TIN ALLOY PLATING SOLUTION

Abstract

A tin alloy plating solution comprising a soluble tin salt, a soluble salt of a metal nobler than tin, and a sulfide compound represented by general formula (I). In formula (I), n is 1 to 3. The metal nobler than tin is preferably silver, copper, gold, or bismuth.

Claims

1. A tin alloy plating solution comprises a soluble tin salt, a soluble salt of a metal nobler than tin, and a sulfide compound represented by general formula (1), wherein a metal nobler than tin is at least 1 or 2 or more kinds of metals selected from silver, copper, gold and bismuth, in general formula (1), n is from 1 to 3
HOCH.sub.2CH.sub.2S(CH.sub.2CH.sub.2OCH.sub.2CH.sub.2S).sub.nCH.sub.2CH.sub.2OH(1)

2. The tin alloy plating solution according to claim 1, further comprising at least 1 or 2 or more surfactants selected from anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants.

3. (canceled)

4. The tin alloy plating solution according to claim 1, further comprising an antioxidant.

5. The tin alloy plating solution according to claim 1, further comprising a complexing agent for tin.

6. The tin alloy plating solution according to claim 1, further comprising a pH adjusting agent.

7. The tin alloy plating solution according to claim 1, further comprising a brightening agent.

8. The tin alloy plating solution according to claim 2, further comprising an antioxidant.

9. The tin alloy plating solution according to claim 2, further comprising a complexing agent for tin.

10. The tin alloy plating solution according to claim 4, further comprising a complexing agent for tin.

11. The tin alloy plating solution according to claim 8, further comprising a complexing agent for tin.

12. The tin alloy plating solution according to claim 2, further comprising a pH adjusting agent.

13. The tin alloy plating solution according to claim 4, further comprising a pH adjusting agent.

14. The tin alloy plating solution according to claim 5, further comprising a pH adjusting agent.

15. The tin alloy plating solution according to claim 8, further comprising a pH adjusting agent.

16. The tin alloy plating solution according to claim 2, further comprising a brightening agent.

17. The tin alloy plating solution according to claim 4, further comprising a brightening agent.

18. The tin alloy plating solution according to claim 5, further comprising a brightening agent.

19. The tin alloy plating solution according to claim 6, further comprising a brightening agent.

20. The tin alloy plating solution according to claim 8, further comprising a brightening agent.

21. The tin alloy plating solution according to claim 9, further comprising a brightening agent.

Description

EXAMPLES

[0051] Next, Examples of the present invention will be described in detail along with Comparative Examples.

(Bath Preparation of SnAg Plating Solution)

Example 1

[0052] With an aqueous tin methanesulfonate solution were mixed methanesulfonic acid as a free acid, a sulfide compound wherein n=1 of the general formula (1) as a complexing agent, and a nonionic surfactant (polyoxyethylene and polyoxypropylene were added to ethylenediamine with a ratio of 50:50) and dissolved, and a silver methanesulfonate liquid was further added and mixed. And finally, ion exchange water was added to prepare a bath of an SnAg plating solution having the following composition. Incidentally, the aqueous tin methanesulfonate solution was prepared by electrolyzing a metal tin plate and the aqueous silver methanesulfonate solution was prepared by electrolyzing a metal silver plate, both in an aqueous methanesulfonic acid solution, respectively.

(Composition of SnAg Plating Solution)

[0053] Tin methanesulfonate (as Sn.sup.2): 50 g/L

[0054] Silver methanesulfonate (as Ag.sup.+): 0.5 g/L

[0055] Methanesulfonic acid (as free acid): 150 g/L

[0056] Sulfide compound (n=1): 5 g/L

[0057] Nonionic surfactant: 5 g/L

[0058] Ion exchange water: balance

Example 2

[0059] An SnAg plating solution was prepared as a bath in the same manner as in Example 1 except that a sulfide compound wherein n=2 of the general formula (1) was used as a complexing agent.

Example 3

[0060] An SnAg plating solution was prepared as a bath in the same manner as in Example 1 except that a sulfide compound wherein n=3 of the general formula (1) was used as a complexing agent.

Example 4

[0061] An aqueous tin methanesulfonate solution was mixed with methanesulfonic acid as a free acid and a sulfide compound wherein n=2 of the general formula (1) as a complexing agent and dissolved, and an aqueous copper methanesulfonate solution was further added and mixed. After making the solution uniform by mixing, a nonionic surfactant was further added thereto. And finally, ion exchange water was added to the mixture to prepare a bath of an SnCu plating solution having the following composition. Incidentally, the aqueous tin methanesulfonate solution was prepared by electrolyzing a metal tin plate, and the aqueous copper methanesulfonate solution was prepared by electrolyzing a metal copper plate in an aqueous methanesulfonic acid solution, respectively.

(Composition of SnCu Plating Solution)

[0062] Tin methanesulfonate (as Sn.sup.2+): 50 g/L

[0063] Copper methanesulfonate (as Cu.sup.2+): 0.3 g/L

[0064] Methanesulfonic acid (as free acid): 150 g/L

[0065] Sulfide compound (n=2): 5 g/L

[0066] Nonionic surfactant: 5 g/L

[0067] Ion exchange water: balance

Example 5

[0068] An aqueous tin methanesulfonate solution was mixed with methanesulfonic acid as a free acid, a sulfide compound wherein n=1 of the general formula (1) as a complexing agent and a nonionic surfactant (20 mol of polyoxyethylene was added to 1 mol of bisphenol A) to dissolve these materials, then, sodium gluconate as a complexing agent of tin and mercaptotetrazole were added, and benzalacetone was mixed as a glossing agent. Further, a silver methanesulfonate solution was added and mixed. And finally, ion exchange water was added to prepare a bath of an SnAg plating solution having the following composition.

(Composition of SnAg Plating Solution)

[0069] Tin methanesulfonate (as Sn.sup.2+): 80 g/L

[0070] Silver methanesulfonate (as Ag.sup.+): 1.0 g/L

[0071] Methanesulfonic acid (as free acid): 100 g/L

[0072] Sulfide compound (n=1): 3 g/L

[0073] Nonionic surfactant: 8 g/L

[0074] Sodium gluconate: 10 g/L

[0075] Mercaptotetrazole: 1 g/L

[0076] Benzalacetone: 0.01 mg/L

[0077] Ion exchange water: balance

Comparative Example 1

[0078] An SnAg plating solution was prepared as a bath in the same manner as in Example 1 except that a sulfide compound wherein n=0 of the general formula (1) was used as a complexing agent.

Comparative Example 2

[0079] An SnAg plating solution was prepared as a bath in the same manner as in Example 1 except that a sulfide compound wherein n=4 of the general formula (1) was used as a complexing agent.

Comparative Example 3

[0080] An SnAg plating solution was prepared as a bath in the same manner as in Example 1 except that 3,6-dithia-1,8-octanediol was used as a complexing agent.

Comparative Example 4

[0081] An SnAg plating solution was prepared as a bath in the same manner as in Example 5 except that a sulfide compound wherein n=4 of the general formula (1) was used as a complexing agent.

<Comparative Test and Evaluation>

[0082] By using nine kinds of the prepared baths of the plating solutions in Examples 1 to 5 and Comparative Examples 1 to 4, stability and plating performance of the tin alloy plating solution were evaluated. Stability of the tin alloy plating solution was evaluated by performing an electrolytic stability test and a temporal stability test. The plating performance was evaluated by performing Hull cell test and a plating test.

(a) Electrolytic Stability Test

[0083] Nine kinds of the prepared baths of the tin alloy plating solutions were used as an electrolyte, a copper plate was located as a cathode and a platinum plate as an anode in the electrolyte, nine kinds of the prepared baths of the tin alloy plating solutions were performed to electroplating each separately at a bath temperature of 25 C. and a cathode current density of 10 ASD. Since metal components in the plating solution were consumed by electroplating, while powders of stannous oxide (SnO) and silver oxide (Ag.sub.2O) were added to, mixed with and dissolved in the plating solution every 5 Ah/L of electroplating to supply the metal components to the plating bath, electroplating was performed up to 200 Ah/L. A concentration of the sulfide compound which is a complexing agent remaining in the tin alloy plating solution after electroplating was quantitatively analyzed by the following HPLC (High Performance Liquid Chromatography) method. The tin alloy plating solution was filtered with a disposable syringe, and analysis was performed using L-Column ODS kept at 40 C. using an HPLC apparatus (Model No.: Prominence) manufactured by Shimadzu Corporation and making a mobile phase MeOH (methanol). The concentration of the complexing agent immediately after preparation of the bath was made 100%, and a remaining ratio (%) of the complexing agent after electroplating was evaluated as the remaining amount of the complexing agent.

(b) Temporal Stability Test

[0084] Nine kinds of the prepared baths of the tin alloy plating solutions were separately charged in a sealed bottle made of a glass, and stored in a clean oven manufactured by Panasonic Corporation at 50 C. for 6 months. Using an ICP Automatic Emission Spectrometer (ICP-AES, Model No.: ICPE-9800) manufactured by Shimadzu Corporation, metal concentrations other than Sn in the tin alloy plating solution immediately after preparation of the bath, that is, in the case of the SnAg alloy plating solution, the Ag concentration, and in the case of the SnCu plating solution, the Cu concentration was made 100%, respectively, and metal concentrations other than Sn remained after storage of 6 months, that is, in the case of the SnAg alloy plating solution, the Ag concentration, and in the case of the SnCu plating solution, the Cu concentration was measured and the remaining ratio (%) thereof was each calculated.

(c) Hull Cell Test

[0085] Nine kinds of the prepared baths of the tin alloy plating solutions were each separately placed in a hull cell tank manufactured by Yamamoto-MS Co., Ltd., and a hull cell plate made of copper was arranged in the liquid as a cathode and a platinum plate as an anode, respectively, to perform the Hull cell test. The plating conditions were such that the liquid temperature was 25 C., the applied current was 3 A, and the plating processing time was 5 minutes. During the plating processing, the plating solution was stirred by a cathode rocker. The hull cell evaluation was performed by observing the film appearance of a plating film on the hull cell plate subjected to plating treatment confirming with naked eyes using a current density quick reference plate, and evaluated with three judgement criteria that the film with gloss or semi-gloss was regarded as good, the film without gloss or cloudy was regarded as acceptable and the film with scorching or burning was regarded as poor.

(d) Plating Test

[0086] Nine kinds of the prepared baths of the tin alloy plating solutions were used as electrolytes and a plating test was carried out separately. The electrolyte was adjusted to a liquid temperature of 25 C., and a substrate made of copper (10 cm in length, 10 cm in width and 0.3 mm in thickness) was immersed in the electrolyte and subjected to 10 minutes at a current density of 5 A/dm.sup.2. The film thickness of ten portions of the obtained plating film was measured by a fluorescent X-ray film thickness measuring device (manufactured by Hitachi High-Technologies Corporation). The maximum value (T.sub.max) the minimum value (T.sub.min) and the average value (T.sub.average) of the film thickness at the 10 portions were obtained, and uniformity of a film thickness was calculated by the following equation (2) to evaluate whether electrodeposition was uniformly performed or not. The test results as above are shown in Table 1.

Uniformity of film thickness=(T.sub.maxT.sub.min)/(2T.sub.average)100(%)(2)

TABLE-US-00001 TABLE 1 Plating characteristics Tin alloy plating solution of plating Complexing agent solution Compound Stability of Hull cell Plating other Metal plating solution test test than other Electrolytic Temporal (plating (film Sulfide sulfide than stability stability film thickness compound compound Sn test test appearance) uniformity) Example 1 n = 1 Ag 90% 93% Good 2.1% Example 2 n = 2 Ag 92% 84% Good 3.3% Example 3 n = 3 Ag 95% 97% Acceptable 4.0% Example 4 n = 2 Cu 88% 89% Good 3.2% Example 5 n = 1 Ag 91% 92% Good 4.2% Comparative n = 0 Ag 86% 27% Good 2.7% Example 1 Comparative n = 4 Ag 98% 98% Poor 15.8% Example 2 Comparative 3, 6-Di- Ag 21% 9% Good 3.1% Example 3 thia- 1,8- octane- diol Comparative n = 4 Ag 93% 92% Poor 24.6% Example 4

[0087] As clearly seen from Table 1, in the case of Examples 1 to 5 using the sulfide compound represented by n=0 to 3 in the general formula (1), even after electrolytic plating, the complexing agent remained with a high ratio as 90% to 95% in the SnAg plating solution and as 88% in the SnCu plating solution, and even after lapse of time, the remaining ratio of Ag or Cu in the solution was as high as 84% to 97% in the SnAg plating solution, and 89% in the SnCu plating solution, and in the plating performance, appearance of the film was good and uniformity of a film thickness was as good as 2.1% to 4.2% in the SnAg plating solution and 3.2% in the SnCu plating solution. On the other hand, in Comparative Example 1, while electrolytic stability and plating performance were good, the residual ratio of Ag decreased after lapse of time. This is considered that the compound of n=0 used in Comparative Example 1 has one S atom in one molecule, so that an ability of forming a complex with Ag ion is not sufficient, and Ag was reduced and deposited. Also, in Comparative Example 2 and Comparative Example 4, while stability of the plating solution was good, the plating performance worsened. This is presumed that the compound of n=4 has high hydrophobicity and is strong in adsorbing power to the surface of the electrode, so that it interfered with the smoothening action of the surfactant used in combination. Further, in Comparative Example 3, while the plating performance was good, the sulfide compound of the present invention as a complexing agent was not contained in the tin alloy plating solution, so that a concentration of the complexing agent was lowered after the electrolytic plating.

UTILIZABILITY IN INDUSTRY

[0088] The plating solution of the present invention can be utilized for forming a part of an electronic component such as a bump electrode of a semiconductor wafer or a printed circuit board.