Surface modified polyimide and preparation method thereof

Abstract

The invention relates to the technical field of surface treatment, and discloses surface modified polyimide and a preparation method thereof, the preparation method adopts a hydrolysis solution comprising strong base, potassium permanganate, sodium carbonate and sodium phosphate to treat the surface of polyimide; then mixing the polyimide with a solution containing silver ions to adsorb the silver ions in situ, freezing the polyimide in liquid nitrogen after adsorption, and then performing vacuum freeze-drying; and baking the freeze-dried polyimide at a high temperature in the atmosphere of a mixed gas of argon and hydrogen to finish modification. A hydrolysis solution with specific components is adopted to modify the surface of polyimide, and in-situ self-adsorption and in-situ pyrolysis reduction methods are combined, so that the surface of polyimide is uniformly coated with a layer of silver nanoparticles with good binding force, and the silver nanoparticles serve as a catalytic activity center of chemical plating; and uniform, compact and high-binding-force adhesion of a polyimide surface coating is realized. The modified polyimide can be suitable for preparing uniformly attached copper active particles on the surface of the polyimide, and has high flexibility and applicability.

Description

Technical Field

[0001] The present application relates to the field of surface treatment technology, and in particular to a surface-modified polyimide and a preparation method thereof. Background Art

[0002] Polyimide (PI) material is a type of polymer whose main chain contains an imide ring (CO-NH-CO) structure. It has an operating temperature of -250℃-+450℃ and has excellent mechanical properties, chemical stability, low dielectric constant and good radiation resistance. It can be widely used in electronics, aerospace, microelectronics and other fields.

[0003] As a typical non-metallic material, polyimide has high volume resistivity and surface resistivity, and high surface insulation. Therefore, when it is used in products such as electronic circuits and radar antennas, it needs to be subjected to surface metallization treatment. Since the surface of polyimide materials is smooth and dense, chemically inert and has poor hydrophilicity, it is necessary to perform surface roughening and activation treatment when depositing metal layers such as chemical plating and electroplating. Using the traditional alkaline hydrolysis ring-opening-hydrolysis method, the activation is uneven, and the density and bonding strength of the metal layer after chemical plating are poor. In addition, due to the difference in thermal expansion coefficient between the polyimide material and the metal material, higher requirements are placed on the interface bonding strength between the polyimide material and the metal layer to meet the thermal stability requirements during application. Therefore, it is necessary to find a surface modification method for polyimide materials to improve the bonding strength between polyimide and surface coating. Summary of the Invention

[0004] In view of this, the purpose of the present application is to provide a surface-modified polyimide and a preparation method thereof, so that the bonding strength between the surface-modified polyimide and the metal coating is significantly improved and can adapt to a wider temperature range environment.

[0005] In order to solve the above technical problems / achieve the above objectives or at least partially solve the above technical problems / achieve the above objectives, as a first aspect of the present application, a method for preparing a surface-modified polyimide is provided, comprising:

[0006] S1 using a hydrolysis solution to treat the polyimide surface; the hydrolysis solution comprises a strong base, potassium permanganate, sodium carbonate and sodium phosphate;

[0007] S2. The surface hydrolyzed polyimide was mixed with a silver ion-containing solution to adsorb silver ions in situ. After adsorption, the polyimide was frozen in liquid nitrogen and then freeze-dried in vacuum;

[0008] S3. The freeze-dried polyimide is baked at high temperature in an atmosphere of a mixed gas of argon and hydrogen to obtain the surface-modified polyimide.

[0009] Optionally, the hydrolysis solution comprises 300-400 g / L of a strong base, 80-160 g / L of potassium permanganate, 30-40 g / L of sodium carbonate, and 5-10 g / L of sodium phosphate. Further optionally, the strong base comprises sodium hydroxide and / or potassium hydroxide.

[0010] Optionally, the silver ion-containing solution comprises silver nitrate.

[0011] Optionally, the high-temperature baking is baking at a temperature of 350-370°C.

[0012] Optionally, the preparation method further comprises performing metal plating on the surface-modified polyimide.

[0013] As a second aspect of the present application, a surface-modified polyimide prepared by the preparation method is provided.

[0014] As a third aspect of the present application, a polyimide surface hydrolysis solution is provided, comprising a strong base, potassium permanganate, sodium carbonate and sodium phosphate.

[0015] Optionally, the hydrolysis solution includes 300-400 g / L of strong base, 80-160 g / L of potassium permanganate, 30-40 g / L of sodium carbonate, and 5-10 g / L of sodium phosphate.

[0016] As a fourth aspect of the present application, provided is the use of the hydrolysis solution in preparing a polyimide surface modifier.

[0017] This application utilizes a hydrolysis solution of specific components to hydrolyze and modify the polyimide surface, combined with in-situ self-adsorption of silver ions and in-situ thermal reduction methods, to achieve a uniform coating of the polyimide surface with a layer of highly adhesive silver nanoparticles. These serve as catalytic active centers for electroless plating, resulting in a uniform, dense, and highly adhesive coating on the polyimide surface. The modified polyimide described in this application is suitable for preparing uniformly adhered copper active particles on its surface, demonstrating high flexibility and applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application.

[0019] Figure 1 Shown are microscopic morphologies of the polyimide surface after hydrolysis treatment in Example 1 at different magnifications;

[0020] Figure 2 The figure shows the morphology of silver nanoparticles attached to the surface of polyimide after being treated with silver nitrate at different concentrations in Example 1;

[0021] Figure 3The figure shows the EDS analysis of silver nanoparticles attached to the surface of the polyimide treated with different concentrations of silver nitrate in Example 1;

[0022] Figure 4 Shown is the microscopic morphology of the polyimide-plated copper metal layer after surface treatment in Example 1;

[0023] Figure 5 Shown is a visual sample image of the polyimide-plated copper metal layer after surface treatment in Example 1;

[0024] Figure 6 The figure shows a visual sample of the polyimide copper-plated metal layer after surface treatment in Example 1 after thermal shock test and high temperature cycle test of -196℃~+120℃;

[0025] Figure 7 The figure shows a visual sample picture of the polyimide copper-plated metal layer after surface treatment in comparative example 1 after thermal shock test;

[0026] Figure 8 Shown is a visual sample picture of the polyimide copper-plated metal layer after surface treatment in comparative example 2 after thermal shock test. DETAILED DESCRIPTION

[0027] The present application discloses a surface-modified polyimide and a preparation method thereof. Those skilled in the art can refer to the contents of this article and appropriately improve the process parameters to achieve the desired effect. It should be noted in particular that all similar replacements and modifications are obvious to those skilled in the art, and they are all deemed to be included in this application. The products, processes and applications described in this application have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods described herein without departing from the content, spirit and scope of this application to implement and apply the technology of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0028] It should be noted that, in this document, if relational terms such as "first" and "second", "step 1" and "step 2", and "(1)" and "(2)" appear, they are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "including a..." do not exclude the presence of other identical elements in the process, method, article or device comprising the elements. At the same time, the embodiments in this application and the features in the embodiments can be combined with each other in the absence of conflict.

[0029] The traditional alkaline hydrolysis ring-opening-hydrolysis method for polyimide surface modification usually uses an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide. The imide ring is hydrolyzed and opened in the alkaline solution to generate a carboxyl group and an amide bond. The hydrogen at the carboxyl end is replaced with sodium or potassium (i.e., an alkali metal in an alkaline aqueous solution) through an ion exchange reaction. The polyimide in the open ring state is then immersed in an aqueous solution containing metal ions such as Ni or Cu, and the alkali metal of the carboxyl group is replaced with the metal (Ni or Cu, etc.). Furthermore, if the polyimide in this state is treated with an aqueous solution of a reducing agent, the metal ions such as Ni or Cu are reduced to metal, forming a thin metal film of Ni or Cu on the polyimide resin. However, the imide bond of polyimide is the most critical part of its molecular structure. The hydrolysis reaction causes the imide bond to break and reduces the strength of the polyimide. Therefore, when using a strong alkaline solution to perform alkaline hydrolysis on polyimide, the hydrolysis area will increase the surface activity, thereby achieving coating deposition, but it will also cause changes in the molecular structure of the polyimide surface, reduce the material strength, and affect the bonding strength between the coating and the substrate. This application uses a mixed solution of alkali, sodium carbonate, sodium phosphate and potassium permanganate to treat polyimide. On the one hand, the weak alkaline effect of sodium carbonate and sodium phosphate is utilized. The sodium carbonate and sodium phosphate are gradually hydrolyzed to release OH - , so that under the same alkaline hydrolysis effect, the concentration of strong alkali is reduced, thereby weakening the impact on the polyimide substrate; on the other hand, the strong oxidizing property of potassium permanganate is used to etch the polyimide surface, thereby improving the surface activity of the polyimide.

[0030] Based on the above technical problems, in a first aspect of the present application, a method for preparing a surface-modified polyimide is provided, comprising:

[0031] S1 using a hydrolysis solution to treat the polyimide surface; the hydrolysis solution comprises a strong base, potassium permanganate, sodium carbonate and sodium phosphate;

[0032] S2. The surface hydrolyzed polyimide was mixed with a silver ion-containing solution to adsorb silver ions in situ. After adsorption, the polyimide was frozen in liquid nitrogen and then freeze-dried in vacuum;

[0033] S3. The freeze-dried polyimide is baked at high temperature in an atmosphere of a mixed gas of argon and hydrogen to obtain the surface-modified polyimide.

[0034] In certain embodiments of the present application, the hydrolysis solution includes 300-400 g / L of a strong base, 80-160 g / L of potassium permanganate, 30-40 g / L of sodium carbonate, and 5-10 g / L of sodium phosphate, wherein the strong base includes sodium hydroxide and / or potassium hydroxide.

[0035] In some other embodiments of the present application, step S1 includes:

[0036] The polyimide surface is treated with a mixed solution of 300-400 g / L sodium hydroxide, 80-160 g / L potassium permanganate, 30-40 g / L sodium carbonate and 5-10 g / L sodium phosphate for 10-30 min at a temperature of 60-70° C., with ultrasonic stirring for 10 min, and then washed with water.

[0037] In certain embodiments of the present application, the silver ion-containing solution comprises silver nitrate; more specifically, the silver ion-containing solution is a 0.4-1 g / L silver nitrate solution. In other embodiments of the present application, step S2 comprises:

[0038] Prepare a 0.4-1g / L silver nitrate solution and add it to the aqueous solution containing the polyimide material while stirring. Ultrasonic stirring is performed for 2-3 hours. The polyimide material is then removed and frozen in liquid nitrogen. The solution is then freeze-dried in a freeze dryer for 24-32 hours to remove moisture.

[0039] After the polyimide material and silver nitrate react, the conventional method generally adopts the method of adding water and then filtering to neutrality, and then drying in an oven. In this way, the silver active particles are easy to agglomerate, thereby affecting the catalytic activity. The present application adopts a vacuum freeze-drying method for processing. Vacuum freeze-drying is a stabilized material drying process. It is a method of first freezing the water-containing material into a solid state, and then allowing the water therein to directly sublimate from the solid state into a gaseous state to be removed to remove the disposal. After the solution state sample is frozen, it undergoes sublimation and desorption, so that the solvent in the product is reduced to a certain extent, thereby preventing the chemical reaction between the solute and the solvent. The vacuum freeze-drying method is a liquid-solid-gas process. During the freeze-drying process, the liquid bridges between the solute particles have been freeze-dried into solid bridges, the relative positions between the particles are fixed, and there is no surface tension at the gas-liquid interface between the particles, which is conducive to retaining the original structure of the polyimide adsorbed silver, and realizing the in-situ adsorption and reduction of silver on the polyimide surface without agglomeration.

[0040] In certain embodiments of the present application, the high-temperature baking of the polyimide surface loaded with silver is mainly to reduce the silver ions to silver particles. The argon hydrogen atmosphere is used, mainly because the hydrogen at high temperature promotes the gasification of carbon in the polyimide, which is beneficial to retain the stable S2 site and remove the unstable S1 site. At the same time, at high temperatures, silver generates highly active hydrogen atoms by dissociating H2, which reduces the metal reduction energy barrier and is beneficial to the reduction of active metals such as silver. In other embodiments of the present application, the high-temperature baking is baked at a temperature of 350 to 370°C. When the baking temperature is lower than 350°C, the effect of high-temperature thermal decomposition reduction is affected, and the silver ions are partially reduced to silver particles, reducing the catalytic activity effect; when the baking temperature is higher than 370°C, the polyimide is easily denatured. In other embodiments of the present application, the baking time is 2h to 3h, and the heating rate is 3 to 5°C / min.

[0041] In certain embodiments of the present application, the preparation method further comprises performing metal plating on the surface-modified polyimide. In other embodiments of the present application, the metal plating is electroless copper plating; wherein the electroless copper plating solution comprises 7 g / L copper sulfate, 10 mL / L formaldehyde, 5 g / L potassium hydroxide, 28 g / L potassium sodium tartrate, and 0.2 mg / L stabilizer, the solution is used at a temperature of 33°C, the electroless copper plating time is 2 hours, and the electroless copper plating layer has a thickness of approximately 4 microns.

[0042] In other embodiments of the present application, electroless copper plating is used to deposit copper on the surface-modified polyimide. The coating has a complete appearance and uniform color. It withstands thermal shock tests from 200°C to cold water and thermal cycling tests from -196°C to +120°C. The coating's solder joint pull-off strength is ≥5 MPa, indicating good bonding strength between the polyimide coating and the substrate. The polyetheretherketone surface coating maintains good bonding strength over a wide temperature range.

[0043] In the second aspect of the present application, a surface-modified polyimide prepared by the preparation method is provided, which can be a polyimide that has been surface-modified only, or a polyimide that has been surface-modified and then plated with a metal layer, such as a polyimide after chemical copper plating.

[0044] In the third aspect of the present application, according to the role of the hydrolysis solution in the modification of polyimide in the present application, the present application provides a polyimide surface hydrolysis solution, including a strong base, potassium permanganate, sodium carbonate and sodium phosphate. Wherein, the strong base can be sodium hydroxide and / or potassium hydroxide.

[0045] In certain embodiments of the present application, the hydrolysis solution includes 300-400 g / L of a strong base, 80-160 g / L of potassium permanganate, 30-40 g / L of sodium carbonate, and 5-10 g / L of sodium phosphate. The concentration of the strong base can be selected from 300 g / L, 320 g / L, 340 g / L, 360 g / L, 380 g / L, 400 g / L, etc.; the concentration of potassium permanganate can be selected from 80 g / L, 100 g / L, 120 g / L, 140 g / L, 160 g / L, etc.; the concentration of sodium carbonate can be selected from 30 g / L, 32 g / L, 34 g / L, 36 g / L, 38 g / L, 40 g / L, etc.; and the concentration of sodium phosphate can be selected from 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, etc.

[0046] In a fourth aspect of the present application, a use of the hydrolysis solution in preparing a polyimide surface modifier is provided. The surface modifier may further include a silver ion-containing solution, such as a 0.4-1 g / L silver nitrate solution.

[0047] In the comparative experiments provided in this application, unless otherwise specified, all experimental conditions and materials, except for the differences noted in each group, were kept consistent to ensure comparability. In addition, all materials used in this application can be purchased from commercial sources.

[0048] The following further describes a surface-modified polyimide and its preparation method provided in this application.

[0049] Example 1:

[0050] The polyimide surface was treated with a mixed solution of 300 g / L sodium hydroxide, 80 g / L potassium permanganate, 30 g / L sodium carbonate, and 5 g / L sodium phosphate for 10 minutes at a temperature of 60°C, with ultrasonic stirring for 10 minutes, and then washed with water. The surface microporous structure formed after the polyimide surface hydrolysis treatment is shown in FIG. Figure 1 .

[0051] Prepare 0.5g / L and 1g / L silver nitrate solutions, then add them to the polyimide-soaked aqueous solution while stirring. Ultrasonic stirring is performed for 2 hours, and then the polyimide is removed and frozen in liquid nitrogen. The solution is then freeze-dried in a freeze dryer for 24 hours to remove moisture.

[0052] The polyimide material obtained after freeze-drying was placed in a high-temperature furnace at 350°C, with a mixture of argon and hydrogen (90% argon, 10% hydrogen) flowing, and baked for 2 hours at a heating rate of 5°C / min to obtain silver nanoparticles deposited on the polyimide surface. The microscopic image of silver attached to the polyimide surface is shown in Figure 2 , EDS analysis diagram see Figure 3 .

[0053] Example 2:

[0054] The treated polyimide material was electrolessly plated with copper. The electroless copper plating solution included 7 g / L copper sulfate, 10 mL / L formaldehyde, 5 g / L potassium hydroxide, 28 g / L potassium sodium tartrate, and 0.2 mg / L stabilizer. The solution temperature was 33° C. The electroless copper plating time was 2 h, and the thickness of the electroless copper plating layer was about 4 microns.

[0055] The microscopic image of the copper metal layer attached to the polyimide surface is shown in Figure 4 , sample intuitive diagram see Figure 5 .

[0056] Comparative Example 1: The silver loading method adopts a conventional activation method.

[0057] The polyimide surface was treated with a mixed solution of 300 g / L sodium hydroxide, 80 g / L potassium permanganate, 30 g / L sodium carbonate and 5 g / L sodium phosphate for 10 min at a temperature of 60°C, with ultrasonic stirring for 10 min, and then washed with water.

[0058] The polyimide substrate was immersed in a 0.5 g / L silver nitrate solution for 2 minutes, then placed in a sodium hypophosphite solution (sodium hypophosphite solution concentration 18-22 g / L), and then baked in a 300°C oven to obtain silver nanoparticles deposited on the polyimide surface.

[0059] Copper plating was performed in the same manner as in Example 2.

[0060] Comparative Example 2: The hydrolysis solution adopts sodium hydroxide solution.

[0061] The polyimide surface was treated with a 300 g / L sodium hydroxide solution for 10 min at a temperature of 60° C., with ultrasonic stirring for 10 min, and then washed with water.

[0062] Prepare a 0.5g / L silver nitrate solution and add it to the polyimide-soaked aqueous solution while stirring. Ultrasonic stirring is performed for 2 hours. The polyimide is then removed and frozen in liquid nitrogen. The solution is then freeze-dried in a freeze dryer for 24 hours to remove moisture.

[0063] The polyimide material obtained after freeze-drying was placed in a high-temperature furnace at 350°C, with a mixed gas flow of argon and hydrogen (90% argon, 10% hydrogen), baked for 2 hours at a heating rate of 5°C / min to obtain silver nanoparticles deposited on the polyimide surface.

[0064] Copper plating was performed in the same manner as in Example 2.

[0065] Experimental example:

[0066] According to the "QJ832B-2011 Test Method for Multilayer Printed Circuit Boards for Aerospace Use" standard, the surface mount pad pull-off strength test method is used to test the pull-off strength of the solder joints between the surface coating of the polyimide material and the substrate.

[0067] A thermal shock test (QJ 479 Metal Coating Bond Strength Test Method - Thermal Shock Test) was used to place the test piece in a +200°C oven for 10 minutes, then quickly take it out and place it in cold water for 10 minutes.

[0068] The high and low temperature environment test (GJB 150.5A-2009) was adopted. The test piece was placed in a +120℃ oven, baked at high temperature for 10 minutes, then quickly taken out and placed in liquid nitrogen for 10 minutes.

[0069] The copper-plated samples of Example 1, Comparative Example 1 and Comparative Example 2 were tested, and the results were shown in Table 1 and Figure 6-8 ;

[0070] Table 1

[0071]

[0072]

[0073] According to the results in Table 1, the copper plating of the surface-modified polyimide of the present application has a solder joint pull-out strength of 5.62 MPa, while the solder joint pull-out strengths of Comparative Example 1 and Comparative Example 2 do not exceed 2 MPa;

[0074] according to Figure 6-Figure 8The results show that after copper plating on the surface-modified polyimide of the present application and then undergoing thermal shock testing and -196°C to +120°C thermal cycling testing, the coating exhibited good appearance, with no bulging or cracking. However, the copper coatings of Comparative Examples 1 and 2 exhibited significant cracking and shedding during the thermal shock test, so the -196°C to +120°C thermal cycling test was not performed. These test results demonstrate that modifying polyimide according to the present method significantly improves the bonding strength of the metal coating and its tolerance to high and low temperature environments.

[0075] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A method for preparing a surface-modified polyimide, characterized in that: include: S1. treating the polyimide surface with a hydrolysis solution; The hydrolysis solution includes a strong base, potassium permanganate, sodium carbonate and sodium phosphate; S2. The surface hydrolyzed polyimide was mixed with a silver ion-containing solution to adsorb silver ions in situ. After adsorption, the polyimide was frozen in liquid nitrogen and then freeze-dried in vacuum; S3. The freeze-dried polyimide is baked at high temperature in an atmosphere of a mixed gas of argon and hydrogen to obtain the surface-modified polyimide.

2. The preparation method according to claim 1, characterized in that The hydrolysis solution comprises 300-400 g / L of strong alkali, 80-160 g / L of potassium permanganate, 30-40 g / L of sodium carbonate, and 5-10 g / L of sodium phosphate.

3. The preparation method according to claim 1 or 2, characterized in that The strong base includes sodium hydroxide and / or potassium hydroxide.

4. The preparation method according to claim 1, characterized in that The silver ion-containing solution includes silver nitrate.

5. The preparation method according to claim 1, characterized in that The high temperature baking is baking at a temperature of 350-370°C.

6. The preparation method according to any one of claims 1 to 5, characterized in that Also included is metal plating on surface-modified polyimides.

7. A surface-modified polyimide prepared by the preparation method according to any one of claims 1 to 6.

8. A polyimide surface hydrolysis solution, characterized in that: These include strong bases, potassium permanganate, sodium carbonate, and sodium phosphate.

9. The hydrolysis solution according to claim 8, characterized in that The hydrolysis solution comprises 300-400 g / L of strong alkali, 80-160 g / L of potassium permanganate, 30-40 g / L of sodium carbonate, and 5-10 g / L of sodium phosphate.

10. Use of the hydrolysis solution according to claim 8 or 9 in preparing a polyimide surface modifier.

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