U.S. patent application number 10/775075 was filed with the patent office on 2004-08-12 for copper foil for high frequency circuit and method of production of same.
This patent application is currently assigned to FURUKAWA CIRCUIT FOIL CO., LTD.. Invention is credited to Shinozaki, Kensaku.
Application Number | 20040154930 10/775075 |
Document ID | / |
Family ID | 32820978 |
Filed Date | 2004-08-12 |
United States Patent
Application |
20040154930 |
Kind Code |
A1 |
Shinozaki, Kensaku |
August 12, 2004 |
Copper foil for high frequency circuit and method of production of
same
Abstract
An electrodeposited copper foil having a rough surface having
knob-like projections and a surface roughness of 2 to 4 .mu.m at
part of a surface thereof produced by electrolysis using an
electrolyte containing copper as a main component and a compound
having mercapto groups, at least one type of another organic
compound, and chloride ions and an electrodeposited copper foil
obtained by roughening treating an untreated copper foil having a
matte side, for bonding with a resin substrate, having knob-like
projections and a surface roughness of 2 to 4 .mu.m by running a
predetermined current through it for a predetermined time in an
electroforming bath.
Inventors: |
Shinozaki, Kensaku;
(Tochigi, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW
SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
FURUKAWA CIRCUIT FOIL CO.,
LTD.
Tokyo
JP
|
Family ID: |
32820978 |
Appl. No.: |
10/775075 |
Filed: |
February 11, 2004 |
Current U.S.
Class: |
205/296 ;
428/687 |
Current CPC
Class: |
C25D 5/12 20130101; Y10T
428/12993 20150115; C25D 5/48 20130101; H05K 2203/0723 20130101;
C25D 11/38 20130101; C25D 5/605 20200801; H05K 2201/0355 20130101;
H05K 3/384 20130101; C25D 1/04 20130101; C25D 5/627 20200801; C25D
5/34 20130101; H05K 2203/0307 20130101; C25D 3/38 20130101 |
Class at
Publication: |
205/296 ;
428/687 |
International
Class: |
C25D 003/38 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2003 |
JP |
2003-033159 |
Claims
What is claimed is
1. An electrodeposited copper foil wherein part of its surface
comprises a rough surface having knob-like projections and a
surface roughness of 2 to 4 .mu.m.
2. An electrodeposited copper foil as set forth in claim 1, wherein
said rough surface having said knob-like projections and said
surface roughness of 2 to 4 .mu.m is a surface of an untreated
copper foil for bonding with a resin substrate and is further
roughening treated by running a predetermined current through the
foil for a predetermined time in an electroforming bath.
3. An electrodeposited copper foil as set forth in claim 2, wherein
said electroforming bath is an acidic electroforming bath
containing at least one of molybdenum, cobalt, nickel, iron,
tungsten and arsenic.
4. An electrodeposited copper foil as set forth in claim 2 or 3,
wherein said rough surface is further formed with a copper plating
layer.
5. An electrodeposited copper foil as set forth in claim 2 or 3,
wherein said rough surface is further formed with a copper plating
layer and at least one layer of nickel plating, zinc plating,
cobalt plating, plating of an alloy of the same and a chromate
treatment layer on that, and according to need further formed with
a coupling agent treatment layer.
6. An electrodeposited copper foil as set forth in claim 1, wherein
said rough surface having said knob-like projections and said
surface roughness of 2 to 4 .mu.m is a surface of an untreated
copper foil for bonding with a resin substrate and is further
formed with a copper plating layer and at least one layer of nickel
plating, zinc plating, cobalt plating, plating of an alloy of the
same and a chromate treatment layer on that, and according to need
further formed with a coupling agent treatment layer.
7. A method of producing an electrodeposited copper foil comprising
electrolysis using an electrolyte containing copper as a main
component and a compound having mercapto groups, at least one type
of another organic compound, and chloride ions to form a copper
foil wherein part of its surface comprises a rough surface having
knob-like projections and a surface roughness of 2 to 4 .mu.m.
8. A method of producing an electrodeposited copper foil as set
forth in claim 7, wherein an electroforming bath for a roughening
treatment is an acidic electroforming bath containing at least one
of molybdenum, cobalt, nickel, iron, tungsten and arsenic.
9. A method of producing an electrodeposited copper foil comprising
producing an electrodeposited copper foil having a matte side
having a surface roughness of 2 to 4 .mu.m using an electrolyte
containing a compound having mercapto groups, at least one type of
another organic compound, and chloride ions and roughening treating
said matte side of said electrodeposited copper foil by running a
predetermined current through it for a predetermined time in an
electroforming bath.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a copper foil having a
small surface roughness of the matte side particularly suitable for
a conductive material of printed circuits for high frequency
applications and a method of production of the copper foil.
[0003] While the main use of the present invention is a conductive
material of printed circuits for high frequency applications, the
electrodeposited copper foil of the present invention is not
limited to that use.
[0004] 2. Description of the Related Art
[0005] Electrodeposited copper foil used for conductive material
for a printed circuit has to give the peel strength, electric
characteristic, etching characteristics, heat resistance, etc.
required for the surface bonded with a resin substrate (hereinafter
called the "matte side"). In order to satisfy these
characteristics, various methods of treatment for roughening the
matte side and improving its chemical properties have been proposed
and put practical in use.
[0006] As an example, the method is proposed of performing
electrolysis in an acidic copper electroforming bath using the
copper foil as the cathode near the limit current density for burnt
plating to obtain a rough surface (see for example Japanese
Examined Patent Publication (Kokoku) No. 40-15327). Further, the
method is proposed of covering the burnt plating surface of the
rough surface by smooth copper plating to bind the plurality of the
projections stably by the copper foil surface (see for example
specification of U.S. Pat. No. 3,293,109).
[0007] In recent years, mobile phones and other mobiles have spread
rapidly. Along with this, copper foil superior in high frequency
characteristics has become demanded for base stations of mobile
phones and supercomputers. At a high frequency, the skin effect
arises, passage of an alternating current through the conductor
results in a change in the magnetic flux and therefore the
occurrence of an electromotive force at the center of the conductor
and a consequent difficulty in flow in current. The higher the
frequency of the alternating current, the more remarkable this
phenomenon. The current comes to flow almost all at the skin
portion. Due to this, in the high frequency band, the current flows
only at the shiny side surface and the matte side surface.
Therefore, it has been considered that if the roughness (Rz) of the
shiny side and the matte side of the copper foil were large, the
transmission distance would become longer and attenuation and delay
of the signal or other problem would occur and that copper foil
with a low profile is suitable as copper foil for a conductive
material of printed circuits for high frequency applications.
[0008] However, the inventors engaged in various experiments in
order to meet the demands for copper foil superior in high
frequency characteristics and as a result obtained different
results from the above theory.
[0009] Table 1 shows the transmission loss when transmitting a high
frequency signal of 3 GHz to copper foils having various surface
roughnesses of the matte side. Table 1 demonstrates that the
roughness of the matte side has an extremely small influence on the
transmission loss.
1TABLE 1 Roughening treating conditions Roughness (roughening
current Roughness after 3 GHZ divided by of roughening Peel
transmission roughening speed untreated treating strength loss (A
.multidot. min/m) foil (.mu.m) (.mu.m) (kN/m) (dB/m) 400 1.70 1.99
0.74 3.97 400 1.12 1.33 0.61 3.98 1000 1.60 3.77 1.00 4.03 1000
1.20 1.72 0.74 4.01 300 4.74 5.14 0.92 3.92
[0010] Therefore, the inventors engaged in further study about
factors causing transmission loss and as a result found that the
strength of the roughening (here, "strength of roughening treating"
defined as roughening current divided by roughening speed, that is,
A.multidot.min/m) for causing deposition of copper particles on the
matte side has a large influence.
[0011] Namely, in the related art, the roughening treating needed
to be strong (roughing current large or roughening time long) to
obtain a sufficient peel strength. Doing that made the transmission
loss worse.
[0012] Therefore, it may be considered to make the roughening
treating weak (roughing current small or roughening time short).
However, if the roughening treating is made weak, a new problem
will occur that a sufficient peel strength will not be obtained.
Table 2 shows the result of measurement of the strength of the
roughening treating, peel strength, and transmission loss observed
for the same untreated copper foil. If the roughening treating is
strong, the peel strength becomes improved but the transmission
loss is also influenced, while if the roughening treating is weak,
the transmission loss becomes improved but the peel strength
declines.
2TABLE 2 Roughening treating conditions Roughness (roughening
Roughness after 3 GHZ current divided by of roughening Peel
transmission roughening speed untreated treating strength loss (A
.multidot. min/m) foil (.mu.m) (.mu.m) (kN/m) (dB/m) 2600 0.83 2.30
1.07 4.38 2000 0.83 1.80 0.95 4.06 1600 0.83 1.60 0.87 4.00 1300
0.83 1.25 0.80 3.83
[0013] The same trend appears in almost all types of foils. The
same applies when using untreated foil having a large roughness of
the matte side. That is, it was not possible to realize both a high
transmission characteristic and high peel strength even if using
untreated foil which has a large roughness of the matte side.
[0014] Note that the value of the transmission loss is influenced
largely by the measurement environment. In the present
specification, the transmission loss was measured under the same
environment to compare the measured values. Therefore, the values
in Table 1, Table 2, and other values can be compared.
[0015] An invention for producing a copper foil using an
electrolyte of copper added with a compound having a mercapto
group, at least one kind of other organic compounds and chloride
ion (see Japanese Patent Publication No. 3313277). The copper foil
produced in this invention has a shiny and very smooth surface at
the matte side too. By burnt plating or otherwise treating this
copper foil, a copper foil that has a matte side having a very low
roughness and is suitable for fine patterns can be produced.
[0016] Therefore, from conventional theory, it had been considered
that if the roughness of the shiny side and the matte side were
small, the transmission loss could be improved. Due to this, the
foil with shiny side at the two sides obtained by the art disclosed
above was expected to give extremely excellent transmission loss
characteristics. However, that foil needed strong roughening
treating to obtain a peel strength (while roughness of the matte
side was small, the roughening treating was strong). As a result,
the transmission loss ended up becoming very poor. The reason is
the transmission loss is more dependent on the strength of the
roughening treating than the surface roughness as shown in
experimental results of Table 1 and Table 2.
SUMMARY OF THE INVENTION
[0017] An object of the present invention is to provide
electrodeposited copper foil having a high enough peel strength to
meet the demands for recent printed circuit boards and an excellent
high frequency transmission characteristic and a method of
production of the same.
[0018] Another object of the present invention is to provide a
copper foil having a high peel strength, capable of being applied
to a fine pattern-compatible copper foil having small roughness of
the matte side, and able to be used to give an excellent printed
circuit board with fine patterns improved in high frequency
transmission loss.
[0019] According to a first aspect of the present invention, there
is provided an electrodeposited copper foil wherein part of its
surface comprises a rough surface having knob-like projections and
a. surface roughness of 2 to 4 .mu.m.
[0020] Preferably, the rough surface having the knob-like
projections and the surface roughness of 2 to 4 .mu.m is a surface
of an untreated copper foil for bonding with a resin substrate and
is further roughening treated by running a predetermined current
through the foil for a predetermined time in an electroforming
bath.
[0021] More preferably, the electroforming bath is an acidic
electroforming bath containing at least one of molybdenum, cobalt,
nickel, iron, tungsten and arsenic.
[0022] Still more preferably, the rough surface is further formed
with a copper plating layer.
[0023] Alternatively, the rough surface is further formed with a
copper plating layer, at least one layer of nickel plating, zinc
plating, cobalt plating, plating of an alloy of the same and a
chromate treatment on that, and a coupling agent treatment layer
according to need on that.
[0024] Preferably, the rough surface having the knob-like
projections and the surface roughness of 2 to 4 .mu.m is a surface
of an untreated copper foil for bonding with a resin substrate and
is further is further formed with a copper plating layer, at least
one layer of nickel plating, zinc plating, cobalt plating, plating
of an alloy of the same and a chromate treatment on that, and a
coupling agent treatment layer according to need on that.
[0025] According to a second aspect of the present invention, there
is provided a method of producing an electrodeposited copper foil
comprising electrolysis using an electrolyte containing copper as a
main component and a compound having mercapto groups, at least one
type of another organic compound, and chloride ions to form a
copper foil wherein part of its surface comprises a rough surface
having knob-like projections and a surface roughness of 2 to 4
.mu.m.
[0026] Preferably, an electroforming bath for a roughening
treatment is an acidic electroforming bath containing at least one
of molybdenum, cobalt, nickel, iron, tungsten and arsenic.
[0027] According to a third aspect of the present invention, there
is a method of producing an electrodeposited copper foil comprising
producing an electrodeposited copper foil having a matte side
having a surface roughness of 2 to 4 .mu.m using an electrolyte
containing a compound having mercapto groups, at least one type of
another organic compound, and chloride ions and roughening treating
the matte side of the electrodeposited copper foil by running a
predetermined current through it for a predetermined time in an
electroforming bath.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] These and other objects and features of the present
invention will become clearer from the following description of the
preferred embodiments given with reference to the attached
drawings, wherein:
[0029] FIG. 1 is an electron micrograph of the surface of a copper
foil of one example of the present invention;
[0030] FIG. 2 is an electron micrograph of the surface of a copper
foil of another example of the present invention; and
[0031] FIG. 3 is an electron micrograph of the surface of a copper
foil of a further example of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] Preferred embodiments of the present invention will be
described in detail below while referring to the attached
figures.
[0033] The electrodeposited copper foil according to the preset
embodiment is characterized in that part of its surface is a rough
surface having knob-like projections and having a surface roughness
of 2 to 4 .mu.m. Such an electrodeposited copper foil is produced
by electrolysis using an electrolyte containing a compound having
mercapto groups, at least one type of another organic compound, and
chloride ions. The thus prepared surface to be bonded to a resin
substrate (bonding surface) is finished to a smooth surface of a
surface roughness of 2 to 4 .mu.m, has knob-like projections formed
on part of the smooth matte side, and can provide copper foil
superior in high frequency transmission loss.
[0034] However, the above electrodeposited copper foil lacks peel
strength. Stronger peel strength is demanded according to the
application. In order to satisfy this demand, the electrodeposited
copper foil is run through by a predetermined current as untreated
copper foil for a predetermined time in an electroforming bath to
roughen the matte side. The roughening treating performed on the
untreated copper foil is performed under weaker treatment
conditions than the conventional roughening treating. Due to the
weak roughening treating, an electrodeposited copper foil has a
peel strength equal to or stronger than a conventional one (namely,
the roughness of the matte side is large but the roughening
treating is weak) and is superior in high frequency transmission
loss.
[0035] As the roughening electroforming bath for the roughening
treating, an acidic electroforming bath containing at least one of
molybdenum, cobalt, nickel, iron, tungsten, and arsenic can be
used. Note that by performing the roughening treated copper foil by
at least one of nickel plating, zinc plating, cobalt plating,
plating of an alloy of the same, treating it by chromate treatment
and a coupling agent treatment, the heat resistance, resistance to
HC1, stain proofing, and peel strength can be improved.
[0036] Further, by performing the untreated copper foil by at least
on of nickel plating, zinc plating, cobalt plating, plating of an
alloy of the same, chromate treatment and a coupling agent
treatment, a copper foil having a surface roughness smaller than a
roughening treated copper foil and having a high peel strength to a
certain type of substrate can be produced. Further, by plating and
treating by a coupling agent, the heat resistance, resistance to
HC1, and stain proofing can be further improved.
[0037] Next, production conditions for the electrodeposited copper
foil and examples of surface treatment of an untreated copper foil
using it as an untreated copper foil will be shown. Note, however,
that the present invention is not limited to these examples.
EXAMPLE 1
[0038] (1) Electrodeposited Copper Foil-Making Conditions and
Solution Composition
[0039] Electrodeposited copper foils were produced under the
electrolyte composition and the electrolysis conditions shown in A
to C of Table 3 (hereinafter, referred as Examples A to C) as the
electrodeposited foil-making conditions of the present invention.
Further, untreated copper foil was produced under the electrolyte
composition and the electrolysis conditions as shown in D of Table
3 as a comparative example.
3TABLE 3 Conditions for producing copper foils and solution
compositions Sulfuric Current Solution Copper acid MPS HEC Glue Cl
density temp. Conditions (g/l) (g/l) (ppm) (ppm) (ppm) (ppm)
(A/dm.sup.2) (.degree. C.) A 90 80 0.8 5 40 60 60 B 90 80 1 5.5 40
60 60 C 90 80 1 4 2 40 60 60 D 90 80 1 3 6 40 60 60 MPS: Sodium
3-mercapto propane sulfonate HEC: Hydroxyethylcellulose
[0040] The performances of the produced electrodeposited copper
foils are shown in Table 4, while the surface states are shown in
the electron micrographs of the surfaces of the copper foils of
FIGS. 1 to 3.
4TABLE 4 Performance of copper foils Foil Roughness of thickness
shiny side Roughness of Conditions (.mu.m) (.mu.m) matte side
(.mu.m) A 35 1.5 3.5 B 35 1.5 3.6 C 35 1.5 2.4 D 35 1.5 0.8
[0041] FIG. 1 shows the surface state of foil produced under the
foil-making conditions A. The knob-like projections are dispersed
evenly. FIG. 2 shows the surface state of foil produced under the
foil-making conditions B. The knob-like projections are closely
concentrated. FIG. 3 shows the surface state of foil produced under
the foil-making conditions C. The knob-like projections are small
and dispersed evenly with longer distances between them than in
FIG. 1.
[0042] (2) Roughening Treating Conditions and Roughening Solution
Composition
[0043] The surfaces of the electrodeposited copper foils A to D
produced above were roughening treated by the roughening solution
composition shown in Table 5.
5TABLE 5 Roughening solution compositions Sulfuric Cu acid Mo Ni Fe
W As Co (g/l) (g/l) (ppm) (g/l) (g/l) (ppm) (ppm) (g/l) 1 25 160
350 4.0 0.2 2 25 160 50 8.0 0.4 3 25 160 250 2.0 4 25 160 250 2.0 5
25 160 350 4.0 6 25 160 350
[0044] The roughening treating was performed under the following
conditions:
[0045] Roughening current density: 5 to 30 A/dm.sup.2
[0046] Treatment time: 2 to 15 seconds
[0047] Temperature: 20 to 40.degree. C.
[0048] The roughening current density (5 to 30 A/dm.sup.2) is lower
than the roughening current density used conventionally. Note that
the reason the treatment time is made 2 to 15 seconds is the sizes
of the anodes were changed for treatment. The line speed was the
same for the solution compositions.
[0049] The surface of the roughening treated copper foil was
encapsulation plated under the conditions shown in Table 6.
6TABLE 6 Encapsulation plating solution condition Sulfuric Current
Copper acid Solution density Treatment (g/l) (g/l) temp. (.degree.
C.) (A/dm.sup.2) time (sec) 65 100 50 10 to 60 2 to 15
[0050] The roughening treating and the encapsulation plating
treatment may be performed several times in the present
invention.
[0051] (3) Performance After Roughening Treating (Treatment Under
Same Conditions)
[0052] The performances of the roughening treated and encapsulation
plated copper foils are shown in Table 7.
7TABLE 7 Peel Untreated Roughening Untreated Rz after strength
copper solution copper roughening with FR-4 foil composition foil
Rz treating (kN/m) A 1 3.5 4.9 1.54 A 2 3.5 5.2 1.53 A 3 3.5 6.2
1.50 A 4 3.5 6.4 1.51 A 5 3.5 7.1 1.62 A 6 3.5 7.1 1.51 C 1 2.4 4.0
1.52 C 2 2.4 4.2 1.50 C 3 2.4 5.1 1.47 C 4 2.4 5.5 1.48 C 5 2.4 6.0
1.60 C 6 2.4 6.3 1.51 D 1 0.8 1.1 0.60 D 6 0.8 1.3 0.54
[0053] As clear from Table 7, the differences between untreated
copper foils, that is, the peel strengths to FR-4 among Examples A
and C and Comparative Example D, are extremely different. The
present invention gives untreated copper foils having a surface
roughness of 2 to 4 .mu.m and knob-like projections on part of the
foil surface. The result is remarkable.
[0054] Note that the untreated copper foils A and B produced above
exhibited almost the same performances as shown in Table 4, so only
Example A was roughening treated. The roughening treating for
Example B was omitted. Further, by plating the plated surface of
the copper foil by one of nickel, zinc, cobalt, or an alloy of the
same or treating it by chromate or a coupling agent, the heat
resistance, resistance to HCl, stain proofing, and peel strength
can be improved.
[0055] (4) Comparison of Transmission Loss and Peel Strength
[0056] The foils of Example C and Comparative Example D of the
present invention were measured for high frequency transmission
loss and peel strength while changing the roughening current
divided by roughening speed. The results are shown in Table 8.
8TABLE 8 Roughening current Comparative Comparative Comparative
divided by Example C Example C Example C Example D Example D
Example D roughening surface peel transmission surface peel
transmission speed roughness strength loss roughness strength loss
2600 7.20 1.57 4.45 2.40 1.07 4.38 900 3.95 1.42 3.79 1.25 0.77
3.77 400 2.90 1.22 3.7 0.90 0.60 3.71 200 2.55 1.21 3.62 0.90 0.59
3.64
[0057] As clear from Table 8, almost no difference in transmission
loss between the untreated copper foil of Example C and the
untreated copper foil of Comparative Example D can be recognized
even when changing the conditions of the roughening current divided
by roughening speed. As described above, it is considered that the
transmission loss depends on the roughening current divided by the
roughening speed (current density and line speed). It is verified
from the examples that both with the untreated foils C and D, when
the roughening current and the roughening speed are set the same,
there is no difference in the transmission loss.
[0058] On the other hand, for the peel strength, as shown in Table
8, the untreated copper foil of Comparative Example D cannot be
used due to the decline of the peel strength when the roughening
current divided by the roughening speed becomes small. However, the
copper foil of Example C of the present invention has a high peel
strength even when the roughening current divided by the roughening
speed becomes small and further has a transmission loss
characteristic that is equal to untreated copper foil D.
[0059] As described above, in Comparative Example D, a clear
decline of the peel strength was observed due to the weakening of
the roughening treating. In Example C of the present invention, a
slight decline of the peel strength was observed due to the
weakening of the roughening treating, but the peel strength was
sufficient compared with Comparative Example D. Further, the
transmission loss is almost the same as Comparative Example D.
Therefore, copper foil with excellent transmission loss and further
high peel strength and a method for producing the same are
available according to the present invention. Needless to say, the
copper foil produced in the present invention has a small surface
roughness and high peel strength, so is suitable for copper foil
for a printed circuit other than for high frequency applications as
well.
EXAMPLE 2
[0060] (1) Untreated Copper Foil-Making Conditions, Types of
Surface Plating, and Amounts of Deposition (mg/dm.sup.2)
[0061] Untreated copper foils were produced having thicknesses of
35 .mu.m according to the untreated copper foil-making conditions
and solution compositions of Example C and Comparative Example D of
Example 1 and treated on their surfaces as shown in Table 9.
9 TABLE 9 Condition no. Ni Zn Cr Co Si 1 0.30 0.02 0.03 0 0.005 2
0.30 0.20 0.03 0.2 0.005 3 0.05 0.02 0.03 0 0.005 4 0.05 0.25 0.03
0 0.005 5 0.10 0.04 0.03 0 0.005 6 0.25 0.03 0.03 0.15 0.005 7 0.10
0.03 0.03 0 0
[0062] (2) Performances
[0063] The Rz's of the copper foil treated on the surface at Table
9 and the peel strength to polyimide substrate are shown in Table
10.
10TABLE 10 Comparative Example C Example D peel Comparative peel
Example C strength Example D strength Rz after with Rz after with
treatment polyimide treatment polyimide Condition (treated
substrate (treated substrate no. side) (kN/m) side) (kN/m) 1 2.4
1.78 0.8 1.40 2 2.4 0.40 0.8 0.25 3 2.4 1.13 0.8 0.82 4 2.4 0.33
0.8 0.24 5 2.4 1.69 0.8 1.38 6 2.4 1.83 0.8 1.43 7 2.4 0.80 0.8
0.55
[0064] As shown in Table 10, by plating untreated copper foil by
nickel, zinc, cobalt, or an alloy of the same or treating it by
chromate or a coupling agent, the heat resistance, resistance to
HC1, and stain proofing can be improved. On the other hand, the
transmission loss of copper foil treated on its surface by 3GHz is
measured and shown in Table 11.
11TABLE 11 Condition Untreated copper no. foil C Untreated copper
foil D 1 3.58 3.60 2 3.56 3.60 3 3.56 3.55 4 3.57 3.58 5 3.60 3.58
6 3.60 3.58 7 3.58 3.57
[0065] As clear from Table 11, the transmission loss did not change
so much in both Example C and Comparative example D even when
plating the untreated copper foil.by nickel, zinc, cobalt, or an
alloy of the same or treating it by chromate or a coupling
agent.
[0066] Thus, by using untreated copper foil produced under the
conditions of present invention, copper foil having a high peel
strength can be provided without detracting from the transmission
characteristic compared with copper foil produced by conventional
methods.
[0067] Summarizing the effects of the invention, as described
above, according to the present invention, there is the superior
effect that a superior copper foil can be provided which is given a
slightly higher surface roughness to make the peel strength to a
resin substrate high without detracting from the high frequency
characteristic. Therefore, it is very effective according to the
applications in the case where a high peel strength is needed more
than surface roughness and is a very suitable copper foil for high
frequency applications.
[0068] While the invention has been described with reference to
specific embodiments chosen for purpose of illustration, it should
be apparent that numerous modifications could be made-thereto by
those skilled in the art without departing from the basic concept
and scope of the invention.
* * * * *