JP2010205884A - Method of manufacturing electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electronic component for forming a plating film having a substantial thickness even by using a plating bath that is weak acid to neutral to weak alkaline with less damage to the electronic component when forming the plating film having Cu as a principal component to the electrode surface of the electronic component without using a power supply and performing catalytic treatment. <P>SOLUTION: A method of manufacturing an electronic component includes a step of forming a plating film on an electrode by mixing an electronic component element assembly having an electrode containing Cu or Ag as a principal component and a conductive medium having at least a surface showing catalytic activity to the oxidation reaction of hypophosphorous acid in the plating bath containing Cu ions and hypophosphorous acid. In the method of manufacturing the electronic component, the plating bath contains Ni ions. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an electronic component and an electronic component, and more particularly to a method for manufacturing a chip-type electronic component such as a multilayer capacitor or a noise filter, and an electronic component manufactured using the manufacturing method.

  Conventionally, electronic parts with Cu electrodes and Ag electrodes formed on the surface of the ceramic body have been subjected to Cu plating, Ni plating, Sn plating, etc. to improve the heat resistance and solder wettability of the electrodes. A plating film is formed on the substrate.

  This Cu plating is generally performed by electrolytic plating using a power source, specifically, electrolytic barrel plating in which energization is performed while stirring together with a conductive medium in a container filled with a plating bath.

  This electrolytic barrel plating has a problem that a large power source is required. Moreover, there is a problem that the plating film thickness deposited on the electronic component also varies due to current density variation in the container. If electroless Cu plating is used, the above-mentioned problems can be solved. However, it is necessary to perform the catalytic treatment for activating the reducing agent's reducing action only on the portion to be plated by masking or the like, and this process is complicated. .

  Therefore, Patent Document 1 discloses a method of performing electroless plating on the electrodes of a chip-type electronic component without using a power source without using a prior catalyst treatment. That is, the method is characterized in that a conductive medium exhibiting catalytic activity for the oxidizing reaction of the reducing agent is mixed with the electronic component body in a plating bath to form a plating film on the electrode.

JP 2003-183843 A

  In the method of manufacturing an electronic component described in Patent Document 1, formaldehyde is required as a reducing agent for electroless Cu plating, and the pH of the plating bath needs to be made high alkali in order to develop the reducing ability of formaldehyde. . The practical complexing agent that stabilizes Cu as a complex in a highly alkaline solution is about EDTA. However, this EDTA dissolves the ceramic body of the electronic component and causes a defect in the reliability of the electronic component.

  Therefore, the pH of the plating solution needs to be weak acid, neutral, or weak alkali, but hypophosphorous acid is a practical reducing agent in this range.

  However, when hypophosphorous acid was used as the reducing agent, there was a problem that the Cu precipitation reaction stopped early. This seems to be because once Cu is deposited even a little, the portion to be plated loses the catalytic ability for the reducing agent. In this case, the construction method using a conductive medium exhibiting catalytic activity is not sufficient, and complicated catalyst treatment such as thick application of Pd particles becomes necessary.

  Therefore, an object of the present invention is to eliminate the need for a complicated catalyst application step when forming a plating film containing Cu as a main component by electroless plating on a Cu electrode or an Ag electrode, and to provide an electronic component body. It is to provide a plating method for obtaining a plating film having a smooth and practical thickness without being eroded.

  That is, the present invention relates to an electronic component body having an electrode mainly composed of Cu or Ag, and a conductive medium having at least a surface having catalytic activity for an oxidation reaction of hypophosphorous acid. In the method of manufacturing an electronic component including a step of mixing in a plating bath containing an acid and forming a plating film on the electrode, the plating bath contains Ni ions, .

  Further, the present invention is characterized in that in the step of forming the plating film, the content of Cu ions in the plating bath at the start of plating is reduced in advance, and the operation of replenishing Cu ions after the start of plating is characterized. It is also preferable to do. More preferably, the Cu ion content in the plating bath at the start of plating may be substantially zero.

  Furthermore, in the present invention, it is also preferable that the plating bath contains citric acid.

  The present invention is also directed to an electronic component having an electrode mainly composed of Cu or Ag on the surface of the electronic component element body. In this electronic component, the Cu-Ni-P plating layer is provided on the electrode, and the Cu concentration in the vicinity of the surface of the plating layer near the electrode is Cu in the vicinity of the surface of the plating layer far from the electrode. The Ni concentration in the vicinity of the surface of the plating layer that is lower than the concentration and closer to the electrode of the plating layer is higher than the Ni concentration in the vicinity of the surface of the plating layer that is far from the electrode.

  According to the method for manufacturing an electronic component of the present invention, Ni ions contained in the plating bath suppress preferential precipitation of Cu ions, and Cu ions and Ni ions co-precipitate. Due to the coprecipitation state and the mixing of a conductive medium having catalytic activity for hypophosphorous acid, the surface to be plated is kept in good catalytic activity for hypophosphorous acid. A plating film is obtained.

  In addition, this method makes it possible to form a plating film containing Cu as a main component without using formaldehyde and EDTA, so that the body of the electronic component is not eroded and a highly reliable electronic component can be obtained.

  Furthermore, this method eliminates the need for a complicated catalyst application step such as applying Pd particles thickly, which simplifies the plating step and is also expected to improve yield.

  In the present invention, when the content of Cu ions in the plating bath at the start of plating is reduced in advance and the operation of replenishing Cu ions after the start of plating is included, the preferential precipitation of Cu ions is more reliably suppressed. Therefore, the co-precipitation state of Cu ions and Ni ions continues for a relatively long time. Therefore, it is possible to form a thicker plating film.

  In the method for producing an electronic component of the present invention, citric acid is preferable as the complexing agent for the Cu plating bath, and stable deposition behavior of Cu can be ensured.

  In the electronic component of the present invention, in the Cu—Ni—P plating layer formed on the electrode, the Ni concentration is high on the side close to the electrode, and the Cu concentration is high on the side close to the plating layer surface. Therefore, both the solder erosion resistance and the solder wettability can be made better.

It is a cross-sectional photograph of a Cu-Ni-P plating layer. It is a line analysis result of the composition concentration in the layer direction of a Cu-Ni-P plating layer.

  In the electronic component according to the present invention, an electrode made of a conductor is formed on an element body of the electronic component. Examples of the electronic component element body include ceramics, and may be a laminate having internal electrodes.

  The electrodes formed on the electronic component body are mainly composed of Cu or Ag, and may be alloys thereof. For example, an external electrode coated with a conductive paste containing metal powder such as Ag or Cu, an organic vehicle, or glass frit and baked can be used. Other examples include metal films formed by sputtering or vapor deposition.

  The conductive medium is a metal having at least a surface having a catalytic action on hypophosphorous acid which is a reducing agent of the plating bath. Examples thereof include at least one metal selected from gold, nickel, palladium, cobalt, platinum, or an alloy thereof. The size of the conductive medium is not particularly limited, but those having a diameter of 0.1 to several mm are preferably used.

  The salt as a Cu source in the Cu plating bath is not particularly limited as long as the object of the present invention is not impaired. For example, copper sulfate, copper nitrate, copper chloride and the like are included. The same applies to the salt as the Ni source, for example, nickel sulfate, nickel chloride, nickel sulfamate and the like.

  As the reducing agent in the Cu plating bath, hypophosphorous acid or hypophosphite is mainly used. Hypophosphorous acid has a reducing action even in weak acids, medieval times, and weak alkalis, so that it can be plated while preventing dissolution of the electronic component body.

  As the complexing agent in the Cu plating bath, a carboxylic acid type is preferably used, but citric acid is particularly preferable in order to keep the precipitation behavior of Cu and Ni stable.

  Moreover, a plating bath may contain a electrically conductive agent, a pH adjuster, surfactant for improving film quality, etc. as needed. The pH of the plating bath is particularly preferably around 8.5 to 11.0 in order to keep the precipitation behavior of Cu and Ni stable.

  In the plating step of the present invention, the Cu plating film is formed by stirring the conductive medium and the electronic component element body in a plating container such as a barrel filled with a Cu plating bath and bringing them into contact with each other. . When a metal having a catalytic action on hypophosphorous acid on the surface of the conductive medium comes into contact with an electrode on the electronic component body, the vicinity of the contact portion in the electrode is activated. At this time, metal ions existing in the vicinity of the contact portion are deposited on the electrode. This is the principle that electroless plating is possible without a catalyst application step such as prior Pd particles (the same action as in Patent Document 1).

  However, when electroless plating is performed using the above-described principle, the precipitation reaction stops as soon as the Cu plating film is thinly formed on the electrode. This is because Cu does not have a catalytic ability for hypophosphorous acid and the catalyst application by the conductive medium having the above-mentioned catalytic activity is not as strong as the conventional Pd application process.

  Therefore, in the present invention, the plating bath contains not only Cu ions but also Ni ions. As a result, since Cu ions and Ni ions co-precipitate, Ni having a catalytic ability for hypophosphorous acid is always present on the surface of the portion to be plated. Together with the application of the catalyst by the conductive media having Cu, both Ni and Cu continue to precipitate. As a result, a Cu—Ni—P plating layer having a practical thickness can be obtained.

  In order to stably continue the co-precipitation behavior of Cu and Ni for a long time, the Cu / Ni ratio of the Cu plating bath at the start of plating should be lowered in advance, and additional Cu after that may be additionally replenished. preferable. This is because, in order to maintain good catalytic performance for hypophosphorous acid in the portion to be plated, it is preferable to make Ni precipitation at the initial stage of the reaction more reliable. However, since the plating layer in the present invention is a Cu alloy film mainly containing Cu, it is preferable to replenish a necessary Cu source later. Further, the Cu concentration at the start of plating may be made zero as long as the object of the present invention is not impaired.

  In the Cu—Ni—P plating layer thus obtained, the Ni concentration is high on the side close to the electrode, and the Cu concentration is high on the side close to the plating layer surface. The solder wettability is ensured at the high Cu concentration portion on the side close to the surface while preventing the solder erosion at the high Ni concentration portion. The change in Cu concentration or Ni concentration depending on the thickness direction of the plating layer may be a linear concentration gradient or a stepwise change. Moreover, the form where the level of a density is repeated periodically may be sufficient.

  In addition, as a method for stirring the conductive medium and the electronic component body, there are a method of using a horizontal rotating barrel, a swinging barrel, an inclined barrel, or the like, or a method of vibrating a container.

  Next, experimental examples carried out to confirm the effects of the present invention will be described.

[Experimental Example 1] 1000 electronic component bodies in which Ag electrodes were formed on both ends of a ceramic body having a length of 2.0 mm, a width of 1.2 mm, and a thickness of 0.85 mm were produced. Next, the electronic component element was immersed in a barrel container having an inner volume of 150 cm ³ filled with a plating bath having the following plating composition, and 100 Ni balls having an average diameter of 1 mmφ were added. The container was rotated after maintaining the plating bath at 70 ° C., and plating was performed so that the surface plating film of the Ag electrode was formed.

<Plating bath composition at the start of plating>
Nickel sulfate hexahydrate: 0.1 mol / L
Citric acid monohydrate: 0.5 mol / L
Boric acid: 0.4 mol / L
Sodium hypophosphite monohydrate: 0.3 mol / L
Bismuth hydroxide: 5 wtppm.
pH: 8.5
The copper ion concentration was zero at the start of plating, but 1 g / L of copper sulfate pentahydrate was replenished 1 minute after the start of plating, and thereafter 1 g / L was replenished every 5 minutes. Thereafter, the plating was stopped when 25 minutes passed from the start of the plating.

  As described above, a Cu—Ni—P plating layer was obtained on the Ag electrode. A cross-sectional photograph of this plating layer is shown in FIG. Moreover, Cu density | concentration and Ni density | concentration were calculated | required by the line analysis (SAM: Auger electron spectroscopy) along the thickness direction about the location shown by the arrow of FIG. FIG. 2 shows the relationship between the strength representing the concentration of each metal and the distance in the thickness direction.

  As a result, a Cu—Ni—P plating layer of about 3 μm could be formed on the Ag electrode. Further, FIG. 2 shows that Ni is mainly precipitated at the initial stage of the reaction, and Ni precipitation decreases with time. However, it can be seen that once Cu deposition is on track, Cu deposition continues stably even if the amount of Ni deposition decreases.

  The method for producing an electronic component of the present invention is effective for an electronic component in which Cu plating is applied to the electrode surface, such as a multilayer ceramic capacitor, a circuit board, and a chip inductor.

Claims (5)

A plating bath containing Cu ions and hypophosphorous acid, an electronic component element having an electrode mainly composed of Cu or Ag, and a conductive medium having a catalytic activity at least on the surface for the oxidation reaction of hypophosphorous acid In the method of manufacturing an electronic component including a step of mixing in and forming a plating film on the electrode,
The method for manufacturing an electronic component, wherein the plating bath contains Ni ions.   The step of forming the plating film includes an operation of previously reducing the content of Cu ions in the plating bath at the start of plating and replenishing Cu ions after the start of plating. The manufacturing method of the electronic component of description.   3. The method of manufacturing an electronic component according to claim 2, wherein in the step of forming the plating film, the content of Cu ions in the plating bath at the start of plating is substantially zero.   The method for manufacturing an electronic component according to claim 1, wherein the plating bath contains citric acid. In an electronic component having an electrode mainly composed of Cu or Ag on the surface of the electronic component element body,
While having a Cu-Ni-P plating layer on the electrode,
The Cu concentration in the vicinity of the surface near the electrode of the plating layer is lower than the Cu concentration in the vicinity of the surface far from the electrode of the plating layer, and the Ni concentration in the vicinity of the surface near the electrode of the plating layer Is higher than the Ni concentration in the vicinity of the surface far from the electrode of the plating layer.

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