Press-fit die for forming local recess in specific BGA (ball grid array) area on PCB (printed circuit board)

Abstract

The utility model provides the press-fit die for forming the local recess in the specific BGA area on the PCB, and the press-fit die is adopted to form the concave structure at the specific site where the BGA area needs to be formed on the to-be-pressed PCB, so that the deformation tolerance of the BGA area and the surface of the PCB in the press-fit manufacturing process is improved; and the probability of unsoldering and pulling of the BGA area due to board bending in the manufacturing process of the PCB is reduced. Specifically, according to the pressing die, the edges of an upper shell and a lower shell are fused to form a shell containing a containing cavity, the lower shell is of a straight structure, and a plane for transmitting uniform pressure is provided for overall pressing; meanwhile, the containing cavity is filled with the supporting structure and the filler, so that the upper shell protrudes to form a stable upward-protruding structure, the external deformation outline of the upward-protruding structure is obscured through cooperation of the hard supporting structure and the flowing filler, and the edge of the formed concave position can be subjected to uniform transition while shaping is conducted on the PCB to be pressed in the using process; and the plate surface is not damaged.

Description

Technical Field

[0001] This utility model relates to the field of electronic manufacturing technology, and more specifically, to a pressing mold for forming local depressions in specific BGA areas on a PCB. Background Technology

[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 reliability of the connection between BGA and printed circuit board (PCB) has become increasingly prominent, especially the bending problem caused by the mismatch of their coefficients of thermal expansion (CTE).

[0003] During manufacturing and use, BGAs and PCBs undergo various temperature changes, such as soldering and fluctuations in ambient temperature. Because different materials respond differently to temperature changes, variations in CTE (Coefficient of Thermal Expansion) can lead to relative displacement and stress between the BGA and PCB during temperature variations. When this stress accumulates to a certain level, it can cause localized or overall bending of the PCB, thereby affecting the soldering quality and electrical connection performance of the BGA. In particular, the risk of board bending increases significantly when the BGA size is large.

[0004] To address this issue, one common industry practice is to adjust the PCB design, recessing the BGA area by a certain depth (e.g., 40 mil) to fix the BGA's position and reduce the direct impact of bending on BGA mounting reliability. This method mitigates the impact of board bending on BGA component mounting reliability to some extent, reducing the risk of desoldering and pulling. However, in actual production, precisely controlling the size, position, and depth of the recessed area, and ensuring that this area does not move or deform during continuous lamination and other processes, has become a pressing technical challenge.

[0005] Therefore, under the current technological background, a more refined solution is needed to address the mismatch in thermal expansion coefficients between BGA components and PCBs. This includes, but is not limited to, developing materials with higher thermal expansion coefficient matching, optimizing the lamination process to achieve precise local control, and introducing advanced positioning and monitoring technologies to ensure processing accuracy and stability. Through the comprehensive application of these technologies, the installation reliability between BGA components and PCBs can be further improved, meeting the increasingly stringent performance requirements of electronic products. Utility Model Content

[0006] The present invention aims to overcome at least one of the defects of the prior art and provide a pressing mold for forming local depressions in specific BGA areas on a PCB.

[0007] To solve the above-mentioned technical problems, this utility model provides a pressing mold for forming a local recess in a specific BGA area on a PCB. The pressing mold is pressed with the PCB board to be pressed, and is used to form a recessed structure on the side of the PCB board that contacts the pressing mold. The structure of the pressing mold includes:

[0008] The outer shell includes an upper shell and a lower shell, the edges of which are fused to form a sealing edge, and the middle is separated to form a receiving cavity;

[0009] The support structure includes multiple layers of filling with varying sizes, stacked and distributed within the receiving cavity;

[0010] The filler material is used to fill the cavity and between the filler layers.

[0011] The cavity includes at least one local area where the number of filling layers of the support structure is greater than in other areas, causing the upper shell to bulge to form an upward convex structure, while the lower shell is a flat structure. The position of the upward convex structure corresponds to the downward concave structure.

[0012] In this technical solution, during the lamination process of the PCB to which BGA components need to be connected, a recessed structure is formed at a specific point on the PCB to be laminated where the BGA area needs to be formed by using a lamination mold. This structure is used to support the BGA components, thereby improving the deformation tolerance of the BGA area and the PCB surface during the lamination process. This reduces the probability of desoldering and pulling of the BGA area during PCB manufacturing, reduces the impact of board bending on the connection and installation of BGA components and the PCB surface, and improves the installation reliability of BGA components and the PCB surface. Specifically, the pressing mold includes an outer shell, a support structure, and filler. The outer shell containing a cavity is formed by fusing the edges of the upper and lower shells. The upper shell is raised to form an upward convex structure, while the lower shell is flat, which facilitates the fit with the plane of the pre-pressed board structure, providing a plane for uniform pressure transmission during the overall pressing process. At the same time, a certain amount of support structure and filler are filled into the cavity to form a complete and leak-proof upward convex structure, which facilitates the formation of a corresponding concave structure on the PCB surface to be pressed. During the pressing process, the internal support structure can provide flexible support through the filler, which allows for uniform edge transition while shaping the PCB during pressing, without damaging the board surface.

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

[0014] The base layer, the area and shape of which are matched to the PCB;

[0015] Several first overlay layers are positioned and superimposed on the local area, with an area larger than the concave structure;

[0016] Several second overlay layers are positioned and superimposed on the first overlay layer, with an area smaller than the concave structure.

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

[0018] Furthermore, the number of the first superimposed layers n1 decreases gradually from bottom to top in terms of the area of ​​the first superimposed layers, and the number of the second superimposed layers n2 decreases gradually from bottom to top in terms of the area of ​​the second superimposed layers, and 2≤n1-n2≤5.

[0019] Furthermore, in order to better construct the required concave structure on the PCB board to be laminated, and at the same time provide appropriate concave curvature in other areas of the PCB board to match the bending of the entire board during the lamination process, the number of the first stacked layers is controlled to be n1, and the area of ​​the first stacked layer gradually decreases from bottom to top. The number of the second stacked layers is n2, and the area of ​​the second stacked layer gradually decreases from bottom to top, and 2≤n1-n2≤5. This ensures that the concave structure formed on the PCB can achieve the required BGA mounting depth, and the outline of the concave structure can gradually change on the PCB board, thereby ensuring the overall rigidity and stability of the PCB board after the concave structure is created.

[0020] Furthermore, to balance the impact of lamination on the overall PCB board bending and improve the reliability of the PCB board manufacturing, in addition to the overall recessed design of the BGA area, a stepped buffer design is also required around the BGA area on the PCB board surface. This minimizes the impact of lamination-induced board bending on the BGA area and the overall PCB board manufacturing. Specifically, in the fabrication of the lamination mold, the support structure includes at least one transition layer. This transition layer is superimposed between the base layer and the first superimposed layer, with an area smaller than the base layer but larger than the first superimposed layer. When there is more than one transition layer, the area of ​​the transition layer gradually decreases from bottom to top. The transition layer effectively connects the area between the base layer and the first superimposed layer, causing the edge of the convex structure on the lamination mold to change from the edge of the base layer to the inside of the convex structure in a stepped manner. As a result, during lamination, the degree of concavity on the overall PCB board surface gradually deepens from the edge to the BGA area, creating the required board height difference in the BGA area during the lamination process. This better balances the board bending of the entire PCB board and ensures the overall reliability of the PCB manufacturing.

[0021] Preferably, to better balance the bending of the entire PCB board and ensure the overall manufacturing reliability of the PCB, when the convex structure is located in the center of the pressing mold; when the base layer area is 4-9 times the area of ​​the first superimposed layer, 1-2 transition layers are set; when the base layer area is 9-12 times the area of ​​the first superimposed layer, 2-4 transition layers are set; when the base layer area is 12-16 times the area of ​​the first superimposed layer, 4-5 transition layers are set; when the base layer area is more than 16 times the area of ​​the first superimposed layer, the number of transition layers does not exceed 8 layers.

[0022] Furthermore, when the pressing mold includes two or more upper convex structures, and all upper convex structures are arranged adjacent to each other, the transition layer is arranged with all upper convex structures as the center;

[0023] When the pressing mold includes two or more convex structures, and the convex structures are set separately, the transition layer is set separately with each convex structure as the center.

[0024] In this technical solution, to address the situation where the PCB board has multiple BGA sites, when the laminating mold includes two or more convex structures, if all convex structures are adjacent, the entire PCB board is buffered as a whole. If all convex structures are separated, a board surface buffering design is performed around each convex structure, thus forming a height difference step on the overall panel of the laminating mold. This ensures that the laminating mold deforms most at the convex structures and gradually decreases towards the edge of the laminating mold. Correspondingly, the PCB board after lamination shows the greatest concave deformation at the concave structure, and the degree of concavity decreases towards the edge of the PCB. This ensures that a groove is formed at the concave structure to facilitate the installation of BGA devices. The edge deformation of the groove transitions naturally with the slight concavity of the overall PCB board surface, thus avoiding damage to the board surface and internal structure, ensuring the rigidity and stability of the laminating PCB board, and better balancing the bending and pulling of the BGA mounting sites and the bending of the entire PCB board during the lamination process, ensuring the overall reliability of the PCB manufacturing. Preferably, the two convex structures are arranged adjacently, with the distance between them not exceeding the full size of one of the convex structures; otherwise, they are arranged separately.

[0025] In a preferred embodiment, both the upper and lower housings are made of copper foil, and the cavity is filled with a prepreg that has been stacked and melted and solidified. The fiber layers stacked in the prepreg form the support structure, and the molten resin in the prepreg forms a filler that fills the gap between the outer shell and the support structure.

[0026] In this technical solution, a prepreg is wrapped with upper and lower copper foil layers. The upper and lower copper foil layers are fused together to form an encapsulation structure on the periphery of the base layer. The prepreg is then stacked on the base layer and fills the cavity formed inside the encapsulation structure. Specifically, the fiber cloth of the prepreg forms a filling layer, and the filling layers are stacked to form a support structure. Through pressing, in the BGA area, the upper copper foil layer tightly wraps the support structure to form an upward convex structure. In other areas, the surface texture of the lower die PCB is imprinted to form an upper shell, and the lower copper foil layer forms a lower shell. Pressing causes the resin of the prepreg to melt and flow to form a filler, which fills the cavity formed between the upper and lower copper foil layers and between the filling layers, thereby forming a stable pressing mold. In other words, by utilizing the properties of prepregs—combining the stable support of fiber layers with the heat-melting and flowing properties of resin—the layered fiber layers serve as the support structure for the pressing mold. The molten resin, flowing during pressing, acts as a filler to fill the gaps in the pressing mold before cooling and solidifying, forming a stable and cured pressing mold. This fully utilizes the buffering effect of the prepregs, allowing the height difference of the pressing mold at the convex structure to change gradually. While constructing the required deformation convex structure on the pressing mold through layered prepregs, it also avoids damage to the PCB board surface during use, improving the reliability of PCB manufacturing. Preferably, the prepregs used in the pressing mold are low-flow prepregs, which are more conducive to alignment and shaping during the pressing mold manufacturing process.

[0027] Furthermore, the prepreg includes a base prepreg, layers of prepregs corresponding to the BGA area, and one or more transition prepregs with an area between the area of ​​the PCB to be laminated and the area of ​​the BGA area, which are stacked between the base prepreg and the prepregs corresponding to the BGA area.

[0028] The prepreg layers corresponding to the BGA regions are stacked one by one, including:

[0029] Several first prepregs have an area larger than the BGA region but not more than 20% of the area of ​​the BGA region;

[0030] Several second prepregs have an area smaller than the BGA region, but not less than 60% of the area of ​​the BGA region;

[0031] The total number of the first and second prepregs is N = [H / d] + n, where the maximum recessed size of the BGA area of ​​the PCB to be laminated is H, the thickness of the prepreg is d, n is a compensation quantity of 2-5 sheets, and [] is the rounding symbol.

[0032] Furthermore, the number of first cured sheets n1 decreases gradually from bottom to top in terms of area, and the number of second cured sheets n2 decreases gradually from bottom to top in terms of area, and 2≤n1-n2≤5;

[0033] After melting and solidification, the fiber cloth of the first semi-cured sheet forms a first superimposed layer, the fiber cloth of the second semi-cured sheet forms a second superimposed layer, and the fiber cloth of the transition semi-cured sheet forms a transition layer.

[0034] In this technical solution, a progressively increasing upward convex structure is formed on one side of the lamination mold by layering prepregs, with the convexity gradually increasing from the edge of the substrate to the center corresponding to the BGA area. The first and second prepregs are combined to form the upward convex structure corresponding to the BGA area. Therefore, the total number of the first and second prepregs used in the lamination mold is set to N = [H / d] + n. Where the maximum recessed size of the BGA area of ​​the PCB to be laminated is H, and the thickness of a single prepreg is d, in addition to filling the recessed size of the BGA area as much as possible with prepregs, n more prepregs are further stacked to compensate for the thickness loss after resin flow and gap filling during the lamination process, ensuring that the upward convex structure after lamination achieves a predetermined deformation. Specifically, the value of n depends on the type and characteristics of the selected prepregs; preferably, n is 2-5 sheets. Furthermore, after lamination, the fiber layer of the first prepreg forms the first superimposed layer, and the fiber layer of the second prepreg forms the second superimposed layer. Therefore, similar to the first and second superimposed layers, in order to enable the lamination mold to better construct the required concave structure on the PCB board to be lamination during lamination, and to provide appropriate concave curvature in other areas of the PCB board to match the bending of the entire board during lamination, the number of the first prepreg is controlled to be n1, and the number of the second prepreg is n2, and 2≤n1-n2≤5. This ensures that the concave structure formed on the PCB can achieve the required BGA mounting depth. The contour of the concave structure is buffered by the resin flowing through the first and second prepregs during lamination, so that the deformation on the PCB board gradually changes, thereby ensuring the overall rigidity and stability of the PCB board after the concave structure is created. Meanwhile, the use of a prepreg between the base layer and the convex structure allows the edge of the convex structure to change from the base layer edge to the interior of the convex structure in the lamination mold in a stepped manner. The resin melts and flows during lamination using the prepreg to fill the part with the height difference at the edge, softening the stepped deformation at the edge of the convex structure. As a result, the concavity of the PCB board surface gradually deepens from the edge to the BGA area during lamination, so that the BGA area generates the board surface height difference required by the design during the lamination process. This better balances the board curvature of the entire PCB board and ensures the overall reliability of the PCB manufacturing.

[0035] Preferably, the copper foil used in the pressing mold has a thickness of not less than 1 oz. By using thick copper foil, the rigidity of the pressing mold is improved, preventing the fiber layer from penetrating or the resin from overflowing when the stacked prepreg forms an upward convex structure. This improves the manufacturing yield of the pressing mold and extends its service life.

[0036] Preferably, in order to ensure the stable installation of the recessed structure formed by the BGA components on the PCB, the recess in the BGA area on the PCB should not be too large to avoid damaging the reliability of the PCB board surface. At the same time, it is convenient for the solder ball pins of the BGA components to be reliably connected to the metallized holes provided on the PCB board surface. The maximum deformation of the recessed structure is set to not exceed 45mil.

[0037] The beneficial effects of this utility model are as follows:

[0038] 1. A pressing mold is provided for forming local recesses in specific BGA areas on a PCB. During the pressing process of a PCB that needs to connect BGA components, a recessed structure is formed at a specific point on the PCB where the BGA area needs to be formed by the pressing mold. This structure is used to support the BGA components, thereby improving the tolerance for deformation of the BGA area and the PCB surface during the pressing process. This reduces the probability of desoldering and pulling of the BGA area during PCB manufacturing and reduces the impact of board bending on the connection and installation of BGA components and the PCB surface. Specifically, the pressing mold includes an outer shell, a support structure, and filler. The outer shell containing a receiving cavity is formed by fusing the edges of the upper and lower shells. The upper shell is raised to form an upward convex structure, while the lower shell is flat, which facilitates the fit with the plane of the board arrangement structure before pressing, providing a plane for uniform pressure transmission during the overall pressing. At the same time, a certain amount of support structure and filler are filled into the receiving cavity to form a complete and leak-proof upward convex structure, which facilitates the formation of a corresponding concave structure on the surface of the PCB to be pressed. During the pressing process, the internal support structure can blur the external deformation contour of the upward convex structure through the filler and provide flexible support during pressing. This allows the edges of the concave positions formed during the shaping on the PCB to be pressed to transition evenly without damaging the board surface. Attached Figure Description

[0039] Figure 1 This is one of the structural schematic diagrams of a pressing mold used to form local depressions in specific BGA areas on a PCB according to this utility model.

[0040] Figure 2 This is a cross-sectional schematic diagram of the pressing mold used by this utility model to form local depressions in specific BGA areas on a PCB.

[0041] Figure 3This is the second schematic diagram of the pressing mold used to form local depressions in specific BGA areas on a PCB according to the present invention.

[0042] Figure description: Upper shell 110, lower shell 120, base layer 210, first superimposed layer 220, second superimposed layer 230, transition layer 240, filler 300. Detailed Implementation

[0043] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this invention. To better illustrate the following embodiments, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0044] Example 1

[0045] like Figures 1-3 As shown, this embodiment provides a pressing mold for forming a local recess in a specific BGA area on a PCB. The pressing mold is pressed with the PCB to be pressed, and is used to form a recessed structure on the side of the PCB to be pressed that contacts the pressing mold. The structure of the pressing mold includes:

[0046] The outer shell includes an upper shell 110 and a lower shell 120, the edges of the upper shell 110 and the lower shell 120 are fused together to form a sealing edge, and the middle is separated to form a receiving cavity;

[0047] The supporting structure includes multiple layers of filling of varying sizes, stacked and distributed within the receiving cavity;

[0048] Packing material 300 is used to fill the cavity and between the packing layers.

[0049] Within the cavity, there is at least one local area where the number of filler layers of the supporting structure is greater than in other areas, causing the upper shell 110 to bulge to form an upward-convex structure, while the lower shell 120 has a flat structure. The position of the upward-convex structure corresponds to the downward-concave structure. By using a pressing mold to form a concave structure at a specific point on the PCB to be pressed where the BGA area needs to be formed, the BGA components are subsequently supported. This improves the tolerance for deformation of the BGA area and the PCB surface during the pressing process, reduces the probability of desoldering and pulling of the BGA area during PCB manufacturing, reduces the impact of board bending on the connection and installation of BGA components and the PCB surface, and improves the installation reliability of BGA components and the PCB surface.

[0050] Furthermore, such as Figure 2 As shown, in order to match the lamination surface of the PCB to be laminated, and at the same time fix the shape and position of the upper and lower recessed structures of the PCB on one side, the support structure includes at least:

[0051] Base layer 210, the area and shape of base layer 210 are matched with PCB;

[0052] Several first overlay layers 220 are positioned and overlaid in a local area, with an area larger than the concave structure;

[0053] Several second overlay layers 230 are positioned and overlaid on the first overlay layer 220, with an area smaller than that of the recessed structure.

[0054] Furthermore, in order to better construct the required concave structure on the PCB board to be laminated, and at the same time provide appropriate concave curvature in other areas of the PCB board to match the bending of the entire board during the lamination process, the number of the first stacked layer 220 is controlled to be n1, and the area of ​​the first stacked layer 220 gradually decreases from bottom to top. The number of the second stacked layer 230 is n2, and the area of ​​the second stacked layer 230 gradually decreases from bottom to top, and 2≤n1-n2≤5. This ensures that the concave structure formed on the PCB can achieve the required BGA mounting depth, and the outline of the concave structure can gradually change on the PCB board, thereby ensuring the overall rigidity and stability of the PCB board after the concave structure is created.

[0055] Furthermore, to balance the impact of lamination on the overall PCB board bending and improve the reliability of the PCB board manufacturing, in addition to the overall recessed design of the BGA area, a stepped buffer design is also required around the BGA area on the PCB board surface. This minimizes the impact of lamination-induced board bending on the BGA area and the overall PCB board manufacturing. Specifically, in the fabrication of the lamination mold, the support structure includes an additional transition layer 240. The transition layer 240 is superimposed between the base layer 210 and the first superimposed layer 220, and its area is smaller than that of the base layer 210. The transition layer 240 is larger than the first superimposed layer 220. When the transition layer 240 exceeds one layer, the area of ​​the transition layer 240 gradually decreases from bottom to top. The transition layer 240 effectively connects the area between the base layer 210 and the first superimposed layer 220, so that the edge of the convex structure on the pressing mold changes from the edge of the base layer 210 to the inside of the convex structure in a stepped manner. As a result, the degree of concavity on the PCB board surface gradually increases from the edge to the BGA area during pressing, so that the BGA area generates the board surface height difference required by the design during the pressing process, thereby better balancing the board bending of the entire PCB board and ensuring the overall manufacturing reliability of the PCB.

[0056] Preferably, to better balance the bending of the entire PCB board and ensure the overall manufacturing reliability of the PCB, when the convex structure is located in the center of the lamination mold; when the area of ​​the base layer 210 is 4-9 times the area of ​​the first superimposed 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 superimposed 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 superimposed 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 superimposed layer 220, the number of transition layers 240 does not exceed 8 layers.

[0057] Optionally, to address situations where the PCB board has multiple BGA mounting points, when the lamination mold includes two or more raised structures, and all raised structures are adjacent to each other, the transition layer 240 is centered on all raised structures; when the lamination mold includes two or more raised structures, and the raised structures are separated, the transition layer 240 is individually centered on each raised structure. This ensures that the board surface and internal structure are not damaged, guaranteeing the rigidity and stability of the laminated PCB board. It also better balances the bending and pulling of the BGA mounting points and the overall PCB board bending during the lamination process, ensuring the overall reliability of the PCB manufacturing. Preferably, adjacent raised structures are defined as those whose distance between them does not exceed the full dimension of one of the raised structures. Figure 1 As shown; otherwise, for separate settings, such as Figure 3 As shown.

[0058] Preferably, in order to ensure the stable installation of the recessed structure formed by the BGA components on the PCB, the recess in the BGA area on the PCB should not be too large to avoid damaging the reliability of the PCB board. At the same time, it is convenient for the solder ball pins of the BGA components to be reliably connected to the metallized holes on the PCB board. The maximum deformation of the recessed structure is set to not exceed 45mil.

[0059] Example 2

[0060] like Figures 1-3 As shown, this embodiment also provides a pressing mold for forming local depressions in specific BGA areas on a PCB. The difference from Embodiment 1 is that in this embodiment, both the upper shell 110 and the lower shell 120 are made of copper foil. The cavity is filled with a prepreg that is stacked and melted and solidified. The fiber layer stacked in the prepreg forms a support structure, and the molten resin in the prepreg forms a filler 300 that fills the gap between the shell and the support structure.

[0061] Specifically, the prepreg includes a base prepreg, layers of prepregs corresponding to the BGA area, and one or more transition prepregs with an area between the area of ​​the PCB to be laminated and the area of ​​the BGA area, which are stacked between the base prepreg and the prepregs corresponding to the BGA area.

[0062] The prepreg layers corresponding to the BGA regions are stacked one by one, including:

[0063] Several first prepregs have an area larger than the BGA region but not more than 20% of the area of ​​the BGA region;

[0064] Several second prepregs have an area smaller than the BGA region, but not less than 60% of the area of ​​the BGA region;

[0065] The total number of the first and second prepregs is N = [H / d] + n, where the maximum recessed size of the BGA area of ​​the PCB to be laminated is H, the thickness of the prepreg is d, and n is the compensation quantity of 2-5 sheets. [] is the rounding symbol.

[0066] Furthermore, the number of first curing sheets n1 decreases gradually from bottom to top, and the number of second curing sheets n2 decreases gradually from bottom to top, with 2≤n1-n2≤5;

[0067] After melting and solidification, the fiber cloth of the first semi-cured sheet forms a first superimposed layer 220, the fiber cloth of the second semi-cured sheet forms a second superimposed layer 230, and the fiber cloth of the transition semi-cured sheet forms a transition layer 240.

[0068] By using a prepreg wrapped with upper and lower copper foil layers, and fusing the upper and lower copper foil layers around the base layer 210 to form an encapsulation structure, the prepreg is stacked on the base layer 210 and fills the cavity formed inside the encapsulation structure. Specifically, the fiber cloth of the prepreg forms a filling layer, and the filling layers are stacked to form a support structure. Through pressing, in the BGA area, the upper copper foil layer tightly wraps the support structure to form an upward convex structure. Pressing also causes the resin of the prepreg to melt and flow to form filler 300, which fills the cavity formed between the upper and lower copper foil layers and between each filling layer, thereby forming a stable pressing mold. By utilizing the properties of prepregs—combining the stable support of fiber layers with the heat-melting and flowing properties of resin—the stacked fiber layers serve as the support structure for the pressing mold. The resin, flowing molten during pressing, acts as filler 300 to fill gaps in the mold before cooling and solidifying, forming a stable and cured pressing mold. This fully utilizes the buffering effect of the prepregs, allowing the height difference at the convex structure of the pressing mold to change gradually. While constructing the required convex structure on the pressing mold using stacked prepregs, it also avoids damage to the PCB board surface during pressing, thus improving the reliability of PCB manufacturing.

[0069] Preferably, the copper foil used in the pressing mold has a thickness of not less than 1 oz. By using thick copper foil, the rigidity of the pressing mold is improved, preventing the fiber layer from penetrating or the resin from overflowing when the stacked prepreg forms an upward convex structure. This improves the manufacturing yield of the pressing mold and extends its service life.

[0070] Obviously, the above embodiments of this utility model are merely examples for clearly illustrating the technical solution of this utility model, and are not intended to limit the specific implementation of this utility model. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of this utility model should be included within the protection scope of the claims of this utility model.

Claims

1. A pressing mold for forming localized recesses in specific BGA areas on a PCB, characterized in that, The pressing mold presses against the PCB board to be pressed, forming a recessed structure on the side of the PCB board that contacts the pressing mold. The structure of the pressing mold includes: The outer shell includes an upper shell and a lower shell, the edges of which are fused to form a sealing edge, and the middle is separated to form a receiving cavity; The support structure includes multiple layers of filling with varying sizes, stacked and distributed within the receiving cavity; The filler material is used to fill the cavity and between the filler layers. The cavity includes at least one local area where the number of filling layers of the support structure is greater than in other areas, causing the upper shell to bulge to form an upward convex structure, while the lower shell is a flat structure. The position of the upward convex structure corresponds to the downward concave structure.

2. The pressing mold according to claim 1, characterized in that, The support structure includes at least: The base layer, the area and shape of which are matched to the PCB; Several first overlay layers are positioned and superimposed on the local area, with an area larger than the concave structure; Several second overlay layers are positioned and superimposed on the first overlay layer, with an area smaller than the concave structure.

3. The pressing mold according to claim 2, characterized in that, The number of first superimposed layers, n1, decreases gradually from bottom to top in area, and the number of second superimposed layers, n2, decreases gradually from bottom to top in area, with 2≤n1-n2≤5.

4. The pressing mold according to claim 2, characterized in that, The support structure also includes: At least one transition layer is provided, which is superimposed between the base layer and the first superimposed layer. The area of ​​the transition layer is smaller than that of the base layer and larger than that of the first superimposed layer. When there is more than one transition layer, the area of ​​the transition layer gradually decreases from bottom to top.

5. The pressing mold according to claim 4, 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 overlay layer, 1-2 transition layers are set. When the area of ​​the base layer is 9-12 times the area of ​​the first overlay layer, 2-4 transition layers are set. When the area of ​​the base layer is 12-16 times the area of ​​the first overlay layer, 4-5 transition layers are set. When the area of ​​the base layer is more than 16 times the area of ​​the first superimposed layer, the number of the transition layers shall not exceed 8.

6. The pressing mold according to claim 4, characterized in that, When the pressing mold includes two or more upper convex structures, and all upper convex structures are arranged adjacent to each other, the transition layer is arranged with all upper convex structures as the center. When the pressing mold includes two or more convex structures, and the convex structures are set separately, the transition layer is set separately with each convex structure as the center.

7. The pressing mold according to any one of claims 1-6, characterized in that, Both the upper and lower housings are made of copper foil. The cavity is filled with a prepreg that has been stacked and melted and solidified. The fiber layers stacked in the prepreg form the support structure, and the molten resin in the prepreg forms a filler that fills the gap between the outer shell and the support structure.

8. The pressing mold according to claim 7, characterized in that, The prepreg includes a base prepreg, a progressively stacked transition prepreg, and progressively stacked prepregs corresponding to the BGA region. The prepreg layers corresponding to the BGA regions are stacked one by one, including: Several first prepregs have an area larger than the BGA region but not more than 20% of the area of ​​the BGA region; Several second prepregs have an area smaller than the BGA region, but not less than 60% of the area of ​​the BGA region; The total number of the first and second prepregs is N = [H / d] + n, where the maximum recessed size of the BGA area of ​​the PCB to be laminated is H, the thickness of the prepreg is d, n is a compensation quantity of 2-5 sheets, and [] is the rounding symbol. Furthermore, the number of the first semi-cured sheets n1 gradually decreases from bottom to top in terms of the area of ​​the first cured sheets, and the number of the second semi-cured sheets n2 gradually decreases from bottom to top in terms of the area of ​​the second cured sheets, and 2≤n1-n2≤5; After melting and solidification, the fiber cloth of the first semi-cured sheet forms a first superimposed layer, the fiber cloth of the second semi-cured sheet forms a second superimposed layer, and the fiber cloth of the transition semi-cured sheet forms a transition layer.

9. The pressing mold according to claim 7, characterized in that, The thickness of the copper foil is not less than 1 oz.

10. The pressing mold according to any one of claims 1-6, characterized in that, The maximum deformation of the concave structure is no more than 45 mil.

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