A flux for spot soldering of solder paste and a method for preparing the same

Abstract

The application provides a flux for spot soldering of soldering paste; raw materials of the flux include, by total mass: 2-7% of acid modified rosin, 25-38% of disproportionated rosin, 1.3-4% of compound active agent, and solvent supplementing the rest to 100%; the compound active agent includes halogen-containing active agent and / or organic acid active agent; the organic acid active agent includes at least two of organic acid with normal pressure boiling point of 90-180 DEG C, organic acid with normal pressure boiling point of 200-300 DEG C, and organic acid with normal pressure boiling point of 305 DEG C or more; the solvent includes organic matter with at most 3 unsaturated structures and at least 1 polar group, and reduces post-soldering residue; the application effectively reduces the amount of acid modified rosin, and expands the soldering temperature range of the flux; the soldering paste of the flux is very suitable for spot soldering operation process due to excellent flow viscosity, wettability and expansion rate, and has high soldering reliability.

Description

Technical Field

[0001] This invention relates to the field of flux technology, B23K35 / 00, and particularly to a flux for spot-applied solder paste and its preparation method. Background Technology

[0002] Flux directly determines the soldering quality and performance of solder paste. Current solder paste fluxes mainly consist of rosin, activators, antioxidants, thixotropic agents, and solvents. Rosin protects the solder powder in the paste from oxidation during reflow soldering, improving soldering performance. Conventional industry techniques require higher rosin content for thickening, but this exacerbates post-soldering residue. Therefore, reducing rosin usage while maintaining solder paste viscosity is an industrially valuable problem. Furthermore, the use of lead in solder alloys is gradually being replaced by non-toxic lead-free solders such as tin-silver-copper alloys, which have become mainstream. However, these lead-free solders have high melting points. To ensure sufficient melting of the lead-free solder, reflow soldering temperatures need to be increased. However, high temperatures increase substrate instability and the possibility of flux component degradation, affecting soldering performance and reflow soldering yield. Therefore, expanding the reflow soldering temperature range for fluxes is imperative.

[0003] With the upgrading and development of electronic products, new soldering processes require the use of spot coating to ensure soldering accuracy. However, traditional canned solder paste cannot meet the requirements of spot coating. How to improve the extrudability and wettability of traditional solder paste and flux to meet the requirements of rapid spot coating is also a problem that needs to be solved.

[0004] Chinese patent CN101077555A discloses a flux for dot-applied solder paste, comprising rosin, solvent, thixotropic agent, activator, and surfactant. The paste is applied evenly with no solder spikes or tails. However, its rosin content is as high as 75%, resulting in high residue levels. Chinese patent CN 107931891B discloses a solder paste flux that uses acrylic resin instead of rosin, resulting in a wider reflow soldering temperature range. However, its soldering performance, such as wettability, still has room for improvement. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention first provides a flux for dot-applied solder paste; the flux comprises, by total mass, 2-7% acid-modified rosin, 25-38% disproportionated rosin, 1.3-4% compound activator, and 100% solvent replenishment.

[0006] Furthermore, the acid-modified rosin includes, but is not limited to, at least one of acrylic acid-modified rosin, maleic acid-modified rosin, fumaric acid-modified rosin, and marinic acid-modified rosin.

[0007] Preferably, the acid-modified rosin is an acrylic acid-modified rosin.

[0008] Further, the dehydroabietic acid content of the disproportionated rosin is ≥45wt%, and the unsaponifiable matter content is ≤12wt%.

[0009] Preferably, the dehydroabietic acid content of the disproportionated rosin is ≥52wt%, and the unsaponifiable matter content is ≤10wt%. The disproportionated rosin of the present application has the characteristics of being less prone to crystallization and more excellent stability than the acrylic rosin, but the effects produced by different disproportionated rosins are not consistent. Only when the dehydroabietic acid content of the disproportionated rosin is ≥52wt% and the unsaponifiable matter content is ≤10wt%, the surface residue and tin beads can be significantly reduced, and the reflow soldering yield reaches the best value; it may be because the aromatic structure in the dehydroabietic acid enhances the rigid structure of the rosin protective film, which can provide good wrapping and support strength for the molten tin powder during welding, avoiding the collapse of the solder paste and reducing the generation of tin beads; in addition, the disproportionated rosin also includes sterols, high molecular alcohols, hydrocarbons, pigments, and fat-soluble vitamins, etc. unsaponifiable matter, these components will increase the residue of the flux, and the content needs to be strictly controlled.

[0010] Further, the complex active agent includes a halogen-containing active agent and / or an organic acid active agent.

[0011] Further, the addition amount of the halogen-containing active agent is 0.1-1% of the total amount of the flux.

[0012] Further, the halogen-containing active agent includes, but is not limited to, at least one of 2-fluoro-4-bromobenzoic acid, 2-chloro-4-bromobenzoic acid, dibromosuccinic acid, and dibromobutenediol.

[0013] Further, the organic acid active agent includes at least two of an organic acid with a normal boiling point of 90-180℃, an organic acid with a normal boiling point of 200-300℃, and an organic acid with a normal boiling point ≥305℃. The normal pressure condition is 760mmHg.

[0014] In a preferred embodiment, the organic acid active agent comprises an organic acid with a normal boiling point of 90-180℃, an organic acid with a normal boiling point of 200-300℃, and an organic acid with a normal boiling point of ≥ 305℃. The present application uses a complex organic acid active agent to enhance the removal of tin powder and the surface oxide film of the welded substrate, and to reduce the surface tension between the two interfaces to enhance the wetting performance of the soldering paste. Different organic acids have different activities at different temperatures. By compounding organic acids with different temperature activities, the use range is expanded while ensuring the reactivity of the organic acid. The soldering paste has the most excellent wetting effect and the widest temperature range when the organic acid with a normal boiling point of 90-180℃, the organic acid with a normal boiling point of 200-300℃, and the organic acid with a normal boiling point of ≥ 305℃ are used in a mass ratio of (0.1-0.5):(0.8-1.5):(0.1-0.5); when the content of the organic acid with a normal boiling point of 90-180℃ is too high, a large amount of organic acid is decomposed and inactivated at high welding temperature, and the welding effect is poor; when the content of the organic acid with a normal boiling point of ≥ 305℃ is too high, the activity is insufficient at low temperature welding conditions, and the wetting performance and welding performance are also poor.

[0015] Preferably, the mass ratio of the organic acid with a normal boiling point of 90-180℃, the organic acid with a normal boiling point of 200-300℃, and the organic acid with a normal boiling point of ≥ 305℃ is (0.1-0.5):(0.8-1.5):(0.1-0.5).

[0016] More preferably, the mass ratio is (0.2-0.4):(1-1.3):(0.2-0.4).

[0017] In a preferred embodiment, the mass ratio of the organic acid with a normal boiling point of 90-180℃, the organic acid with a normal boiling point of 200-300℃, and the organic acid with a normal boiling point of ≥ 305℃ is 0.3:1.1:0.3.

[0018] Further, the organic acid with a normal boiling point of 90-180℃ is selected from at least one of oxalic acid, malonic acid, propionic acid, butyric acid, and dimethylol propionic acid.

[0019] Preferably, the organic acid with a normal boiling point of 90-180℃ is malonic acid.

[0020] Further, the organic acid with a normal boiling point of 200-300℃ includes, but is not limited to, at least one of succinic acid, glutaric acid, adipic acid, pimelic acid, and suberic acid.

[0021] Preferably, the organic acid with a normal boiling point of 200-300℃ includes at least two of succinic acid, adipic acid, and suberic acid.

[0022] Further preferably, the organic acid having an atmospheric boiling point of 200-300℃ includes succinic acid, adipic acid and suberic acid, with a mass ratio of (0.3-0.55):(0.2-0.4):(0.3-0.55).

[0023] More preferably, the mass ratio of the succinic acid, adipic acid and suberic acid is 0.4:0.3:0.4.

[0024] Further, the organic acid having an atmospheric boiling point of ≥ 305℃ includes, but is not limited to, at least one of azelaic acid, sebacic acid, dodecanoic acid, behenic acid, malic acid, tartaric acid, and phenylsuccinic acid.

[0025] Preferably, the organic acid having an atmospheric boiling point of ≥ 305℃ includes azelaic acid.

[0026] Further, the raw material of the flux further includes 1-6% of a release agent, based on the total mass.

[0027] Further, the release agent includes, but is not limited to, at least one of triethylamine, triethanolamine, benzotriazole, 5-phenyltetrazole, dodecylbenzimidazoline, N-methylpiperazine, and N-diethylpiperazine.

[0028] Further, the release agent includes triethanolamine and benzotriazole, with a mass ratio of (0.3-1):(1.1-3.7).

[0029] Preferably, the mass ratio of the triethanolamine and benzotriazole is (0.4-0.8):(1.5-3.0); more preferably, 0.6:2.1.

[0030] Further, the raw material of the flux further includes 2-8% of a thixotropic agent, based on the total mass.

[0031] Further, the thixotropic agent includes, but is not limited to, at least one of hydrogenated castor oil, polyamide, polyethylene wax, and ethylene glycol bis-stearamide.

[0032] Further, the solvent includes at least one of ethylene glycol, isopropyl alcohol, propylene glycol, glycerol, ethylene glycol dimethyl ether, ethylene glycol butyl ether, ethylene glycol hexyl ether, dipropylene glycol methyl ether, dipropylene glycol propyl ether, diethylene glycol ethyl ether, and dipropylene glycol ethyl ether.

[0033] Preferably, the solvent includes ethylene glycol butyl ether and / or ethylene glycol hexyl ether.

[0034] Further, the solvent further includes an organic substance having at most 3 unsaturated structures and at least 1 polar group; the unsaturated structure is at least one of a double bond, a triple bond, and a cyclic structure; the polar group is selected from a hydroxyl group or a carboxyl group.

[0035] Further, the organic substance having at most 3 unsaturated structures and at least including 1 polar group is selected from at least one of terpineol, terpineic acid, and hydrated terpene diol.

[0036] Preferably, the unsaturated structure is a double bond and / or a cyclic structure, and the organic substance having at most 3 unsaturated structures and at least including 1 polar group is terpineol and / or hydrated terpene diol.

[0037] In a preferred embodiment, the organic substance having at most 3 unsaturated structures and at least including 1 polar group is terpineol. In conventional technology, a large amount of acrylic modified rosin needs to be used to protect the tin powder from being re-oxidized during soldering by the film-forming effect thereof, but the viscosity of the soldering paste is relatively high due to the fact that the acrylic modified rosin contains a large number of polar groups, the needle tube extrusion effect is very poor, and the head is easily blocked, but if the acrylic modified rosin is not used, the adhesion of the soldering paste is also very low, and the overall performance is too dry; when terpineol is added in the formula, the amount of acrylic modified rosin used in the formula can be greatly reduced, the flow performance and needle extrusion effect of the soldering paste are effectively improved, and the tackiness of the soldering paste is not lost; it is worth noting that the addition of terpineol also significantly reduces the spreading thickness of the residue, increases the brightness of the solder joint, and makes it easier to clean the residue. The reason is that, on the one hand, the acrylic modified rosin contains double bonds and polar bonds with high reactivity, and under high-temperature oxygen-containing conditions, the resin acid undergoes polymerization reaction, and the polymer molecules formed have long chain length and poor flowability, which causes the appearance of the solder joint to be poor, and when the amount of acrylic modified rosin is reduced, the residue is naturally reduced; on the other hand, in the high-temperature oxygen-containing environment of soldering, terpineol will chemically react with part of the organic acid, and the generated substance forms a hybrid system with the post-soldering residue, and because of its suitable chain length and reduced molecular polarity, the interaction force between the residues is reduced, and the generated substance and the acrylic modified rosin, thixotropic agent, etc. in the system work together to enhance the flowability of the latter and its spreading on the surface of the solder joint, thereby improving the brightness and soldering reliability of the solder joint.

[0038] Further, the organic substance having at most 3 unsaturated structures and at least including 1 polar group accounts for 48-60% of the total mass of the flux.

[0039] Further, the raw materials of the flux further include 0.05-2% of an antioxidant, according to the total mass. The antioxidant in the present application is not strictly required, and is a conventional antioxidant used in the industry, such as BHT, etc.

[0040] Secondly, the present application also provides a preparation method of the flux for the spot-coating type soldering paste, which comprises the following steps:

[0041] S1, adding acid modified rosin, disproportionated rosin and solvent into a container and mixing and heating to stir;

[0042] S2, the organic acid active agent is mixed with the benzotriazole and then added to S1;

[0043] S3, the halogen-containing active agent and the thixotropic agent are mixed and then added to S2 for stirring and dissolving, and then filtered through a filter screen at a temperature not lower than 110°C, and then cooled to 35-50°C;

[0044] Further, the heating temperature in step S1 is not higher than 130°C, and preferably 120-130°C.

[0045] Further, an antioxidant is added in step S1.

[0046] Further, a part of the release agent is added in step S2.

[0047] Further, a thixotropic agent is added in step S3.

[0048] Further, a 1000-1800 mesh filter screen is used in step S3.

[0049] Further, another part of the release agent is added after cooling.

[0050] In a preferred embodiment, the preparation method comprises the following steps:

[0051] S1, the acid-modified rosin, the disproportionated rosin, the antioxidant and the solvent are added to a container for mixing and stirring under heating, and the heating temperature is 120-130°C;

[0052] S2, the organic acid active agent and the benzotriazole are mixed and then added to S1;

[0053] S3, the halogen-containing active agent and the thixotropic agent are mixed and then added to S2 for stirring and dissolving, and then filtered through a filter screen at a temperature not lower than 110°C, and then cooled to 35-50°C;

[0054] S4, the triethanolamine is added to S3 for stirring and dispersing.

[0055] Further, the flux described in the present application can be used in a spot-coating solder paste, and the flux accounts for 10-20wt% and the tin powder accounts for 80-90wt% based on the total amount of the solder paste.

[0056] Further, the tin powder includes but is not limited to at least one of tin bismuth powder, tin copper powder, tin silver copper powder, and tin antimony powder.

[0057] In a preferred embodiment, the tin powder is tin silver copper powder, and can be selected from SAC305 and SAC307.

[0058] Further, the particle size (i.e. the average diameter of the particles) of the tin powder is 2-25μm.

[0059] Further, the particle size (i.e. the average diameter of the particles) of the tin powder is 2-25μm.Beneficial effects

[0060] 1、The application unexpectedly found that the solvent component can be used instead of rosin by optimizing the solvent system, effectively reducing the use amount of rosin such as acrylic modified rosin, not only reducing the post-welding residue of the flux, but also significantly reducing the production cost (about 20% saved); by selecting specific replaceable components, the wettability and welding yield of the flux paste can also be effectively improved;

[0061] 2、The application can make the prepared flux and solder paste have excellent needle extrusion effect and flow viscosity by using specific content of acrylic modified rosin, disproportionated rosin and specific types of solvents;

[0062] 3、The application expands the activity of the flux and solder paste at different temperatures by optimizing different organic acid active agent components, compounding organic acids with normal boiling point of 90-180°C, organic acids with normal boiling point of 200-300°C and organic acids with normal boiling point ≥305°C, and by optimizing their types and amounts, the activity of the flux is maximized without causing copper plate corrosion, further improving the welding yield;

[0063] 4、The application optimizes the preparation process of the flux, so that the raw material components in the flux are fully mixed and will not be degraded in the process, ensuring the reliability of the flux effect;

[0064] 5、The solder paste prepared by the flux of the application has excellent flow viscosity, wettability and expansion rate, and is very suitable for spot coating type soldering operation process, and has very high welding reliability. DETAILED DESCRIPTION

[0065] EMBODIMENT

[0066] EMBODIMENT 1

[0067] The embodiment provides a flux for spot coating type solder paste; the raw materials of the flux include: 4% of acrylic modified rosin (ke604), 30% of disproportionated rosin, 0.4% of halogen-containing active agent, 1.7% of organic acid active agent, 2.7% of slow-release agent, 5% of thixotropic agent, 0.2% of antioxidant BHT, 4% of ethylene glycol butyl ether and 52% of terpineol, based on the total mass;

[0068] The dehydroabietic acid content of the disproportionated rosin is ≥52wt%, and the unsaponifiable matter content is ≤10wt%, which is purchased from Dongban Chemical and the model is a-100;

[0069] The halogen-containing active agent is dibromobutene diol;

[0070] The organic acid active agent is an organic acid with a normal boiling point of 90-180°C (malonic acid), an organic acid with a normal boiling point of 200-300°C, and an organic acid with a normal boiling point of ≥ 305°C (azelaic acid), with a mass ratio of 0.3:1.1:0.3;

[0071] The organic acid with a normal boiling point of 200-300°C includes succinic acid, adipic acid, and octanedioic acid, with a mass ratio of 0.4:0.3:0.4;

[0072] The slow-release agent includes triethanolamine and benzotriazole, with a mass ratio of 0.6:2.1;

[0073] The thixotropic agent is hydrogenated castor oil;

[0074] The embodiment also provides a preparation method of the flux, including the following steps:

[0075] S1, add acrylic modified rosin, disproportionated rosin, antioxidant, ethylene glycol butyl ether, and terpineol into a container, mix and heat stir, and the heating temperature is 125°C;

[0076] S2, mix the organic acid active agent and benzotriazole, and then add them into S1;

[0077] S3, mix the halogen-containing active agent and the thixotropic agent, then add them into S2 and stir to dissolve, and then filter through a 1000-mesh filter screen at about 110°C, and cool to 43°C;

[0078] S4, add triethanolamine into S3, stir and disperse, and then obtain the flux.

[0079] Embodiment 2

[0080] The embodiment provides a flux for spot coating type solder paste; the raw materials of the flux include, based on the total mass, 2% of acrylic modified rosin (ke604), 38% of disproportionated rosin, 0.8% of a halogen-containing active agent, 0.5% of an organic acid active agent, 1% of a slow-release agent, 2% of a thixotropic agent, 0.05% of antioxidant BHT, 1% of ethylene glycol butyl ether, and 54.65% of terpineol;

[0081] The disproportionated rosin has a dehydroabietic acid content of ≥ 52 wt%, and a unsaponifiable matter content of ≤ 10 wt%, and is purchased from Toho Chemical, and the model is a-100;

[0082] The halogen-containing active agent is dibromobutenediol;

[0083] The organic acid active agent is an organic acid with a normal boiling point of 90-180°C (malonic acid), an organic acid with a normal boiling point of 200-300°C, and an organic acid with a normal boiling point of ≥ 305°C (azelaic acid), with a mass ratio of 0.4:1:0.2;

[0084] The organic acid with normal boiling point of 200-300℃ includes succinic acid, adipic acid and octanedioic acid, and the mass ratio of the three is 0.3:0.2:0.55;

[0085] The slow-release agent includes triethanolamine and benzotriazole, and the mass ratio of the two is 0.4:1.5;

[0086] The thixotropic agent is hydrogenated castor oil;

[0087] The embodiment also provides a preparation method of the flux, including the following steps:

[0088] S1, acrylic modified rosin, dismutation rosin, antioxidant, ethylene glycol butyl ether and terpineol are added into a container and mixed and heated and stirred, and the heating temperature is 120℃;

[0089] S2, the organic acid active agent and benzotriazole are mixed and then added into S1;

[0090] S3, the halogen-containing active agent and the thixotropic agent are mixed and then added into S1 and stirred and dissolved, and then filtered through a 1000-mesh filter screen at about 110℃, and cooled to 35℃;

[0091] S4, triethanolamine is added into S1 and stirred and dispersed.

[0092] Embodiment 3

[0093] The embodiment provides a flux for spot soldering; the raw materials of the flux include, based on the total mass, 7% of acrylic modified rosin (ke604), 25% of dismutation rosin, 0.1% of a halogen-containing active agent, 3.9% of an organic acid active agent, 4% of a slow-release agent, 6% of a thixotropic agent, 2% of antioxidant BHT, 4% of ethylene glycol butyl ether and 48% of terpineol;

[0094] The dehydroabietic acid content of the dismutation rosin is greater than or equal to 52wt%, and the unsaponifiable matter content is less than or equal to 10wt%, and the dismutation rosin is purchased from Dongban Chemical and the model is a-100;

[0095] The halogen-containing active agent is dibromobutene diol;

[0096] The organic acid active agent is an organic acid with normal boiling point of 90-180℃ (malonic acid), an organic acid with normal boiling point of 200-300℃ and an organic acid with normal boiling point greater than or equal to 305℃ (azelaic acid), and the mass ratio is 0.2:1.3:0.4;

[0097] The organic acid with normal boiling point of 200-300℃ includes succinic acid, adipic acid and octanedioic acid, and the mass ratio of the three is 0.55:0.4:0.3;

[0098] The slow-release agent includes triethanolamine and benzotriazole, and the mass ratio of the two is 0.8:3.0;

[0099] The thixotropic agent is hydrogenated castor oil;

[0100] The embodiment also provides a preparation method of the flux, comprising the following steps:

[0101] S1, add acrylic modified rosin, disproportionated rosin, antioxidant, ethylene glycol butyl ether and terpineol into a container, mix and heat and stir, and the heating temperature is 130℃;

[0102] S2, mix the organic acid active agent and benzotriazole, and then add into S1;

[0103] S3, mix the halogen-containing active agent and the thixotropic agent, then add into S1 and stir to dissolve, and then filter through a 1000 mesh filter at about 110℃, and cool to 50℃;

[0104] S4, add triethanolamine into S3, stir and disperse.

[0105] Comparative Example 1

[0106] The embodiment is basically the same as Example 1, except that the organic acid active agent is an organic acid (malonic acid) with a normal boiling point of 90-180℃, an organic acid with a normal boiling point of 200-300℃ and an organic acid (azelaic acid) with a normal boiling point of ≥305℃, and the mass ratio is 0.4:0.5:0.3.

[0107] Comparative Example 2

[0108] The embodiment is basically the same as Example 1, except that the organic acid active agent is an organic acid (malonic acid) with a normal boiling point of 90-180℃, an organic acid with a normal boiling point of 200-300℃ and an organic acid (azelaic acid) with a normal boiling point of ≥305℃, and the mass ratio is 0.3:1.1:0.8.

[0109] Comparative Example 3

[0110] The embodiment is basically the same as Example 1, except that the organic acid with a normal boiling point of 200-300℃ includes succinic acid and octanedioic acid, and the mass ratio is 0.55:0.55.

[0111] Comparative Example 4

[0112] The embodiment is basically the same as Example 1, except that the raw materials of the flux include: acrylic modified rosin (ke604) 30%, disproportionated rosin 30%, halogen-containing active agent 0.4%, organic acid active agent 1.7%, release agent 2.7%, thixotropic agent 5%, antioxidant BHT 0.2%, ethylene glycol butyl ether 4%, and terpineol 26%, based on the total mass.

[0113] Comparative Example 5

[0114] The flux of the above examples is mixed with SAC305 tin powder in a mass ratio of 15:85 and stirred uniformly in a double-planet mixer to prepare a solder paste suitable for needle tube extrusion. The particle size specification of the SAC305 tin powder is 5# powder, and the needle specification used is: 0.25 mm inner diameter, 1 cm in length.

[0115] Performance test method:

[0116] The solder paste of the above examples is mixed with SAC305 tin powder in a mass ratio of 15:85 and stirred uniformly in a double-planet mixer to prepare a solder paste suitable for needle tube extrusion. The particle size specification of the SAC305 tin powder is 5# powder, and the needle specification used is: 0.25 mm inner diameter, 1 cm in length.

[0117] 1. Extrusion effect test: The same mass of the solder paste of the above examples is placed in a needle tube, and under the condition of 1.5 kg air pressure, it is observed whether 10 mL (30 g) of the solder paste is smoothly and completely extruded in 12 h;

[0118] 2. Flux residue rate: The prepared solder paste is quantitatively point-coated on an alumina ceramic plate, the mass of the solder paste is weighed and the flux content (m1) in the solder paste is calculated, the solder paste and the alumina ceramic plate are heated and melted at 250°C, and after cooling, the total mass (m2) is weighed, the alumina ceramic plate and the solder ball are thoroughly cleaned and dried, and the mass (m3) after removing the residues is weighed, and the residue rate calculation formula is obtained: residue rate = (m2-m3) / m1 x 100%.

[0119] 3. Wettability test: according to GB / 31475-2015 standard.

[0120] Performance test results:

[0121] The test results are shown in Table 1.

[0122] Table 1

[0123] Sample No. Extrusion effect / g Soldering flux residue rate / % Wettability Example 1 Complete extrusion 25 First class Example 2 Complete extrusion 38 First class Example 3 Complete extrusion 31 First class Comparative Example 1 Complete extrusion 28 Second class Comparative Example 2 Complete extrusion 30 Second class Comparative Example 3 Complete extrusion 27 First class Comparative Example 4 5g clogging 60 First class Comparative Example 5 Complete extrusion 52 Second class

[0124] From the above test results, it can be seen that:

[0125] The flux and solder paste prepared in Examples 1-3 have excellent extrudability, wettability and high-temperature soldering reliability, and less post-soldering residue.

[0126] The wetting property and reflow soldering yield in Comparative Example 1-2 are relatively small, which can be because the content of organic acid with normal boiling point of 200-300°C in Comparative Example 1 is small, leading to low activity of the organic acid active agent in the flux in removing oxides in the temperature range of 160-200°C, and the oxide film on the surface of the soldering substrate cannot be effectively removed in a short time, and the surface tension between the two-phase interface is still high; and Comparative Example 2 is the same, when the content of organic acid with normal boiling point of ≥305°C is too much, and the content of other organic acids is small, the flux can only have excellent oxide film removal activity in a relatively high temperature range, however, when the temperature is too high, the content of other organic acids decomposed increases, which also leads to low activity; and Comparative Example 3 also proves that only the organic acid with special combination can work together, which can broaden the soldering temperature of the flux and has higher activity.

[0127] Comparative Example 4 shows that when the content of modified rosin is too much, the solder paste prepared by the flux is easy to block the needle, which is not suitable for spot soldering, and there are many residues after soldering.

[0128] In Comparative Example 5, no terpineol is added, the flux residue is large, and the wetting property is poor, which can be because there is no component corresponding to a surfactant to wrap the post-soldering residue in the soldering, the residue layer is not effectively spread, and the residue is accumulated thick.

Claims

1. A flux for spot soldering of solder paste, characterized by, The raw materials of the flux include, by total mass: acid-modified rosin 2-7%, disproportionated rosin 25-38%, compounded active agent 1.3-4%, and solvent to make up the balance to 100%; the compounded active agent includes halogen-containing active agent and / or organic acid active agent; The organic acid active agent includes organic acid with normal pressure boiling point of 90-180℃, organic acid with normal pressure boiling point of 200-300℃, and organic acid with normal pressure boiling point ≥305℃; the normal pressure condition is 760mmHg; The mass ratio of the organic acid with normal pressure boiling point of 90-180℃, the organic acid with normal pressure boiling point of 200-300℃, and the organic acid with normal pressure boiling point ≥305℃ is (0.2-0.4):(1-1.3):(0.2-0.4); The solvent includes ethylene glycol butyl ether and / or ethylene glycol hexyl ether, and also includes terpineol.

2. The flux according to claim 1, characterized in that, The organic acid with normal pressure boiling point of 200-300℃ includes succinic acid, adipic acid, and suberic acid.

3. A method of producing the flux according to any one of claims 1 to 2, characterized by, The method includes the following steps: S1, adding acid-modified rosin, disproportionated rosin, and solvent into a container, mixing, and heating and stirring; S2, adding the mixed organic acid active agent into S1; S3, adding the halogen-containing active agent into the mixture, stirring and dissolving, then filtering through a filter screen, and cooling.