Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2001-11-07
2003-11-18
Jackson, Monique R. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of metal
C428S458000
Reexamination Certificate
active
06649274
ABSTRACT:
TECHNICAL FIELD
The present invention relates to electrodeposited copper foil with carrier predominantly employed for producing printed wiring boards.
BACKGROUND ART
Conventionally, electrodeposited copper foil with carrier has been employed as a material for producing printed wiring boards, which are widely used in the electric and electronic industries. In general, electrodeposited copper foil with carrier is bonded, through hot-pressing, onto an electrically insulating polymer material substrate such as glass-epoxy substrate, phenolic polymer substrate, or polyimide, to thereby form a copper-clad laminate, and the thus-prepared laminate is used for producing printed wiring boards of high density mounting.
In hot-pressing, a copper foil, a prepreg (substrate) which is cured into a B-stage, and mirror plates serving as spacers are laid-up in a multilayered manner, and the copper foil and the prepreg are hot-press-bonded at high temperature and pressure (hereinafter the step may be referred to as “press-forming”). When wrinkles are in turn generated in the copper foil to be pressed, cracks are generated in the wrinkled portions, thereby possibly causing bleeding of resin from a prepreg, or open circuit of a formed electric circuit during an etching step followed in production steps of printed wiring boards. In an electrodeposited copper foil with carrier, the carrier foil prevents generation of wrinkles in the electrodeposited copper foil.
Electrodeposited copper foils with carrier are generally divided into two types; i.e., foils with peelable carriers and foils with etchable carriers. Briefly, the difference between the two types of foils lies in the method for removing the carrier after completion of press-forming. In foil with peelable carrier, the carrier is removed by peeling, whereas in foil with etchable carrier, the carrier is removed by etching. The present invention is directed to electrodeposited copper foil with peelable carrier.
However, the peel strength of conventional peelable carriers after completion of press-forming varies considerably, and a preferable strength of 50-300 gf/cm is generally required. In some cases, a carrier foil cannot be removed from the copper foil. Thus, conventional peelable carriers have a drawback; i.e., target peel strength is difficult to attain. The drawback prevents the widespread use of the electrodeposited copper foil with carrier employed for general use.
Causes of variation in peel strength of a carrier foil will next be described. Conventional electrodeposited copper foil with carrier, regardless of whether the carrier is peelable or etchable, has a metallic—e.g., zinc-containing—adhesive interface layer between the carrier foil and the electrodeposited copper foil. The amount of metal components forming the adhesive interface layer determines, with slight dependence on the type of the carrier foil, whether the formed copper foil with carrier has peelable carrier foil or etchable carrier foil.
In many cases, such a metallic adhesive interface layer is formed electrochemically; i.e., through electrodeposition by use of a solution containing a predetermined metallic element. However, in electrodeposition, controlling the amount of deposition on a very minute scale is difficult, and reproduction of the deposition is unsatisfactory as compared with other methods for forming the adhesive interface layer. In addition, the boundary line of the required deposition amount determining whether the formed carrier becomes peelable or etchable is difficult to adjust; i.e., small variations in amount of a metallic component contained in the adhesive interface layer determine the type of the carrier. Thus, stable peeling performance may be difficult to attain.
From another point of view, such a carrier foil is removed by peeling after completion of press-forming, typically at a temperature as high as 180° C. under high pressure for 1 to 3 hours. Components contained in the carrier foil and copper atoms contained in the electrodeposited copper foil may be mutually diffused through the adhesive interface layer. Such mutual diffusion strengthens the adhesion, thereby failing to attain moderate peel strength.
In order to solve the aforementioned drawbacks, the present inventors have proposed electrodeposited copper foil with carrier in which the adhesive interface layer between the carrier foil layer and the electrodeposited copper foil comprises an organic agent such as CBTA, and a method for producing the electrodeposited copper foil with carrier.
The aforementioned electrodeposited copper foil with carrier which the present inventors have proposed completely solves the drawback that the carrier foil cannot be peeled; i.e., the proposed foil can be peeled at a strength of 3-200 gf/cm. However, there has been still increasing demand for a copper foil which can be peeled with a moderate and constant peel strength after a copper-clad laminate is produced by use of an electrodeposited copper foil with carrier.
Meanwhile, an advantage of electrodeposited copper foil with carrier per se is the state where one surface of the carrier foil are placed as if it were bonded in a lamination manner to one surface of an electrodeposited copper layer. In other words, the electrodeposited copper foil with carrier can prevent staining the surface of the electrodeposited copper foil with foreign matter and damaging the electrodeposited copper foil layer by maintaining the bonding state at least immediately before an etching step for forming printed circuits, which step is carried out after production of a copper-clad laminate through hot-pressing the electrodeposited copper foil with carrier and a prepreg (substrate).
Thus, separation of a carrier foil and an electrodeposited copper foil during handling of the electrodeposited copper foil with carrier before hot-press-forming is not acceptable. Although the carrier foil must be peeled with a moderate peel strength after completion of hot-pressing, lamination-type bonding of the carrier foil to one surface of an electrodeposited copper foil of a copper-clad laminate must also be maintained, at least immediately before an etching step so as to prevent contamination and staining the surface of the copper clad laminate with foreign matter.
SUMMARY OF THE INVENTION
In view of the foregoing, the present inventors have conducted extensive studies, and have concluded that the peel strength between a carrier foil and an electrodeposited copper foil should be controlled to 3 gf/cm to 100 gf/cm so as to maintain lamination-type bonding of the carrier to one surface of the electrodeposited copper foil at least immediately before an etching step with lower peel strength.
Thus, the aforementioned demands can be satisfied by selecting combination of materials of a carrier foil and an electrodeposited copper foil, which materials are predominant materials for forming an electrodeposited copper foil with carrier. This approach differs from the approach of modifying an organic agent which is employed in an adhesive interface layer and the approach of improving interface-forming techniques, such as a method for forming the adhesive interface layer. Since an electrodeposited copper foil with carrier is hot-pressed during production of a copper-clad laminate, the copper foil with carrier is subjected to a certain amount of thermal stress. The present inventors have found that, among properties of the materials, coefficient of thermal expansion is an important factor. The present invention has been accomplished on the basis of this finding.
Accordingly, the present invention provides an electrodeposited copper foil with carrier comprising a carrier foil layer, an organic adhesive interface layer formed on the carrier foil layer, and an electrodeposited copper foil layer formed on the organic adhesive interface layer, wherein the difference between the coefficient of thermal expansion of material forming the carrier foil layer at a certain temperature and that of material forming the electrodeposited copper foil at the same temperat
Dobashi Makoto
Sugimoto Akiko
Taenaka Sakiko
Takahashi Naotomi
Jackson Monique R.
Mitsui Mining & Smelting Co. Ltd.
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