JP2017048468A - Manufacturing method of printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure good heat release property by using an aluminum material for a base sheet, enhance adhesiveness between the base sheet and a circuit layer and enhance durability.SOLUTION: In a method for manufacturing a printed substrate, a fine porous anodic oxide film 3 having porosity of over 5% and 30% or less with a thickness of 0.03 to 2.0 μm is formed on at least a part of surface of a base sheet 2 made of pure aluminum or an aluminum alloy, and a circuit layer 5 made of copper or a copper alloy is formed on the fine porous anodic oxide film 3 via a thermal conductive adhesive layer 4 containing an inorganic filler of 50 to 95 mass%, and the fine porous anodic oxide film is formed by two-step electrolytic treatment.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing a printed circuit board on which electronic components are mounted, and more particularly to a method for manufacturing a printed circuit board based on an aluminum material.

  As electronic components have been mounted with higher density, printed circuit boards have been required to have high heat dissipation. In particular, in recent years, when an LED is mounted on a printed circuit board, a printed circuit board that can quickly dissipate heat with respect to extremely large heat generation of the LED has been demanded. In order to meet this demand, it has become necessary to be based on metal.

In particular, when an aluminum material is used as the base plate, since the aluminum material is lightweight, the plate thickness can be increased to improve heat dissipation, which is suitable for use on a printed circuit board that places importance on heat dissipation.
However, the adhesive bonding aluminum and copper foil has low thermal conductivity. For this reason, inorganic fillers have been added to the adhesive layer in order to increase thermal conductivity. However, the addition of this filler reduces the adhesive strength of the adhesive and causes peeling at the interface with the aluminum material. The number of bugs to be increased has increased.

On the other hand, the usage environment of printed circuit boards is becoming more severe. In particular, there has been an increase in the case where adhesion to aluminum is lowered due to the increase in the temperature of the reflow furnace for shortening the mounting process time.
Furthermore, in the printed circuit boards used in automobiles, troubles in which the aluminum and the adhesive peel off due to the high temperature and high humidity environment in the vehicle and engine room have increased.
In order to prevent these problems, aluminum has been used with a surface treatment material that has been subjected to a chromate treatment or a surface treatment such as anodization with sulfuric acid or phosphoric acid.
Patent Document 1 discloses that an aluminum plate is anodized with phosphoric acid, and the oxide film is heated and dried at a temperature of 150 to 300 ° C. for 0.5 hours or more.

JP 2006-24906 A

  However, there is a case where sufficient heat resistance, moisture resistance, and heat dissipation may not be obtained only by anodizing treatment as described in Patent Document 1, and for application to a base plate of a small and high current type, there is a conventional case. Higher adhesion and heat dissipation are required.

  The present invention has been made in view of the above circumstances, and by using an aluminum material for the base plate, it ensures good heat dissipation and improves the adhesion between the base plate and the circuit layer, thereby improving durability. An object of the present invention is to provide a method for manufacturing a printed circuit board.

  In the method for producing a printed board according to the present invention, a microporous anodic oxide film having a porosity of more than 5% and not more than 30% is formed on 0.03 to 2 on the surface of at least a part of a base plate made of pure aluminum or an aluminum alloy. A circuit layer made of copper or a copper alloy is formed on the microporous anodic oxide film with a thickness of 0.0 μm through a heat conductive adhesive layer containing 50 to 95% by mass of an inorganic filler. A method for producing a printed circuit board, wherein the microporous anodic oxide film is an electrolysis comprising one or more of sulfuric acid, phosphoric acid, chromic acid and oxalic acid up to a thickness of 0.15 μm. The film is formed by electrolytic treatment using a liquid, and the film thickness is from 0.15 μm to 2.0 μm by electrolytic treatment using an electrolytic solution made of an aqueous solution of phosphate or silicate.

As the base plate, pure aluminum having a purity of 99.0% or more, or various aluminum alloys of 1000 series, 3000 series (Al-Mn series), 5000 series (Al-Mg series) can be used. In, the composition is not limited.
A microporous anodic oxide film refers to pores that are regularly formed from the surface of the film toward the aluminum substrate in the cross-sectional observation of the part where the film is uniformly formed (usually the opening is 1 to 10 nm in thickness of the film) Is a film having a depth of more than 60% and exceeding 5% and not more than 30% (ratio of the total area of the holes as viewed from the surface).
In general anodic oxide coatings (porous coatings) are formed containing several to tens of percent of moisture and electrolytes, so these moisture and the like are released during the drying process of the adhesive and heating in a reflow furnace. Cause deterioration of adhesion. Moreover, although the anodized film by phosphoric acid has a three-dimensional network structure and has good adhesion due to the shape effect, since the film contains moisture, a heat drying step is performed as a post-treatment as in Patent Document 1. Necessary.
A microporous anodic oxide film having a porosity of more than 5% and not more than 30% has less water content compared to a general porous anodic oxide film or phosphoric acid anodic oxide film, so there is no decrease in adhesion and heat drying. A process is also unnecessary. Moreover, it has sufficient durability even in a humid environment.
Compared with a non-porous film having a porosity of 5% or less, the surface of the microporous film is roughened, so that the adhesion surface area is increased, and both the adhesion and heat dissipation properties are excellent due to the shape effect. In particular, it is effective in adhesion to a thermally conductive adhesive layer containing an inorganic filler at a high concentration.

However, this microporous anodic oxide film should be as thin as possible from the viewpoint of thermal conductivity, and is preferably 2.0 μm or less. On the other hand, if it is too thin, it is difficult to form a uniform film, and the adhesiveness with the resin is lowered in a wet environment or the like. Therefore, the film thickness is preferably 0.03 μm or more.
The heat conductive adhesive layer has high heat conductivity by containing an inorganic filler. If the content of the inorganic filler is less than 50% by mass, the thermal conductivity is insufficient, and if it exceeds 95% by mass, the adhesion may be impaired. As described above, the microporous anodic oxide film is effective for adhesion to an adhesive layer having an inorganic filler at a high concentration (for example, 70 to 95% by mass).
In this production method, the phosphate may be selected from ammonium phosphate, ammonium hydrogen phosphate, and ammonium dihydrogen phosphate, and the silicate may be selected from sodium silicate, potassium silicate, and lithium silicate.

In the printed circuit board manufactured according to the present invention, the inorganic filler may be aluminum oxide.
Since aluminum oxide (alumina) has high thermal conductivity, it promotes heat dissipation from the circuit layer to the base plate and also has good adhesion. Moreover, it is excellent also in electrical insulation, and electrical insulation between the circuit layer and the base plate is also good.

In the printed board manufactured by the present invention, a silane coupling agent may be applied on the nonporous anodic oxide film at an application amount of 0.1 to 30 mg / m ² .
As the silane coupling agent, amino-based, epoxy-based, acrylic-based and the like can be used, and the present invention is not limited to a specific one.
The application amount of the silane coupling agent is preferably an appropriate amount in order to improve its function. If it is less, the effect of improving the adhesion is not recognized. 0.1 mg / m ² or more is preferable, and 1 mg / m ² is more preferable. On the other hand, if too much silane coupling agent is applied, the cohesive strength of the silane coupling agent itself may be reduced, and the coating film is easily peeled off. For this reason, 30 mg / m ² or less is preferable, and 8 mg / m ² or less is more preferable.

  According to the present invention, since the circuit layer is formed on the microporous anodic oxide film on the surface of the base plate via the heat conductive adhesive containing the inorganic filler, sufficient heat resistance, moisture resistance, and heat dissipation are provided. It is suitable as a printed circuit board for an electronic component having a large calorific value such as an LED.

It is sectional drawing which shows embodiment of the printed circuit board which concerns on this invention. It is a model figure which shows the relationship between the film thickness in the case of forming an anodized film, and a porosity. It is a model figure which shows the cross-section of a porous anodic oxide film. It is a model figure which shows the cross-section of a microporous anodic oxide film.

Embodiments of a printed circuit board according to the present invention will be described below with reference to the drawings.
As shown in FIG. 1, the printed circuit board 1 of the present embodiment has a microporous anode having a porosity of more than 5% and not more than 30% on at least a part of the surface of a base plate 2 made of pure aluminum or an aluminum alloy. An oxide film 3 is formed to a thickness of 0.03 to 2.0 μm, and a heat conductive adhesive layer 4 is formed on the microporous anodic oxide film 3 via a silane coupling agent. A circuit layer 5 made of copper or a copper alloy is formed on the adhesive layer 4.

[Base plate]
As the aluminum constituting the base plate 2, pure aluminum having a purity of 99.0% or more, 1000 series, 3000 series (Al-Mn series), 5000 series (Al-Mg series) aluminum alloys are used. This aluminum material has a microporous anodic oxide film 3 formed on the surface.

[Microporous anodic oxide film]
The anodizing treatment is performed using an electrolytic solution having a low dissolving power of the oxide film, and the microporous anodic oxide film 3 having a suitable thickness is formed by adjusting the voltage.
Pretreatment is performed prior to the microporous anodic oxidation treatment. The pretreatment is not particularly limited. For example, it is washed with an alkaline degreasing solution, alkali etched with an aqueous sodium hydroxide solution, and desmutted with an aqueous nitric acid solution.

  The microporous anodic oxide film 3 is formed by anodizing the base plate 2. This anodizing treatment (so-called alumite treatment) is to form an anodized film by anodizing treatment in which aluminum or aluminum alloy constituting the base material is immersed in an electrolytic solution. By such anodizing treatment, a microporous anodic oxide film (microporous alumite film) having a porosity exceeding 5% and 30% or less can be formed. Here, the porosity is a value obtained by dividing the area of the portion where pores are formed in the measurement region on the surface of the anodized film by the total measurement area, that is, porosity = (area where holes are present) / ( It is shown by the relational expression of (total measurement area). The porosity of the microporous anodic oxide film is in the range of more than 5% and not more than 30%, more preferably in the range of more than 5% and not more than 10%.

Next, a method for producing a microporous anodic oxide film 3 having a porosity of more than 5% and not more than 30% used as an underlayer will be described below.
In order to produce the microporous anodic oxide coating 3, the electrolysis is stopped at a stage before the coating is made porous, thereby obtaining a coating that is almost nonporous at the stage before the porous coating grows. The method performed by is preferable.
As the electrolytic solution used here, a solution of one or more of sulfuric acid, phosphoric acid, chromic acid, and oxalic acid can be used.
When the base plate 2 made of aluminum or an aluminum alloy is anodized using these electrolytic solutions, an anodized film called a nonporous barrier layer grows in the initial stage of electrolysis, and this nonporous film is formed. When the growth of the anodized film proceeds to a predetermined stage, the porous layer grows rapidly and a porous anodized film is generated. However, in this specification, the term “porous anodic oxide film” means a porous layer grown on a nonporous thin barrier layer.

Here, a growth model of this type of anodized film will be described with reference to FIG.
The horizontal axis in FIG. 2 indicates the thickness of the anodic oxide film, and the vertical axis indicates the porosity. Normally, when a porous anodic oxide film is produced, a nonporous film having a thickness of about 0.1 to 0.2 μm is produced. After the formation of, a rapid increase in porosity occurs with almost no increase in film thickness, and the relationship between the increase in film thickness and the increase in porosity starts to shift to a proportional relationship when the porosity exceeds 30%. Such a growth curve is shown. The growth curve shown in FIG. 2 is a model example of an anodic oxide film, but a nonporous layer having a certain thickness can be obtained even if the concentration and type of electrolyte, applied voltage, and applied current density are slightly different. After the formation, the porosity rapidly increases, and after that, when the porosity exceeds 30%, the relationship between the increase in the film thickness and the increase in the porosity shifts to a proportional relationship, and a porous anodic oxide film is formed. The tendency to do is the same.

  In view of the growth model of the anodic oxide film shown in FIG. 2, in order to obtain a microporous anodic oxide film having a porosity of more than 5% and not more than 30% used as an underlayer, there is It is only necessary to stop the electrolytic treatment in a state where the porosity is low. From the growth model shown in FIG. 2, there is a nonporous layer anodic oxide film having a porosity of 5% or less in the initial stage of electrolysis. Alternatively, the base layer may be formed so as to obtain a non-porous anodic oxide film by stopping electrolysis at the initial stage of the anodizing treatment when producing a porous anodic oxide film described below.

In order to obtain the microporous anodic oxide coating 3, the electrolysis treatment may be stopped under electrolysis conditions such that the film thickness ranges from 0.03 to 0.15 μm, for example, the porosity is 30% or less. A more preferable range of the microporous anodic oxide film 3 under these conditions is a film thickness of 0.05 to 0.1 μm and a porosity of 10%.
When one or more of sulfuric acid, phosphoric acid, chromic acid, and oxalic acid is selected as the electrolytic solution used here, the thickness of the barrier layer of the anodized film is generally an electrolytic voltage (V) × (0.0010 ~ 0.0016) (μm), and it is known that when the thickness of the anodized film exceeds 0.15 μm, the porous structure is started.
Further, in the case of using sulfuric acid as the electrolytic solution, if the electrolytic voltage is set high, a large amount of surface film defects may be formed and a defect called so-called “burn” may occur, so the electrolytic voltage is set to 25 V or less. It is desirable. In the treatment at this electrolytic voltage, the microporous film is obtained by stopping the electrolysis by controlling the film thickness of the anodized film to be 0.15 μm or less.

  When the thickness of the microporous anodic oxide film is less than 0.03 μm, it is difficult to obtain corrosion resistance, and when the thickness exceeds 0.15 μm, the formation of porosity tends to proceed. 1 μm. In the range of 5 to 30%, the porosity is preferably more than 5% and not more than 20%. In the case of an anodized film having a porosity of 5 to 20%, the anode having a porosity of 20% to 30% There is an advantage that the release of moisture can be better suppressed with respect to the oxide film, the decrease in the adhesion area can be prevented, and the film breakage can be easily prevented. From such a viewpoint, the porosity of the microporous anodic oxide film 3 is preferably more than 5% and 10% or less.

From the background as described above, the electrolyte concentration in the electrolytic bath when producing the microporous anodic oxide film is selected in the range of 2% by mass to the saturated concentration of the electrolyte. The bath temperature of the electrolytic bath is sufficient in the range of 5 to 30 ° C.
In such an electrolytic solution, the aluminum material is anodic electrolyzed by being connected to a power source so as to be an anode even if it is continuous or intermittent. An insoluble conductive material such as a carbon electrode is used for the cathode. As the electrolytic current, a direct current or the like is used. In direct current electrolysis, electrolysis is performed with a direct current density of about 0.5 to 2.5 A / dm ² and an electrolysis time of about several seconds to 10 minutes.
Further, in the case where sulfuric acid is used as the electrolytic solution, the electrolysis is performed with the electrolysis voltage set to 25 V or less for the reasons described above.

FIG. 3 is a model diagram of a cross-sectional structure of the anodized film made porous by increasing the porosity shown in FIG. 2, and FIG. 4 is a nonporous material obtained by setting the porosity shown in FIG. 2 to about 10%. It is a model figure of the cross-sectional structure of a microporous anodic oxide film close to.
A porous anodic oxide film 10 shown in FIG. 3 is composed of a nonporous barrier layer 10a and a porous layer 10b formed on the nonporous barrier layer 10a. 11 shows a cross-sectional structure in which some irregularities exist on the surface without holes growing. In the microporous anodic oxide film 11, 5-30% of the holes exist, and this ratio of holes is present. However, in FIG. 4, clear-shaped holes are not shown.

The film thickness of the microporous anodic oxide film 3 is preferably 0.03 to 2.0 μm. From the viewpoint of thermal conductivity, it should be as thin as possible and is preferably 2.0 μm or less. However, if it is too thin, it is difficult to form a uniform film, and the adhesiveness to the resin is lowered in a wet environment. It is preferable that it is the film thickness. From the viewpoint of thermal conductivity, adhesion, etc., the film thickness is more preferably 0.1 to 1.5 μm.
As described above, in order to obtain a microporous anodic oxide film, the film thickness is preferably up to 0.15 μm, but when the film thickness is 0.15 to 2.0 μm, it is porous by electrolytic treatment. Therefore, it is preferable to control so that the porosity is 5 to 30% by performing two-stage electrolytic treatment.
The electrolytic solution for anodization performed in the two-stage electrolytic treatment is a phosphate such as ammonium phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, or ammonium phosphate, or a silicate such as sodium silicate, potassium silicate, or lithium silicate. If it is an aqueous solution, the dissolving power of the oxide film is low, and the porosity can be reduced.

[Silane coupling agent]
By applying an amino-based, epoxy-based, acrylic-based or other silane coupling agent to the surface of the microporous anodic oxide coating 3, the adhesion with the resin is improved. The coating amount of the silane coupling agent is preferably 0.1 mg / m ² or more, more preferably 1 mg / m ² or more, preferably 30 mg / m ² or less, more preferably 8 mg / m ² or less.

[Thermal conductive adhesive layer]
A heat conductive adhesive layer 4 is provided on the surface of the microporous anodic oxide film 3 coated with a silane coupling agent. This heat conductive adhesive layer 4 is made by containing 50 to 95% by mass of an inorganic filler in an adhesive such as an epoxy resin. As the inorganic filler, powders having thermal conductivity such as Al ₂ O ₃ , MgO, BN, SiO ₂ , Si ₃ N ₄ , AlN, and carbon can be used, and one or a combination of two or more thereof can be used. Added. Among them, _Al 2 _{O 3} is obtained by adding (aluminum oxide) good adhesion, preferred. Excellent electrical insulation. The addition amount is preferably 50 to 95% by mass, and if it is less than 50% by mass, the thermal conductivity is insufficient, and if it exceeds 95% by mass, the adhesion may be impaired. More preferably, it is 60-85 mass%.
Although the thickness of this heat conductive contact bonding layer 4 is not specifically limited, It shall be 30-50 micrometers.

[Circuit layer]
A circuit layer 5 is formed on the heat conductive adhesive layer 4 in a predetermined pattern. The circuit layer 5 is formed by a method in which a foil made of copper or a copper alloy is attached to the base plate 2 by the heat conductive adhesive layer 4 and then masked into a predetermined pattern and etched. The film thickness of the circuit layer 5 is not particularly limited, and is set to an appropriate thickness, but 10 to 100 μm is appropriate.

The printed circuit board 1 obtained as described above has a significantly improved adhesion due to the microporous anodic oxide film 3 of the base plate 2, and the occurrence of peeling or the like of the circuit layer 5 bonded via the heat conductive adhesive layer 4. Can be prevented.
Since a general anodized film is a porous film, it contains a large amount of moisture and electrolyte, such as several percent to several tens of percent. During the drying process of the adhesive layer and subsequent heating in a reflow furnace, these moisture and the like are contained. As a result of the release, adhesion is reduced. Further, in the chromate treatment, the film is denatured by the heating and the adhesion is reduced.
On the other hand, the microporous anodic oxide film 3 does not contain moisture and has a high barrier property, so that the adhesion is not lowered and has sufficient durability even in a wet environment.

  For example, in an endurance test in which the deterioration of adhesion is observed when exposed to a moist environment, the normal anodized film progresses rapidly and peels off, whereas the use of a microporous anodized film significantly improves the durability. To improve. The reason is that a normal anodic oxide film is a porous film, and therefore, corrosive substances easily enter the aluminum material from the film and corrosion is likely to occur. On the other hand, infiltration of corrosive substances is suppressed in the microporous anodic oxide film.

Furthermore, since the microporous anodic oxide film is excellent in the above-mentioned corrosion resistance, the film thickness can be made as thin as 0.03 to 2.0 μm, and the heat dissipation is also improved with respect to a normal anodic oxide film exceeding 2.0 μm. it can.
Of the various materials described above, silica, carbon, aluminum oxide (alumina), and the like are suitable as the inorganic filler, but adhesion is particularly excellent when alumina is used.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
As the base plate, an Al—Mg JIS 5052 plate rolled to 1.0 mm was used. This material was immersed in a 50 ° C. degreasing solution containing 2% of a surfactant for 60 seconds and then washed with water for 30 seconds. Next, the substrate was etched with a 10% NaOH aqueous solution at 50 ° C. for 30 seconds, and then washed with water for 30 seconds. Subsequently, the substrate was washed with a 10% HNO ₃ solution for 30 seconds and then washed with water for 30 seconds.

Next, electrolytic treatment was performed using sulfuric acid as an electrolytic solution and the aluminum alloy as an anode. The sulfuric acid concentration in the electrolytic solution was appropriately adjusted in the range of 10 to 20%, the electrolytic bath temperature was 15 to 25 ° C., the electrolytic voltage was 15 to 25 V, and the current density was 1 to ² A / dm ² . In this way, an anodized film having a thickness shown in Table 1 was formed on the aluminum alloy surface. Moreover, the thing which formed the porous anodic oxide film by the normal anodic oxidation process which used sulfuric acid aqueous solution as electrolyte solution, and the thing which carried out the phosphoric acid chromate process for the base treatment were also produced.

Next, a silane coupling agent was applied to the surface of the base plate subjected to the base treatment, and then a copper foil was bonded via an adhesive in which various fillers were added to an epoxy resin. Table 1 shows the type and amount of filler. The numerical value in () is the addition amount, which is mass%. The thickness of the adhesive was 40 μm, and the thickness of the copper foil was 50 μm.
The printed circuit board (copper-clad laminate) thus obtained was evaluated for adhesion, moisture resistance, and heat dissipation.

  Adhesive evaluation: After the sample was heated at 180 ° C. for 15 minutes, the peel strength was measured by a peel test according to JIS C6481 “Test method for copper-clad laminate for printed wiring board”. Those having a peel strength of 3.0 kgf / cm (29.4 N / cm) or more, ◎, 2.5 kgf / cm (24.5 N / cm) or more, 3.0 kgf / cm (29.4 N / cm) What was less than (circle) and what was less than 2.5 kgf / cm (24.5 N / cm) was made into x.

  Wetability evaluation: The sample was heated at 180 ° C. for 15 minutes, then exposed to 85% wet environment at 85 ° C. for 1000 hours, and then peeled off in accordance with JIS C6481 “Testing method for copper-clad laminates for printed wiring boards” The peel strength was measured by the test. Those having a peel strength of 3.0 kgf / cm (29.4 N / cm) or more, ◎, 2.5 kgf / cm (24.5 N / cm) or more, 3.0 kgf / cm (29.4 N / cm) What was less than (circle) and what was less than 2.5 kgf / cm (24.5 N / cm) was made into x.

Evaluation of heat dissipation: LED was mounted on a square printed board of 20 mm × 20 mm, and the temperature at the center of the board when emitting light for 30 minutes was measured with a radiation thermometer. A sample having a temperature of less than 50 ° C. was evaluated as “◎”, a sample having a temperature of 50 ° C. or more and less than 60 ° C. was evaluated as “◯”, and a sample having a temperature of 60 ° C. or more was evaluated as “X”.
These evaluation results are shown in Table 1. Comprehensive evaluation: ◎ if all evaluations of adhesiveness, moisture resistance and heat dissipation were ◎, 接着 if adhesive was ◎ and other evaluation was 又 は or ◎, 他 if adhesiveness was 他The case where the evaluation was ○ or ◎ was Δ, and the case where any evaluation was × was ×.

  As shown in Table 1, the base plate was microporous anodized and the thickness of the microporous anodized film having a porosity of more than 5% and not more than 30% was 0.03 to 2.0 μm. When the copper foil is formed on the microporous anodic oxide film via a heat conductive adhesive layer containing 50 to 95% by mass of an inorganic filler such as alumina or silica, the overall evaluation is Δ to ◎. It can be seen that it is excellent in adhesiveness, moisture resistance and heat dissipation.

In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.
In the above embodiment, the microporous anodic oxide film is formed on the entire surface of the base plate and the copper foil is adhered. However, when the circuit layer is partially provided, at least the part where the circuit layer is provided. A microporous anodic oxide film may be formed on the surface.

DESCRIPTION OF SYMBOLS 1 Printed circuit board 2 Base board 3 Microporous anodic oxide film 4 Thermal conductive adhesive layer 5 Circuit layer

Claims (2)

A microporous anodic oxide film having a porosity of more than 5% and not more than 30% is formed on a surface of at least a part of a base plate made of pure aluminum or an aluminum alloy to a thickness of 0.03 to 2.0 μm. A method for producing a printed circuit board in which a circuit layer made of copper or a copper alloy is formed on a microporous anodic oxide film through a heat conductive adhesive layer containing 50 to 95% by mass of an inorganic filler. ,
The microporous anodic oxide film is formed by electrolytic treatment using an electrolytic solution composed of one or more of sulfuric acid, phosphoric acid, chromic acid, and oxalic acid until the film thickness reaches 0.15 μm. The method for producing a printed circuit board, wherein the thickness is 0.15 μm to 2.0 μm by electrolytic treatment using an electrolytic solution made of an aqueous solution of phosphate or silicate.   2. The phosphate according to claim 1, wherein the phosphate is selected from ammonium phosphate, ammonium hydrogen phosphate, and ammonium dihydrogen phosphate, and the silicate is selected from sodium silicate, potassium silicate, and lithium silicate. Manufacturing method for printed circuit boards.

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