CN114589433A

CN114589433A - Soldering flux and preparation method and application thereof

Info

Publication number: CN114589433A
Application number: CN202210275316.6A
Authority: CN
Inventors: 杨宗美; 张小春; 翁行尚; 王飞; 赵鹏; 庄学文; 陈伟健; 吴正旭
Original assignee: Institute of Chemical Engineering of Guangdong Academy of Sciences
Current assignee: Institute of Chemical Engineering of Guangdong Academy of Sciences
Priority date: 2022-03-21
Filing date: 2022-03-21
Publication date: 2022-06-07
Anticipated expiration: 2042-03-21
Also published as: CN114589433B

Abstract

The invention belongs to the technical field of welding materials, and particularly relates to a soldering flux as well as a preparation method and application thereof. The soldering flux comprises the following components: film forming agent, flux activator, surfactant and corrosion inhibitor; the surface active agent comprises fatty alcohol-polyoxyethylene ether and cardanol polyoxyethylene ether, and the corrosion inhibitor comprises fluorobenzimidazole, secondary amine and chitosan. The soldering flux prepared by the invention has good oxidation resistance and antibacterial property, high appearance stability, excellent tinning performance, no halogen and little ionic pollution to a PCB (printed circuit board); the solder resist ink does not contain Volatile Organic Solvents (VOCs), has no aggressivity to the solder resist ink, is environment-friendly and healthy, fundamentally solves the problem of reaction between the solvents and the solder resist ink, and has clean PCB surface and no white oil mark. Except that the cardanol polyoxyethylene and the chitosan do not contain VOCs, the cardanol polyoxyethylene and the chitosan which are adopted by the invention are natural green biodegradable environment-friendly raw materials, so that the cardanol polyoxyethylene and the chitosan are more environment-friendly and healthier.

Description

Soldering flux and preparation method and application thereof

Technical Field

The invention belongs to the technical field of welding materials, and particularly relates to a soldering flux as well as a preparation method and application thereof.

Background

The hot air leveling (also known as hot air solder leveling) technology is one of the surface treatment modes of Printed Circuit Boards (PCBs), and is a mature technology applied at present. Because the hot air leveling has the advantages of reliable welding, simple operation, no need of chemical control, low requirement on production environment, flexible production scale applicability and the like, and the application of advanced technologies and equipment such as automation and the like, the hot air leveling technology is developed again, has an irreplaceable status in practical application, and is widely applied to important fields such as military, aviation, mobile phones, notebooks, industry and the like.

As a final surface treatment process of a PCB, the final quality of a product is directly influenced by the welding quality of hot air leveling, and the soldering flux is a key material for ensuring the welding quality of the hot air leveling. The soldering flux is mainly used for tightly combining the solder and the metal to be soldered through the following actions: (1) removing oxides and impurities on the surface of the welded metal to ensure that the metal surface reaches necessary cleanliness; (2) the surface tension of the solder is reduced, and the wettability is enhanced; (3) the solder and the surface of the welded substrate are prevented from being oxidized again during welding; (4) the auxiliary heat conduction makes the heat transfer to the welding area evenly. The ideal soldering flux has strong chemical activity, and also has good wettability, thermal stability, film forming property, oxidation resistance, low corrosivity, low ion pollution, environmental protection, health and the like.

At present, most of the soldering fluxes for hot air leveling in the market are water-soluble soldering fluxes. From the perspective of active ingredients, the halogen-containing water-soluble soldering flux and the halogen-free water-soluble soldering flux are mainly divided. Halogen such as hydrochloric acid, hydrofluoric acid, zinc chloride, ammonium chloride and the like is added into the halogen-containing water-soluble soldering flux, so that the halogen-containing water-soluble soldering flux has strong chemical action, good soldering-assisting performance and low cost, but has large corrosion effect and serious ion pollution, thus causing the reduction of the surface insulation resistance of a circuit board and seriously affecting the reliability and the service life of an electronic product. Therefore, the method is gradually eliminated in practical application. The halogen-free water-soluble flux can be classified into organic solvent type flux and water-based flux according to the type of the solvent. The organic solvent type soldering flux mainly takes volatile organic solvents such as alcohol and ether as solvents, has high volatility and smoke, seriously pollutes the environment and harms the health of human bodies; the water-based soldering flux takes deionized water as a main solvent, is a great trend for the environmental protection development of the soldering flux, and greatly reduces the pollution to the atmospheric environment and the health hazard of operators.

Although the water-based soldering flux for hot air leveling is more environment-friendly and healthier, the following problems still exist: (1) poor wetting spreadability, poor soldering-assisting performance, poor tin-coating, tin connection, copper exposure, tin accumulation and the like. The poor tin-coating performance is caused by various reasons, such as large surface tension, insufficient impurity and oxide removing capability, poor wetting and spreading performance of the soldering flux, insufficient antioxidant protection force caused by poor film-forming property and the like, which can greatly reduce the soldering assisting performance of the soldering flux, particularly, the water-based soldering flux contains more water, the surface tension of water is large, so that the wetting performance of the soldering flux is poor, and tin connection and tin stacking are more easily caused. (2) The residues after welding are too much or the organic solvent in the soldering flux reacts with the solder resist ink, so that the cleanliness and the product performance of the PCB surface are seriously influenced. Although the main solvent of the water-based soldering flux is water, the solubility of water to various active ingredients in the soldering flux is limited, for example, the conventional antioxidant BHT cannot be dissolved in water, so that alcohol ether organic solvents are added to most soldering fluxes as cosolvent in practice. (3) The active substances are added too much, the corrosivity is strong, and the service life of the product is influenced. (4) The heat resistance and the heat conductivity are poor, so that the surface of the circuit board is locally overheated in the welding process, and the product performance is influenced. Lead-free solder makes higher demands on the heat resistance of the soldering flux. (5) The deionized water content is too high, the viscosity of the soldering flux is low, and the solder is seriously splashed. (6) The water-based soldering flux is particularly easy to breed bacteria, mould and the like, so that the storage stability of the soldering flux is poor. In addition, the flux is prone to color deepening and even color change during storage and use due to oxidation.

Therefore, it is necessary to develop a soldering flux which is halogen-free, free of VOC, good in soldering performance, free of continuous tin, free of tin accumulation, less in residue, clean in board surface, low in corrosivity, stable in heat resistance and low in cost.

Disclosure of Invention

The present invention has been made to solve at least one of the above-mentioned problems occurring in the prior art. Therefore, the invention provides the soldering flux which has good wetting and spreading properties, strong solderability and excellent tin coating.

The invention also provides a preparation method and application of the soldering flux.

In a first aspect of the present invention, a flux is provided, which comprises the following components: film forming agent, flux activator, surfactant and corrosion inhibitor; the surface active agent comprises fatty alcohol-polyoxyethylene ether and cardanol polyoxyethylene ether, and the corrosion inhibitor comprises fluorobenzimidazole, secondary amine and chitosan.

According to the first aspect of the present invention, at least the following advantageous effects are obtained:

the surface tension of a welding material can be seriously influenced by a very small amount of pollutants on the surface of a workpiece, the wettability is directly influenced by the surface tension, and the cleaning force of the soldering flux on the surface of the workpiece is very important for successful welding. According to the soldering flux, the fatty alcohol-polyoxyethylene ether and the cardanol-polyoxyethylene ether are compounded, so that the foaming force of the soldering flux is low, and the cleaning capability of the soldering flux on a PCB is good; the surface tension of the soldering flux can be greatly reduced, the uniform distribution of all components of the soldering flux on a PCB is effectively promoted, and the activity of the soldering flux activator can be better exerted; the flowing, the expansion and the wetting of the solder on the PCB are effectively promoted, and the wetting spreadability of the soldering flux is greatly improved. Meanwhile, fluorobenzimidazole, secondary amine and chitosan are used as corrosion inhibitors, and fluorobenzimidazole can be self-assembled on the surface of a workpiece to form a compact and ordered molecular protective film, so that the workpiece and a welding flux are effectively prevented from being oxidized in the welding process. In addition, the fluorobenzimidazole, the chitosan and the secondary amine are combined through F … H, N … H, O … H hydrogen bonds to form a multilayer structure, so that the problem caused by incomplete film formation of a single corrosion inhibitor can be effectively avoided.

Preferably, the mass percentage of the surfactant in the soldering flux is 0.2-0.6%, more preferably 0.2-0.5%, and even more preferably about 0.4%. The soldering flux prepared by controlling the mass percent of the surfactant in the soldering flux to be 0.2-0.6% has good wetting spreadability and good film forming property, and the foam of the soldering flux is increased along with the increase of the dosage of the surfactant.

Preferably, the mass ratio of the fatty alcohol-polyoxyethylene ether to the cardanol polyoxyethylene ether is 1-11: 1, more preferably 2 to 10: 1; further preferably 8: about 1. The use ratio is 1-11: 1, the soldering flux prepared by compounding the fatty alcohol-polyoxyethylene ether and the cardanol-polyoxyethylene ether as a surfactant has good wetting spreadability and film-forming property; with the increase of the ratio of the fatty alcohol-polyoxyethylene ether, the foam of the soldering flux is increased, and the wettability is improved.

Preferably, the hydroxyl value of the fatty alcohol-polyoxyethylene ether is 90-120mgKOH/g, and more preferably 95-115 mgKOH/g.

Preferably, the pH value of the fatty alcohol-polyoxyethylene ether is 5-7, and more preferably 6.0-7.5; the HLB value of the fatty alcohol-polyoxyethylene ether is 10-14, and more preferably 12-13.

Preferably, the fatty alcohol-polyoxyethylene ether comprises at least one of AEO7 and AEO 9.

Preferably, the mass percentage of the corrosion inhibitor in the soldering flux is 0.4-3.0%, more preferably 0.5-2.0%, and even more preferably 0.92-1.62%.

Preferably, the mass percentage of the fluorobenzimidazole in the soldering flux is 0.01-0.05%, more preferably 0.01-0.03%, such as 0.02%.

Preferably, the fluorobenzimidazole comprises at least one of 2- (2-fluorobenzyl) benzimidazole, 2- (3-fluorobenzyl) benzimidazole, and 2- (4-fluorobenzyl) benzimidazole. The fluorobenzimidazole can be self-assembled on the copper surface to form a compact and ordered molecular protective film.

Preferably, the mass percentage of the secondary amine in the soldering flux is 0.5-2.0%, and more preferably 0.85-1.75%.

Preferably, the secondary amine comprises at least one of diethylamine and diethanolamine. The boiling point of the diethylamine or the diethanolamine is not high, the residue after welding is less, and the problem of more residue after welding by using the triethanolamine is solved. In addition, secondary amines also act as pH adjusters.

Preferably, the mass percentage of the chitosan in the soldering flux is 0.01-0.08%, such as 0.05%.

Preferably, the chitosan is water-soluble chitosan; the chitosan has a degree of deacetylation of 70% or more, and preferably 80% or more. The water-soluble chitosan with the deacetylation degree of more than 70 percent is adopted, so that on one hand, the water solubility of the chitosan is increased, and meanwhile, the compatibility between the chitosan and other components of the soldering flux is improved, on the other hand, the deacetylation degree of more than 70 percent can ensure that the chitosan contains enough primary amino groups and can be cooperatively acted with secondary amine to form amine copper complexes on the copper surface, so that the wettability of the soldering flux is improved, and the soldering flux has a soldering assisting effect.

Preferably, the mass percentage of the flux activator in the soldering flux is 1.0-3.0%, and more preferably 1.5-2.0%.

Preferably, the fluxing active agent comprises oxalic acid, succinic acid, adipic acid, gallic acid. According to the invention, multiple acid compounds are adopted as an active agent to prepare the soldering flux, and on one hand, an activation gradient is formed by adopting organic acid compounds with different boiling points and without activity; on the other hand, the activity of the soldering flux is synergistically improved by adding gallic acid and utilizing the active phenolic hydroxyl and carboxyl contained in the gallic acid.

Preferably, the mass ratio of the oxalic acid to the succinic acid to the adipic acid to the gallic acid is (1-13): (1-13): (1-23): 1; more preferably (2-10): (2-10): (2-20): 1.

preferably, the mass percentage of the film forming agent in the soldering flux is 30-60%, more preferably 35-55%, and even more preferably 48-55%.

Preferably, the film forming agent comprises polyethylene glycol, sorbitol. Sorbitol in the soldering flux contains a large number of hydroxyl groups, can form a large number of hydrogen bonds with polyethylene glycol, and is crosslinked with each other under the interaction of the hydrogen bonds to form a uniform network, so that the soldering flux has good film forming property, and solder and base metal can be effectively protected from being oxidized in the soldering process. Such materials not only act as film formers, but also act as heat resistant carriers.

Preferably, the mass ratio of the polyethylene glycol to the sorbitol is 3-10: 1, more preferably 4 to 6: 1, further preferably 5: about 1.

Preferably, the polyethylene glycol has an average molecular weight of 200 to 1000, more preferably 600 to 800. The low molecular weight polyethylene glycol can keep the viscosity of the soldering flux low without influencing the spreading fluidity of the soldering flux, has excellent thermal conductivity and can prevent the soldering point from influencing the soldering quality due to local overheating.

Preferably, the pH of the soldering flux is 4.5-5.5, more preferably 4.8-5.2, such as 5.0. The pH of the soldering flux is controlled within the range of 4.5-5.5, the soldering flux has high activity, and when the pH is more than 5.5, the activity of the soldering flux can be greatly reduced.

Preferably, the flux further comprises water. The soldering flux contains a large amount of hydroxyl and water, so that the soldering flux has a better ionization environment, and the activation performance of active acid is effectively improved.

In a second aspect of the present invention, a method for preparing the soldering flux comprises the following steps: and mixing the components of the soldering flux to obtain the soldering flux.

Preferably, the soldering flux comprises a film forming agent, a soldering flux active agent, a surfactant and a corrosion inhibitor; wherein the film forming agent comprises polyethylene glycol and sorbitol, the fluxing active agent comprises oxalic acid, succinic acid, adipic acid and gallic acid, and the corrosion inhibitor comprises fluorobenzimidazole, secondary amine and chitosan; the preparation method of the soldering flux comprises the following steps:

dissolving the gallic acid, oxalic acid, succinic acid, sorbitol, chitosan and fluorobenzimidazole to obtain a component A;

dissolving the adipic acid, the polyethylene glycol and the surfactant to obtain a component B;

and mixing the component A, the component B and secondary amine to obtain the soldering flux.

Preferably, the solvent of component a is water.

Preferably, the preparation process of the component B specifically comprises the following steps: and adding the adipic acid into polyethylene glycol for dissolving, then adding the surfactant, and mixing to obtain a component B.

Preferably, the step of mixing the component A, the component B and the secondary amine specifically comprises the following steps: mixing the component A and the component B, adding secondary amine, and adjusting the pH value to be between 4.5 and 5.5.

In a third aspect of the invention, the flux is applied to workpiece welding.

Preferably, the workpiece comprises a PCB board.

Compared with the prior art, the invention at least has the following beneficial effects:

(1) the soldering flux disclosed by the invention completely does not contain Volatile Organic Solvents (VOCs), and is environment-friendly and healthy; through the synergistic effect of various components, the soldering flux has strong solderability and no copper exposure, and can effectively inhibit the generation of tin connection and tin accumulation; after hot air leveling, the tinning is excellent, the tin surface is flat, and the PCB surface is clean and has few residues after welding; heat resistance and stability; the corrosivity is low; good antibacterial effect, good storage stability, and no discoloration.

(2) The soldering flux disclosed by the invention does not contain halogen, and has small ionic pollution to a workpiece (PCB); the solder resist ink does not contain Volatile Organic Solvents (VOCs), has no aggressivity to the solder resist ink, is environment-friendly and healthy, fundamentally solves the problem of reaction of the solvents and the solder resist ink, and has clean PCB surface and no white oil mark. Except that the cardanol polyoxyethylene and the chitosan do not contain VOCs, the cardanol polyoxyethylene and the chitosan which are adopted by the invention are natural green biodegradable environment-friendly raw materials, so that the cardanol polyoxyethylene and the chitosan are more environment-friendly and healthier.

(3) The invention has high appearance stability and can not generate color change in the process of storage and use. Mainly because the gallic acid has better oxidation resistance than common antioxidant (such as dibutyl hydroxy toluene BHT), and the sorbitol and the chitosan have good antibacterial property, and the synergistic effect of the gallic acid and the sorbitol overcomes the problem that the scaling powder (especially the water-based scaling powder) is easy to breed bacteria and mildew due to containing a large amount of water and is easy to change color due to air oxidation.

(4) The soldering flux has the advantages of simple preparation process and low cost, and is suitable for large-scale industrial production.

Drawings

The invention is further described with reference to the following figures and examples, in which:

FIG. 1 is a diagram illustrating the tin-coating effect of the flux prepared in examples 1-6 of the present invention;

FIG. 2 is a diagram illustrating the tin-coating effect of the flux prepared in examples 7 to 13 of the present invention;

FIG. 3 is a graph showing the tin-coating effect of the flux prepared in comparative examples 1 to 6 according to the present invention;

FIG. 4 is a graph of water contact angles of fluxes prepared in examples 1 to 8 of the present invention;

FIG. 5 is a graph of water contact angles of fluxes prepared in examples 9 to 13 of the present invention;

FIG. 6 is a water contact angle chart of the flux prepared in comparative examples 1 to 6 of the present invention.

Detailed Description

The concept and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention.

Example 1

The soldering flux prepared by the embodiment comprises the following components in percentage by mass: the film forming agent is 48%, and comprises polyethylene glycol 600 and sorbitol, wherein the mass ratio of the polyethylene glycol 600 to the sorbitol is 5: 1; 2.0% of a flux activator, wherein the mass ratio of oxalic acid, succinic acid, adipic acid and gallic acid is 5: 5: 10: 1; 0.4% of surfactant, wherein the mass ratio of fatty alcohol-polyoxyethylene ether to cardanol-polyoxyethylene ether is 8: 1; 1.22 percent of corrosion inhibitor, wherein the fluorobenzimidazole is 0.02 percent, the water-soluble chitosan with the deacetylation degree of 90 percent is 0.05 percent, the diethanolamine is 1.15 percent, and the balance is water. The flux has a pH of 5.0.

The preparation method of the soldering flux comprises the following steps:

s1: sequentially dissolving weighed gallic acid, sorbitol, oxalic acid, succinic acid, water-soluble chitosan and fluorobenzimidazole in deionized water completely to obtain a component A;

s2: adding adipic acid into polyethylene glycol, stirring until the adipic acid is completely dissolved, adding a surfactant, and uniformly stirring to obtain a component B;

s3: adding the component A into the component B while stirring, and continuously stirring uniformly; additional secondary amine was added to adjust the pH to 5.0.

Example 2

The soldering flux prepared by the embodiment comprises the following components in percentage by mass: the film forming agent is 48%, and comprises polyethylene glycol 600 and sorbitol, wherein the mass ratio of the polyethylene glycol 600 to the sorbitol is 5: 1; 1.5% of flux activator, wherein the mass ratio of oxalic acid, succinic acid, adipic acid and gallic acid is 5: 5: 10: 1; 0.4% of surfactant, wherein the mass ratio of the fatty alcohol-polyoxyethylene ether to the cardanol-polyoxyethylene ether is 8: 1; 0.92% of corrosion inhibitor, wherein the content of fluorobenzimidazole is 0.02%, the content of water-soluble chitosan with the deacetylation degree of 90% is 0.05%, the content of diethanol amine is 0.85%, and the balance is water. The flux has a pH of 5.0.

The preparation method of the soldering flux comprises the following steps:

Example 3

The difference from example 1 is that: the flux activator is 1.5 percent, wherein the mass ratio of oxalic acid, succinic acid, adipic acid and gallic acid is 5: 5: 10: 1; the corrosion inhibitor is 1.82 percent, wherein the fluorobenzimidazole is 0.02 percent, the water-soluble chitosan with the deacetylation degree of 90 percent is 0.05 percent, and the diethanolamine is 1.75 percent; the other components are used in the amounts shown in Table 1; the preparation method is the same as that of example 1.

Example 4

The difference from example 1 is that: the flux activator is 2.0 percent, wherein the mass ratio of oxalic acid, succinic acid, adipic acid and gallic acid is 2: 2: 2: 1; the corrosion inhibitor is 1.82 percent, wherein the fluorobenzimidazole is 0.02 percent, the water-soluble chitosan with the deacetylation degree of 90 percent is 0.05 percent, and the diethanolamine is 1.75 percent; the other components are used in the amounts shown in Table 1; the preparation method is the same as that of example 1.

Example 5

The difference from example 1 is that: the flux activator is 2.0 percent, wherein the mass ratio of oxalic acid, succinic acid, adipic acid and gallic acid is 10: 10: 20: 1; 1.62 percent of corrosion inhibitor, wherein the fluorobenzimidazole is 0.02 percent, the water-soluble chitosan with the deacetylation degree of 90 percent is 0.05 percent, and the diethanolamine is 1.55 percent; the other components are used in the amounts shown in Table 1; the preparation method is the same as in example 1.

Example 6

The difference from example 1 is that: the surfactant accounts for 0.4%, wherein the mass ratio of the fatty alcohol-polyoxyethylene ether to the cardanol-polyoxyethylene ether is 2: 1; the other components are used in the amounts shown in Table 1; the preparation method is the same as that of example 1.

Example 7

The difference from example 1 is that: the surfactant accounts for 0.4%, wherein the mass ratio of the fatty alcohol-polyoxyethylene ether to the cardanol-polyoxyethylene ether is 10: 1; the other components are used in the amounts shown in Table 1; the preparation method is the same as that of example 1.

Example 8

The difference from example 1 is that: the surfactant accounts for 0.2%, wherein the mass ratio of the fatty alcohol-polyoxyethylene ether to the cardanol-polyoxyethylene ether is 8: 1; the other components are used in the amounts shown in Table 1; the preparation method is the same as in example 1.

Example 9

The difference from example 1 is that: the surfactant accounts for 0.5 percent, wherein the mass ratio of the fatty alcohol-polyoxyethylene ether to the cardanol-polyoxyethylene ether is 8: 1; the other components are used in the amounts shown in Table 1; the preparation method is the same as that of example 1.

Example 10

The difference from example 1 is that: the film forming agent is 35 percent, and comprises polyethylene glycol 600 and sorbitol, wherein the mass ratio of the polyethylene glycol 600 to the sorbitol is 5: 1; the other components are used in the amounts shown in Table 1; the preparation method is the same as that of example 1.

Example 11

The difference from example 1 is that: the film forming agent is 55%, and comprises polyethylene glycol 600 and sorbitol, wherein the mass ratio of the polyethylene glycol 600 to the sorbitol is 5: 1; the other components are used in the amounts shown in Table 1; the preparation method is the same as that of example 1.

Example 12

The difference from example 1 is that: the film forming agent is 48%, and comprises polyethylene glycol 600 and sorbitol, wherein the mass ratio of the polyethylene glycol 600 to the sorbitol is 10: 1; the other components are used in the amounts shown in Table 1; the preparation method is the same as in example 1.

Example 13

The difference from example 1 is that: the film forming agent is 48%, and the film forming agent comprises polyethylene glycol 600 and sorbitol, wherein the mass ratio of the polyethylene glycol 600 to the sorbitol is 3: 1; the other components are used in the amounts shown in Table 1; the preparation method is the same as that of example 1.

Comparative example 1

The difference from example 1 is that: the active agent does not contain gallic acid; the preparation method is the same as that of example 1.

Comparative example 2

The difference from example 1 is that: the surfactant does not contain cardanol polyoxyethylene ether; the preparation method is the same as that of example 1.

Comparative example 3

The difference from example 1 is that: the preparation method is the same as example 1 without the surfactant.

Comparative example 4

The difference from example 1 is that: the corrosion inhibitor is free of fluorobenzimidazole and water soluble chitosan and is prepared in the same manner as in example 1.

Comparative example 5

The difference from example 1 is that: the film former is sorbitol free; the preparation method is the same as that of example 1.

Comparative example 6

The difference from example 1 is that: the film forming agent does not contain polyethylene glycol 600; the preparation method is the same as that of example 1.

Table 1 amount of main components of flux (mass fraction/%)

Test examples

The performance of the fluxes prepared in the examples and comparative examples was tested in this test example, and the test results are shown in table 2.

TABLE 2 Performance Table of fluxes prepared in examples of the present invention and comparative examples

The contact angle was measured as follows: cutting a copper plate with the thickness of 50mm multiplied by 0.3mm, treating the copper plate with a micro-etching solution for 30-50 s, cleaning the copper plate with deionized water and absolute ethyl alcohol in sequence, drying, dropping soldering flux on the surface of the horizontal copper plate, measuring a contact angle of the soldering flux on the copper plate for 0-60 s by using a contact angle measuring instrument and observing the wetting and spreading performance of the soldering flux on the copper plate.

Measurement of surface tension: and measuring the surface tension of the soldering flux by using a surface tension meter.

Determination of corrosivity-copper mirror corrosion test: according to the standard GB/T2040, a copper plate with the thickness of 50mm multiplied by 0.3mm is cut, soldering flux is dripped on the copper plate, the copper plate is placed in a constant temperature box with the temperature of 80 ℃ for processing for two hours, then the copper plate is placed in a constant temperature and humidity box with the temperature of 40 ℃ and the humidity of 93% for processing for 72 hours, the change of the surface color of the copper plate is observed, and once the color of the surface of the copper plate is obviously changed, such as the surface color is changed into green or black, the copper plate is corroded. As a result: the copper plate had no apparent corrosion, slight corrosion, severe corrosion, no corrosion observed, corrosion observed locally, corrosion observed.

Testing of tin-coating effect: cutting a PCB into small pieces, soaking the small pieces in soldering flux for 5s, then placing the small pieces in a tin furnace at the temperature of 260 ℃ for tinning for 6s, wherein the solder in the tin furnace is lead-free tin molten solder. And (3) observing the tin coating effect: whether the tin coating is good or not has the problems of copper exposure, tin connection and tin accumulation.

Evaluation of appearance stability: and (3) placing the prepared soldering flux at normal temperature, and observing color change and whether precipitation, delamination and other phenomena occur.

As can be seen from Table 2, the water-based soldering flux prepared by the invention has good wetting and spreading properties, strong weldability, excellent tin coating after hot air leveling, brightness and smoothness; solves the common problems of tin connection, tin stacking and copper exposure in the actual production. The problems of tin connection, tin stacking and copper exposure are closely related to the wettability, activity, film-forming property and the like of the soldering flux, and are particularly prominent for water-based soldering flux because the surface tension of water is relatively large and the water has poor solubility to a plurality of effective organic components.

According to the invention, the fatty alcohol-polyoxyethylene ether and the cardanol polyoxyethylene ether are compounded for use, so that the cleaning capability of the PCB is good; and the surface tension of the soldering flux can be greatly reduced. As is clear from Table 2 and FIGS. 4 to 5, the surface tensions of the fluxes in examples 1 to 13 of the present invention were 19.90 to 24.90 mN. mol^-1The contact angle is 14.0-23.8 degrees, the wetting and spreading performance of the PCB is good, the tin coating effect is good, and the phenomena of copper exposure, tin connection, tin lamination and the like are avoided. As is clear from Table 2 and FIG. 6, the flux prepared by omitting the surfactant in comparative example 3 has a sharply increased surface tension and contact angle, as compared with example 1, and the surface tension is the surface tension (21.277 mN. mol.) of example 1^-1) At a contact angle of 37.4 degrees higher than that of example 1, very poor wet spreadability, copper deposit,The conditions of tin connection and tin stacking are serious, which shows that the addition of the surfactant can effectively reduce the surface tension and further improve the tin coating performance. Compared with the example 1, the soldering flux prepared by the cardanol polyoxyethylene ether is omitted in the comparative example 2, the surface tension and the contact angle are obviously increased, the surface tension is about 1.8 times of that of the example 1, the contact angle is 37.4 degrees higher than that of the example 1, the wetting spreadability is poor, and the copper exposure phenomenon is avoided in a tinning test, but the tin connection and tin stacking conditions are severe, so that the soldering flux prepared by compounding the fatty alcohol polyoxyethylene ether and the cardanol polyoxyethylene ether as the surfactant is better in performance.

As can be seen from the table 2 and the figures 1 to 2, the mass percent of the surfactant in the soldering flux is controlled to be 0.2 to 0.6 percent, and the comprehensive performance of the soldering flux is good; it is understood from examples 8, 1 and 9 that the surface tension of the flux is reduced and the foam is slightly increased with the increase of the amount of the surfactant, and the tin plating is good without copper exposure, tin connection and tin accumulation. The mass ratio of the fatty alcohol-polyoxyethylene ether to the cardanol-polyoxyethylene ether is controlled to be 1-11: the soldering flux prepared in the step 1 has good comprehensiveness, and as can be seen from the examples 6, 1 and 7, the fatty alcohol-polyoxyethylene ether content is increased, the surface tension is reduced overall, the foam is slightly increased, and the tinning effect is good.

The mass percent of the surfactant is controlled within the range of 0.2-0.6%, and the mass ratio of the fatty alcohol-polyoxyethylene ether to the cardanol-polyoxyethylene ether is 1-11: 1, the surface tension of the prepared soldering flux is obviously reduced, the flowing, the expansion and the wetting of all components of the soldering flux on a PCB are effectively promoted, the wetting spreadability of the soldering flux is improved, and the activity of a soldering flux activator is better exerted.

In the embodiments 1-13 of the invention, the mass ratio of (1-13): (1-13): (1-23): 1, oxalic acid, succinic acid, adipic acid and gallic acid are compounded to be used as the soldering flux prepared by the soldering flux active agent, so that the soldering flux has good wetting spreadability and film forming property, good tinning property, no copper exposure, tin connection and tin accumulation phenomena and good appearance stability (is light yellow transparent liquid, and has no change in color and state after being placed for 6 months). As can be seen from fig. 3, compared with comparative example 1 provided in example 1, the soldering flux prepared by omitting gallic acid has the advantages of large surface tension, poor wetting and spreading properties, low activity, copper exposure, and poor appearance stability (the color changes from light yellow to dark yellow after being placed for 6 months), which indicates that gallic acid can synergistically improve the activity of the soldering flux, and simultaneously, the gallic acid, sorbitol and aqueous chitosan synergistically act to avoid the problems of bacterial mildew breeding, oxidative discoloration and the like in the water-based soldering flux.

In the embodiment 10, the embodiment 1 and the embodiment 11 of the invention, the film forming agent with the mass percent of 30-60% is added into the soldering flux, the soldering flux also plays a role of a heat-resistant carrier, and the prepared soldering flux has good tin coating, no copper exposure, tin connection and tin accumulation phenomena and good wettability and spreadability. The addition amount of the film forming agent in the soldering flux prepared in example 10 is relatively small, the comprehensive performance is slightly poorer than that of examples 1 and 11, and the film forming agent splashes during tinning and is poor in heat resistance and film forming property, so that the dosage of the film forming agent is preferably 48-55%. The film forming agents of the embodiment 12, the embodiment 1 and the embodiment 13 are used in the same amount, but the mass ratio of the polyethylene glycol to the sorbitol is different. In examples 12, 1 and 13, the mass ratio of polyethylene glycol to sorbitol is 3 to 10: 1 the prepared soldering flux has good wetting and spreading performance, good tin coating, no copper exposure, tin connection and tin accumulation, good appearance stability and basically meets the requirements of the soldering flux. Among them, the scaling powder prepared by the larger (10: 1) and smaller (3: 1) polyethylene glycol ratios in example 12 and example 13, respectively, has slightly inferior film forming property compared with example 1 (5: 1), and the scaling powder of example 13 has relatively inferior heat resistance, so the mass ratio of polyethylene glycol to sorbitol is preferably 5: about 1.

The flux prepared by omitting sorbitol and polyethylene glycol in comparative examples 5 and 6, respectively, had significantly deteriorated film forming properties compared to example 1. The copper exposure point appears in the soldering flux tin applying test prepared in the comparative example 5, and the coating bubbling, uneven heating and severe splashing condition appears in the soldering flux tin applying test prepared in the comparative example 6, which shows that the film forming property of the soldering flux can be effectively improved by using the sorbitol and polyethylene glycol compounded film forming agent, so that the tin applying effect is improved.

The scaling powder prepared by chitosan and fluorobenzimidazole in the corrosion inhibitor is omitted in the comparative example 4, the phenomena of bubbling of a coating, tin connection and tin accumulation are avoided, and corrosion can be observed, but in the examples 1 to 13 of the invention, the scaling powder prepared by compounding fluorobenzimidazole, chitosan and secondary amine as the corrosion inhibitor has a good tin coating effect, no corrosion phenomenon is observed, the secondary amine is used as a pH regulator at the same time, and the pH value of the scaling powder is controlled to be between 4.5 and 5.5.

In conclusion, the soldering flux disclosed by the invention completely does not contain volatile organic solvents VOCs, is environment-friendly and healthy, and fundamentally solves the problem of reaction between the solvent and the solder resist ink; through the synergistic effect of various components, the soldering flux has strong solderability and no copper exposure, and can effectively inhibit the generation of tin connection and tin accumulation; after hot air leveling, the tinning is excellent, the tin surface is flat, and the PCB surface after welding is clean and has few residues; heat resistance and stability; the corrosivity is low; the antibacterial and antibacterial effects are good, the storage stability is good, and the color is not changed; and the preparation method is simple and low in cost.

The present invention can achieve the above-described effects mainly for the following reasons:

according to the invention, the fatty alcohol-polyoxyethylene ether and the cardanol polyoxyethylene ether are compounded for use, so that the foaming force of the soldering flux is low, and the cleaning capability of the soldering flux on a PCB is good; the surface tension of the soldering flux can be reduced, the uniform distribution of all components of the soldering flux on the PCB is effectively promoted, and the activity of the active agent can be better exerted; effectively promotes the flowing, the spreading and the wetting of the solder on the PCB, and greatly improves the wetting and spreading performance of the soldering flux.

Secondly, organic acids which do not use activity and have different boiling points are compounded to form an activation gradient; gallic acid is further added, and the activity of the soldering flux is synergistically improved by utilizing active phenolic hydroxyl and carboxyl contained in the gallic acid. Meanwhile, the gallic acid has better oxidation resistance than a common antioxidant BHT, and the sorbitol and the chitosan have good antibacterial property, and the synergistic effect of the two components overcomes the problem that the water-based soldering flux contains a large amount of water, is easy to breed bacteria and mildew, and is easy to discolor due to air oxidation. In addition, the soldering flux contains a large amount of hydroxyl and water, so that the soldering flux has a better ionization environment, and the activation performance of active acid (such as oxalic acid, succinic acid, adipic acid and gallic acid) is effectively improved.

Furthermore, the sorbitol and the chitosan used in the invention both contain a large amount of hydroxyl groups, can form a large amount of hydrogen bonds with polyethylene glycol or the three, and are mutually crosslinked under the interaction of the hydrogen bonds to construct a relatively uniform network, so that the film forming property is good, and the solder and the base metal can be effectively protected from being oxidized in the welding process. The selection of the low molecular weight polyethylene glycol can keep the viscosity of the soldering flux low without influencing the spreading fluidity of the soldering flux, has excellent heat conductivity, and can prevent the soldering flux from influencing the soldering quality due to local overheating.

Finally, water-soluble chitosan with the deacetylation degree of more than 80% (such as water-soluble chitosan with the deacetylation degree of 90%) is adopted, on one hand, the water solubility of the chitosan is increased, and meanwhile, the compatibility between the chitosan and other components of the soldering flux is improved, on the other hand, the deacetylation degree of more than 80% can ensure that the chitosan contains enough primary amino groups and can be used for forming an amine copper complex on the surface of copper in a synergistic effect with secondary amine, the wettability of the soldering flux can be improved, and the soldering flux has a soldering assisting effect; however, the flux activity is greatly reduced when the secondary amine is used in an excessive amount and the pH is more than 5.5. And the boiling point of the diethylamine or the diethanolamine is not high, the residue after welding is less, and the problem of more residue after welding by using the triethanolamine is solved. In addition, the fluorobenzimidazole can be self-assembled on the copper surface to form a compact and ordered molecular protective film, can be combined with chitosan and secondary amine through F … H, N … H, O … H hydrogen bonds to form a multilayer structure, and can effectively avoid the corrosion problem caused by incomplete film formation of a single corrosion inhibitor.

The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention. Furthermore, the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict.

Claims

1. The soldering flux is characterized by comprising the following components: film forming agent, flux activator, surfactant and corrosion inhibitor; the surface active agent comprises fatty alcohol-polyoxyethylene ether and cardanol polyoxyethylene ether, and the corrosion inhibitor comprises fluorobenzimidazole, secondary amine and chitosan.

2. The soldering flux according to claim 1, wherein the surfactant is 0.2-0.6% by mass of the soldering flux.

3. The soldering flux according to claim 1 or 2, wherein the mass ratio of the fatty alcohol-polyoxyethylene ether to the cardanol polyoxyethylene ether is 1-11: 1.

4. the soldering flux according to claim 1, wherein the fluorobenzimidazole accounts for 0.01-0.05% by weight of the soldering flux.

5. The solder flux according to claim 1, wherein the fluorobenzimidazole comprises at least one of 2- (2-fluorobenzyl) benzimidazole, 2- (3-fluorobenzyl) benzimidazole, and 2- (4-fluorobenzyl) benzimidazole.

6. The flux of claim 1, wherein the flux active agent comprises oxalic acid, succinic acid, adipic acid, gallic acid; the mass ratio of the oxalic acid to the succinic acid to the adipic acid to the gallic acid is (1-13): (1-13): (1-23): 1.

7. the soldering flux of claim 1, wherein the film forming agent comprises polyethylene glycol and sorbitol.

8. The solder flux of claim 1, further comprising water.

9. The method for preparing the soldering flux of any one of claims 1 to 8, comprising the steps of: and mixing the components of the soldering flux to obtain the soldering flux.

10. Use of the flux of any one of claims 1 to 8 in workpiece soldering.