Tin-Silver Alloy Electroplating Solution, Its Preparation Method and Application

Abstract

The present invention relates to the field of electroplating, and discloses a tin-silver alloy electroplating solution, a preparation method and an application thereof. The electroplating solution comprises a soluble stannous salt, a soluble silver salt, a compound defoamer, an anti-coking agent, free acid, an antioxidant, a complexing agent and a solvent. The compound defoamer comprises a first defoamer and a second defoamer. The first defoamer is selected from naphthol sulfonic acid, and the second defoamer is selected from naphthol ether. The molar ratio of the first defoamer to the second defoamer is 1:1-4. The tin-silver alloy electroplating solution provided by the present invention comprises a compound defoamer prepared by compounding naphthol sulfonic acid and naphthol ether, which can effectively prevent foam formation and simultaneously destroy the formed foam, thereby avoiding the appearance of voids in the tin-silver alloy bumps after reflow. In addition, the compound defoamer has good water solubility and a high cloud point, and will not cause the electroplating solution to become turbid at a higher temperature, which can avoid affecting the normal use of the electroplating solution.

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. Background Art

[0002] Wafer bump plating is mainly connected by electric welding, which has high temperature requirements. Pure metals cannot meet this requirement, but alloys can meet higher welding temperatures, so alloy plating is mainly used. Currently, tin-lead alloys and tin-silver alloys are mainly used, with a small amount of tin-indium alloys, tin-copper alloys, tin-silver-copper alloys, etc. From the perspective of solderability, wafer bump plating uses welding plating, which has high requirements for the solderable temperature range. The solderable temperature of tin-silver alloy is 200-250℃, which has a good match with the solderable temperature.

[0003] The mainstream tin-silver electroplating solution on the market currently uses a current density of about 1-10ASD. When the tin-silver electroplating solution continues to work at a medium-to-high current density, a large number of bubbles will be generated in the plating solution due to the occurrence of hydrogen evolution at the cathode and oxygen evolution at the anode. If the defoaming ability or foam suppression ability of the plating solution is poor, these generated bubbles cannot be dissipated in time and are enriched in large quantities on the surface and in the plating solution. This will cause the plating solution to overflow the electroplating tank of the machine and cause pollution to the machine and the working environment. In addition, when these generated bubbles cannot be dissipated in time, they will be mixed in the electroplating coating during the electroplating process. After reflow, these bubbles in the coating will cause void problems and reduce the yield rate. For example, as disclosed in JP11256390A, since the precious metal component (silver) is preferentially precipitated at low current density, the silver content increases sharply at locations where the current density is low and cannot be controlled. As a result of this phenomenon, the current density becomes uneven on the uneven surface to be plated, and the alloy composition of the plated film becomes uneven, making it difficult to control the physical properties of the film, such as solderability. In addition, when using insoluble materials such as platinum, platinum-plated titanium, titanium coated with precious metal oxides, carbon, etc. as anodes, the following problems will occur: (1) divalent tin ions are oxidized on the anode and tetravalent tin ions accumulate in the plating solution; (2) a large amount of indelible foam layer will appear on the anode, which will affect the conductivity of the plating solution and increase the voltage, that is, when an insoluble anode is used, there will be a problem of reduced current efficiency. In addition, when a soluble anode is used, there is also the problem of silver displacement and deposition on the surface of the tin electrode. In order to solve the electroplating problem caused by high foam, JP11229174A discloses a low-foaming Sn or Sn-Pb alloy electroplating solution, but it can only be applied to pure tin or tin-lead alloy plating solution systems. Therefore, in view of the above technical problems, it is necessary to provide a low-foaming tin-silver alloy electroplating solution.

[0004] Generally speaking, in a high-speed electroplating tin-silver alloy plating solution, in order to ensure the normal operation of the plating solution at high current density, cationic surfactants such as ester-based quaternary ammonium salts or dialkyl and trialkyl ammonium salts are added to the plating solution to inhibit the deposition rate of stannous ions at high current density, thereby preventing the occurrence of burning and powdering problems at high current density. However, this type of cationic surfactant often makes the plating solution more prone to generating bubbles, and these generated bubbles will not dissipate in a short time. If some non-ionic surfactants are added to inhibit bubbles, these non-ionic surfactants often have poor solubility and low turbidity, and adding them to the plating solution will cause the problem of turbidity of the plating solution, affecting the normal use of the plating solution. In addition, TW202202661A discloses that it uses betaine-based amphoteric surfactants, and a large amount of foam is likely to appear during electroplating. If too much foam is generated during electroplating, voids will appear in the tin-silver alloy bumps after reflow, which will further affect subsequent functional problems such as solderability and uniformity. Summary of the Invention

[0005] In order to overcome the problem that the tin-silver alloy electroplating solution in the prior art is prone to generating a large amount of foam during electroplating, resulting in voids in the tin-silver alloy bumps obtained by electroplating after reflow, the present invention provides a tin-silver alloy electroplating solution, its preparation method and application. The tin-silver alloy electroplating solution contains a composite defoaming agent composed of a complex of naphthol sulfonic acid and naphthol ether, which can effectively prevent foam formation and simultaneously destroy the formed foam, thereby avoiding the appearance of voids in the tin-silver alloy bumps after reflow.

[0006] In addition, the composite defoaming agent has good water solubility and a high cloud point, and will not cause turbidity of the electroplating solution at a higher temperature, and can avoid affecting the normal use of the electroplating solution.

[0007] In order to achieve the above object, the first aspect of the present invention provides a tin-silver alloy electroplating solution, which contains a soluble stannous salt, a soluble silver salt, a composite defoaming agent, an anti-burning agent, free acid, an antioxidant, a complexing agent and a solvent. The composite defoaming agent contains a first defoaming agent and a second defoaming agent;

[0008] The first defoaming agent is selected from naphthol sulfonic acid, and the second defoaming agent is selected from naphthol ether;

[0009] The molar ratio of the first defoaming agent to the second defoaming agent is 1:1 - 4.

[0010] The second aspect of the present invention provides a preparation method of the tin-silver alloy electroplating solution provided in the first aspect of the present invention. The method includes: in the presence of a solvent, mixing a soluble stannous salt, a soluble silver salt, a composite defoaming agent, free acid, an antioxidant, a complexing agent, an anti-burning agent and an optional brightening agent to obtain the tin-silver alloy electroplating solution.

[0011] The third aspect of the present invention provides an application of the tin-silver alloy electroplating solution provided by the first aspect of the present invention in electroplating.

[0012] The beneficial technical effects of the present invention are as follows:

[0013] The tin-silver alloy electroplating solution provided by the present invention contains a composite defoamer composed of a compound of naphthol sulfonic acid and naphthol ether, which can effectively prevent foam formation and simultaneously destroy the formed foam, thereby avoiding the appearance of voids in the tin-silver alloy bumps after reflow.

[0014] In addition, the composite defoamer has good water solubility and a high cloud point, and will not cause the electroplating solution to become turbid at a relatively high temperature, which can avoid affecting the normal use of the electroplating solution. Description of the Drawings

[0015] Figure 1 X-Ray CT diagram of the tin-silver alloy bumps after reflow obtained from the electroplating solution of Example 1;

[0016] Figure 2 X-Ray CT diagram of the tin-silver alloy bumps after reflow obtained from the electroplating solution of Comparative Example 1;

[0017] Figure 3 Section scanning electron microscope diagram of the tin-silver alloy bumps after reflow obtained from the electroplating solution of Example 1;

[0018] Figure 4 Section scanning electron microscope diagram of the tin-silver alloy bumps after reflow obtained from the electroplating solution of Comparative Example 1. Detailed Description of the Invention

[0019] The endpoints and any values within the ranges disclosed herein 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, the endpoints of each range, between the endpoints of each range, between the endpoints 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.

[0020] The first aspect of the present invention provides a tin-silver alloy electroplating solution, the electroplating solution contains a soluble stannous salt, a soluble silver salt, a composite defoamer, an anti-coking agent, a free acid, an antioxidant, a complexing agent and a solvent, and the composite defoamer contains a first defoamer and a second defoamer;

[0021] The first defoamer is selected from naphthol sulfonic acid, and the second defoamer is selected from naphthol ether;

[0022] The molar ratio of the first defoamer to the second defoamer is 1:1-4.

[0023] The tin-silver alloy electroplating solution provided by the present invention contains a composite defoamer composed of a compound of naphthol sulfonic acid and naphthol ether, which can effectively prevent foam formation and simultaneously destroy the formed foam, thereby avoiding voids in the tin-silver alloy bumps after reflow.

[0024] According to the present invention, preferably, the molar ratio of the first defoamer to the second defoamer is 1:1.5 - 3.

[0025] According to a preferred embodiment of the present invention, the first defoamer is selected from at least one of the substances represented by formula (I):

[0026] (I)

[0027] Wherein, R 1 -R 8 Each independently selected from H, a halogen atom, a substituted or unsubstituted C1-C 20 alkyl group, a C2-C 20 alkenyl group, a C4-C 20 dienyl group, a C3-C 20 cycloalkyl group, a C3-C 20 cycloalkenyl group, a C4-C 20 cyclodienyl group, an alkoxy group, an amino group, a nitro group, a nitroso group, an azo group, a diazo group, an anilino group, a hydroxyl group, and -SO3M x wherein M is H or a first metal ion, and x is a stoichiometric number that satisfies charge balance;

[0028] R 1 -R 8 has at least one hydroxyl group and at least one -SO3M x .

[0029] In the present invention, there is no particular limitation on the valence state of the first metal ion, and the first metal ion can be monovalent, divalent or a higher valence state. For example, when M is a monovalent metal ion (Na + , K + , etc.), to satisfy charge balance, x = 1; when M is a divalent metal ion (Mg 2+ , Ca 2+ , etc.), to satisfy charge balance, x = 1 / 2.

[0030] Specifically, R 1 -R 8 Each independently selected from H, a halogen atom, a substituted or unsubstituted C1-C6 alkyl group, a C2-C6 alkenyl group, a C4-C8 dienyl group, a C3-C8 cycloalkyl group, a C3-C8 cycloalkenyl group, a C4-C8 cyclodienyl group, an alkoxy group, an amino group, a nitro group, a nitroso group, an azo group, a diazo group, an anilino group, a hydroxyl group, and -SO3M x wherein one of them.

[0031] According to a preferred embodiment of the present invention, the second defoaming agent is selected from at least one of the substances represented by formula (II):

[0032] (II)

[0033] wherein, R 9 is a C1-C6 alkylene group, R 10 is -N y or a C1-C6 alkyl group, N is H or a second metal ion, and y is a stoichiometric number that satisfies charge balance.

[0034] In the present invention, there is no particular limitation on the valence state of the second metal ion, and the second metal ion can be monovalent, divalent or a higher valence state. For example, when N is a monovalent metal ion (such as Na + , K + , etc.), to satisfy charge balance, y = 1; when N is a divalent metal ion (such as Mg 2+ , Ca 2+ , etc.), to satisfy charge balance, y = 1 / 2.

[0035] According to the present invention, more preferably, the first defoaming agent is selected from at least one of naphthol ethoxysulfonic acid, 1-naphthol-5-sulfonic acid, 1-amino-2-naphthol-4-sulfonic acid, 2-nitroso-1-naphthol-4-sulfonic acid, 2-diazo-1-naphthol-4-sulfonic acid, 7-anilino-1-naphthol-3-sulfonic acid, 2-naphthol-6,8-disulfonic acid, 6-nitro-1-amino-2-naphthol-4-sulfonic acid, and their salts.

[0036] When the first defoaming agent is naphthol ethoxysulfonic acid, in R 1 -R 8 : R 1 is an ethoxy group, R 2 is a hydroxyl group, R 4 is a sulfonic acid group, and the rest are H.

[0037] When the first defoaming agent is 1-naphthol-5-sulfonic acid, in R 1 -R 8 : R 4 is a sulfonic acid group, R 8 is a hydroxyl group, and the rest are H.

[0038] When the first defoaming agent is 1-amino-2-naphthol-4-sulfonic acid, in R 1 -R 8 : R 1 is an amino group, R 2 is a hydroxyl group, R 4 is a sulfonic acid group, and the rest are H.

[0039] When the first defoamer is 2-nitroso-1-naphthol-4-sulfonic acid, R 1 -R 8 In: R 1 is a hydroxyl group, R 2 is a nitroso group, R 4 is a sulfonic acid group, and the rest are H.

[0040] When the first defoamer is 2-diazo-1-naphthol-4-sulfonic acid, R 1 -R 8 In: R 5 is a sulfonic acid group, R 7 is a diazo group, R 8 is a hydroxyl group, and the rest are H.

[0041] When the first defoamer is 7-anilino-1-naphthol-3-sulfonic acid, R 1 -R 8 In: R 4 is an anilino group, R6 is a hydroxyl group, R 8 is a sulfonic acid group, and the rest are H.

[0042] When the first defoamer is 2-naphthol-6,8-disulfonic acid, R 1 -R 8 In: R 3 is a hydroxyl group, R 6 and R 8 are sulfonic acid groups, and the rest are H.

[0043] When the first defoamer is 6-nitro-1-amino-2-naphthol-4-sulfonic acid, R 1 -R 8 In: R 3 is a nitro group, R 5 is an amino group, R 6 is a hydroxyl group, R 8 is a sulfonic acid group, and the rest are H.

[0044] In the present invention, when the first defoamer is selected from the above more preferred range, it can further improve the stability of stannous ions while suppressing and eliminating foam, and avoid the oxidation of stannous ions to stannic ions, thereby further improving the stability and service life of the plating solution.

[0045] Further preferably, the first defoamer is selected from at least one of naphthol ethoxysulfonic acid, 1-naphthol-5-sulfonic acid, 1-amino-2-naphthol-4-sulfonic acid, and 2-naphthol-6,8-disulfonic acid.

[0046] According to the present invention, more preferably, the second defoamer is selected from at least one of ethyl 1-naphthyloxyacetate, methyl 2-(1-naphthyloxy)propionate, ethyl 2-(1-naphthyloxy)propionate, and tert-butyl 2-(1-naphthyloxy)propionate.

[0047] When the second defoamer is ethyl 1-naphthoxyacetate, R 9 is methylene, and R 10 is ethyl.

[0048] When the second defoamer is methyl 2-(1-naphthyloxy)propionate, R 9 is 1,2-ethylene, and R 10 is methyl.

[0049] When the second defoamer is ethyl 2-(1-naphthyloxy)propionate, R 9 is 1,2-ethylene, and R 10 is ethyl.

[0050] When the second defoamer is tert-butyl 2-(1-naphthyloxy)propionate (CAS: 1519509-92-2), R 9 is 1,2-ethylene, and R 10 is tert-butyl.

[0051] In the present invention, when the second defoamer is selected from the above more preferred range, it can further improve the foam suppression and defoaming effects without affecting the silver ion deposition rate.

[0052] Further preferably, the first defoamer is ethyl 1-naphthoxyacetate.

[0053] According to a preferred embodiment of the present invention, the content of the composite defoamer in the electroplating solution is 5 - 20 g / L.

[0054] In the present invention, when the content of the composite defoamer in the electroplating solution is within the above range, it can better inhibit foam formation and destroy the formed foam.

[0055] More preferably, the content of the composite defoamer in the electroplating solution is 8 - 15 g / L.

[0056] According to a specific embodiment of the present invention, the soluble stannous salt is selected from at least one of stannous methylsulfonate, stannous sulfate, and stannous fluoroborate.

[0057] According to a specific embodiment of the present invention, the soluble silver salt is selected from at least one of silver methylsulfonate, silver acetate, and silver sulfate.

[0058] According to a specific embodiment of the present invention, based on the metal ions, the content of the soluble stannous salt in the electroplating solution is 60 - 100 g / L, and the content of the soluble silver salt is 0.8 - 4 g / L.

[0059] More specifically, based on metal ions, the content of soluble stannous salt in the electroplating solution is 80 - 95 g / L, and the content of soluble silver salt is 1 - 3 g / L.

[0060] According to a specific embodiment of the present invention, the free acid is selected from at least one of methanesulfonic acid, sulfuric acid, and formic acid.

[0061] According to the present invention, specifically, the hydrogen ion concentration of the electroplating solution is 0.5 - 1.6 mol / L.

[0062] More specifically, the hydrogen ion concentration of the electroplating solution is 0.8 - 1.2 mol / L.

[0063] According to the present invention, specifically, the antioxidant is selected from at least one of catechol, hydroquinone, potassium hydroquinone monosulfonate, potassium hydroquinone sulfonate, 2 - naphthol - 7 - sulfonic acid, pyrogallol, antipyrine, hydroquinone, catechol sulfonic acid, resorcinol sulfonic acid, catechol, aminocatechol, potassium hydroquinone sulfonate, methyl hydroquinone, hydroquinone sulfonic acid, potassium hydroquinone sulfonate, ascorbic acid.

[0064] More specifically, the antioxidant is antipyrine.

[0065] According to the present invention, specifically, the content of antioxidant in the electroplating solution is 1 - 10 g / L.

[0066] More specifically, the content of antioxidant in the electroplating solution is 1 - 5 g / L.

[0067] According to the present invention, specifically, the complexing agent is selected from at least one of thiol compounds, thioether compounds, and thiourea compounds, such as 3,6 - dithia - 1,8 - octanediol, thiodiglycol, thiourea, 4,4’ - dihydroxydiphenyl sulfide, 3,6 - dithiaoctane - 1,8 - diol, thio - bis(triglyceride), 1,10 - diamino - 4,7 - dithiahexadecane, 4,7 - dithiahexadecane - 1,2,9,10 - tetraol, thio - bis(dodecaethylene glycol), thioethylene glycol, 4,7 - dithiahexadecane - 1,10 - diol, thio - bis(eicosylene glycol), 3,6 - dithiaoctane - 1,8 - diol, 1,10 - diamino - 4,7 - dithiadecane, thio - bis(dodecaethylene glycol), thio - bis(decaglycol), 4,7 - dithia - 1,10 - diol, dithio - bis(pentadecaethylene glycol), dithio - bis(decaglycerol), 1 - (2 - dimethylaminoethyl) - 5 - mercaptotetrazole, 1 - (m - sulfophenyl) - 5 - mercapto - 1H - tetrazole sodium salt, and octyldimethylethylammonium sulfate.

[0068] More specifically, the complexing agent is thiodiglycol.

[0069] According to the present invention, specifically, the molar ratio of the complexing agent to the soluble silver salt in terms of silver ions in the electroplating solution is 2-30:1.

[0070] More specifically, the molar ratio of the complexing agent to the soluble silver salt in terms of silver ions in the electroplating solution is 10-20:1.

[0071] According to a preferred embodiment of the present invention, the anti-coking agent is a cationic surfactant and / or an amphoteric surfactant.

[0072] More preferably, the anti-coking agent is selected from at least one of dodecyldimethylbenzylammonium chloride, cetyl dimethyl benzyl ammonium chloride, lauryldimethylamine oxide, dodecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, lauryl hydroxy sulfobetaine, lauryl sulfobetaine, stearyl sulfobetaine, cetyltrimethylammonium hydroxide, tetrabutylammonium hydroxide, tris(2-hydroxyethyl)methylammonium hydroxide, benzyltrimethylammonium hydroxide, polyoxyethylene bisphenol ether, polyoxyethylene phenyl ether, N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine, ethoxylated phenol, and ethoxylated bisphenol.

[0073] In the present invention, when the anti-coking agent is selected from the above range, it can better prevent coking during electroplating at a high current density, and at the same time refine the grains on the surface of the coating, thereby improving the overall uniformity of the coating.

[0074] More preferably, the anti-coking agent is selected from at least one of dodecyldimethylbenzylammonium chloride, cetyl dimethyl benzyl ammonium chloride, lauryldimethylamine oxide, lauryl hydroxy sulfobetaine, and dodecyldimethylbenzyl bromide.

[0075] According to the present invention, preferably, the content of the anti-coking agent in the electroplating solution is 2-10 g / L.

[0076] More preferably, the content of the anti-coking agent in the electroplating solution is 2-6 g / L.

[0077] According to a specific embodiment of the present invention, the electroplating solution further contains a brightening agent, and the brightening agent is selected from at least one of 1-acetyl-1-cyclohexene, 4-hexene-3-one, pentahydroxyflavone, benzalacetone, benzaldehyde, cinnamaldehyde, β-ionone, benzylideneacetone, benzoylacetone, benzylideneacetone, morin, and quercetin.

[0078] More specifically, the brightening agent is benzylideneacetone.

[0079] According to the present invention, specifically, the content of the brightening agent in the electroplating solution is 5-60 mg / L.

[0080] More specifically, the content of the brightener in the electroplating solution is 30 - 50 mg / L.

[0081] In the present invention, the solvent is preferably water, but the technical solution provided by the present invention does not exclude the applicability of non-aqueous solvents, such as polar organic solvents and ionic liquids.

[0082] 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, and the method includes: in the presence of a solvent, mixing a soluble stannous salt, a soluble silver salt, a compound defoamer, a free acid, an antioxidant, a complexing agent, an anti-coking agent, and an optional brightener to obtain the tin-silver alloy electroplating solution.

[0083] According to the specific embodiments of the present invention, the method includes the following steps:

[0084] (1) In the presence of a solvent, sequentially add a free acid, an antioxidant, a complexing agent, a soluble tin salt, and a soluble silver salt;

[0085] (2) Mix the solution obtained in step (1) with a compound defoamer, an anti-coking agent, and an optional brightener to obtain the electroplating solution.

[0086] The third aspect of the present invention provides an application of the tin-silver alloy electroplating solution provided by the first aspect of the present invention in electroplating.

[0087] The present invention will be described in detail below through examples.

[0088] In the following examples, the turbidity of the electroplating solution was measured by a Hach TL2310 turbidimeter using 90° scattered light, and the light source wavelength was 830 - 890 nm;

[0089] The proportion of voids after bump reflow was measured by X-ray computed tomography (X-Ray CT).

[0090] Unless otherwise specified, all reagents and raw materials are commercially available.

[0091] Examples and Comparative Examples

[0092] (1) At room temperature, sequentially add a free acid, an antioxidant, a complexing agent, a soluble tin salt, and a soluble silver salt to water, and stir for 30 s;

[0093] (2) Sequentially add a defoamer, an anti-coking agent, and an optional brightener to the solution obtained in step (1), and stir for 60 s to obtain the electroplating solution.

[0094] The specific types and contents of the above substances are shown in Table 1.

[0095] Table 1

[0096]

[0097] Table 1 (continued)

[0098]

[0099] Table 1 (continued)

[0100]

[0101] Table 1 (continued)

[0102]

[0103] Table 1 (continued)

[0104]

[0105] Test Example 1

[0106] Take 100 mL of the electroplating solutions obtained from the above-mentioned examples and comparative examples respectively, place them in a 1-L glass graduated cylinder, and place a catheter with an inner diameter of 5 mm in the graduated cylinder. The outlet of the catheter is about 5 mm away from the bottom of the graduated cylinder. Let it stand for 10 min. After there are no visible bubbles in the electroplating solution to the naked eye, pass air through the catheter at a flow rate of 0.5 L / min. When the height of the foam in the plating solution is observed to be stable and no longer rising, stop passing air and start timing simultaneously. Record the maximum graduated cylinder scale reached by the foam and the time elapsed until all visible bubbles are completely eliminated. The results are shown in Table 2.

[0107] Table 2

[0108]

[0109] Test Example 2

[0110] Take the electroplating solutions obtained from the above-mentioned examples and comparative examples respectively, place them in a constant temperature water bath at 55 °C and heat for 360 h, then observe the appearance of the electroplating solution and whether there is precipitation, and measure the turbidity of the electroplating solution with a turbidimeter. The results are shown in Table 3.

[0111] Table 3

[0112]

[0113] Test Example 3

[0114] Cut out a test piece of a pattern wafer with a seed layer of copper covered with photoresist from a 12-inch diameter wafer. The size of the test piece is 6.25 cm × 6.25 cm, and it contains a total of 9 chip units (DIE) of 3 × 3. The area of a single DIE is about 0.64 cm 2 . The thickness of the photoresist is 80 μm, the pore diameter is 85 μm, and the aperture ratio is 12%.

[0115] Take 500 mL of the electroplating solutions obtained in the above examples and comparative examples respectively, and perform electroplating in a constant temperature water bath at 30 °C according to the following segmented current density conditions:

[0116] The first stage: Use a current density of 1 ASD, the electroplating time is 1 min, and the stirring speed is 15 m / min;

[0117] The second stage: Use a current density of 4 ASD, the electroplating time is 8 min 45 s, and the stirring speed is 15 m / min;

[0118] The third stage: Use a current density of 7 ASD, the electroplating time is 37 s, and the stirring speed is 15 m / min;

[0119] The fourth stage: Use a current density of 7 ASD, the electroplating time is 8 min 20 s, and the stirring speed is 60 m / min to obtain tin-silver alloy bumps.

[0120] After electroplating, wash the test piece with deionized water and dry it; then, use a stripping solution to remove the photoresist on the surface. Perform a reflow treatment on the stripped test piece, specifically: in a nitrogen atmosphere, heat the test piece from room temperature to 200 °C at a rate of 2 °C / s and hold for 80 s; then heat it to 240 °C at a rate of 2 °C / s and hold for 110 s, and finally cool it naturally to room temperature. Use X-Ray CT to detect whether there are voids and the void ratio in the reflowed tin-silver alloy bumps, and the results are shown in Table 4.

[0121] Table 4

[0122]

[0123] Figure 1 、 Figure 2 are the X-Ray CT diagrams of the reflowed tin-silver alloy bumps obtained from the electroplating solutions of Example 1 and Comparative Example 1 respectively.

[0124] Figure 3 、 Figure 4 are the sliced scanning electron microscope diagrams of the reflowed tin-silver alloy bumps obtained from the electroplating solutions of Example 1 and Comparative Example 1.

[0125] It can be seen through Figures 1-4 that there are no voids in the reflowed tin-silver alloy bumps obtained from the electroplating solution of Example 1, while there are obvious voids in the reflowed tin-silver alloy bumps obtained from the electroplating solution of Comparative Example 1.

[0126] As can be seen from the results in Table 2-4, the compound defoamer provided by the present invention, which contains a compound of naphthol sulfonic acid and naphthol ether, can effectively prevent foam formation in the electroplating solution and at the same time destroy the formed foam, thereby avoiding the appearance of voids in the tin-silver alloy bumps after reflow.

[0127] In addition, the compound defoamer provided by the present invention has good water solubility and a high cloud point, and will not cause the electroplating solution to become turbid at a higher temperature, which can avoid affecting the normal use of the electroplating solution.

[0128] 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 also 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 defoamer, an anti-scorching agent, a free acid, an antioxidant, a complexing agent and a solvent, and the composite defoamer comprises a first defoamer and a second defoamer; The first defoamer is selected from naphthol sulfonic acid, and the second defoamer is selected from naphthol ether; The molar ratio of the first defoaming agent to the second defoaming agent is 1:1-4; The first defoaming agent is selected from at least one of naphthol ethoxy sulfonic acid, 1-naphthol-5-sulfonic acid, 1-amino-2-naphthol-4-sulfonic acid, 2-nitroso-1-naphthol-4-sulfonic acid, 2-diazo-1-naphthol-4-sulfonic acid, 7-anilino-1-naphthol-3-sulfonic acid, 2-naphthol-6,8-disulfonic acid, and 6-nitro-1-amino-2-naphthol-4-sulfonic acid; The second defoaming agent is selected from at least one of ethyl 1-naphthoxylate, methyl 2-(1-naphthoxy)propionate, ethyl 2-(1-naphthoxy)propionate and tert-butyl 2-(1-naphthoxy)propionate; The content of the composite defoamer in the electroplating solution is 5-20 g / L; The electroplating solution contains 60-100 g / L soluble stannous salt and 0.8-4 g / L soluble silver salt in terms of metal ions. The hydrogen ion concentration of the electroplating solution is 0.5-1.6 mol / L; The anti-scorching agent is at least one of dodecyl dimethyl benzyl ammonium chloride, lauryl dimethyl ammonium oxide, hexadecyl dimethyl benzyl ammonium chloride and lauryl hydroxysulfobetaine.

2. The electroplating solution according to claim 1, characterized in that The content of antioxidant in the electroplating solution is 1-10g / L; And / or, the molar ratio of the complexing agent to the soluble silver salt calculated as silver ions in the electroplating solution is 2-30:

1.

3. The electroplating solution according to claim 1 or 2, characterized in that: The content of the anti-scorch agent in the electroplating solution is 2-10 g / L.

4. The electroplating solution according to claim 1 or 2, characterized in that: The electroplating solution further comprises a brightener, wherein the brightener is selected from at least one of benzaldehyde, cinnamaldehyde, β-ionone, benzoyl acetone, benzyl acetone, morin and quercetin; And / or, the content of brightener in the electroplating solution is 5-60 mg / L.

5. A method for preparing the tin-silver alloy electroplating solution according to any one of claims 1 to 4, characterized in that: The method comprises: mixing soluble stannous salt, soluble silver salt, composite defoamer, free acid, antioxidant, complexing agent, anti-scorch agent and optional brightener in the presence of solvent to obtain the tin-silver alloy electroplating solution.

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

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