High dielectric constant, low dielectric loss aluminum-polymer composites and methods of making the same

Abstract

High dielectric constant, low dielectric loss polymer-based composite material has important application in electronic industry, especially embedded circuit. The application discloses a high dielectric constant, low dielectric loss aluminum-polymer composite material and a preparation method thereof. The composite material is prepared from surface passivated aluminum powder and liquid polymer monomer by the following method: surface passivated aluminum powder is applied with a certain pressure to form aluminum powder body, and then is immersed in liquid polymer monomer. After the liquid fills the pores in the aluminum powder body, in-situ solidification is carried out to obtain the aluminum-polymer composite material. The aluminum-polymer composite material has high dielectric constant, low dielectric loss and good dielectric performance temperature stability, and is easy to be machined and compatible with PCB manufacturing process, and can be widely applied to modern electronic industry as high-performance embedded capacitor. Meanwhile, the material preparation process is simple, low in cost and stable in performance, and is beneficial to scale production.

Description

Technical Field

[0001] This invention relates to polymer-based dielectric composite materials applicable to the modern electronics industry, and more particularly to an aluminum-polymer composite material with high dielectric constant and low dielectric loss for embedded capacitors, and a method for preparing the same. Background Technology

[0002] In modern electrical and electronic equipment, passive components typically occupy more than 40% of the surface area of ​​printed circuit boards (PCBs). Embedding passive components, especially capacitors, into PCBs can significantly reduce circuit size and achieve miniaturization of electronic devices, as well as reduce solder joints and enhance the reliability of circuit systems. This poses a significant challenge to dielectric materials that simultaneously possess high dielectric constant, low dielectric loss, and good PCB compatibility. Metal-polymer dielectric composites, with their high dielectric constant and good PCB compatibility, have the potential to become ideal materials for manufacturing embedded capacitors, thus attracting widespread research and attention. These composites are typically prepared by uniformly dispersing metal powders such as silver, nickel, and iron in a polymer matrix. By controlling the volume fraction of the metal phase to be close to but slightly below the percolation threshold corresponding to the formation of an overall conductive network, a high dielectric constant can be obtained. However, because the metal phase is close to forming an overall conductive network, the dielectric loss of these composites is usually high, and even small fluctuations in composition and preparation conditions near the percolation threshold can cause drastic changes in the dielectric constant, greatly limiting their large-scale production applications. When aluminum powder is used as the metallic phase, aluminum particles are easily passivated by oxygen, forming an insulating amorphous alumina shell on the particle surface. Therefore, in aluminum-polymer composites, the conductive aluminum cores cannot directly contact each other to form a conductive network, and the composite material no longer exhibits percolation characteristics. This results in aluminum-polymer composites having a much lower dielectric loss than other metal-polymer composites, but also significantly reduces their dielectric constant, which is detrimental to further miniaturization of electronic devices. Therefore, simultaneously achieving high dielectric constant, low dielectric loss, and good performance stability in metal-polymer composites remains a major challenge. Developing novel metal-polymer composites with excellent comprehensive performance suitable for embedded capacitors is of great significance for advancing the electrical and electronic industries. Summary of the Invention

[0003] The purpose of this invention is to provide a high dielectric constant, low loss aluminum-polymer composite material for embedded capacitors and a method for preparing the same. The dielectric composite material provided by this invention can be prepared using the following method.

[0004] First, a certain pressure is applied to passivated aluminum powder to form pressed aluminum powder. Then, the pressed aluminum powder is immersed in liquid polymer monomers, allowing the liquid to fully fill the pores in the pressed aluminum powder. Finally, the polymer monomers are cured in situ to obtain the aluminum-polymer composite material. The passivated aluminum powder particles used consist of a metallic aluminum core and an alumina shell, with the alumina shell thickness ranging from 0.5 to 20 nm. The pressure applied during the preparation of the pressed aluminum powder is uniaxial or isostatic, ranging from 5 to 180 MPa. The polymer used is an electrically insulating solid, and its monomer is liquid, which can be cured in situ by adding a curing agent, heating, absorbing moisture from the air, or ultraviolet irradiation. The polymers used include, but are not limited to, epoxy resin, silicone resin, ethylene cyanoacrylate, and acrylic resin.

[0005] In the aluminum-polymer composite material provided by this invention, aluminum particles are deformed by mutual compression during the pressure molding process, thus forming large flat direct contact areas at the particle contact points. These flat direct contact areas are composed of an insulating alumina shell layer on the surface of the passivated aluminum particles, which acts as a dielectric layer and together with the conductive aluminum cores on both sides as electrodes, constitutes a microcapacitor. These microcapacitors are numerous, and the alumina dielectric layer has a large area and extremely small thickness, resulting in a large total capacitance. Under the action of an external electric field, it can store a large amount of charge and electrical energy, thereby giving the composite material a high dielectric constant macroscopically. Furthermore, the presence of the amorphous alumina shell layer on the surface of the passivated aluminum particles avoids direct contact between the conductive aluminum cores, thus significantly suppressing leakage current and giving the composite material very low dielectric loss.

[0006] The aluminum-polymer composite material provided by this invention has a dielectric constant of 20–260 at room temperature and 10 kHz, a dielectric loss of no more than 0.03, and good frequency and temperature stability. Its dielectric constant is comparable to that of composite materials with percolation characteristics prepared by uniformly dispersing metal powders such as silver, nickel, and iron in a polymer matrix, but its dielectric loss is much lower. Compared with composite materials prepared by uniformly dispersing passivated aluminum particles in a polymer matrix, the aluminum-polymer composite material provided by this invention has a much higher dielectric constant and similar dielectric loss. Therefore, the aluminum-polymer composite material provided by this invention can be used as a novel dielectric material with high dielectric strength, low loss, and stable performance, and can be widely applied in embedded capacitors, effectively reducing the size of circuit systems and enhancing their reliability. Furthermore, the aluminum-polymer composite material provided by this invention also has a series of advantages such as simple processing, stable performance, and low cost, thus facilitating low-cost mass production and possessing broad application prospects. Detailed Implementation

[0007] The aluminum powder used in this invention can be purchased directly or prepared, or the obtained aluminum powder can be subjected to subsequent thermal oxidation treatment to control the thickness of the alumina passivation shell in the aluminum powder. Tables 1 and 2 show specific examples and dielectric properties of the aluminum-polymer composite materials constituting this invention. Both examples yielded aluminum-epoxy resin composite materials with high dielectric constant, low dielectric loss, and excellent dielectric constant frequency and temperature stability. In Table 1, the average thickness of the alumina passivation shell in the aluminum powder is 2 nm, and the polymer used is epoxy resin. After the mixture of its liquid monomer and curing agent fully fills the pores in the pressed aluminum powder, it is in-situ cured at 80°C for 3 hours. In Table 2, the average thickness of the alumina passivation shell in the aluminum powder is 15 nm, and the polymer used is ethyl cyanoacrylate. After its liquid monomer fully fills the pores in the pressed aluminum powder, it is in-situ cured after absorbing moisture from the air at room temperature. The dielectric constant (ε) of the composite material is... r The dielectric loss (tanδ) and dielectric loss (tanδ) were tested using a high-precision impedance analyzer.

[0008] Table 1. Dielectric properties of aluminum-epoxy resin composites.

[0009]

[0010] Table 2. Dielectric properties of aluminum-polycyanoacrylate composite materials.

[0011]

[0012]

[0013] Tables 1 and 2 show that when the aluminum powder preparation pressure is low (≤20 MPa), its density (i.e., the volume fraction of aluminum in the composite material) increases slowly with pressure, indicating that low preparation pressure has limited effect on promoting aluminum particle rearrangement, and the distribution of aluminum particles in the composite material remains relatively loose. Since good contact has not yet been formed between the aluminum particles, a large-area alumina microcapacitor cannot be constructed; therefore, the dielectric constant of the composite material is relatively low (ε). r<50), but the table also shows that the composite material has a very low dielectric loss (not higher than 0.03). Further increasing the aluminum powder preparation pressure to 60 MPa, the aluminum volume fraction in the composite material increases rapidly. For aluminum powders with average alumina shell thicknesses of 2 nm and 15 nm used in Tables 1 and 2, the aluminum volume fraction in the composite material increases rapidly from 42.9% and 53.6% to 53.0% and 62.7%, respectively. This indicates that the current preparation pressure can drive aluminum particles to overcome friction and rearrange. After rearrangement, the aluminum particles are tightly packed, in contact with each other, and begin to undergo extrusion deformation. During this process, more and more aluminum particles form flat direct contact areas between particles through extrusion deformation, thus constructing alumina microcapacitors. Therefore, the dielectric constants of the two composite materials increase rapidly to 127.0 and 128.1 (20℃, 10kHz) with increasing aluminum powder preparation pressure. Further increasing the aluminum powder preparation pressure makes it difficult for the tightly packed aluminum particles to move relative to each other after rearrangement, so the aluminum volume fraction in the composite material only increases slightly. However, the deformation of aluminum particles intensifies, significantly increasing the area of ​​direct contact between aluminum particles and the capacitance of the alumina microcapacitor, thereby further significantly improving the dielectric constant of the composite material. For aluminum powder with an average alumina shell thickness of 2 nm used in Table 1, the dielectric constant of the composite material reaches a maximum of 188.9 (20℃, 10kHz) when the aluminum pressing pressure is 100 MPa; while for aluminum powder with an average alumina passivation shell thickness of 15 nm used in Table 2, the dielectric constant of the composite material reaches a maximum of 259.7 (20℃, 10kHz) when the aluminum pressing pressure is 180 MPa. At higher preparation pressures, the friction between aluminum particles becomes too great, damaging the alumina shell on their surface, allowing the conductive aluminum cores to directly contact and form a conductive network. The composite material then exhibits conductivity and can no longer be used as a dielectric material. Meanwhile, the aluminum powder preparation pressure corresponding to the destruction of the alumina shell increases with the increase of the shell thickness. Therefore, the highest preparation pressure and the corresponding highest dielectric constant of the aluminum-polymer composite material (average alumina shell thickness of 15 nm) in Table 2 are significantly higher than those of the composite material (average alumina shell thickness of 2 nm) in Table 1.

[0014] The above examples are only some embodiments of the present invention, and are only used to illustrate the technical solution of the present invention. They do not constitute a limitation on the scope of the present invention. The thickness of the alumina shell layer of the aluminum powder in the solution can typically be 0.5–20 nm. The pressure applied when preparing the aluminum powder can be uniaxial pressure or isostatic pressure, typically ranging from 5 to 180 MPa. The polymer used only needs to meet the following requirements: it is an electrically insulating solid, its monomer is liquid, and it can be cured in situ by adding a curing agent, heating, absorbing moisture from the air, or ultraviolet irradiation. Polymers include, but are not limited to, epoxy resin, silicone resin, ethylene cyanoacrylate, and acrylic resin. The aluminum-polymer composite material prepared by the present invention has high dielectric constant, low dielectric loss, and good dielectric performance temperature stability, and has good application prospects.

Claims

1. An aluminum-polymer composite material with high dielectric constant and low dielectric loss, characterized in that: The material is a composite material made by filling the pores of aluminum powder with polymer. It has the characteristics of high dielectric constant and low dielectric loss. The dielectric constant is 20~260 at room temperature and 10 kHz, and the dielectric loss is not higher than 0.

03. The preparation method includes the following steps: First, a certain pressure is applied to the surface passivated aluminum powder, the pressure being uniaxial pressure or isostatic pressure, with a magnitude of 5~180 MPa, to form aluminum pressed powder; then, the aluminum pressed powder is immersed in liquid polymer monomer, so that the liquid fully fills the pores in the aluminum pressed powder; finally, the polymer monomer is cured in situ to obtain aluminum-polymer composite material. The surface passivated aluminum powder particles consist of a metallic aluminum core and an aluminum oxide shell, with the aluminum oxide shell having a thickness of 0.5~20 nm.

2. A method for preparing an aluminum-polymer composite material with high dielectric constant and low dielectric loss, characterized in that... The process includes the following steps: First, a certain pressure is applied to passivated aluminum powder to form pressed aluminum powder; then, the pressed aluminum powder is immersed in liquid polymer monomers to fully fill the pores in the pressed aluminum powder; finally, the polymer monomers are cured in situ to obtain an aluminum-polymer composite material; the passivated aluminum powder particles consist of a metallic aluminum core and an alumina shell, with the thickness of the alumina shell being 0.5~20 nm; the pressure applied during the preparation of pressed aluminum powder is uniaxial pressure or isostatic pressure, ranging from 5 to 180 MPa.

3. The method for preparing the aluminum-polymer composite material with high dielectric constant and low dielectric loss as described in claim 2, characterized in that: The polymer used is an electrically insulating solid, and its monomer is liquid. In-situ curing is achieved by adding a curing agent, heating, absorbing moisture from the air, or irradiating with ultraviolet light. The polymer used is epoxy resin, silicone resin, ethyl cyanoacrylate, or acrylic resin.

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