Low dielectric constant film of sandwich structure

Abstract

This invention provides a sandwich-structured low dielectric constant thin film, comprising a lower (1) cellulose nanofiber layer, an upper (3) cellulose nanofiber layer, and a middle (2) cellulose nanofiber / hollow microsphere composite layer. The lower (1) and upper (3) cellulose nanofiber layers have a network structure with pore sizes distributed in the range of 10-200 nm, formed by interlaced cellulose nanofibers with diameters of 3-100 nm. The middle (2) layer has a bilevel pore structure composed of large-sized closed pores of hollow microspheres and large-sized open pores of the cellulose fiber network, with the ratio of large-sized closed pores to large-sized open pores in the range of 0.5-2. This sandwich structure design simultaneously endows the material with low dielectric constant and good mechanical properties, solving the problem of balancing dielectric and mechanical properties in traditional homogeneous thin films. It is particularly suitable for insulating encapsulation of 5G high-frequency circuit substrates.

Description

Technical Field

[0001] This utility model relates to the field of insulating materials for electronic devices, specifically to a sandwich-structured low dielectric constant thin film, which is particularly suitable for high-frequency communication devices (such as 5G antennas, millimeter-wave radar), wearable electronic devices, millimeter-wave antennas and other fields. Background Technology

[0002] With the rapid development of 5G communication technology and other fields, high-frequency signal transmission places stringent demands on the dielectric properties of insulating materials. Traditional dielectric materials (such as polyimide k≈3.5 and epoxy resin k≈4.0) experience significantly increased polarization losses at high frequencies, leading to increasingly prominent signal attenuation and transmission delay problems. Thin film materials with low dielectric constants (k<3.0) and low dielectric losses (tanδ<0.01) have become key to overcoming the bottleneck of high-frequency signal transmission. Introducing air pores or lightweight fillers is a conventional approach to reducing the dielectric constant, but it can lead to insufficient mechanical strength and poor flexibility. Therefore, by controlling the distribution of structural components in the thin film to achieve an optimized structure, it is hoped that a balance between the dielectric and mechanical properties of the material can be achieved. Utility Model Content

[0003] The purpose of this invention is to provide a low dielectric constant thin film with a sandwich structure. The low dielectric constant thin film provided in this application combines low dielectric constant with good mechanical properties.

[0004] Therefore, this application provides the following aspects:

[0005] <1> A sandwich-structured low dielectric constant thin film, comprising a lower cellulose nanofiber layer 1, an upper cellulose nanofiber layer 3, and a middle cellulose nanofiber / hollow microsphere composite layer 2, characterized in that:

[0006] The lower cellulose nanofiber layer 1 and the upper cellulose nanofiber layer 3 have a network structure with a pore size distribution of 10-200 nm, formed by interlaced cellulose nanofibers with a diameter of 3-100 nm.

[0007] The intermediate layer 2 has a bilevel porous structure consisting of large-sized closed pores of hollow microspheres and large-sized open pores of the cellulose fiber network, and the ratio of the large-sized closed pores to the large-sized open pores is in the range of 0.5-2.

[0008] <2> The low dielectric constant thin film with the sandwich structure described above is characterized in that the thicknesses of the lower cellulose nanofiber layer 1 and the upper cellulose nanofiber layer 3 are 5-500 μm, respectively.

[0009] <3> The low dielectric constant thin film with a sandwich structure according to any one of the above is characterized in that the thickness of the middle layer 2 cellulose nanofiber / hollow microsphere composite layer is 50-1000 μm.

[0010] <4> The low dielectric constant thin film with a sandwich structure according to any one of the above claims is characterized in that the average particle size of the hollow microspheres 21 is 5-50 μm, and D 10 Greater than 3 μm, D 90 It is less than 55 μm and the wall thickness is 1 / 10 to 1 / 100 of its outer diameter.

[0011] <5> The low dielectric constant thin film with a sandwich structure according to any of the above is characterized in that the intermediate layer 2 further comprises channels formed by stacking hollow microspheres of different particle sizes, and the channels are a network filled with cellulose nanofibers.

[0012] <6> The low dielectric constant thin film with a sandwich structure according to any one of the above features a hollow microsphere 21 uniformly distributed in the intermediate layer 2, wherein the volume of the hollow microsphere 21 accounts for 30-70% of the volume of the intermediate layer 2.

[0013] <7> The low dielectric constant thin film with a sandwich structure according to any one of the above features, characterized in that the pore size of the large-size closed pore is in the range of 1-60 μm, and the pore size of the large-size open pore is in the range of 1-20 μm.

[0014] <8> The low dielectric constant thin film with a sandwich structure according to any one of the above is characterized in that, in the middle layer 2 cellulose nanofiber / hollow microsphere composite layer, the diameter of the cellulose nanofiber is in the range of 3-100 nm.

[0015] <9> The low dielectric constant thin film with a sandwich structure according to any of the above is characterized in that the thickness of the intermediate layer 2 is greater than the thickness of the lower layer 1 and greater than the thickness of the upper layer 3.

[0016] <10> The low dielectric constant thin film with a sandwich structure according to any one of the above claims is characterized in that the low dielectric constant thin film has an integral structure without interlayer interfaces. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the sandwich structure low dielectric constant thin film of the present invention, wherein: 1 is the lower cellulose nanofiber layer, 2 is the middle cellulose nanofiber / hollow microsphere composite layer, 3 is the upper cellulose nanofiber layer, and 21 is a hollow microsphere.

[0018] Figure 2 This is a scanning electron microscope image of the middle layer of the sandwich structure low dielectric constant film of the present invention. The middle layer has a bilevel pore structure consisting of large-sized closed pores of hollow microspheres and large-sized open pores of the bacterial cellulose fiber network.

[0019] Figure 3 The image shows an interlayer focused ion beam scanning electron microscope image of the sandwich structure low dielectric constant thin film described in this invention, illustrating an example of a structure where the material has an integrated structure without interlayer interfaces.

[0020] Figure 4 The height profile scan of the surface of the low dielectric constant thin film with the sandwich structure described in this invention shows that its surface undulations are at the nanometer level. Detailed Implementation

[0021] To more clearly illustrate the purpose, technical solution, and advantages of this utility model, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the utility model and are not intended to limit its scope. Furthermore, the technical features involved in the various embodiments of this utility model described below can be combined with each other as long as they do not conflict with each other.

[0022] like Figure 1 As shown, this utility model provides a sandwich structure low dielectric constant film, including a lower layer 1 and an upper layer 3 cellulose nanofiber layers, and a middle layer 2 cellulose nanofiber / hollow microsphere composite layer, wherein the oblique line filling density represents the difference in cellulose content.

[0023] In this invention, the terms "upper layer," "middle layer," and "lower layer" are distinguished by the composition and location of each layer, but do not necessarily imply that there is an interlayer interface between them. The upper and lower layers are composed of bacterial cellulose nanofiber layers, while the middle layer is a composite layer composed of bacterial cellulose nanofibers and hollow microspheres.

[0024] In this application, the low dielectric constant of the film is primarily due to the introduction of a large number of pores, particularly a "gradient pore structure." The "gradient pore structure" refers to a bilevel pore structure that transitions from small-sized open pores in the upper bacterial cellulose nanofiber layer to large-sized closed pores in the middle hollow glass microspheres combined with large-sized open pores in the fiber network, and then back to small-sized open pores in the lower bacterial cellulose nanofiber layer. Therefore, the "large" in the terms "large-sized closed pores" and "large-sized open pores" referring to the middle layer is relative to the pore size of the upper and lower layers. The upper and lower cellulose nanofiber layers are 5-500 μm thick and consist of a network structure with pore sizes distributed in the 10-200 nm range, formed by interlaced cellulose nanofibers with diameters of 3-100 nm, thereby introducing air into the film. The middle cellulose nanofiber / hollow microsphere composite layer is 50-1000 μm thick. An example of the hollow microspheres is glass microspheres. The average particle size of the hollow microspheres is 5-50 μm, and D... 10 Greater than 3 μm, D 90 The microspheres are less than 55 μm in diameter, with a wall thickness of 1 / 10 to 1 / 100 of their outer diameter. The volume fraction of hollow microspheres is 30-70%. The introduction of a large number of closely packed hollow microspheres introduces numerous closed pores, while only a small amount of cellulose nanofibers is needed to achieve efficient bonding and assembly of the hollow microspheres, resulting in a fiber network with large-sized open pores. This high-porosity structure endows the cellulose / hollow microsphere film with an extremely low dielectric constant.

[0025] Furthermore, the upper and lower cellulose nanofiber layers enhance the material's mechanical strength. In composites of cellulose nanofibers and hollow microspheres, the mechanical properties originate from fiber-fiber and fiber-hollow microsphere interactions. Since the diameter of the hollow microspheres is much larger than that of the bacterial cellulose nanofibers, the interaction between them is very limited compared to fiber-fiber interactions; therefore, the strength of the cellulose nanofiber network determines the material's mechanical properties. Compared to a homogeneous mixture of cellulose nanofibers and hollow microspheres, the low-dielectric-constant film of this invention exhibits a higher hydrogen bond density in the cellulose nanofiber network, resulting in a stronger network density and endowing the low-dielectric-constant film with excellent mechanical strength.

[0026] The upper and lower bacterial cellulose nanofiber layers also improve the smoothness of the material. The two layers of cellulose nanofiber reduce the micron-level undulations caused by the hollow microspheres to the nanometer level (see appendix). Figure 4 ).

[0027] Due to the finely aggregated structure of the orderly and tightly arranged semi-crystalline cellulose chains in cellulose nanofibers, they have an extremely low coefficient of thermal expansion, and this advantage is inherited by thin films with low dielectric constants.

[0028] The thin film obtained by this invention has a low dielectric constant of at least 2.5 (at 1 MHz), and can even reach below 1.4 (at 1 MHz).

[0029] Because of the special structural features mentioned above, this invention can design a thin film material that has a low dielectric constant, good mechanical properties, flatness, and an extremely low coefficient of thermal expansion. This solves the problem that traditional homogeneous thin films cannot achieve both dielectric and mechanical properties, and is especially suitable for the insulating encapsulation of 5G high-frequency circuit boards.

Claims

1. A sandwich-structured low dielectric constant thin film, comprising a lower (1) cellulose nanofiber layer and an upper (3) cellulose nanofiber layer, and an intermediate layer (2), characterized in that: The lower (1) cellulose nanofiber layer and the upper (3) cellulose nanofiber layer have a network structure with a pore size distribution of 10-200 nm formed by interlaced cellulose nanofibers with a diameter of 3-100 nm, and The intermediate layer (2) has a bilevel pore structure consisting of large-sized closed pores of hollow microspheres and large-sized open pores of cellulose nanofiber fiber network, and the ratio of the large-sized closed pores to the large-sized open pores is in the range of 0.5-2.

2. The low dielectric constant thin film of sandwich structure according to claim 1, wherein The thicknesses of the lower (1) cellulose nanofiber layer and the upper (3) cellulose nanofiber layer are 5-500 μm, respectively.

3. The low dielectric constant thin film of sandwich structure according to claim 1, wherein The thickness of the intermediate layer (2) is 50-1000 μm.

4. The low dielectric constant thin film of sandwich structure according to claim 1, wherein The hollow microspheres (21) have an average particle diameter of 5 to 50 μm, and D 10 greater than 3 μm, D 90 less than 55 μm, and a wall thickness of 1 / 10 to 1 / 100 of the outer diameter thereof.

5. The low dielectric constant thin film of sandwich structure according to claim 1, wherein The intermediate layer (2) also includes channels formed by stacking hollow microspheres of different particle sizes, and the channels are a network filled with the cellulose nanofibers.

6. The low dielectric constant thin film with a sandwich structure according to claim 1, characterized in that, Hollow microspheres (21) are uniformly distributed in the intermediate layer (2).

7. The low dielectric constant thin film of sandwich structure according to claim 1, wherein The diameter of the large-size closed pore is in the range of 1-60 μm, and the diameter of the large-size open pore is in the range of 1-20 μm.

8. The low dielectric constant thin film of sandwich structure according to claim 1, wherein In the intermediate layer (2), the diameter of the cellulose nanofibers is in the range of 3-100 nm.

9. The low dielectric constant thin film of sandwich structure according to claim 1, wherein The thickness of the intermediate layer (2) is greater than the thickness of the lower layer (1) and greater than the thickness of the upper layer (3).

10. The low dielectric constant thin film of sandwich structure according to claim 1, wherein The low dielectric constant thin film has an integrated structure without interlayer interfaces.

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