Cavity package structure of radio frequency filter and preparation method thereof

Abstract

The application provides a cavity packaging structure of a radio frequency filter and a preparation method thereof, and comprises a packaging substrate, a green oil layer, a glue layer and a radio frequency front-end component; the green oil layer is arranged on the packaging substrate, the radio frequency front-end component is connected and arranged on the green oil layer through the glue layer, and a closed cavity is formed between the packaging substrate, the green oil layer, the glue layer and the radio frequency front-end component; one side of the radio frequency front-end component provided with a functional circuit is located in the cavity. The filter circuit is protected in a closed cavity by surrounding the filter with glue.

Description

Technical Field

[0001] This invention relates to wafer-level packaging technology, specifically to a cavity packaging structure for an RF filter and its fabrication method. Background Technology

[0002] Existing technologies typically employ lamination or a combination of lamination and molding to shape the cavity. During the lamination process, the cavity is susceptible to contamination, which can lead to damage to the filter chip's circuitry. After lamination, stress concentration at the bottom gap opening of the filter can cause the thin film in that area to crack, resulting in damage to the cavity structure and consequently deteriorating the filter chip's performance.

[0003] Patent document CN112688655A discloses a filter wafer-level packaging process and structure. The filter wafer includes a substrate, with functional areas and multiple pads disposed on the upper surface of the substrate. The filter wafer-level packaging process includes: forming a groove on one side of a silicon wafer to form a cover wafer; bonding the side of the cover wafer with the groove to the upper side of the substrate using an adhesive layer to form a mating body, with the functional areas accommodated in the space enclosed by the substrate and the groove; forming blind vias on the mating body from the cover wafer side to expose the conductive layer of the pads; and electrically connecting micro-bump solder joints to the conductive layer. However, this patent document involves multiple processes such as bonding, thinning, electroplating, coating, etching, and photolithography, making the fabrication process complex and difficult, and significantly increasing the packaging cost of the filter chip.

[0004] Patent document CN114499433A discloses a cavity filter packaging structure and its manufacturing method. This packaging structure includes a filter chip, a cap layer, and a sealing structure. The sealing structure forms a closed ring on the non-resonant region of the filter chip. Bumps are provided above the chip pads of the filter chip, which are located inside or outside the closed ring. The cap layer includes a reinforcing structure layer and annular and block metal structures embedded in the reinforcing structure layer at intervals. The cap layer and the filter chip are aligned via an alignment structure, which bonds the sealing structure and bumps to the annular and block metal structures, forming a cavity above the resonant region. A metal lead is provided on the surface of the cap layer away from the cavity. However, this patent document differs from the technical solution of this application. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the purpose of this invention is to provide a cavity packaging structure for a radio frequency filter and its fabrication method.

[0006] A cavity packaging structure for a radio frequency filter according to the present invention includes: a packaging substrate, an oil-based coating, an adhesive layer, and a filter.

[0007] The green varnish layer is disposed on the encapsulation substrate, and the filter is connected to the green varnish layer through the adhesive layer. A closed cavity is formed between the encapsulation substrate, the green varnish layer, the adhesive layer, and the filter.

[0008] The filter has a functional circuitry on one side located inside the cavity.

[0009] Preferably, there is a gap opening between the upper surface of the green oil layer and the lower surface of the filter in a direction perpendicular to the upper surface of the green oil layer.

[0010] Preferably, the adhesive layer is disposed around the outer side wall of the filter;

[0011] The thickness of the adhesive layer is greater than the vertical opening length of the gap; the vertical height of the upper surface of the adhesive layer is less than the height of the upper surface of the filter.

[0012] Preferably, the adhesive layer includes an integrally formed surrounding structure and a filling structure; the surrounding structure is disposed around the outer sidewall of the filter;

[0013] The thickness of the surrounding structure is greater than the vertical opening length of the gap; the vertical height of the upper surface of the surrounding structure is less than the height of the upper surface of the filter.

[0014] The filling structure is filled within the gap opening.

[0015] Preferably, solder pads are connected and disposed on the packaging substrate;

[0016] A metal pillar is provided on one side of the filter where the functional circuitry is provided, and a solder ball is provided at the end of the metal pillar away from the filter. The solder ball is connected to the solder pad.

[0017] The metal pillar, the solder pad, and the solder ball are all located within the enclosed cavity.

[0018] Preferably, the metal pillar is a tin pillar or a copper pillar.

[0019] Preferably, the opening length of the gap in the vertical direction is 0 to 25 μm.

[0020] Preferably, the packaging substrate is provided with leads, and the filter is electrically connected to the leads through the solder pads and then connected to an external electrical signal or ground.

[0021] Preferably, the encapsulation substrate is an organic encapsulation substrate or a ceramic encapsulation substrate.

[0022] The present invention also provides a method for fabricating a cavity packaging structure for an RF filter, comprising the following steps:

[0023] Substrate processing steps: Provide a packaging substrate, in which functional circuits are provided, and on the surface of the packaging substrate, several solder pads are provided.

[0024] Green oil coating step: Green oil coating forms a green oil layer, which forms a groove structure with the encapsulation substrate. Solder pads are placed inside the groove structure, and there is a gap between the solder pads and the green oil layer.

[0025] Chip fabrication steps: Provide a filter chip, and set a metal pillar on the side of the filter chip where the functional circuit is set, and set a solder ball on the end of the metal pillar away from the filter chip;

[0026] Chip mounting steps: Mount the filter chip by soldering the solder balls on the filter to the pads. In a direction perpendicular to the upper surface of the solder mask, create a gap between the upper surface of the solder mask and the lower surface of the filter.

[0027] Adhesive application step: Apply adhesive in dots, and the adhesive surrounds the filter chip to form an adhesive layer, so that the adhesive layer, green oil layer, filter and packaging substrate form a closed cavity.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. This invention protects the filter circuitry by surrounding the filter with glue within a closed cavity;

[0030] 2. By setting a green oil layer, the present invention can protect the functional circuits on the package substrate it covers, and also provide support for subsequent filters to a certain extent.

[0031] 3. By setting a gap opening, the present invention can ensure a good electrical connection between the solder balls of the filter and the pads on the packaging substrate, so as to avoid the filter being placed on the green solder mask layer, which can easily cause gaps between the solder balls and the pads and lead to poor contact.

[0032] 4. For single or multiple filters, this invention replaces the existing film coating process with adhesive spraying around the filter to complete the cavity shaping, thereby solving problems such as film breakage (gap position) and poor mechanical stability of the cavity, and greatly reducing the packaging cost;

[0033] 5. For the SIP (system in package) module of the RF front-end module, other devices are also set on the packaging substrate. When the devices on the packaging substrate are coated, the presence of the adhesive layer ensures that the film covering the filter surface and surrounding area does not break. Attached Figure Description

[0034] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0035] Figure 1 This is a top view of the cavity packaging structure of the radio frequency filter of the present invention;

[0036] Figure 2 for Figure 1 Cross-sectional view along line aa;

[0037] Figure 3 This is a schematic diagram of the packaging substrate in Example 1;

[0038] Figure 4 This is a schematic diagram of the filter chip structure;

[0039] Figure 5 This is a schematic diagram of the assembly of the encapsulation substrate and the green oil layer in Example 1;

[0040] Figure 6 and Figure 7 This is a schematic diagram of the filter chip mounting in Example 1;

[0041] Figure 8 This is a schematic diagram of the cavity encapsulation structure when the gap opening size is zero.

[0042] Figure 9 and Figure 10 Schematic diagrams showing different settings for the adhesive layer;

[0043] Figure 11 This is a schematic diagram of the packaging substrate in Example 2;

[0044] Figure 12 This is a schematic diagram of the assembly of the substrate and the green oil layer in Example 2;

[0045] Figure 13 This is a schematic diagram of the glue application in Example 2;

[0046] Figure 14 and Figure 15 This is a schematic diagram of the filter chip mounting in Example 2.

[0047] The diagram shows:

[0048] Packaging substrate 101, solder pad 106

[0049] Green oil layer 102, solder ball 107

[0050] Enclosed cavity 103, copper column 108

[0051] Adhesive layer 104, gap opening 109

[0052] RF front-end component 105 Detailed Implementation

[0053] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0054] Example 1:

[0055] like Figure 1 and Figure 2 As shown, this embodiment provides a cavity packaging structure for an RF filter, including: a packaging substrate 101, an oleophobic layer 102, an adhesive layer 104, and a filter 105. The oleophobic layer 102 is disposed on the packaging substrate 101, and the filter 105 is connected to the oleophobic layer 102 through the adhesive layer 104. A closed cavity 103 is formed between the packaging substrate 101, the oleophobic layer 102, the adhesive layer 104, and the filter 105. The side of the filter 105 with functional circuits is located inside the cavity.

[0056] A solder pad 106 is connected and disposed on the packaging substrate 101. A metal pillar 108 is disposed on the side of the filter 105 where the functional circuitry is disposed. A solder ball 107 is disposed at the end of the metal pillar 108 away from the filter. The solder ball 107 is connected and disposed to the solder pad 106. The metal pillar 108, the solder pad 106, and the solder ball 107 are all located within the enclosed cavity 103. The metal pillar 108 is a solder pillar or a copper pillar.

[0057] A gap opening 109 exists between the upper surface of the green oil layer 102 and the lower surface of the filter 105 in a direction perpendicular to the upper surface of the green oil layer 102. An adhesive layer 104 partially surrounds the outer wall of the filter 105. The thickness of the adhesive layer 104 is greater than the vertical opening length of the gap opening 109, and the vertical height of the upper surface of the adhesive layer 104 is less than the vertical height of the upper surface of the filter 105. The vertical opening length of the gap opening 109 is 0–25 μm.

[0058] The packaging substrate 101 has leads, and the filter 105 is electrically connected to the leads via solder pads 106 to connect to external electrical signals or ground. The packaging substrate 101 is an organic packaging substrate or a ceramic packaging substrate.

[0059] This embodiment also provides a method for fabricating a cavity packaging structure for an RF filter, which, based on the above-mentioned cavity packaging structure for an RF filter, includes the following steps:

[0060] Substrate processing steps: Provide a packaging substrate 101, in which functional circuits are provided and several solder pads are provided on the surface of the packaging substrate 101.

[0061] Green oil coating step: Green oil coating forms a green oil layer 102, so that the green oil layer 102 and the encapsulation substrate 101 form a groove structure. A solder pad 106 is placed inside the groove structure, and there is a gap between the solder pad 106 and the green oil layer 102; the gap is 5~20um.

[0062] Chip fabrication steps: Provide a filter 105 chip, and set a metal pillar 108 on the side of the filter 105 chip where the functional circuit is set, and set a solder ball 107 at the end of the metal pillar 108 away from the filter 105 chip.

[0063] Chip mounting steps: Mount the filter 105 chip, solder the solder balls 107 on the filter 105 to the pads 106, and make a gap opening 109 between the upper surface of the green solder layer 102 and the lower surface of the filter 105 in a direction perpendicular to the upper surface of the green solder layer 102.

[0064] Adhesive application step: Apply adhesive in dots, and the adhesive surrounds the filter 105 chip to form an adhesive layer 104, so that the adhesive layer 104, the green oil layer 102, the filter 105 and the packaging substrate 101 form a closed cavity 103.

[0065] In other embodiments, a PA, LNA, and Switch are also provided at the location of the filter, which together constitute an RF front-end assembly, and a coating is provided on the RF front-end assembly.

[0066] Example 2:

[0067] The difference between this embodiment and embodiment 1 is that the adhesive layer 104 includes an integrally formed surrounding structure and a filling structure. The surrounding structure is disposed around the outer wall of the filter 105, and the thickness of the surrounding structure is greater than the opening length of the gap opening 109 in the vertical direction. The height of the upper surface of the surrounding structure in the vertical direction is less than the height of the upper surface of the filter 105, and the filling structure is disposed within the gap opening 109.

[0068] Example 3:

[0069] Those skilled in the art can understand this embodiment as a more specific description of Embodiment 1 and Embodiment 2.

[0070] This embodiment provides a cavity packaging structure for an RF filter, including: a packaging substrate 101, an oil-based coating 102; a cavity 103, an adhesive layer 104, a filter, solder pads 106, solder balls 107, and copper pillars 108.

[0071] The location of the filter is not limited to a filter itself; it can also be other components of the RF front-end module, such as PA / LNA / Switch, etc.

[0072] like Figure 2 As shown, the packaging substrate has internal leads. The filter can be electrically connected to the internal leads of the packaging substrate via solder pads to connect to external electrical signals or ground. A certain gap opening 109 is maintained vertically between the lower surface of the solder mask layer and the upper surface of the filter chip. The gap opening 109 is preferably in the range of 0-25µm. Setting the gap opening 109 ensures good electrical connection between the filter's solder balls and the solder pads on the packaging substrate; otherwise, if the filter is placed on the solder mask, a gap opening 109 may easily form between the solder balls and the solder pads, leading to poor contact. Figure 1 As shown, the packaging substrate can extend in all directions, and RF front-end module devices other than filters, such as PA / LNA / Switch, can also be placed on the packaging substrate; the arrangement and size of the copper pillars in the figure do not represent actual applications, but are only to illustrate the existence of copper pillars.

[0073] like Figure 3 As shown, the encapsulation substrate can be an organic encapsulation substrate or a ceramic encapsulation substrate. In a preferred embodiment, a resin encapsulation substrate (belonging to the organic system) is used. Metal leads are provided inside the encapsulation substrate, and solder pads are provided on the upper surface of the encapsulation substrate. The solder pads are made of metal with good conductivity.

[0074] like Figure 4 As shown, the filter chip has copper pillars with a height of 25–50 μm and solder balls with a height of 25–60 μm; alternatively, copper pillars can be omitted, and solder pillars of 25–80 μm (with spherical ends) can be directly used. The former configuration provides better conductivity; the latter is simpler to manufacture. Additionally, functional circuitry is located on the side of the filter with the copper pillars and solder balls.

[0075] like Figure 5 As shown, green solder mask is applied around the substrate to form a groove, which forms a closed cavity with the subsequent filter and adhesive. Functionally, the green solder mask can protect the functional circuitry on the packaged substrate it covers, and can also provide some support for the subsequent filter.

[0076] like Figures 6-8 As shown, in chip mounting, the filter chip is flipped and soldered onto the packaging substrate. After mounting, there is a certain gap opening 109 in the vertical direction (refer to...). Figure 7The two dashed lines in the diagram indicate that the gap opening 109 ranges from 0 to 25 μm. Ideally, the gap opening 109 is 0 μm and the solder ball makes good contact with the pad. A smaller gap opening 109 makes the cavity more sealed after subsequent adhesive application. In actual processes, when the gap opening 109 is 0 μm, there is a possibility that the chip may be suspended on the solder mask. If it is suspended, the solder ball and the pad will have poor electrical contact, leading to device failure. Setting a certain gap opening 109 can ensure good electrical connection between the pad and the solder ball. In addition, the outer boundary of the filter should exceed the inner boundary of the cavity (refer to the two dashed lines in the diagram). Figure 7 (The vertical dotted lines in the text) are used to ensure that the green paint can provide support after the glue is applied.

[0077] like Figure 9 and Figure 10 As shown, adhesive is applied by dotting the filter chip using a dotting process, referring to... Figure 1 In a preferred embodiment, the adhesive is made of epoxy resin; the height of the adhesive is not less than the height of the gap opening 109 and does not exceed the height of the upper surface of the filter chip; the adhesive has a certain degree of fluidity and good viscosity. The fluidity allows the adhesive to fully surround the filter and seal the gap opening 109, while the good viscosity ensures a firm bond between the filter and the solder mask and prevents breakage during subsequent processes that could affect the cavity's airtightness; the filling range of the adhesive on the gap opening 109 is within... Figures 9-10 Between the indicated ranges: Figure 9 If the glue is applied to the outer boundary of the gap opening 109, the dispensing process is simpler. Figure 10 If the glue completely fills the gap opening 109 at the inner boundary of the green oil, the mechanical stability of the cavity will be higher.

[0078] At this point, the packaging substrate, solder mask, adhesive, and filter chip are arranged to form a closed cavity, completing the cavity shaping. This closed cavity design helps prevent packaging material from contaminating the filter chip during the packaging process. This is especially important because the filter surface has very precise circuitry (refer to the attached diagram of the filter chip). Contamination can cause defects such as short circuits, open circuits, or detachment, leading to performance degradation of the filter chip.

[0079] Example 4:

[0080] like Figures 11-15 As shown, the difference between this embodiment and embodiment 3 is that the order of chip mounting and adhesive spraying is reversed, with adhesive spraying performed first and then chip mounting performed.

[0081] This invention protects the filter circuitry by surrounding the filter with glue, placing it within a closed cavity.

[0082] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0083] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A cavity packaging structure for a radio frequency filter, characterized in that, include: The package substrate (101), the green oil layer (102), the adhesive layer (104), and the filter (105); The green oil layer (102) is disposed on the encapsulation substrate (101), and the filter (105) is connected to the green oil layer (102) through the adhesive layer (104). A closed cavity (103) is formed between the encapsulation substrate (101), the green oil layer (102), the adhesive layer (104) and the filter (105). The filter (105) has a side with functional circuitry located inside the cavity; In a direction perpendicular to the upper surface of the green oil layer (102), there is a gap opening (109) between the upper surface of the green oil layer (102) and the lower surface of the filter (105). A solder pad (106) is connected and disposed on the packaging substrate (101). A metal pillar (108) is provided on one side of the filter (105) where the functional circuit is provided. A solder ball (107) is provided at the end of the metal pillar (108) away from the filter. The solder ball (107) is connected to the solder pad (106). The metal pillar (108), the solder pad (106), and the solder ball (107) are all located within the enclosed cavity (103); The green oil layer (102) and the encapsulation substrate (101) form a groove structure; By setting the gap opening (109), the solder balls (107) of the filter can be electrically connected to the pads (106) on the packaging substrate (101).

2. The cavity packaging structure of the radio frequency filter according to claim 1, characterized in that, The adhesive layer (104) is partially disposed around the outer wall of the filter (105); The thickness of the adhesive layer (104) is greater than the vertical opening length of the gap opening (109); the vertical height of the upper surface of the adhesive layer (104) is less than the height of the upper surface of the filter (105).

3. The cavity packaging structure of the radio frequency filter according to claim 1, characterized in that, The adhesive layer (104) includes an integrally formed surrounding structure and a filling structure; the surrounding structure is disposed around the outer wall of the filter (105); The thickness of the surrounding structure is greater than the vertical opening length of the gap opening (109); the height of the upper surface of the surrounding structure in the vertical direction is less than the height of the upper surface of the filter (105); The filling structure is filled within the gap opening (109).

4. The cavity packaging structure of the radio frequency filter according to claim 1, characterized in that, The metal pillar (108) is a tin pillar or a copper pillar.

5. The cavity packaging structure of the RF filter according to claim 1, characterized in that, The gap opening (109) has an opening length of 25 μm in the vertical direction.

6. The cavity packaging structure of the radio frequency filter according to claim 1, characterized in that, The packaging substrate (101) is provided with leads, and the filter (105) is electrically connected to the leads through the solder pad (106) and then connected to an external electrical signal or ground.

7. The cavity packaging structure of the radio frequency filter according to claim 1, characterized in that, The encapsulation substrate (101) is an organic encapsulation substrate or a ceramic encapsulation substrate.

8. A method for fabricating a cavity packaging structure for an RF filter, characterized in that, The cavity packaging structure of the radio frequency filter according to any one of claims 1 to 7 includes the following steps: Substrate processing steps: Provide a packaging substrate (101), in which functional circuits are provided and several solder pads are provided on the surface of the packaging substrate (101); Green oil coating step: Green oil coating forms a green oil layer (102), so that the green oil layer (102) and the encapsulation substrate (101) form a groove structure, and a solder pad (106) is set inside the groove structure, and there is a gap between the solder pad (106) and the green oil layer (102). Chip fabrication steps: Provide a filter (105) chip, and set a metal pillar (108) on the side of the filter (105) chip where the functional lines are set, and set a solder ball (107) at the end of the metal pillar (108) away from the filter (105) chip. Chip mounting steps: Mount the filter (105) chip, solder the solder balls (107) on the filter (105) to the pads (106), and make a gap opening (109) between the upper surface of the green solder layer (102) and the lower surface of the filter (105) in a direction perpendicular to the upper surface of the green solder layer (102). Adhesive application step: Apply adhesive and surround the filter (105) chip to form an adhesive layer (104), so that the adhesive layer (104), the green oil layer (102), the filter (105) and the packaging substrate (101) form a closed cavity (103).

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