KR100261441B1 - Process for plating iron-nickel substrate for improved corrosion resistance and flexibility - Google Patents

Abstract

PURPOSE: A four layer plating method is provided to obtain a plating layer which does not have almost no hydrogen brittleness and hair crack, and is flexible, particularly superior corrosion resistance on an Fe-Ni alloy material. CONSTITUTION: In a method for plating a palladium plating layer or a palladium alloy plating layer on an Fe-Ni alloy material, the plating method for improving corrosion resistance and crack resistance of an Fe-Ni alloy material comprises the processes of first substrate plating before plating a palladium layer or palladium alloy layer on a material to be plated so that a tin plating layer, a tin-lead alloy plating layer or a tin-bismuth alloy plating layer is formed on the material to be plated; second substrate plating thereon so that a copper plating layer or a copper-bismuth alloy plating layer is formed; and third substrate plating thereon so that a nickel plating layer is formed, wherein the material to be plated of the Fe-Ni alloy material is a semiconductor lead frame, and the palladium alloy layer is formed of an alloy selected from the group consisting of palladium-gold, palladium-silver and palladium-bismuth.

Description

Plating method to improve corrosion and crack resistance of iron-nickel alloy

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plating method for improving the corrosion resistance and crack resistance of an iron-rock alloy material, and more particularly, to a four-layer plating method that can be used for a semiconductor lead frame made of an iron-nickel alloy material.

In general, semiconductor lead frames have been made of copper alloy materials, but more and more iron-nickel alloy materials are being used in consideration of various characteristics. Stamping process was mainly used when manufacturing semiconductor lead frame made of copper alloy material. However, iron-nickel alloy material is harder than copper alloy material. There is a problem of losing, and thus there is a problem that can not make a compact and fine lead frame. In order to solve this problem, an etching process has been developed and used.

On the other hand, conventionally, the semiconductor lead frame is mainly silver-plated and then tin-lead alloy plating, and has been relatively thick compared to other platings in order to obtain a certain level of characteristics, for example, corrosion resistance and solderability. The higher the lead (higher capacity), that is, the higher the capacity between the legs becomes very fine, when the thick plating is a phenomenon that they stick together. In order to overcome these problems, many studies have been carried out to obtain a plating thinner exhibiting properties such as excellent corrosion resistance and solderability even as a very thin plating layer, that is, a thin film. The typical method is palladium plating, palladium alloy plating or gold plating.

In the case of iron-nickel alloy materials, for example, alloy # 42 (42% Ni, 56% Fe, 0.5% Mn, 0.3% Si, 0.035% Ca, 0.035% p 0.025%), the Si and Ca contained in the material itself Due to the components, it is difficult to chemically activate the process, and if the nickel plating is applied as a base plating layer before palladium plating, palladium alloy plating or gold plating on this material, corrosion resistance is reduced due to the Fe component. There are many problems such as deterioration.

Accordingly, the present inventors have conducted many research experiments to obtain higher reliability in applying palladium plating or palladium alloy plating to an iron-nickel alloy plated material, and as a result, to plate with palladium plating or palladium alloy plating composition It is possible to obtain excellent characteristics by performing three layers of base plating before.

That is, it is an object of the present invention to provide a four-layer plating method capable of obtaining a plating layer having little hydrogen brittleness and fine cracks on the iron-nickel alloy material, which is flexible and particularly excellent in corrosion resistance.

In order to achieve the above object, in the present invention, the primary base plate is plated to form a tin plated worm, tin-lead alloy plated layer or tin-bismuth alloy plated layer on the plated body of the iron-nickel alloy material, and the copper plated layer or copper- Secondary base plating to form a bismuth alloy plating layer, and a third base plating to form a nickel plating layer thereon, and then iron-nickel alloy material, characterized in that the plating to form a palladium plating layer or a palladium alloy plating layer as an upper plating layer It provides a four-layer plating method of.

Hereinafter, the present invention will be described in more detail.

In the present invention, the first base plating, the second base plating, the third base plating are sequentially applied to the iron-nickel alloy material, and then palladium or palladium alloy plating is formed thereon to form four plating layers. According to the present invention, the structure of the plated plated with four plating layers is shown in Table 1 below.

The plated body used in the present invention includes any conventional electronic devices such as lead frames, printed circuit boards, and connectors made of iron-nickel alloys. In particular, a lead frame made of alloy # 42 is preferred.

In the present invention, as the primary underlying plating layer, a tin plating layer, a tin-lead alloy plating layer or a tin-bismus alloy plating layer is used.

It is preferable that the tin plating composition for forming a tin plating layer consists of an aqueous solution containing a tin compound in the density | concentration of 20-100 g / L on a tin metal basis. The tin compound is then supplied in a suitable salt form, and examples of the salt include tin methanesulfonic acid tin, first tin sulfate, first tin chloride or mixtures thereof. In addition, the composition may further comprise one or more conductive compounds selected from the group consisting of methanesulfonic acid, sulfuric acid, potassium phosphate and ammonium chloride.

As a plating composition for forming a tin-lead alloy plating layer, it is preferable that it consists of the aqueous solution containing 10-30 g / L of a tin compound on the basis of a tin metal, and 0.5-5 g / L of a lead compound on the basis of a lead metal. . The lead compound is then supplied in a suitable salt form, examples of which include lead methanesulfonate, lead nitrate, lead sulfate, lead acetate or mixtures thereof. Tin compounds which can be used in the composition are as mentioned above. The composition may contain methanesulfonic acid, sulfuric acid, potassium phosphate, ammonium chloride or a mixture thereof as a conductive compound at a concentration of 50 to 300 g / l.

As a plating composition for forming the tin-bismuth alloy plating layer, the tin compound is composed of an aqueous solution containing 10-30 g / l of tin compound on the basis of tin metal and 0.5-5 g / l of bismuth compound on the basis of bismuth metal. desirable. The bismuth compound is then supplied in a suitable salt form, examples of which include bismuth sulfate, bismuth sodium hydrate, bismuth nitrate or mixtures thereof. Tin compounds which can be used in the composition are as mentioned above. The composition may contain methanesulfonic acid, potassium carbonate, sodium carbonate, sulfuric acid, ammonium sulfate or a mixture thereof as a conductive compound at a concentration of 50 to 300 g / L.

In the present invention, a copper plating layer or a copper-bismus plating layer is used as the secondary base plating layer.

The plating composition for forming the copper plating layer is preferably made of an aqueous solution containing 20-50 g / l of the non-cyanide copper compound based on the copper metal, as described in the applicant's Korean Patent Application No. 96-14102. At this time, the non-cyanide copper compound is supplied in an appropriate salt form, and examples of the salt include copper sulfate pentahydrate, cupric pyrophosphate, cupric copper carbonate or a mixture thereof. The composition may contain methanesulfonic acid, potassium pyrophosphate, sodium carbonate, ammonium sulfate, potassium carbonate or a mixture thereof as a conductive compound at a concentration of 50 to 300 g / l.

Plating composition for forming a copper-bismuth alloy plating layer is a bismuth-based copper compound 10 to 50g / L, based on the copper metal, as described in the applicant's Korean Patent Application No. 96-34830 It is preferable to contain at the density | concentration of 0.5-2 g / L on a mus metal basis. At this time, the non-cyanide copper compound and bismuth compound used are as mentioned above. The composition may contain methanesulfonic acid, potassium pyrophosphate, sodium carbonate, ammonium sulfate, calcium carbonate or a mixture thereof as a conductive compound at a concentration of 50 to 300 g / l.

In the present invention, a nickel plating layer is used as the tertiary base plating layer.

The plating composition for forming the nickel plating layer is preferably made of an aqueous solution containing a nickel compound at a concentration of 30 to 100 g / l based on the nickel metal, as described in Korean Patent Application No. 96-2912 of the applicant. . At this time, the nickel compound is supplied in an appropriate salt form, and examples of the salt may include nickel sulfamate, nickel sulfate hexahydrate, nickel carbonate tetrahydrate, amine nickel sulfate or a mixture thereof, so as not to precipitate or neutralize in the plating composition. After reacting with a conductive salt in advance, it is preferable to add to the composition. The conductive compound should be appropriately selected according to the type of metal salt. For example, a concentration of 50 to 300 g / l of methanesulfonic acid, potassium citrate, citric acid, sodium citrate, ammonium sulfate, sodium sulfate, sulfuric acid, or mixtures thereof Can be used as

In the present invention, the plating composition for forming a palladium plating layer or a palladium alloy plating layer is 100% palladium plating, palladium-gold alloy plating, palladium-silver alloy plating or as described in the applicant's Korean Patent Application No. 96-21467 or Palladium-bismuth alloy plating compositions are preferably used.

It is preferable that the dog composition for general palladium plating consists of an aqueous solution containing a palladium compound at a concentration of 2 to 10 g / l based on the palladium metal. Palladium for palladium plating is supplied in a suitable salt form, and examples of the salt include tetrachlorodiammonium palladium, tetraammonium dichloride palladium, diamine palladium dichloride, palladium chloride, tetraamine palladium dichloride or mixtures thereof. . Also. Potassium phosphate, ammonium phosphate, potassium pyrophosphate, ammonium chloride, ammonium sulfate or mixtures thereof can be used as the conductive compound in an amount of 20 to 200 g / l.

The plating composition for the palladium-gold alloy plating is preferably made of an aqueous solution containing a palladium compound at a concentration of 5 to 10 g / l based on the palladium metal and 0.3 to 2.5 g / l based on the gold metal. At this time, the gold compound is supplied in an appropriate salt form, and examples of the salt include tetrachlorogold (111) potassium, gold oxide (111) potassium, gold cyanide (I) potassium or a mixture thereof. Palladium compounds that can be used are as mentioned above. In addition, ammonium phosphate, potassium phosphate, ammonium sulfate, ammonium chloride, potassium pyrophosphate or a mixture thereof can be used in an amount of 20 to 200 g / L as the conductive compound.

The plating composition for the palladium-silver alloy plating is preferably made of an aqueous solution containing a palladium compound at a concentration of 5 to 25 g / l based on the palladium metal, and a silver compound at a concentration of 0.5 to 2.5 g / l based on the silver metal. At this time, the silver compound is supplied in an appropriate salt form, and examples of the salt include silver (I) potassium cyanide, silver nitrate, silver orthophosphoric acid, and mixtures thereof. Palladium compounds that can be used are as mentioned above.

In addition, potassium phosphate, ammonium phosphate. Ammonium sulfate, ammonium chloride. Potassium pyrophosphate or a mixture thereof can be used as the conductive compound in an amount of 20 to 200 g / L.

The plating composition for the palladium-bismuth alloy plating is preferably made of an aqueous solution containing a palladium compound of 5 to 25g / l based on the palladium metal, 0.5-2.5g / l based on the bismuth metal. . In this case, the bismuth compound is supplied in an appropriate salt form, and examples of the salt include bismuth sodium hydrate, bismuth nitrate or a mixture thereof. Palladium compounds that can be used are as mentioned above. In addition, potassium phosphate, ammonium phosphate, ammonium sulfate, ammonium chloride, potassium pyrophosphate or a mixture thereof can be used as the conductive salt in an amount of 20 to 200 g / L.

The primary, secondary and tertiary base plating compositions may include one or more conventional complexing agents, surface modifiers and stress reducing agents in addition to the conductive salts. The base plating compositions are prepared by directly dissolving a plating metal compound, a conductive salt, a complexing agent, and other additives in water, or by reacting the metal salt with a conductive salt or a complexing agent in advance and then dissolving in water to sufficiently react.

Complexing agents that can be used in the present invention include acetic acid series, amine series, imine series, amide series compounds or mixtures thereof, ethylenediaminetetraacetate, nitrilotriacetic acid trisodium monohydrate, nitrilotriacetic acid, triethylenediamine , Triethanolamine, ethanol, polyimine, thioacetamide or mixtures thereof are preferred. The complexing agent is used in an amount of 0.01 to 50 g / l.

Surface improving agents that can be used in the present invention include ammonium series, aldehyde series, imine series, benzene series compounds or mixtures thereof, ammonia water, ammonium citrate, thiodiglycolic acid, sodium tetraphenylborate, 1-phenylsemi Carbazide, ethylenediamine, 2-methoxy-naphthoaldehyde or mixtures thereof are preferred. The surface improver is used in an amount of 0.01 to 50 g / l.

Stress reducing agents that can be used in the present invention include pyridine-based, alcohol-based, sulfone-based, ether-based compounds or mixtures thereof, N-arylpyridinun glolide, tridecyloxyl poly (ethyleneoxy) ethanol (III Naphthalene-1-sulfonic acid (alpha) sodium polyethylene monocetyl ether or a mixture thereof is preferable. The surface improver is used in an amount of 0.01 to 50 g / l.

In the case of forming the primary base plating layer according to the present invention, the primary base plating composition is maintained at 25 to 60 ° C., and the anode of the plated body and the corresponding metal, which is the cathode, is immersed and the current is 2 to 10 ASD (Ampere per). Square Decimeter) to form a primary underlying plating layer having a thickness of 0.5-2 占 퐉 on the plated body.

In the case of forming the secondary base plating layer, while maintaining the composition for secondary base plating at 40 to 60 ° C., the primary base plated object to be a cathode and the anode of the corresponding metal are immersed and the current flows through 2 to 5 ASD. Then, a secondary base plating layer having a thickness of 0.7-1.0 µm is formed on the plated body.

In the case of forming the tertiary base plating layer, while maintaining the tertiary base plating composition at 40-50 ° C, the secondary base plated to-be plated body and the anode of the corresponding metal are respectively immersed and the current is flowed through 4 to 8 ASD The third base plating layer having a thickness of 0.5 to 1.0 mu m is formed on the plated body.

In the case of forming the upper plating layer, while maintaining the upper plating composition at 30 to 45 ° C, the third base plated plated body, which is the cathode, and the anode or insoluble platinum network of the corresponding metal, respectively, are immersed in the anode, and the current is 0.7 to 1.5. It is made to flow to ASD, and the plating layer of 0.1-0.2 micrometer in thickness is formed in a to-be-plated body.

It is preferable to adjust specific gravity of the plating composition used for this invention to 4-25 Be (Baume), and pH to 4-13.5.

The present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited only to the following examples.

The adhesion, crack resistance, corrosion resistance and solderability of the plating layers prepared in the following Examples and Comparative Examples are evaluated according to the following Reference Examples.

Reference Example 1

Adhesion Test

The plated plated body was baked for 2 minutes at 400 ° C. ± 5 ° C. according to Examples and Comparative Examples, and the plated surface of the sample was observed with a magnifying glass 20X or visually to evaluate as follows.

i) There should be no blistering, peeling, lifting and bleeding of the plated material after the baking test (0: excellent, x: poor).

ii) After the baking test, there shall be no scratching, peeling, or plating separation between the flag and the end of the lead with a scratch test with forceps or pointed objects (0: excellent, x: bad).

iii) After the baking test, the scotch sticking tape # 540, # 610, # 810 or the same shall be attached across the strip, pressed firmly with the tip of the nail, and then peeled off quickly so that the plated part does not stick to the tape. (0: good, x: bad).

Reference Example 2

[Crack resistance test]

The plated plated according to the Examples and Comparative Examples were baked at 400 ° C ± 5 ° C for 2 minutes. Subsequently, the test of bending the external lead in one direction by more than 90 °, and then no peeling or lifting when observed with a magnifying glass (20X) or visually (0: excellent) , x: defect).

Reference Example 3

Corrosion Resistance Test

After spraying a 5% NaCl solution on a plated plated body at 40 ° C. ± 5 ° C. for 24 hours according to the Examples and Comparative Examples, it was corroded in a magnifying glass (20 ×) or in the entire portion of the plated lead frame when visually observed. There should be no phenomena such as occurrence, blistering and peeling (0: good, x: bad).

Reference Example 4

[Soldering test]

The plated plated body according to the Examples and Comparative Examples were mold cured at 175 ° C. for 3 minutes, and then mold cured at 175 ° C. for 3 hours. After 96 hours of combustion testing at 145 ° C., steam aging for 32 hours in 95 ° C. steam and flux treatment on Kester solder or α-100. When observed with a magnifying glass (20 X) or visually, a uniform lead application without any pinholes should be at least 95% of the total surface of the sample (0: good, x: poor).

The composition, pH and specific gravity of the composition used in the following examples and comparative examples, temperature and current density conditions at the time of their plating are as follows.

Composition 1: Tin Plating Composition (pH 1, Be 14, 25 ° C., 5ASD)

Methanesulfonic Acid Tin 45g / L

Methanesulfonic acid 210g / ℓ

N-butylidene sulfanic acid 5g / l

Catechol 1g / ℓ

Benzaldehyde 0.05g / ℓ

Resorcinol 0.02 g / l

Composition 2: Tin Plating Composition (pH 1, Be 5, 25 ° C., 2ASD)

20 g / l of first tin sulfate

Sulfuric acid 100g / ℓ

N-cinnamoldenesulfanylic acid 2 g / L

Hydroquinone 3g / ℓ

Aldehyde 1g / ℓ

Benzylidene Acetone 0.01g / ℓ

Composition 3: Tin Plating Composition (pH 7, Be 6, 25 ° C, 2ASD)

30 g / l of first tin chloride

Potassium Phosphate 50g / ℓ

Ammonium Chloride 20g / L

o-chlorobenzaldehyde 2g / ℓ

Pyridinecarboxaldehyde 0.1g / l

Propioaldehyde 0.01 g / l

Composition 4: Tin-Lead Alloy Plating Composition (pH 1, Be 1, 25 ° C., 2ASD)

Methanesulfonic Acid Tin 25g / L

Methanesulfonic acid lead 3g / ℓ

Methanesulfonic acid 200g / ℓ

N-butylidene sulfanic acid 5g / l

Polyethyleneglycol Monoacetyl Ether 15g / L

Composition 5: Tin-bismus Alloy Plating Composition (pH 1 Be 14, 25 ° C., 3ASD)

Methanesulfonic Acid Tin 30g / L

Bismuth Sulfate 5g / ℓ

Methanesulfonic acid 200g / ℓ

N-butylidene sulfanic acid 5g / l

β-naphthol 3 g / l

Pyrocatechol 1g / ℓ

Benzaldehyde 0.4g / ℓ

Composition 6: Tin-Bismouth Alloy Plating Composition (PH 1, Be 14, 25 ° C, 3ASD)

Potassium Tartrate 35g / ℓ

Bismuth Natrun Hydrate 2g / ℓ

Potassium Carbonate 50g / ℓ

Thiodi glycolic acid 13 g / l

5 g / l sodium propionate

Composition 7: Copper Plating Composition (pH 8, Be 8, 50 ° C., 3ASD)

Sulfuric acid pentahydrate 50g / ℓ

Ammonium Sulfate 45g / ℓ

Potassium Sulfate 20g / ℓ

Ethylenediaminetetraacetate Dihydrate 5g / l

Sodium Tetraphenyl Borate 0.5g / ℓ

Diethylene glycol monodecyl ether 0.1g / ℓ

Composition 8: Copper Bismuth Alloy Plating Composition (pH 1, Be 14, 25 ° C, 2ASD)

50 g / l of cuprous pyroic acid

Bismuth Sodium Hydrate 2g / ℓ

Potassium Pyroate 120g / ℓ

1-Penyl Senmi Cabazide 0.5g / L

0.3 g / l N-arylpyridinium chloride

Polyethylene imine 0.03 g / l

Composition 9: Nickel Plating Composition (pH 5, Be 25, 45 ° C, 5ASD)

Nickel sulfamate 450g / ℓ

Ammonium Sulfate 90g / ℓ

Borax 50g / ℓ

Amino acetic acid 5g / l

2-methoxy-1-naphthoaldehyde 0.3g / l

Tridecyloxypoly (ethyleneoxy) ethanol (III) 1 g / L

Composition 10: Pure 100% Palladium Plating Composition (pH 5, Be 7, 30 ° C, 1ASD)

Tetrachlorodiammoniumpalladium 12g / l

Potassium Sulfate 50g / ℓ

Nitrilotriacetic acid 5g / l

Naphthalene-1-sulfonic acid (α) sodium salt 0.1 g / L

Triethylenetetraamine 0.07 g / l

Composition 11: Palladium-Gold Alloy Plating Composition (pH 5, Be 8, 35 ° C, 1ASD)

Tetraammonium Palladium Dichloride 10g / L

Potassium cyanide (I) potassium 0.74 g / ℓ

Ammonium Phosphate 50g / ℓ

4-oxo-pentanoic acid 2 g / l

Benzenesulfonate 0.01 g / l

Composition 12: palladium-silver alloy plating composition (pH 9.5, Be 8, 45 ° C, 1ASD)

Diamine Palladium Dichloride 11g / L

Orthophosphoric acid is 2g / ℓ

Pyrophosphate 60g / ℓ

20 g / l sodium pyrophosphate

Aminoacetic acid 3g / l

2-propene-1-sulfonic acid sodium salt 0.15 g / l

Polyethyleneimine 0.07g / ℓ

Composition 13: palladium-bismuth alloy plating composition (pH 6.5, Be 7, 40 ℃, 1ASD)

Diamine Palladium Dichloride 10g / L

Bismuth Sodium Hydrate 2g / ℓ

Ammonium Chloride 50g / ℓ

Ammonium Sulfate 35g / ℓ

1-phenylsemicarbazide 0.5 g / l

4-methoxybenzaldehyde 0.2 g / l

Example 1

Plating composition 1, a tin primary base plating composition, on a lead frame of iron-nickel alloy (alloy # 42) under a current density of 5 ASD, and composition 7, a secondary base plating composition, on a tin primary base plating layer under a current density of 3 ASD. Plated, and the composition 9, which is a tertiary base plating composition, was plated under a current density of 5 ASD on the copper secondary base plated layer, and the compositions 10 to 13 were plated on the tertiary base plated layer, respectively, to provide a uniform surface of palladium, Pd-Au, and Pd-. A plated body having Ag and Pd-Bi top plating layers and three base plating layers was obtained.

The adhesion, crack resistance, corrosion resistance and solderability of the plated final leadframe were tested according to the methods of Reference Examples 1 to 4 and shown in Table 3.

As can be seen from Table 3, the adhesion, crack resistance, corrosion resistance and solderability of the plated plated according to Example 1 were all excellent.

[Examples 2 to 7]

A plated semiconductor lead frame having a uniform surface was repeated by repeating the method of Example 1 except for changing the types of the first base plating composition, the second base plating composition, the third base plating composition, and the top plating composition as shown in Table 3 below. Got.

The adhesion, crack resistance, corrosion resistance and solderability of the plated final leadframes were tested according to the methods of Reference Examples 1-4 and shown in Table 3.

As can be seen from Table 3, the adhesion, crack resistance, corrosion resistance and solderability of the plated plated according to Examples 2 to 7 were all excellent.

[Comparative Examples 1 to 6]

The method of Example 1 was repeated except that the types of the primary base plating composition, secondary base plating composition, tertiary base plating composition, and top plating composition were changed as shown in Table 2, respectively.

The adhesion, crack resistance, corrosion resistance and solderability of the plated final leadframes were tested according to the methods of Reference Examples 1-4 and shown in Table 3.

As can be seen in Table 3, although the corrosion resistance of the plated plated according to Comparative Examples 1 to 6 was excellent, the adhesion, crack resistance and solderability were generally poor.

As in the present invention, by performing a four-layer plating of the first base plating, the second base plating, the third base plating and the third base plating on the semiconductor lead frame made of the iron-nickel alloy material sequentially, the corrosion resistance is reduced due to the characteristics of the material itself. The phenomenon was suppressed to the maximum, so that excellent properties, especially excellent corrosion resistance, could be obtained even as a thin film.

Claims (9)

In a method of plating a palladium plating layer or a palladium alloy plating layer on an iron-nickel alloy plated body, before the palladium or palladium alloy plating on the plated body, a tin plating layer, tin-lead alloy plating layer or tin-bismusmus A primary base plating to form an alloy plating layer, a secondary base plating to form a copper plating layer, a copper-bismuth alloy plating layer thereon, and a tertiary base plating to form a nickel plating layer thereon. The method of claim 1, wherein the plated body of the iron-nickel alloy material is a semiconductor lead frame. The method of claim 1 wherein the palladium alloy plating layer is formed of an alloy selected from the group consisting of palladium-gold, palladium-silver and palladium-bismus. The method of claim 2, wherein the plated material of the iron-nickel alloy material is a semiconductor leadframe of alloy (Alloy) # 42. The method of claim 1, wherein the tin plating layer is formed using a tin plating composition consisting of an aqueous solution containing 20 to 100 g / l of tin. 6. The method of claim 5, wherein the tin is selected from the group consisting of methanesulfonic acid tin, first tin sulfate, first tin chloride, and mixtures thereof. The method of claim 5 wherein the tin plating composition further comprises at least one conductive salt selected from the group consisting of methanesulfonic acid, sulfuric acid, potassium phosphate and ammonium chloride. The method of claim 1 wherein the tin-lead alloy plating layer is formed using a tin-lead alloy plating composition consisting of an aqueous solution comprising 10-50 g / l tin and 0.5-15 g / l lead. The method of claim 1, wherein the tin-bismuth alloy plating layer is formed using a tin-lead alloy plating composition composed of an aqueous solution comprising 10-30 g / l tin and 0.5-20 g / l bismuth. .