A die-bonding solder paste that can be air-reflow soldered and its preparation method

Abstract

This invention discloses a die-bonding solder paste capable of air reflow soldering and its preparation method. It consists of 15% ultrasonically atomized 2-25µm Sn96.5Ag3.0Cu0.5 alloy solder powder and 85% nano-treated flux. The flux comprises the following mass percentages: solvent 40-50%, resin 35-40%, imidazole 5-8%, thixotropic agent 5-10%, and antioxidant 1-5%. It can be applied to high-power LED soldering. By using ultrasonically atomized solder powder with high sphericity, smooth surface, and low oxygen content, and preferably incorporating adsorbent film-type organic imidazoles and phenolic antioxidants with complexing metal ions, the flux is further nano-ground using a nano-grinding machine. The nano-ground flux completely coats the surface of the solder powder, forming a nanomaterial protective layer. This die-bonding solder paste differs from existing die-bonding solder pastes on the market, achieving air reflow soldering capability and further improving wetting performance, reducing production costs and contributing to environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, specifically relating to a die-bonding solder paste that can be air-reflow soldered and its preparation method. Background Technology

[0002] Currently, high-power LEDs are experiencing rapid market growth due to their superior performance, expanding beyond lighting into new fields such as automobiles, mobile phones, and medical devices. However, in practical applications, high-power LED devices can only convert 15% to 20% of the input power into electrical energy, with the remainder dissipating as heat. As devices become smaller and their power increases, this causes a redshift in the chip's emission spectrum, reducing the LED's light power, accelerating device aging, and reducing permanent light decay. To better address the heat dissipation problem of LED devices, researchers have developed a new encapsulation bonding material—die-bonding solder paste—based on die-bonding adhesives and conductive silver paste. After soldering, die-bonding solder paste readily forms a reliable third phase with the silver plating on the ceramic substrate and the gold layer at the bottom of the chip, which is highly beneficial for heat dissipation. High thermal conductivity die-bonding solder paste can replace the previously widely used die-bonding adhesives and conductive silver paste, effectively solving the chip's heat dissipation problem and meeting the normal operating requirements of high-power LEDs.

[0003] In its design, die-bonding solder paste typically uses Sn96.5Ag3.0Cu0.5 alloy solder powder with a powder diameter of 2-25µm to meet the soldering requirements of high-power chips ranging from 10 to 75mil. Because the diameter of the tin powder is small, the larger the specific surface area, the higher the oxygen content on the surface of the tin powder. Furthermore, since die-bonding solder paste is currently applied to the surface to be soldered via dispensing or printing, and reflow soldering typically takes 2-12 hours, this prolonged exposure to oxygen makes the tin powder highly susceptible to oxidation, thus affecting the wetting performance of the solder paste. Currently, all commercially available die-bonding solder pastes require nitrogen gas during reflow soldering to reduce the oxygen concentration during the soldering process, preventing re-oxidation and thus minimizing oxidation of the tin powder surface, ensuring the wetting performance of the solder paste during soldering.

[0004] Chinese Publication No. CN102069314A discloses a die-bonding solder paste for high-power LEDs and its preparation method. It is made by mixing lead-free metal alloy powder with die-bonding flux. This invention features higher thermal conductivity, shorter die-bonding time, and stable performance. Its preparation method is simple, and the prepared die-bonding solder paste exhibits excellent wettability to gold layers, low porosity, a uniform and delicate consistency, no odor, and a high thixotropic index, resulting in excellent soldering strength and mechanical properties. Chinese Patent Publication No. CN105855748A discloses a die-bonding solder paste for chip packaging, its preparation method, and its application process. The die-bonding solder paste described in this invention effectively ensures the uniformity of the die-bonding process during long-term operation in an open environment, improves oxidation resistance, reduces void ratio, and enhances the electrical performance of semiconductor devices.

[0005] Based on existing invention patents and core technologies of market products, current die-bonding solder pastes require nitrogen gas during reflow soldering. The drawback is that this increases nitrogen consumption and production costs. Summary of the Invention

[0006] The purpose of this invention is to provide a die-bonding solder paste that can be air-reflow soldered and its preparation method, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a die-bonding solder paste that can be air-reflow soldered, comprising 15% ultrasonically atomized 2-25µm Sn96.5Ag3.0Cu0.5 alloy solder powder and 85% nano-treated flux; the flux is composed of the following mass percentages: solvent 40-50%, resin 35-40%, imidazole 5-8%, thixotropic agent 5-10%, and antioxidant 1-5%.

[0008] A method for preparing a die-bonding solder paste suitable for air reflow soldering is characterized by the following steps: Step 1: Weigh solvent, resin, imidazole, thixotropic agent, and antioxidant according to their mass percentages and add them to a reaction vessel. While stirring, heat to 100 degrees Celsius. After complete dissolution, seal the vessel and allow it to stand at room temperature for 24 hours. Then, perform two grinding operations using a nano-grinding machine to control the particle size of all materials in the flux to below the nanometer level, thus obtaining the desired nano-flux. The nano-grinding machine grinds the flux, and because the particle size of all materials is below the nanometer level, it can completely coat the surface of the tin powder, forming a nanomaterial protective layer and reducing the possibility of the tin powder surface coming into contact with oxygen. Due to the protection of this nano-flux layer, it can be directly exposed to the air environment before and during soldering.

[0009] Step 2: According to the mass percentage, mix the nano flux and ultrasonically atomized solder powder prepared above in a solder paste mixer and vacuum mix for more than 0.5 hours. Set the vacuum degree to -0.1 MPa and the mixing speed to 20 rpm / min. Mix until completely homogeneous.

[0010] Preferably, the ultrasonically atomized 2-25µm Sn96.5Ag3.0Cu0.5 alloy solder powder utilizes ultrasonic vibration to form micro-droplets from a liquid solder solution in a protective atmosphere. This process produces solder alloy powder with high sphericity, low oxygen content, good sphericity, smooth surface, and good powder consistency. The ultrasonically atomized solder powder also possesses advantages such as high sphericity, low oxygen content, good sphericity, smooth surface, and good powder consistency. Because of its high sphericity, smooth surface, low oxygen content, and good alloy fusion, the solder paste requires less activity even in air, thus improving its wetting performance.

[0011] Preferably, the solvent is one or a combination of diethylene glycol monooctyl ether and diethylene glycol hexyl ether; the solvent provides a dissolving environment for components such as resin and thixotropic agent, and also affects the ionization of active components; the preferred solvent has good dissolving properties for other materials added in this invention, does not easily volatilize at room temperature, increases the service life of solder paste, and because the carbon chain segment is greater than 8, it also acts as a surfactant in the later stage of soldering, reducing the surface tension of the surface to be soldered.

[0012] Preferably, the resin is one or a combination of lead-free 685 rosin, water-white rosin, and hydrogenated rosin glycerol ester. The main function of the resin is to remove the oxide film from the surface of the solder and the welding plate, achieving the necessary cleanliness of the metal surface. This prevents re-oxidation during welding, reduces the surface tension of the solder, improves welding performance, and makes the solder joints more solid, reducing the probability of cold solder joints and resulting in brighter, fuller solder joints. The resin residue after welding has good electrical insulation properties, increases surface insulation resistance, effectively prevents electron migration, and thus prevents short circuits between solder joints.

[0013] Preferably, the imidazole is one or a combination of 2-ethylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, and 2-phenylimidazole. Imidazole organic compounds are all adsorption film type materials. After being added to the flux, they can quickly generate electrostatic attraction and van der Waals forces with the surface charge of the tin powder, forming a complete adsorption film in the active reaction area on the surface of the tin powder, thereby achieving a good corrosion inhibition effect. Because of the presence of this corrosion inhibition effect, the antioxidant effect of the solder paste of the present invention is improved. Simultaneously, during the heating of the die-bonding solder paste, hydrogen ions on the imidazole functional groups are released, acting as activators. This removes oxides from the substrate and solder surfaces, wets the substrate, provides an acidic atmosphere to prevent secondary oxidation of the solder, reduces post-soldering oxide residue, and ensures the spread area of ​​the solder joints. The thixotropic agent is one or a combination of hydrogenated castor oil and modified hydrogenated castor oil (ST). The thixotropy of these two materials is caused by hydrogen bonds, which easily form a three-dimensional network structure. Their main function is to impart certain thixotropic properties to the solder paste. Under no stress, its viscosity increases to maintain its inherent shape and prevent solder paste collapse. Under stress, the viscosity decreases to facilitate solder paste dispensing and printing, and decreases further with increasing shear force.

[0014] Preferably, the antioxidant is one or more combinations of antioxidant BHT, antioxidant 1024, and antioxidant 245. The mechanism of action of these phenolic antioxidants includes two pathways: indirect scavenging of free radicals and direct scavenging of free radicals. The former refers to phenolic antioxidants preventing oxygen atoms from attacking metal ions by complexing them, while the latter refers to phenolic antioxidants generating stable phenoxy free radicals through the hydrogen extraction reaction of phenolic hydroxyl groups, thereby interrupting the chain reaction. This invention achieves the protective effect on the metal surface of tin powder by adding one or more of these antioxidants.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The die-bonding solder paste and its preparation method that can be air-reflow soldered provided by the present invention can be applied to high-power LED soldering. By using solder powder with high sphericity, smooth surface, low oxygen content, and ultrasonic atomization, and preferably adding adsorbent film-type organic imidazole and phenolic antioxidants with complexing metal ions, the flux paste is nano-ground using a nano-grinding machine. The nano-ground flux paste can completely coat the surface of the solder powder, forming a nano-material protective layer. The die-bonding solder paste of the present invention is different from the existing die-bonding solder pastes on the market. It can be air-reflow soldered and the wetting performance is further improved, reducing production costs and playing a role in environmental protection. Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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. Example

[0017] A die-bonding solder paste that can be air-reflow soldered and its preparation method: 40% diethylene glycol monooctyl ether, 40% lead-free 685 rosin, 8% 2-ethylimidazole, 10% hydrogenated castor oil, and 2% antioxidant BHT are weighed by mass percentage and added to a reaction vessel. The mixture is heated to 100 degrees Celsius while stirring. After complete dissolution, the mixture is sealed and allowed to stand at room temperature for 24 hours. Then, it is ground twice using a nano-grinding machine to obtain the nano-flux.

[0018] Weigh out 15% of the nano flux and 85% of the ultrasonic atomized solder powder according to the mass percentage and put them into a solder paste mixer. Stir under vacuum for more than 0.5 hours, with the vacuum degree set to -0.1 MPa and the stirring speed set to 20 rpm / min. After being completely stirred evenly, a die-bonding solder paste that can be air reflow soldered is obtained. After dispensing, it is stored in a cold storage at 2-10 degrees Celsius. Example

[0019] A die-bonding solder paste that can be air-reflow soldered and its preparation method: 43% diethylene glycol hexyl ether, 39% water-based rosin, 7% 2-methylimidazole, 9% modified hydrogenated castor oil (ST), and 3% antioxidant 1024 are weighed by mass percentage and added to a reaction vessel. The mixture is stirred and heated to 90-100 degrees Celsius until completely dissolved. After sealing, the mixture is allowed to stand at room temperature for 24 hours and then ground twice using a nano-grinding machine to obtain the nano-flux paste.

[0020] Weigh out 15% of the nano flux and 85% of the ultrasonic atomized solder powder according to the mass percentage and put them into a solder paste mixer. Stir under vacuum for more than 0.5 hours, with the vacuum degree set to -0.1 MPa and the stirring speed set to 20 rpm / min. After being completely stirred evenly, a die-bonding solder paste that can be air reflow soldered is obtained. After dispensing, it is stored in a cold storage at 2-10 degrees Celsius. Example

[0021] A die-bonding solder paste that can be air-reflow soldered and its preparation method: 24% diethylene glycol hexyl ether, 20% diethylene glycol hexyl ether, 38% hydrogenated rosin glycerol ester, 6% 2-ethyl-4-methylimidazolium, 4% hydrogenated castor oil, 4% modified hydrogenated castor oil (ST), and 4% antioxidant 245 are weighed by mass percentage and added to a reaction vessel. The mixture is stirred and heated to 90-100 degrees Celsius until completely dissolved. After sealing, the mixture is allowed to stand at room temperature for 24 hours and then ground twice using a nano-grinding machine to obtain the nano-flux paste.

[0022] Weigh out 15% of the nano flux and 85% of the ultrasonic atomized solder powder according to the mass percentage and put them into a solder paste mixer. Stir under vacuum for more than 0.5 hours, with the vacuum degree set to -0.1 MPa and the stirring speed set to 20 rpm / min. After being completely stirred evenly, a die-bonding solder paste that can be air reflow soldered is obtained. After dispensing, it is stored in a cold storage at 2-10 degrees Celsius. Example

[0023] A die-bonding solder paste that can be air-reflow soldered and its preparation method: 10% diethylene glycol monooctyl ether, 37% diethylene glycol hexyl ether, 10% lead-free 685 rosin, 27% hydrogenated rosin glycerol ester, 5% 2-phenylimidazole, 4% hydrogenated castor oil, 3% modified hydrogenated castor oil (ST), 2% antioxidant BHT, 1% antioxidant 1024, and 1% antioxidant 245 are weighed by mass percentage and added to a reaction vessel. While stirring, the temperature is raised to 90-100 degrees Celsius. After complete dissolution, the mixture is sealed and allowed to stand at room temperature for 24 hours. Then, it is ground twice using a nano-grinding machine to obtain the nano-flux paste.

[0024] Weigh out 15% of the nano flux and 85% of the ultrasonic atomized solder powder according to the mass percentage and put them into a solder paste mixer. Stir under vacuum for more than 0.5 hours, with the vacuum degree set to -0.1 MPa and the stirring speed set to 20 rpm / min. After being completely stirred evenly, a die-bonding solder paste that can be air reflow soldered is obtained. After dispensing, it is stored in a cold storage at 2-10 degrees Celsius. Example

[0025] A die-bonding solder paste that can be air-reflow soldered and its preparation method are disclosed. The following ingredients are weighed by mass percentage: 38% diethylene glycol monooctyl ether, 10% diethylene glycol hexyl ether, 26% lead-free 685 rosin, 10% water-white rosin, 2-ethylimidazole, 2-methylimidazole, 1% 2-ethyl-4-methylimidazole, 1% 2-phenylimidazole, 4% hydrogenated castor oil, 5% modified hydrogenated castor oil (ST), and 2455% antioxidant. The mixture is added to a reaction vessel, heated to 90-100 degrees Celsius while stirring. After complete dissolution, the mixture is sealed and allowed to stand at room temperature for 24 hours. It is then ground twice using a nano-grinding machine to obtain the nano-flux.

[0026] Weigh out 15% of the nano flux and 85% of the ultrasonic atomized solder powder according to the mass percentage and put them into a solder paste mixer. Stir under vacuum for more than 0.5 hours, with the vacuum degree set to -0.1 MPa and the stirring speed set to 20 rpm / min. After being completely stirred evenly, a die-bonding solder paste that can be air reflow soldered is obtained. After dispensing, it is stored in a cold storage at 2-10 degrees Celsius. Example

[0027] A die-bonding solder paste that can be air-reflow soldered and its preparation method: 50% diethylene glycol hexyl ether, 20% water-based rosin, 15% hydrogenated rosin glycerol ester, 3% 2-ethylimidazole, 2% 2-ethyl-4-methylimidazole, 6% hydrogenated castor oil, 3% modified hydrogenated castor oil (ST), and 1% antioxidant BHT are weighed by mass percentage and added to a reaction vessel. The mixture is heated to 90-100 degrees Celsius while stirring. After complete dissolution, the mixture is sealed and allowed to stand at room temperature for 24 hours. Then, it is ground twice using a nano-grinding machine to obtain the nano-flux paste.

[0028] Weigh out 15% of the nano flux and 85% of the ultrasonic atomized solder powder according to the mass percentage and put them into a solder paste mixer. Stir under vacuum for more than 0.5 hours, with the vacuum degree set to -0.1 MPa and the stirring speed set to 20 rpm / min. After being completely stirred evenly, a die-bonding solder paste that can be air reflow soldered is obtained. After dispensing, it is stored in a cold storage at 2-10 degrees Celsius. Example

[0029] A die-bonding solder paste capable of air reflow soldering and its preparation method: 20% diethylene glycol monooctyl ether, 25% diethylene glycol hexyl ether, 10% lead-free 685 rosin, 15% water-based white rosin, 10% hydrogenated rosin glycerol ester, 3% 2-ethylimidazole, 1% 2-methylimidazole, 2% 2-phenylimidazole, 3% 2-ethyl-4-methylimidazole, 3% hydrogenated castor oil, 3% modified hydrogenated castor oil (ST), 2% antioxidant BHT, 2% antioxidant 1024, and 1% antioxidant 245 are added to a reaction vessel while stirring and heating to 90-100 degrees Celsius. After complete dissolution, the mixture is sealed and allowed to stand at room temperature for 24 hours. It is then ground twice using a nano-grinding machine to obtain the nano-flux.

[0030] Weigh out 15% of the nano flux and 85% of the ultrasonic atomized solder powder according to the mass percentage and put them into a solder paste mixer. Stir under vacuum for more than 0.5 hours, with the vacuum degree set to -0.1 MPa and the stirring speed set to 20 rpm / min. After being completely stirred evenly, a die-bonding solder paste that can be air reflow soldered is obtained. After dispensing, it is stored in a cold storage at 2-10 degrees Celsius.

[0031] The solder paste in the above embodiments underwent tests for solder balls, collapse, wetting, and anti-wetting effects according to the Japanese Industrial Solder Paste Standard JIS Z3284, and tests for copper plate corrosion, copper mirror corrosion, surface insulation resistance, and electron migration according to the IPC TM-650 standard. All test results were satisfactory. When the above embodiments were directly subjected to air reflow soldering, the solder strength, void ratio, solder joint brightness, and residual characteristics achieved the same effect as commercially available die-bonding solder pastes that require nitrogen gas soldering.

[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A die-bonding solder paste that can be air-reflow soldered, characterized in that: The solder paste is composed of 85% ultrasonically atomized 2-25µm Sn96.5Ag3.0Cu0.5 alloy solder powder and 15% nano-treated flux. The flux is composed of the following mass percentages: solvent 40-50%, resin 35-40%, imidazole 5-8%, thixotropic agent 5-10%, and antioxidant 1-5%. The imidazole is one or a combination of 2-ethylimidazolium, 2-methylimidazolium, 2-ethyl-4-methylimidazolium, and 2-phenylimidazolium. The thixotropic agent is one or a combination of hydrogenated castor oil and modified hydrogenated castor oil.

2. The die-bonding solder paste capable of air reflow soldering according to claim 1, characterized in that: The solvent is one or a combination of two of diethylene glycol monooctyl ether and diethylene glycol hexyl ether.

3. The die-bonding solder paste capable of air reflow soldering according to claim 1, characterized in that: The resin is one or more of lead-free 685 rosin, water-white rosin, and hydrogenated rosin glycerol ester.

4. The die-bonding solder paste capable of air reflow soldering according to claim 1, characterized in that: The antioxidant is one or more of antioxidant BHT, antioxidant 1024, and antioxidant 245.

5. A method for preparing a die-bonding solder paste capable of air reflow soldering as described in claim 1, characterized in that: Step 1: Weigh the solvent, resin, imidazole, thixotropic agent, and antioxidant according to the mass percentage and add them to the reaction vessel. While stirring, heat to 100 degrees Celsius. After complete dissolution, seal the vessel and let it stand at room temperature for 24 hours. Then, use a nano milling machine to grind the materials twice to control the particle size of all materials in the flux to below the nanometer level to obtain the required nano flux. Step 2: According to the mass percentage, mix the nano flux and ultrasonically atomized solder powder in a solder paste mixer and vacuum mix for at least 0.5 hours. Set the vacuum degree to 0.1 MPa and the mixing speed to 20 rpm / min. Once completely mixed, it is ready.

6. The method for preparing a die-bonding solder paste capable of air reflow soldering according to claim 5, characterized in that: The ultrasonically atomized 2-25µm Sn96.5Ag3.0Cu0.5 alloy solder powder utilizes ultrasonic vibration to form micro-droplets from a liquid solder solution in a protective atmosphere.