Tin-silver alloy electroplating solution, its preparation method and application, electroplating method

Abstract

The present invention relates to the field of electroplating, and discloses a tin-silver alloy electroplating solution, a preparation method and application thereof, and an electroplating method. The electroplating solution contains a soluble stannous salt, a soluble silver salt, a composite surfactant, a free acid, an antioxidant, a complexing agent and a solvent. When electroplating with the electroplating solution, the available current density can reach 25 ASD, the electroplating efficiency is high, and the tin-silver alloy bumps obtained by electroplating are uniform, the proportion of voids after bump reflow is small, and no collapse occurs.

Description

Technical Field

[0001] The present invention relates to the field of electroplating, and specifically relates to a tin-silver alloy electroplating solution, a preparation method and application thereof, and an electroplating method. Background Art

[0002] Through the flip-chip bump interconnection technology, chips can be stacked layer by layer to achieve high density and realize the high-density three-dimensional packaging of chips. Tin and tin alloys have excellent solderability due to their low melting point, high boiling point, and good wettability. They also have good electrical and thermal conductivity and chemical stability, making them very suitable for use as chip bumps and welding materials. There are various methods for manufacturing tin and tin alloy bumps, such as stencil printing, evaporation / sputtering, electroplating method, etc. Among them, the electroplating method has low cost, and the size, size, and height of the bumps are uniformly controllable. Therefore, developing a tin and tin alloy electroplating solution applicable to wafer electroplating and improving its electroplating performance are the keys to manufacturing tin and tin alloy bumps.

[0003] However, in actual production, due to the tin whisker problem of pure tin coatings, short circuits are likely to occur in high-density fine-pitch bump flip-chip products, resulting in device failure. Lead-tin alloys have been replaced due to the pollution of lead to the environment. Gold-tin alloys have disadvantages such as high gold price and slow plating speed. Tin-copper alloys and tin-bismuth alloys are prone to voids after reflow and have poor reliability. Tin-silver alloy is an ideal "bump interconnection" material in terms of environmental protection, reliability, and usage cost.

[0004] CN116529428A provides a tin alloy plating solution for manufacturing bumps as protrusion electrodes of tin alloys on a substrate when a semiconductor integrated circuit chip is mounted on the circuit substrate. The plating solution contains: (A) a soluble salt containing at least stannous salt; (B) a soluble salt of a metal less active than tin; (C) an alkanesulfonic acid or its salt containing 9 to 18 carbon atoms in the molecule; (D) a nonionic surfactant containing more than 1 phenyl group in the molecule; and (E) a leveling agent. This plating solution uses a leveling agent composed of an alkanesulfonic acid or its salt containing 9 to 18 carbon atoms in the molecule; it does not use aromatic carbonyl compounds (such as benzalacetone, cinnamic acid, cinnamaldehyde, benzaldehyde, etc.) as leveling agents. Without replenishing the leveling agent for a long time during electroplating, a coating can be formed evenly and densely, and the coating can be made smooth. In actual operation, since the solubility of alkanesulfonic acid or its salt containing 9 to 18 carbon atoms is often poor, additional cosolvents need to be added for dissolution, increasing the complexity of the plating solution. Moreover, such alkanesulfonic acid or its salt has too much foam during operation and is prone to form voids during electroplating. Furthermore, in the examples and comparative examples, the current density used is only 4 ASD.

[0005] CN108474127A mentions a tin-silver alloy plating solution, which is a Sn-Ag alloy plating solution containing a water-soluble tin compound and a water-soluble silver compound. With respect to 1 mole of silver in the water-soluble silver compound, a specific thioether compound is contained in the range of not less than 0.25 mole and not more than 10 moles. In order to stably dissolve the silver compound in the Sn-Ag alloy plating solution, a sulfur-containing compound such as a heterocyclic compound having a mercapto group or a thioether compound is added as a complexing agent to form a silver complex. Even when this plating solution is used or stored for a long time, silver is hardly precipitated as a metal or an insoluble salt in the plating solution, and it is a Sn-Ag alloy plating solution capable of stably forming a Sn-Ag alloy coating film. However, the current density mentioned in its examples and comparative examples is only 5 ASD.

[0006] JP2022063889A provides a tin or tin alloy plating solution for suppressing the generation of voids in bumps under a wide range of current densities from 2 ASD to 14 ASD, and a method for forming bumps using this solution. The inventors conducted in-depth research and found that by incorporating polypropylene glycol having a specific weight average molecular weight into the plating solution at a specific mass ratio, the generation of voids in bumps can be suppressed within a wide range of current densities. The first aspect includes a soluble salt (A) containing at least a stannous salt, an acid or its salt (B) selected from organic acids and inorganic acids, and a surfactant (C). A plating solution containing polypropylene glycol in an amount of 0.05 g / L to 5 g / L, and the weight average molecular weight of the polypropylene glycol is 610 to 740. The second aspect is the invention according to the first aspect, wherein the surfactant (C) is a nonionic surfactant obtained by condensation of polyoxyethylene (EO) and polyoxypropylene (PO), and it is a tin or tin alloy plating solution. The third aspect is to form a tin or tin alloy plating deposit layer that will become precursors of a plurality of bumps on a substrate using the tin or tin alloy plating solution of the first aspect or the second aspect.

[0007] CN104032337A provides a tin alloy plating solution having high continuous stability, with very little change in the co-deposition ratio of tin and alloy metals caused by changes in the current density and substantially free of cyanide. A series of test results of the inventors show that by mixing a peptide having a cysteine residue in the plating solution, even when there are metal ions more inert than tin in the plating solution, this plating solution can be stably used for a long time, and with respect to an increase or decrease in the current density, this plating solution can obtain a substantially unchanged co-deposition ratio of tin and metal ions. The current used for the tin alloy plating solution can be direct current or pulsed current. The current density is preferably in the range of 0.5 - 10 A / dm 2 and more preferably 1 - 8 A / dm 2 .

[0008] JP11256390A relates to a tin-silver alloy electroplating solution for plating tin-silver alloys. This plating solution is used for joining electronic components, components for solder joining during installation, surface treatment of lead frames and printed circuit boards, etc. It is considered that in all conventional tin-silver alloy electroplating solutions, the composition of the electroplated product varies greatly with the current density. For example, at a relatively high current density of 2 ASD, the silver content is 3-5% (by weight), but at a relatively low current density, the silver content rapidly increases to 15-25% (by weight), increasing by several times or more. In this patent application, silver compounds are dissolved in the tin plating solution to form metallic silver particles with a particle size of about 5 nm, which do not agglomerate or settle and exist stably dispersed in the plating bath. Then, during subsequent electroplating, they are incorporated into the tin coating to form a tin-silver alloy coating. The temperature range of the plating bath of this invention is 20°C to 70°C, preferably 30°C to 60°C, and the cathode current density is 0.1-10 ASD, more preferably 0.1-5.0 ASD.

[0009] US20070037377A1 provides a tin-silver alloy electroplating solution that can be used for solder wafer bumps. This plating solution is added with additives to enhance the stability of silver, N-allylthiourea compounds and quaternary ammonium salt surfactants, allowing electroplating of Sn-Ag wafer bumps at a high current density of 1-20 ASD, thereby greatly reducing or completely eliminating voids between the bumps and Cu and UBM. However, the maximum current density used in all its examples and comparative examples is only 12 ASD.

[0010] JP2006265572A provides a cyanide-free tin-silver alloy electroplating solution. The tin-silver alloy film obtained from this plating solution has excellent solder wettability and appearance. The inventor adds aliphatic sulfides and aliphatic thiols as stabilizers for silver ions in the plating solution, and adds aliphatic amino acids such as glycine and nitrogen-containing aromatic carboxylic acids such as picolinic acid in the plating solution. The thin film obtained from this plating solution can effectively improve solderability and appearance. However, for the tin-silver alloy electroplating solutions obtained in Examples 1-10 and Comparative Examples 1-5, the current density used at the cathode is 5-15 ASD.

[0011] CN106757212A discloses an electroplating tin-silver alloy solution for wafer-level packaging. The solution comprises components with the following concentrations: 50 - 450 g / L of methanesulfonic acid, 20 - 60 g / L of tin ions, 0.1 - 1.0 g / L of silver ions, 10 - 50 g / L of silver ion chelating agent, and 0.52 - 5.08 g / L of organic additive. When electroplating with this tin-silver alloy solution, the current density is between 1 - 10 ASD, and the temperature is between 15 - 35 °C. This invention's solution comprises methanesulfonic acid, tin ions, silver ions, silver ion chelating agent, and organic additive, and when electroplating, the current density is between 1 - 10 ASD, and the temperature is between 15 - 35 °C. The above components electroplate to form a tin-silver alloy solution, and the electroplating tin-silver plating solution is used to replace the traditional electroplating pure tin solution, solving the problem that existing pure tin bumps are prone to tin whiskers, effectively preventing defects such as tin whiskers generated by the pure tin coating, and further improving the reliability of electronic products.

[0012] CN118639288A provides a tin-silver alloy electroplating solution and its preparation method, for electroplating tin-silver alloy bumps. The electroplating solution for preparing the tin-silver alloy contains a mercapto compound, an amino acid, nonylphenol polyoxyethylene ether, and a fluorinated surfactant, which can significantly improve the coplanarity of the tin-silver alloy bumps and the uniformity of the silver content in the alloy, and its available current density is 1 - 10 ASD.

[0013] It can be seen that the current density during electroplating with the tin-silver alloy electroplating solutions disclosed in the prior art is relatively low and cannot reach above 20 ASD. Summary of the Invention

[0014] To overcome the problem of relatively low electroplating current density existing in the prior art, the present invention provides a tin-silver alloy electroplating solution, its preparation method and application, and an electroplating method. The available current density during electroplating with this electroplating solution can reach 25 ASD, the electroplating efficiency is high, and the obtained tin-silver alloy bumps are uniform, the proportion of voids after bump reflow is small, and no collapse occurs.

[0015] To achieve the above object, in the first aspect of the present invention, a tin-silver alloy electroplating solution is provided. The electroplating solution comprises a soluble stannous salt, a soluble silver salt, a composite surfactant, a free acid, an antioxidant, a complexing agent, and a solvent. The composite surfactant comprises a first surfactant, a second surfactant, a third surfactant, and a fourth surfactant;

[0016] The first surfactant is selected from at least one of linear alkylphenol polyethers, linear alkylphenol polyether esters and their salts, aromatic phenol polyethers, aromatic phenol polyether esters, styryl phenol polyethers, and EO-PO-EO block copolymers with a weight average molecular weight of 2000 - 4000 Da;

[0017] The second surfactant is a polyhydric alcohol;

[0018] The third surfactant is a cationic surfactant and / or an amphoteric surfactant;

[0019] The fourth surfactant is a thio-polyoxyethylene ether;

[0020] The mass ratio of the first surfactant, the second surfactant, the third surfactant and the fourth surfactant is 1:1 - 12:0.05 - 2:0.25 - 8;

[0021] The content of the composite surfactant in the electroplating solution is 30 - 180 g / L.

[0022] In the second aspect of the present invention, a method for preparing the tin-silver alloy electroplating solution provided in the first aspect of the present invention is provided. The method includes mixing a soluble stannous salt, a soluble silver salt, a composite surfactant, a free acid, an antioxidant, a complexing agent and an optional brightening agent in the presence of a solvent to obtain the tin-silver alloy electroplating solution.

[0023] In the third aspect of the present invention, an application of the tin-silver alloy electroplating solution provided in the first aspect of the present invention in electroplating is provided.

[0024] In the fourth aspect of the present invention, a method for electroplating using the tin-silver alloy electroplating solution provided in the first aspect of the present invention is provided. The current density of the electroplating is 1 - 25 ASD.

[0025] The beneficial effects of the present invention are as follows:

[0026] The available current density during electroplating with the electroplating solution provided by the present invention can reach 25 ASD, the electroplating efficiency is high, and the tin-silver alloy bumps obtained by electroplating are uniform, the proportion of voids after bump reflow is small, and no collapse occurs. Description of the Drawings

[0027] Figure 1 It is a photograph of the coating appearance. Among them, (a) is the photograph of the coating appearance obtained in Example 1, (b) is the photograph of the coating appearance obtained in Comparative Example 1, (c) is the photograph of the coating appearance obtained in Comparative Example 2, (d) is the photograph of the coating appearance obtained in Comparative Example 3, (e) is the photograph of the coating appearance obtained in Comparative Example 4, (f) is the photograph of the coating appearance obtained in Comparative Example 5, and (g) is the photograph of the coating appearance obtained in Comparative Example 6;

[0028] Figure 2 It is a scanning electron microscope image of the bumps before reflow obtained with the electroplating solution of Example 2;

[0029] Figure 3 It is a scanning electron microscope image of the cross-section of the bumps before reflow obtained with the electroplating solution of Example 2;

[0030] Figure 4SEM image after bump reflow obtained with the electroplating solution of Example 2;

[0031] Figure 5 SEM cross-sectional image after bump reflow obtained with the electroplating solution of Example 2;

[0032] Figure 6 X-Ray CT image after bump reflow obtained with the electroplating solution of Example 1;

[0033] Figure 7 X-Ray CT image after bump reflow obtained with the electroplating solution of Comparative Example 3;

[0034] Figure 8 X-Ray CT image after bump reflow obtained with the electroplating solution of Comparative Example 4;

[0035] Figure 9 X-Ray CT image after bump reflow obtained with the electroplating solution of Comparative Example 6. Detailed Description of the Invention

[0036] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0037] In the present invention, ASD refers to amperes per square decimeter, i.e., A / dm 2 .

[0038] The first aspect of the present invention provides a tin-silver alloy electroplating solution, which comprises a soluble stannous salt, a soluble silver salt, a composite surfactant, a free acid, an antioxidant, a complexing agent and a solvent, and the composite surfactant comprises a first surfactant, a second surfactant, a third surfactant and a fourth surfactant;

[0039] The first surfactant is selected from at least one of linear alkylphenol polyethers, linear alkylphenol polyether esters and their salts, aromatic phenol polyethers, aromatic phenol polyether esters, styrylphenol polyethers and EO-PO-EO block copolymers with a weight average molecular weight of 2000-4000 Da;

[0040] The second surfactant is a polyhydric alcohol;

[0041] The third surfactant is a cationic surfactant and / or an amphoteric surfactant;

[0042] The fourth surfactant is a thio-polyoxyethylene ether;

[0043] The mass ratio of the first surfactant, the second surfactant, the third surfactant and the fourth surfactant is 1:1 - 12:0.05 - 2:0.25 - 8;

[0044] The content of the composite surfactant in the electroplating solution is 30 - 180 g / L.

[0045] In the present invention, the first surfactant can promote the precipitation of tin in the low current density range (0.1 - 2 ASD); the second surfactant can inhibit the precipitation of silver in the low current density range (0.1 - 2 ASD); the third surfactant can promote the normal precipitation of tin in the ultra - high current density range (12 - 25 ASD); the fourth surfactant can refine the tin - silver grains.

[0046] The above four surfactants cooperate to improve the available current density during electroplating of the electroplating solution provided by the present invention, improve the electroplating efficiency, and the tin - silver alloy bumps obtained by electroplating are uniform, the proportion of voids after bump reflow is small, and no collapse occurs.

[0047] In the present invention, the EO value has its conventional meaning in the art, that is, the molar amount of - CH 2 CH 2 O - segments contained in each mole of polymer molecules.

[0048] For the first surfactant:

[0049] According to the present invention, preferably, the first surfactant is selected from at least one of cardanol polyoxyethylene ether, cardanol polyoxyethylene ether sulfate and its salts, phenol polyoxyethylene ether, stilbene diphenol polyoxyethylene ether and triphenylethylene phenol polyoxyethylene ether.

[0050] Preferably, the EO value of the first surfactant is 5 - 25.

[0051] For the second surfactant:

[0052] According to the present invention, preferably, the polyhydric alcohol is at least one of polyethylene glycol (PEG), polypropylene glycol (PPG) and EO - PO - EO block copolymer.

[0053] Preferably, the weight - average molecular weight of the second surfactant is 200 - 2000 Da.

[0054] More preferably, PEG is selected from at least one of PEG 200 - 2000, and can be, for example, PEG 200, PEG 400, PEG 600, PEG 1000, PEG 1500, PEG 2000.

[0055] More preferably, the PPG is selected from at least one of PPG 400 - 1000, and may be, for example, PPG 400, PPG 600, PPG 800, or PPG 1000.

[0056] More preferably, the EO-PO-EO block copolymer is selected from at least one of polyethylene oxide - polypropylene oxide alcohol, polyoctylene glycol - polypropylene ether, and polyvinyl alcohol - polypropylene oxide alcohol.

[0057] For the third surfactant:

[0058] According to the present invention, preferably, the third surfactant is selected from C 12 -C 18 alkyltrimethylammonium chloride, C 12 -C 18 alkyldimethylbenzylammonium chloride, C 12 -C 18 alkyltrimethylammonium bromide, C 12 -C 18 alkyldimethylbenzylammonium bromide, C 12 -C 18 alkyltrimethylammonium p-toluenesulfonate, lauryldimethylamine oxide, citric acid betaine, and at least one of 3-sulfopropyltetradecyldimethylbetaine.

[0059] For the fourth surfactant:

[0060] According to the present invention, preferably, the fourth surfactant is C 12 -C 18 alkylthiol polyoxyethylene ether and / or thiodiglycol ethoxylate;

[0061] Preferably, the EO value of the fourth surfactant is 5 - 25.

[0062] According to a particularly preferred embodiment of the present invention, the first surfactant is cardanol polyoxyethylene ether BGF-10, the second surfactant is PEG 1000, the third surfactant is dodecyldimethylbenzylammonium bromide, and the fourth surfactant is thiodiglycol ethoxylate (EO = 10).

[0063] According to a preferred embodiment of the present invention, the mass ratio of the first surfactant, the second surfactant, the third surfactant, and the fourth surfactant is 1:3 - 6:0.2 - 1:3 - 5.

[0064] According to a preferred embodiment of the present invention, the content of the composite surfactant in the electroplating solution is 50 - 150 g / L.

[0065] The present invention does not particularly limit the specific type of the soluble stannous salt, and those skilled in the art can make a conventional choice. According to a specific embodiment of the present invention, the soluble stannous salt is selected from at least one of stannous sulfonate, stannous sulfate, and stannous fluoborate.

[0066] According to a preferred embodiment of the present invention, based on the metal ions, the content of the soluble stannous salt in the electroplating solution is 30-150 g / L.

[0067] In the present invention, when the content of the soluble stannous salt in the electroplating solution is within the above range, it can further promote the precipitation of tin, and at the same time keep the electroplating solution at a moderate viscosity to avoid voids in the coating.

[0068] More preferably, based on the metal ions, the content of the soluble stannous salt in the electroplating solution is 50-120 g / L.

[0069] The present invention does not particularly limit the specific type of the soluble silver salt, as long as it is soluble in acid, and those skilled in the art can make a conventional choice. According to a specific embodiment of the present invention, the soluble silver salt is selected from at least one of silver sulfonate, silver acetate, and silver sulfate.

[0070] According to the present invention, preferably, based on the metal ions, the content of the soluble silver salt in the electroplating solution is 0.01-5 g / L.

[0071] In the present invention, when the content of the soluble silver salt in the electroplating solution is within the above range, a tin-silver alloy coating with a more suitable melting point can be obtained.

[0072] More preferably, based on the metal ions, the content of the soluble silver salt in the electroplating solution is 0.5-3 g / L, and further preferably 1.5-2.5 g / L.

[0073] The present invention does not particularly limit the specific type of the free acid, and those skilled in the art can make a conventional choice. For example, the free acid can be at least one of soluble strong acids such as sulfuric acid, hydrochloric acid, alkylsulfonic acid, aminosulfonic acid, and arylsulfonic acid.

[0074] The present invention does not particularly limit the specific type and content of the antioxidant, and those skilled in the art can make a conventional choice.

[0075] According to a specific embodiment of the present invention, the antioxidant can be phenolic compounds and their derivatives, such as phenol, benzenediol, benzenetriol, naphthol; it can be hydroxybenzoic acid and its derivatives, such as p-hydroxybenzoic acid, o-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid, gallic acid; it can be hydroxybenzenesulfonic acid, naphtholsulfonic acid and their derivatives, such as cresolsulfonic acid, naphtholsulfonic acid, 1-amino-2-naphthol-4-sulfonic acid, 4-hydroxy-1-naphthalenesulfonic acid monosalt; it can be flavonoid compounds, such as flavone, flavonol, dihydroflavone and dihydroflavonol, chalcone, dihydrochalcone, aurone, anthocyanidin and flavanol.

[0076] According to the present invention, specifically, the content of the antioxidant in the electroplating solution is 0.5 - 5 g / L.

[0077] The present invention does not particularly limit the specific type and content of the complexing agent, and those skilled in the art can make conventional selections.

[0078] According to a specific embodiment of the present invention, the complexing agent can be selected from at least one of hydroxyethylidene diphosphonic acid, gluconic acid, N-hydroxyethyl ethylenediamine triacetic acid, malic acid, N-acetyl-L-histidine; the complexing agent can also be selected from at least one of thioether compounds, thiol compounds and mercapto compounds, such as 4,4'-dihydroxydiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 2-hydroxyethyl ethyl sulfide, methylthioethanol, methylthioacetic acid, 3-methylthiopropanol, 3-methylthiopropionic acid, methylthio pyridine, methylthio pyrazine, methylthio pyrimidine, thiodiglycol, 1-(2-dimethylaminoethyl)-1H-tetrazole-5-thiol, 3,6-dithia-1,8-octanediol, 3,6-dioxa-1,8-octanedithiol, 1-thioglycerol, mercaptoacetic acid, mercaptopropionic acid, mercaptoimidazole, thioproline, disulfide compounds such as 2,2'-dithiopyridine, dithiophene disulfide, bis(thiobenzoyl) disulfide, 4-amino-4H-1,2,4-triazole-3,5-dithiol, dithiodiacetic acid.

[0079] According to the present invention, specifically, the molar ratio of the complexing agent to the soluble silver salt in terms of silver ions is 2 - 10:1.

[0080] According to the present invention, preferably, the electroplating solution further contains a brightening agent.

[0081] The present invention does not particularly limit the specific type and content of the brightener, and those skilled in the art can make a conventional selection. According to a specific embodiment of the present invention, the brightener is selected from at least one of polyquaternary ammonium salt, polyvinylpyrrolidone, polyethyleneimine, benzalacetone, 2',3,4',5,7-pentahydroxyflavone, 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-4H-1-benzopyran-4-one, glutaraldehyde, cinnamaldehyde, anisaldehyde, and vanillin.

[0082] According to the present invention, specifically, the content of the brightener in the electroplating solution is 0.01 - 1 g / L.

[0083] The second aspect of the present invention provides a method for preparing the tin-silver alloy electroplating solution provided in the first aspect of the present invention. The method includes mixing a soluble stannous salt, a soluble silver salt, a composite surfactant, a free acid, an antioxidant, a complexing agent, and an optional brightener in the presence of a solvent to obtain the tin-silver alloy electroplating solution.

[0084] The third aspect of the present invention provides an application of the tin-silver alloy electroplating solution provided in the first aspect of the present invention in electroplating.

[0085] The fourth aspect of the present invention provides a method for electroplating using the tin-silver alloy electroplating solution provided in the first aspect of the present invention. The current density of the electroplating is 1 - 25 ASD.

[0086] According to the present invention, preferably, the method includes energizing at 1 - 2 ASD for 30 - 90 s, at 3 - 5 ASD for 300 - 480 s, and at 20 - 25 ASD for 120 - 240 s in sequence.

[0087] The present invention will be described in detail below through examples. In the following examples, the silver content in the bumps was measured by X-ray fluorescence spectrometry (XRF);

[0088] The proportion of voids after bump reflow was measured by X-ray computed tomography (X-Ray CT);

[0089] The surface roughness Ra of the coating was measured using a Keyence laser microscope, and the definition of Ra refers to GB / T 3505 - 2009;

[0090] The content of each substance in the electroplating solution was calculated based on the feeding amount.

[0091] Unless otherwise specified, all reagents and raw materials are commercially available.

[0092] Examples 1 - 15 and Comparative Examples 1 - 6

[0093] Stannous methyl sulfonate, silver methyl sulfonate, methyl sulfonic acid, catechol, hydroquinone, gluconic acid, 3,6-dithia-1,8-octanediol, 2,2'-dithiopyridine and benzylidene acetone are added to water, stirred and mixed, and then a first surfactant, a second surfactant, a third surfactant and a fourth surfactant are added, stirred and mixed to obtain a tin-silver alloy electroplating solution.

[0094] The stannous content in the electroplating solution is 85 g / L, the silver content is 2 g / L, the catechol content is 1 g / L, the hydroquinone content is 1 g / L, the gluconic acid content is 15 g / L, the 3,6-dithia-1,8-octanediol content is 5 g / L, the 2,2'-dithiopyridine content is 1 g / L, the benzylidene acetone content is 0.1 g / L, and the pH value of the electroplating solution is 0.

[0095] The mass ratios of the four surfactants and the total content of the surfactants in the electroplating solution are shown in Table 1.

[0096] Table 1

[0097]

[0098] Table 1 (continued)

[0099]

[0100] Table 1 (continued)

[0101]

[0102] Test Example 1

[0103] Using a titanium-based platinum-coated electrode as the anode and a copper sheet of 100 mm × 65 mm as the cathode. The copper sheet is successively subjected to electrolytic degreasing, cleaning, acid activation and cleaning. The anode and the cathode are placed in a Hull cell, and 250 mL of the electroplating solutions obtained in the above-mentioned examples and comparative examples are respectively added, 5 A of direct current is passed for 5 min, the appearance of the coating within the range of 1-25 ASD is observed, and the surface roughness Ra of the coating is measured. The results are shown in Table 2.

[0104] Table 2

[0105]

[0106] Figure 1 It is a photograph of the coating appearance. Among them, (a) is the photograph of the coating appearance obtained in Example 1, (b) is the photograph of the coating appearance obtained in Comparative Example 1, (c) is the photograph of the coating appearance obtained in Comparative Example 2, (d) is the photograph of the coating appearance obtained in Comparative Example 3, (e) is the photograph of the coating appearance obtained in Comparative Example 4, (f) is the photograph of the coating appearance obtained in Comparative Example 5, and (g) is the photograph of the coating appearance obtained in Comparative Example 6.

[0107] It can be seen that the coating obtained from the electroplating solution of Example 1 has a uniform and delicate appearance without abnormalities;

[0108] For the electroplating solution of Comparative Example 1, large-area burning occurs at high potentials, and the covering power at low potentials is poor;

[0109] For the electroplating solution of Comparative Example 2, the color of the coating is slightly blackened and the silver content is on the high side;

[0110] For the electroplating solution of Comparative Example 3, the tin-silver alloy cannot be deposited in the low-potential range of the coating, resulting in serious non-plating;

[0111] For the electroplating solution of Comparative Example 4, the color of the coating test piece is overall on the black side;

[0112] For the electroplating solution of Comparative Example 5, the coating burns at high potentials;

[0113] For the electroplating solution of Comparative Example 6, the coating is rough.

[0114] Application Example

[0115] Using a titanium-based platinum-coated electrode as the anode and a wafer pattern piece as the cathode. The wafer pattern piece is silicon-based copper-coated and coated with a photoresist with a thickness of 80 μm. The size of the wafer pattern piece is about 23 mm × 23 mm, and there are 9 individual chip units (DIEs). Each DIE contains 1351 small holes with a diameter of 85 μm and a depth of 80 μm. The anode and cathode are placed in a cube-shaped small tank with a volume of 500 mL, and 500 mL of the electroplating solutions obtained from the above-mentioned examples and comparative examples are added respectively. Electrolysis is carried out successively at 1 ASD for 60 s, at 4 ASD for 360 s, and at 25 ASD for 180 s to deposit 50-μm tin-silver alloy bumps in the small holes, and then the photoresist is removed.

[0116] The wafer pattern piece with the photoresist removed is heated to 100 °C at a rate of 2 °C / s and held for 60 s, heated to 200 °C at a rate of 2 °C / s and held for 100 s, heated to 240 °C at a rate of 2 °C / s and held for 120 s, and then naturally cooled to room temperature to obtain the bumps after reflow.

[0117] Test Example 2

[0118] Use a scanning electron microscope to observe the morphology of the bumps before and after reflow.

[0119] Figure 2 Figure 38 is a scanning electron microscope image of the bumps before reflow obtained from the electroplating solution of Example 2. The accelerating voltage is 10 kV, the focal length is 10.9 mm, the magnification is 200 times, and the receiving signal probe is a secondary electron detector;

[0120] Figure 3This is a scanning electron microscope image of the front section of the bump reflow obtained by the electroplating solution of Example 2, with an acceleration voltage of 5 kV, a focal length of 5.6 mm, a magnification of 1000 times, and a secondary electron detector as the receiving signal probe;

[0121] Figure 4 This is a scanning electron microscope image of the bump after reflow obtained by the electroplating solution of Example 2, with an acceleration voltage of 5 kV, a focal length of 8.5 mm, a magnification of 200 times, and a secondary electron detector as the receiving signal probe;

[0122] Figure 5 This is a scanning electron microscope image of the cross-section of the bump after reflow obtained by the electroplating solution of Example 2, with an acceleration voltage of 5 kV, a focal length of 5.8 mm, a magnification of 1000 times, and a secondary electron detector as the receiving signal probe.

[0123] It can be seen that by selecting the appropriate type, proportion and addition amount of surfactant, qualified tin-silver alloy bumps can be obtained on the silicon wafer.

[0124] XRF was used to measure the silver content in the bumps after removing the photoresist and before reflow, and X-Ray CT testing equipment was used to observe the percentage of bump voids after reflow. The results are shown in Table 3.

[0125] Table 3

[0126]

[0127] NA means not applicable or no data.

[0128] Figure 6 The X-Ray CT image of the bump after reflow obtained by the electroplating solution of Example 1;

[0129] Figure 7 The X-Ray CT image of the bump after reflow obtained by the electroplating solution of Comparative Example 3;

[0130] Figure 8 The X-Ray CT image of the bump after reflow obtained by the electroplating solution of Comparative Example 4;

[0131] Figure 9 This is an X-Ray CT image of the bump after reflow obtained from the electroplating solution of Comparative Example 6.

[0132] It can be seen that the bumps obtained by the electroplating solution of Example 1 are normal without voids, the bumps obtained by the electroplating solutions of Comparative Examples 3 and 6 have more voids, and some bumps obtained by the electroplating solution of Comparative Example 4 are completely collapsed.

[0133] From the results in Table 2 and Table 3, it can be found that the available current density during electroplating with the electroplating solution provided by the present invention can reach 25 ASD, with high electroplating efficiency. Moreover, the obtained tin-silver alloy coating is uniform, delicate, has a low roughness, an appropriate silver content, a small proportion of voids after bump reflow, and no collapse occurs.

[0134] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should equally be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A tin-silver alloy electroplating solution, characterized in that: The electroplating solution comprises a soluble stannous salt, a soluble silver salt, a composite surfactant, a free acid, an antioxidant, a complexing agent and a solvent, and the composite surfactant comprises a first surfactant, a second surfactant, a third surfactant and a fourth surfactant; The mass ratio of the first surfactant, the second surfactant, the third surfactant and the fourth surfactant is 1:1-12:0.05-2:0.25-8; The content of the composite surfactant in the electroplating solution is 30-180 g / L; The first surfactant is selected from at least one of cardanol polyoxyethylene ether, phenol polyoxyethylene ether, distyrylphenol polyoxyethylene ether and tristyrylphenol polyoxyethylene ether; The second surfactant is selected from at least one of polyethylene glycol, polypropylene glycol and EO-PO-EO block copolymer; The third surfactant is selected from C 12 -C 18 Alkyl dimethyl benzyl ammonium chloride, C 12 -C 18 At least one of alkyl dimethyl benzyl ammonium bromide and lauryl dimethyl amine oxide; The fourth surfactant is C 12 -C 18 Alkyl mercaptan polyoxyethylene ethers and / or thiodiglycol ethoxylates; The content of soluble stannous salt in the electroplating solution is 30-150 g / L in terms of metal ions; The content of soluble silver salt in the electroplating solution is 0.01-5 g / L in terms of metal ions; The pH value of the electroplating solution is 0.

2. The electroplating solution according to claim 1, characterized in that The EO value of the first surfactant is 5-25; and / or, the weight average molecular weight of the second surfactant is 200-2000 Da; And / or, the EO value of the fourth surfactant is 5-25.

3. The electroplating solution according to claim 1 or 2, characterized in that: The mass ratio of the first surfactant, the second surfactant, the third surfactant and the fourth surfactant is 1:3-6:0.2-1:3-5.

4. The electroplating solution according to claim 1 or 2, characterized in that: The content of the composite surfactant in the electroplating solution is 50-150 g / L.

5. The electroplating solution according to claim 1 or 2, characterized in that: The content of antioxidant in the electroplating solution is 0.5-5 g / L; and / or, the molar ratio of the complexing agent to the soluble silver salt calculated as silver ions is 2-10:1; And / or, the electroplating solution further comprises 0.01-1 g / L of brightener.

6. A method for preparing the tin-silver alloy electroplating solution according to any one of claims 1 to 5, characterized in that: The method comprises mixing a soluble stannous salt, a soluble silver salt, a complex surfactant, a free acid, an antioxidant, a complexing agent and an optional brightener in the presence of a solvent to obtain the tin-silver alloy electroplating solution.

7. Use of the tin-silver alloy electroplating solution according to any one of claims 1 to 5 in electroplating.

8. A method for electroplating using the tin-silver alloy electroplating solution according to any one of claims 1 to 5, characterized in that: The current density of the electroplating is 1-25 ASD.

9. The method according to claim 8, characterized in that The method includes sequentially applying power at 1-2 ASD for 30-90 s, applying power at 3-5 ASD for 300-480 s, and applying power at 20-25 ASD for 120-240 s.

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