Tin electroplating bath and method for depositing tin or tin alloy on a substrate surface

Abstract

The invention relates to a tin electroplating bath comprising tin ions; titanium ions as a reducing agent suitable for reducing tin ions to metallic tin; and at least one compound selected from the group consisting of sulfite, dithiosulfonate, thiosulfate, tetra-thiosulfonate, polythiosulfonate, pyrosulfite, sulfide, disulfide, polysulfide, elemental sulfur or mixtures thereof. The invention further discloses a method for depositing tin or tin alloys on a substrate surface. The tin electroplating bath is particularly suitable for use in the electronics and semiconductor industry.

Description

Technical Field

[0001] This invention relates to a tin plating bath comprising tin ions and titanium ions as a reducing agent suitable for reducing the tin ions to metallic tin. The invention further relates to a method for depositing tin or a tin alloy on a substrate surface. The tin plating bath is particularly suitable for depositing tin or a tin alloy on at least one surface of a substrate, and is preferably used in the electronics and semiconductor industries. Background Technology

[0002] Deposits of tin and tin alloys on electronic components such as printed circuit boards, IC substrates, and semiconductor wafers are used in particular as solderable and adhesive coatings in subsequent manufacturing steps of such electronic components.

[0003] Tin and tin alloy deposits typically form on metal contact areas, such as contact pads and bump structures. These contact areas are usually made of copper or copper alloys. In cases where such contact pads are electrically contactable for depositing tin and tin alloy layers, these layers are deposited using conventional electroplating methods. However, in many cases, individual contact areas cannot be electrically contacted. In such cases, electroless plating is required. The method chosen in industry for electroless plating of tin and tin alloy layers has historically been immersion plating. The main disadvantage of immersion plating is the limited thickness of the tin or tin alloy deposit. Immersion plating is based on the exchange between tin ions and the copper contact area to be plated. With immersion plating of tin or tin alloy layers, the deposition rate decreases significantly with increasing tin layer thickness because the exchange between copper and tin is hindered by the growing tin layer.

[0004] In situations where a thicker tin or tin alloy layer is required and electrical connections cannot be provided, a self-catalytic electroless electroplating process is needed. The plating bath composition for self-catalytic tin or tin alloy plating includes a (chemical) reducing agent.

[0005] US 2005 / 077186 A1 discloses an acidic electrolytic tin plating bath comprising an aliphatic complexing agent having sulfide groups and amino groups attached to different carbon atoms. Furthermore, such sulfur compounds are used in electrolytic bronze plating (DE 10 2013226 297 B3 and EP 1 001 054 A2) and in electrolytic tin plating as described in CN 1804142 A and CN 103173807 A.

[0006] WO 2009 / 157334 A1 relates to an electroless tin plating bath that includes organic complexing agents and organic sulfides. However, the disclosed plating bath exhibits a rapid decrease in plating rate over time and results in a low overall plating rate (see comparative example in WO 2018 / 122058 A1). This is a major drawback of many tin plating baths known in the art, especially electroless tin plating baths.

[0007] US 8,801,844 B2 relates to a self-catalytic tin plating bath composition comprising water-soluble Sn. 2+ Ion source, water-soluble Ti 3+ An ion source and 1,10-phenanthroline and / or at least one 1,10-phenanthroline derivative as a stabilizing additive.

[0008] Typically, conventional tin plating baths exhibit plating behavior that begins with an extremely high plating rate, followed by a significant decrease over time. In some cases, the plating rate spikes within the first few minutes, then declines even more rapidly. This behavior is highly undesirable because it makes it extremely difficult to control plating results, such as the uniformity and thickness of the tin deposit.

[0009] The purpose of this invention

[0010] Therefore, the object of the present invention is to overcome the shortcomings of the prior art. Another object is to provide a tin plating bath that has an increased plating rate compared to the electroless tin plating baths known from the prior art.

[0011] Another objective is to provide a tin plating bath that has a constant plating rate over time.

[0012] Another objective is to provide a tin plating bath that is (sufficiently) stable and prevents plate-out (e.g., for at least 4 hours after replenishment or during use).

[0013] Another objective is to reduce the amount of compounds and / or reduce the amount of compounds in the tin plating bath. Summary of the Invention

[0014] The aforementioned objective is achieved through an electroless tin plating bath, which includes...

[0015] (a) Tin ions;

[0016] (b) Titanium ions, as a suitable reducing agent for reducing tin ions to metallic tin;

[0017] (c) At least one accelerator selected from the group consisting of: sulfites, dithiosulfinates, thiosulfates, tetrathiosulfates, polythiosulfates, metabisulfites, sulfides, disulfides, polysulfides, elemental sulfur and mixtures thereof;

[0018] (d) at least one complexing agent; and

[0019] (e) Optionally at least one hypophosphite

[0020] The pH value of the tin plating bath is 5 to 10.5, provided that if thiosulfate is included in the tin plating bath, then the upper limit of pH is less than 9.5.

[0021] The aforementioned objective is further achieved by using a tin plating bath according to the invention to deposit tin or a tin alloy on at least one surface of a substrate (preferably in the electronics and semiconductor industry) and a method for depositing tin or a tin alloy on at least one surface of at least one substrate, the method comprising the following steps:

[0022] (i) providing a substrate; and

[0023] (ii) Contacting at least one surface of the substrate with the inventive tin plating bath according to the invention, such that tin or a tin alloy is deposited on at least one surface of the substrate.

[0024] As shown in the examples below, it has been unexpectedly found that significantly higher plating rates can be achieved using the tin plating bath according to the invention (see, for example, Examples 1 to 10 of the invention compared with Comparative Examples C1 and C2).

[0025] Advantageously, the tin plating bath of the present invention exhibits no or minimal loss in plating rate over time. Even after several hours of using the tin plating bath of the present invention, a high and constant plating rate can still be observed after inserting a new (or rinsed) substrate into the tin plating bath. Independent research has found that the tin plating bath of the present invention can be used for many hours (some exceeding eight hours) without exhibiting precipitation and maintaining a high and constant plating rate throughout the process. Furthermore, the tin plating bath of the present invention allows for the formation of uniform tin or tin alloy deposits. If two or more surfaces of different sizes are plating simultaneously, the thickness of the tin or tin alloy deposit is non-dependent or has a very low dependence. When tin is deposited simultaneously on substrates of different sizes using a conventional plating bath, plating typically produces unevenly covered surfaces (especially in terms of the thickness of the tin or tin alloy deposit). The present invention overcomes the disadvantage of conventional tin plating baths, namely that larger surface areas typically produce thinner deposits compared to smaller surface areas.

[0026] Another advantage of the present invention is that the tin plating bath according to the invention exhibits a sufficiently high initial plating rate (e.g., after 5 minutes) and a sufficiently high plating rate during use.

[0027] Another advantage of this invention is that it provides a glossy tin deposit without the need for organic brighteners or surfactants. The tin deposit also does not contain visible, detectable defects such as burning or blistering. Detailed Implementation

[0028] Advantageously, compared with conventional tin plating baths known in the art, the tin plating bath of the present invention minimizes the loss of plating rate over time. Ideally, the tin plating bath of the present invention allows for a constant plating rate, at least for a certain period of time.

[0029] Tin plating baths that minimize the loss of plating rate over time, and ideally tin plating baths with a constant plating rate, allow for improved process control because the tin deposit thickness can be easily controlled. This eliminates the need for tedious optimization when a specific tin deposit thickness is required. Furthermore, tin deposits formed at a constant plating rate are more uniform (especially in terms of tin or tin alloy deposit thickness) compared to deposits from plating baths with different plating rates. Therefore, a tin plating bath with a constant plating rate is highly desirable.

[0030] The tin plating bath of the present invention comprises tin ions. Typical sources of tin ions are water-soluble tin salts or water-soluble tin complexes. Preferably, the tin ions are tin(II) ions (compared to tin(IV) ions) that facilitate reduction to their metallic state. More preferably, at least one source of tin ions is selected from the group consisting of: organic sulfonates of tin in the +II oxidation state, such as tin(II) methanesulfonate; tin(II) sulfate; tin(II) halides, such as tin(II) chloride, tin(II) bromide; tin(II) pyrophosphate; linear tin(II) polyphosphate; cyclic tin(II) polyphosphate; and mixtures thereof. Even more preferably, at least one source of tin ions is selected from the group consisting of other anions selected to avoid undesirable anions in tin or tin alloy plating: tin(II) chloride, tin(II) pyrophosphate, linear tin(II) polyphosphate, cyclic tin(II) polyphosphate; and mixtures thereof. Alternatively and more preferably, tin ions can be prepared by anodic dissolution of metallic tin.

[0031] The total concentration of tin ions in the tin plating bath of the present invention is preferably between 0.02 and 0.2 mol / L, more preferably between 0.04 and 0.15 mol / L, and even more preferably between 0.05 and 0.08 mol / L. Concentrations above a certain threshold are applicable, depending on the circumstances. However, if the concentration is below the threshold, a longer plating time may be required, and in some cases, concentrations above the threshold may lead to precipitation.

[0032] The electroless tin plating bath of the present invention therefore includes titanium ions suitable for reducing tin ions to metallic tin. Titanium (III) ions are used as at least one reducing agent. Titanium (III) ions may be added in the form of a water-soluble titanium (III) compound. Preferred titanium (III) compounds are selected from the group consisting of titanium (III) chloride, titanium (III) sulfate, titanium (III) iodide, and titanium (III) methanesulfonate. Alternatively, the tin plating bath of the present invention may consist of a titanium (IV) ion source or a mixture of titanium (III) and titanium (IV) ions and be activated prior to use by electrochemically reducing titanium (IV) ions to titanium (III) ions, as described in US 6,338,787. Specifically, the regeneration unit described, for example, in Figure 1 of WO 2013 / 182478 A2, and the method described in the aforementioned document are also suitable for this purpose.

[0033] The total concentration of all titanium(III) ions in the tin-free plating bath of the present invention is preferably between 0.02 mol / L and 0.2 mol / L, more preferably between 0.04 mol / L and 0.15 mol / L, and even more preferably between 0.05 and 0.08 mol / L.

[0034] Therefore, the electroless tin plating bath of the present invention comprises at least one accelerator selected from the group consisting of: sulfites, dithiosulfinates, thiosulfates, tetrathiosulfates, polythiosulfates, metabisulfites, sulfides, disulfides, polysulfides, elemental sulfur, and mixtures thereof. Our own research has demonstrated that a) sulfites and / or b) dithiosulfinates, c) thiosulfates, d) tetrathiosulfates, e) polythiosulfates, f) metabisulfites, g) elemental sulfur and / or h) sulfides, disulfides, and polysulfides can be used as accelerators to improve the tin plating rate. Preferably, at least one accelerator is inorganic. If two or more accelerators are selected, they are preferably all inorganic.

[0035] The preferred sources of sulfites, dithiosulfinates, thiosulfates, tetrathiosulfates, polythiosulfates, sulfides, disulfides, polysulfides, and metabisulfites are individual salts, such as basic salts (e.g., sodium sulfite, potassium sulfite, sodium bisulfite), alkaline earth metal salts (e.g., magnesium sulfite, calcium sulfite), ammonium salts, and mixtures thereof. Preferably, at least one accelerator is water-soluble and the relative ions used (e.g., sodium or potassium) will not co-deposit.

[0036] For the purposes of this invention, the term polysulfonate refers to a salt having the formula S n (SO3)2 2- Oxygen-containing anions, where n = 0, 1, 3, 4, 5, 6, 7 or ≥ 8.

[0037] Dithiosulfinates, thiosulfates, tetrathiosulfates, polythiosulfates, metabisulfites, disulfides, polysulfides, and elemental sulfur are compounds containing at least one SS moiety.

[0038] The tin plating bath according to the present invention is preferred, wherein the accelerator is selected from the group consisting of: alkali metal sulfites, alkali metal bisulfites, alkaline earth metal sulfites, alkaline earth metal bisulfites, ammonium sulfite, ammonium bisulfite, alkali metal dithiosulfinates, alkali metal dithiosulfinates, alkaline earth metal dithiosulfinates, alkaline earth metal dithiosulfinates, alkali metal thiosulfates, alkali metal bisulfates, alkaline earth metal thiosulfates, alkaline earth metal bisulfates, ammonium thiosulfate, ammonium thiosulfate, and alkali metal tetrathiosulfates. Alkali metal tetrasulfonates, alkaline earth metal tetrasulfonates, alkaline earth metal tetrasulfonates, ammonium tetrasulfonates, ammonium tetrasulfonates, alkali metal polysulfonates, alkali metal polysulfonates, alkaline earth metal polysulfonates, alkaline earth metal polysulfonates, ammonium polysulfonates, ammonium polysulfonates, alkali metal metabisulfites, alkali metal metabisulfites, alkaline earth metal metabisulfites, alkaline earth metal metabisulfites, ammonium metabisulfites, ammonium metabisulfites, alkali metal sulfides, alkali metal disulfides, alkali metal polysulfides, ammonium sulfide, and octasulfite (S8).

[0039] The tin plating bath according to the invention is more preferably wherein the accelerator is selected from the group consisting of: sodium sulfite, potassium sulfite, sodium hydrogen sulfite, potassium hydrogen sulfite, calcium bisulfite, and magnesium bisulfite. (bisulfite), ammonium sulfite, ammonium bisulfite, sodium dithiosulfinate, potassium dithiosulfinate, calcium dithiosulfinate, magnesium dithiosulfinate, sodium thiosulfate, sodium bithiosulfate, potassium thiosulfate, calcium thiosulfate, potassium thiosulfate, barium thiosulfate, ammonium thiosulfate, ammonium thiosulfate, ammonium thiosulfate, sodium tetrathiosulfate, potassium tetrathiosulfate, ammonium tetrathiosulfate, ammonium tetrathiosulfate, barium tetrathiosulfate, sodium polysulfate, potassium polysulfate, ammonium polysulfate, ammonium polysulfate, sodium metabisulfite, potassium metabisulfite, ammonium metabisulfite, ammonium metabisulfite, sodium or potassium sulfide, sodium or potassium disulfide, sodium polysulfide or potassium polysulfide, ammonium sulfide and granular cyclooctasulfide (S8).

[0040] In one embodiment, if the selected accelerator includes an inorganic sulfide, such as an alkali metal sulfide, then at least one pH adjuster is selected from the group consisting of ammonia or inorganic ammonium derivatives, such as ammonium hydroxide or ammonium chloride.

[0041] According to the invention, sodium dithiosulfinate and / or sodium sulfite and / or sodium thiosulfate and / or sodium tetrathiosulfate and / or sodium polythiosulfate and / or sodium metabisulfite are particularly preferred. When elemental sulfur is used in the tin plating bath according to the invention, sulfur in its S8 cyclic configuration is preferred. Sulfur is particularly preferred to be present in the form of sulfur particles, especially sulfur particles with an aerodynamic diameter of less than 300 nm, preferably less than 200 nm, and more preferably less than 100 nm, as determined by an aerodynamic particle size analyzer (APS). While it is not desirable to be bound by any particular theory, it is believed that sulfur transforms into two different compounds, namely sulfites and sulfides.

[0042] Preferably, the molar ratio of all accelerators used in this invention to tin ions is at least 1:300. More preferably, the molar ratio of all accelerators used in this invention to tin ions is between 1:200 and 1:5.000, even more preferably between 1:300 and 1:4.000, still even more preferably between 1:500 and 1:1.500, and most preferably in the range of 1:550 to 1:1.000.

[0043] The total concentration of sulfite, dithiosulfinate, thiosulfate, tetrathiosulfate, polythiosulfinate, metabisulfite, sulfide, disulfide, polysulfide, and sulfur in the electroless tin plating bath of the present invention is preferably between 0.0008 and 0.80 mmol / L, more preferably between 0.008 and 0.40 mmol / L, and even more preferably between 0.04 and 0.16 mmol / L.

[0044] Preferably, the total amount of accelerator in the tin plating bath by weight is between 0.01 and 300 ppm, more preferably between 0.1 and 200 ppm, and even more preferably between 0.5 and 175 ppm.

[0045] Preferably, the tin plating bath of the present invention is free of organic sulfites. The inventors have discovered that these compounds occasionally have a negative impact on the plating rate and increase the loss of plating rate over time and during the use of tin plating baths containing such organic sulfites.

[0046] The electroless tin plating bath according to the present invention preferably comprises tin chloride (II), titanium chloride (III) and at least one accelerator selected from the group consisting of sodium sulfite, sodium dithiosulfinate, sodium thiosulfate and mixtures thereof.

[0047] The tin plating bath of the present invention further comprises (d) at least one complexing agent (also known in the art as a chelating agent), preferably selected from the group consisting of:

[0048] - Organic polycarboxylic acids, their salts, anhydrides, and esters

[0049] - Organophosphonic acids, their salts and esters

[0050] -Organic polyphosphoric acid, its salts and esters, and

[0051] -Inorganic polyphosphoric acid, its salts and esters.

[0052] In the context of this invention, organic polycarboxylic acids are organic compounds having a plurality of (at least two) carboxylic acid functional groups. The tin plating bath according to the invention is more preferably wherein the organic polycarboxylic acid, its salts, anhydrides, and esters are selected from the group consisting of: oxalic acid, tartaric acid, citric acid, hypozoxytriacetic acid, ethylenediaminetetraacetic acid, dimercaptosuccinic acid, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, 3,6,9,12-tetra(carboxymethyl)-3,6,9,12-tetraazatetradecane-1,14-dicarboxylic acid, diethylenetriaminepentaacetic acid, iminodiacetic acid, and their salts, anhydrides, or esters.

[0053] Preferred salts of the organic polycarboxylic acid according to the present invention are alkali metal salts or alkaline earth metal salts of the organic polycarboxylic acid (e.g., lithium salts, sodium salts, potassium salts, magnesium salts, calcium salts, beryllium salts) or ammonium salts of the organic polycarboxylic acid. Preferred esters of the organic polycarboxylic acid according to the present invention are methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester, pentyl ester, octyl ester, decyl ester, and dodecyl ester or organic polycarboxylic acid.

[0054] The preferred salts or anhydrides of citric acid (citric acid esters) according to the present invention are alkali metal salts, alkaline earth metal salts or ammonium salts of citric acid (e.g., sodium citrate, potassium citrate, magnesium citrate) and citric anhydrides.

[0055] Preferred salts or anhydrides of hypotriacetic acid according to the present invention are hypotriacetic anhydride and alkali metal salts, alkaline earth metal salts or ammonium salts of hypotriacetic acid (e.g., sodium hypotriacetic acid (mono, di or tri), potassium hypotriacetic acid (mono, di or tri), magnesium hypotriacetic acid).

[0056] The tin plating bath according to the present invention is more preferably wherein the organophosphonic acid, its salt, and ester are selected from the group consisting of: 1-hydroxyethane-1,1-diphosphonic acid (HEDP, CAS No. 2809-21-4), its salt, and ester; aminotris(methylenephosphonic acid) (ATMP, CAS No. 6419-19-8), its salt, and ester; diethylenetriaminepenta(methylenephosphonic acid) (DTPMP, CAS No. 22042-96-2 for the sodium salt), its salt, and ester; ethylenediaminetetra(methylenephosphonic acid) (EDTMP, CAS No. 22042-96-2 for the sodium salt), its salt, and ester; and ethylenediaminetetra(methylenephosphonic acid) (EDTMP, CAS No. 22042-96-2 for the sodium salt). Item No.: 15142-96-8), its salts and esters; Phosphonic butanetricarboxylic acid (PBTC, CAS No. 37971-36-1), its salts and esters; Hexamethylenediaminetetra(methylenephosphonic acid) (HDTMP, CAS No. 23605-74-5), its salts and esters; Hydroxyethylaminodi(methylenephosphonic acid) (HDTMP, CAS No. 23605-74-5), its salts and esters; and Bis(hexamethylene)triamine-penta(methylphosphonic acid) (BHMTMP, CAS No. 34690-00-1), its salts and esters.

[0057] Preferred salts of the organophosphonic acids according to the present invention are alkali metal salts or alkaline earth metal salts of organophosphonic acids (e.g., lithium salts, sodium salts, potassium salts, magnesium salts, calcium salts, beryllium salts) or ammonium salts of organophosphonic acids. Preferred esters of the organophosphonic acids according to the present invention are methyl esters, ethyl esters, propyl esters, isopropyl esters, butyl esters, pentyl esters, octyl esters, decyl esters, and dodecyl esters or organophosphonic acids.

[0058] The tin plating bath according to the invention is more preferably wherein the inorganic polyphosphoric acid, its salt, and ester are linear or cyclic, and more preferably selected from the group consisting of potassium pyrophosphate, sodium pyrophosphate, and sodium hydrogen pyrophosphate. Potassium pyrophosphate is particularly preferred according to the invention.

[0059] The tin plating bath according to the invention is more preferably wherein the organic and / or inorganic polyphosphoric acid, the salt and ester of which comprise 2 to 10 phosphate building units linked together, preferably 2 to 5, more preferably 2 or 3.

[0060] A mixture of two or more of the complexing agents may be used appropriately.

[0061] The total concentration of all complexing agents in the tin plating bath of the present invention is preferably between 0.1 and 3.5 mol / L, more preferably 0.1 to 2 mol / L, and even more preferably 0.15 to 1.5 mol / L, even more preferably 0.2 to 1.2 mol / L, still more preferably 0.25 to 1.0 mol / L, and most preferably within the range of 0.5 to 1.0 mol / L. Depending on the specific circumstances, concentrations above a certain threshold are applicable. However, if the concentration is below the threshold, the stability of the tin plating bath of the present invention may be insufficient to cause precipitation, and in some cases, concentrations above the threshold may reduce the plating rate of the tin plating bath of the present invention. The complexing agent performs various functions in the tin plating bath of the present invention. Firstly, it buffers the pH of the bath. Secondly, it prevents the precipitation of tin ions, and thirdly, it reduces the concentration of free (i.e., uncomplexed tin ions). Specifically, for the last two reasons mentioned, a preferred embodiment of the present invention uses at least one complexing agent in excess relative to the molar amount of tin ions.

[0062] Preferably, the molar ratio of all complexing agents to tin ions used according to the present invention is at least 1:1. More preferably, the molar ratio of all complexing agents to tin ions used according to the present invention is between 2 / 1 and 25 / 1, even more preferably 2.5 to 20 / 1, still even more preferably 5 / 1 to 15 / 1, and most preferably in the range of 7.5 / 1 to 12.5 / 1.

[0063] Preferably, the tin plating bath of the present invention is free of 1,10-phenanthroline and / or 1,10-phenanthroline derivatives (including dibenzo[b,j][1,10]phenanthroline and dibenzo[b,j][1,10]phenanthroline derivatives). The inventors have found that these compounds can occasionally have a negative impact on the plating rate and increase the loss of plating rate over time and during the use of tin plating baths containing such compounds.

[0064] Optionally, the electroless tin plating bath of the present invention includes (e) at least one hypophosphite. While not wishing to be bound by any particular theory, it is generally believed that hypophosphites act as antioxidants that inhibit the oxidation of tin(II) ions to tin(IV) ions. Hypophosphites are conceptually a class of phosphorus compounds based on the structure of hypophosphite (H3PO2). In this document, the term hypophosphite is used to describe both inorganic species (e.g., sodium hypophosphite or potassium hypophosphite) and organophosphite species. Preferred hypophosphites are selected from the group consisting of alkali metal hypophosphites or alkaline earth metal hypophosphites (e.g., lithium, sodium, potassium, magnesium, calcium, beryllium salts) and ammonium hypophosphite, more preferably sodium hypophosphite, potassium hypophosphite, and ammonium hypophosphite. Sodium hypophosphite is particularly preferred according to the present invention.

[0065] The total concentration of all hypophosphites in the electroless tin plating bath of the present invention is preferably between 1 and 570 mmol / L, more preferably between 10 and 230 mmol / L, and even more preferably between 30 and 170 mmol / L. Concentrations above the threshold are applicable, depending on the circumstances. However, if the concentration is below the threshold, the antioxidant effect will be reduced, and in some cases, concentrations above the threshold may lead to precipitation.

[0066] Optionally, the tin plating bath of the present invention includes (in addition) at least one antioxidant that is not a hypophosphite. The additional antioxidant advantageously inhibits the oxidation of tin(II) ions to tin(IV) ions. The additional antioxidant is preferably a hydroxylated aromatic compound, such as catechol, resorcinol, hydroquinone, pyrogallol, α-naphthol or β-naphthol, or pyrogallol; or a sugar-based compound, such as ascorbic acid and sorbitol. The antioxidant is typically used at a total concentration of 0.1 to 1 g / L.

[0067] Optionally, the tin plating bath of the present invention further comprises (f) at least one stabilizing additive selected from the group consisting of: 2-mercaptopyridine, 2-mercaptobenzothiazole, 2-mercapto-2-thiazoline, and mixtures thereof.

[0068] The total concentration of all stabilizing additives in the tin plating bath of the present invention is preferably between 0.5 and 200 mmol / L, more preferably 1 to 100 mmol / L, even more preferably 5 to 30 mmol / L, and even more preferably 6 to 25 mmol / L. Concentrations above the threshold are applicable, depending on the circumstances. However, if the concentration is below the threshold, the positive effects of the present invention may not be sufficiently apparent, and in some cases, concentrations above the threshold do not further increase the benefits but only increase the cost.

[0069] The inventors have unexpectedly discovered that the combination of the complexing agent described above with the stabilizing additives described above allows the beneficial effects described in this specification to be maintained, for example, during use and over time, the plating rate of the tin plating bath of the present invention.

[0070] The tin plating bath of this invention is an electroless (autocatalytic) tin plating bath. The terms "electroless tin plating bath" and "autocatalytic tin plating bath" are used interchangeably herein. In the context of this invention, electroless plating should be understood as autocatalytic deposition using a (chemical) reducing agent (referred to herein as "reducing agent"). A distinction should be made between electroless plating baths and immersion plating baths. The latter does not require the addition of a (chemical) reducing agent but relies on the exchange of metal ions in the bath with metal components (e.g., copper) from the substrate (see above). Therefore, there are fundamental differences between these two types of plating baths.

[0071] The tin plating bath of the present invention is an aqueous solution. This means that the main solvent is water. Optionally, other solvents miscible with water, such as polar organic solvents, including alcohols, glycols, and glycol ethers, may be added. For its eco-friendly characteristics, it is preferable to use only water (i.e., more than 99 wt% of all solvents, more preferably more than 99.9 wt% of all solvents).

[0072] The pH value of the tin plating bath of the present invention is preferably between 5 and 9, more preferably between 6 and 8.5, and even more preferably between 6.4 and 8.3. These pH ranges allow for an improved tin plating rate retention, or ideally a stable tin plating bath with a constant plating rate.

[0073] If thiosulfate is included in the tin plating bath of the present invention, then the pH value of the tin plating bath of the present invention is less than 9.5, preferably in the range of 5 to 9.5, more preferably in the range of 6 to 9, more preferably in the range of 6.4 to 8.5 and even more preferably in the range of 8.0 to 8.3.

[0074] Optionally, the tin plating bath of the present invention includes at least one pH adjuster. The pH adjuster is an acid, base, or buffer compound. Preferred acids are selected from the group consisting of inorganic and organic acids. Inorganic acids are preferably selected from the group consisting of phosphoric acid, hydrochloric acid, sulfuric acid, nitric acid, and mixtures thereof. Organic acids are generally carboxylic acids, such as formic acid, acetic acid, malic acid, lactic acid, and the like, and mixtures thereof. Preferred bases are selected from the group consisting of inorganic and organic bases. Inorganic bases are preferably selected from the group consisting of ammonia, potassium hydroxide, sodium hydroxide, calcium hydroxide, and mixtures thereof, more preferably from the group consisting of ammonia and sodium hydroxide. Organic bases are generally amines, such as ethylenediamine, methylamine, dimethylamine, trimethylamine, ethylamine, propylamine, triethylamine, aniline, pyridine, and the like, and mixtures thereof. Buffer compounds are preferably boric acid and / or phosphate-based buffers. At least one pH adjuster is typically used at a certain concentration to adjust the pH of the tin plating bath of the present invention to the stated range.

[0075] In one embodiment, at least one pH adjuster is selected from the group consisting of ammonia or inorganic ammonium derivatives, such as ammonium hydroxide, ammonium chloride, and ammonium acetate. These pH adjusters also exhibit good stability and prevent precipitation for at least 3 to 9 hours, preferably 4 to 8 hours, and more preferably 6 to 8 hours. Optionally, the tin plating bath of the present invention includes at least one other type of reducible metal ion besides tin ions. The term "reducible metal ion" should be understood in the context of the present invention as a metal ion that can be reduced to its respective metallic state under given conditions (e.g., typical plating conditions and specifically those outlined in this specification). Exemplarily, alkali metal ions and alkaline earth metal ions are generally not reducible to their respective metallic states under the applied conditions. If such other types of reducible metal ions besides tin ions are present in the tin plating bath, a tin alloy will be deposited when the tin plating bath of the present invention is used. Typical tin alloys used as solderable or adhesive coatings on contact areas are tin-silver alloys, tin-bismuth alloys, tin-nickel alloys, and tin-copper alloys. Therefore, suitable other types of reducible metal ions besides tin ions are preferably selected from the group consisting of silver ions, copper ions, bismuth ions, and nickel ions.

[0076] The sources of optional silver, bismuth, copper, and nickel ions are selected from water-soluble silver, bismuth, copper, and nickel compounds. Preferred water-soluble silver compounds are selected from the group consisting of: silver nitrate, silver sulfate, silver oxide, silver acetate, silver citrate, silver lactate, silver phosphate, silver pyrophosphate, and silver methanesulfonate. Preferred water-soluble bismuth compounds are selected from the group consisting of: bismuth nitrate, bismuth oxide, bismuth methanesulfonate, bismuth acetate, bismuth carbonate, bismuth chloride, and bismuth citrate. Preferred water-soluble copper compounds are selected from the group consisting of: copper sulfate; alkyl sulfonates, such as copper methanesulfonate; copper halides, such as copper chloride; copper oxide; and copper carbonate. Preferred sources of water-soluble nickel compounds are selected from the group consisting of: nickel chloride, nickel sulfate, nickel acetate, nickel citrate, nickel phosphate, nickel pyrophosphate, and nickel methanesulfonate.

[0077] The concentration of at least one other type of reducible metal ion besides tin ions is preferably between 0.01 g / L and 10 g / L, more preferably between 0.02 g / L and 5 g / L.

[0078] In one embodiment of the invention, the tin plating bath of the invention is substantially free of other reducible metal ions besides tin ions. This means that, based on the amount of tin ions, the amount of other reducible metal ions is 1 mol% or less. Preferably, only tin ions, as reducible metal ions, are present in the tin plating bath. Then, pure tin is deposited using the tin plating bath.

[0079] In some embodiments of the invention, the tin plating bath of the invention is free of organophosphorus compounds, such as organophosphonates or organophosphorus compounds, such as nitrazine tris(methylenephosphonate) (NTMP), particularly organophosphorus compounds, wherein the phosphorus atom in said compound is in the +III oxidation state. The inventors have found that these compounds can occasionally have a negative impact on the plating rate and increase the loss of plating rate over time and during the use of tin plating baths containing such organophosphorus compounds.

[0080] Preferably, the tin plating bath of the present invention is free of thiourea due to its acute toxicity and tendency to dissolve metal ions on metal surfaces, such as copper ions on cuprous surfaces. Thiourea further increases the loss of plating rate over time and during the use of a tin plating bath containing said compound.

[0081] Preferably, due to its toxicity, the tin plating bath of the present invention is preferably free of cyanide ions (CN). - In one embodiment of the invention, the tin plating bath of the invention comprises only complexing agents selected from the group consisting of: pyrophosphate ions, linear polyphosphate ions, and cyclic polyphosphate ions.

[0082] Preferably, the tin plating bath of the present invention is free of polysulfides, such as basic polysulfides, to avoid the release of hydrogen sulfide.

[0083] Optionally, the tin plating bath of the present invention includes at least one surfactant. At least one surfactant improves the wetting of the substrate by the tin plating bath of the present invention and thus facilitates tin deposition. It further contributes to the deposition of a smooth tin deposit. Suitable surfactants can be determined by those skilled in the art through routine experiments. The surfactant is typically used at a total concentration of 0.01 to 20 g / L.

[0084] For the reasons outlined above, the tin plating bath of the present invention can be prepared by dissolving all components in at least one solvent, preferably in water. Particularly suitable alternative preparation methods are as follows:

[0085] First, a solution of tin(II) ions and a complexing agent is prepared in a solvent, preferably water. Second, the solution comprising the complexing agent and a titanium(IV) salt is acidified with an (preferably inorganic) acid (e.g., phosphoric acid), since its solubility is typically in a solution of alkoxylated titanium(IV). The solution is then subjected to high temperature to remove all volatile components, such as alcohols and the like. Subsequently, preferably using a constant cathode current, electrolysis is performed to reduce the titanium(IV) ions to titanium(III) ions. The two solutions are then mixed and other components, such as stabilizing additives, are added.

[0086] In step (i) of the method according to the invention, a substrate is provided. The substrate has at least one surface suitable for treatment with the tin plating bath of the invention. Preferably, the at least one surface is selected from the following: copper, nickel, cobalt, gold, palladium, tungsten, tantalum, titanium, platinum alloys, and mixtures thereof. The surface consists of or comprises only the aforementioned materials, preferably at least 50 wt%, more preferably at least 90 wt%. The substrate is entirely made of the materials listed above or comprises only one or more surfaces made of the materials listed above. In the context of the invention, it is also possible to treat more than one surface simultaneously or sequentially.

[0087] More preferably, at least one surface is selected from the group consisting of surfaces including (or composed of): copper, nickel, cobalt, gold, palladium, platinum, alloys and mixtures of any of the foregoing.

[0088] Specifically, the method according to the invention uses a substrate having one or more of the aforementioned surfaces, commonly used in the electronics and semiconductor industries. Such substrates particularly include printed circuit boards, IC substrates, flat panel displays, wafers, interconnect devices, ball grid arrays, and the like.

[0089] Optionally, at least one substrate is subjected to one or more pretreatment steps. The pretreatment steps are known in the art. Pretreatment steps may include, for example, cleaning, etching, and activation steps. The cleaning step typically uses an aqueous solution comprising one or more surfactants to remove contaminants, such as those from at least one surface of at least one substrate, that are detrimental to tin plating deposition. The etching step typically employs an acidic solution optionally comprising one or more oxidants, such as hydrogen peroxide, to increase the surface area of ​​at least one surface of at least one substrate. The activation step typically involves depositing a noble metal catalyst, most commonly palladium, on at least one surface of at least one substrate to make said at least one surface more suitable for tin deposition. Sometimes, a pre-dip step precedes the activation step or a post-dip step follows it; both are steps known in the art.

[0090] In step (ii) of the method according to the invention, at least one surface of the substrate to be treated is brought into contact with the tin plating bath of the invention. By bringing at least one surface of the substrate into contact with the tin plating bath of the invention, tin or a tin alloy is deposited on at least one surface of at least one substrate.

[0091] The tin plating bath of the present invention preferably contacts individual surfaces through immersion, dip coating, spin coating, spraying, curtain coating, roller coating, printing, screen printing, inkjet printing, or brushing. In one embodiment of the present invention, the tin plating bath is used in a horizontal or vertical electroplating apparatus.

[0092] The contact time between at least one surface and the tin plating bath of the present invention is preferably between 1 min and 4 h, more preferably between 15 min and 2 h, and even more preferably between 30 min and 1 h. If a particularly thin or thick tin or tin alloy deposit is required, the contact time may exceed the threshold. The preferred thickness of the tin or tin alloy deposit is between 1 and 30 μm, preferably between 2 and 20 μm, and more preferably between 4 and 10 μm.

[0093] Using the tin plating bath of the present invention, the tin plating rate, which controls the tin layer thickness on at least one surface, increases over time to preferably greater than 4 μm / h, more preferably greater than 5 μm / h, and even more preferably greater than 6 μm / h. Practical applications typically require a plating rate of at least 2 μm / h. The tin plating bath of the present invention demonstrates that, within the used plating time (the time at least one surface of the substrate is in contact with the tin plating bath – plating time), the plating rate value remains preferably 2 to 6 μm / h or greater, preferably 3 to 5 μm / h.

[0094] In other words, the tin plating bath according to the invention does not even exhibit an initial high plating rate of 2 to 6 μm per hour or greater, preferably 3 to 5 μm per hour, nor a high plating rate during use. The plating rate is preferably between 2 and 6 μm per hour for at least two hours of use (plating time), more preferably between 3 and 6 μm per hour for at least one hour of use (plating time). In any case, the plating rate preferably does not decrease below 2 μm per hour during the used plating time, and preferably not less than 3 μm per hour for at least two hours.

[0095] The application temperature depends on the application method used. For example, for dip coating, roll coating, or spin coating applications, the application temperature is typically between 40°C and 90°C, preferably between 50°C and 85°C, and even more preferably between 65°C and 75°C.

[0096] Optionally, the tin plating bath of the present invention is regenerable. Regeneration of the tin plating bath is exemplary for reducing titanium(IV) ions to titanium(III) ions. Suitable methods and apparatus for this purpose are described in particular in EP 2 671 968 A1.

[0097] The components in the tin plating bath of the present invention may optionally be supplemented, for example by anodic dissolution of metallic tin or by adding the components themselves or the components mentioned above in the solution.

[0098] Optionally, the tin or tin alloy deposit is post-treated with a rust-preventive composition known in the art.

[0099] The method of the present invention optionally includes one or more rinsing steps. Rinsing can be achieved by treating at least one surface of at least one substrate with at least one solvent, said at least one solvent optionally including one or more surfactants. The at least one solvent is preferably selected from the group consisting of: water, more preferably deionized water (DI water); alcohols, such as ethanol and isopropanol; glycols, such as DEG; and glycol ethers, such as BDG, and mixtures thereof.

[0100] The method of the present invention optionally further includes a drying step. Drying can be accomplished by any method known in the art, such as subjecting the substrate to high temperature and / or air drying.

[0101] The present invention further relates to products manufactured using the methods of the present invention or using the tin plating bath of the present invention. Specifically, it relates to printed circuit boards, IC substrates, flat panel displays, wafers, interconnect devices, and spherical grid arrays comprising at least one tin or tin alloy deposit formed by the tin plating bath and / or the methods of the present invention.

[0102] Unless otherwise stated, percentages throughout this specification are weight percentages (wt%). Yields are given as a percentage of theoretical yield. Unless otherwise stated, concentrations given in this specification refer to the volume or mass of the total solution.

[0103] The terms “deposition” and “electroplation” are used interchangeably in this document.

[0104] The present invention will now be described with reference to the following non-limiting examples.

[0105] Example

[0106] Unless otherwise specified below, use the product as described in the corresponding technical data sheet (concentration, parameters, other derivatives) (if available at the application date). Practical applications typically require an electroplating rate of at least 2 μm / h.

[0107] Determining the thickness of metal or metal alloy deposits The deposit thickness was measured at 10 locations on each substrate and used to determine the layer thickness via XRF using the Fischerscope XDV-SDD XRF instrument (Helmut Fischer GmbH, Germany). The layer thickness can be calculated from this type of XRF data by assuming a layered structure of the deposit. Alternatively, the deposit thickness was determined based on frequency variations in a quartz crystal using a quartz crystal microbalance (SRS QCM200, Stanford Research Systems, Inc.).

[0108] Measurement of electroplating rateThe electroplating rate is obtained by dividing the thickness of the tin deposit by the time required to achieve the thickness.

[0109] The pH value was measured at 25°C using a SevenMulti S40 professional pH meter (electrode: InLab Semi-Micro-L, Mettler-Toledo GmbH), which has Ag... + Use the ARGENTHAL™ filtration device (reference electrolyte: 3 mol / L KCl) for measurement. Continue measuring until the pH becomes constant, but in any case, continue for at least 3 minutes. Calibrate the pH meter using three high pH standards (7.00, 9.00, and 12.00) provided by Merck KGaA before use.

[0110] Example 1 of the present invention: Sodium sulfite as an accelerator in an electroless tin plating bath

[0111] In a beaker, 660.66 g of potassium pyrophosphate was dissolved in deionized water, and 220 g of titanium(III) chloride was added to the solution while stirring to dissolve it. The volume of the resulting solution was adjusted to 1000 mL with deionized water.

[0112] The resulting solution was stirred at 60°C for two to three hours until a dark blue solution with a precipitate was formed. The solution was filtered (10 μm) and the titanium concentration was determined by titration. The titanium concentration should generally be in the range of 190 to 215 mM. The resulting solution had a pH of approximately 7.8 to 8.3.

[0113] The solution described above is used to prepare the tin plating bath of the present invention, which comprises the following components:

[0114] c(Sn 2+ = 60 mmol / L

[0115] c(Ti 3+ = 60 mmol / L

[0116] c(pyrophosphate) = 700 mmol / L

[0117] c(2-mercaptopyridine) = 20 mmol / L

[0118] Sodium hypophosphite = 5g / L

[0119] Sodium sulfite = 30 ppm

[0120] pH = 8.2

[0121] Temperature = 75℃

[0122] The circuit board is coated with Cu as a substrate, 5×5cm = 25cm 2Furthermore, XRF measurements were performed on BGA structures coated with Sn layers of 150 μm diameter or less. The results are summarized in Table I.

[0123] The tin plating bath is stable and exhibits no precipitation or depreciation.

[0124] Example 2 of the present invention: Sulfur as an accelerator in an electroless tin plating bath

[0125] The method described for Example 1 of the present invention was repeated, but sodium sulfite was replaced with 1 ppm sulfur nanoparticles, and the aerodynamic diameter, as measured by an aerodynamic particle size analyzer (APS), was less than 100. The results are summarized in Table I.

[0126] The tin plating bath is stable and exhibits no precipitation or depreciation.

[0127] Example 3 of the present invention: Sodium dithiosulfinate as an accelerator in an electroless tin plating bath

[0128] The method described for Example 1 of the present invention was repeated, but sodium sulfite was replaced with 20 ppm sodium dithiosulfinate. Only BGA structures were electroplated during this example. The results are summarized in Table I.

[0129] The tin plating bath is stable and exhibits no precipitation or depreciation.

[0130] Example 4 of the present invention: Sodium thiosulfate as an accelerator in an electroless tin plating bath

[0131] The method described in Example 1 of the present invention is repeated, but the tin plating bath of the present invention comprises the following components:

[0132] c(Sn 2+ =50mmol / L

[0133] c(Ti 3+ = 60 mmol / L

[0134] c(pyrophosphate) = 700 mmol / L

[0135] c(2-mercaptopyridine) = 0 mmol / L (absent)

[0136] Sodium hypophosphite = 5g / L

[0137] Sodium thiosulfate = 150 ppm

[0138] pH = 8.0

[0139] Temperature = 75℃

[0140] The tin plating bath is stable and exhibits no precipitation or depreciation.

[0141] In this example, only the BGA structure was electroplated. The results are summarized in Table I.

[0142] Example 5 of the present invention: Sodium dithiosulfinate as an accelerator in an electroless tin plating bath

[0143] The method described in Example 1 of the present invention is repeated, but the tin plating bath of the present invention comprises the following components:

[0144] c(Sn 2+ =50mmol / L

[0145] c(Ti 3+ = 60 mmol / L

[0146] c(pyrophosphate) = 700 mmol / L

[0147] c(2-mercaptopyridine) = 0 mmol / L (absent)

[0148] Sodium hypophosphite = 5g / L

[0149] Sodium dithionite = 100 ppm

[0150] pH = 8.0

[0151] Temperature = 75℃

[0152] The tin plating bath is stable and exhibits no precipitation or depreciation.

[0153] In this example, only the BGA structure was electroplated. The results are summarized in Table I.

[0154] Example 6 of the present invention: Sodium sulfite as an accelerator in an electroless tin plating bath

[0155] The method described in Example 1 of the present invention is repeated, but the tin plating bath of the present invention comprises the following components:

[0156] c(Sn 2+ =50mmol / L

[0157] c(Ti 3+ = 60 mmol / L

[0158] c(pyrophosphate) = 700 mmol / L

[0159] c(2-mercaptopyridine) = 0 mmol / L (absent)

[0160] Sodium hypophosphite = 5g / L

[0161] Sodium sulfite = 150 ppm

[0162] pH = 8.0

[0163] Temperature = 75℃

[0164] The tin plating bath is stable and exhibits no precipitation or depreciation.

[0165] In this example, only the BGA structure was electroplated. The results are summarized in Table I.

[0166] Example 7 of the present invention: Sodium sulfite as an accelerator in an electroless tin plating bath

[0167] The method described in Example 1 of the present invention is repeated, but the tin plating bath of the present invention comprises the following components:

[0168] c(Sn 2+ = 60 mmol / L

[0169] c(Ti 3+ =50mmol / L

[0170] c(1-hydroxyethane-1,1-diphosphonic acid (HEDP)) = 600 mmol / L

[0171] c(2-mercaptopyridine) = 0 mmol / L (absent)

[0172] Sodium sulfite = 20 ppm

[0173] pH = 8.2

[0174] Temperature = 75℃

[0175] The circuit board is coated with Cu as a substrate, 5×5cm = 25cm 2 Furthermore, XRF measurements were performed on BGA structures coated with Sn layers of 150 μm diameter or less. The results are summarized in Table I.

[0176] The tin plating bath is stable and exhibits no precipitation or depreciation.

[0177] Example 8 of the present invention: Sulfur as an accelerator in an electroless tin plating bath

[0178] The method described in Example 1 of the present invention is repeated, but the tin plating bath of the present invention comprises the following components:

[0179] c(Sn2+)=60mmol / L

[0180] c(Ti3+) = 60 mmol / L

[0181] c(potassium pyrophosphate) = 720 mmol / L

[0182] c(sodium hypophosphite) = 56 mmol / L

[0183] Sulfur nanoparticles = sulfur nanoparticles at the tip of a spatula

[0184] pH = 8.2

[0185] Temperature = 75℃

[0186] The sulfur nanoparticles used had an aerodynamic diameter of less than 100, as determined by an aerodynamic particle size analyzer (APS).

[0187] In this example, only the BGA structure was electroplated. The results are summarized in Table I.

[0188] The tin plating bath is stable and exhibits no precipitation or depreciation.

[0189] Example 9 of the present invention: Sodium tetrathionate as an accelerator in an electroless tin plating bath

[0190] The method described in Example 1 of the present invention is repeated, but the tin plating bath of the present invention comprises the following components:

[0191] c(Sn2+)=50mmol / L

[0192] c(Ti3+) = 60 mmol / L

[0193] c(potassium pyrophosphate) = 700 mmol / L

[0194] c(sodium hypophosphite) = 5 g / L

[0195] Sodium tetrathionate = 50 ppm

[0196] pH = 8.0

[0197] Temperature = 75℃

[0198] In this example, only the BGA structure was electroplated. The results are summarized in Table I.

[0199] The tin plating bath is stable and exhibits no precipitation or depreciation.

[0200] Example 10 of the present invention: Sodium metabisulfite as an accelerator in an electroless tin plating bath

[0201] The method described in Example 1 of the present invention is repeated, but the tin plating bath of the present invention comprises the following components:

[0202] c(Sn2+)=50mmol / L

[0203] c(Ti3+) = 60 mmol / L

[0204] c(potassium pyrophosphate) = 700 mmol / L

[0205] c(sodium hypophosphite) = 5 g / L

[0206] Sodium metabisulfite = 20 ppm

[0207] pH = 8.0

[0208] Temperature = 75℃

[0209] In this example, only the BGA structure was electroplated. The results are summarized in Table I.

[0210] The tin plating bath is stable and exhibits no precipitation or depreciation.

[0211] Example 11 of the present invention: Sodium sulfite as an accelerator in an electroless tin plating bath

[0212] The method described in Example 1 of the present invention is repeated, but the tin plating bath of the present invention comprises the following components:

[0213] c(Sn 2+ = 60 mmol / L

[0214] c(Ti 3+ =50mmol / L

[0215] c(sodium hypophosphite) = 5 g / L

[0216] Sodium sulfite = 5 ppm

[0217] Ammonia (15% by weight) = 1.5 mL / L

[0218] pH = 8.2

[0219] Temperature = 70℃

[0220] The circuit board is coated with Cu as a substrate, 5×5cm = 25cm 2 Furthermore, XRF measurements were performed on BGA structures coated with Sn layers of 150 μm diameter or less. The results are summarized in Table I.

[0221] The tin plating bath stabilized within 8 hours, during which time the deposition rate remained constant at approximately 5 μm / h. No precipitation or depreciation occurred.

[0222] Example 12 of the present invention: Ammonium sulfide as an accelerator in an electroless tin plating bath

[0223] The method described in Example 1 of the present invention is repeated, but the tin plating bath of the present invention comprises the following components:

[0224] c(Sn2+)=50mmol / L

[0225] c(Ti3+) = 60 mmol / L

[0226] c(potassium pyrophosphate) = 700 mmol / L

[0227] c(sodium hypophosphite) = 5 g / L

[0228] c(2-mercaptopyridine) = 20 mmol / L

[0229] Ammonium sulfide = 3 ppm

[0230] pH = 8.0

[0231] Temperature = 70℃

[0232] The circuit board is coated with Cu as a substrate, 5×5cm = 25cm 2 Furthermore, XRF measurements were performed on BGA structures coated with Sn layers of 150 μm diameter or less. The results are summarized in Table I. The tin plating bath was stable and showed no precipitation or deposition.

[0233] Example 13 of the present invention: Ammonium sulfide as an accelerator in an electroless tin plating bath

[0234] The method described in Example 1 of the present invention is repeated, but the tin plating bath of the present invention comprises the following components:

[0235] c(Sn2+)=50mmol / L

[0236] c(Ti3+) = 60 mmol / L

[0237] c(potassium pyrophosphate) = 700 mmol / L

[0238] c(sodium hypophosphite) = 5 g / L

[0239] c(2-mercaptopyridine) = 20 mmol / L

[0240] Sodium sulfide = 3 ppm

[0241] pH = 8.0

[0242] Temperature = 70℃

[0243] The circuit board is coated with Cu as a substrate, 5×5cm = 25cm 2 Furthermore, XRF measurements were performed on BGA structures coated with Sn layers of 150 μm diameter or less. The results are summarized in Table I. The tin plating bath was stable and showed no precipitation or deposition.

[0244] Comparative Example C1: No accelerator in the electroless tin plating bath

[0245] The method described for Example 1 of the present invention is repeated, but sodium sulfite or sulfur is omitted. Therefore, sulfites, dithiosulfinates, and sulfur are not used in this example.

[0246] The tin plating bath was stable and showed no precipitation or deposition. Results for all examples are summarized in Table I.

[0247] Comparative Example C2: No accelerator in the electroless tin plating bath

[0248] The method described for Example 8 of the present invention was repeated, but 2-mercaptopyridine (40 mM) was used instead of sulfur nanoparticles. Therefore, sulfites, dithiosulfinates, and sulfur were not used in this example. The BGA structure was not electroplated during this example.

[0249] The tin plating bath was stable and showed no precipitation or deposition. Results for all examples are summarized in Table I.

[0250] Table I: Tin deposit thickness depending on accelerator

[0251]

[0252] The tin deposits obtained from Examples 1 to 13 of the present invention are lustrous and free from defects detectable to the naked eye, such as blistering, burning, and the like. The tin deposits obtained from Examples 1, 3 to 7, 9, and 10 to 13 of the present invention are slightly better than the tin deposits obtained from Examples 2 and 8 of the present invention.

[0253] Compared with comparative examples C1 and C2, the electroplating rate was significantly improved by using at least one accelerator selected from the group consisting of sulfites, dithiosulfinates, thiosulfates, elemental sulfur and mixtures thereof in the electroless tin plating bath.

Claims

1. A non-electro-metal plating bath, comprising: (a) Tin ions; (b) Titanium ions, as a suitable reducing agent for reducing tin ions to metallic tin; (c) At least one accelerator selected from the group consisting of: sulfites, dithiosulfinates, tetrathiosulfinates, polythiosulfinates, metabisulfites, elemental sulfur, and mixtures thereof, wherein "polythiosulfinate" refers to an accelerator having the formula S n (SO3)2 2- oxyanions, where n = 0, 1, 3, 4, 5, 6, 7 or ≥ 8; (d) at least one complexing agent; and (e) Optionally at least one hypophosphite The tin plating bath has a pH of 6.4 to 8.3, and the electroless tin plating bath is free of 1,10-phenanthroline and / or 1,10-phenanthroline derivatives.

2. The tin plating bath according to claim 1, wherein the at least one accelerator is inorganic.

3. The tin plating bath according to claim 1, wherein the at least one accelerator comprises two or more accelerators, wherein the two or more accelerators are all inorganic.

4. The tin plating bath according to claim 1 or 2, wherein the accelerator is selected from the group consisting of: alkali metal sulfites, alkali metal bisulfites, alkaline earth metal sulfites, alkaline earth metal bisulfites, ammonium sulfite, ammonium bisulfite, alkali metal dithiosulfinates, alkali metal dithiosulfinates, alkaline earth metal dithiosulfinates, alkaline earth metal dithiosulfinates, alkali metal tetrathiosulfinates, alkali metal tetrathiosulfinates, alkaline earth metal tetrathiosulfinates, alkaline earth metal tetrathiosulfinates, ammonium tetrathiosulfinates, ammonium tetrathiosulfinates, alkali metal polythiosulfinates, alkali metal polythiosulfinates, alkaline earth metal polythiosulfinates, alkaline earth metal polythiosulfinates, ammonium polythiosulfinates, ammonium polythiosulfinates, ammonium polythiosulfinates, alkali metal metabisulfites, alkali metal metabisulfites, alkaline earth metal metabisulfites, alkaline earth metal metabisulfites, ammonium metabisulfite, ammonium metabisulfite, and octasulfite (S8).

5. The tin plating bath according to claim 1 or 2, wherein the accelerator is selected from the group consisting of: sodium sulfite, potassium sulfite, sodium bisulfite, potassium bisulfite, calcium bisulfite, magnesium bisulfite, ammonium sulfite, ammonium bisulfite, sodium dithiosulfinate, potassium dithiosulfinate, calcium dithiosulfinate, magnesium dithiosulfinate, sodium tetrathiosulfate, potassium tetrathiosulfate, ammonium tetrathiosulfate, ammonium tetrathiosulfate, barium tetrathiosulfate, sodium polythiosulfate, potassium polythiosulfate, ammonium polythiosulfate, ammonium polythiosulfate, sodium metabisulfite, potassium metabisulfite, ammonium metabisulfite, ammonium metabisulfite, and particulate cyclooctasulfite (S8).

6. The tin plating bath according to claim 1 or 2, wherein the total amount of the accelerator in the tin plating bath by weight is in the range of 0.01 to 300 ppm.

7. The tin plating bath according to claim 1 or 2, wherein the total amount of the accelerator in the tin plating bath by weight is in the range of 0.1 to 200 ppm.

8. The tin plating bath according to claim 1 or 2, wherein the total amount of the accelerator in the tin plating bath by weight is in the range of 0.5 to 175 ppm.

9. The tin plating bath according to claim 1 or 2, wherein the at least one complexing agent is selected from the group consisting of: - Organic polycarboxylic acids, their salts, anhydrides, and esters - Organophosphonic acids, their salts and esters -Organic polyphosphoric acid, its salts and esters, and -Inorganic polyphosphoric acid, its salts and esters.

10. The tin plating bath according to claim 9, wherein the organic polycarboxylic acid, its salts and esters are selected from the group consisting of: oxalic acid, tartaric acid, citric acid, hypozoxytriacetic acid, ethylenediaminetetraacetic acid, dimercaptosuccinic acid, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, 3,6,9,12-tetra(carboxymethyl)-3,6,9,12-tetraazatetradecane-1,14-dicarboxylic acid, diethylenetriaminepentaacetic acid, iminodiacetic acid and its salts or esters.

11. The tin plating bath according to claim 9, wherein the organophosphonic acid compound, its salt, and ester are selected from the group consisting of: 1-Hydroxyethane-1,1-Diphosphonic acid, its salts and esters, Aminotris(methylenephosphonic acid), its salts and esters, Diethylenetriaminepenta (methylenephosphonic acid), its salts and esters, Ethylenediaminetetra(methylenephosphonic acid), its salts and esters, Phosphonobutanetricarboxylic acid, its salts and esters, Hexamethylenediaminetetra(methylenephosphonic acid), its salts and esters, Hydroxyethylaminobis(methylenephosphonic acid), its salts and esters, and Bis(hexamethylene)triamine-penta(methylphosphonic acid), its salts and esters.

12. The tin plating bath according to claim 9, wherein the inorganic polyphosphoric acid is selected from the group consisting of potassium pyrophosphate, sodium pyrophosphate, and sodium hydrogen pyrophosphate.

13. The tin plating bath according to claim 9, wherein the organic and / or inorganic polyphosphoric acid compound, its salt and ester comprising 2 to 10 phosphate building blocks linked together.

14. The tin plating bath according to claim 9, wherein the organic and / or inorganic polyphosphoric acid compound, its salt and ester comprising 2 to 5 phosphate building blocks linked together.

15. The tin plating bath according to claim 9, wherein the organic and / or inorganic polyphosphoric acid compound, its salt and ester comprising two or three phosphate building blocks linked together.

16. The tin plating bath according to claim 1 or 2, characterized in that... A) The total concentration of all tin ions is in the range of 0.02 to 0.2 mol / L. and / or B) The total concentration of all titanium ions is in the range of 0.02 mol / L to 0.2 mol / L.

17. The tin plating bath according to claim 16, wherein the total concentration of all tin ions is in the range of 0.04 to 0.15 mol / L.

18. The tin plating bath according to claim 16, wherein the total concentration of all tin ions is in the range of 0.05 to 0.08 mol / L.

19. The tin plating bath according to claim 16, wherein the total concentration of all titanium ions is in the range of 0.04 mol / L to 0.15 mol / L.

20. The tin plating bath according to claim 16, wherein the total concentration of all titanium ions is in the range of 0.05 mol / L to 0.08 mol / L.

21. The tin plating bath according to claim 1 or 2, characterized in that... The tin plating bath does not contain organic sulfites.

22. The tin plating bath according to claim 1 or 2, further comprising: (f) at least one stabilizing additive selected from the group consisting of 2-mercaptopyridine, 2-mercaptobenzothiazole, 2-mercapto-2-thiazoline and mixtures thereof.

23. Use of a tin plating bath according to any one of claims 1 to 22, for depositing tin or a tin alloy on at least one surface of a substrate.

24. A method for depositing tin or a tin alloy on at least one surface of a substrate, comprising the following steps: (i) providing the substrate; and (ii) Contacting at least one surface of the substrate with a tin plating bath according to any one of claims 1 to 22, such that tin or a tin alloy is deposited on at least one surface of the substrate.

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