Method for wet chemical formation of stable tin oxide layers for printed circuit boards - Patents.com

Abstract

The present invention relates to a method for treating a tin or tin alloy layer on a metal surface, preferably a copper surface, comprising the steps of: (i) providing a metal surface, preferably a copper surface; (ii) contacting said metal surface, preferably said copper surface, with a tin or tin alloy plating bath; and (iii) oxidizing said tin or tin alloy layer obtained by step (ii).

Description

[Technical field]

[0001] The present invention relates to a method comprising a wet chemical oxidation step of a tin layer as a top layer, the method preferably serving to manufacture electric circuit carriers, more particularly to manufacture printed circuit boards, in particular to produce contacts, such as edge connector contacts and push button contacts of printed circuit boards, on the circuit carrier. [Background technology]

[0002] During the fabrication of the electric circuit carrier, organic and / or metallic layers are applied onto the copper surface of the base material. These layers may perform different functions. The organic layers may, for example, be used to structure the copper surface in a subsequent process. For this purpose, a photoresist is applied onto the copper surfaces so as to completely cover them. The layer may then be partially exposed to light using a special photomask that images the desired line structures into the photoresist. The imaged structures are then developed using corresponding chemicals. Depending on the type of photoresist, which may be negative or positive, both the exposed and unexposed areas are removed by development so as to expose the areas of the copper layer located directly underneath. These areas may then be selectively etched or plated with copper or other metals using electroless, chemical or electrochemical methods.

[0003] When metal layers are partially etched or deposited as described, the resulting circuit carrier has a specific line structure. To build complex structures, the steps of the method may be repeated. Individual layers are packed together to form multi-layer circuits.

[0004] To enable the mounting of electronic components on the circuit carrier provided with the line structure, additional layers, such as gold, silver, tin, nickel layers, are then deposited using, for example, electroless, chemical or electrochemical methods, with the aid of a solder resist, to form surface top layers. On one side, these surface top layers serve to form the solderable surface areas required for mounting the components. On the other side, the gold surface areas are also suitable for bonding housed and unhoused semiconductor components.

[0005] WO 2012 / 095334 discloses a tin plating bath.

[0006] These top surface layers also serve as protective layers intended to prevent the copper surface from oxidizing and to preserve its solderability. These top layers are necessary because the fabrication of the circuit carrier and its further processing, such as the mounting of components thereon, usually does not take place at the same fabrication site, and therefore further processing takes place only at a later stage.

[0007] Gold and silver layers are formed as surface top layers, for example also by inserting them into contact areas for the production of separable electrical contacts, e.g. contact sockets and push buttons, for the production of plug connectors for plugging into circuit carriers.

[0008] Once the circuit carriers are completed, i.e. after the top surface layer has been applied, they are dried and then, before being stored or subjected to further processing, thoroughly rinsed once more to clean them from any ionic contaminants originating from the various method steps, more particularly caused by the deposition method for the creation of the top surface layer.

[0009] Such cleaning is disclosed, for example, in WO 2007 / 025675.

[0010] Due to the very high quality requirements in the electronics industry, impurities, such as air pollution, must be avoided. Therefore, today, products, in particular circuit carriers with a freshly produced tin layer, are immediately packaged under vacuum.

[0011] However, these metallic tin layers have been found to exhibit stability problems in the final assembly process. In extreme cases, there is a tendency for poor wetting leading to sphere formation and / or copper diffusion from the underlying copper layer through the tin layer to the surface. This effect becomes more evident with increasing temperature. In modern lead-free solder reflow processes, which have peak temperatures higher than the melting point of pure tin, the described undesirable poor wetting is a continuing challenge.

[0012] Another problem is that in automated optical inspection (AOI) with pure tin metal surfaces, the mark points are not correctly recognized. There are at least two reasons for this. One is the gloss of the tin metal layer. The other is the unclear optical properties of the surface, e.g. the PCB surface. The unclear optical properties can be attributed to at least one poor or partial poor wetting. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] International Publication No. 2012 / 095334 [Patent Document 2] International Publication No. 2007 / 025675 Summary of the Invention [Problem to be solved by the invention]

[0014] Objective of the invention Therefore, the object of the present invention is to find a way to minimize or even avoid the above mentioned problems.

[0015] A further object of the invention is to find a method that does not negatively affect the tin layer, for example by chemical contamination, especially ionic contamination. As a control measure, the conductivity of the medium should remain below 10 μS / cm in the final rinsing step.

[0016] A further object of the present invention is to find a method which is cost effective and easy to operate. [Means for solving the problem]

[0017] The above mentioned object is solved by the inventive method according to claim 1. Preferred embodiments of the invention can be found in the dependent claims.

[0018] The method of the invention involves a wet chemical oxidation step of the tin layer. The advantage is that such a step can be easily integrated into existing processes. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 shows the thickness of the tin oxide layer on tin depending on different parameters: (a) concentration of the oxidant H2O2, pH and residence time (at constant temperature); (b) concentration of the oxidant H2O2, pH, Ionix and residence time (at constant pH). [Diagram 2] 1 shows printed circuit boards treated (a) according to comparative process C-1; (b) according to comparative process C-2; (c) and (d) according to process P using different concentrations of oxidizing agent. [Diagram 3] Zoomed-in views of the lower right corner (center column) and upper middle part (right column) of FIG. 2 are shown: (a) by comparative process C-1; (b) by comparative process C-2; (c) and (d) by process P using different concentrations of oxidizing agent. [Figure 4] FIG. 1 shows surface tension measurements of tin oxide layers of printed circuit boards prepared under different conditions, namely with and without aging; with and without oxidation step (iii); with and without another post-immersion step different from oxidation step (iii). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Percentages throughout this specification are weight percent (wt%) unless otherwise specified. One exception is yields given as a percentage of theoretical yield. Concentrations given herein refer to the total volume of the solution unless otherwise specified.

[0021] The method of the present invention for treating a tin or tin alloy layer on a metal surface, preferably a copper surface, comprises the following process steps: (i) providing a metal surface, preferably a copper surface; (ii) contacting a metal surface, preferably a copper surface, with a tin or tin alloy plating bath; and (iii) a step of oxidizing the tin or tin alloy layer obtained by step (ii).

[0022] Step (i) - Providing a metal surface, preferably a copper surface In principle, any metal surface can be used in the method of the invention. Preferably, the metal of the metal surface is selected from the group consisting of nickel, gold, palladium, copper and silver. In particular, it is preferred that the metal surface is a copper surface.

[0023] Step (ii) - contacting a metal surface, preferably a copper surface, with a tin or tin alloy plating bath. Contacting a metal surface with a tin or tin alloy plating bath is used as a deposition method to deposit tin or tin alloy on the metal surface.

[0024] In principle, any of the methods known to those skilled in the art can be used. These include electroless, chemical and electrochemical methods. Preference is given to methods in which the tin or tin alloy plating bath is an immersion plating bath. In an alternative preferred method, the tin or tin alloy plating bath is an electroless plating bath.

[0025] The tin or tin alloy plating bath may further comprise at least one stabilizer.

[0026] The at least one stabilizer may be selected from stannates, organic acids, inorganic acids, and combinations thereof.

[0027] Examples of stannates are potassium stannate or sodium stannate.

[0028] Examples of the organic acid include organic sulfonic acids, aliphatic carboxylic acids, oxycarboxylic acids, aminocarboxylic acids, and the like.

[0029] Among organic acids, organic sulfonic acids are superior because they are easy to treat in wastewater, have high solubility in metal salts, allow high-speed plating, and have high electrical conductivity.

[0030] Examples of organic sulfonic acids include methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, 2-propanesulfonic acid, 1-butanesulfonic acid, 2-butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, decanesulfonic acid, alkanesulfonic acids such as dodecanesulfonic acid, 2-hydroxyethane-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid (2-propanolsulfonic acid), 2-hydroxybutane-1-sulfonic acid, 2-hydroxypentane-1-sulfonic acid, etc.; alkanolsulfonic acids such as , 1-hydroxypropane-2-sulfonic acid, 3-hydroxypropane-1-sulfonic acid, 4-hydroxybutane-1-sulfonic acid, 2-hydroxyhexane-1-sulfonic acid, 2-hydroxydecane-1-sulfonic acid, 2-hydroxydodecane-1-sulfonic acid; 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, p-phenolsulfonic acid, cresolsulfonic acid, sulfosalicylic acid, nitrobenzenesulfonic acid, sulfobenzoic acid, diphenylamine-4-sulfonic acid, etc.

[0031] Furthermore, the above-mentioned aliphatic carboxylic acids, oxycarboxylic acids, aminocarboxylic acids, etc. are effective in preventing hydrolysis of metal salts in the pH range of about 1-10.

[0032] Generally, carboxylic acids having 1 to 6 carbons can be used as the aliphatic carboxylic acid, specific examples of which include acetic acid, propionic acid, butyric acid, sulfosuccinic acid, trifluoroacetic acid, and the like.

[0033] Examples of oxycarboxylic acids include lactic acid, citric acid, gluconic acid, tartaric acid, malic acid, and the like.

[0034] Aminocarboxylic acids include ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), and iminodipropionic acid (IDP); These include hydroxyethylethylenediaminetriacetic acid (HEDTA), triethylenetetraaminehexaacetic acid (TTHA), glycine, alanine, N-methylglycine, lysine, glutamic acid, aspartic acid, etc.

[0035] Examples of inorganic acids include phosphonic acid, phosphoric acid, sulfuric acid, hydrochloric acid, boric acid, hydrofluoric acid, silicic acid, sulfamic acid, and the like.

[0036] Various known additives such as surfactants, complexing agents, stabilizers, brighteners, semi-brighteners, pH adjusters, buffers, etc. may be suitably mixed with the tin plating bath in step (ii) of the process according to purpose.

[0037] Step (iii) - Oxidizing the tin or tin alloy layer obtained by step (ii). Process step (iii) is performed by contacting the tin or tin-alloy layer obtained by step (ii) with a composition comprising at least one solvent and at least one oxidizing agent.

[0038] Preferably, at least one solvent contains water in an amount of 50 vol.% or more. The remainder is selected from the group consisting of water-miscible organic solvents. A preferred water-miscible organic solvent is ethanol.

[0039] More preferably, the at least one solvent is water.

[0040] The at least one oxidizing agent is selected from non-decomposable and decomposable oxidizing agents, for example peroxides such as hydrogen peroxide, metal peroxides such as sodium peroxide, potassium peroxide; metal superoxides such as potassium superoxide; copper ions and iron ions.

[0041] However, ionic species have a negative effect on conductivity and are less preferred.

[0042] Preferably, the at least one oxidizing agent is a decomposable oxidizing agent, more preferably, the at least one oxidizing agent comprises hydrogen peroxide, and most preferably, the at least one oxidizing agent is hydrogen peroxide.

[0043] To prevent decomposition of the peroxides, other additional compounds such as p-phenolsulfonic acid, phosphoric acid, stannates and / or organic acids and their respective derivatives, e.g. oxalic acid and the respective esters, α-ketocarboxylic acid esters or aldehyde carboxylic acid esters, may be added.

[0044] The concentration of at least one oxidizing agent in the composition is usually in the range of about 0.1 to about 20 g / l, preferably about 0.2 to about 10 g / l, more preferably about 0.3 to about 5 g / l, and even more preferably about 0.5 to about 3 g / l.

[0045] The pH of the composition is usually in the range of about 3 to about 12. Preferably, the pH of the composition is in the range of about 3.5 to about 10. More preferably, the pH of the composition is in the range of about 4.0 to about 8.0. Even more preferably, the pH of the composition is in the range of about 4.5 to about 6.5. Most preferably, the pH of the composition is in the range of about 4.5 to about 5.5. The pH can be adjusted by any chemical known to those skilled in the art. However, non-ionic compounds are preferred. In particular, ammonia is preferred.

[0046] The residence time in step (iii) is usually about 0.1 to about 5 minutes, preferably about 0.2 to about 2 minutes, more preferably about 0.3 to about 1.5 minutes, and even more preferably about 0.4 to about 1 minute.

[0047] The temperature in step (iii) is usually above 40°C, preferably the temperature is from about 40°C to about 90°C, more preferably from about 50°C to about 80°C, even more preferably from about 60°C to about 75°C.

[0048] In a preferred embodiment, the method of the present invention is used in the manufacture of electrical circuit carriers with vertical and / or horizontal lines.

[0049] In a preferred embodiment, the method according to any one of the preceding embodiments in making electrical contacts on an electrical circuit carrier.

[0050] The process typically further comprises rinsing the tin or tin-alloy layer at least once with deionized water before and / or after step (iii).

[0051] In a preferred embodiment, the process further comprises step (ii-a) between step (ii) and step (iii), wherein step (ii-a) comprises a) at least one first compound selected from the group comprising ethanolamine compounds and salts thereof; b) at least one second compound selected from the group comprising alcoholic solvents, and c) Optionally, treating the tin or tin-alloy layer with an aqueous solution comprising at least one third compound selected from the group comprising guanidine compounds and salts thereof.

[0052] It was discovered early on that this process has an overall positive impact on reducing conductivity, and is believed to act both as a surface cleaner and as a swelling agent at the same time.

[0053] Embodiment A. A method for treating a tin or tin alloy layer on a metal surface, preferably a copper surface, comprising the steps of: (i) providing a metal surface, preferably a copper surface; (ii) contacting the metal surface, preferably the copper surface, with a tin or tin alloy plating bath; and (iii) oxidizing the tin or tin alloy layer obtained by step (ii); The method includes:

[0054] B. The method of embodiment A, wherein the tin or tin alloy plating bath is an immersion plating bath.

[0055] C. The method of embodiment A or embodiment B, wherein step (iii) is accomplished by contacting the tin or tin alloy layer obtained by step (ii) with a composition comprising at least one solvent and at least one oxidizing agent, wherein preferably the at least one solvent comprises water, more preferably the at least one solvent is water.

[0056] D. The method of embodiment C, wherein the composition further comprises at least one stabilizer.

[0057] E. The method of embodiment C or embodiment D, wherein the at least one oxidizing agent is selected from non-degradable and degradable oxidizing agents, preferably degradable oxidizing agents, more preferably the at least one oxidizing agent comprises hydrogen peroxide, and most preferably the at least one oxidizing agent is hydrogen peroxide.

[0058] F. The method according to any one of embodiments C to E, wherein the concentration of the at least one oxidizing agent in the composition is in the range of about 0.1 to about 20 g / l, preferably about 0.2 to about 10 g / l, more preferably about 0.3 to about 5 g / l, and even more preferably about 0.5 to about 3 g / l.

[0059] G. The method according to any one of embodiments C to F, wherein the pH of the composition is in the range of about 3 to about 12, preferably about 3.5 to about 10, more preferably about 4.0 to about 8.0, even more preferably about 4.5 to about 6.5, and even more preferably about 4.5 to about 5.5.

[0060] H. The method according to any one of embodiments A to G, wherein the residence time in step (iii) is from about 0.1 minutes to about 5 minutes, preferably from about 0.2 minutes to about 2 minutes, more preferably from about 0.3 minutes to about 1.5 minutes, and even more preferably from about 0.4 minutes to about 1 minute.

[0061] I. The method according to any one of embodiments A to H, wherein the temperature in step (iii) is greater than 40°C, preferably the temperature is from about 40°C to about 90°C, more preferably from about 50°C to about 80°C, and even more preferably from about 60°C to about 75°C.

[0062] J. The method of any one of embodiments A to I in the manufacture of electrical circuit carriers of vertical and / or horizontal lines.

[0063] K. The method of any one of embodiments A through J in making electrical contacts on an electrical circuit carrier.

[0064] L. The method of any one of embodiments A through K, further comprising rinsing the tin or tin-alloy layer at least once with deionized water before and / or after step (iii).

[0065] M. The method further comprises a step (ii-a) between steps (ii) and (iii), wherein step (ii-a) comprises: a) at least one first compound selected from the group comprising ethanolamine compounds and salts thereof; b) at least one second compound selected from the group comprising alcoholic solvents, and The method of any one of embodiments A to L, comprising optionally treating the tin or tin-alloy layer with an aqueous solution comprising at least one third compound selected from the group comprising guanidine compounds and salts thereof.

[0066] The method according to any one of embodiments A to M, characterized in that the surface tension of the tin oxide layer after dry aging at 90° C. for 14 hours has a value of 70 mN / m or more, preferably 75 mN / m or more, more preferably 80 mN / m or more, even more preferably 85 mN / m or more.

[0067] O. The surface tension of the tin oxide layer after dry aging at 90°C for 14 hours is 70 mN / m to 100 mN / m; The method according to any one of embodiments A to M, characterized in that it has a value of 80 mN / m to 95 mN / m, more preferably 85 mN / m to 95 mN / m.

[0068] P. An article comprising a metal layer, preferably a copper layer, a tin layer and a tin oxide layer, characterized in that the tin oxide layer has a thickness of 1 to 3 nm as measured by SERA.

[0069] Q. The article of embodiment P, wherein the surface tension of the tin oxide layer after dry aging at 90° C. for 14 hours has a value of 70 mN / m or more, preferably 75 mN / m or more, more preferably 80 mN / m or more, and even more preferably 85 mN / m or more.

[0070] R. The surface tension of the tin oxide layer after dry aging at 90°C for 14 hours is 70 mN / m to 100 mN / m; The article of embodiment P, characterized in that it has a value of more preferably between 80 mN / m and 95 mN / m, even more preferably between 85 mN / m and 95 mN / m.

[0071] The following non-limiting examples further illustrate the invention. EXAMPLES

[0072] SERA measurement: The dried specimen is placed in a SERA® QC-100. The Sn(II) oxide layer is measured by coulometry with a sealing aperture diameter of 1.6 mm using a Bor Acid / Borat buffer with a pH value of approximately 9 and a current density of -30 μA / cm2. The results are verified by the cumulative current between the reduction potentials of -0.8 and -1.1 V.

[0073] Tin gloss measurements: Dried specimens were aged in a reflow oven with a reduced oxygen concentration of approximately 100 ppm and a reflow profile for Senju M31-GRN360-KV solder paste (peak 245°C). After aging, a flatbed scanner was used to create digital photographs of the specimens. Due to the typical angle of approximately 45° of the flatbed scanner between the light source and the RGB sensor, the RGB sensor can only detect diffuse reflected light. Not all the total reflected light (mirror) of the tin surface reaches the RGB sensor. Depending on the optical properties of the tin surface, more or less light reaches the RGB sensor. A normal tin surface produces a bright white color. Shiny tin is detected as a dark area with much less brightness.

[0074] Surface tension measurement: Contact angle measuring instrument OCA15 - Water and Young's equation: cosθ = (σ S -σ LS ) / σ L (In the formula, σ L = 72.85 mN / m and σ LS = 12.3 mN / m); droplet size: 1 µL; measurement time: 3 seconds. Alternatively, commercially available water / ethanol test inks can be used in the range of 30-72 mN / m.

[0075] Example 1 A printed circuit board having a solder resist mask (Taiyo PSR-4000 AM03TS) was treated using the tin deposition method according to Table 1 to apply a 1 μm thick layer of immersion tin. The tin deposition bath contained tin(II) methanesulfonate, methanesulfonic acid, and thiourea.

[0076] After tin deposition, the samples were examined with SERA using different post-immersion parameters, and the parameters and the respective tin oxide thickness are shown in Figure 1.

[0077] [Table 1]

[0078] Example 2 A printed circuit board having a solder resist mask (Taiyo PSR-4000 AM03TS) was treated using the tin deposition method according to Table 1 to apply a 1 μm thick layer of immersion tin. The tin deposition bath contained tin(II) methanesulfonate, methanesulfonic acid, and thiourea.

[0079] FIG. 2 shows the results of the experiment (a) according to comparative process C-1; (b) according to comparative process C-2; and (c) with a concentration of 0.3% H 2 O 2 (d) according to process P (post-soaking) using 1.0% H 2 O 2 2. FIG. 3 shows a magnified view of the lower right corner (center column) and the upper middle part of FIG. 2 (right column).

[0080] The results are shown in Figure 2 / Figure 3 and Table 2.

[0081] [Table 2]

[0082] Example 3 A printed circuit board having a solder resist mask (Taiyo PSR-4000 AM03TS) was treated using the tin deposition method according to Table 1 to apply a 1 μm thick layer of immersion tin. The tin deposition bath contained tin(II) methanesulfonate, methanesulfonic acid, and thiourea.

[0083] Treatments were performed involving different combinations of the following: - with aging / without aging; - in the post-immersion step of Table 1: oxidation step (iii) of process P, i.e. with / without application of PD2020; - In the post-immersion step of Table 1: an already established process for purifying the tin surface, with / without application of PD270.

[0084] Different combinations can be expressed as follows: a) Ionix-Rinse-No Post-Soak (=Table 1, Process C-2) b) Ionix-Rinse-Post-soak PD270-Rinse (= Table 1, Process C-2 with an inserted post-soak step different from the inventive post-soak step) c) Ionix-Rinse-Post-Soak PD2020-Rinse (=Table 1, Process P) d) Ionix-Rinse-Postsoak 270-Rinse-Postsoak PD2020-Rinse (=Table 1, process P with an inserted postsoak step different from the inventive postsoak step before the inventive postsoak step).

[0085] The surface tension of the tin oxide layer on the PCB was measured, and the results are shown in Figure 4.

[0086] Metals and metal oxides exhibit high surface tension, while organic materials tend to exhibit low surface tension. Surfactants, in particular, have very low surface tension values. Therefore, achieving and maintaining high surface tension is advantageous.

[0087] Measurements show that chemical oxidation of printed circuit boards not only has a positive effect on the formation of the tin oxide layer, but also increases the chemical purity of the surface by reducing the risk of organic substances migrating to the tin / tin oxide surface during storage and thereby contaminating it. This migration can occur not only during storage or transport from the PCB factory to the assembly plant, but also within the assembly process itself.

[0088] It is understood that the examples and embodiments described herein are for illustrative purposes only, and that various modifications and variations in light thereof, and combinations of the features described in this application will be suggested to those skilled in the art and are to be included within the spirit and scope of the described invention and the scope of the appended claims. All publications, patents, and patent applications cited herein are incorporated herein by reference.

Claims

1. 1. A method for treating a tin or tin alloy layer on a metal surface, preferably a copper surface, comprising the steps of: (i) providing a metal surface, preferably a copper surface; (ii) contacting the metal surface, preferably the copper surface, with a tin or tin alloy plating bath; and (iii) oxidizing the tin or tin alloy layer obtained by step (ii); The method includes:

2. 2. The method of claim 1, wherein the tin or tin alloy plating bath is an immersion plating bath.

3. 3. The method of claim 1 or 2, wherein step (iii) is performed by contacting the tin or tin alloy layer obtained by step (ii) with a composition comprising at least one solvent and at least one oxidizing agent, wherein preferably said at least one solvent comprises water, more preferably said at least one solvent is water.

4. The method of claim 3 , wherein the composition further comprises at least one stabilizer.

5. 5. The method according to claim 3 or 4, wherein said at least one oxidizing agent is selected from non-degradable and degradable oxidizing agents, preferably degradable oxidizing agents, more preferably said at least one oxidizing agent comprises hydrogen peroxide, most preferably said at least one oxidizing agent is hydrogen peroxide.

6. 6. The method according to any one of claims 3 to 5, characterized in that the concentration of the at least one oxidizing agent in the composition ranges from about 0.1 to about 20 g / l, preferably from about 0.2 to about 10 g / l, more preferably from about 0.3 to about 5 g / l, even more preferably from about 0.5 to about 3 g / l.

7. 7. The method according to any one of claims 3 to 6, characterized in that the pH of the composition ranges from about 3 to about 12, preferably from about 3.5 to about 10, more preferably from about 4.0 to about 8.0, even more preferably from about 4.5 to about 6.5, even more preferably from about 4.5 to about 5.

5.

8. 8. The process according to any one of claims 1 to 7, characterized in that the residence time of step (iii) is from about 0.1 min to about 5 min, preferably from about 0.2 min to about 2 min, more preferably from about 0.3 min to about 1.5 min, even more preferably from about 0.4 min to about 1 min.

9. 9. The method according to any one of claims 1 to 8, characterized in that the temperature in step (iii) is above 40°C, preferably the temperature is between about 40°C and about 90°C, more preferably between about 50°C and about 80°C, even more preferably between about 60°C and about 75°C.

10. 10. A method according to any one of claims 1 to 9 in the manufacture of electrical circuit carriers with vertical and / or horizontal lines.

11. 11. A method according to any one of claims 1 to 10 in the production of electrical contacts on an electrical circuit carrier.

12. 12. The method according to claim 1, further comprising the step of rinsing the tin or tin alloy layer at least once with deionized water before and / or after step (iii).

13. The method further comprises a step (ii-a) between step (ii) and step (iii), wherein step (ii-a) comprises: a) at least one first compound selected from the group comprising ethanolamine compounds and salts thereof; b) at least one second compound selected from the group comprising alcoholic solvents, and 13. The method according to claim 1, further comprising the step of c) optionally treating the tin or tin-alloy layer with an aqueous solution comprising at least one third compound selected from the group comprising guanidine compounds and their salts.

14. 1. An article comprising a metal layer, preferably a copper layer, a tin layer and a tin oxide layer, characterized in that the tin oxide layer has a thickness of 1-3 nm as measured by SERA.

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