U.S. patent application number 09/888151 was filed with the patent office on 2001-11-29 for method of drying copper foil and copper foil drying apparatus.
Invention is credited to Imada, Nobuyuki, Oshima, Kazuhide.
Application Number | 20010046458 09/888151 |
Document ID | / |
Family ID | 16478272 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010046458 |
Kind Code |
A1 |
Imada, Nobuyuki ; et
al. |
November 29, 2001 |
Method of drying copper foil and copper foil drying apparatus
Abstract
A method employed to dry a copper foil having been subjected to
various surface treatments, which method comprises irradiating at
least one surface-treated side of the copper foil with near
infrared rays to dry the copper foil, and an apparatus suitable to
the method. The drying of the copper foil having undergone surface
treatments can be accomplished by a simple apparatus with low
electric power while controlling the heating of the surface of the
copper foil so that the drying temperature can be held at
100.degree. C. or higher at which a eutectic alloying of rust
preventive metal and copper foil, for example, alloying (brass
formation) of zinc and copper on the surface of the copper foil is
effected.
Inventors: |
Imada, Nobuyuki;
(Hasuda-shi, JP) ; Oshima, Kazuhide; (Ageo-shi,
JP) |
Correspondence
Address: |
Harold N. Wells
JENKENS & GILCHRIST
Suite 3200
1445 Ross Avenue
Dallas
TX
75202-2799
US
|
Family ID: |
16478272 |
Appl. No.: |
09/888151 |
Filed: |
June 22, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09888151 |
Jun 22, 2001 |
|
|
|
09354626 |
Jul 16, 1999 |
|
|
|
6269551 |
|
|
|
|
Current U.S.
Class: |
422/186 |
Current CPC
Class: |
H05K 3/384 20130101;
H05K 3/227 20130101; H05K 2201/0355 20130101; H05K 2203/0723
20130101; F26B 3/283 20130101; F26B 13/10 20130101; H05K 2203/0307
20130101 |
Class at
Publication: |
422/186 |
International
Class: |
B01J 019/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 17, 1998 |
JP |
203692/1998 |
Claims
what is claimed is:
1. A method of drying a copper foil subjected to surface
treatments, comprising irradiating one surface or both surfaces of
the copper foil with near infrared rays to thereby dry the copper
foil.
2. The method as claimed in claim 1, wherein the copper foil is an
electrodeposited copper foil.
3. The method as claimed in claim 1, wherein at least one
surface-treated side of the copper foil is irradiated with near
infrared rays to dry the copper foil.
4. The method as claimed in claim 3 wherein nodularization
comprising depositing fine particles on the surface of the copper
foil is done prior to a passivation.
5. The method as claimed in claim 4, wherein the passivation
comprises applying a rust preventive metal.
6. The method as claimed in claim 5, wherein the passivation
comprises applying at least one rust preventive metal selected from
the group consisting of Zn, Ni, Sn, Cr, Mo and Co.
7. The method as claimed in any of claims 1 to 6, wherein the
drying by near infrared irradiation is done under condition such
that the surface or surfaces of the copper foil have a temperature
of 100 to 170.degree. C.
8. A copper foil drying apparatus for drying a copper foil
subjected to surface treatments, comprising a drying chamber and,
arranged therein, a near infrared irradiating unit, said drying
chamber adapted to allow the copper foil to be continuously fed
therethrough, said near infrared irradiating unit arranged opposite
to a surface-treated side of the copper foil so that at least the
surface-treated side of the copper foil is irradiated with near
infrared rays.
9. The apparatus as claimed in claim 8, wherein the copper foil is
an electrodeposited copper foil.
10. The apparatus as claimed in claim 8, which further comprises
means for controlling the output of the near infrared irradiating
unit so that the surface of the copper foil has a controlled drying
temperature.
11. The apparatus as claimed in any of claims 8 to 10, wherein near
infrared irradiating units are arranged so that they face each
other with the copper foil interposed therebetween, the apparatus
provided with control means for selectively operating either a near
infrared ray irradiating unit arranged on one side or near infrared
irradiating units arranged on both sides in conformity with surface
condition of the copper foil fed through the drying chamber.
12. The method of claim 1, wherein said near infrared rays have a
wavelength of about 0.8 to 2 .mu.m.
13. The apparatus of claim 8, wherein said near infrared
irradiation unit supplies infrared rays having a wavelength of
about 0.8 to 2 .mu.m.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method of drying a copper
foil and a copper foil drying apparatus for use in the method. In
particular, the present invention relates to a method of drying the
copper foils used in copper clad laminates, each of such laminates
comprising an insulating resin clad with a copper foil, the copper
clad laminates are used, for example, in printed wiring boards, the
invention also relates to a copper foil drying apparatus used in
the method.
BACKGROUND OF THE INVENTION
[0002] The demand for printed wiring boards having electronic
components such as IC (integrated circuits) and LSI (large scale
integrated circuits) mounted thereon is rapidly increasing in
accordance with the progress of electronic industry.
[0003] In the production of the printed wiring boards, kraft paper,
glass cloth, glass nonwoven fabric or the like are impregnated with
a thermosetting resin such as a phenolic resin or an epoxy resin to
obtain a pre-preg.
[0004] This pre-preg and a copper foil are bonded with each other
by, for example, hot pressing. Thereafter, resist printing and
masking film lamination are used to form circuit patterns. Unwanted
portions of the copper foil are etched away with the use of an acid
or an alkali to form a desired circuit pattern, and the resist and
masking film are removed. After the formation of the desired
circuit pattern, electronic components are set at the predetermined
positions of the printed wiring board and dipped in a solder bath
so that the electronic components are fixed on the printed wiring
board.
[0005] Two types of copper foils, namely electrodeposited copper
foil and rolled copper foil, are available for use in printed
wiring boards. These days, however, electrolytic copper foil is
more often employed because of its wide applicability and because
of the ease and low cost in forming a thinner copper foil.
[0006] Electrodeposited copper foil for use in printed wiring
boards is conventionally produced through the following
process.
[0007] That is, a copper sulfate solution is placed in a
electrolyzing bath and anodes composed of insoluble electrodes, are
disposed in the electrolyzing bath.
[0008] Furthermore, a rotating cathode drum is disposed in the
electrolyzing bath so that almost half of the drum is immersed in
the copper sulfate solution and the surface of the drum is opposite
to the anodes. Then, high current density is passed through the
anodes and cathode drum to produce continuously the copper foil. In
this case, the surface of the foil which was in contact with the
surface of the cathode drum, is the shiny side of the
electrodeposited copper foil and the outer surface of the copper
foil is the matte side.
[0009] The copper foil obtained through this electrolytic process
is subjected to surface treatments. In these surface treatments,
nodularization of the copper foil is performed for exerting an
anchoring effect when bonding with a substrate, followed by zinc
plating, chromating or silane coupling treatments for exerting a
passivation effect. Finally, drying is performed to obtain the
electrodeposited copper foil for making printed circuits.
[0010] On the other hand, in case of as-rolled copper foil, both
surface sides of the copper foil are shiny or smooth. One side or
both sides of these shiny sides is subjected to a surface
treatment.
[0011] The copper foil having undergone the above surface
treatments, because, for example, the electrolyte adheres to the
surface thereof, must be washed with water (not shown) prior to the
drying by means of a dryer for removing water from the surface of
copper foil.
[0012] Therefore, it is common practice to perform drying of the
electrolytic copper foil. This drying is generally accomplished by
drying using hot air or using far infrared rays. The current
situation is that drying by these methods is to about such an
extent that the water adhering to the surface of the copper foil is
removed and, thus, the drying temperature is held at up to
100.degree. C.
[0013] Heating the surface of the copper foil to 100.degree. C. or
higher, for example, causes the zinc of the plated zinc layer
provided on the surface of the copper foil to diffuse into the
copper foil so that a zinc-copper alloying (brass formation) is
effected. As a result, the dezincing phenomenon, which is the
leaching of zinc into an acid such as hydrochloric acid used in the
formation of circuit pattern, does not occur, thereby enhancing the
acid resistance. Further, according to the inventors'
investigations, the higher the surface temperature of the copper
foil, the greater the peel strength relative to the resin
substrate, until a peel strength peak at about 130.degree. C. as
shown in FIG. 3.
[0014] Drying using hot air enables heating the copper foil and
regulating the temperature at 130.degree. C. or higher. However,
this method relies on the heating (drying) through the heat
transfer from hot air, so that the energy loss attributed to
discharged hot air is large. Further, as shown in FIG. 5, hot air
drying apparatus 700 requires heater 701, fan 702 and circulation
path 704 including path 703 for discharging a large volume of
exhaust gas containing steam outside the apparatus. Therefore,
unfavorably, the size of the apparatus is large, the space required
is large, and the cost is high.
[0015] On the other hand, drying using far infrared rays, the
surface of the copper foil reflects almost about 97% or more of the
far infrared rays whose wavelength range is from 4 to 1000 .mu.m
(see pages 6 to 120 of American Institute of Physics Handbook) and,
hence, exhibits low absorption of far infrared rays. Therefore, the
energy loss is large, and the temperature of the surface of the
copper foil cannot be readily increased. Accordingly, a
multiplicity of far infrared ray irradiating units must be arranged
for attaining temperatures of 130.degree. C. or higher, thereby
resulting in disadvantages in terms of apparatus, power consumption
and cost.
OBJECT OF THE INVENTION
[0016] The present invention has been made taking the above state
of the art into account. Accordingly, an object of the present
invention is to provide a method of drying a copper foil, by which
the drying of surface-treated copper foil can be accomplished by a
simple apparatus with low electric power while controlling the
heating of the surface of the copper foil so that the drying
temperature can be held at 100.degree. C. or higher, at which
condition a eutectic alloying of a rust preventive metal and copper
foil, for example, alloying (brass formation) of zinc and copper on
the surface of the copper foil is effected. Another object of the
present invention is to provide a copper foil drying apparatus
suitable for use in this method.
SUMMARY OF THE INVENTION
[0017] The present invention has been made with a view toward
solving the above problems of the prior art and attaining the above
object. Thus, the present invention provides a method of drying a
copper foil, which has been subjected to surface treatments, which
method comprises irradiating a surface or surfaces of the copper
foil with near infrared rays to thereby dry the copper foil.
[0018] In this invention, term "surface treatments" includes not
only nodularization and passivation, but also any other surface
treatments, in combination or independently.
[0019] In particular, the copper foil drying method of the present
invention is characterized in that the copper foil is an
electrolytic copper foil.
[0020] Near infrared rays are easily absorbed by the copper foil
surface so that the copper foil surface can be heated to a given
temperature with a high energy efficiency. Also, the copper foil
surface can be heated and regulated at a given temperature by
changing voltage and electric current applied to a near infrared
irradiating unit. As a result, the copper foil surface can be
heated and dried at 100.degree. C. or higher at which temperature
the alloying (brass formation) of zinc-copper occurs. Not only is
the acid resistance improved but also, the bonding strength to a
resin substrate is increased, thereby exhibiting an increased peel
strength and avoiding separation of the copper foil from the resin
substrate.
[0021] Further, the copper foil drying method of the present
invention may be characterized in that at least one surface-treated
side of the copper foil is irradiated with near infrared rays to
dry the copper foil.
[0022] In this instance, the absorptivity of near infrared rays is
increased on the surface-treated side of the copper foil, so that
the heating and drying of the copper foil surface can be done with
enhanced energy efficiency.
[0023] Still further, the copper foil drying method of the present
invention may be characterized in that fine particles are applied
to a copper foil surface to roughen the copper foil surface and the
modularized surface of the copper foil is irradiated with near
infrared rays.
[0024] Surface nodularization for increasing the bonding strength
(peel strength) with a resin substrate, is performed prior to
passivation, and thereafter the modularized surface is irradiated
with near infrared rays. Thus, by virtue of the unevenness formed
by the nodularization, the absorptivity of near infrared rays is
increased to enable heating and drying of the copper foil surface
with enhanced energy efficiency.
[0025] Still further, the copper foil drying method of the present
invention may be characterized in that the copper foil surface is
furnished with passivation and, thereafter, the nodularized surface
of the copper foil is irradiated with near infrared rays.
[0026] It is preferred that the passivation comprise applying a
rust preventive metal preferably, at least one rust preventive
metal selected from the group consisting of Zn, Ni, Sn, Cr, Mo and
Co.
[0027] Furthermore, the copper foil drying method of the present
invention may be characterized in that the drying by near infrared
irradiation be performed under conditions such that the surface of
the copper foil has a temperature of 100 to 170.degree. C.,
preferably 120 to 150.degree. C.
[0028] When the copper foil surface is heated at 100 to 170.degree.
C., the formation of a eutectic alloy of a rust preventive metal
and copper foil, for example, alloying (brass formation) of
zinc-copper is effected on the copper foil surface. Further, the
dezincing phenomenon in which zinc is leached is prevented, thereby
enhancing the acid resistance. Still further, the bonding strength
with a resin substrate, namely the peel strength, is also
enhanced.
[0029] In another aspect of the present invention, there is
provided a copper foil drying apparatus for drying a copper foil
which has been subjected to various surface treatments, which
apparatus comprises a drying chamber and, arranged therein, a near
infrared irradiating unit, said drying chamber adapted to allow the
copper foil to be continuously fed therethrough, said near infrared
irradiating unit arranged opposite to a surface-treated side of the
copper foil so that at least the surface-treated side of the copper
foil is irradiated with near infrared rays.
[0030] In particular, the copper foil drying apparatus of the
present invention is characterized in that the copper foil is an
electrodeposited copper foil.
[0031] Further, the copper foil drying apparatus of the present
invention may be characterized in that it further comprises means
for controlling output to near infrared ray lamps of the near
infrared irradiating unit so that the surface of the copper foil
has a controlled drying temperature.
[0032] In this construction, lead time required for start-up of
near infrared ray lamps is short, so that the temperature is
rapidly raised to the desired level. Moreover, the surface
temperature of the copper foil can continuously be regulated by
controlling the voltage or electric current applied to near
infrared ray lamps. Therefore, the drying can be performed while
heating and regulating the copper foil surface at 100 to
170.degree. C. so that the formation of a eutectic alloy of rust
preventive metal and copper foil, for example, alloying (brass
formation) of zinc-copper is effected on the copper foil surface to
enhance the acid resistance, and inhibit the dezincing phenomenon
(leaching) and so that the bonding strength with a resin substrate,
namely the peel strength, is also enhanced.
[0033] Still further, the copper foil drying apparatus of the
present invention may be characterized in that near infrared ray
irradiating units are arranged so that these face each other with
the copper foil interposed therebetween, the apparatus provided
with control means for selectively operating either a near infrared
irradiating unit arranged on one side or near infrared irradiating
units arranged on both sides in conformity with surface condition
of the copper foil fed through the drying chamber.
[0034] When the electrodeposited copper foil is dried with only its
matte side subjected to nodularization, passivation, etc., this
apparatus selectively operates the near infrared irradiating unit
arranged on the one side. For the shiny side treated
electrodeposited copper foil having a shiny side bond enhancing
treatment in order to increase the insulation reliability after
etching or to enhance the circuit characteristics, this apparatus
selectively operates the near infrared ray irradiating units
arranged on both sides. Thus, there is no limit on the copper foil
to be dried.
BRIEF DESCRIPTION OF THE DRAWING
[0035] FIG. 1 is a schematic sectional view of the first form of
drying apparatus for use in carrying out the copper foil drying
method of the present invention;
[0036] FIG. 2 is a schematic sectional view of the second form of
drying apparatus for use in carrying out the copper foil drying
method of the present invention;
[0037] FIG. 3 is a graph showing the relationship between copper
foil drying temperature and peel strength;
[0038] FIG. 4 is a graph showing the relationship between time and
foil temperature when the copper foil surface is heated by near
infrared rays or far infrared rays; and
[0039] FIG. 5 is a schematic diagram of the conventional hot air
drying apparatus.
DETAILED DESCRIPTION OF THE INVENTION
[0040] Embodiments (Examples) of the present invention will be
described below with reference to the drawings.
[0041] FIG. 1 is a schematic sectional view of the first form of
drying apparatus for use in carrying out the copper foil drying
method of the present invention.
[0042] The copper foil is obtained by the conventional foil
producing process in which an acidic copper sulfate solution is fed
into an electrolytic cell and copper is deposited by elctrolysis on
a rotating cathode drum arranged opposite to an insoluble anode and
after which copper is continuously wound up. The matte side of
electrodeposited copper foil is subjected to surface treatment
steps including, for example, nodularization, zinc plating and
chromating steps and, as required, further subjected to a silane
coupling treatment step for increasing the bonding strength with a
resin substrate. The electrolyte and other matter adhere to the
surface of the copper foil having undergone these surface treatment
steps. Therefore, the copper foil must be washed with water,
although not shown, prior to being fed to the drying step for
removing water from the copper foil surface by means of a
dryer.
[0043] Accordingly, referring to FIG. 1, the copper foil 1 having
undergone these surface treatments is passed between rolls 2, 3 so
that water, etc. are squeezed off to a certain degree. The squeezed
copper foil 1 is fed through copper foil inlet opening 22 disposed
at a lower side of drying apparatus body 20 of drying apparatus 10,
dried inside the drying apparatus body 20 and discharged through
copper foil outlet opening 24 disposed at an upper side of the
drying apparatus body 20. The dried copper foil 1 discharged
through the copper foil outlet opening 24 is wound on wind-up roll
30.
[0044] Inside the drying apparatus body 20, near infrared ray
irradiating unit 40 is arranged in a direction parallel to the
direction of feeding the copper foil 1 and a direction opposite to
a surface treatment matte side 1a of the copper foil 1. A plurality
of mutually parallel halogen lamps 42 are disposed in a direction
parallel to the direction of feeding of the copper foil in the near
infrared ray irradiating unit 40. The halogen lamps 42 are backed
with a deflector 44 having a specular surface such that near
infrared rays emitted from the halogen lamps 42 are reflected to
irradiate the surface-treated matte side 1a of the copper foil
1.
[0045] Moreover, air feeding unit 26 is disposed in the vicinity of
the copper foil inlet opening 22 of the drying apparatus body 20,
so that, by means of a blower not shown, outside dry fresh air is
introduced into the drying apparatus body 20. On the other hand,
exhaust unit 28 is disposed in the vicinity of the copper foil
outlet opening 24 of the drying apparatus body 20, so that the air
containing steam evaporated from the surface of the copper foil 1
is exhausted from the drying apparatus body 20. These accelerate
the evaporation of moisture from the surface of the copper foil
1.
[0046] The individual halogen lamps 42 of the near infrared
irradiating unit 40 are connected to control unit 50. Thus, the
output of the halogen lamps 42 toward the surface of the copper
foil 1, is regulated by controlling the voltage or electric current
supplied to the individual halogen lamps 42 by means of the control
unit 50 to enable regulating the temperature of the surface-treated
side 1a of the copper foil 1 during drying.
[0047] The above control of voltage or electric current can be done
by, for example, the ON-OFF controlling method in which the time is
regulated by voltage ON-OFF, the phase controlling method in which
voltage/electric current regulation and control are carried out or
the zero cross switching method in which the loading power time
ratio is regulated (ON-OFF control).
[0048] With respect to the method of controlling the voltage or
electric current by means of the control unit 50, although the
control can be done so that all the individual halogen lamps 42
have the same values of voltage or electric current, the control
can also be done so that the individual halogen lamps 42 have
selected values of voltage or electric current or so that the
voltage or electric current applied to the individual halogen lamps
42 is selectively switched on or off.
[0049] Further, with respect to the method of controlling the
voltage or electric current applied to the halogen lamps 42,
automatic continuous control can be effected by disposing a
temperature sensor in the vicinity of the surface-treated side 1a
of the copper foil 1, although not shown, and controlling the
voltage or electric current supplied to the halogen lamps 42 by
means of the control unit 50 on the basis of the temperature
detected by the temperature sensor.
[0050] Regarding the wavelength of near infrared rays, it is
preferred that the wavelength peak be in the range of 0.8 to 2
.mu.m, especially 1 to 1.5 .mu.m, so that the surface of the copper
foil 1 has a high absorptivity of near infrared rays. Therefore, it
is desirable to regulate the wavelength of emitted near infrared
rays so as to fall within the above range by raising the
temperature of the halogen lamps 42 to 2000-2200.degree. C. by
controlling the voltage or electric current applied to the halogen
lamps 42 by means of the control unit 50. By virtue of this
control, the temperature of the surface-treated side 1a of the
copper foil 1 is preferably set at 100 to 170.degree. C., more
preferably 120 to 150.degree. C.
[0051] Referring to FIG. 3, the peel strength from the resin
substrate is increased in accordance with the increase of the
temperature of the surface of the copper foil 1. The peel strength
reaches its peak at about 130.degree. C. When the surface of the
copper foil 1 is heated at 150.degree. C. or higher, for example,
zinc contained in the zinc plating layer formed on the copper foil
surface is diffused into the copper foil to effect the alloying
(brass formation) of zinc-copper. Thus, the dezincing phenomenon,
namely the leaching of zinc into an acid such as hydrochloric acid
used in the formation of circuit patterns, would not occur, thereby
realizing an enhancement of acid resistance. Accordingly, taking
into account both the formation of a eutectic alloy from rust
preventive metal and copper foil and the peel strength representing
the bonding strength with the resin substrate, the temperature of
the surface-treated side 1a of the copper foil 1 is preferably set
at 100 to 170.degree. C., more preferably 120 to 150.degree. C.
When the temperature of the surface-treated side 1a of the copper
foil 1 is lower than 100.degree. C., the formation of a eutectic
alloy from rust preventive metal and copper foil such as the
alloying (brass formation) of zinc-copper would not occur at the
surface of the copper foil 1 with the result that the acid
resistance is not satisfactory. On the other hand, when the
temperature of the surface-treated side 1a of the copper foil 1 is
higher than 170.degree. C., the chromate used as a rust preventive
is destroyed although the advance of the alloying is rapid. The
bonding strength between the copper foil 1 and the resin substrate,
namely the peel strength is lowered.
[0052] The residence time of the copper foil 1 in the drying
apparatus body 20 is generally about 10 sec from the viewpoint of
the capacity of facilities.
[0053] From the viewpoint of energy efficiency, it is preferred
that the distance between the halogen lamps 42 and the
surface-treated side 1a of the copper foil 1 be set at 20 to 100
mm, especially 30 to 50 mm.
[0054] By irradiating the surface-treated side 1a of the copper
foil 1 with near infrared rays as described above, near infrared
rays are easily absorbed by the copper foil surface, so that the
copper foil surface can be heated to a given temperature with a
high energy efficiency. Moreover, the copper foil surface can be
heated and regulated at a given temperature by changing voltage and
electric current outputs applied to near infrared ray lamps of a
near infrared irradiating unit. As a result, the copper foil
surface can be heated and dried at 100.degree. C. or higher at
which the formation of a eutectic alloy from rust preventive metal
and copper foil such as the alloying (brass formation) of
zinc-copper is carried out, so that not only is the acid resistance
improved but also, when bonding with a resin substrate, the bonding
strength, namely the peel strength, is increased to avoid
separation of the copper foil from the resin substrate.
[0055] FIG. 2 is a schematic sectional view of the second form of
drying apparatus for use in carrying out the copper foil drying
method of the present invention.
[0056] This form of drying apparatus has a structure similar to
that of the above first form of drying apparatus. Like reference
numbers are employed to designate fundamentally like structural
members throughout FIGS. 1 and 2, and the detailed description
thereof will not be repeated.
[0057] This form of drying apparatus 10 is different from the above
first form of drying apparatus in that near infrared ray unit 60
like the near infrared ray irradiating unit 40 is disposed in a
vertical direction opposite to a surface-treated shiny side 1b of
the copper foil 1 inside the drying apparatus body 20. The
structure of this near infrared ray unit 60 is the same as that of
the near infrared ray irradiating unit 40 of the above first form
of drying apparatus, so that detailed description thereof will not
be repeated.
[0058] Depending on the type of copper foil, the surface-treated
shiny side may be a substrate bonding side in order to improve the
circuit characteristics and the insulation reliability after
etching, and the shiny side 1b may be roughened in order to
increase the adherence to the substrate. In this instance, the
surface-treated shiny side 1b is a modularized surface, so that
near infrared rays can be absorbed. Therefore, the drying of the
copper foil 1 can be carried out with enhanced energy efficiency by
simultaneously irradiating the surface-treated shiny side 1b with
near infrared rays to dry the copper foil surface.
[0059] In this drying apparatus 10, the individual halogen lamps 62
of the near infrared ray unit 60 are connected to the control unit
50 in the same manner as in the above near infrared ray irradiating
unit 40. Thus, the output of the halogen lamps 62, namely the level
of radiation of near infrared rays emitted from the halogen lamps
62 toward the shiny side 1b of the copper foil 1, is regulated by
controlling the voltage or electric current supplied to the
individual halogen lamps 62 from the power source by means of the
control unit 50 to enable regulating the temperature of the shiny
surface 1b of the copper foil 1 during the drying.
[0060] This drying apparatus can be so constructed as to enable
selectively operating either one or both of the near infrared ray
irradiating unit 40 and the near infrared ray unit 60 by means of
the control unit 50.
[0061] Therefore, when the copper foil is dried with only its
surface-treated matte side subjected to bond enhancing reatement,
for instance, nodularization, passivation, etc., this apparatus
selectively operates the near infrared irradiating unit arranged on
that side. For copper foil having its shiny side roughened in order
to increase the insulation reliability after etching or to enhance
the circuit characteristics, this apparatus selectively operates
the near infrared ray irradiating units arranged on both sides.
Thus, there is no limit on the copper foil to be dried.
[0062] In the above first and second forms of drying apparatus 10,
in place of the use of the near infrared ray irradiating units
40,60 only, it is naturally feasible to employ a hot air dryer or a
far infrared ray irradiating unit, although not shown, in
combination with the near infrared ray irradiating units 40,60.
[0063] In the above embodiments the copper foil having been
subjected to surface treatment steps including, for example,
nodularization, zinc plating and chromating steps and, as needed,
further subjected to a silane coupling treatment step for
increasing the bonding strength with a resin substrate is dried by
means of the drying apparatus to remove water from the copper foil
surface. However, drying by means of the drying apparatus may be
done after any of these steps or after a combination of steps
selected from thereamong. Furthermore, these passivation steps are
not limited to those mentioned above, and may include, for example,
a rust preventive treatment in which at least one rust preventive
metal selected from the group consisting of Zn, Ni, Sn, Cr, Mo and
Co.
[0064] Moreover, although in the above embodiments the
electrodeosited copper foil has been employed as the copper foil to
be dried, the present drying is naturally applicable to, for
example, a rolled copper foil which is subjected to surface
treatments such as nodularization, passivation and the like.
EFFECT OF THE INVENTION
[0065] In the present invention, the near infrared rays with which
the copper foil surface is irradiated to thereby dry the copper
foil are easily absorbed by the copper foil surface, so that the
copper foil surface can be heated to a given temperature with a
high energy efficiency. Moreover, the copper foil surface can be
heated and regulated at a given temperature by changing voltage and
electric current outputs applied to the unit irradiating near
infrared rays.
[0066] As a result, the copper foil surface can be heated and dried
at 100.degree. C. or higher at which the alloying (brass formation)
of zinc-copper occurs, so that not only is the acid resistance
improved but also, the bonding strength with a resin substrate is
increased to provide increased peel strength and avoid separation
of the copper foil from the resin substrate.
[0067] The surface of the copper foil exhibits a low absorption of
far infrared rays, so that the energy loss is large. Much time and
energy must be spent for raising the temperature to a given level
and, because of poor efficiency, the apparatus must be large and
the residence time of the copper foil therein must be prolonged.
Further, the hot air drying also exhibits poor energy efficiency
and must be equipped with a heater, a blower and circulation paths
including a path for discharging a large volume of exhaust gas
containing steam outside the apparatus. Therefore, unfavorably, the
size of the apparatus is large, the installation space thereof is
large, and the cost is high. With respect to energy efficiency and
quick response, the drying method using near infrared rays is
strikingly superior to the above far infrared ray and hot air
methods.
[0068] Therefore, the present invention is remarkably excellent in
view of the many effects including the compact apparatus, high
energy efficiency, capability of heating and drying the copper foil
surface at a given temperature, enhancement of acid resistance and
production of copper foil exhibiting a high bonding strength when
bonded with a resin substrate.
EXAMPLE
[0069] The present invention will now be illustrated in greater
detail with reference to the following Examples, which in no way
limit the scope of the invention.
Example 1
[0070] Electrodeposited copper foil having a thickness of 35 .mu.m
was electrolyzed in an acidic copper sulfate solution so that the
electrodposited copper foil was provided with copper plating to
roughen the matte side of the electrodeposited copper foil. Thus,
the copper foil having its matte side overlaid with a particulate
copper layer was obtained (nodularization).
[0071] The resultant copper foil was electrolyzed in a zinc
solution bath of pH 11.0 containing 10 g/L. of zinc pyrophosphate
and 100 g/L. of potassium pyrophosphate at room temperature at a
current density of 5 A/m.sup.2 for 6 sec so that the copper foil on
its matte side was overlaid with 400 mg/m.sup.2 (in terms of zinc)
of a zinc plating.
[0072] Subsequently, the zinc plated copper foil was electrolyzed
in a chromating solution of pH 10 containing 2 g/L. of chromic acid
at room temperature at a current density of 0.5 A/m.sup.2 for 5 sec
so that the copper foil surface on its matte side was overlaid with
a chromate coating layer composed of zinc chromate.
[0073] Thereafter, a 5 g/L. aqueous
.gamma.-glycidoxypropyltrimethoxysilan- e solution containing 0.5
g/lit. of chromic acid was sprayed on the foil so that a silane
coupling treatment was provided for the copper foil. The surface
treated copper foil was passed through a water washing bath and
then between dewatering rolls and dried by means of the near
infrared drying apparatus of the present invention as shown in FIG.
1.
[0074] The drying of the copper foil was performed under various
temperature conditions by regulating output voltage applied to the
near infrared ray lamps while measuring the temperature of the
surface-treated matte side of the copper foil by the change of
color of a thermotape stuck to the shiny side of the copper
foil.
[0075] The dried copper foil was hot-pressed with glass epoxy
substrate (produced by NELCO) and etched in 10 mm width. 90.degree.
peeling thereof was performed in accordance with Japanese
Industrial Standard C-6481 to determine the peel strength.
[0076] For comparison, the above copper foil was dried by hot air,
in place of near infrared rays, at varied copper foil surface
temperatures while checking the change of color of a thermotape
stuck to the shiny side of the copper foil. The peel strength
thereof was measured in the same manner.
[0077] The results are shown in FIG. 3. As apparent from FIG. 3,
the peel strength reaches its peak when the drying temperature of
the copper foil surface is in the vicinity of 130.degree. C.
[0078] It is also apparent that, even at the same temperature
employed in the drying of copper foil surface after dewatering, the
peel strength is greater when the drying is performed with the use
of near infrared rays than when the drying is performed with the
use of hot air.
[0079] The reason is presumed to be that some texture change is
made in the silane coupling layer, chromating layer and zinc
plating layer by the irradiation of near infrared rays to thereby
increase the adherence to the resin substrate.
Example 2
[0080] With respect to the energy required for raising the
temperature of the surface of the copper foil after dewatering
obtained in the same manner as in Example 1 to given level, near
infrared ray, far infrared ray and hot air drying were compared to
each other in the power and time spent for raising the temperature
of the surface of the copper foil to given level. The results are
given in Table 1 and FIG. 4.
1 TABLE 1 Index of electric energy (KWH/t) for increasing foil
temp. to 130.degree. C. Near I.R. ray drying 100 Far I.R. ray
drying 350 Hot air drying 250
[0081] As apparent from the results of FIG. 4, in the comparison of
the time spent for raising the temperature of the surface of the
copper foil to 130.degree. C., the time was only 1 sec when near
infrared ray drying was used while about 15 sec was needed when far
infrared ray drying was used although the far infrared heater had
the same capacity as that of the near infrared heater.
[0082] Further, as apparent from the results of Table 1, the
electric energy per weight required by far infrared ray and hot air
drying were 350 and 250, respectively, while that required by the
near infrared ray drying was 100, and hence the near infrared ray
drying was found to be strikingly superior to the far infrared ray
and hot air drying in respect of both energy efficiency and
response characteristics.
Example 3
[0083] Copper foils produced by drying after dewatering in the same
manner as in Example 1 with the use of near infrared rays at varied
copper foil surface drying temperatures were hot-pressed to glass
epoxy substrates, etched in 0.8 mm width and immersed in a 12%
hydrochloric acid solution at room temperature for 30 min to
thereby compare the acid resistances thereof with each other.
[0084] For comparison, the copper foils were dried by hot air at
the same varied drying temperatures, and the acid resistances
thereof were compared with each other.
[0085] The results are given in Table 2 below.
2 TABLE 2 Peel loss after Drying temp. (.degree. C.) HCL (%) Near
I.R. ray 1 85 21 drying 2 110 6 3 150 0 4 170 12 Hot air drying 5
85 22 (Comp.) 6 110 10 7 150 6
[0086] It is apparent from the results of Table 2 that the
hydrochloric acid resistance (improvement of peel loss after HCL)
is enhanced by near infrared ray drying conducted with the drying
temperature of the surface of the copper foil held at 100.degree.
C. or higher. The reason is that, at 100.degree. C. or higher, the
zinc of the zinc plating is diffused into the copper foil to
thereby form a copper-zinc binary eutectic alloy with the result
that the dezincing phenomenon can be avoided.
[0087] Similar results are obtained in the hot air drying as
well.
* * * * *