JP4539960B2 - Metal materials for printed wiring boards - Google Patents

Description

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

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 wiring boards on which semiconductor components are mounted, and high-density mounting technology for passive components on printed wiring 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, so that substantial high-density mounting and cost reduction are possible. 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.
JP 11-26943 A

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.

Conventionally, copper foils (base copper foils) used for printed wiring boards of such electric / electronic parts include electrolytic copper foils and rolled copper foils. In general, an electrolytic copper foil is manufactured by continuously depositing a copper foil on the surface of a rotating drum made of Ti or stainless steel by continuously electrodepositing Cu, and then peeling the copper foil continuously. ing. The produced copper foil usually has a glossy surface on the rotating drum side and 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, although the surface roughness is smoother than that of a normal electrolytic copper foil, it is generally rougher than that of a 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 is finished to a desired thickness 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 a flexible printed circuit (FPC), the softening temperature is low, and softening at the time of adhesion 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 some 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.

  Therefore, 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 plated with Ni.

  As a result of intensive studies, the inventor found a metal material suitable for a printed wiring board by applying a copper alloy foil having a smooth surface and heat resistance and Ni plating.

That is, the present invention
(1) Even if heated at 300 ° C. for 1 hour, the tensile strength after heating does not decrease to 60% or less of the tensile strength before heating. Ni plating of 3 μm or more, and the surface roughness of the Ni plating is 0.15 μm or less in Ra. (2) Ni plating applied to the glossy surface is a nickel plating brightener The metal material for a printed wiring board according to (1) above, wherein the surface roughness of the Ni plating is Ra of 0.10 μm or less because the Ni plating is performed using a watt bath containing
(3) The chemical composition of the copper alloy foil is 0.05 to 0.25% by mass of Sn balance Cu and unavoidable impurities, and for printed wiring boards according to (1) to (2) above Metal material.
(4) 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, and the balance is Cu and inevitable impurities. (1) It is a metal material for printed wiring boards as described in (2).

  According to the present invention, by using 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 plating, passive components (for example, inductors, capacitors, resistors) are formed on the inner layer of the printed wiring board. 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 the electrodes of the capacitor are mounted, and a stable distance between the electrodes, which is an important characteristic of the capacitor, cannot be secured. Therefore, one side of the copper alloy foil on which the capacitor or the like is mounted on the copper alloy foil needs to be finished to a glossy surface. Since the surface of the Ni plating after the Ni plating shown below is applied to the glossy surface is also smooth, the surface roughness is preferably 0.15 μm or less in terms of Ra. Furthermore, Ra is preferably 0.10 μm or less. Here, Ra is selected as the surface roughness index because the average smoothness of the surface has the greatest influence on the mounting of capacitors and the like. However, Rz (10-point average roughness) and Ry (maximum roughness) can be evaluated in a pseudo manner. This is because Ra (arithmetic mean roughness) is also increased as a result in the case of a surface having a specifically rough portion, and the specifically rough portion is disadvantageous at the time of mounting. Accordingly, Ra can be paraphrased as Rz, Ry, or another roughness index. Of course, it is clear from the object of the invention that Ra is most suitable as an index.
From the viewpoint of smoothness, the present invention is limited to a rolled copper alloy foil that can provide a smooth surface.

(2) Ni plating By subjecting the alloy foil to Ni plating, Cu oxidation of the glossy surface at a 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 smoothness of the surface is required for mounting, it is more preferable to use bright Ni plating for Ni plating. That is, by using glossy Ni plating for the rolled foil, the surface roughness Ra of the glossy surface can be 0.12 μm or less and Rz can be 0.7 μm or less, and the yield of mounted components such as capacitors and resistors can be improved.

  Here, it is also possible to apply Ni alloy plating, for example, alloy plating such as Ni—P or Ni—Co. However, since the method of controlling the gloss and the method of stabilizing the composition are difficult as compared with the simple Ni plating, the Ni plating and the bright Ni plating are used here.

(3) Heat resistance of the metal foil The metal foil is subjected to a high temperature environment of 300 ° C. to 400 ° C. in order to cure the resin. Here, softening refers to a reduction to 60% or less of the tensile strength before heating due to heating.
In this invention, the rolled copper alloy foil which does not soften even if it heats at 300 degreeC for 1 hour is prescribed | regulated. Specifically, it is shown below.

(A) Copper foil containing Sn The heat resistance of Cu improves by adding Sn. As its 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 with the addition of 0.05 mass% or more of Sn. This level of tensile strength is 50 MPa or more higher than when Ag is added (Japanese Patent Application No. 2001-216411). Considering the effect of improving the strength after rolling as described above, the preferable Sn addition amount is 0.05 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, one or more elements such as Zn, Ni, Ti, Sn, Si, Mn, P, Mg, Co, Te, Al, B, In, Ag, and Hf are added in a total amount of 0.005% by mass to 1.5% by mass. If it is contained, 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.

Furthermore, Ni plating having a thickness shown in Table 3 was applied using a Watt bath having a bath composition shown in Table 2 under the conditions of a current density of 5 A / dm ² and a bath temperature of 55 ° C. Further, Ni plating having the thickness shown in Table 3 was applied using the gloss watt bath shown in Table 2 under the conditions of current density bath temperature and 55 ° C.
Capacitor parts were assembled using this copper foil and the performance was confirmed. The results are shown in Table 3.

Invention Example No. 6 to 9 are alloys having a composition satisfying claim 4, satisfying the condition of not softening even when heated at 300 ° C. for 1 hour according to claim 1, and surface roughness (Ra, Rz) after Ni plating Was in the scope of the claims, so good results were obtained. Furthermore, Invention Example No. In Nos. 8 to 9, since the bright Ni plating was used for the Ni plating, Ra satisfies 0.1 μm or less. It was better than 5-7.
Invention Example No. 10 is an alloy having a composition satisfying claim 5 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 tough pitch 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 was oxidized during 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 Ni plating thickness does not satisfy claim 1, and therefore, the oxidation performance of copper is not sufficient, so that the component performance is not sufficient.

Claims (4)

  In a rolled copper alloy foil in which the tensile strength after heating does not decrease to 60% or less of the tensile strength before heating even when heated at 300 ° C. for 1 hour, at least one surface is finished to a glossy surface, and 0.3 μm or more is formed on the surface A metal material for a printed wiring board, characterized in that the surface roughness of the applied Ni plating is 0.15 μm or less in terms of Ra. The Ni plating applied to the glossy surface is Ni plating performed using a Watt bath containing a nickel plating brightener, whereby the surface roughness of the Ni plating is Ra of 0.10 μm or less. The metal material for printed wiring boards as described. The metal composition for a printed wiring board according to claim 1 or 2, wherein the chemical composition of the copper alloy foil is 0.05 to 0.25% by mass of Sn balance Cu and unavoidable impurities. The chemical composition of the copper alloy foil, 0.02 to 0.4 mass% of Cr and 0.01 to 0.25 wt% of Zr, claim the balance being a Cu and unavoidable impurities 1 or 2. The metal material for printed wiring boards according to 2.