A three-dimensional wafer level packaging structure and a preparation method thereof

Abstract

This application relates to the field of semiconductor packaging technology, specifically providing a three-dimensional wafer-level packaging structure and its fabrication method. The structure includes: a first acoustic filter chip; a second acoustic filter chip; and a double-sided cap substrate, including a solid support portion, a solid isolation portion, a first recessed portion, and a second recessed portion. The first and second recessed portions are respectively disposed on a first side and a second side of the double-sided cap substrate. The first acoustic filter chip and the first recessed portion enclose a first packaging protection cavity, and the second acoustic filter chip and the second recessed portion enclose a second packaging protection cavity. The projection of a first functional sensitive area in the top view direction is located within the projection of the first packaging protection cavity in the top view direction, and the projection of the second functional sensitive area in the top view direction is located within the projection of the second packaging protection cavity in the top view direction. The solid isolation portion is a continuous structure located between the first and second recessed portions. The structure has the advantages of compact structure, stable performance, and good process compatibility.

Description

Technical Field

[0001] This application relates to the field of semiconductor packaging technology, and more specifically, to a three-dimensional wafer-level packaging structure and its fabrication method. Background Technology

[0002] As RF front-end modules evolve towards miniaturization, high integration, and multi-frequency, multi-channel designs, acoustic filter chips, such as bulk acoustic wave filters, are increasingly adopting wafer-level 3D packaging to reduce package area and interconnect length. Existing solutions primarily involve packaging two filter chips side-by-side or individually capping them before stacking them. However, side-by-side packaging still occupies a significant area, making it difficult to meet high-density integration requirements. The solution of individually capping two chips before stacking involves repeated capping, sealing rings, and bonding layers, increasing package thickness and process complexity. Furthermore, for existing solutions using a double-sided interposer structure with sequential bonding, if the double-sided cap substrate lacks physical support areas corresponding to the upper and lower bonding positions, the compressive load generated during the bonding process of the second-side chip may be transferred to the functionally sensitive areas of the acoustic filter chip via the cavity span area or the already packaged first-side device, adversely affecting the chip's acoustic performance and potentially causing device damage. Therefore, achieving a balance between reliability and integration through structural optimization is a pressing issue in the current packaging field.

[0003] There is currently no effective technical solution to the above problems. Summary of the Invention

[0004] The purpose of this application is to provide a three-dimensional wafer-level packaging structure and its fabrication method, which has the advantages of compact structure, stable performance and good process compatibility.

[0005] In a first aspect, this application provides a three-dimensional wafer-level packaging structure, which includes: The first acoustic filter chip has a first functional sensitive area; The second acoustic filter chip has a second functional sensitive area; A double-sided cap substrate, comprising a solid support portion, a solid isolation portion, a first recessed portion, and a second recessed portion; The first recess and the second recess are respectively disposed on the first and second opposite sides of the double-sided cap substrate. The first acoustic filter chip is connected to the first side of the solid support, and the second acoustic filter chip is connected to the second side of the solid support. The first acoustic filter chip and the first recess form a first encapsulation protection cavity, and the second acoustic filter chip and the second recess form a second encapsulation protection cavity. The projection of the first functional sensitive area in the top view direction is located within the projection of the first encapsulation protection cavity in the top view direction, and the projection of the second functional sensitive area in the top view direction is located within the projection of the second encapsulation protection cavity in the top view direction. The solid isolation part is a continuous structure located between the first recess and the second recess, and the solid isolation part is used to block the communication between the first encapsulation protection cavity and the second encapsulation protection cavity.

[0006] Optionally, the projection of the first recess in the top view direction overlaps with the projection of the second recess in the top view direction, and the projection of the first functional sensitive area in the top view direction overlaps with the projection of the second functional sensitive area in the top view direction.

[0007] Optionally, the first acoustic filter chip is connected to the first side of the physical support through the first bonding support structure, and the second acoustic filter chip is connected to the second side of the physical support through the second bonding support structure. The projection of the first bonding support structure in the top view direction is located outside the projection of the first functional sensitive area in the top view direction, and the projection of the second bonding support structure in the top view direction is located outside the projection of the second functional sensitive area in the top view direction.

[0008] Optionally, the projections of the first bonded support structure and the second bonded support structure in the top view direction overlap with the projection of the solid support portion in the top view direction to form a pressure bearing path that avoids the first and second functionally sensitive areas.

[0009] Optionally, both the first bonding support structure and the second bonding support structure are made of conductive materials. The three-dimensional wafer-level packaging structure also includes a vertical conductive structure, a first horizontal conductive structure, and a second horizontal conductive structure. The vertical conductive structure penetrates the double-sided cap substrate and is located outside the first packaging protection cavity and the second packaging protection cavity. The first horizontal conductive structure is connected to one side of the first bonding support structure and the vertical conductive structure, respectively. The second horizontal conductive structure is connected to the other side of the second bonding support structure and the vertical conductive structure, respectively.

[0010] Optionally, the vertical conductive structure includes a conductive metal pillar.

[0011] Optionally, the first recess is directly opposite the second recess.

[0012] Alternatively, the double-sided cap substrate may be made of glass, silicon, or ceramic.

[0013] Optionally, the ratio of the depth of the first encapsulation protection cavity to the thickness of the solid isolation portion and the ratio of the depth of the second encapsulation protection cavity to the thickness of the solid isolation portion are both 1-2.

[0014] Secondly, this application also provides a method for fabricating a three-dimensional wafer-level packaging structure, used to fabricate the three-dimensional wafer-level packaging structure provided in the first aspect. The method for fabricating the three-dimensional wafer-level packaging structure includes the following steps: S1. A first recess and a second recess are formed on the first side and the second side of the double-sided cap substrate, respectively. The sum of the depth of the first recess and the depth of the second recess is less than the thickness of the double-sided cap substrate, so as to retain a solid isolation portion between the first recess and the second recess. The area of ​​the double-sided cap substrate other than the first recess, the second recess and the solid isolation portion constitutes a solid support portion. S2. Bond the first acoustic filter chip to the first side of the physical support portion so that the first acoustic filter chip and the first recessed portion form a first encapsulation protection cavity. S3. Bond the second acoustic filter chip to the second side of the physical support portion so that the second acoustic filter chip and the second recessed portion form a second encapsulation protection cavity.

[0015] As can be seen from the above, the three-dimensional wafer-level packaging structure and fabrication method provided in this application, by setting a solid support part and a solid isolation part in the double-sided cap substrate, provides a reliable mechanical support path for the bonding process while realizing double-sided chip integrated packaging, avoiding the load from directly acting on the functionally sensitive area, thereby solving the problem of poor reliability of double-sided packaging in the prior art, and has the advantages of compact structure, stable performance and good process compatibility. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a three-dimensional wafer-level packaging structure provided in an embodiment of this application.

[0017] Figure 2 This is a flowchart illustrating a method for fabricating a three-dimensional wafer-level packaging structure, as provided in an embodiment of this application.

[0018] Reference numerals: 1. First acoustic filter chip; 2. Second acoustic filter chip; 3. Double-sided cap substrate; 31. Solid support portion; 32. Solid isolation portion; 4. First functional sensitive area; 5. Second functional sensitive area; 6. First encapsulation protection cavity; 7. Second encapsulation protection cavity; 8. First bonding support structure; 9. Second bonding support structure; 10. Vertical conductive structure; 11. First horizontal conductive structure; 12. Second horizontal conductive structure. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0020] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0021] Firstly, such as Figure 1 As shown, this application provides a three-dimensional wafer-level packaging structure, which includes: The first acoustic filter chip 1 has a first functional sensitive area 4; The second acoustic filter chip 2 has a second functional sensitive area 5; The double-sided cap substrate 3 includes a solid support portion 31, a solid isolation portion 32, a first recessed portion, and a second recessed portion; The first recess and the second recess are respectively disposed on the first and second opposite sides of the double-sided cap substrate 3. The first acoustic filter chip 1 is connected to the first side of the solid support 31, and the second acoustic filter chip 2 is connected to the second side of the solid support 31. The first acoustic filter chip 1 and the first recess form a first encapsulation protection cavity 6, and the second acoustic filter chip 2 and the second recess form a second encapsulation protection cavity 7. The projection of the first functional sensitive area 4 in the top view direction is located within the projection of the first encapsulation protection cavity 6 in the top view direction, and the projection of the second functional sensitive area 5 in the top view direction is located within the projection of the second encapsulation protection cavity 7 in the top view direction. The solid isolation part 32 is a continuous structure located between the first recess and the second recess, and the solid isolation part 32 is used to block the communication between the first encapsulation protection cavity 6 and the second encapsulation protection cavity 7.

[0022] For ease of understanding, some key terms in this embodiment are explained below. The first acoustic filter chip 1 and the second acoustic filter chip 2 in this embodiment are the core functional units of the three-dimensional wafer-level packaging structure, used to implement the filtering function of radio frequency signals. They typically include one or more acoustic resonators and related diaphragm regions, electrode overlap regions, release structures, acoustic reflection structures, or other areas sensitive to mechanical loads. These regions are collectively referred to as functionally sensitive areas (the functionally sensitive area of ​​the first acoustic filter chip 1 is the first functionally sensitive area 4, and the functionally sensitive area of ​​the second acoustic filter chip 2 is the second functionally sensitive area 5). The performance of the functionally sensitive areas directly affects the working effect of the filter chips. Therefore, these areas need to be specially protected during the packaging process to avoid damage or interference. The double-sided cap substrate 3 in this embodiment is a key structure connecting the first acoustic filter chip 1 and the second acoustic filter chip 2. Its design aims to achieve vertical integration of the two chips. The double-sided cap substrate 3 has opposing first and second sides, respectively used for connecting to the two chips. The physical support portion 31 in this embodiment is part of the double-sided cap substrate 3, providing physical support for the bonding of the first acoustic filter chip 1 and the second acoustic filter chip 2. Its function is to ensure that the bonding pressure can be transmitted through the physical support portion 31 during the packaging process, thereby preventing the pressure from directly acting on the functionally sensitive areas of the chip. The physical isolation portion 32 in this embodiment is a continuous structure located between the first recess and the second recess in the double-sided cap substrate 3. Its main function is to block the communication between the first packaging protection cavity 6 and the second packaging protection cavity 7, ensuring that the two packaging cavities are independent of each other. It should be understood that "independence" here means that there is no direct open communication between the two packaging protection cavities in the design, and does not mean that the two packaging protection cavities are completely isolated in terms of heat, mechanics, electromagnetics, or substrate acoustics. The first recess and the second recess in this embodiment are cavity structures formed on the double-sided cap substrate 3. These two recesses, together with the first acoustic filter chip 1 and the second acoustic filter chip 2, respectively enclose the first packaging protection cavity 6 and the second packaging protection cavity 7. These packaging protection cavities provide the necessary free space for the functionally sensitive areas of the chip to ensure that the chip can work normally.

[0023] This application proposes a three-dimensional wafer-level packaging structure, which includes a first acoustic filter chip 1, a second acoustic filter chip 2, and a double-sided cap substrate 3. The first acoustic filter chip 1 has a first functional sensitive area 4, the second acoustic filter chip 2 has a second functional sensitive area 5, and the double-sided cap substrate 3 includes a solid support portion 31, a solid isolation portion 32, a first recess portion, and a second recess portion.

[0024] The first recess and the second recess are respectively disposed on a first side and a second side opposite to each other on the double-sided cap substrate 3. For example, the first recess can be disposed on the bottom surface of the double-sided cap substrate 3, while the second recess is disposed on the top surface of the double-sided cap substrate 3. This opposite arrangement allows the two acoustic filter chips to be mounted on opposite sides of the substrate, thereby achieving vertical stacking packaging.

[0025] The first acoustic filter chip 1 is connected to the first side of the physical support portion 31 (corresponding to the first side of the double-sided cap substrate 3), and the second acoustic filter chip 2 is connected to the second side of the physical support portion 31 (corresponding to the second side of the double-sided cap substrate 3). Various bonding technologies can be used for the connection, such as eutectic bonding, thermoforming bonding, or adhesive bonding. In one embodiment, the first acoustic filter chip 1 can be connected to the first side of the physical support portion 31 via a first bonding support structure 8, while the second acoustic filter chip 2 can be connected to the second side of the physical support portion 31 via a second bonding support structure 9. These bonding support structures provide a robust mechanical connection and serve as the sealing boundary of the encapsulation protection cavity.

[0026] The first acoustic filter chip 1 and the first recess together form a first encapsulation protection cavity 6, and the second acoustic filter chip 2 and the second recess together form a second encapsulation protection cavity 7. Specifically, when the first acoustic filter chip 1 is bonded to the first side of the physical support portion 31, the surface of the chip and the inner wall of the first recess together form a closed cavity, namely the first encapsulation protection cavity 6. Similarly, the second acoustic filter chip 2 and the second recess together form the second encapsulation protection cavity 7. These encapsulation protection cavities provide necessary free space for the functionally sensitive areas of the chip, preventing capping materials or other encapsulation materials from directly occupying or pressing against the acoustically sensitive working areas.

[0027] The projection of the first functionally sensitive area 4 in the top view direction lies within the projection of the first encapsulation protection cavity 6 in the top view direction, and the projection of the second functionally sensitive area 5 in the top view direction lies within the projection of the second encapsulation protection cavity 7 in the top view direction. This means that the size and position of the recess and the encapsulation protection cavity are designed to completely cover and protect the corresponding functionally sensitive areas. For example, the first functionally sensitive area 4 can be located in the central region of the first encapsulation protection cavity 6 to ensure that it is adequately protected during the encapsulation process.

[0028] The solid isolation portion 32 is a continuous structure located between the first recess and the second recess. For example, in the thickness direction of the double-sided cap substrate 3, the solid isolation portion 32 can be an unetched or uncut intermediate layer, with the etched or cut-out areas being the first and second recesses. The solid isolation portion 32 is used to block the communication between the first package protection cavity 6 and the second package protection cavity 7. This means that the two package protection cavities are physically completely independent, with no direct open communication path, thus providing relatively independent package-level free space for the acoustic filter chips on both sides.

[0029] The following example provides a more detailed explanation of the above technical solutions: Suppose we need to package two acoustic filter chips, each used to process RF signals in different frequency bands, and the package structure is required to have high integration and anti-interference capabilities. Traditional side-by-side packaging solutions occupy a large planar area, while solutions that independently cap and then stack them increase package thickness and process complexity. Furthermore, in double-sided packaging, if effective physical support is lacking, the compressive load generated by the bonding on the second side may be transferred to the acoustically sensitive area of ​​the already packaged first-side device, thus affecting device performance.

[0030] To address the aforementioned issues, this application proposes a three-dimensional wafer-level packaging structure. First, a double-sided cap substrate 3 is fabricated using glass material, with a first recess and a second recess formed on its opposing first and second sides, respectively. These recesses are formed using wet or dry etching processes, with their depth precisely controlled to ensure a continuous solid isolation portion 32 is maintained between the two recesses. The thickness of this solid isolation portion 32 is sufficient to provide adequate mechanical strength and effectively block the connection between the two recesses. The area of ​​the double-sided cap substrate 3 excluding the first recess, the second recess, and the solid isolation portion 32 constitutes a solid support portion 31.

[0031] Next, the first acoustic filter chip 1 is bonded to the first side of the physical support portion 31. During the bonding process, the non-functional sensitive area of ​​the first acoustic filter chip 1 contacts the physical support portion 31, while the first functional sensitive area 4 faces the first recess. Through precise alignment and bonding, the first acoustic filter chip 1 and the first recess form a first encapsulation protection cavity 6. The projection of the first functional sensitive area 4 in the top view direction is ensured to be completely within the projection of the first encapsulation protection cavity 6 in the top view direction, thereby providing the first functional sensitive area 4 with an independent, protected free space.

[0032] Subsequently, the second acoustic filter chip 2 is bonded to the second side of the physical support portion 31. During the second-side bonding, due to the presence of the physical support portion 31, the compressive load generated during bonding is mainly transmitted through the physical support portion 31, avoiding direct application to the functionally sensitive area of ​​the first acoustic filter chip 1. The non-functionally sensitive area of ​​the second acoustic filter chip 2 is in contact with the physical support portion 31, and the second functionally sensitive area 5 is directly opposite the second recess. After bonding, the second acoustic filter chip 2 and the second recess together form the second encapsulation protection cavity 7. Similarly, the projection of the second functionally sensitive area 5 in the top view direction is ensured to be completely within the projection of the second encapsulation protection cavity 7 in the top view direction.

[0033] In this process, the physical isolation portion 32, as a continuous structure located between the first recess and the second recess, ensures complete physical isolation between the first encapsulation protection cavity 6 and the second encapsulation protection cavity 7. This means that even if a leak or pressure anomaly occurs inside the first encapsulation protection cavity 6, it will not be directly transmitted to the second encapsulation protection cavity 7, and vice versa. This isolation is crucial for acoustic filter chips that require high Q values ​​and low crosstalk.

[0034] Through the above implementation method, two acoustic filter chips are successfully integrated into a compact three-dimensional package structure. The first acoustic filter chip 1 and the second acoustic filter chip 2 are independently packaged on both sides of the double-sided cap substrate 3, achieving high-density integration in the vertical direction and effectively reducing the planar area occupied by the package. The presence of the solid support portion 31 ensures that the bonding pressure can be transmitted through the solid support portion 31 during the double-sided bonding process, thereby avoiding the pressure from directly acting on the functionally sensitive areas of the acoustic filter chips and protecting the acoustic performance of the device. The solid isolation portion 32 effectively blocks the communication between the two package protection cavities, prevents interference between the cavities, and enhances the structural strength of the substrate.

[0035] The three-dimensional wafer-level packaging structure proposed in this application achieves vertical integration of two acoustic filter chips by introducing a double-sided cap substrate 3. Compared with the existing traditional side-by-side packaging scheme, this significantly reduces the planar area occupied by the package. For example, under the same functional requirements, the packaging structure of this application can reduce the board area occupied by the device by nearly half.

[0036] Furthermore, compared to existing solutions where two chips are independently capped before being stacked, this application provides a packaging protection cavity for both chips simultaneously using a single double-sided capped substrate 3. This avoids the need for repeated capping, sealing rings, and bonding layers, effectively reducing packaging thickness and process complexity. For example, traditional solutions may require two separate capping and bonding layers, while this application only requires one double-sided capped substrate 3 to achieve double-sided packaging, thus optimizing the overall packaging thickness.

[0037] More importantly, this application solves the problem of bonding load being transferred to the acoustically sensitive area and affecting device performance due to the lack of physical support during double-sided packaging by including a solid support portion 31 and a solid isolation portion 32 in the double-sided cap substrate 3. The solid support portion 31 provides a stable physical support for the bonding of the first acoustic filter chip 1 and the second acoustic filter chip 2, ensuring that the bonding pressure can be transferred through the solid support portion 31 during the second-side bonding, thereby avoiding the pressure directly acting on the functionally sensitive area of ​​the acoustic filter chip. The solid isolation portion 32 physically achieves effective isolation between the two packaging protection cavities, preventing interference between the cavities and further enhancing the structural strength of the double-sided cap substrate 3. This design ensures that the functionally sensitive area of ​​the acoustic filter chip is fully protected during packaging and operation, thereby guaranteeing the performance and reliability of the device. For example, during the second-side bonding, the solid support portion 31 can effectively disperse and bear the bonding pressure, preventing the pressure from concentrating on the functionally sensitive area of ​​the first-side chip, and avoiding problems such as resonant frequency drift or Q value decrease caused by bonding stress.

[0038] In some preferred embodiments, the projection of the first recess in the top view direction overlaps with the projection of the second recess in the top view direction, and the projection of the first functional sensitive area 4 in the top view direction overlaps with the projection of the second functional sensitive area 5 in the top view direction.

[0039] The projections of the first recess and the second recess in the top view direction overlap, meaning that when viewed from a direction perpendicular to the plane of the double-sided cap substrate 3, the outlines of the first and second recesses share at least a portion of their plane contours. This overlap can be achieved in various ways. For example, the central regions of the first and second recesses can be perfectly aligned, causing their projection areas to largely overlap; or, the two recesses can be partially offset, but still have some areas overlapping each other in the top view direction. This design aims to optimize space utilization and reduce the overall planar size of the package structure. Simultaneously, the projections of the first functional sensitive area 4 and the second functional sensitive area 5 in the top view direction overlap, meaning that when viewed from a direction perpendicular to the chip plane, the projection areas of the first functional sensitive area 4 on the first acoustic filter chip 1 and the second functional sensitive area 5 on the second acoustic filter chip 2 share at least a portion of their plane contours. This can manifest as two functionally sensitive regions being perfectly aligned vertically, resulting in a high degree of overlap in their projected areas; or, the two functionally sensitive regions can be partially offset, but still have portions that overlap in the top-view direction, for example, one functionally sensitive region being located above the edge of another. This overlapping design allows the core functional regions of the two chips to be closely arranged vertically, further reducing the planar size of the package and potentially shortening internal interconnect paths.

[0040] This solution overlaps the first and second recesses on the double-sided cap substrate 3 in a top-view orientation, and overlaps the first functional sensitive area 4 on the first acoustic filter chip 1 and the second functional sensitive area 5 on the second acoustic filter chip 2 in a top-view orientation. This allows two acoustic filter chips, which might otherwise need to be arranged side-by-side or completely staggered, to be stacked and packaged more compactly on both sides of the double-sided cap substrate 3. The double-sided cap substrate 3 provides overlapping package protection cavity space for the chips on both sides through its overlapping first and second recesses. Simultaneously, the functional sensitive areas of the first acoustic filter chip 1 and the second acoustic filter chip 2 also overlap vertically, allowing the core working area of ​​the chip to efficiently utilize the shared vertical space. This layout significantly reduces the projected area in the horizontal direction while maintaining independent package protection cavities on both sides of the entire three-dimensional wafer-level packaging structure. The physical isolation portion 32 ensures the independence of the two package protection cavities within the overlapping area, avoiding mutual interference. This compact vertical stacking design effectively solves the problem of excessive planar area caused by the staggered chip layout in traditional solutions, achieving high integration.

[0041] In some preferred embodiments, the first acoustic filter chip 1 is connected to the first side of the physical support portion 31 through the first bonding support structure 8, and the second acoustic filter chip 2 is connected to the second side of the physical support portion 31 through the second bonding support structure 9. The projection of the first bonding support structure 8 in the top view direction is located outside the projection of the first functional sensitive area 4 in the top view direction, and the projection of the second bonding support structure 9 in the top view direction is located outside the projection of the second functional sensitive area 5 in the top view direction.

[0042] The first bonding support structure 8 and the second bonding support structure 9 are structures used to provide mechanical connection, force transmission, and cavity sealing between the acoustic filter chip and the double-sided cap substrate 3. They simultaneously serve as sealing and mechanical support, and at least constitute a portion of the sealing boundary of the corresponding package protection cavity. As one implementation, the bonding support structure can use metal bumps, such as gold or copper bumps, connected to the chip and substrate via thermoforming or ultrasonic bonding to form a robust mechanical support. Alternatively, the bonding support structure can consist of annular or frame-shaped sealing rings made of polymer materials (such as epoxy resin, benzocyclobutene BCB) or metal solders (such as AuSn, SnAg), providing both sealing and mechanical support. Furthermore, the bonding support structure can also be a micropillar array made of silicon, polymer, or metal materials, connected via adhesive or eutectic bonding. The solid support portion 31 is the solid part in the double-sided cap substrate 3 that provides mechanical strength and load-bearing capacity. It, together with the recessed portion and the solid isolation portion 32, constitutes the overall structure of the substrate and can be made of materials such as glass, silicon, or ceramic. The connection between the chip and the solid support portion 31 can be achieved by various methods such as eutectic bonding, thermoforming bonding, adhesive bonding, or glass fusion bonding. The projection of the first bonding support structure 8 in the top view direction is outside the projection of the first functionally sensitive area 4 in the top view direction, and the projection of the second bonding support structure 9 in the top view direction is outside the projection of the second functionally sensitive area 5 in the top view direction. This positional relationship is achieved through precise layout design and alignment technology, ensuring that the bonding support structure does not overlap with the functionally sensitive area in the direction perpendicular to the chip plane, thereby arranging the bonding support structure in the area surrounding the functionally sensitive area, such as at the edge of the chip or in a non-sensitive area.

[0043] This solution effectively guides and isolates bonding pressure by introducing a first bonding support structure 8 and a second bonding support structure 9 as physical connection media between the first acoustic filter chip 1, the second acoustic filter chip 2, and the physical support portion 31 of the double-sided cap substrate 3. In the three-dimensional wafer-level packaging structure, the double-sided cap substrate 3 provides a compact stacked packaging method, and the physical isolation portion 32 ensures the independence of the first packaging protection cavity 6 and the second packaging protection cavity 7. Based on this, by setting the projection of the first bonding support structure 8 in the top view direction outside the projection of the first functional sensitive area 4 in the top view direction, and setting the projection of the second bonding support structure 9 in the top view direction outside the projection of the second functional sensitive area 5 in the top view direction, it is ensured that the pressure applied during chip bonding operations can be directly transmitted to the physical support portion 31 of the double-sided cap substrate 3 and the non-functional sensitive area of ​​the chip through these bonding support structures, rather than directly acting on the fragile functional sensitive area. This layout utilizes the physical support portion 31 and the non-functional sensitive area of ​​the chip as the main force-bearing components. Through spatial avoidance design, it effectively avoids mechanical stress damage to the functional sensitive area caused by bonding pressure. The bonding support structure, acting as a connecting bridge, not only ensures a stable mechanical connection between the chip and the substrate but also, through its specific positional definition, spatially decouples the functional sensitive area from the pressure-bearing path. This ensures the integrity of the packaging structure while maximizing the protection of the core functional areas of the acoustic filter chip.

[0044] In some preferred embodiments, the projections of the first bonded support structure 8 in the top view, the second bonded support structure 9 in the top view, and the solid support portion 31 in the top view overlap to form a pressure bearing path that avoids the first functional sensitive area 4 and the second functional sensitive area 5.

[0045] The projections of the first bonding support structure 8 and the second bonding support structure 9 in the top view represent the two-dimensional outlines of the first bonding support structure 8 and the second bonding support structure 9 in the direction perpendicular to the packaging plane, respectively. These bonding support structures are used to connect the first acoustic filter chip 1 and the second acoustic filter chip 2 to the solid support portion 31 of the double-sided cap substrate 3, respectively. They can be formed from bonding materials such as metal solder, polymer adhesive, or glass paste. The shape and size of their projections can be designed according to the bonding area and stress distribution requirements of the chip, for example, they can be ring-shaped, rectangular, or dot-shaped arrays. The projection of the solid support portion 31 in the top view represents the two-dimensional outline of the solid portion of the double-sided cap substrate 3 that is not part of the recessed area in the vertical direction. This solid support portion 31 provides structural integrity and mechanical strength to the double-sided cap substrate 3 and is the main area that bears external pressure. "Overlap" means that at least a portion of the projections of the first bonding support structure 8, the second bonding support structure 9, and the solid support portion 31 in the top view direction are shared spatially. This ensures a direct force transmission path between the bonding support structure and the solid support portion 31 in the vertical direction. For example, by precisely aligning the bonding area, the bonding support structure can be positioned directly above or below the solid support portion 31, thereby forming a continuous force channel in the vertical direction. In this way, this embodiment can form a pressure-bearing path that avoids the first functional sensitive area 4 and the second functional sensitive area 5. That is, during the packaging process, the physical channel through which the externally applied mechanical pressure is transmitted from the point of application to the bonded support structure is designed to bypass the first functional sensitive area 4 of the first acoustic filter chip 1 and the second functional sensitive area 5 of the second acoustic filter chip 2.

[0046] This solution optimizes the pressure-bearing path by specifically arranging the spatial positions of the bonding support structure and the physical support portion 31. In the aforementioned three-dimensional wafer-level packaging structure, the first acoustic filter chip 1 is connected to the first side of the physical support portion 31 via the first bonding support structure 8, and the second acoustic filter chip 2 is connected to the second side of the physical support portion 31 via the second bonding support structure 9. Simultaneously, the projection of the first bonding support structure 8 in the top view direction is outside the projection of the first functionally sensitive area 4 in the top view direction, and the projection of the second bonding support structure 9 in the top view direction is outside the projection of the second functionally sensitive area 5 in the top view direction. Based on this, by overlapping the projections of the first bonding support structure 8, the second bonding support structure 9, and the physical support portion 31 in the top view direction, it is ensured that during the packaging bonding process, the applied pressure can be directly transmitted to the physical support portion 31 of the double-sided cap substrate 3 through the bonding support structure, rather than acting on the functionally sensitive area of ​​the chip. This design utilizes the physical support portion 31 as the primary load-bearing point, effectively avoiding functionally sensitive areas and thus achieving physical structural protection for these areas. When chip bonding is completed on the first side and preparation is underway for chip bonding on the second side, at least a portion of the compressive load generated by the second-side bonding can be sequentially transferred to the non-sensitive areas on the first-side chip via the second bonding support portion, the physical support portion 31, and the first bonding support portion. This pressure path effectively diverts mechanical stress during the packaging process to non-sensitive areas, preventing deformation or performance degradation of sensitive areas due to bonding pressure, and ensuring the reliability and stability of the acoustic filter chip after double-sided packaging.

[0047] In some preferred embodiments, the materials of the first bonding support structure 8 and the second bonding support structure 9 are both conductive. The three-dimensional wafer-level packaging structure also includes a vertical conductive structure 10, a first horizontal conductive structure 11, and a second horizontal conductive structure 12. The vertical conductive structure 10 penetrates the double-sided cap substrate 3 and is located outside the first packaging protection cavity 6 and the second packaging protection cavity 7. The first horizontal conductive structure 11 is connected to one side of the first bonding support structure 8 and the vertical conductive structure 10, respectively. The second horizontal conductive structure 12 is connected to the other side of the second bonding support structure 9 and the vertical conductive structure 10, respectively.

[0048] The materials of the first bonding support structure 8 and the second bonding support structure 9 are both designed to be conductive. This means that in addition to providing mechanical support and pressure bearing functions, these bonding support structures can also serve as transmission paths for electrical signals. For example, their materials can be conductive adhesive, metal solder (such as tin-silver-copper alloy), or conductive layers formed through metallization processes. Furthermore, the three-dimensional wafer-level packaging structure of this application also includes a vertical conductive structure 10, a first horizontal conductive structure 11, and a second horizontal conductive structure 12. The vertical conductive structure 10 is configured to penetrate the double-sided cap substrate 3 to achieve electrical connection between the two sides of the double-sided cap substrate 3. This vertical conductive structure 10 can take various forms; for example, it can be a through-glass via (TGV) formed through a glass substrate filled with conductive material, or a through-silicon via (TSV) formed through a silicon substrate filled with conductive material. The vertical conductive structure 10 is arranged in the external region of the first packaging protection cavity 6 and the second packaging protection cavity 7, thereby ensuring the physical isolation between the conductive path and the acoustic filter cavity, avoiding the impact on the cavity's airtightness and potential electromagnetic interference from signal transmission to the acoustic filter performance, and preventing disruption of the isolation relationship between the first packaging protection cavity 6 and the second packaging protection cavity 7. The first horizontal conductive structure 11 and the second horizontal conductive structure 12 are used for electrical connection in the horizontal direction. Specifically, the first horizontal conductive structure 11 is designed to connect to one side of the first bonding support structure 8 and the vertical conductive structure 10, while the second horizontal conductive structure 12 is connected to the other side of the second bonding support structure 9 and the vertical conductive structure 10. These horizontal conductive structures can take the form of redistribution layers (RDLs) or pads, and their function is to lead out the electrical signals on the first bonding support structure 8 and the second bonding support structure 9 and connect them to the vertical conductive structure 10, thereby realizing signal transfer from the chip to the inside of the substrate and then to the outside.

[0049] This solution integrates mechanical support and electrical interconnection functions to construct a highly efficient and compact vertical interconnection system. Specifically, the first bonding support structure 8 and the second bonding support structure 9 not only serve as mechanical support points for the first acoustic filter chip 1 and the second acoustic filter chip 2, bearing pressure during bonding and protecting the first functional sensitive area 4 and the second functional sensitive area 5 from damage, but also, due to their conductivity, act as the first-level nodes for the chip's electrical leads. This design avoids the need for additional independent conductive pillars near sensitive areas, thus saving valuable packaging space. The vertical conductive structure 10 is cleverly placed in the double-sided cap substrate 3 and extends through its thickness direction, enabling electrical signal transmission on both sides of the double-sided cap substrate 3. Positioned outside the first packaging protection cavity 6 and the second packaging protection cavity 7, i.e., outside the sealing area, this layout ensures that the vertical conductive structure 10 does not compromise the sealing integrity of the packaging protection cavity, which is crucial for the performance of the acoustic filter chip. Simultaneously, this isolation effectively avoids electromagnetic interference that electrical signal transmission might cause to the acoustic filter chip. The first horizontal conductive structure 11 and the second horizontal conductive structure 12 act as bridges, electrically connecting the conductive bonding support structure located at the inner edge of the encapsulation protection cavity to the vertical conductive structure 10 located outside the encapsulation protection cavity. The first horizontal conductive structure 11 leads out the electrical signal on the first bonding support structure 8 and connects it to one side of the vertical conductive structure 10, while the second horizontal conductive structure 12 leads out the electrical signal on the second bonding support structure 9 and connects it to one side of the vertical conductive structure 10. This horizontal wiring design allows electrical signals to be efficiently transmitted from the chip surface to the vertical conductive path inside the double-sided cap substrate 3, and then further led out to the external circuit. Through the above structural combination, the solution of this application, while inheriting the above three-dimensional wafer-level packaging structure, forms a pressure-bearing path that avoids the first functional sensitive area 4 and the second functional sensitive area 5 through the first bonding support structure 8, the second bonding support structure 9, and the solid support portion 31, further realizes effective electrical interconnection between the upper and lower acoustic filter chips and the external circuit. This integrated design allows for a high degree of spatial reuse of mechanical support and electrical interconnection functions, avoiding the increased package size and process complexity caused by independently setting interconnection structures in traditional solutions, while ensuring signal integrity and package reliability.

[0050] In some preferred embodiments, the vertical conductive structure 10 includes a conductive metal pillar.

[0051] A conductive metal pillar is a columnar structure made of conductive metal material. Its main function is to provide a vertical path for electrical signal transmission, while also providing a certain degree of mechanical support. The conductive metal pillar can be designed to penetrate the thickness of the solid support portion 31, thereby achieving electrical interconnection between the two sides of the double-sided cap substrate 3. The conductive metal pillar can be implemented in various ways. For example, it can be formed by filling conductive materials (such as copper, tungsten, etc.) inside pre-formed through-holes (such as through-glass vias (TGV) or through-silicon vias (TSV)) on the double-sided cap substrate 3; or it can be directly grown or formed in the surface or internal trenches of the double-sided cap substrate 3 using processes such as electroplating, sputtering, and chemical vapor deposition, combined with photolithography and etching techniques, to create a conductive metal structure with a columnar morphology.

[0052] This solution concretizes the vertical conductive structure 10 as a conductive metal pillar, providing a clear physical implementation for vertical signal transmission within a 3D package. In 3D wafer-level packaging, since electrical interconnection between upper and lower chips needs to be achieved across the double-sided cap substrate 3, using a conductive metal pillar as the vertical conductive structure 10 leverages the excellent conductivity and mechanical strength of the metal material to ensure low-resistance signal transmission during the substrate penetration process. Compared to other possible conductive forms, the conductive metal pillar has stronger structural rigidity and can better withstand thermal stress and mechanical loads during the packaging process, thereby enhancing the physical stability of the entire package structure while ensuring electrical connectivity. Through this specific structural definition, the vertical conductive structure 10 can form a stable electrical path with the first horizontal conductive structure 11 and the second horizontal conductive structure 12, effectively supporting the signal transmission requirements of acoustic filter chips in multi-frequency, multi-channel applications, and solving the technical challenge of achieving high-reliability connections in a small space for vertical interconnect structures.

[0053] In some preferred embodiments, the first recess is directly opposite the second recess.

[0054] "Alignment" refers to the spatial alignment of the first and second recessed portions in the thickness direction of the double-sided cap substrate 3. Specifically, when viewed from a direction perpendicular to the plane of the double-sided cap substrate 3 (i.e., from a top view), the projections of the first and second recessed portions in the top view at least partially overlap. Preferably, the horizontal coordinates of the center of the first and second recessed portions are the same. This alignment ensures that the distribution of recessed areas on the upper and lower sides of the double-sided cap substrate 3 is consistent. This alignment can be achieved in various ways, for example, by employing high-precision double-sided photolithography alignment technology during the manufacturing process of the double-sided cap substrate 3 to ensure that the patterns of the first and second recessed portions are precisely aligned when etching or molding on both sides of the substrate.

[0055] This solution achieves symmetry in the spatial geometry of the upper and lower packaging cavities by aligning the first and second recesses on the double-sided cap substrate 3. In the three-dimensional wafer-level packaging structure, the double-sided cap substrate 3 supports the first acoustic filter chip 1 and the second acoustic filter chip 2, and respectively encloses the first and second recesses to form the first packaging protection cavity 6 and the second packaging protection cavity 7. During chip bonding or subsequent packaging processes, the packaging structure will be subjected to a certain compressive load. If the first and second recesses are not precisely aligned, the load may cause uneven local stress on the double-sided cap substrate 3, resulting in stress concentration, especially at the junction of the solid support portion 31 and the solid isolation portion 32. By aligning the first recess with the second recess, it can be ensured that the stress points on the upper and lower sides can remain on the same vertical axis when subjected to bonding pressure. This symmetrical and aligned layout allows the solid support portion 31 of the double-sided cap substrate 3 to form a more stable and uniform pressure bearing path. The loads acting on the first acoustic filter chip 1 and the second acoustic filter chip 2 can be effectively guided to the physical support portion 31 and uniformly transmitted along the thickness direction of the substrate. This avoids local stress concentration on the substrate caused by misalignment of the recessed portion, and protects the first functional sensitive area 4 and the second functional sensitive area 5 located in the first packaging protection cavity 6 and the second packaging protection cavity 7 from unnecessary mechanical stress interference. In addition, by setting the first recessed portion and the second recessed portion on the double-sided cap substrate 3 to be in a direct facing relationship, the space required by the first recessed group and the second recessed group in the thickness direction of the double-sided cap substrate 3 can be reduced, so as to reduce the overall size of the three-dimensional wafer-level packaging structure.

[0056] In some preferred embodiments, the double-sided cap substrate 3 is made of glass, silicon, or ceramic.

[0057] When the double-sided cap substrate 3 is made of glass, its excellent electrical insulation properties effectively reduce parasitic capacitance and inductance within the package, thus ensuring the signal integrity of the acoustic filter chip. Furthermore, the transparency of glass facilitates optical inspection and alignment during the packaging process, improving production efficiency and yield. Its processing flexibility also makes it possible to form precise first and second recesses, as well as other vias, through processes such as wet etching or laser drilling. When the double-sided cap substrate 3 is made of silicon, silicon has a good coefficient of thermal expansion matching with the acoustic filter chip (which is typically also based on silicon or silicon-based materials). This matching significantly reduces the risk of deformation or cracking due to thermal stress mismatch when the package structure is subjected to temperature changes, effectively protecting the first functional sensitive area 4 and the second functional sensitive area 5. Simultaneously, silicon is a mature material in semiconductor micromachining, and the first and second recesses, as well as the solid support portion 31 and the solid isolation portion 32, can be precisely formed using techniques such as deep reactive ion etching (DRIE). If the double-sided cap substrate 3 is made of ceramic, ceramic, known for its excellent mechanical strength and thermal stability, can provide robust physical support for the entire three-dimensional wafer-level packaging structure. Especially during multi-layer stacking and bonding processes, it can effectively withstand external pressure, ensuring the structural integrity of the physical support portion 31 and the physical isolation portion 32, and preventing bonding loads from being directly transferred to the functionally sensitive areas of the acoustic filter chip. Furthermore, ceramic materials also possess good chemical inertness, resisting various chemical attacks and improving the long-term reliability of the package.

[0058] This solution ensures the overall performance and reliability of the three-dimensional wafer-level packaging structure by selecting specific materials (glass, silicon, or ceramic) for the double-sided cap substrate 3. In the aforementioned three-dimensional wafer-level packaging structure, the double-sided cap substrate 3 is the core supporting component, comprising a solid support portion 31, a solid isolation portion 32, a first recess, and a second recess. The first recess and the first acoustic filter chip 1 enclose a first packaging protection cavity 6, and the second recess and the second acoustic filter chip 2 enclose a second packaging protection cavity 7, used to protect their respective functionally sensitive areas. The solid isolation portion 32 is used to block the connection between the two packaging protection cavities. When the double-sided cap substrate 3 is made of glass, its excellent electrical insulation helps maintain the electrical performance of the acoustic filter chip and reduces parasitic effects. At the same time, the processing characteristics of glass allow it to precisely form the required recess and solid structure, ensuring the geometric accuracy of the packaging protection cavity. When silicon is used, its high coefficient of thermal expansion, which closely matches that of the acoustic filter chip, effectively alleviates thermal stress generated during temperature cycling, thus preventing relative deformation between the double-sided cap substrate 3 and the chip, and protecting the first functional sensitive area 4 and the second functional sensitive area 5 from mechanical stress. If ceramic is used, its high mechanical strength and thermal stability provide robust physical support for the entire package structure. Especially in subsequent bonding processes, it ensures that the physical support portion 31 and the physical isolation portion 32 maintain structural integrity under bonding pressure, effectively preventing pressure from being transmitted to the sensitive area through the cavity span region, thereby maintaining the performance stability of the acoustic filter chip. By selecting these materials, the double-sided cap substrate 3 provides stable physical support, ensuring the integrity of the first package protection cavity 6 and the second package protection cavity 7, and effectively isolating the two cavities. This material selection, combined with the aforementioned three-dimensional wafer-level packaging structure design, allows the package structure to maintain its intended geometry and function under external mechanical loads and thermal stress, fundamentally solving the technical problem of package structure deformation caused by improper substrate material selection, which in turn affects the performance of the sensitive area of ​​the acoustic filter chip.

[0059] In some preferred embodiments, the ratio of the depth of the first encapsulation protection cavity 6 to the thickness of the solid isolation portion 32 and the ratio of the depth of the second encapsulation protection cavity 7 to the thickness of the solid isolation portion 32 are both 1-2.

[0060] The depth of the first encapsulation protection cavity 6 refers to the dimension of the cavity formed by the first acoustic filter chip 1 and the first recess in the direction perpendicular to the plane of the acoustic filter chip. This depth can be precisely controlled in various ways. For example, the first recess can be formed by a precision etching process on the double-sided cap substrate 3, thereby directly determining the cavity depth. The thickness of the solid isolation portion 32 refers to the dimension of the continuous structure located between the first recess and the second recess in the direction perpendicular to the plane of the acoustic filter chip. This thickness can be precisely defined by controlling the overall thickness of the double-sided cap substrate 3 and the etching depth of the first and second recesses to ensure that a solid layer with a specific thickness is formed inside the double-sided cap substrate 3. Alternatively, a solid isolation portion 32 with a predetermined thickness can be formed by using a layered stacking and selective material removal manufacturing process. The ratio of the depth of the first encapsulation protection cavity 6 to the thickness of the solid isolation portion 32 and the ratio of the depth of the second encapsulation protection cavity 7 to the thickness of the solid isolation portion 32 are both limited to the range of 1-2, aiming to achieve a balance between the internal space requirements of the encapsulation cavity and the overall structural strength of the substrate.

[0061] This solution optimizes the reliability of 3D packaging from a structural mechanics perspective by precisely defining the ratio between the depth of the packaging cavity and the thickness of the solid isolation portion 32. As the core support and isolation structure of the double-sided cap substrate 3, the thickness of the solid isolation portion 32 directly determines the substrate's resistance to deformation under vertical pressure. By controlling the ratio of the packaging cavity depth to the thickness of the solid isolation portion 32 within the range of 1 to 2, sufficient material thickness is ensured in the solid isolation portion 32 to provide structural rigidity, while guaranteeing sufficient vibration space for the functionally sensitive area of ​​the acoustic filter chip. This ratio balances the contradiction between the internal space requirements of the packaging cavity and the overall structural strength of the substrate, enabling the solid isolation portion 32 to effectively resist pressure loads from both sides during double-sided bonding processes. This prevents structural weakness due to excessive cavity depth or stress transmission due to excessively thin isolation portion, thereby ensuring the working performance and structural integrity of the acoustic filter chip after packaging. This ratio setting allows the double-sided cap substrate 3 to effectively form a thickness-direction bonding support structure when acting as a double-sided intermediate cap body. In the subsequent second-side bonding process, the thickness-direction bearing path is used to transfer at least part of the bonding load, avoiding direct stress impact on the functionally sensitive area of ​​the acoustic filter chip.

[0062] Secondly, such as Figure 2 As shown, this application also provides a method for fabricating a three-dimensional wafer-level packaging structure, used to fabricate the three-dimensional wafer-level packaging structure provided in the first aspect. The method for fabricating the three-dimensional wafer-level packaging structure includes the following steps: S1. A first recess and a second recess are formed on the first and second sides of the double-sided cap substrate 3, respectively. The sum of the depth of the first recess and the depth of the second recess is less than the thickness of the double-sided cap substrate 3, so as to retain the solid isolation portion 32 located between the first recess and the second recess. The area of ​​the double-sided cap substrate 3 other than the first recess, the second recess and the solid isolation portion 32 constitutes the solid support portion 31. S2. Bond the first acoustic filter chip 1 to the first side of the physical support portion 31 so that the first acoustic filter chip 1 and the first recessed portion form the first encapsulation protection cavity 6. S3. Bond the second acoustic filter chip 2 to the second side of the physical support portion 31 so that the second acoustic filter chip 2 and the second recessed portion form a second encapsulation protection cavity 7.

[0063] In step S1, the formation of the first and second recesses aims to create spaces on both sides of the double-sided cap substrate 3 to accommodate the acoustic filter chip and form a protective encapsulation cavity. These recesses can be achieved through various microfabrication techniques, such as wet etching (e.g., etching a glass substrate with hydrofluoric acid or etching a silicon substrate with KOH solution) or dry etching (e.g., reactive ion etching, RIE), or by laser drilling or mechanical milling. The sum of the depths of the first and second recesses is less than the thickness of the double-sided cap substrate 3. This limitation ensures that there is always a partially penetrated material layer between the first and second recesses inside the double-sided cap substrate 3. This design is a key prerequisite for achieving subsequent physical isolation, preventing direct connection between the two recesses and thus providing the necessary physical isolation and structural integrity for the double-sided encapsulation structure. The solid isolation portion 32 is a continuous material layer inside the double-sided cap substrate 3. Its main function is to physically block the communication between the first encapsulation protection cavity 6 and the second encapsulation protection cavity 7, ensuring the independence and sealing of each cavity. In addition, the solid isolation portion 32 also provides important structural strength for the double-sided cap substrate 3, preventing deformation or cracking during subsequent processing or use. The area of ​​the double-sided cap substrate 3 other than the first recess, the second recess, and the solid isolation portion 32 constitutes the solid support portion 31. This solid support portion 31 is the area on the double-sided cap substrate 3 used for bonding with the acoustic filter chip. This area is usually located around the recess and its function is to provide a robust and flat bonding interface for the chip to withstand the mechanical pressure generated during the bonding process and effectively transfer these pressures to the non-sensitive areas of the substrate, thereby protecting the functionally sensitive areas of the acoustic filter chip from stress damage.

[0064] In step S2, the first acoustic filter chip 1 is bonded to the first side of the physical support portion 31. This step fixes the first acoustic filter chip 1 to the first side of the double-sided cap substrate 3. Various bonding techniques can be used, such as wafer-level bonding (e.g., eutectic bonding, glass paste bonding, polymer bonding) or chip-level bonding (e.g., thermoforming bonding, ultrasonic bonding). The purpose of bonding is to form a strong and sealed connection between the first acoustic filter chip 1 and the physical support portion 31 to ensure the integrity of the package. The first encapsulation protection cavity 6 is formed by bonding the first acoustic filter chip 1 to the first recess, creating a closed internal space, i.e., the first encapsulation protection cavity 6. This cavity provides a protected microenvironment for the functionally sensitive area of ​​the first acoustic filter chip 1, preventing it from being contaminated by the external environment (e.g., moisture, particulate matter) or affected by mechanical stress, thereby ensuring the normal operating performance of the chip.

[0065] In step S3, the second acoustic filter chip 2 is bonded to the second side of the physical support portion 31. This step is similar to S2, fixing the second acoustic filter chip 2 to the second side of the double-sided cap substrate 3. The bonding method can also employ wafer-level bonding or chip-level bonding techniques. This bonding process is usually performed after the first side bonding is completed. It may be necessary to flip, transfer, or support the bonded first side structure to ensure smooth bonding of the second side and effectively manage the stress generated during the bonding process. A second encapsulated protective cavity 7 is formed by bonding the second acoustic filter chip 2 to the second recess, creating a second enclosed internal space, i.e., the second encapsulated protective cavity 7. This cavity also provides protection for the functionally sensitive areas of the second acoustic filter chip 2, ensuring its performance and reliability after packaging.

[0066] This fabrication method, through ingenious step design, constructs a structure with specific mechanical support and cavity isolation functions on a double-sided capped substrate 3, and on this basis, achieves reliable bonding of the double-sided acoustic filter chip. The method first forms a first recess and a second recess on the first and second sides of the double-sided capped substrate 3, respectively. Crucially, by precisely controlling the depths of the first and second recesses, their sum is less than the overall thickness of the double-sided capped substrate 3. This design cleverly preserves a continuous solid isolation portion 32 within the substrate. This solid isolation portion 32 not only physically separates the first and second recesses, ensuring the independence between the subsequently formed first and second encapsulation protection cavities 6 and 7, but more importantly, it provides the necessary structural strength and rigidity for the entire double-sided capped substrate 3. Simultaneously, the area on the double-sided capped substrate 3 other than the recesses and the solid isolation portion 32 is explicitly defined as a solid support portion 31. This solid support portion 31 plays a vital role in the subsequent bonding process, providing a robust bonding interface and mechanical load-bearing area for the acoustic filter chip. After the double-sided capped substrate 3 has undergone structuring, the method proceeds to chip bonding. First, the first acoustic filter chip 1 is bonded to the solid support portion 31 on the first side of the double-sided capped substrate 3. This bonding process causes the first acoustic filter chip 1 and the first recessed portion to jointly enclose and form a first encapsulation protection cavity 6, thereby providing a protected microenvironment for the first functionally sensitive area 4 of the first acoustic filter chip 1. Subsequently, the bonded first-side structure undergoes necessary processing (such as flipping, transferring, or supporting), and then the second acoustic filter chip 2 is bonded to the solid support portion 31 on the second side of the double-sided capped substrate 3. Similarly, this bonding process causes the second acoustic filter chip 2 and the second recessed portion to jointly enclose and form a second encapsulation protection cavity 7, protecting the second functionally sensitive area 5 of the second acoustic filter chip 2. By constructing a substrate with support and isolation functions first, and then performing double-sided sequential bonding, this method effectively solves the problems of insufficient structural strength and bonding stress damage in double-sided packaging. During the bonding process, the bonding pressure can be effectively transmitted and dispersed through the physical support portion 31, preventing the pressure from acting directly on the functionally sensitive area of ​​the acoustic filter chip, thereby protecting the chip's performance. This fabrication method, combined with a three-dimensional wafer-level packaging structure, allows the double-sided cap substrate 3 to simultaneously provide independent packaging protection cavities and robust mechanical support, thus achieving high-density, high-reliability three-dimensional integration of the acoustic filter chip, significantly reducing the packaging area and thickness, and simplifying the process complexity.

[0067] As can be seen from the above, the three-dimensional wafer-level packaging structure and fabrication method provided in this application, by setting a solid support portion 31 and a solid isolation portion 32 in the double-sided cap substrate 3, provides a reliable mechanical support path for the bonding process while realizing double-sided chip integrated packaging, avoiding the load from directly acting on the functionally sensitive area, thereby solving the problem of poor reliability of double-sided packaging in the prior art, and has the advantages of compact structure, stable performance and good process compatibility.

[0068] In the embodiments provided in this application, it should be understood that relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0069] The above are merely embodiments of this application and are not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A three-dimensional wafer-level packaging structure, characterized in that, The three-dimensional wafer-level packaging structure includes: The first acoustic filter chip has a first functional sensitive area; The second acoustic filter chip has a second functional sensitive area; A double-sided cap substrate includes a solid support portion, a solid isolation portion, a first recessed portion, and a second recessed portion; The first recess and the second recess are respectively disposed on a first side and a second side opposite to each other on the double-sided cap substrate. The first acoustic filter chip is connected to the first side of the solid support portion, and the second acoustic filter chip is connected to the second side of the solid support portion. The first acoustic filter chip and the first recess form a first encapsulation protection cavity, and the second acoustic filter chip and the second recess form a second encapsulation protection cavity. The projection of the first functional sensitive area in the top view direction is located within the projection of the first encapsulation protection cavity in the top view direction, and the projection of the second functional sensitive area in the top view direction is located within the projection of the second encapsulation protection cavity in the top view direction. The solid isolation portion is a continuous structure located between the first recess and the second recess, and the solid isolation portion is used to block the communication between the first encapsulation protection cavity and the second encapsulation protection cavity.

2. The three-dimensional wafer-level packaging structure according to claim 1, characterized in that, The projection of the first recess in the top view direction overlaps with the projection of the second recess in the top view direction, and the projection of the first functional sensitive area in the top view direction overlaps with the projection of the second functional sensitive area in the top view direction.

3. The three-dimensional wafer-level packaging structure according to claim 1, characterized in that, The first acoustic filter chip is connected to the first side of the physical support through a first bonding support structure, and the second acoustic filter chip is connected to the second side of the physical support through a second bonding support structure. The projection of the first bonding support structure in the top view direction is outside the projection of the first functional sensitive area in the top view direction, and the projection of the second bonding support structure in the top view direction is outside the projection of the second functional sensitive area in the top view direction.

4. The three-dimensional wafer-level packaging structure according to claim 3, characterized in that, The projections of the first bonded support structure in the top view, the second bonded support structure in the top view, and the solid support portion in the top view overlap to form a pressure bearing path that avoids the first functionally sensitive area and the second functionally sensitive area.

5. The three-dimensional wafer-level packaging structure according to claim 4, characterized in that, Both the first bonding support structure and the second bonding support structure are made of conductive materials. The three-dimensional wafer-level packaging structure further includes a vertical conductive structure, a first horizontal conductive structure, and a second horizontal conductive structure. The vertical conductive structure penetrates the double-sided cap substrate and is located outside the first packaging protection cavity and the second packaging protection cavity. The first horizontal conductive structure is connected to one side of the first bonding support structure and the vertical conductive structure, respectively. The second horizontal conductive structure is connected to the other side of the second bonding support structure and the vertical conductive structure, respectively.

6. The three-dimensional wafer-level packaging structure according to claim 5, characterized in that, The vertical conductive structure includes conductive metal pillars.

7. The three-dimensional wafer-level packaging structure according to claim 1, characterized in that, The first recess is directly opposite the second recess.

8. The three-dimensional wafer-level packaging structure according to claim 1, characterized in that, The double-sided cap substrate is made of glass, silicon, or ceramic.

9. The three-dimensional wafer-level packaging structure according to claim 1, characterized in that, The ratio of the depth of the first encapsulation protection cavity to the thickness of the solid isolation portion and the ratio of the depth of the second encapsulation protection cavity to the thickness of the solid isolation portion are both 1-2.

10. A method for fabricating a three-dimensional wafer-level packaging structure, characterized in that, The method for fabricating the three-dimensional wafer-level packaging structure is used to fabricate the three-dimensional wafer-level packaging structure according to claim 1. The method for fabricating the three-dimensional wafer-level packaging structure includes the following steps: S1. A first recess and a second recess are formed on the first and second sides of the double-sided cap substrate, respectively; the sum of the depths of the first recess and the second recess is less than the thickness of the double-sided cap substrate, so as to retain a solid isolation portion between the first recess and the second recess, and the area of ​​the double-sided cap substrate other than the first recess, the second recess and the solid isolation portion constitutes a solid support portion. S2. Bond the first acoustic filter chip to the first side of the physical support portion so that the first acoustic filter chip and the first recessed portion form a first encapsulation protection cavity. S3. Bond the second acoustic filter chip to the second side of the physical support portion, so that the second acoustic filter chip and the second recessed portion form a second encapsulation protection cavity.

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