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

Abstract

The invention relates to the field of electroplating, and discloses a tin-silver alloy electroplating solution as well as a preparation method and application thereof and an electroplating method, and the electroplating solution comprises soluble stannous salt, soluble silver salt, a composite surfactant, free acid, an antioxidant, a complexing agent and a solvent. When the electroplating liquid is used for electroplating, the available current density can reach 25 ASD, the electroplating efficiency is high, tin-silver alloy salient points obtained through electroplating are uniform, the cavity proportion is small after the salient points flow back, and collapse is avoided.

Description

Technical Field

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

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

[0003] However, in actual production, pure tin plating is prone to short circuits and device failure in high-density fine-pitch bump flip-chip products due to tin whisker problems. Lead-tin alloys have been replaced due to lead pollution to the environment. Gold-tin alloys have disadvantages such as high gold prices and slow plating speeds. Tin-copper alloys and tin-bismuth alloys are prone to voids after reflow and have poor reliability. Tin-silver alloys are superior in terms of environmental protection, reliability, and cost of use, and are a more ideal "bump interconnect" material.

[0004] CN116529428A provides a tin alloy plating solution for manufacturing bumps as protruding electrodes of tin alloy on a substrate when a semiconductor integrated circuit chip is mounted on a circuit substrate, the plating solution comprising: (A) a soluble salt containing at least a 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 one or more phenyl groups in the molecule; and (E) a leveling agent. The plating solution is composed of a leveling agent composed of an alkanesulfonic acid or its salt containing 9 to 18 carbon atoms in the molecule; it does not use an aromatic carbonyl compound (benzylideneacetone, cinnamic acid, cinnamaldehyde, benzaldehyde, etc.) as a leveling agent, does not replenish the leveling agent for a long time during electroplating, can form a plated film uniformly and densely, and can make the plated film smooth. In actual operation, since the solubility of alkanesulfonic acid or its salt containing 9 to 18 carbon atoms is often poor, it is necessary to add another co-solvent to dissolve it, which increases the complexity of the plating solution. Moreover, such alkanesulfonic acid or its salt produces too much foam during operation and is prone to form voids during electroplating. Moreover, in the examples and comparative examples, the current density used is only 4ASD.

[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, and contains a specific sulfide compound in a range of 0.25 moles or more and 10 moles or less relative to 1 mole of silver in the water-soluble silver compound. In order to stably dissolve the silver compound in the Sn-Ag alloy plating solution, a sulfur-containing compound such as a heterocyclic compound or a sulfide compound having a mercapto group is added as a complexing agent to form a silver complex. Even if the plating solution is used or stored for a long time, it is difficult for silver to precipitate in the plating solution as a metal or an insoluble salt, and the Sn-Ag alloy plating solution can stably form a Sn-Ag alloy film. However, the current density mentioned in the embodiments and comparative examples is only 5ASD.

[0006] JP2022063889A provides a tin or tin alloy plating solution that suppresses the generation of voids in the bump under a current density in a wide range of 2ASD-14ASD, and a method for forming a bump using the solution. The inventors conducted in-depth research and found that by adding polypropylene glycol with a specific mass average molecular weight to the plating solution at a specific mass ratio, the generation of voids in the bump can be suppressed over a wide current density range. The first aspect includes a soluble salt (A), which contains at least a stannous salt, an acid or its salt (B) selected from an organic acid and an inorganic acid, and a surfactant (C). A plating solution, the plating solution contains polypropylene glycol, the content of which is 0.05g / L-5g / L, and the mass average molecular weight of the polypropylene glycol is 610-740. The second aspect is an invention according to the first aspect, wherein the surfactant (C) is a nonionic surfactant condensed from polyoxyethylene (EO) and polyoxypropylene (PO), and is a tin or tin alloy plating solution. The third aspect is to use the tin or tin alloy plating solution of the first aspect or the second aspect to form a tin or tin alloy plating deposit layer, which will become a plurality of bump precursors, on a substrate.

[0007] CN104032337A provides a tin alloy plating solution, which has high continuous stability, the co-deposition ratio of tin and alloy metal caused by the change of current density changes very little and basically does not contain cyanide. The inventor's series of test results show that by mixing a peptide with a cysteine ​​residue into the plating solution, even if there are metal ions more inert than tin in the plating solution, the plating solution can be stably used for a long time, and the plating solution can obtain a substantially unchanged co-deposition ratio of tin and metal ions relative to an increase or decrease in current density. The current used in the tin alloy plating solution can be a direct current or a pulse current. The current density is preferably 0.5-10A / dm 2 In the range of 1-8A / dm 2 .

[0008] JP11256390A relates to a tin-silver alloy electroplating solution for plating tin-silver alloy. The plating solution is used for joining electronic components, solder joint parts during installation, surface treatment of lead frame printed circuit boards, etc. It is believed that in all conventional tin-silver alloy electroplating solutions, the composition of the electroplated product varies greatly with the current density. For example, 2ASD has a silver content of 3-5% (weight) at a higher current density, but at a lower current density, the silver content increases rapidly to 15-25% (weight), which is more than several times the increase. However, the patent application dissolves the silver compound in the tin plating solution to form metallic silver particles with a particle size of about 5nm, which do not condense or settle, and are dispersed and stably present in the plating bath. Then, during the subsequent electroplating, it is mixed in the tin plating layer to form a tin-silver alloy plating layer. The temperature range of the plating bath of the invention is 20°C to 70°C, preferably 30°C to 60°C, and the cathode current density is 0.1-10ASD, more preferably 0.1-5.0ASD.

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

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

[0011] CN106757212A discloses a tin-silver alloy electroplating solution for wafer-level packaging, the solution comprising the following concentrations of components: 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 additives; the current density of the tin-silver alloy solution during electroplating is between 1-10ASD, and the temperature is between 15-35°C. The invention discloses that the solution comprises methanesulfonic acid, tin ions, silver ions, silver ion chelating agent and organic additives, and the current density during electroplating is between 1-10ASD, and the temperature is between 15-35°C; the above components are electroplated to form a tin-silver alloy solution, and the electroplating tin-silver plating solution is used to replace the traditional electroplating pure tin solution, solves the problem that the existing pure tin bumps are prone to produce tin whiskers, can effectively prevent the shortcomings of tin whiskers produced by the pure tin coating, and further improves the reliability of electronic products.

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

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

[0014] In order to overcome the problem of low electroplating current density in the prior art, the present invention provides a tin-silver alloy electroplating solution and its preparation method and application, and an electroplating method. The available current density of the electroplating solution during electroplating can reach 25ASD, the electroplating efficiency is high, and the tin-silver alloy bumps are uniform. After the bumps are reflowed, the proportion of voids is small and no collapse occurs.

[0015] In order to achieve the above-mentioned object, the first aspect of the present invention provides a tin-silver alloy electroplating solution, 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; The first surfactant is at least one selected from linear alkylphenol polyethers, linear alkylphenol polyether esters and salts thereof, aromatic phenol polyethers, aromatic phenol polyether esters, styrylphenol polyethers and EO-PO-EO block copolymers with a weight average molecular weight of 2000-4000Da; The second surfactant is a polyol; The third surfactant is a cationic surfactant and / or an amphoteric surfactant; The fourth surfactant is thiopolyoxyethylene ether; 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.

[0016] The second aspect of the present invention provides a method for preparing the tin-silver alloy electroplating solution provided by the first aspect of the present invention, the method comprising 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.

[0017] The third aspect of the present invention provides a use of the tin-silver alloy electroplating solution provided by the first aspect of the present invention in electroplating.

[0018] The fourth aspect of the present invention provides a method for electroplating using the tin-silver alloy electroplating solution provided by the first aspect of the present invention, wherein the current density of the electroplating is 1-25 ASD.

[0019] The beneficial effects of the present invention are: The available current density of the electroplating solution provided by the present invention can reach 25ASD during electroplating, the electroplating efficiency is high, and the tin-silver alloy bumps obtained by electroplating are uniform, the void ratio is small after the bumps are reflowed, and no collapse occurs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 are photos of the coating appearance, wherein (a) is a photo of the coating appearance obtained in Example 1, (b) is a photo of the coating appearance obtained in Comparative Example 1, (c) is a photo of the coating appearance obtained in Comparative Example 2, (d) is a photo of the coating appearance obtained in Comparative Example 3, (e) is a photo of the coating appearance obtained in Comparative Example 4, (f) is a photo of the coating appearance obtained in Comparative Example 5, and (g) is a photo of the coating appearance obtained in Comparative Example 6; Figure 2 The scanning electron microscope image of the bump obtained by the electroplating solution of Example 2 before reflow; Figure 3 The scanning electron microscope image of the front section of the bump reflow obtained by the electroplating solution of Example 2; Figure 4 This is a scanning electron microscope image of the bumps obtained by the electroplating solution of Example 2 after reflow; Figure 5 The scanning electron microscope image of the cross section of the bump after reflow obtained by the electroplating solution of Example 2; Figure 6The X-Ray CT image of the bump after reflow obtained by the electroplating solution of Example 1; Figure 7 The X-Ray CT image of the bump after reflow obtained by the electroplating solution of Comparative Example 3; Figure 8 The X-Ray CT image of the bump after reflow obtained by the electroplating solution of Comparative Example 4; Fig. 9 This is an X-Ray CT image of the bump after reflow obtained from the electroplating solution of Comparative Example 6. DETAILED DESCRIPTION

[0021] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0022] In the present invention, ASD refers to ampere per square decimeter, i.e. A / dm 2 .

[0023] The first aspect of the present invention provides a tin-silver alloy electroplating solution, the electroplating solution comprising 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 comprising a first surfactant, a second surfactant, a third surfactant and a fourth surfactant; The first surfactant is at least one selected from linear alkylphenol polyethers, linear alkylphenol polyether esters and salts thereof, aromatic phenol polyethers, aromatic phenol polyether esters, styrylphenol polyethers and EO-PO-EO block copolymers with a weight average molecular weight of 2000-4000Da; The second surfactant is a polyol; The third surfactant is a cationic surfactant and / or an amphoteric surfactant; The fourth surfactant is thiopolyoxyethylene ether; 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.

[0024] 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.

[0025] The above four surfactants work together to increase the available current density of the electroplating solution provided by the present invention during electroplating, improve the electroplating efficiency, and the tin-silver alloy bumps obtained by electroplating are uniform, the proportion of voids after the bumps are reflowed is small, and no collapse occurs.

[0026] In the present invention, the EO value has the conventional meaning in the art, that is, the molar amount of -CH2CH2O- fragments contained per mole of polymer molecules.

[0027] For the first surfactant: 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 salt, phenol polyoxyethylene ether, distyrylphenol polyoxyethylene ether and tristyrylphenol polyoxyethylene ether.

[0028] Preferably, the EO value of the first surfactant is 5-25.

[0029] For the second surfactant: According to the present invention, preferably, the polyol is at least one of polyethylene glycol (PEG), polypropylene glycol (PPG) and EO-PO-EO block copolymer.

[0030] Preferably, the weight average molecular weight of the second surfactant is 200-2000 Da.

[0031] More preferably, PEG is selected from at least one of PEG 200-2000, for example, PEG 200, PEG 400, PEG 600, PEG 1000, PEG 1500, or PEG 2000.

[0032] More preferably, the PPG is selected from at least one of PPG 400-1000, for example, it may be PPG 400, PPG 600, PPG 800, or PPG 1000.

[0033] More preferably, the EO-PO-EO block copolymer is selected from at least one of polyethylene oxide-polypropylene oxide alcohol, polyoctanediol-polypropylene oxide ether and polyvinyl alcohol-polypropylene oxide alcohol.

[0034] For the third surfactant: According to the present invention, preferably, the third surfactant is selected from C 12 -C 18 Alkyl trimethyl ammonium chloride, C 12 -C 18 Alkyl dimethyl benzyl ammonium chloride, C 12 -C 18 Alkyltrimethylammonium bromide, C 12 -C 18 Alkyl dimethyl benzyl ammonium bromide, C 12 -C 18 At least one of alkyltrimethylammonium p-toluenesulfonate, lauryl dimethylamine oxide, betaine citrate and 3-sulfopropyltetradecyl dimethyl betaine.

[0035] For the fourth surfactant: According to the present invention, preferably, the fourth surfactant is C 12 -C 18 Alkyl mercaptan polyoxyethylene ethers and / or thiodiglycol ethoxylates; Preferably, the EO value of the fourth surfactant is 5-25.

[0036] 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 dodecyl dimethyl benzyl ammonium bromide, and the fourth surfactant is thiodiglycol ethoxylate (EO=10).

[0037] 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.

[0038] According to a preferred embodiment of the present invention, the content of the composite surfactant in the electroplating solution is 50-150 g / L.

[0039] The present invention does not particularly limit the specific type of the soluble stannous salt, and those skilled in the art can routinely select. 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 fluoroborate.

[0040] According to a preferred embodiment of the present invention, the content of soluble stannous salt in the electroplating solution is 30-150 g / L in terms of metal ions.

[0041] In the present invention, when the content of the soluble stannous salt in the electroplating solution is within the above range, the precipitation of tin can be further promoted, while the electroplating solution can maintain a moderate viscosity to avoid voids in the plating layer.

[0042] More preferably, the content of soluble stannous salt in the electroplating solution is 50-120 g / L, calculated as metal ions.

[0043] 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 routinely select it. 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.

[0044] According to the present invention, preferably, the content of soluble silver salt in the electroplating solution is 0.01-5 g / L in terms of metal ions.

[0045] 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 plating layer with a more suitable melting point can be obtained.

[0046] More preferably, the content of soluble silver salt in the electroplating solution is 0.5-3 g / L, and further preferably 1.5-2.5 g / L, calculated as metal ions.

[0047] The present invention does not particularly limit the specific type of the free acid, and those skilled in the art can routinely select. For example, the free acid can be at least one of soluble strong acids such as sulfuric acid, hydrochloric acid, alkyl sulfonic acid, aminosulfonic acid, and aryl sulfonic acid.

[0048] The present invention has no particular limitation on the specific type and content of the antioxidant, and those skilled in the art can make routine selections.

[0049] According to a specific embodiment of the present invention, the antioxidant can be a phenolic compound and its derivatives, such as phenol, dihydroquinone, benzyltriol, and 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, and gallic acid; it can be hydroxybenzenesulfonic acid, naphtholsulfonic acid and its derivatives, such as cresolsulfonic acid, naphtholsulfonic acid, 1-amino-2-naphthol-4-sulfonic acid, and 4-hydroxy-1-naphthalenesulfonic acid monosalt; it can be a flavonoid compound, such as flavones, flavonols, dihydroflavones and dihydroflavonols, chalcones, dihydrochalcones, aurones, anthocyanidins and flavanols.

[0050] According to the present invention, specifically, the content of the antioxidant in the electroplating solution is 0.5-5 g / L.

[0051] The present invention has no particular limitation on the specific type and content of the complexing agent, and those skilled in the art can make routine selections.

[0052] 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-hydroxyethylethylenediaminetriacetic acid, malic acid, and N-acetyl-L-histidine; the complexing agent can also be selected from at least one of sulfide compounds, thiol compounds, and sulfhydryl compounds, such as 4,4-dihydroxydiphenyl sulfide, 4,4-diaminodiphenyl sulfide, 2-hydroxyethyl ethyl sulfide, methylthioethanol, methylthioacetic acid, 3-methylthiopropanol, 3-methylthiopropionic acid, methylthiopyrimidine, pyridine, methylthiopyrazine, methylthiopyrimidine, thiodiglycol, 1-(2-dimethylaminoethyl)-1H-tetrazolyl-5-thiol, 3,6-dithia-1,8-octanediol, 3,6-dioxa-1,8-octanedithiol, 1-thioglycerol, thioglycolic acid, mercaptopropionic acid, mercaptoimidazole, thioproline, disulfide compounds such as 2,2'-disulfide dipyridine, dithiophene disulfide, bis(thiobenzoyl) disulfide, 4-amino-4H-1,2,4-triazole-3,5-dithiol, dithiodiacetic acid.

[0053] According to the present invention, specifically, the molar ratio of the complexing agent to the soluble silver salt calculated as silver ions is 2-10:1.

[0054] According to the present invention, preferably, the electroplating solution further comprises a brightener.

[0055] The present invention does not particularly limit the specific type and content of the brightener, and those skilled in the art can make conventional selections. According to a specific embodiment of the present invention, the brightener is selected from at least one of polyquaternary ammonium salts, polyvinyl pyrrolidone, polyethylene imine, benzylidene acetone, 2',3,4',5,7-pentahydroxyflavone, 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-4H-1-benzopyran-4-one, glutaraldehyde, cinnamaldehyde, anisaldehyde, and vanillin.

[0056] According to the present invention, specifically, the content of the brightener in the electroplating solution is 0.01-1 g / L.

[0057] The second aspect of the present invention provides a method for preparing the tin-silver alloy electroplating solution provided by the first aspect of the present invention, the method comprising 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.

[0058] The third aspect of the present invention provides a use of the tin-silver alloy electroplating solution provided by the first aspect of the present invention in electroplating.

[0059] The fourth aspect of the present invention provides a method for electroplating using the tin-silver alloy electroplating solution provided by the first aspect of the present invention, wherein the current density of the electroplating is 1-25 ASD.

[0060] According to the present invention, preferably, the method comprises 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.

[0061] The present invention will be described in detail below through examples. In the following examples, the silver content in the bumps is determined by X-ray fluorescence spectrometry (XRF); The void fraction after bump reflow was measured by X-ray computed tomography (X-Ray CT); The roughness Ra of the coating surface was measured using a Keyence laser microscope. The definition of Ra was based on GB / T 3505-2009. The content of each substance in the plating solution is calculated by the amount of material added.

[0062] Unless otherwise specified, all reagents and raw materials were purchased from commercial sources.

[0063] Examples 1-15 and Comparative Examples 1-6 Stannous methanesulfonate, silver methanesulfonate, methanesulfonic acid, catechol, hydroquinone, gluconic acid, 3,6-dithia-1,8-octanediol, 2,2'-disulfide dipyridine and benzyl acetone are added into water and stirred to mix, and then a first surfactant, a second surfactant, a third surfactant and a fourth surfactant are added and stirred to mix to obtain a tin-silver alloy electroplating solution.

[0064] The stannous content in the plating 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'-dithiodipyridine content is 1 g / L, the benzyl acetone content is 0.1 g / L, and the pH value of the plating solution is 0.

[0065] The mass ratio of the four surfactants and the total content of the surfactants in the electroplating solution are shown in Table 1.

[0066] Table 1

[0067] Table 1 (continued)

[0068] Table 1 (continued)

[0069] Test Example 1 The titanium-based platinum coating was used as the anode and the copper sheet of 100 mm × 65 mm was used as the cathode. The copper sheet was subjected to electrolytic degreasing, cleaning, acid activation, and cleaning in sequence. The anode and cathode were placed in a Hull cell, and 250 mL of the electroplating solution obtained in the above embodiments and comparative examples were added respectively. A 5A direct current was passed for 5 minutes, and the appearance of the coating within the range of 1-25 ASD was observed, and the roughness Ra of the coating surface was measured. The results are shown in Table 2.

[0070] Table 2

[0071] Figure 1 are photos of the coating appearance, wherein (a) is a photo of the coating appearance obtained in Example 1, (b) is a photo of the coating appearance obtained in Comparative Example 1, (c) is a photo of the coating appearance obtained in Comparative Example 2, (d) is a photo of the coating appearance obtained in Comparative Example 3, (e) is a photo of the coating appearance obtained in Comparative Example 4, (f) is a photo of the coating appearance obtained in Comparative Example 5, and (g) is a photo of the coating appearance obtained in Comparative Example 6.

[0072] It can be seen that the coating obtained by the electroplating solution of Example 1 has a uniform and fine appearance without any abnormality; The electroplating solution of Comparative Example 1 resulted in large-area scorching at high potential and poor coverage at low potential; The coating obtained by the electroplating solution of Comparative Example 2 is slightly black in color and has a high silver content; The plating layer obtained by the electroplating solution of Comparative Example 3 cannot deposit tin-silver alloy in the low potential range, and serious leakage plating; The color of the coating test piece obtained by the electroplating solution of Comparative Example 4 is overall black; The coating obtained from the electroplating solution of Comparative Example 5 was burnt due to high potential; The plating layer obtained by the electroplating solution of Comparative Example 6 was rough.

[0073] Application Examples The titanium-based platinum coating is used as the anode, and the wafer pattern piece is used as the cathode. The wafer pattern piece is a silicon-based copper-coated wafer, and is 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 single chip units (DIEs), each of which contains 1351 small holes with a diameter of 85 μm and a depth of 80 μm. The anode and cathode are placed in a cubic small tank with a volume of 500 mL, and 500 mL of the plating solution obtained in the above embodiments and comparative examples are added respectively. The power is applied at 1 ASD for 60 s, 4 ASD for 360 s, and 25 ASD for 180 s, and 50 μm tin-silver alloy bumps are plated in the small holes, and then the photoresist is removed.

[0074] The wafer graphic piece with the photoresist removed is heated to 100°C at a rate of 2°C / s, maintained for 60s, heated to 200°C at a rate of 2°C / s, maintained for 100s, heated to 240°C at a rate of 2°C / s, maintained for 120s, and then naturally cooled to room temperature to obtain the reflowed bumps.

[0075] Test Example 2 The morphology of the bumps before and after reflow was observed using a scanning electron microscope.

[0076] Figure 2 This is a scanning electron microscope image of the bump obtained by the electroplating solution of Example 2 before reflow, with an acceleration voltage of 10 kV, a focal length of 10.9 mm, a magnification of 200 times, and a secondary electron detector as the receiving signal probe; Figure 3 This 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; 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; 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.

[0077] 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.

[0078] 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.

[0079] Table 3

[0080] NA means not applicable or no data.

[0081] Figure 6 The X-Ray CT image of the bump after reflow obtained by the electroplating solution of Example 1; Figure 7 The X-Ray CT image of the bump after reflow obtained by the electroplating solution of Comparative Example 3; Figure 8 The X-Ray CT image of the bump after reflow obtained by the electroplating solution of Comparative Example 4; Fig. 9This is an X-Ray CT image of the bump after reflow obtained from the electroplating solution of Comparative Example 6.

[0082] 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.

[0083] From the results in Table 2 and Table 3, it can be found that the available current density during electroplating of the electroplating solution provided by the present invention can reach 25ASD, the electroplating efficiency is high, and the tin-silver alloy coating obtained by electroplating is uniform and fine, with low roughness and appropriate silver content. The proportion of voids after the bump reflow is small, and no collapse occurs.

[0084] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to 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 first surfactant is selected from at least one of linear alkylphenol polyethers, linear alkylphenol polyether esters and salts thereof, aromatic phenol polyethers, aromatic phenol polyether esters and styrylphenol polyethers; The second surfactant is a polyol; The third surfactant is a cationic surfactant and / or an amphoteric surfactant; The fourth surfactant is thiopolyoxyethylene ether; 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.

2. The electroplating solution according to claim 1, characterized in that The first surfactant is selected from at least one of cardanol polyoxyethylene ether, cardanol polyoxyethylene ether sulfate and its salt, phenol polyoxyethylene ether, distyrylphenol polyoxyethylene ether and tristyrylphenol polyoxyethylene ether; and / or, the second surfactant is selected from at least one of polyethylene glycol, polypropylene glycol and EO-PO-EO block copolymer; And / or, the third surfactant is selected from C 12 -C 18 Alkyl trimethyl ammonium chloride, C 12 -C 18 Alkyl dimethyl benzyl ammonium chloride, C 12 -C 18 Alkyl trimethyl ammonium bromide, C 12 -C 18 Alkyl dimethyl benzyl ammonium bromide, C 12 -C 18 At least one of alkyltrimethylammonium p-toluenesulfonate, lauryl dimethylamine oxide, betaine citrate and 3-sulfopropyltetradecyl dimethyl betaine; And / or, the fourth surfactant is C 12 -C 18 Alkyl mercaptan polyoxyethylene ether and / or thiodiglycol ethoxylate.

3. The electroplating solution according to claim 2, 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.

4. 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.

5. 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.

6. The electroplating solution according to claim 1 or 2, characterized in that: The content of soluble stannous salt in the electroplating solution is 30-150 g / L in terms of metal ions; And / or, the content of soluble silver salt in the electroplating solution is 0.01-5 g / L in terms of metal ions.

7. 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.

8. A method for preparing the tin-silver alloy electroplating solution according to any one of claims 1 to 7, 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.

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

10. A method for electroplating using the tin-silver alloy electroplating solution according to any one of claims 1 to 7, characterized in that: The current density of the electroplating is 1-25 ASD.

11. The method according to claim 10, 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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