Multilayer printed circuit board with built-in radio frequency filter

Abstract

The invention discloses a multi-layer printed circuit board with a built-in radio frequency filter. The multi-layer printed circuit board is provided with a first metal layer, a second metal layer and a third metal layer from the top end to the bottom end in sequence, a first substrate layer is arranged between the first metal layer and the second metal layer, and a second substrate layer is arranged between the second metal layer and the third metal layer; a radio frequency filter to be embedded is arranged in a groove in the second substrate layer, a window is formed in the position, located at the top of the radio frequency filter, in the first metal layer, and a lower metal layer of the radio frequency filter is electrically connected with the third metal layer through a first metal via hole. And the upper metal layer of the radio frequency filter is electrically connected with the first metal layer through the second metal via hole. Compared with a traditional mode that the filter is packaged and then welded on the printed circuit board, the multilayer printed circuit board is smaller in size and better in electrical performance, and the problems that the occupied area is large when the surface-mounted filter is welded on the traditional printed circuit board, but the filter cannot be directly processed in the printed circuit board through patterns are solved.

Description

Technical Field

[0001] The present application belongs to the field of microwave circuits, and in particular to a multilayer printed circuit board with an embedded radio frequency filter. Background Art

[0002] Multilayer printed circuit boards are used to realize signal interconnection and carry electronic components, and are the most critical components of electronic devices. The embedding technology of multilayer printed circuit boards can embed components that are traditionally mounted on the surface of printed circuit boards inside the components, which has the advantage of improving the integration and performance of printed circuit boards.

[0003] There are two main types of embedded passive device technologies for multilayer printed circuit boards. One is to directly embed components in the graphics of the substrate, such as embedded resistors, embedded capacitors, embedded power dividers, filters, etc. This technology directly embeds passive components in the graphics, and the process is relatively simple, but the accuracy is poor. Taking embedded passive filters as an example, the minimum processing width of the existing technology line width is generally above 70um, and the relative dielectric constant is generally below 4. The thinner the line width of the transmission line in the printed circuit board and the larger the dielectric constant, the greater the achievable characteristic impedance. Therefore, this technology is difficult to achieve the high impedance line required in the filter, and because of the small dielectric constant, the size of the filter is very large. In addition, the line width and line spacing accuracy of the printed circuit board are generally within ±25um, which will have a serious impact on the performance of the filter.

[0004] Another embedded technology is to embed independent components in the printed circuit board. This technology is difficult to process, and currently mainly embeds digital devices after packaging, which are large in size and have large parasitic parameters. It is rare to see the embedding of RF components. Summary of the invention

[0005] The purpose of the present application is to overcome the problems of the prior art and disclose a multilayer printed circuit board with an embedded radio frequency filter, so as to solve the problems encountered in the integration process of the multilayer printed circuit board and the passive radio frequency filter, such as the large size of the surface-mount filter, the difficulty in directly processing the filter in the substrate, the poor processing accuracy and the easy frequency deviation, so as to realize the embedding of the radio frequency filter directly in the multilayer printed circuit board.

[0006] The purpose of this application is achieved through the following technical solutions:

[0007] A multilayer printed circuit board with an embedded radio frequency filter, wherein the multilayer printed circuit board is provided with: a first metal layer, a second metal layer and a third metal layer in sequence from the top to the bottom;

[0008] A first substrate layer is provided between the first metal layer and the second metal layer, and a second substrate layer is provided between the second metal layer and the third metal layer;

[0009] The radio frequency filter to be buried is arranged in the groove in the second substrate layer, and a window is arranged at the top position of the radio frequency filter in the first metal layer.

[0010] The lower metal layer of the radio frequency filter is electrically connected to the third metal layer through the first metal via, and the upper metal layer of the radio frequency filter is electrically connected to the first metal layer through the second metal via.

[0011] According to a preferred embodiment, the window size is larger than the filter pattern size in the upper metal layer of the radio frequency filter.

[0012] According to a preferred embodiment, the second substrate layer is formed by stacking a first stacking layer and a second stacking layer, a cavity structure is provided in the first stacking layer, the size of the cavity structure matches the RF filter, and when the first stacking layer and the second stacking layer are stacked, the through hole structure forms a groove.

[0013] According to a preferred embodiment, a notch is provided in the second metal layer at the top of the radio frequency filter, and the size of the notch is larger than the size of the upper metal layer of the radio frequency filter.

[0014] According to a preferred embodiment, the first metal layer, the second metal layer, the third metal layer, the first substrate layer and the second substrate layer are laminated by heat pressing to form a circuit board.

[0015] According to a preferred embodiment, during the hot pressing lamination process, the bottom portion of the first substrate layer is in a molten state and fills into the gap in the second metal layer.

[0016] According to a preferred embodiment, the first metal via and the second metal via are formed by laser drilling.

[0017] According to a preferred embodiment, the thickness of the upper metal layer and the lower metal layer of the radio frequency filter is 15 um.

[0018] According to a preferred embodiment, the filter substrate is made of a material with a dielectric constant greater than 9.

[0019] According to a preferred embodiment, the filter substrate is made of a high-K ceramic substrate or an Al2O3 ceramic substrate.

[0020] The aforementioned main scheme of the present application and its further options can be freely combined to form multiple schemes, all of which are schemes that can be adopted and claimed for protection in the present application. After understanding the scheme of the present application, those skilled in the art can understand that there are multiple combinations based on the prior art and common knowledge, all of which are technical schemes to be protected by the present application, and they are not exhaustively listed here.

[0021] Beneficial effects of this application:

[0022] This application embeds the RF filter into a multi-layer printed circuit board, and the filter does not need to be packaged. The embedding is achieved by substrate lamination and laser drilling. Compared with the traditional method of packaging the filter and then welding it on the printed circuit board, it has a smaller size and better electrical performance. It solves the problem that the surface mount filter welded on the traditional printed circuit board occupies a large area, but the filter cannot be directly processed in the printed board through graphics. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a cross-sectional view of a multilayer printed circuit board of the present application;

[0024] Figure 2 is a top view of the second substrate layer in the multi-layer printed circuit of the present application;

[0025] Figure 3 is a cross-sectional view of the second substrate layer of the multi-layer printed circuit of the present application;

[0026] Figure 4 It is a schematic diagram of the three-dimensional structure of the multilayer printed circuit of the present application;

[0027] Figure 5 is a measured curve of a multilayer printed circuit board with an embedded low-pass filter in an embodiment of the present application;

[0028] Among them, 11-first metal layer, 12-second metal layer, 13-third metal layer, 14-first substrate layer, 15-second substrate layer, 151-first stacking layer, 152-second stacking layer, 153-groove, 16-RF filter, 161-upper metal layer, 162-lower metal layer, 163-filter substrate, 17-first metal via, 18-second metal via, 19-window. DETAILED DESCRIPTION

[0029] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0030] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0031] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the application is usually placed when in use. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0032] In addition, the terms "horizontal", "vertical", "overhanging" and the like do not mean that the components are required to be absolutely horizontal or overhanging, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0033] In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0034] In addition, the present application would like to point out that, in the present application, unless the specific structure, connection relationship, positional relationship, power source relationship, etc. are specifically written out, the structure, connection relationship, positional relationship, power source relationship, etc. involved in the present application are all known by those skilled in the art on the basis of the prior art without creative work.

[0035] refer to Figures 1 to 4 As shown in the figure, a multilayer printed circuit board with an embedded radio frequency filter 16 is shown, and the multilayer printed circuit board is provided with: a first metal layer 11, a second metal layer 12 and a third metal layer 13 from top to bottom; a first substrate layer 14 is provided between the first metal layer 11 and the second metal layer 12, and a second substrate layer 15 is provided between the second metal layer 12 and the third metal layer 13, and the radio frequency filter 16 to be embedded is arranged in a groove 153 in the second substrate layer 15.

[0036] Preferably, the lower metal layer 162 of the RF filter 16 is electrically connected to the third metal layer 13 via the first metal via 17 , and the upper metal layer 161 of the RF filter 16 is electrically connected to the first metal layer 11 via the second metal via 18 .

[0037] Preferably, the first metal layer 11 , the second metal layer 12 , the third metal layer 13 , the first substrate layer 14 and the second substrate layer 15 are laminated by heat pressing to form a circuit board.

[0038] Furthermore, during the hot pressing lamination process, the bottom portion of the first substrate layer 14 is in a molten state and fills the gap in the second metal layer 12 , so that the first substrate layer 14 is in close contact with the RF filter 16 .

[0039] Preferably, a window 19 is provided in the first metal layer 11 at the top of the radio frequency filter 16. The size of the window 19 is larger than the size of the filter pattern in the upper metal layer 161 of the radio frequency filter 16, thereby effectively reducing the influence of the height change of the upper dielectric on the electrical performance of the radio frequency filter after the radio frequency filter is buried in the multi-layer printed circuit board.

[0040] Furthermore, a notch is provided in the second metal layer 12 at the top position of the RF filter 16, and the size of the notch is larger than the size of the upper metal layer 161 of the RF filter 16. By providing the notch on the second metal layer 12, the influence of the height change of the upper dielectric on the electrical performance of the RF filter after the RF filter is buried in the multi-layer printed circuit board can be effectively reduced.

[0041] Preferably, the second substrate layer 15 is formed by stacking a first stacking layer 151 and a second stacking layer 152, and a cavity structure is provided in the first stacking layer 151, and the size of the cavity structure matches the RF filter 16, and when the first stacking layer 151 and the second stacking layer 152 are stacked, the through hole structure forms a groove 153.

[0042] By dividing the second substrate layer 15 into two layers for prefabrication, the first stacking layer 151 can be used to quickly complete the precise processing of the accommodating space of the RF filter 16, ensuring that the size of the cavity structure matches the RF filter 16 with high precision.

[0043] Preferably, the first metal via 17 and the second metal via 18 are formed by laser drilling. The laser drilling technology is used to electrically connect the front surface pad of the RF filter 16 to the multi-layer printed circuit board, and the metal ground on the back of the RF filter 16 is connected to the ground of the multi-layer printed circuit board. That is, the embedding of the RF filter 16 does not require a welding process, and the grounding and electrical connection can be achieved through the first metal via 17 and the second metal via 18, which further reduces the processing complexity of the circuit board and reduces the volume of the circuit board.

[0044] Furthermore, the filter substrate 163 is made of a material with a high dielectric constant greater than 9, such as a high-K ceramic substrate, an Al2O3 ceramic substrate, etc., which can effectively achieve miniaturization of the filter.

[0045] Furthermore, unlike the 4um thickness of the thin gold of the traditional filter, the thickness of the upper metal layer 161 and the lower metal layer 162 of the RF filter 16 is 15um, which facilitates laser drilling to form an electrical connection structure and ensures the qualified rate of the circuit board.

[0046] This application embeds the RF filter into a multi-layer printed circuit board, and the filter does not need to be packaged. The embedding is achieved by substrate lamination and laser drilling. Compared with the traditional method of packaging the filter and then welding it on the printed circuit board, it has a smaller size and better electrical performance. It solves the problem that the surface mount filter welded on the traditional printed circuit board occupies a large area, but the filter cannot be directly processed in the printed board through graphics.

[0047] Example

[0048] Using the structure proposed in the present invention, a multilayer printed circuit board with a built-in 6GHz low-pass filter is designed. The printed circuit board substrate used is Panasonic Megtron6, the filter substrate used is ceramic with a dielectric constant of 25, and the filter size is 3mm*2.4mm*0.381mm. The measured response curve is as follows Figure 5 As shown, it has good insertion loss and out-of-band suppression.

[0049] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A multilayer printed circuit board with an embedded radio frequency filter, characterized in that: The multilayer printed circuit board is provided with, from top to bottom, a first metal layer (11), a second metal layer (12) and a third metal layer (13); A first substrate layer (14) is provided between the first metal layer (11) and the second metal layer (12), and a second substrate layer (15) is provided between the second metal layer (12) and the third metal layer (13); The radio frequency filter (16) to be buried is arranged in a groove (153) in the second substrate layer (15), and a window (19) is provided in the first metal layer (11) at a top position of the radio frequency filter (16). The lower metal layer (162) of the radio frequency filter (16) is electrically connected to the third metal layer (13) via the first metal via (17), and the upper metal layer (161) of the radio frequency filter (16) is electrically connected to the first metal layer (11) via the second metal via.

2. The multilayer printed circuit board according to claim 1, characterized in that The size of the opening window (19) is larger than the size of the filter pattern in the upper metal layer (161) of the radio frequency filter (16).

3. The multilayer printed circuit board according to claim 1, characterized in that The second substrate layer (15) is formed by stacking a first stacking layer (151) and a second stacking layer (152). A cavity structure is provided in the first stacking layer (151), the size of the cavity structure matches the radio frequency filter (16), and when the first stacking layer (151) and the second stacking layer (152) are stacked, the through hole structure forms a groove (153).

4. The multilayer printed circuit board according to claim 1, characterized in that A notch is provided in the second metal layer (12) at the top of the radio frequency filter (16), and the size of the notch is larger than the size of the upper metal layer (161) of the radio frequency filter (16).

5. The multilayer printed circuit board according to claim 4, characterized in that: The first metal layer (11), the second metal layer (12), the third metal layer (13), the first substrate layer (14) and the second substrate layer (15) are laminated by heat pressing to form a circuit board.

6. The multilayer printed circuit board according to claim 5, characterized in that: During the hot pressing lamination process, the bottom portion of the first substrate layer (14) is in a molten state and fills the gap in the second metal layer (12).

7. The multilayer printed circuit board according to claim 1, characterized in that: The first metal via (17) and the second metal via (18) are formed by laser drilling.

8. The multilayer printed circuit board according to claim 1, characterized in that The thickness of the upper metal layer (161) and the lower metal layer (162) of the radio frequency filter (16) is 15 um.

9. The multilayer printed circuit board according to claim 1, characterized in that: The filter substrate (163) is made of a material with a dielectric constant greater than 9.

10. The multilayer printed circuit board according to claim 9, characterized in that The filter substrate (163) is made of a high-K ceramic substrate or an Al2O3 ceramic substrate.

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