Pressing mold and preparation method thereof

Abstract

The present invention provides a pressing mold and a preparation method thereof. A pressing mold is used to form a concave structure at a specific position where a BGA area is to be formed on a circuit board to be pressed, so as to carry BGA components in the future, thereby improving the deformation tolerance of the BGA area and the circuit board surface during the pressing process, and reducing the probability of desoldering and pulling of the BAG area during the circuit board production process. Secondly, a stable pressing mold is formed by pre-pressing a semi-cured sheet stacked with upper and lower copper foils and a sleeve circuit board matching plate. The characteristics of the semi-cured sheet are used as a supporting structure of the pressing mold by using a stacked fiber layer, and the resin that melts and flows during pressing is used as a filler to fill the gap in the pressing mold, so that the height difference of the pressing mold at the upper convex structure changes slowly, avoiding damage to the circuit board surface to be pressed when the pressing mold is used, and improving the reliability of circuit board production.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic manufacturing, and more specifically, to a pressing mold and a preparation method thereof. Background Art

[0002] In modern electronic packaging technology, ball grid array (BGA) packaging is widely used in various high-end electronic devices due to its high density and high performance. However, with the continuous miniaturization and integration of electronic products, the connection reliability problem between BGA and printed circuit board (PCB) has become increasingly prominent, especially the bending problem caused by the mismatch of the coefficient of thermal expansion (CTE) of the materials.

[0003] During the manufacturing and use process, BGA and circuit boards will experience a variety of temperature changes, such as welding, temperature fluctuations in the working environment, etc. Since different materials respond differently to temperature changes, the difference in CTE will cause relative displacement and stress between BGA and circuit board when the temperature changes. When this stress accumulates to a certain extent, it will cause partial or overall bending of the circuit board, which will in turn affect the welding quality and electrical connection performance of the BGA. In particular, when the BGA size is larger, the corresponding board bending risk also increases significantly.

[0004] In order to deal with this problem, one of the measures commonly taken by the industry is to adjust the design of the circuit board surface, designing the BGA position to be recessed a certain depth (such as 40 mil) than the normal board surface, so as to fix the position of the BGA area and reduce the direct impact of bending on the BGA installation reliability. This method alleviates the impact of board bending on the installation reliability of BGA components to a certain extent, and reduces the risk of desoldering and pulling. However, in actual production, how to accurately control the size, position and depth of the recessed area, and how to ensure that the area does not move or deform during continuous pressing and other processes have become technical problems that need to be solved urgently.

[0005] Therefore, under the existing technical background, a more sophisticated solution is needed to solve the problem of mismatched thermal expansion coefficients between BGA components and circuit boards, including but not limited to developing materials with higher thermal expansion coefficient matching, optimizing the pressing process to achieve local precise control, and introducing advanced positioning and monitoring technologies to ensure processing accuracy and stability. Through the comprehensive application of these technical means, the installation reliability between BGA components and circuit boards can be further improved to meet the increasingly stringent performance requirements of electronic products. Summary of the invention

[0006] The present invention aims to overcome at least one of the above-mentioned deficiencies of the prior art and provides a pressing mold and a preparation method thereof.

[0007] The object of the present invention is to provide a pressing mold, which is in the shape of a flat plate as a whole and is used to form a concave structure on one side of a circuit board during the lamination process of the circuit board, comprising:

[0008] The housing comprises an upper housing and a lower housing, wherein the edges of the upper housing and the lower housing are fused to form an edge seal and the middle is separated to form a receiving cavity;

[0009] A supporting structure, comprising multiple filling layers of different sizes, stacked and distributed in the accommodating cavity;

[0010] Filler, filled in the containing cavity and between each filling layer;

[0011] The accommodating cavity includes at least one local area, in which the number of filling layers of the supporting structure is greater than that of other areas, so that the upper shell bulges to form an upward convex structure, the lower shell is a flat structure, and the position of the upward convex structure corresponds to the downward concave structure.

[0012] In the present technical scheme, during the pressing and manufacturing process of a circuit board to which BGA components need to be connected, a pressing mold is used to form a concave structure at a specific location on the circuit board to be pressed where a BGA area is required to be formed, so as to carry the BGA components later. This improves the deformation tolerance of the BGA area and the circuit board surface during the pressing and manufacturing process, reduces the probability of desoldering and pulling of the BAG area during the circuit board manufacturing process, reduces the influence of the board bending phenomenon on the connection and installation of the BGA components and the circuit board surface, and improves the installation reliability of the BGA components and the circuit board surface. Specifically, the pressing mold includes an outer shell, a supporting structure and a filler. The outer shell containing the accommodating cavity is formed by fusing the edges of the upper and lower shells. The upper shell is raised to form an upper convex structure, and the lower shell is a flat structure, which is convenient for fitting with the plane of the panel structure before pressing, and provides a plane for transmitting uniform pressure for the overall pressing. At the same time, a certain amount of supporting structure and filler are filled in the accommodating cavity to form a complete and non-leaking upper convex structure, which is convenient for forming a concave structure corresponding to the upper convex structure on the surface of the circuit board to be pressed, and during the pressing process, the supporting structure filled inside can be flexibly supported by the filler, which is convenient for shaping on the circuit board to be pressed during pressing while the edges can be evenly transitioned without damaging the board surface.

[0013] Furthermore, the support structure at least comprises:

[0014] A base layer, the area and shape of which match those of the circuit board;

[0015] A plurality of first stacked layers, positioned and stacked in the local area, having an area larger than the concave structure;

[0016] A plurality of second stacking layers are positioned and stacked on the first stacking layer, and have an area smaller than the concave structure.

[0017] In the present technical scheme, in order to fix the shape and position of the upper and lower concave structures of the circuit board, the convex structure formed on the pressing mold includes a hard supporting structure. Specifically, the supporting structure includes a base layer whose area and shape match the surface of the circuit board, which is used to fit the lower shell body and construct a flat and uniform pressing surface. In order to better construct the concave structure of the required shape on the entire circuit board to be pressed, it also includes a plurality of first superimposed layers positioned and superimposed on the local area. The area of ​​the first superimposed layer is smaller than the base layer, and is slightly larger than the concave structure required to be formed on the circuit board to be pressed. Furthermore, a plurality of second superimposed layers are positioned and superimposed on the first superimposed layer, and the area of ​​the second superimposed layer is slightly smaller than the concave structure. Specifically, the second superimposed layer is used to fix the basic outline of the concave structure, and can cooperate with the introduction of filler to construct the required concave structure size. The first superimposed layer is used to balance and buffer the board surface height difference generated by the BGA area during the pressing process when the concave structure is formed, thereby better balancing the board bending of the entire circuit board and ensuring the overall manufacturing reliability of the circuit board.

[0018] Furthermore, in order to better construct a concave structure of a desired shape on the entire circuit board to be pressed, and at the same time provide an appropriate concave curvature on other areas of the circuit board surface to match the bending of the entire board during the pressing process, the number of first stacking layers is controlled to be n1, and the area of ​​the first stacking layer gradually decreases from bottom to top, and the number of second stacking layers is n2, and the area of ​​the second stacking layer gradually decreases from bottom to top, and 2≤n1-n2≤5, so that the concave structure formed on the circuit board can achieve the BGA installation depth required by the design, and the contour of the concave structure can gradually change on the circuit board surface, thereby ensuring the overall rigidity and stability of the circuit board surface after the concave structure is opened.

[0019] Furthermore, in order to balance the influence of lamination on the board bending of the overall board surface of the circuit board and improve the reliability of the production of the entire circuit board, in addition to the overall concave design of the BGA area on the entire board of the circuit board, it is also necessary to perform a stepped buffer design on the overall board surface of the circuit board around the BGA area on the entire board surface of the circuit board, so as to minimize the influence of the board bending caused by lamination on the BGA area and the overall board surface of the circuit board; specifically, in the production of the lamination mold, it is arranged that the support structure also includes one less transition layer, the transition layer is superimposed between the base layer and the first superimposed layer, and the area is smaller than the base layer and larger than the first superimposed layer. When the transition layer exceeds one layer, the area of ​​the transition layer gradually decreases from bottom to top. The area between the base layer and the first superimposed layer is effectively connected by the setting of the transition layer, so that the edge of the upper convex structure on the lamination mold changes in steps from the edge of the base layer to the inside of the upper convex structure, so that the concave degree on the overall board surface of the circuit board slowly and gradually deepens from the edge to the BGA area during lamination, so that the BGA area produces the board surface height difference required by the design during the lamination process, thereby better balancing the board bending of the entire circuit board and ensuring the overall production reliability of the circuit board.

[0020] Preferably, the bending of the entire circuit board is better balanced to ensure the overall manufacturing reliability of the circuit board when the convex structure is located in the center of the pressing mold; when the base area is 4-9 times the area of ​​the first stacking layer, 1-2 transition layers are set; when the base area is 9-12 times the area of ​​the first stacking layer, 2-4 transition layers are set; when the base area is 12-16 times the area of ​​the first stacking layer, 4-5 transition layers are set; when the base area is more than 16 times the area of ​​the first stacking layer, the number of transition layers does not exceed 8 layers.

[0021] Further, when the pressing mold includes two or more convex structures, and all the convex structures are arranged adjacent to each other, the transition layer is arranged with all the convex structures as the center;

[0022] When the pressing mold includes two or more convex structures, and the convex structures are separately arranged, the transition layer is separately arranged with each convex structure as the center.

[0023] In the present technical scheme, in order to cope with the situation where the circuit board surface has multiple BGA sites, when the pressing mold includes two or more convex structures, if all the convex structures are arranged adjacent to each other, all the convex structures are taken as a whole and then a buffer design is performed on the entire circuit board. If all the convex structures are arranged separately from each other, a board surface buffer design is performed around each convex structure to form a height difference step on the overall panel of the pressing mold, ensuring that the pressing mold is deformed the most at the convex structure and then gradually decreases to the edge of the pressing mold. Correspondingly, the concave deformation is the largest at the concave structure on the circuit board panel after pressing, and the degree of concaveness decreases as a whole to the edge of the circuit board, ensuring that a groove is formed at the concave structure to facilitate the installation of BGA devices, and the edge deformation of the groove and the slight depression of the overall board surface of the circuit board have a natural transition, thereby not damaging the board surface and the internal structure, ensuring the stiffness and stability of the circuit board produced by pressing, and at the same time better balancing the bending and pulling of the BGA installation site and the bending of the entire circuit board during the pressing process, ensuring the overall production reliability of the circuit board. Preferably, the two upward convex structures are adjacently arranged if the distance between them does not exceed the full size of one of the upward convex structures; otherwise, they are separated.

[0024] Another object of the present invention is to provide a method for manufacturing a pressing mold, which is used to manufacture the pressing mold provided in the technical solution, specifically, comprising the following steps:

[0025] S1. Cut a prepreg sheet to match the size of the circuit board to be pressed as the base layer;

[0026] S2. Corresponding to the BGA area of ​​the circuit board to be pressed, a prepreg corresponding to the BGA area is stacked layer by layer on the base layer;

[0027] S3. Copper foil layers are respectively covered on the upper and lower sides of the laminated prepreg, and the upper and lower copper foil layers are fused around the periphery of the base layer to form a packaging structure;

[0028] S4. Take a circuit board with the same wiring as the circuit board to be pressed as a sleeve mold circuit board, and fit the package structure with a laminated prepreg on one side of the sleeve mold circuit board on which the BGA is mounted, and align the laminated prepreg with the BGA area to form a composite structure;

[0029] S5. Heating and pressurizing the composite structure:

[0030] The resin of the prepreg is melted and flowed to form a filler;

[0031] The fiber cloth of the prepreg forms a filling layer, and the filling layers are stacked to form a supporting structure;

[0032] The filler is filled in the accommodation cavity formed between the upper and lower copper foil layers and between each filling layer;

[0033] In the BGA area, the copper foil layer located on the upper layer forms an upward convex structure, and the surface texture of the lower mold circuit board is printed on other areas to form an upper shell, and the lower copper foil layer forms a lower shell;

[0034] S6. Cool and solidify to form a pressed mold.

[0035] In the present technical scheme, a preparation method of a pressing mold is also provided. Specifically, a semi-cured sheet stacked with upper and lower copper foils is firstly wrapped, and the upper and lower copper foil layers are fused at the periphery of the base layer to form a packaging structure, and the semi-cured sheet is stacked on the base layer and fills the accommodating cavity formed inside the packaging structure, and specifically, the fiber cloth of the semi-cured sheet forms a filling layer, and the filling layers are stacked to form a supporting structure, and through pressing, in the BGA area, the copper foil layer located on the upper layer tightly wraps the supporting structure to form an upper convex structure, and the surface texture of the lower mold circuit board is printed in other areas to form an upper shell, and the lower copper foil layer forms a lower shell, and pressing makes the resin of the semi-cured sheet melt and flow to form a filler, which is filled in the accommodating cavity formed between the upper and lower copper foil layers and between the filling layers, thereby forming a stable pressing mold. That is, by utilizing the characteristics of the semi-cured sheet, the stacked fiber layers are used as the supporting structure of the laminating mold, and the molten resin during laminating is used as filler to fill the gaps in the laminating mold, so that the height difference of the laminating mold at the convex structure changes slowly. While the stacked semi-cured sheets are used to construct the convex structure with the required deformation amount on the laminating mold, damage to the surface of the circuit board to be pressed when the laminating mold is used is avoided, thereby improving the reliability of circuit board production. In the preparation process of the lamination mold, it also includes the process of using pre-lamination to solidify the lamination mold and form an upper convex structure. Specifically, when the lamination mold is pre-lamination, first, the setting position of the laminated semi-cured sheet in the lamination template is positioned by using a positioning system consistent with the circuit board to be pressed, so as to ensure that the setting position of the laminated semi-cured sheet corresponds to the BGA area of ​​the circuit board to be pressed; secondly, a circuit board with the same wiring as the circuit board to be pressed is used as a sleeve mold circuit board, and the side of the package structure with the laminated semi-cured sheet is laminated with the side of the sleeve mold circuit board to be installed with the BGA components to form a composite structure. The specific shape of the upper convex structure on the lamination mold is fixed by the lamination process with the sleeve mold circuit board, and the concave structure formed by lamination on the sleeve mold circuit board can also be connected and adapted with the BGA components to check the position accuracy of the formed lamination mold and the degree of improvement of the depression. Preferably, the semi-cured sheet used to prepare the lamination mold adopts a low-flow semi-cured sheet, which is more conducive to the alignment and shaping of the lamination mold during the production process.

[0036] Furthermore, in step S2, stacking the prepregs corresponding to the BGA area layer by layer includes:

[0037] A plurality of first prepreg sheets, the area of ​​which is larger than the BGA area and not larger than 20% of the area of ​​the BGA area;

[0038] A plurality of second prepreg sheets, the area of ​​which is smaller than the BGA area and not less than 60% of the area of ​​the BGA area;

[0039] The total number of the first prepreg and the second prepreg is N=[H / d]+n, wherein the maximum concave dimension of the BGA area of ​​the circuit board to be pressed is H, the thickness of the prepreg is d, n is the compensation number of 2-5 sheets, and [] is the rounding symbol;

[0040] The number n1 of the first cured sheets is such that the area of ​​the first cured sheets decreases gradually from bottom to top, the number n2 of the second cured sheets is such that the area of ​​the second cured sheets decreases gradually from bottom to top, and 2≤n1-n2≤5;

[0041] After the step S6 is cooled and solidified:

[0042] The fiber cloth of the first prepreg forms a first superimposed layer;

[0043] The fiber cloth of the second prepreg forms a second superposition layer.

[0044] In the technical scheme, a convex structure with a gradually increasing convexity from the edge of the substrate to the center of the position corresponding to the BGA area is formed on one side of the lamination mold by stacking semi-cured sheets layer by layer; wherein, the first semi-cured sheet and the second semi-cured sheet are combined to form the convex structure corresponding to the BGA area, and thus the total number of the first semi-cured sheets and the second semi-cured sheets used in the lamination mold is set to be N=[H / d]+n, wherein, when the maximum concave size of the BGA area of ​​the circuit board to be pressed is H and the thickness of the single semi-cured sheet used is d, on the basis of filling the concave size of the BGA area with the semi-cured sheets as much as possible, n semi-cured sheets are further stacked to compensate for the thickness loss after the resin in the semi-cured sheets flows and fills the gaps during the lamination process, so as to ensure that the convex structure after lamination can reach a predetermined deformation amount; specifically, the value of n depends on the type and characteristics of the selected semi-cured sheets, and preferably, the value of n is 2-5 sheets. Furthermore, after lamination, the fiber layer of the first semi-cured sheet constitutes the first superimposed layer, and the fiber layer of the second cured sheet constitutes the second superimposed layer. Therefore, similar to the first superimposed layer and the second superimposed layer, in order to enable the lamination mold to better construct a concave structure of a desired shape on the entire circuit board to be laminated during lamination, and at the same time provide an appropriate concave curvature on other areas of the circuit board surface for matching the bending of the entire board during the lamination process, the number of first semi-cured sheets is controlled to be n1, and the number of second semi-cured sheets is n2, and 2≤n1-n2≤5, so that the concave structure formed on the circuit board can achieve the BGA installation depth required by the design, and the contour of the concave structure is buffered by the adjustment action of the molten flow of resin of the first semi-cured sheet and the second semi-cured sheet during lamination, so that the deformation amount on the circuit board surface changes gradually, thereby ensuring the overall rigidity and stability of the circuit board surface after the concave structure is opened.

[0045] Preferably, the following steps are also included between steps S1 and S2: S12. stacking one or more layers of transitional semi-cured sheets with an area between the area of ​​the circuit board to be laminated and the area of ​​the BGA area on the base semi-cured sheet; the specific step S2 is to stack the semi-cured sheets corresponding to the BGA area layer by layer on the transitional semi-cured sheets; by using the transitional semi-cured sheets, the edge of the convex structure on the lamination mold changes in steps from the edge of the base layer to the inside of the upper convex structure, and the resin melt flow of the semi-cured sheet during lamination is used to fill the part with a height difference at the edge, so as to soften the edge of the step-shaped convex structure from the edge of the base layer, so that the concave degree on the entire board surface of the circuit board is slowly and gradually deepened from the edge to the BGA area during lamination, so that the BGA area produces the board surface height difference required by the design during the lamination process, thereby better balancing the board bending of the entire circuit board and ensuring the overall manufacturing reliability of the circuit board.

[0046] Preferably, the following step is further included between steps S2 and S3: S22. All prepregs are fused and positioned to fix the relative positions of the prepregs. The fusion positioning allows the prepregs forming the support layer in the pressing mold to be firmly connected, and the prepregs can be heated, melted and solidified. The positioning fusion can achieve a firm connection between the layers without introducing an additional positioning and connection procedure, which improves the accuracy of the pressing mold and simplifies the preparation process.

[0047] Preferably, the sleeve mold circuit board is specifically configured such that at least one side of the wiring is the same as the side of the concave structure formed by the circuit board to be pressed, and no holes are opened in the wiring area, and the periphery is provided with the same positioning holes as the circuit board to be pressed, and the upper shell forms positioning columns at the positioning holes; by providing a sleeve mold circuit board that has undergone circuit production but has not undergone outer layer drilling, the influence of the drilling process on the surface area of ​​the circuit board to be pressed is avoided, and at the same time, by providing positioning columns on the edge of the upper shell in the pressing mold so as to more accurately correspond to the positioning system of the circuit board to be pressed, the installation position of the BGA device on the circuit board to be pressed and the site of the positioning system are more accurately simulated, thereby improving the accuracy of positioning and production of the pressing mold.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. A pressing mold is provided. In the pressing process of a circuit board to be connected with BGA components, a concave structure is formed at a specific position on the circuit board to be pressed where a BGA area is to be formed, so as to carry BGA components in the future. This improves the deformation tolerance of the BGA area and the circuit board surface during the pressing process, reduces the probability of desoldering and pulling of the BAG area during the circuit board production process, and reduces the influence of the board bending phenomenon on the connection and installation of the BGA components and the circuit board surface. Specifically, the pressing mold includes an outer shell, a supporting structure and a filler. The outer shell containing the accommodating cavity is formed by fusing the edges of the upper and lower shells. The upper shell is raised to form an upper convex structure, and the lower shell is a flat structure, which is convenient for fitting with the plane of the panel structure before pressing, and provides a plane for transmitting uniform pressure for the overall pressing. At the same time, a certain amount of supporting structure and filler are filled in the accommodating cavity to form a complete and non-leaking upper convex structure, which is convenient for forming a concave structure corresponding to the upper convex structure on the surface of the circuit board to be pressed, and during the pressing process, the supporting structure filled inside can be flexibly supported by the filler, which is convenient for shaping on the circuit board to be pressed during pressing while the edges can be evenly transitioned without damaging the board surface.

[0050] 2. A preparation method for a pressing mold is provided, in which a stable pressing mold is formed by pre-pressing a semi-cured sheet stacked with upper and lower copper foils and a sleeve circuit board. The characteristics of the semi-cured sheet are utilized, and the stacked fiber layers are used as the supporting structure of the pressing mold. The molten resin flowing during pressing is used as a filler to fill the gap in the pressing mold, so that the height difference of the pressing mold at the convex structure changes slowly, and the convex structure with the required deformation amount is conveniently and quickly constructed on the sub-mold, while avoiding damage to the surface of the circuit board to be pressed when the pressing mold is used, thereby improving the reliability of circuit board production. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is one of the structural schematic diagrams of a pressing mold of the present invention.

[0052] Figure 2 This is the second structural schematic diagram of a pressing mold of the present invention.

[0053] Figure 3 It is a schematic structural diagram of the pressing mold in Example 2 of the present invention.

[0054] Figure 4 The present invention is a schematic diagram of a process for preparing a pressing mold.

[0055] Description of the drawings: upper shell 110 , lower shell 120 , base layer 210 , first stacking layer 220 , second stacking layer 230 , transition layer 240 , filler 300 . DETAILED DESCRIPTION

[0056] The drawings of the present invention are only for illustrative purposes and should not be construed as limiting the present invention. In order to better illustrate the following embodiments, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; it is understandable to those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0057] Example 1

[0058] like Figure 1-Figure 2 As shown, this embodiment provides a pressing mold, which is in the shape of a flat plate as a whole and is used in the lamination process of a circuit board to form a concave structure on one side of the circuit board, including:

[0059] The housing comprises an upper housing 110 and a lower housing 120, wherein the edges of the upper housing 110 and the lower housing 120 are fused to form an edge seal and the middle is separated to form a receiving cavity;

[0060] The supporting structure includes multiple filling layers of different sizes, which are stacked and distributed in the accommodating cavity;

[0061] Filler 300, filled in the containing cavity and between each filling layer;

[0062] The accommodating cavity includes at least one local area, in which the number of filling layers of the supporting structure is greater than that of other areas, so that the upper shell 110 is raised to form an upper convex structure, and the lower shell 120 is a flat structure, and the position of the upper convex structure corresponds to the lower concave structure. The pressing mold is a flat plate structure as a whole, which is convenient for laminating with other plates during the pressing process of the circuit board, but the side that cooperates with the circuit board to be pressed has an upper convex structure, which is used to cooperate with the pressing to form a lower concave structure on the side where the circuit board and the pressing mold cooperate. Specifically, the pressing mold includes an outer shell, a supporting structure and a filler 300. The outer shell containing the accommodating cavity is formed by fusing the edges of the upper and lower shells. The upper shell 110 is raised to form an upper convex structure, and the lower shell 120 is a flat structure, which is convenient for fitting with the plane of the panel structure before pressing, and provides a plane for transmitting uniform pressure for the overall pressing; at the same time, a certain amount of supporting structure and filler 300 are filled in the accommodating cavity to form a complete and non-leaking upper convex structure, which is convenient for forming a concave structure corresponding to the upper convex structure on the surface of the circuit board to be pressed, and during the pressing process, the supporting structure filled inside can be flexibly supported by the filler 300, which is convenient for shaping on the circuit board to be pressed during pressing while the edges can be evenly transitioned without damaging the board surface.

[0063] Furthermore, in order to fix the shape and position of the upper and lower concave structures of the circuit board, the upper convex structure formed on the pressing mold includes a hard support structure, and the support structure at least includes: a base layer 210, the area and shape of the base layer 210 match the circuit board, and is used to construct a flat and uniform pressing surface; secondly, in order to better construct the concave structure of the desired shape on the entire circuit board to be pressed, it also includes a plurality of first stacking layers 220 positioned and stacked in the local area, the area of ​​the first stacking layer 220 is smaller than the base layer 210, and is smaller than the required shape on the circuit board to be pressed. The concave structure is slightly larger. Furthermore, several second stacking layers 230 are positioned and stacked on the first stacking layer 220, and the area of ​​the second stacking layer 230 is slightly smaller than the concave structure. Specifically, the second stacking layer 230 is used to fix the basic outline of the concave structure, and can cooperate with the introduction of the filler 300 to construct the required concave structure size. The first stacking layer 220 is used to balance and buffer the board height difference generated by the BGA area during the pressing process when the concave structure is formed, so as to better balance the board bending of the entire circuit board and ensure the overall manufacturing reliability of the circuit board.

[0064] Furthermore, in order to better construct a concave structure of a desired shape on the entire circuit board to be pressed, and at the same time provide an appropriate concave curvature on other areas of the circuit board surface to match the bending of the entire board during the pressing process, the number of first stacking layers 220 is controlled to be n1, and the area of ​​the first stacking layer 220 gradually decreases from bottom to top, and the number of second stacking layers 230 is n2, and the area of ​​the second stacking layer 230 gradually decreases from bottom to top, and 2≤n1-n2≤5, so that the concave structure formed on the circuit board can achieve the BGA installation depth required by the design, and the contour of the concave structure can gradually change on the circuit board surface, thereby ensuring the overall rigidity and stability of the circuit board surface after the concave structure is opened.

[0065] Furthermore, in order to balance the influence of lamination on the board bending of the overall board surface of the circuit board and improve the reliability of the overall board surface of the circuit board, in addition to the overall concave design of the BGA area on the entire board of the circuit board, it is also necessary to perform a stepped buffer design on the overall board surface of the circuit board around the BGA area on the entire board surface of the circuit board, so as to minimize the influence of the board bending caused by lamination on the BGA area and the overall board surface of the circuit board; specifically, in the production of the lamination mold, it is arranged that the support structure also includes one less transition layer 240, and the transition layer 240 is superimposed between the base layer 210 and the first superimposed layer 220, and the area is smaller than the base layer 210. The transition layer 240 is larger than the first stacking layer 220. When the transition layer 240 exceeds one layer, the area of ​​the transition layer 240 decreases gradually from bottom to top. The transition layer 240 is effectively connected to the area between the base layer 210 and the first stacking layer 220, so that the edge of the convex structure on the laminating mold changes in steps from the edge of the base layer 210 to the inside of the convex structure. Therefore, during laminating, the concave degree on the entire surface of the circuit board slowly and gradually deepens from the edge to the BGA area, so that the BGA area produces the required board height difference during the laminating process, thereby better balancing the board bending of the entire circuit board and ensuring the overall manufacturing reliability of the circuit board.

[0066] Preferably, the bending of the entire circuit board is better balanced to ensure the overall manufacturing reliability of the circuit board when the convex structure is located in the center of the pressing mold; when the area of ​​the base layer 210 is 4-9 times the area of ​​the first stacking layer 220, 1-2 transition layers 240 are set; when the area of ​​the base layer 210 is 9-12 times the area of ​​the first stacking layer 220, 2-4 transition layers 240 are set; when the area of ​​the base layer 210 is 12-16 times the area of ​​the first stacking layer 220, 4-5 transition layers 240 are set; when the area of ​​the base layer 210 is more than 16 times the area of ​​the first stacking layer 220, the number of transition layers 240 does not exceed 8 layers.

[0067] Furthermore, in order to cope with the situation where the circuit board surface has multiple BGA sites, when the pressing mold includes two or more convex structures, and all the convex structures are arranged adjacent to each other, the transition layer 240 is arranged with all the convex structures as the center, and all the convex structures are taken as a whole to perform buffer design on the entire circuit board; when the pressing mold includes two or more convex structures, and the convex structures are arranged separately, the transition layer 240 is arranged with each convex structure as the center, and the board surface buffer design is performed around each convex structure, thereby forming a height difference step on the overall panel of the pressing mold to ensure that the pressing mold is on the convex structure. The deformation is the largest at the bottom and then gradually decreases to the edge of the pressing mold. Correspondingly, the concave deformation is the largest at the concave structure on the circuit board panel after pressing, and the overall degree of concave decreases to the edge of the circuit board, ensuring that a groove convenient for the installation of BGA devices is formed at the concave structure, and the edge deformation of the groove and the slight concave of the overall surface of the circuit board have a natural transition, so as not to damage the board surface and internal structure, thereby ensuring the rigidity and stability of the circuit board produced by pressing, and at the same time better balancing the bending and pulling of the BGA installation site and the bending of the entire circuit board during the pressing production process, thereby ensuring the overall production reliability of the circuit board.

[0068] Preferably, two convex structures are arranged on the pressing mold provided in this embodiment, and the distance between the two convex structures does not exceed the complete size of any one of the convex structures, that is, the two convex structures are arranged adjacent to each other.

[0069] Example 2

[0070] like Figure 3 As shown, this embodiment also provides a pressing mold, which is different from Embodiment 1 in that two separately arranged upper convex structures are provided on one side of the pressing mold.

[0071] Example 3

[0072] like Figure 1-Figure 4 As shown, this embodiment provides a method for manufacturing a pressing mold, which is used to manufacture the pressing mold provided in Example 1 or Example 2, specifically, comprising the following steps:

[0073] S1. Forming the base layer 210: Cutting a prepreg to match the size of the circuit board to be laminated as the base layer 210;

[0074] S2. Forming a laminated prepreg: corresponding to the BGA area of ​​the circuit board to be pressed, the prepreg corresponding to the BGA area is stacked layer by layer on the base layer 210;

[0075] S3. Forming a packaging structure: Copper foil layers are respectively covered on the upper and lower sides of the laminated prepreg, and the upper and lower copper foil layers are fused around the base layer 210 to form a packaging structure;

[0076] S4. Forming a composite structure: Take a circuit board with the same wiring as the circuit board to be pressed as a sleeve mold circuit board, and fit the package structure with one side of the laminated prepreg and the side of the sleeve mold circuit board on which the BGA is mounted, and align the laminated prepreg with the BGA area to form a composite structure;

[0077] S5. Pre-pressing the composite structure: heating and pressurizing the composite structure:

[0078] The resin of the prepreg is melted and flowed to form a filler 300;

[0079] The fiber cloth of the prepreg forms a filling layer, and the filling layers are stacked to form a supporting structure;

[0080] The filler 300 is filled in the accommodation cavity formed between the upper and lower copper foil layers and between each filling layer;

[0081] In the BGA area, the copper foil layer located at the upper layer forms an upward convex structure, and the surface texture of the lower mold circuit board is printed on other areas to form an upper shell 110, and the lower copper foil layer forms a lower shell 120;

[0082] S6. Cool and solidify to form a pressed mold.

[0083] Specifically, a semi-cured sheet with upper and lower copper foils wrapped in layers is first used, and the upper and lower copper foil layers are fused at the periphery of the base layer 210 to form a packaging structure, and the semi-cured sheet is stacked on the base layer 210 and fills the accommodating cavity formed inside the packaging structure, and specifically, the fiber cloth of the semi-cured sheet forms a filling layer, and the filling layers are stacked to form a supporting structure, and through pressing, in the BGA area, the copper foil layer located on the upper layer tightly wraps the supporting structure to form an upper convex structure, and other areas are traced with the surface texture of the lower sleeve circuit board to form an upper shell 110, and the lower copper foil layer forms a lower shell 120, and pressing makes the resin of the semi-cured sheet melt and flow to form a filler 300, which is filled in the accommodating cavity formed between the upper and lower copper foil layers and between the filling layers, thereby forming a stable pressing mold. That is, by utilizing the characteristics of the semi-cured sheet, the stacked fiber layers are used as the supporting structure of the laminating mold, and the molten resin during laminating is used as filler 300 to fill the gap in the laminating mold, so that the height difference of the laminating mold at the convex structure changes slowly. While the stacked semi-cured sheets are used to construct the convex structure with the required deformation amount on the laminating mold, damage to the surface of the circuit board to be pressed when the laminating mold is used is avoided, thereby improving the reliability of circuit board production. The preparation process of the lamination mold also includes a process of pre-lamination to solidify the lamination mold and form an upper convex structure. Specifically, when the lamination mold is pre-laminated, the setting position of the stacked semi-cured sheet in the lamination template is first located by using a positioning system consistent with the circuit board to be laminated, so as to ensure that the setting position of the stacked semi-cured sheet corresponds to the BGA area of ​​the circuit board to be laminated; secondly, a circuit board with the same wiring as the circuit board to be laminated is used as a sleeve mold circuit board, and the side of the packaging structure with the stacked semi-cured sheet is laminated with the side of the sleeve mold circuit board where the BGA components are to be installed to form a composite structure. The specific shape of the upper convex structure on the lamination mold is fixed through the lamination process with the sleeve mold circuit board, and the concave structure formed by lamination on the sleeve mold circuit board can also be connected and adapted with the BGA components to check the position accuracy and the degree of improvement of the depression of the formed lamination mold.

[0084] Furthermore, in step S2, stacking the prepregs corresponding to the BGA area layer by layer includes:

[0085] A plurality of first prepreg sheets, the area of ​​which is larger than the BGA area and not larger than 20% of the area of ​​the BGA area;

[0086] A plurality of second prepreg sheets, the area of ​​which is smaller than the BGA area and not less than 60% of the area of ​​the BGA area;

[0087] The total number of the first prepreg and the second prepreg is N=[H / d]+n, where the maximum concave dimension of the BGA area of ​​the circuit board to be pressed is H, the thickness of the prepreg is d, n is the compensation number of 2-5 sheets, and [] is the rounding symbol;

[0088] The number of first cured sheets n1, the area of ​​the first cured sheets gradually decreases from bottom to top, the number of second cured sheets n2, the area of ​​the second cured sheets gradually decreases from bottom to top, and 2≤n1-n2≤5;

[0089] After cooling and solidification in step S6:

[0090] The fiber cloth of the first prepreg forms a first superimposed layer 220;

[0091] The fiber cloth of the second prepreg forms the second stacking layer 230. Specifically, a convex structure with a gradually increasing convexity from the edge of the substrate to the center of the position corresponding to the BGA area is formed on one side of the pressing mold by stacking the prepregs layer by layer; wherein, the first prepreg and the second prepreg are combined to form the convex structure corresponding to the BGA area, and the maximum concave size of the BGA area of ​​the circuit board to be pressed is H, and when the thickness of the single prepreg used is d, on the basis of filling the concave size of the BGA area with the prepreg as much as possible, n prepregs are further stacked to compensate for the thickness loss after the resin in the prepreg flows and fills the gaps during the pressing process, so as to ensure that the convex structure after pressing can reach the predetermined deformation amount; specifically, the value of n depends on the type and characteristics of the selected prepreg, and preferably, the value of n is 2-5 sheets. Furthermore, after lamination, the fiber layer of the first semi-cured sheet constitutes the first stacking layer 220, and the fiber layer of the second semi-cured sheet constitutes the second stacking layer 230. Therefore, similar to the first stacking layer 220 and the second stacking layer 230, in order to enable the lamination mold to better construct a concave structure of a desired shape on the entire circuit board to be laminated during lamination, and at the same time provide an appropriate concave curvature on other areas of the circuit board surface for matching the bending of the entire board during the lamination process, the number of first semi-cured sheets is controlled to be n1, and the number of second semi-cured sheets is n2, and 2≤n1-n2≤5, so that the concave structure formed on the circuit board can achieve the BGA installation depth required by the design, and the contour of the concave structure is buffered by the adjustment of the molten flow of resin of the first semi-cured sheet and the second semi-cured sheet during lamination, so that the deformation amount on the circuit board surface changes gradually, thereby ensuring the overall rigidity and stability of the circuit board surface after the concave structure is opened.

[0092] Preferably, the following steps are further included between steps S1 and S2:

[0093] S12. Overlaying transition semi-cured sheet: Overlaying one or more transition semi-cured sheets with an area between the area of ​​the circuit board to be pressed and the area of ​​the BGA area on the semi-cured sheet of the base layer 210 as a transition layer 240; step S2 specifically involves overlaying the semi-cured sheets corresponding to the BGA area layer by layer on the transition semi-cured sheet; by using the transition semi-cured sheet, the edge of the convex structure on the pressing mold changes in steps from the edge of the base layer 210 to the inside of the convex structure, and the resin melt flow of the semi-cured sheet during pressing is used to fill the part with a height difference at the edge, softening the step-deformed edge of the convex structure from the edge of the base layer 210, so that the concave degree on the entire board surface of the circuit board slowly and gradually deepens from the edge to the BGA area during pressing, so that the BGA area produces the board surface height difference required by the design during the pressing process, thereby better balancing the board bending of the entire circuit board and ensuring the overall manufacturing reliability of the circuit board.

[0094] Preferably, the following steps are further included between steps S2 and S3:

[0095] S22. All prepregs are fused and positioned to fix the relative positions of each layer of prepregs. Through fusion positioning, each layer of prepregs forming the support layer in the pressing mold is firmly connected. The prepregs can be heated, melted and solidified. Through positioning and fusion, a firm connection between the layers can be achieved without introducing additional positioning and connection procedures, which not only improves the accuracy of pressing mold production, but also simplifies the preparation process.

[0096] Preferably, in the preparation process of the lamination mold, at least one side of the wiring of the sleeve mold circuit board used is the same as the side of the concave structure formed by the circuit board to be pressed, and the wiring area is not opened, and the surrounding area is opened with the same positioning holes as the circuit board to be pressed, and the upper shell 110 forms positioning columns at the positioning holes; by setting a sleeve mold circuit board that has been processed with circuits but has not been drilled on the outer layer, the influence of the drilling process on the surface area of ​​the circuit board to be pressed is avoided. At the same time, by setting positioning columns on the edge of the upper shell 110 in the lamination mold so as to more accurately correspond to the positioning system of the circuit board to be pressed, the installation position of the BGA device on the circuit board to be pressed and the site of the positioning system are more accurately simulated, thereby improving the accuracy of positioning and manufacturing of the lamination mold.

[0097] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation methods of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the claims of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A pressing mold, which is flat as a whole and is used in the lamination process of a circuit board to form a concave structure on one side of the circuit board, characterized in that: include: The housing comprises an upper housing and a lower housing, wherein the edges of the upper housing and the lower housing are fused to form an edge seal and the middle is separated to form a receiving cavity; A supporting structure, comprising multiple filling layers of different sizes, stacked and distributed in the accommodating cavity; Filler, filled in the containing cavity and between each filling layer; The accommodating cavity includes at least one local area, in which the number of filling layers of the supporting structure is greater than that of other areas, so that the upper shell is raised to form an upper convex structure, the lower shell is a straight structure, and the position of the upper convex structure corresponds to the lower concave structure; The support structure comprises at least: A base layer, the area and shape of which match those of the circuit board; A plurality of first stacked layers, positioned and stacked in the local area, having an area larger than the concave structure; A plurality of second stacking layers, positioned and stacked on the first stacking layer, having an area smaller than the concave structure; The number n1 of the first stacking layers is such that the area of ​​the first stacking layers decreases gradually from bottom to top, and the number n2 of the second stacking layers is such that the area of ​​the second stacking layers decreases gradually from bottom to top, and 2≤n1-n2≤5; The support structure also includes: At least one transition layer is stacked between the base layer and the first stacked layer, and has an area smaller than the base layer and larger than the first stacked layer. When there is more than one transition layer, the area of ​​the transition layer decreases gradually from bottom to top.

2. A pressing mold according to claim 1, characterized in that: The convex structure is located in the center of the pressing mold; When the area of ​​the base layer is 4-9 times the area of ​​the first superimposed layer, 1-2 transition layers are provided; When the area of ​​the base layer is 9-12 times the area of ​​the first superimposed layer, 2-4 transition layers are provided; When the area of ​​the base layer is 12-16 times the area of ​​the first superimposed layer, 4-5 transition layers are provided; When the area of ​​the base layer is more than 16 times the area of ​​the first stacking layer, the number of the transition layers shall not exceed 8.

3. A pressing mold according to claim 1, characterized in that: When the pressing mold includes two or more convex structures, and all the convex structures are arranged adjacent to each other, the transition layer is arranged with all the convex structures as the center; When the pressing mold includes two or more convex structures, and the convex structures are separately arranged, the transition layer is separately arranged with each convex structure as the center.

4. A method for manufacturing the pressing mold according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Cut a prepreg sheet to match the size of the circuit board to be pressed as the base layer; S2. Corresponding to the BGA area of ​​the circuit board to be pressed, a prepreg corresponding to the BGA area is stacked layer by layer on the base layer; S3. Copper foil layers are respectively covered on the upper and lower sides of the laminated prepreg, and the upper and lower copper foil layers are fused around the periphery of the base layer to form a packaging structure; S4. Take a circuit board with the same wiring as the circuit board to be pressed as a sleeve mold circuit board, and fit the package structure with a laminated prepreg on one side of the sleeve mold circuit board on which the BGA is mounted, and align the laminated prepreg with the BGA area to form a composite structure; S5. Heating and pressurizing the composite structure: The resin of the prepreg is melted and flowed to form a filler; The fiber cloth of the prepreg forms a filling layer, and the filling layers are stacked to form a supporting structure; The filler is filled in the accommodation cavity formed between the upper and lower copper foil layers and between each filling layer; In the BGA area, the upper copper foil layer forms an upward convex structure, and the surface texture of the lower mold circuit board is printed on other areas to form an upper shell, and the lower copper foil layer forms a lower shell; S6. Cool and solidify to form a pressed mold.

5. The method according to claim 4, characterized in that: The step S2 of stacking the prepregs corresponding to the BGA area layer by layer includes: A plurality of first prepreg sheets, the area of ​​which is larger than the BGA area and not larger than 20% of the area of ​​the BGA area; A plurality of second prepreg sheets, the area of ​​which is smaller than the BGA area and not less than 60% of the area of ​​the BGA area; The total number of the first prepreg and the second prepreg is N=[H / d]+n, wherein the maximum concave dimension of the BGA area of ​​the circuit board to be pressed is H, the thickness of the prepreg is d, n is the compensation number of 2-5 sheets, and [] is the rounding symbol; The number n1 of the first prepregs is such that the area of ​​the first prepregs decreases gradually from bottom to top, the number n2 of the second prepregs is such that the area of ​​the second prepregs decreases gradually from bottom to top, and 2≤n1-n2≤5; After the step S6 is cooled and solidified: The fiber cloth of the first prepreg forms a first superimposed layer; The fiber cloth of the second prepreg forms a second superposition layer.

6. The method according to claim 4, characterized in that: The following steps are also included between steps S1 and S2: S12. One or more transition prepregs having an area between the circuit board area to be laminated and the BGA area are superimposed on the base prepreg; The step S2 specifically comprises stacking prepregs corresponding to the BGA area layer by layer on the transition prepreg; The following steps are also included between steps S2 and S3: S22. All prepregs are fused and positioned to fix the relative positions of the prepregs of each layer.

7. The method according to claim 4, characterized in that: Specifically, the sleeve mold circuit board has at least one side whose wiring is the same as the side of the circuit board to be pressed to form a concave structure, and the wiring area has no holes, and the periphery is provided with the same positioning holes as the circuit board to be pressed; The upper shell forms a positioning column at the positioning hole.

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