Gold-based alloy solder paste with good dispensing performance and preparation method thereof

Abstract

A gold-based alloy solder paste with good dispensing performance, comprising, in mass percentage, 87-93% of gold-based alloy powder, the gold-based alloy powder containing 75-90% of gold; and 7-13% of flux, the flux mainly comprising modified rosin, organic solvent, active agent and thixotropic agent; the modified rosin being hydrogenated rosin and polymerized rosin; the organic solvent being two or more of ethylene glycol, glycerol, isopropyl alcohol, diethylene glycol ethyl ether, propylene glycol methyl ether or dipropylene glycol butyl ether; the active agent being one or more of acetic acid, glutaric acid, o-hydroxybenzoic acid, pimelic acid and heptanedioic acid; and the thixotropic agent being ethylene bis-stearamide and modified fatty acid amide resin; the gold-based alloy solder paste prepared by the application is free of halogen, easy to clean, low in oxygen content, has bright solder joints and high expansion rate, can realize continuous dispensing, and is applied to the field of high-reliability electronic packaging.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electronic packaging, and particularly relates to a gold-based alloy solder paste with good dispensing performance and a preparation method thereof. BACKGROUND

[0002] The gold-based alloy solder paste has excellent electric conductivity, heat conductivity and corrosion resistance, and excellent mechanical properties, and has been widely applied in the fields of JG and aerospace with high reliability requirements. As a high-temperature solder paste with high reliability, the gold-based alloy solder paste can be used in occasions with a high service temperature range (more than 150 DEG C), and has the characteristics of good thermal fatigue performance, high strength at high temperature, and excellent corrosion resistance and oxidation resistance.

[0003] The gold-based alloy solder paste has two modes of dispensing and screen printing in the use process. The dispensing process is that the solder paste is filled in an injection dispenser, a specific mass of the solder paste is pressed out from a needle nozzle by controlling the pressure of compressed air, and is accurately positioned at a specific position on the surface of a substrate. Under the action of gravity, the solder paste is formed into a film layer with a specific shape, and the initial connection between the electronic component and the substrate is realized. Then, the organic carrier is decomposed and volatilized, the flux plays a cleaning and wetting role, and then flows out from the film layer, and the solder is melted and spread, so that the electronic component and the substrate are well electrically connected. The main factor affecting the dispensing performance of the solder paste is the thixotropy of the solder paste, that is, the characteristic that the viscosity of the solder paste is reduced under the action of shear force. Whether the high viscosity can be maintained under static state and whether the solder paste can be instantaneously thinned after being stressed are important bases for evaluating the quality of the solder paste. The domestic gold-based alloy solder paste on the market generally has unstable dispensing performance and the problem of stratification of the flux and the powder in the injection dispenser. SUMMARY

[0004] In order to overcome the defects of the prior art, the purpose of the present application is to provide a gold-based alloy solder paste with good dispensing performance and a preparation method thereof, and the specific technical solutions are as follows.

[0005] The first aspect of the present application is to provide a gold-based alloy solder paste. The solder paste comprises 87-93% of gold-based alloy powder and 7-13% of flux by mass percentage. The main components of the flux are modified rosin, organic solvent, active agent and thixotropic agent.

[0006] Preferably, the gold content in the gold and alloy powder is 75-90%.

[0007] In the present application, the modified rosin is hydrogenated rosin and polymerized rosin, and the ratio of hydrogenated rosin and polymerized rosin is 2-4:1-2, and the content accounts for 25-35% of the total amount of the flux. Different kinds of rosin have different solubility and crystallization tendency in alcohol ether solvents, and the present application selects two kinds of modified rosin resins, and selects appropriate ratio to achieve better flux effect. The polymerized rosin has relatively low acid value and high viscosity, the hydrogenated rosin has good oxidation resistance, small brittleness and high thermal stability.

[0008] In the present application, the organic solvent is two or more of ethylene glycol, glycerol, isopropyl alcohol, diethylene glycol ether, propylene glycol methyl ether or dipropylene glycol butyl ether, and the ratio of alcohol and ether is 2-4:1-2, and the content accounts for 50-70% of the total amount of the flux; each organic solvent has different viscosity and boiling point, and different alcohol and ether are selected to adjust the viscosity of the flux, and the flux is completely volatilized at the temperature close to the formed solder joint, thereby reducing the post-soldering residue.

[0009] In the present application, the active agent is one or more of acetic acid, glutaric acid, o-hydroxybenzoic acid, sunflower acid and heptanedioic acid, and the content accounts for 2-10% of the total amount of the flux.

[0010] In the present application, the thixotropic agent is ethylene bis-stearamide and modified fatty acid amide, and the ratio is 1-2:2-4, and the content accounts for 2-10% of the total amount of the flux. The thixotropic agent has a significant influence on the final viscosity of the gold-based alloy paste.

[0011] In the present application, the gold-based alloy powder is a gold-based alloy powder with liquidus line at 250-400 DEG C and oxygen content ≤50ppm; the gold-based alloy powder has high sphericity, no satellite ball and no hollow ball, uniform particle size distribution, and particle size is between 25-45 microns. The gold-based alloy powder prepared by the gold-based alloy powder has good flowability, the solder powder is easy to combine with the flux, and the soldering performance is good.

[0012] The second aspect of the present application is to provide a preparation method of the gold-based alloy solder paste of the first aspect of the present application, and the method comprises:

[0013] (1) The rosin, organic solvent and active agent are weighed according to the weight ratio, and are placed in a water bath heating reactor at 80-100 DEG C, and are stirred at a speed of 800-1200 revolutions per minute for 20-40 minutes until a uniform mixture is formed, and is cooled to room temperature;

[0014] (2) The thixotropic agent is added to the mixture of (1), and is stirred at a speed of 1000 revolutions per minute for more than 5 minutes, so that it is uniformly mixed into the mixture;

[0015] (3) Take the flux and gold-based alloy powder by weight ratio, stir them uniformly by using a stirrer, and then roll the soldering paste by using a rolling mill. The gold-based alloy soldering paste should be rolled for 3-5 passes, and the fineness should be less than the maximum gold and alloy powder particle size.

[0016] The present application has the following advantages:

[0017] (1) The gold-based alloy soldering paste prepared according to the present application does not contain halogen, and is friendly to electronic components and environment;

[0018] (2) The gold-based alloy soldering paste prepared according to the present application is easy to clean, has good dispensing performance, and good spreading performance;

[0019] (3) The gold-based alloy soldering paste prepared according to the present application has low boiling point of organic solvent, which is completely removed during welding. The antioxidant can effectively inhibit or reduce the oxidation of metal particles, and improve the heat shock resistance and mechanical properties of the welding layer. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The gold-based soldering paste prepared in Examples 1-3 was subjected to spreading experiments on a gold-plated plate, wherein, Figure 1 a is the effect picture of Example 1, Figure 1 b is the effect picture of Example 2, Figure 1 c is the effect picture of Example 3. DETAILED DESCRIPTION

[0021] The present application provides a preparation method of gold-based alloy soldering paste with good dispensing performance, which is further described below in combination with examples.

[0022] In the following examples, the gold-based alloy powder is smelted gold with gold content of 75-90%, which is obtained by atomization, and other substances are industrial pure products.

[0023] Example 1

[0024] Take 87% gold-based alloy powder and 13% flux by mass percentage; the main components of the flux are 35% hydrogenated rosin and polymerized rosin, and the mass ratio of hydrogenated rosin to polymerized rosin is 2:1; 60% organic solvent, wherein the mass ratio of glycerol to diethylene glycol ethyl ether is 2:1; 2% acetic acid; 3% thixotropic agent, wherein the mass ratio of ethylene bis-stearamide to modified fatty acid amide resin is 1:2; the liquidus of the gold-based alloy powder is 280℃, the gold content of the gold-based alloy powder is 80%, and the oxygen content is 46ppm; the sphericity is high, there are no satellite balls and hollow balls, and the particle size distribution is 25-45μm. The following are the preparation steps of the gold-based alloy soldering paste:

[0025] (1) The weighed rosin, organic solvent and active agent were placed in a water bath heating reactor at 80°C and stirred at 800 rpm for 30 minutes until a uniformly dispersed mixture was formed, and then cooled to room temperature;

[0026] (2) The thixotropic agent was added to the mixture of (1) and stirred in a blender at 1000 rpm for 5 minutes to uniformly mix into the mixture, thereby obtaining the flux;

[0027] (3) 26 grams of the flux and 174 grams of the gold-based alloy powder were stirred uniformly using a stirrer, and then the solder paste was rolled using a three-roll mill. The gold-based alloy solder paste was rolled for 3 passes by the three-roll mill. The obtained gold-based alloy solder paste had a viscosity of 80 Pa·s, bright soldering spots, easy cleaning, and could be continuously dispensed.

[0028] Example 2

[0029] The gold-based alloy powder and the flux were weighed in a mass percentage of 90% and 10%, respectively. The main components of the flux included 30% hydrogenated rosin, 65% organic solvent, 2.5% glutaric acid, and 2.5% thixotropic agent. The mass ratio of hydrogenated rosin to polymeric rosin was 3:1. The mass ratio of glycerol, isopropyl alcohol, diethylene glycol ethyl ether, and dipropylene glycol butyl ether in the organic solvent was 1:2:2:1. The mass ratio of ethylene bis-stearamide to modified fatty acid amide resin in the thixotropic agent was 2:3. The liquidus of the gold-based alloy powder was 356°C, the gold content was 88%, and the oxygen content was 39 ppm. The gold-based alloy powder had high sphericity, no satellite balls, and no hollow balls, and the particle size distribution was 25-45 μm. The following were the preparation steps of the gold-based alloy solder paste:

[0030] (1) The weighed rosin, organic solvent and active agent were placed in a water bath heating reactor at 90°C and stirred at 900 rpm for 32 minutes until a uniformly dispersed mixture was formed, and then cooled to room temperature;

[0031] (2) The thixotropic agent was added to the mixture of (1) and stirred in a blender at 1000 rpm for 5 minutes to uniformly mix into the mixture, thereby obtaining the flux;

[0032] (3) 20 grams of the flux and 180 grams of the gold-based alloy powder were stirred uniformly using a stirrer, and then the solder paste was rolled using a three-roll mill. The gold-based alloy solder paste was rolled for 3 passes by the three-roll mill. The obtained gold-based alloy solder paste had a viscosity of 75 Pa·s, bright soldering spots, easy cleaning, and could be continuously dispensed.

[0033] Example 3

[0034] Take 85% of gold-based alloy powder and 15% of flux by mass percentage; the main components of the flux are 32% hydrogenated rosin, polymerized rosin, the mass ratio of hydrogenated rosin to polymerized rosin is 2:1; 62% organic solvent, the mass ratio of ethylene glycol, isopropyl alcohol, diethylene glycol ether, and propylene glycol methyl ether is 2:1:1:1; 3% sunflower acid; 4% thixotropic agent, the mass ratio of ethylene bis-stearamide to modified fatty acid amide resin is 1:2; the liquidus of the gold-based alloy powder is 290℃, the gold-based alloy powder contains 88% of gold, and the oxygen content of the gold-based alloy powder is 36ppm; the sphericity is high, there are no satellite balls and hollow balls, and the particle size distribution is 25-45μm. The following are the preparation steps of the gold-based alloy paste:

[0035] (1) The rosin, organic solvent, and active agent weighed by mass are placed in a 95℃ water bath heating reactor, stirred at a speed of 1000rpm for 38 minutes until a uniformly dispersed mixture is formed, and cooled to room temperature;

[0036] (2) The thixotropic agent is added to the mixture in (1), placed in a stirrer, and stirred at a speed of 1000rpm for 5 minutes to uniformly mix into the mixture, thereby obtaining the flux;

[0037] (3) 30g of the flux and 170g of the gold-based alloy powder are weighed, uniformly stirred using a stirrer, and then rolled into a paste using a three-roll mill, and the gold-based alloy paste is rolled for 3 passes. The obtained gold-based alloy paste has a viscosity of 90Pa·s, the welding spot is bright, easy to clean, and can be continuously dispensed.

[0038] The flux prepared by the embodiments of the present application does not contain halogen, is friendly to electronic components and environment, has good physical stability, is easy to clean and dispense, has good spreading property, the boiling point of the flux in the gold-based alloy paste is low, it is completely removed during welding, effectively inhibits the oxidation of the gold-based alloy powder, improves the heat shock resistance and mechanical properties of the welding layer, has good wettability, the welding spot is bright in appearance, has excellent welding performance, and can ensure the reliability of high-end electronic packaging.

Claims

1. A gold-based alloy solder paste having good dispensing properties, characterized in that The soldering paste comprises, in mass percentage, 87-93% of gold-based alloy powder, the gold content of which is 75-90%; 7-13% of flux, the main components of which include modified rosin, organic solvent, active agent and thixotropic agent; the modified rosin is hydrogenated rosin and polymerized rosin, the ratio of which is 2-4:1-2, and the content of which is 15-25% of the flux; the organic solvent is two or more of ethylene glycol, glycerol, isopropyl alcohol, diethylene glycol ethyl ether, propylene glycol methyl ether or dipropylene glycol butyl ether, the ratio of which is 2-4:1-2, and the content of which is 50-70% of the flux; the thixotropic agent is ethylene bis-stearamide and modified fatty acid amide, the ratio of which is 1-2:2-4, and the content of which is 2-10% of the flux.

2. The gold-based alloy paste of claim 1, wherein, The active agent is one or more of acetic acid, glutaric acid, o-hydroxybenzoic acid, sebacic acid and heptanedioic acid, and the content of which is 2-10% of the flux.

3. The gold-based alloy paste of claim 1, wherein, The gold-based alloy powder is a gold-based alloy powder with liquidus line at 270-360℃ and oxygen content ≤50ppm, and the particle size distribution is 25-45μm.

4. A preparation method of the gold-based alloy soldering paste according to claim 1, comprising: (1) weighing rosin, organic solvent and active agent according to weight ratio, and placing them in a water bath heating reactor at 80-100℃, and stirring at 800-1200rpm for 20-40 minutes until a uniformly dispersed mixture is formed, and cooling to room temperature; (2) adding thixotropic agent to the mixture in (1), and stirring at 1000rpm for more than 5 minutes to make it uniformly mixed in the mixture; (3) weighing flux and gold-based alloy powder according to weight ratio, stirring them uniformly using a stirrer, and then using a rolling mill to roll the soldering paste, and the fineness of the gold-based alloy soldering paste should be less than the maximum gold and alloy powder particle size after 3-5 rolling passes.

Images