A copper electrode paste for COB packaging glass substrates and its preparation method

Abstract

This invention provides a copper electrode paste for COB encapsulation glass substrates and its preparation method. The copper electrode paste formulation comprises the following components in weight percentages: 65-75% copper powder, 15-30% organic carrier, 5-10% glass powder, and 0.2-0.5% organic additives. The copper powder is a mixture of several copper powders with different particle sizes and morphologies, and the glass powder is a mixture of two glass powders with different sintering properties. The copper electrode paste prepared by this invention exhibits good conductivity, printability, and compatibility with the substrate during sintering. After high-temperature sintering in a N2 atmosphere, the copper layer shows no significant shrinkage, exhibits high dry film adhesion, and possesses excellent acid and alkali resistance and adhesion, making it a complete replacement for silver paste on glass substrates.

Description

Technical Field

[0001] This invention relates to the field of conductive copper electrode paste technology, and more particularly to a copper electrode paste for COB packaging glass substrates and its preparation method. Background Technology

[0002] Thick-film electronic paste refers to electrode circuits printed on a ceramic substrate and then sintered at high temperature. Compared with ordinary PCBs, it has significant advantages in heat dissipation and stability, and has obvious value advantages in harsh environments such as high temperature, high humidity, high power, and high vibration. It is mainly used in automotive electronics, communication systems, aerospace, and military fields.

[0003] Thick-film circuits mainly consist of a substrate and thick-film electronic paste. The substrate is the carrier of the thick-film circuit and mainly includes ceramic substrates, polymer substrates, glass substrates, and composite substrates. Its material properties have a significant impact on the quality of the thick-film circuit. Currently, ceramic substrates are the most widely used.

[0004] Thick-film electronic pastes are the core and key components of thick-film circuits. Based on their application, they can be categorized into resistive pastes, conductor pastes, and dielectric pastes. Their quality directly affects the performance of the subsequent film components and printed circuit boards.

[0005] With the development of technology, the substrates used for packaging COB light sources in LED lighting have evolved and been updated from aluminum substrates to copper substrates to ceramic substrates to glass substrates and finally to sapphire substrates. Since the luminous efficacy of glass substrates used for packaging COB light sources in LED lighting is ≥140 lm / W, a 4W LED lamp is equivalent to the brightness of a 40W incandescent bulb (approximately 600 lumens). This means energy savings of 9 times (or 90%) and a lifespan increase of 10 times (at least 20,000 hours, up to 250,000 hours). Currently, glass substrates (especially high thermal conductivity types) for COB light sources in LED lighting offer better luminous efficacy and lower costs than metal substrates (Al substrates, Cu substrates) and ceramic substrates. Therefore, glass substrates for LED lighting have broad application value and a large market.

[0006] Traditionally, silver paste is the primary electrode paste used in COB packaging substrates due to its excellent conductivity and sintering activity. Under high-temperature sintering, silver forms a dense metal layer with excellent solderability, solder resistance, and conductivity. The sintering process is simple and easily achievable for mass production. However, as product applications become more widespread and usage increases, cost will become a major consideration for manufacturers. Copper, as a base metal, possesses similar conductivity to silver, and its price is only 1 / 5 to 1 / 10 that of silver. Therefore, replacing silver paste with copper paste as the electrode paste for thick-film coatings offers significant cost reduction advantages and will become the future development trend for thick-film pastes.

[0007] The patent application publication number "CN105934416 A" mentions "a glass substrate provided with a copper-based conductive strip". The patent mentions the preparation method and application scope of copper paste for glass substrates. However, the text focuses more on the product design and application of glass-based copper paste and does not elaborate on the formulation and preparation method of copper paste for glass substrates.

[0008] The patent application publication number "CN104658633 A" mentions "a formula and preparation method of conductive copper paste for automotive glass heating wires". The patent mentions a method for preparing conductive copper paste for glass substrates, which is applied in the field of automotive rear windshield heating wires. The sintering temperature is >600℃, which does not meet the sintering process conditions of copper paste for glass substrates used in COB packaging.

[0009] The patent application publication number "CN112125527A" also mentions "a high thermal expansion glass powder for copper paste and its preparation method and application", which focuses on the preparation and testing methods of glass powder from the perspective of glass preparation, but does not introduce the application performance of copper paste prepared by this glass powder on different ceramic matrices.

[0010] Given the limited research in China on copper paste for glass substrates, especially for COB-packaged glass substrates, and the lack of comparable achievements to foreign products, it is necessary to provide a copper electrode paste to address these issues. Summary of the Invention

[0011] To address the aforementioned issue of limited research on copper paste for glass substrates in China, this invention provides a copper electrode paste for COB encapsulation glass substrates and its preparation method. Starting with glass substrates used for COB light source encapsulation in LED lighting, this invention primarily considers the combination of different types of copper powder, glass powder, and polymer resin to achieve a conductive copper paste on the glass substrate with performance comparable to silver paste. By using copper paste instead of silver paste as the printed electrode circuit paste, cost reduction is achieved, ultimately resulting in a conductive copper paste product with high conductivity, high solder pull strength, and high sintering density, comparable to foreign products.

[0012] The technical means employed in this invention are as follows:

[0013] A copper electrode paste for COB packaging glass substrates comprises the following components in weight percentages:

[0014] The copper powder comprises 65-75% copper powder, wherein the copper powder is a mixture of spherical powder and flake powder, wherein the particle size D50 of the spherical powder is 0.2-1.5 μm and the particle size D50 of the flake powder is 3.0-7.0 μm.

[0015] 15%–30% organic carrier;

[0016] 5% to 10% glass powder, wherein the glass powder is a mixture of two glass powders with different sintering properties. Calculated by mass percentage, glass powder A is a mixture of 40% to 70% bismuth oxide, 5% to 20% boric acid, 5% to 20% silicon oxide, 5% to 10% basic copper carbonate, 0.5% to 2% manganese dioxide, 0% to 5% alkaline earth metal oxides, and 0% to 3% alkali metal oxides; glass powder B is a mixture of 40% to 60% bismuth oxide, 20% to 40% boric acid, 0% to 5% zinc oxide, 0% to 1% aluminum oxide, 5% to 10% alkaline earth metal oxides, and 0% to 3% alkali metal oxides.

[0017] 0.2% to 0.5% organic additives.

[0018] Copper powder, as a functional phase in conductive pastes, possesses excellent electrical and thermal conductivity, superior physical and mechanical properties, and its price is significantly more advantageous than that of precious metals such as gold, platinum, palladium, and silver. It is widely used in various conductive and resistive pastes. Different types, particle sizes, and morphologies of silver powder play different roles in the application areas of pastes.

[0019] The copper powders used in this invention are quite diverse, including spherical copper powder and flake copper powder. The particle size D50 of the spherical powder is 0.2 to 1.5 μm, and the particle size D50 of the flake powder is 3.0 to 7.0 μm. They exhibit good dispersibility and packing density in the slurry, which is beneficial for improving the density and conductivity of the sintered silver layer.

[0020] Glass powder acts as a sintering aid and binder in copper paste, improving the densification of the sintered copper layer and forming an effective bond between the copper layer and the substrate. The main factor affecting the role of glass powder in the paste is its characteristic softening temperature. If the softening point is too high, the sintering activity is low, the wettability of the copper powder is poor, and the sintering density of the copper powder decreases, affecting the conductivity of the copper layer. Conversely, if the softening point is too low, it will cause excessive erosion of the substrate, resulting in a decline in the electrical properties of the substrate itself. Therefore, selecting a suitable glass system is of significant importance to the performance of conductive copper paste.

[0021] The present invention provides a combination of two glass powders with different sintering properties. Glass powder A has a wide adjustable temperature range and good wettability to both the glass substrate and copper powder, improving the sintering activity of the copper powder and enhancing the density of the copper layer. Glass powder B is a microcrystalline glass that microcrystallizes during sintering, improving the acid and alkali resistance of the copper film and increasing its mechanical strength with the glass substrate. The combination of these two powders ensures that the copper layer possesses excellent weld adhesion, electrical properties, and anti-aging properties.

[0022] Furthermore, the organic carrier is prepared from 65-75% polymer resin and 70-90% organic solvent.

[0023] Furthermore, the polymer resin is a mixture of ethyl cellulose and acrylic resin in a predetermined ratio.

[0024] Furthermore, the organic solvent is selected from one or more alcohols or ethers, wherein the alcohols include one or a mixture of terpineol, turpentine, and dodecyl alcohol ester, and the ethers include one or two of diethylene glycol butyl ether and diethylene glycol butyl ether acetate.

[0025] Furthermore, the organic additives include leveling agents, coupling agents, defoamers, thixotropic agents, etc., wherein the coupling agent can be a silane coupling agent, etc.; the thixotropic agent can be hydrogenated castor oil, polyamide waxes, etc.

[0026] This invention also discloses a method for preparing copper electrode paste for COB packaging glass substrates, characterized by comprising the following steps:

[0027] S1. Mix different types of polymer resins according to a preset ratio, and then mix them with organic solvents and organic additives in a certain ratio until fully dissolved to obtain the required organic carrier.

[0028] S2. The organic carrier prepared in step S1 is mixed with copper powder, glass powder and organic additives according to the slurry ratio to obtain a mixture.

[0029] S3. Grind the above mixture thoroughly using a three-roll mill to obtain a pre-finished copper electrode slurry. Filter, test, and adjust the viscosity of the pre-finished copper slurry until a copper electrode slurry that meets the requirements is obtained.

[0030] Furthermore, in step S1, the organic solvent is added to the reaction vessel in the order of adding the polymer resin first, and the water bath heating temperature of the reaction vessel is stable and the mixture is completely dissolved by stirring. The pre-set organic additive is added to the completely dissolved and transparent carrier, and stirring and heating are continued to obtain the desired organic carrier.

[0031] Furthermore, in step S2, the preparation of the two types of glass powder includes the following steps:

[0032] S21. Calculate the specific raw material mass ratio according to the preset glass oxide formula, and weigh accurately;

[0033] S22. Thoroughly mix the weighed raw materials in the mixer to ensure uniform mixing of different raw materials;

[0034] S23. Place the mixed raw materials in an alumina crucible, then place the crucible in a muffle furnace and melt it at 1100-1350℃ for 30-60 minutes.

[0035] S24. Pour the molten glass into deionized water for water quenching to obtain glass fragments of about 1mm.

[0036] S25. Place the glass fragments into a ball mill jar and ball mill for 8-12 hours. After passing through a 500-mesh sieve, dry them in an oven at 120°C to obtain the required glass powder. The particle size of the glass powder is controlled within D50: 3-5μm.

[0037] Furthermore, in step S3, the mixture is thoroughly ground 5 to 8 times using a three-roll mill, and the viscosity is controlled at 50 to 100 Pa·s.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] 1. This invention starts with the formulation of copper paste. The copper powder selected is a composite combination. The copper powder is prepared by combining nano-sized copper powder with certain flakes and balls. It has high sintering activity and meets the requirements of low-temperature sintering.

[0040] 2. Copper paste has very low adhesion to glass substrates. This invention uses two glass powders with different properties to improve the adhesion of the metal layer: Glass A is made of bismuth, copper, manganese, silicon and lithium glass, which improves the wettability and corrosion resistance between glass and glass substrates. Glass B has excellent acid resistance and mechanical strength. The copper paste prepared by the combination of the two not only has high sintering activity and high copper layer density, but also has high adhesion to the glass substrate and good metal layer resistance.

[0041] In summary, the copper electrode paste prepared by combining different types of copper powder, glass powder, and polymer resin exhibits excellent conductivity, printability, and compatibility with the substrate during sintering. After sintering the conductive copper paste on a glass substrate at temperatures below 600°C under a nitrogen atmosphere, the copper layer shows no significant shrinkage, exhibits high dry film adhesion, and possesses excellent acid and alkali resistance and adhesion, making it a complete replacement for silver paste on glass substrates.

[0042] Therefore, the copper electrode paste provided by this invention has a wide sintering window, which can be matched with different sintering curves of customers, and finally achieves high conductivity, high welding pull and high sintering density. It fills the gap in the application of this technology in China and is a conductive copper paste product that can be compared with foreign products. It plays a key role in promoting the development of domestic glass substrates in the COB packaging field. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a SEM image of the glass powder of the present invention.

[0045] Figure 2 This is a metallographic microscope image of copper paste sintering in Embodiment 1 of the present invention. Detailed Implementation

[0046] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0049] This invention provides a copper electrode paste for COB packaging glass substrates. The formulation of the copper electrode paste, calculated by mass percentage, includes the following components:

[0050] The copper powder comprises 65-75% copper powder, wherein the copper powder is a mixture of spherical powder and flake powder, wherein the particle size D50 of the spherical powder is 0.2-1.5 μm and the particle size D50 of the flake powder is 3.0-7.0 μm.

[0051] The organic carrier, comprising 15% to 30%, is prepared from 65% to 75% polymer resin and 70% to 90% organic solvent; the polymer resin is a mixture of ethyl cellulose and acrylic resin in a certain proportion; the organic solvent is selected from one or more alcohols or ethers, wherein the alcohols include one or more of terpineol, turpentine oil, and dodecyl alcohol ester, and the ethers include one or two of diethylene glycol butyl ether and diethylene glycol butyl ether acetate;

[0052] 5% to 10% glass powder, wherein the glass powder is a mixture of two glass powders with different sintering properties. Calculated by mass percentage, glass powder A is a mixture of 40% to 70% bismuth oxide, 5% to 20% boric acid, 5% to 20% silicon oxide, 5% to 10% basic copper carbonate, 0.5% to 2% manganese dioxide, 0% to 5% alkaline earth metal oxides, and 0% to 3% alkali metal oxides; glass powder B is a mixture of 40% to 60% bismuth oxide, 20% to 40% boric acid, 0% to 5% zinc oxide, 0% to 1% aluminum oxide, 5% to 10% alkaline earth metal oxides, and 0% to 3% alkali metal oxides.

[0053] 0.2% to 0.5% organic additives, including at least leveling agents, coupling agents, and thixotropic agents. Among them, coupling agents can be silane coupling agents, etc.; thixotropic agents can be hydrogenated castor oil, polyamide waxes, etc.

[0054] This invention also discloses a method for preparing copper electrode paste for COB packaging glass substrates, comprising the following steps:

[0055] S1. Mix polymer resins of different molecular weights in a certain proportion, and then mix them with organic solvents and organic additives in a certain proportion to obtain the desired organic carrier.

[0056] To ensure the viscosity of the conductive silver paste and the stability of printing, a method for preparing the aforementioned preferred carrier is proposed as follows:

[0057] (1) Weigh the above-mentioned preferred organic solvent and polymer resin precisely according to the designed formula ratio.

[0058] (2) Add the above raw materials into the reactor in the order of adding organic solvent first and then polymer resin, ensuring that the resin does not clump or settle to the bottom. The water bath heating temperature of the reactor is kept stable at 85°C and the stirring speed is 150 rpm. Stir and dissolve for 3 to 5 hours.

[0059] (3) Add the designed organic additives to the completely dissolved and transparent carrier, and continue stirring and heating for 0.5 min. The organic resin should be fully dissolved in organic solvent until it is transparent, and there should be no undissolved particles. The addition of these additives can ensure that the paste has good printability and stability.

[0060] (4) After stirring, the prepared organic carrier is placed in a pre-prepared stainless steel bucket, covered and placed at room temperature to cool down naturally, so as to avoid the evaporation of organic solvent and the instability of carrier viscosity, thus obtaining the organic carrier required by the present invention.

[0061] S2. According to the proportion, mix the organic carrier with silver powder and glass powder evenly to obtain a mixture;

[0062] To ensure the excellent performance of the conductive copper paste, the following method for preparing the glass powder matrix is ​​proposed:

[0063] (1) Calculate the specific raw material mass ratio according to the designed glass oxide formula and weigh it accurately.

[0064] (2) The weighed raw materials are thoroughly mixed in the mixer to ensure uniform mixing of different components.

[0065] (3) Place the mixed raw materials in an alumina crucible, then place the crucible in a muffle furnace and melt it at 1100-1350℃ for 30-60 minutes.

[0066] (4) Pour the molten glass into deionized water for water quenching to obtain glass fragments of about 1 mm.

[0067] (5) Put the glass fragments into a ball mill jar and ball mill for 8 to 12 hours. After passing through a 500-mesh sieve, dry them in an oven at 120°C to obtain the required glass powder. The particle size of the glass powder is controlled within D50: 3 to 5 μm.

[0068] S3. Grind the above mixture thoroughly 5 to 8 times using a three-roll mill to obtain a pre-finished hole electrode paste. Filter, test, and adjust the viscosity of the pre-finished silver paste until a hole electrode conductive silver paste that meets the requirements is obtained.

[0069] To ensure excellent printability of the conductive copper paste, the viscosity of the conductive copper paste of this invention is preferably controlled between 50 and 100 Pa·s. Unless otherwise specified, the viscosity of this invention is measured using a Broodfield (DV2T) viscometer at 14# / 10 rpm.

[0070] Table 1 lists examples of conductive copper paste preparation according to the present invention. The organic solvents in the examples are a mixture of three solvents: terpineol, dodecyl alcohol ester, and diethylene glycol butyl ether acetate, with a solvent ratio of 1:1:5 (volume ratio). The ratio of spherical copper powder to flake copper powder is fixed at 3:1. The comparative sample is a commercially available silver paste.

[0071] Table 1

[0072]

[0073] Table 2 shows the composition of glass powder A in the above cases, as follows:

[0074] Table 2

[0075] mass ratio Example 1 Example 2 Example 3 Example 4 Bismuth oxide 45 55 60 70 boric acid 20 20 15 10 silicon dioxide 20 10 10 5 Basic copper carbonate 8 8 8 8 Manganese dioxide 1 1 1 1 Mixed alkaline earth metal oxides 4 2 2 2 Mixed alkali metal oxides 2 4 4 4 total 100 100 100 100

[0076] Table 3 shows the composition of glass powder B in the above cases, as follows:

[0077] Table 3

[0078] mass ratio Example 1 Example 2 Example 3 Example 4 Bismuth oxide 50 55 60 60 boric acid 35 30 25 30 Zinc oxide 0.5 0.5 0.5 0.5 Alumina 1 1 1 1 Mixed alkaline earth metal oxides 10 10 10 5 Mixed alkali metal oxides 3.5 3.5 3.5 3.5 total 100 100 100 100

[0079] Conductive copper pastes A1, A2, A3, and A4, as well as a comparative silver paste AD1, were prepared according to the above method, and comparative experiments were conducted to verify the prepared copper pastes.

[0080] Test results:

[0081] Surface printing tests were conducted on copper pastes A1, A2, A3, and A4 prepared according to the example, as well as the comparative silver paste AD1. The samples were then sintered in a chain furnace under a nitrogen atmosphere at a peak sintering temperature of 580℃ for 150 min. The conductivity, sintering density, and interlayer continuity of each sample were then tested. The test results are shown in Table 4 below.

[0082] Table 4

[0083]

[0084]

[0085] In summary, this invention provides a method for preparing copper electrode paste for COB packaging glass substrates. This conductive copper paste exhibits good adhesion to the glass substrate, and after printing and sintering, it does not exhibit phenomena such as metal layer blistering or peeling. Performance testing shows that all indicators are comparable to those of comparative silver paste, thus it can replace silver paste as the electrode electronic paste for glass substrates. Figure 1 The morphology of the glass powder can be observed; Figure 2 These are microscope images of the copper layer.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A copper electrode paste for COB encapsulation glass substrates, characterized in that, It consists of the following components in the following mass percentages: The copper powder comprises 65-75% copper powder, wherein the copper powder is a mixture of spherical powder and flake powder, wherein the particle size D50 of the spherical powder is 0.2-1.5 μm and the particle size D50 of the flake powder is 3.0-7.0 μm. 15%~30% organic carrier; 5%~10% glass powder, wherein the glass powder is a mixture of two glass powders with different sintering properties. Calculated by mass percentage, glass powder A consists of 40%~70% bismuth oxide, 5%~20% boric acid, 5%~20% silicon oxide, 5%~10% basic copper carbonate, 0.5%~2% manganese dioxide, 0~5% alkaline earth metal oxides, and 0~3% alkali metal oxides; glass powder B consists of 40%~60% bismuth oxide, 20%~40% boric acid, 0%~5% zinc oxide, 0%~1% aluminum oxide, 5~10% alkaline earth metal oxides, and 0~3% alkali metal oxides. 0.2%~0.5% organic additives.

2. The copper electrode paste for COB packaging glass substrates according to claim 1, characterized in that, The organic carrier is prepared from 65-75% polymer resin and 70-90% organic solvent.

3. The copper electrode paste for COB packaging glass substrates according to claim 2, characterized in that, The polymer resin is a mixture of ethyl cellulose and acrylic resin in a preset ratio.

4. The copper electrode paste for COB encapsulation glass substrates according to claim 2, characterized in that, The organic solvent is selected from one or more alcohols or ethers, wherein the alcohols include one or more of terpineol, turpentine, and dodecyl alcohol ester, and the ethers include one or two of diethylene glycol butyl ether and diethylene glycol butyl ether acetate.

5. The copper electrode paste for COB packaging glass substrates according to claim 1, characterized in that, The organic additives include at least one or a mixture of several of the following: leveling agents, coupling agents, defoamers, and thixotropic agents.

6. The copper electrode paste for COB packaging glass substrates according to claim 1, characterized in that, The preparation of the two types of glass powder includes the following steps: S21. Calculate the specific raw material mass ratio according to the preset glass oxide formula, and weigh accurately; S22. Thoroughly mix the weighed raw materials in the mixer to ensure uniform mixing of different raw materials; S23. Place the mixed raw materials in an alumina crucible, then place the crucible in a muffle furnace and melt it at 1100~1350℃ for 30~60min. S24. Pour the molten glass into deionized water for water quenching to obtain 1mm glass fragments. S25. Put the glass fragments into a ball mill jar and ball mill for 8~12 hours. After passing through a 500-mesh sieve, dry them in an oven at 120℃ to obtain the required glass powder. The particle size of the glass powder is controlled within D50: 3~5μm.

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