JPH10256708A - Manufacture of circuit electrode portion and circuit electrode portion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce spots and discolorations appearing on the surface of the gold film of a circuit electrode portion or the generations of the cracks of its pad portion and to form the circuit electrode portion with a good bonding ability by suppressing the erosions of its nickel film, when performing its electroless gold plating of a substitution type. SOLUTION: On the surface of a pad base portion 2, formed by a copper plating, a palladium film 3 is formed by an electroless plating to form thereon a nickel film 4 containing phosphorus by an electroless plating. On the surface of the nickel film 4, a gold film 5 is formed by a substitution type electroless plating. Since the phosphorus concentration of the nickel film 4 is lowers as it is nearer the palladium film 3 to its upper layer, the erosions of the nickel film 4 when forming the gold film 5 are suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a circuit electrode and a circuit electrode, and more particularly to a technique suitable for forming a bonding pad on a printed circuit board.

[0002]

2. Description of the Related Art Conventionally, when a bonding pad provided on a substrate such as a printed board and a terminal such as an IC chip are conductively connected to each other, a conductive material such as solder is used between the bonding pad and the terminal. Fix it with paste,
A method of connecting via a gold wire has been adopted. Here, in many cases, a gold film is formed on the pad base for the purpose of increasing the adhesion between the bonding pad and the conductive material and reducing the contact resistance.

When the pad base is formed of a copper pattern, it is difficult to form a gold coating directly, so a nickel coating is formed on the pad base, and the gold coating is formed on the nickel coating. It is formed. Conventionally, as a method of forming such a coating, an electroplating method in which an electrode is attached to a wiring pattern on a substrate to form a coating has been generally used. However, it has become difficult to mount electrodes on wiring patterns as electronic equipment parts have become smaller or denser, and therefore, a method of coating a pad base by electroless plating that does not require electrodes is often used. It has become.

In the conventional manufacturing process, first, FIG.
As shown in (a), the wiring board 20 on which the copper pattern including the pad base 21 is formed is immersed in a palladium chloride solution having a concentration of about 10 ppm so that palladium is adsorbed on the surface of the pad base 21. Next, a nickel coating 22 containing phosphorus is formed by electroless plating on the pad base 21 on which palladium has been adsorbed. Thereafter, a gold film was thinned to a thickness of about 0.05 μm on the nickel film 22 by electroless gold plating using a substitution mold.
Approximately 0.5μm thick by electroless gold plating by reduction type
A gold coating 23 is formed.

Here, in order to form a gold film as thick as about 0.5 μm, reduction type electroless gold plating is usually used. However, when the content of phosphorus in the nickel coating 22 is low, a thick gold coating can be formed even by using substitution-type gold plating which does not require much time for managing the plating bath.

[0006]

However, in the conventional manufacturing process, as shown in FIG. 5B, some irregularities are formed on the surface of the pad base 21 or the adhesion of the plating layer is improved. Therefore, when irregularities are intentionally formed, a portion where the film quality is deteriorated is formed on the nickel film 22 formed thereon. Such nickel coating 2
When the substitution type electroless gold plating is performed on the surface 2, an infiltrated portion is partially formed in the nickel film 22 by a substitution reaction. The eroded portion progresses deeper from the surface of the nickel coating 22 to the inside as the plating processing time becomes longer to thicken the gold coating, and in some cases, penetrates the nickel coating to reach the copper surface. Due to this immersion action, the gold coating 2
There is a problem that stains or discoloration occurs on the surface 23a of the third surface, and cracks are generated by heat when the substrate is heated in a later manufacturing process.

Here, if the nickel coating 22 contains a certain amount of phosphorus, it is possible to prevent the nickel coating 22 from eroding when performing the substitutional gold plating, but at the same time, the formation rate of the substitutional plating decreases. However, there is a problem that the plating layer itself cannot be formed depending on the phosphorus content.

Accordingly, the present invention has been made to solve the above problems, and its object is to suppress the contact of the nickel film when performing the substitution type electroless gold plating, so that the problem appears on the surface of the gold film. An object of the present invention is to form a circuit electrode portion having good bonding properties by reducing the occurrence of spots, discoloration, or cracks in a pad portion.

[0009]

Means taken by the present invention to solve the above-mentioned problem is that at least a surface of a circuit pattern provided on a substrate is formed on a circuit electrode portion made of a material mainly composed of copper. Forming a palladium film entirely by electroless plating, forming a nickel film containing phosphorus by electroless plating on the palladium film, and electroless gold plating by a substitution reaction on the nickel film. And forming a gold film by performing the method.

According to this means, when a palladium film is entirely formed by electroless plating on a circuit electrode portion composed of a material mainly composed of copper, and a nickel film is formed thereon, it is close to a palladium film. In the lower layer, the content of phosphorus in the nickel coating increases, and as it goes to the upper layer, the content of phosphorus decreases. Therefore, when the substitutional electroless gold plating is performed on the nickel film, the upper layer portion of the nickel film can form the gold film without any trouble since the phosphorus content is low, and the quality of the film of the nickel film is temporarily reduced. Even if the erosion occurs in the inferior part, the erosion stops in the lower part where the phosphorus content is high, and the erosion occurs more uniformly in the upper part where the phosphorus content is low rather than in the vertical direction. In addition, contact of the nickel coating is suppressed as compared with the related art, and spots and discoloration of the surface of the gold coating are reduced, and generation of cracks is also prevented.

In addition, the gold film formed by the substitutional electroless plating formed on the nickel film has a fine texture and a smooth surface with few irregularities. improves.

Further, by forming the palladium coating entirely by electroless plating, the nickel coating can be formed more easily than in the prior art, the nickel coating formation speed can be improved, and the upper layer of the nickel coating contains phosphorus. The lower the rate, the higher the rate of gold film formation. Therefore, the processing time of the plating coating step can be reduced.

Here, the plating solution used in the step of forming the nickel film is preferably prepared so that the average content of phosphorus in the formed nickel film is 3 to 10 wt%. .

According to this means, by setting the average phosphorus content of the nickel coating within the range of 3 to 10 wt%, the lower layer having high corrosion resistance and the upper layer capable of performing substitutional electroless gold plating can be obtained. Can be formed. The average phosphorus content of the nickel coating is 10
If the content exceeds 5 wt%, the phosphorus concentration in the upper layer of the nickel coating becomes too high, making it difficult to form a gold coating. On the other hand, if the average phosphorus content of the nickel coating is less than 3 wt%,
It is not possible to obtain a sufficient phosphorus content in the lower layer of the nickel coating to obtain corrosion resistance to substitution type electroless gold plating.

The phosphorus content of the nickel coating is about 3 to 7 wt% in the upper layer, and 8 to 1 wt.
Desirably, it is about 2 wt%. It is difficult to make the phosphorus content of the upper layer lower than the above range in a single plating step, and if it is higher than the above range, it becomes difficult to perform substitutional electroless gold plating. On the other hand, if the phosphorus content of the lower layer portion is lower than the above range, there is a problem in corrosion resistance when performing substitution type electroless gold plating, and if it is higher than the above range, the phosphorus content in the upper layer portion falls within the above range. It becomes difficult to fit.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a method for manufacturing a circuit electrode portion and a structure of the circuit electrode portion according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a sectional process view showing a manufacturing process in this embodiment. In the present embodiment, FIG.
As shown in (a), a wiring pattern is previously formed on a wiring board 1 such as a printed board or an insulating board by copper plating or the like, and a pad base 2 for terminal connection is formed as a part of this wiring pattern. . The plan shape of the pad base 2 is shown in FIG. A slightly widened pad base 2 at the tip of a wiring pattern 11 formed on a wiring board 1
Are formed in parallel. The wiring pattern 11 on the wiring board 1 is covered with a resist 12 except for the surface of the pad base 2.

After sequentially performing degreasing and soft etching with an acid on the surface of the wiring substrate 1, the PDC
Immerse in -10W (manufactured by Ishihara Chemical Co., Ltd., product number)
Activate the copper surface. This PDC-10W is an aqueous solution containing 0.42% of palladium chloride and 20% of sodium acetate as main components.

Next, the wiring board 1 is immersed in an electroless palladium plating bath, and a palladium coating 3 is formed as shown in FIG. The plating solution used for this electroless palladium plating is APP to 1 liter of ion-exchanged water.
-10 (Ishihara Pharmaceutical Co., Ltd., product number) from 160 to 2
40 ml, preferably 200 ml, A
PP-20W (manufactured by Ishihara Chemical Co., Ltd., product number) 40
６０60 ml, preferably 50 ml, were added and mixed, and the bath temperature was 45-55 ° C., preferably 50 ° C. The pH of the plating bath is 7.5-
8.5, preferably 8.2.

The above APP-10 contains 0.9% of palladium chloride and 6.0% of tetrasodium ethylenediaminetetraacetate as main components. In addition, APP-20
W contains 20% of sodium phosphinate. The plating solution contains a small amount of a phosphorus compound, and the alloy composition of the palladium coating is about 96% by weight of palladium and about 4% by weight of phosphorus.

In the present embodiment, the plating process is performed for 5 minutes under the above conditions, and the palladium coating 3 is formed on the pad base 2 so as to have a thickness of about 0.1 to 0.2 μm.

Next, as shown in FIG. 1C, a nickel coating 4 is formed on the palladium coating 3 by electroless plating. For this electroless nickel plating, 150 ml of Nimden NPR-4-M (manufactured by Uemura Kogyo Co., Ltd., product number) per 1 liter of ion-exchanged water and Nimden NPR-4-A (manufactured by Uemura Kogyo Co., Ltd.) , Product number) and Nimden NPR-4-D
(Manufactured by Uemura Kogyo Co., Ltd., product number) was added to each of 5 ml, and the mixture was stirred and adjusted to a liquid temperature of 79 to 81 ° C, preferably 80 ° C. PH of plating solution is 4.5-
4.7, preferably 4.6.

Immerse in the above plating solution for about 30 minutes,
A nickel coating 4 of μm was formed. The above plating solution contains a compound of phosphorus together with nickel (hypophosphite, etc.)
The nickel coating 4 is prepared so that the average composition of the nickel coating 4 is about 93 wt% nickel and about 7 wt% phosphorus.

Finally, on the nickel coating 4, FIG.
As shown in (d), a gold film 5 is formed by performing substitution type electroless gold plating. The electroless gold plating in this embodiment is performed in two stages. First, the surface 4a of the nickel coating is subjected to displacement plating by thinning a gold coating (not shown) to a thickness of about 0.05 μm in about 10 minutes by using a strike bath. Next, on the thinned gold film, substitution type electroless gold plating is performed for about 10 to 15 minutes using a neutral bath to finally form a gold film 5 having a thickness of about 0.5 μm. I do.

The strike bath includes Orical TSS
-22 (manufactured by Uemura Kogyo Co., Ltd., product name). This is equivalent to 1 liter of ion-exchanged water per Oral TSS
22-M20 (product name, manufactured by Uemura Kogyo Co., Ltd.)
0 ml, 6.0 g of potassium gold cyanide,
Potassium cyanide was mixed at a rate of 100 ml, and the pH was adjusted to 4.5 with ammonia water or citric acid.
6.0, preferably 4.8, and the liquid temperature is 75-85.
° C, preferably 75 ° C.

In addition, the above-mentioned neutral bath contains Orical TTT.
-11 (manufactured by Uemura Kogyo Co., Ltd., product name). This is equivalent to the Oral TTT per liter of ion-exchanged water.
500--11-M2 (product name, manufactured by Uemura Kogyo Co., Ltd.)
Milliliter, 5.9 g of potassium gold cyanide and 0.05 ml of potassium cyanide were mixed to adjust the pH, and each component was appropriately replenished.
Gold concentration of 3.6 to 4.1 g / liter, preferably 4 g
/ Liter, pH 4.6-5.0, preferably 4.8
It is what it was.

The pad base 2 formed as described above
The upper laminate structure is shown in FIG. FIG. 2 shows a state in which a cross section of the wiring substrate 1 is observed by a scanning electron microscope (SEM). A thin palladium coating 3 is entirely coated on the surface of the pad base 2 made of copper, and a nickel coating 4 is laminated thereon. In the cross section of the nickel coating 4, a portion (hereinafter, referred to as a lower layer) substantially below the intermediate position 4 b of the thickness of the nickel coating 4.
In the figure, horizontal stripes (not shown) are seen, and it is observed that a plurality of layers are stacked. In the portion above the intermediate position 4b (hereinafter, referred to as an upper layer portion), the above-mentioned stripes are not seen, and it is observed that almost the entire film is formed uniformly.

An eroded portion 4c extending downward from an interface 5a with the gold coating 5 covering the nickel coating 4 is formed in the upper layer of the nickel coating 4. These eroded portions 4c are:
It is a cavity formed by the erosion of the nickel film 4 generated by the substitution type electroless plating process, or a denatured portion whose film quality is roughened by the erosion. These eroded portions 4c
Of the deepest ones, the tip position is stopped at the lower part of the upper part or the upper part of the lower part.

Compared with the cross section of the conventional laminated structure shown in FIG. 5B, in the conventional structure, the eroded portion penetrates to the lower portion of the nickel layer, and in extreme cases, extends to the copper pattern portion. In the cross section of the present embodiment, the eroded portion 4c
Are stopped inside the nickel coating 4 and do not enter the lower layer of the nickel coating 4.

Further, it is thought that this is related to the above-mentioned change in the cross-sectional structure, but the surface aspect of the surface 5b of the gold coating 5 is also considerably changed. Observation with a microscope or the like on the surface of the conventional gold film reveals that rough irregularities are formed, but in the present embodiment, it has changed to a fine irregular shape of about 1/10 times that of the related art. The vertical height of the irregularities is also small,
It has been smoothed. In addition, almost no stains or discoloration observed on the surface of the conventional gold film occurred.

In the laminated structure formed according to the present embodiment, the cross section observed by the SEM was analyzed by electron beam microprobe X-ray analysis. In this analysis, the atomic species constituting the nickel coating were specified, and a quantitative analysis was performed for each atomic species by the ZAF method. As a result, the phosphorus content in the lower layer was 5.18 wt%, whereas the phosphorus content in the upper layer was 3.18 wt%.
It was 92% by weight. Further, after the surface damage layer formed on the polished surface of the cross section was removed by soft etching with an acid, the same measurement and quantification were performed. As a result, the phosphorus content in the lower layer was 7.32 wt%, and the phosphorus in the upper layer was The phosphorus content was 6.59 wt%.

As described above, in the present embodiment, the film quality and the phosphorus content are different between the upper layer portion and the lower layer portion of the nickel coating. Since gold plating can be easily performed and the phosphorus content in the lower layer is high, the nickel film is hardly eroded in the depth direction, and the eroded portion 4c does not penetrate into the lower layer. Therefore, the surface state of the nickel coating 4 is smoother than before, the gold coating can be formed uniformly, and the surface of the gold coating can be formed more evenly and flatter than before.

In the above-described manufacturing process, the formation speed of the nickel coating 4 is improved by forming the palladium coating 3, the surface condition of the nickel coating 4 is also improved, and the phosphorus in the upper layer of the nickel coating is improved. Due to the decrease in the content, the formation rate of the gold film was also improved. It takes about 25 minutes to form a 0.5 μm thick gold film using the same plating solution as in the present embodiment on a nickel film formed using the same plating solution as in the present embodiment by the conventional method. However, in the present embodiment, it can be formed in about 10 minutes.

In the above embodiment, the palladium plating solution and the palladium coating contain phosphorus.
A similar effect can be obtained without any problem even with a palladium coating containing no phosphorus.

Further, according to the present embodiment, the palladium coating is formed to a thickness of 0.1 μm to 0.2 μm, but the palladium coating may be formed entirely on the pad base 2. Actually, it is considered that the coating is almost entirely formed when the thickness of the palladium coating is 0.01 μm or more. The upper limit of the thickness of the palladium coating is 0.2
It is preferably about μm. This is because even if the film is formed thicker than this, there is no difference in the effect, and it takes time and material for the plating process, so that it is not economical.

In this embodiment, a phosphoric acid compound is mixed in the electroless nickel plating bath so that the nickel film contains about 6 to 7 wt% of phosphorus as a whole. It was found that the lower layer of the nickel film contained about 5 to 9 wt% of phosphorus and the upper layer contained about 3 to 7 wt%. Although the cause is not clear, it is considered that phosphorus in the nickel plating solution is more easily deposited on the palladium coating than nickel. Further, since the film quality of the upper layer portion and the lower layer portion is different, the deposition composition may be different depending on the film quality.

If a plating solution is prepared for the nickel coating so that the average phosphorus content in the coating is 3 to 10 wt% as a whole, it is effective as a base for gold coating on the pad base. is there. If the average phosphorus content in the nickel coating is less than 3 wt%, even in the lower part close to the palladium coating, sufficient corrosion resistance to the substitutional electroless gold plating solution cannot be obtained. If the average phosphorus content exceeds 10% by weight, it is not possible to obtain a low phosphorus content of the nickel film to such an extent that substitutional electroless gold plating can be effectively performed even in the upper layer portion close to the surface.

In general, in substitutional electroless gold plating, the lower the phosphorus content of the nickel coating 4, the more easily the substitution reaction occurs. Conversely, the higher the phosphorus content in the nickel coating 4, the higher the substitution reaction. Is less likely to occur. It is considered that the critical region of the phosphorus content of the nickel film in which the substitution type electroless gold plating can be performed is about 6 to 8 wt%. In the present embodiment, since the phosphorus content of the upper layer of the nickel coating 4 is lower than the average content in the nickel coating, the nickel coating 4 is easily formed. Therefore, the average content in the nickel coating is 10%.
When the amount is less than wt%, it is sufficiently possible to form a gold film on the nickel film by substitution type electroless gold plating.

In particular, the phosphorus content of the nickel coating is desirably about 3 to 7 wt% in the upper layer and about 8 to 12 wt% in the lower layer. It is difficult to make the phosphorus content of the upper layer lower than the above range in a single plating step, and if it is higher than the above range, it becomes difficult to perform substitutional electroless gold plating. On the other hand, if the phosphorus content of the lower layer portion is lower than the above range, there is a problem in corrosion resistance when performing substitution type electroless gold plating, and if it is higher than the above range, the phosphorus content in the upper layer portion falls within the above range. It becomes difficult to fit.

The eroded portion 4c extends downward from the interface 5a between the gold coating 5 and the nickel coating 4. It is considered that the eroded portion 4c is formed when a weak portion of the nickel coating 4 is dissolved in the plating solution. Although the depth of the eroded portion 4c varies depending on the location, even the deepest formed portion stops at the upper portion of the lower layer of the nickel coating 4. This is because in the nickel coating 4, the phosphorus content increases toward the lower layer, so that the substitution reaction between the plating solution and the nickel coating does not easily occur, so that the eroded portion 4 c does not easily extend downward. It seems to be because.

The immersion of the gold plating in the lower layer of the nickel coating 4 is stopped, so that the contamination of the gold plating bath by the copper caused by the erosion 4c reaching the pad base 2 as in the prior art is prevented. Can be prevented, and the life of the gold plating bath can be increased.

FIG. 4 shows a resist layer 1 according to this embodiment.
FIG. 4 is a longitudinal sectional view showing a laminated structure on a pad base near an outer edge of the pad base; Since the structure of each plating film is the same as that shown in FIG. 1D, the same components are denoted by the same reference numerals and description thereof will be omitted. As shown in FIG. 4, the thickness of each of the coatings at the portion in contact with the side surface 12a of the resist layer 12 covering the wiring pattern 11 is slightly increased, and there is no particular disorder in the film formation. It has a smooth outer edge.

On the other hand, FIG. 6 shows a case where a film is formed by the above-mentioned conventional manufacturing method, in which the concentration of palladium chloride in the solution in which the wiring substrate 1 is immersed before the nickel plating step is 1%.
The contact portion with the resist layer 12 when the concentration is increased from 0 ppm to 20 ppm is shown. Here, a nickel film 22 and a gold film 23 are laminated on the pad base 21 in this order. Palladium as a catalyst is only adhered between the pad base 21 and the nickel coating 22, and the palladium coating is not entirely formed on the surface of the pad base 21. In this case, the nickel coating 22 in a portion in contact with the side surface 24a of the resist 24 is formed to be unusually thick, and the nickel coating 22 has a cross-sectional shape that rises upward along the side surface 24a of the resist layer 24. ing.

Although the cause of the abnormal shape of the outer edge of the nickel coating 22 shown in FIG. 6 is not clear, the immersion in the conventional palladium chloride solution used as a catalyst solution will
The palladium solution accumulates at the interface between the pad base 21 and
From this, it is considered that the nickel coating 22 grows abnormally.

In this embodiment, since the palladium coating is formed on the pad base, it is not necessary to bring the catalyst solution into contact with the periphery of the pad base and maintain the adhered state of the deposited palladium. It is considered that abnormal precipitation of nickel at the step can be prevented.

[0046]

As described above, according to the present invention, a palladium film is entirely formed by electroless plating on a circuit electrode portion composed of a material mainly composed of copper, and a nickel film is formed thereon. When formed, the phosphorus content in the nickel coating increases in the lower layer near the palladium coating, and the phosphorus content decreases as it goes to the upper layer. For this reason,
When the substitution type electroless gold plating is performed on the nickel film, the upper layer portion of the nickel film can form the gold film without any trouble due to the low phosphorus content, and the portion of the nickel film having poor film quality can be temporarily formed. Even if erosion occurs, erosion stops in the lower part with a high phosphorus content, and erosion occurs uniformly in the upper part with a low phosphorus content rather than in the vertical direction. Also, the contact of the nickel coating is suppressed, the stain and discoloration of the surface of the gold coating are reduced, and the generation of cracks is also prevented.

The gold film formed on the nickel film by the substitutional electroless plating has a smooth surface with fine texture and little unevenness, so that the bonding property of the circuit electrode portion is improved. improves.

Further, since the palladium film is entirely formed by electroless plating, the nickel film can be formed more easily than in the conventional case, the formation speed of the nickel film can be improved, and the upper layer of the nickel film contains phosphorus. The lower the rate, the higher the rate of gold film formation. Therefore, the processing time of the plating coating step can be reduced.

[Brief description of the drawings]

FIGS. 1A to 1D are process cross-sectional views illustrating an embodiment of a method for manufacturing a circuit electrode portion according to the present invention.

FIG. 2 is an enlarged vertical sectional view showing an embodiment of a laminated structure of a circuit electrode portion according to the present invention.

FIG. 3 is an enlarged plan view showing a part of the planar shape of the wiring board in the embodiment.

FIG. 4 is an enlarged longitudinal sectional view showing a shape of a contact portion between a resist layer and each plating film in the embodiment.

FIG. 5A is an enlarged longitudinal sectional view showing a conventional laminated structure of a plating film on a pad base and FIG. 5A is an enlarged longitudinal sectional view showing a state of a laminated plating film.

FIG. 6 is an enlarged vertical sectional view showing a shape of a contact portion between a resist layer and each plating film in a conventional laminated structure of a plating film of a pad base.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 20 Wiring board 2, 21 Pad base 3 Palladium coating 4, 22 Nickel coating 5, 23 Gold coating 11, 24 Resist layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Mayumi Minato 1528 Toyohira, Chino-shi, Nagano Pref.

Claims (5)

[Claims] A step of forming a palladium coating entirely by electroless plating on a circuit electrode portion at least a surface of a circuit pattern provided on a substrate is made of a material mainly composed of copper; A circuit comprising: a step of forming a phosphorous-containing nickel film on a film by electroless plating; and a step of forming a gold film by performing electroless gold plating by a substitution reaction on the nickel film. Manufacturing method of the electrode part. 2. The nickel plating solution according to claim 1, wherein the nickel plating solution used in the step of forming the nickel coating comprises:
The average content of phosphorus in the nickel film to be formed is 3 to 10.
A method for producing a circuit electrode portion, wherein the method is prepared so as to be wt%. 3. The nickel coating according to claim 1, wherein the content of phosphorus in the upper layer of the nickel coating is less than 7 wt% and the content of phosphorus in the lower layer of the nickel coating is 8 wt% or more. A method for manufacturing a circuit electrode portion, wherein a film is formed by adjusting a phosphorus concentration of a nickel plating solution in a forming step. 4. A palladium film entirely formed on a circuit electrode portion at least a surface of a circuit pattern provided on a substrate is made of a material mainly composed of copper;
A nickel coating containing phosphorus formed on the surface of the palladium coating; and a gold coating formed by substituting the surface of the nickel coating. The lower layer of the nickel coating has a relative phosphorus content. A circuit electrode portion formed so as to have a relatively high phosphorus content in an upper layer portion of the nickel coating. 5. The method according to claim 4, wherein the upper layer of the nickel coating has a phosphorus content of 3 to 7 wt%, and the lower layer of the nickel coating has a phosphorus content of 8 to 12 wt%. Circuit electrode part.