JP2008294432A - Printed wiring board, method of manufacturing the same, and electrolytic copper foil for copper clad laminate used for manufacturing printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed wiring board easy for micro-miniaturization of wiring, in particular, a flexible printed wiring board easy for micro-miniaturization of wiring and excellent in durability against bending. <P>SOLUTION: The printed wiring board has wiring lines formed on the surface of an insulating substrate and having a layered structure in which a first copper layer and a second copper layer are laminated, wherein the first copper layer side is affixed to the insulating substrate, and the average crystal grain size of the second copper layer is larger than that of the first copper layer. The printed wiring board can be manufactured by steps of preparing a metal clad laminate which is provided with a conductive layer of a layered construction capable of forming wiring lines having the structure on the surface of the insulating substrate, forming a resist pattern for etching on the surface of the second copper layer of the conductive layer, forming wiring lines by an etching process, and subsequently removing the resist pattern for etching to form the printed wiring board. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a printed wiring board, a method for manufacturing the printed wiring board, and an electrolytic copper foil for a copper-clad laminate used for manufacturing the printed wiring board.

With the spread of mobile devices such as mobile phones, personal computers, music players and portable game machines in recent years, the trend of making electronic devices lighter, thinner and smaller continues. Many of these mobile devices are equipped with a video display function, and various display devices are used. However, liquid crystal display panels are mainly used. As a method for mounting electronic components such as driver ICs and LSIs of this liquid crystal display panel, COF (Chip On Film) tape, TCP (Tape Carrier Package) tape, BGA (Ball Grid Array) tape, ASIC (Application Specific Integrated Circuit) Mounting methods using film carrier tape for mounting electronic components such as tape (hereinafter simply referred to as “film carrier tape” or “TAB (Tape Automated Bonding) tape”) and FPC (Flexible Printed Circuit) are used. . Therefore, further fine wiring is required for these printed wiring boards.

  In manufacturing the above-described COF tape or the like, wiring is formed by etching using copper as a main conductor. In order to make the wiring formed here finer and facilitate subsequent surface mounting, it is required to increase the etching factor of the wiring. Therefore, it is necessary to shorten the setting of the over-etching time, and it has been attempted to adopt a thin copper layer with a smooth adhesion surface between the copper layer forming the wiring and the insulating substrate. That is, in the electrolytic copper foil, various organic additives have been used in the manufacturing process, the copper crystal grain size has been reduced, and the low profile of the adhesive surface with the insulating substrate has been achieved. However, even if the bonding surface with the insulating substrate is flat, the top width of the formed wiring becomes narrower than the bottom width due to the undercut phenomenon that occurs during the etching process. Therefore, if the wiring pitch of the COF tape or the like is further reduced, the top width necessary for device connection cannot be secured. That is, unless wiring having a better etching factor than before is formed, it becomes impossible to cope with the miniaturization of wiring.

  On the other hand, a flexible printed wiring board such as a TAB tape such as a COF tape or a TCP tape or an FPC may be mounted on an electronic device or the like in a bent state or may be repeatedly bent. Also, if these wiring boards are subjected to vibration during transportation or vibration due to the operation of electronic equipment, if the wiring is composed of conductors with poor flex resistance, disconnection will occur at the bent part of the wiring, etc. Tend to.

  Also, looking at the history of liquid crystal driving drivers represented by TAB tape, flex resistance has been required from the beginning. However, as described above, priority has been given to the miniaturization of the wiring, and the crystal grain size of the electrolytic copper foil has been miniaturized to lower the profile of the bonding surface with the insulating substrate. Thus, when the crystal grain size of copper decreases, the tensile strength increases but the elongation rate tends to decrease. That is, a copper foil that has been affected by additives that are considered to be unevenly distributed in the crystal grain boundary and hardly obtains an annealing effect even when heated has been used. As described above, the ability to form a fine circuit has been prioritized even at the sacrifice of bending resistance. However, for example, in order to reduce the area of the frame in the liquid crystal panel, the output side wiring portion of the TAB tape is folded at the end portion of the liquid crystal panel and connected to the wiring of the liquid crystal panel. It can be considered that there is an increasing tendency to be more demanded than before.

  As a technique for improving the etching factor, Patent Document 1 provides a copper-clad board for a printed wiring board capable of suitably forming a fine-pitch wiring pattern and a printed wiring board using the same. A copper-clad board for a printed wiring board having a structure in which the grain size of the copper foil crystal grains is successively reduced in the thickness direction from the copper-clad board surface toward the insulating base material side, and the printed wiring having such a structure A technique for applying a subtractive construction method to a copper clad sheet for board is disclosed.

  In addition, Patent Document 2 discloses a copper foil that enables high-etching photoetching and a method for producing the same, an etching method, a copper foil pattern, and a storage method, from a low current density to a high current density. By continuously controlling the plating current density, a copper foil having a different structure from a copper foil having a saddle etching structure to a copper foil having a difficult etching structure is formed continuously or stepwise to form a difficult etching structure. In order to form a structure gradient copper foil pattern by etching from the copper foil side having a copper foil pattern in which the pattern is subjected to heat treatment at 170 ° C. for 30 minutes or more to relax the structure inclination state is disclosed. .

Certainly, if the techniques disclosed in Patent Document 1 and Patent Document 2 are used, it is possible to form a wiring exhibiting a good etching factor as long as a conductor layer having the same thickness is used.
JP 2003-324258 A JP 2004-190073 A

However, even if the technical content disclosed in the above-mentioned patent document is applied to wiring such as a liquid crystal driver wiring board of a mobile device, the risk of disconnection of the wiring as described above is not reduced.
Therefore, in the wiring of rigid printed wiring boards and flexible printed wiring boards (hereinafter, all of these are collectively referred to as “printed wiring boards”), miniaturization while maintaining a good etching factor is possible. A possible technology has been demanded. For COF tapes, TCP tapes, and FPCs, products with improved flex resistance as well as finer wiring have been required.

  Therefore, the present inventors have conceived the following invention for the purpose of achieving both the miniaturization of the wiring in the printed wiring board and the bending resistance in the case of the flexible printed wiring board.

Printed wiring board according to the present invention:
The printed wiring board according to the present invention is a printed wiring board in which wiring is formed on the surface of an insulating substrate, and the wiring has a layer configuration in which a first copper layer and a second copper layer are laminated, The copper layer side is bonded to the insulating substrate, and the average crystal grain size of the second copper layer has an average crystal grain size larger than the average crystal grain size of the first copper layer.

  In the printed wiring board according to the present invention, the first copper layer has an average crystal grain size of 0.1 μm or more and less than 1.0 μm, and the second copper layer has an average crystal grain size of 1.0 μm to 5.0 μm. Is preferred.

In the printed wiring board according to the present invention, the thickness of the second copper layer is preferably 5% to 500% of the thickness of the first copper layer.
In the printed wiring board according to the present invention, the second copper layer is composed of n-layer (where n ≧ 1) sub-metal layers, and the n-th sub-metal is the (n−1) -th sub-metal layer. It is also preferable to have an average crystal grain size larger than the average crystal grain size.

In the printed wiring board according to the present invention, in the cross-sectional shape of the wiring at an arbitrary position, the thickness of the wiring is T _c , the top width of the wiring upper surface is W _t , and the bottom width of the wiring lower surface is W _{When b} is set, the etching factor obtained by the following formula (1) is 2.5.
It is characterized by the above.

In the printed wiring board which concerns on this invention, it becomes a printed wiring board which is flexible and can be bent by using the base material for flexible printed wiring boards for an insulated substrate.
In the printed wiring board according to the present invention, a rigid printed wiring board base material is used for the insulating substrate, whereby a plate-like rigid printed wiring board is obtained.

A method for producing a printed wiring board according to the present invention:
The method for manufacturing a printed wiring board according to the present invention includes the following steps A to D. For convenience of explanation, this is referred to as a first manufacturing method.

  Step A: A conductive layer having a layer structure in which a first copper layer and a second copper layer are laminated on the surface of an insulating substrate, and the average crystal grain size of the second copper layer is the average crystal grain of the first copper layer. A step of preparing a metal-clad laminate having an average crystal grain size larger than the diameter and having the first copper layer side bonded to the insulating substrate.

Step B: A step of forming an etching resist pattern on the surface of the second copper layer of the conductor layer.
Step C: A step of etching the metal-clad laminate having the etching resist pattern to dissolve and remove a portion of the conductor layer where the etching resist pattern is not formed to form a wiring.

Step D: A step of removing the etching resist pattern present on the surface of the wiring to obtain a printed wiring board.
In the first manufacturing method, the metal-clad laminate used in the step A has a layer configuration in which a first copper layer and a second copper layer are laminated, and the average crystal grain size of the second copper layer is the first It is preferable to use a copper clad laminate in which an electrolytic copper foil having an average crystal grain size larger than the average crystal grain size of the copper layer is used and the first copper layer side is bonded to an insulating substrate.

  In the first manufacturing method, the metal-clad laminate used in the step A includes a first copper layer and a second copper layer that is recrystallized by heating at 170 ° C. to 180 ° C. for 15 minutes or more. Is a laminated copper foil with a layer structure, and when the metal-clad laminate is molded, a temperature of 170 ° C. to 180 ° C. is applied to the first copper layer side for 15 minutes or more to bond the insulating substrate and the electrolytic copper foil together. Thus, it is also preferable to use a copper-clad laminate in which the average crystal grain size of the second copper layer is larger than the average crystal grain size of the first copper layer.

  Further, in the first manufacturing method, in the metal-clad laminate used in the step A, a first copper layer is formed on an insulating substrate by an electroless plating method, and 170 ° C. is formed on the first copper layer. By forming a second copper layer to be recrystallized by heating at ˜180 ° C. for 15 minutes or more to form a conductor layer, and then heating by applying a temperature of 170 ° C. to 180 ° C. for 15 minutes or more, It is also preferable to use a copper-clad laminate in which the average crystal grain size of the second copper layer is larger than the average crystal grain size of the first copper layer.

And in the said 1st manufacturing method, the formation of the said 2nd copper layer employ | adopts the electrolytic copper plating method using a sulfuric acid acidic copper plating solution, The copper concentration is 0.8 mol in the said sulfuric acid copper plating solution. / Liter to 1.2 mol / liter, free sulfuric acid concentration of 0.8 mol / liter to 1.2 mol / liter, chlorine concentration of 5 ppm to 50 ppm, and more than 1/2 volume of the sulfuric acid copper plating solution It is preferable to use one that has been subjected to activated carbon treatment.

  Moreover, it is preferable to employ | adopt the manufacturing method of the printed wiring board characterized by including the following process a-process f as another manufacturing method which concerns on this invention. For convenience of explanation, this is referred to as a second manufacturing method.

Step a: Step of manufacturing a temporary copper clad laminate having only the first copper layer on the surface of the insulating substrate.
Step b: forming a plating resist pattern on the surface of the first copper layer of the temporary copper clad laminate.

Step c: A step of forming a wiring-shaped second copper layer by performing copper plating on the surface of the first copper layer on which the plating resist pattern of the temporary copper-clad laminate is not formed.
Step d: A step of removing the plating resist pattern to obtain a temporary printed wiring board.

Step e: A step of heat treating the temporary printed wiring board obtained in step d to make the crystals of the second copper layer macrocrystalline.
Step f: Thereafter, the temporary printed wiring board in which the crystal of the second copper layer is macrocrystallized is etched to dissolve and remove the exposed first copper layer where the second copper layer is not formed. The process which makes a wiring board.

In this second production method, an electrolytic copper plating method using a sulfuric acid copper plating solution is employed for forming the second copper layer, and the sulfuric acid copper plating solution has a copper concentration of 0.8 mol / 1 to 1.2 mol / liter, free sulfuric acid concentration of 0.8 mol / liter to 1.2 mol / liter, chlorine concentration of 5 ppm to 50 ppm, and more than 1/2 volume of the sulfuric acid acidic copper plating solution It is preferable to use one that has been subjected to activated carbon treatment.

In the second manufacturing method, the heat treatment in the step e is preferably performed at a temperature of 170 ° C. to 180 ° C. for 15 minutes or more.
Electrolytic copper foil according to the present invention:
The electrolytic copper foil according to the present invention is an electrolytic copper foil used for the production of the metal-clad laminate, comprising a layer structure in which a first copper layer and a second copper layer are laminated, and after heating at 175 ° C. for 15 minutes. The first copper layer has an average crystal grain size of 0.1 μm or more and less than 1.0 μm, and the second copper layer has an average crystal grain size of 1.0 μm or more and 5.0 μm or less.

  The printed wiring board obtained by the present invention is provided with wiring having a good etching factor. In addition, when a flexible printed wiring board is used, wiring with a good etching factor is provided and at the same time good bending resistance is exhibited. Therefore, even if the wiring of a liquid crystal driver wiring board or the like for a mobile device is miniaturized, there is little risk of disconnection. Moreover, the method for producing a printed wiring board according to the present invention is optimal as a method for efficiently obtaining the printed wiring board.

The printed wiring board and the method for producing the printed wiring board according to the present invention will be described below. The manufacturing method will be described separately for the first manufacturing method and the second manufacturing method.
<Configuration of Printed Wiring Board According to the Present Invention>
The printed wiring board according to the present invention is a printed wiring board in which wiring is formed on the surface of an insulating substrate, and the wiring has a layer configuration in which a first copper layer and a second copper layer are laminated, The copper layer side is bonded to the insulating substrate, and the average crystal grain size of the second copper layer is larger than the average crystal grain size of the first copper layer. A printed wiring board provided with wiring having such a layer configuration can be easily miniaturized by using a manufacturing method described later, and can obtain good bending resistance when a flexible printed wiring board is used. It is.

  Since the average crystal grain size of the second copper layer on the outer layer side of the wiring has an average crystal grain size larger than the average crystal grain size of the first copper layer, the bending resistance performance when a flexible printed wiring board is obtained Improve dramatically. Here, a bending resistance test is performed on the flexible printed wiring board, and a process from repeated bending stress to circuit disconnection is considered. When bending stress is repeatedly applied, the amount of displacement associated with bending (the amount of displacement associated with elongation or contraction) is larger when going to the outer surface of the flexible printed wiring board and smaller when going to the center. Become. Therefore, it is normal that the bending operation of the flexible printed wiring board causes micro cracks on the outer surface of the wiring, and crack propagation occurs along the crystal grain boundary during repeated bending, leading to wiring breakage. is there. Therefore, in the printed wiring board according to the present invention, it was considered to increase the average crystal grain size of the second copper layer so as to form a layer having few crystal grain boundaries serving as crack propagation routes and to have a large elongation rate. .

  Accordingly, considering only the bending resistance, it is possible to further improve the bending performance by setting the average crystal grain size of the first copper layer to the same level as the average crystal grain size of the second copper layer. However, increasing the crystal grain size of the metal layer is contrary to the purpose of forming a low profile plane. Therefore, only the first crystal grain size of the first copper layer constituting the wiring of the printed wiring board according to the present invention is made smaller than the second crystal grain size, so that the insulating resin group of the conductive layer is formed. The low profile of the bonding surface with the material was made possible to form a wiring with an excellent etching factor. That is, it can be said that it is a printed wiring board capable of simultaneously obtaining good bending resistance and good etching characteristics.

  In the printed wiring board according to the present invention, the first copper layer has an average crystal grain size of 0.1 μm or more and less than 1.0 μm, and the second copper layer has an average crystal grain size of 1.0 μm to 5.0 μm. The average crystal grain size referred to here is obtained by sampling and observing a 200 μm long section with respect to the wiring thickness using an SEM (Scanning Electron Microscope), an FIB (Focused Ion Beam) apparatus, or a metal microscope. It is the value which measured and averaged the major axis and minor axis of the crystal which exist in each copper layer of the range. Here, when the average crystal grain size is less than 0.1 μm, it is impossible to accurately measure the crystal grain size using any of the above-described crystal grain size observation methods. Therefore, in the first copper layer, the average crystal grain size is not excluded in the strict sense of less than 0.1 μm. On the other hand, when the average crystal grain size of the first copper layer is 1.0 μm or more, the crystal size distribution becomes wide and it becomes difficult to obtain a stable etching rate. A typical example of a crystal constituting the first copper layer is shown in FIG.

  And it is preferable that the average crystal grain diameter of a 2nd copper layer is 1.0 micrometer-5.0 micrometers. The average crystal grain size in the second copper layer is also a value obtained by measuring and averaging the major axis and minor axis of the crystals present in the second copper layer. When the average crystal grain size is less than 1.0 μm, the bending resistance performance when a flexible printed wiring board is formed cannot be improved. On the other hand, when the average crystal grain size exceeds 5.0 μm, the etching processing speed becomes slow, and it becomes difficult to obtain a wiring having a good etching factor. A representative example of a crystal constituting the second copper layer is shown in FIG.

The metal constituting each of the first copper layer and the second copper layer can have different levels of average crystal grain size by changing the content level of impurities and the like. . Furthermore, the difference in crystal grain size can be clarified by heating. This is because even if the crystal grain size immediately after production is almost the same, it is possible to create different crystal structures with different recrystallization behaviors by heating. This will be described in detail in the manufacturing method described later.

  In the printed wiring board according to the present invention, the thickness of the second copper layer is 5% to 500% of the thickness of the first copper layer. In determining the thickness relationship, the average crystal grain size of the first copper layer and the second copper layer affects. That is, when the average crystal grain size of the second copper layer is 5.0 μm at the maximum, and when the combination of 0.1 μm with the minimum average crystal grain size of the first copper layer is considered, Consider the etching rate. As a result, when the thickness of the second copper layer exceeds 500% of the thickness of the first copper layer, when etching is performed from the state of the metal-clad laminate, the erosion rate on the first copper layer side that is easily etched is increased. This is not preferable because it becomes faster, the etching state of the first copper layer and the second copper layer become significantly different, and the etching factor seen in the circuit cross section becomes worse. On the other hand, when the thickness of the second copper layer is less than 5% of the thickness of the first copper layer, the bending resistance cannot be improved.

  In the printed wiring board according to the present invention, the second copper layer is composed of n sublayers (where n ≧ 1), and the nth submetal layer is the (n−1) th submetal layer. The average crystal grain size is larger than the average crystal grain size. As described above, when the difference in the average crystal grain size between the first copper layer and the second copper layer is large and the ratio of the thickness is large, the etching of the first copper layer becomes large, and there is a step in the observation of the wiring cross section. May be observed. In such a case, it is effective to make the average crystal grain size of the second copper layer close to the first copper layer close to the average crystal grain size of the first copper layer in order to reduce the step. Therefore, the number of layers may be set as necessary.

In the printed wiring board according to the present invention, in the cross-sectional shape of the wiring at an arbitrary position, the thickness of the wiring is T _c , the top width of the wiring upper surface is W _t , and the bottom width of the wiring lower surface is W _{When b} is set, the etching factor obtained by the following formula (1) is 2.5.
That's it. FIG. 3 schematically shows the cross-sectional shape of the wiring.

This etching factor indicates how the shape of the wiring cross section is rectangular and the difference between the top width of the upper surface of the wiring and the bottom width of the lower surface of the wiring is small. The top width (W _t ) of the upper surface of the wiring =
The bottom width (W _b ) on the lower surface of the wiring is ideal, and at this time, the value of the etching factor approaches infinity (∞). Therefore, strictly speaking, in the case of a manufacturing method in which the first copper layer and the second copper layer are simultaneously etched (corresponding to the case where the following first manufacturing method is adopted), the etching factor is 2.5 or more, More preferably, it is 3.0 or more. On the other hand, when the second copper layer is formed by pattern plating (corresponding to the case where the following second manufacturing method is adopted), the etching factor may be 3.0 or more, more preferably 4.0 or more. It becomes possible. A larger etching factor is preferable because the top width of the upper surface of the wiring is wider and a mounting area can be increased when the electronic component is surface-mounted.

It is also important to pay attention to the linearity of the wiring. In particular, in a wiring that transmits a high-frequency signal, good linearity is required for both the top line and the bottom line. Considering the skin effect when a high-frequency current flows through the wiring, a shape having no irregularities is preferable from the viewpoint of reducing noise signals and causing no abnormal operation. In addition, in terms of bending resistance, when tensile stress is applied, if the wiring width becomes wider or narrower, the stress concentrates on the narrowest part of the wiring width, causing microcracks in the wiring. There is a high possibility that this will be the starting point. Considering the above, the variation required for the formed wiring width is about 10%. For example, the conductor thickness used for manufacturing the COF tape or the like is about 5 μm to 20 μm. The wiring pitch (line width + space width) is a fine pattern of 40 μm or less. At this time, when the variation in the wiring width exceeds 10%, the etching factor tends to be less than 2.5. Therefore, it is important that the etching factor is 2.5 or more in order to obtain a flexible printed wiring board that is easy to surface-mount electronic components and has excellent bending resistance.

An insulating substrate that can be used in the printed wiring board according to the present invention will be described. The wiring provided in the printed wiring board according to the present invention can be applied to either a flexible printed wiring board or a rigid printed wiring board. In the case of a flexible printed wiring board, a flexible resin film such as a polyimide resin film, a polyimide amide resin film, a PET resin film, or a liquid crystal polymer resin can be widely used for the insulating substrate. In the case of a rigid printed wiring board, it is cured into a plate shape after heating, and is a known rigid insulating substrate such as a glass-epoxy resin prepreg, a glass-polyimide resin prepreg, or a BT resin prepreg containing a skeleton material. The use of charge is possible.
<Manufacturing Form 1 of Printed Wiring Board According to the Present Invention>
Here, the form of the first manufacturing method will be described. The 1st manufacturing method of the printed wiring board concerning the present invention includes the following process A-process D, It is characterized by the above-mentioned. Hereinafter, it demonstrates for every process.
Process A:
In this step, a conductive layer having a layer structure in which a first copper layer and a second copper layer are laminated is provided on the surface of the insulating substrate, and the average crystal grain size of the second copper layer is the average crystal of the first copper layer. A metal-clad laminate having an average crystal grain size larger than the grain size and having the first copper layer side bonded to the insulating substrate is prepared. Several methods can be adopted as a method for producing the metal-clad laminate.

The manufacturing method of the first metal-clad laminate is a method using electrolytic copper foil.
The electrolytic copper foil at this time has a layer structure in which a first copper layer and a second copper layer are laminated, and the average crystal grain size of the second copper layer is larger than the average crystal grain size of the first copper layer. It has a particle size. The electrolytic copper foil as used herein means that the average crystal grain size of the first copper layer and the average crystal grain size of the second copper layer are clearly different at the stage of the electrolytic copper foil. Therefore, the electrolytic copper foil manufactured through the two-stage electrolysis process by separating the formation conditions of the first copper layer and the second copper layer, the copper electrolyte, and the like corresponds. However, the electrolytic copper foil referred to here does not refer to a copper foil manufactured entirely by an electrolytic method. For example, it includes the case where an electrolytic copper foil is once manufactured, and one of the first copper layer and the second copper layer is manufactured on one side of the surface by an electroless plating method or a physical vapor deposition method. It is. A metal-clad laminate is prepared by bonding the first copper layer side of the electrolytic copper foil described above having a small average crystal grain size to the insulating substrate via hot press molding or an adhesive layer.

  The method for producing the second metal-clad laminate uses an electrolytic copper foil having a layer structure in which a first copper layer and a second copper layer are laminated, and the second copper layer is 170 ° C. to 180 ° C. And those which are recrystallized by heating for 15 minutes or longer.

  That is, at the stage of the electrolytic copper foil, the difference between the average crystal grain size of the first copper layer and the average crystal grain size of the second copper layer cannot be classified. However, the first copper layer side of this electrolytic copper foil is loaded with a temperature of 170 ° C. to 180 ° C. for 15 minutes or more on the first copper layer side during molding of the metal-clad laminate, and the insulating substrate, the electrolytic copper foil, Are bonded together, the average crystal grain size of the second copper layer becomes larger than the average crystal grain size of the first copper layer. That is, the copper crystal structure of the second copper layer is recrystallized by heating at the time of lamination, and becomes larger than the average crystal grain size of the first copper layer.

In order to obtain the copper crystal structure of the second copper layer, an electrolytic copper plating method using a sulfuric acid copper plating solution is employed, and the copper acid concentration of the sulfuric acid copper plating solution is 0.8 mol / Liter to 1
. 2 mol / liter, free sulfuric acid concentration of 0.8 mol / liter to 1.2 mol / liter, chlorine concentration of 5 ppm to 50 ppm is used, and a sulfuric acid-treated copper plating solution with a volume of 1/2 volume or more is activated carbon. be able to. What is characteristic here is that a part of the copper sulfate plating solution treated with activated carbon is used. In other words, compared to the normal copper electrolyte used for the production of electrolytic copper foil industrially, by using a cleaned copper plating solution, the electrolytic copper recrystallized when heated at 170 ° C. to 180 ° C. for 15 minutes or more. A foil is obtained. What activated 1/2 volume or more of the said sulfuric acid acidic copper plating solution means that when preparing 100 liters of copper plating solution, 50 liters or more are used after activated carbon filtration. When the activated carbon treatment amount of the sulfuric acid copper plating solution is less than ½ volume, recrystallization does not occur even if heated for about 15 minutes at 170 ° C. to 180 ° C., or crystals are generated even if recrystallization occurs. The variation in particle size is large, which is not preferable. Furthermore, regarding the electrolysis conditions, the dimension stable anode (Dimension Stable)
Anode: DSA) and the liquid temperature is preferably 40 ° C. to 60 ° C., and electrolysis is preferably performed at a current density of 5 A / dm ^{2 to} 70 A / dm ² . The same applies to the sulfuric acid copper plating solution and the electrolysis conditions when forming the second copper layer that causes recrystallization.

  Here, the heat treatment is preferably performed at 170 ° C. to 180 ° C. for 15 minutes or longer. As described above, when the copper layer having good low-temperature annealing property is heated at 170 ° C. for 10 minutes, the mechanical properties change greatly. That is, the crystal grain size begins to change by heating at 170 ° C. for 10 minutes. And if it heats for 15 minutes or more at the temperature of 170 degreeC or more, the average crystal grain diameter of a 2nd copper layer will become larger than the average crystal grain diameter of a 1st copper layer. However, if the heating temperature is too high or if the heating time is too long, the crystal structure of the first copper layer tends to recrystallize and become macrocrystalline, so the heating temperature is set to 170 ° C. to 180 ° C., and the heating time Is more preferably 15 minutes to 30 minutes. Within this range, an epoxy resin can be used as the insulating substrate, and a urethane adhesive can be used as the adhesive with the insulating layer. The same applies to the heating conditions.

The third method for producing a metal-clad laminate is a method that does not use electrolytic copper foil.
That is, first, a first copper layer is formed on an insulating substrate by an electroless plating method. Since the electroless plating method is used, the first copper layer can be formed directly on the surface of the insulating substrate. For the electroless plating at this time, copper electroless plating is applied, and any known electroless plating method may be used. Then, on the first copper layer, the above-mentioned method is adopted, and a second copper layer to be recrystallized is formed by heating at 170 ° C. to 180 ° C. for 15 minutes or more to form a conductor layer. .

Then, as described above, the average crystal grain size of the second copper layer is larger than the average crystal grain size of the first copper layer by applying a temperature of 170 ° C. to 180 ° C. for 15 minutes or more and heating. This is used as a copper clad laminate so as to have a particle size.
Process B:
In this step, an etching resist pattern is formed on the surface of the second copper layer of the conductor layer. Any known resist such as ink, dry film, or liquid resist may be used as the etching resist for forming the etching resist pattern. However, in order to obtain a good resolution in consideration of the above-described miniaturization and linearity of the wiring, it is preferable to select a liquid resist. In the case of using a liquid resist, the surface of the second copper layer is pickled and washed with water to clean and dry the surface, and after applying the liquid resist to the surface, the surface is dried to form a resist film. Then, the etching resist pattern is exposed on the resist film, and developed to remove unnecessary portions, thereby obtaining a metal-clad laminate having the etching resist pattern on the surface.
Process C:
In this step, the metal-clad laminate having the etching resist pattern is etched to dissolve and remove all the conductor layers where the etching resist pattern is not formed to form wiring. In this etching process, the etching process and etching conditions used in the conventional printed wiring board manufacturing can be used as they are.

That is, an acid-based etching solution or an alkaline etching solution using cupric chloride or ferric chloride can be used. In particular, in order to carry out a stable etching process, it is preferable to use an acid-based etching solution that allows easy liquid quality management. The overetching time set in the etching process is preferably set to 0% to 50% of the time required for etching the entire copper layer using the data obtained from the strobe etching or the like as a reference. However, the overetching time is more preferably set to 0% to 10% in order to minimize the occurrence of undercut phenomenon on the first copper layer.
Process D:
In this step, a printed wiring board is obtained by removing the etching resist pattern present on the surface of the wiring. A specific method for removing the etching resist pattern has been widely known, and a method corresponding to the type of the etching resist may be selected and used. For example, when the above-described liquid resist is used, the etching resist pattern is swelled and peeled using an alkaline solution such as a caustic soda solution.
<Manufacturing Form 2 of Printed Wiring Board According to the Present Invention>
The second manufacturing method according to the present invention includes the following steps a to f. Hereinafter, in order to avoid duplicating description about the part which overlaps with description of a 1st manufacturing method, the description is abbreviate | omitted as much as possible.

Step a:
In this step, a temporary copper clad laminate having only the first copper layer on the surface of the insulating substrate is manufactured. The first copper layer has a small average crystal grain size, and a method of bonding the electrolytic copper foil to the insulating substrate can be employed. Alternatively, it can be directly formed on the insulating substrate using electroless plating, physical vapor deposition, or the like. It is only necessary to have a crystal structure in which the crystal grain size does not change greatly in the step e described later. However, in order to obtain a certain level of adhesive strength between the first copper layer and the insulating substrate, a copper-clad laminate manufactured using an electrolytic copper foil and in the case of a hot press method or a flexible printed wiring board by a casting method. It is preferable to use a plate. And when obtaining a thin 1st copper layer, it is also preferable to use electrolytic copper foil with a carrier.

Step b:
In this step, a plating resist pattern is formed on the surface of the first copper layer of the temporary copper clad laminate. As the plating resist pattern here, a known one such as an ink, a dry film, or a liquid resist can be used similarly to the etching resist. When a thin plated copper layer is formed, a fine wiring pattern can be easily obtained by using a liquid resist. However, the thickness of the plated copper layer is often set in consideration of etching processing in a later process. As described above, when a certain thickness is required as the plating resist pattern, it is preferable to use a dry film in consideration of resolution and the like. When using a dry film, the surface of the first copper layer is dried by pickling the surface by pickling or the like, and a dry film is attached using a laminator. A plating resist pattern is exposed on this dry film, developed to remove unnecessary portions, and a copper-clad laminate provided with a plating resist pattern is obtained.

Step c:
In this step, copper plating is performed on the surface of the first copper layer on which the plating resist pattern of the temporary copper-clad laminate is not formed to form a second copper layer along the wiring shape. That is, the second copper layer is formed using a pattern plating method. By using the pattern plating method, the cross-sectional shape of the wiring formed as the second copper layer can be formed close to an ideal shape. Therefore, as a result, it becomes easy to obtain a wiring shape having an excellent etching factor. The formation of the second copper layer at this time may be any method as long as it can form a copper layer with good low-temperature annealing property that is recrystallized when heated at a temperature of 170 ° C. to 180 ° C. for 15 minutes or more. Of course, an electrolytic copper plating method, an electroless copper plating method, a physical vapor deposition method, or the like can be used. However, in view of mass productivity and cost, it is preferable to perform copper plating under the same conditions using the above-mentioned sulfuric acid copper plating solution.

Step d:
In this step, the plating resist pattern is removed to obtain a temporary printed wiring board. Since the same concept as the removal of the etching resist pattern can be applied to the removal of the plating resist pattern, the description thereof is omitted to avoid redundant description.

Step e:
In this step, the temporary printed wiring board obtained in step d is heat-treated to crystallize the crystals of the second copper layer. Since the heating conditions at this time are as described above, description thereof is omitted here.

Step f:
In this step, after that, the temporary printed wiring board in which the crystal of the second copper layer is macrocrystallized is etched to dissolve and remove the exposed first copper layer where the second copper layer is not formed. A printed wiring board. In this process, it is possible to form and etch a metal resist layer that is thinly plated with tin or the like on the surface of the second copper layer formed along the circuit shape. It is preferable to employ an etching method.

When the flash etching method is applied, the above-described copper etching method may be used. This is because the plated second copper layer functions as an etching resist for the first copper layer.
That is, the second copper layer having a large average crystal grain size is etched slowly, and the first copper layer having a small average crystal grain size is etched quickly, whereby a wiring pattern having a good etching factor is obtained. The overetching time set by the etching process is 0% of the time required for etching the first copper layer using the data obtained by performing the strobe etching or the like on the first copper layer as a reference. It is preferable to set it to -50%. However, in order to minimize the wear of the plated copper layer and the undercut phenomenon with respect to the first copper layer, the overetching time is more preferably set to 0% to 10%.

In any of the manufacturing forms, after the wiring is formed, the wiring is plated with metal such as Sn, Sn-Bi, or Au, or alloy plating containing these metals. Next, an insulating protective layer is formed on the wiring using a solder resist or a coverlay except for the terminal portion of the wiring, and a printed wiring board is obtained. In addition, you may perform the plating to the said terminal part after formation of an insulating protective layer.
<Form of electrolytic copper foil according to the present invention>
The electrolytic copper foil according to the present invention is an electrolytic copper foil used for producing the metal-clad laminate, and the average crystal grain size of the first copper layer after heating at 175 ° C. for 15 minutes is 0.1 μm or more and 1.0 μm. The average crystal grain size of the second copper layer is 1.0 μm or more and 5.0 μm or less.

The electrolytic copper foil having the above-described configuration can be manufactured by using two types of bath compositions having different bath compositions as the electrolytic solution used for manufacturing the electrolytic copper foil, and employing a two-stage electrolytic process. For example, the first copper layer has a copper concentration of 0.8 mol / liter to 1.2 mol / liter and a free sulfuric acid concentration of 0.8 mol / liter.
1 to 1.2 mol / liter, a copper electrolyte solution having a chloride ion concentration of 3 to 10 ppm and a gelatin additive concentration of 0.3 to 5 ppm, a liquid temperature of 40 to 60 ° C., and 5 to 50 A / it can be formed by electrolysis at a current density of dm ^2. For the formation of the second copper layer, the copper concentration is 0.8 mol.
/ Liter to 1.2 mol / liter, free sulfuric acid concentration is 0.8 mol / liter to 1.2 mol
/ Liter, and a copper electrolyte having a chlorine ion concentration of 5 ppm to 50 ppm is used. And when supplying this sulfuric acid acidic copper electrolyte to an electrolytic cell, it is set as the liquid which processed activated carbon more than 1/2 of the amount of supply liquid, and the current density of 5-70 A / dm < ² > at the liquid temperature of 40-60 degreeC. By electrolyzing, a second copper layer can be formed.

As equipment for producing such an electrolytic copper foil, various kinds of proposed equipment can be arranged and used, including equipment used for producing electrolytic copper foil with a carrier. Whether the second copper layer is formed on the first copper layer or the first copper layer is formed on the second copper layer depends on the setting of the thickness of each layer and the state of the process at that time. To select.
〔Example〕
Hereinafter, the present invention will be described with reference to examples of the present invention, but the present invention is not limited thereto.

  In Example 1, on the surface of a long polyimide film having a thickness of 35 μm, a first copper layer having an average crystal grain size of 0.5 μm and a thickness of 4 μm, and an average crystal grain size of 2.0 μm and a thickness of 4 μm. FCCL with a second copper layer was used.

  The FCCL was washed with dilute sulfuric acid having a sulfuric acid concentration of 30 g / liter, washed with water and dried, and a commercially available liquid photoresist ink (etching resist ink) was applied to the surface of the second copper layer. The FCCL on which the liquid resist film was formed was dried, and a wiring pattern was projected and exposed.

The wiring pattern used for the evaluation is a linear pattern with a wiring pitch of 30 μm.
After the exposure, development was performed using an aqueous sodium carbonate solution, and unnecessary portions of the resist were peeled and removed, followed by washing with water and drying to obtain FCCL having an etching resist pattern.

  The FCCL provided with the etching resist pattern obtained above was etched to obtain a printed wiring board having a linear pattern of wiring with a wiring pitch of 30 μm. With respect to this printed wiring board, the cross-sectional shape of the wiring was evaluated at 10 points to determine the etching factor.

Moreover, the MIT folding-proof test was implemented as another characteristic.
In the MIT folding endurance test, as shown in FIG. 4, a wiring pattern 7 is formed on an insulating substrate 6 and used as a test piece 4 in which an insulating protective layer 5 is formed on a portion 8 where the folding endurance test is performed. did. This test piece was carried out using the MIT folding test apparatus shown in FIG. 5 under the conditions of bending curvature R: 0.5 mm / load: 100 gf. The breakage of the wiring pattern 7 was detected by the absence of conduction between the conduction detection terminals 9 at both ends.

  As a result of the above evaluation and test, the etching factor was an average of 5.3 (copper layer thickness 8 μm / top width 12 μm / bottom width 15 μm). The number of bendings in the MIT folding endurance test up to disconnection was 200 times.

The above is summarized and shown in Table 1 together with the evaluation and test results of Comparative Example 1.
[Comparative Example 1]
In Comparative Example 1, an electrolytic copper foil having the same grain size as that of the first copper layer in Example 1 was provided as a conductive layer, and FCCL used for COF tape production was used as a starting material.

The method of forming the wiring for evaluation and the method of evaluation / test were the same as in the examples. The description here is omitted to avoid redundant description.
As a result of the evaluation and the test, as shown in Table 1, the etching factor was an average of 2.0 (copper layer thickness 8 μm / top width 7 μm / bottom width 15 μm).

  The number of bendings in the MIT folding endurance test until disconnection was 150.

<Contrast between Example 1 and Comparative Example 1>
From the above, the cross-sectional shape of the wiring obtained in Example 1 shows a favorable rectangular shape with an etching factor of 2.7 times that of the conventional cross-sectional shape obtained in Comparative Example 1. . And in the bending resistance in the MIT test, the durability is about 1.3 times. Therefore, it is clear that a printed wiring board provided with a metal layer having a configuration in which the crystal grain size increases from the insulating substrate side toward the surface of the metal layer as a wiring has an advantage in the shape and bending resistance of the wiring. is there.

In Example 1, the same FCCL was used except that the average crystal grain size of copper in the first copper layer was 0.2 μm and the average crystal grain size of the second copper layer was 1.1 μm.
A printed wiring board having a linear pattern of wiring with a wiring pitch of 30 μm was obtained in the same manner as in Example 1 except that the above FCCL was used. With respect to this printed wiring board, the cross-sectional shape of the wiring was evaluated at 10 points to determine the etching factor.

Moreover, the MIT folding-proof test was implemented as another characteristic.
The etching factor of this printed wiring board was 5.0, and the number of bendings in the MIT folding resistance test until disconnection was 165 times.

In Example 1, the same FCCL was used except that the average crystal grain size of copper in the first copper layer was 0.9 μm and the average crystal grain size of the second copper layer was 3.5 μm.
A printed wiring board having a linear pattern of wiring with a wiring pitch of 30 μm was obtained in the same manner as in Example 1 except that the above FCCL was used. With respect to this printed wiring board, the cross-sectional shape of the wiring was evaluated at 10 points to determine the etching factor.

Moreover, the MIT folding-proof test was implemented as another characteristic.
The etching factor of this printed wiring board was 4.6, and the number of bendings in the MIT folding endurance test until disconnection was 230.

In Example 1, the same FCCL was used except that the average crystal grain size of copper in the first copper layer was 1.1 μm and the average crystal grain size of the second copper layer was 2.0 μm.
A printed wiring board having a linear pattern of wiring with a wiring pitch of 30 μm was obtained in the same manner as in Example 1 except that the above FCCL was used. With respect to this printed wiring board, the cross-sectional shape of the wiring was evaluated at 10 points to determine the etching factor.

Moreover, the MIT folding-proof test was implemented as another characteristic.
The printed wiring board had an etching factor of 2.6. However, when the average crystal grain size of the first copper layer is 1 μm or more, the crystal size distribution becomes wide, and due to this, the value of the individual etching factor varies within the range of 2.0 to 3.6, The variation width became large.

  Further, the number of bendings in the MIT folding endurance test up to the disconnection was 180 times.

In Example 1, the same FCCL was used except that the average crystal grain size of copper in the first copper layer was 0.5 μm and the average crystal grain size of the second copper layer was 0.9 μm.
A printed wiring board having a linear pattern of wiring with a wiring pitch of 30 μm was obtained in the same manner as in Example 1 except that the above FCCL was used. With respect to this printed wiring board, the cross-sectional shape of the wiring was evaluated at 10 points to determine the etching factor.

Moreover, the MIT folding-proof test was implemented as another characteristic.
The etching factor of this printed wiring board was 3.0, but the number of folds in the MIT folding test until disconnection was 155, and the average crystal grain size of the second copper layer was less than 1 μm. Although the folding performance in the MIT folding test is improved, it cannot be said that the improvement effect is sufficient.

  Examining the above Examples 1 to 5, when the average crystal grain size of the copper crystal forming the second copper layer is larger than the average crystal grain size of the copper crystal forming the first copper layer, However, when the average crystal grain size of the first copper layer is larger than 1 μm, the average value of the etching factor is within a good range, but the distribution range of the etching factor values measured individually tends to be wide. If the average crystal grain size of the second copper layer is less than 1 μm, it is not always sufficient to improve the number of bendings until the wire breaks in the MIT folding resistance test. That's not true. The average crystal grain size of the copper crystal of the first copper layer is not less than 0.1 μm and less than 1.0 μm, and the average crystal grain size of the copper crystal of the second copper layer is in the range of 1.0 μm to 5 μm. In some cases, this tendency does not occur. Therefore, in the average crystal grain size of the copper crystals forming the first copper layer and the second copper layer, the average crystal grain size of 1.0 μm is a boundary point that causes various characteristic changes in the obtained wiring.

  In the printed wiring board obtained by the present invention, the wiring formed on the surface of the insulating substrate has a good etching factor, and when it is a flexible printed wiring board, the product is excellent in bending resistance. Therefore, the wiring of a liquid crystal driver mounting printed circuit board for mobile devices and the like can be easily miniaturized, and the risk of circuit disconnection is reduced. Moreover, the printed wiring board manufacturing process can be carried out using conventional manufacturing equipment, and does not require new capital investment. Therefore, the printed wiring board is excellent in economy and has good quality. Enables the provision of

FIG. 1 is a photograph showing an example of a copper layer having fine crystals. FIG. 2 is a photograph showing an example of a macrocrystalline copper layer. FIG. 3 is a schematic diagram showing the cross-sectional shape of the wiring. FIG. 4 is a schematic view showing a test piece for MIT folding resistance test. FIG. 5 is a schematic diagram of the MIT test apparatus.

Explanation of symbols

1 Top width (W _t )
2 ... Bottom width (W _b )
3 ... Total thickness of copper layer ( _Tc )
4 ... MIT Folding test specimen 5 ... Insulating protective layer 6 ... Insulating substrate 7 ... Copper wiring 8 ... Folding test part 9 ... Conduction detection terminal 10 ... Test piece 11 ... Bending device 12 ... Bending device mounting base 13 ... Plunger 14 ... Grip 15 for applying a load ... Conductor 16 ... Test piece exposed part (length: 50 mm to 70 mm)
17 ... Bending angle (135 ° ± 5 °)
18 ... Bending angle (135 ° ± 5 °)

Claims (16)

A printed wiring board in which wiring is formed on the surface of an insulating substrate,
The wiring has a layer structure in which a first copper layer and a second copper layer are laminated, and the first copper layer side is bonded to the insulating substrate,
A printed wiring board comprising an average crystal grain size of the second copper layer larger than that of the first copper layer.   2. The print according to claim 1, wherein the average crystal grain size of copper in the first copper layer is 0.1 μm or more and less than 1.0 μm, and the average crystal grain size of copper in the second copper layer is 1.0 μm to 5.0 μm. Wiring board.   The printed wiring board according to claim 1 or 2, wherein the thickness of the second copper layer is 5% to 500% of the thickness of the first copper layer. The second copper layer is composed of n sublayers (where n ≧ 1),
4. The printed wiring according to claim 1, wherein the n-th sub-metal layer has an average crystal grain size larger than that of the (n−1) -th sub-metal layer. Board. When the wiring has a cross-sectional shape at an arbitrary position, the thickness of the wiring is T _c , the top width of the wiring upper surface is W _t , and the bottom width of the wiring lower surface is W _b , The printed wiring board according to any one of claims 1 to 4, wherein an etching factor obtained by calculation in (2) is 2.5 or more.
  The printed wiring board in any one of Claims 1-5 which used the base material for flexible printed wiring boards for the insulated substrate.   The printed wiring board in any one of Claims 1-5 which used the base material for rigid printed wiring boards for the insulated substrate. It is a manufacturing method of the printed wiring board in any one of Claims 1-7, Comprising: The manufacturing method of the printed wiring board characterized by including the following process A-process D.
Step A: A conductive layer having a layer structure in which a first copper layer and a second copper layer are laminated on the surface of an insulating substrate, and the average crystal grain size of the second copper layer is the average crystal grain of the first copper layer. A step of preparing a metal-clad laminate having an average crystal grain size larger than the diameter and having the first copper layer side bonded to the insulating substrate.
Step B: A step of forming an etching resist pattern on the surface of the second copper layer of the conductor layer.
Step C: A step of etching the metal-clad laminate having the etching resist pattern to dissolve and remove a portion of the conductor layer where the etching resist pattern is not formed to form a wiring.
Step D: A step of removing the etching resist pattern present on the surface of the wiring to obtain a printed wiring board.   The metal-clad laminate used in Step A has a layer structure in which a first copper layer and a second copper layer are laminated, and the average crystal grain size of the second copper layer is the average crystal grain size of the first copper layer. The manufacturing method of the printed wiring board of Claim 8 using the copper clad laminated board which used the electrolytic copper foil provided with a bigger average crystal grain diameter, and bonded the 1st copper layer side with the insulated substrate. The metal-clad laminate used in the step A is an electrolytic copper foil having a layer structure in which a first copper layer and a second copper layer that is recrystallized by heating at 170 ° C. to 180 ° C. for 15 minutes or more are laminated. Then, at the time of forming the metal-clad laminate, a temperature of 170 ° C. to 180 ° C. is applied to the first copper layer side for 15 minutes or more, and the insulating substrate and the electrolytic copper foil are bonded to each other. The method for producing a printed wiring board according to claim 8, wherein a copper-clad laminate having an average crystal grain size larger than that of the first copper layer is used. In the metal-clad laminate used in the step A, a first copper layer is formed on an insulating substrate by an electroless plating method, and heating is performed at 170 ° C. to 180 ° C. for 15 minutes or more on the first copper layer. By forming a second copper layer to be recrystallized to form a conductor layer, and then heating at a temperature of 170 ° C. to 180 ° C. for 15 minutes or more, thereby heating the average crystal grain size of the second copper layer The method for producing a printed wiring board according to claim 8, wherein a copper-clad laminate is used which has an average crystal grain size larger than the average crystal grain size of the first copper layer.   For the formation of the second copper layer, an electrolytic copper plating method using a sulfuric acid copper plating solution is employed. The sulfuric acid copper plating solution has a copper concentration of 0.8 mol / liter to 1.2 mol / liter, A free sulfuric acid concentration of 0.8 mol / liter to 1.2 mol / liter and a chlorine concentration of 5 ppm to 50 ppm is used, and a product obtained by subjecting the sulfuric acid acidic copper plating solution to activated carbon treatment for 1/2 volume or more is used. The manufacturing method of the printed wiring board of Claim 10 or Claim 11. It is a manufacturing method of the printed wiring board in any one of Claims 1-7, Comprising: The manufacturing method of the printed wiring board characterized by including the following process a-process f.
Step a: Step of manufacturing a temporary copper clad laminate having only the first copper layer on the surface of the insulating substrate.
Step b: forming a plating resist pattern on the surface of the first copper layer of the temporary copper clad laminate. Step c: A step of forming a wiring-shaped second copper layer by performing copper plating on the surface of the first copper layer on which the plating resist pattern of the temporary copper-clad laminate is not formed.
Step d: A step of removing the plating resist pattern to obtain a temporary printed wiring board.
Step e: A step of heat treating the temporary printed wiring board obtained in step d to make the crystals of the second copper layer macrocrystalline.
Step f: Thereafter, the temporary printed wiring board in which the crystal of the second copper layer is macrocrystallized is etched to dissolve and remove the exposed first copper layer where the second copper layer is not formed. The process which makes a wiring board.   For the formation of the second copper layer, an electrolytic copper plating method using a sulfuric acid copper plating solution is employed. The sulfuric acid copper plating solution has a copper concentration of 0.8 mol / liter to 1.2 mol / liter, A free sulfuric acid concentration of 0.8 mol / liter to 1.2 mol / liter and a chlorine concentration of 5 ppm to 50 ppm is used, and a product obtained by subjecting the sulfuric acid acidic copper plating solution to activated carbon treatment for 1/2 volume or more is used. The manufacturing method of the printed wiring board of Claim 13.   The method for manufacturing a printed wiring board according to claim 13, wherein the heat treatment in the step e is performed at a temperature of 170 ° C. to 180 ° C. for 15 minutes or more. An electrolytic copper foil used for producing the metal-clad laminate according to claim 9,
The electrolytic copper foil has a layer structure in which a first copper layer and a second copper layer are laminated, and the average crystal grain size of the first copper layer after heating at 175 ° C. for 15 minutes is 0.1 μm or more and less than 1.0 μm. An electrolytic copper foil, wherein the second copper layer has an average crystal grain size of 1.0 μm or more and 5.0 μm or less.