Polyimide composite film and its preparation method

Abstract

This invention relates to a polyimide composite film, comprising: a carrier layer; a sputtered copper layer laminated to the surface of the carrier layer; an electroplated copper layer laminated to the surface of the sputtered copper layer; and an electroplated tin layer laminated to the surface of the electroplated copper layer. The carrier layer is a polyimide film with a thickness of 5-30 μm, the sputtered copper layer has a thickness of 0.5-2 μm, the electroplated copper layer has a thickness of 2-5 μm, and the electroplated tin layer has a thickness of 1-5 μm. The surface roughness Rz of the electroplated copper layer is 1-3 μm. This invention also relates to a method for preparing the above-mentioned polyimide composite film.

Description

Technical Field

[0001] This invention relates to the field of thermal conductivity and electromagnetic shielding materials, and in particular to a polyimide (PI) composite film with both high thermal conductivity and electromagnetic shielding and its preparation method. Background Technology

[0002] This section provides background information relevant to this application, which does not necessarily constitute prior art.

[0003] Currently, electronic devices face the following technical challenges: 1. Miniaturization and thinning of electronic devices restrict the rapid dissipation of heat; 2. Electromagnetic waves radiated by high-frequency electronic devices during operation often induce currents in circuits and electronic components. Electromagnetic interference can cause signal distortion, shorten the lifespan of electronic components, and even damage the equipment.

[0004] To address the aforementioned technical problems, existing solutions involve incorporating electromagnetic shielding and thermally conductive materials into electronic devices. However, materials that simultaneously offer both thermal conductivity and electromagnetic shielding are rare. Traditional single-metal or alloy materials used for electromagnetic shielding, such as copper, aluminum, iron, and their alloys, are heavy and have limited thermal conductivity and dissipation. Most existing electromagnetic shielding materials are composite films comprising a base film, a shielding film, and a conductive film. The shielding film is typically a silver metal layer prepared using electroplating. However, existing electromagnetic shielding films exhibit poor shielding performance, failing to meet the shielding requirements for ultra-high frequency signals, and also suffer from poor reliability and heat resistance. Summary of the Invention

[0005] To address the technical problems existing in the prior art, the present invention provides a polyimide composite film that combines high thermal conductivity and excellent electromagnetic shielding performance. The polyimide composite film uses a polyimide film as a carrier layer and prepares multiple metal layers on the surface of the carrier layer.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a polyimide composite film, comprising:

[0007] A polyimide composite film, comprising:

[0008] Carrier layer;

[0009] A sputtered copper layer composited on the surface of the carrier layer;

[0010] An electroplated copper layer is composited on the surface of the sputtered copper layer;

[0011] An electroplated tin layer is laminated onto the surface of the electroplated copper layer.

[0012] The sputtered copper layer, electroplated copper layer, and electroplated tin layer constitute a metal layer. The sputtered copper layer can serve as the bottom layer, the electroplated copper layer can serve as the connecting layer, and the electroplated tin layer can serve as both the functional layer and the protective layer.

[0013] The carrier layer is a PI film.

[0014] The thickness of the carrier layer is not particularly limited, but it can be adjusted to an appropriate thickness while still fulfilling its function as a carrier; for example, it can be 5 μm or more. However, if the carrier layer is too thick, the production cost increases, so a thickness of 30 μm or less is generally preferred.

[0015] The total thickness of the metal layer is not particularly limited, and it is generally thinner than the carrier, typically not exceeding 20 μm. It can be noted that metal layers can be formed on both sides of the carrier layer. Preferably, the thickness of the sputtered copper is 0.5-2 μm, the thickness of the electroplated copper layer is 2-5 μm, and the thickness of the electroplated tin layer is 1-5 μm.

[0016] In one or more embodiments, the average particle size of the electroplated copper layer is 0.25-0.45 μm; the average particle size of the electroplated tin layer is not greater than 0.35 μm. The lower limit of the average particle size of the electroplated tin layer does not need to be particularly limited, for example, it is 0.05 μm or more, or 0.09 μm or more, or 0.10 μm or more, or 0.12 μm or more, or 0.15 μm or more.

[0017] Forming an electroplated copper layer on the surface of a sputtered copper layer can be considered as a roughening treatment of the sputtered copper layer surface using a plating method. Specifically, a matte copper plating method is used to form a microparticle-like copper layer, thereby improving the adhesion strength between the electroplated tin layer and the sputtered copper layer. The reasonable range for the surface roughness Rz (micro-irregularity height at ten points) of the electroplated copper layer is 1-3 μm. If the surface roughness Rz is below 1 μm, the effect weakens; furthermore, even if Rz is above 3 μm, the effect becomes saturated. The adhesion strength between the electroplated tin layer and the electroplated copper layer formed in this way can reach 0.80 kg / cm². 2 Furthermore, the bonding strength can reach 0.90 kg / cm². 2 above.

[0018] The beneficial effects of this invention are as follows:

[0019] This invention provides a polyimide composite film, comprising: a carrier layer; and a metal layer laminated to the surface of the carrier layer. The polyimide composite film provided by this invention exhibits excellent shielding performance against ultra-high frequency electromagnetic signals (1GHz-50GHz), while also demonstrating high reliability and heat resistance. This polyimide composite film achieves a balance between high thermal conductivity and excellent electromagnetic shielding performance, simultaneously addressing the thermal and electromagnetic interference problems of electronic components. Furthermore, the polyimide composite film provided by this invention achieves a tight bond between the metal layer and the carrier layer, with a dense coating free from peeling or flaking.

[0020] The following description is based on specific embodiments. Detailed Implementation

[0021] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0022] It should be noted that the average particle size described in this invention was determined by observing and photographing particles using a scanning electron microscope at 30,000x magnification. Based on the obtained photographs, the particle size of each primary and secondary particle was measured separately. Furthermore, the arithmetic mean of the obtained particle sizes of each primary and secondary particle was set as the average particle size of the primary and secondary particles. It should be noted that when drawing a straight line across the particles in the scanning electron microscope photographs, the length of the particle whose straight line has the longest length was defined as its particle size.

[0023] It should be noted that the surface roughness Rz described in this invention is a value measured using a stylus-type surface roughness meter.

[0024] It should be noted that the polyimide composite film has a structure in which sputtered copper layer, electroplated copper layer, and electroplated tin layer are sequentially stacked in a symmetrical manner on both sides of the carrier layer. Unless otherwise specified, the thickness of sputtered copper layer, electroplated copper layer, and electroplated tin layer described in this invention refer to the thickness of the layered structure formed on one side of the carrier layer, and this thickness is a value determined by analyzing the cross-section of the polyimide film using a transmission electron microscope with energy dispersive X-ray spectroscopy (TEM-EDX).

[0025] Examples 1-3 and Comparative Examples 1-10 all provide a polyimide composite film.

[0026] In the polyimide composite films provided in Examples 1-3, a polyimide film is used as the carrier layer, and a sputtered copper layer, an electroplated copper layer, and an electroplated tin layer are formed on the surface of the carrier layer in sequence from the inside to the outside. The difference is as follows: In the polyimide composite film provided in Example 1, the thickness of the polyimide film is 25 μm, the thickness of the sputtered copper layer is 0.5 μm, the thickness of the electroplated copper layer is 2 μm, and the thickness of the electroplated tin layer is 1 μm; In the polyimide composite film provided in Example 2, the thickness of the polyimide film is 30 μm, the thickness of the sputtered copper layer is 2 μm, the thickness of the electroplated copper layer is 5 μm, and the thickness of the electroplated tin layer is 5 μm; In the polyimide composite film provided in Example 3, the thickness of the polyimide film is 28 μm, the thickness of the sputtered copper layer is 1 μm, the thickness of the electroplated copper layer is 2.6 μm, and the thickness of the electroplated tin layer is 1.8 μm.

[0027] The preparation methods of the polyimide composite films provided in Examples 1-3 all include the following steps:

[0028] Step 1: Form a sputtered copper layer on the surface of the polyimide film.

[0029] The sputtered copper layer constituting the polyimide composite film of the present invention can be manufactured using any sputtering method disclosed in the prior art. Sputtered copper layers manufactured by sputtering are preferred from the viewpoints of in-plane uniformity of film thickness and productivity in sheet or roll form. When using sputtering, the sputtering method can be any known method such as magnetron sputtering or bipolar sputtering, but magnetron sputtering is preferred for its fast film formation speed and high productivity. Furthermore, sputtering can be performed using either DC (direct current) or RF (high frequency) power supplies. Additionally, the vacuum level reached in the chamber before sputtering is preferably less than 1 × 10⁻⁴ Pa. Argon is preferred as the gas used in sputtering, and the flow rate of argon, etc., is not particularly limited as long as it is appropriately determined according to the size of the sputtering chamber and the film formation conditions. Furthermore, from the viewpoint of avoiding operational malfunctions such as abnormal discharge and poor plasma irradiation, and maintaining continuous and stable film formation, the pressure during film formation is preferably in the range of 0.1-2.0 Pa. This pressure range can be set by adjusting the flow rates of the film-forming power and argon gas based on the device structure, capacity, vacuum pump exhaust capacity, and rated capacity of the film-forming power source. Furthermore, for sputtering power, considering factors such as film thickness uniformity and productivity, the range is 0.05-10.0 W / cm² per unit area of ​​the target. 2 The appropriate settings can be made within the specified range. For example, a sputtered copper layer is formed on the surface of a polyimide film by sputtering under the following apparatus and conditions. The sputtered copper layer is then measured using a non-contact surface shape measuring machine, and the result shows that the sputtered copper layer has an extremely flat surface (e.g., the arithmetic mean deviation Ra of the profile is no greater than 100 nm):

[0030] - Equipment: Roll-up DC sputtering device;

[0031] -Target: Copper target;

[0032] -Achieved vacuum level Pu: less than 1×10 -4 Pa;

[0033] - Gas: Argon (flow rate: 100 sccm);

[0034] -Sputtering pressure: 0.45 Pa;

[0035] -Sputtering power: 1.0kW (3.1W / cm²) 2 ).

[0036] Step two: An electroplated copper layer is formed on the surface of the sputtered copper layer by electroplating. The electrolyte used for electroplating is a sulfuric acid-copper sulfate electrolyte, which includes 60-100 g / L of sulfuric acid, 160-240 g / L of copper sulfate, and 60-100 ppm of chloride ions. Additives with the composition shown in Table 1 are added to this sulfuric acid-copper sulfate electrolyte, and the electroplating is carried out under the following electrolysis conditions to prepare the electroplated copper layer:

[0037] - Electrolyte temperature: 25-50℃;

[0038] - Current density: 1-3A / dm 2 .

[0039] Step 3: Activate the surface of the electroplated copper layer with a solution containing 5-7 wt% sulfuric acid for no more than 15 seconds.

[0040] Step four: A tin plating layer is formed on the surface of the copper plating layer by electroplating. The electrolyte used for electroplating is a sulfuric acid-stannous sulfate electrolyte, which contains 30-60 g / L of Sn. 2+ A tin-plated layer is prepared by electroplating with 60-90 g / L sulfuric acid (derived from stannous sulfate) and additives as shown in Table 2 in the sulfuric acid-stannous sulfate electrolyte, and under the following electrolysis conditions:

[0041] -Liquid temperature: 30-50℃;

[0042] - Current density: 1-2A / dm 2 .

[0043] The steps described above also include a surface cleaning step using deionized water.

[0044] The difference between the polyimide composite film provided in Comparative Examples 1-8 and the polyimide composite film provided in Example 3 is that different sulfuric acid-copper sulfate electrolytes were used to prepare the electroplated copper layer and / or different sulfuric acid-stannous sulfate electrolytes were used to prepare the electroplated tin layer, as shown in Tables 1 and 2.

[0045] The only difference between the polyimide composite film provided in Comparative Example 9 and the polyimide composite film provided in Example 3 is that the polyimide composite film provided in Comparative Example 9 does not include an electroplated tin layer, and the thickness of the electroplated copper layer of the polyimide composite film provided in Comparative Example 9 is 4.4 μm.

[0046] The difference between the polyimide composite film provided in Comparative Example 10 and the polyimide composite film provided in Example 3 is that the polyimide composite film provided in Comparative Example 10 does not include an electroplated copper layer, but instead forms a 4.4 μm thick electroplated tin layer directly on the sputtered copper layer.

[0047] It should be noted that for copper electroplating using sulfuric acid-copper sulfate electrolyte, existing technologies commonly employ a combination of additives A and B to achieve a bright and smooth plating layer. Additive A is one or more additives selected from thiourea or thiourea derivatives. Examples of thiourea and thiourea derivatives include water-soluble thiourea and thiourea derivatives such as thiourea, N,N'-dimethylthiourea, N,N'-diethylthiourea, tetramethylthiourea, aminothiourea, N-allylthiourea, and ethylenethiourea. Additive B is a high-molecular-weight polysaccharide such as animal glue, gelatin, polyethylene glycol, polypropylene glycol, starch, water-soluble cellulose polymers (carboxymethyl cellulose, hydroxyethyl cellulose, etc.), polyethyleneimine, or polyacrylamide. The synergistic effect of additives A and B can achieve a surface roughness Rz of less than 0.8 μm for the obtained electroplated copper layer, more typically less than 0.5 μm. A surface roughness Rz of less than 1 μm weakens the adhesion between the electroplated copper layer and the electroplated tin layer.

[0048] Table 1

[0049]

[0050] Table 2

[0051]

[0052] The following tests were performed on the polyimide composite films provided in Examples 1-3 and Comparative Examples 1-10:

[0053] 1. The adhesion of the coating is tested according to the standard of GB / T 2792-2014 Test Method for Peel Strength of Adhesive Tape. In this invention, the adhesion of the coating is tested by bonding the surfaces of 3M 610 tape and polyimide composite film, and the adhesion of the coating is measured while the 3M 610 tape is pulled in a 90° direction.

[0054] 2. The thermal diffusivity of the polyimide composite film was tested according to the standard of ASTM E1461-2013, "Standard Test Method for Determination of Thermal Diffusivity by Flash Method".

[0055] 3. The shielding effectiveness of the polyimide composite film was tested in the electromagnetic wave frequency range of 1GHz-50GHz according to the standard of ASTM D4935-10 Test Method for Measuring Electromagnetic Shielding Effect of Planar Materials.

[0056] The test results are shown in Table 3. The polyimide composite film provided by this invention has a shielding effectiveness greater than 85 dB in the electromagnetic wave frequency range of 1 GHz to 50 GHz, and an average thermal diffusivity of not less than 410 mm. 2 Furthermore, the adhesion test results show that the coating adhesion of the polyimide composite film provided by the present invention is not less than 3010gf, and the coating did not peel off or fall off after the adhesion test.

[0057] Table 3

[0058] Shielding effectiveness (dB) <![CDATA[Average thermal diffusivity (mm 2 / s)]]> Coating adhesion (gf) Example 1 86.2 411 3020 Example 2 85.7 413 3010 Example 3 87.1 421 3040 Comparative Example 1 78.1 392 2720 Comparative Example 2 80.7 403 2780 Comparative Example 3 77.2 395 2830 Comparative Example 4 78.1 401 2840 Comparative Example 5 80.4 405 2870 Comparative Example 6 79.2 401 2750 Comparative Example 7 80.2 402 2810 Comparative Example 8 80.9 404 2770 Comparative Example 9 76.1 388 2120 Comparative Example 10 72.4 372 2470

[0059] As can be seen from the test data in Table 3, the polyimide composite films provided in Comparative Examples 1-10 all showed a decrease in shielding effectiveness, average thermal diffusivity, and coating adhesion compared to the polyimide composite film provided in Example 3. This verifies that the coating adhesion can be significantly improved by roughening the electroplated copper layer and controlling the additives in the sulfuric acid-stannous sulfate electrolyte. By increasing the bonding sites between the electroplated copper layer and the electroplated tin layer, the polyimide composite films provided in Examples 1-3 have a higher average thermal diffusivity, and unexpectedly, their shielding effect is also improved.

[0060] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a polyimide composite film, characterized in that, The polyimide composite film comprises: Carrier layer; A sputtered copper layer composited on the surface of the carrier layer; An electroplated copper layer is composited on the surface of the sputtered copper layer; An electroplated tin layer is laminated onto the surface of the electroplated copper layer; The carrier layer is a polyimide film with a thickness of 5-30 μm, the sputtered copper layer has a thickness of 0.5-2 μm, the electroplated copper layer has a thickness of 2-5 μm, and the electroplated tin layer has a thickness of 1-5 μm. The surface roughness Rz of the electroplated copper layer is 1-3 μm; The preparation method includes the following steps: Step 1: Form the sputtered copper layer on the surface of the polyimide film by sputtering. Step 2: An electroplated copper layer is formed on the surface of the sputtered copper layer by electroplating. The electrolyte used for electroplating is a sulfuric acid-copper sulfate electrolyte, which includes 60-100 g / L of sulfuric acid, 160-240 g / L of copper sulfate, 60-100 ppm of chloride ions, and an organic additive. The organic additive is one of thiourea, N,N'-dimethylthiourea, N,N'-diethylthiourea, tetramethylthiourea, aminothiourea, N-allylthiourea, and ethylenethiourea. Step 3: Activate the surface of the electroplated copper layer with a solution containing 5-7 wt% sulfuric acid for no more than 15 seconds. Step four: A tin plating layer is formed on the surface of the copper plating layer by electroplating. The electrolyte used for electroplating is a sulfuric acid-stannous sulfate electrolyte, which includes 30-60 g / L of Sn. 2+ 60-90 g / L sulfuric acid, 6-8 g / L thiourea, 15-20 g / L citric acid, 5-7 ml / L glutaraldehyde, and 2-4 ml / L benzylidene acetone.

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