No-clean low-residue soldering paste and preparation method thereof

Abstract

The invention relates to the technical field of soldering paste production, in particular to no-clean low-residue soldering paste and a preparation method thereof.The no-clean low-residue soldering paste is prepared from, by weight, 93-99 parts of soldering powder alloy, 11-17 parts of scaling powder and 2-4 parts of additives, the solder powder alloy is one or a composition of more of a SnB i alloy, a SnB iAg alloy, a SnAgCu alloy, a SnPb alloy, a SnCu I n alloy, a SnAgCuSb alloy, a SnAgSb alloy, a SnPbB i alloy or a SnPbAg alloy; the soldering flux comprises the following components in parts by weight: 60-80 parts of a homogeneous solvent, 15-20 parts of at least one thixotropic agent, 13-28 parts of at least one activating agent and 12-15 parts of rosin. According to the invention, under the condition of ensuring the stability, wettability and bonding strength of the soldering paste, the use of rosin can be reduced, so that the overall residual quantity after soldering is reduced, the requirement that the residual quantity of soldering flux after reflow soldering is up to 2% is met, and the purpose of no cleaning is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of solder paste production, and in particular to a no-cleaning low-residue solder paste and a preparation method thereof. Background Art

[0002] Solder paste is a new type of welding material that came into being with SMT. It is generally a paste-like mixture formed by mixing solder powder, flux, etc. It is mainly used for welding electronic components such as resistors, capacitors, and ICs on the surface of PCBs in the SMT industry. One disadvantage of these traditional fluxes is that a large amount of rosin and other solid components of the flux are actually left as flux residues on or near the resulting solder joints. During the reflow process, many chemical reactions occur between the rosin, other components of the flux, and metal oxides on the surface of the solder alloy. The non-volatile part of the reaction product and the inert components of the raw materials are still left on the workpiece as residues.

[0003] If the amount of these residues is large, it will cause the morphology of the soldering area to deteriorate and damage the contact effect of the pins of the electronic parts soldered by the solder paste. In addition, the flux residue can cause the insulation resistance between the workpiece circuits to decrease due to the moisture it absorbs, and it may also cause circuit damage or disconnection due to corrosion products formed by the flux residue. Therefore, the workpiece to be used in electronic equipment that requires high reliability must be washed with a cleaning agent after reflow soldering to remove the flux residue remaining in the soldering area.

[0004] Currently, most flux paste formulas use a rosin resin system. Although it can meet the no-cleaning standard after welding, rosin is a high-boiling point, non-volatile substance. After welding, the rosin remains completely on the solder joint. For products with high requirements for residues, a cleaning agent is still needed to clean the residues. Summary of the invention

[0005] Technical issues solved

[0006] In view of the above-mentioned shortcomings of the prior art, the present invention provides a no-clean low-residue solder paste and a preparation method thereof, which can effectively solve the problem that most of the existing flux paste formulas use a rosin resin system. Although the no-cleaning standard can be achieved after welding, rosin is a high-boiling point and non-volatile substance. After welding, the rosin completely remains on the solder joint. For products with high residue requirements, a cleaning agent is still needed to clean the residue.

[0007] Technical Solution

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] The invention provides a no-cleaning low-residue solder paste, which is prepared from 93-99 parts by weight of a solder powder alloy, 11-17 parts by weight of a soldering flux, and 2-4 parts by weight of an additive, wherein the solder powder alloy is one or a combination of several of the following: SnBi alloy, SnBiAg alloy, SnAgCu alloy, SnPb alloy, SnCuIn alloy, SnAgCuSb alloy, SnAgSb alloy, SnPbBi alloy or SnPbAg alloy; and the soldering flux comprises, by weight, 60-80 parts of a uniform solvent, 15-20 parts of at least one thixotropic agent, 13-28 parts of at least one activator, and 12-15 parts of rosin.

[0010] During use, the solder paste is heated to 140-260°C during reflow, at which time the flux begins to activate and the solvent begins to evaporate. As the temperature continues to rise, the activator begins to remove oxides from the surface of the alloy and components, thereby improving the wettability for forming a good bond. The rosin begins to melt and forms a protective coating around the solder powder particles, thereby minimizing the possibility of re-oxidation due to continued temperature increases. Afterwards, the solvent and rosin evaporate completely, leaving almost no residue, which can meet the requirements of a residue-free process without the use of organic solvents.

[0011] Furthermore, the solder powder alloy is one or a combination of Sn42Bi58, SnB i 35Ag0.3-1.5, SnAg0.3-3.0Cu0.3-1.0, Sn63Pb37, Sn43Pb43Bi 14, Sn62.8Pb36.8Ag0.4, Pb92.5Sn5Ag2.5.

[0012] Further, the homogeneous solvent comprises one or more glycol ethers and one or more alcohols, wherein the glycol ether is selected from the following group: mono-, di- or tri-propylene glycol methyl ether, mono-, di- or tri-propylene glycol n-butyl ether, mono-, di- or tri-ethylene glycol n-butyl ether, and ethylene glycol methyl ether, triethylene glycol methyl ether, diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, or a combination thereof. This solvent system improves the stability of the flux.

[0013] Furthermore, the alcohol is one or a combination of isobornyl cyclohexanol, hexadecanol, 1,8-octanediol, 1,2-octanediol, terpineol and isopropyl alcohol. The use of the above alcohols can reduce the use of rosin while ensuring the bonding effect, thereby reducing the overall residual amount after welding, thereby meeting the requirement of a maximum of 2% residual flux after reflow soldering.

[0014] Furthermore, the thixotropic agent is a composition of glyceryl tri-12-hydroxystearate, modified glyceryl tri-12-hydroxystearate, modified hydrogenated castor oil and polyamide. The rheological properties of the flux can be changed by selecting the thixotropic agent, thereby meeting different requirements.

[0015] Furthermore, the activator is one or a combination of several of benzoic acid, salicylic acid, aminobenzoic acid, succinic acid, glutaric acid and adipic acid.

[0016] Furthermore, the rosin is one or a combination of tall oil rosin, hydrogenated rosin and dehydrogenated rosin.

[0017] Furthermore, the additive is one or a combination of rosin methyl ester, n-oleyl sarcosine and oleyl imidazoline. The addition of the additive can improve the wettability and bonding strength of the solder paste, and the additive itself has good volatility and will not increase the overall residual amount after welding, thereby meeting the requirement of a maximum of 2% residual flux after reflow soldering.

[0018] Furthermore, it is characterized in that it is made of 95 parts by weight of solder powder alloy, 16 parts by weight of flux, and 3 parts by weight of additives.

[0019] A method for preparing a no-clean low-residue solder paste comprises the following steps:

[0020] S1. Weigh the raw materials of soldering flux by weight, mix the solvent evenly at a constant temperature of 60°C, and allow it to fully react for 20 hours. Remove the unreacted raw materials and raise the temperature to 150-170°C. Then, add a thixotropic agent, an activator and rosin in sequence and stir until they are completely blended to obtain soldering flux for use.

[0021] S2, cooling the above soldering flux to 95-105°C, adding additives and continuing to stir until completely melted, cooling to obtain a paste, and storing it in a cold storage at 0-10°C for later use;

[0022] S3. Weigh the solder powder alloy and paste by weight, pour them into a vacuum mixer, stir at a low speed for 15 minutes, then fill with nitrogen and stir at a medium speed for 50 minutes to fully mix the solder powder alloy and the paste, then evacuate and stir at a medium speed for 15 minutes to obtain the solder paste.

[0023] Beneficial Effects

[0024] Compared with the known public technology, the technical solution provided by the present invention has the following beneficial effects:

[0025] The present invention can reduce the use of rosin while ensuring the stability, wettability and bonding strength of the solder paste, thereby reducing the overall residue after soldering, thereby meeting the requirement of a maximum of 2% of the flux residue after reflow soldering, thereby achieving the purpose of no cleaning. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The present invention will be further described below in conjunction with the embodiments.

[0028] Embodiment 1:

[0029] A no-clean low-residue solder paste is prepared from 96 parts by weight of a solder powder alloy, 12 parts by weight of a soldering flux, and 2 parts by weight of an additive, wherein the solder powder alloy is Sn42Bi58, and the soldering flux comprises, by weight, 30 parts of ethylene glycol methyl ether, 38 parts of isobornyl cyclohexanol, 15 parts of glyceryl tri-12-hydroxystearate, 13 parts of aminobenzoic acid, 12 parts of tall oil rosin, and 2 parts of n-oleyl sarcosine.

[0030] A method for preparing a no-clean low-residue solder paste comprises the following steps:

[0031] S1. Weigh the raw materials of soldering flux by weight, mix the solvent evenly at a constant temperature of 60°C, and allow it to fully react for 20 hours. Remove the unreacted raw materials and raise the temperature to 150-170°C. Then, add a thixotropic agent, an activator and rosin in sequence and stir until they are completely blended to obtain soldering flux for use.

[0032] S2, cooling the above soldering flux to 95-105°C, adding additives and continuing to stir until completely melted, cooling to obtain a paste, and storing it in a cold storage at 0-10°C for later use;

[0033] S3. Weigh the solder powder alloy and paste by weight, pour them into a vacuum mixer, stir at a low speed for 15 minutes, then fill with nitrogen and stir at a medium speed for 50 minutes to fully mix the solder powder alloy and the paste, then evacuate and stir at a medium speed for 15 minutes to obtain the solder paste.

[0034] During use, the solder paste is heated to 140-300°C during reflow, at which time the flux begins to activate and the solvent begins to evaporate. As the temperature continues to rise, the activator begins to remove oxides from the surface of the alloy and components, thereby improving the wettability for forming a good bond. The rosin begins to melt and forms a protective coating around the solder powder particles, thereby minimizing the possibility of re-oxidation due to continued temperature increases. Afterwards, the solvent and rosin evaporate completely, leaving almost no residue, which can meet the requirements of a residue-free process without the use of organic solvents for cleaning.

[0035] Embodiment 2:

[0036] The difference from Example 1 is that it is made of 96 parts by weight of solder powder alloy, 12 parts by weight of flux, and 3 parts by weight of additives, wherein the solder powder alloy is Sn42Bi58, and the flux includes 30 parts of ethylene glycol methyl ether, 38 parts of isobornyl cyclohexanol, 15 parts of glyceryl tri-12-hydroxystearate, 13 parts of aminobenzoic acid, 12 parts of tall oil rosin, 1 part of n-oleyl sarcosine and 2 parts of oleyl imidazoline in parts by weight.

[0037] Embodiment 3:

[0038] The difference from Example 1 is that it is made of 92 parts by weight of solder powder alloy, 12 parts by weight of flux, and 2 parts by weight of additives, wherein the solder powder alloy is Sn42Bi58, and the flux includes 22 parts of ethylene glycol methyl ether, 5 parts of triethylene glycol methyl ether, 5 parts of diethylene glycol dibutyl ether, 2 parts of tetraethylene glycol dimethyl ether, 30 parts of 1,8-octanediol, 15 parts of modified glyceryl tri-12-hydroxystearate, 11 parts of benzoic acid, 13 parts of salicylic acid, 12 parts of hydrogenated rosin, 1 part of rosin methyl ester and 1 part of n-oleyl sarcosine.

[0039] Embodiment 4:

[0040] The difference from Example 3 is that it is made of 92 parts by weight of solder powder alloy, 12 parts by weight of flux, and 2 parts by weight of additives, wherein the solder powder alloy is Sn42Bi58, and the flux includes 22 parts of ethylene glycol methyl ether, 5 parts of triethylene glycol methyl ether, 5 parts of diethylene glycol dibutyl ether, 2 parts of tetraethylene glycol dimethyl ether, 30 parts of hexadecanol, 15 parts of modified glyceryl tri-12-hydroxystearate, 11 parts of benzoic acid, 13 parts of salicylic acid, 12 parts of hydrogenated rosin, 1 part of rosin methyl ester and 1 part of n-oleyl sarcosine.

[0041] Embodiment 5:

[0042] The difference from Example 3 is that it is made of 92 parts by weight of solder powder alloy, 12 parts by weight of flux, and 2 parts by weight of additives, wherein the solder powder alloy is Sn42Bi58, and the flux includes, by weight, 22 parts of ethylene glycol methyl ether, 5 parts of triethylene glycol methyl ether, 5 parts of diethylene glycol dibutyl ether, 2 parts of tetraethylene glycol dimethyl ether, 22 parts of 1,2-octanediol, 11 parts of pinene alcohol, 15 parts of modified glyceryl tri-12-hydroxystearate, 11 parts of benzoic acid, 13 parts of salicylic acid, 12 parts of hydrogenated rosin, 1 part of rosin methyl ester and 1 part of n-oleyl sarcosine.

[0043] Control group

[0044] It is a rosin resin solder paste commonly used on the market. The model used in this application is Sn60Pb40 lead solder paste produced by Xinghongtai Tin Industry Co., Ltd.

[0045] Examples 1-5, the control group, and the comparative example were applied to SMT assembly and placed in an air reflow oven with a peak temperature of 260° C. The final residue was observed after reflow. The test results are shown in Table 1:

[0046]

[0047] Therefore, the present invention can reduce the use of rosin while ensuring the stability, wettability and bonding strength of the solder paste, thereby reducing the overall residual amount after soldering, thereby meeting the requirement of a maximum of 2% residual flux after reflow soldering, thereby achieving the purpose of no-cleaning.

[0048] Embodiment 6:

[0049] The difference from Example 1 is that the solder powder alloy is Sn42Bi57Ag1.0.

[0050] Embodiment 7:

[0051] The difference from Example 1 is that the solder powder alloy is Sn42B i57.6Ag0.4.

[0052] Embodiment 8:

[0053] The difference from Example 1 is that the solder powder alloy is Sn64Bi35Ag1.0.

[0054] Embodiment 9:

[0055] The difference from Example 1 is that the solder powder alloy is Pb92.5Sn5Ag2.5.

[0056] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the embodiments of the present invention.

Claims

1. A no-clean low-residue solder paste, characterized in that: The invention is prepared from 93-99 parts by weight of solder powder alloy, 11-17 parts by weight of soldering flux and 2-4 parts by weight of additives, wherein the solder powder alloy is one or a combination of SnBi alloy, SnBiAg alloy, SnAgCu alloy, SnPb alloy, SnCuIn alloy, SnAgCuSb alloy, SnAgSb alloy, SnPbBi alloy or SnPbAg alloy; and the soldering flux comprises 60-80 parts by weight of a uniform solvent, 15-20 parts by weight of at least one thixotropic agent, 13-28 parts by weight of at least one activator and 12-15 parts by weight of rosin.

2. The no-clean low-residue solder paste according to claim 1, characterized in that: The solder powder alloy is one of Sn42Bi58, SnBi 35Ag0.3-1.5, SnAg0.3-3.0Cu0.3-1.0, Sn63Pb37, Sn43Pb43Bi 14, Sn62.8Pb36.8Ag0.4, Pb92.5Sn5Ag2.5 or a combination of several thereof.

3. The no-clean low-residue solder paste according to claim 2, characterized in that: The homogeneous solvent comprises one or more glycol ethers and one or more alcohols, wherein the glycol ether is selected from the following group: mono-, di- or tri-propylene glycol methyl ether, mono-, di- or tri-propylene glycol n-butyl ether, mono-, di- or tri-ethylene glycol n-butyl ether, and ethylene glycol methyl ether, triethylene glycol methyl ether, diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, or a combination thereof.

4. The no-clean low-residue solder paste according to claim 3, characterized in that: The alcohol is one or a combination of isobornyl cyclohexanol, hexadecanol, 1,8-octanediol, 1,2-octanediol, terpineol and isopropanol.

5. The no-clean low-residue solder paste according to claim 4, characterized in that: The thixotropic agent is a composition of glyceryl tri-12-hydroxystearate, modified glyceryl tri-12-hydroxystearate, modified hydrogenated castor oil and polyamide.

6. The no-clean low-residue solder paste according to claim 5, characterized in that: The activator is one or a combination of several of benzoic acid, salicylic acid, aminobenzoic acid, succinic acid, glutaric acid and adipic acid.

7. The no-clean low-residue solder paste according to claim 6, characterized in that: The rosin is one or a combination of tall oil rosin, hydrogenated rosin and dehydrogenated rosin.

8. The no-clean low-residue solder paste according to claim 7, characterized in that: The additive is one or a combination of rosin methyl ester, n-oleyl sarcosine and oleyl imidazoline.

9. The no-clean low-residue solder paste according to any one of claim 8, characterized in that: The invention is prepared from 95 parts by weight of solder powder alloy, 16 parts by weight of soldering flux and 3 parts by weight of additives.

10. A method for preparing a no-cleaning low-residue solder paste according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Weigh the raw materials of soldering flux by weight, mix the solvent evenly at a constant temperature of 60°C, and allow it to fully react for 20 hours. Remove the unreacted raw materials and raise the temperature to 150-170°C. Then, add a thixotropic agent, an activator and rosin in sequence and stir until they are completely blended to obtain soldering flux for use. S2, cooling the above soldering flux to 95-105°C, adding additives and continuing to stir until completely melted, cooling to obtain a paste, and storing it in a cold storage at 0-10°C for later use; S3. Weigh the solder powder alloy and paste by weight, pour them into a vacuum mixer, stir at a low speed for 15 minutes, then fill with nitrogen and stir at a medium speed for 50 minutes to fully mix the solder powder alloy and the paste, then evacuate and stir at a medium speed for 15 minutes to obtain the solder paste.

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