Lamination method for realizing base recess in specific BGA area of PCB

Abstract

According to the lamination method for realizing the base recess in the specific BGA area of the PCB, the die and the to-be-laminated PCB are combined to perform total lamination together, and the base recess is formed at the specific site where the BGA area needs to be formed on the to-be-laminated PCB and is used for subsequently bearing the BGA component, so that the probability of unsoldering and pulling after the BAG component is mounted on the PCB is reduced, and the production efficiency is improved. And the influence of the board bending phenomenon on the connection and installation of the BGA component and the PCB board is reduced. Furthermore, in the laminating method provided by the invention, during hot pressing, the mold and the PCB to be laminated are arranged in groups, and buffer structures are synchronously and fully arranged on two sides of the mold and the PCB to be laminated, so that a symmetrically arranged laminated plate structure is formed; according to the invention, the problem that the board bending of the to-be-pressed PCB in the pressing process is aggravated due to non-uniform pressure and temperature conduction of the board surface of the to-be-pressed PCB caused by an upward convex structure arranged on the die during pressing is avoided, the pressing stability is improved, and the pressing precision and reliability of the to-be-pressed PCB are improved.

Description

Technical Field

[0001] The present invention relates to the field of electronic manufacturing technology, and more specifically, to a lamination method for realizing a base recess 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 connection reliability problem between BGA and printed PCB (PCB) has become increasingly prominent, especially the bending problem caused by the mismatch of the coefficient of thermal expansion (CTE) of the two materials.

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

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

[0005] Therefore, under the existing technical background, a more sophisticated solution is needed for the CTE mismatch problem between BGA and PCB. This includes but is not limited to developing materials with higher CTE matching, optimizing the pressing process to achieve local precision control, and introducing advanced positioning and monitoring technologies to ensure processing accuracy and stability. Through the comprehensive application of these technical means, the connection reliability between BGA and PCB can be further improved to meet the increasingly stringent performance requirements of electronic products. Summary of the invention

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

[0007] The object of the present invention is to provide a lamination method for realizing a base depression in a specific BGA area on a PCB, wherein a mold is covered on one side of a PCB to be pressed with a BGA area and a corresponding plate is formed into a laminated structure, and the laminated structure is sent into a hot press to be heated and pressurized to form a base depression in the specific BGA area on the PCB; the laminated structure comprises a first buffer layer, a first isolation layer, a PCB to be pressed and a mold, a second isolation layer and a second buffer layer stacked in sequence between steel plates of the hot press, and the mold is used to form a concave structure at the corresponding BGA area on the PCB to be pressed 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 bulges to form an upward convex structure, the lower shell is a flat structure, and the position of the upward convex structure corresponds to the downward concave structure.

[0008] In the technical scheme, a base depression is formed at a specific position where a BGA area is to be formed on the PCB to be pressed by using a mold, which is used to carry the BGA chip. Among them, the mold has a convex structure on one side of the PCB to be pressed, which is used to form a concave structure on the PCB by pressing. Specifically, the mold includes a shell, a support structure and a filler. The upper and lower shell edges are fused to form a shell containing a housing cavity. The upper shell is raised to form a convex structure, and the lower shell is a straight structure, which is convenient for fitting with the plane of the panel structure before pressing, and provides a plane for transmitting uniform pressure for the overall pressing; at the same time, a certain amount of support structure and filler are filled in the housing cavity to form a complete and non-leaking convex structure, which is convenient for forming a concave structure corresponding to the convex structure on the surface of the PCB to be pressed, and the support structure filled in the interior can be flexibly supported by the filler during the pressing process, which is convenient for shaping on the PCB to be pressed and the edge can be uniformly transitioned during pressing, so as not to damage the board surface. Furthermore, due to the convex structure provided on the mold, it is easy to cause uneven pressure and temperature conduction on the surface of the PCB to be pressed during pressing, which aggravates the board bending of the PCB to be pressed during the pressing process. In order to improve the precision and reliability of the pressing and manufacturing of the PCB to be pressed, specifically, 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 stacked in sequence between the steel plates of the hot press. By fully arranging the buffer structure on both sides of the PCB to be pressed and the mold during the pressing and arranging of the plates, the conduction speed of pressure and temperature in the stacked plate structure during the pressing process is delayed, thereby improving the stability of the pressing.

[0009] Furthermore, the support structure at least comprises: 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 are positioned and stacked on the first stacking layer, and have an area smaller than the concave structure.

[0010] In the present technical scheme, in order to fix the shape and position of the upper and lower concave structures of the PCB, the convex structure formed on the mold includes a hard supporting structure. Specifically, the supporting structure includes a base layer whose area and shape match the PCB board surface, which is used to fit the lower shell body and construct a flat and uniform pressing surface. In order to better construct the concave structure of the required shape on the entire PCB to be pressed, it also includes a plurality of first superimposed layers positioned and superimposed on the local area. The area of ​​the first superimposed layer is smaller than the base layer, and is slightly larger than the concave structure required to be formed on the PCB to be pressed. Furthermore, a plurality of second superimposed layers are positioned and superimposed on the first superimposed layer, and the area of ​​the second superimposed layer is slightly smaller than the concave structure. Specifically, the second superimposed layer is used to fix the basic outline of the concave structure, and can cooperate with the introduction of filler to construct the required concave structure size. The first superimposed layer is used to balance and buffer the board surface height difference generated by the BGA area during the pressing process when the concave structure is formed, thereby better balancing the board bending of the entire PCB board and ensuring the overall manufacturing reliability of the PCB.

[0011] Furthermore, in order to better construct a concave structure of a desired shape on the entire PCB to be pressed, and at the same time provide an appropriate concave curvature on other areas of the PCB surface to match the bending of the entire board during the pressing process, the number of first stacking layers is controlled to be n1, and the area of ​​the first stacking layer gradually decreases from bottom to top, and the number of second stacking layers is n2, and the area of ​​the second stacking layer gradually decreases from bottom to top, and 2≤n1-n2≤5, so that the concave structure formed on the PCB can achieve the BGA installation depth required by the design, and the contour of the concave structure can gradually change on the PCB surface, thereby ensuring the overall rigidity and stability of the PCB surface after the concave structure is opened.

[0012] Furthermore, in order to balance the influence of pressing on the board bending of the whole PCB board surface and improve the reliability of the whole PCB board production, in addition to the overall concave design of the BGA area on the whole PCB board, it is also necessary to perform a stepped buffer design on the whole PCB board surface around the BGA area on the whole PCB board surface, so as to minimize the influence of the board bending caused by pressing on the BGA area and the whole PCB board surface production; specifically, in the production of the mold, it is arranged that the support structure also includes one less transition layer, the transition layer is superimposed between the base layer and the first superimposed layer, and the area is smaller than the base layer and larger than the first superimposed layer. When the transition layer exceeds one layer, the area of ​​the transition layer gradually decreases from bottom to top. The area between the base layer and the first superimposed layer is effectively connected by the setting of the transition layer, so that the edge of the upper convex structure on the mold changes in steps from the edge of the base layer to the inside of the upper convex structure, so that the concave degree on the whole PCB board surface slowly and gradually deepens from the edge to the BGA area during pressing, so that the BGA area produces the board surface height difference required by the design during the pressing process, thereby better balancing the board bending of the whole PCB board and ensuring the overall production reliability of the PCB.

[0013] Preferably, the board bending of the entire PCB is better balanced to ensure the overall manufacturing reliability of the PCB when the convex structure is located in the center of the mold; when the base area is 4-9 times the area of ​​the first stacking layer, 1-2 transition layers are set; when the base area is 9-12 times the area of ​​the first stacking layer, 2-4 transition layers are set; when the base area is 12-16 times the area of ​​the first stacking layer, 4-5 transition layers are set; when the base area is more than 16 times the area of ​​the first stacking layer, the number of transition layers does not exceed 8 layers.

[0014] Further, 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.

[0015] In the present technical scheme, in order to cope with the situation where the PCB board surface has multiple BGA sites, when the mold includes two or more convex structures, if all the convex structures are arranged adjacent to each other, all the convex structures are taken as a whole and then a buffer design is performed on the entire PCB board. If all the convex structures are arranged separately from each other, a board surface buffer design is performed around each convex structure to form a height difference step on the overall panel of the pressing mold, ensuring that the mold is deformed the most at the convex structure and then gradually decreases to the edge of the mold. Correspondingly, the concave deformation is the largest at the concave structure on the PCB panel after pressing, and the degree of concaveness decreases as a whole to the edge of the PCB, ensuring that a groove that is convenient for the installation of BGA devices is formed at the concave structure, and the edge deformation of the groove and the slight concave transition of the overall PCB board surface are natural, thereby not damaging the board surface and the internal structure, ensuring the rigidity and stability of the PCB board manufactured by pressing, and also better balancing the bending and pulling of the BGA installation site and the board bending of the entire PCB board during the pressing process, ensuring the overall manufacturing reliability of the PCB. Preferably, the two upward convex structures are adjacently arranged if the distance between them does not exceed the full size of one of the upward convex structures; otherwise, they are separated.

[0016] Furthermore, in the laminate 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; wherein the copper foil can be a copper foil layer on the surface of the PCB to be pressed, or a separately arranged copper foil layer, which is used to separate the PCB to be pressed and the mold, avoiding the risk of damage caused by direct contact between the two, and at the same time, the flexible characteristics of the copper foil are used to further disperse the stress of the contact surface of the PCB to be pressed and the mold during pressing, so that the edge transition is smoother when forming the upper and lower concave structures of the PCB to be pressed. The laminate structure includes multiple groups of the PCB to be pressed and the mold group, and the multiple groups of the PCB to be pressed and the mold group are isolated by the third isolation layer and the third buffer layer. By setting a uniform and symmetrical stacking structure in the pressing arrangement, multiple PCBs to be pressed can also be processed at the same time. Specifically, the concave structure on the PCB to be pressed is molded by mold pressing, so the PCB to be pressed and the mold are arranged in a group, and the first buffer layer, the first isolation layer, the PCB to be pressed and the mold, the second isolation layer and the second buffer layer are stacked in sequence between the steel plates of the hot press, and 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 stacking structure can be evenly pressurized.

[0017] Preferably, in the mold, the upper shell and the lower shell are both made of copper foil, the accommodating cavity is filled with stacked and melt-cured semi-cured sheets, the fiber layers stacked in the semi-cured sheets form the supporting structure, and the molten resin in the semi-cured sheets forms a filler to fill the gap between the shell and the supporting structure; the semi-cured sheets include a base semi-cured sheet, a transitional semi-cured sheet stacked layer by layer, and a semi-cured sheet stacked layer by layer corresponding to the BGA area; by utilizing the characteristics of the semi-cured sheets, the fiber layers in the stacked semi-cured sheets are used as the supporting structure of the mold, and the molten resin flowing during pressing is used as a filler to fill the gap in the mold, so that the height difference of the mold at the convex structure changes slowly, and while the convex structure with the required deformation amount on the mold is constructed by the stacked semi-cured sheets, damage to the PCB board surface to be pressed when the mold is used is avoided, thereby improving the reliability of PCB production.

[0018] Furthermore, before lamination, it also includes a step of using pre-pressing to make the mold correspond to the PCB to be pressed. Specifically, the semi-cured sheet stacked by upper and lower copper foils is first wrapped, and the upper and lower copper foil layers are fused around the periphery of the base semi-cured sheet to form a packaging structure, and the semi-cured sheet is stacked on the base semi-cured sheet and fills the accommodating cavity formed inside the packaging structure, and specifically the fiber cloth of the semi-cured sheet forms a filling layer, the filling layers are stacked to form a supporting structure, and through pressing, in the BGA area, the upper copper foil layer tightly wraps the supporting structure to form an upper convex structure, and other areas are traced with the surface texture of the lower mold PCB to form an upper shell, and the lower copper foil layer forms a lower shell, and pressing makes the resin of the semi-cured sheet melt and flow to form a filler, which is filled in the accommodating cavity formed between the upper and lower copper foil layers and between the filling layers, thereby forming a stable mold. Specifically, the prepregs stacked layer by layer corresponding to the BGA area include a number of first prepregs with an area larger than the BGA area and a number of second prepregs with an area smaller than the BGA area; and the number n1 of the first prepregs, the area of ​​the first prepregs gradually decreases from bottom to top, the number n2 of the second prepregs, the area of ​​the second prepregs gradually decreases from bottom to top, and 2≤n1-n2≤5; after melting and solidification, the fiber cloth of the first prepreg forms a first stacking layer, the fiber cloth of the second prepreg forms a second stacking layer, and the fiber cloth of the transition prepreg forms a transition layer. Specifically, when the mold is pre-pressed, the setting position of the laminated semi-cured sheet in the pressing template is first located by using a positioning system consistent with the PCB to be pressed, so as to ensure that the setting position of the laminated semi-cured sheet 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 also used as the sleeve mold PCB, and the side of the package structure with the laminated semi-cured sheet is laminated with the side of the sleeve mold PCB where the BGA components are to be installed to form a composite structure, and the specific shape of the upper convex structure on the mold is fixed through the pressing process with the sleeve mold PCB, and the concave structure formed by pressing on the sleeve mold PCB can also be connected and adapted with the BGA components to check the position accuracy of the formed mold and the degree of improvement of the depression. Preferably, the semi-cured sheet used in the mold is a low-flow semi-cured sheet, which is more conducive to the alignment and shaping of the mold during the production process.

[0019] Optionally, the PCB to be pressed is a stacked structure that has not been pressed together, and 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 2-5 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; The number n1 of the first cured sheets is such that the area of ​​the first cured sheets decreases gradually from bottom to top, and the number n2 of the second cured sheets is such that the area of ​​the second cured sheets decreases gradually from bottom to top, and 2≤n1-n2≤3; 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.

[0020] Optionally, the PCB to be pressed is a finished PCB that has undergone total pressing, and stacking the prepregs corresponding to the BGA area layer by layer includes: 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 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; The number n1 of the first cured sheets is such that the area of ​​the first cured sheets decreases gradually from bottom to top, the number n2 of the second cured sheets is such that the area of ​​the second cured sheets decreases gradually from bottom to top, and 2≤n1-n2≤5; 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.

[0021] In the present technical solution, the pressing process of the PCB that has not been pressed together can be participated in by using the mold pressing method, and the required concave structure can be formed on the surface of the PCB during the total pressing process of the PCB; the PCB that has undergone a total pressing can also be subjected to a secondary board surface shaping process by using the mold pressing method. In the pressing process of the PCB that has not been pressed together, the part of the PCB to be pressed that is adjacent to the mold is a laminated copper foil and other metal layers and a semi-cured sheet, and its surface is relatively soft. When the required concave structure is formed on its surface, the mold only needs to form a convex structure and pressure corresponding to the concave structure in the corresponding BGA area to form a depression. The secondary shaping process of the completed PCB board requires the mold to provide a larger convex structure and a larger pressure at the corresponding position to complete.

[0022] Specifically, during the lamination process of the PCB, a convex structure with a gradually increasing convexity from the edge of the substrate to the center of the position corresponding to the BGA area is formed on one side of the mold by stacking prepregs layer by layer; wherein, the first prepreg and the second prepreg are combined to form the convex structure corresponding to the BGA area, and thus the total number of the first prepreg and the second prepreg used in the mold is set to be N=[H / d]+n, wherein, when the maximum concave size of the BGA area of ​​the PCB to be laminated is H and the thickness of the single prepreg used is d, on the basis of filling the concave size of the BGA area with the prepreg as much as possible, n prepregs are further stacked to compensate for the thickness loss after the resin in the prepreg flows and fills the gaps during the lamination process, so as to ensure that the convex structure after lamination can reach a predetermined deformation amount; specifically, the value of n depends on the type and characteristics of the selected prepreg, and preferably, the value of n is 2-5 sheets. Furthermore, after lamination, the fiber layer of the first semi-cured sheet constitutes the first superimposed layer, and the fiber layer of the second cured sheet constitutes the second superimposed layer. Therefore, similar to the first superimposed layer and the second superimposed layer, in order to enable the mold to better construct a concave structure of a desired shape on the entire PCB to be laminated during lamination, and at the same time provide an appropriate concave curvature on other areas of the PCB surface for matching the bending of the entire board during the lamination process, the number of first semi-cured sheets is controlled to be n1, and the number of second semi-cured sheets is controlled to be n2. Preferably, when the PCB to be pressed is a PCB that has not been pressed together, the area of ​​the first semi-cured sheet is set to be no more than 20% of the area of ​​the BGA area; the area of ​​the second semi-cured sheet is no less than 80% of the area of ​​the BGA area; and 2≤n1-n2≤3, so that the concave structure formed on the PCB can achieve the BGA installation depth required by the design, and the contour of the concave structure is buffered and changed under the regulation of the molten flow of resin by the first semi-cured sheet and the second semi-cured sheet during pressing, so that the deformation amount on the PCB board surface changes gradually, thereby ensuring the overall rigidity and stability of the PCB board surface after the concave structure is opened. When the PCB to be pressed is a PCB that has undergone one total pressing, the area of ​​the first prepreg is set to be no more than 20% of the area of ​​the BGA area; the area of ​​the second prepreg is no less than 60% of the area of ​​the BGA area; and 2≤n1-n2≤5, so as to construct a convex structure with a slightly larger position area, which makes it more suitable for pressing under a greater pressing pressure, so that the concave structure formed on the PCB can achieve the BGA installation depth required by the design, and the deformation amount on the PCB board surface changes gradually, ensuring the overall rigidity and stability of the PCB board surface after the concave structure is opened.

[0023] Compared with the prior art, the present invention has the following beneficial effects: 1. A lamination method for realizing a base depression in a specific BGA area on a PCB is provided. In the process of pressing and manufacturing a PCB to be connected with BGA components, a mold is used to perform a total pressing together with the PCB to be pressed, and a base depression is formed at a specific position on the PCB to be pressed where the BGA area is to be formed, which is used to carry BGA components in the future, thereby improving the deformation tolerance of the BGA area and the PCB surface during the pressing and manufacturing process, reducing the probability of desoldering and pulling of the BAG area during the PCB manufacturing process, and reducing the influence of the board bending phenomenon on the connection and installation of the BGA components and the PCB surface. Furthermore, 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 to form a symmetrically arranged stacked plate structure, thereby avoiding the uneven pressure and temperature conduction of the PCB surface to be pressed caused by the convex structure arranged on the mold during pressing, which aggravates the problem of board bending of the PCB to be pressed during pressing, improving the stability of pressing, and improving the precision and reliability of pressing and manufacturing of the PCB to be pressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The schematic diagram of the structure of the stacked plate structure in a lamination method for realizing a base depression in a specific BGA area on a PCB according to the present invention.

[0025] Figure 2 This is one of the structural schematic diagrams of a mold used in a lamination method for realizing a base depression in a specific BGA area on a PCB according to the present invention.

[0026] Figure 3 The cross-sectional schematic diagram of a mold used in a lamination method for realizing a base depression in a specific BGA area on a PCB according to the present invention.

[0027] Figure 4 This is the second structural schematic diagram of the mold used in the lamination method of realizing the base depression of a specific BGA area on a PCB of the present invention.

[0028] Figure 5 The schematic diagram of the board surface of a PCB manufactured by a laminating method of the present invention for realizing a base depression in a specific BGA area on a PCB.

[0029] Description of the drawings: upper shell 110 , lower shell 120 , base layer 210 , first stacking layer 220 , second stacking layer 230 , transition layer 240 , filler 300 . DETAILED DESCRIPTION

[0030] The drawings of the present invention are only for illustrative purposes and should not be construed as limiting the present invention. In order to better illustrate the following embodiments, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; it is understandable to those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0031] Example 1 like Figure 1-Figure 4 As shown, this embodiment provides a lamination method for realizing the base depression of a specific BGA area on a PCB, a mold is covered on one side of the PCB to be pressed with a BGA area, and a corresponding plate is formed into a stacked plate structure, and the stacked plate structure is sent into a hot press to heat and pressurize so that a base depression is formed in the specific BGA area on the PCB; the stacked plate structure includes a first buffer layer, a first isolation layer, a 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 at the corresponding BGA area on the PCB to be pressed during the lamination process. Due to the convex structure set on the mold, it is easy to cause uneven pressure and temperature conduction on the surface of the PCB to be pressed during pressing, which aggravates the plate bending of the PCB to be pressed during the pressing process. In order to improve the precision and reliability of the pressing and manufacturing of the PCB to be pressed, specifically, the first buffer layer, the first isolation layer, the PCB to be pressed and the mold, the second isolation layer and the second buffer layer are stacked in sequence between the steel plates of the hot press. Preferably, in the laminated structure, the PCB to be laminated and the mold are arranged in a group, and the PCB to be laminated and the mold are separated by copper foil, which may be a copper foil layer on the surface of the PCB to be laminated or a separately arranged copper foil; the laminated structure includes multiple groups of PCBs to be laminated and mold groups, and the multiple groups of PCBs to be laminated and the mold groups are isolated by a third isolation layer and a third buffer layer. By fully 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 stacking structure during the pressing process is delayed, thereby improving the stability of the pressing; at the same time, by setting a uniform and symmetrical stacking structure in the pressing arrangement, multiple PCBs to be pressed can also be processed at the same time. Specifically, the concave structure on the PCB to be pressed is molded by the mold pressing, so the PCB to be pressed and the mold are set in groups, and the first buffer layer, the first isolation layer, the PCB to be pressed and the mold, the second isolation layer and the second buffer layer are stacked in sequence between the steel plates of the hot press. 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 stacking structure can be evenly pressed. The buffer material used in all buffer layers used in the stacking structure can be kraft paper or VIPAD, so as to play the role of buffering, equalizing temperature and equalizing pressure during the pressing process. The number of sheets of buffer material can be adjusted according to the actual effect. The basic selection principle is that the larger the depression of the concave structure of the PCB to be pressed, the more sheets of buffer material are set.

[0032] Among them, the structure of the mold used includes: an outer shell, including an upper shell 110 and a lower shell 120, the edges of the upper shell 110 and the lower shell 120 are fused to form a sealed edge, and the middle is separated to form a accommodating cavity; a supporting structure, including multiple filling layers of different sizes, which are stacked and distributed in the accommodating cavity; a filler 300, which is filled in the accommodating 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 110 bulges to form an upper convex structure, and the lower shell 120 is a flat structure, and the position of the upper convex structure corresponds to the lower concave structure. An outer shell containing a receiving cavity is formed by fusing the edges of the upper and lower shells. The upper shell 110 is raised to form a convex structure, and the lower shell 120 is a flat structure, which is convenient for fitting with the plane of the panel structure before pressing, and provides a plane for transmitting uniform pressure for the overall pressing. At the same time, a certain amount of supporting structure and filler 300 are filled in the receiving cavity to form a complete and non-leaking convex structure, which is convenient for forming a concave structure corresponding to the convex structure on the surface of the PCB to be pressed, and during the pressing process, the supporting structure filled inside can be flexibly supported by the filler 300, which is convenient for shaping on the PCB to be pressed during pressing and the edges can be evenly transitioned at the same time, so as not to damage the board surface. Among them, Figure 3 As shown, the support structure of the pressing mold includes at least: a base layer 210, the area and shape of the base layer 210 match the PCB; a plurality of first stacking layers 220, which are positioned and stacked in a local area and have an area larger than the concave structure; and a plurality of second stacking layers 230, which are positioned and stacked on the first stacking layer 220 and have an area smaller than the concave structure. Specifically, the second stacking layer 230 is used to fix the basic profile of the concave structure, and can also cooperate with the introduction of the filler 300 to construct the required concave structure size. The first stacking layer 220 is used to balance and buffer the board height difference generated by the BGA area during the pressing process when the concave structure is formed, so as to better balance the board bending of the entire PCB and ensure the overall manufacturing reliability of the PCB.

[0033] Preferably, in order to better construct a concave structure of a desired shape on the entire PCB to be pressed, and at the same time provide an appropriate concave curvature on other areas of the PCB surface for matching the bending of the entire board during the pressing process, the number of first stacking layers 220 is controlled to be n1, and the area of ​​the first stacking layer 220 gradually decreases from bottom to top, the number of second stacking layers 230 is n2, and the area of ​​the second stacking layer 230 gradually decreases from bottom to top, and 2≤n1-n2≤5, so that the concave structure formed on the PCB can achieve the BGA installation depth required by the design, and the contour of the concave structure can gradually change on the PCB surface, thereby ensuring the overall rigidity and stability of the PCB surface after the concave structure is opened.

[0034] Preferably, in order to balance the influence of pressing on the board bending of the whole PCB board surface and improve the reliability of the whole PCB board surface, in addition to the overall concave design of the BGA area on the whole PCB board, it is also necessary to perform a stepped buffer design on the whole PCB board surface around the BGA area, so as to minimize the influence of the board bending caused by pressing on the BGA area and the whole PCB board surface. Specifically, in the production of the mold, it is arranged that the support structure also includes one less transition layer 240, and the transition layer 240 is superimposed between the base layer 210 and the first superimposed layer 220, and the area is smaller than the base layer 210. The transition layer 240 is larger than the first stacking layer 220. When the transition layer 240 exceeds one layer, the area of ​​the transition layer 240 decreases gradually from bottom to top. The transition layer 240 is effectively connected to the area between the base layer 210 and the first stacking layer 220, so that the edge of the convex structure on the mold changes from the edge of the base layer 210 to the inside of the convex structure. Therefore, during pressing, the concave degree on the entire PCB surface slowly and gradually deepens from the edge to the BGA area, so that the BGA area produces the required board height difference during the pressing process, thereby better balancing the board bending of the entire PCB and ensuring the overall manufacturing reliability of the PCB.

[0035] Preferably, in order to better balance the board bending of the entire PCB 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 stacking layer 220, 1-2 transition layers 240 are set; when the area of ​​the base layer 210 is 9-12 times the area of ​​the first stacking layer 220, 2-4 transition layers 240 are set; when the area of ​​the base layer 210 is 12-16 times the area of ​​the first stacking layer 220, 4-5 transition layers 240 are set; when the area of ​​the base layer 210 is more than 16 times the area of ​​the first stacking layer 220, the number of transition layers 240 does not exceed 8 layers.

[0036] Furthermore, in order to cope with the situation where the PCB board surface has multiple BGA sites, when the mold includes two or more convex structures, if all the convex structures are arranged adjacent to each other, all the convex structures are taken as a whole and then a buffer design is performed on the entire PCB board. If all the convex structures are arranged separately from each other, a board surface buffer design is performed around each convex structure to form a height difference step on the overall panel of the pressing mold, ensuring that the mold is deformed the most at the convex structure and then gradually decreases to the edge of the mold. Correspondingly, the concave deformation is the largest at the concave structure on the PCB panel after pressing, and the degree of concaveness decreases as a whole to the edge of the PCB, ensuring that a groove that is convenient for the installation of BGA devices is formed at the concave structure, and the edge deformation of the groove and the slight concave transition of the overall PCB board surface are natural, thereby not damaging the board surface and the internal structure, ensuring the rigidity and stability of the PCB board manufactured by pressing, and also better balancing the bending and pulling of the BGA installation site and the board bending of the entire PCB board during the pressing process, ensuring the overall manufacturing reliability of the PCB. 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 Otherwise, it is a separate setting, such as Figure 4 shown.

[0037] Example 2 This embodiment also provides a lamination method for realizing the base depression of a specific BGA area on a PCB. The difference from the embodiment 1 is that in the mold used, the upper shell 110 and the lower shell 120 are both made of copper foil, the accommodating cavity is filled with a prepreg that is stacked and melted and solidified, the fiber layers stacked in the prepreg form a support structure, and the molten resin in the prepreg forms a filler 300 to fill the gap between the shell and the support structure; the prepreg includes a base layer 210 prepreg, a transition prepreg stacked layer by layer, and a prepreg stacked layer by layer corresponding to the BGA area; by utilizing the characteristics of the prepreg, the fiber layers in the stacked prepreg are used as the support structure of the mold, and the molten resin flowing during pressing is used as the filler 300 to fill the gap in the mold, so that the height difference of the mold at the upper convex structure changes slowly, and while the upper convex structure with the required deformation amount on the mold is constructed by the stacked prepreg, the damage to the PCB board surface to be pressed when the mold is used is avoided, thereby improving the reliability of PCB production.

[0038] Furthermore, before lamination, the method further includes the step of using pre-pressing to match the mold with the PCB to be pressed. Specifically, the upper and lower copper foils are used to wrap the stacked semi-cured sheets, and the upper and lower copper foil layers are fused around the periphery of the semi-cured sheets of the base layer 210 to form a packaging structure. The semi-cured sheets are stacked on the base layer 210 semi-cured sheets and fill the accommodating cavity formed inside the packaging structure. Specifically, the fiber cloth of the semi-cured sheets forms a filling layer, and the filling layers are stacked to form a supporting structure. By pressing, the upper copper foil layer tightly wraps the supporting structure in the BGA area to form an upper convex structure, and the surface texture of the lower mold PCB is printed in other areas to form an upper shell 110, and the lower copper foil layer forms a lower shell 120. The pressing makes the resin of the semi-cured sheets melt and flow to form a filler 300, which is filled in the accommodating cavity formed between the upper and lower copper foil layers and between the filling layers, thereby forming a stable mold. Specifically, the semi-cured sheets stacked layer by layer corresponding to the BGA area include a plurality of first semi-cured sheets with an area larger than the BGA area and a plurality of second semi-cured sheets with an area smaller than the BGA area; and the number of first cured sheets n1, the area of ​​the first cured sheets gradually decreases from bottom to top, the number of second cured sheets n2, the area of ​​the second cured sheets gradually decreases from bottom to top, and 2≤n1-n2≤5; after melting and solidification, the fiber cloth of the first semi-cured sheet forms a first stacking layer 220, the fiber cloth of the second semi-cured sheet forms a second stacking layer 230, and the fiber cloth of the transitional semi-cured sheet forms a transitional layer 240.

[0039] In this embodiment, the PCB to be pressed is a laminated structure that has not been pressed together, and the total number of the first prepreg and the second prepreg is N=[H / d]+n, wherein the maximum concave size 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; The area of ​​the first prepreg is not greater than 20% of the BGA area; The area of ​​the second prepreg is not less than 80% of the BGA area; The number of first cured sheets n1, the area of ​​the first cured sheets gradually decreases from bottom to top, the number of second cured sheets n2, the area of ​​the second cured sheets gradually decreases from bottom to top, and 2≤n1-n2≤3; After melting and solidification, the fiber cloth of the first prepreg forms a first superimposed layer 220 , the fiber cloth of the second prepreg forms a second superimposed layer 230 , and the fiber cloth of the transition prepreg forms a transition layer 240 .

[0040] Example 3 This embodiment also provides a lamination method for realizing a base depression 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 undergone total lamination, and in the mold used, the prepreg sheets corresponding to the BGA area are laminated layer by layer, including: The area of ​​the first prepreg is not greater than 20% of the BGA area; The area of ​​the second prepreg is not less than 60% of the BGA area; The total number of the first prepreg and the second prepreg is N=[H / d]+n, where the maximum concave size 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; The number of first cured sheets n1, the area of ​​the first cured sheets gradually decreases from bottom to top, the number of second cured sheets n2, the area of ​​the second cured sheets gradually decreases from bottom to top, and 2≤n1-n2≤5; After melting and solidification, the fiber cloth of the first prepreg forms a first superimposed layer 220 , the fiber cloth of the second prepreg forms a second superimposed layer 230 , and the fiber cloth of the transition prepreg forms a transition layer 240 .

[0041] Example 4 like Figure 5 As shown, the present embodiment provides a PCB manufactured by a lamination method for realizing a base depression in a specific BGA area on a PCB as in any one of Embodiments 1-3, wherein two adjacent concave structures are formed on at least one side surface of the PCB, and are used to carry BGA components BGA-U1 and BGA-U2, wherein the concave structure has the largest degree of deformation at its center, and its deformation decreases and smoothly transitions toward the edge of the concave structure; on the overall board surface of the PCB, the concave structure is centrally arranged, and the deformation decreases and smoothly transitions toward the edge of the PCB board surface with the concave structure as the center.

[0042] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation methods of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the claims of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A 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 bulges to form an upward convex structure, the lower shell is a flat structure, and the position of the upward convex structure corresponds to the downward concave structure.

2. The lamination method according to claim 1, characterized in that 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 are positioned and stacked on the first stacking layer, and have an area smaller than the concave structure.

3. The lamination method according to claim 2, characterized in that 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.

4. The lamination method according to claim 2, characterized in that: 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.

5. The lamination method according to claim 4, 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.

6. The lamination method according to claim 4, 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.

7. The lamination method according to any one of claims 1 to 6, 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.

8. The lamination method according to any one of claims 1 to 6, 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.

9. The lamination method according to claim 7, 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 cured sheets be n1, the area of ​​the first cured sheets gradually decreases from bottom to top, let the number of second cured sheets be n2, the area of ​​the second cured sheets 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.

10. The lamination method according to claim 7, 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 cured sheets be n1, the area of ​​the first cured sheets gradually decreases from bottom to top, let the number of second cured sheets be n2, the area of ​​the second cured sheets 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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