JP2009203505A - Electroless plating method, and electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroless plating method for forming an electroless plating layer on the surface of a conductive layer formed on the surface of a base material, where the formation of the electroless plating layer on a region other than the conductive layer can be more effectively prevented. <P>SOLUTION: Disclosed is an electroless plating method for forming an electroless plating layer on the surface of a conductive layer formed on the surface of a base material and essentially consisting of silver, and includes: a stage where an iodine-containing substance is applied to the surface of the base material comprising the conductive layer; a stage where, after the application of the iodine-containing substance, a catalyst essentially consisting of palladium is applied to the surface of the base material comprising the conductive layer; and a stage where, after the application of the catalyst, the electroless plating layer is formed on the surface of the conductive layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention generally relates to an electroless plating method and an electronic component, and specifically, forms an electroless plating layer on the surface of a conductive layer mainly composed of silver formed on the surface of a substrate. The present invention relates to an electroless plating method and an electronic component obtained thereby.

  Conventionally, in a circuit board or electronic component in which a conductive layer such as a wiring pattern layer is formed on the surface of a base material, an electroless plating layer is formed on the surface of the conductive layer. The electroless plating layer is composed of, for example, a nickel layer and a gold layer formed on the nickel layer. The gold layer has a high electrical conductivity and has good solder wettability when electronic components are mounted. Therefore, the gold layer is used to form a surface layer such as a wiring pattern layer. The nickel layer constituting the underlayer of the gold layer has a property of high resistance to solder erosion.

  In general, the electroless plating layer is formed by depositing metal ions as a metal by the action of a reducing agent. For this reason, a catalytic substance such as palladium that exhibits a catalytic action for the reduction reaction needs to be applied to the surface to be electrolessly plated.

  For example, when the electroless plating layer is formed on the surface of the wiring pattern layer as the conductive layer, if the above-mentioned catalytic substance is applied to the surface of the substrate on which the wiring pattern layer is formed, the catalytic substance becomes the wiring pattern. Selectively deposit on the surface of the layer. However, on the surface of the base material to which the catalytic substance is applied, a minute conductor portion is also present in a region where the wiring pattern layer is not formed. For example, in a base material such as a ceramic substrate, when a metal thick film paste applied to form a wiring pattern layer and a ceramic that forms the substrate are co-sintered, a metal is formed in a region other than the wiring pattern layer. Ingredients may be diffused or scattered. Due to such a metal component, a minute conductor portion exists in a region other than the wiring pattern layer.

  For this reason, the catalytic substance may adhere to the region other than the wiring pattern layer. There is a problem that a metal is deposited by electroless plating using the attached catalytic substance as a nucleus.

An electroless nickel-gold plating method for solving such a problem is proposed in, for example, Japanese Patent Application Laid-Open No. 2004-332035 (hereinafter referred to as Patent Document 1). This electroless nickel-gold plating method includes an electroless nickel plating process in which an electroless nickel plating film is formed on a conductor formed on a substrate, and a replacement gold plating film is formed on the electroless nickel plating film. In an electroless nickel-gold plating method including a gold plating step and an electroless gold plating step of further forming an electroless gold plating layer on the replacement gold plating layer, the electroless nickel plating step and the replacement gold plating step In the meantime, it includes a sulfur treatment step of treating an object to be plated obtained by the electroless nickel plating step using an aqueous solution containing an inorganic sulfur compound. The inorganic sulfur compound formed by this sulfur treatment process is adsorbed on a small amount of conductor formed at a position protruding from the conductor pattern region, thereby preventing the formation of a gold plating film on the small amount of conductor. It is supposed to be possible.
JP 2004-332035 A

  In the method proposed in Patent Document 1, the inorganic sulfur compound formed before the replacement gold plating step is a replacement between nickel and gold in the electroless nickel plating film formed in the electroless nickel plating step. It is thought to work to suppress the reaction. However, a catalytic substance such as palladium applied before the electroless nickel plating step is also attached to a minute conductor portion existing in a region other than the conductor pattern. Due to the presence of the catalytic substance, gold is deposited on the minute conductor portion existing in the region other than the conductor pattern in the electroless gold plating step. For this reason, there exists a problem that formation of the gold plating film to areas other than a conductor pattern cannot fully be prevented. Furthermore, since the application of the sulfur compound is performed after electroless nickel plating, a portion where electroless nickel remains attached outside the pattern also occurs.

  Therefore, an object of the present invention is to provide an electroless plating method for forming an electroless plating layer on the surface of a conductive layer formed on the surface of a substrate. It is to provide an electroless plating method capable of preventing formation more effectively.

  The electroless plating method according to the present invention is an electroless plating method for forming an electroless plating layer on the surface of a conductive layer mainly composed of silver formed on the surface of a base material. A step of applying an iodine-containing substance on the surface of the substrate including the layer, a step of applying a catalyst mainly composed of palladium on the surface of the substrate including the conductive layer after applying the iodine-containing substance, and a catalyst Then, an electroless plating step of forming an electroless plating layer on the surface of the conductive layer is provided.

  In the electroless plating method of the present invention, first, an iodine-containing substance is applied on the surface of a substrate including a conductive layer mainly composed of silver. When silver in the conductive layer reacts with iodine in the provided iodine-containing substance, silver iodide is generated on the surface of the conductive layer. At this time, silver iodide is also generated in a region where the conductive layer is not formed on the surface of the substrate. This silver iodide has an effect of preventing the adhesion of palladium by a substitution reaction between silver and palladium.

  Thereafter, when a catalyst containing palladium as a main component is applied, the silver iodide produced in the region where the conductive layer is not formed on the surface of the base material adheres to the region where the conductive layer is not formed. Effectively hinder. Thereby, even if it performs an electroless-plating process after that, the electroless plating by a reducing action is not performed to the area | region in which the conductive layer is not formed. On the other hand, silver iodide is also generated on the surface of the conductive layer. However, since a certain amount of palladium adheres on the surface of the conductive layer, an electroless plating layer is formed on the surface of the conductive layer. This is considered as follows.

  Since the conductor portion made of silver existing in a region other than the conductive layer is very small, most of the silver reacts with iodine to generate silver iodide. On the other hand, since the silver forming the conductive layer has a certain amount of area, even if some silver existing on the surface of the conductive layer reacts with iodine to produce silver iodide, a considerable amount of silver is formed. Silver remains on the surface of the conductive layer. As a result, a certain amount of palladium is deposited on the surface of the conductive layer by a substitution reaction of silver and palladium, so that an electroless plating layer is formed on the surface of the conductive layer. The silver iodide produced as described above may remain as it is after the electroless plating layer is formed.

  Accordingly, it is possible to more effectively prevent the formation of the electroless plating layer in the region other than the conductive layer.

  In the electroless plating method of the present invention, the step of providing the iodine-containing substance is preferably performed by applying an aqueous solution containing iodine and potassium iodide or sodium iodide. In this case, the iodine-containing substance can be easily applied on the surface of the substrate including the conductive layer by immersing the substrate as the object to be plated in the iodine-containing solution.

  In the electroless plating method of the present invention, the electroless plating step preferably includes at least a step of forming an electroless nickel plating layer.

  The electronic component obtained by the electroless plating method of the present invention includes a conductive layer mainly composed of silver formed on the surface of the substrate, and an electroless plated layer formed on the surface of the conductive layer. In the electronic component provided with the above, an adhesive containing silver iodide as a main component is provided in a region where the conductive layer is not formed on the surface of the substrate.

  As described above, according to the present invention, it is possible to more effectively prevent the formation of the electroless plating layer in the region other than the conductive layer only by adding one simple process.

  As an object to be plated of sample numbers 1 to 8 shown in Table 1 below, 8 low temperature co-fired ceramics (LTCC: Low Temperature Co-fired Ceramic) mainly composed of 100 mm square alumina and glass components are used. I prepared a sheet. A wiring pattern layer having a width of 5 mm and a thickness of 10 μm is formed on the surface of the substrate as a conductive layer mainly composed of silver. The area ratio of the wiring pattern layer was 50%. In addition, on the surface region of the substrate other than the wiring pattern layer, there are several tens of fine silver deposits having an outer diameter of about 1 to 10 μm.

  First, each substrate prepared above was degreased by immersing it in a degreasing liquid (trade name LT-2000C manufactured by World Metal Co., Ltd.) maintained at a temperature of 50 ° C. for 2 minutes.

  Next, an iodine-containing substance is imparted on the surface of each substrate including the wiring pattern layer by immersing each substrate in an iodine-containing solution (a solution containing potassium iodide and iodine) maintained at a temperature of 25 ° C. for 2 minutes. did. Here, in the sample numbers 1-7, the board | substrate was immersed in the iodine containing solution whose density | concentration of an iodine and potassium iodide is a value shown in Table 1. In sample number 8, the substrate was not immersed in the iodine-containing solution.

  Thereafter, each substrate is immersed for 3 minutes in a palladium catalyst applying liquid (trade name AT-909 manufactured by World Metal Co., Ltd.) maintained at a temperature of 25 ° C., so that palladium is deposited on the surface of each substrate including the wiring pattern layer. A catalyst having a main component was added.

  Further, each substrate is immersed in an electroless nickel plating solution (trade name Linden 204L manufactured by World Metal Co., Ltd.) maintained at a temperature of 70 ° C. for 30 minutes, whereby an electroless nickel plating layer is formed on the surface of the wiring pattern layer. Formed.

  In each sample Nos. 1 to 8 obtained as described above, the presence or absence of nickel deposition by electroless nickel plating on 20 minute silver deposits existing in the surface region of the substrate other than the wiring pattern layer Were examined using an optical microscope (50 times magnification). The results were evaluated as follows.

A: 0% of the number of nickel deposits observed in 20 minute silver deposits
B: Less than 30% of the number of nickel deposits observed in 20 fine silver deposits C: 30% or more of the number of nickel deposits observed in 20 fine silver deposits D: A portion where there is no nickel plating on the surface of the wiring pattern layer regardless of the presence or absence of nickel deposition on the surface region of the substrate other than the wiring pattern layer.

  The evaluation results are shown in Table 1.

  From the results of sample numbers 4 to 6 shown in Table 1, by applying a certain concentration of iodine-containing substance to the substrate, formation of an electroless nickel plating layer on the surface region of the substrate other than the wiring pattern layer, that is, precipitation of nickel It can be seen that can be prevented more effectively.

  Moreover, in the samples of sample numbers 4 to 6, deposits mainly composed of silver iodide were formed in a region where the wiring pattern layer was not formed on the surface of the substrate. From this, for example, when the electroless plating method of the present invention is applied to an electronic component, a wiring pattern layer mainly composed of silver formed on the surface of the substrate and an electroless pattern on the surface of the wiring pattern layer In the electronic component on which the nickel plating layer is formed, the deposit containing silver iodide as a main component is formed in a region where the wiring pattern layer is not formed on the surface of the base material.

  In order to prevent nickel plating from adhering to the surface of the wiring pattern layer, the iodine concentration of the iodine-containing substance applied on the substrate may be adjusted as appropriate.

  The iodine concentration of the iodine-containing substance provided on the substrate may be appropriately adjusted depending on the size of the substrate to be plated, the area of the wiring pattern layer, the type of plating metal, the concentration of palladium in the catalyst, and the like. .

  In the above embodiment, the iodine-containing liquid as the iodine-containing substance is a solution containing iodine and potassium iodide. However, a solution containing iodine and sodium iodide may be used. The iodine-containing liquid may be iodic acid obtained by adding an oxidizing agent such as nitric acid to iodine or potassium iodide.

  In the above embodiment, an example of electroless nickel plating was described as electroless plating. However, electroless gold plating may be performed after electroless nickel plating, and if palladium is used as a catalyst for electroless plating. The type of electroless plating metal and the number of plating layers are not particularly limited.

  It should be considered that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the embodiments described above, and is intended to include any modifications and variations within the scope and meaning equivalent to the terms of the claims.

  The electroless plating method of the present invention can be used to coat and finish the surface of an external electrode of an electronic component such as a chip capacitor.

Claims (4)

An electroless plating method for forming an electroless plating layer on the surface of a conductive layer mainly composed of silver formed on the surface of a substrate,
Providing an iodine-containing substance on the surface of the substrate including the conductive layer;
After providing the iodine-containing substance, applying a catalyst mainly composed of palladium on the surface of the base material including the conductive layer;
An electroless plating method comprising: an electroless plating step of forming an electroless plating layer on the surface of the conductive layer after applying a catalyst.   The electroless plating method according to claim 1, wherein the step of applying the iodine-containing substance is performed by applying an aqueous solution containing iodine and potassium iodide or sodium iodide.   The electroless plating method according to claim 1, wherein the electroless plating step includes at least a step of forming an electroless nickel plating layer. An electronic component comprising a conductive layer mainly composed of silver formed on the surface of a substrate and an electroless plating layer formed on the surface of the conductive layer,
The electronic component which has the deposit | attachment which has silver iodide as a main component in the area | region in which the said conductive layer is not formed on the surface of the said base material.