Lamination method to achieve recessed base of specific BGA area on PCB

Abstract

The present invention provides a lamination method for realizing a base depression in a specific BGA area of ​​a PCB, wherein a mold is used to perform total lamination together with a PCB to be pressed, and a base depression is formed at a specific position on the PCB to be pressed where a BGA area is to be formed, which is used to carry BGA components in the future, thereby reducing the probability of desoldering and pulling after the BAG components are installed on the PCB, and reducing the influence of the board bending phenomenon on the connection and installation of the BGA components and the PCB board surface. Furthermore, in the lamination method provided by the present invention, during hot pressing, the mold and the PCB to be pressed are arranged in a group, and a buffer structure is synchronously and fully arranged on both sides of the mold and the PCB to be pressed, forming a symmetrically arranged stacked plate structure, thereby avoiding uneven pressure and temperature conduction on the surface of the PCB to be pressed due to the convex structure arranged on the mold during pressing, aggravating the problem of board bending of the PCB to be pressed during the pressing process, improving the stability of pressing, and improving the precision and reliability of pressing and manufacturing of the PCB to be pressed.

Description

Technical Field

[0001] This invention relates to the field of electronic manufacturing technology, and more specifically, to a lamination method for achieving a recessed base in a specific BGA area of ​​a PCB. 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 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 to a certain depth compared to the normal board surface. This fixes the BGA's position and reduces the direct impact of bending on the BGA. This method mitigates the effects of board bending on the BGA to some extent, reducing the risk of desoldering and tearing. 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, have become pressing technical challenges.

[0005] Therefore, under the current technological background, a more refined solution is needed to address the CTE mismatch issue between BGA and PCB. This includes, but is not limited to, developing materials with higher CTE matching, optimizing the lamination process to achieve precise local control, and introducing advanced positioning and monitoring technologies to ensure processing accuracy and stability. The comprehensive application of these technologies can further improve the reliability of the connection between BGA and PCB, meeting the increasingly stringent performance requirements of electronic products. Summary of the Invention

[0006] The present invention aims to overcome at least one of the shortcomings of the prior art and provide a lamination method for achieving a recessed base in a specific BGA area of ​​a PCB.

[0007] The purpose of this invention is to provide a lamination method for creating a recessed base in a specific BGA area on a PCB. A mold is placed over the side of the PCB to be laminated where the BGA area is located, and corresponding boards are fitted to form a stacked structure. The stacked structure is then fed into a hot press for heating and pressurization, causing a recessed base to form in the specific BGA area on the PCB. The stacked structure includes a first buffer layer, a first isolation layer, the PCB to be laminated, the mold, a second isolation layer, and a second buffer layer, sequentially stacked between the steel discs of the hot press. The mold is used to create a recessed structure at the corresponding BGA area on the PCB to be laminated during the lamination process.

[0008] The structure of the mold includes:

[0009] 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;

[0010] The support structure includes multiple layers of filling with varying sizes, stacked and distributed within the receiving cavity;

[0011] The filler material is used to fill the cavity and between the filler layers.

[0012] 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.

[0013] In this technical solution, a mold is used to form a base recess at a specific location on the PCB where the BGA area needs to be formed, to support the BGA chip. The mold has a convex structure on the side that mates with the PCB, used to form a concave structure on the PCB during pressing. Specifically, the mold includes a shell, a support structure, and filler. The upper and lower shells are fused together to form a cavity. The upper shell is raised to form the convex structure, while the lower shell is flat, facilitating alignment with the plane of the pre-pressed board structure and providing a plane for uniform pressure transmission during the overall pressing process. Simultaneously, a certain amount of support structure and filler is filled into the cavity to form a complete and leak-proof convex structure, facilitating the formation of a corresponding concave structure on the PCB surface. During pressing, the internal support structure provides flexible support through the filler, allowing for uniform edge transition during shaping on the PCB and preventing damage to the board surface. Furthermore, due to the upward-convex structure on the mold, uneven pressure and temperature conduction on the PCB board to be pressed is easily caused during pressing, which aggravates the bending of the PCB board during the pressing process. In order to improve the precision and reliability of the pressing of the PCB board, specifically, a first buffer layer, a first isolation layer, the PCB board to be pressed and the mold, a second isolation layer and a second buffer layer are stacked sequentially between the steel discs of the hot press. By fully setting buffer structures on both sides of the PCB board to be pressed and the mold during the pressing process, the speed of pressure and temperature conduction in the stacked structure is slowed down, and the stability of pressing is improved.

[0014] Furthermore, the support structure includes at least:

[0015] The base layer, the area and shape of which are matched to the PCB;

[0016] Several first overlay layers are positioned and superimposed on the local area, with an area larger than the concave structure;

[0017] Several second overlay layers are positioned and superimposed on the first overlay layer, with an area smaller than the concave structure.

[0018] 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 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.

[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 mold manufacturing process, 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 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 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 mold includes two or more convex structures and all convex structures are arranged adjacent to each other, the transition layer is arranged with all convex structures as the center.

[0023] When the 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 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 buffer design is performed around each convex structure to create a height difference step on the overall panel of the mold. This ensures that the mold deforms most at the convex structures and gradually decreases towards the edge of the mold. Correspondingly, the PCB board after lamination has 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. This ensures the rigidity and stability of the laminated PCB board and better balances 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] Furthermore, in the stacked structure, the PCBs to be pressed and the molds are arranged in groups, separated by copper foil. The copper foil can be a copper foil layer on the surface of the PCBs to be pressed, or it can be a separately arranged copper foil layer, used to separate the PCBs and the molds, avoiding the risk of damage from direct contact. Simultaneously, the flexibility of the copper foil further disperses the stress on the contact surfaces of the PCBs and the molds during pressing, resulting in a smoother edge transition when forming the concave and convex structures of the PCBs to be pressed. The stacked structure includes multiple groups of PCBs and molds to be pressed, and these groups are separated by a third isolation layer and a third buffer layer. By setting a uniform and symmetrical stacked plate structure in the pressing plate, multiple PCBs to be pressed can be processed simultaneously. Specifically, the concave structure on the PCB to be pressed is shaped by the mold pressing. Therefore, the PCBs to be pressed and the mold are set up in groups. By stacking the first buffer layer, the first isolation layer, the PCBs to be pressed and the mold, the second isolation layer and the second buffer layer in sequence between the steel plates of the hot press, and the multiple groups of PCBs to be pressed and the mold are isolated by the third isolation layer and the third buffer layer, so that the PCBs to be pressed in the stacked plate structure can be uniformly pressed.

[0026] Preferably, in the mold, both the upper and lower shells are made of copper foil, and the cavity is filled with stacked and melt-cured prepreg sheets. The stacked fiber layers in the prepreg sheets form the support structure, and the molten resin in the prepreg sheets forms filler to fill the gaps between the shell and the support structure. The prepreg sheets include a base prepreg sheet, progressively stacked transition prepreg sheets, and progressively stacked prepreg sheets corresponding to the BGA area. By utilizing the characteristics of the prepreg sheets, the fiber layers in the stacked prepreg sheets serve as the support structure of the mold, and the molten resin flowing during pressing serves as filler to fill the gaps in the mold, so that the height difference of the mold at the convex structure changes gradually. While constructing the required convex structure on the mold using the stacked prepreg sheets, damage to the PCB board surface to be pressed is avoided during mold use, thus improving the reliability of PCB manufacturing.

[0027] Furthermore, before lamination, a pre-pressing step is included to match the mold with the PCB to be laminated. Specifically, a prepreg is first wrapped with upper and lower copper foil layers, which are then fused together to form an encapsulation structure around the base prepreg. The prepreg is then stacked on top of the base prepreg 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 lamination, 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 molded PCB is imprinted to form an upper shell, and the lower copper foil layer forms a lower shell. The lamination also 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 mold. Specifically, the layered prepregs corresponding to the BGA regions include several first prepregs with areas larger than the BGA regions and several second prepregs with areas smaller than the BGA regions; and the number of first prepregs n1, the area of ​​the first prepregs gradually decreases from bottom to top, the number of second prepregs n2, the area of ​​the second prepregs gradually decreases from bottom to top, and 2≤n1-n2≤5; after melt curing, the fiber cloth of the first prepregs forms a first layer, the fiber cloth of the second prepregs forms a second layer, and the fiber cloth of the transition prepregs forms a transition layer. Specifically, during mold pre-pressing, the placement of the laminated prepreg in the pressing template is first determined using a positioning system identical to that of the PCB to be pressed, ensuring that the placement of the laminated prepreg corresponds to the BGA area of ​​the PCB to be pressed. Secondly, a PCB with the same wiring as the PCB to be pressed is used as a mold PCB. The side of the package structure with the laminated prepreg is attached to the side of the mold PCB where the BGA components will be mounted, forming a composite structure. The pressing process with the mold PCB fixes the specific shape of the convex structure on the mold. Simultaneously, the concave structure formed by pressing on the mold PCB can be connected and adapted to the BGA components to verify the positional accuracy and the degree of concavity improvement of the formed mold. Preferably, the prepreg used in the mold is a low-flow prepreg, which is more conducive to mold alignment and shaping during the manufacturing process.

[0028] Optionally, the PCB to be laminated is a stacked structure without total lamination, and 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.

[0029] The area of ​​the first prepreg is no more than 20% of the area of ​​the BGA region;

[0030] The area of ​​the second prepreg is not less than 80% of the area of ​​the BGA region;

[0031] 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≤3;

[0032] 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.

[0033] Optionally, the PCB to be laminated is a finished PCB that has already undergone overall lamination, and the prepreg layered with the BGA area includes:

[0034] The area of ​​the first prepreg is no more than 20% of the area of ​​the BGA region;

[0035] The area of ​​the second prepreg is not less than 60% of the area of ​​the BGA region;

[0036] 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.

[0037] 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;

[0038] 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.

[0039] In this technical solution, a mold pressing method can be used to participate in the lamination process of a PCB that has not undergone total lamination, forming the required recessed structure on the PCB surface during the total lamination process. Alternatively, a mold pressing method can be used to perform a secondary shaping process on a PCB that has already undergone one total lamination. During the lamination process of a PCB that has not undergone total lamination, the part of the PCB to be laminated adjacent to the mold consists of stacked copper foil and other metal layers and prepreg. Its surface is relatively soft, and when forming the required recessed structure on its surface, the mold only needs to form an upward convex structure corresponding to the recessed structure and apply pressure in the corresponding BGA area to form the depression. The secondary shaping process of a PCB that has already been made requires the mold to provide a larger upward convex structure and greater pressure at the corresponding points to complete the process.

[0040] Specifically, during the PCB lamination process, a progressively increasing upward convex structure is formed on one side of the 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 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 mold to better construct the required concave structure on the PCB board to be laminated 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. Preferably, when the PCB to be laminated is a PCB that has not been fully laminated, the area of ​​the first prepreg is set to be no more than 20% of the BGA area; the area of ​​the second prepreg is no less than 80% of the BGA area; and 2≤n1-n2≤3, so that the recessed structure formed on the PCB can achieve the BGA mounting depth required by the design. The contour of the recessed structure is buffered by the resin flowing through the first and second prepregs during lamination, so that the deformation on the PCB surface changes gradually, thereby ensuring the overall rigidity and stability of the PCB surface after the recessed structure is formed. When the PCB to be laminated is a PCB that has already undergone one total lamination, the area of ​​the first prepreg is set to be no more than 20% of the BGA area; the area of ​​the second prepreg is no less than 60% of the BGA area; and 2≤n1-n2≤5, thereby constructing a slightly larger convex structure, which is more adaptable to lamination with greater lamination pressure. This ensures that the recessed structure formed on the PCB can achieve the required BGA mounting depth, and the deformation on the PCB surface changes gradually, guaranteeing the overall rigidity and stability of the PCB surface after the recessed structure is created.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] 1. A lamination method for creating recessed bases in specific BGA areas on a PCB is provided. During the lamination process of a PCB to be connected to BGA components, a mold and the PCB to be laminated are combined for overall lamination. A recessed base is formed at specific locations on the PCB where the BGA area needs to be formed, serving to support the BGA components. This improves the tolerance for deformation of the BGA area and the PCB surface during lamination, reduces the probability of BGA desoldering and pulling during PCB fabrication, and minimizes the impact of board bending on the connection and installation of BGA components to the PCB surface. Furthermore, during hot lamination, the mold and the PCB to be laminated are grouped together. By simultaneously and adequately setting buffer structures on both sides of the mold and the PCB to be laminated, a symmetrical stacked structure is formed. This avoids uneven pressure and temperature conduction on the PCB surface caused by the convex structure on the mold during lamination, which could exacerbate board bending during lamination. This improves the stability of lamination and enhances the precision and reliability of the PCB lamination process. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the laminate structure in a lamination method for realizing a recessed base in a specific BGA area on a PCB according to the present invention.

[0044] Figure 2 This is one of the schematic diagrams of the mold used in the lamination method for realizing the recess of the base in a specific BGA area on a PCB according to the present invention.

[0045] Figure 3 This is a cross-sectional schematic diagram of the mold used in the lamination method for creating a recessed base in a specific BGA area on a PCB according to the present invention.

[0046] Figure 4 This is the second schematic diagram of the mold used in the lamination method for realizing the recessed base of a specific BGA area on a PCB according to the present invention.

[0047] Figure 5 This is a schematic diagram of a PCB fabricated using a lamination method for creating a recessed base in a specific BGA area on a PCB, as described in this invention.

[0048] 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

[0049] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention. To better illustrate the following embodiments, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions; it is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0050] Example 1

[0051] like Figures 1-4 As shown, this embodiment provides a lamination method for creating a recessed base in a specific BGA area on a PCB. A mold is placed over the side of the PCB to be laminated where the BGA area is located, and corresponding boards are fitted to form a stacked structure. The stacked structure is then fed into a hot press for heating and pressurization, causing a recessed base to form in the specific BGA area on the PCB. The stacked structure includes a first buffer layer, a first isolation layer, the PCB to be laminated and the mold, a second isolation layer, and a second buffer layer, sequentially stacked between the steel plates of the hot press. The mold is used to create a recessed structure at the corresponding BGA area on the PCB during the lamination process. Due to the convex structure on the mold, uneven pressure and temperature conduction on the PCB surface during lamination can easily occur, exacerbating the bending of the PCB during lamination. To improve the precision and reliability of the lamination process, specifically, a first buffer layer, a first isolation layer, the PCB to be laminated and the mold, a second isolation layer, and a second buffer layer are sequentially stacked between the steel plates of the hot press. Preferably, in the stacked structure, the PCB to be pressed and the mold are arranged in groups, and the PCB to be pressed and the mold are separated by copper foil, which can be a copper foil layer on the surface of the PCB to be pressed or a separate copper foil; the stacked structure includes multiple groups of PCBs to be pressed and molds, and the multiple groups of PCBs to be pressed and molds are separated by a third isolation layer and a third buffer layer. By adequately setting buffer layers on both sides of the PCB to be pressed and the mold during the pressing process, the conduction speed of pressure and temperature in the stacked structure is slowed down, thus improving the stability of the pressing process. Simultaneously, by setting a uniform and symmetrical stacked structure in the pressing assembly, multiple PCBs to be pressed can be processed simultaneously. Specifically, the recessed structure on the PCB to be pressed is shaped by the mold during pressing. Therefore, the PCBs to be pressed and the mold are grouped together. A first buffer layer, a first isolation layer, the PCB to be pressed and the mold, a second isolation layer, and a second buffer layer are sequentially stacked between the steel discs of the hot press. Multiple groups of PCBs to be pressed and the mold are separated by a third isolation layer and a third buffer layer, ensuring that all PCBs to be pressed in the stacked structure are uniformly pressurized. All buffer layers used in the stacked structure can use kraft paper or VIPAD as the buffering material to achieve buffering, temperature equalization, and pressure equalization during the pressing process. The number of buffer sheets can be adjusted according to the actual effect; the basic selection principle is that the larger the recess of the PCB to be pressed, the more buffer sheets are used.

[0052] The mold structure includes: an outer shell, comprising an upper shell 110 and a lower shell 120, the edges of which are fused to form a sealing edge and separated in the middle to form a receiving cavity; a support structure, comprising multiple layers of filling layers of different sizes, stacked and distributed within the receiving cavity; filler 300, filling the receiving cavity and between the filling layers; the receiving cavity includes at least one local area, in which the number of filling layers of the support structure is greater than in other areas, causing the upper shell 110 to bulge to form an upward convex structure, and the lower shell 120 to be a flat structure, with the position of the upward convex structure corresponding to the downward concave structure. The upper and lower shells are fused together to form an outer shell containing a cavity. The upper shell 110 is raised to form a convex structure, while the lower shell 120 is a flat structure, which facilitates the fit with the plane of the pre-pressed board structure and provides a plane for uniform pressure transmission during the overall pressing. At the same time, a certain amount of support structure and filler 300 are filled into the cavity to form a complete and leak-proof 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 be flexibly supported by the filler 300, which facilitates the uniform transition of the edges while shaping the PCB during pressing, without damaging the board surface.

[0053] Among them, such as Figure 3 As shown, the support structure of the lamination mold includes at least: a base layer 210, the area and shape of which match the PCB; several first stacked layers 220, positioned and stacked in a local area, with an area larger than the recessed structure; and several second stacked layers 230, positioned and stacked on the first stacked layers 220, with an area smaller than the recessed structure. Specifically, the second stacked layers 230 are used to fix the basic outline of the recessed structure and can also cooperate with the introduction of filler 300 to construct the required recessed structure size. The first stacked layers 220 are used to balance and buffer the board height difference generated in the BGA area during the lamination process when the recessed structure is formed, thereby better balancing the board bending of the entire PCB and ensuring the overall manufacturing reliability of the PCB.

[0054] Preferably, in order to better construct the desired 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] Preferably, in order 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 on the PCB board, a stepped buffer design is also required around the BGA area on the PCB board surface to minimize the impact of lamination-induced board bending on the BGA area and the overall PCB board manufacturing. Specifically, in the mold manufacturing process, the support structure is configured to include an additional transition layer 240, which is superimposed between the base layer 210 and the first superimposed layer 220, and has a smaller area than 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 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 lamination. This causes the BGA area to generate the board surface height difference required by the design during the lamination process, thereby better balancing the board bending of the entire PCB board and ensuring the overall manufacturing reliability of the PCB.

[0056] Preferably, in order 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 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] Furthermore, to address situations where the PCB board has multiple BGA mounting points, when the 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 buffer design is implemented around each convex structure to create a height difference step on the overall panel of the mold. This ensures that the mold deforms most at the convex structures and gradually decreases towards the edge of the mold. Correspondingly, the PCB board after lamination shows the greatest deformation at the concave structures, with the degree of concavity decreasing towards the edge of the PCB. This ensures that grooves are formed at the concave structures to facilitate the installation of BGA devices. The edge deformation of the grooves transitions naturally with the slight concavity of the overall PCB board surface, thus avoiding damage to the board surface and internal structure. This ensures the rigidity and stability of the laminated PCB board and better balances the bending and pulling of the BGA mounting points and the bending of the entire PCB board during the lamination process, ensuring the overall reliability of the PCB manufacturing. Preferably, the distance between the two convex structures does not exceed the full size of one of the convex structures, and they are arranged adjacent to each other, such as... Figure 2 As shown; otherwise, for separate settings, such as Figure 4 shown.

[0058] Example 2

[0059] This embodiment also provides a lamination method for creating a recessed base in a specific BGA area on a PCB. The difference from Embodiment 1 is that in the mold used, both the upper shell 110 and the lower shell 120 are made of copper foil. The cavity is filled with stacked and melt-cured prepreg sheets. The stacked fiber layers in the prepreg sheets form a support structure, and the molten resin in the prepreg sheets forms filler 300, filling the gaps between the shell and the support structure. The prepreg sheets include a base layer 210 prepreg sheet, progressively stacked transition prepreg sheets, and progressively stacked prepreg sheets corresponding to the BGA area. By utilizing the characteristics of the prepreg sheets, using the fiber layers in the stacked prepreg sheets as the support structure of the mold, and using the molten resin flowing during lamination as filler 300 to fill the gaps in the mold, the height difference of the mold at the convex structure changes gradually. While constructing the required convex structure on the mold using the stacked prepreg sheets, damage to the PCB surface to be laminated is avoided during mold use, improving the reliability of PCB manufacturing.

[0060] Furthermore, before lamination, a pre-pressing process is included to match the mold with the PCB to be laminated. Specifically, a prepreg is first wrapped with upper and lower copper foil layers. The upper and lower copper foil layers are fused around the prepreg in the base layer 210 to form an encapsulation structure. The prepreg is then stacked on the base layer 210 and fills the cavity formed inside the encapsulation structure. The fiber cloth of the prepreg forms a filling layer, and the filling layers are stacked to form a support structure. 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 molded PCB is imprinted to form an upper shell 110 and a lower copper foil layer forms a lower shell 120. The resin of the prepreg melts and flows during the pressing process to form a filler 300, which fills the cavity formed between the upper and lower copper foil layers and between the filling layers, thereby forming a stable mold. Specifically, the prepregs corresponding to the BGA regions are stacked layer by layer, including a number of first prepregs with an area larger than the BGA regions and a number of second prepregs with an area smaller than the BGA regions; and the number of first prepregs n1, the area of ​​the first prepregs gradually decreases from bottom to top, the number of second prepregs n2, the area of ​​the second prepregs gradually decreases from bottom to top, and 2≤n1-n2≤5; after melt curing, the fiber cloth of the first prepregs forms a first stacked layer 220, the fiber cloth of the second prepregs forms a second stacked layer 230, and the fiber cloth of the transition prepregs forms a transition layer 240.

[0061] In this embodiment, the PCB to be laminated is a stacked structure without total lamination. 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.

[0062] The area of ​​the first prepreg is no more than 20% of the area of ​​the BGA region;

[0063] The area of ​​the second prepreg is not less than 80% of the area of ​​the BGA region;

[0064] 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, and 2≤n1-n2≤3;

[0065] 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.

[0066] Example 3

[0067] This embodiment also provides a lamination method for creating a recessed base in a specific BGA area on a PCB. The difference from Embodiment 2 is that the PCB to be laminated is a finished PCB that has already undergone overall lamination. The mold used involves layering prepregs corresponding to the BGA areas, including:

[0068] The area of ​​the first prepreg is no more than 20% of the area of ​​the BGA region;

[0069] The area of ​​the second prepreg is not less than 60% of the area of ​​the BGA region;

[0070] 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.

[0071] 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;

[0072] 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.

[0073] Example 4

[0074] like Figure 5 As shown, this embodiment provides a PCB manufactured by lamination method of realizing the base recess of a specific BGA area on the PCB as in any of the embodiments 1-3. The PCB has two adjacent recessed structures formed on at least one side surface, which are used to support BGA components BGA-U1 and BGA-U2. The recessed structure has the greatest deformation at its center, and its deformation decreases and smoothly transitions to the edge of the recessed structure. On the overall surface of the PCB, the recessed structure is centrally located, and the deformation decreases and smoothly transitions to the edge of the PCB surface with the recessed structure as the center.

[0075] 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 of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A lamination method for realizing a base depression in a specific BGA area of ​​a PCB, characterized in that: A mold is covered on one side of the PCB to be pressed with a BGA area and a corresponding plate is formed to form a laminate structure, and the laminate structure is sent to a hot press to heat and pressurize so that a base depression is formed in a specific BGA area on the PCB; the laminate structure includes a first buffer layer, a first isolation layer, the PCB to be pressed and a mold, a second isolation layer and a second buffer layer stacked in sequence between the steel plates of the hot press, and the mold is used to form a concave structure on one side of the PCB to be pressed corresponding to the BGA area during the lamination process; The structure of the mold includes: 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 the PCB; 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. The lamination method according to claim 1, characterized in that The convex structure is located in the center of the 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. The lamination method according to claim 1, characterized in that When the 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 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. The lamination method according to any one of claims 1 to 3, characterized in that: In the stacked plate structure, the PCB to be pressed and the mold are arranged in a group, and the PCB to be pressed and the mold are separated by copper foil; the stacked plate structure includes multiple groups of PCB to be pressed and mold groups, and the multiple groups of PCB to be pressed and mold groups are isolated by a third isolation layer and a third buffer layer.

5. The lamination method according to any one of claims 1 to 3, characterized in that: In the mold, the upper shell and the lower shell are both made of copper foil, the accommodating cavity is filled with laminated and melted prepregs, the laminated fiber layers in the prepregs form the supporting structure, and the melted resin in the prepregs forms a filler to fill the gap between the shell and the supporting structure; the prepregs include a base prepreg, a transition prepreg stacked layer by layer, and a prepreg stacked layer by layer corresponding to the BGA area; The prepregs stacked layer by layer corresponding to the BGA area include a plurality of first prepregs with an area larger than the BGA area and a plurality of second prepregs with an area smaller than the BGA area; After melting and solidification, the fiber cloth of the first prepreg forms a first superimposed layer, the fiber cloth of the second prepreg forms a second superimposed layer, and the fiber cloth of the transition prepreg forms a transition layer.

6. The lamination method according to claim 4, characterized in that The PCB to be pressed is a laminated structure that has not been pressed together. 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 PCB to be pressed is H, the thickness of the prepreg is d, n is a compensation number of 2-3 sheets, and [] is a rounding symbol; The area of ​​the first prepreg is not greater than 20% of the area of ​​the BGA area; The area of ​​the second prepreg is not less than 80% of the area of ​​the BGA area; Let the number of first prepregs be n1, and the area of ​​the first prepregs gradually decreases from bottom to top; let the number of second prepregs be n2, and the area of ​​the second prepregs gradually decreases from bottom to top, and 2≤n1-n2≤3; After melting and solidification, the fiber cloth in the first prepreg forms a first superimposed layer, the fiber cloth in the second prepreg forms a second superimposed layer, and the fiber cloth in the transition prepreg forms a transition layer.

7. The lamination method according to claim 4, characterized in that: The PCB to be pressed is a finished PCB that has undergone total pressing, and the prepregs corresponding to the BGA area are stacked layer by layer, including: 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 PCB 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; Let the number of first prepregs be n1, and the area of ​​the first prepregs gradually decreases from bottom to top; let the number of second prepregs be n2, and the area of ​​the second prepregs gradually decreases from bottom to top, and 2≤n1-n2≤5; After melting and solidification, the fiber cloth in the first prepreg forms a first superimposed layer, the fiber cloth in the second prepreg forms a second superimposed layer, and the fiber cloth in the transition prepreg forms a transition layer.

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