KR890004785B1 - Sensitizing agent for electroless plating and method for sensitizing substrate with the agent - Google Patents

Abstract

A sensitizing agent for an electroless plating consists of a water or alcohol and a soln. of one or more of palladium(II), silver(I), copper(I), copper(II) or niclel(II) cpds. dissolved in an amide solvent. The concentration of the metal cpd. in the agent is 0.01- 1.0 wt.%, and the agent has PH 11-13. The agent is useful for plating through-holes in multilayer printed circuit boards.

Description

Sensitizers and Substrates for Electroless Plating

The present invention relates to a sensitizer for electroless plating and a method for sensitizing a substrate with a sensitizer.

Electroless plating techniques including electroless copper plating are widely used in the field of manufacturing printed circuit boards that form circuits on electrically insulating substrates such as plastic thin plates. In this case, before the substrate to be electroless plated is immersed in the electroless plating bath, a sensitization treatment is performed, i.e., a catalyst nuclei for electroless plating is formed on the substrate. For example, a circuit is formed by isothermal ions in a bath precipitated with a metal or the like around the catalyst nucleus to grow into a copper film. To increase or decrease the electrically insulating substrate, particulate metal palladium, silver, copper, or nickel, which acts as a catalyst nucleus for electroless plating, must be formed on the surface of the substrate. As an example, palladium particles for this purpose in the prior art are produced according to the following scheme.

The PdCl ₂ -SnCl ₂ -HCl-sensitized systems are disposed in U.S. Patent No. 3, 011, 920 and No. 3, 960, 573 call. PdCl ₂ -SnCl ₂ -HCl-sensitized system is damaged device that is exposed to the system because it is a strong acid, in an inner layer circuit in the multilayer circuit board pink containing many impurities, including Sn and Cl - present a ring (pink-ring) developing do.

The pink-ring phenomenon of the inner layer circuit occurs as follows.

In the method of manufacturing a multilayer printed circuit board, a circuit is formed by etching (clad) a copper clad thin plate, and the base material such as the inner layer circuit and prepreg (paper and glass fiber) is transferred to a thermosetting resin. Impregnated and dried), one by one, and the top layer is overlapped with a copper foil or a copper-bonded thin plate on one side, and the whole laminate is heated and pressed into a single body, and the copper of the top layer is treated. A circuit corresponding to the pattern of the inner layer circuit is formed, and then a layer is drilled (including a portion of the inner layer circuit) at a desired position to form a through hole, followed by electroless plating to form a metal layer on the inner wall of each through hole. In the above step, copper oxide (usually 1 to 3 mu m thickness) is coated on the surface of the inner layer circuit to improve the adhesion between each inner layer circuit and the prepreg in contact with the inner layer circuit. The inner wall of each through hole is increased or decreased before electroless plating. When the PdCl ₂ -SnCl ₂ -HCl-sensitized system is used to increase or decrease the process, a portion of the oxide coating on the exposed through-hole is dissolved in hydrochloric acid, hydrochloric acid, separation by diffusion at the interface between the surface of the prepregs and the resin layer of the inner layer circuit ( cause delamination. This is a pink-ring phenomenon, and when this occurs, the adhesive strength and insulation resistance will be reduced.

It is an object of the present invention to provide a sensitizer for electroless plating that minimizes damage to the exposed device and does not cause pink-ring phenomena.

Another object of the present invention is to provide a method for sensitizing a substrate with the sensitizer.

The sensitizer for electroless plating according to the present invention may be a solution of at least one of palladium (II) compounds, copper (I) compounds, copper (I) compounds, copper (II) compounds and nickel (II) compounds dissolved in amides. Configure.

Amides suitable for the present invention consist of formamide, dimethyl formamide, diethylformamide, dimethylacetamide, dimethylarylamide and mixtures of these amides.

Suitable compounds of palladium (II), silver (I), copper (I), copper (II) and nickel (II) suitable for the present invention include chlorides, fluorides, bromide, iodides, nitrates, sulfates, oxides, sulfides and the like. There is a mixture of compounds. Especially chloride is preferable among the said compounds.

The compound is dissolved in each of the amides described above, and the solution is diluted with water or alcohol so that the concentration of the compound is 0.01-1.0 wt%, pH is 3-14, preferably 11-13, most preferably 11.5-12.5. To prepare a phosphor sensitizer. Compounds dissolved in these amides are believed to form complexes with the amide.

Substrates to be plated, such as plastic sheets, ceramic plates, plastic molded articles and plastic films, are immersed in a sensitizer and then immersed in a reducing solution to form metal nuclei of palladium, silver, copper and / or nickel on the substrate surface.

Examples of suitable reducing solution used herein is an aqueous solution or an alcohol solution such as formaldehyde, tin chloride (Ⅱ), NaBH _4, glucose. The concentration is preferably 0.01-10 wt%, preferably 0.1-1 wt%, and pH 3-14.

The reducing substances may be used alone or in combination with each other, or in combination with a stabilizer that acts as a buffer, for example, methanol in formaldehyde, hydrochloric acid in tin (II) chloride or hydroxide in NaBH ₄ . Sodium may be used in combination.

Electroless plating is performed by immersing a substrate in which nucleus such as palladium is formed for plating in an electroless plating bath, and the electroless plating bath may be an electroless plating solution such as copper or nickel which is commonly used.

The sensitization effect can be further improved by pretreating the substrate to be plated before immersing it in the electroless plating sensitizer of the present invention.

For this pretreatment, 0.1 to 10% aqueous hydrogen peroxide solution, the same concentration and hydrogen peroxide solution adjusted to pH 3-6 with sulfuric acid, hydrochloric acid pH3-6, sulfuric acid pH3-6, water alcohol or methyl ethyl ketone 0.1 to 10% of the 10% bisphenol A epoxy resin solution and the above-described reducing solution can be used.

Instead of immersing in the sensitizer and reducing solution for electroless plating, the solution may be sprayed onto the substrate.

Example 1

The through-holes were drilled through a glass epoxy thin film (1.6 mm thick), which was previously immersed in an aqueous solution of a mixture of sodium hydroxide, potassium chloride and sodium phosphate, and formed an oxide coating on each copper surface, followed by 2.0 weight in formamide. The% PdCl ₂ solution was immersed in water for 5 minutes in a sensitizer solution prepared by diluting the PdCl ₂ concentration with water to 0.1% and the pH to 12.5. After the liquid was removed, the plate was immersed in a 1% NaBH ₄ solution in 1% NaOH aqueous solution for 5 minutes while shaking the plate, and then immersed in the electroless plating solution CUST-201 (Hirachi Chemical Co., Ltd.) for 20 minutes. After, washed with water. As a result of the electroless copper plating, copper was uniformly deposited on the inner wall of the through-hole of the glass epoxy sheet, and no chemical erosion of the oxide coating covering the copper surface was observed.

Example 2

As in Example 1, an oxide was coated on a glass epoxy thin plate (1.6 mm thick) copper-bonded on both sides to drill through-holes, followed by washing.

The thin plates were then treated with a 1.0% NaBH ₄ solution in 0.1% NaOH aqueous solution.

A sensitizer was prepared by diluting a 1% PdCl ₂ solution in formamide with 0.05% aqueous NaOH solution and diluting PdCl ₂ concentration to 0.05% and pH 1.2.

The thin plate was immersed in the sensitizer and shaken well for 5 minutes. After removing the liquid, the thin plate was treated with a 10% NaBH ₄ reducing solution in 0.1% NaCH aqueous solution, and then immersed in electroless copper plating solution CUST-201 (the same as Example 1), followed by washing with water. As a result of the electroless copper plating, copper was uniformly deposited on the inner wall of the through hole of the thin plate, and no chemical erosion of the oxide thin film covering the copper surface was observed.

Effects according to the present invention are as follows.

(1) The damage of the apparatus exposed to the electroless plating sensitizer with the pH of solution 3-14 is reduced.

(2) Plating can be made uniform.

(3) No chemical erosion of the inner layer circuit of the multilayer circuit board occurs.

Claims (6)

Palladium (II) compound, silver (I) compound, copper (I) compound, copper (II) compound and nickel (II) compound dissolved in amide, and water or alcohol. A sensitizer for electroless plating without erosion, wherein the pH range of the sensitizer is 11 to 13, and the concentration range of the metal compound in the sensitizer is 0.01 to 1.0% by weight. The sensitizer for electroless plating according to claim 1, wherein the amide is at least one selected from the group consisting of formamide, dimethyl formamide, diethyl formamide, dimethyl acetamide and dimethyl arylamide. The sensitizer for electroless plating according to claim 2, wherein the metal compound is at least one selected from the group consisting of chloride, fluoride, bromide, iodide, nitrate, sulfate, oxide and sulfide of the metal. One or more solutions selected from the group consisting of palladium (II) compounds, silver (I) compounds, copper (I) compounds, copper (II) compounds, and nickel (II) compounds dissolved in amides for increasing or decreasing the substrate to be electroless plated. The substrate is treated with a sensitizer, consisting of water or alcohol, which does not chemically corrode copper oxide, has a pH range of 11-13, and a concentration range of 0.01-1.0% by weight of the metal compound. Treating the substrate to impart the metal in the form of a metal to the substrate. The method of claim 4, wherein the amide is at least one selected from the group consisting of formamide, dimethyl formamide, diethyl formamide, dimethyl acetamide and dimethyl arylamide. The method according to claim 5, wherein the metal compound is at least one selected from the group consisting of chloride, fluoride, bromide, iodide, nitrate, sulfate, oxide and sulfide of the metal. .