U.S. patent application number 09/833059 was filed with the patent office on 2002-01-31 for method for surface treatment of copper foil.
This patent application is currently assigned to FUKUDA METAL FOIL & POWDER CO., LTD.. Invention is credited to Hirose, Masaru, Manabe, Hisanori, Takami, Masasto.
Application Number | 20020011418 09/833059 |
Document ID | / |
Family ID | 18624899 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020011418 |
Kind Code |
A1 |
Manabe, Hisanori ; et
al. |
January 31, 2002 |
Method for surface treatment of copper foil
Abstract
Disclosed is a process of treating the surface of copper foil
without using harmful elements such as arsenic, selenium and
tellurium unlike in the prior art. It is possible to, in an easy
way, obtain a uniform rough condition and low rougheness and
produce a high adhesive strength to such resin base materials as
polymide resin which is weak in adhesive strength. The process
comprises a roughening treatment involving a cathodic electrolysis
of at least one side of copper foil near or above the limiting
current density in an electrolytic bath containing titanium ions
and tungsten ions and prepared by adding sulfuric acid and copper
sulfate so as to have copper protrusions deposited and then coating
the depositions with copper or a copper alloy in a cathodic
electrolysis, followed by giving to the surface of the
above-mentioned copper or the copper alloy at least one of the
following rust-proofing treatments--chromate treatment, organic
rust-proofing treatment and silane coupling agent treatment.
Inventors: |
Manabe, Hisanori; (Kurisuno,
JP) ; Takami, Masasto; (Gokasho, JP) ; Hirose,
Masaru; (Higashino Minami, JP) |
Correspondence
Address: |
RONALD E. GREIGG
GREIGG & GREIGG P.L.L.C.
1423 POWHATAN STREET, UNIT ONE
ALEXANDRIA
VA
22314
US
|
Assignee: |
FUKUDA METAL FOIL & POWDER CO.,
LTD.
|
Family ID: |
18624899 |
Appl. No.: |
09/833059 |
Filed: |
April 12, 2001 |
Current U.S.
Class: |
205/191 ;
205/219 |
Current CPC
Class: |
C25D 1/04 20130101; C25D
3/38 20130101; H05K 2203/0307 20130101; C25D 5/48 20130101; H05K
2203/0723 20130101; H05K 2201/0355 20130101; C25D 5/605 20200801;
H05K 3/384 20130101; C25D 3/58 20130101 |
Class at
Publication: |
205/191 ;
205/219 |
International
Class: |
C25D 005/34 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 14, 2000 |
JP |
2000-112808 |
Claims
What is claimed:
1. A process of treating the surface of copper foil which comprises
the steps of: Roughening the surface to deposit copper protrusions
by subjecting at least one side of copper foil near or above the
limiting current density in an electrolytic bath containing
titanium ions and tungsten ions and prepared by adding sulfuric
acid and copper sulfate coating the depositions with copper or a
copper alloy by a cathodic electrolysis, giving to the surface of
said copper or the copper alloy at least one of the following
rust-proofing treatments--chromate treatment, organic rust-proofing
treatment and silane coupling agent treatment.
2. The process of treating the surface of copper foil wherein the
electrolytic bath contains 0.03 to 5 g/l of titanium ions and 0.001
to 0.3 g/l of tungsten ions.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the surface treatment of
copper foil. More specifically, this invention concerns the method
of treating the surface of copper foil to create a surface with a
rough and uniform condition and with a high adhesion to resins for
use in the semiconductor field represented by printed circuit
boards.
[0003] 2. Description of the Prior Art
[0004] Copper foil is used in printed circuit boards for
electronics and electric materials in large quantities.
[0005] Printed circuit boards are made in the following process.
First, the matte side of copper foil is put on an insulating
resin-impregnated base material, heated and press-bonded into a
copper-coated laminated board. The glass-epoxy resin base material
(FR-4) which is widely used is pressed at 170.degree. C. for one to
two hours. Some base materials like glass and high heat-resistant
resins such as polyimide require pressing for two hours at
220.degree. C.
[0006] Printed circuit boards have been improved in performance and
reliability, and the properties required in the printed circuit
boards are getting complicated and diversified.
[0007] The copper foil, one of the constituent materials of the
printed circuit board, too, has to meet vigorous quality
requirements.
[0008] Copper foil for printed circuit boards is available in two
kinds, that is, rolled copper foil and electrodeposited copper
foil. The electrodeposited copper foil which has a matte side and a
shiny side is used in predominantly large quantities.
[0009] The electrodeposited copper foil is generally made in the
following process. Copper is deposited from a copper electrolytic
solution in an electrodeposition apparatus to obtain a crude foil
which is called untreated copper foil. Then, the matte side
(non-shiny side) of the untreated copper foil is pickled for
roughening treatment to secure adhesion to the resin. Then, the
copper foil is treated to improve and stabilize such properties as
heat resistance and chemical resistance and etching properties.
[0010] A number of techniques for those treatments have been
developed and proposed, which make available copper foils with
high-functional surfaces.
[0011] Printed circuit boards have been highly densified in recent
years, and the insulating layer or the resin layer is made very
thin in thin printed circuit boards and build-up process printed
circuit boards, for example. Such printed circuit boards can
present problems with interlayer insulating properties if the
roughened side of copper foil is high in degree of rougheness.
[0012] In a recent trend toward fine lining, furthermore, a matte
side with a low profile is being sought, because a lower degree of
rougheness on the roughened side of copper foil can keep the
inter-line insulation better. However, if the adhesion is not
sufficient, the copper foil circuit will present such problems as
peeling, lifting, and delamination in the course of or after
manufacturing. Those requirements are conflicting with each other,
and a process of surface treatment that meet those conflicting
requirements is sought.
[0013] Furthermore, as base material for printed circuit boards,
glass-epoxy resin base material (FR-4) has been widely used, while
base materials impregnated with special resins like polyimide
resin, high heat-resistant and low dielectric constant resins are
finding increasing use in printed circuit boards because of the
high reliability.
[0014] Such special resins are low in adhesion for copper foil. It
is hoped that a process of surface treatment should be developed
that solves the adhesion problem on the low profiled surface.
[0015] Meanwhile, the shiny side or the reverse side of the matte
side of copper foil requires properties different from those on the
matte side. They include resistance to heat color change, solder
wettability and resist adhesion. The matte side needs a process of
surface treatment different from that for the shiny side.
[0016] In the past, no solder wettability is required in the shiny
side of copper foil for use in multi-layer printed circuit boards,
especially as inner layer and did not need to be roughened.
[0017] But even in an application called DT (double treatment) foil
other than copper foil, light roughening has come to be hoped for
to improve the adhesion for resist and the adhesive strength in
treatment of inner layers in forming a printed circuit board.
[0018] Sophisticated treatments have been developed to meet a
variety of requirements made on the matte side and the shiny side
of copper foil.
[0019] A number of processes of roughening copper foil are
disclosed. For example, Japanese publicized examined patent
application gazette No. 53-38700 discloses a process involving a
three-step electrolytic treatment in an acid electrolytic bath
containing arsenic. Japanese publicized examined patent application
gazettes Nos. 53-39327 and 54-38053 disclose processes comprising
carrying out electrolysis at around the limiting current density in
a acid copper electrolytic bath containing arsenic, antimony,
bismuth, selenium, and tellurium. Japanese patent No. 2717911
discloses a process involving electrolysis at around the limiting
current density in an acid copper electrolytic bath containing
either chromium or tungsten or both.
[0020] But some of the above-mentioned processes use such
substances as arsenic, selenium and tellurium that are harmful to
humans and have to be extremely limited in their uses in the light
of the environmental protection. It is feared that the harmful
components contained in copper foil could pollute the environment
when printed circuit boards are recycled or disposed of as
industrial waste. One of the disclosed processes of surface
treatment involves treatment in a bath containing chromium and
tungsten. In this process, the roughened surface condition improves
in uniformity but is low in adhesive strength to glass epoxy resin
base material (FR-4) and especially glass-polyimide resin base
material etc. and is not practically useful.
SUMMARY OF THE INVENTION
[0021] In view of the prior art described above, including the
disadvantages and problems of the prior art, it is an object of the
present invention to provide an easy process of copper foil surface
treatment which does not use such harmful substances as arsenic,
selenium and tellurium and which produces a copper foil with a
uniform matte condition, a low surface rougheness and a high
adhesive strength for such base resins with a weak adhesion as
polyimide resin.
[0022] The foregoing object is effected by the invention as will be
apparent from the following description. That is, at least one side
of copper foil is subjected to a roughening treatment involving a
cathodic electrolysis near or above the limiting current density in
an electrolytic bath containing titanium ions and tungsten ions and
prepared by adding sulfuric acid and copper sulfate so as to have
copper protrusions deposited and then the depositions are coated
with copper or a copper alloy in a cathodic electrolysis. Then the
surface of the above-mentioned copper or the copper alloy is given
at least one of the following rust-proofing treatments--chromate
treatment, organic rust-proofing treament and silane coupling agent
treatment.
[0023] It is preferable that the concentration of titanium ions is
0.03 to 5 g/l and the concentration of tungsten is 0.001 to 0.3 g/l
in the electrolytic bath.
[0024] The roughening treatment method according to the present
invention will be described. First, untreated copper foil is
pickled to remove oxides and stains on the surface.
[0025] Then, the matte surface of the copper foil is subjected to
cathodic electrolysis near or above the limiting current density in
an electrolytic bath so as to have copper protrusions deposited on
the surface, thus forming an uneven surface.
[0026] The deposited copper protrusions are weak in adhesive
strength to the surface of the copper foil. After that, therefore,
a coat of copper or copper alloy is formed by cathodic electrolysis
so as to coat the protrusions with the copper, thus keeping copper
foil and copper protrusions from peeling off.
[0027] Then, the coat of copper or copper alloy is subjected to
rust proofing treatment.
[0028] The cathodic electrolysis conditions to deposit copper
protrusions on the copper foil surface are different depending on
the concentration of the electrolytic bath, time, temperature, the
requred extent of roughing, and not limited in particular. But the
preferable conditions are treatment time 2 to 60 seconds, bath
temperature 10 to 50.degree. C., current density 5 to 100
A/dm.sup.2, quantity of electricity 20 to 200 C/dm.sup.2, more
preferably 40 to 130 C/dm.sup.2. Under those conditions, cathodic
electrolysis can be carried out near or above the limiting current
density.
[0029] It is preferable that the electrolytic bath contains 0.03 to
5 g/l of titanium ions and 0.001 to 0.3 g/l of tungsten. Sulfuric
acid may be used in 50 to 200 g/l and copper sulfate in 5 to 200
g/l, but the addition is not limited to these ranges, because the
bath temperature, current density etc. have effects on the
electrolysis conditions.
[0030] As titanium ion source, it is preferable to use titanic
sulfate solution. The addition of titanium ion is preferably 0.03
to 5 g/l, more preferably 0.2 to 0.8 g/l.
[0031] The reason why the concentration range is restricted as
mentioned above is to make copper deposited protrusions uniform and
fine. The addition of not larger than 0.03 g/l is not desirable
because the copper deposited protrusions will not be uniform. The
concentration of not smaller than 5 g/l is not desirable, because
the copper deposited protrusion will be too fine and could leave
copper on the printed circuit board side after etching.
[0032] As tungsten ion sources, it is possible to use tungstic acid
and its salts such as its salt, sodium salt, potassium salt,
ammonium salt etc.
[0033] Tungstic acid is added in 0.001 to 0.3 g/l, preferably 0.005
to 0.08 g/l.
[0034] The reason why the concentration range is limited as
mentioned above is to curb the growth of the projection of copper
and to improve the adhesion for the surface of copper foil. If the
concentration is not larger than 0.001 g/l, it will be less
effective in making copper deposited protrusions uniform and it is
possible that a uniform matte condition can not be obtained. If, on
the other hand, the concentration is not smaller than 0.3 g/l, it
will be so effective in curbing the growth of copper protrusions
that sufficient adhesive strength can not be obtained. To increase
the adhesive strength, it will be necessary to increase the
concentration of titanium ions. That is bad economy.
[0035] The reason why titanium ions and tungsten ions are used in
combination is this. Titanium ions are effective in micronizing the
copper deposited protrusion and making the rougheness on the rough
surface uniform but tends to leave copper on the printed circuit
board surface after etching. That is why the use of titanium ions
alone is not desirable. On the other hand, tungsten ions are
effective in curbing the formation of dendrites by controlling the
spawning of nuclei. But tungsten alone is not effective in
imparting adhesive strength, especially to the glass polyimide
resin base material. Without either titanium or tungsten, no
desired results can be expected in a roughening treatment.
[0036] If titanium and tungsten ions are added, the rough condition
is unfirom with a low rougheness. In addition, a high adhesive
strength can be imparted to such base materials as glass-polyimide
which is generally weak in adhesive strength.
[0037] As set forth above, the copper foil subjected to roughening
treatment in an electrolytic solution with titanium and tungsten
ions added thereto is generally uniform in rough surface condition
with a low rougheness on the surface. That is a rough surface just
for a fine pattern.
[0038] On the other hand, in case neither titanium ions nor
tungsten ions are added, the rough condition with copper
protrusions is quite ununiform with rough and large dendrites
formed. And copper can remain on the etched surface of the printed
circuit board after press molding. This defect is fatal to the
printed circuit board. The wiring density is high nowdays, and even
if no copper is found left, the wiring edge formed in a delicate
etching time is poor in fineness. There is a possible of a short
circuit being caused. That is, there arises a problem with
insulation. Such a printed circuit board is problematical.
[0039] After copper protrusions or dendrites are deposited on the
surface of copper foil, the copper protrusions or dendrites are
coated with copper or a copper alloy in a cathodic electrolysis to
improve the adhesion of the rough surface.
[0040] This treatment is carried out in the following bath under
the following conditions, for example.
1 CuSO.sub.4.5H.sub.2O 250 g/l H.sub.2SO.sub.4 100 g/l
[0041] bath temperature 50.degree. C., current density 5
A/dm.sup.2, cathodic electrolysis time about 80 seconds. Under
those conditions, roughening is finished.
[0042] The thickness of the coat formed in the cathodic
electrolysis is 2.5 to 40 g/m.sup.2, preferably 4.5 to 20
g/m.sup.2.
[0043] If the thickness of the coat is smaller than 2.5 g/m.sup.2,
the deposited protrusions can not be coated well. Deposited
protrusions sticking to the surface of the copper foil can fall
off, which is undesirable. Furthermore, it is feared that copper
will remain after etching. If, on the other hand, the coat is
thicker than 40 g/m.sup.2, the treated surface is so thick that
there are such problems as decreased mechanical anchoring
effect.
[0044] The copper alloy is an alloy formed of copper as main
component and one or two elements selected from among Ni, Co, Zn,
Sn etc. The preferred alloys include Cu--Ni, Cu--Co, Ci--Ni--Co,
Cu--Zn, Cu--Sn etc.
[0045] The coated layer (plated layer) formed of copper or a copper
alloy by the cathodic electrolysis further strengthens the adhesive
strength between the base material and the copper foil, determining
the final condition on the roughened surface.
[0046] The coating with copper or a copper alloy is followed by
rust-proofing treatment.
[0047] For rust-proofing, the organic rust-proofing treatment
represented by chromate treatment and benzotriazole and silane
coupling agent treatment can be named. One treatment alone or more
in combination are performed.
[0048] For chromating treatment, an aqueous solution containing
potassium dichromate ions is adjusted to a suitable pH. In this
solution, the copper foil is dipped or subjected to cathodic
electrolysis. The chemicals used include trichromate oxide,
potassium dischlormate, sodium dichromate.
[0049] For organic rust-proofing, a variety of organic
rust-proofing agents are prepared into an aqueous solution. The
solution is applied by dipping or spraying. Among the suitable
organic rust-proofing agents are methylbenzotriazole,
aminobenzotriazole, benzotriazole.
[0050] The silane coupling agent treatment is carried out by
dipping or spraying an aqueous solution of silane coupling agent.
Many suitable silane coupling agents can be named, including epoxy
group, amino group, methylcapto group, and vinyl group. A group
compatible with the resin is used, and no restriction is imposed on
the selection.
[0051] After going through those treatments, a finished printed
circuit board can be obtained.
[0052] In this connection, the heat resistance may be increased by
forming a barrier layer of Co--Mo, W or Cu--Zn disclosed in
Japanese examined patent application gazettes Nos. 2-24037 and
8-19550 or another known barrier layer before the rust-proofing
treatment.
[0053] In the past, as set forth above, there was no need to
roughen the shiny side of the copper foil except for one used as
inner DT (double treated) foil. In recent years, however, it is
hoped that copper foil is given beforehand fine, uniform and light
roughening treatment to improve the adhesion of resist, to drop the
soft etching step and to increase the adhesive strength of the
inner layers.
[0054] Copper foils given the surface treatment according to the
present invention are uniform in surface condition and have a high
adhesion for the resin used, and can be used as DT foils meeting
those requirements.
[0055] In treating the copper foil according to the present
invention, the shiny side of the copper foil is roughened lightly
than the roughened side.
[0056] In treatment of copper foil according to the present
invention, the matte side and the shiny side may be reversed. In
case the matte side and the shiny side are reversed, the shiny side
of the untreated copper foil is first brought in contact with the
resin when making a copper-coated laminated board. In such a method
in which the matte side and the shiny side are reversed, the side
not in contact with the resin has a better adhesion for resist
after molding with the resin than in case one side is not treated
at all. In the inner layer processing step in the printed circuit
board manufacturer, the preceding treatment, that is, soft etching
can be dropped. Furthermore, the step of treating the surface of
copper is light as compared with the conventional method of making
copper foil with two treated sides. That makes manufacuturing much
easier at the copper manufacturer.
[0057] Embodiments
[0058] Copper foils obtained by the surface treatment method
according to the present invention is used in copper-coated
laminated boards, that is, printed circuit boards.
[0059] There will now be described properties of copper-coated
laminated board embodying the present invention.
[0060] Embodiment 1
[0061] The matte side of an untreated electrodeposited copper foil
35 .mu.m thick was subjected to cathodic electrolysis for 2.5
seconds at 50 A/dm.sup.2 at a temperaure of 40.degree. C. in
[0062] (A) bath prepared of:
2 CuSO.sub.4.5H.sub.2O 50 g/l H.sub.2SO.sub.4 100 g/l 24% solution
of Ti(SO.sub.4).sub.2 6.1 ml/l (Ti.sup.4+: 0.4 g/l)
Na.sub.2WO.sub.4.2H.sub.2O 0.018 g/l (W.sup.6+: 0.01 g/l)
[0063] rinsed and was subjected to cathodic electrolysis for 60
seconds at 10 A/dm.sup.2 at a temperaure of 40.degree. C. in
[0064] (B) bath prepared of:
3 CuSO.sub.4.5H.sub.2O 200 g/l H.sub.2SO.sub.4 100 g/l
[0065] followed by rinsing.
[0066] Then, for rust-proofing, the copper foil was subjected to
cathodic electrolysis for 5 seconds at 0.5 A/dm.sup.2 in
[0067] (C) bath prepared of:
4 Na.sub.2Cr.sub.2O.sub.7.2H.sub.2O 3 g/l NaOH 10 g/l
[0068] followed by rinsing and drying.
[0069] The surface properties (uniformity, surface rougheness) of
this copper foil were determined. The results are shown in Table
1.
[0070] Furthermore, the roughened surface of this copper foil as
coated surface was pressed to a glass-polyimide resin base material
under a pressure of 3.9 Mpa for 100 minutes at 200.degree. C. Also,
the copper foil was laminated with a glass-epoxy resin and pressed
under a pressure of 3.9 Mpa for 60 minutes at 170.degree. C. in the
molding step.
[0071] The properties (adhesive strength, copper residue) of the
copper-coated laminated board were determined. The results are
shown in Table 1.
[0072] Embodiment 2
[0073] The same treatment as Embodiment 1 was carried out at
40.degree. C. except that (A) bath was replaced with
[0074] (D) bath prepared of:
5 CuSO.sub.4.5H.sub.2O 50 g/l H.sub.2SO.sub.4 100 g/l 24% solution
of Ti(SO.sub.4).sub.2 8.4 ml/l (Ti.sup.4+: 0.55 g/l)
Na.sub.2WO.sub.4.2H.sub.2O 0.054 g/l (W.sup.6+: 0.03 g/l)
[0075] and the properties were determined the same way, and the
results are shown in Table 1.
[0076] Embodiment 3
[0077] The same treatment as Embodiment 1 was carried out by
cathodic electrolysis for 3 seconds at 40 A/dm.sup.2 at 40.degree.
C. except that (A) bath was replaced with
[0078] (E) bath prepared of:
6 CuSO.sub.4.5H.sub.2O 60 g/l H.sub.2SO.sub.4 150 g/l 24% solution
of Ti(SO.sub.4).sub.2 9.1 ml/l (Ti.sup.4+: 0.6 g/l)
Na.sub.2WO.sub.4.2H.sub.2O 0.018 g/l (W.sup.6+: 0.01 g/l)
[0079] and the properties were determined the same way, and the
results are shown in Table 1.
[0080] Embodiment 4
[0081] The same treatment as Embodiment 1 was carried out by
cathodic electrolysis for 4.2 seconds at 30 A/dm.sup.2 at
40.degree. C. except that (A) bath was replaced with
[0082] (F) Bath prepared of:
7 CuSO.sub.4.5H.sub.2O 60 g/l H.sub.2SO.sub.4 150 g/l 24% solution
of Ti(SO.sub.4).sub.2 12.1 ml/l (Ti.sup.4+: 0.8 g/l)
Na.sub.2WO.sub.4.2H.sub.2O 0.09 g/l (W.sup.6+: 0.05 g/l)
[0083] and the properties were determined the same way, and the
results are shown in Table 1.
[0084] Embodiment 5
[0085] The same treatment as Embodiment 1 was carried out by
cathodic electrolysis for 4.2 seconds at 30 A/dm.sup.2 at
40.degree. C. except that (A) bath was replaced with
[0086] (G) bath prepared of:
8 CuSO.sub.4.5H.sub.2O 60 g/l H.sub.2SO.sub.4 150 g/l 24% solution
of Ti(SO.sub.4).sub.2 12.1 ml/l (Ti.sup.4+: 0.8 g/l)
Na.sub.2WO.sub.4.2H.sub.2O 0.144 g/l (W.sup.6+: 0.08 g/l)
[0087] and the properties were determined the same way, and the
results are shown in Table 1.
[0088] Embodiment 6
[0089] The same treatment as Embodiment 1 was carried out by
cathodic electrolysis for 2.5 seconds at 60 A/dm.sup.2 except that
(A) bath was replaced with
[0090] (H) bath prepared of:
9 CuSO.sub.4.5H.sub.2O 60 g/l H.sub.2SO.sub.4 100 g/l 24% solution
of Ti(SO.sub.4).sub.2 4.6 ml/l (Ti.sup.4+: 0.3 g/l)
Na.sub.2WO.sub.4.2H.sub.2O 0.009 g/l (W.sup.6+: 0.005 g/l)
[0091] and the properties were determined the same way, and the
results are shown in Table 1.
[0092] Embodiment 7
[0093] The same treatment as Embodiment 1 was carried out at
40.degree. C. except that (A) bath was replaced with
[0094] (I) bath prepared of:
10 CuSO.sub.4.5H.sub.2O 40 g/l H.sub.2SO.sub.4 150 g/l 24% solution
of Ti(SO.sub.4).sub.2 9.1 ml/l (Ti.sup.4+: 0.6 g/l)
Na.sub.2WO4.2H.sub.2O 0.054 g/l (W.sup.6+: 0.03 g/l)
[0095] and the properties were determined the same way, and the
results are shown in Table 1.
COMPARATIVE EXAMPLES
Comparative Example 1
[0096] The same treatment as Embodiment 1 was carried out at
40.degree. C. except that (A) bath was replaced with
[0097] (J) bath prepared of:
11 CuSO.sub.4.5H.sub.2O 50 g/l H.sub.2SO.sub.4 100 g/l 24% solution
of Ti(SO.sub.4).sub.2 9.1 ml/l (Ti.sup.4+: 0.6 g/l)
[0098] and the properties were determined the same way, and the
results are shown in Table 1.
Comparative Example 2
[0099] The same treatment as Embodiment 1 was carried out at
40.degree. C. except that (A) bath was replaced with
[0100] (K) bath prepared of:
12 CuSO.sub.4.5H.sub.2O 50 g/l H.sub.2SO.sub.4 100 g/l
Na.sub.2WO.sub.4.2H.sub.2O 0.018 g/l (W.sup.6+: 0.01 g/l)
[0101] and the properties were determined the same way, and the
results are shown in Table 1.
Comparative Example 3
[0102] The same treatment as Embodiment 1 was carried out at
40.degree. C. except that (A) bath was replaced with
[0103] (L) bath prepared of:
13 CuSO.sub.4.5H.sub.2O 50 g/l H.sub.2SO.sub.4 100 g/l
[0104] and the properties were determined the same way, and the
results are shown in Table 1.
14 TABLE 1 Adhesive Adhesive strength strength (FR-4) Roughness
(N/mm) (N/mm) Copper Rz (.mu.m) to glass- to glass- found left Uni-
on roughened polyimide epoxy resin on etched formity side resin
base base base side Embod- Ments (1) 0 8.9 2.05 2.00 0 (2) 0 8.7
2.01 1.95 0 (3) 0 7.6 2.11 1.82 0 (4) 0 9.0 1.84 2.03 0 (5) 0 8.5
1.86 1.86 0 (6) 0 8.3 1.85 1.82 0 (7) 0 8.4 1.98 1.97 0 Com-
parative example (1) .DELTA. 8.8 1.57 1.87 X (2) 0 8.4 1.58 1.91 0
(3) X 11.1 1.90 2.15 X
[0105] "Uniformity" was evaluated by examining the surface
condition under an electronic microscope at a maginification of
about 1,000. The evaluation results are indicated by the following
symbols:
[0106] .smallcircle.: roughened particles on the matte side are not
large and uniform with little differences in size found among
them.
[0107] .DELTA.: roughened particles on the matte side are not large
but some differences in size are found among them.
[0108] .times.: roughened particles on the matte side are very
large and ununiform.
[0109] "Adhesive strength" means a degree of strength required to
tear the copper foil from the base material. The strength was
determined in accordance with JIS-C-6481 (1986) 5.7.
[0110] "Copper found left on etched base side" was checked under a
stereomicroscope at a magnification of 50 after copper was removed
by cupric chloride etching. Table 1 shows the evaluation results on
the glass-polyimide resin base material. The evaluation results are
indicated by the following symbols:
[0111] .smallcircle.: no copper found left
[0112] .times.: copper found left
[0113] The results in Table 1 show that the roughened surface
condition treated according to the present invention is high in
uniformity and low in rougheness as compared with those by the
prior art. According to the present invention, while the adhesive
strength to the glass-epoxy resin base material (Grade FR-4) is
somewhat low, a high degree of adhesion is exhibited with
glass-polyimide. Thus, excellent surface treated copper foil can be
obtained.
[0114] As set forth above, the surface treatment process according
to the present invention has the following advatanges:
[0115] (1) roughens the surface without using such harmful element
as arsenic, selenium and tellurium, presenting no environmetal
problems and having no fear of harmful effects on humans.
[0116] (2) Produces a surface treated copper foil with a uniform
roughness condition on the matte side and with a high adhesive
strength to the resins, especially glass-polymide resin base
material which is weak in adhesive strength, thus adapted to high
density printed circuit boards.
[0117] (3) Needs only light treatment and easy to include in the
copper production process, thus permitting mass production.
* * * * *