In accordance with requirement on so-called down-sizing to reduce in size and weight of electronic and electric apparatuses, same kind of performance is required on the printed wiring boards also. For the printed wiring boards, formation of a miniaturized and high functional wiring is required in a limited mounting area. Thus, a fine-pitch wiring must be formed to prepare a high density wiring. To obtain such a fine-pitch wiring, a thinner copper foil having the lower surface roughness on the bonding side to a base material has been employed to reduce over-etching time.
For this purpose, a low-profile electro-deposited copper foil is generally used. Also, to ease handling of the copper foil and a copper clad laminate when the copper foil thickness is reduced, efforts have been made to increase mechanical strength of the copper foil. Such a low-profile electro-deposited copper foil having excellent mechanical strength is disclosed in Patent Documents 1 and 2, which will be more specifically described below.
Object of Patent Document 1 is to provide a low-profile electro-deposited copper foil, which has a low-profile surface suitable for practical use in a printed wiring board and a negative-electrode collector of a lithium ion secondary battery as well as excellent fatigue ductility. More specifically, object of the document is to provide a low-profile electro-deposited copper foil having a surface roughness (Rz) of 2.0 μm or less, which has a low-profile surface without wavy undulation and having an elongation of 10.0% or more at 180° C. For this purpose, Patent Document 1 discloses a method of manufacturing an electro-deposited copper foil by using an aqueous sulfuric acid/copper sulfate solution as an electrolytic solution, an insoluble anode made of a titanium plate coated with a platinum metal or an oxide thereof and a cathode drum (which faces to the anode) made of a titanium and supplying direct current between the electrodes. In this manufacturing method, the electrolytic solution contains an oxyethylene surfactant, polyethylene imine or a derivative thereof, a sulfonic acid salt of an active organic sulfur compound and chloride ions. By the presence of these compounds, a low-profile electro-deposited copper foil (which has a low-profile surface with uniform roughness and having a surface roughness (Rz) of 2.0 μm or less without wavy undulation and having an elongation of 10.0% or more at 180° C.) can be obtained. Examples of Patent Document 1 discloses that the electro-deposited copper foil obtained had a deposit surface having a surface roughness (Rz) of 0.9 μm to 2.0 μm, an elongation as received of 10% to 18%, an elongation at 180° C. of 10% to 20%, a tensile strength as received of 340 MPa to 500 MPa, and a tensile strength at 180° C. of 180 MPa to 280 MPa. The document also discloses that the deposit surface of the electro-deposited copper foil had a gloss [Gs(85°)] of 120 to 132, which was measured at an angle of 85° for the transverse direction.
Patent Document 2 discloses the technologies which object to provide a low-profile electro-deposited copper foil having a low-profile surface and less tensile strength loss after heating, and having an excellent elongation at high temperature, and object to provide a method for manufacturing the same also. For this purpose, five additives, namely, hydroxyethylcellulose, polyethylene imine, acetylenic glycol, a sulfonic acid salt of an active organic sulfur compound and chloride ions are added in an electrolytic solution, which is an aqueous sulfuric acid/copper sulfate solution. By the presence of these five additives, it enables to obtain a low-profile electro-deposited copper foil having a surface roughness (Rz) of 2.5 μm or less, a tensile strength (at 25° C. measured within 20 minutes after finishing electro-deposition) of 500 MPa or more, a reduction rate of the tensile strength (at 25° C. measured at 300 minutes after finishing electro-deposition) of 10% or less or a tensile strength loss (at 25° C. measured after a foil is heated at 100° C. for 10 minutes after finishing electro-deposition) of 10% or less, and an elongation at 180° C. of 6% or more.
Examples of Patent Document 2 disclose that
an electrolytic solution, which consists of an aqueous sulfuric acid/copper sulfate solution containing 100 g/L sulfuric acid (H2SO4) and 280 g/L copper sulfate 5 hydrates (CuSO45H2O), was used as a basic solution;
additives, hydroxyethylcellulose, polyethylene imine, sodium 3-mercapto-1-propanesulfonic acid, acetylenic glycol and hydrochloric acid were added to the basic solution;
the electrolytic solution was filled in the gap between an insoluble anode made of platinum oxide coated titanium and a cathode drum made of titanium;
electrolysis was performed at a current density of 40 A/dm2 and a temperature of the electrolytic solution of 40° C. to obtain an electro-deposited copper foil of 18 μm in thickness; and
the electro-deposited copper foil thus obtained had a deposit surface having a surface roughness (Rz) of 1.5 μm to 2.3 μm, a tensile strength as received of 650 MPa to 900 MPa and a tensile strength loss (measured after heated at 100° C. for 10 minutes) of 0% to 7.7%.
As described above, according to each of the Examples of these documents, the electro-deposited copper foils manufactured by these methods have low-profile deposit surfaces. The quality level thereof is excellent as a conventional low-profile electro-deposited copper foil and may be effective for forming a fine-pitch wiring. It is also disclosed that more excellent mechanical strength than that of a conventional electro-deposited copper foil can be obtained. It should be noted that the term “low-profile” used in a copper foil for a printed wiring board means that the height between peak and valley of a bonding side of a copper foil to be bonded to an insulating layer-forming material is low.
[Patent Document 1] Japanese Patent Laid-Open No. 2004-263289
[Patent Document 2] Japanese Patent Laid-Open No. 2004-339558