U.S. patent application number 11/173126 was filed with the patent office on 2006-01-05 for printed circuit board and method for manufacturing printed circuit board.
This patent application is currently assigned to Nitto Denko Corporation. Invention is credited to Kei Nakamura, Takeshi Yamato.
Application Number | 20060000637 11/173126 |
Document ID | / |
Family ID | 34941781 |
Filed Date | 2006-01-05 |
United States Patent
Application |
20060000637 |
Kind Code |
A1 |
Nakamura; Kei ; et
al. |
January 5, 2006 |
Printed circuit board and method for manufacturing printed circuit
board
Abstract
An insulating layer made of an insulator film or the like is
prepared. Then, a thin metal film and a thin copper film are formed
in sequence on the insulating layer. The thin copper film is
subsequently laminated with a dry film or the like, and exposed and
developed to form a plating resist thereon that have patterns
opposite to conductor patterns which are formed in a subsequent
step. This is followed by forming conductor patterns made of
copper, by electrolytic plating using an electrolytic copper
sulfate plating solution, on the surfaces of the thin copper film
where the plating resist is not formed. The plating resist is then
removed by, for example, stripping. After this, the thin copper
film is held at a temperature of not less than 200.degree. C. and
not more than 300.degree. C. for approximately an hour to be
thermally treated. Then, the thin copper film and the thin metal
film are removed by chemical etching except the portions under the
conductor patterns.
Inventors: |
Nakamura; Kei; (Osaka,
JP) ; Yamato; Takeshi; (Osaka, JP) |
Correspondence
Address: |
AKIN GUMP STRAUSS HAUER & FELD L.L.P.
ONE COMMERCE SQUARE
2005 MARKET STREET, SUITE 2200
PHILADELPHIA
PA
19103
US
|
Assignee: |
Nitto Denko Corporation
|
Family ID: |
34941781 |
Appl. No.: |
11/173126 |
Filed: |
July 1, 2005 |
Current U.S.
Class: |
174/257 |
Current CPC
Class: |
H05K 3/108 20130101;
H05K 2203/1105 20130101; H05K 1/0393 20130101; H05K 3/388 20130101;
H05K 1/056 20130101 |
Class at
Publication: |
174/257 |
International
Class: |
H05K 1/09 20060101
H05K001/09 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 1, 2004 |
JP |
2004-195939 |
Claims
1. A printed circuit board comprising, in sequence, an insulating
layer, a thin copper film, and a conductor layer, wherein said
conductor layer and said thin copper film have prescribed patterns,
and said thin copper film has a first surface in contact with said
insulating layer and a second surface in contact with said
conductor layer, and contains a grain of a size that extends
between said first surface and said second surface.
2. The printed circuit board according to claim 1, wherein said
thin copper film has a thickness of not less than 50 nm and not
more than 300 nm.
3. The printed circuit board according to claim 1, wherein said
conductor layer includes copper.
4. The printed circuit board according to claim 1, further
comprising a thin metal film between said insulating layer and said
thin copper film.
5. The printed circuit board according to claim 4, wherein said
thin metal film includes at least one of chromium and nickel.
6. The printed circuit board according to claim 4, wherein said
thin metal film has a thickness of not less than 5 nm and not more
than 50 nm.
7. The printed circuit board according to claim 1, wherein said
insulating layer includes a flexible substrate.
8. A method for manufacturing a printed circuit board by a
semi-additive method, comprising the steps of: forming a thin
copper film on an insulating layer; forming a conductor layer
having prescribed patterns on said thin copper film; removing said
thin copper film except portions on which said conductor layer is
formed; and applying a thermal treatment to said thin copper film
between said step of forming said thin copper film and said step of
forming said conductor layer or between said step of forming said
conductor layer and said step of removing said thin copper
film.
9. The method for manufacturing a printed circuit board according
to claim 8, wherein a temperature during said thermal treatment of
said thin copper film is not less than 200.degree. C. and not more
than 300.degree. C.
10. The method for manufacturing a printed circuit board according
to claim 8, wherein said step of forming said conductor layer
includes the steps of: forming a resist on said thin copper film
that has patterns opposite to said prescribed patterns; forming a
conductor layer on said thin copper film except portions on which
said resist is formed; and removing said resist after forming said
conductor layer, and wherein said step of applying said thermal
treatment to said thin copper film is provided between said step of
forming said thin copper film and said step of forming said resist
or between said step of removing said resist and said step of
removing said thin copper film.
11. The method for manufacturing a printed circuit board according
to claim 8, further comprising the step of forming a thin metal
film between said insulating film and said thin copper film.
12. The method for manufacturing a printed circuit board according
to claim 11, wherein said step of forming said thin metal film
includes the step of forming at least one of chromium and nickel as
said thin metal film.
13. The method for manufacturing a printed circuit board according
to claim 11, wherein said step of forming said thin metal film
includes the step of forming said thin metal film having a
thickness of not less than 5 nm and not more than 50 nm.
14. The method for manufacturing a printed circuit board according
to claim 8, wherein said step of forming said thin copper film on
said insulating layer includes the step of forming said thin copper
film on a flexible substrate that serves as said insulating layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to printed circuit boards and
a method for manufacturing such printed circuit boards.
[0003] 2. Description of the Background Art
[0004] Printed circuit boards such as flexible printed circuit
boards are widely used in a variety of electrical and electronic
devices. A printed circuit board includes, for example, an
insulating layer of, e.g., polyimide, having on one side or both
sides thereof conductor layers of, e.g., a copper foil with
prescribed patterns.
[0005] Conventionally, conductor layers having prescribed patterns
in printed circuit boards such as flexible printed circuit boards
are formed by the known methods such as the semi-additive,
substractive, and full-additive methods (refer to JP 2002-176259,
for example).
[0006] The above-mentioned semi additive method is now described
with reference to the drawings.
[0007] FIGS. 4 (a), 4 (b), 4 (c), 4 (d), 4 (e), and 4 (f) are
schematic cross sectional views showing the steps of a method for
manufacturing a printed circuit board by the semi additive
method.
[0008] In the semi-additive method, for example, an insulating
layer 11 of a resin film is first prepared, as shown in FIG. 4
(a).
[0009] Next, as shown in FIG. 4 (b), a thin conductive film 12 is
formed on the insulating layer 11 by sputtering or electroless
plating.
[0010] Then, as shown in FIG. 4 (c), a plating resist 13 is formed
on the thin conductive film 12 using a dry film resist or the like.
The plating resist 13 has patterns opposite to the prescribed
patterns of a conductor layer formed in a step shown below.
[0011] After this, as shown in FIG. 4 (d), a conductor layer 14 is
formed by electrolytic plating on the surfaces of the thin
conductive film 12 where the plating resist 13 is not formed.
[0012] This is followed by removing the plating resist 13 by, e.g.,
stripping, as shown in FIG. 4 (e). Then, the thin conductive film
12 except the portions on which the conductor layer 14 is formed is
removed by chemical etching or the like, as shown in FIG. 4 (f). In
this manner, the conductor layer 14 with prescribed patters is
formed on the insulating layer 11.
[0013] However, in the conventional method for forming a printed
circuit board, side etching of the thin conductive film 12 under
the conductor layer 14 may occur during the removal of the thin
conductive film 12 except the portions under the conductor layer 14
by chemical etching or the like. The term "side etching" is
described now with reference to the figure below.
[0014] FIG. 5 is a magnified view of the region B in FIG. 4 (f).
During the removal of the thin conductive film 12 by chemical
etching or the like, the thin conductive film 12 under the
conductor layer 14 was etched together with both ends thereof being
gouged as shown in FIG. 5. This results in a deterioration of the
adhesion of the conductor layer 14 to the thin conductive film 12.
In the case of a significant decrease in the adhesion, the
conductor layer 14 may be stripped off.
SUMMARY OF THE INVENTION
[0015] It is an object of the present invention to provide printed
circuit boards that provide improved adhesion of conductor layers
and a method for manufacturing such printed circuit boards.
[0016] A printed circuit board according to one aspect of the
invention comprises, in sequence, an insulating layer, a thin
copper film, and a conductor layer, wherein the conductor layer and
the thin copper film have prescribed patterns, and the thin copper
film has a first surface in contact with the insulating layer and a
second surface in contact with the conductor layer, and contains a
grain of a size that extends between the first surface and the
second surface.
[0017] In the printed circuit board, the thin copper film and
conductor layer with the prescribed patterns are formed in sequence
on the insulating layer. The thin copper film contains a grain of a
size that extends between the first surface in contact with the
insulating layer and the second surface in contact with the
conductor layer. This reduces or prevents the incidence of side
etching of the thin copper film under the conductor layer during
the removal of the thin copper film except the portions on which
the conductor layer is formed. In this manner, a sufficient
adhesion area of the thin copper film to the insulating layer is
ensured to improve the adhesion.
[0018] The thin copper film preferably has a thickness of not less
than 50 nm and not more than 300 nm. This further improves the
adhesion of the conductor layer to the thin copper film.
[0019] The conductor layer may include copper. This even further
improves the adhesion of the conductor layer to the thin copper
film.
[0020] The printed circuit board may further comprise a thin metal
film between the insulating layer and the thin copper film. In this
manner, a sufficient adhesion area of the thin copper film to the
thin metal film is ensured to improve the adhesion.
[0021] The thin metal film may include at least one of chromium and
nickel. This further improves the adhesion between the insulating
layer and the thin copper film.
[0022] The thin metal film preferably has a thickness of not less
than 5 nm and not more than 50 nm. This still further improves the
adhesion between the insulating layer and the thin copper film.
[0023] The insulating layer may include a flexible substrate. The
flexible substrate having flexibility allows the flexibility of the
printed circuit board to be improved.
[0024] A method for manufacturing a printed circuit board by a
semi-additive method according to another aspect of the invention
comprises the steps of forming a thin copper film on an insulating
layer, forming a conductor layer having prescribed patterns on the
thin copper film, removing the thin copper film except portions on
which the conductor layer is formed, and applying a thermal
treatment to the thin copper film between the step of forming the
thin copper film and the step of forming the conductor layer or
between the step of forming the conductor layer and the step of
removing the thin copper film.
[0025] In the method for manufacturing the printed circuit board,
the thin copper film is thermally treated between the step of
forming the thin copper film and the step of forming the conductor
layer or between the step of forming the conductor layer and the
step of removing the thin copper film, which increases the size of
grains contained in the thin copper film. This reduces or prevents
the incidence of side etching of the thin copper film under the
conductor layer during the removal of the thin copper film except
the portions on which the conductor layer is formed. Thus, a
sufficient adhesion area of the thin copper film to the insulating
layer is ensured to improve the adhesion. In addition, where a thin
metal film is present between the insulating layer and the thin
copper film, a sufficient adhesion area of the thin copper film to
the thin metal film is ensured to improve the adhesion.
[0026] A temperature during the thermal treatment of the thin
copper film may be not less than 200.degree. C. and not more than
300.degree. C. This allows the size of grains contained in the thin
copper film to be sufficiently increased.
[0027] The method for manufacturing a printed circuit board may
include the steps of forming a resist on the thin copper film that
has patterns opposite to the prescribed patterns, forming a
conductor layer on the thin copper film except portions on which
the resist is formed, and removing the resist after forming the
conductor layer, and wherein the step of applying the thermal
treatment to the thin copper film is provided between the step of
forming the thin copper film and the step of forming the resist or
between the step of removing the resist and the step of removing
the thin copper film.
[0028] In this manner, the step of applying the thermal treatment
to the thin copper film is provided between the step of forming the
thin copper film and the step of forming the resist or between the
step of removing the resist and the step of removing the thin
copper film. This prevents the resist from dissolving by the
thermal treatment of the thin copper film.
[0029] The manufacturing method may further comprise the step of
forming a thin metal film between the insulating film and the thin
copper film. In this manner, a sufficient adhesion area of the thin
copper film to the thin metal film is ensured to improve the
adhesion.
[0030] The step of forming the thin metal film may include the step
of forming at least one of chromium and nickel as the thin metal
film. This further improves the adhesion between the insulating
layer and the thin copper film.
[0031] The step of forming the thin metal film may include the step
of forming the thin metal film having a thickness of not less than
5 nm and not more than 50 nm. This still further improves the
adhesion between the insulating layer and the thin copper film.
[0032] The step of forming the thin copper film on the insulating
layer may include the step of forming the thin copper film on a
flexible substrate that serves as the insulating layer. The
flexible substrate having flexibility allows the flexibility of the
printed circuit board to be improved.
[0033] According to the invention, the thin copper film contains a
grain of the size that extends between the first surface in contact
with the insulating layer and the second surface in contact with
the conductor layer. This reduces or prevents the incidence of side
etching of the thin copper film under the conductor layer during
the removal of the thin copper film except the portions on which
the conductor layer is formed. In this manner, a sufficient
adhesion area of the thin copper film to the insulating layer is
ensured to improve the adhesion. In addition, where the thin metal
film is present between the insulating layer and the thin copper
film, a sufficient adhesion area of the thin copper film to the
thin metal film is ensured to improve the adhesion.
[0034] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIGS. 1 (a), 1 (b), 1 (c), and 1 (d) are schematic cross
sectional views showing the steps of a method for manufacturing a
printed circuit board according to an embodiment of the
invention;
[0036] FIGS. 2 (e), 2 (f), and 2 (g) are schematic cross sectional
views showing the steps of a method for manufacturing a printed
circuit board according to an embodiment of the invention;
[0037] FIG. 3 is a magnified view of the region A in FIG. 2 (f)
[0038] FIGS. 4 (a), 4 (b), 4 (c), 4 (d), 4 (e), and 4 (f) are
schematic cross sectional views showing the steps of a method for
manufacturing a printed circuit board by the semi additive method;
and
[0039] FIG. 5 is a magnified view of the region B in FIG. 4 (f)
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] A printed circuit board according to an embodiment of the
invention and a method for manufacturing the printed circuit board
will be described below with reference to the drawings.
[0041] A method for manufacturing a printed circuit board according
to an embodiment will be described first. FIGS. 1 (a), 1 (b), 1
(c), and 1 (d) as well as FIGS. 2 (e), 2 (f), and 2 (g) are
schematic cross sectional views showing the steps of a method for
manufacturing a printed circuit board according to an embodiment of
the invention.
[0042] To begin with, as shown in FIG. 1 (a), an insulating layer 1
made of, e.g., an insulator film, is prepared. Such an insulator
film is made of polyimide or polyester, for example. Alternatively,
the insulating layer 1 may be formed by applying a resin onto a
substrate made of a metal foil.
[0043] Next, a thin metal film 2 and a thin copper film 3 are
formed in sequence on the insulating layer 1, as shown in FIG. 1
(b). The thin metal film 2, which is provided to improve the
adhesion between the insulating layer 1 and the thin copper film 3,
may only be provided when necessary. Each of the thin metal film 2
and thin copper film 3 is formed by sputtering, electroless
plating, or other suitable means.
[0044] The thin metal film 2 as used here includes at least either
of chromium and nickel. For example, the thin metal film 2 may be
made of a single layer of chromium, a laminated film of chromium
and nickel, or a film of a chromium-nickel alloy. The thickness of
the thin metal film 2 is preferably in the range of not less than 5
nm and not more than 50 nm, for example. This further improves the
adhesion of the thin copper film 3 to the insulating layer 1.
[0045] The thickness of the thin copper film 3 is preferably in the
range of not less than 50 nm and not more than 300 nm, for example.
This further improves the adhesion of conductor patterns 5
described below to the thin copper film 3.
[0046] Then, as shown in FIG. 1 (c), the thin copper film 3 is
laminated with, e.g., a dry film, and exposed and developed to form
plating resist 4 thereon. The plating resist 4 have patterns
opposite to the conductor patterns 5 which are formed in a step
shown below.
[0047] After this, as shown in FIG. 1 (d), the conductor patterns 5
are formed on the surfaces of the thin copper film 3 where the
plating resist 4 is not formed by electrolytic plating using, e.g.,
a copper sulfate electrolytic plating solution. A metal or an alloy
other than copper may also be used as the material of the conductor
patterns 5.
[0048] The plating resist 4 is subsequently removed by, for
example, stripping, as shown in FIG. 2 (e). Then, a thermal
treatment is applied to the thin copper film 3. During the thermal
treatment, the thin copper film 3 is held at a temperature of not
less than 200.degree. C. and not more then 300.degree. for
approximately an hour, preferably not less than half an hour and
not more than two hours. Setting the time to not less than half an
hour and not more than two hours as described above allows the
grain size to be sufficiently increased while preventing
consumption of an excessive energy.
[0049] The above-described thermal treatment allows the grain size
of the thin copper film 3 to be increased. For example, in this
embodiment, the grain size of the thin copper film 3 is as large as
approximately not less than 40 nm and not more than 300 nm.
[0050] After this, as shown in FIG. 2 (f), the thin copper film 3
and thin metal film 2 are removed, by chemical etching using, e.g.,
a mixed solution of a sulfuric acid and oxygenated water, except
the portions on which the conductor patterns 5 are formed.
[0051] Then, as shown in FIG. 2 (g), a protective insulating layer
6 of polyimide or the like having prescribed patterns is formed. In
this case, a terminal is provided on the portion of each conductor
pattern 5 that is not covered with the protective insulating layer
6 (i.e., an aperture).
[0052] Note that the above-described thermal treatment is possible
without a plating resist being formed. For example, the thermal
treatment may be performed between the step of FIG. 1 (b) and the
step of FIG. 1 (c).
[0053] Now, advantageous effects provided by the above-described
thermal treatment of the thin copper film 3 will be described.
[0054] FIG. 3 is a magnified view of the region A in FIG. 2 (f). As
shown in FIG. 3, thermally treating the thin copper layer 3 allows
the size of grains contained in the thin copper layer 3 to be
increased.
[0055] That is, in this embodiment, the thermally treated thin
copper film 3 contains a grain 21 of such size as to extend between
one surface of the thin copper film 3 in contact with the
insulating layer 1 and the other surface of the thin copper film 3
in contact with the conductor pattern 5. That is, the thin copper
film 3 has a point where only a single grain 21 is present in the
thickness direction V. This reduces or prevents the incidence of
side etching of the thin copper film 3 under the conductor pattern
5 during the removal of the thin copper film 3 except the portion
on which the conductor pattern 5 is formed. This ensures a
sufficient adhesion area of the thin copper film 3 to the
insulating layer 1 to improve the adhesion. Where the thin metal
film 2 is present between the insulating layer 1 and the thin
copper film 3, a sufficient adhesion area of the thin copper film 2
to the thin metal film 2 is ensured to improve the adhesion.
[0056] Although in this embodiment, the use of polyimide,
polyester, or the like as the material of the insulating layer 1 is
described, any other highly insulating films of plastics may also
be used as the insulating layer 1. For example, a polyethylene
terephthalate film, a polyethylene naphthalate film, a polyether
nitril film, polyethersulfone film, a polyvinyl chloride film or
the like may be used.
[0057] It is preferred to use, in particular, a polyimide film, a
polyethylene terephthalate film, or a polyethylene naphthalate
film, since they are superior in such properties as thermal
resistance, dimensional stability, electrical properties,
mechanical properties, and chemical resistant properties.
EXAMPLES
Inventive Example
[0058] A printed circuit board according to Inventive Example and
the method for manufacturing the printed circuit board will be
described below. The manufacturing method according to Inventive
Example is based upon the manufacturing method according to the
above-described embodiment, and therefore the description of
drawings is omitted.
[0059] First, an insulating layer 1 made of a 25-.mu.m polyimide
insulator film was prepared.
[0060] Next, a thin metal film 2 made of 30-nm nichrome and a
200-nm thin copper film 3 were formed in sequence on the insulating
layer 1 by sputtering.
[0061] Then, the thin copper film 3 was laminated with a dry film,
and then exposed and developed to form a plating resist 4 thereon
having patterns opposite to conductor patterns that are formed in a
step shown below.
[0062] After this, conductor patterns 5 of copper with a thickness
of 8 .mu.m, a width of 15 .mu.m, and a pitch of 15 .mu.m were
formed, by electrolytic plating using a copper sulfate electrolytic
plating solution, on the surfaces of the thin copper film 3 where
the plating resist 4 was not formed.
[0063] The plating resist 4 was then stripped off, after which the
thin copper film 3 was held at 250.degree. C. for an hour to be
thermally treated.
[0064] Then, the thin copper film 3 and thin metal film 2 were
removed except the portions under the conductor patterns 5 by
chemical etching using a mixed solution of a sulfuric
acid/oxygenated water. This was followed by the formation of a
protective insulating film 6 of polyimide having prescribed
patterns.
[0065] A cross section of thus fabricated printed circuit board was
observed with a scanning electron microscope (SEM).
[0066] The results showed that the thin copper film 3 contained
grains of the size equal to the thickness of the thin copper film
3, 200 nm; i.e., grains of such size as to extend between one
surface of the thin copper film 3 in contact with the thin metal
film 2 and the other surface of the thin copper film 3 in contact
with the conductor patterns 5 in the thickness direction V.
[0067] In addition, the thin copper film 3 under the conductor
patterns 5 did not show any side etching.
[0068] Stripping tests using an adhesive tape were also conducted
in order to check the conductor patterns 5 for adhesion to the thin
copper film 3. The results confirmed that the conductor patterns 5
were not stripped at all, and possessed good adhesion.
Comparative Example
[0069] The method for manufacturing a printed circuit board
according to Comparative Example differed from the above-described
method according to Inventive Example in that the thin copper film
3 was not thermally treated.
[0070] After the fabrication of the printed circuit board, a cross
section of the printed circuit board was observed with SEM, as in
the above-described Inventive Example.
[0071] The results showed that the sizes of all of grains contained
in the thin copper film 3 were less than 200 nm, and there always
existed two or more grains between one surface of the thin copper
film 3 in contact with the thin metal film 2 and the other surface
of the thin copper film 3 in contact with the conductor patterns 5
in the thickness direction V.
[0072] Further, the thin copper film 3 under the conductor patterns
5 showed side etching.
[0073] Stripping tests using an adhesive tape were also conducted
in order to check the conductor patterns 5 for adhesion to the thin
copper film 3. The results confirmed that part of the conductor
patterns 5 was stripped off, and did not possess good adhesion.
[0074] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *