JPH05306470A - Catalytic solution for selective electroless plating - Google Patents

Abstract

PURPOSE:To selectively deposit Pd metal only on a conductive pattern and to facilitate production control at the time of applying electroless plating on the conductive pattern of a substrate for electronic parts. CONSTITUTION:In a catalytic solution for electroless plating containing mainly a water soluble Pd salt, an ammonium compound as a complexing agent of Pd ion, an inorganic acid and a pH adjusting agent, the ammonium compound of 750-1500mol. to Pd salt of 1mol. is used and the value of pH is 2.5-4. As a result, Pd metal is selectively deposited only on the conductive pattern and the optimum application condition area of the solution is wide, that is, production control is facilitated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst solution for electroless plating for selective electroless plating only on a conductor pattern on a substrate such as an electronic component.

[0002]

2. Description of the Related Art After a wiring (conductor) pattern of copper (Cu) is formed on a synthetic resin substrate such as glass epoxy resin, paper phenol resin, or polyimide resin, nickel (Ni) or gold (Au) is further formed on the conductor pattern. ) Etc. may be selectively applied. In that case, the conductor pattern must be activated. As the activation means, a catalyst liquid containing Pd is generally used. The metal of the conductor pattern is replaced by Pd, and the electroless plating film is made of this metal Pd.
Precipitates on d. A first method for selectively depositing the electroless plating based on the activity of Pd is a method of coating the portion other than the plated portion of the metal pattern with a resist and depositing Pd only on the conductor pattern. This method is electroless N
In more detail, an example of i plating will be described. After immersing the substrate on which the conductor pattern is provided in a sensitizing liquid (SnCl ₂ —HCl) containing first tin (Sn) ions, an activity containing Pd ions is activated. Liquid (PdCl ₂ -HCl)
Or an activation liquid containing first Sn ions and Pd ions. However, the first Sn ion,
Since Pd ions have strong adsorptivity, it is said that Pd eventually deposits on the entire surface of the substrate (JP-A-2-24027).
(See No. 1). Therefore, after that, the resist is peeled off to leave only Pd deposited on the conductor pattern, and the initial deposition of electroless Ni plating is performed only on the conductor pattern using Pd as a catalyst. The second method is as follows.
As disclosed in Japanese Patent No. 31188, the two-step treatment of performing Pd activation with high catalytic activity on a substrate provided with a conductor pattern for a short time and gold activation with gold cyanide with low catalytic activity is performed. Due to the synergistic effect of using the two together, there is a method of performing electroless plating without causing bridges between conductor patterns at the stage of electroless plating.
Then, in the third method, as shown in JP-A-62-238374, a part of the substrate on which the conductor pattern is provided is subjected to Pd treatment, and then electroless plating treatment is performed. Then, it is possible to selectively deposit a plating metal, such as nickel, on the conductor pattern of the Pd-untreated portion several tens of seconds after the plating deposition starts from the Pd-treated portion. In the Pd-treated portion, the electroless plating is also applied outside the conductor pattern, so the conductor pattern is in an electrically short-circuited state. Therefore, the Pd treated part is removed (cut)
However, there is a method of obtaining a desired conductor pattern which is circuit-independent from this. Further, as a fourth method, Japanese Patent Application Laid-Open No. Hei 2
As disclosed in Japanese Patent Application Laid-Open No. 101172, a ceramic part having a tungsten (W) or molybdenum (Mo) coating is selectively metallized on the W and Mo films by a two-step treatment with an aqueous cyanide solution and an aqueous PdCl ₂ solution. There is a method of precipitating Pd and then immersing it in an electroless nickel plating solution so that plating is not deposited on the ceramic portion and an electroless plating coating is formed only on the W and Mo films. As a fifth method, it is possible to add P by adding an inorganic acid to a water-soluble Pd salt without directly coating the substrate on which the conductor pattern is formed with a resist.
Conventionally, there is a method of immersing in a d-active liquid to selectively activate the conductor pattern. This method is not the adsorption of Pd
Since it is based on the substitution reaction of Pd with the metal (for example, Cu) of the conductor pattern, it is said that the fact that the adsorptivity of Pd is different between on the conductor and on the non-conductor is used (Japanese Patent Laid-Open No. Hei 10 (1999) -135242) 2-240271).

[0003]

In the methods shown in the first to fourth prior arts, the number of steps is large and complicated, the work efficiency is poor, and the cost is high. In addition, the methods shown in the second and fourth methods are not so preferable because the demand for non-cyanation has recently been increasing from the viewpoint of environment and health of workers. Therefore, as a solution to these problems, the fifth method is desirable and has been widely used recently.
However, this method reduces the amount of Pd adsorbed on the non-conductive substrate to O
It is difficult to perform K, and therefore an electrical short circuit is likely to occur between the conductor patterns. Since the longer the immersion time in the catalyst solution is, the more likely the bridge is to occur, the optimum use range of the catalyst solution is narrow, and it can be said that work management is difficult. Therefore, the present invention is a method of selectively depositing metal Pd only on a conductor pattern, in which no bridges are formed between conductor patterns, the optimum use range of the catalyst liquid is wide, and work management is easy, and selective electroless A plating catalyst is applied.

[0004]

In the present invention, various studies have been made in order to achieve the above object. As a result, the water-soluble Pd salt and ammonium compound were mixed at 1: 750 to 1: 1.
By adjusting the molar ratio to 500, adjusting the pH to 2.5 to 4.0, and treating the substrate on which the conductor pattern is provided with this solution, the activation step can be performed on the conductor pattern in a single treatment. It has been found that the metal Pd can be selectively precipitated only, and the range of optimum use conditions is wide, which can facilitate process control. Therefore,
This method will be described in detail. When the molar ratio of the water-soluble Pd salt to the ammonium compound is less than 1: 750 or the pH is less than 2.5, activation of the conductor pattern is performed at a treatment temperature of 25.
In case of performing electroless Ni plating treatment at 5 ° C for 5 minutes,
It was found that Ni bridges are likely to occur between the conductor patterns, and Ni bridges are more likely to occur as the treatment time becomes longer. In other words, under these conditions, the range of optimum use conditions is narrow, which makes it difficult to control the process. Also, the pH
When the value exceeds 4, the Pd catalytic activity on the conductor pattern is weakened, and the time for starting the electroless plating deposition on the conductor pattern is delayed. If the molar ratio of PdCl ₂ and NH ₄ Cl exceeds 1: 1,500, it is difficult to dissolve NH ₄ Cl, which is a defect in production. The molar ratio of the water-soluble Pd salt to the ammonium compound is 1: 750 to 1: 1.
When the pH is adjusted to the range of 2.5 to 4 in the range of 500, the metal Pd can be selectively deposited only on the conductor pattern, and even if the activation treatment time is long, after the electroless plating, a space between the conductor patterns is formed. No metal bridge is generated. Therefore, it can be said that the range of optimum use conditions is wide and process control is easy. From the above, in order to selectively deposit the metal Pd only on the conductor pattern and to widen the range of the optimum use condition, the Pd salt Pd formed in the liquid is simply added.
It has been found that the properties of the palladium ammonium complex of the ion with the ammonium ion of the ammonium compound do not achieve the above objectives. Rather, this complex functions to stabilize Pd ions in the solution, and it can be said that an excess amount of ammonium compound contained in the solution is necessary to achieve the above object. ..

[0005]

Example An electroless plating catalyst solution having the composition shown in Table 1 was prepared. (However, pH was adjusted with NaOH.) Next, the glass epoxy substrate on which the Cu pattern was formed was subjected to electroless nickel (Ni) plating by the steps shown in Table 2. Table 1 also shows the deposition state of the electroless Ni plating for each substrate treatment time of the electroless plating catalyst solution at that time.

[0006]

[Table 1]

[0007]

[Table 2]

From Table 1, the glass epoxy substrate treated with the electroless plating catalyst solution of the present invention surely selectively deposits metal Pd only on the conductor pattern, and the electroless Ni
The plating could be coated.

Comparative Example A catalyst solution for electroless plating having the composition shown in Table 3 was prepared (however, the pH was adjusted with NaOH). Next, the catalyst solutions for electroless plating shown in Table 3 were applied in the same manner as in the examples.
Table 3 also shows the deposition state of the electroless Ni plating for each substrate treatment time of the electroless plating catalyst solution at that time.

[0010]

[Table 3]

From Table 3, with the PdCl ₂ --HCl system electroless plating catalyst solution, when the treatment time was 30 seconds and the pH was 3 or more, Ni bridges did not occur between the conductor patterns. However, when the treatment time exceeded 30 seconds, Ni bridges were generated at any pH. Also PdCl ₂ / NH ₄ Cl
With the catalyst liquid for electroless plating of> 1/750 and pH <2.5, Ni bridges were generated when the treatment time was long.

[0012]

EFFECTS OF THE INVENTION By treating a substrate provided with a conductor pattern with the electroless plating catalyst solution of the present invention, metal Pd is selectively deposited only on the conductor pattern, and electroless plating is selectively performed. be able to. Further, the catalyst liquid has a wide optimum use range, and therefore work management is easy.

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[Procedure amendment]

[Submission date] June 2, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

[0010]

[Table 3]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Yamamoto 1245 Morisoejima, Shimodate-shi, Ibaraki Hitachi Boden Co., Ltd.

Claims (3)

[Claims] 1. A catalyst solution for electroless plating, which comprises a water-soluble palladium (Pd) salt, an ammonium compound as a complexing agent for Pd ions, an inorganic acid, and a pH adjuster as essential components. 2. The catalyst solution for electroless plating according to claim 1, wherein the molar ratio of the water-soluble Pd salt to the ammonium compound is in the range of 1: 750 to 1: 1500. 3. The catalyst solution for electroless plating according to claim 1, wherein the pH is in the range of 2.5 to 4.0.