Compositions: coating or plastic – Coating or plastic compositions – Silicon containing other than solely as silicon dioxide or...
Reexamination Certificate
2003-05-01
2004-12-28
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Silicon containing other than solely as silicon dioxide or...
C106S287140, C428S447000, C428S450000
Reexamination Certificate
active
06835241
ABSTRACT:
TECHNICAL FIELD
This invention relates to a copper foil surface treatment agent which increases the adhesion between the copper foil and an insulating resin. More particularly, the invention relates to a copper foil surface treatment agent that provides excellent adhesion between an insulating resin and a low-profile copper foil used on high-frequency-adaptable substrates.
BACKGROUND ART
As computers and communication devices have improved in their performance and functions and such computers and devices become increasingly network-oriented in recent years, the signals trend toward higher frequencies for the high-speed transmission of large volumes of information.
Because of their excellent adhesion characteristics, epoxy resins have been used fairly widely for the insulating materials of printed wiring boards. However, epoxy resins generally have a high dielectric constant or dielectric tangent and thus unsatisfactory high frequency characteristics. A resin with excellent dielectric characteristics has to be used in order to cope with the high-frequency signals used in the above-mentioned communication field. But resins with low dielectric constant or dielectric tangent have few functional groups with high polarity that contribute to adhesion, so the adhesion characteristics of the resins tend to suffer. Then, improvement is need on this front.
Also, the copper foil for a high-frequency-adaptable substrate needs to have as little surface roughness as possible, that is, to be low-profile. The reason that this lower profile is preferable for a copper foil is theorized that electric current flow becomes concentrated in the surface of a copper foil as the signal frequency rises (this is called the epidermal effect), meaning that the surface roughness of a copper foil greatly affects transmission loss.
Therefore, with a high-frequency-adaptable substrate, due both to the change in resin and to the lower profile of the copper foil, the adhesive strength between the copper foil and the insulating resin is lower, and there is an urgent need for improvement of this adhesion.
Standard means employed for improving the adhesion between an insulating resin and a copper foil of a high-frequency-adaptable substrate are a surface treatment of a copper foil with a silane coupling agent, or addition of a silane coupling agent to the resin. The inventors have already disclosed in Japanese Patent Publication H8-295736 a silane coupling agent whose active components are specific organosilicic compounds expressed by General Formulas (1) and (2) given below. In addition, commercially available epoxy-based and amino-based silane coupling agents are effective, and have been in use for many years. But, the cases that the required characteristics cannot be achieved increase in the above-mentioned higher frequency applications of today.
DISCLOSURE OF THE INVENTION
Therefore, an object of the present invention is to provide a copper foil surface treatment agent with which an insulating resin and a copper foil used for a printed wiring board can be securely bonded together. More particularly, an object of the present invention is to provide a copper foil surface treatment agent that is effective even with low-profile copper foils and insulating resins used in high-frequency-adaptable substrates.
As a result of diligent research aimed at improving the adhesion between a copper foil and an insulating resin, the inventors discovered that the above-mentioned problems can be solved by combining a specific organosilicic compound with an olefin-based silane coupling agent. In particular, it was discovered that an aqueous solution whose active components are an organosilicic compound expressed by the following General Formula (1) and/or (2) and an olefin-based silane coupling agent is favorable as a copper foil surface treatment agent for a high-frequency-adaptable substrate, thereby, the adhesive strength between the insulating substrate and the copper foil can be dramatically increased. Specifically, the present invention provides the copper foil surface treatment agent and copper foil of [1] to [4] below.
[1] A copper foil surface treatment agent, comprising an olefin-based silane coupling agent and an organosilicic compound expressed by a following General Formula (1) and/or an organosilicic compound expressed by a General Formula (2) as active components thereof:
wherein, in the Formulas (1) and (2), R
1
is a hydroxyl group or a C
1
to C
5
alkyl group, R
2
is a C
1
to C
10
alkylene group that optionally contains oxygen, X is
including the former group having two hydroxyl groups produced by cleavage of an epoxy group, n is an integer of at least 2, and m is an integer of at least 1.
[2] A copper foil surface treatment agent comprising a solution as an active component, said solution being obtained by stirring an organosilicic compound having an epoxy group expressed by a following General Formula (3) under heating in an aqueous solution, returning said solution to room temperature, adding an olefin-based silane coupling agent and stirring:
wherein R
3
is a C
1
to C
5
alkyl group, R
4
is a hydroxyl group or a C
1
to C
5
alkyl group, R
5
is a single bond or a C
1
to C
10
alkyl group that optionally contains oxygen, and L is 2 or 3.
[3] A copper foil being surface treated with the copper foil surface treatment agent according to [1] or [2] above.
[4] The copper foil according to [3] above, wherein said copper foil is a low-profile copper foil whose surface roughness (Rz) is 3.5 &mgr;m or less.
The mechanism by which adhesion between a copper foil and an insulating resin is improved with applying the surface treatment agent of the present invention is theorized to be as follows: First, because the organosilicic compound expressed by the above-mentioned General Formula (1) and/or (2) is an oligomer component, it readily sticks to a copper foil; Next, it is accepted that adhesion between the copper foil and the insulating resin strengthens when the olefin-based silane coupling agent reacts with the insulating resin, and also reacts with the organosilicic compound expressed by the above-mentioned General Formula (1) and/or (2).
The improvement in adhesion between the copper foil and the insulating resin will be inadequate if just the organosilicic compound expressed by the above-mentioned General Formula (1) and/or (2) or just the olefin-based silane coupling agent is used alone. Research on the part of the inventors has confirmed that particularly good adhesive strength can be obtained by combining the two of these (the organosilicic compound expressed by the above-mentioned General Formula (1) and/or (2) and the olefin-based silane coupling agent).
The constitution of the present invention will now be described.
The surface treatment agent of the present invention contains an organosilicic compound expressed by the above-mentioned General Formula (1) and/or (2), and, in addition, may also contain an intermolecular condensate produced through a condensation reaction between the .Si.OH groups of these compounds. Also, in the above-mentioned General Formulas (1) and (2), n is at least 2, and preferably 2 to 50, and m is at least 1, and preferably 1 to 50. Stability is highest when m=2.
As will be described below, the organosilicic compound expressed by General Formula (1) or (2) is obtained by heating and stirring a compound expressed by General Formula (3). In General Formula (3), R
3
is a C
1
to C
5
alkyl group, but from the standpoint of ease of hydrolysis, an alkyl group with one or two carbons is preferable. In terms of solubility in water, R
4
preferably has one or two carbons. If L is 2 or 3, the hydrolysis and condensation of alkoxysilyl groups will proceed so the effect of the present invention will be satisfactorily achieved. Furthermore, L=3 is particularly favorable, because the greater is the number of alkoxysilyl groups, the more hydrolysis and condensation will occur and the gr
Akase Fumiaki
Kumagai Masashi
Tsuchida Katsuyuki
Brunsman David
Flynn ,Thiel, Boutell & Tanis, P.C.
Nikko Materials Co., Ltd.
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