JP2006339304A - Metal material for printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal material for printed circuit board where the copper alloy foil including smooth surfaces and having heat resistance property is plated by Ni or Ni-alloy. <P>SOLUTION: In the metal material for printed circuit board, at least one surface of the rolled copper alloy foil, which is not softened even when it is heated for an hour at 300°C, is finished as the glossy surface. The surface thereof is plated by Ni or Ni alloy of 0.3 μm or more. The surface roughness is 0.10 μm or less in terms of Ra, and the a value of the relative skewness (Rsk) of the surface roughness is a negative value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to the surface of a heat-resistant copper alloy foil used for a printed wiring board.

Various electric and electronic devices such as mobile phones are rapidly becoming lighter and thinner. The development is supported by microfabrication technology for various semiconductor components, multilayer technology for printed circuit boards on which semiconductor components are mounted, and high-density mounting technology for passive components on printed circuit boards.
With the remarkable development of semiconductor materials, electrical and electronic parts are required to be further miniaturized and mounted with high density, and such demands can be satisfied by miniaturization of the passive parts. It was gone.

As one of the attempts to meet such demands, passive components (for example, inductors, capacitors, resistors, etc.) that occupy a large mounting area are built in the inner layer of the printed wiring board to achieve substantial high-density mounting and cost reduction. Efforts are being made to achieve performance improvements.
With regard to the technology for incorporating components, for example, as a method of providing a capacitor on a printed wiring board, a method of attaching an external capacitor such as a chip capacitor to the printed wiring board, or using a high dielectric constant material for the inner layer of the printed wiring board There is known a method of giving a printed circuit board itself a capacitor function. In view of the recent miniaturization of electronic products, the latter method using a high dielectric constant material as an inner layer to form a capacitor is desirable.
Various methods for incorporating a dielectric layer into a printed wiring board have been studied, but a dielectric resin is applied onto a film on which an electrode has been formed in advance and then cured in the second half. After further forming an electrode on the film, it is transferred to the substrate. Japanese Patent Application Laid-Open No. H10-228707 discloses a method for performing the above.
However, since the smoothness of the copper foil directly affects the quality of the capacitor when the electrode is formed, the smoothness of the copper foil becomes a problem.

  Resistance produced by laminating a copper foil with a resistance layer formed by forming a material layer (referred to as a resistance layer) for forming a resistance circuit on one or both sides of a copper foil for forming a conductor circuit on a resin substrate A circuit-embedded printed wiring board is known. This printed wiring board is generally manufactured as follows. First, the surface of the copper foil on the resistance layer side and a base material made of an insulating resin are laminated to form a copper-clad laminate. Next, primary etching is performed with a predetermined etchant to form a predetermined circuit pattern in which the copper foil and the resistance layer are integrated, and then a conductor circuit (copper circuit (copper copper) located on the surface side of the circuit pattern is formed. The foil) is subjected to secondary etching to selectively remove only the necessary portion of the copper foil, and the resistance layer at that portion is left behind. Thereafter, an insulating base material is further laminated on the entire surface, and a resistance layer is incorporated.

JP 11-26943 A

  Conventionally, copper foils (base copper foils) used for printed wiring boards of such electric / electronic parts include electrolytic copper foils and rolled copper foils. Generally, an electrolytic copper foil is manufactured by continuously depositing Cu on a surface of a rotating drum made of Ti or stainless steel to form a copper foil, and then continuously peeling the copper foil. ing. The manufactured copper foil has a rough surface on the electrolytic plating solution side. However, since the surface of the rotating drum has streaky irregularities due to corrosion of the electrolytic solution or the like, the surface roughness of the glossy surface to which it is transferred is very rough compared to the rolled copper foil described later.

  Recently, flatness has been demanded on the surface of the copper foil, and an additive for making electrodeposits finer is added to the electrolytic plating solution to grow a smooth plating so that the surface on the electrolytic plating solution side Electrolytic copper foil used as a glossy surface is also used. However, the surface roughness is generally smoother than the electrolytic copper foil, but is generally rougher than the rolled copper foil.

On the other hand, for the rolled copper foil, an ingot is melted and formed into a plate by hot rolling, and then recrystallization annealing and cold rolling are repeated, and finally the foil having a desired thickness is finished by cold rolling. Thus, since it is manufactured by plastic working with a rolling roll, it is known that a smooth surface in which the surface form of the rolling roll is transferred to the surface of the foil is obtained.
However, unlike the electrolytic copper foil, the softening temperature is relatively low at about 150 ° C. When flexibility is required as in FPC, the softening temperature is low, and softening at the time of bonding or resin curing is an advantageous characteristic.

However, in order to impart a capacitor function to the surface of the copper foil, if the resin containing the dielectric is cured or if the dielectric is softened at that temperature when formed by sputtering or the like, the copper foil will be deformed. This is not preferable because there are cases. The curing temperature of the resin varies depending on the type of resin, but considering the heat resistance during use, a resin that cures at a high temperature is desirable, and treatment at a high temperature of 300 ° C. to 400 ° C. is increasing. A rolled copper foil such as tough pitch copper cannot withstand this temperature and deforms.

In addition, resin curing is often performed in the air. In that case, oxidation of the copper surface is also a problem. For example, in the case of a capacitor, oxygen may be supplied through the resin, and the copper surface is oxidized. If it becomes like this, the performance as a capacitor cannot be obtained. The same applies to the resistance layer, and oxidation of the copper surface is not preferable.
In order to prevent this, it is necessary to heat in an inert gas such as nitrogen or argon, which has the disadvantage of increasing capital investment.

Accordingly, an object of the present invention is to provide a metal material for a printed wiring board in which a copper alloy foil having a smooth surface and heat resistance is subjected to Ni or Ni alloy plating.

As a result of diligent research, the inventor has found that the surface roughness relative skewness (indicating the smoothness of the surface of the copper alloy foil for printed wiring boards subjected to Ni or Ni alloy plating with a smooth surface and heat resistance ( It has been found effective to use the value of Rsk). The value of relative skewness (Rsk) was defined.

That is, the present invention (1) finishes at least one surface of a rolled copper alloy foil that does not soften even when heated at 300 ° C. for 1 hour to a glossy surface, and Ni or Ni alloy plating of 0.3 μm or more is applied to the surface, A metal material for a printed wiring board, characterized in that the surface roughness Ra is 0.10 μm or less and the value of the surface roughness relative skewness (Rsk) is negative,
(2) The metal composition for printed wiring boards according to (1) above, wherein the chemical composition of the copper alloy foil is 0.05 to 0.25% by mass of Sn balance Cu and unavoidable impurities,
(3) The chemical composition of the copper alloy foil is 0.02 to 0.4% by mass of Cr and 0.01 to 0.25% by mass of Zr, the balance being Cu and unavoidable impurities It is a metal material for printed wiring boards as described in (1).

According to the present invention, by using a metal material for printed wiring boards in which a copper alloy foil having a smooth surface and heat resistance is subjected to Ni or Ni alloy plating, passive components (for example, inductors, capacitors, etc.) are formed on the inner layer of the printed wiring board. , Resistors, etc.) can be built in.

The reasons for limitation are shown below.
(1) Surface Roughness The alloy foil used for the printed wiring board is subjected to roughening plating on one surface and is in close contact with the resin. On the other surface, for example, in the case of a passive component built-in substrate, a capacitor, an inductance, a resistance, and the like are mounted.
In particular, in order to mount the capacitor on the surface, the surface of the copper alloy foil is required to be smooth. This is because, when the surface roughness of the foil is rough, it is affected by the surface roughness when mounting the electrodes of the capacitor, and a stable distance between the electrodes, which is an important characteristic of the capacitor, cannot be secured. Accordingly, it is necessary to finish the one side on which the copper alloy foil capacitor or the like is mounted with a glossy surface. It is desirable that the roughness of the surface after Ni or Ni alloy plating described below is applied to this surface is 0.1 μm or less, preferably 0.06 μm or less in terms of Ra.

Furthermore, in the case of a capacitor, if there is a portion where the thickness of the capacitor film is thin, the portion may be destroyed or current may leak when a voltage is applied. This may be caused by protrusions and depressions on the surface of the copper foil serving as the substrate. Accordingly, it is desirable that the surface roughness of the copper foil be a curved convex distribution above the upward convex convex distribution, that is, a convex concave distribution below. This can be indicated by surface roughness relative skewness (Rsk). Rsk is a value indicating the relativity of the amplitude distribution curve with respect to the average line and can be expressed by the following equation.

FIG. 1A shows a schematic diagram of the surface shape when Rsk is positive, but the protrusion shape is a projection shape upward. On the other hand, when Rsk is negative, as shown in FIG. 1 (b), the projection has a concave shape downward, and a flat portion of the surface shape is seen on the surface.
If a capacitor is formed on a flat portion of the surface seen when Rsk is negative, a stable one can be secured.

  In addition, roughness indices such as Rmax, Rz, and Ry other than Ra and Rsk also have a large effect on capacitor performance. These are indicators that are greatly influenced by the maximum roughness, and it is apparent that a smaller capacitor is preferable. However, since the values of these indexes vary greatly depending on the position to be evaluated and the evaluation length, they are not used here because they have large variations compared to the average roughness indexes Ra and Rsk. However, it does not exclude the provision of these values.

  Such a surface shape in which Rsk has a negative value can be obtained by adjusting the surface shape of the rolling roll transferred during final rolling. However, in the present invention, not only Rsk but also Ra is defined, and in order to satisfy both conditions, the surface roughness of the rolling roll may be reduced. It is also effective to apply bright plating to the roll surface. Furthermore, adjustment is possible by selecting the roll diameter of the rolling roll and controlling the rolling oil viscosity and rolling speed.

(2) Ni or Ni alloy plating By applying Ni and Ni alloy plating to the alloy foil, Cu oxidation of the glossy surface at high temperature can be prevented.
This is because oxidation of the glossy surface adversely affects the mounting of the capacitor and the resistance layer.
Furthermore, since surface smoothness is required for mounting, it is more preferable to use a plating that can provide gloss for Ni or Ni alloy plating. For example, in the case of Ni plating, it is effective to use bright plating that adds an additive to the plating bath to give the plating film a gloss. Further, when alloy plating such as Ni-P is performed, the electrodeposited grains can be made finer, the surface can be smoothed, and the diffusion barrier ability due to the heat of Cu is higher than that of Ni plating. can do. In addition to Ni-P plating, Ni alloy plating such as Ni-Fe plating or Ni-Co plating may be used.

(3) Heat resistance of the metal foil Since the metal foil is subjected to a high temperature environment of 300 ° C. or higher in order to cure the resin or to sinter oxide such as BTO which is a capacitor component, The condition is that it does not soften at least at 300 ° C. Here, softening refers to a reduction to 60% or less of the tensile strength before heating due to heating.
In the present invention, a rolled copper alloy foil that does not soften even when heated at 300 ° C. for 1 hour is specified. Specifically, it is shown below.

(A) Copper foil containing Sn The heat resistance of Cu improves by adding Sn. As an effect, the amount of decrease in tensile strength when heated at 300 ° C. for 1 hour becomes small, and it becomes possible to maintain a tensile strength of 350 MPa or more by adding 0.05 mass% or more of Sn. This tensile strength level is 50% higher than when Ag is added (Japanese Patent Application No. 2001-216411).
Higher than MPa. Considering the effect of improving the strength after rolling as described above, the preferable Sn addition amount is 0.05% by mass or more, and the upper limit value of Sn is determined from the target conductivity.
As for impurities of this copper alloy, it is desirable that O is 60 ppm or less, S is 10 ppm or less, and the total concentration of Bi, Pb, Sb, Se, As, Fe, and Te is 10 ppm or less.

(B) Copper foil containing Cr and Zr It is a copper alloy obtained by adding 0.02% to 0.4% by mass of Cr and 0.01 to 0.25% by mass of Zr to pure copper, with the balance being copper and inevitable impurities In the case of the alloy, the heat resistance is further improved and there is almost no decrease in tensile strength even after heating at 350 ° C. for 1 hour.
Furthermore, the total amount of one or more elements such as Zn, Ni, Ti, Sn, Si, Mn, P, Mg, Co, Te, Al, B, In, Ag, and Hf is 0.005% by mass to 1.5% by mass. If it contains, it is possible to further improve the strength, and it is more advantageous when strength is required. Further, since there is no adverse effect on heat resistance, addition of these third elements is not excluded.

  An ingot having the composition shown in Table 1 was melted and formed into a plate by hot rolling, and then recrystallization annealing and cold rolling were repeated. Finally, the material was finished to a thickness of 35 μm by cold rolling. In the final pass of the final rolling process, the surface roughness was adjusted using rolling rolls having different roughness. Comparative Example No. For the foils 3 to 5, the rolling degree in the final rolling step is 90%, the surface roughness Ra of the rolling roll in the final pass is 0.10 μm, the rolling oil viscosity is 8.0 cst, and the roll biting angle is 0 0058 rad, the rolling speed was 600 m / min. On the other hand, Invention Example No. The foils 6 to 11 have a negative Rsk value with a rolling roll surface roughness Ra of 0.02 μm, a rolling oil viscosity of 6.5 cst, a roll biting angle of 0.0031 rad, a rolling speed of 500 m / min. Rolled as follows.

Further, Comparative Example No. 1, 2, 4, 5 and Invention No. 6 and 7, Ni plating having a thickness shown in Table 4 was applied using a Watt bath having a bath composition shown in Table 2 under conditions of a current density of 5 A / dm ² and a bath temperature of 55 ° C. In addition, Invention Example No. For 8, 9, and 11, Ni plating having a thickness shown in Table 3 was applied using the gloss watt bath shown in Table 2 under the conditions of a current density of 5 A / dm ² and a bath temperature of 55 ° C. Furthermore, Invention Example No. 10 was subjected to Ni-P plating with the thickness shown in Table 4 under the conditions of a current density of 5 A / dm ² and a bath temperature of 55 ° C. using the Watt bath shown in Table 3.

The surface after plating was measured according to JIS standard (B0601) using a stylus type surface roughness meter.
Capacitor parts were assembled using this copper foil and the performance was confirmed. The results are shown in Table 4.

Legend: Foil deformation ×: Deformation by heating ○: No deformation (300 ° C x 1h)
A: Deformation-free component performance up to higher temperature (350 ° C. × 1 h) ×: Yield 10% or less Δ: Yield 10-60%
○: Yield 60-80%
: Yield 80% or more

Invention Example No. 6 to 11 are alloys having a composition satisfying claim 2, satisfying the condition of not softening even when heated at 300 ° C. for 1 hour according to claim 1, and surface roughness (Ra) after Ni or Ni alloy plating And Rsk) are within the scope of the claims, and good results were obtained. Furthermore, Invention Example No. In Nos. 8 to 10, since the bright Ni plating is used for the Ni plating, Ra satisfies 0.05 μm or less. It was better than 5-7.
Invention Example No. 11 is an alloy having a composition satisfying claim 3 and can withstand high temperature processing.

On the other hand, Comparative Example No. 1-2 are electrolytic copper foils and are examples in which the surface roughness Ra is not satisfied, and good results were not obtained. In particular, no. Although 2 is a smooth electrolytic copper foil, it was a performance that did not reach the example of the present invention.
Comparative Example No. Although 3 is a rolled copper foil made of pure copper, the surface roughness Ra is within the scope of the claims, but when heated at 300 ° C. for 1 hour, it softens and is not suitable for this application.
Comparative Example No. 4 is an alloy having a composition satisfying claim 5, but since Ni plating was not applied, copper oxidation occurred at the time of component mounting, and the component performance could not be satisfied.
Comparative Example No. Although 5 is an alloy having a composition satisfying claim 5, the roughness after Ni plating did not satisfy claim 1, and therefore the performance of the parts was not sufficient.

It is a schematic diagram which shows the difference in the measurement surface shape by the positive / negative of Rsk.

Claims (3)

At least one surface of the rolled copper alloy foil that does not soften even when heated at 300 ° C. for 1 hour is finished to a glossy surface, and Ni or Ni alloy plating of 0.3 μm or more is applied to the surface, and the surface roughness is 0 in terms of Ra. A metal material for a printed wiring board, which is 10 μm or less and has a negative surface roughness relative skewness (Rsk) value. 2. The metal material for a printed wiring board according to claim 1, wherein the chemical composition of the copper alloy foil is 0.05 to 0.25 mass% of Sn remaining Cu and unavoidable impurities. The chemical composition of the copper alloy foil is 0.02 to 0.4% by mass of Cr and 0.01 to 0.25% by mass of Zr, with the balance being Cu and inevitable impurities. The metal material for printed wiring boards as described.

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