Active solder substrate and method for its production

Abstract

An active solder substrate and a method for producing the same are provided. The active solder substrate comprises a ceramic substrate layer (1), an active metal layer (2), and a conductive metal layer (3). The active metal layer (2) is disposed between the ceramic substrate layer (1) and the conductive metal layer (3). The active metal layer (2) is formed from an active metal solder and an organic dispersion medium. The active metal solder contains silver, copper, and an active metal. Based on the total weight of the active metal solder of 100 wt.%, the silver content ranges from 10 wt.% to 60 wt.%. The tensile strength of the active solder substrate ranges from 165 N / cm to 270 N / cm.

Description

[0001] Some references, which may include patents, patent applications, and various publications, may be cited and discussed in the description of this disclosure. The citation and / or discussion of such references is merely intended to clarify the description of the present disclosure and does not constitute an admission that such reference is "prior art" to the disclosure described herein. All references cited and discussed in this specification are incorporated into this specification in their entirety and to the same extent as if each reference were individually incorporated by reference.

[0002] The present disclosure relates to an active solder substrate and a method for producing the same, and more particularly to an active solder substrate having a good bonding force and a method for producing the same.

[0003] The promotion of energy conservation and carbon reduction measures in various countries has led to a strong upswing in the global electric vehicle market. In recent years, a variety of high-voltage (800 volt) vehicle products have been successfully launched, leading to increasing demand for silicon carbide (SiC) ceramic substrates.

[0004] However, as the voltage, frequency, and operating temperature requirements of power components of silicon carbide (SiC) ceramic substrate materials continue to increase, the ceramic substrates must also have better heat dissipation and reliability.

[0005] A widely used direct bonded copper (DBC) ceramic substrate is typically manufactured by eutectic bonding. There is no bonding agent between a copper layer and the ceramic substrate. However, during high-temperature operation, due to the different thermal expansion coefficients of the copper layer and the ceramic substrate (such as Al), 2 O 3 (AlN) generates large thermal stress, causing the copper layer to peel off from one surface of the ceramic substrate. Therefore, the conventional direct-bonded copper-ceramic substrate can no longer meet the requirements of high temperature, high performance, high heat dissipation, and high reliability.

[0006] Currently, the use of active brazing alloy (AMB) substrate materials is gradually being replaced by the use of direct bonded copper-ceramic substrate materials as the main substrate material.

[0007] Active solder substrate materials typically contain silver. The silver content in active solder substrate materials often exceeds 50 wt% and can even reach 70 wt%. However, due to the high silver content, the material cost of active solder ceramic substrates is high, and the problem of electromigration by silver atoms in a solder layer can occur.

[0008] Therefore, how to reduce the amount of silver in the solder layer by adjusting the materials and structure of the active solder ceramic substrate to overcome the above problems has become one of the most important issues facing the industry.

[0009] In response to the above-mentioned technical deficiencies, the present disclosure provides an active solder substrate and a method for producing the same.

[0010] To solve the above-mentioned problems, one of the technical aspects of the present disclosure is to provide an active solder substrate. The active solder substrate includes a ceramic substrate layer, an active metal layer, and a conductive metal layer. The active metal layer is sandwiched between the ceramic substrate layer and the conductive metal layer. The active metal layer is formed from an active metal solder and an organic dispersion medium. The active metal solder contains silver, copper, and an active metal. Based on the total weight of the active metal solder of 100 wt%, the silver content ranges from 10 wt% to 60 wt%. The tensile strength of the active solder substrate ranges from 165 N / cm to 270 N / cm.

[0011] To solve the above-mentioned problems, another of the technical aspects of the present disclosure is to provide a method for manufacturing an active solder substrate. The method includes the steps of applying an active metal solder paste to a ceramic substrate to form an active metal layer on the ceramic substrate, depositing a conductive metal layer on the active metal layer, and then implementing an active soldering process to obtain an active solder substrate. The active metal solder paste comprises an active metal solder and an organic dispersion medium. The active metal solder contains silver, copper, and an active metal. Based on the total weight of the active metal solder of 100 wt%, the silver content ranges from 10 wt% to 60 wt%. The tensile strength of the active solder substrate ranges from 165 N / cm to 270 N / cm.

[0012] Therefore, in the active solder substrate and the method for producing the same provided by the present disclosure, due to “the active metal solder containing silver, copper, and an active metal” and “based on the total weight of the active metal solder of 100 wt%, the amount of silver is in the range of 10 wt% to 60 wt%,” a bonding force between the ceramic substrate layer and the conductive metal layer can be improved.

[0013] These and other aspects of the present disclosure will become apparent from the following description of the embodiment taken in conjunction with the following drawings and their captions, although variations and modifications may be made therein without departing from the spirit and scope of the novel concepts of the disclosure.

[0014] The described embodiments can be better understood with reference to the following description and the accompanying drawings. Fig. 1 is a schematic side view of an active solder substrate according to the present disclosure and Fig. 2 is a schematic side view of another active solder substrate according to the present disclosure.

[0015] The present disclosure is described in more detail in the following examples, which are given for illustrative purposes only, since numerous modifications and variations therein will be apparent to those skilled in the art. Like numerals in the drawings indicate like components throughout the several views. As used herein in the specification and in the following claims, the meaning of "a" and "the" includes plural references unless the context clearly dictates otherwise, and the meaning of "in" includes "in" and "on." For the convenience of the reader, titles or subtitles may be used herein, but these do not affect the scope of the present disclosure.

[0016] The terms used herein generally have the meaning commonly used in the art. In the event of a conflict, this document, including all definitions contained herein, shall control. The same may be expressed in multiple ways. Alternative expressions and synonyms may be used for all terms discussed herein, and it is not particularly important whether a term is further explained or discussed herein. The inclusion of one or more synonyms does not preclude the use of other synonyms. The use of examples anywhere in this specification, including examples of any term, is for illustrative purposes only and in no way limits the scope and meaning of the present disclosure or any exemplary term. Likewise, the present disclosure is not limited to the various embodiments given herein.Numerals such as "first," "second," or "third" may be used to describe various components, signals, or the like, solely to distinguish one component / signal from another, and these numerals are neither intended nor designed to impose any substantial limitations on the components, signals, or the like.

[0017] To overcome the problem of peeling of a copper layer from a ceramic substrate due to differences in thermal expansion coefficients in a conventional direct-bonded copper-ceramic substrate, the present disclosure provides an active solder substrate. In the active solder substrate, the use of a solder paste of the active metal enables a good bonding force between the copper layer and the ceramic substrate. Therefore, the active solder substrate can be used in certain package structures that operate at high temperature and high power and require high reliability. According to the present disclosure, the bonding force between the copper layer and the ceramic substrate is quantified as the tensile strength of the active solder substrate for clarity.

[0018] In Fig.1, the active solder substrate according to the present disclosure comprises a ceramic substrate layer 1, an active metal layer 2, and a conductive metal layer 3. The active metal layer 2 is disposed between the ceramic substrate layer 1 and the conductive metal layer 3 to combine the ceramic substrate layer 1 and the conductive metal layer 3.

[0019] In Fig. 1, the active metal layer 2 and the conductive metal layer 3 are arranged only on one side of the ceramic substrate layer 1, but the present disclosure is not limited thereto. The active metal layer 2 and the conductive metal layer 3 may be arranged on both sides of the ceramic substrate layer 1 (as in Fig. 2).

[0020] In Fig.2, the active solder substrate can have a symmetrical structure. The active metal layers 2, 2' and the conductive metal layers 3, 3' are each arranged on two opposite sides of the ceramic substrate layer 1. Accordingly, the active solder substrate can be used to manufacture a package structure with double conductive layers. [Ceramic substrate layer]

[0021] The ceramic substrate layer 1 may be a ceramic substrate made of silicon nitride (SiN), silicon carbide (SiC), aluminum nitride (AIN) or aluminum oxide (Al 2 O 3 ). The ceramic substrate layer 1 is preferably a ceramic substrate containing silicon, and more preferably a ceramic substrate made of silicon nitride (SiN). The thickness of the ceramic substrate layer 1 may be between 100 µm and 1000 µm, but the present disclosure is not limited thereto. [Layer of the active metal]

[0022] The active metal layer 2 is formed from a solder of the active metal and an organic dispersion medium.

[0023] The active metal solder contains silver (Ag), copper (Cu) and an active metal.

[0024] Based on the total weight of the active metal solder of 100 wt%, the silver content ranges from 10 wt% to 60 wt%. Because the silver content in the active metal solder is lower than in conventional technology, the material cost of the active solder substrate can be reduced, and the probability of silver electromigration can also be reduced.

[0025] In particular, based on the total weight of the solder of the active metal of 100 wt%, the silver content may be in the range of 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt% or 55 wt%.

[0026] According to one exemplary embodiment, the silver content is between 30 wt% and 50 wt%. According to another exemplary embodiment, the silver content is between 10 wt% and 20 wt%. When the silver content is changed, the copper content, the active metal content, and the active soldering temperature must be adjusted accordingly to maintain a high bonding strength between the ceramic substrate layer 1 and the conductive metal layer 3.

[0027] During a vacuum sintering process, the silver of the active metal layer 2 can partially diffuse into an interface between the active metal layer 2 and the conductive metal layer 3 and form a silver-copper alloy with copper atoms of the conductive metal layer 3.

[0028] According to an exemplary embodiment, based on the total weight of the solder of the active metal of 100 wt.%, the copper content is in the range of 30 wt.% to 80 wt.% and the active metal content is in the range of 1 wt.% to 10 wt.%.

[0029] In particular, the copper content can be 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt% or 75 wt%.

[0030] In particular, the active metal content may be 2 wt%, 4 wt%, 6 wt%, or 8 wt%. Preferably, based on the total active metal weight of the solder paste of 100 wt%, the active metal content is in the range of 2 wt% to 4 wt%.

[0031] It should be noted that the melting point of the active metal is low, so the active metal is melted in advance during the vacuum sintering process. The molten active metal can be filled into small openings of the ceramic substrate layer 1 or the conductive metal layer 3 and even react with the ceramic substrate layer 1. On the other hand, the active metal can also reduce the electrical impedance of the active metal layer 2.

[0032] The active metal can in particular be selected from the group consisting of titanium (Ti), zirconium (Zr), tantalum (Ta), niobium (Nb), vanadium (V) and hafnium (Hf).

[0033] During the vacuum sintering process, the active metal of the active metal layer 2 may partially diffuse into an interface between the active metal layer 2 and the ceramic substrate layer 1, forming a metal silicide containing silicon atoms of the ceramic substrate layer 1 or a metal nitride containing nitrogen atoms of the ceramic substrate layer 1. Similarly, the active metal of the active metal layer 2 may also partially diffuse into the interface between the active metal layer 2 and the conductive metal layer 3 to form an alloy. Therefore, the ceramic substrate layer 1 and the conductive metal layer 3 can exhibit good bonding strength.

[0034] According to an exemplary embodiment, the active metal is titanium metal. During the vacuum sintering process, titanium atoms partially diffuse into the ceramic substrate layer 1 and form titanium silicide (TiSi), silicon nitride (TiN), or titanium disilicide (TiSi 2) with silicon atoms or nitrogen atoms. Furthermore, the titanium atoms may also diffuse into the conductive metal layer 3 and form a titanium-copper alloy with the copper atoms of the conductive metal layer 3, but the present disclosure is not limited thereto.

[0035] If the active metal layer 2 is too thin, the bonding force between the ceramic substrate layer 1 and the conductive metal layer 3 decreases. If the active metal layer 2 is too thick, the material cost of the active metal layer 2 may be too high, which is not advantageous for mass production. Therefore, the thickness of the active metal layer 2 may be greater than or equal to 6 µm. Preferably, the thickness of the active metal layer 2 may be between 10 µm and 30 µm, for example, 12 µm, 14 µm, 16 µm, 18 µm, 20 µm, 22 µm, 24 µm, 26 µm, or 28 µm. More preferably, the thickness of the active metal layer 2 may be between 18 µm and 24 µm. [Conductive metal layer]

[0036] The conductive metal layer 3 can be arranged on the ceramic substrate layer 1 over the active metal layer 2. In particular, the conductive metal layer 3 can be a copper foil, an aluminum foil, or a copper-aluminum alloy foil. According to an exemplary embodiment, the conductive metal layer 3 is a copper foil.

[0037] The thickness of the conductive metal layer 3 may be between 50 µm and 1200 µm. Preferably, the thickness of the conductive metal layer 3 may be between 200 µm and 800 µm, but the present disclosure is not limited thereto. [Method for producing an active solder substrate]

[0038] In step S1, the active metal solder paste is prepared. The active metal solder paste is used to form active metal layer 2.

[0039] The active metal solder paste includes the active metal solder and the organic dispersion medium mentioned above.

[0040] The active metal solder contains silver, copper, and the active metal mentioned above. According to one exemplary embodiment, the active metal solder is a combination of a silver powder, a copper powder, and an active metal powder. According to another exemplary embodiment, the active metal solder may also be a combination of an active metal powder and at least one of silver powder, copper powder, and silver-copper alloy powder.

[0041] As mentioned above, based on the total weight of the solder of the active metal of 100 wt%, the silver content is in the range of 10 wt% to 60 wt%.

[0042] The organic dispersion medium can help disperse the active metal solder and solidify the active metal solder paste to form the active metal layer 2. Specifically, the organic dispersion medium contains a paste-forming agent, an organic solvent, and a thixotropic agent. Based on the total weight of the organic dispersion medium of 100 wt%, the proportion of the paste-forming agent ranges from 20 wt% to 30 wt%, the proportion of the organic solvent ranges from 50 wt% to 70 wt%, and the proportion of the thixotropic agent ranges from 1 wt% to 5 wt%.

[0043] For example, the paste-forming agent can be selected from the group consisting of silicone oil, white oil, polyvinyl alcohol, acrylic resin, nitrocellulose, ethylcellulose, dimethyl phthalate, and carboxymethylcellulose. Preferably, the paste-forming agent is ethylcellulose,

[0044] The organic solvent can be selected from the group consisting of ethylene glycol butyl ether acetate, diethylene glycol, triethanolamine, butyl cellosolve (ethylene glycol monobutyl ether), tert-butyl alcohol, N,N-dimethylformamide, terpineol, and nonylphenol polyglycol ether. Preferably, the organic solvent can be terpineol or ethylene glycol butyl ether acetate.

[0045] The thixotropic agent can be selected from the group consisting of polyamide wax, hydrogenated castor oil, and polyurea. Preferably, the thixotropic agent is polyamide wax.

[0046] The active solder and the organic dispersion medium are mixed in a weight ratio of 70% to 95%: 5% to 30% to form the active metal solder paste with a viscosity of 50 mPa s to 300 mPa s. Preferably, the weight ratio of the active metal solder to the organic dispersion medium is 75% to 90%: 10% to 25%.

[0047] However, the present disclosure is not limited to the above-mentioned examples, and as long as the active metal solder and the organic solvent can be processed into an active metal solder paste having a suitable viscosity to be applied to the ceramic substrate layer 1 and form the active metal layer 2, such a method or configuration for achieving this purpose is considered to be within the spirit and scope of the present disclosure.

[0048] In step S2, the active metal solder paste may be applied to the ceramic substrate layer 1 by screen printing and dried at a temperature of 90°C to 110°C for 5 to 15 minutes. In this way, most of the organic solvent in the active metal solder paste evaporates, forming the active metal layer 2.

[0049] In step S3, the conductive metal layer 3 is disposed on the active metal layer 2, after which an active soldering process is implemented to fix the conductive metal layer 3 on the ceramic substrate layer 1.

[0050] The active brazing process includes a first heat treatment step and a second heat treatment step, which can be implemented in a vacuum environment. The processing temperature of the first heat treatment step is not higher than 500°C. The processing temperature of the second heat treatment step is between 900°C and 1100°C (i.e., the active brazing temperature). The processing temperature of the second heat treatment step is higher than the processing temperature of the first heat treatment step.

[0051] Specifically, the processing temperature in the first heat treatment step is between 300°C and 500°C, and the processing time is between 30 minutes and 60 minutes. The processing temperature in the second heat treatment step is between 900°C and 1100°C, and the processing time is between 60 minutes and 240 minutes. Additionally, the temperature rise rates of the aforementioned heat treatment steps can be between 5°C / min and 30°C / min, and the temperature decrease rates of the aforementioned heat treatment steps can be between 2°C / min and 30°C / min.

[0052] It should be noted that the active brazing temperature of the active brazing process can be adjusted according to the silver content in the active metal layer 2 to ensure that the active brazing substrate has good tensile strength. Specifically, when the silver content in the active metal layer 2 is in the range of 30 wt% to 50 wt%, the active brazing temperature of the active brazing process can be in the range of 900°C to 950°C. When the silver content in the active metal layer 2 is in the range of 10 wt% to 20 wt%, the active brazing temperature of the active brazing process can be in the range of 1000°C to 1100°C.

[0053] During the active soldering process, the organic dispersion medium is partially evaporated. A surface of the ceramic substrate layer 1 is wetted by the active metal, and the ceramic substrate layer 1 reacts with the active metal to increase the bonding force between the active metal layer 2 and the ceramic substrate layer 1. Furthermore, at the interface between the active metal layer 2 and the conductive metal layer 3, the active metal and metal atoms of the conductive metal layer 3 undergo a micrometer-scale eutectic reaction, forming a strong eutectic structure. This firmly bonds the active metal layer 2 and the conductive metal layer 3. [Tests 1 to 10]

[0054] In order to compare the influences of the silver content in the active metal layer 2, the active soldering temperature and the thickness of the active metal layer 2 on the tensile strength of the active solder substrate, the metal-ceramic substrates from Test 1 to Test 10 are manufactured in the above-mentioned steps S1 to S3.

[0055] In the metal-ceramic substrates of Tests 1 to 10, ceramic substrate layer 1 is a silicon nitride ceramic substrate, active metal layer 2 includes silver, copper, and titanium, and conductive metal layer 3 is a copper layer. In Tests 1 to 10, the titanium composition is controlled within 1 to 5 wt%. For example, the titanium composition is 4 wt%, and the remainder can be copper.

[0056] During the preparation of the active metal solder paste, ethyl cellulose is used as the paste-forming agent, ethylene glycol butyl ether acetate is used as the organic solvent, and polyamide wax is used as the thixotropic agent. Based on the total weight of the organic dispersion medium of 100 wt%, the proportion of the paste-forming agent is in the range of 20 wt% to 30 wt%, the proportion of the organic solvent is in the range of 50 wt% to 70 wt%, and the proportion of the thixotropic agent is in the range of 1 wt% to 5 wt%. According to this embodiment, the composition of the organic dispersion medium consists of the paste-forming agent (30 wt%), the organic solvent (67 wt%), and the thixotropic agent (3 wt%).

[0057] The specific silver content in the active metal solder (in active metal layer 2), the specific active soldering temperature, and the specific thickness of active metal layer 2 are listed in Table 1. The tensile strength of the active solder substrate is measured at 25 °C according to JIS-C-6481, and the results are listed in Table 1. Table 1 Silver content in the active metal solder (wt%) Active soldering temperature (°C) Thickness of the active metal layer Tensile strength of the active solder substrate (N / cm) Test 1 54 950 24 170 Test 2 48,75 950 24 266,64 Test 3 36,5 950 24 196,14 Test 4 18,45 950 24 N / A Test 5 48,75 950 18 251,04 Test 6 35,6 950 18 201,15 Test 7 18,9 950 18 12,31 Test 8 18,9 1015 18 248,84 Test 9 15,75 1015 18 142,92 Test 10 73 950 24 178

[0058] According to the results in Table 1, the tensile strength of the active solder substrate can range from 165 N / cm to 270 N / cm when the silver content in the active metal layer is between 10 wt% and 60 wt%. According to Test 1 to Test 4, the tensile strength of the active solder substrate can range from 180 N / cm to 270 N / cm when the silver content in the active metal layer is between 20 wt% and 50 wt%.

[0059] Even if the thickness of the active metal layer is reduced to 18 µm, the active solder substrate can still exhibit high tensile strength. According to Tests 5 to 7, the tensile strength of the active solder substrate can range from 180 N / cm to 270 N / cm when the silver content in the active metal layer is between 20 wt% and 50 wt%.

[0060] The experimental results show that the tensile strength of the active solder substrate can be improved by increasing the active soldering temperature. According to Tests 8 and 9, the tensile strength of the active solder substrate can still be between 140 N / cm and 250 N / cm when the active soldering temperature is increased to 1015 °C, even when the silver content in the active metal layer is only between 10 wt% and 20 wt%.

[0061] According to the above results, by adjusting the silver content in the active metal layer and the active soldering temperature, the active solder substrate according to the present disclosure can have good tensile strength and can be used in certain package structures that operate at high temperature and high power and require high reliability. [Advantageous effects of the embodiment]

[0062] In summary, in the active solder substrate and the method for producing the same provided by the present disclosure, due to “the active metal solder containing silver, copper, and an active metal” and “based on the total weight of the active metal solder of 100 wt%, the amount of silver is in the range of 10 wt% to 60 wt%,” a bonding force between the ceramic substrate layer and the conductive metal layer can be improved.

[0063] The foregoing description of the exemplary embodiments of the disclosure has been presented for purposes of illustration and description only and is not intended to be exhaustive or to limit the disclosure to the precise forms. Many modifications and variations are possible in light of the above teachings.

[0064] The embodiments were chosen and described in order to explain the principles of the disclosure and its practical application, thereby enabling others skilled in the art to utilize the disclosure and various embodiments with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present disclosure belongs without departing from its spirit and scope. List of reference symbols 1 ceramic substrate layer 2, 2' layer of the active metal 3, 3' conductive metal layer

Claims

[1] Active solder substrate, comprising: • a ceramic substrate layer (1), • a layer (2) of the active metal formed from a solder of the active metal and an organic dispersion medium, wherein the solder of the active metal contains silver, copper and an active metal, wherein, based on the total weight of the solder of the active metal of 100 wt.%, the silver content is in the range of 10 wt.% to 60 wt.%, and • a conductive metal layer (3), wherein the layer (2) of the active metal is arranged between the ceramic substrate layer (1) and the conductive metal layer (3), • the tensile strength of the active solder substrate is in the range of 165 N / cm to 270 N / cm. [2] The active solder substrate according to claim 1, wherein, based on the total weight of the active metal solder of 100 wt%, the silver content is in the range of 30 wt% to 50 wt%. [3] The active solder substrate according to claim 1 or 2, wherein, based on the total weight of the active metal solder of 100 wt%, the silver content is in the range of 10 wt% to 20 wt%. [4] The active solder substrate according to any one of claims 1 to 3, wherein, based on the total weight of the solder of the active metal of 100 wt%, the content of the active metal is in the range of 2 wt% to 4 wt%. [5] Active solder substrate according to one of claims 1 to 4, wherein the active metal is selected from the group consisting of titanium (Ti), zirconium (Zr), tantalum (Ta), niobium (Nb), vanadium (V) and hafnium (Hf). [6] Active solder substrate according to one of claims 1 to 5, wherein the thickness of the layer (2) of the active metal is greater than or equal to 6 µm. [7] Active solder substrate according to claim 6, wherein the thickness of the layer (2) of the active metal is in the range of 18 µm to 24 µm. [8] A method for producing an active solder substrate, comprising: • Applying an active metal solder paste to a ceramic substrate to thereby form an active metal layer (2) on the ceramic substrate, wherein the active metal solder paste comprises an active metal solder and an organic dispersion medium, wherein the active metal solder comprises silver, copper and an active metal, wherein, based on the total weight of the active metal solder of 100 wt%, the silver content is in the range of 10 wt% to 60 wt%, and • Applying a conductive metal layer (3) to the layer (2) of the active metal and then implementing an active soldering process to obtain an active solder substrate, wherein the tensile strength of the active solder substrate is in the range of 165 N / cm to 270 N / cm. [9] The method of claim 8, wherein, based on the total weight of the active metal solder of 100 wt%, the silver content is in the range of 30 wt% to 50 wt%, wherein the active soldering temperature of the active soldering process is in the range of 900°C to 950°C. [10] The method of claim 8, wherein, based on the total weight of the active metal solder of 100 wt%, the silver content is in the range of 10 wt% to 20 wt%, wherein the active soldering temperature of the active soldering process is in the range of 1000 °C to 1100 °C.

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