JP2023013674A - Two layer flexible substrate - Google Patents

Abstract

To provide a two layer flexible wiring board excellent in heat resistant adhesion, applied even to a flexible wiring board including a wiring part having a narrow width and a narrow pitch, industrially useful and having higher reliability.SOLUTION: A two layer flexible wiring board includes: an insulating base material having a surface subjected to plasma treatment; a ground metal layer laminated on the surface of the insulating base material subjected to the plasma treatment; and a copper conductor layer laminated on the surface of the ground metal layer. The half width of the crystal plane (111) of the ground metal layer by X ray diffraction is 0.40-0.50 degrees; and the half value width of the crystal plane (111) of the copper conductor layer by the X ray diffraction is 0.20-0.50 degrees; and a crystalline orientation ratio (K (200)/K (111)) after being exposed at 100°C for 120 hours is 0.2-0.3.SELECTED DRAWING: None

Description

The present invention relates to a two-layer flexible substrate. More specifically, the present invention has excellent heat-resistant adhesion, can be applied to a flexible wiring board having a narrow-width, narrow-pitch wiring portion, and is industrially useful and has a higher reliability. It relates to flexible substrates.

Conventionally, electronic devices (for example, LCDs (liquid crystal displays), smart phones, digital cameras, etc.) using flexible printed circuit boards (FPCs) with copper clad laminates (CCLs) have been developed. A CCL (for example, a two-layer CCL in which an insulating film and a copper foil are directly bonded) is formed on an insulating film by a dry process (sputtering method, ion plating method, vacuum deposition method, CVD method, etc.) to form a thin underlying metal layer. on which copper electroplating is performed (metallizing method).

However, the two-layer CCL produced by the metallizing method is inferior in heat resistance, and the adhesion strength tends to be greatly reduced compared to the initial adhesion strength. Therefore, techniques for improving the heat resistance of the two-layer CCL have been proposed (for example, Patent Document 1).

WO2008/090654

However, the invention described in Patent Document 1 is still insufficient in the heat-resistant adhesive strength of the two-layer CCL. Therefore, the invention described in Patent Document 1 is particularly unsuitable for FPCs having narrow width and narrow pitch wiring portions.

The present invention has been made in view of such conventional inventions, and is industrially useful because it can be applied to flexible wiring boards having excellent heat-resistant adhesion and narrow-width, narrow-pitch wiring portions. It is an object of the present invention to provide a more reliable flexible wiring board.

As a result of intensive studies, the present inventors have discovered an insulating substrate having a plasma-treated surface, a base metal layer laminated on the plasma-treated surface of the insulating base, and the surface of the base metal layer. In a two-layer flexible substrate comprising a copper conductor layer laminated on a substrate, the half-value width of the crystal plane (111) of the underlying metal layer and the copper conductor layer by X-ray diffraction is within a predetermined numerical range, and under high temperature conditions When the orientation ratio (K(200)/K(111)) of the crystalline after being exposed to heat is within a predetermined numerical range, the interlayer adhesion can be strengthened, and the above problems can be solved. perfected the invention. That is, the two-layer flexible substrate of the present invention for solving the above problems mainly includes the following configurations.

(1) an insulating substrate having a plasma-treated surface, a base metal layer laminated on the plasma-treated surface of the insulating base, and copper laminated on the surface of the base metal layer and a conductor layer, wherein the crystal plane (111) of the base metal layer has a half-value width of 0.40 to 0.50 deg by X-ray diffraction, and the crystal plane (111) of the copper conductor layer has an X-ray The half width by diffraction is 0.20 to 0.50 deg, and the crystalline orientation ratio (K(200)/K(111)) after exposure at 100° C. for 120 hours is 0.2 to 0.2. 3, two-layer flexible substrate.

According to such a configuration, the two-layer flexible substrate has good crystallinity. As a result, the two-layer flexible substrate is less likely to be changed by heat and has excellent heat-resistant adhesion. As a result, the two-layer flexible substrate can be applied to a flexible wiring board having wiring portions of narrow width and narrow pitch, and is industrially useful and highly reliable.

(2) The two-layer flexible substrate according to (1), wherein the base metal layer does not contain nitrogen.

According to such a configuration, the two-layer flexible substrate has improved heat-resistant adhesion. In addition, the two-layer flexible substrate tends to have improved etching characteristics when wiring is formed.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to apply to a flexible wiring board having excellent heat-resistant adhesiveness and narrow-width, narrow-pitch wiring portions, which is industrially useful and provides a highly reliable flexible wiring board. can do.

FIG. 1 is a schematic diagram for explaining pulses applied to electrodes in a plasma processing step. FIG. 2 is a graph obtained by measuring the plasma state during film formation in the DC method and the high-pressure pulse method with a plasma emission spectrometer for the copper conductor layer.

<Two-layer flexible substrate>
A two-layer flexible substrate according to one embodiment of the present invention includes an insulating substrate having a plasma-treated surface, a base metal layer laminated on the plasma-treated surface of the insulating base, and a base metal and a copper conductor layer laminated on the surface of the layer. The X-ray diffraction half width of the crystal plane (111) of the underlying metal layer is 0.40 to 0.50 deg. The X-ray diffraction half width of the crystal plane (111) of the copper conductor layer is 0.20 to 0.50 deg. The crystalline orientation ratio (K(200)/K(111)) after exposure at 100° C. for 120 hours is 0.2-0.3. Each configuration will be described below.

(Insulating base material)
The insulating substrate is not particularly limited. For example, the insulating substrate is a polymer film such as polyethylene terephthalate, biaxially oriented polypropylene, non-oriented polypropylene, polyamide, polystyrene, polyvinyl chloride, polycarbonate, polyacrylonitrile, polyimide, and the like. Among these, the insulating substrate is preferably polyimide because of its good dimensional stability in a high-temperature environment.

The thickness of the insulating substrate is not particularly limited. For example, the thickness of the insulating substrate is preferably 5 μm or more, more preferably 8 μm or more. Moreover, the thickness of the insulating substrate is preferably 200 μm or less, more preferably 30 μm or less. When the thickness of the insulating substrate is within the above range, the insulating substrate can be easily transported during processing, the film is less likely to be bent, and the continuous processability is excellent. Also, the obtained two-layer flexible substrate can exhibit appropriate rigidity and strength.

The insulating base material of the present embodiment is plasma-treated on the surface. As a result, the surface of the insulating substrate is cleaned, gas is released from the insulating substrate (degassing), fine irregularities are formed on the surface, and the surface is modified. .

The plasma treatment method is not particularly limited. Examples of plasma processing methods include DC (a method of processing with constant power from a DC power source), high-voltage pulse method, RF, and the like. In this embodiment, the plasma treatment is preferably performed by a high voltage pulse method.

The high-pressure pulse method is a film-forming method that achieves high adhesion and throwing power by improving the ionization rate with high-density plasma while maintaining the low-temperature film-forming feature of the sputtering method. In the high-voltage pulse method, a capacitor is charged by a DC power supply, and the accumulated electric charge is sent all at once to the target material, which becomes an electrode. improve the ionization rate of Power is supplied in very short and extremely powerful pulses. The pulses are delivered with a relatively low duty cycle (duty cycle, ie, relatively long period between pulses). As a result, the time-averaged power (electric power) falls within the same range as typical DC sputtering methods. The high-voltage pulse power source can output instantaneous power 10 to 10,000 times that of the conventional plasma processing while the average power is almost the same as that of the conventional plasma processing.

FIG. 1 is a schematic diagram for explaining pulses applied to electrodes in a plasma processing step. The pulse shown in FIG. 1 is a square wave that generates a negative high voltage only for a predetermined pulse time (Ton). Moreover, in this embodiment, such a square wave can be generated for each predetermined pulse repetition time (Ton+Toff). As a result, in the present embodiment, the ratio (Ton/Ton+Toff) of the pulse time (Ton) to the pulse repetition time (Ton+Toff) can be reduced, forming high-density plasma and improving the ionization rate of the target material. obtain.

For example, the plasma treatment of Example 1, which will be described later, is performed at an average power density of 0.24 W/cm ² . By reducing the ratio (Ton/Ton+Toff) of the pulse time (Ton) to the pulse repetition time (Ton+Toff), processing with a maximum power density of 2.4 W/cm ² is performed. The ratio of the maximum power density to the average power density of the pulse is 10 or more. As a result, the plasma density in the atmosphere in plasma processing can be greatly improved, and the ionization rate of the target material and gas in the atmosphere can be greatly increased.

Also, by increasing the maximum power density with the high voltage pulse method, the sputtered particles and ionized gas will adhere and collide with the insulating substrate in a higher energy state. In addition, degassing (mainly moisture) contained in the substrate can be removed more efficiently, and deterioration of adhesion properties can be easily prevented. Furthermore, it is possible to more effectively form fine irregularities on the surface of the substrate and to modify the surface. As a result, chemical bonding with the underlying metal layer and the copper conductor layer, which will be described later, is promoted, and adhesion can be improved.

The maximum power density during plasma processing can be adjusted by the pulse time (Ton) and the number of repetitions (frequency). Therefore, according to the high-pressure pulse method, it is easy to adjust how much the adhesion property is improved according to the type of substrate.

In addition, the high-voltage pulse method has a low duty ratio (ratio of pulse time (Ton) to pulse repetition time (Ton+Toff) (Ton/Ton+Toff). Therefore, even with the same average power, comparison with other plasma processing methods Therefore, the heat load during film formation can be reduced.As a result, the insulating substrate is less likely to form a fragile layer and the adhesive strength is less likely to decrease.The high-pressure pulse method is suitable for substrates with low glass temperatures. Even with (for example, COP, PPS, etc.), it is possible to obtain good adhesion properties like polyimide (PI) films.

(Base metal layer)
The underlying metal layer is laminated to the plasma-treated surface of the insulating substrate. The base metal layer is provided to improve interlayer adhesion between the copper conductor layer and the insulating substrate.

The base metal layer is not particularly limited. For example, the base metal layer is a base metal layer formed using nickel (Ni), titanium (Ti), or the like as a sputtering target. Among these, the base metal layer of the present embodiment is preferably a layer made of a Ni alloy. The Ni alloy layer prevents the copper contained in the copper conductor layer from diffusing into the inside of the insulating base material, and also prevents gases such as oxygen and water vapor that cause copper to diffuse inside the insulating base material. can improve gas barrier properties against

When the base metal layer is a Ni alloy layer, the metal components (alloy components) other than Ni contained in the Ni alloy layer are not particularly limited. For example, the alloy components are Cr, Ti, Mo, Cu, Fe, and the like. Among these, Cr and Ti are particularly preferred as the alloying components because they exhibit excellent adhesion to the insulating substrate.

The content of the alloy component in the Ni alloy layer is not particularly limited. As an example, the content of the alloy component is preferably 4% by mass or more, more preferably 7% by mass or more, in the Ni alloy. In addition, the content of the alloy component is preferably 50% by mass or less, more preferably 35% by mass or less, in the Ni alloy. When the content of the alloy component is within the above range, the obtained two-layer flexible substrate has more excellent adhesion between the insulating substrate and the copper conductor layer.

The thickness of the underlying metal layer is not particularly limited. For example, the thickness of the base metal layer is preferably 3 nm or more, more preferably 10 nm or more. The thickness of the underlying metal layer is preferably 30 nm or less, more preferably 20 nm or less. When the thickness of the base metal layer is within the above range, the time required for film formation of the base metal layer is appropriate, resulting in good productivity. Moreover, the resulting two-layer flexible substrate has excellent adhesion between the insulating substrate and the copper conductor layer.

The X-ray diffraction half width of the crystal plane (111) of the underlying metal layer may be 0.50 deg or less, preferably 0.04 deg or less. If the half-value width exceeds 0.50 deg, the two-layer flexible substrate has a problem of reduced adhesion in a 150° C. heat resistance test.

The underlying metal layer preferably does not contain nitrogen. As a result, the heat-resistant adhesiveness of the two-layer flexible substrate is more likely to be improved. In addition, the two-layer flexible substrate is more likely to improve etching characteristics during wiring formation.

The method of providing the base metal layer is not particularly limited. For example, the base metal layer can be provided by laminating an alloy such as Ni on the surface of the insulating base material by sputtering. In this embodiment, the underlying metal layer is preferably provided by a high voltage pulse method. As a result, the plasma density during sputtering is likely to increase, and the ionization rate of sputtered particles is improved, so that the base metal layer can be formed in a plasma state completely different from that of the conventionally used DC method.

When the underlying metal layer is formed by the high voltage pulse method, the conditions for the high voltage pulse method are not particularly limited. In one example, deposition of the underlying metal layer may be performed at an average power density of 4 W/cm ² . At this time, by reducing the ratio (Ton/Ton+Toff) of the pulse time (Ton) to the pulse repetition time (Ton+Toff), processing with a maximum power density of 800 W/cm ² can be performed. The ratio of the maximum power density to the average power density of the pulse is preferably 200 or more. As a result, the plasma density in the atmosphere for forming the base metal layer is likely to be improved, and the ionization rate of the target material and the gas in the atmosphere is likely to be increased.

The effect of adopting the high voltage pulse method is considered as follows. That is, by adopting the high-pressure pulse method, plasma (mainly sputtered particles) during film formation can reach the substrate in a high-energy state. This allows the sputtered particles to adhere to the insulating substrate and then move around on the insulating substrate, so that the thin film can be formed in a more stable manner. As a result, the sputtered particles of the base metal (for example, Ni alloy) are arranged in a more stable manner and aligned with the (111) plane, thereby making the half width of the diffraction line smaller.

Also, in the high voltage pulse method, the instantaneous power can be easily adjusted by adjusting parameters. As a result, the high pressure pulse method can easily control the plasma state during film formation. In addition, the high-pressure pulse method makes it possible to easily adjust the crystalline state. As a result, according to the high-pressure pulse method, the underlying metal layer can be controlled to a crystalline state (half-value width) that is less susceptible to thermal changes, and the adhesion characteristics are likely to be improved.

Moreover, according to the high pressure pulse method, the ionization rate of the sputtering material during film formation is high at the same time. As a result, the two-layer flexible substrate is more likely to promote chemical bonding with the outermost layer of the insulating base material, thereby improving adhesion characteristics. That is, since the high voltage pulse method has a low duty ratio, the heat load during film formation can be reduced even with the same average power. Therefore, the brittle layer of the insulating base material is less likely to be formed, and a decrease in adhesion can be prevented. In the case of conventional plasma treatment and plasma during film formation, if the heat load is large, there is a possibility that the film surface will oligomerize and the film surface temperature will exceed the glass transition temperature. In this case, a brittle layer is formed on the surface layer portion of the insulating base material, and the strength of the surface layer portion of the insulating base material is reduced, which may result in deterioration of adhesion characteristics. On the other hand, with the high-pressure pulse method, it is possible to obtain good adhesion properties similar to polyimide (PI) films even with insulating substrates having a low glass transition temperature such as COP and PPS.

(copper conductor layer)
The copper conductor layer is laminated on the surface of the underlying metal layer.

The thickness of the copper conductor layer is not particularly limited. For example, the thickness of the copper conductor layer is preferably 50 nm or more, more preferably 100 nm or more. Also, the thickness of the copper conductor layer is preferably 500 nm or less, more preferably 400 nm or less. When the thickness of the copper conductor layer is within the above range, the copper conductive layer can easily obtain the necessary conductivity in the process of electrolytic Cu plating or the like. Also, copper conductive layers are easy to produce and easy to handle.

The X-ray diffraction half width of the crystal plane (111) of the copper conductor layer may be 0.40 deg or less, preferably 0.30 deg or less. When the half-value width exceeds 0.40 deg, the two-layer flexible substrate has reduced adhesion in a 150° C. heat resistance test.

The method of providing the copper conductor layer is not particularly limited. In one example, the copper conductor layer can be applied by a high voltage pulse method. This makes it easier to increase the plasma density during sputtering and improves the ionization rate of sputtered particles, making it possible to form a copper conductor layer in a completely different plasma state from the conventionally used DC method. .

For example, film formation of a copper conductive layer in Example 1, which will be described later, was performed at an average power density of 4 W/cm ² . Further, by reducing the ratio (Ton/Ton+Toff) of the pulse time (Ton) to the pulse repetition time (Ton+Toff), processing was performed at a maximum power density of 1000 W/cm ² . The ratio of the maximum power density to the average power density of the pulse was 250 or more. As a result, the plasma density in the atmosphere for Cu film formation can be greatly improved, and the ionization rate of the target material and gas in the atmosphere can be greatly increased.

The effect of using the high voltage pulse method is considered as follows. That is, by adopting the high-pressure pulse method, the plasma density during sputtering is likely to increase, and the ionization rate of the sputtered particles is improved. It becomes possible to form a film.

FIG. 2 is a graph obtained by measuring the plasma state during film formation in the DC method and the high-pressure pulse method with a plasma emission spectroscope for the copper conductor layer. The measurement conditions and Cu sputtering output (gas pressure, average power) are the same. A plasma emission monitor manufactured by HORIBA was used as a measuring instrument. Integration Time (ms) (exposure time) is 20 ms, Binning Level (sensitivity) is 50%, Cu sputtering conditions are average power density of 4 W/cm ² and gas pressure of 0.3 Pa.

As shown in FIG. 2, it is clear from the plasma emission state that the plasma state during film formation is completely different between the high voltage pulse method and the DC method. For example, looking at the emission peak at a wavelength of 324 nm, which is observed as the strongest peak in the wavelength range from 200 nm to 800 nm, the high pressure pulse method has a peak intensity ten times or more that of the DC method. This also shows that the high-pressure pulse method has a high plasma density during film formation.

The effects obtained by using high voltage pulses are considered as follows. That is, by adopting the high-pressure pulse method, plasma of higher density can be obtained. This allows the sputtered particles to reach the insulating substrate in a higher energy state, allowing the sputtered particles to adhere to the insulating substrate and then move around on the substrate. As a result, the copper conductor layer can be formed into a thin film in a more stable manner. In addition, Cu is arranged in a more stable manner in the copper conductor layer. Since Cu is a face-centered cubic lattice, it is preferentially arranged in the (111) plane corresponding to the closest packing plane of the face-centered cubic lattice, and the crystallites are aligned and a good crystal state is obtained. becomes smaller.

If the deposited Cu sputtered particles exist in a random microcrystalline state, the crystallinity tends to deteriorate and the half width tends to increase. In this case, the obtained two-layer flexible substrate does not have a uniform crystalline state due to heat, which is likely to cause deterioration in heat-resistant adhesion.

The area ratio of the (200) plane and the (111) plane of the Cu crystal plane immediately after film formation, calculated from the diffraction lines of X-ray diffraction, is preferably 0.2 or less, more preferably 0.1 or less. more preferred. When the area ratio is within the above range, the two-layer flexible substrate is less likely to deteriorate in heat-resistant strength, and easily suppresses changes in the orientation ratio due to heat.

The two-layer flexible substrate of the present embodiment may have a crystalline orientation ratio (K(200)/K(111)) of 0.2 or more after being exposed at 100° C. for 120 hours. Also, the orientation ratio may be 0.3 or less. If the orientation ratio exceeds 0.3, the two-layer flexible substrate has a problem of reduced adhesion in a 150° C. heat resistance test.

As described above, the two-layer flexible substrate of the present embodiment has good crystallinity. As a result, the two-layer flexible substrate is less likely to be changed by heat and has excellent heat-resistant adhesion. As a result, the two-layer flexible substrate can be applied to a flexible wiring board having wiring portions of narrow width and narrow pitch, and is industrially useful and highly reliable.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is by no means limited to these examples.

In the following examples, a roll-to-roll sputtering apparatus (MIC-350MS, Hirano Koon Co., Ltd.) was used for the plasma treatment step and the film formation of the Ni alloy layer (base metal layer) and the copper conductive layer. A target size of 750 cm ² was used.

The half width and orientation ratio of the Ni alloy layer and the copper conductive layer were adjusted by changing the plasma atmosphere during film formation using the high voltage pulse method. Specifically, by adjusting the pulse time (Ton), peak current value, and frequency, the instantaneous maximum power density is adjusted by changing the ratio of the pulse time (Ton) to the pulse repetition time (Ton + Toff) and the instantaneous maximum power. By doing so, the half width and orientation ratio of the Ni alloy layer and the copper conductive layer were adjusted.

<Example 1>
Plasma treatment is performed on one side of a 25 μm-thick polyimide film insulating substrate (manufactured by Ube Industries, Ltd., registered trademark “Upilex”) in a vacuum chamber in an oxygen gas atmosphere using a high-voltage pulse power supply. was performed (plasma treatment step).

Next, on the insulating substrate, in an argon gas atmosphere, a film was formed using a 7% by mass Cr—Ni alloy target using a high-voltage pulse power source so that the half-value width was 0.445 deg (Ni alloy layer deposition process). At this time, the average power density was 4 W/cm ² and the instantaneous maximum power density was 800 W/cm ² .

As a copper conductive layer, a copper film was formed on the Ni alloy layer using a Cu target and a high-voltage pulse power source in an argon gas atmosphere so that the half width was 0.255 deg and the thickness was 100 nm. (conductive layer forming step). At this time, the average power density was 4 W/cm ² and the instantaneous maximum power was 1000 W/cm ² . The orientation ratio (K(200)/K(111)) between the (111) plane and the (200) plane of the copper conductor layer is 0.05, and the orientation ratio (K( 200)/K(111)) was 0.27.

Subsequently, a Cu film was formed to a thickness of 20 μm on the sputtered copper conductive layer by electroplating. The obtained two-layer flexible substrate had an initial peel strength of 0.85 N/mm and a peel strength of 0.75 N/mm after the 150° C. heat resistance test.

<Example 2>
Plasma treatment is performed on one side of a 25 μm-thick polyimide film insulating substrate (manufactured by Ube Industries, Ltd., registered trademark “Upilex”) in a vacuum chamber in an oxygen gas atmosphere using a high-voltage pulse power supply. was performed (plasma treatment step).

Next, on the insulating substrate, in an argon gas atmosphere, a film was formed using a 7% by mass Cr—Ni alloy target using a high-voltage pulse power source so that the half-value width was 0.451 deg (Ni alloy layer deposition process). At this time, the average power density was 4 W/cm ² and the instantaneous maximum power density was 400 W/cm ² .

On this NiCr alloy layer, a copper film was formed as a copper conductive layer so that the half width was 0.268 deg and the thickness was 100 nm using a Cu target and a high voltage pulse power source in an argon gas atmosphere. (conductive layer forming step). At this time, the average power density was 4 W/cm ² and the instantaneous maximum power density was 650 W/cm ² . The orientation ratio (K(200)/K(111)) between the (111) plane and the (200) plane of the copper conductor layer is 0.07, and the orientation ratio (K( 200)/K(111)) was 0.30.

Subsequently, a Cu film was formed to a thickness of 20 μm on the copper conductive layer by electrolytic plating. The obtained two-layer flexible substrate had an initial peel strength of 0.83 N/mm and a peel strength of 0.70 N/mm after the 150° C. heat resistance test.

<Example 3>
Plasma treatment is performed on one side of a 25 μm-thick polyimide film insulating substrate (manufactured by Ube Industries, Ltd., registered trademark “Upilex”) in a vacuum chamber in an oxygen gas atmosphere using a high-voltage pulse power supply. was performed (plasma treatment step).

Next, on the insulating substrate, in an argon gas atmosphere, a film was formed using a 7% by mass Cr—Ni alloy target using a high-voltage pulse power source so that the half-value width was 0.445 deg (Ni alloy layer deposition process). At this time, the average power density was 4 W/cm ² and the instantaneous maximum power density was 800 W/cm ² .

On this NiCr alloy layer, a copper film was formed as a copper conductive layer so that the half-width was 0.235 deg and the thickness was 100 nm using a Cu target and a high-voltage pulse power source in an argon gas atmosphere. (conductive layer forming step). At this time, the average power density was 4 W/cm ² and the instantaneous maximum power density was 400 W/cm ² . The orientation ratio (K(200)/K(111)) between the (111) plane and the (200) plane of the copper conductor layer is 0.07, and the orientation ratio (K( 200)/K(111)) was 0.25.

Subsequently, a Cu film was formed to a thickness of 20 μm on the sputtered copper conductive layer by electroplating. The obtained two-layer flexible substrate had an initial peel strength of 0.83 N/mm and a peel strength of 0.74 N/mm after the 150° C. heat resistance test.

<Example 4>
Plasma treatment is performed on one side of a 25 μm-thick polyimide film insulating substrate (manufactured by Ube Industries, Ltd., registered trademark “Upilex”) in a vacuum chamber in an oxygen gas atmosphere using a high-voltage pulse power supply. was performed (plasma treatment step).

Next, on the insulating substrate, under an argon gas atmosphere, a film was formed using a 7% by mass Cr—Ni alloy target using a high voltage pulse power source so that the half width was 0.295 deg (Ni alloy layer deposition process). At this time, the average power density was 6 W/cm ² and the instantaneous maximum power density was 1200 W/cm ² .

As a copper conductive layer on this NiCr alloy layer, a Cu target is used and a high voltage pulse power supply is used in an argon gas atmosphere to form a copper film having a half width of 0.322 deg and a thickness of 100 nm. (conductive layer forming step). At this time, the average power density was 4 W/cm ² and the instantaneous maximum power density was 270 W/cm ² . The orientation ratio (K(200)/K(111)) between the (111) plane and the (200) plane of the copper conductor layer is 0.09, and the orientation ratio (K( 200)/K(111)) was 0.30.

Subsequently, a Cu film was formed to a thickness of 20 μm on the sputtered copper conductive layer by electroplating. The obtained two-layer flexible substrate had an initial peel strength of 0.85 N/mm and a peel strength of 0.69 N/mm after the 150° C. heat resistance test.

<Comparative Example 1>
Plasma treatment is performed on one side of a 25 μm-thick polyimide film insulating substrate (manufactured by Ube Industries, Ltd., registered trademark “Upilex”) in a vacuum chamber in an oxygen gas atmosphere using a high-voltage power supply. was performed (plasma treatment step).

Next, on the insulating substrate, under an argon gas atmosphere, a film was formed using a DC power supply using a 7 wt% Cr—Ni alloy target so that the half-value width was 0.729 deg (Ni alloy layer film formation process). At this time, the average power density was 4 W/cm ² .

On this NiCr alloy layer, a Cu target is used as a copper conductive layer, and a DC power source is used in an argon gas atmosphere to form a copper film having a half width of 0.461 deg and a thickness of 100 nm. (conductive layer forming step). At this time, the average power density was 4 W/cm ² . The orientation ratio (K(200)/K(111)) between the (111) plane and the (200) plane of the copper conductor layer is 0.10, and the orientation ratio (K( 200)/K(111)) was 0.32.

Subsequently, a Cu film was formed to a thickness of 20 μm on the sputtered copper conductive layer by electroplating. The obtained two-layer flexible substrate had an initial peel strength of 0.83 N/mm and a peel strength of 0.60 N/mm after the 150° C. heat resistance test.

<Comparative Example 2>
Plasma treatment is performed on one side of a 25 μm-thick polyimide film insulating substrate (manufactured by Ube Industries, Ltd., registered trademark “Upilex”) in a vacuum chamber in an oxygen gas atmosphere using a high-voltage pulse power supply. was performed (plasma treatment step).

Next, on the insulating substrate, under an argon gas atmosphere, a film was formed using a 7 wt% Cr—Ni alloy target using a high-voltage pulse power source so that the half-value width was 0.445 deg (Ni alloy layer deposition process). At this time, the average power density was 4 W/cm ² and the instantaneous maximum power density was 800 W/cm ² .

As a copper conductive layer on this NiCr alloy layer, a Cu target is used and a high-voltage pulse power source is used in an argon gas atmosphere to form a copper film having a half width of 0.412 deg and a thickness of 100 nm. (conductive layer forming step). At this time, the average power density was 4 W/cm ² and the instantaneous maximum power density was 40 W/cm ² . The orientation ratio (K(200)/K(111)) between the (111) plane and the (200) plane of the copper conductor layer is 0.21, and the orientation ratio (K( 200)/K(111)) was 0.38.

Subsequently, a Cu film was formed to a thickness of 20 μm on the sputtered copper conductive layer by electroplating. The obtained two-layer flexible substrate had an initial peel strength of 0.80 N/mm and a peel strength of 0.52 N/mm after the 150° C. heat resistance test.

<Comparative Example 3>
Plasma treatment is performed on one side of a 25 μm-thick polyimide film insulating substrate (manufactured by Ube Industries, Ltd., registered trademark “Upilex”) in a vacuum chamber in an oxygen gas atmosphere using a high-voltage power supply. was performed (plasma treatment step).

Then, on the insulating substrate, in an argon gas atmosphere, a film was formed using a DC power supply using a 7 wt% Cr—Ni alloy target so that the half-value width was 0.665 deg (Ni alloy layer film formation process). At this time, the average power density was 6 W/cm ² .

As a copper conductive layer on this NiCr alloy layer, a Cu target is used and a high-voltage pulse power source is used in an argon gas atmosphere to form a copper film having a half width of 0.447 deg and a thickness of 100 nm. (conductive layer forming step). At this time, the average power density was 4 W/cm ² and the instantaneous maximum power density was 160 W/cm ² . The orientation ratio (K(200)/K(111)) between the (111) plane and the (200) plane of the copper conductor layer is 0.23, and the orientation ratio (K( 200)/K(111)) was 0.44.

Subsequently, a Cu film was formed to a thickness of 20 μm on the sputtered copper conductive layer by electroplating. The obtained two-layer flexible substrate had an initial peel strength of 0.79 N/mm and a peel strength of 0.48 N/mm after the 150° C. heat resistance test.

For the two-layer flexible substrates produced in the above examples and comparative examples, the film thickness, adhesion strength, heat resistance, and Ni alloy layer of the Ni alloy layer and the Cu conductor layer are analyzed by X-ray diffraction analysis by the following method. Half-value width of the diffraction peak of the crystal lattice (111) plane, the half-value width of the diffraction peak of the Cu crystal lattice (111) plane obtained by X-ray diffraction analysis in the copper conductor layer, the copper conductor layer obtained by X-ray diffraction analysis The orientation index ratio between the (111) plane and the (200) plane of the fcc structure obtained was measured. The results are shown in Tables 1-3.

(adhesion strength)
After the base metal layer and the copper conductor layer were formed on the insulating base material, copper was plated to a thickness of 20 μm by electroplating on the film forming surface side. After that, it is cut into strips with a width of 5 mm, and a peel strength tester (Autograph tensile tester, AGS-100G, manufactured by Shimadzu Corporation) is used to measure the separation between the insulating base material and the metal side including the plating. The peel strength (peel strength) was measured by pulling at a speed of 50 mm/min at 180° peeling.

(Heat-resistant)
For heat resistance, a sample was prepared by the method shown in the method for measuring adhesion strength, and the obtained sample was heat-treated by holding it in an oven at 150 ° C. for one week, taken out, and allowed to stand until it reached room temperature. The adhesion strength of the sample was measured by the same method as above. The adhesion strength (%) of the sample after heat treatment relative to the adhesion strength of the sample before heat treatment was calculated to evaluate the heat resistance.

(Half width of diffraction peak of Ni crystal lattice (111) plane obtained by X-ray diffraction analysis in Ni alloy layer)
It was measured using an X-ray diffractometer (RINT-Ultima III, manufactured by Rigaku Denki Co., Ltd.). The Ni alloy side of the substrate was irradiated with characteristic X-rays of CuKα rays, and the half-value width was derived from the diffraction line of the (111) plane of the Ni crystal lattice appearing near 2θ=44.5°. Since the diffraction peak of Ni and the diffraction peak of Cu are close to each other, an accurate value cannot be calculated because they overlap. Measurement was carried out on a film formed of Ni alone as described above.

(Half width of diffraction peak of Cu crystal lattice (111) plane obtained by X-ray diffraction analysis in copper conductor layer)
It was measured using the same device and method as the half-value width of the Ni alloy layer. The half width was calculated from the maximum peak of the diffraction spectrum of the (111) plane of the Cu crystal lattice appearing around 2θ=43.3°. The thickness of the copper conductor layer at this time was adjusted to 100 nm.

(Orientation index ratio between (111) plane and (200) plane of fcc structure obtained by X-ray diffraction analysis in copper conductor layer)
It was measured and calculated using an X-ray diffractometer (RINT-Ultima III, manufactured by Rigaku Denki Co., Ltd.). For the (111) plane, the peak of the diffraction spectrum of the Cu crystal lattice (111) plane appearing near 2θ=43.3° is taken, and for the (200) plane, the peak of the diffraction spectrum appearing near 2θ=50.4° is taken. It was calculated from the respective area ratios from the peaks. In addition, a base metal layer and a copper conductor layer were formed on an insulating substrate, and copper was plated to a thickness of 20 μm by electrolytic plating. .

As shown in Tables 1 to 3, the two-layer flexible substrate of the present invention exhibited excellent adhesion and heat resistance of 80% or more. Therefore, the two-layer flexible substrate of the present invention can be applied to a flexible wiring board having narrow width and narrow pitch wiring portions, and is industrially useful and more reliable.

Claims (2)

an insulating base material having a plasma-treated surface;
a base metal layer laminated on the plasma-treated surface of the insulating base;
A copper conductor layer laminated on the surface of the underlying metal layer,
The X-ray diffraction half width of the crystal plane (111) of the base metal layer is 0.40 to 0.50 deg,
The crystal plane (111) of the copper conductor layer has a half width of 0.20 to 0.50 deg by X-ray diffraction,
A two-layer flexible substrate having a crystalline orientation ratio (K(200)/K(111)) of 0.2-0.3 after exposure at 100° C. for 120 hours. 2. The two-layer flexible substrate of claim 1, wherein the underlying metal layer does not contain nitrogen.

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