CN102918937B - Printed circuit board and method of manufacturing the printed circuit board - Google Patents

Abstract

According to the method for manufacturing a printed wiring board of the present invention, first, a through hole (41) leading to a conductive substrate (10) is formed in an insulating layer (20). Next, a conductive ink containing conductive particles is applied to the region including the through-hole (41) on the insulating layer (20) to form a conductive particle layer (31). Subsequently, a plating layer (33) is formed on the conductive particle layer (31) by plating. Then, the conductive particle layer (31) and the electroless plating layer (32) around the blind via (40) are removed.

Description

Printed circuit board and method of manufacturing the printed circuit board

technical field

The invention relates to a printed circuit board with blind holes and a method for manufacturing the printed circuit board.

Background technique

As a blind hole of a printed circuit board, the technique of patent document 1 is known. As shown in FIG. 6 , the first conductive pattern 110 and the second conductive pattern 120 are formed on the surface of the insulating layer 130 . In the insulating layer 130 , a blind hole 140 penetrating through the insulating layer 130 is formed. The first conductive pattern 110 and the second conductive pattern 120 are connected to each other by a blind hole 140 . The blind hole 140 is formed by filling the through hole 141 with a conductive paste 143 .

In recent years, the diameter of the blind hole 140 needs to be made smaller in accordance with the high-density wiring of the printed circuit board. Therefore, it is necessary to make the inner diameter of the through hole 141 smaller. In addition, in order to fill a sufficient amount of conductive paste 143 into the through holes 141 , it is also necessary to reduce the viscosity of the conductive paste 143 . However, when using a low-viscosity conductive paste 143 , the conductive paste 143 will flow during thermal curing, and the blind hole diameter BD will easily vary. That is, the diameter BD of the blind hole sometimes extends beyond the land pattern 142 , and in this case, the adjacent conductive pattern may be short-circuited.

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2008-181915

Contents of the invention

The problem to be solved by the invention

An object of the present invention is to provide a printed wiring board capable of suppressing small variations in diameter of blind holes, and a method of manufacturing the printed wiring board.

means of solving problems

In order to solve the above problems, according to the first embodiment of the present invention, a method of manufacturing a printed circuit board is provided, the printed circuit board has an insulating layer, a first conductive layer formed on the first surface of the insulating layer, and a first conductive layer formed on the insulating layer. The second conductive layer formed on the second surface of the layer, and the blind hole connecting the first conductive layer and the second conductive layer. The manufacturing method includes the following steps: a through-hole forming step, in which a through-hole leading to the first conductive layer is formed in the insulating layer; conductive ink to form a conductive particle layer; the second layer forming process, wherein an electroplating layer is formed on the conductive particle layer by electroplating; and a pattern layer forming process, wherein the conductive particle layer around the through hole is removed, and a conductive Particle layer and 2nd conductive layer of electroplated layer.

According to this method, the conductive particle layer is removed after forming the blind via. Therefore, in order to form the conductive particle layer, a conductive ink having a low viscosity can be used. Thereby, variation in the diameter of the blind hole due to the low viscosity of the conductive ink can be suppressed.

In the above-mentioned method of manufacturing a printed circuit board, it is preferable that after the blind hole is formed, the blind hole is subjected to an electrical heat treatment. Blind vias contain a layer of conductive particles. In addition, the resistance value of the conductive particle layer is easily affected by the contact resistance at the portion where the conductive particles are in contact with each other. In this regard, according to this method, the portions where the conductive particles are in contact with each other are melted or sintered by subjecting the blind holes to an energization heat treatment. In this way, the contact resistance between the conductive particles can be reduced, thereby reducing the resistance value of the blind hole.

In the manufacturing method of the above-mentioned printed circuit board, the first layer forming step preferably includes the following steps: a step of applying conductive ink; a step of evaporating the solvent of the conductive ink to form a layer of conductive particles; and forming a layer of conductive particles on the layer of conductive particles. Electroless plating process. According to this method, since the gaps between the conductive particles in the conductive particle layer are filled with the plating material, the conductive particle layer can be densified. As a result, the resistance value of the blind via can be reduced.

In the above method of manufacturing a printed circuit board, preferably, the first layer forming step further includes a step of applying an oxide remover on the conductive particle layer before the electroless plating layer is formed, and the oxide remover removes the first layer. 1 Oxide on the surface of the conductive layer. According to this method, since the oxide on the surface of the first conductive layer is removed by the oxide remover, the bonding strength between the first conductive layer and the conductive particle layer increases. As a result, peeling between the first conductive layer and the conductive particle layer is suppressed.

In the above method of manufacturing a printed wiring board, preferably, the first layer forming step further includes a step of heat-treating the oxide remover in an inert atmosphere after applying the oxide remover. According to this method, after the oxide remover is applied onto the conductive particle layer, it is heat-treated in an inert atmosphere. Therefore, compared with heat treatment in air, the reaction between the oxide remover and oxygen in the air is suppressed, and the reaction between the oxide remover and the oxide of the first conductive layer is accelerated. Therefore, peeling between the first conductive layer and the conductive particle layer is further suppressed compared to the case where the heat treatment is performed in air.

In the above method of manufacturing a printed wiring board, it is preferable that the oxide remover contains at least one of a reducing agent that reduces the oxide and a dissolved substance that dissolves the oxide. The reducing agent reduces the oxide to decompose the oxide. The dissolving substance dissolves the oxide to decompose the oxide. According to this method, since the oxide of the first conductive layer is decomposed, the joining force between the first conductive layer and the conductive particle layer increases.

In the above method for producing a printed wiring board, preferably, the reducing agent reduces the oxide on the surface of the first conductive layer, and the dissolving substance dissolves the oxide. According to this method, since the conductive ink contains at least one of the reducing agent and the dissolved substance, at least one of the reducing agent and the dissolved substance can be brought into contact with the oxide of the first conductive layer by applying the conductive ink. Thereby, the oxide of the first conductive layer can be decomposed.

In the above method of manufacturing a printed wiring board, the first conductive layer is preferably a stainless steel substrate. According to this method, the printed circuit board can have higher elasticity than the case where copper is used for the first conductive layer. In addition, a component in which a circuit is formed on a stainless steel surface can be used for a component requiring vibration buffering (for example, a circuit board for head suspension such as a hard disk).

In the above method of manufacturing a printed wiring board, it is preferable that the stainless steel substrate has a nickel layer on a surface in contact with the insulating layer. Generally, because the surface of stainless steel is easily oxidized, the connection strength of stainless steel and blind holes may be reduced. In this regard, according to this method, the nickel layer suppresses the oxidation of the surface of the stainless steel, thereby making it possible to suppress a decrease in connection strength to the blind hole.

In order to solve the above problems, according to the second embodiment of the present invention, there is provided a printed circuit board having an insulating layer, a first conductive layer formed on the first surface of the insulating layer, a first conductive layer formed on the first surface of the insulating layer, The second conductive layer formed on the two sides, and the blind hole connecting the first conductive layer and the second conductive layer. The second conductive layer has: a conductive particle layer formed on the insulating layer and containing a plurality of conductive particles; an electroless plating layer laminated on the conductive particle layer; and an electroplating layer laminated on the electroless plating layer, and the blind hole has: A conductive particle layer formed at a position corresponding to a through-hole penetrating the insulating layer and containing a plurality of conductive particles; an electroless plating layer laminated on the conductive particle layer of the blind hole; and an electroplating layered on the electroless plating layer of the blind hole layer, the blind via is connected to the first conductive layer at the bottom of the through hole.

Blind holes are sequentially stacked by insulating layers, electroless plating layers and electroplating layers. However, in this configuration, since the bonding strength between the insulating layer and the electroless plating layer is weak, the electroless plating layer may be peeled off from the insulating layer. In this regard, according to the method, the electroplated layer is connected to the first conductive layer through the layer of conductive particles and the electroless plated layer. In this case, the bonding force between the conductive particle layer and the insulating layer is greater than the bonding strength between the electroless plating layer and the insulating layer. Therefore, peeling of the conductive particle layer from the insulating layer can be suppressed.

In the above-mentioned printed circuit board, it is preferable that the plurality of conductive particles are fused or sintered to be connected to each other at the parts that are in contact with each other, and the conductive particles and the first conductive layer are fused or sintered to be connected to each other at the parts that are in contact with each other. connect. According to this method, a plurality of conductive particles are fused or sintered to be connected to each other, and the conductive particles and the first conductive layer are fused or sintered to be connected to each other. Therefore, the current density of the conduction path of the blind hole increases, so that the resistance value of the blind hole can be reduced.

In the above printed circuit board, preferably, the diameter of the through hole is 10 μm or more, and the thickness of the conductive particle layer is 0.5 μm or less. When the conductive particle layer is formed throughout the through hole, since the conductive particle layer contains many gaps, the strength of the blind hole is reduced. In this regard, according to this method, the electroless plating layer and the electroplating layer are laminated on the conductive particle layer formed on the bottom surface and the side surface of the through hole. Therefore, compared with the case where the conductive particle layer is formed in the entire through hole, the strength of the blind hole can be improved.

Brief description of the drawings

[ Fig. 1 ] A partial sectional view of a printed circuit board according to an embodiment of the present invention.

[Fig. 2] A partial sectional view of a blind hole.

[ FIG. 3 ] (A) to (D) are partial cross-sectional views showing the manufacturing process of the printed circuit board.

[ FIG. 4 ] (A) to (D) are partial cross-sectional views showing the manufacturing process of the printed circuit board.

[ Fig. 5 ] A table showing the relationship between the manufacturing conditions of the printed circuit board and the resistance value of the blind via.

[FIG. 6] A partial sectional view of a conventional printed circuit board.

detailed description

An embodiment will be described with reference to FIGS. 1 and 2. This embodiment is: the printed circuit board of the present invention is embodied as a circuit board for suspending a magnetic head, and the circuit board for suspending a magnetic head is used for mounting a magnetic head in a hard disk drive.

As shown in FIGS. 1 and 2 , the printed circuit board 1 has a conductive substrate 10 as a first conductive layer, an insulating layer 20 laminated on the upper surface of the conductive substrate 10 , and a second conductive layer formed on the upper surface of the insulating layer 20 . The conductive pattern 30. In this embodiment, the lower surface of the insulating layer 20 is the first surface, and the upper surface of the insulating layer is the second surface.

As the conductive substrate 10 , for example, a stainless steel substrate with a thickness of 10 μm to 500 μm is used. In addition, as the conductive substrate 10, an aluminum plate, an iron plate, a copper plate, a conductive metal plywood, or a conductive alloy can be used. The thickness of the conductive substrate 10 is set according to the application. As the conductive substrate 10, a stainless steel substrate having a nickel layer formed on the surface may also be used. In this case, the nickel layer acts as a protective film that suppresses the oxidation of stainless steel.

The insulating layer 20 is formed of a stretchable insulating resin, for example, a polyimide film. Therefore, the insulating layer 20 can be deformed corresponding to the vibration of the printed circuit board 1 .

The conductive pattern 30 is composed of a conductive particle layer 31 formed of metal particles, an electroless plating layer 32 formed on the conductive particle layer 31 , and an electroplating layer 33 formed on the electroless plating layer 32 . The layer composed of the conductive particle layer 31 and the electroless plating layer 32 is regarded as the first layer, and the electroplating layer 33 is regarded as the second layer, which will be described below.

The conductive particle layer 31 is formed by laminating conductive particles 31A having an average particle diameter of several tens of nm. The average particle diameter is a value (D50) at which the cumulative value of the cumulative distribution of particle diameters represents 50%. The cumulative distribution was created based on the value obtained by analyzing the image of 500 particles with a scanning electron microscope (SEM), and then converting the value of the particle circle radius into volume. The thickness of the conductive particle layer 31 is 0.5 μm or less.

The conductive particles 31A are made of copper (Cu). As the conductive particles 31A, for example, particles containing at least one selected from the group of Ag, Au, Pt, Pd, Ru, Sn, Ni, Fe, Co, Ti, and In other than Cu can be used. In addition, the conductive particle layer 31 may be formed from a mixture of these conductive particles 31A. The particle size of the conductive particles 31A is preferably in the range of 30 nm to 100 nm. By setting the particle diameter within the above range, the surface of the conductive particle layer 31 can be smoothed.

Adjacent conductive particles 31A are sintered or fused at portions in contact with each other, thereby connecting the plurality of conductive particles 31A to each other. In addition, the portion where the conductive particles 31A and the conductive substrate 10 are in contact is also sintered or melted, thereby connecting the conductive particles 31A and the conductive substrate 10 to each other.

The electroless plated layer 32 is formed by electroless plating of metals such as copper, silver, and nickel (hereinafter referred to as electroless plated metal). When electroconductive particle 31A is a copper particle, it is preferable to form the electroless plating layer 32 with copper or nickel from a viewpoint of the adhesiveness with copper particle. The electroless plating layer 32 is composed of a lower layer formed on the same layer as the conductive particle layer 31 , and an upper layer laminated on the lower layer. The lower layer is a layer formed of electroless-plated metal filled in the gaps between the conductive particles 31A. The upper layer is a layer containing electroless-plated metal as a main component. The thickness of the electroless plating layer 32 is 0.1 μm˜0.5 μm.

The plated layer 33 is formed by plating metal such as copper or nickel. The thickness of the electroplating layer 33 is 5 μm˜30 μm. The thickness of the electroplating layer 33 is larger than that of the electroless plating layer 32 . The thickness of the plating layer 33 is set according to the application of the printed circuit board 1 .

A through hole 41 leading to the conductive substrate 10 is formed in the insulating layer 20 . The blind hole 40 is formed by sequentially stacking the conductive particle layer 31 , the electroless plating layer 32 and the electroplating layer 33 at positions corresponding to the through holes 41 . The blind hole 40 has the same configuration as the conductive pattern 30 .

Next, a method of manufacturing the printed wiring board 1 will be described with reference to FIGS. 3(A) to 4(D).

As shown in FIG. 3(A), on the conductive substrate 10 having a thickness of 10 μm to 500 μm, a solution-like polyimide precursor resin is coated. Thereafter, the polyimide precursor resin is heated at 300° C. or higher to be cured. Thus, the insulating layer 20 with a thickness of 10 μm to 200 μm is formed on the conductive substrate 10 .

As shown in FIG. 3(B) , in the insulating layer 20 , a through hole 41 having a diameter of 10 μm to 200 μm is formed at a portion corresponding to the blind hole 40 (through hole forming step). For the formation of the through hole 41, a laser method or an etching method can be used. At this time, the through hole 41 is formed until the bottom surface of the through hole 41 reaches the conductive substrate 10 , that is, the depth of the through hole 41 is the same as the thickness of the insulating layer 20 . The inner diameter of the through hole 41 is 10 μm to 200 μm. After the through hole 41 is formed, a desmear process is performed to remove resin burrs, resin powder, and the like generated by laser or etching.

As shown in FIG. 3(C), after surface treatment of the insulating layer 20, conductive ink is applied to the entire surface of the conductive substrate 10, and the applied conductive ink is further dried (first layer formation process) . After the conductive ink is dried, an oxide remover is applied to remove oxides formed on the surface of the conductive particles 31A and the surface of the conductive substrate 10 , and the applied oxide remover is further dried. In addition, heat treatment is performed in order to sinter the conductive particles 31A. Each step will be described in detail below.

As the surface treatment method of the insulating layer 20, plasma treatment, alkali treatment for making the surface hydrophilic with an alkaline solution, corona treatment for modifying the surface of the object by corona discharge, and making the surface of the object by ultraviolet rays Modified UV treatment, etc. These surface treatment methods can roughen the surface of the insulating layer 20 or introduce hydrophilic groups into the surface of the insulating layer 20 . As a result, the surface tension between the conductive ink and the insulating layer 20 decreases.

The conductive ink is prepared by dispersing conductive particles 31A in a predetermined solvent. For dispersion of the conductive particles 31A, a particle dispersant can be used. As a solvent, for example, water can be used. The viscosity of conductive ink is almost the same as that of water. Therefore, even if the diameter of the through-hole 41 is as small as 10 μm, the conductive ink can be easily filled in the through-hole 41 . As the solvent, a volatile solvent such as ethanol, or a mixed solution of water and a volatile solvent can also be used. As the conductive particles 31A, particles having an average particle diameter of several tens of nm can be used.

As the particle dispersant, for example, a polymer dispersant having a molecular weight of 2,000 to 100,000 can be used. Specifically, as the particle dispersant, an amine-based polymer dispersant such as polyethyleneimine or polyvinylpyrrolidone can be used. In addition, as a particle dispersant, a hydrocarbon polymer dispersant having a carboxylic acid group in a molecule such as polyacrylic acid or carboxymethyl cellulose may also be used.

The conductive ink is coated on the entire surface of the conductive substrate 10 using a roller. The thickness of the applied conductive ink was adjusted so that the thickness of the conductive ink after drying was 0.1 μm. For the coating of the conductive ink, methods such as spin coating, spray coating, bar coating, die coating, slit coating, and dip coating can also be used. When the conductive ink is dried, the temperature of 80° C. is maintained for a predetermined time in an air atmosphere in order to evaporate water in the conductive ink. Thereby, a thin layer of conductive particles 31A is formed on the surface of insulating layer 20 .

After the conductive ink is dried, an oxide remover is applied on the surface of the conductive particles 31A and the surface of the conductive substrate 10 . The oxide removal agent is adjusted so that the oxide removal substance is dissolved in a predetermined solvent. As a solvent, for example, water can be used. As the solvent, a volatile solvent such as ethanol, or a mixed solution of water and a volatile solvent can also be used.

After the oxide remover is applied, heating is performed in an inert gas atmosphere. The heating temperature of the oxide remover is 50°C to 450°C, more preferably 100°C to 400°C. The heat treatment time is 1 minute to 200 minutes, more preferably 10 minutes to 60 minutes. By heat treatment, the oxide layer present on the surfaces of the conductive particles 31A and the conductive substrate 10 reacts with the oxide removing substance to decompose the oxide layer.

There are two types of oxide removal substances as follows.

The first type of oxide removal material is a reducing material that reduces oxides. Hypophosphorous acid, phosphorous acid, ascorbic acid, ethylenediaminetetraacetic acid (EDTA), alcohol, hydrazine, formaldehyde, etc. are mentioned as a reducing substance.

The second type of oxide removal substance is an acidic or alkaline substance that dissolves oxides. Examples of such substances include allylamine, formic acid, glutamic acid, fatty acid, lactic acid, phthalic acid, maleic acid, malic acid, boric acid, ammonium chloride, magnesium chloride, methyl chloride, chloroform, sodium acetate, bromide Potassium, calcium bromide, trichlorethylene, sodium sulfide, sodium iodide, aluminum sulfate, hexachloroethane, etc. In particular, allylamine, formic acid, glutamic acid, fatty acid, lactic acid, phthalic acid, maleic acid, and malic acid do not allow ionic elements to remain even after the oxide remover is dried. preferred.

The oxide remover can be used by dissolving either or both of the first type of oxide remover and the second type of oxide remover in a solvent. In addition, a dispersant for an oxide-removing substance or a pH adjuster for adjusting the pH of the solution may be added to the solvent.

In the heat treatment after the conductive ink is dried, organic substances other than the conductive particles 31A (hereinafter referred to as “residual organic substances”) are removed while the conductive particles 31A are sintered. Examples of the residual organic matter include a particle dispersant, an oxide remover, and the like contained in the conductive ink. In order to suppress oxidation of the conductive particles 31A, heat treatment is performed, for example, in a nitrogen atmosphere. In the heat treatment, the temperature was raised to 350° C. at a rate of temperature increase of 5° C./minute, and the temperature of 350° C. was maintained for 30 minutes. Thus, the conductive particles 31A are sintered, and the conductive particles 31A are connected to each other, thereby forming the conductive particle layer 31 . The reason why sintering can be performed at a relatively low temperature as described above is that the surface energy of the conductive particles 31A having an average particle diameter of several tens of nm is high.

Next, as shown in FIG. 3(D), the electroless plating layer 32 is formed so that the thickness from the insulating layer 20 is about 0.2 μm. Specifically, after coating a metal catalyst such as Pd—Sn on the conductive particle layer 31 and the insulating layer 20 , Sn is dissolved to allow Pd to adhere to the conductive particle layer 31 . Then, the electroless plating layer 32 is formed on the conductive particle layer 31 and the insulating layer 20 by immersion in a copper plating solution. In this way, the gaps between the adjacent conductive particles 31A and the gaps between the conductive particles 31A and the conductive substrate 10 are filled with the electroless plating metal. Thus, while the density of the conductive particle layer 31 is increased, a dense electroless plating layer 32 is formed on the surface of the conductive particle layer 31 .

Next, the conductive pattern 30 and the blind hole 40 are formed by a semi additive-pattern method. Each step will be specifically described below.

As shown in FIG. 4(A) , on the surface of the electroless plating layer 32 other than the portions corresponding to the blind holes 40 and the conductive patterns 30 , a resist 50 is formed. The resist 50 is formed by laminating a photoresist on a substrate, exposing and developing using a photomask.

As shown in FIG. 4(B) , copper electroplating is performed to form an electroplating layer 33 on the electroless plating layer 32 (second layer forming step). Thus, the conductive pattern 30 and the blind hole 40 are formed on the conductive particle layer 31 and the insulating layer 20 .

As shown in FIG. 4(C), after the resist 50 is stripped, the seed layer, that is, the electroless plating layer 32 and the conductive particle layer 31 is removed with sulfuric acid hydrogen peroxide. Pd adhering to the insulating layer 20 during electroless plating is further removed. Through the above steps, blind holes 40 and conductive patterns 30 are formed (pattern layer forming step).

Next, the manufacturing method of the present embodiment will be compared with a conventional manufacturing method and explained.

In a conventional manufacturing method, after forming the through hole 41 in the insulating layer 20 , a pad pattern is formed around the through hole 41 . Next, the land pattern is connected to the conductive substrate 10 by filling the through hole 41 with a conductive paste. According to this method, in order to solve the problem that the conductive paste cannot be filled due to the reduction in the diameter of the through-hole 41 , it is necessary to reduce the viscosity of the conductive paste. However, the decrease in the viscosity of the conductive paste causes a problem that the conductive paste spreads over the land pattern when thermally cured, and thus the diameter of the blind hole deviates.

In this respect, the invention of the present application is characterized by each process of FIG. 4(A) to FIG. 4(C). In other words, unlike the conventional method of manufacturing blind vias 40 , since the process of filling conductive material into through holes 41 , that is, coating of conductive ink is performed before electroplating, low-viscosity conductive ink can be used. In addition, since it is sufficient to remove the seed layer (electroless plating layer 32 and conductive particle layer 31 ) after the conductive ink is applied, occurrence of dimensional variation in the blind hole 40 can be suppressed. Therefore, the dimensional accuracy of the blind hole 40 can be made the same as the pattern accuracy of the semi-additive-pattern method.

In addition, in the manufacturing method of the printed circuit board 1 of this embodiment, after forming the blind hole 40 and the conductive pattern 30, in order to reduce the resistance value of the blind hole 40, the blind hole 40 is energized and heated. This processing will be described below.

As shown in FIG. 4(D) , the probe 61 on the high potential side of the constant current power supply 60 is brought into contact with the plating layer 33 of the blind hole 40 . In addition, the probe 62 on the ground side is brought into contact with the conductive substrate 10 . Then, a constant current is passed through the blind hole 40 using the two probes 61 and 62 .

The resistance of the conductive particle layer 31 and the electroless plating layer 32 is determined by the conductivity of the conductive particles 31A, the conductivity of the electroless plating, the contact resistance between the conductive particles 31A, and the contact resistance between the conductive particles 31A and the conductive substrate 10. , the contact resistance between the electroless plating and the conductive particles 31A, etc. are determined. Among the above elements, the electrical resistance of the conductive particle layer 31 and the electroless plated layer 32 is greatly influenced by the contact resistance between the conductive particles 31A and the contact resistance between the conductive particles 31A and the conductive substrate 10 . In addition, in the case where an oxide layer is formed on the surface of the conductive particle 31A and the surface of the conductive substrate 10 , each of the above contact resistances contributes more to the resistance of the conductive particle layer 31 and the electroless plated layer 32 . Therefore, in order to reduce each contact resistance, a pulse current is passed through the blind hole 40 to sinter or melt the contact portion between the conductive particles 31A and the contact portion between the conductive particle 31A and the conductive substrate 10 . Accordingly, the conductive particles 31A are connected to each other, and at the same time, the conductive particles 31A and the conductive substrate 10 are connected to each other. In addition, in this case, the contact resistance between the conductive particles 31A and the contact resistance between the conductive particles 31A and the conductive substrate 10 become small, respectively.

Next, the effect of applying an oxide remover in the method of manufacturing the printed circuit board 1 and the effect of heating the blind vias 40 will be described with reference to the embodiments and comparative examples of the printed circuit board 1 shown in FIG. 5 . .

In Examples 1 to 3, the oxide remover was applied and then energized and heated. In the comparative example, energization heating was performed without applying an oxide remover. Then, for each of the examples and comparative examples, the resistance values of the blind holes 40 before and after heating were measured.

<Example 1>

· The base material is the conductive substrate 10 on which the insulating layer 20 is laminated.

·The conductive substrate 10 is a SUS304 substrate with a thickness of 20 μm.

· The insulating layer 20 is formed of polyimide resin. The thickness of the insulating layer was set to 10 μm.

· The insulating layer 20 is irradiated with a YAG laser to form the through hole 41 of the blind hole 40 . The diameter of the through hole 41 was set to 60 μm.

・The conductive ink used was an aqueous solution in which copper particles with an average particle diameter of 40 nm were dispersed in water at only 8% by mass.

· After coating the conductive ink on the substrate, it was heated at 80° C. for about 30 seconds to dry the conductive substrate 10 .

· After the conductive ink was dried, a 1.0% by mass aqueous solution of ascorbic acid was applied as an oxide remover (reducing agent) on the dried conductive ink. Thereafter, in an inert gas atmosphere, a temperature of 90° C. was maintained for 30 minutes. Next, the temperature was raised to 350° C. at a rate of 5° C./minute, and then heated at 350° C. for 30 minutes to form the conductive particle layer 31 .

- Electroless copper plating is performed on the conductive particle layer 31 . The thickness of the electroless plating layer was set to 0.2 μm.

• On the electroless plating layer, the conductive pattern 30 and the blind hole 40 are formed by a semi-additive-patterning method.

• A pulse current with a current of 5 A and a pulse width of 100 μs was passed through the blind hole 40 .

(result)

· The resistance value of the blind hole 40 before power-on is 1.4Ω.

· The resistance value of the blind hole 40 after electrification is 0.11Ω.

<Example 2>

・The production conditions were the same as in Example 1, except that after the conductive ink was dried, a 1.0% by mass aqueous solution of glutamic acid was applied as an oxide remover (oxide dissolver) to the dry conductive ink. things.

(result)

· The resistance value of the blind hole 40 before power-on is 1.2Ω.

· The resistance value of the blind hole 40 after electrification is 0.09Ω.

<Example 3>

・The production conditions were the same as in Example 1, except that after the conductive ink was dried, a 1.0% by mass aqueous solution of maleic acid was applied as an oxide remover (oxide dissolver) to the dry conductive ink. things.

(result)

· The resistance value of the blind hole 40 before power-on is 1.2Ω.

· The resistance value of the blind hole 40 after electrification is 0.09Ω.

<Comparative example>

·The production conditions were the same as in Examples 1 to 3 except that no oxide remover was applied.

(result)

· The resistance value of the blind hole 40 before power-on is 1.8Ω.

· The resistance value of the blind hole 40 after electrification is 0.14Ω.

<Evaluation>

The examples and comparative examples are compared with reference to FIG. 5 .

For any of the examples and comparative examples, the effects of the pulsed current are the same when the pulsed current is applied in the blind hole 40 . That is, the resistance value after energization is smaller than the resistance value before energization. This is considered to be because the resistance value is relatively high at the contact portion between the conductive particles 31A and the contact portion between the conductive particle 31A and the conductive substrate 10 before the pulse energization, whereas the pulse energization Afterwards, each contact part is heated and melted or sintered, so that the resistance value of each contact part is reduced.

On the other hand, comparing the resistance values of the blind vias 40 before energization, the resistance values of the respective examples were smaller than the resistance values of the comparative examples. This is considered to be because in any of the examples, the oxide on the surface of the conductive particles 31A and the oxide on the surface of the conductive substrate 10 (the bottom surface of the blind hole 40 ) were removed due to the application of the oxide remover.

Hereinafter, according to the present embodiment, the following operational effects can be achieved.

(1) Coating conductive ink on the insulating layer 20 to form the conductive particle layer 31 . Next, blind holes 40 are formed on the conductive particle layer 31 by electroplating. Further, the conductive particle layer 31 and the electroless plating layer 32 around the blind hole 40 are removed. According to this method, the conductive particle layer 31 is removed after the blind hole 40 is formed. Therefore, a low-viscosity conductive ink for forming the conductive particle layer 31 can be used. Thereby, variation in the diameter of the blind hole due to the low viscosity of the conductive film can be suppressed.

(2) After the blind hole 40 is formed, the blind hole 40 is energized and heated. The blind hole 40 contains the conductive particle layer 31 . In addition, the resistance value of the conductive particle layer 31 is easily affected by the contact resistance at the contact portion between the conductive particles 31A. According to the present embodiment, the contact portions between the conductive particles 31A are melted or sintered by subjecting the blind vias 40 to heat treatment with electricity. Accordingly, the contact resistance between the conductive particles 31A can be reduced, thereby reducing the resistance value of the blind hole 40 .

(3) After evaporating the solvent of the conductive ink to form the conductive particle layer 31 , the electroless plating layer 32 is formed on the conductive particle layer 31 . According to this method, since the gaps between the conductive particles 31A are filled with the plating material, the conductive particle layer 31 can be made dense. As a result, the resistance value of the blind via 40 can be reduced.

(4) After the conductive particle layer 31 is formed, an oxide remover is applied on the conductive particle layer 31 . According to this configuration, since the oxide on the surface of the conductive substrate 10 is removed by the oxide remover, the bonding strength between the conductive substrate 10 and the conductive particle layer 31 increases. As a result, peeling between the conductive substrate 10 and the conductive particle layer 31 is suppressed.

(5) After applying the oxide remover, it is heat-treated in an inert atmosphere. According to this method, the reaction of the oxide remover with oxygen in the air is suppressed compared to the heat treatment performed in air, thereby promoting the reaction of the oxide remover with the oxide of the conductive substrate 10 . Therefore, peeling between the conductive substrate 10 and the conductive particle layer 31 is further suppressed.

(6) As the oxide removal agent, at least one of a reducing agent that reduces oxides and a dissolved substance that dissolves oxides can be used. The reducing agent reduces the oxide to decompose the oxide. The dissolved substance dissolves the oxide to decompose the oxide. According to this method, since the oxide of the conductive substrate 10 is decomposed, the joining force between the conductive substrate 10 and the conductive particle layer 31 becomes large.

(7) The conductive substrate 10 may be a stainless steel substrate. According to this configuration, the printed wiring board 1 can have higher elasticity than when a copper material is used for the conductive substrate 10 .

(8) The blind hole 40 has the conductive particle layer 31 , the electroless plating layer 32 and the electroplating layer 33 . The blind hole 40 is formed by sequentially laminating the electroless plating layer and the electroplating layer 33 on the insulating layer 20 . However, in this configuration, since the bonding strength between the insulating layer 20 and the electroless plating layer 32 is weak, the electroless plating layer 32 may peel off from the insulating layer 20 . In this regard, according to the present embodiment, the plating layer 33 is connected to the conductive substrate 10 through the conductive particle layer 31 and the electroless plating layer 32 . In this case, the bonding force between the conductive particle layer 31 and the insulating layer 20 is greater than the bonding strength between the electroless plating layer and the insulating layer 20 . Therefore, peeling of the conductive particle layer 31 from the insulating layer 20 is suppressed.

(9) The plurality of conductive particles 31A are fused or sintered to be connected to each other at portions in contact with each other. In addition, the conductive particles 31A and the conductive substrate 10 are fused or sintered to be connected to each other at portions in contact with each other. According to this configuration, since the current density of the conduction path of the blind hole 40 increases, the resistance value of the blind hole 40 can be reduced.

It should be noted that the following modifications can also be made to this embodiment.

· Generally, since the surface of stainless steel is prone to oxidation, the connection strength of the stainless steel substrate and the blind hole 40 may be reduced. In order to prevent this, the stainless steel substrate as the conductive substrate 10 may have a nickel layer on its contact surface with the insulating layer 20 . According to this configuration, since the nickel layer suppresses oxidation of the surface of the stainless steel, it is possible to suppress a decrease in connection strength between the stainless steel substrate and the blind hole 40 .

· After the conductive ink is dried, the oxide remover is applied on the conductive particle layer 31 , but the oxide remover may be added to the conductive ink in advance. Even so, the reducing agent and dissolved substances in the conductive ink can be brought into contact with the oxide of the conductive substrate 10 to decompose the oxide of the conductive substrate 10 . According to this method, the steps of applying the oxide removing agent and drying the solution containing the oxide removing agent are unnecessary, thereby simplifying the manufacturing process.

- After the conductive ink is dried, the application and drying of the oxide remover are performed, but the drying of the oxide remover may be included in the sintering process of the conductive particles 31A. For example, the oxide remover coating is heated under an inert atmosphere using two stages of heating temperature. The temperature in the first stage is set to a temperature at which moisture in the oxide remover evaporates (that is, 50° C. to 100° C.), and is maintained for 30 minutes. Then, the temperature of the second stage was set to 350° C. and maintained for 30 minutes.

• The conductive pattern 30 and the blind hole 40 may also be formed by a semi-additive panel method. In any manufacturing method, the conductive particle layer 31 and the electroless plating layer 32 can be removed after the conductive pattern 30 is formed, and therefore, the dimensional accuracy of the blind hole 40 can be improved compared with the conventional method.

· The present invention is also applicable to the blind hole 40 connecting the conductive pattern 30 and the conductive pattern 30 disposed above or below it.

- The present invention is applicable to various printed circuit boards 1 other than the printed circuit board 1 for head suspension used for mounting a magnetic head in a hard disk drive.

Claims (10)

1. a manufacture method for printed circuit board (PCB), described printed circuit board (PCB) have insulating barrier, On the 1st of described insulating barrier formed the 1st conductive layer, at the 2nd of described insulating barrier On face formed the 2nd conductive layer and connect described 1st conductive layer and described 2nd conductive layer Blind hole, described manufacture method is characterised by including following operation:

Through hole formation process, wherein, is formed in described insulating barrier and passes to the described 1st and lead The through hole of electric layer；

1st layer of formation process, wherein, is coated with in the region containing described through hole and contains The electric conductivity ink of conductive particle is to form conductive particle layer, and described 1st layer of formation process includes Following operation: be coated with described electric conductivity ink operation, make described electric conductivity ink solvent evaporation with Form the operation of described conductive particle layer, and coating oxide goes on described conductive particle layer After agent, described conductive particle layer forms the operation of electroless plating, described oxide removal Agent removes the oxide of described 1st conductive layer surface；

2nd layer of formation process, wherein, forms electricity by plating on described conductive particle layer Coating；And

Patterned layer formation process, wherein, removes the described conductive particle around described through hole Layer, and form described 2nd conductive layer comprising described conductive particle layer and described electrodeposited coating.

The manufacture method of printed circuit board (PCB) the most according to claim 1, it is characterised in that

After forming described blind hole, described blind hole is carried out electrified regulation process.

The manufacture method of printed circuit board (PCB) the most according to claim 1, it is characterised in that

In described 1st layer of formation process, be additionally included in coating described oxide remover it After, in an inert atmosphere described oxide remover is carried out the operation of heat treated.

The manufacture method of printed circuit board (PCB) the most according to claim 1, it is characterised in that

Described oxide remover contains and reduces the reducing agent of described oxide and dissolve described At least one dissolved in material of oxide.

The manufacture method of printed circuit board (PCB) the most according to claim 4, it is characterised in that

The oxide of described 1st conductive layer surface is reduced by described reducing agent, and described molten Solve material to be dissolved by described oxide.

The manufacture method of printed circuit board (PCB) the most according to claim 1 and 2, its feature It is,

Described 1st conductive layer is stainless steel substrate.

The manufacture method of printed circuit board (PCB) the most according to claim 6, it is characterised in that

Described stainless steel substrate has nickel dam on its contact surface with described insulating barrier.

8. a printed circuit board (PCB), this printed circuit board (PCB) is according to claim 1 and 2 Method manufacture, have insulating barrier, on the 1st of described insulating barrier formed the 1st conductive layer, On the 2nd of described insulating barrier formed the 2nd conductive layer and connect described 1st conduction Layer and the blind hole of described 2nd conductive layer, it is characterised in that

Described 2nd conductive layer has:

It is formed on described insulating barrier and contains the conductive particle layer of multiple conductive particles；

It is laminated in the electroless plating on described conductive particle layer；And

It is laminated in the electrodeposited coating on described electroless plating,

Described blind hole has:

Formed in the position corresponding with the through hole running through described insulating barrier and lead containing multiple The conductive particle layer of conductive particles；

It is laminated in the electroless plating on the conductive particle layer of described blind hole；And

It is laminated in the electrodeposited coating on the electroless plating of described blind hole,

Described blind hole is connected with described 1st conductive layer in the bottom surface of described through hole.

Printed circuit board (PCB) the most according to claim 8, it is characterised in that

The plurality of conductive particle is melted at the part contacted with each other or sinters and be mutual Connect,

Described conductive particle and described 1st conductive layer are melted at the part contacted with each other Or sinter and be connected with each other.

Printed circuit board (PCB) the most according to claim 8 or claim 9, it is characterised in that

More than a diameter of 10 μm of described through hole, and the thickness of described conductive particle layer It it is below 0.5 μm.