KR102398247B1 - Nitride circuit board manufactured using molten salt titanizing and manufacturing method thereof - Google Patents

Abstract

An object of the present invention is to provide a circuit board and a method for manufacturing the same using molten salt in a liquid state in modifying the surface of a dielectric substrate. According to one aspect of the present invention, (a) forming a mixture comprising a Ti powder and molten salt; (b) immersing the dielectric substrate in the mixture; and (c) heating the mixture to form a Ti-containing layer on the surface of the dielectric substrate.

Description

Nitride circuit board manufactured using molten salt titanizing and manufacturing method thereof

The present invention relates to a circuit board and a method of manufacturing the same, and more particularly, to a circuit board in which the surface of a dielectric substrate is modified by reacting molten salt with Ti, and to a method of manufacturing the same.

AlN (Aluminum Nitride, aluminum nitride) and Si ₃ N ₄ (Silicon Nitride, silicon nitride) have high thermal conductivity of 150~250 W/mK and 60~90 W/mK, respectively, so they are applied to parts that require heat dissipation. . In order to efficiently remove the heat generated from the LED chip or power semiconductor, a substrate with good thermal conductivity is required, and typical materials are AlN and Si ₃ N ₄ . A conductor such as copper is bonded to one or both surfaces of the nitride substrate, or copper wiring is formed in a given pattern.

Several methods are known for forming a copper-nitride circuit board by bonding copper to a nitride substrate. For one, it is known that a brazing alloy is placed between a nitride and copper and heat-treated at a high temperature. The brazing alloy is composed of Ag as a main element and a small amount of Ti or Zr added thereto. During the heat treatment at high temperature, Ti or Zr in the brazing alloy reacts with the nitride to increase the bonding strength of the bonding interface. As an example, in Japanese Unexamined Patent Publication (A) Unexamined Patent Application Publication (A) 2014-91673, a brazing agent containing 25 wt% or less of Cu, 8-40 wt% of Sn, 2-6 wt% of at least one type of Ti and Zr, and the remainder being Ag is used. A technique for bonding AlN and copper using a vacuum atmosphere of 650 ~ 780 °C and a vacuum atmosphere of 1.0Х10 ^-3 Pa or less was known. As another method, there is a method of forming a Ti layer on a nitride substrate by sputtering, forming a copper layer thereon by sputtering or electroless plating, and then growing a copper layer to a desired thickness by electroplating. A third method is to form a copper layer directly on a nitride substrate by electroless plating and then to grow a copper layer to a desired thickness by electroplating.

In the case of using the first brazing, an expensive material containing Ag must be used as a brazing bonding agent, and since bonding in a vacuum atmosphere is required, there is a disadvantage in that equipment and process costs are increased. The second method has problems with high equipment cost and low productivity because high vacuum sputtering must be used. In the third method, since AlN is unstable in aqueous solution, the adhesion of the electroless plating layer during electroless plating is low, so peeling during electroplating There is a problem that the process is difficult to control. In Korea Patent Registration No. 10-1642009, AlN water is surface-modified using Ti in an inert/reducing atmosphere instead of in a vacuum, and Cu is electroless-plated there, followed by electrolytic plating sequentially to form Cu and AlN water (thing). ) and a method for producing a Cu-AlN composite having excellent adhesion is disclosed. However, in this method, when the reaction temperature is increased, the Ti powder is sintered after the reaction, and it is difficult to separate the reacted AlN from the Ti powder.

Korean Patent Registration No. 10-1642009

An object of the present invention is to provide a method for manufacturing a circuit board using molten salt in a liquid state for the purpose of modifying the surface of a dielectric substrate and facilitating recovery of the modified substrate, and a circuit board thereby. However, these problems are exemplary, and the scope of the present invention is not limited thereto.

According to one aspect of the present invention, (a) forming a mixture comprising a Ti powder and molten salt; (b) immersing the dielectric substrate in the mixture; and (c) heating the mixture to form a Ti-containing layer on the surface of the dielectric substrate.

According to an embodiment of the present invention, the molten salt may include at least one of chloride and fluoride.

According to an embodiment of the present invention, as the chloride, at least one selected from the group consisting of NaCl, KCl, LiCl and CaCl ₂ , BaCl ₂ is used, and as the fluoride, NaF, KF, MgF ₂ , CaF ₂ and At least one selected from the group consisting of BaF ₂ may be used.

According to an embodiment of the present invention, the dielectric substrate may include a nitride, and the nitride may include any one of AlN, Si ₃ N ₄ and BN.

According to an embodiment of the present invention, (d) removing the residual salt by contacting the reactants in which the reactions (a) to (c) are completed with a solvent capable of dissolving the salt; may further include. Another method is to take out the nitride substrate from the molten salt existing in the molten state when the reaction of step (c) is finished. A small amount of molten salt is attached to the surface of the nitride substrate taken out from a high temperature, and when it is cooled, it remains on the surface in a salt state. It can be removed using the above-mentioned solvent.

According to an embodiment of the present invention, (e) forming an electroless plating layer on the Ti-containing layer; (f) forming an electroplating layer on the electroless plating layer; and (g) forming a metal pattern on the dielectric by patterning the electroless plating layer and the electrolytic plating layer.

According to an embodiment of the present invention, (h) forming an electrolytic plating layer on the Ti-containing layer; and (i) forming a metal pattern on the dielectric by patterning the electrolytic plating layer.

According to an embodiment of the present invention, the electroless plating layer may include Cu, Ni, Co, Au, Pd, or an alloy thereof.

According to an embodiment of the present invention, the electrolytic plating layer may include Cu, Ni, Fe, Co, Cr, Zn, Au, Ag, Pt, Pd, Rh, or an alloy thereof.

According to an embodiment of the present invention, the method may further include a step of performing at least one heat treatment after step (c).

According to an embodiment of the present invention, the method may further include a step in which heat treatment is performed after step (e) before step (f) or step (f) in which heat treatment is performed before step (g).

According to an embodiment of the present invention, the method may further include a step in which heat treatment is performed after step (h) and before step (i).

According to an embodiment of the present invention, the method may further include a step of performing a heat treatment after the step of forming the metal pattern.

According to an embodiment of the present invention, the electrolytic plating layer may include a Fe-Ni alloy layer or a Ni-Cr alloy layer. For example, the Fe-Ni alloy layer may include an INVAR alloy. As another example, the Ni-Cr alloy layer may include a nichrome alloy.

According to an embodiment of the present invention, the electrolytic plating layer may include a soft magnetic thin film made of any one or more of Fe, Ni, and Co.

According to an embodiment of the present invention made as described above, it is easy to separate the dielectric substrate surface-modified with Ti from molten salt or salt, and the bonding force between the plating layer and the dielectric substrate is improved, so that it has excellent durability even when there is a change in temperature. A circuit board can be easily manufactured. Of course, the scope of the present invention is not limited by these effects.

1 is a flowchart illustrating a method of forming a metal pattern on a dielectric substrate according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. In addition, the embodiments of the present invention are provided in order to more completely explain the present invention to those of ordinary skill in the art. Accordingly, the shapes and sizes of elements in the drawings may be exaggerated for clearer description, and elements indicated by the same reference numerals in the drawings are the same elements.

Hereinafter, a method of manufacturing a circuit board according to an aspect of the present invention will be described in detail.

1 is a flowchart of an embodiment of a method of manufacturing a circuit board according to the present invention.

Referring to FIG. 1 , an embodiment of a method of manufacturing a circuit board according to the present invention begins with forming a Ti-containing layer 20 on a surface of a dielectric substrate. The dielectric substrate is preferably nitride. For example, it may include any one of AlN, Si ₃ N ₄ and BN.

The Ti-containing layer 20 may be formed by heating the dielectric substrate by immersing it in a mixture of titanium (Ti) powder and molten salt. The mixture may be formed by adding Ti in powder form into liquid molten salt. The molten salt used in the present invention is a salt exhibiting a molten state in a wide temperature range including room temperature (room temperature), and may be in the form of a liquid in which an ionic substance is melted. In the present invention, Ti ions formed during the reaction of Ti and molten salt introduced move to the surface of the dielectric substrate submerged in the molten salt, and these Ti ions react with the constituents of the substrate to form the Ti-containing layer 20 .

The above-mentioned molten salt may be an ionic molecular group consisting of a chemical bond with a group 1 (alkaline element group) and group 2 (alkaline element group) element of the periodic table, and chlorine or fluorine element, which is a halo group element system. That is, the above-described molten salt may be at least one of chloride and fluoride. More specifically, as the chloride, at least one selected from the group consisting of alkali metal chlorides such as LiCl, NaCl, and KCl and alkaline earth metal chlorides such as CaCl ₂ and BaCl ₂ may be used, and as the fluoride, NaF, KF, MgF ₂ , CaF ₂ and BaF ₂ At least one selected from the group consisting of may be used.

In one embodiment, Ti powder injected into the molten salt composed of chloride reacts with the molten salt to become Ti chloride such as TiCl ₂ , TiCl ₃ or TiCl ₄ , and thus Ti is present as Ti ions in the molten salt. These Ti ions come into contact with the nitride surface to precipitate as Ti, and the precipitated Ti reacts with Al (or Si, B) and nitrogen (N), which are components of AlN (or Si ₃ N ₄ , BN) to form a Ti-containing layer to form

More specifically, when Ti powder is added to a molten salt made of an alkali metal chloride or alkaline earth metal chloride, Ti reacts with the chloride to form a chloride containing Ti, that is, TiCl ₂ , TiCl ₃ , TiCl ₄ etc. can Such Ti chloride exists as an ion in the molten salt. Therefore, Ti ions such as Ti ²⁺ , Ti ³⁺ , Ti ⁴⁺ may exist in the molten salt. Ti ²⁺ or Ti ³⁺ ions migrated to the AlN (or Si ₃ N ₄ , BN) surface are Ti on the AlN (or Si ₃ N ₄ , BN) surface through the following reaction (1) or reaction (2) to precipitate

2 Ti ²⁺ = Ti(s) + Ti ⁴⁺ --------(1)

3 Ti ³⁺ = Ti(s) + 2 Ti ⁴⁺ ------(2)

Thereafter, the precipitated Ti reacts with AlN (or Si ₃ N4, BN) through the following reaction (3) to form Ti-nitride (TiN) and Ti-Al (or Ti-Si, Ti-B) alloy A Ti-containing layer 20 is formed.

2 Ti(s) + AlN= Ti-Al + TiN ------(4)

If a Si ₃ N ₄ nitride substrate is used, compounds such as TiN, Ti ₅ Si ₃ , TiSi, and TiSi ₂ may be generated as reactants.

One of the purposes of forming the Ti-containing layer 20 is to more easily form the electroless plating layer formed on the surface of the dielectric substrate. Therefore, the Ti-containing layer 20 does not need to be thick, and a thickness of several tens of nm to several μm is sufficient. The thickness of the Ti-containing layer 20 can be controlled by adjusting the reaction temperature and time, and the amount of molten salt.

Since the thickness of the Ti-containing layer 20 is usually about several μm, the high-temperature reaction time for forming the Ti-containing layer 20 is preferably about 0.2 to 600 minutes. More preferably, it can be heated for 0.2 minutes to 240 minutes. The thickness of the Ti-containing layer 20 may be increased or decreased by adjusting the reaction temperature or reaction time.

An embodiment of the method for manufacturing a circuit board according to the present invention includes removing the salt remaining after the reaction of forming the Ti-containing layer 20 described above. More specifically, using a solvent (eg, water, alcohol, etc.) capable of dissolving the above-mentioned salt (eg, extraction and removal by immersing the salt in the above-mentioned solvent, or washing with the above-mentioned solvent) ) a process of removing salts may be performed. Another method is to take out the dielectric substrate from the molten salt existing in the molten state at the time the reaction is finished. A small amount of molten salt is attached to the surface of the nitride substrate taken out from a high temperature, and when it is cooled, it remains on the surface in a salt state. It can be removed using the above-mentioned solvent.

Next, the electroless plating layer 30 is formed on the Ti-containing layer 20 , and the electroless plating layer 40 is sequentially formed on the electroless plating layer 30 . In the specification of the present invention, the electroless plating layer 30 and the electrolytic plating layer 40 stacked in order will be collectively referred to as a 'plating layer'. In some cases, the electroless plating layer 30 may be referred to as a first metal layer and the electrolytic plating layer 40 may be referred to as a second metal layer. The plating layer on the dielectric substrate 10 covered with the Ti-containing layer 20 may cover the entire dielectric substrate 10 and may have a desired pattern. The formation of a wiring suitable for a given pattern can be formed by an etching process or a semi-additive process.

According to the technical idea of the present invention, at least one heat treatment may be performed after the Ti-containing layer 20 is formed in order to increase bonding strength by mutual diffusion between the Ti-containing layer 20 and the plating layers 30 and 40 . For example, the heat treatment may be performed during the process of forming the plating layers 30 and 40 or after forming a metal pattern using the plating layers 30 and 40 .

1 (a) and (b) schematically show a method of manufacturing a circuit board by an etching method and a semi-additive method, respectively.

The etching method of FIG. 1 (a) is a method used when the thickness of the plating layer is not thick. After performing electroless plating and electroplating, and attaching the desired circuit pattern 45 film, parts other than the circuit pattern 45 are removed. A metal pattern is obtained by etching away. The heat treatment process to further improve the adhesion between the Ti-containing layer 20 and the plating layer may be introduced after obtaining the metal pattern (case 1), and may be introduced before etching the plating layer, that is, before attaching the circuit pattern 45 film. It can also be (case 2). Also, the first metal layer may be formed by electroless plating, heat treated, and then the second metal layer may be formed by an electrolytic plating process (case 3).

The purpose of introducing the heat treatment process is to increase the bonding force due to mutual diffusion between the plating layers 30 and 40 and the Ti-containing layer 20, so that it can be introduced anywhere in the entire process if suitable.

According to the semi-additive method of FIG. 1( b ), a partial region on the substrate 10 on which the Ti-containing layer 20 and the electroless plating layer 30 are formed on the substrate 10 and the electroless plating layer 30 is formed on the substrate 10 . A circuit pattern 45 is attached to the Next, after the electrolytic plating layer 40 is formed, the circuit pattern 45 previously formed is removed, and the metal pattern can be formed by etching up to the Ti-containing layer 10 formed on the surface of the substrate 10 . In the semi-additive method, a heat treatment process may be introduced at an appropriate time in accordance with the above principle.

In one embodiment, the etching of the plating layer in the step of forming the metal pattern may use a conventional etching solution. In addition, any known etchant capable of etching Ti may be used for etching the Ti-containing layer 20 .

In one embodiment, the heat treatment temperature may be 400 to 1000 ℃. Since the thickness of the Ti-containing layer 20 is usually about several micrometers, the heat treatment time is preferably about 0.1 to 600 minutes. More preferably, it may be 0.1 minutes to 120 minutes. The degree of mutual diffusion can be controlled by adjusting the heat treatment temperature or time. In this case, the heat treatment is preferably performed in a weakly reducing atmosphere in order to prevent oxidation of the metal.

In one embodiment, the electroless plating layer 30 or the first metal layer 30 formed by electroless plating may be any one of Cu, Ni, Co, Au, and Pd or an alloy thereof. Such electroless plating may be performed by a conventionally known method, for example, a conventional method using Pd as a catalyst. Conditions for electroless plating can be appropriately set according to the required plating thickness.

After the first metal layer is formed, an electrolytic plating layer 40 or a second metal layer 40 is formed thereon by electroplating. The second metal layer may include Cu, Ni, Fe, Co, Cr, Zn, Au, Ag, Pt, Pd, Rh, or an alloy thereof. Electrolytic plating of the second metal layer may also be performed using a conventional method.

The second metal layer 40 may be an alloy of various compositions according to the use of the circuit board.

In an embodiment, the first metal layer 30 may be formed of an electroless copper plating layer, and the second metal layer 40 may be formed of an electrolytic copper plating layer. Electroless plating may use a conventional method using Pd as a catalyst. For example, in the case of copper (Cu) electroless plating, a method of reducing the Rochelle copper salt with formalin may be selected, but other conventional methods may be used. Electrolytic plating may also be performed using a conventional method. For example, in the electrolytic plating of copper, an electrolyte using copper sulfate or sulfuric acid may be selected and used, but the present invention is not limited thereto, and other conventional methods may be used.

As another embodiment, when the Fe-Ni alloy layer is formed as the second metal layer 40, the thermal expansion coefficient can be adjusted to a ceramic level by controlling the composition of the alloy layer, and it can be applied as a high-temperature heating material. For example, when forming an Fe-Ni alloy layer having an INVAR alloy composition in which the content of Ni is 36% by weight and the remainder is Fe and unavoidable impurities, it is difficult to manufacture a circuit board having a metal layer having an extremely low coefficient of thermal expansion. It is possible. As another example, the Fe-Ni alloy layer may be used as a high-temperature heating material.

As another embodiment, when the Ni-Cr alloy layer is formed as the second metal layer 40, it may be used as a heat generating material. For example, when an alloy layer of a nichrome composition including 80% Ni and 20% Cr by weight% is formed on the substrate, it can be applied as a planar heater.

As another embodiment, by forming a Fe-Ni alloy layer or a Ni-Cr alloy layer capable of generating heat as the second metal layer 40 locally on a part of the circuit board, it becomes possible to locally heat only the corresponding part. A circuit board capable of such local heating is applicable when composing a sensor circuit operating at a high temperature. For example, by forming a Ni-Cr alloy interconnection in the middle of the Cu interconnection, only the nickel-chromium hot wire portion may generate heat.

As another embodiment, by forming the soft magnetic thin film made of any one or more of Fe, Ni, and Co as the second metal layer 40, it can be used for various purposes as a magnetic element or a magnetic sensor.

As a modified embodiment, the electroplating layer 40 may be directly formed on the Ti-containing layer 20 without the formation of the electroless plating layer 30 . In this case, the step of forming the electroless plating layer 30 may be omitted. The various metals described above may be directly formed by electroplating, and the heat treatment process may be performed in the above-described sequence.

Hereinafter, the present invention will be described in more detail through Examples and Comparative Examples.

<Example>

Formation of Ti-containing layer using a mixture of Ti powder and molten salt

So that the weight ratio of NaCl, KCl, CaCl ₂ becomes 27:8:65, put a total of 450g and 45g of Ti powder (average particle size 20㎛, purity 99%) into an alumina crucible, and raise the temperature while maintaining the argon atmosphere to 850℃ Hold for 1 hour and dissolve to make molten salt. Three AlN plates with a thickness of 1 mm and a width of 50 mm each fixed with a stainless steel wire are immersed here at the same time. The gap between the AlN plates was made to be 3 to 4 mm. After 1 hour has elapsed, the stainless steel wire is raised upwards to take the AlN plate out of the molten salt and place it on the top of the alumina crucible. After cooling in the furnace, the AlN plate was removed by dissolving the salt on the surface with distilled water. A Pd catalyst seed was formed on the AlN plate on which the Ti-containing layer was formed, and the Cu layer was formed by electroless plating at room temperature for 30 minutes. In this case, for the electroless plating, an electroless plating solution using a Rossel salt was used. Using an insulating tape on one side of the electroless plated substrate, a rectangular shape with a width of 10 mm and a length of 20 mm was left in the center of the side, and the rest was insulated, and the other side was insulated. Using the electroless-plated Cu layer as an electrode, Cu was electrolytically plated only in an area of 10×20 mm. The electrolytic plating solution used was a general plating solution using copper sulfate and sulfuric acid. After the plating was completed, the thickness of the Cu layer was 50 μm. After the plating was completed, the insulating tape was removed and the copper electroless plating layer was removed using a FeCl ₃ solution. Thereafter, the Ti-containing reaction layer was removed using the SC-1 etchant to form a Cu pattern with a width of 10 mm and a length of 20 mm on the AlN substrate. After the pattern was completed, it was heat treated at 650° C. for 1 hour in a hydrogen atmosphere to prepare a Cu-AlN circuit board with excellent interfacial adhesion.

A thermal history test was performed on the manufactured Cu-AlN circuit board. The heat history test was carried out by 1 cycle of maintaining at -40°C for 30 minutes, maintaining at room temperature for 10 minutes, maintaining at 125°C for 30 minutes, and maintaining at room temperature for 10 minutes. In the case of this example, it could be observed that even after 50 cycles had elapsed, the adhesion was observed, and it was confirmed that the adhesion did not come off even after a peel test using a scotch tape.

From the above results, it can be seen that, when the dielectric surface is modified using a mixture of Ti powder and molten salt according to an embodiment of the present invention, a metal layer having excellent adhesion can be formed on the dielectric substrate. In the case of using the liquid molten salt, there is an advantage in that separation from the nitride substrate having the Ti-containing reaction layer is very easy. In addition, since the liquid molten salt has superior thermal conductivity and fluidity compared to the solid powder form, the reactivity with the Ti powder is further improved and the uniformity can be secured. It is expected.

The terminology used in the present invention is for describing specific embodiments, and is not intended to limit the present invention. The singular expression should be regarded as including the plural meaning unless the context clearly shows it. Terms such as “comprise” or “have” mean that the features, numbers, steps, operations, components, or combinations thereof described in the specification exist, but are not intended to exclude them. The present invention is not limited by the above-described embodiments and the accompanying drawings, but is intended to be limited by the appended claims. Therefore, various types of substitution, modification and change will be possible by those skilled in the art within the scope not departing from the technical spirit of the present invention described in the claims, and it is also said that it falls within the scope of the present invention. something to do.

10: dielectric substrate
20: Ti-containing layer
30: electroless plating layer
40: electrolytic plating layer
45: circuit pattern

Claims (18)

(a) forming a mixture comprising Ti powder and molten salt;
(b) immersing the dielectric substrate in the mixture; and
(c) heating the mixture to form a Ti-containing layer on the surface of the dielectric substrate;
In the mixture, the weight ratio of the Ti powder and the molten salt is 1:10, the method of manufacturing a circuit board. The method of claim 1,
The molten salt comprises at least one of a chloride and a fluoride, a method of manufacturing a circuit board. 3. The method of claim 2,
As the chloride, at least one selected from the group consisting of NaCl, KCl, LiCl and CaCl ₂ , and BaCl ₂ is used, and as the fluoride, one or more selected from the group consisting of NaF, KF, MgF ₂ , CaF ₂ and BaF ₂ The manufacturing method of the circuit board including the above. The method of claim 1,
wherein the dielectric substrate comprises a nitride. 5. The method of claim 4,
The nitride includes any one of AlN, Si ₃ N ₄ and BN, a method of manufacturing a circuit board. The method of claim 1,
(d) removing the remaining salt by contacting the reactant in which the (a) to (c) reaction is completed, with a solvent capable of dissolving the salt; Further comprising, a method of manufacturing a circuit board. 7. The method of claim 6,
After step (d),
(e) forming an electroless plating layer on the Ti-containing layer;
(f) forming an electroplating layer on the electroless plating layer; and
(g) patterning the electroless plating layer and the electrolytic plating layer to form a metal pattern on the dielectric; further comprising a method of manufacturing a circuit board. 7. The method of claim 6,
After step (d),
(h) forming an electrolytic plating layer on the Ti-containing layer; and
(i) patterning the electrolytic plating layer to form a metal pattern on the dielectric; further comprising a method of manufacturing a circuit board. 8. The method of claim 7,
The electroless plating layer comprises Cu, Ni, Co, Au, Pd or an alloy thereof, a method of manufacturing a circuit board. 8. The method of claim 7,
The electroplating layer is, Cu, Ni, Fe, Co, Cr, Zn, Au, Ag, Pt, Pd, Rh or an alloy thereof, the method of manufacturing a circuit board comprising an alloy. The method of claim 1,
The method of manufacturing a circuit board, further comprising the step of performing at least one heat treatment after step (c). 8. The method of claim 7,
After the step (e), the step of performing a heat treatment before the step (f) or after the step (f) further comprising the step of performing a heat treatment before the step (g), the manufacturing method of the circuit board. 9. The method of claim 8,
After the (h) step, the method of manufacturing a circuit board further comprising the step of performing a heat treatment before step (i). 9. The method according to claim 7 or 8,
Further comprising the step of performing a heat treatment after the step of forming the metal pattern, the manufacturing method of the circuit board. 9. The method according to claim 7 or 8,
The electrolytic plating layer is a Fe-Ni alloy layer or a Ni-Cr alloy layer comprising a, a method of manufacturing a circuit board. 16. The method of claim 15,
The Fe-Ni alloy layer comprises an INVAR alloy, a method of manufacturing a circuit board. 16. The method of claim 15,
The Ni-Cr alloy layer comprises a nichrome alloy, a method of manufacturing a circuit board. 9. The method according to claim 7 or 8,
The electroplating layer comprises a soft magnetic thin film made of any one or more of Fe, Ni, and Co, a method of manufacturing a circuit board.

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