first pad 121 and the second pad 122 are welded, not shaped by the whole surface bonding between the first area 101 and the second area 102, so it can weaken the rigid constraint force of the third area 103 after the welding site is formed (the closer the welding site is to the third area 103, the stronger the rigid constraint force of the third area 103). Therefore, the foldable circuit board 100 provided in the present application can reduce the stress concentration at the bend caused by welding. Therefore, the foldable circuit board 100 of the present application can solve the problem of stress concentration to improve the reliability of the foldable circuit board 100. At the same time, the present application shapes the foldable circuit board 100 by means of pad welding, which is also beneficial to the heat conduction inside the foldable circuit board.

[0055] In some embodiments, in conjunction with reference Figure 1 , the number of the first area 101 and the number of the third area 103 are both two. Each first area 101 is connected to the second area 102 through a third area 103. A first pad 121 is provided at one end of each first area 101 connected to the third area 103. A second pad 122 is provided at both ends of the second area 102. Before the substrate 10 is bent, the two first areas 101 can be arranged at intervals along the second direction Y perpendicular to the first direction X and are both located on the same side of the second area 102. Optionally, the two first areas 101 extend along the third direction Z. The third direction Z is perpendicular to the first direction X and the second direction Y. The angle between the third area 103 and the second direction Y is an acute angle. Optionally, the angle between the third area 103 and the second direction Y can be 45 degrees. In the foldable circuit board 100, the first pad 121 of a first area 101 is welded to the second pad 122 on one side of the substrate layer 11. The first pad 121 of another first area 101 is welded to the second pad 122 on the other side of the substrate layer 11. The first region 101 is overlapped on two opposite sides of the second region 102 , which is beneficial to reducing the size of the foldable circuit board 100 in the second direction Y.

[0056] In another embodiment, in another embodiment, the two first regions 101 may be stacked on the same side of the second region 102 to reduce the size of the folded circuit board 100 in the first direction X.

[0057] In some embodiments, the projection of the second region 102 in the first direction X is located within the range of each first region 101 (see Figure 7 ).

[0058] In some embodiments, reference Figure 1 and Figure 3 Before the substrate 10 is bent, when viewed along the first direction X, the shapes of the first surface 1211 and the second surface 1221 are a combination of a trapezoid and an inverted trapezoid, a combination of a square and a rectangle, a combination of cross-placed quadrilaterals, or a combination of a circle and an ellipse. Figure 3 (a), the first surface 1211 may be a square, and the corresponding second surface 1221 may be a rectangle. Conversely, when the first surface 1211 is a rectangle, the second surface 1221 may be a square. The length of the long side of the rectangle may be greater than the side length of the square. At this time, the shape setting of the first surface 1211 and the second surface 1221 is conducive to the first surface 1211 and the second surface 1221 having a good contact area in the subsequent welding steps, thereby improving the welding stability between the first surface 1211 and the second surface 1221. Alternatively, refer to Figure 3 (b), the first surface 1211 may be circular, and the corresponding second surface 1221 may be elliptical. Conversely, when the first surface 1211 is elliptical, the second surface 1221 may be circular. The long diameter of the ellipse may be greater than the diameter of the circle. In this case, the shape of the first surface 1211 and the second surface 1221 is conducive to improving the stability and tensile strength of the first surface 1211 and the second surface 1221 after welding. Alternatively, refer to Figure 3 (c), both the first surface 1211 and the second surface 1221 can be inclined quadrilaterals (e.g., rectangles or parallelograms), and the first surface 1211 and the second surface 1221 can form a cross pattern with an acute angle (e.g., a 45-degree angle) after being stacked. In this case, the shape of the first surface 1211 and the second surface 1221 is conducive to improving the ability of the first surface 1211 and the second surface 1221 to resist tensile or shearing after welding. Or, refer to Figure 3 (d), the first surface 1211 may be a trapezoid (e.g., an isosceles trapezoid), and the corresponding second surface 1221 may be an inverted trapezoid (e.g., an inverted isosceles trapezoid). The lengths of the sides and the angles between the trapezoid and the inverted trapezoid may be completely equal. The shape setting of the first surface 1211 and the second surface 1221 can improve the welding stability between the first surface 1211 and the second surface 1221.

[0059] In another embodiment, the first surface 1211 and the second surface 1221 may be of the same shape and of the same size. For example, the first surface 1211 and the second surface 1221 may be a combination of a rectangular, a square, a polygon, or a circle. The first surface 1211 and the second surface 1221 have the same shape, which facilitates the molding and preparation of the first pad 121 and the second pad 122.

[0060] In some embodiments, reference Figure 6 The foldable circuit board 100 further includes an anti-oxidation layer 30 . The anti-oxidation layer 30 covers the first side surface 1212 and the second side surface 1222 .

[0061] Embodiment 3:

[0062] An embodiment of the present application also provides a method for preparing a foldable circuit board 200. The difference from the first embodiment is that the substrate 10 includes a conductive circuit layer 12. In step 2, a welding layer 40 (see FIG. 1 ) covering the first surface 1211, the first side surface 1212, the second surface 1221 and the second side surface 1222 is formed in the opening 21. Figure 8 In step 4, the first pad 121 and the second pad 122 are connected by the soldering layer 40, rather than soldering the first pad 121 to the second pad 122 (refer to Fig. 9 ).

[0063] In another embodiment, the substrate 10 may also include two conductive circuit layers 12 , and the two conductive circuit layers 12 are respectively disposed on two opposite surfaces of the base material layer 11 .

[0064] The foldable circuit board 200 provided in this embodiment can also solve the problems of stress concentration and glue overflow.

[0065] Since the materials of the elements in Embodiment 2 and Embodiment 3 are the same as those of the corresponding elements in Embodiment 1, they will not be described in detail.

[0066] The above description is only an optimized specific implementation of the present application, but it cannot be limited to this implementation in the actual application process. For ordinary technicians in this field, other variations and changes made according to the technical concept of the present application should all fall within the protection scope of the present application.

Claims

1. A foldable circuit board, comprising a substrate and an insulating protective layer, wherein the substrate comprises a base material layer and a conductive circuit layer stacked along a first direction, the insulating protective layer covers a portion of the conductive circuit layer, and the insulating protective layer is provided with a window, characterized in that: The substrate includes a first area, a second area and a third area connected between the first area and the second area, the first area is bent and arranged on one side of the second area in the first direction through the third area; the conductive circuit layer includes a first solder pad located in the first area and a second solder pad located in the second area, the first solder pad includes a first surface, the second solder pad includes a second surface, the first surface and the second surface are both arranged away from the base material layer and exposed in the window, and the second surface is welded to the first surface.

2. The foldable circuit board according to claim 1, characterized in that: There are two first regions and two third regions, each of which is connected to the second region via one third region, one end of each first region connected to the third region is provided with the first pad, both ends of the second region are provided with the second pad, and the angle between the third region and the second direction perpendicular to the first direction is an acute angle; There are two conductive circuit layers, which are respectively arranged on two opposite surfaces of the substrate layer and both include the first soldering pad and the second soldering pad. The first soldering pad in one first area is welded to the second soldering pad on one side of the substrate layer, and the first soldering pad in another first area is welded to the second soldering pad on the other side of the substrate layer.

3. The foldable circuit board according to claim 2, characterized in that: The projection of the second area in the first direction is located within the range of each of the first areas.

4. The foldable circuit board according to any one of claims 1 to 3, characterized in that: Before the substrate is bent, when observed along the first direction, the shape combination of the first surface and the second surface is a combination of a trapezoid and an inverted trapezoid, a combination of a square and a rectangle, a combination of cross-placed quadrilaterals, or a combination of a circle and an ellipse.

5. The foldable circuit board according to any one of claims 1 to 3, characterized in that: The foldable circuit board also includes an anti-oxidation layer, the first solder pad also includes a first side surface connected to the substrate layer and the first surface, the second solder pad also includes a second side surface connected to the substrate layer and the second surface, the first side surface and the second side surface are also exposed in the window, and the anti-oxidation layer covers the first side surface and the second side surface.

6. A method for preparing a foldable circuit board, characterized in that: The steps include: A substrate is provided, the substrate comprising a base material layer and a conductive circuit layer stacked along a first direction, the substrate comprising a first area, a second area, and a third area connected between the first area and the second area, the conductive circuit layer comprising a first pad located in the first area and a second pad located in the second area, the first pad comprising a first surface, the second pad comprising a second surface, and the first surface and the second surface are both arranged away from the base material layer; forming an insulating protective layer covering a portion of the conductive circuit layer, wherein the insulating protective layer is provided with a window, and the first surface and the second surface are both exposed at the window; The first region is bent around the third region and then overlapped on one side of the second region in the first direction, so that the first surface and the second surface overlap in the first direction; The first side and the second side are welded.

7. The preparation method according to claim 6, characterized in that: The first pad further includes a first side surface connected to the substrate layer and the first surface, the second pad further includes a second side surface connected to the substrate layer and the second surface, the first side surface and the second side surface are both exposed from the opening, and before the welding, the preparation method further includes the steps of: forming an anti-oxidation layer covering the first surface, the first side surface, the second surface and the second side surface in the opening; The anti-oxidation layer disposed on the first surface and the second surface is removed.

8. The preparation method according to claim 6 or 7, characterized in that: There are two first regions and two third regions, each of which is connected to the second region via one third region; one end of each first region connected to the third region is provided with the first pad, and both ends of the second region are provided with the second pad; before the bending, the two first regions are arranged at intervals along a second direction perpendicular to the first direction and are located on the same side of the second region, and the angle between the third region and the second direction is an acute angle; There are two conductive circuit layers, and the two conductive circuit layers are respectively arranged on two opposite surfaces of the substrate layer and both include the first soldering pad and the second soldering pad. After the bending, the two first regions are respectively stacked on the opposite sides of the second region in the first direction. After the welding, the first soldering pad of one first region is welded to the second soldering pad on one side of the substrate layer, and the first soldering pad of the other first region is welded to the second soldering pad on the other side of the substrate layer.

9. The preparation method according to claim 8, characterized in that: After the welding, a projection of the second region in the first direction is located within the range of each of the first regions.

10. The preparation method according to claim 7, characterized in that: Before the bending, when observed along the first direction, the shape combination of the first surface and the second surface is a combination of a trapezoid and an inverted trapezoid, a combination of a square and a rectangle, a combination of cross-placed quadrilaterals, or a combination of a circle and an ellipse.

Images