A stable tin chemical plating solution and its application

Abstract

The present invention relates to C23C18, and more specifically, to a stable tin chemical plating solution and its application. The raw materials for preparing the plating solution include stannous salt, organic acid, thiourea accelerator and reducing agent, and the organic acid includes C1-C5 organic acid. The present invention provides a chemical plating solution, which can realize continuous tin plating under acidic conditions by using suitable thiourea accelerator and reducing agent, and realize higher smoothness and brightness on the tin layer with higher thickness. By adding suitable dispersant and organic acid, the stability of the plating solution can be improved while reducing the aggressiveness to ink. Through the joint action of the components of the plating solution provided by the present invention, a dense plating layer can be achieved at a faster plating speed, and the solderability of subsequent electronic components such as PCB boards can be improved.

Description

Technical Field

[0001] The present invention relates to C23C18, and more particularly to a stable tin-based chemical plating solution and application thereof. Background Art

[0002] As the requirements for the soldering performance of electronic components increase, the demand for providing a coating, such as a tin layer, on the circuits of electronic components also increases. However, the tin-lead solder currently used has problems such as high lead content and environmental pollution, which affects the use of solder.

[0003] CN101705482A provides an alkyl sulfonic acid chemical tin plating solution and a tin plating process based on the chemical tin plating solution, which comprises an organic sulfonic acid tin salt, an organic acid, a complexing agent, a reducing agent, a surfactant, an antioxidant, a noble metal salt, and a brightener. The invention adopts a two-step method of pre-dipping and chemical plating to deposit a tin layer with a thickness of 2.0 μm on a copper and copper alloy substrate, and is suitable for chemical tin plating processes such as printed circuit boards (PCB boards) and integrated circuits, and has the advantages of good solderability, strong anti-whisker growth ability, low cost, stable process, and the like.

[0004] However, due to the oxidation of tin during the tin plating process, the brightness and stability of the coating will be affected. In addition, due to the high potential of tin during the tin plating process, it is difficult to achieve a thicker tin layer and the adhesion is low. Summary of the invention

[0005] In order to solve the above problems, the first aspect of the present invention provides a stable tin-based chemical plating solution, wherein the raw materials for preparing the plating solution include stannous salt, organic acid, thiourea accelerator and reducing agent.

[0006] As a preferred technical solution of the present invention, in 1L of plating solution, the mass of stannous salt is 20-30g.

[0007] As a preferred technical solution of the present invention, the stannous salt is selected from one or more of stannous sulfate, stannous fluoroborate, stannous halide, and stannous methanesulfonate.

[0008] As a preferred technical solution of the present invention, the weight ratio of the organic acid to the stannous salt is (2.5-3):1.

[0009] As a preferred technical solution of the present invention, the organic acid includes C1-C5 organic acid, and the C1-C5 organic acid is selected from one or more of methanesulfonic acid, citric acid, and tartaric acid, preferably methanesulfonic acid and citric acid, with a weight ratio of 1: (6-8).

[0010] As a preferred technical solution of the present invention, the organic acid also includes C10-C20 unsaturated acid, and the weight ratio of the C10-C20 unsaturated acid to the C1-C5 organic acid is 1:(3-5).

[0011] As a preferred technical solution of the present invention, the C10-C20 unsaturated acid is selected from one or more of oleic acid, 9-octadecenoic acid, 2-hexadecenoic acid, 2-tetradecenoic acid, and 9-hexadecenoic acid.

[0012] As a preferred technical solution of the present invention, the reducing agent is selected from one or more of hydrazine hydrate, ascorbic acid, sodium hypophosphite, and ammonium hypophosphite, preferably ascorbic acid and sodium hypophosphite, with a weight ratio of 1: (4-6).

[0013] As a preferred technical solution of the present invention, the weight ratio of the reducing agent to the stannous salt is (1.5-2):1.

[0014] As a preferred technical solution of the present invention, the thiourea accelerator is selected from one or more of thiosemicarbazide, phenylthiourea and vinylthiourea.

[0015] As a preferred technical solution of the present invention, the weight ratio of the thiourea accelerator to the stannous salt is (2.5-3):1.

[0016] In the process of tin plating on PCB boards, because tin has a high potential, it is difficult to replace copper, and when a reducing agent is used for reduction, it is difficult to achieve continuous reduction to obtain a tin layer. In addition, because stannous tin is easily oxidized, blackening may occur during the electroplating process, affecting the brightness and flatness of the coating. The inventors have found that by using a thiourea accelerator and a small molecule organic acid environment, the copper potential can be reduced, thereby promoting the plating of stannous tin, and by using a suitable reducing agent for continuous reduction deposition, tin plating is performed.

[0017] The inventors have found that in order to avoid oxidation and blackening during the tin plating process, a relatively high amount of small molecule organic acid is required to provide a relatively stable chelating site. However, the relatively high amount of small molecule organic acid also increases the stability of the chelated coordination of stannous substance, affecting the further replacement with copper and the thickening of the tin layer. The inventors have found that by adding citric acid as a small molecule organic acid as the main component and adding an unsaturated medium-chain organic acid, the medium-chain organic acid can be involved while citric acid and the like stabilize stannous substance, and the unsaturated medium-chain organic acid can be used to regulate the number of citric acid, methanesulfonic acid and the like chelated with stannous substance, so that citric acid and the like tend to form a mono-coordinated or di-coordinated structure with stannous substance, thereby reducing the realization of more coordinated structures, promoting continuous tin plating, and obtaining a brighter coating of suitable thickness.

[0018] As a preferred technical solution of the present invention, the raw materials for preparing the plating solution also include a dispersant, and the weight ratio of the dispersant to the aliphatic alcohol amine is (0.2-0.6):1.

[0019] As a preferred technical solution of the present invention, the dispersant is selected from one or more of polyether, sulfonate, and polyvinyl amide, preferably polyether and sulfonate, with a weight ratio of 1:(2-3).

[0020] Examples of polyethers include polyoxyethylene ethers, polyoxypropylene ethers, and polyoxyethylene-polyoxypropylene block copolymers. The weight average molecular weight of the polyether is 2000-4000, and the HLB value is 12-18. Examples include polyoxyethylene-polyoxypropylene block copolymers of sea stone flowers, such as L45 (weight average molecular weight of 2400, HLB value of 15), L65 (weight average molecular weight of 3500, HLB value of 15), and L64 (weight average molecular weight of 2900, HLB value of 13).

[0021] As a preferred technical solution of the present invention, the sulfonate is selected from one or more of disodium 4-octadecenol 2-sulfosuccinate, calcium di(2-ethylhexyl)succinate sulfonate, magnesium di(2-ethylhexyl)succinate sulfonate, and disodium 4-isodecyl 2-sulfosuccinate, preferably calcium di(2-ethylhexyl)succinate sulfonate and magnesium di(2-ethylhexyl)succinate sulfonate.

[0022] In addition, the inventors found that during the tinning process of the PCB board, etching problems such as the window openings on the copper surface are prone to occur, so it is necessary to add ink to the PCB board to reduce the impact on the window openings. However, this also causes the plating solution, especially the acidic plating solution, to attack the ink. The inventors added polyethers and sulfonates to effectively reduce the attack on the ink while further improving the stability of the ink.

[0023] This may be because in the tin-plating process, by using a polyether with a suitable molecular weight and HLB value, the solubility of the polyether in the plating solution water and the spreadability of the PCB ink part and the copper surface are improved, while utilizing the effects of sulfonates, especially sulfonates containing divalent ions such as magnesium and calcium and organic acids, etc., to reduce the attack of the plating solution on the ink layer while promoting the stability of the plating solution. The inventors have found that by adding a di-branched sulfonate and a polyoxyethylene-polyoxypropylene block copolymer containing polyoxy and polybranched chains, the attack of the plating solution on the ink layer can be further reduced, thereby improving the placement stability of the plating solution.

[0024] As a preferred technical solution of the present invention, the raw materials for preparing the plating solution also include aliphatic alcohol amines, and the weight ratio of the thiourea accelerator to the aliphatic alcohol amine is 1:(0.1-0.2).

[0025] As a preferred technical solution of the present invention, the aliphatic alcohol amine is selected from aliphatic monoalcohol amine and / or aliphatic diol amine.

[0026] As a preferred technical solution of the present invention, the aliphatic monoalcohol amine is selected from one or more of lauric acid monoethanolamide, stearic acid monoethanolamide, myristic acid monoethanolamide, and oleic acid monoethanolamide.

[0027] As a preferred technical solution of the present invention, the aliphatic diol amine is selected from one or more of lauric acid diethanolamide, stearic acid diethanolamide, myristic acid diethanolamide, and oleic acid diethanolamide.

[0028] The inventors found that when adding long chains of polyether, it will affect the compactness and adhesion of the tin layer deposition, and affect the adhesion of the tin-plated layer and the PCB board. The inventors found that by adding suitable aliphatic alcohol amines, especially aliphatic monoalcohol amines, the adhesion of the coating can be improved while further obtaining a fully bright coating.

[0029] This may be because by adding aliphatic monoalcohol amines, due to the interaction and competitive adsorption between the fatty chain and the long polyether chain, as well as the structure of the NHROH bond of the monoalcohol amine, chelation can occur with copper, etc. to further reduce the potential and promote the substitution effect, so that cross-adsorption of polyether and fatty monoalcohol amine is formed in the early stage of tin plating, thereby promoting the lattice formation and lattice density of the initial tin deposition. When the reaction continues, the potential reduction of the thiourea accelerator and the competitive effect of calcium, magnesium, etc. in the sulfonate and stannous tin are utilized to increase the reaction activity and concentration of stannous tin, thereby forming a coating with better adhesion and density, and promoting the improvement of coating adhesion and brightness.

[0030] As a preferred technical solution of the present invention, the raw materials for preparing the plating solution also include metal oxides, and the weight ratio of the metal oxides to stannous salts is (0.1-0.2):1.

[0031] As a preferred technical solution of the present invention, the metal oxide is selected from Na 2 WO 4 、CuSb 2 O 6 、Na 2 SnO 3 One or more of .

[0032] The inventors found that by using a relatively high amount of organic acid to stabilize stannous tin, using thiourea and alcohol amine to promote the replacement of stannous tin and copper, and continuously depositing through a suitable reducing agent, a tin-plated layer of suitable thickness can be obtained, and problems such as blackening of the plating layer can be avoided. In addition, the present invention uses a certain amount of polyether and sulfonate as a disperser, and adds metal powder to act together, so as to adjust the formation and growth of crystals in the tin-plating process, obtain a smooth and fully bright plating layer, and improve the bonding strength of the plating layer.

[0033] The second aspect of the present invention provides an application of the stable tin-based chemical plating solution for tin plating of electronic components and semiconductors.

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

[0035] (1) The present invention provides a chemical plating solution, which can achieve continuous tin plating under acidic conditions by using a suitable thiourea accelerator and a reducing agent, and achieve higher smoothness and brightness on a tin layer of higher thickness.

[0036] (2) By adding appropriate dispersants and organic acids, the stability of the plating solution can be improved while reducing its aggressiveness to the ink.

[0037] (3) By adding appropriate amides and dispersants, it is beneficial to improve the binding ability and brightness while avoiding attack on the ink.

[0038] (4) Through the combined action of the components of the plating solution provided by the present invention, a dense plating layer can be obtained at a faster plating speed, thereby improving the solderability of subsequent electronic components such as PCB boards. DETAILED DESCRIPTION

[0039] Example

[0040] Example 1

[0041] This example provides a plating solution, wherein the raw materials for preparing the plating solution include stannous salt, organic acid, thiourea accelerator and reducing agent. In 1L of plating solution, the mass of stannous salt is 30g, the stannous salt is stannous methanesulfonate, the weight ratio of the organic acid to the stannous salt is 3:1, the organic acid includes C1-C5 organic acid, the C1-C5 organic acid is methanesulfonic acid and citric acid, the weight ratio is 1:8, the organic acid also includes C10-C20 unsaturated acid, the weight ratio of the C10-C20 unsaturated acid to the C1-C5 organic acid is 1:3, the C10-C20 unsaturated acid is 9-octadecenoic acid, the reducing agent is ascorbic acid and sodium hypophosphite, the weight ratio is 1:6, the weight ratio of the reducing agent to the stannous salt is 1:1. The weight ratio of the thiourea accelerator to the stannous salt is 2:1, the thiourea accelerator is phenylthiourea, the weight ratio of the thiourea accelerator to the stannous salt is 3:1, the raw materials for preparing the plating solution also include a dispersant, the weight ratio of the dispersant to the aliphatic alcohol amine is 0.5:1, the dispersant is polyether L45 and sulfonate, the weight ratio is 1:3, the sulfonate is di(2-ethylhexyl) calcium succinate sulfonate, the raw materials for preparing the plating solution also include aliphatic alcohol amine, the weight ratio of the thiourea accelerator to the aliphatic alcohol amine is 1:0.2, the aliphatic alcohol amine is lauric acid monoethanolamide, the raw materials for preparing the plating solution also include a metal oxide, the weight ratio of the metal oxide to the stannous salt is 0.2:1, the metal oxide is Na 2 WO 4 .

[0042] Example 2

[0043] This example provides a plating solution, wherein the raw materials for preparing the plating solution include stannous salt, organic acid, thiourea accelerator and reducing agent. In 1L of the plating solution, the mass of the stannous salt is 25g, the stannous salt is stannous methanesulfonate, the weight ratio of the organic acid to the stannous salt is 2.8:1, the organic acid includes C1-C5 organic acid, the C1-C5 organic acid is methanesulfonic acid and citric acid, the weight ratio is 1:7, the organic acid also includes C10-C20 unsaturated acid, the weight ratio of the C10-C20 unsaturated acid to the C1-C5 organic acid is 1:4, the C10-C20 unsaturated acid is 2-hexadecenoic acid, the reducing agent is ascorbic acid and sodium hypophosphite, the weight ratio is 1:5, the weight ratio of the reducing agent to the stannous salt is 1 .8:1, the thiourea accelerator is phenylthiourea, the weight ratio of the thiourea accelerator to the stannous salt is 2.6:1, the raw materials for preparing the plating solution also include a dispersant, the weight ratio of the dispersant to the fatty alcohol amine is 0.4:1, the dispersant is polyether L65 and sulfonate, the weight ratio is 1:2.5, the sulfonate is di(2-ethylhexyl) calcium succinate sulfonate, the raw materials for preparing the plating solution also include a fatty alcohol amine, the weight ratio of the thiourea accelerator to the fatty alcohol amine is 1:0.15, the fatty alcohol amine is stearic acid monoethanolamide, the raw materials for preparing the plating solution also include a metal oxide, the weight ratio of the metal oxide to the stannous salt is 0.15:1, the metal oxide is Na 2 WO 4 .

[0044] Example 3

[0045] This example provides a plating solution, wherein the raw materials for preparing the plating solution include stannous salt, organic acid, thiourea accelerator and reducing agent, in 1L of plating solution, the mass of stannous salt is 20g, the stannous salt is stannous methanesulfonate, the weight ratio of the organic acid to the stannous salt is 2.5:1, the organic acid includes C1-C5 organic acid, the C1-C5 organic acid is methanesulfonic acid and citric acid, the weight ratio is 1:6, the organic acid also includes C10-C20 unsaturated acid, the weight ratio of the C10-C20 unsaturated acid to the C1-C5 organic acid is 1:5, the C10-C20 unsaturated acid is 2-tetradecenoic acid, the reducing agent is ascorbic acid and sodium hypophosphite, the weight ratio is 1:4, the weight ratio of the reducing agent to the stannous salt is The weight ratio of the thiourea accelerator to the stannous salt is 1.5:1, the thiourea accelerator is phenylthiourea, the weight ratio of the thiourea accelerator to the stannous salt is 2.5:1, the raw materials for preparing the plating solution also include a dispersant, the weight ratio of the dispersant to the aliphatic alcohol amine is 0.4:1, the dispersant is polyether L64 and sulfonate, the weight ratio is 1:2, the sulfonate is di(2-ethylhexyl) magnesium succinate sulfonate, the raw materials for preparing the plating solution also include aliphatic alcohol amine, the weight ratio of the thiourea accelerator to the aliphatic alcohol amine is 1:0.1, the aliphatic alcohol amine is myristic acid monoethanolamide, the raw materials for preparing the plating solution also include a metal oxide, the weight ratio of the metal oxide to the stannous salt is 0.1:1, the metal oxide is Na 2 WO 4 .

[0046] Example 4

[0047] This example provides a plating solution, wherein the raw materials for preparing the plating solution include stannous salt, organic acid, thiourea accelerator and reducing agent. In 1L of the plating solution, the mass of the stannous salt is 25g, the stannous salt is stannous methanesulfonate, the weight ratio of the organic acid to the stannous salt is 2.8:1, the organic acid includes C1-C5 organic acid, the C1-C5 organic acid is methanesulfonic acid and citric acid, the weight ratio is 1:7, the organic acid also includes C10-C20 unsaturated acid, the weight ratio of the C10-C20 unsaturated acid to the C1-C5 organic acid is 1:4, the C10-C20 unsaturated acid is 2-hexadecenoic acid, and the reducing agent is ascorbic acid. The weight ratio of the reducing agent to the stannous salt is 1.8:1, the thiourea accelerator is phenylthiourea, and the weight ratio of the thiourea accelerator to the stannous salt is 2.6:1. The raw materials for preparing the plating solution also include a dispersant, and the weight ratio of the dispersant to the fatty alcohol amine is 0.4:1. The dispersant is polyether L65 and a sulfonate, and the weight ratio is 1:2.5. The sulfonate is di(2-ethylhexyl) calcium succinate sulfonate. The raw materials for preparing the plating solution also include a metal oxide, and the weight ratio of the metal oxide to the stannous salt is 0.15:1. The metal oxide is Na 2WO 4 .

[0048] Example 5

[0049] This example provides a plating solution, wherein the raw materials for preparing the plating solution include stannous salt, organic acid, thiourea accelerator and reducing agent. In 1L of the plating solution, the mass of the stannous salt is 25g, the stannous salt is stannous methanesulfonate, the weight ratio of the organic acid to the stannous salt is 2.8:1, the organic acid includes C1-C5 organic acid, the C1-C5 organic acid is methanesulfonic acid and citric acid, the weight ratio is 1:7, the organic acid also includes C10-C20 unsaturated acid, the weight ratio of the C10-C20 unsaturated acid to the C1-C5 organic acid is 1:4, the C10-C20 unsaturated acid is 2-hexadecenoic acid, the reducing agent is ascorbic acid and sodium hypophosphite, the weight ratio is 1 : 5, the weight ratio of the reducing agent to the stannous salt is 1.8: 1, the thiourea accelerator is phenylthiourea, the weight ratio of the thiourea accelerator to the stannous salt is 2.6: 1, the raw materials for preparing the plating solution also include a dispersant, the weight ratio of the dispersant to the aliphatic alcohol amine is 0.4: 1, the dispersant is polyether L65, the raw materials for preparing the plating solution also include aliphatic alcohol amine, the weight ratio of the thiourea accelerator to the aliphatic alcohol amine is 1: 0.15, the aliphatic alcohol amine is stearic acid monoethanolamide, the raw materials for preparing the plating solution also include a metal oxide, the weight ratio of the metal oxide to the stannous salt is 0.15: 1, the metal oxide is Na 2 WO 4 .

[0050] Performance Evaluation

[0051] 1. Ink aggressiveness test: Place the PCB board containing the ink layer in the plating solution at 45°C for chemical plating to obtain a 3μm plating layer. Then use a microscope to observe whether the ink on the PCB board is loose. The results are shown in Table 1.

[0052] 2. Coating morphology: Place the PCB board containing the ink layer in the plating solution at 45°C for chemical plating. After obtaining a 3μm coating, observe whether the coating is completely bright and smooth. The results are shown in Table 1.

[0053] 3. Stability: Place the plating solution at room temperature for 5 days and observe whether there are precipitation, stratification and other problems. The results are shown in Table 1.

[0054] 4. Binding strength: Place the copper plate in the plating solution and perform chemical plating at 45°C to obtain a 3μm coating. Then heat the tin-plated substrate to 250°C and immerse it in cold water at 20°C after 1 hour to observe whether the coating appears bubbling or peeling. The results are shown in Table 1.

[0055] Table 1

[0056] Example Ink aggressiveness Coating morphology stability Binding force 1 No looseness Full Brightness No turbidity No blistering or peeling 2 No looseness Full Brightness No turbidity No blistering or peeling 3 No looseness Full Brightness No turbidity No blistering or peeling 4 - Most of the light - Slightly bubbling 5 Slightly loose Most of the light Slightly turbid -

[0057] The plating solution provided by the invention has high stability and tinning ability, and can obtain a tinning layer with high brightness and adhesion.

[0058] It should be understood that the embodiments described herein should be considered in a descriptive sense only and not for limiting purposes. The description of features, advantages or aspects within each embodiment should be considered as applicable to other similar features, advantages or aspects in other embodiments.

Claims

1. A stable tin chemical plating solution, characterized in that: The raw materials for preparing the plating solution include stannous salt, organic acid, thiourea accelerator and reducing agent, and the organic acid includes C1~C5 organic acid; The weight ratio of the thiourea accelerator to the stannous salt is (2.5-3):1; The raw materials for preparing the plating solution include a dispersant and a sulfonate, the dispersant includes a polyether, the weight average molecular weight of the polyether is 2000-4000, and the HLB value is 12-18; The weight ratio of the polyether to the sulfonate is 1:(2-3), and the sulfonate is selected from di(2-ethylhexyl) succinate calcium sulfonate and di(2-ethylhexyl) succinate magnesium sulfonate; The C1-C5 organic acid is methanesulfonic acid and citric acid, and the weight ratio is 1:(6-8); the organic acid also includes C10-C20 unsaturated acid, and the weight ratio of the C10-C20 unsaturated acid to the C1-C5 organic acid is 1:(3-5); the C10-C20 unsaturated acid is selected from one or more of oleic acid, 9-octadecenoic acid, 2-hexadecenoic acid, 2-tetradecenoic acid, and 9-hexadecenoic acid; The reducing agent is ascorbic acid and sodium hypophosphite in a weight ratio of 1:(4-6); The raw materials for preparing the plating solution also include aliphatic alcohol amine, and the weight ratio of the thiourea accelerator to the aliphatic alcohol amine is 1: (0.1-0.2); The raw materials for preparing the plating solution also include metal oxide, and the weight ratio of the metal oxide to stannous salt is (0.1-0.2):1; The weight ratio of the dispersant to the aliphatic alcohol amine is (0.2-0.6):1; The weight ratio of the organic acid to the stannous salt is (2.5-3):

1.

2. The stable tin-based chemical plating solution according to claim 1, characterized in that: The thiourea accelerator is selected from one or more of thiosemicarbazide, phenylthiourea and vinylthiourea.

3. An application of the stable tin-based chemical plating solution according to claim 1, characterized in that: Used for tinning of electronic components and semiconductors.