JP2005138310A - Copper foil for electronic part - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a copper foil for an electronic part stable in its structure, excellent in heat resistance, causing no shrinkage, not changing a wiring pitch and excellent in dimensional stability even if heat-treated at a high temperature by employing a two-layered structure in FPC or TAB. <P>SOLUTION: The rolled copper foil containing 10 wt.ppm or below of oxygen and 0.01-0.20 wt.% of Zr and used in the lamination with a polyimide film is preliminarily heat-treated at 350-550°C before laminated to the polyimide film to recrystallize and organize copper crystal particles. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a copper foil for electronic parts used as a conductor for wiring patterns such as FPC (flexible printed wiring board) and TAB (Tape Automated Bonding).

  For FPC and TAB, in which wiring patterns are formed by bonding copper foil to polyimide resin film, etc., and etching copper foil as wiring materials and IC packaging materials for miniaturization, weight reduction, and densification of electronic devices These film carriers are widely used.

  In many cases, a rolled copper foil that is more flexible than an electrolytic copper foil is used as a copper foil used for a film carrier for FPC or TAB. The rolled copper foil material is made of tough pitch copper (oxygen concentration 100-500 ppm by weight), oxygen-free copper (oxygen concentration 10 ppm by weight or less), or a trace component added to oxygen-free copper to increase the softening temperature of oxygen-free copper. A lowered one is used (for example, see Patent Document 1), and after hot rolling these ingots, cold rolling and annealing are repeated to a predetermined thickness to produce a rolled copper foil. Thereafter, the surface of the rolled copper foil is roughened to improve the adhesion to the resin substrate. The copper foil after the rough plating is cut and then bonded to the resin substrate. For the bonding of the copper foil and the resin, for example, an adhesive made of a thermosetting resin such as epoxy is used, and after the bonding, it is cured by heating at a temperature of 130 to 170 ° C. for several hours to several tens of hours. . Next, various circuit patterns are formed by etching the copper foil.

As described above, a three-layer structure in which a polyimide resin substrate film and a copper foil are laminated via an adhesive layer made of an epoxy resin or the like has been conventionally used as a structure of an FPC or a film carrier. However, in recent years, a two-layer structure in which a polyimide resin layer and a copper foil are directly laminated without using an adhesive layer with inferior heat resistance due to reasons such as the use of lead-free solder having a higher melting point than conventional solders is widely used. It has come to be used.
JP 2001-262296 A

  In the case of a two-layer structure, the polyimide resin is directly bonded to the copper foil, so that it is necessary to pressurize at a temperature of 300 ° C. or higher during production. However, since the softening temperature of the conventionally used rolled copper foil is 250 ° C. or less, the structure of the copper foil after heating is not stable, and the strength may drop and the subsequent line handling may deteriorate. .

  In addition, the two-layer structure is excellent in dimensional stability as compared with the conventional three-layer structure, but the dimensional stability during use becomes a problem due to the progress of fine pitch. In other words, after pattern formation, heat treatment when bonding printed wiring boards or mounting an integrated chip with a narrow pitch is performed at a high temperature (about 250 ° C.) by using lead-free solder. Tend to be. At this time, the copper foil forming the circuit has a tendency to shrink by heating, and the pitch of the wiring patterns changes during use, and there is a problem that the wiring patterns cannot be connected stably.

  Accordingly, the object of the present invention is to provide a stable structure and excellent heat resistance even when heat treatment is performed at a high temperature by adopting a two-layer structure, and to achieve dimensional stability without changing the wiring pitch without causing shrinkage of copper foil It is in providing the copper foil for electronic components excellent in.

In order to achieve the above object, the present inventors have taken the following two measures.
First, the crystal structure of copper foil is not affected by conventional carbon-free copper or tough pitch copper as a copper foil material, but by adding an additive element that increases the heat-resistant temperature, even if heat treatment is performed at a temperature of about 300 to 400 ° C. To stabilize.
Secondly, the shrinkage of the copper foil due to heating when using the copper foil is thought to be due to the recrystallized texture of the copper crystal grains constituting the copper foil after the rolling process. By performing heat treatment in advance and shrinking the copper foil to recrystallize the copper crystal grains when the copper foil is used, shrinkage due to heating during use is suppressed.

  That is, the copper foil for electronic components of the present invention is a rolled copper foil having an oxygen content of 10 ppm by weight or less, containing 0.01 to 0.20 wt% of Zr, and being bonded to a resin substrate. The copper crystal grains are recrystallized by heat treatment at a predetermined temperature before being bonded to the resin substrate.

  In the two-layer structure, the predetermined temperature is equal to or higher than the temperature at which the resin substrate is manufactured by the casting method, specifically, for example, 350 ° C. or higher and 550 ° C. or lower, particularly 400 ° C. or higher and 500 ° C. or lower. preferable.

  The resin substrate can be a polyimide film.

  According to the copper foil for electronic parts of the present invention, the heat-resistant temperature is improved because a predetermined amount of Zr is added, and when the polyimide resin and the copper foil are bonded or when the printed wiring boards are joined together, However, the crystal structure of the copper foil is stable and the strength does not drop.

  In addition, before the copper foil is bonded to the resin substrate, the copper foil is preheated at a predetermined temperature and the crystal grains of the copper foil are recrystallized in advance. Can be suppressed. Therefore, the dimensional stability is excellent without changing the wiring pitch.

The present invention will be described with reference to examples.
An oxygen-free copper having an oxygen content of 10 ppm was used as a base material, and Zr was added in an amount of 0.01 to 0.20 wt%, followed by melt casting. The ingot was hot-rolled and processed into a material having a thickness of 12 mm, and then processed by a method of repeating cold rolling and annealing to produce a fabric material having a thickness of 200 μm. Furthermore, after this dough material was annealed, it was cold-rolled to a thickness of 10 μm to prepare a sample.

  About the sample copper foil manufactured as mentioned above, initial tensile strength at normal temperature, softening temperature, and tensile strength after heating at 450 ° C. for 4 hours were examined. Further, the amount of shrinkage after heat treatment at 250 ° C. for 30 minutes was measured. For the measurement, marking was performed with a span of about 200 mm, and the difference before and after heating was compared. 250 ° C. for 30 minutes is a temperature simulating the temperature at the time of joining. The results are shown in Table 1.

From the results in Table 1, sample No. The heat-resistant temperatures of 1 to 5 are all 350 ° C. or higher, and it can be seen that the structural influence is generally small at a temperature of 350 ° C. at which polyimide is cast. In addition, each sample had a sufficient strength of 300 N / mm ² after 4 hours at 450 ° C. Furthermore, it was confirmed that the amount of shrinkage before and after reheating at 250 ° C. for 30 minutes was −0.03%, and the dimensional stability was excellent.

  Next, sample Nos. Sample No. 1 in which the amount of Zr added was lower than 1-5. Sample Nos. 6 and 7 with a large amount of addition. 8 was examined for applicability. In addition, as a conventional material, Sample No. The amount of dimensional change during heating of No. 9 was confirmed. The results are shown in Table 2.

  From the results in Table 2, the sample No. In 6 and 7, the softening temperature is 250 ° C. or lower, and the strength is lowered at the temperature at which the polyimide is cast. For this reason, since subsequent line handling property deteriorates, application is difficult. Even if the handling property is improved by increasing the thickness of the copper foil, the softening temperature is 250 ° C or lower, so when the bonding temperature is high, such as lead-free solder, the structure is not stable and dimensional changes are likely to occur Not suitable. Conversely, No. with a large addition amount. No. 8 is not suitable for a wiring material because of a decrease in conductivity. Furthermore, the conventional material No. No. 9 of the present example. Compared with 1-5, the dimensional change after heating at 250 ° C. for 30 minutes is large and unsuitable. From the above, the effect of the present invention was confirmed.

  In the present invention, Zr is added to the copper foil, but other elements may be added instead of Zr or in addition to Zr as long as the heat resistance temperature of the copper foil can be secured at 300 ° C. or higher. You can also. For this reason, addition of Sn, Ag, Fe or the like can be expected to have the same effect.

Claims (3)

  A rolled copper foil having an oxygen content of 10 ppm by weight or less and containing Zr of 0.01 to 0.20% by weight and being bonded to a resin substrate, A copper foil for electronic parts, wherein the copper crystal grains are recrystallized by heat treatment at a predetermined temperature.   The copper foil for electronic parts according to claim 1, wherein the predetermined temperature is 350 ° C or higher and 550 ° C or lower. The copper foil for electronic parts according to claim 1, wherein the resin substrate is a polyimide film.