Printed circuit board and electronic device

Abstract

The embodiment of the present application provides a printed circuit board, comprising a core plate and a substrate, the core plate is arranged on the outer wall surface of the substrate; the core plate comprises a first conductive layer, a second conductive layer and a first dielectric layer, wherein the first conductive layer is located on the side of the core plate away from the substrate; the second conductive layer is located on the side of the core plate close to the substrate; the first dielectric layer is located between the first conductive layer and the second conductive layer, and comprises a soft dielectric layer with a Young's modulus less than or equal to a preset Young's modulus. The printed circuit board provided by the embodiment of the present application reduces the modulus of the PCB at the bottom of the power device welding point on the one hand, thereby improving the reliability of the welding point between the power device and the PCB, meeting the service life requirement of the product, and on the other hand, strengthening the voltage resistance between the outermost conductive layer and the second outer conductive layer.

Description

Technical Field

[0001] This application relates to the field of printed circuit boards, and more particularly to a printed circuit board and an electronic device. Background Technology

[0002] As energy products evolve towards higher power and higher density, the increased number of layers and copper thickness of printed circuit boards (PCBs) leads to an increase in the coefficient of thermal expansion (CTE) and Young's modulus of PCBs. This, in turn, makes the reliability of solder joints in high-power devices more challenging. Traditional PCB materials are unable to meet the long-term reliability testing requirements of solder joints and are prone to solder joint cracking. Summary of the Invention

[0003] This application provides a printed circuit board and electronic device that reduces the Young's modulus of the printed circuit board and improves the reliability of the solder joints between the power device and the PCB.

[0004] In a first aspect, embodiments of this application provide a printed circuit board, including a core board and a substrate. The core board covers one of the two outer wall surfaces opposite to the substrate. The core board includes a first conductive layer, a second conductive layer, and a first dielectric layer. The first conductive layer is located on the side of the core board away from the substrate. The second conductive layer is located on the side of the core board closer to the substrate. The first dielectric layer is located between the first conductive layer and the second conductive layer and includes a soft dielectric layer with a Young's modulus less than or equal to a preset Young's modulus.

[0005] The printed circuit board provided in this application reduces the Young's modulus of the dielectric layer between the outermost conductive layer and the second outermost conductive layer by mixing a soft dielectric layer between the dielectric layer and the second outermost conductive layer. On the one hand, this reduces the modulus of the PCB at the bottom of the power device solder joint, thereby improving the reliability of the solder joint between the power device and the PCB and meeting the product lifespan requirements. On the other hand, it strengthens the withstand voltage capability between the outermost conductive layer and the second outermost conductive layer.

[0006] In one possible implementation, the preset Young's modulus is less than or equal to 15 GPa.

[0007] In another possible implementation, the core board is also covered on the other of the two opposing outer wall surfaces of the substrate.

[0008] In another possible implementation, the first dielectric layer further includes a prepreg (PP), which is formed by mixing and pressing a flexible dielectric layer and the prepreg.

[0009] In one example, the prepreg partially or completely covers the surface of the flexible dielectric layer near the second conductive layer, wherein the surface of the flexible dielectric layer near the first conductive layer is in close contact with the first conductive layer, and the prepreg is in close contact with the flexible dielectric layer and the second conductive layer respectively. In this way, a single-sided board is formed by first pressing the first conductive layer and the flexible dielectric layer together, and then the single-sided board and the inner core board are bonded together using the prepreg to form a PCB motherboard.

[0010] In another example, the surfaces of the flexible dielectric layer near the first conductive layer and near the second conductive layer are partially or completely covered by a prepreg; wherein the flexible dielectric layer is tightly connected to the first conductive layer and the second conductive layer respectively through the prepreg.

[0011] Optionally, the prepreg is an FR4 prepreg.

[0012] In another possible implementation, the surface of the flexible dielectric layer near the first conductive layer is in close contact with the first conductive layer, and the surface near the second conductive layer is in close contact with the second conductive layer.

[0013] In another possible implementation, the first conductive layer is provided with pads, and a flexible dielectric layer is provided on the first dielectric layer at the corresponding pad positions.

[0014] In one possible implementation, the substrate includes N third conductive layers and M second dielectric layers, which are alternately stacked, wherein N = M + 1, and N and M are both natural numbers; the Young's modulus of the first dielectric layer is less than that of the second dielectric layer. In another possible implementation, the substrate includes N third conductive layers and M second dielectric layers, which are alternately stacked, wherein M = N + 1, and N and M are both natural numbers; some of the M second dielectric layers include flexible dielectric layers; or each of the M second dielectric layers includes a flexible dielectric layer.

[0015] In another possible implementation, the coefficient of thermal expansion of the flexible dielectric layer in the XY axis direction is less than or equal to a preset threshold.

[0016] Optionally, the preset threshold is less than or equal to 30.

[0017] The printed circuit board provided in this application embodiment achieves a simultaneous reduction in the Young's modulus and CET of the PCB by mixing a flexible dielectric layer between the outermost conductive layer and the next outermost conductive layer with a Young's modulus less than a preset Young's modulus and a CTE less than a preset threshold in the XY axis direction, thereby further increasing the reliability of the power devices and the solder joints of the PCB.

[0018] Optionally, the flexible dielectric layer is made of polyimide.

[0019] Secondly, embodiments of this application also provide an electronic device, including a power device and a printed circuit board provided in the first aspect, wherein the power device is electrically connected to the printed circuit board, thereby improving the service life of the electronic device. Attached Figure Description

[0020] The accompanying drawings used in the description of the embodiments or prior art are briefly introduced below.

[0021] Figure 1 This is a schematic diagram of the structure of a printed circuit board provided in an embodiment of this application;

[0022] Figure 2 Provided for the embodiments of this application Figure 1 The flowchart shown is a production process diagram for printed circuit boards.

[0023] Figure 3 This is a schematic diagram of another printed circuit board structure provided in an embodiment of this application;

[0024] Figure 4 Provided for the embodiments of this application Figure 3 The flowchart shown is a production process diagram for printed circuit boards.

[0025] Figure 5 This is a schematic diagram of another printed circuit board structure provided in an embodiment of this application;

[0026] Figure 6 Provided for the embodiments of this application Figure 5 The diagram shown is a flowchart of the printed circuit board manufacturing process. Detailed Implementation

[0027] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0028] In the description of this application, the terms “center,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” and “outer,” etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0029] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation", "connection" and "joining" should be interpreted broadly, for example, they can be fixed connections, detachable connections, mating connections or integral connections; those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0030] This application provides a printed circuit board comprising a stacked structure of multiple conductive layers and dielectric layers alternately stacked, such as... Figure 1 As shown, the conductive layer may include 4 layers (e.g., Figure 1 The dielectric layer (comprising two first conductive layers 11 and two second conductive layers 12) may include three layers (e.g., ...). Figure 1 The two first dielectric layers (composed of a flexible dielectric layer 21 and a PP layer 22) and the central dielectric layer 23 (core) located in the central layer of the stacked structure, of course, Figure 1 The diagram shown is only one possible structure of the printed circuit board. The number of conductive layers and dielectric layers can be set according to actual needs. This application does not limit the number of conductive layers and dielectric layers.

[0031] The conductive layer and the dielectric layer are stacked alternately, with the conductive layer disposed on the upper surface of the dielectric layer.

[0032] Generally speaking, the outer surface of a PCB refers to the side of the PCB used to set pads or solder power devices. The upper surface of the dielectric layer refers to the side of the dielectric layer closest to the outer surface of the PCB, while the lower surface of the dielectric layer refers to the side of the dielectric layer furthest from the outer surface of the PCB.

[0033] The conductive layer is made of conductive materials, usually copper, aluminum or silver, which are conductors with good conductivity. The conductive layer can be connected to the ground wire to shield and protect the signal.

[0034] The dielectric layer is made of insulating material, so it is often called the insulating layer. The dielectric layer mainly serves to support the conductive layer.

[0035] See also Figure 1 The first conductive layer 11 and the second conductive layer 12 are respectively the outermost and second outermost conductive layers in the multi-layered structure. That is, the first conductive layer 11 and the second conductive layer 12 are respectively the outermost and second outermost conductive layers in the multi-layered structure in the direction away from the core layer 23 (i.e.,...). Figure 1 The arrows in the diagram indicate the outermost and second-outermost conductive layers.

[0036] The first dielectric layer is located between the first conductive layer 11 and the second conductive layer 12.

[0037] It is easy to understand that the direction away from the core layer 23 has two opposite directions starting from the core layer 23 (see the arrow directions in the figure). Therefore, there are two first conductive layers 11 and two second conductive layers 12, and consequently, there are also two first dielectric layers.

[0038] The first dielectric layer includes a soft dielectric layer 21 with a Young's modulus less than or equal to a preset Young's modulus.

[0039] Optionally, the Young's modulus is preset to be less than or equal to 15 GPa, that is, the Young's modulus of the soft dielectric layer is less than or equal to 15 GPa.

[0040] The printed circuit board provided in this application reduces the Young's modulus of the dielectric layer between the outermost conductive layer and the second outermost conductive layer by mixing a soft dielectric layer between the dielectric layer and the second outermost conductive layer. On the one hand, this reduces the modulus of the PCB at the bottom of the power device solder joint, thereby improving the reliability of the solder joint between the power device and the PCB and meeting the product lifespan requirements. On the other hand, it strengthens the withstand voltage capability between the outermost conductive layer and the second outermost conductive layer.

[0041] In one example, the first dielectric layer is formed by laminating a PP layer and a flexible dielectric layer. Since the Young's modulus of the flexible dielectric layer is lower than that of the PP layer, the Young's modulus of the first dielectric layer after laminating the PP and flexible dielectric layers will also be lower than that of the PP layer, effectively reducing the Young's modulus of the first dielectric layer. For example...

[0042] Figure 1 In this structure, the PP layer 22 is composed of PP that partially or completely covers the surface of the flexible dielectric layer 21 near the second conductive layer 12. The surface of the flexible dielectric layer 21 near the first conductive layer is tightly bonded to the first conductive layer 11. The PP is tightly bonded to the flexible dielectric layer 21 and the second conductive layer 12 respectively, so as to firmly bond the flexible dielectric layer 21 and the second conductive layer 12.

[0043] PP acts as an interlayer adhesive. Under the high temperature and pressure of a laminator, it softens and then hardens, transforming from B-stage to C-stage, thus bonding the two layers together. For example... Figure 1 In this process, PP bonds the flexible dielectric layer 21 and the second conductive layer 12 together.

[0044] PP can be made from thermosetting or thermoplastic materials, such as phenolic resin, urea-formaldehyde resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin, polyurethane, etc. This application does not limit the choice of materials, and appropriate materials can be selected to prepare PP as needed.

[0045] Figure 2 Provided for the embodiments of this application Figure 1 The diagram shows the manufacturing process of a printed circuit board. Figure 2 As shown, Figure 1 The manufacturing process of the printed circuit board shown includes steps S201-S204.

[0046] In step S201, a flexible dielectric layer single panel is provided, which includes a flexible dielectric layer and a conductive layer, such as a copper foil layer, formed on the surface of the flexible dielectric layer.

[0047] In step S202, the interface of the flexible dielectric layer is roughened to make the single-sided flexible dielectric layer easier to bond and fix to the inner core board.

[0048] In step S203, the flexible dielectric layer single-sided board is laminated with the inner core board using PP to form a PCB motherboard.

[0049] For example, a flexible dielectric layer single-sided board (with the flexible dielectric layer single-sided board facing the PP away from the conductive layer), PP, inner core board, PP and flexible dielectric layer single-sided board are stacked in sequence, and then they are pressed together to form a PCB motherboard.

[0050] In this step, a release film can be wrapped around the stacked structure formed by the overlapping flexible dielectric layer single-sided board, PP, inner core board, and PP and flexible dielectric layer single-sided board before the pressing operation is performed. The purpose is to prevent the PP from melting and flowing out as glue under pressure during the pressing process.

[0051] It's easy to understand that "inner core board" refers to the core board located in the inner layer of the PCB, for example, Figure 1 The core layer 23 and the second conductive layer 12 covering the upper and lower surfaces of the core layer 23.

[0052] In step S204, through holes / blind holes are drilled on the PCB and electroplated to achieve conductivity between the conductive layers.

[0053] At least one dielectric layer and one conductive layer have vias formed along the stacking direction of the dielectric and conductive layers. When there are dielectric and conductive layers without vias, a blind via is formed on the PCB. When every dielectric and conductive layer has a via, a through-hole is formed on the PCB.

[0054] Blind vias are generally used to connect surface layer circuitry to underlying inner layer circuitry. The depth and diameter of the via typically do not exceed a certain ratio.

[0055] Through holes are generally used to enable internal interconnection or as mounting and positioning holes for components.

[0056] Vias are used to make traces located on different layers conductive. The via is filled with a material medium to form a core. The core is insulated from the conductive layer but electrically connected to the trace that needs to be conductive.

[0057] Vias can be configured independently, with the via core electrically connected to other structures, such as pads on a conductive layer, via traces. Alternatively, pads can be directly placed on the vias, and power devices can be soldered onto these pads, achieving electrical connection between the power devices and the via core. Power devices can be, for example, MOSFETs, chips, or other electrical components.

[0058] In practice, the core hole and the conductive layer can be spaced apart to achieve insulation between the core hole and the conductive layer; alternatively, an insulating material, such as coating with insulating resin or setting with insulating rubber, can be placed between the core hole and the conductive layer to achieve insulation between the core hole and the conductive layer.

[0059] The drilling process for through holes or blind holes can be plasma drilling, photosensitive drilling, laser drilling, etc. This application does not limit the drilling process, and the appropriate drilling process can be selected according to the actual situation.

[0060] Figure 3 This is a schematic diagram of another printed circuit board structure provided in an embodiment of this application. For example... Figure 3 As shown, it is similar to Figure 1 The difference in the printed circuit board shown is that the first dielectric layer includes a PP layer 22 covering the upper and lower surfaces of the flexible dielectric layer 21. The PP layer 22 is composed of PP partially or completely covering the upper and lower surfaces of the flexible dielectric layer 21. The flexible dielectric layer 21 is tightly connected to the first conductive layer and the second conductive layer through the PP.

[0061] It should be explained that the upper surface of the flexible dielectric layer 21 refers to the surface of the flexible dielectric layer that is closer to the first conductive layer 11, and the lower surface of the flexible dielectric layer refers to the surface that is closer to the second conductive layer 12. In other words, the upper surface of the flexible dielectric layer refers to the surface of the flexible dielectric layer that is away from the core layer 23, and the lower surface of the flexible dielectric layer refers to the surface that is closer to the core layer 23.

[0062] In one example, the PP mentioned above is FR4 PP.

[0063] Figure 4 Provided for the embodiments of this application Figure 3 The diagram shows the manufacturing process of a printed circuit board. Figure 4 As shown, Figure 3 The manufacturing process of the printed circuit board shown includes steps S401-S404.

[0064] In step S401, a soft dielectric layer is prepared.

[0065] The flexible dielectric material is fabricated into a plate shape, for example, by laminating a flexible dielectric layer into a plate-shaped flexible dielectric layer.

[0066] In step S402, the interface of the soft dielectric layer is roughened.

[0067] The upper and lower surfaces of the flexible dielectric layer are roughened to make it easier for the flexible dielectric layer to bond and fix with PP.

[0068] In step S403, the first conductive layer, PP layer, flexible dielectric layer, PP layer, and inner core board are laminated to form a PCB motherboard.

[0069] For example, the first conductive layer, PP layer, flexible dielectric layer, PP layer, inner core board, PP layer, flexible dielectric layer, PP layer, and first conductive layer are stacked sequentially, and then they are pressed together to form a PCB motherboard.

[0070] The first dielectric layer forms a sandwich structure consisting of a PP layer, a flexible dielectric layer, and another PP layer.

[0071] It's easy to understand that "inner core board" refers to the core board located in the inner layer of the PCB, for example, Figure 3 The core layer 23 and the second conductive layer 12 covering the upper and lower surfaces of the core layer 23.

[0072] In step S404, through holes / blind holes are drilled on the PCB and electroplated to achieve conductivity between the conductive layers.

[0073] Figure 5 This is a schematic diagram of another printed circuit board structure provided in an embodiment of this application. For example... Figure 5 As shown, it is similar to Figure 1 and Figure 3 The difference in the printed circuit board shown is that the first dielectric layer only includes a flexible dielectric layer, and the upper and lower surfaces of the flexible dielectric layer are tightly bonded to the first conductive layer and the second conductive layer, respectively.

[0074] It should be explained that the upper surface of the flexible dielectric layer 21 refers to the surface of the flexible dielectric layer 21 that is closer to the first conductive layer 11, and the lower surface of the flexible dielectric layer 21 refers to the surface of the flexible dielectric layer 21 that is closer to the second conductive layer 12. In other words, the upper surface of the flexible dielectric layer 21 refers to the surface of the flexible dielectric layer 21 that is away from the core layer 23, and the lower surface of the flexible dielectric layer 21 refers to the surface of the flexible dielectric layer 21 that is closer to the core layer 23.

[0075] Figure 6 Provided for the embodiments of this application Figure 5 The diagram shows the manufacturing process of a printed circuit board. Figure 6 As shown, Figure 5 The manufacturing process of the printed circuit board shown includes steps S601-S603.

[0076] In step S601, the soft dielectric PP material is prepared.

[0077] That is, PP materials are prepared by selecting dielectric materials with a Young's modulus of less than 15 GPa. For example, polyimide (PI) is selected to prepare PP materials.

[0078] In step S602, the first conductive layer, the flexible dielectric PP layer, and the inner core board are laminated to form a PCB motherboard.

[0079] For example, the first conductive layer, the flexible dielectric PP layer, the inner core board, the flexible dielectric PP layer, and the first conductive layer are stacked in sequence, and then they are pressed together to form a PCB motherboard.

[0080] It's easy to understand that "inner core board" refers to the core board located in the inner layer of the PCB, for example, Figure 5 The core layer 23 and the second conductive layer 12 covering the upper and lower surfaces of the core layer 23.

[0081] In step S603, through holes / blind holes are drilled on the PCB and electroplated to achieve conductivity between the conductive layers.

[0082] It is understood that the embodiments of this application Figure 2 , Figure 4 and Figure 6 Provided for Figure 1 , Figure 3 and Figure 5 The manufacturing process of the printed circuit board is a partial process. For example, after step S204, step S404, or step S603, it also includes subsequent manufacturing steps such as outer layer patterning, outer layer etching, outer layer inspection, solder mask / characters, surface treatment, milling, electrical performance testing, finished product inspection, and packaging.

[0083] In one example, a layer of soft dielectric material can be integrally mixed within the first dielectric layer, for example, Figure 1 , Figure 3 , Figure 5 The printed circuit board shown has a full-layer mixed-pressure flexible dielectric layer in the first dielectric layer. This not only improves the reliability of the solder joints between the power devices and the PCB by reducing the Young's modulus of the first dielectric layer, but also facilitates the fabrication and processing of the first dielectric layer.

[0084] In another example, a soft dielectric layer may be locally mixed within the first dielectric layer, for example, Figure 1 , Figure 3 , Figure 5 The first conductive layer of the printed circuit board shown is provided with pads (not shown in the figure), and a flexible dielectric layer is provided on the first dielectric layer corresponding to the pad positions.

[0085] It should be explained that the meaning of the corresponding pad position on the first dielectric layer refers to the area on the first dielectric layer that affects the solder joint when power devices are soldered onto the pads. For example, it could be the area on the first dielectric layer below the pad, or the area of ​​the orthographic projection of the pad on the first dielectric layer, or the area of ​​the orthographic projection of the pad on the first dielectric layer that is slightly larger, or the area of ​​the orthographic projection of the pad on the first dielectric layer that is slightly smaller. In this way, the reliability of the solder joint between the power device and the PCB can be improved by reducing the Young's modulus of the first dielectric layer, while saving flexible dielectric material.

[0086] Pads include functional pads and non-functional / redundant pads, used to achieve electrical and mechanical connections between power devices (such as MOSFETs and chips) and the PCB, thereby correctly packaging the power devices on the PCB.

[0087] It is easy to understand that, Figure 1 , Figure 3 , Figure 5 The first conductive layer 11, the flexible dielectric layer 21 and the PP layer 22 constitute the dielectric layer, and the second conductive layer constitutes the core board. The core layer 23 is the substrate. The core board is disposed on the two opposite outer walls of the substrate in the extension direction to reduce the Young's modulus of the outer layers on both sides of the PCB and improve the reliability of the solder joints between the power devices and the PCB.

[0088] In another example, for the sake of simplifying the printed circuit board manufacturing process, the core board can be provided only on one side of the substrate, that is, the core board is covered only on one outer wall surface in the extension direction of the substrate, while the other outer wall surface still uses a conventional core board. For example, only on one outer wall surface in the extension direction of the substrate. Figure 1 , Figure 3 , Figure 5 A flexible dielectric layer is disposed within the dielectric layer between the first conductive layer 11 and the second conductive layer in the direction of one of the arrows.

[0089] In one example, the substrate includes N third conductive layers and M second dielectric layers, which are alternately stacked, where M = N + 1, and N and M are both natural numbers; for example, the substrate can be a single-layer structure, i.e., N = 0, M = 1, for example... Figure 1 , Figure 3 and Figure 5 The substrate in this paper has only one dielectric layer, namely the core layer 23. The substrate can also be a multilayer structure, for example, N=1, M=2, meaning the substrate has one conductive layer and two dielectric layers, with the dielectric and conductive layers alternately stacked to form a multilayer structure. The structure of the substrate can be selected as needed; this application does not limit the specific structure of the substrate.

[0090] To save on flexible dielectric materials, the dielectric layer (i.e., the second dielectric layer) in the substrate is made of conventional materials, such as epoxy resin. The Young's modulus of the second dielectric layer is greater than 20 GPa. Therefore, the Young's modulus of the first dielectric layer is less than that of the second dielectric layer.

[0091] In another example, a flexible dielectric layer is provided within all or part of the dielectric layer in the substrate. On the one hand, this reduces the Young's modulus of the PCB as a whole and improves the PCB's voltage resistance. On the other hand, it ensures that the material of multiple core boards in the PCB is the same, guaranteeing that the modulus and CTE of multiple core boards are equal or approximately equal.

[0092] Preferably, the thickness of the flexible dielectric layer is 2-8 mil, the thickness of the PP layer is 2-5 mil, and the thickness of the conductive layer is 3-5 ounces.

[0093] In one example, the CTE in the XY axis direction of the flexible dielectric layer is less than or equal to a preset threshold, for example, the preset threshold is less than or equal to 30, that is, the CTE in the XY axis direction of the flexible dielectric layer is less than or equal to 30.

[0094] It is easy to understand that the XY axis direction of the flexible dielectric layer refers to the surface extension direction of the flexible dielectric layer, that is, the direction perpendicular to the thickness direction of the flexible dielectric layer.

[0095] Therefore, the Young's modulus of the flexible dielectric layer must be less than or equal to 15 GPa, and the CTE in the XY axis direction of the flexible dielectric layer must be less than or equal to 30.

[0096] Optionally, the flexible dielectric layer is made of polyimide (PI) material.

[0097] In another example, Figure 1 , Figure 3 and Figure 5 The inner core board can also be a multi-layer board structure.

[0098] This application also provides an electronic device, including a power device and a printed circuit board as described in the above embodiments, wherein the power device is electrically connected to the printed circuit board.

[0099] For example, the outermost layer of a printed circuit board is provided with pads, and power devices (such as MOSFETs and chips) are soldered to the pads to be electrically connected to the pre-defined traces in the printed circuit board.

[0100] Alternatively, a connector hole can be provided on the outer layer of the printed circuit board, and the power device can be plugged into the connector hole to achieve electrical connection with the preset traces in the printed circuit board.

[0101] Electronic devices include, but are not limited to, mobile phones, tablets, wearable devices, laptops, ultra-mobile personal computers (UMPCs), handheld computers, walkie-talkies, netbooks, POS machines, personal digital assistants (PDAs), dashcams, or virtual reality devices.

[0102] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0103] In the description of this specification, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A printed circuit board, characterized in that, include: A core board and a substrate, the core board covering one of two opposing outer wall surfaces of the substrate; the core board comprises: The first conductive layer is located on the side of the core board away from the substrate; The second conductive layer is located on the side of the core board closest to the substrate; A first dielectric layer, located between the first conductive layer and the second conductive layer, includes a flexible dielectric layer, wherein the Young's modulus of the flexible dielectric layer is less than or equal to a preset Young's modulus. Wherein, the Young's modulus of the first dielectric layer is smaller than that of the substrate, the first dielectric layer further includes a prepreg, and the first dielectric layer is formed by mixing and pressing the flexible dielectric layer and the prepreg. The first conductive layer is provided with pads, and the flexible dielectric layer is provided on the first dielectric layer corresponding to the pad positions.

2. The printed circuit board according to claim 1, characterized in that, The preset Young's modulus is less than or equal to 15 GPa.

3. The printed circuit board according to claim 1 or 2, characterized in that, The core board is also covered on the other of the two outer wall surfaces opposite to the substrate.

4. The printed circuit board according to claim 1, characterized in that, The prepreg partially or completely covers the surface of the flexible dielectric layer near the second conductive layer, wherein the surface of the flexible dielectric layer near the first conductive layer is in close contact with the first conductive layer, and the prepreg is in close contact with the flexible dielectric layer and the second conductive layer respectively.

5. The printed circuit board according to claim 1, characterized in that, The flexible dielectric layer partially or completely covers the prepreg on both the surface near the first conductive layer and the surface near the second conductive layer; wherein the flexible dielectric layer is tightly connected to the first conductive layer and the second conductive layer respectively through the prepreg.

6. The printed circuit board according to any one of claims 1-5, characterized in that, The prepreg is an FR4 prepreg.

7. The printed circuit board according to any one of claims 1-3, characterized in that, The surface of the flexible dielectric layer near the first conductive layer is in close contact with the first conductive layer, and the surface near the second conductive layer is in close contact with the second conductive layer.

8. The printed circuit board according to any one of claims 1-7, characterized in that, The substrate includes N third conductive layers and M second dielectric layers, which are alternately stacked, wherein M = N + 1, and N and M are both natural numbers; The Young's modulus of the first dielectric layer is less than that of the second dielectric layer.

9. The printed circuit board according to any one of claims 1-7, characterized in that, The substrate includes N third conductive layers and M second dielectric layers, which are alternately stacked, wherein M = N + 1, and N and M are both natural numbers; Some of the M second dielectric layers include the soft dielectric layer; Alternatively, each of the M second dielectric layers may include the soft dielectric layer.

10. The printed circuit board according to any one of claims 1-9, characterized in that, The coefficient of thermal expansion of the flexible dielectric layer in the XY axis direction is less than or equal to a preset threshold.

11. The printed circuit board according to claim 10, characterized in that, The preset threshold is less than or equal to 30.

12. The printed circuit board according to any one of claims 1-11, characterized in that, The flexible dielectric layer is made of polyimide material.

13. An electronic device, characterized in that, It includes a power device and a printed circuit board as described in any one of claims 1-12, wherein the power device is electrically connected to the printed circuit board.

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