A low-stress tin plating additive, a preparation method and application thereof

Abstract

The application relates to a low-stress tinning additive, a preparation method and application thereof, and belongs to the technical field of tinning additives. The additive comprises biodegradable organic-inorganic hybrid microcapsules and a solvent. The microcapsules comprise a core and a shell layer. The core is a substance which is liquid at a tinning service temperature, is not miscible with tin and has a surface energy lower than 30 mN / m. The shell layer comprises silicon dioxide and biodegradable polymer monomers. The mass ratio of the core to the shell of the microcapsules is (1-2):1. The particle size of the core is 0.5-2 mu m. The thickness of the shell layer is 0.1-0.3 mu m. The biodegradable hybrid microcapsules are co-deposited with tin, and a low-surface-energy liquid core material is released in subsequent heat treatment, a large number of micro stress buffer points are actively formed in the coating, tin whiskers are effectively removed, and the long-term reliability of electronic components is greatly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of tin plating additives, and particularly relates to a low-stress tin plating additive, a preparation method thereof and application thereof. BACKGROUND

[0002] Electrodeposited tin and its alloys have been widely used in the manufacture of electronic components, such as IC lead frames, precision connectors, printed circuit boards, etc., due to their low toxicity, excellent solderability and conductivity. Among them, the acid tin plating system (such as sulfate, methyl sulfonate system) has become the mainstream technology because of its high operating current density and fast deposition rate.

[0003] However, the internal stress of the coating is a key indicator affecting the quality and reliability of the tin coating, and it is also a long-standing technical problem. During electrodeposition, significant internal stress will accumulate in the coating due to factors such as lattice defects, hydrogen penetration, impurity adsorption, and uneven crystal growth. Excessive internal stress, whether tensile stress or compressive stress, can cause a series of serious quality problems: (1) it can cause the coating to blister, crack, and even peel off from the substrate, seriously affecting the adhesion and long-term reliability of the product; (2) it is the main cause of tin whisker growth. Tin whiskers are self-grown single-crystal tin structures that can cause micro-pitch circuit short circuits, posing a serious threat to modern electronic equipment; (3) for ultra-precision or thin-walled electronic components, internal stress can cause micro-deformation of the workpiece, affecting the final assembly precision and product performance.

[0004] Currently, the industry generally uses organic additives including brighteners, leveling agents, carrier surfactants, etc. to improve the quality of the coating. These additives mainly adsorb on the cathode surface to refine the grains and inhibit the growth of dendrites to reduce the internal stress to some extent. However, this adsorption-inhibition-based mechanism has limited effect and obvious drawbacks: first, the reduction in internal stress is often unsatisfactory, making it difficult to meet the requirements of high-reliability electronic components; second, excessive use of additives in pursuit of low stress often sacrifices other properties of the coating such as deposition rate, hardness, and ductility; third, the accumulation of additive decomposition products in the plating solution complicates process control.

[0005] Therefore, there is an urgent need in the prior art for a new additive solution that can fundamentally and effectively reduce the internal stress of the tin coating without compromising other comprehensive properties of the coating and is easy to integrate into existing production processes. SUMMARY

[0006] In order to overcome some of the problems mentioned in the background above, the present application provides a low-stress tin plating additive and a preparation method thereof to at least partially solve the above problems.

[0007] According to the technical scheme of the present application, a low-stress tinning additive is provided, which comprises biodegradable organic-inorganic hybrid microcapsules and a solvent, wherein the microcapsules comprise a core and a shell layer;

[0008] The core is a substance that is liquid at a tinning service temperature, is not miscible with tin, and has a surface energy lower than 30 mN / m, and the shell layer comprises silica and biodegradable polymer monomers, and the silica and biodegradable polymer monomers form a "ceramic-polymer" shell layer with silica as a skeleton and biodegradable polymer monomers as fillers, which is stable under electroplating conditions and biodegradable in subsequent heat treatment or long-term storage.

[0009] The mass ratio of the core to the shell of the microcapsules is (1-2):1, the particle size of the core is 0.5-2 μm, and the thickness of the shell layer is 0.1-0.3 μm.

[0010] Preferably, the core comprises one or more of silicone oil, perfluoropolyether oil, and gallium-indium-tin alloy.

[0011] The biodegradable polymer monomers comprise lactic acid-glycolic acid copolymer.

[0012] Preferably, the microcapsules further comprise an auxiliary brightener and a carrier surfactant.

[0013] The auxiliary brightener comprises one or more of o-methoxybenzaldehyde, vanillin, and o-chlorobenzaldehyde.

[0014] The carrier surfactant comprises one or more of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, and polyethylene glycol.

[0015] Preferably, the preparation method of the microcapsules comprises the following steps:

[0016] S1. Mixing the core with an aqueous phase, adding an emulsifier, and performing high-speed shearing emulsification to form a stable oil-water primary emulsion;

[0017] S2. Adding tetraethyl orthosilicate to the primary emulsion to form a silica inorganic skeleton on the surface of the core material droplets under the action of an alkaline catalyst;

[0018] S3. Adding an organic solvent in which lactic acid-glycolic acid copolymer is dissolved, and continuing the reaction to deposit and crosslink the lactic acid-glycolic acid copolymer on the silica skeleton to form a hybrid shell layer;

[0019] S4. Performing centrifugation, washing, and redispersion on the product obtained in step S3 to obtain a dispersion of the organic-inorganic hybrid microcapsules.

[0020] Preferably, the step S1 comprises adding Span-80 as oil-soluble surfactant into the core, stirring uniformly at 40-50°C to obtain the oil phase;

[0021] Adding Tween-80 or sodium dodecyl sulfate as water-soluble emulsifier into deionized water, then adding concentrated ammonia water with a concentration of 25-28% as catalyst, stirring uniformly to obtain the water phase;

[0022] Slowly adding the oil phase into the water phase to obtain a mixture, and shearing the mixture at high speed for 5-20 min to obtain a stable primary oil-water emulsion.

[0023] Preferably, the step S2 comprises mixing and diluting tetraethyl orthosilicate with an equal volume of anhydrous ethanol to obtain a precursor solution;

[0024] Slowly adding the precursor solution into the primary oil-water emulsion under the condition of continuous stirring at 300-500 rpm, and reacting at 30-50°C for 8-24 h to form a dense inorganic silica network framework on the surface of the core droplets of the primary oil-water emulsion.

[0025] Preferably, the step S3 comprises adding lactic acid-glycolic acid copolymer into an organic solvent dichloromethane or ethyl acetate to completely dissolve, to obtain an organic solvent in which lactic acid-glycolic acid copolymer is dissolved;

[0026] Slowly adding the organic solvent in which lactic acid-glycolic acid copolymer is dissolved into the product of step S2 under the condition of continuous stirring at 300-500 rpm, and reacting at 35-45°C for 4-12 h, and cooling to room temperature to obtain a pre-dispersion.

[0027] Preferably, the step S4 comprises centrifuging the pre-dispersion at a speed of 5000-10000 rpm for 10-20 min to precipitate the microcapsules in the pre-dispersion;

[0028] Discarding the supernatant, and washing the precipitate with deionized water and anhydrous ethanol alternately for 3-5 times to completely remove unreacted raw materials, emulsifiers and solvents, to obtain purified wet microcapsules;

[0029] Re-dispersing the purified wet microcapsules in deionized water to prepare a hybrid microcapsule stock dispersion with a solid content of 5%-15%.

[0030] Preferably, the additive comprises the following contents of raw materials:

[0031] 1-10 g / L of microcapsules, 5-20 ml / L of auxiliary brightener, 10-30 ml / L of carrier surfactant, and the balance of water.

[0032] In another aspect, the application also provides a use of the low-stress tin plating additive, and the low-stress tin plating additive is used in the field of tin plating.

[0033] The additive is added in the tin plating solution in an amount of 10-100 ml / L, and the plated layer is subjected to heat treatment after the electroplating is completed, the heat treatment temperature is 80-150 DEG C, and the heat treatment time is 30-120 min.

[0034] Compared with the prior art, the application has the following beneficial effects:

[0035] The application actively forms numerous micro stress buffer points in the plated layer by co-depositing the biodegradable hybrid microcapsule with tin and releasing the low surface energy liquid core material in subsequent heat treatment, effectively removes tin whiskers, and greatly improves the long-term reliability of electronic components.

[0036] The application can not only realize extremely low internal stress, but also obtain full-brightness and mirror-level plated layer appearance by using the microcapsule as a functional component and cooperating with traditional brightener and carrier surfactant, and the plated layer is still dense and has good corrosion resistance.

[0037] The application can actively control the degree and timing of stress release by designing the types of core materials of the microcapsule, such as silicone oil and perfluoropolyether oil, and the viscosity, wall material thickness and degradation rate of the core material, can be directly added to the existing acid or methyl sulfonate tin plating system, does not need to change the existing electroplating equipment and main process flow, and only needs to add a standard heat treatment step. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments will be described below in a clear and complete manner. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments. Based on the embodiments, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope.

[0039] The application provides a low-stress tin plating additive, which comprises biodegradable organic-inorganic hybrid microcapsules and a solvent.

[0040] The core is a substance that is liquid at the service temperature of tin plating, is not co-soluble with tin and has a surface energy lower than 30 mN / m, and the shell layer comprises silicon dioxide and biodegradable polymer monomers.

[0041] The mass ratio of the core to the shell of the microcapsule is (1-2):1, the particle size of the core is 0.5-2 μm, and the thickness of the shell layer is 0.1-0.3 μm.

[0042] In further embodiments of the present application, the core comprises one or more of silicone oil, perfluoropolyether oil, and gallium-indium-tin alloy.

[0043] The biodegradable polymer monomer comprises lactic acid-glycolic acid copolymer.

[0044] In further embodiments of the present application, the microcapsule further comprises an auxiliary brightener and a carrier surfactant.

[0045] The auxiliary brightener comprises one or more of o-methoxybenzaldehyde, vanillin, and o-chlorobenzaldehyde.

[0046] The carrier surfactant comprises one or more of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, and polyethylene glycol.

[0047] In further embodiments of the present application, the method for preparing the microcapsule comprises the following steps:

[0048] S1. Mixing the core with an aqueous phase, adding an emulsifier, and performing high-speed shearing emulsification to form a stable oil-water primary emulsion;

[0049] S2. Adding tetraethyl orthosilicate to the primary emulsion to form a silica inorganic framework on the surface of the core material droplets under the action of an alkaline catalyst;

[0050] S3. Adding an organic solvent in which lactic acid-glycolic acid copolymer is dissolved, and continuing the reaction to deposit and crosslink the lactic acid-glycolic acid copolymer on the silica framework to form a hybrid shell layer;

[0051] S4. Centrifuging, washing, and redispersing the product obtained in step S3 to obtain a dispersion of the organic-inorganic hybrid microcapsule.

[0052] In further embodiments of the present application, step S1 comprises adding Span-80 as an oil-soluble surfactant to the core, and stirring uniformly at 40-50°C to obtain an oil phase;

[0053] Adding Tween-80 or sodium dodecyl sulfate as a water-soluble emulsifier to deionized water, then adding concentrated ammonia water with a concentration of 25-28% as a catalyst, and stirring uniformly to obtain an aqueous phase;

[0054] Slowly adding the oil phase to the aqueous phase to obtain a mixture, and passing the mixture through high-speed shearing for 5-20 min to obtain a stable oil-water primary emulsion.

[0055] In further embodiments of the present application, step S2 comprises mixing and diluting tetraethyl orthosilicate with an equal volume of anhydrous ethanol to obtain a precursor solution;

[0056] The precursor solution is slowly added into the primary oil-water emulsion under continuous stirring at 300-500 rpm, and a dense inorganic silica network framework is formed on the surface of the core liquid droplets of the primary oil-water emulsion under the condition of 30-50 ℃ for 8-24 h.

[0057] In a further implementation form of the embodiment, the step S3 comprises: adding the lactic acid-glycolic acid copolymer into an organic solvent dichloromethane or ethyl acetate for complete dissolution, to obtain an organic solvent in which the lactic acid-glycolic acid copolymer is dissolved;

[0058] The organic solvent in which the lactic acid-glycolic acid copolymer is dissolved is slowly added into the product of the step S2 under the condition of continuous stirring at a rotation speed of 300-500 rpm, and the reaction is carried out at 35-45 ℃ for 4-12 h, and the pre-dispersion liquid is obtained after cooling to room temperature.

[0059] In a further implementation form of the embodiment, the step S4 comprises: centrifuging the pre-dispersion liquid at a rotation speed of 5000-10000 rpm for 10-20 min, to precipitate the microcapsules in the pre-dispersion liquid;

[0060] The supernatant is discarded, and the precipitate is washed with deionized water and anhydrous ethanol alternately for 3-5 times, to completely remove the unreacted raw materials, emulsifiers and solvents, to obtain the purified wet microcapsules;

[0061] The purified wet microcapsules are dispersed in deionized water again, to configure a hybrid microcapsule stock dispersion liquid with a solid content of 5% - 15%.

[0062] In a further implementation form of the embodiment, the additive comprises the following contents of raw materials:

[0063] 1-10 g / L of microcapsules, 5-20 ml / L of auxiliary brightener, 10-30 ml / L of carrier surfactant, and the balance of water.

[0064] In another aspect, the embodiment of the present application also provides an application of the low-stress tinning additive. The low-stress tinning additive is applied in the field of tinning.

[0065] The additive is added into the tinning solution in an amount of 10-100 ml / L, and the plated layer is subjected to heat treatment after electroplating, the heat treatment temperature is 80-150 ℃, and the heat treatment time is 30-120 min.

[0066] It should be noted that the present application is no longer limited to the traditional organic molecule adsorption theory, but introduces the concept of "in-situ stress buffering". A biodegradable organic-inorganic hybrid microcapsule is designed as the core component of the additive. These microcapsules are co-deposited with tin ions during electroplating and embedded in the interior of the coating. Subsequently, during subsequent heat treatment or natural storage, the microcapsule shell degrades, releasing the internal low surface energy liquid material, forming a small "cavity" or "buffer layer" at the coating grain boundary, thereby actively releasing and offsetting internal stress.

[0067] Due to the extremely small particle size of the microcapsules and the hydrophilic modification of the surface, they can stably suspend in the plating solution. Under the action of the electroplating electric field, these negatively charged or neutral microcapsules are brought to the surface of the cathode (workpiece) and are "wrapped" into the tin crystals that are rapidly growing, becoming part of the coating.

[0068] After electroplating is completed, a large number of intact microcapsules are uniformly distributed in the coating. During the necessary heat treatment such as hydrogen removal, aging or natural storage, the organic layer in the hybrid shell begins to slowly hydrolyze, and the shell strength decreases.

[0069] After the biodegradable biopolymer monomer in the shell degrades, the low surface energy liquid core material such as silicone oil inside is released. Since the silicone oil is not wetted by tin, it will form a micron-scale "soft cavity" at the original microcapsule position. This cavity can effectively absorb and release the tensile stress or compressive stress in the surrounding tin lattice, similar to adding elastic particles in concrete. At the same time, the released silicone oil can also play a lubricating role at the grain boundary, allowing small slip to occur between the grains, further relaxing the stress. This fundamentally changes the stress state of the coating, transforming it from a continuous, high-energy stress state to a low stress state separated by numerous micro-buffer zones.

[0070] Preparation Example 1: S1. 1g of Span-80 was added as an oil-soluble surfactant to 100g of dimethyl silicone oil, and stirred uniformly at 45°C to obtain an oil phase;

[0071] 5g of Tween-80 was added as a water-soluble emulsifier to 1000ml of deionized water, and then 15ml of concentrated ammonia water with a concentration of 28% was added as a catalyst, and stirred uniformly to obtain an aqueous phase;

[0072] The oil phase was slowly added to the aqueous phase to obtain a mixed solution, and the mixed solution was subjected to high-speed shearing at 12000rpm for 10min to obtain a stable oil-water primary emulsion.

[0073] S2. 30g of tetraethyl orthosilicate was mixed and diluted with an equal volume of anhydrous ethanol to obtain a precursor solution;

[0074] The precursor solution is slowly added dropwise into the oil-water primary emulsion under continuous stirring at 400 rpm, and a dense inorganic silica network framework is formed on the surface of the core liquid droplets of the oil-water primary emulsion under the condition of 40°C for 12 h.

[0075] S3. 15 g of lactic acid-glycolic acid copolymer (molar ratio of lactic acid-glycolic acid being 1:1) is added into 150 ml of organic solvent dichloromethane for complete dissolution, to obtain an organic solvent dissolving lactic acid-glycolic acid copolymer;

[0076] The organic solvent dissolving lactic acid-glycolic acid copolymer is slowly added into the product of step S2 under the condition of continuous stirring at 400 rpm, and a pre-dispersion liquid is obtained by cooling to room temperature under the condition of 40°C for 6 h.

[0077] S4. The pre-dispersion liquid is centrifuged at a speed of 8000 rpm for 15 min to precipitate the microcapsules in the pre-dispersion liquid;

[0078] The supernatant is discarded, and the precipitate is washed with deionized water and anhydrous ethanol alternately for 4 times to completely remove unreacted raw materials, emulsifiers and solvents, to obtain purified wet microcapsules;

[0079] The purified wet microcapsules are redispersed in deionized water to configure a hybrid microcapsule stock dispersion liquid with a solid content of 10%.

[0080] Preparation Example 2: The difference from Preparation Example 1 is that the core material in S1 is selected as perfluoropolyether oil.

[0081] Preparation Example 3: The difference from Preparation Example 1 is that:

[0082] S2. 50 g of tetraethyl orthosilicate is mixed and diluted with an equal volume of anhydrous ethanol to obtain a precursor solution;

[0083] The precursor solution is slowly added dropwise into the oil-water primary emulsion under continuous stirring at 400 rpm, and a dense inorganic silica network framework is formed on the surface of the core liquid droplets of the oil-water primary emulsion under the condition of 40°C for 12 h.

[0084] S3. 25 g of lactic acid-glycolic acid copolymer (molar ratio of lactic acid-glycolic acid being 1:1) is added into 150 ml of organic solvent dichloromethane for complete dissolution, to obtain an organic solvent dissolving lactic acid-glycolic acid copolymer;

[0085] The organic solvent dissolving lactic acid-glycolic acid copolymer is slowly added into the product of step S2 under the condition of continuous stirring at 400 rpm, and a pre-dispersion liquid is obtained by cooling to room temperature under the condition of 40°C for 6 h.

[0086] The following experimental examples use the microcapsules obtained in Preparation Examples 1-3 in the plating solutions of the tin plating experimental examples obtained by combining the additive compositions and plating solutions in different proportions. All plating solutions are based on a base solution of stannous methanesulfonate 60 g / L, methanesulfonic acid 120 mL / L.

[0087] Experimental Example 1: The additive was obtained by uniformly mixing 0.1 part of the dispersion obtained in Preparation Example 1, 1 part of o-methoxybenzaldehyde, 2 parts of nonylphenol polyoxyethylene ether, and the balance water.

[0088] 50 ml of the additive was added to 1 L of the base plating solution, i.e., the actual concentration of the microcapsules in the plating solution was 0.05 g / L.

[0089] Experimental Example 2: The additive was obtained by uniformly mixing 0.5 part of the dispersion obtained in Preparation Example 1, 1 part of o-methoxybenzaldehyde, 2 parts of nonylphenol polyoxyethylene ether, and the balance water.

[0090] 20 ml of the additive was added to 1 L of the base plating solution, i.e., the actual concentration of the microcapsules in the plating solution was 0.1 g / L.

[0091] Experimental Example 3: The additive was obtained by uniformly mixing 0.5 part of the dispersion obtained in Preparation Example 1, 2 parts of o-methoxybenzaldehyde, 1.5 parts of nonylphenol polyoxyethylene ether, and the balance water.

[0092] 15 ml of the additive was added to 1 L of the base plating solution, i.e., the actual concentration of the microcapsules in the plating solution was 0.075 g / L.

[0093] Experimental Example 4: The additive was obtained by uniformly mixing 0.1 part of the dispersion obtained in Preparation Example 1, 1 part of o-methoxybenzaldehyde, 2 parts of nonylphenol polyoxyethylene ether, and the balance water.

[0094] 20 ml of the additive was added to 1 L of the base plating solution, i.e., the actual concentration of the microcapsules in the plating solution was 0.02 g / L.

[0095] Experimental Example 5: The additive was obtained by uniformly mixing 0.5 part of the dispersion obtained in Preparation Example 2, 1 part of o-methoxybenzaldehyde, 2 parts of nonylphenol polyoxyethylene ether, and the balance water.

[0096] 20 ml of the additive was added to 1 L of the base plating solution, i.e., the actual concentration of the microcapsules in the plating solution was 0.1 g / L.

[0097] Experimental Example 6: The additive was obtained by uniformly mixing 0.5 part of the dispersion obtained in Preparation Example 3, 1 part of o-methoxybenzaldehyde, 2 parts of nonylphenol polyoxyethylene ether, and the balance water.

[0098] 20 ml of the additive was added to 1 L of the base plating solution, i.e., the actual concentration of the microcapsules in the plating solution was 0.1 g / L.

[0099] Comparative Example 1: The additive was prepared by mixing 1 part of o-methoxybenzaldehyde, 2 parts of nonylphenol polyoxyethylene ether and the balance of water.

[0100] Comparative Example 2: The additive was prepared by mixing 5 parts of the dispersion prepared in Preparation Example 1, 1 part of o-methoxybenzaldehyde, 2 parts of nonylphenol polyoxyethylene ether and the balance of water.

[0101] 40 ml of the additive was added to 1 L of the base plating solution, so that the actual concentration of the microcapsules in the plating solution was 2 g / L.

[0102] The plating solutions of Experimental Examples 1-6 and Comparative Examples 1 and 2 were respectively subjected to electroplating at a cathode current density of 2 A / dm 2 , a plating temperature of 25°C and a plating time of 30 min. After plating, the plating layer was heated at 120°C for 1 h, and then the following tests were performed on the plating layer:

[0103] The internal stress of the plating layer was measured by an X-ray diffraction stress analyzer. Accelerated aging was performed at a temperature of 55°C and a relative humidity of 85%, and after 1000 hours, the number of tin whiskers with a length of more than 10 μm per unit area was observed and counted using a scanning electron microscope. The brightness and uniformity of the plating layer were observed by the naked eye as the appearance of the plating layer. The time at which a color spot appeared was recorded by the potassium ferricyanide drop test, to indicate the porosity of the plating layer. The experimental data obtained are shown in Table 1 below.

[0104] Table 1

[0105]

[0106] The internal stress values of all of the Experimental Examples 1-6 of the present application were significantly lower than those of Comparative Examples 1 and 2. In the optimal ratio of Experimental Example 2, the internal stress was greatly reduced from -42.1 MPa in Comparative Example 1 to -5.8 MPa. Correspondingly, the number of tin whiskers was also drastically reduced. The number of tin whiskers in Experimental Example 2 was only 2 per mm

[0107] It can be seen from experimental examples 1-3 that the microcapsule content is best within the range defined in the present application, too low will weaken the effect, too high although the stress is lower, but will affect the brightness of the coating and may lead to uneven microstructure. It can be seen from experimental example 4 that under the premise of reasonable addition of core microcapsules within the range defined in the present application, the proportion of brightener and carrier is properly adjusted, and excellent low stress effect can still be obtained. And through comparative example 2, the addition amount of microcapsules needs to be within the range defined in the present application, and if it exceeds the range, although the stress can be further reduced, the apparent quality and density of the coating will be seriously sacrificed.

[0108] It can be seen from experimental example 5 that since the perfluoropolyether oil has a lower surface tension than the silicon oil, after being released from the microcapsule, it can more effectively spread on the tin grain boundary to form a more excellent stress buffer interface, but because of its slightly poor compatibility with the plating solution system, it slightly affects the uniformity of the electrocrystallization process. It can be seen from experimental example 6 that the internal stress of the wall material with too thick thickness is high and the number of tin whiskers is also large, which cannot be fully degraded under the set heat treatment condition of 120℃ / 60min, resulting in that most of the microcapsules cannot effectively release the core material, so that the "in-situ stress buffer" mechanism fails, and the heat treatment time needs to be increased to achieve the effect of the remaining experimental examples. However, the appearance of the coating is still bright, so thickening the wall material has no negative effect on the electroplating process itself.

[0109] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A low-stress tinning additive characterized in that, The additive comprises biodegradable organic-inorganic hybrid microcapsules and a solvent, the microcapsules comprising a core and a shell layer; The core is a substance that is liquid at a tin plating service temperature, is not miscible with tin, and has a surface energy lower than 30 mN / m, and the shell layer comprises silica and biodegradable polymer monomers, the silica and biodegradable polymer monomers forming a "ceramic-polymer" shell layer with silica as a skeleton and biodegradable polymer monomers as fillings, the shell layer being stable under electroplating conditions and biodegradable in subsequent heat treatment or long-term storage; The core-shell mass ratio of the microcapsules is (1-2):1, the particle size of the core is 0.5-2 μm, and the thickness of the shell layer is 0.1-0.3 μm; The core comprises one or more of silicone oil, perfluoropolyether oil, and gallium-indium-tin alloy; The biodegradable polymer monomers comprise lactic acid-glycolic acid copolymer.

2. The low stress tinning additive according to claim 1, characterized in that, The microcapsules further comprise an auxiliary brightener and a carrier surfactant; The auxiliary brightener comprises one or more of o-methoxybenzaldehyde, vanillin, and o-chlorobenzaldehyde; The carrier surfactant comprises one or more of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, and polyethylene glycol.

3. A process for the preparation of a low-stress tinning additive according to any one of claims 1-2, characterized in that, The preparation method of the microcapsules comprises the following steps: S1. Mixing the core with an aqueous phase, adding an emulsifier, and performing high-speed shearing emulsification to form a stable oil-water primary emulsion; S2. Adding tetraethyl orthosilicate to the primary emulsion to form a silica inorganic skeleton on the surface of the core material droplets under the action of an alkaline catalyst; S3. Adding an organic solvent in which lactic acid-glycolic acid copolymer is dissolved, and continuing the reaction to make the lactic acid-glycolic acid copolymer deposit and crosslink on the silica skeleton to form a hybrid shell layer; S4. Performing centrifugation, washing, and redispersion on the product obtained in step S3 to obtain a dispersion of the organic-inorganic hybrid microcapsules.

4. The method of claim 3, wherein the low-stress tinning additive is prepared by adding the compound of formula (1) to the aqueous solution of tin sulfate. The step S1 comprises: adding Span-80 as an oil-soluble surfactant to the core, stirring uniformly at 40-50°C to obtain an oil phase; Adding Tween-80 or sodium dodecyl sulfate as a water-soluble emulsifier to deionized water, then adding concentrated ammonia water with a concentration of 25-28% as a catalyst, and stirring uniformly to obtain an aqueous phase; Slowly adding the oil phase to the aqueous phase to obtain a mixed solution, and passing the mixed solution through high-speed shearing for 5-20 min to obtain a stable oil-water primary emulsion.

5. The method of claim 3, wherein the low-stress tinning additive is prepared by adding the compound of formula (1) to the aqueous solution of tin sulfate. The step S2 comprises: mixing and diluting tetraethyl orthosilicate with an equal volume of anhydrous ethanol to obtain a precursor solution; Slowly dropping the precursor solution into the oil-water primary emulsion under continuous stirring at 300-500 rpm, reacting at 30-50°C for 8-24 h, and forming a dense inorganic silica network skeleton on the surface of the core droplets of the oil-water primary emulsion.

6. The method of claim 3, wherein the low-stress tinning additive is prepared by the steps of: The step S3 comprises: adding lactic acid-glycolic acid copolymer to an organic solvent dichloromethane or ethyl acetate to completely dissolve the lactic acid-glycolic acid copolymer, and obtaining an organic solvent in which the lactic acid-glycolic acid copolymer is dissolved; The organic solvent containing lactic acid-glycolic acid copolymer is slowly added into the product of step S2 under the condition of continuous stirring at a rotating speed of 300-500 rpm, and the reaction is carried out at 35-45℃ for 4-12 h, and then the pre-dispersion is obtained by cooling to room temperature.

7. The method of claim 3, wherein the low-stress tinning additive is prepared by the steps of: The step S4 comprises centrifuging the pre-dispersion at a rotating speed of 5000-10000 rpm for 10-20 min to precipitate the microcapsules in the pre-dispersion; The supernatant is discarded, and the precipitate is washed with deionized water and anhydrous ethanol alternately for 3-5 times to completely remove the unreacted raw materials, emulsifiers and solvents, and then the purified wet microcapsules are obtained; The purified wet microcapsules are dispersed in deionized water again to prepare a hybrid microcapsule stock dispersion with a solid content of 5%-15%.

8. The method of claim 3, wherein the low-stress tinning additive is prepared by the steps of: The additive comprises the following contents of raw materials: 1-10 g / L of microcapsules, 5-20 ml / L of auxiliary brightener, 10-30 ml / L of carrier surfactant, and the balance of water.

9. Use of a low-stress tinning additive, characterized in that The application of the low-stress tin plating additive according to any one of claims 1-3 in the field of tin plating; The additive is added in the tin plating solution in an amount of 10-100 ml / L, and the final concentration of the microcapsules in the tin plating solution is 0.02-0.1 g / L, and the coating is subjected to heat treatment after electroplating, the heat treatment temperature is 80-150℃, and the heat treatment time is 30-120 min.

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