KR20220053469A - Hole filling method of circuit board using different species metal - Google Patents

Abstract

The present invention relates to a method for filling a through-hole in a circuit board, which comprises the steps of: forming a through-hole in the substrate; forming an electroless plating part in the through-hole; forming a bridge electrolytic plating part containing first metal in the electroless plating part; and forming a filling part containing second metal on the substrate on which the bridge electrolytic plating part is formed. The melting point of the first metal is higher than the melting point of the second metal.

Description

Method of filling through-holes of a circuit board using different metals {Hole filling method of circuit board using different species metal}

The present invention relates to a through-hole filling method of a circuit board in which a conductive material is filled in the through-hole in order to electrically connect circuits provided on different surfaces of the substrate.

A circuit board in which a predetermined circuit is integrated is widely used in electronic devices such as mobile terminals and display devices. The circuit board is a board in which a circuit pattern is formed on an insulating substrate by using a printing technique, a plating technique, an etching technique, or the like. Such a circuit board is divided into a single-sided printed circuit board, a double-sided printed circuit board, a multi-layered printed circuit board, etc. according to the formation structure of the circuit pattern. The double-sided printed circuit board and the multilayer printed circuit board have through-holes (through-holes or via holes) formed by using a CNC drill or a laser drill to connect circuit patterns formed on different surfaces of the board. ) is filled with a conductive material.

As one method of filling the through-holes with the conductive material, a method of filling the through-holes by applying a stack via structure may be used. However, the method has a problem in that the upper and lower portions of the through-holes cannot be completely filled in the process of filling the through-holes and performing the build-up process. Also, there was a problem in that the process was difficult because the build-up had to be done by controlling the positions between the through-holes.

Another method for filling the through-holes with a conductive material is to form an electroless plating layer on the inner surface of the through-holes with an electroless plating solution, and then perform electrolytic filling plating on the electroless plating layer with an electroless plating solution. . However, in this method, an electroless plating solution and an electrolytic plating solution must be prepared, respectively, and since the electroless plating and the electrolytic plating must be performed respectively, there is a problem in that process efficiency is reduced and high cost is consumed. In addition, there was a problem in that a considerable amount of time was consumed during the electrolytic filling plating.

Republic of Korea Patent No. 10-1418034

An object of the present invention is to provide a through-hole filling method capable of increasing the efficiency of a through-hole filling process of a circuit board.

In order to solve the above problems, the present invention includes the steps of forming a through hole in a substrate; forming an electroless plating part in the through hole; forming a bridge electroplating part containing a first metal in the electroless plating part; and forming a filling part containing a second metal on the substrate on which the bridge electrolytic plating part is formed, wherein the melting point of the first metal is higher than the melting point of the second metal. do.

The forming of the filling part may include: putting the substrate on which the bridge electrolytic plating part is formed into a plating solution containing the second metal and performing electrolytic plating; and putting the electrolytically plated substrate into a vacuum chamber to reflow the substrate.

The forming of the filling part may include: spraying the metal powder containing the second metal onto the substrate on which the bridge electrolytic plating part is formed to apply the metal powder; and heat-treating the substrate to which the metal powder is applied.

The forming of the filling part may include: applying a conductive paste containing the second metal to the substrate on which the bridge electrolytic plating part is formed; and heat-treating the substrate to which the conductive paste is applied.

The second metal may be a low-melting-point metal having a melting point of 1000° C. or less.

The second metal may be at least one selected from the group consisting of tin, bismuth, aluminum, zinc, silver, and copper.

The present invention fills the through hole of the circuit board with a simple process of performing electroless plating and electrolytic plating so that some areas inside the through hole are bridged (connected), and then filling the through hole with a low melting point metal and/or an alloy thereof. It is possible to improve the efficiency of the filling process.

1 illustrates a through-hole filling process of a circuit board according to an embodiment of the present invention.
2 and 3 are optical microscope images for explaining Experimental Example 2 of the present invention.

The terms or words used in the description and claims of the present invention should not be construed as being limited to their ordinary or dictionary meanings, and the inventor must properly understand the concept of the term in order to best describe his invention. Based on the principle that can be defined, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

The present invention relates to a through-hole filling method of a circuit board derived to solve the problem of the prior art in which a long time was consumed for filling the through-holes as the through-holes of the circuit board were filled through electroless plating and electrolytic plating, It is characterized in that the time consumed for filling the through-holes is reduced by applying a dissimilar metal when filling the through-holes. Specifically, the method for filling a through-hole in a circuit board according to the present invention comprises the steps of: forming a through-hole in the substrate; forming an electroless plating part in the through hole; forming a bridge electroplating part containing a first metal in the electroless plating part; and forming a filling part containing a second metal on the substrate on which the bridge electrolytic plating part is formed, which will be described in detail with reference to FIG. 1 as follows.

The step of forming the through hole H in the substrate (FIG. 1 (a)) may be performed using a CNC drill or a laser drill. The substrate is not particularly limited as long as it is commonly known, and specifically, may be a plastic substrate, a glass substrate, or a ceramic substrate.

The step of forming the electroless plating part 10 in the through hole (H) (FIG. 1 (b)) may be performed by electroless plating using an electroless plating solution. The electroless plating is performed in order to ensure uniform electrodeposition on the inner surface (front surface) of the through hole (H) and the surface of the substrate. The electroless plating solution is not particularly limited, but may include a copper ion source, a complexing agent, a reducing agent, a pH adjuster, and an additive.

The copper ion source may be copper sulfate. The complexing agent is for stabilizing the alkali plating solution, and may be EDTA. The reducing agent may be formalin or sodium borohydride. The pH adjusting agent is for supplying OH required for the oxidation reaction, and may be sodium hydroxide, potassium hydroxide, or the like. The additive may be ethylenediaminetetraacetic acid, hydroxyethylethylenetriacetic acid, cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, tetrakis(2-hydroxypropyl)ethyldiamine, or the like.

The electroless plating may be performed at a plating rate of 10 μm/hr at a pH of 11-14 and a temperature of 20 to 60°C.

The step of forming the bridge electroplating part 20 containing the first metal on the electroless plating part 10 (FIG. 1(c)) may be performed by electroplating using an electrolytic plating solution containing the first metal. there is. The electroplating is to form a bridge connecting some regions inside the through hole H in which the electroless plating part 10 is formed. The electrolytic plating solution is not particularly limited, but may include sulfuric acid, copper sulfate, chlorine, a brightener, a carrier, and a leveler. As such an electroplating solution is used, the first metal contained in the bridge electroplating part 20 may be copper.

The brightener is (O-ethyldithiocarbonato)-S-(3-sulfopropyl)-ester, 3-[(amino-iminomethyl)-thiol]-1-propane sulfonic acid, 3-(benzothiazole- 2-Mercapto)-propyl sulfonic acid, sodium bis-(sulfopropyl)-disulfide, N,N-dimethyl dithiocarbamyl propyl sulfonic acid, 3,3-thiobis(1-propane sulfonic acid), 2-hydroxy-3 -[tris(hydroxymethyl)methylamino]-1-propane sulfonic acid, sodium 2,3-dimercaptopropane sulfonic acid, 3-mercapto-1-propane sulfonic acid, 5,5'-dithiobis (2-nitrobenzoic acid) , DL-cysteine, 4-mercapto-benzene sulfonic acid, and 5-mercapto-1H-tetrazol-1-methane sulfonic acid may be at least one selected from the group consisting of sulfonic acid.

The carrier is polyoxyalkylene glycol, carboxymethyl cellulose, octanediol bis glycol ether, oleic acid polyglycol ester, polyethylene glycol, polyethylene glycol dimethyl ether, polyethylene glycol-block-polypropylene glycol-block-polyethylene glycol, polypropylene glycol, Polyvinyl alcohol, stearyl alcohol polyglycol ether, stearic acid polyglycol ester, 3-methyl-1-butane-3-ol, 3-methyl-penten-3-ol, L-ethynylcyclohexanol, phenylpropynol , 3-phenyl-1-butane-3-ol, propargyl alcohol, methyl butynol-ethylene oxide, 2-methyl-4-chloro-3-butain-2-ol, dimethyl hexaindiol, dimethyl octa It may be at least one selected from the group consisting of indiol, phenylbutinol, and 1,4-butanediol diglycidyl ether.

The leveler may be a saturated heterocyclic compound containing at least one of nitrogen, oxygen, sulfur, and phosphorus. Specifically, aziridine, oxirane, thiirane, diaziridine, oxaziridine, dioxirane, azetidine, oxetane, thietane, diazetidine, dioxetane, dithiethane, pyrrolidine, thiolane, phosphorane , imidazolidine, pyrazolidine, oxazolidine, isoxazolidine, thiazolidine, isothiazolidine, dioxolane, dithiolane, piperidine, oxane, thiane, phosphinan, piperazine, morpholine , thiomorpholine, dioxane, dithiane, azepan, homopyrerazine, azocan, oxokane, thiocane, azonan, may be at least one selected from the group consisting of oxonane and thionane.

The composition ratio of the electrolytic plating solution may be 200 to 300 parts by weight of copper sulfate, 50 to 150 parts by weight of a carrier, 0.5 to 5 parts by weight of a brightener, and 1 to 10 parts by weight of a leveler based on 100 parts by weight of sulfuric acid, and chlorine is 30 to 30 parts by weight based on the total weight of the plating solution. 120 ppm. In this case, the chlorine may mean chlorine ions generated by adding diluted hydrochloric acid to the plating solution.

The step of forming the filling part 30 containing the second metal on the substrate on which the bridge electrolytic plating part 20 is formed (FIG. 1 (d)) is a through hole (H) except for the bridge electrolytic plating part 20 to allow the area to be filled. The filling part 30 is formed by electrolytic plating and heat melting (reflow) using a plating solution containing a second metal; thermal spraying of a metal powder containing a second metal; Alternatively, it may be achieved through application (printing) of a conductive paste (conductive ink) containing the second metal. As the filling part 30 is formed through this process, the through-hole filling time can be greatly shortened and voids can be prevented from being formed during the filling process.

Specifically, the step of forming the filling part 30 may include: putting the substrate on which the bridge electrolytic plating part 20 is formed into a plating solution containing the second metal and performing electrolytic plating; And it may include the step of heating and melting (reflow) by putting the substrate on which the electrolytic plating is made into a vacuum chamber. The plating solution containing the second metal is not particularly limited as long as it is an electrolytic plating solution containing the second metal. For example, the electrolytic plating solution may include an electrolyte solution, a second metal ion source, a brightener, a carrier, and a leveler. The electrolytic plating may be performed at 20 to 30° C. for 1 to 3 hours under application of a current density of 1 to 5 ASD. In the heat-melting step, the conditions (temperature and time) may be appropriately adjusted according to the melting point of the second metal.

In addition, the forming of the filling part 30 may include: spraying a metal powder containing a second metal onto the substrate on which the bridge electrolytic plating part 20 is formed to apply the metal powder; and heat-treating the substrate coated with the metal powder. The application of the metal powder may be made through a commonly known spraying method, and the average particle diameter of the metal powder may be appropriately adjusted according to the diameter of the through hole (H). In addition, the heat treatment may be performed under an inert atmosphere, and the conditions (temperature and time) may be appropriately adjusted according to the melting point of the second metal.

In addition, forming the filling part 30 may include applying a conductive paste containing a second metal to the substrate on which the bridge electrolytic plating part 20 is formed; and heat-treating the substrate to which the conductive paste is applied. The conductive paste may include commonly known components (eg, binder resin, solvent, dispersant, defoaming agent, surfactant, thickener, wetting agent, colorant, etc.) in addition to the second metal. The heat treatment may be performed under conditions that allow thermal diffusion of the second metal while the solvent contained in the conductive paste is volatilized.

Meanwhile, the second metal may not be particularly limited as long as it has a lower melting point than the first metal. As such, when the filling part 30 is formed of the second metal having a melting point lower than the melting point of the first metal, the filling part 30 is relatively formed through the thermal diffusion principle while preventing the bridge electrolytic plating part 20 from collapsing. It can be filled in a short time. Specifically, the second metal may be a low-melting-point metal having a melting point of 1000 °C or less (specifically 700 °C or less, more specifically 250 °C or less). More specifically, the second metal may be a single metal selected from the group consisting of tin, bismuth, aluminum, zinc, silver, and copper, or a mixture thereof. For example, the second metal may be Sn (MP: 231.93 °C), Sn-58Bi (MP: 139 °C), Sn-Zn-Bi (MP: 198 °C), or Sn-Zn-Al.

The method of filling the through-holes of the circuit board according to the present invention as described above can fill the through-holes formed in the substrate having a thickness of 200 µm or more (specifically, 800 to 1500 µm) with a conductive material in a relatively short time. Specifically, the present invention can reduce the time consumed in the conventional through-hole filling process by 10 to 50%.

Hereinafter, the present invention will be described in more detail by way of Examples. However, the following examples are intended to illustrate the present invention, and it is apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention, and the scope of the present invention is not limited thereto.

[ Example One]

An epoxy resin substrate having a thickness of 1000 μm was processed with a laser to form a through hole having a diameter of 200 μm. Next, electroless plating is performed with an electroless copper plating solution containing copper sulfate, EDTA (complexing agent), formalin (reducing agent), and other additives (ethylenediaminetetraacetic acid, caustic soda), and electroless plating is performed inside the through hole and on the surface of the substrate. A plating portion was formed. At this time, the electroless plating was performed at pH 12 and a bath temperature of 65 °C. After degreasing and pickling, sulfuric acid, copper sulfate, (O-ethyldithiocarbonato)-S-(3-sulfopropyl)-ester (bright agent), polyoxyalkylene glycol (carrier), aziridine (leveler) and electrolytic plating with an electrolytic copper plating solution containing chlorine ions to form a bridge electroplating part inside the through hole. At this time, the electrolytic plating was performed for 90 minutes under the application of 2-4 ASD current density at 27 ℃. Next, after electrolytic plating with a tin plating solution (YMT, Tinomat NFJ), it was put into a vacuum chamber and heated and melted at 230° C. to form a filling part. At this time, the electrolytic plating of the tin plating solution was performed for 2 hours at 23 °C under the application of 2 ASD current density.

[ comparative example One]

The through-holes were filled in the same manner as in Example 1, except that the filling part was formed by electrolytic plating with an electrolytic copper plating solution used for forming the bridge electrolytic plating part, rather than tin plating and heat melting.

[ Experimental example One]

The time consumed for filling the through-holes in Example 1 and Comparative Example 1 was measured, respectively, and the results are shown in Table 1 below.

division electroless plating
formation time Bridge electroplating part
formation time filling part
formation time total time Example 1 10 minutes 90 minutes 120 minutes 220 minutes Comparative Example 1 10 minutes 90 minutes 500 minutes 600 minutes

Referring to Table 1, in the case of Example 1 in which the through-holes were filled by the method according to the present invention, it was confirmed that the time consumed for filling the through-holes was reduced by about 1/3 compared to Comparative Example 1.

[ Experimental example 2]

After cutting the substrate filled with the through-holes through Example 1 and Comparative Example 1, a cross-section sample was prepared through mold molding using an epoxy resin. After processing the cross-section by polishing the prepared cross-section sample, the cross-section was confirmed with an optical microscope, and the results are shown in FIGS. 2 and 3 .

Referring to FIGS. 2 and 3 , in Example 1 in which the through-holes were filled by the method according to the present invention, it was confirmed that the through-holes were filled in a state in which void generation was minimized compared to Comparative Example 1.

H: through hole
10: electroless plating part
20: bridge electrolytic plating part
30: filling part

Claims (6)

forming a through hole in the substrate;
forming an electroless plating part in the through hole;
forming a bridge electroplating part containing a first metal in the electroless plating part; and
and forming a filling part containing a second metal on the substrate on which the bridge electrolytic plating part is formed,
The melting point of the first metal is higher than the melting point of the second metal, the through-hole filling method of the circuit board. The method according to claim 1,
The step of forming the filling part,
electroplating by putting the substrate on which the bridge electrolytic plating part is formed into a plating solution containing the second metal; and
Through-hole filling method of a circuit board comprising the step of heating and melting (reflow) by putting the substrate on which the electrolytic plating is made into a vacuum chamber. The method according to claim 1,
The step of forming the filling part,
spraying the metal powder containing the second metal onto the substrate on which the bridge electrolytic plating part is formed to apply the metal powder; and
The method for filling through-holes in a circuit board comprising the step of heat-treating the substrate coated with the metal powder. The method according to claim 1,
The step of forming the filling part,
applying a conductive paste containing the second metal to the substrate on which the bridge electrolytic plating part is formed; and
A method for filling through-holes in a circuit board, comprising the step of heat-treating the substrate to which the conductive paste is applied. The method according to claim 1,
The second metal is a low-melting-point metal having a melting point of 1000 °C or less. The method according to claim 1,
The second metal is at least one selected from the group consisting of tin, bismuth, aluminum, zinc, silver and copper.

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