CN114286494A - PCB structure, manufacturing method thereof and electronic equipment - Google Patents
PCB structure, manufacturing method thereof and electronic equipment Download PDFInfo
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- CN114286494A CN114286494A CN202011033555.8A CN202011033555A CN114286494A CN 114286494 A CN114286494 A CN 114286494A CN 202011033555 A CN202011033555 A CN 202011033555A CN 114286494 A CN114286494 A CN 114286494A
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Abstract
The application provides a PCB structure, including first core, tie coat and the second core of range upon range of setting, bond through the tie coat between second core and the first core, the coefficient of thermal expansion of second core is less than the coefficient of thermal expansion of first core, and the surface of first core is equipped with the circuit layer, does not have the circuit layer between tie coat and the second core. This application is through setting up the second core that at least one coefficient of expansion is less than first core in a plurality of first cores to change the coefficient of thermal expansion of whole PCB structure, with the whole rigidity that promotes the PCB structure, solve the warpage problem of PCB structure in the reflow soldering in-process. Meanwhile, the application also provides a manufacturing method of the PCB structure and electronic equipment.
Description
Technical Field
The present invention relates to the field of Printed Circuit Board (PCB) technology, and in particular, to a PCB structure and a method for manufacturing the same, and an electronic device.
Background
The PCB (printed circuit board) is one of the very important and critical components in the electronic products in the ICT industry, and plays a role in physical support of different components (including chips, capacitors, resistors, etc.) in the system and signal transmission between the components. When the components are mounted on the PCB, the components and the pads on the surface of the PCB are often soldered together by melting the lead-free solder through reflow soldering. In the reflow soldering process of the PCB, the PCB generally warps and deforms due to heating, and the flatness of the board surface deteriorates, i.e., the warping degree increases. With the increasing complexity of ICT industry systems, the used chips are larger and larger in package size, heavier and heavier in weight and more in number of solder balls, and the local areas of the PCB at the chip welding positions are more sensitive to the warping degree of the PCB. Therefore, how to improve the rigidity of the PCB and reduce the warpage of the PCB after reflow soldering becomes the research and development focus of the industry.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a PCB structure, and the overall rigidity of the PCB structure is improved by adding a second core board with a small thermal expansion coefficient, so that the problem of warping of the PCB structure in the reflow soldering process is solved.
In order to achieve the above object, the embodiments of the present invention provide the following technical solutions:
in a first aspect, the present invention provides a PCB structure, including a first core board, a bonding layer, and a second core board, which are stacked, wherein the second core board is bonded to the first core board through the bonding layer, a thermal expansion coefficient of the second core board is smaller than a thermal expansion coefficient of the first core board, a metal layer is disposed on a surface of the first core board, and no metal layer is disposed between the bonding layer and the second core board. The first core board and the second core board are copper clad boards, and are plate composite structures with resin glue solution and glass fiber cloth as raw materials and copper foil coated on one or two surfaces of the outermost layer of the first core board and the second core board through operations of pre-dipping, pre-drying, heating, pressurizing and the like. The bonding sheet is a prepreg, which is a sheet formed by soaking degreased glass fiber cloth in resin glue solution and then pre-drying, and has the function of bonding different copper clad laminates, such as the first core board and/or the second core board mentioned in the embodiment. It can be understood that the PCB structure is formed by laminating and bonding a first core board and a second core board, which is different from the design in the conventional scheme in that the copper-clad board in the PCB structure in the embodiment includes the second core board having a thermal expansion coefficient smaller than that of the first core board in addition to the first core board. It can be understood that, because the thermal expansion coefficient of the second core board is smaller than that of the first core board, in the reflow soldering process, when the first core board and the second core board absorb heat and deform, because the expansion amount of the second core board is smaller than that of the first core board, and because the second core board is bonded with the first core board into a whole, the second core board with small expansion amount can inhibit the first core board with large expansion amount, and further reduce the expansion amount of the whole PCB structure, so as to reduce the warpage caused by reflow soldering. For the second core board of the present application, the design aims to improve the thermal expansion performance and rigidity of the PCB structure, and the first core board and the second core board are integrated by the adhesive layer, so that when the first core board is deformed by thermal expansion, the first core board can be effectively inhibited by the second core board adhered thereto. It can be understood that the larger the bonding range of the second core plate and the first core plate, the more obvious the improvement effect of the corresponding second core plate. Meanwhile, it should be noted that the circuit pattern in the embodiment is manufactured by selectively etching the copper foil on the copper-clad plate to obtain the required circuit pattern. The first core board and the second core board are both of copper clad plate structures, copper foils are arranged on the surfaces of the first core board and the second core board, the purpose is to obtain needed circuit patterns on the copper foils through selective etching, and for the embodiment of the application, the second core board is designed to improve the thermal expansion performance and rigidity of the whole PCB structure, and does not need to participate in circuit design in the PCB structure. Therefore, for the second core board, the surface of the copper-clad plate is subjected to chemical cleaning, pad pasting exposure, development etching and other processing to remove the copper foil on the surface, so that no circuit layer is arranged on the second core board. The design has the advantages that the functions of the first core board and the second core board are clear, and the influence of the residual copper foil of the second core board on the circuit layer in the first core board is avoided. Another reason for etching the copper foil on the surface of the second core board is to reduce the influence of the copper foil on the second core board on the overall thermal expansion coefficient of the phase-stretched PCB structure and the overall thermal expansion performance of the PCB structure.
In one possible embodiment, the second core panel has a coefficient of expansion less than or equal to 10 ppm/deg.C and the first core panel has a coefficient of expansion in a range from 15 ppm/deg.C to 20 ppm/deg.C. In the embodiment, the first core plate belongs to a conventional copper-clad plate, and the thermal expansion coefficient of the first core plate is generally between 15 ppm/DEG C and 20 ppm/DEG C. While the second core board in the embodiment is designed to adjust the thermal expansion performance of the entire PCB structure, the thermal expansion coefficient of the second core board is less than or equal to 10 ppm/c in this respect.
In one possible embodiment, the second core plate has an elastic modulus greater than or equal to 25 Gpa. In the embodiment, the elastic modulus of the second core board is greater than or equal to 25Gpa, so as to enhance the rigidity of the second core board, and thus when the PCB structure is heated and thermally expanded, the deformation amount of the second core board with higher elastic modulus is smaller, and for the whole PCB structure, because the second core board with higher elastic modulus exists, the overall rigidity of the PCB structure is improved. It can be understood that when the modulus of elasticity of the second core board is greater than or equal to 25Gpa, the rigidity of the second core board to the whole PCB structure is significantly improved.
In one possible embodiment, the second core plate has a thickness in the range of 0.3mm to 1 mm. In the embodiment, the second core board is used for improving the thermal expansion performance and the elastic modulus of the whole PCB structure, and if the thickness of the second core board is too low, for example, less than 0.3mm, the improvement effect is not obvious enough, and the thermal expansion performance of the whole PCB structure cannot be adjusted; if the thickness is too large, the most direct effect is to increase the overall thickness of the PCB structure, and it can be understood that the effect on the second core board is limited to improving the thermal expansion performance and the elastic modulus of the PCB structure, and does not participate in the circuit layout, so if the thickness of the second core board is too large, for example, exceeding 1mm, the thickness of the PCB structure is inevitably increased, which is not favorable for the miniaturization design.
In one possible embodiment, the second core plate includes a first face and a second face, and the number of the first core plates and the number of the adhesive layers are both two, wherein one of the adhesive layer stacks is provided between the first face and one of the first core plates, and the other of the adhesive layer stacks is provided between the second face and the other of the first core plates. In this embodiment, the second core board is sandwiched by the two first core boards and is bonded to the first core board through the bonding layer, so that the first surface and the second surface of the second core board are bonded to the first core board, and the second core board is prevented from thermal expansion deformation of the first core boards on two sides effectively, thereby improving the thermal expansion performance of the whole PCB structure.
In one possible embodiment, the adhesive layer covers the first face and the second face entirely. The second core plate is bonded with the first core plates on the two sides into a whole through the bonding layers, the second core plate inhibits the thermal expansion deformation of the first core plates on the two sides through bonding force, and when the bonding layers completely cover the first surface and the second surface, the maximization of the bonding force can be ensured under the same size, so that the influence of the second core plate on the thermal expansion deformation of the first core plate is facilitated; meanwhile, the increase of the bonding force can also avoid the cracking phenomenon among different layer structures.
In a possible embodiment, the number of the first core plates is multiple, and multiple first core plates are stacked and symmetrically distributed on two sides of the second core plate. The number of the second core boards in the embodiment is one, the number of the corresponding first core boards is multiple, and because the thermal expansion coefficient and the elastic modulus of the second core boards are different from those of the first core boards, the second core boards are arranged at the center of the whole PCB structure, and the first core boards are symmetrically arranged at two sides of the second core boards, so that the stress concentration influence caused by a reflow soldering process can be reduced, and the warping problem of the whole PCB structure is improved.
In a possible embodiment, the PCB structure includes a central layer, the number of the second core boards is multiple, and the multiple second core boards are symmetrically distributed on two sides of the central layer. In an embodiment, the PCB structure includes a central layer, which may be a first core board or a second core board, and the specific situation is selected according to actual needs. The second core board in the embodiment functions to improve thermal expansion performance and rigidity of the entire PCB structure, so when the second core board is selectively added to the PCB structure, it is preferable that the plurality of second core boards are symmetrically distributed regardless of whether the central layer of the PCB structure is the first core board or the second core board. The symmetrically distributed second core boards have the advantages that the thermal expansion performance and rigidity of the PCB structure can be improved more effectively, and meanwhile, the problem of stress concentration can be relieved. The copper clad plates with the same thermal expansion coefficient are selected from the existing multilayer PCB structure, the design aims to reduce the stress problem caused by thermal expansion deformation among different copper clad plates, and for the application, the warping of the heated PCB is overcome, so that the stress problem caused by different thermal expansion coefficients is reduced as far as possible after the second core plates with different thermal expansion coefficients are introduced. The symmetrical distribution can effectively and evenly distribute the stress between the first core board and the second core board, and the stress is prevented from being concentrated in a certain area in the PCB structure.
In a possible embodiment, when the number of the second core boards is odd, the central layer of the PCB structure is the second core board. In this embodiment, the number of the second core boards is odd, such as 3, 5, etc., and in order to ensure the symmetrical distribution of the second core boards in the PCB structure, the central layer corresponding to the PCB structure is the second core board, and the first core boards bonded by the adhesive layers are located at two sides of the second core board of the central layer.
In a possible embodiment, when the number of the second core boards is even, the central layer of the PCB structure is the first core board or the adhesive layer, and the plurality of second core boards are symmetrically distributed on two sides of the central layer. The number of the second core boards in the embodiment is even, such as 2/4/6, etc., and in this case, in order to ensure the symmetrical distribution of the second core boards in the PCB structure, the central layer of the corresponding PCB structure is the first core board or the adhesive layer. When the central layer is the first core plate, the two sides of the first core plate are respectively provided with the second core plates which are bonded through the bonding layers, and then the outer sides of the second core plates are provided with the first core plates which are bonded through the bonding layers, so that each second core plate is clamped by the two first core plates. When the center layer is the tie coat, the both sides of this tie coat set up first core respectively, are equipped with the second core that sets up through the tie coat bonding again in the outside of this first core, are equipped with the first core that sets up through the tie coat again in the outside of this second core simultaneously to ensure that every second core is all established by two first core clamps.
In a possible embodiment, the thickness of the second core board in the PCB structure is greater than or equal to 10%. The thickness of the PCB structure is determined by the thickness of the first core plate, the thickness of the second core plate and the thickness of the adhesive layer. For the whole PCB structure, the first core plate is used for bearing high-speed circuit work, so that the plurality of first core plates are the main body part of the whole PCB structure, and the second core plate is used as an intermediate layer structure for adjusting the thermal expansion performance and rigidity of the PCB structure and plays an auxiliary role. Therefore, for the whole PCB structure, the thickness ratio of the second core board in the PCB structure is smaller than that of the first core board, but in order to ensure the improvement of the thermal expansion performance and rigidity of the whole PCB structure by the second core board, the thickness ratio of the second core board in the PCB structure is greater than or equal to 10%, and if the ratio is lower than the ratio, the improvement effect of the second core board is not obvious, and the problem of warping of the PCB structure after the reflow soldering process cannot be overcome. It should be noted that, in the embodiments, regardless of whether the number of the second core boards is one or more, the thickness ratio here refers to the thickness ratio of all the second core boards in the whole PCB structure.
In a possible embodiment, the surface of the second core plate is provided with a micro-protrusion structure for increasing the bonding force between the second core plate and the bonding layer. The design of the micro-protrusion structure in the embodiment aims to increase the contact area between the second core board and the bonding layer, so that the bonding force between the second core board and the bonding layer is increased, and the situation of warping and cracking is avoided.
In a possible embodiment, the second core plate comprises an edge region and a central region, the edge region surrounds the central region, and the distribution density of the microprojection structures in the edge region is greater than the distribution density of the microprojection structures in the central region. In the embodiment, the micro-protrusion structures are mainly distributed in the edge area of the second core plate, so that the bonding force of the edge area in the pressing process is improved. It can be understood that, for the PCB structure, the position where the warpage deformation occurs is mostly at the edge position of the board, and in this embodiment, the distribution density of the micro-protrusion structure of the second core board at the edge area is increased, so that the contact surface between the second core board and the bonding layer at the edge area is further increased, the adhesive force between the second core board and the bonding layer is improved, and the situation of warpage cracking is avoided.
In a second aspect, the present invention further provides a method for manufacturing a PCB structure, comprising the following steps: providing a first core board, wherein the first core board is a copper-clad board, and etching a copper foil on the first core board to obtain a circuit layer; providing a second core board, wherein the second core board is a copper-clad board, and etching away copper foil on the second core board to ensure that no circuit layer exists on the surface of the second core board, and the thermal expansion coefficient of the second core board is smaller than that of the first core board; and pressing and bonding the first core plate and/or the second core plate by using a bonding layer. In the embodiment, the first core board and the second core board are both of a plate-shaped composite structure in which resin glue is used as a raw material, and after glass fiber cloth is added, copper foil is coated on one surface or two surfaces of the outermost layer of the first core board and the second core board through operations such as pre-drying, heating, pressurizing and the like. The manufacturing process is the same as that of the traditional PCB structure, bonding sheets (prepregs) are adopted, and a plurality of first core plates and at least one second core plate which are arranged in a stacked mode are pressed through a high-temperature press machine, so that the needed PCB structure is obtained. The difference lies in that the thermal expansion coefficient of the second core board is smaller than that of the first core board, so that the thermal expansion performance and rigidity of the whole PCB can be improved through the second core board, and the PCB structure capable of overcoming the warping caused by reflow soldering is obtained. And simultaneously, in the process of manufacturing the first core board, etching the copper foil on the first core board to obtain the circuit layer, and in the process of manufacturing the second core board, etching away the copper foil on the second core board to ensure that no circuit layer exists on the surface of the second core board.
In a third aspect, the present invention further provides an electronic device, where the electronic device includes a component and the PCB structure described above, the PCB structure includes a pad, and the component is soldered on the pad. The components can be chips, capacitors, resistors and other devices, the pads refer to welding structures exposed out of the metal layer on the outermost side of the PCB structure, and in the etching process of the metal layer, on one hand, etching can be performed according to the requirements of a circuit layout, and meanwhile, appropriate pads can be provided for the components according to the design of the circuit layout so as to realize matching of the components and the circuit. The components are welded with the PCB structure through the bonding pads arranged on the surface of the PCB structure, so that the components and the PCB structure are fixedly installed. In the embodiment of the component, the mode that the component passes through reflow soldering welds with PCB structure, compare in traditional PCB structure can lead to warpage because of the thermal expansion of copper-clad plate after reflow soldering, cause the risk of desoldering, the electronic equipment that this application provided is equipped with the second core that improves thermal expansion performance in its PCB structure, can overcome the warpage problem of PCB structure after reflow soldering.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic diagram of an electronic device in one embodiment of the invention;
FIG. 2 is a schematic illustration of warpage of a prior art PCB structure;
FIG. 3 is a cross-sectional view of a first PCB construction in an embodiment of the invention;
FIG. 4 is a cross-sectional view of a second PCB construction in an embodiment of the invention;
FIG. 5 is a cross-sectional view of a third PCB construction in an embodiment of the invention;
FIG. 6 is a cross-sectional view of a fourth PCB configuration in an embodiment of the present invention;
FIG. 7 is a graph comparing the performance of PCB structures in the prior art and the present application embodiments;
FIG. 8 is a graph comparing warp maxima for prior art and present embodiments of PCB structures;
FIG. 9 is a graph comparing warpage ripple of a PCB structure in the prior art and the present embodiment;
FIG. 10a is a prior art PCB structure test cloud at 30 deg.C;
FIG. 10b is a prior art PCB structure test cloud at 250 deg.C;
FIG. 10c is a prior art PCB structure test cloud at 130 deg.C;
FIG. 11a is a test cloud of a PCB structure of the present application at 30 ℃;
FIG. 11b is a test cloud of a PCB structure of the present application at 250 ℃;
FIG. 11c is a test cloud of the PCB structure of the present application at 130 ℃;
fig. 12 is a sectional view of a second core plate provided by the present invention;
fig. 13 is a top view of a second core plate provided by the present invention;
fig. 14 is a flow chart of the PCB structure fabrication provided by the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly described below with reference to the accompanying drawings in the embodiments of the present invention.
The use of the terms first, second, etc. in this disclosure is to distinguish one element, component, or ingredient from another, and is not intended to indicate or imply the relative importance or number of such elements, components, or ingredients. "plurality" means two or more unless otherwise specified.
Fig. 1 shows a specific application of the PCB structure 100 provided in the present application in an electronic device 200, where the electronic device 200 may be a radio, a player, a telephony device, a computer, or other electronic products. In this application scenario, the PCB structure 100 is used to support the physical support and signal transmission of different components 110 in the electronic device 200, and fig. 1 illustrates the PCB structure 100 and the components with a chip as a specific component 110. As shown in fig. 1, a pad 120 is disposed on one side surface of the PCB structure 100, where the pad 120 refers to a soldering structure formed on an outer metal layer (not shown) of the PCB structure, and during an etching process of the metal layer, on one hand, etching is performed according to a circuit layout requirement, and meanwhile, an appropriate pad is provided for a component according to a design of the circuit layout, so as to match the component with a circuit. The chip (component 110) is reflow soldered to the pad 120, thereby mounting the chip (component 110) on the PCB structure 100. In the implementation, the surface of the package substrate 115 corresponding to the component 110 and the surface of the PCB structure 100 opposite to the pad 120 are coated with the lead-free solder 150, and then the lead-free solder 150 is melted by a reflow process and then cooled and solidified to complete the fixing and mounting.
In the process of mounting the chip on the PCB structure in a reflow soldering manner, as shown in fig. 2, the conventional PCB structure 300 may expand and warp due to local heating, which may cause solder separation and solder connection between the PCB structure 300 and the package board 115, thereby affecting the performance stability of the whole electronic device.
In view of the above problem, as shown in fig. 3, the present application provides a PCB structure 100, where the PCB structure 100 includes a first core board 10, an adhesive layer 30, and a second core board 20, which are stacked, the second core board 20 and the first core board 10 are adhered by the adhesive layer 30, a thermal expansion coefficient of the second core board 20 is smaller than that of the first core board 10, a metal layer 12 is disposed on a surface of the first core board 10, and no metal layer 12 is disposed between the adhesive layer 30 and the second core board 20. The PCB structure 100 in the embodiment is a multi-core structure in which a first core 10, an adhesive layer 30, and a second core 20 are sequentially stacked, and each first core 10 and each second core 20 are bonded by the adhesive layer 30 to form an integral body. The first core board 10 and the second core board 20 are Copper Clad Laminates (CCLs), and are plate-shaped composite structures in which resin glue and glass fiber cloth are used as raw materials, and one or both surfaces of the outermost layer of the core boards are covered with Copper foil by operations such as pre-impregnation, pre-drying, heating, and pressing. The adhesive sheet 30 (prepeg, PP) is a Prepreg, which is a sheet formed by immersing degreased glass fiber cloth in resin glue solution and then pre-drying, and is different from a copper-clad plate (a first core plate 10 and a second core plate 20), the surfaces of both sides of the adhesive sheet 30 are not covered with copper foil, and the adhesive sheet 30 is used for bonding different copper-clad plates, such as the first core plate 10 and/or the second core plate 20 mentioned in the embodiments. It can be understood that the copper-clad plate (the first core plate 10 and the second core plate 20) is a resin substrate with copper foil bonded on the surface, a required circuit pattern can be carved on the copper foil by an etching technique, then the first core plate 10 and/or the second core plate 20 with different circuit patterns are bonded by using the bonding sheet 20, and the PCB structure 100 is manufactured and processed by processes of drilling, electroplating, and the like.
In this embodiment, the PCB structure 100 is formed by stacking and bonding a first core board 10 and a second core board 20, and unlike the conventional scheme, the copper-clad board in the PCB structure 100 of the present application further includes the second core board 20 having a thermal expansion coefficient smaller than that of the first core board 10 in addition to the first core board 10. It can be understood that, since the thermal expansion coefficient of the second core board 20 is smaller than that of the first core board 10, in the reflow soldering process, when the first core board 10 and the second core board 20 absorb heat and deform, since the expansion amount of the second core board 20 is smaller than that of the first core board 10, and the second core board 20 and the first core board 10 are bonded into a whole, the second core board with a small expansion amount can inhibit the first core board with a large expansion amount, and further reduce the expansion amount of the whole PCB structure, so as to reduce the warpage deformation caused by reflow soldering.
It is understood that in the fabrication of PCB structure 100, three primary substrates are included: a first core board 10, a second core board 20, and an adhesive sheet 30. The first core board 10 and the second core board 20 are copper clad boards, that is, glass fiber cloth is dipped in a resin glue solution, and then dried to form a prepreg (an adhesive sheet 30), and then a plurality of prepregs are stacked together according to a certain thickness requirement, one side or two sides of the outermost layer of the prepreg are covered with copper foil, and the prepreg are heated and pressurized to be cured to form a plate-shaped composite material. The copper-clad plate made of the glass fiber cloth has good electrical performance and higher working temperature, and meets the working requirements of high-speed circuits. Similarly, the adhesive sheet 30 is a sheet of prepreg material prepared by impregnating a degreased glass fiber cloth with a resin paste and prebaking, and is not covered with copper foil on both surfaces thereof. As can be seen by comparing the manner in which the first core board 10, the second core board 20 and the bonding sheet 30 are manufactured, the first core board 10 and the second core board 20 can be understood as the main body layers of the PCB structure 100, and the bonding sheet 30 is the connection layer (serving as the bonding layer) between the main body layers. It should be noted that, taking the first core board 10 as an example, in the manufacturing process, in order to enhance the adhesion between the copper foil and the resin material, the adhesion surface is usually subjected to a micro-etching and oxidation treatment (also referred to as a browning treatment) to obtain a micro-rough adhesion surface.
In this embodiment, the circuit layer 12 is formed by selectively etching the copper foil on the copper-clad plate. The raw materials of the first core board 10 and the second core board 20 in this application are copper clad board structures, and the surfaces thereof are provided with copper foils in order to obtain desired circuit patterns on the copper foils by selective etching, but for the embodiment of this application, the second core board 20 is designed in order to improve the thermal expansion performance of the entire PCB structure 100 without participating in the circuit design in the PCB structure 100. Therefore, for the second core board 20, the surface of the copper-clad plate is subjected to chemical cleaning, pad-pasting exposure, development etching and other processing to remove the copper foil on the surface, thereby ensuring that no circuit layer 12 exists on the second core board 20. The advantage of this design is that the first core board 10 and the second core board 20 have definite functions, and the influence of the residual copper foil of the second core board 20 on the circuit layer 12 in the first core board 10 is avoided. Another reason for etching the copper foil on the surface of the second core board 20 is to avoid the influence of the copper foil on the second core board 20 on the overall thermal expansion coefficient of the PCB structure 100, and it can be understood that the thermal expansion coefficient of the copper foil is larger than that of the copper-clad board, so that unnecessary copper foil can be removed to reduce the overall thermal expansion coefficient of the PCB structure 100.
In one particular embodiment, as shown in FIG. 3, the coefficient of thermal expansion of the second core plate 20 is less than 10 ppm/deg.C. In the embodiment, the first core board 10 is a conventional copper clad board, and the thermal expansion coefficient of the first core board is generally between 10 ppm/deg.c and 20 ppm/deg.c for the electrical performance of the PCB structure 100, for example, the thermal expansion coefficient of the copper clad board made of the material model S7439HW is about 12 ppm/deg.c to 14 ppm/deg.c. While the second core board 20 in the embodiment is designed to adjust the thermal expansion performance of the entire PCB structure 100, in this respect, the thermal expansion coefficient of the second core board 20 needs to be less than or equal to 10 ppm/c.
In one particular embodiment, the modulus of elasticity of the second core plate 20 is greater than or equal to 25 Gpa. In this embodiment, the elastic modulus of the second core board 20 is greater than or equal to 25Gpa to enhance the rigidity of the second core board 20, so that when the PCB structure 100 is heated and thermally expands, the deformation amount of the second core board 20 with a higher elastic modulus is smaller, and the overall rigidity of the PCB structure 100 is improved for the whole PCB structure 100 due to the existence of the second core board 20 with a higher elastic modulus. It can be understood that when the modulus of elasticity of the second core board 20 is greater than or equal to 25Gpa, the rigidity of the entire PCB structure 100 is significantly improved by the second core board 20.
It will be appreciated that two factors are primarily responsible for the warpage problem of the PCB structure 100, one is the coefficient of thermal expansion of the material and the other is the modulus of elasticity of the material. For the solution of the present application, since the warpage problem of the PCB structure 100 is derived from the heating problem in the reflow soldering, the thermal expansion of the material caused by the temperature change is the root cause of the warpage problem, and therefore, the thermal expansion coefficient of the second core board 20 is first defined in the embodiment of the present application. On the basis of the definition, the elastic modulus of the material is simultaneously improved so as to further reduce the occurrence of the warping problem after heating.
In one possible embodiment, the second core plate has a thickness in the range of 0.3mm to 1 mm. In the embodiment, the second core board is used for improving the thermal expansion performance and the elastic modulus of the whole PCB structure, and if the thickness of the second core board is too low, for example, less than 0.3mm, the improvement effect is not obvious enough, and the thermal expansion performance of the whole PCB structure cannot be adjusted; if the thickness is too large, the most direct effect is to increase the overall thickness of the PCB structure, and it can be understood that the effect on the second core board is limited to improving the thermal expansion performance and the elastic modulus of the PCB structure, and does not participate in the circuit layout, so if the thickness of the second core board is too large, for example, exceeding 1mm, the thickness of the PCB structure is inevitably increased, which is not favorable for the miniaturization design.
In some possible embodiments, as shown in fig. 4, 5 and 6, the second core plate 20 comprises a first face 21 and a second face 22, the number of the first core plates 10 and the number of the adhesive layers 20 are both two, wherein one adhesive layer 20 is arranged between the first face 21 and one of the first core plates 22 in a stacked manner, and the other adhesive layer 20 is arranged between the second face 22 and the other first core plate 10 in a stacked manner. In the PCB structure 100 shown in fig. 4 to 6, the number of the second core boards 20 is 1, 2 and 3, respectively, and for the second core boards 20 with different numbers in different embodiments, each second core board 20 is sandwiched by two first core boards 10 and bonded by the bonding layer 30. In the second core plates 20 of the present application, which are designed to improve the thermal expansion performance and rigidity of the PCB structure 100, in order to better perform the functions thereof, it is preferable that each second core plate 20 is sandwiched between different first core plates 10, so that when the first core plates 10 are deformed by thermal expansion, the second core plates 20 bonded thereto can effectively suppress the deformation. It can be understood that the larger the range of bonding the second core plate 20 to the first core plate 10 is, the more obvious the improvement effect of the corresponding second core plate 20 is, therefore, the first face 21 and the second face 22 of each second core plate 20 are bonded to the first core plate 10, and the improvement effect of the second core plate 20 can be exerted most effectively. The second core board 20 is sandwiched by the two first core boards 10, and the second core board 20 and the first core board 10 are bonded by the bonding layer 20, so that the first surface 21 and the second surface 22 of the second core board 20 are both bonded with the first core board 10, the second core board 20 can effectively inhibit the thermal expansion deformation of the first core boards 10 at two sides of the second core board 20, and the thermal expansion performance of the whole PCB structure 100 is improved.
In a specific embodiment, as shown in fig. 5, the number of the first core plates 10 is multiple, and a plurality of the first core plates 10 are stacked and symmetrically distributed on two sides of the second core plate 20. In fig. 5, the number of the second core boards 20 of the PCB structure 100 is one, and the number of the corresponding first core boards 10 is multiple, because the thermal expansion coefficient and the elastic modulus of the second core boards 20 are different from those of the first core boards 10, the second core boards 20 are disposed at the center of the whole PCB structure 100, so that the multiple first core boards 10 are symmetrically disposed at two sides of the second core board 20, which can reduce the stress concentration effect caused by the reflow soldering process and improve the warpage problem of the whole PCB structure 100.
In some specific embodiments, as shown in fig. 5 and 6, the PCB structure 100 includes a central layer 50, the number of the second core boards 20 is plural, and the plural second core boards 20 are symmetrically distributed on two sides of the central layer 50. As can be seen from fig. 5 and 6, the number of the second core boards 20 is 2 and 3, respectively, and for the second core boards 20 with different numbers, the second core boards 20 in the embodiment are always symmetrically distributed about the central layer 50 in the PCB structure 100. As shown in fig. 5, the number of the second core boards 20 is 2, and the central layer 50 of the PCB structure 100 is the adhesive layer 20, and the corresponding 2 second core boards 20 are symmetrically distributed on two sides of the central layer 50. PCB structure it can be understood that the second core board 20 functions to improve thermal expansion performance and rigidity of the entire PCB structure 100, so that it is preferable that the second core boards 20 are symmetrically distributed when selectively adding the second core boards 20 between the plurality of first core boards 10. The symmetrically distributed second core boards 20 have the advantage of more effectively improving the thermal expansion performance and rigidity of the PCB structure, and simultaneously alleviating the problem of stress concentration. Copper clad plates with the same thermal expansion coefficient are selected from the existing multilayer PCB structure 100, the design aims to reduce the stress problem caused by thermal expansion deformation among different copper clad plates, and for the application, the warping of the PCB structure 100 after being heated is overcome, so that the stress problem caused by different thermal expansion coefficients needs to be reduced as much as possible after the second core plates 20 with different thermal expansion coefficients are introduced. The symmetrical distribution can effectively share the stress between the first core board 10 and the second core board 20, and avoid the stress from concentrating on a certain area in the PCB structure 100.
In some specific embodiments, as shown in fig. 6, when the number of the second core boards 20 is odd, the central layer of the PCB structure 100 is the second core board 20. Fig. 6 corresponds to 3 second core boards 20, and in order to ensure the symmetrical distribution of the second core boards 20 in the PCB structure 100, the central layer 50 corresponding to the PCB structure 100 is the second core board 20, and two sides of the second core board 20 belonging to the central layer 50 are the first core boards 10 adhesively arranged by the adhesive layers 30.
In some specific embodiments, as shown in fig. 5, when the number of the second core boards is even, the central layer 50 of the PCB structure 100 is the first core board 10 or the adhesive layer 30, and the plurality of second core boards 20 are symmetrically distributed on two sides of the central layer 50. The number of the second core boards in the embodiment is even, such as 2/4/6, etc., and in this case, in order to ensure the symmetrical distribution of the second core boards in the PCB structure, the central layer of the corresponding PCB structure is the first core board or the adhesive layer. As shown in fig. 5, the central layer of the PCB structure 100 is the adhesive layer 30, and the number of the second core boards 20 is 2, and the 2 second core boards 20 are symmetrically distributed on two sides of the adhesive layer 30 as the central layer 50.
In order to better understand the beneficial effects of the present technical solution, three specific embodiments are described below, as shown in fig. 4, fig. 5 and fig. 6, which are the cases of 1, 2 and 3 second core plates 20 respectively.
As shown in fig. 4, in this embodiment, the PCB structure 100 includes 4 first core boards 10 and a second core board 20, and 6 bonding layers 30 for bonding the first core board 10 and the second core board 20, wherein the second core board 20 is located between two middle boards of the 4 first core boards 10, and specifically, the PCB structure 100 includes, from top to bottom, the bonding layer 30, the first core board 10, the bonding layer 30, the second core board 20 (central layer), the bonding layer 30, the first core board 10, and the bonding layer 30. In this embodiment, the second core plate 20 is formed by laminating 8 sheets of 2116 glass fiber cloth, and has a thermal expansion coefficient less than 10 ppm/DEG C and an elastic modulus greater than or equal to 25 Gpa. The corresponding 4 first core panels 10 and 6 tie layers 30 still used M4S material, which is a conventional substrate stock.
To better appreciate the benefits of the present application, a conventional PCB structure without the second core board 20 and a PCB structure 100 including the second core board 20 were tested here. As shown in fig. 7, the histogram represents the thermal expansion coefficient and elastic coefficient value plots of the conventional PCB structure (white shading) and the PCB structure (black shading) provided in the application document. As can be seen from fig. 6, the PCB structure 100 including the second core board 20 has a coefficient of thermal expansion of 11.66 ppm/c and an elastic modulus of 26.27 Gpa. The thermal expansion coefficient is reduced by about 25% and the elastic modulus is increased by about 14% compared to the conventional PCB structure without the second core board 20. Thereby reducing the CTE of the overall PCB structure and increasing the stiffness of the overall PCB structure.
To better illustrate this beneficial effect, the thermal deformation of a simulated reflow solder of two PCB structures (PCB structure 100 containing the second core board 20 and a conventional PCB structure not containing the second core board 20) of the same external dimension (420mm x 400mm), the same chip site dimension (75 x 60mm) was actually tested below using a Shadow Moire apparatus. As shown in fig. 8 and 9, the histograms in fig. 8 represent the maximum value of the warpage of the conventional PCB structure (white shading) and the PCB structure provided in the document (black shading), respectively, and the histograms in fig. 9 represent the warpage fluctuation of the conventional PCB structure (white shading) and the PCB structure provided in the document (black shading), respectively. Referring to fig. 10a, 10b and 10c together, wherein fig. 10a, 10b and 10c are schematic views of thermal deformation of a conventional PCB structure without the second core board 20 at 30 c, 250 c and 130 c, respectively, and fig. 11a, 11b and 11c are schematic views of thermal deformation of the PCB structure 100 with the second core board 20 at 30 c, 250 c and 130 c, respectively. The 30, 250, and 130 degrees are chosen to reduce the temperature drop of the PCB structure 100 after the temperature is raised during the reflow process. It is apparent that the maximum value of the warpage of the PCB structure 100 having the second core board 20 is reduced by 42% compared to that of the conventional PCB structure, and the fluctuation of the warpage is improved by 22%. Meanwhile, the second core board 20 changes the deformation direction (from convex to concave) of the corresponding warping degree of the projection area of the PCB structure and the component (taking the chip as an example here), so that the deformation direction can be better matched with the deformation of the component.
As shown in fig. 5, in this embodiment, the PCB structure 100 includes 4 first core boards 10 and 2 second core boards 20, and 7 adhesive layers 30 for adhering the first core boards 10 and the second core boards 20, wherein each second core board 20 is located between two first core boards 10, and a central layer of the PCB structure 100 is the adhesive layer 30, specifically, the PCB structure 100 sequentially includes, from top to bottom, the adhesive layer 30, the first core board 10, the adhesive layer 30, the second core board 20, the adhesive layer 30, the first core board 10, the adhesive layer 30 (central layer), the first core board 10, the adhesive layer 30, the second core board 20, the adhesive layer 30, the first core board 10, and the adhesive layer 30. In this embodiment, the second core plate 20 is formed by laminating 8 sheets of 2116 glass fiber cloth, and has a thermal expansion coefficient less than 10 ppm/DEG C and an elastic modulus greater than or equal to 25 Gpa. The corresponding 4 first core panels 10 and 7 tie layers 30 still used M4S material, which is a conventional substrate stock. By the design of the second core board 20, the thermal expansion coefficient (decrease) and the elastic modulus (increase) of the entire PCB structure 100 can be greatly improved.
As shown in fig. 6, in this embodiment, the PCB structure 100 includes 4 first core boards 10 and 3 second core boards 20, and 8 bonding layers 30 for bonding the first core boards 10 and the second core boards 20, wherein each second core board 20 is located between two first core boards 10, and a central layer of the PCB structure 100 is the second core board 20, and specifically, the PCB structure 100 includes, from top to bottom, a bonding layer 30, a first core board 10, a bonding layer 30, a second core board 20 (intermediate layer), a bonding layer 30, a first core board 10, a bonding layer 30, a second core board 20, a bonding layer 30, a first core board 10, and a bonding layer 30. In this embodiment, the second core plate 20 is formed by laminating 8 sheets of 2116 glass fiber cloth, and has a thermal expansion coefficient less than 10 ppm/DEG C and an elastic modulus greater than or equal to 25 Gpa. The corresponding 4 first core panels 10 and 8 tie layers 30 still used M4S material, which is a conventional substrate stock. By designing the three second core boards 20, the thermal expansion coefficient (decrease) and the elastic modulus (increase) of the entire PCB structure 100 can be greatly improved.
In the above three embodiments, the outermost side of the PCB structure 100 is provided with the adhesive layer 20, and then the outer side surface of the adhesive layer 20 is provided with a metal layer 12, where the design of the metal layer 12 is to prepare for the pad fabrication. It is understood that in the manufacturing process of the conventional PCB structure 100, an adhesive layer 20 is attached to the outermost side of the board, which serves to adhere the outermost metal layer 12 on the one hand and to save the cost on the other hand, and if the outermost layer is designed as the first core board 10, the cost is increased.
In a specific embodiment, the thickness of the second core board 20 in the PCB structure 100 is 10% or more, and the expansion coefficient of the first core board 10 ranges from 15 ppm/c to 20 ppm/c. In the embodiment, the first core plate belongs to a conventional copper-clad plate, and the thermal expansion coefficient of the first core plate is generally between 15 ppm/DEG C and 20 ppm/DEG C. As can be seen from fig. 3, the main components determining the thickness of the PCB structure 100 in the embodiment are the thickness of the first core board 10, the thickness of the second core board 20 and the thickness of the adhesive layer 30. For the whole PCB structure 100, it is the first core board 10 (both sides are covered with copper foil) that undertakes the high-speed circuit work, so the plurality of first core boards 10 are the main body part of the whole PCB structure 100, and the second core board 20 plays an auxiliary role as an intermediate layer structure for adjusting the thermal expansion performance and rigidity of the PCB structure. Therefore, the thickness of the second core board in the PCB structure is smaller than that of the first core board, but in order to ensure the improvement of the thermal expansion performance and rigidity of the second core board to the whole PCB structure, the thickness of the second core board in the PCB structure is greater than or equal to 10%, and if the thickness of the second core board is lower than the thickness of the first core board, the improvement effect of the second core board 20 is not obvious, and the problem of warpage of the PCB structure 100 after the reflow soldering process cannot be overcome.
Specifically, for the design considerations of the PCB structure 100, the thickness of the second core board 20 is 0.3mm to 1.0mm, and the thickness of the PCB structure 100 excluding the second core board 20 is 2.0mm to 3.6 mm. In one specific embodiment, as shown in fig. 3, the second core board 20 is laminated by eight 2116 glass fiber cloths to have a thickness of 0.8mm, and the thickness of the corresponding 4 first core boards 10 and the adhesive layer 30 is 2.0mm, so that it can be seen that the thickness of the second core board 20 is 28% in the entire PCB structure 100.
It is understood that the thicknesses of the 4 first core boards 10 in the specific implementation are not consistent, and the relative thicknesses can be selected according to specific requirements, such as the design of circuit patterns and the requirement of drilling holes, and in general, the conventional copper-clad plate includes non-standard specifications of 0.1mm, 0.2mm, 0.3mm, 0.5mm and standard specifications of 0.8mm, 1.0mm, 1.2mm, 1.6mm, 2.0mm, etc.
In a specific embodiment, as shown in fig. 12, the surfaces (the first face 21 and the second face 22) of the second core panel 20 are provided with a micro-protrusion structure 25, and the micro-protrusion structure 25 is used to increase the bonding force between the second core panel 20 and the adhesive layer 30. The design of the micro-protrusion structure 25 in the embodiment aims to increase the contact area between the second core board 20 and the adhesive layer 30, so as to increase the bonding force between the second core board 20 and the adhesive layer 30 and avoid the situation of warping and cracking.
Specifically, as shown in fig. 13, the second core plate 20 includes an edge region 23 (outside the dotted line) and a central region 24 (inside the dotted line), the edge region 24 surrounds the central region 23, and the distribution density of the microprojection structure 25 in the edge region 24 is greater than the distribution density of the microprojection structure 25 in the central region 23. In the embodiment, the micro-protrusion structures 25 are mainly distributed on the edge regions 24 of the second core plate 20, so as to improve the bonding force of the edge regions 24 during the pressing process. It can be understood that, for the PCB structure 100, the position where the warpage deformation occurs is mostly at the edge position of the board, and in the present embodiment, by increasing the distribution density of the micro-protrusion structures 25 of the second core board 20 at the edge area 24, the contact surface between the second core board 20 and the bonding layer 30 at the edge area 24 is further increased, so as to improve the adhesive force therebetween, and avoid the occurrence of the warpage cracking.
As shown in fig. 14, the present application further provides a method for manufacturing a PCB structure, including the following steps:
s110, providing a first core board, wherein the first core board is a copper-clad board, and etching a copper foil on the first core board to obtain a circuit layer;
the first core plate is a conventional copper-clad plate, and in order to ensure the overall electrical performance of the PCB structure, a plate-shaped base material obtained by impregnating glass fiber cloth with resin glue and then coating copper foil on the surface is selected.
S120, providing a second core board, wherein the second core board is a copper-clad board, and etching away copper foil on the second core board to ensure that no circuit layer exists on the surface of the second core board, and the thermal expansion coefficient of the second core board is smaller than that of the first core board;
the second core board is also a plate-shaped base material which is obtained by impregnating glass fiber cloth with resin glue and then coating the surface with copper foil. Unlike the first core board, the thermal expansion coefficient of the second core board in the embodiment is smaller than that of the first core board, aiming at improving the thermal expansion performance of the whole PCB structure. Note that, the purpose of performing full etching on the copper foils on both sides of the second core board is to remove the copper foils on both sides of the second core board, so as to avoid the copper foils from affecting the circuit pattern on the first core board. In the manufacturing process of the PCB structure, the second core board is processed by the existing copper clad board, and the copper clad boards are purchased with copper foils already coated on the surfaces of both sides, so that the copper foils need to be etched away to avoid the influence of the copper foils on the circuit pattern on the first core board. Specifically, the second core plate may be composed of 8 sheets of 2116 glass fiber cloth.
It should be noted that, there is no context between step S110 and step S120, and the two steps may be performed selectively in sequence or simultaneously, and the specific situation may be selected according to the processing requirement.
And S130, pressing and bonding the first core board and/or the second core board by using the bonding layer.
The bonding layer is a sheet formed by soaking degreased glass fiber cloth in resin glue solution and then pre-drying, and the bonding layer is used for bonding different copper clad plates. The bonding layer is used for bonding the stacked and adjacent copper-clad plates in the middle, can be bonding between the first core plate and the second core plate, and can also be bonding between the first core plate and the first core plate, and the specific bonding object is determined according to the actual stacking condition of the PCB structure.
In a specific embodiment, after a plurality of first core boards, at least one second core board and a plurality of bonding layers are stacked, a complete PCB structure is formed only by pressing through a high-temperature press, and then the finished product of the PCB structure is obtained through necessary processing steps such as drilling, electroplating, outer layer pattern, solder mask, character, surface treatment, shape processing and the like.
The PCB fabrication method provided above will be described with reference to the PCB structure 100 shown in fig. 5.
Firstly, providing 4 first core boards 10, wherein the first core boards 10 are copper-clad boards made of M4S materials, and then etching copper foils on two sides of the first core boards 10 to obtain a required circuit pattern 12;
similarly, 1 second core board 20 is provided, the second core board 20 is a copper-clad board formed by laminating 8 2116 glass fiber cloths, the specific board model is MCL-E-705G, the corresponding thermal expansion coefficient of the obtained second core board 20 ranges from 5 ppm/deg.c to 7 ppm/deg.c, and the elastic modulus ranges from 32Gpa to 34 Gpa. And then, the copper foils on the two sides of the copper-clad plate are fully etched, so that the two sides of the second core plate 20 are ensured to be free of copper foils, and the phenomenon that the normal operation of the whole PCB structure 100 high-speed circuit is influenced by the residual copper foils on the second core plate 20 is avoided.
And then, stacking 4 first core boards 10 and 1 second core board 20, wherein the second core board 20 is placed at the center, and meanwhile, arranging bonding sheets 30 on two sides of each copper-clad plate (the first core board or the second core board) for a total of six, so that a stacked structure formed by 6 bonding sheets 30, 4 first core boards 10 and 1 second core board 20 is formed.
And then, carrying out high-temperature lamination by using a hot press to obtain a PCB structure with a stable structure. And finally, carrying out necessary processing steps such as drilling, electroplating, outer layer graphics, resistance welding, characters, surface treatment, appearance processing and the like on the PCB structure to obtain a final PCB structure finished product.
It can be understood that the manufacturing method of the PCB structure provided by the present application is different from the conventional manufacturing method in the design of the second core board. The second core board with smaller thermal expansion coefficient and larger elastic modulus is added in the original PCB structure formed by the first core board and the bonding layer, so that the thermal expansion coefficient and the elastic modulus of the whole PCB structure are changed. As shown in the simulation experiment data of fig. 6, in the conventional PCB structure without the first core board, the thermal expansion coefficient is 15.55 ppm/c, and the elastic modulus is 22.98 Gpa. After a second core board is added at the center of the PCB structure, the thermal expansion coefficient of the obtained new PCB structure is 11.66 ppm/DEG C, and the Young modulus is 26.27 Gpa. In comparison, the thermal expansion coefficient of the PCB structure is reduced by about 25% and the elastic modulus is increased by about 14% after the second core board is added. Therefore, the thermal expansion coefficient of the whole PCB structure is reduced, the rigidity of the whole PCB structure is improved, and the phenomena of open welding and continuous welding caused by warping of the PCB structure in reflow soldering are avoided.
The foregoing is a preferred embodiment of the present invention, and it should be noted that it would be apparent to those skilled in the art that various modifications and enhancements can be made without departing from the principles of the invention, and such modifications and enhancements are also considered to be within the scope of the invention.
Claims (15)
1. The PCB structure is characterized by comprising a first core board, a bonding layer and a second core board which are arranged in a stacking mode, wherein the second core board is bonded with the first core board through the bonding layer, the thermal expansion coefficient of the second core board is smaller than that of the first core board, and a circuit layer is arranged on the surface of the first core board.
2. The PCB structure of claim 1, wherein the second core board has a coefficient of expansion less than or equal to 10ppm/° c, and the first core board has a coefficient of expansion in a range from 15ppm/° c to 20ppm/° c.
3. The PCB structure of claim 1, wherein the second core board has a modulus of elasticity greater than or equal to 25 Gpa.
4. The PCB structure of claim 1, wherein the second core board has a thickness in a range of 0.3mm to 1 mm.
5. The PCB structure of claim 1, wherein the second core board includes a first face and a second face, the number of the first core boards and the number of the adhesive layers are both two, wherein one of the adhesive layers is stacked and disposed between the first face and one of the first core boards, and the other of the adhesive layers is stacked and disposed between the second face and the other of the first core boards.
6. The PCB structure of claim 5, wherein the adhesive layer completely covers the first and second faces.
7. The PCB structure of claim 1, wherein the number of the first core boards is plural, and a plurality of the first core boards are stacked and symmetrically distributed on both sides of the second core board.
8. The PCB structure of claim 1, wherein the PCB structure comprises a central layer, the number of the second core boards is plural, and the plural second core boards are symmetrically distributed on two sides of the central layer.
9. The PCB structure of claim 8, wherein one of the second core boards is the center layer when the number of the second core boards is an odd number.
10. The PCB structure of claim 9, wherein when the number of the second core boards is an even number, the central layer of the PCB structure is the first core board or the adhesive layer.
11. The PCB structure of any of claims 1-10, wherein the thickness of the second core board in the PCB structure is greater than or equal to 10%.
12. The PCB structure of claim 11, wherein the surface of the second core board is provided with a micro-protrusion structure for increasing the bonding force between the second core board and the bonding layer.
13. The PCB structure of claim 12, wherein the second core board includes an edge region and a central region, the edge region surrounding the central region, the microprojection structure having a distribution density in the edge region that is greater than a distribution density of the microprojection structure in the central region.
14. A manufacturing method of a PCB structure is characterized by comprising the following steps:
providing a first core board, wherein the first core board is a copper-clad board, and etching a copper foil on the first core board to obtain a circuit layer;
providing a second core board, wherein the second core board is a copper-clad board, and etching away copper foil on the second core board to ensure that no circuit layer exists on the surface of the second core board, and the thermal expansion coefficient of the second core board is smaller than that of the first core board;
and pressing and bonding the first core plate and/or the second core plate by using a bonding layer.
15. An electronic device comprising a component and a PCB structure as claimed in any of claims 1 to 13, wherein the PCB structure comprises pads and the component is soldered to the pads.
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| CN117812855A (en) * | 2024-03-01 | 2024-04-02 | 深圳市众阳电路科技有限公司 | Method for pressing row plates by asymmetric structure in printed circuit board and circuit board member |
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| CN117812855B (en) * | 2024-03-01 | 2024-04-26 | 深圳市众阳电路科技有限公司 | Method for pressing row plates by asymmetric structure in printed circuit board and circuit board member |
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