Circuit board and manufacturing method thereof

Abstract

The invention discloses a circuit board and a manufacturing method thereof, the circuit board is provided with an uncovered area and a non-uncovered area, the circuit board comprises a first circuit layer and a first insulating layer and a second insulating layer which are located on two opposite surfaces of the first circuit layer, and the first circuit layer comprises at least one connecting pad located in the uncovered area. The first insulating layer in the uncovering area forms an opening corresponding to each connecting pad, and the connecting pads are exposed from the openings. According to the circuit board provided by the invention, the metal part of the uncovering area is firstly removed, and then the first insulating layer of part of the uncovering area is removed, so that the opening capable of exposing the connecting pad of the inner layer is formed for welding the functional component, the surface mounting stability and reliability can be improved, the risk of bridging short circuit during welding can be reduced, and the product yield is high.

Description

Technical Field

[0001] The present application relates to the technical field of printed circuit boards, and in particular to a circuit board and a manufacturing method thereof. Background Art

[0002] Currently, electronic devices are increasingly developing towards multifunctionality, high integration, and miniaturization. Therefore, the requirements for circuit boards are getting higher and higher. It is usually necessary to mount functional components such as chips, board-to-board connectors (BTB) or other circuit boards on the circuit board through surface mounting technology (SMT). If the Z-axis thickness of the circuit board after mounting is limited, the inner connection pads of the circuit board need to be electrically connected to the above functional components, which requires the circuit board to be opened to expose the inner connection pads.

[0003] The traditional circuit board cover opening process is complicated, short circuits are easy to occur between different connection pads, there is a risk of failure, the product yield is low, and the connection reliability between the connection pads and other functional components is poor. Summary of the invention

[0004] In view of this, in order to overcome at least one of the above-mentioned defects, it is necessary to provide a circuit board.

[0005] In addition, it is also necessary to provide a method for manufacturing the aforementioned circuit board.

[0006] An embodiment of the present application provides a circuit board, which has an open cover area and a non-open cover area connected to the periphery of the open cover area. The circuit board includes a first circuit layer, and a first insulating layer and a second insulating layer located on two opposite surfaces of the first circuit layer. The first circuit layer includes at least one connection pad located in the open cover area, and the first insulating layer located in the open cover area forms an opening corresponding to each of the connection pads, and the connection pads are exposed in the opening.

[0007] In some possible embodiments, along the extension direction of the circuit board, the size of the opening is smaller than the size of the connection pad.

[0008] In some possible embodiments, an angle is formed between a side wall of the first insulating layer close to the opening and a surface of the connection pad, and the angle is in a range of 90° to 135°.

[0009] In some possible embodiments, along a first extension direction of the circuit board, the size of the opening is larger than the size of the connection pad; along a second extension direction of the circuit board, the size of the opening is smaller than the size of the connection pad, and the first extension direction and the second extension direction are perpendicular to each other.

[0010] In some possible embodiments, along the first extension direction, a gap is respectively formed between two opposite side walls of the connection pad and the first insulation layer, and the gap extends to the second insulation layer.

[0011] In some possible embodiments, the circuit board also includes at least one second circuit layer provided on the surface of the second insulating layer facing away from the first circuit layer, and at least one third circuit layer provided on the surface of the first insulating layer facing away from the first circuit layer, the third circuit layer is located in the non-opening area, and the first circuit layer is electrically connected to the second circuit layer and the third circuit layer, respectively.

[0012] In some possible embodiments, the second circuit layer close to the first circuit layer is electrically connected to the connection pad via a conductive column, and the conductive column penetrates the second insulating layer and the second circuit layer and contacts the connection pad.

[0013] In some possible embodiments, the cover opening area includes an opening area and a bending area connected to each other, the opening is located in the opening area, and the bending area is not provided with the opening.

[0014] The present application also provides a method for manufacturing a circuit board, the method comprising:

[0015] A circuit substrate is provided, wherein the circuit substrate has an open cover area and a non-open cover area connected to the periphery of the open cover area, the circuit substrate comprises: a first circuit layer, and a first insulating layer and a second insulating layer located on two opposite surfaces of the first circuit layer, the first circuit layer comprising at least one connection pad located in the open cover area; and

[0016] The portion of the first insulating layer located in the cover opening area is penetrated to form an opening corresponding to each of the connection pads, so that the connection pads are exposed in the openings to obtain the circuit board.

[0017] In some possible embodiments, along the extension direction of the circuit board, the size of the opening is smaller than the size of the connection pad.

[0018] In some possible embodiments, an angle is formed between a side wall of the first insulating layer close to the opening and a surface of the connection pad, and the angle is in a range of 90° to 135°.

[0019] In some possible embodiments, along a first extension direction of the circuit board, the size of the opening is larger than the size of the connection pad; along a second extension direction of the circuit board, the size of the opening is smaller than the size of the connection pad, and the first extension direction and the second extension direction are perpendicular to each other.

[0020] In some possible embodiments, after forming the opening, the manufacturing method further includes:

[0021] Along the first extension direction, a gap is formed between two opposite side walls of the connection pad and the first insulation layer respectively, and the gap extends to the second insulation layer.

[0022] Compared with the prior art, the circuit board provided in the embodiment of the present application first removes the metal part of the cover opening area, and then removes the first insulating layer of part of the cover opening area to form an opening that can expose the inner layer connection pad. The opening is surrounded by the first insulating layer, and there is no need to set a separate covering film, which simplifies the structure of the circuit board; the thickness uniformity of the first insulating layer is high, which is conducive to improving the subsequent mounting yield of functional components, reducing the stress concentration of functional components, and thus improving product reliability; the connection pad is formed when the first circuit layer circuit is made, and there is no need to electroplate the surface of the connection pad. The surface of the connection pad is flat, which further improves the subsequent mounting yield of functional components and the reliability of the product. The first insulating layer is partially removed. If there are multiple connection pads, the first insulating layer acts as a covering film between two adjacent connection pads, which can also reduce the risk of bridging short circuit during welding and improve the product yield. The formation of an inverted trapezoidal opening is conducive to the discharge of gas in the corners of the opening, and improves the welding yield of functional components. By extending the first insulating layer to the peripheral surface of the connection pad, the stability of the connection pad can be improved, thereby improving the reliability of the mounting of functional components. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is a schematic diagram of the structure of a rear-opening circuit board based on a PI substrate in the prior art.

[0024] Figure 2 The figure is a schematic diagram of the structure of a front-opening circuit board based on a thermoplastic substrate in the prior art.

[0025] Figure 3 A schematic diagram of the structure of a circuit board provided in one embodiment of the present application.

[0026] Figure 4 for Figure 3 The schematic diagram of the structure of the circuit board after being connected with other functional components is shown.

[0027] Figure 5A for Figure 4 Magnified view of part C.

[0028] Figure 5B This is a partial photo of the circuit board after openings are formed in an embodiment of the present application.

[0029] Figure 6 A top view of a circuit board provided in accordance with another embodiment of the present application.

[0030] Figure 7 A schematic diagram of the structure of a circuit board provided in yet another embodiment of the present application.

[0031] Figure 8 for Figure 7 When there are multiple connection pads in the device, a schematic diagram of the arrangement of the connection pads is shown.

[0032] Fig. 9 for Figure 8 Cross-sectional view along line IX-IX.

[0033] Fig.10 for Figure 8 Cross-sectional view along XX.

[0034] Fig.11 for Fig. 9 A magnified schematic diagram of the support structure and connection pads.

[0035] Fig.12 for Fig.11 Actual photos of the support structure and connection pads.

[0036] Fig.13 It is a schematic diagram of the structure of a copper column formed by two copper plating steps in the prior art.

[0037] Fig.14 for Fig.13 Actual photo of the copper column.

[0038] Fig.15 A flowchart of manufacturing a circuit board provided in one embodiment of the present application.

[0039] Figures 16 to 22 A schematic diagram of the structure of a circuit board manufacturing process provided in one embodiment of the present application.

[0040] Fig.23 A flowchart of manufacturing a circuit board provided in another embodiment of the present application.

[0041] Figure 24 to Figure 26 A structural schematic diagram of a circuit board manufacturing process provided in another embodiment of the present application.

[0042] Fig. 27 This is a local scanning electron microscope photograph of a circuit board according to an embodiment of the present application.

[0043] Main component symbols

[0044] Circuit board 100,200 Conductive paste 20

[0045] First circuit layer 1 Circuit substrate 30, 80

[0046] Connection pad 11 Substrate 40

[0047] First insulating layer 2 First metal layer 51

[0048] Second insulating layer 3 Second metal layer 52

[0049] Support structure 31 Third metal layer 53

[0050] Opening 4 Fourth metal layer 54

[0051] Gap 41 First single-sided copper clad laminate 61

[0052] Second circuit layer 5 Second single-sided copper clad board 62

[0053] Third circuit layer 6 Open cover area A

[0054] First protective layer 71 Opening area A1

[0055] Second protective layer 72 bending area A2

[0056] Covering film 73 Non-opening area B

[0057] Conductive pillar 8 extending direction a, b, c

[0058] Functional Part 10

[0059] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0060] 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 of the embodiments.

[0061] 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.

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0063] Traditional PI substrate circuit boards are mostly opened from behind, such as Figure 1As shown, when the copper-clad laminate with a PI substrate is laminated to increase the layers, the PI substrate needs to be bonded through an adhesive layer, so that the adhesive layer corresponding to the cover opening area on the PI substrate is first washed off, and after laminating and increasing the layers, the increased layer part of the cover opening area is cut off to form an open cover. However, the inventors of the present application have found that if the PI substrate is replaced with a thermoplastic substrate, such as an aromatic thermoplastic polyester such as liquid crystal polymer (LCP), the thermoplastic substrate in the cover opening area will combine with the copper surface during high-temperature lamination, and subsequent cutting and opening of the cover cannot be achieved.

[0064] In order to realize the opening of the thermoplastic substrate, the inventor of the present application has tried to adopt the front opening method, that is, during the inner layer circuit manufacturing process, such as Figure 2 As shown, the cover opening area is first produced, and then the non-cover opening area is subjected to subsequent processing (such as black shadow, surface electroplating, etc.). However, during the black shadow processing process, in order to avoid carbon on the thermoplastic substrate in the cover opening area, the cover opening area needs to be masked with a masking material, and the masking material is removed after the black shadow. However, during the outer layer electroplating process, the metal circuit in the cover opening area may be stained by the black shadow residual carbon, causing a short circuit in the circuit and product failure. In addition, if a temporary protective film is pressed or a protective ink is printed on the cover opening area, residual glue or residual ink will be left, and the number of steps is increased, which increases the complexity of the process. In addition, after the front cover is opened, the following defects exist when connecting other functional components: (1) After the cover is opened, before soldering other functional components (such as chips, other circuit boards, etc.) on the connection pads, it is necessary to electroplate the surface of the connection pads to thicken them. After electroplating, the surface of the electroplated layer is in an arc shape, and then tin is applied to the arc-shaped pads, and then solder mask printing is performed. In this way, there is a dead angle at the contact edge of the solder paste ball and the electroplated layer, which is easy to cause residual gas and is difficult to discharge, resulting in poor welding; (2) There are line gaps between different connection pads (such as Figure 2 (as shown), this gap will cause stress concentration in the mounted functional components, reduce reliability, and there is a risk of bridging short circuit during welding; (3) After the protective printing, the thickness uniformity of the solder mask is poor, and it is also easy to cause poor welding of other functional components, reducing reliability.

[0065] In order to solve the above thermoplastic substrate (such as LCP substrate) cover opening problem, please refer to Figure 3, an embodiment of the present application provides a circuit board 100, wherein the circuit board 100 has an open cover area A and a non-open cover area B connected to the periphery of the open cover area A. The circuit board 100 includes a first circuit layer 1, and a first insulating layer 2 and a second insulating layer 3 located on two opposite surfaces of the first circuit layer 1, the first circuit layer 1 includes at least one connection pad 11 located in the open cover area A, and the first insulating layer 2 located in the open cover area A forms an opening 4 corresponding to each of the connection pads 11, and the connection pads 11 are exposed in the opening 4. After the connection pads 11 are exposed, solder paste can be set on the connection pads 11 to connect other functional components (such as chips, BTB connectors or other circuit boards, etc.). Figure 4 As shown, when the functional component 10 needs to be mounted on the cover opening area A of the circuit board 100, a conductive paste 20 needs to be set in the opening 4, and the pins of the functional component 10 are flattened with the conductive paste 20 and welded to achieve the mounting of the functional component 10 on the circuit board 100.

[0066] See also Figure 3 , and refer to Figure 4 and Figure 5A , along any extension direction a of the circuit board 100, the size of the opening 4 is smaller than the size of the connection pad 11. That is, the first insulating layer 2 partially extends to the peripheral surface of the connection pad 11. Specifically, the opening 4 is formed by laser opening. Since part of the first insulating layer 2 covers the periphery of the connection pad 11, the stability of the connection pad 11 can be improved, thereby improving the overall yield of the product after the subsequent mounting of the functional component 10. Moreover, if a plurality of connection pads 11 are provided, the adjacent connection pads 11 are directly isolated by the first insulating layer 2, and there is no need to add a solder mask between different connection pads to form isolation as in the traditional opening process. The thickness of the first insulating layer 2 is uniform, which can improve the flatness of the overall connection surface of the opening area A, thereby facilitating the improvement of the process yield of the subsequent mounting of the functional component 10, avoiding the problem of stress concentration in the connected functional component 10, improving reliability, and reducing the risk of failure. In addition, the first insulating layer 2 of the opening area A can be used as a covering film (CVL), and only the opening 4 is provided in the opening area A1, which can reduce the subsequent gold plating area and save costs.

[0067] In some embodiments, the thickness tolerance of the first insulating layer 2 is approximately ±5um, and the thickness uniformity of the first insulating layer 2 is high, which is conducive to improving the yield of subsequent surface mounting of functional components (such as SMT process). In addition, the connection pad 11 is formed during the production process of the first circuit layer 1, and there is no need to electroplate the surface of the connection pad 11. The surface flatness is high, which is also conducive to improving the mounting yield of functional components.

[0068] In some embodiments, along any of the extension directions a, the dimension x of the overlapping portion of the first insulating layer 2 and the connection pad 11 is greater than or equal to 25 μm, and by limiting the minimum width of the overlapping portion to 25 μm, the reliability of the connection pad 11 can be further improved. The size of the opening 4 is adjustable, with high dimensional accuracy, usually around 0.05 mm, and the opening 4 can be designed according to different welding requirements to ensure that the cover opening area A has the best reliability.

[0069] In some embodiments, an angle α is formed between the side wall of the first insulating layer 2 close to the opening 4 and the upper surface of the connection pad 11, and the angle α is in the range of 90° to 135°, and further, the angle α is in the range of 100° to 120°. By setting the side wall of the first insulating layer 2 corresponding to the opening 4 as an inclined side wall, an inverted trapezoidal opening 4 is obtained, which can make it easier to discharge the gas in the corner of the opening 4 close to the first insulating layer 2 and the connection pad 11, thereby improving the mounting yield of functional components and reducing the risk of failure.

[0070] like Figure 5B As shown, it is a partial physical photo of the circuit board 100, and is combined with Figure 5A It can be seen that after the opening 4 is set in the cover opening area, the side wall of the first insulating layer 2 is inclined, and the first insulating layer 2 will not overflow onto the connection pad 11 due to hot pressing.

[0071] In some embodiments, the first insulating layer 2 may be a thermoplastic substrate, and the material may be a thermoplastic polymer, for example, an LCP substrate. The second insulating layer 3 may also be a thermoplastic substrate, and the material may be a thermoplastic polymer, for example, an LCP substrate. When a thermoplastic substrate is used, there is no need to add a glue layer like a PI substrate during layer addition and lamination, and the thermoplastic substrate itself has a bonding effect during the heating process. Moreover, it is easier to form the opening 4 on the thermoplastic substrate.

[0072] See also Figure 6 , the cover opening area A is divided into an opening area A1 and a bending area A2, wherein the opening 4 is located in the opening area A1, and the bending area A2 is not provided with the opening 4, and the bending area A2 can realize the bending of the circuit board 100. The opening 4 is provided only in the opening area A1, so that only the first insulating layer 2 is partially removed, and the first insulating layer 2 of other cover opening areas A can be retained, thereby serving as a covering film of the cover opening area A, improving the reliability of the entire circuit board 100, and making it easier to bend and shape the bending area A2, and the inner layer circuit of the bending area A2 is not easy to bend and break, thereby improving the yield of the circuit board 100.

[0073] Please refer again Figure 3, the circuit board 100 further includes at least one second circuit layer 5 located on the surface of the second insulating layer 3 away from the first circuit layer 1, and at least one third circuit layer 6 located on the surface of the first insulating layer 2 away from the first circuit layer 1, the third circuit layer 6 is located in the non-opening area B, and the first circuit layer 1 is electrically connected to the second circuit layer 5 and the third circuit layer 6 respectively. The circuit board 100 can be designed with the number of circuit layers according to actual needs, and the connection pads 11 of the inner layer circuit corresponding to the opening area A are exposed to realize mounting with other functional components, thereby reducing the thickness of the overall circuit board after mounting to meet the needs of miniaturization of electronic equipment.

[0074] Please refer again Figure 3 The circuit board 100 further includes a first protective layer 71 located on the surface of the second circuit layer 5 at the outermost layer, and a second protective layer 72 located on the surface of the third circuit layer 6 at the outermost layer. The second protective layer 71 is located in the non-opening area B, and is used to protect the outer circuits of the non-opening area B. Figure 6 The second protective layer 72 is located in the non-opening area B and extends to the opening area A1 of the opening area A, and the second protective layer 72 is not provided in the bending area A2, which can make the circuit board 100 easier to bend.

[0075] Specifically, the circuit board 100 provided in the embodiment of the present application may be a high-frequency circuit board based on a thermoplastic substrate, realizing a Solder Mask Defined (NSMD) structure.

[0076] The circuit board 100 provided in the embodiment of the present application forms an opening 4 that can expose the connection pad 11 of the inner layer by removing the first insulating layer 2 of the partially opened cover area A. The opening 4 is surrounded by the first insulating layer 2, and there is no need to set a separate covering film, which simplifies the structure of the circuit board 100; the thickness uniformity of the first insulating layer 2 is high, which is conducive to improving the subsequent mounting yield of functional components, reducing the stress concentration of functional components, and thus improving product reliability; the connection pad 11 is formed when the first circuit layer 1 circuit is made, and there is no need to electroplate the surface of the connection pad 11. The surface of the connection pad 11 is flat, which further improves the subsequent mounting yield of functional components and the reliability of the product. The first insulating layer 2 is partially removed. If there are multiple connection pads 11, the first insulating layer 2 acts as a covering film between two adjacent connection pads 11, which can also reduce the risk of bridging short circuit during welding and improve the product yield. The formation of an inverted trapezoidal opening 4 is conducive to the discharge of gas in the corners of the opening 4 and improves the welding yield of functional components. By extending the first insulating layer 2 to the peripheral surface of the connection pad 11, the stability of the connection pad 11 can be improved, thereby improving the reliability of mounting the functional component.

[0077] See also Figure 7and Figure 8 The present application also provides another circuit board 200. The structure of the circuit board 200 is substantially the same as that of the circuit board 100. The main difference is that along the first extension direction b of the circuit board 200, the size of the opening 4 (e.g. Fig. 9 L1 in the figure) is larger than the size of the connection pad 11 (e.g. Fig. 9 along the second extension direction c of the circuit board 200, the size of the opening 4 (eg Fig.10 L3 in the figure) is smaller than the size of the connection pad 11 (e.g. Fig.10 In the embodiment of the present invention, the first extension direction b and the second extension direction c are perpendicular to each other. That is, part of the edge of the connection pad 11 is covered in the first insulating layer 2, and the other part of the edge is exposed from the opening 4, which can improve the stability of the connection pad 11 and increase the contact area between the connection pad 11 and the conductive paste during the subsequent functional component mounting process.

[0078] In some embodiments, Figures 8 to 10 As shown, along the first extension direction b, a gap 41 is formed between the two opposite side walls of the connection pad 11 and the first insulating layer 2, and the gap 41 extends to the second insulating layer 3, so that the second insulating layer 3 below the connection pad 11 is formed with a support structure 31. By forming the gap 41, the two opposite side walls of the connection pad 11 can be exposed from the gap 41, and the side walls of the connection pad 11 will also contact the conductive paste, which can further increase the contact area between the connection pad 11 and the conductive paste, improve the mounting yield of functional components, and reduce the risk of failure. During the mounting process, the gap 41 can also be used as a space to accommodate excess conductive paste, reducing the risk of short circuit caused by overflow of the conductive paste. In addition, the connection area between the support structure 31 and the second insulating layer 3 is larger, and the support structure 31 is more stable, so that the connection pad 11 is more stable, and a smaller spacing between the connection pads 11 can be achieved, the connection density is improved, and it is not easy to be tilted or damaged by external forces during the process, and it is easy to mass produce. Specifically, in this embodiment, the connecting pad 11 can be roughly a rectangular parallelepiped, wherein the gap 41 is formed between the side walls where the two long sides are located and the first insulating layer 2, and the edges where the two short sides of the connecting pad 11 are located are covered by the first insulating layer 2. This can not only ensure the stability of the connecting pad 11, but also the internal space of the gap 41 is relatively large, which can further increase the exposed area of ​​the connecting pad 11 and can fully accommodate excess conductive paste.

[0079] In the process of forming the gap 41, for example, by removing part of the second insulating layer 3 by laser, the sidewalls of the support structure 31 are not absolutely vertical sidewalls, but are roughly inclined sidewalls, so that the bottom size of the support structure 31 is larger and the top size close to the connection pad 11 is smaller, forming Fig.11The ladder-shaped structure shown can further improve the stability of the support structure 31 without damaging the side wall of the connection pad 11, ensuring the dimensional accuracy of the connection pad 11, and not affecting the bonding force between the connection pad 11 and the support structure 31 and the stability of the connection pad 11.

[0080] In some embodiments, the depth of the gap 41 is preferably such that it does not penetrate the second insulating layer 3. Specifically, the remaining thickness of the second insulating layer 3 below the gap 41 (eg Figure 7 The d) in the figure may be greater than or equal to 20 μm.

[0081] like Fig.11 and Fig.12 As shown, the connection pad 11 is a circuit directly produced on a metal layer (such as a copper layer) by patterning, and has a flat surface. In the traditional opening method, the connection pad needs to be copper-plated twice to form a Fig.13 and Fig.14 The copper pillar shown has an arc-shaped surface. Therefore, the connection pad 11 formed in the circuit board 200 of the embodiment of the present application has a flat surface, high thickness uniformity, and a thickness tolerance of less than 10μm. Compared with the traditional copper pillar with poor thickness uniformity (thickness is approximately 50±16μm, cpk: 1.67), the tolerance level is improved by about 40%; moreover, compared with the traditional copper pillar (diameter / pad=125 / 225μm), the size of the connection pad 11 of this embodiment is 125 / 150μm; in addition, the formation accuracy of the opening 4 (such as laser opening accuracy) is approximately 25μm, which is improved by about 50% compared with the traditional electroplating selective plating accuracy (±50μm). The connection pad 11 of the embodiment of the present application has a flat surface and high dimensional accuracy, which is conducive to the subsequent mounting with functional components, can improve the mounting yield and reliability, and is conducive to increasing the density of the connection pad 11, and is more suitable for designing as follows Figure 8 The high-density connection structure shown. Figure 8 As shown, in this high-density connection structure, the height of the highest point of the conductive paste is measured after reflow soldering, and the height is approximately 75±25μm (when the height of the copper column at the hot pressing welding is 50μm), the size of the connection pad 11 can be 125*400μm, and the spacing between adjacent connection pads 11 is greater than 225μm.

[0082] In some embodiments, the second circuit layer 5 close to the first circuit layer 1 is electrically connected to the connection pad 11 through a conductive column 8, and the conductive column 8 penetrates the second insulating layer 3 and the second circuit layer 5 and contacts the connection pad 11. The conductive column 8 contacts the connection pad 11 to achieve conduction between the first circuit layer 1 and the second circuit layer 5, and there is no need to form a through hole on the connection pad 11, which further ensures the surface flatness of the connection pad 11 and is more suitable for designing a large-area high-density connection structure.

[0083] The circuit board 200 provided in the embodiment of the present application can utilize the space of the first insulating layer 2 to realize a non-solder mask defined pad (NSMD) structure, and fully utilize the space of the first insulating layer 2 to realize a high-density interconnection structure.

[0084] See also Fig.15 , and refer to Figure 3 The present application also provides a method for preparing the circuit board 100, which specifically includes the following steps:

[0085] Step S11, providing a circuit substrate 30, wherein the circuit substrate 30 has an open cover area A and a non-open cover area B connected to the periphery of the open cover area A, and the circuit substrate 30 includes: a first circuit layer 1, and a first insulating layer 2 and a second insulating layer 3 located on two opposite surfaces of the first circuit layer 1, and the first circuit layer 1 includes at least one connection pad 11 located in the open cover area A.

[0086] The circuit substrate 30 may be a multilayer board, wherein the surface of the first insulating layer 2 may be provided with at least one third circuit layer 6, and the surface of the second insulating layer 3 may be provided with at least one second circuit layer 5. The third circuit layer 6 is located in the non-opening area B, and the first circuit layer 1 is electrically connected to the second circuit layer 5 and the third circuit layer 6, respectively.

[0087] Specifically, the method for preparing the circuit substrate 30 includes the following steps:

[0088] The first step, such as Fig.16 As shown, a substrate 40 is provided, wherein the substrate 40 has an open cover area A and a non-open cover area B connected to the periphery of the open cover area A, and the substrate 40 includes a second insulating layer 3 and a first metal layer 51 and a second metal layer 52 located on two opposite surfaces of the second insulating layer 3.

[0089] The second step is, Fig.17 As shown, a through hole is formed through the first metal layer 51, and metal is electroplated in the through hole to make the first metal layer 51 and the second metal layer 52 conductive.

[0090] The third step is Fig.18 As shown, the first metal layer 51 is patterned to form a first circuit layer 1, the first circuit layer 1 includes at least one connection pad 11 located in the open cover area A, and the second metal layer 52 is patterned to form a second circuit layer 5, and the second circuit layer 5 is electrically connected to the first circuit layer 1.

[0091] The fourth step is Fig.19 and Fig. 20As shown, a first single-sided copper clad laminate 61 and a second single-sided copper clad laminate 62 are respectively laminated on the surfaces of the first circuit layer 1 and the second circuit layer 5. The first single-sided copper clad laminate 61 includes a first insulating layer 2 laminated on the surface of the first circuit layer 1 and a third metal layer 53 located on the surface of the first insulating layer 2. The second single-sided copper clad laminate 62 includes another second insulating layer 3 laminated on the surface of the second circuit layer 5 and a fourth metal layer 54 located on the surface of the another second insulating layer 3.

[0092] Step 5: Fig.21 As shown, the third metal layer 53 is patterned to form a third circuit layer 6, and the third circuit layer 6 is located in the non-opening area B. The third metal layer 53 located in the opening area A is removed during the circuit manufacturing process to expose the first insulating layer 2. The fourth metal layer 54 is patterned to form another second circuit layer 5, wherein the second circuit layer 5, the third circuit layer 6 and the first circuit layer 1 are all electrically connected, thereby obtaining the circuit substrate 30. It can be understood that when forming the third circuit layer 6, if there are multiple layers of third circuit layers 6, each layer of the third circuit layer 6 will remove part of the metal located in the opening area A during the patterning process, and the other first insulating layers 2 stacked on the first insulating layer 2 can jointly constitute the first insulating layer 2 to form the subsequent opening 4, or the redundant first insulating layer 2 can be removed by laser or other means in the subsequent process, and the first insulating layer 2 close to the first circuit layer 1 can be retained. Such a molding method facilitates the formation of the subsequent opening 4.

[0093] It is understandable that the structure design with multiple second circuit layers 5 and multiple third circuit layers 6 can be realized by laminating and stacking according to actual needs.

[0094] Step S12, as Fig. 22 As shown, an opening 4 corresponding to each of the connection pads 11 is formed through a portion of the first insulating layer 2 located in the opening area A, so that the connection pad 11 is exposed in the opening 4, thereby obtaining the circuit board 100.

[0095] Compared with the traditional opening method, it is necessary to remove the insulating layer of the entire opening area to expose the inner circuit layer. The embodiment of the present application only needs to partially remove the first insulating layer 2 located in the opening area A to form an opening 4, and retain the first insulating layer 2 in other areas of the opening area A. It can be used as a covering film to protect the first circuit layer 1 in the opening area A, which can improve the yield of the overall process and product reliability. At the same time, for the part with the bending area A2, the protection of the first insulating layer 2 can make the bending area A2 easier to bend and shape.

[0096] In some embodiments, the opening can be performed by laser, and the portion of the first insulating layer 2 located above the connection pad 11 is removed to form the opening 4, for example, a carbon dioxide laser is used to perform drilling to remove the local first insulating layer 2. Specifically, the first insulating layer 2 can be a thermoplastic substrate as described above, such as an LCP substrate.

[0097] In some embodiments, along the extension direction of the circuit board 100 , the size of the opening 4 is smaller than the size of the connection pad 11 .

[0098] In some embodiments, when the opening 4 is formed by laser, an angle α is formed between the side wall of the first insulating layer 4 close to the opening 4 and the surface of the connection pad 11 , and the angle α is in the range of 90° to 135°.

[0099] In some embodiments, after forming the opening 4, the manufacturing method further comprises the steps of: forming a first protective layer 71 on the surface of the second circuit layer 5 of the outermost layer, and forming a second protective layer 72 on the surface of the third circuit layer 6 of the outermost layer. The second protective layer 72 is located in the non-opening area B, and is used to protect the outer circuit of the non-opening area B.

[0100] The circuit board 100 provided in the embodiment of the present application can be a high-frequency circuit board structure based on a thermoplastic substrate. The first metal layer 51 of the opening area A is first removed during circuit formation, and then the first insulating layer 2 is partially opened to form an opening 4, so that the connection pad 11 located on the inner layer is exposed, thereby improving the aforementioned many problems of opening the thermoplastic substrate, simplifying the process technology, further improving the overall process yield and product reliability, and at the same time optimizing the curing risk of solder mask breakage at the opening, and optimizing the angle of the opening 4 in the SMT area (solder mask angle <90 degrees).

[0101] See also Fig.23 The present application also provides a method for manufacturing the aforementioned circuit board 200, which specifically includes the following steps:

[0102] Step S21, as Fig.24 As shown, a circuit substrate 80 is provided, and the circuit substrate 80 includes: a first circuit layer 1, and a first insulating layer 2 and a second insulating layer 3 located on two opposite surfaces of the first circuit layer 1, and the first circuit layer 1 includes at least one connection pad 11 located in the open cover area A.

[0103] The circuit substrate 80 may be a multilayer board, wherein the surface of the first insulating layer 2 may be provided with at least one third circuit layer 6, and the surface of the second insulating layer 3 may be provided with at least one second circuit layer 5. The third circuit layer 6 is located in the non-opening area B, and the first circuit layer 1 is electrically connected to the second circuit layer 5 and the third circuit layer 6, respectively.

[0104] like Fig.24 As shown, the circuit substrate 80 is different from the circuit substrate 30 in step S11 of the above embodiment in that the connection pad 11 is electrically connected to the second circuit layer 5 close to the first circuit layer 1 through the conductive column 8 .

[0105] like Fig.25 and Fig.26 As shown, after the steps of forming the second circuit layer 5 and the third circuit layer 6, the method for manufacturing the circuit substrate 80 further includes the steps of:

[0106] like Fig.25 As shown, a first protective layer 71 is formed on the surface of the second outermost circuit layer 5, and a second protective layer 72 is formed on the surface of the third outermost circuit layer 6. The second protective layer 72 is located in the non-opening area B to protect the outer circuits in the non-opening area B, and the first protective layer 71 is located in the non-opening area B and extends to the partially opened area A.

[0107] like Fig.26 As shown, a covering film 73 is formed on the first protection layer 71 near the cover opening area A, and the outermost second circuit layer 5 is exposed for connecting pads for electrical lead-out.

[0108] Step S22, refer to Figure 7 , an opening 4 corresponding to each of the connection pads 11 is formed through the portion of the first insulating layer 2 located in the opening area A, so that the connection pads 11 are exposed in the openings 4, thereby obtaining the circuit board 200.

[0109] In some embodiments, reference is made to Figure 8 When the opening 4 is formed, along the first extension direction b of the circuit board 200, the size of the opening 4 is larger than the size of the connection pad 11; along the second extension direction c of the circuit board 200, the size of the opening 4 is smaller than the size of the connection pad 11, and the first extension direction b and the second extension direction c are perpendicular to each other. In this embodiment, the connection pad 11 is a substantially rectangular structure.

[0110] After forming the opening 4, the manufacturing method further comprises:

[0111] Along the first extension direction b, a gap 41 is formed between the two opposite side walls of the connection pad 11 and the first insulating layer 2 , and the gap 41 extends to the second insulating layer 3 , so that a portion of the second insulating layer 3 below the connection pad 11 forms a supporting structure 31 .

[0112] In some embodiments, the opening 4 and the gap 41 can be formed by laser, such as carbon dioxide laser opening. It is understandable that the carbon dioxide laser opening can also be replaced by applying a protective film and then using plasma etching and other technologies to remove the redundant first insulating layer 2, which can achieve higher precision, and the plasma etching line accuracy can reach ±3μm. Fig. 27 This is a partial physical photo of the circuit board 200. The gap formed on the side of the connecting pad 11 is formed by partially removing the first insulating layer 2 and partially removing the second insulating layer 3 under the first insulating layer 2. The circuit is flat, and the circuit and opening size accuracy are both high, which is conducive to realizing a high-density connection structure.

[0113] In the embodiment of the present application, the opening 4 above the connection pad 11 is formed at the end of the manufacturing process, which avoids the process of applying a resist coating on the surface of the cover film before the traditional solder mask, reduces the discontinuity difference between the connection pad 11 and the base surface, and avoids the scraper from damaging the connection pad 11. In addition, the surface of the connection pad 11 is flat, the thickness is uniform, and the dimensional accuracy is high, which can realize a high-density connection structure.

Claims

1. A circuit board, characterized in that: The circuit board has an open cover area and a non-open cover area connected to the periphery of the open cover area. The circuit board includes: a first circuit layer, and a first insulating layer and a second insulating layer located on two opposite surfaces of the first circuit layer. The first circuit layer includes at least one connection pad located in the open cover area. The first insulating layer located in the open cover area forms an opening corresponding to each of the connection pads, and the connection pads are exposed in the opening.

2. The circuit board according to claim 1, characterized in that Along the extension direction of the circuit board, the size of the opening is smaller than the size of the connection pad.

3. The circuit board according to claim 1, characterized in that: An angle is formed between the side wall of the first insulating layer close to the opening and the surface of the connection pad, and the angle is in the range of 90° to 135°.

4. The circuit board according to claim 1, characterized in that: Along a first extension direction of the circuit board, the size of the opening is larger than the size of the connection pad; along a second extension direction of the circuit board, the size of the opening is smaller than the size of the connection pad, and the first extension direction and the second extension direction are perpendicular to each other.

5. The circuit board according to claim 4, characterized in that: Along the first extension direction, a gap is formed between two opposite side walls of the connection pad and the first insulation layer respectively, and the gap extends to the second insulation layer.

6. The circuit board according to any one of claims 1 to 5, characterized in that: The circuit board also includes at least one second circuit layer arranged on the surface of the second insulating layer away from the first circuit layer, and at least one third circuit layer arranged on the surface of the first insulating layer away from the first circuit layer, the third circuit layer is located in the non-opening area, and the first circuit layer is electrically connected to the second circuit layer and the third circuit layer respectively.

7. The circuit board according to claim 6, characterized in that: The second circuit layer close to the first circuit layer is electrically connected to the connection pad via a conductive column, and the conductive column penetrates the second insulating layer and the second circuit layer and contacts the connection pad.

8. The circuit board according to claim 6, characterized in that: The cover opening area includes an opening area and a bending area that are connected to each other. The opening is located in the opening area, and the bending area is not provided with the opening.

9. A method for manufacturing a circuit board, characterized in that: include: A circuit substrate is provided, wherein the circuit substrate has an open cover area and a non-open cover area connected to the periphery of the open cover area, the circuit substrate comprises: a first circuit layer, and a first insulating layer and a second insulating layer located on two opposite surfaces of the first circuit layer, the first circuit layer comprising at least one connection pad located in the open cover area; as well as The portion of the first insulating layer located in the cover opening area is penetrated to form an opening corresponding to each of the connection pads, so that the connection pads are exposed in the openings to obtain the circuit board.

10. The method for manufacturing a circuit board according to claim 9, characterized in that: Along the extension direction of the circuit board, the size of the opening is smaller than the size of the connection pad.

11. The method for manufacturing a circuit board according to claim 9, characterized in that: An angle is formed between the side wall of the first insulating layer close to the opening and the surface of the connection pad, and the angle is in the range of 90° to 135°.

12. The method for manufacturing a circuit board according to claim 9, wherein: Along a first extension direction of the circuit board, the size of the opening is larger than the size of the connection pad; along a second extension direction of the circuit board, the size of the opening is smaller than the size of the connection pad, and the first extension direction and the second extension direction are perpendicular to each other.

13. The method for manufacturing a circuit board according to claim 12, wherein: After forming the opening, the manufacturing method further includes: Along the first extension direction, a gap is formed between two opposite side walls of the connection pad and the first insulation layer respectively, and the gap extends to the second insulation layer.

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