JP4918342B2 - Copper foil roughening treatment method - Google Patents

Description

  The present invention provides a roughening treatment method for producing a copper foil suitable for a printed wiring board particularly for high-frequency characteristics and high-density wiring.

Copper foil is used in large quantities for printed wiring board applications, and is roughly classified into rolled copper foil and electrolytic copper foil depending on the production method.
Among these, a general manufacturing method of the electrolytic copper foil is manufactured by electrolytically depositing copper having a target thickness from an acidic copper sulfate electrolytic solution with an electrodeposition apparatus, peeling the precipitate, and winding it. At that time, by adding an appropriate additive to the electrolytic solution, mechanical properties and a surface shape suitable for the application are created. In the case of electrolytic copper foil, the surface characteristics of both surfaces are often different, and the electrodeposition drum side is called the S (Shiny) surface, smooth surface or glossy surface, and the opposite side is called the M (Matt) surface or rough surface. The S plane is affected by the electrodeposition drum, the surface roughness is about 2 μm in Rz, and the crystal is a fine crystal of random orientation. On the other hand, the M surface can greatly vary its surface characteristics depending on the electrodeposition conditions and additive conditions. When an appropriate brightener is added, the surface roughness is 18 μm thick copper foil. Rz can be reduced to 1 μm or less, and the crystal at that time is extremely fine. When glue is added, the surface roughness Rz can be varied to about 4 μm to 12 μm. Becomes columnar crystals.

Moreover, the general manufacturing method of rolled copper foil is rolled and manufactured to a target thickness with a rolling mill from a copper ingot.
These copper foils are called “untreated copper foils” by those skilled in the art. When obtaining copper foils for printed wiring boards, these copper foils are usually not used as they are, but are insulated. Various surface treatments are applied for the purpose of imparting "roughening treatment" for the purpose of improving the adhesion to the resin and chemical adhesion, heat resistance, chemical resistance and rust prevention.
Each step of the plurality of surface treatments is completed within a few seconds to a few dozen seconds from an industrial viewpoint.

Among these, the general roughening process of the copper foil for printed wiring boards is formed with the following form.
First, a surface cleaning process is performed for the purpose of cleaning the surface of the untreated copper foil before the roughening process.
By immersing (spreading) or electrolytically treating the surface of the untreated copper foil in an acidic bath or an alkaline bath, the surface oxides and organic substances are removed.
Next, as roughening treatment, a copper foil is used as a cathode in a sulfuric acid copper bath, and an insoluble anode is arranged opposite to the treated surface to form a copper dendrite with a current exceeding the limit current density. Furthermore, the dendritic protrusions are coated and fixed with a copper foil as a cathode in an acidic copper sulfate bath with a current equal to or lower than the limiting current density.
Conditions such as the composition of the electrolytic solution, additives, current, and temperature are controlled with high accuracy so as to obtain an optimum surface for a printed wiring board.

In addition, the surface roughening treatment is mainly performed on the M surface side, but in recent years, it has been performed on both surfaces as an alternative to the case applied to the S surface and the blackening treatment in the multilayer printed wiring board manufacturing process. There is also a case.
In recent years, as mobile electronic devices have become more sophisticated, the surface of copper foil has been reduced to reduce the etching factor and improve the signal transmission speed delay due to the skin effect in order to satisfy high-frequency characteristics and higher wiring density. There is a flow to do. For lowering the roughness, the roughness of the untreated copper foil is reduced, the roughened particles are reduced in the surface roughening treatment, and the roughened particles are dispersed on the uneven surface of the untreated copper foil. However, there is a conflicting relationship between “reducing the roughness of the copper foil” and “adhesive strength with the resin base material”. It is.

The following are examples of technologies that have been studied so far.
For example, Patent Document 1 below discloses a method for finely roughening a surface by a cathode treatment or an anodic dissolution treatment in advance before the surface roughening treatment step. The conditions are the same for the cathode treatment and the anodic dissolution treatment, and it is shown that an acidic copper sulfate bath having a copper concentration of 5 to 60 g / L is used.
Patent Document 2 below discloses a method of forming a roughened etching surface of a rolled copper foil in an electrolytic solution by AC / DC or a combination thereof.
JP 48-9938 A JP 59-9050 A

  However, simply plating or dissolving in such a simple bath does not provide a high surface area, and a sufficient effect cannot be obtained. This is a simple example shown in Comparative Example 2 described later. It is clear from the results of anodic dissolution treatment using direct current in the bath.

Further, Patent Document 3 below shows that the glossy surface of the copper foil is etched, and chemical etching is most convenient as the means, and an ammonium persulfate bath is suitable.
Japanese Patent Laid-Open No. 7-74464

  However, chemical etchants containing a large amount of peroxide have a high consumption (decomposition) rate of the peroxide itself, and the additive is decomposed by the peroxide, so the etching amount can be stably and highly accurate. Not only is it difficult to control, it is also difficult to circulate and reuse the liquid.

  Also, when chemical etching solution is used, both sides of the copper foil are etched at the same time, and when it is performed only on one side, a special device that touches the etching solution only on one side is required, or a film or the like is applied on one side. It was necessary to paste them together. In particular, thin foils of 18 μm or less, which are frequently used for printed wiring boards for the purpose of high-frequency characteristics and high-density wiring, are inferior in foil permeability and in productivity. Further, when the untreated copper foil is an electrolytic copper foil, the surface roughness of the S plane and the M plane are often different, and the crystal structure is also often different. For such a foil, it is easily guessed that it is difficult to control the etching amount separately on both sides using a chemical etching solution.

Moreover, in the field of chemical etching solutions, as disclosed in the following Patent Document 4, attempts have been made to add azoles to acidic peroxide aqueous solutions for a long time. In the field of printed wiring boards, acidic peroxide aqueous solutions to which azoles are added are called “microetching treatment solutions” and are widely used in alternative techniques for blackening treatments.
US3773577

However, even in the case of azoles, the difference in the etching shape and the etching rate due to the presence or absence of halogen ions is significant depending on the type of the azole. For example, as shown in Patent Document 5 below, the azole is composed of benzotriazole. In some cases, chlorine ions are essential to form irregularities, but the etching rate is slow, and when tetrazoles are used, irregularities can be etched at a high rate regardless of the presence or absence of chlorine ions.
In microetching by the electrolysis method of the present invention described later, as shown in Comparative Example 4, tetrazole does not show a clear effect, and triazoles or thiazoles show an effect. In the (spraying) method (chemical etching), the types of additives that can be microetched are different and the reaction proceeds by another mechanism.
JP 2000-64067 A

In addition, as a pre-process of the roughening treatment, for example, a number of methods for mechanically polishing the surface have been reported as typified by the following Patent Document 6, but not only the process becomes complicated, but also polishing. Mist and polishing residue are generated, and there is a concern that it may affect the subsequent circuit formation process, which is not suitable for the recent high-density printed wiring board process.
JP 59-145800 A

  An object of the present invention is to solve the above-described problems of the prior art and to provide a method for easily obtaining a low-roughness and high-adhesion copper foil surface shape suitable for high-frequency substrate applications and high-density wiring applications. .

The copper foil roughening treatment method of the present invention is characterized in that one or both surfaces of the copper foil are subjected to microetching treatment by an electrolytic method with a sulfuric acid solution containing azoles. The azoles are preferably triazoles and thiazoles, and the concentration is preferably 0.005 to 2 g / L. The copper foil used in the method of the present invention may be either an electrolytic copper foil or a rolled copper foil.
The present invention also provides a roughening treatment method for copper foil, characterized in that after the microetching treatment is performed, a dendritic treatment and a coating plating treatment are further performed by an electrolytic method using a sulfuric acid acidic solution. is there.

  By using the roughening treatment method of the present invention, a low-roughness surface having a high surface area can be obtained separately, simply and uniformly with high accuracy on both sides of the copper foil. In addition, when used in combination with a conventional roughening treatment, a printed wiring board copper foil exhibiting high adhesive strength can be obtained particularly for substrate materials that require low roughness.

The microetching solution by the electrolytic method used in the present invention is based on a sulfuric acid acidic solution, and exhibits an effect by adding an additive of triazoles or thiazoles.
The concentration of sulfuric acid in the microetching solution is preferably 10 to 250 g / L, more preferably 50 to 150 g / L. The additive is selected from triazoles and thiazoles.
Triazoles include benzotriazole, 1-methylbenzotriazole, 1,2,3-triazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, 4-amino-4H-1, Examples include 2,4-triazole, 5-nitrobenzotriazole, and hydroxybenzotriazole. Examples of thiazoles include 2-aminothiazole, benzothiazole, 2-methylbenzothiazole, and 2-mercaptobenzothiazole. It is not limited to.
The effect is recognized when the concentration of the additive is 0.005 to 2 g / L, and more preferably 0.01 to 1 g / L.

When the composition of the treatment liquid is compared, the liquid composition of the conventional immersion system is sulfuric acid, hydrogen peroxide around 40 vol%, and the azoles are 100 mg / L (+ chlorine), whereas the liquid composition for electrolysis of the present invention is Sulfuric acid, azoles 10 mg / L + chlorine, no peroxide or a small amount, and even though the addition amount of azoles is about 1/10 of the immersion (spraying) method, Has the same effect.
In this invention, there exists an advantage that the amount of an additive brings about an effect comparable as immersion (spreading) at about 1/10. In addition, when there is a large amount of hydrogen peroxide, hydrogen peroxide itself is easily decomposed and it is difficult to control micro-etching with high accuracy, but there is no peroxide in the processing solution used in the method of the present invention. Alternatively, since only a small amount is contained, the life of the treatment liquid is long. Further, since the amount of hydrogen peroxide in the treatment liquid is small, there is almost no decomposition of the azole additive, the stability is excellent, and the treatment liquid can be circulated and used.
Furthermore, in the conventional immersion type liquid, both sides of the copper foil are etched at the same time, and in the case of only one side, a film can be stretched on the foil or the electrolytic cell can be processed only on one side (mechanically complicated). However, in the case of the electrolytic method, the amount of microetching on each side can be controlled easily and with high precision by changing the current conditions with a single liquid system.

Moreover, although copper ion melt | dissolves by a microetching process and inevitably mixes in a process liquid, the upper limit density | concentration is not specifically limited, What is necessary is just to manage in the range which does not produce a copper sulfate crystal | crystallization. The triazole and thiazole additives in the treatment liquid in the present invention are considered to form a complex salt with copper in the microetching solution.
Moreover, halogen ion (preferably chlorine ion) is an essential component, and its concentration is 0.5 mg / L to 120 mg / L, preferably 3 mg / L to 70 mg / L. When the concentration is lower than 0.5 mg / L, the unevenness tends not to be deeply formed. When the concentration is higher than 120 mg / L, the copper foil appearance tends to be uneven.

  In addition, although the peroxide does not have to be present in the microetching treatment solution, the presence of a small amount improves the time effect required for etching by the electrolytic method. The upper limit is preferably 10 g / L when hydrogen peroxide is taken as an example, and if it is more than this, not only will the influence on the decomposition of the additive (azoles) itself begin to appear, but also polishing will begin to proceed chemically. It becomes difficult to control micro-etching with high accuracy, and the meaning of individually controlling both surfaces is reduced. In addition, as shown in Comparative Example 3, when only the immersion treatment is performed with hydrogen peroxide at 10 g / L, the effect is not exhibited even if it takes 60 seconds.

As a method of applying electricity, which can be applied to the microetching process by the electrolytic method of the present invention, it is sufficient that the copper foil is finally dissolved, not only DC, but also forward / reverse inversion by a chopper or a high-speed PR pulse power source, The waveform can be selected arbitrarily.
Conventionally, the roughening treatment by electrolysis is a treatment on the side of depositing metal, whereas the microetching treatment of the present invention is distinguished from a treatment on the side of dissolving metal. .
Although the current density of electrolysis depends on the method of applying electricity, in the case of direct current, 1 to 100 ASD is preferable, and if it is 1 ASD or less, it takes too much time to process, and if it is 100 ASD or more, the effect of forming irregularities is reduced. More preferably, it is 10 ASD-50 ASD.
The time required for the treatment is preferably less than 60 seconds, preferably 1 to 30 seconds from an industrial viewpoint, and the shorter the time, the better.
The temperature of the liquid is not particularly limited, but on the basis of room temperature (25 ° C.), the high side tends to increase the etching rate, and the low side tends to have deep irregularities.
The microetching process by the electrolytic method also has an effect of cleaning the surface of the untreated copper foil, and thus can be replaced with a surface cleaning process.

Further, after the microetching treatment by the electrolytic method, a coating plating treatment or a roughening treatment may be performed as necessary. In the present invention, preferably, a copper foil is used as a cathode in a sulfuric acid copper bath, and the treatment surface is treated. An insoluble anode is placed facing the copper dendrite, and a copper dendrite is formed at a current equal to or higher than the limit current density, and the copper foil is used as a cathode in an acidic copper bath, and the current is equal to or lower than the limit current density. The dendrite is covered with copper and fixed.
Furthermore, various surface treatments that can be applied to printed wiring boards such as imparting rust prevention, heat resistance, chemical resistance, improved adhesion, color tone adjustment, solubility, resistance layer, etc. can be applied. .
Below, preferable embodiment of this invention is described based on an Example and a comparative example.

  A list of examples and comparative examples is shown in Table 1 below.

Abbreviated name of additive type
AT: aminothiazole
BTA: Benzotriazole
MBTA: 1-methylbenzotriazole
BT: benzothiazole
TET: 5-amino-1H-tetrazole

Table 2 shows the types of untreated copper foil used in the experiment. Table 3 shows the process sequence and conditions. In Examples 1 to 8 and Comparative Examples 2 and 4, in order of i → ii → v → vi, and in Comparative Example 1, in order of i → v → vi went. In Example 9 and Comparative Example 3, the cleaning was performed in the order of i to vi while sandwiching water washing in each step. Finally, drying with warm air was performed.
Here, the details of the microetching process by the electrolytic method of this example and the comparative example will be described. Copper sulfate pentahydrate and sulfuric acid, chloride ions, hydrogen peroxide, and azoles were prepared in a solution adjusted to satisfy the conditions shown in Table 3 (ii) and Table 1, respectively. Direct current was applied using the copper foil as an anode under the predetermined processing conditions shown in Table 1.
Comparative Example 1 is a case where the additive (azoles) is not added and the micro-etching process is not performed. Comparative Example 2 is a case where the additive (azoles) and hydrogen peroxide are not added. This is a case where the etching treatment is performed, and Comparative Example 3 is a case where the hydrogen peroxide is added without adding the additive (azoles) and the immersion treatment is performed (no electrolytic treatment). Comparative Example 4 is a case where the additive is tetrazole in the microetching process by the electrolytic method.

Surface electron micrographs (magnification: 5000) of the copper foils obtained in Example 3 and Comparative Example 1 (Comparison with and without microetching treatment), Example 9 and Comparative Example 3, and Comparative Example 4 (additive is tetrazole) Times) is shown in FIGS. The surface electron micrograph was observed from an oblique direction of 40 degrees of the sample.
From the comparison between FIG. 1 and FIG. 2, it can be confirmed that extremely fine irregularities are formed on the surface by the microetching treatment according to the present invention.
From the comparison between FIG. 3 and FIG. 4, it can be confirmed that the microetching process according to the present invention contributes to the uniform dispersion of the roughened particles in the roughening process.
From FIG. 5, when the azole is tetrazole, it is observed that fine irregularities are not formed.

Roughness Rz was measured with respect to the obtained copper foil. The measurement was based on JIS B0601 standard, and a surf coder SE1700α manufactured by Kosaka Laboratory was used.
Moreover, the obtained copper foil was laminated | stacked on the high heat resistant multilayer base material suitable for a high frequency circuit use, respectively, and the copper clad laminated board was formed.
Furthermore, the peel strength was measured according to IPC-TM-650 standard 2.4.8.5.
The results are shown in Table 4.

It was confirmed that a high adhesive force was obtained with a low roughness by the microetching process by the electrolytic method. In addition, it was confirmed that the microetching treatment liquid to which no azoles were added could hardly be expected to have an effect on improving the adhesive force.
Normally, “reducing the roughness of the copper foil” and “adhesive strength with the resin base material” are in a contradictory relationship, but the roughening treatment of the present invention has a low roughness and a uniform and high surface area. Since the surface can be obtained, in addition to the high physical surface area, the adhesion amount per unit area of the subsequent chemical adhesion treatment (for example, silane coupling treatment) is also increased, resulting in an adhesive force with the substrate. As a result, it is considered that both the properties of “low roughness” and “high adhesive strength” can be combined.

  Furthermore, in addition to the microetching process by the electrolytic method, it was confirmed that a higher adhesive force can be obtained by performing a roughening process comprising a dendritic process and a coating plating process. This effect is thought to be due to the fact that the surface of the roughening treatment was formed uniformly and finely by the microetching treatment by the electrolytic method, and worked effectively as a nucleus generation point during the dendritic treatment.

  Further, according to the comparative example shown below, performing the microetching process by the electrolytic method instead of the immersion (spreading) process not only contributes to the stability of the liquid but also contributes to the reduction of the absolute amount of the additive. I understood that. That is, while the optimum concentration of azoles by the electrolytic method is 0.005 to 2 g / L, the concentration at which the effect is recognized by the dipping (spreading) method is at least 1 g / L or more, preferably 10 to 15 g / L. Needed.

Table 5 shows the evaluation results of the rough surface state when the additive concentration was changed by the immersion (spreading) method. Moreover, the surface electron micrograph of copper foil is shown in FIGS.
The evaluation of the rough surface state was judged in three stages from micrographs of FIGS. 6 to 11 where micro-etching was sufficiently carried out = ◯, slightly made = Δ, and hardly carried out = ×. A substantial effect is recognized at least Δ, preferably at least ○.
The treatment conditions are 35 μm thick electrolytic copper foil M surface side, and the microetching treatment liquid composition is copper sulfate pentahydrate 10 g / L, sulfuric acid 100 g / L, chloride ions 70 ppm, hydrogen peroxide 100 g / L, Benzotriazole was adjusted to a predetermined concentration, the liquid temperature was 35 ° C., and the spraying time was 50 seconds.

6 to 11 are electron micrographs of a microetching process by a dipping (spreading) method in Comparative Examples 5 to 10, respectively.
From the above results, it was confirmed that the necessary additive (azoles) concentration can be greatly reduced by performing the microetching process not by dipping (spreading) but by electrolysis.

According to the present invention, a low roughness surface having a high surface area can be obtained separately and easily on both sides of the copper foil, and even when used in combination with a conventional roughening treatment, the roughness is particularly low. The present invention provides a method for roughening a copper foil for a printed wiring board, which exhibits high adhesive strength with respect to a substrate material that is required.
Moreover, since the adhesive force with the base material (resin) is improved by the physical shape of the copper foil, the copper foil obtained by the present invention is used for known secondary battery electrodes, plasma displays, and transportation. It is also suitable for electromagnetic shielding applications used for medium windows.
By using the micro-etching process by the electrolytic method, it becomes possible to easily control the etching amount separately on both sides of the untreated copper foil.
Further, it has been found that performing the microetching process by an electrolytic method instead of an immersion (spreading) process not only contributes to the stability of the liquid, but also contributes to a reduction in the absolute amount of the additive.

4 is a surface electron micrograph of the copper foil obtained in Example 3. 2 is a surface electron micrograph of the copper foil obtained in Comparative Example 1. 4 is a surface electron micrograph of the copper foil obtained in Example 9. 4 is a surface electron micrograph of the copper foil obtained in Comparative Example 3. 4 is a surface electron micrograph of the copper foil obtained in Comparative Example 4. 6 is an electron micrograph of microetching treatment by a dipping (dispersing) method in Comparative Example 5. 14 is an electron micrograph of microetching treatment by a dipping (dispersing) method in Comparative Example 6. 14 is an electron micrograph of microetching treatment by a dipping (dispersing) method in Comparative Example 7. 10 is an electron micrograph of microetching treatment by a dipping (spreading) method in Comparative Example 8. 10 is an electron micrograph of microetching treatment by a dipping (spreading) method in Comparative Example 9. 14 is an electron micrograph of microetching treatment by a dipping (spreading) method in Comparative Example 10.

Claims (6)

Roughening of copper foil characterized by subjecting one side or both sides of copper foil to microetching by electrolysis using a halogen ion-containing sulfuric acid acid solution containing at least one of triazoles or thiazoles Processing method. The copper foil roughening method according to claim 1, wherein after the microetching treatment, a dendritic treatment and a coating plating treatment are further performed by an electrolytic method using a sulfuric acid acidic solution. The method for roughening a copper foil according to claim 1 or 2, wherein the concentration of the triazoles or thiazoles in the halogen ion-containing sulfuric acid acidic solution is 0.005 to 2 g / L. The triazole or thiazole is benzotriazole, 1-methylbenzotriazole, 1,2,3-triazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, 4-amino-4H -1,2,4-triazole, 5-nitrobenzotriazole, hydroxybenzotriazole, 2-aminothiazole, benzothiazole, 2-methylbenzothiazole and 2-mercaptobenzothiazole The roughening processing method of the copper foil of any one of Claims 1-3 characterized by the above-mentioned. The halogen ion in the sulfuric acid acidic solution containing the triazoles or thiazoles is a chloride ion, and the chloride ion concentration is 0.5 to 120 mg / L. The roughening method of the copper foil as described in 2. The roughening processing method of the copper foil of Claims 1-5 for manufacturing the copper foil of a printed wiring board use, a secondary battery electrode use, or electromagnetic wave shielding use.