A kovar alloy composite material and a method for manufacturing the same

Abstract

The application discloses a kind of kovar alloy composite materials and preparation method thereof, for this, the preparation method provided in the present application includes the uniform iron or cobalt plating layer that is electroless plated on the surface of kovar alloy powder;Uniform copper plating layer is electroless plated on the surface of the kovar alloy powder plated with iron or cobalt;Kovar alloy powder after step S2 is treated dry reduction;The powder after dry reduction is hot-pressed sintering, and kovar alloy composite material is obtained.The kovar alloy composite material prepared in the application is distributed in three-dimensional network structure, and has higher thermal conductivity on the basis of retaining the low expansion coefficient of kovar alloy, which is beneficial to its application in aerospace, chemical industry, electronics, semiconductor, integrated circuit, instrument, machinery manufacturing, electric light source and other industrial fields.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sealing material preparation, and particularly relates to a Kovar alloy composite material and a preparation method thereof. BACKGROUND

[0002] The Kovar alloy is widely used in the matching sealing of glass ceramic materials due to its low expansion coefficient, and plays an important role in the industrial fields of aerospace, chemical industry, electronics, semiconductor, integrated circuit, instrument, mechanical manufacturing, electric light source and the like. As a sealing material, the material is usually required to have a low thermal expansion coefficient, to reduce or avoid the generation of thermal stress, a very good thermal conductivity to provide heat dissipation, and good processing or forming performance. However, the thermal conductivity of the Kovar alloy is extremely low, which greatly limits the application of the Kovar alloy.

[0003] At present, the commonly used method for improving the thermal conductivity of the Kovar alloy mainly focuses on combining the Kovar alloy with a metal or an alloy with a higher thermal conductivity together to form a composite material, for example, high-pressure rolling and then annealing of Cu and the Kovar alloy to form a solid solution connection, forming a sandwich structure Cu layered composite material, the CTE of which is adjustable, the thermal conductivity of which is variable, but the material performance has heterogeneity; and adding Kovar alloy powder particles into a copper matrix to form a composite material, or mechanically mixing high-thermal-conductivity alloy or metal powder with Kovar alloy powder to form a composite material, the Kovar alloy composite material prepared in this way is easy to cause the thermal expansion coefficient of the material to increase due to element diffusion.

[0004] In summary, how to improve the thermal conductivity of the Kovar alloy composite material while maintaining the thermal expansion coefficient performance of the Kovar alloy composite material is a technical problem to be solved at present. SUMMARY

[0005] The main purpose of the application is to provide a Kovar alloy composite material with high thermal conductivity and excellent thermal expansion coefficient performance and a preparation method thereof.

[0006] To this end, the application provides a preparation method of a Kovar alloy composite material, which comprises the following steps:

[0007] S1, uniformly electroless plating an iron or cobalt plating layer on the surface of the Kovar alloy powder;

[0008] S2, uniformly electroless plating a copper plating layer on the surface of the Kovar alloy powder plated with the iron or cobalt;

[0009] S3, drying and reducing the Kovar alloy powder treated in step S2;

[0010] S4, hot-pressing sintering the dried and reduced powder to obtain the Kovar alloy composite material.

[0011] Principle and advantages

[0012] First, a uniform iron or cobalt plating layer is plated on the surface of the Kovar alloy powder by electroless plating, the iron or cobalt plating layer completely wraps the Kovar alloy powder, and then a uniform copper plating layer is plated on the surface of the Kovar alloy powder. By using the characteristics that iron and cobalt are elements of the Kovar alloy itself and have a low solid solubility with copper, iron or cobalt is introduced as an intermediate protective layer between copper and the powder matrix, so that copper is less diffused into the Kovar alloy matrix during sintering, thereby playing a role in improving the thermal conductivity of the composite material on the basis of less increasing the thermal expansion coefficient of the material.

[0013] In addition, the powder surface after electroless plating may be oxidized during the drying process, causing iron, cobalt, and copper to form oxides. By adding a reduction step, the oxygen content of the surface plating layer is reduced, and the influence of oxides on the performance of the material is reduced.

[0014] Specifically, the specific process of electroless plating iron or cobalt is as follows: configure the iron plating solution or cobalt plating solution according to a certain proportion, adjust the pH value with lye, add the Kovar alloy powder into the plating solution, then slowly add a reducing agent, stir until the reaction is complete, use the reducing agent to reduce metal Fe or Co ions into metal particles and deposit them on the surface of the Kovar alloy powder, and then wash with deionized water until neutral.

[0015] Specifically, the amount of Kovar alloy powder added is 20-50 g / L based on the volume of the plating solution; wherein,

[0016] The iron plating solution contains a main salt and a complexing agent, the main salt is FeSO4·7H2O, and the complexing agent is a mixture of citric acid and sucrose; the concentration of the main salt is 10-20 g / L and the concentration of the complexing agent is 30-40 g / L based on the volume of the iron plating solution, and the mass ratio of citric acid to sucrose is 3:1-10:1.

[0017] The cobalt plating solution contains a main salt and a complexing agent, the main salt is CoSO4·7H2O, and the complexing agent is citric acid; the concentration of the main salt is 10-20 g / L and the concentration of the complexing agent is 30-40 g / L based on the volume of the cobalt plating solution. The reason why the concentrations of the main salt and the complexing agent in the cobalt plating solution are controlled within the above range is similar to that of the iron plating solution, which will not be described here.

[0018] The reason why the plating solution and powder ratio, the concentration of the main salt and the complexing agent in the iron plating solution are controlled within the above range is that if the amount of powder added is too much, the concentration of the plating solution will be too high, which may cause free plating or uneven and non-dense plating layer, and if the amount of powder added is too little, the concentration of the plating solution will be too low, which makes it difficult to plate; if the concentration of the main salt exceeds the above range, it will be difficult to plate; if it is lower than the above range, the plating efficiency will be low; if the concentration of the complexing agent is too high, the reaction will be slow, and if it is too low, the complexing agent will be difficult to complex with the main salt to form a precipitate, causing the plating layer to not wrap the Kovar alloy powder well.

[0019] Specifically, the specific process of electroless copper plating is as follows: configuring copper plating solution in a certain proportion, adjusting pH value with alkali solution, adding Kovar alloy powder plated with iron or cobalt into the copper plating solution, then slowly adding reducing agent, stirring until the reaction is completed, and then washing with deionized water until neutral.

[0020] The adding amount of Kovar alloy powder is 20-50 g / L based on the volume of plating solution, the copper plating solution contains main salt and complexing agent, the main salt is CuSO4·5H2O, and the complexing agent is a mixture of KNaC4H4O6·4H2O (potassium sodium tartrate) and EDTA (ethylenediaminetetraacetic acid); the concentration of main salt is 10-30 g / L based on the volume of copper plating solution, and the concentration of complexing agent is 30-40 g / L, the mass ratio of KNaC4H4O6·4H2O and EDTA is 1:1-4:5. The reason why the concentrations of main salt and complexing agent in the copper plating solution are controlled within the above range is similar to that of the iron plating solution, which will not be repeated here.

[0021] Specifically, the reducing agent added in electroless copper plating is glyoxylic acid or formaldehyde, and the adding amount of reducing agent is 10-40 ml / L based on the volume of copper plating solution, and the temperature of copper plating solution is maintained at 50-60℃.

[0022] Specifically, the reducing agent added in electroless iron or cobalt plating is N2H4, and the adding amount of reducing agent is 10-40 ml / L based on the volume of plating solution, the purity of reducing agent is 80%, and the temperature of plating solution is maintained at 50-60℃.

[0023] The reason why the amount of reducing agent is set within the above range in electroless iron, cobalt or copper plating is that when the amount of reducing agent exceeds the designed range, the reaction speed is too fast, free iron, cobalt or copper is easily produced, and the generated plating layer is relatively loose, and when the amount of reducing agent is lower than the above range, the reaction rate is too low, and the plating layer generation time is too long.

[0024] Specifically, the vacuum degree is controlled to be ≤10 -3 MPa during hot-pressing sintering, the heating rate is 20-50℃ / min, the sintering temperature is 650℃-950℃, the pressure is 5-20 MPa, and the holding time is 5-20 min.

[0025] The reason why the above parameters are set as above is that if the vacuum degree is too low, the material is easily reacted with oxygen at a relatively high temperature, which affects the performance of the material, if the temperature is too high, the plating layer becomes liquid phase, if the temperature is too low, the density of the composite material is too low, the performance is reduced, if the pressure and holding time are too short, the density is not enough, if the holding time is too long, the diffusion time of the plating layer is increased, the thermal conductivity is improved, and the effect is not obvious, and if the pressure is too large, the mold is easily cracked.

[0026] Specifically, the reduction temperature is 300-500℃, the reduction time is 1-3h, and the reduction atmosphere is hydrogen. The reason for controlling the reduction temperature and the reduction time within the above range is that when the reduction temperature exceeds the above range, the plating layer on the surface of the powder diffuses to the substrate at a high speed, and when the reduction time is too long, the diffusion time is too long, which are not conducive to the effective maintenance of the plating layer; and when the temperature is too low and the time is too short, the reduction effect is not good because the oxide reduction temperature is not reached.

[0027] Specifically, the Kovar alloy powder needs to be pretreated before being plated with iron or cobalt. The pretreatment process is to remove oil from the Kovar alloy powder, and then perform sensitization, activation or pickling treatment. Among them,

[0028] The purpose of oil removal is to keep the surface of the powder clean, which is conducive to plating. The specific process of oil removal is to put the Kovar alloy powder into an alkali solution for stirring treatment. The alkali solution is NaOH solution, the concentration of the alkali solution is 100-120g / L, the stirring time is 30-60min, and the stirring temperature is 50-60℃.

[0029] Sensitization is to put the oil-removed Kovar alloy powder into a sensitizing solution for stirring treatment. The sensitizing solution is SnCl2 solution, the concentration of the sensitizing solution is 10-15g / L, the pH value is 1-1.5, the stirring time is 20-30min, and the stirring temperature is room temperature. Activation is to put the sensitized Kovar alloy powder into an activating solution for stirring treatment. The activating solution is PdCl2 solution, the concentration of the activating solution is 0.05-0.07g / L, the activation temperature is 50℃-60℃, and the stirring time is 20-30min. Sensitization treatment forms a thin liquid film with reducing property on the surface of the powder, and activation reduces the divalent tin ions to metallic palladium (Sn2++Pd2+→Sn4++Pd). These elemental palladiums are distributed on the surface of the Kovar alloy powder and become the catalytic active centers on the surface of the Kovar alloy powder, thereby facilitating plating and improving the adhesion of the plating layer.

[0030] Pickling is to put the oil-removed Kovar alloy powder into an acid solution for stirring treatment. The acid solution is HCl solution, the concentration of the acid solution is 15-20vol.%, and the stirring time is 5-10s. Pickling can remove surface oxides and dirt, improve surface roughness, and improve hydrophilicity.

[0031] The Kovar alloy powder is at least one of iron-nickel and iron-nickel-cobalt systems. In steps S1 and S2, the alkali solution is KOH solution, and the pH value is adjusted to 11-13.

[0032] Another aspect of the present application also provides a Kovar alloy composite material prepared by the above method.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] The application uses Kovar alloy powder as a base, and through a chemical plating method, an iron or cobalt intermediate protective plating layer is plated on the surface of the powder, then a copper plating layer is plated, and then a Kovar alloy composite powder is obtained through hydrogen reduction, and finally a high-thermal-conductivity Kovar alloy composite material is prepared through hot-pressing sintering. The Kovar alloy composite material prepared by the method has a low expansion coefficient, and because the copper is distributed in a three-dimensional network structure in the composite material, the composite material has a high thermal conductivity. In addition, the composite material is prepared by a chemical plating method, and the thickness of the plating layer can be adjusted to realize the mutual cooperation of the thermal conductivity and the expansion coefficient of the composite material. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort.

[0036] Figure 1 SEM picture of the iron-nickel powder after chemical plating of cobalt in Example 1;

[0037] Figure 2 SEM picture of the iron-nickel powder after chemical plating of copper on the iron-nickel powder plated with cobalt in Example 1;

[0038] Figure 3 EDS-mapping picture of the Kovar alloy composite material after hot-pressing sintering of the iron-nickel powder plated with iron and copper in Example 5;

[0039] Figure 4 SEM picture of the iron-nickel powder after chemical plating of iron in Comparative Example 3;

[0040] Figure 5 EDS-mapping picture of the Kovar alloy composite material after hot-pressing sintering of the iron-nickel powder plated with iron and copper in Comparative Example 3. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present application.

[0042] A preparation method of a Kovar alloy composite material, comprising:

[0043] S1, uniformly plating an iron or cobalt plating layer on the surface of a Kovar alloy powder;

[0044] S2, electroless plating a uniform copper plating layer on the surface of the iron or cobalt plated Kovar alloy powder;

[0045] S3, drying and reducing the Kovar alloy powder after step S2;

[0046] S4, hot-pressing and sintering the dried and reduced powder to obtain a Kovar alloy composite material.

[0047] The present application first electrolessly plates a uniform iron or cobalt plating layer on the surface of the Kovar alloy powder, and then electrolessly plates a uniform copper plating layer on the surface of the Kovar alloy powder. The iron or cobalt plating layer completely wraps the Kovar alloy powder. The iron or cobalt is introduced as an intermediate protective layer between copper and the powder matrix, which is based on the characteristics that iron and cobalt are elements of the Kovar alloy itself and have a low solid solubility with copper. The copper is less diffused into the Kovar alloy matrix during sintering and finally distributed in a three-dimensional network structure in the composite material, so that the prepared Kovar alloy composite material has a high thermal conductivity while retaining the low expansion coefficient of the Kovar alloy. In addition, the surface of the powder after electroless plating may be oxidized during the drying process, forming oxides of iron, cobalt and copper. By adding a reduction step, the oxygen content of the surface plating layer is reduced, and the influence of the oxides on the performance of the material is reduced.

[0048] The specific preparation process of the above Kovar alloy composite material is as follows:

[0049] (1) Kovar alloy powder pretreatment

[0050] In order to obtain a good plating effect, the Kovar alloy powder needs to be sequentially degreased, sensitized, activated or pickled.

[0051] (2) Electroless plating of iron or cobalt

[0052] An iron plating solution or a cobalt plating solution is prepared according to a certain proportion, an alkali solution is used to adjust the pH value, the Kovar alloy powder after activation or pickling in step (1) is added to the solution, then a reducing agent A is slowly added, stirring until the reaction is complete, and then deionized water is used to wash to neutral.

[0053] (3) Electroless plating of copper

[0054] A copper plating solution is prepared according to a certain proportion, an alkali solution is used to adjust the pH value, the Kovar alloy powder after plating of iron or cobalt in step (2) is added to the solution, then a reducing agent B is slowly added, stirring until the reaction is complete, and then deionized water is used to wash to neutral.

[0055] (4) Preparation of Kovar alloy composite powder

[0056] The powder prepared in step (3) is reduced to obtain a Kovar alloy composite powder.

[0057] (5) Preparation of Kovar alloy composite material

[0058] The prepared preformed composite powder is sintered to obtain the Kovar alloy composite material.

[0059] In the above preparation method, the iron plating solution contains a main salt and a complexing agent, the main salt is FeSO4·7H2O, and the complexing agent is a mixture of citric acid and sucrose; the cobalt plating solution contains a main salt and a complexing agent, the main salt is CoSO4·7H2O, and the complexing agent is citric acid; and the copper plating solution contains a main salt and a complexing agent, the main salt is CuSO4·5H2O, and the complexing agent is a mixture of KNaC4H4O6·4H2O and EDTA.

[0060] The inventors have found that, in order to obtain a uniform iron plating layer that can completely coat the Kovar alloy powder, the ratio of the plating solution to the powder and the addition amount of the main salt and the complexing agent need to be specially limited. The addition amount of the Kovar alloy powder is 20-50 g / L based on the volume of the iron plating solution. If the addition amount of the powder is too large, the main salt concentration of the iron plating solution is too high, a large amount of free iron is generated in the solution after plating, and the powder is almost not plated with iron. If the addition amount of the powder is too small, the main salt concentration of the plating solution is too low, and the plating efficiency is low. The main salt concentration is limited to 10-20 g / L, and the complexing agent concentration is limited to 30-40 g / L. The mass ratio of citric acid to sucrose is limited to 3:1-10:1, which is more appropriate. If the main salt concentration exceeds the above range, it will be difficult to initiate plating. If the main salt concentration is lower than the above range, the plating efficiency is low. If the complexing agent concentration is too high, the reaction will be slow. If the complexing agent concentration is too low, the complexing agent will be difficult to complex with the main salt to generate a precipitate, and the plating layer cannot well coat the Kovar alloy powder.

[0061] Similarly, in the cobalt plating solution, the main salt concentration is controlled to 10-20 g / L based on the volume of the cobalt plating solution, and the complexing agent concentration is controlled to 30-40 g / L, which is more appropriate. In the copper plating solution, the main salt concentration is controlled to 10-30 g / L based on the volume of the copper plating solution, the complexing agent concentration is controlled to 30-60 g / L, and the mass ratio of KNaC4H4O6·4H2O to EDTA (ethylenediaminetetraacetic acid) is controlled to 1:1-4:5, which is more appropriate.

[0062] Specifically, the reducing agent A is N2H4, and the addition amount of the reducing agent is 10-40 ml / L based on the volume of the iron or cobalt plating solution. The purity of the reducing agent is 80%. The reducing agent B is glyoxalic acid and / or formaldehyde, and the addition amount of the reducing agent is 10-40 ml / L based on the volume of the copper plating solution. The reducing agents A and B are set to the above contents because, if the addition amount of the reducing agent exceeds the designed range, the reaction speed will be too fast, free iron, cobalt or copper will be easily generated, and the generated plating layer will be relatively fluffy. If the addition amount of the reducing agent is lower than the above range, the reaction rate will be too low, and the plating layer will be generated for too long.

[0063] The inventor further found that the temperature of the iron or copper plating solution is preferably maintained at 50-60℃ during plating, and the temperature of the copper plating solution is preferably maintained at 50-60℃, because if the plating temperature is too low, the substances do not react or react too slowly, and if the temperature is too high, the reaction speed is too fast, the plating layer is not dense and a large amount of free iron, cobalt or copper can be produced.

[0064] In the above preparation method, in steps (2) and (3), the alkali solution is a KOH solution, and the pH value is adjusted to 11-13.

[0065] The inventor further found that a good reduction effect can be achieved when the reduction temperature is 300-500℃ and the reduction time is 1-3h in a hydrogen atmosphere, because if the reduction temperature exceeds the above range, the plating layer on the surface of the powder diffuses into the matrix at a faster speed, and if the reduction time is too long, the diffusion time is too long, which are not conducive to the effective maintenance of the plating layer; and if the temperature is too low and the time is too short, the reduction effect is not good because the oxide reduction temperature is not reached.

[0066] Specifically, to obtain a Kovar alloy composite material with excellent performance, the vacuum degree is controlled to be ≤10 -3 MPa, the heating rate is 20-50℃ / min, the sintering temperature is 650℃~950℃, the pressure is 5-20Mpa, and the holding time is 5-20min.

[0067] The above parameters are set as above because if the vacuum degree is too low, the material is easily reacted with oxygen at a high temperature, which affects the performance of the material, if the temperature is too high, the plating layer becomes a liquid phase, if the temperature is too low, the density of the composite material is too low and the performance is reduced, if the pressure and holding time are too short, the density is not enough, if the holding time is too long, the diffusion time of the plating layer increases and the thermal conductivity improvement effect is not obvious, and if the pressure is too large, there is a risk of mold cracking.

[0068] In step (1), the oil removal is to put the Kovar alloy powder into an alkali solution and stir, the alkali solution is a NaOH solution, the concentration of the alkali solution is 100-120g / L, the stirring time is 30-60min, and the stirring temperature is 50-60℃;

[0069] The sensitization is to put the oil-removed Kovar alloy powder into a sensitization solution and stir, the sensitization solution is a SnCl2 solution, the concentration of the sensitization solution is 10-15g / L, the pH value is 1-1.5, the stirring time is 20-30min, and the stirring temperature is room temperature;

[0070] The activation is that the sensitized Kovar alloy powder is added into an activation liquid for stirring treatment, the activation liquid is a PdCl2 solution, the concentration of the activation liquid is 0.05-0.07 g / L, the activation temperature is 50-60 ℃, and the stirring time is 20-30 min.

[0071] The pickling is that the oil-removed Kovar alloy powder is added into an acid liquid for stirring treatment, the acid liquid is an HCl solution, the concentration of the acid liquid is 15-20 vol.%, and the stirring time is 5-10 s.

[0072] The composite material prepared by the patent is prepared by the chemical plating method, the mutual cooperation of the thermal conductivity and the expansion coefficient of the composite material can be realized by adjusting the plating layer thickness, the solid solubility between iron or cobalt and copper is small, and the solid solubility between nickel and copper is unlimited, the Kovar alloy composite material prepared by the patent greatly reduces the diffusion between the powder matrix and the copper plating layer because of the iron plating layer or the cobalt plating layer as the intermediate plating layer, and the comprehensive performance of the composite material is improved.

[0073] The copper in the Kovar alloy composite material prepared by the patent is distributed in a three-dimensional network structure, the Kovar alloy composite material has high thermal conductivity on the basis of retaining the low expansion coefficient of the Kovar alloy, and is favorable for application in the industrial fields of aerospace, chemical industry, electronics, semiconductor, integrated circuit, instrument, mechanical manufacturing, electric light source and the like.

[0074] The application will be further described below by combining specific examples. Example 1

[0075] The specific process for preparing the Kovar alloy composite material in the embodiment is as follows:

[0076] (1) Kovar alloy powder pretreatment

[0077] 50 g of spherical iron-nickel-cobalt powder (Fe-29%Ni-17%Co) with a particle size of 40 μm is added into a NaOH solution with a concentration of 100 g / L, and stirring is carried out at 60 ℃ for 30 min, and after oil removal, the powder is washed with deionized water until neutral.

[0078] The oil-removed powder is added into a SnCl2 solution with a concentration of 10 g / L and a pH value of 1.5, and stirring is carried out at room temperature for 30 min, and after sensitization, the powder is washed with deionized water until neutral.

[0079] The sensitized powder is added into a PdCl2 solution with a concentration of 0.05 g / L, and stirring is carried out at 50 ℃ for 30 min, and after activation, the powder is washed with deionized water until neutral.

[0080] (2) Chemical cobalt plating

[0081] The activated iron-nickel-cobalt powder of step (1) is added into the cobalt plating solution, the amount of the iron-nickel-cobalt powder added is 40 g / L based on the volume of the cobalt plating solution, the pH value is adjusted to 12 by using KOH solution, then the reducing agent N2H4 is slowly added, the amount of the reducing agent N2H4 added is 30 ml / L based on the volume of the cobalt plating solution, the stirring is continued until the reaction is completed, the powder is washed by using deionized water until the pH value is neutral, the cobalt plating solution contains the following components: CoSO4·7H2O 15 g / L, C6H8O7 (citric acid) 40 g / L, the temperature of the plating solution is maintained at 50℃;

[0082] (3) Electroless copper plating

[0083] The powder after the electroless cobalt plating of step (2) is added into the copper plating solution, the amount of the powder added is 40 g / L based on the volume of the copper plating solution, then the reducing agent glyoxalic acid is added, the pH value is adjusted to 12 by using KOH solution, the amount of the reducing agent glyoxalic acid added is 30 ml / L based on the volume of the copper plating solution, the stirring is continued until the reaction is completed, the powder is washed by using deionized water until the pH value is neutral and dried, the pH value of the plating solution is adjusted by using KOH solution during the stirring to maintain the pH value at 12; the copper plating solution contains the following components: CuSO4·5H2O 15 g / L, KNaC4H4O6·4H2O 20 g / L, EDTA 20 g / L, the temperature of the plating solution is maintained at 60℃;

[0084] (4) Preparation of Kovar alloy composite powder

[0085] The powder prepared in step (3) is reduced at 450℃ under hydrogen atmosphere for 1 h to obtain the Kovar alloy composite powder;

[0086] (5) Preparation of Kovar alloy composite material

[0087] The Kovar alloy composite powder prepared in step (4) is hot-pressed and sintered, the vacuum degree is controlled to be ≤10 -3 MPa, the heating rate is 50℃ / min, the sintering temperature is 900℃, the pressure is 20 MPa, the holding time is 10 min, and the Kovar alloy composite material is obtained after cooling in air.

[0088] In the process of preparing the Kovar alloy composite material in this embodiment, the SEM pictures of the powder after the cobalt plating and the powder after the copper plating are respectively as Figure 1 and Figure 2 It can be seen that the cobalt plating layer and the copper plating layer are uniformly distributed, the powder particles are completely coated, and the prepared Kovar alloy composite material has a density of 8.15 g / cm 3, the thermal conductivity is 30.5 W / (m·K), and the thermal expansion coefficient (10-6 / ℃) is 5.8. The reason why the thermal conductivity and the thermal expansion coefficient are good is that the cobalt plating layer and the copper plating layer completely wrap the Kovar alloy powder. Since cobalt is a low-solubility element of the Kovar alloy and copper, cobalt acts as an intermediate protective layer between copper and the powder matrix, completely separating the copper from the powder particles, so that the copper is less diffused into the Kovar alloy matrix during sintering, thereby not affecting the thermal expansion performance. The copper is finally distributed in a three-dimensional network structure in the composite material, so that the prepared Kovar alloy composite material has a higher thermal conductivity. Example 2

[0089] Different from example 1, the addition amount of Kovar alloy powder is 40 g / L based on the volume of cobalt plating solution. During electroless cobalt plating, the cobalt plating solution contains the following components CoSO4·7H2O 12 g / L, C6H8O7 (citric acid) 40 g / L based on the volume of cobalt plating solution.

[0090] The addition amount of Kovar alloy powder is 40 g / L based on the volume of copper plating solution. During electroless copper plating, the copper plating solution contains the following components CuSO4·5H2O 15 g / L, KNaC4H4O6·4H2O 16 g / L, EDTA 20 g / L based on the volume of copper plating solution.

[0091] In the preparation of the Kovar alloy composite material in this example, the SEM pictures of the powder after cobalt plating and copper plating show that the cobalt plating layer and the copper plating layer are uniformly distributed, and the powder particles are completely coated. The prepared Kovar alloy composite material has a density of 8.13 g / cm 3 , a thermal conductivity of 28.7 W / (m·K), and a thermal expansion coefficient (10-6 / ℃) of 6.1. Example 3

[0092] Different from example 1, the addition amount of Kovar alloy powder is 40 g / L based on the volume of cobalt plating solution. During electroless cobalt plating, the cobalt plating solution contains the following components CoSO4·7H2O 18 g / L, C6H8O7 (citric acid) 40 g / L based on the volume of cobalt plating solution.

[0093] During electroless copper plating, the addition amount of Kovar alloy powder is 40 g / L based on the volume of copper plating solution. The copper plating solution contains the following components CuSO4·5H2O 25 g / L, KNaC4H4O6·4H2O 16 g / L, EDTA 20 g / L based on the volume of copper plating solution.

[0094] The Kovar alloy composite material prepared in this example has a density of 8.17 g / cm 3 , a thermal conductivity of 32.5 W / (m·K), and a thermal expansion coefficient (10-6 / ℃) of 6.3. Example 4

[0095] Different from Example 1, the Kovar alloy powder is spherical iron-nickel powder (Fe-50%Ni).

[0096] The density of the Kovar alloy composite prepared in this example is 8.31 g / cm 3 , the thermal conductivity is 30.8 W / (m·K), and the thermal expansion coefficient (10-6 / ℃) is 8.9. Example 5

[0097] The specific process for preparing the Kovar alloy composite in this example is as follows:

[0098] (1) Pretreatment of Kovar alloy powder

[0099] 50 g of spherical iron-nickel powder (Fe-50%Ni) with a particle size of 45 μm was added to a NaOH solution with a concentration of 100 g / L and stirred at 60°C for 30 min. After oil removal was completed, it was washed with deionized water until it was neutral.

[0100] The oil-removed Kovar alloy powder was added to a HCl solution with a concentration of 15 vol.% and stirred for 10 s. After pickling was completed, it was washed with deionized water until it was neutral.

[0101] (2) Electroless iron plating

[0102] The iron-nickel powder after pickling in step (1) was added to an iron plating solution, and the amount of iron-nickel powder added was 35 g / L based on the volume of the iron plating solution. The pH value was adjusted to 12 using a KOH solution, and then a reducing agent N2H4 was slowly added, and the amount of reducing agent N2H4 added was 40 ml / L based on the volume of the iron plating solution. Stirring was performed until the reaction was completed, and then it was washed with deionized water until it was neutral. The iron plating solution contained the following components: FeSO4·7H2O 20 g / L, citric acid 30 g / L, and sucrose 10 g / L based on the volume of the iron plating solution. The temperature of the plating solution was maintained at 50°C.

[0103] (3) Electroless copper plating

[0104] The powder after electroless iron plating in step (2) was added to a copper plating solution, and the amount of powder added was 40 g / L based on the volume of the copper plating solution. Then, a reducing agent glyoxalic acid was added, and the amount of reducing agent glyoxalic acid added was 40 ml / L based on the volume of the copper plating solution. The pH value was adjusted to 12 using a KOH solution, and stirring was performed until the reaction was completed. Then, it was washed with deionized water until it was neutral and dried. The pH value of the plating solution was adjusted using a KOH solution during stirring to maintain the pH value at 12. The copper plating solution contained the following components: CuSO4·5H2O 20 g / L, KNaC4H4O6·4H2O 20 g / L, and EDTA 20 g / L based on the volume of the copper plating solution. The temperature of the plating solution was maintained at 55°C.

[0105] (4) Preparation of Kovar alloy composite powder

[0106] The powder prepared in step (3) was reduced at 450°C for 1 hour in a hydrogen atmosphere to obtain Kovar alloy composite powder;

[0107] (5) Preparation of Kovar alloy composite materials

[0108] The Kovar alloy composite powder obtained in step (4) is hot-pressed and sintered, with the vacuum degree controlled to be ≤10. -3 Kovar alloy composite material was obtained by heating at a pressure of MPa, a heating rate of 40℃ / min, a sintering temperature of 850℃, a pressure of 20 MPa, holding at the temperature for 10 min, and then cooling in air.

[0109] The EDS-mapping image of the Kovar alloy composite material prepared in this embodiment is shown below. Figure 3 As shown, copper is distributed in a three-dimensional network structure in the material, and the Kovar alloy powder particles are evenly distributed.

[0110] The density of the Kovar alloy composite material prepared in this embodiment is 8.27 g / cm³. 3 The thermal conductivity is 29.8 W / (m·K), and the coefficient of thermal expansion (10⁻⁶ / ℃) is 8.8. The good thermal conductivity and coefficient of thermal expansion are due to the fact that the iron and copper plating completely encapsulate the Kovar alloy powder. Since iron is an inherent element of Kovar alloy and has low solid solubility with copper, the iron acts as an intermediate protective layer between the copper and the powder matrix, completely separating the powder particles from the copper. This minimizes the diffusion of copper into the Kovar alloy matrix during sintering, thus not affecting the thermal expansion properties. Furthermore, the copper is ultimately distributed in a three-dimensional network structure in the composite material, resulting in a Kovar alloy composite material with high thermal conductivity. Example 6

[0111] Unlike Example 5, in the chemical iron plating process, the amount of Kovar alloy powder added is 30 g / L based on the volume of the iron plating solution. Based on the volume of the iron plating solution, the iron plating solution contains the following components: FeSO4·7H2O 20 g / L, citric acid 30 g / L, sucrose 10 g / L, and formaldehyde is used as the reducing agent.

[0112] Based on the volume of the copper plating solution, the amount of Kovar alloy powder added is 30 g / L. During electroless copper plating, based on the volume of the copper plating solution, the copper plating solution contains the following components: CuSO4·5H2O 25 g / L, KNaC4H4O6·4H2O 20 g / L, and EDTA 20 g / L.

[0113] The density of the Kovar alloy composite material prepared in this embodiment is 8.26 g / cm³. 3 Its thermal conductivity is 29.6 W / (m·K), and its coefficient of thermal expansion (10-6 / ℃) is 8.9. Example 7

[0114] Different from Example 5, the amount of the Kovar alloy powder added in the plating solution is 40 g / L, and the plating solution contains the following components: FeSO4·7H2O 20 g / L, citric acid 25 g / L, and sucrose 5 g / L, based on the volume of the plating solution.

[0115] The amount of the Kovar alloy powder added in the plating solution is 40 g / L, and the plating solution contains the following components: CuSO4·5H2O 20 g / L, KNaC4H4O6·4H2O 15 g / L, and EDTA 15 g / L, based on the volume of the plating solution.

[0116] The Kovar alloy composite material prepared in this example has a density of 8.24 g / cm 3 , a thermal conductivity of 29.2 W / (m·K), and a thermal expansion coefficient (10-6 / ℃) of 9.0.

[0117] Comparative Example 1

[0118] Different from Example 1, in Comparative Example 1, the amount of the Kovar alloy powder added in the plating solution is 60 g / L, and the plating solution contains the following components: CoSO4·7H2O 20 g / L and C6H8O7 (citric acid) 40 g / L, based on the volume of the plating solution; the amount of the Kovar alloy powder added in the plating solution is 60 g / L, and the plating solution contains the following components: CuSO4·5H2O 30 g / L, KNaC4H4O6·4H2O 30 g / L, and EDTA 30 g / L, based on the volume of the plating solution.

[0119] The Kovar alloy composite material prepared in this example has a density of 8.13 g / cm 3 , a thermal conductivity of 23.7 W / (m·K), and a thermal expansion coefficient (10-6 / ℃) of 6.5. The reason for the poor performance of the composite material prepared in this comparative example is that the amount of the powder added is increased, the concentration of the solution is increased accordingly, the plating is difficult, the plating layer is thin and not dense after a long plating time, the isolation of the intermediate protective layer is ineffective, copper diffuses into the Kovar alloy matrix during sintering, the thermal expansion coefficient is increased, and the thermal conductivity is decreased.

[0120] Comparative Example 2

[0121] Unlike Example 1, in the electroless cobalt plating, the cobalt plating solution contains the following components by volume: CoSO4·7H2O 5g / L, C6H8O7 (citric acid) 20g / L; and the copper plating solution contains the following components by volume: CuSO4·5H2O 15g / L, KNaC4H4O6·4H2O 20g / L, EDTA 20g / L.

[0122] The density of the Kovar alloy composite material prepared in this comparative example is 8.12 g / cm³. 3 The thermal conductivity is 23.5 W / (m·K), and the coefficient of thermal expansion (10-6 / ℃) is 6.4. The reason for the deterioration of the composite material prepared in Comparative Example 2 is that the concentration of the plating solution is too low, the reaction is slow, and some cobalt ions cannot be reduced to cobalt due to the low concentration. As a result, less cobalt is plated on the powder, and it is impossible to form an intermediate protective layer that completely covers the Kovar alloy powder. This causes copper to diffuse into the Kovar alloy matrix during sintering, resulting in an increase in the coefficient of thermal expansion.

[0123] Comparative Example 3

[0124] Unlike Example 5, the amount of Kovar alloy powder added is 60 g / L based on the volume of the iron plating solution. In the electroless iron plating, the iron plating solution contains the following components based on the volume: FeSO4·7H2O 30 g / L, citric acid 30 g / L, and sucrose 10 g / L. The amount of Kovar alloy powder added is 40 g / L based on the volume of the copper plating solution. The copper plating solution contains the following components based on the volume: CuSO4·5H2O 20 g / L, KNaC4H4O6·4H2O 20 g / L, and EDTA 20 g / L.

[0125] The Kovar alloy composite material prepared in this comparative example, after iron plating, has the following SEM image of iron-nickel powder: Figure 4 As shown, the EDS-mapping image of Kovar alloy composite material is as follows: Figure 5 As shown, it can be seen that almost no iron is plated on the iron-nickel powder, and copper diffuses significantly in the material.

[0126] The density of the Kovar alloy composite material prepared in this comparative example is 8.31 g / cm³. 3 The thermal conductivity is 22.1 W / (m·K) and the coefficient of thermal expansion (10-6 / ℃) is 9.1. This is because too much powder was added during iron plating, resulting in an excessively high concentration of the main salt in the iron plating solution. After the plating process begins, a large amount of free iron is generated in the solution, and the powder is almost not plated with iron. There is almost no intermediate layer between the copper plating layer and the base powder. During the reduction and sintering process, interdiffusion occurs between the copper and the base powder.

[0127] Comparative Example 4

[0128] Different from example 5, the iron plating solution contains the following components: FeSO4·7H2O 5g / L, citric acid 10g / L, sucrose 2g / L, based on the volume of the iron plating solution; the copper plating solution contains the following components: CuSO4·5H2O 15g / L, KNaC4H4O6·4H2O 20g / L, EDTA 25g / L, based on the volume of the copper plating solution.

[0129] The density of the vanadium alloy composite material prepared in the present comparative example is 8.29g / cm 3 , the thermal conductivity is 21.7W / (m·K), and the thermal expansion coefficient (10-6 / ℃) is 9.2.

[0130] Comparative example 5

[0131] Different from example 1, in the present comparative example, only copper plating is performed without plating a cobalt intermediate protective layer, and the rest of the process is the same as that in example 1. The density of the vanadium alloy composite material prepared in the present comparative example is 8.14g / cm 3 , the thermal conductivity is 20.7W / (m·K), and the thermal expansion coefficient (10-6 / ℃) is 6.6.

[0132] Comparative example 6

[0133] Different from example 1, in the present comparative example, neither cobalt nor copper is plated on the surface of the vanadium alloy, and the spherical iron-nickel-cobalt powder (Fe-29%Ni-17%Co) is directly hot-pressed and sintered into a vanadium alloy material by using the hot-pressing and sintering process in example 1. The density of the vanadium alloy prepared in the present comparative example is 8.12g / cm 3 , the thermal conductivity is 15.9W / (m·K), and the thermal expansion coefficient (10-6 / ℃) is 5.3.

[0134] The above examples are merely illustrative for the present application and are not intended to limit the embodiments. Based on the above description, other different forms of changes or variations can be made by those of ordinary skill in the art. Here, it is neither necessary nor possible to exhaust all the examples. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method of making a Kovar alloy composite material, characterized by, The application relates to a preparation method of a Kovar alloy composite material. S1, uniformly electroless plating iron or cobalt on the surface of the Kovar alloy powder; S2, uniformly electroless plating copper on the surface of the Kovar alloy powder plated with iron or cobalt; S3, drying and reducing the Kovar alloy powder after the step S2; S4, hot-pressing and sintering the dried and reduced powder to obtain the Kovar alloy composite material; Control the vacuum degree ≤10 -3 MPa, the heating rate is 20-50℃ / min, the sintering temperature is 650℃-950℃, the pressure is 5-20Mpa, and the holding time is 5-20min. The specific process of electroless plating iron or cobalt is as follows: iron plating solution or cobalt plating solution is prepared according to a certain proportion, the pH value is adjusted by alkali solution, the Kovar alloy powder is added into the plating solution, then a reducing agent is slowly added, stirring is conducted until the reaction is completed, and then deionized water is used for cleaning until neutral. The adding amount of the Kovar alloy powder is 20-50 g / L in volume of the plating solution; wherein, The iron plating solution contains a main salt and a complexing agent, the main salt is FeSO4.7H2O, and the complexing agent is a mixture of citric acid and sucrose; the concentration of the main salt is 10-20 g / L in volume of the iron plating solution, the concentration of the complexing agent is 30-40 g / L, and the mass ratio of citric acid to sucrose is 3:1-10:1; The cobalt plating solution contains a main salt and a complexing agent, the main salt is CoSO4.7H2O, and the complexing agent is citric acid; the concentration of the main salt is 10-20 g / L in volume of the cobalt plating solution, and the concentration of the complexing agent is 30-40 g / L; The reducing agent added in the electroless plating of iron or cobalt is N2H4, the adding amount of the reducing agent is 10-40 ml / L in volume of the plating solution, and the temperature of the plating solution is maintained at 50-60 DEG C. The specific process of electroless plating copper is as follows: copper plating solution is prepared according to a certain proportion, the pH value is adjusted by alkali solution, the Kovar alloy powder plated with iron or cobalt is added into the copper plating solution, then a reducing agent is slowly added, stirring is conducted until the reaction is completed, and then deionized water is used for cleaning until neutral.

2. The method of claim 1, wherein the cobalt alloy composite is prepared by a process comprising: The adding amount of the Kovar alloy powder is 20-50 g / L in volume of the copper plating solution; wherein, 3. The method of claim 2, wherein the cobalt alloy composite is prepared by a process comprising: The copper plating solution contains a main salt and a complexing agent, the main salt is CuSO4.5H2O, and the complexing agent is a mixture of KNaC4H4O6.4H2O and EDTA; the concentration of the main salt is 10-30 g / L in volume of the copper plating solution, the concentration of the complexing agent is 30-40 g / L, and the mass ratio of KNaC4H4O6.4H2O to EDTA is 1:1-4:

5. The reducing agent added in the electroless plating of copper is glyoxylic acid or formaldehyde, the adding amount of the reducing agent is 10-40 ml / L in volume of the copper plating solution, and the temperature of the copper plating solution is maintained at 50-60 DEG C.

4. The method of claim 3, wherein the cobalt alloy composite is prepared by a process comprising: The preparation method of the Kovar alloy composite material is prepared by the method in any one of claims 1-4.

5. A Kovar alloy composite material, characterized by ​

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