U.S. patent application number 12/867109 was filed with the patent office on 2011-03-10 for etching method.
Invention is credited to Mariko Ishida, Makoto Kato, Kunihiro Nakagawa, Yuji Toyoda.
Application Number | 20110056910 12/867109 |
Document ID | / |
Family ID | 40956978 |
Filed Date | 2011-03-10 |
United States Patent
Application |
20110056910 |
Kind Code |
A1 |
Kato; Makoto ; et
al. |
March 10, 2011 |
ETCHING METHOD
Abstract
Etching is carried out with an etchant that reacts with a metal
to be etched to form an insoluble compound. After the etching using
the above etchant, etching is carried out using an etchant that
does not form an insoluble compound through a reaction with the
metal to be etched, whereby the form of an etched portion comes
close to a rectangular form, and the side surface of a conductor
pattern becomes smooth. Further, after the etching of one surface
of a material to be etched is carried out using an etchant that
reacts with a metal to be etched to form an insoluble compound
nearly from below, the upper and lower sides of the material to be
etched is reversed, and the etching of the opposite surface is
carried out nearly from below, whereby fine conductor patterns can
be formed on both of the surfaces.
Inventors: |
Kato; Makoto; (Tokyo,
JP) ; Toyoda; Yuji; (Tokyo, JP) ; Nakagawa;
Kunihiro; (Tokyo, JP) ; Ishida; Mariko;
(Tokyo, JP) |
Family ID: |
40956978 |
Appl. No.: |
12/867109 |
Filed: |
February 4, 2009 |
PCT Filed: |
February 4, 2009 |
PCT NO: |
PCT/JP2009/052258 |
371 Date: |
September 24, 2010 |
Current U.S.
Class: |
216/41 |
Current CPC
Class: |
C23F 1/18 20130101; H05K
2203/1572 20130101; H05K 2203/075 20130101; H05K 2203/1563
20130101; H05K 3/067 20130101; H05K 2203/1476 20130101 |
Class at
Publication: |
216/41 |
International
Class: |
C23F 1/04 20060101
C23F001/04; C23F 1/18 20060101 C23F001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2008 |
JP |
2008-030367 |
Claims
1. An etching method for etching a material to be etched prepared
by forming a resist pattern on a metal layer containing a metal to
be etched, the method comprising consecutively carrying out the
steps of (1) ejecting an etchant that reacts with the metal to be
etched to form a water-insoluble reaction product, by means of a
spray nozzle, to perform etching until the etching depth reaches
60% or more of the metal layer thickness, and (2) ejecting an
etchant that does not form a water-insoluble reaction product
through a reaction with the metal to be etched, by means of a spray
nozzle, to perform etching.
2. The etching method of claim 1, wherein an etching speed is 0.3
.mu.m/minute or more but 3 .mu.m/minute or less when the metal to
be etched is immersion-etched with the etchant used in the step
(2).
3. The etching method of claim 1, wherein the metal to be etched is
copper or copper alloy and the etchant used in the step (1) is an
etchant containing iron (III) chloride and oxalic acid.
4. The etching method of claim 1, wherein the metal to be etched is
copper or copper alloy and the etchant used in the step (2) is an
etchant containing iron (III) chloride or copper (II) chloride.
5. The etching method of claim 1, wherein the step (3) of removing
said water-insoluble reaction product by using a liquid that
dissolves the above water-insoluble reaction product is carried out
between the step (1) and the step (2).
6. The etching method of claim 5, wherein the metal to be etched is
copper or copper alloy and the etchant used in the step (2) is an
etchant containing copper (II) chloride.
7. An etching method for etching a material to be etched which
material is obtained by stacking metal layers each containing a
metal to be etched on both surfaces of an insulating material and
forming resist patterns on the metal layers, the method comprising
consecutively carrying out the three steps of (4) holding the
material to be etched horizontally or at an angle of 20.degree. or
less from the horizontal and ejecting an etchant containing a
compound that reacts with the metal to be etched to form a
water-insoluble reaction product, by means of a spray nozzle from
below the material to be etched, to etch one surface (surface A) of
the material to be etched, (5) reversing the upper and lower sides
of the material to be etched, and (6) holding the material to be
etched horizontally or at an angle of 20.degree. or less from the
horizontal and ejecting the etchant containing a compound that
reacts with the metal to be etched to form a water-insoluble
reaction product, by means of a spray nozzle from below the
material to be etched, to etch that surface (surface B) which is
opposite to the surface (A).
8. The etching method of claim 7, wherein the metal to be etched is
copper or copper alloy and the etchant containing a compound that
reacts with the metal to be etched to form a water-insoluble
reaction product is an etchant containing iron (III) chloride and
oxalic acid.
9. The etching method of claim 7, wherein the step (7) of removing
said water-insoluble reaction product with a liquid that dissolves
said water-insoluble reaction product is carried out between the
step (4) and the step (6).
10. The etching method of claim 2, wherein the metal to be etched
is copper or copper alloy and the etchant used in the step (2) is
an etchant containing iron (III) chloride or copper (II) chloride.
Description
TECHNICAL FIELD
[0001] This invention relates to an etching method to engrave the
surface of a metal material.
BACKGROUND ART
[0002] An etching technique is used as a technique to engrave the
surface of a metal material. In particular, in the production of
printed wiring boards obtained by forming a conductor pattern
containing a metal on an insulating substrate, a subtractive method
based on an etching technique is widely used for some reasons
including a fast processing speed, which leads to high
productivity, and conductor pattern thickness uniformity as
compared with other production methods such as an additive method,
a semi-additive method, etc.
[0003] In the production of a printed wiring board by an etching
technique, a material to be etched formed by stacking a metal layer
containing a metal to be etched on an insulating substrate with a
resist pattern formed on the metal layer is etched, and a conductor
pattern is formed. The cross-sectional form of the above conductor
pattern frequently comes to be what is called "trapezoidal" in
which a top width is smaller than a bottom width (for example, see
Printed Circuit Gijutsu Binran, compiled by Japan Institute of
Electronics Packaging, issued by Nikkan Kogyo Shimbun, Ltd., May
30, 2006, pages 780-781). When the cross-sectional form of a
conductor pattern becomes trapezoidal, there is caused a problem
that the area of a surface for mounting parts thereon is deficient
or that the wiring resistance increases to increase a transfer
loss.
[0004] For overcoming the above problems, there is proposed, the
technique of improving the cross-sectional form of a conductor
pattern by selectively removing a metal of a foot with an etchant
containing a specific component after etching is finished (for
example, see JP 2004-256901A). The cross-sectional form of a
conductor pattern obtained by the technique in JP 2004-256901A is
still far from rectangular. Further, there is proposed the
technique of using an etchant prepared by adding to an etchant
containing copper (II) chloride as a main component a compound that
reacts with the ion of a metal to be etched to form a
water-insoluble reaction product, such as a benzothiasole (e.g.,
see JP 6-57453A) and an azole compound having nitrogen alone as a
hetero atom (e.g., see Published US Patent Application No.
2005/0016961), etc. However, while a conductor pattern having a top
width and a bottom width which are nearly equivalent can be
obtained according to the techniques proposed in JP 6-57453A and
Published US patent Application No. 2005/0016961, there is still
involved a problem that small texture is formed on side surfaces of
a conductor pattern and the transfer loss is increased due to a
conductor skin effect when it is used in a high-frequency
circuit.
[0005] Further, when a double-sided printed wiring board is
produced, conventionally, etching is applied simultaneously to both
the upper and lower surfaces of a material to be etched obtained by
forming metal layers containing a metal to be etched on both the
surfaces of an insulating substrate with resist patterns formed on
the metal layers. When this method is used, however, there is a
problem that the surface to be etched as the upper surface has a
difficulty in forming a fine conductor pattern as compared with the
surface to be etched as the lower surface (see the paper entitled
"High-precision Etching Conditions in Continuous Circuit-Formation
Method", authored by Koji SATO and Shuji KITAGAWA, Matsushita
Electric Works Technical Report, Matsushita Electrics Works, Ltd.,
August 2001, No. 75, pages 44-50). While one surface (surface A) of
a material to be etched is etched with the one surface (surface A)
being a lower surface, the surface (surface B) as an upper surface
opposite to the surface A is kept from contacting an etchant, and
after the etching of the surface A is finished, the upper and lower
sides of the material to be etched are reversed, and the surface B
as a lower surface is etched while the upper surface is kept from
contacting an etchant, whereby fine patterns can be formed on both
the surfaces. However, it requires a special method to keep the
upper surface from contacting an etchant. For example, it is
required to secure a sufficient margin in the circumference of a
material to be etched in order to prevent that an etchant flowing
around onto the upper surface etches a necessary portion, it is
required to use an etching apparatus having a complicated mechanism
for preventing an etchant from flowing around onto the upper
surface (for example, see JP 5-226809A and JP 6-302935A), or it is
required to use an etching apparatus having a suction device for
removing an etchant from the upper surface (for example, see
Published US Patent Application No. 2003/0150381). In these
methods, however, there is involved a problem that a portion of a
material which forms the margin goes to waste, or that the etching
apparatus is so complicated that its maintenance is
troublesome.
[0006] As means for solving the above problems, there can be
possibly employed a constitution in which a protective layer is
formed on the surface B to be etched later, the surface A is etched
from below, then, the protective layer is removed from the surface
B, a protective layer is formed on the surface A, the upper and
lower sides are reversed, and the surface B is etched from below.
However, the step of forming the protective layer and the step of
separating it need to be carried out twice each, and there is a
problem that the production process is very complicated.
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0007] The first object of this invention is to provide an etching
method for producing a conductor pattern having a nearly
rectangular cross-sectional form and smooth side surfaces. The
second object of this invention is to provide an etching method in
which conductor patterns can be formed on both two surfaces of a
material to be etched without any complicated apparatus or
steps.
Means to Solve the Problems
[0008] The first etching method of this invention is a method for
etching a material to be etched prepared by forming a resist
pattern on a metal layer containing a metal to be etched, the
method comprising consecutively carrying out the steps of (1)
ejecting an etchant containing a compound that reacts with the
metal to be etched to form a water-insoluble reaction product, by
means of a spray nozzle, to perform etching until the etching depth
reaches 60% or more of the metal layer thickness, and (2) ejecting
an etchant which does not form any water-insoluble reaction product
through a reaction with the metal to be etched, by means of a spray
nozzle, to perform etching.
[0009] In the first etching method of this invention, when the
metal to be etched is immersion-etched with the etchant to be used
in the step (2), the etching speed is preferably 0.3 .mu.m/minute
or more but 3 .mu.m/minute or less.
[0010] In the first etching method of this invention, preferably,
the metal to be etched is copper or copper alloy, and the etchant
for use in the step (1) is an etchant containing iron (III)
chloride and oxalic acid. Further, preferably, the metal to be
etched is copper or copper alloy, and the etchant for use in the
step (2) is an etchant containing iron (III) chloride or copper
(II) chloride.
[0011] In the first etching method of this invention, preferably,
the step (3) of removing the above water-insoluble reaction product
with a liquid that dissolves the above water-insoluble reaction
product is carried out between the step (1) and the step (2).
Further, more preferably, the metal to be etched is copper or
copper alloy and the etchant for use in the step (2) is an etchant
containing copper (II) chloride.
[0012] The second etching method of this invention is an etching
method for etching a material to be etched which material is
obtained by stacking metal layers each containing a metal to be
etched on both surfaces of an insulating material and forming
resist patterns on the metal layers, the method comprising
consecutively carrying out the three steps of (4) holding the
material to be etched horizontally or at an angle of 20.degree. or
less from the horizontal and ejecting an etchant that reacts with
the metal to be etched to form a water-insoluble reaction product,
by means of a spray nozzle from below the material to be etched, to
etch one surface (surface A) of the material to be etched, (5)
reversing the upper and lower sides of the material to be etched,
and (6) holding the material to be etched horizontally or at an
angle of 20.degree. or less from the horizontal and ejecting the
etchant that reacts with the metal to be etched to form a
water-insoluble reaction product, by means of a spray nozzle from
below the material to be etched, to etch that surface (surface B)
which is opposite to the surface (A).
[0013] In the second etching method of this invention, preferably,
the metal to be etched is copper or copper alloy, the etchant
containing the compound that reacts with ion of the metal to be
etched to form a water-insoluble reaction product is an etchant
containing iron (III) chloride and oxalic acid.
[0014] Further, in the second etching method of this invention,
preferably, the step (7) of removing the above water-insoluble
reaction product with a liquid that dissolves the above
water-insoluble reaction product is carried out between the step
(4) and the step (6).
EFFECT OF THE INVENTION
[0015] By the first etching method of this invention, there can be
obtained a conductor pattern having a nearly rectangular
cross-sectional form and smooth side surfaces. By the second
etching method of this invention, fine patterns can be formed on
both the surfaces of a material to be etched, without using
complicated apparatus or steps.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1 is a schematic cross-sectional view of a conductor
pattern formed by an etching method.
[0017] FIG. 2 is a schematic cross-sectional view of a concave
portion (narrowed part) that can occur on a side surface of a
conductor pattern.
[0018] FIG. 3 is a schematic cross-sectional view showing a
preferred positional relationship between a plate-shaped work and a
spray nozzle.
[0019] FIG. 4 is a schematic cross-sectional view showing a
preferred positional relationship between a plate-shaped work and a
spray nozzle.
[0020] Reference numerals in FIGS. 1 to 4 will be explained below.
[0021] 1a Resist pattern [0022] 1b Metal layer [0023] 1c Substrate
[0024] 1d Side surface [0025] 1e Bottom space width [0026] 1f Top
space width [0027] 1g Etched portion [0028] 2a Concave portion
(narrowed portion) formed on side surface of conductor pattern
[0029] 2b Upper end portion of narrowed portion [0030] 2c Deepest
portion of narrowed portion [0031] d Depth of narrowed portion 2a
[0032] 3a Material to be etched [0033] 3b Spray nozzle [0034] P
Perpendicular line to etching surface, projected on a vertical
plane in parallel with a conveying direction [0035] C Ejection
center axis of spray nozzle, projected on a vertical plane in
parallel with a conveying direction [0036] x Angle formed by P and
C [0037] P' Perpendicular line to etching surface, projected on a
vertical plane perpendicular to a conveying direction [0038] C'
Ejection center axis of spray nozzle, projected on a vertical plane
perpendicular to a conveying direction [0039] y Angle formed by P'
and C'
EMBODIMENT FOR PRACTICING THE INVENTION
[0040] The first etching method of this invention (To be referred
to as "first etching method" hereinafter) will be explained.
[0041] FIG. 1 shows a schematic cross-sectional view of a conductor
pattern formed by an etching method. A conductor pattern of a metal
layer 1b is formed on a substrate 1c, and the 1a indicates a resist
pattern used during etching. The portion of a space (dent) formed
by etching the metal layer 1b by an etching method will be an
"etched portion" 1g. In the first etching method of this invention,
there are consecutively carried out the steps of (1) ejecting an
etchant that reacts with the metal to be etched to form a
water-insoluble reaction product, by means of a spray nozzle, to
perform etching until the etching depth reaches 60% or more of the
metal layer thickness, and (2) ejecting an etchant that does not
react with the metal to be etched and hence does not form a
water-insoluble reaction product through a reaction with the metal
to be etched, by means of a spray nozzle, to perform etching,
whereby the top space width 1f and bottom space width 1e of the
etched portion come to be closely equivalent, so that a conductor
pattern having a nearly rectangular cross-sectional form can be
obtained. The method of ejecting an etchant with a spray nozzle
will be referred to as a spray method.
[0042] In the step (1), in the etched portion 1g, the etching
proceeds while a water-insoluble reaction product is deposited in a
portion where the flow speed of the etchant is low. In the portion
covered with the deposited water-insoluble reaction product, the
etching proceeds extremely slowly, and in an early stage of the
step (1), the water-insoluble reaction product easily adheres to a
portion that keeps the etching from proceeding in the lateral
direction, so that the etching mainly proceeds only in the depth
direction. However, as the step (1) is proceeded with, the etching
in the lateral direction comes to proceed at a certain speed. In
particular, as shown in FIG. 2, around the middle portion along the
metal layer thickness in the etched portion 1g, a concave portion
(narrowed portion) 2a is liable to occur on a side surface 1d of
the etched portion 1g. Further, since the above water-insoluble
reaction product is deposited non-uniformly to some extent, small
texture is sometimes formed on the side surface 1d of the etched
portion to give a surface in a roughened state. In this invention,
the narrowed portion 2a and small texture formed in the step (1)
can be removed by the etching in the step (2). Therefore, there can
be obtained a conductor pattern having a nearly rectangular
cross-sectional form and smooth surfaces. By the above technique,
there can be produced a printed wiring board that is suitable for
transmitting high-frequency current.
[0043] In the first etching method, as the etching depth in the
step (1) is smaller, the cross-sectional form is more liable to
become trapezoidal, and as the etching depth in the step (1) is
larger, the etching form is more liable to become rectangular. That
is, in the first etching method of this invention, the
cross-sectional form obtained after completion of the step (2) can
be controlled by adjusting the etching depth provided in the step
(1). This relationship will be specifically explained below.
[0044] When the etching in the step (1) is carried out until the
etching depth becomes 60% or more but less than 90% of the metal
layer thickness, and further when the etching in the step (2) is
carried out until a desired bottom space width is obtained, it
comes to be easier to obtain a trapezoidal conductor pattern having
a top space width 1f and a bottom space width 1e closer to each
other in size than that in a conventional etching technique and
having a cross-sectional form closer to a rectangular form than
that in a conventional etching method. When the cross section of a
conductor pattern has the above form, the conductor pattern is
inferior to some extent from the viewpoint of satisfaction of both
high insulation reliability and low conductor resistance when
compared with a conductor pattern having a rectangular
cross-sectional form, while there is an advantage that the quality
control of the conductor pattern can be performed by observation
from above like a conductor pattern produced by a conventional
etching method.
[0045] When the etching in the step (1) is carried out until the
etching depth becomes 90% or more but 100% or less of the metal
layer thickness, and further when the etching in the step (2) is
carried out until a desired bottom space width is obtained, the
cross-sectional form of a conductor pattern can be made far closer
to a rectangular form. Alternatively, when the etching in the step
(1) is carried out for a time period that is 1 to 1.1 times the
time period required until the etching depth becomes equivalent to
the metal layer thickness, and when, further, the etching in the
step (2) is carried out until a desired bottom space width is
obtained, the cross-sectional form of a conductor pattern can be
made far closer to a rectangular form.
[0046] When the etching in the step (1) is carried out for a time
period that is more than 1.1 times the time period required until
the etching depth becomes equivalent to the metal layer thickness,
and further, when the etching in the step (2) is carried out until
a desired top space width 1f is obtained, there can be obtained a
conductor pattern having a reversed trapezoidal form having a
narrow top space width 1f and a wide bottom space width 1e.
[0047] In any one of these cases, it is required to adjust the
etching depth provided by the etching in the step (1) in the above
range in order to obtain a desired form.
[0048] In the first etching method, further, when the etchant for
use in the step (2) has a faster etching speed, there is also an
advantage that the etching can be completed in a shorter period of
time in terms of a total time period of the steps (1) and (2) as
compared with the case of one-step etching with using only one
etchant for use in the step (1).
[0049] In the first etching method, the material to be etched
refers to a material obtained by forming a resist pattern on a
metal layer containing a metal to be etched. When a printed wiring
board is produced, there is used a material obtained by stacking
metal layer(s) on one surface or both surfaces of a substrate and
forming resist pattern(s) on the metal layer(s).
[0050] As a substrate that can be used for producing a printed
wiring board, there can be used various synthetic resins such as an
epoxy resin, a phenolic resin, a melamine resin, a polyester resin,
a polyimide resin, a polyamide resin, a fluororesin, etc.,
fiber-reinforced resins obtained by impregnating fibers such as
paper and a glass fiber, etc., with these synthetic resins, such as
paper phenol, paper epoxy, glass epoxy, etc., and various glasses,
ceramics and metals. When a printed wiring board is produced,
fiber-reinforced resins, heat-resistant resins such as a polyimide,
a fluororesin, etc., and ceramics are preferably used from the
viewpoint of insulating properties, mechanical properties, heat
resistance, etc. There can be also used a substrate obtained by
compounding or stacking two or more materials.
[0051] The metal to be etched refers to a metal material that is
removed by etching. The metal to be etched can be selected from
various metals such as copper, copper alloy, aluminum, tin, etc.
When a printed wiring board is produced, copper or copper alloy is
preferably used from the viewpoint of conductivity, mechanical
properties, soldering properties, etc.
[0052] The method for stacking the metal layer on the substrate is
not specially limited, and the substrate and a metal foil can be
bonded to each other with a phenol-, melamine-, epoxy-, urethane-,
silicon- or modified silicon-containing adhesive, any one of
adhesives containing various rubbers such as chloroprene, nitrile
and acrylic rubbers, or a vinyl-acetate-containing adhesive.
Further, a metal foil can be also stacked on the substrate by a
so-called heat-seal method. There can be also employed a so-called
casting method in which a heat-melted product or solution of a
material for forming a substrate is applied onto a metal foil and
the applied material is cooled or dried to solidify to form a
laminate. There can be also used a laminate produced by forming a
metal layer on the surface of a substrate by electric plating,
electroless plating or a vacuum vapor deposition method such as
sputtering, etc.
[0053] The method for forming a resist pattern is not specially
limited, and it can be selected from various methods such as a
photolithography method, a screen printing method, etc. Of these
methods, the photolithography method is preferably used, since a
fine pattern can be easily formed. As a resist for use in the
photolithography method, there can be used both a negative
photoresist in which a portion other than a portion insolubilized
by exposure to light is removed by dissolving it with an alkali
aqueous solution, etc., and a positive photoresist in which a
portion solubilized by exposure to light is removed by dissolving
it with an alkali aqueous solution, etc., while the positive
photoresist is particularly preferred since no spreading bottom of
a line portion is easily formed so that a highly reliable printed
wiring board can be produced. In addition, in the second etching
method, the resist used on the surface A and the resist used on the
surface B may be the same or may be different.
[0054] The etchant refers to a liquid that dissolves a metal to be
etched, at a processing-wise reasonable speed, that is, at a speed
of 0.1 .mu.m/minute or more under processing conditions where the
etchant is applied. Further, the etchant contains a component that
dissolves a metal to be etched (to be referred to as "etching
component" hereinafter). Examples of the etching component that is
used when the metal to be etched is copper or copper alloy include
iron (III) chloride, copper (II) chloride, a sulfuric acid-hydrogen
peroxide mixture, persulfate, etc.
[0055] In the step (I), there is used an etchant that reacts with a
metal to be etched to form a water-insoluble reaction product. The
etchant in the step (1) contains in addition to the etching
component a compound that is capable of reacting with ion of the
metal to be etched to form a water-insoluble reaction product. In
this invention, the "compound that reacts with ion of the metal to
be etched to form a water-insoluble reaction product" is added
mainly for the purpose of improving the cross-sectional form of a
conductor pattern such that it is closer to the form of a
rectangle, and will be described as "form improver". A
water-insoluble reaction product formed by a reaction between the
ion of a metal to be etched and the form improver will be described
as "water-insoluble reaction product". The content of the form
improver can be any amount if it is sufficient for forming a
water-insoluble reaction product on the surface of the metal to be
etched (including side surfaces of an etched portion).
[0056] As the etchant in the step (2), there is used an etchant
that does not form a water-insoluble reaction product through a
reaction with the metal to be etched. The etching component in the
etchant in the step (1) and the etching component in the etchant in
the step (2) may be the same or may be different. The etchant for
use in the step (2) may contain a small amount of a form improver
so long as the water-insoluble reaction product does not remain on
the surface of a metal to be etched (including side surfaces of the
etched portion). Therefore, it is preferred, but is not essential,
to keep the form improver from being contained in the etchant in
the step (2) by carrying out the procedures of liquid removal or
rinsing with water between the step (1) and the step (2) so that
the etchant in the step (1) is kept from being included in the
etchant in the step (2).
[0057] When the metal to be etched is copper or copper alloy,
examples of the form improver include oxalic acid and various azole
compounds proposed in JP 6-57453A and Published US Patent
Application No. 2005/0016961.
[0058] In the first etching method, when the metal to be etched is
copper or copper alloy, the etchant in the step (1) preferably
contains 1 to 20 mass % of iron (III) chloride as an etching
component and 5 to 50 mass %, based on the iron (III) chloride, of
oxalic acid as a form improver. When the above etchant is used,
there can be easily obtained a conductor pattern having an etched
portion in which the top space width 1f and the bottom space width
1e are very close to each other and having a cross-sectional form
close to a rectangular form.
[0059] In the first etching method, when the metal to be etched is
copper or copper alloy, an aqueous solution containing iron (III)
chloride or copper (II) chloride as an etching component is
preferably used as the etchant in the step (2). And, it is
particularly preferred to use an aqueous solution containing copper
(II) chloride. These etching components have lower concentrations
that are required for obtaining certain constant etching speeds
than other etching components, so that their viscosities are low
when compared on the basis of the constant etching speeds. As a
result, etching uniformly proceeds even in a fine etched portion,
and a good cross-sectional form closer to a rectangular form can be
obtained. Further, when copper (II) chloride is used as the etchant
in the step (2), there is also another advantage that side surfaces
of a conductor pattern can be made remarkably smooth.
[0060] For obtaining an etching form that is very close to a
rectangular form in the first etching method, it is preferred to
use an etchant having an etching speed of 0.3 .mu.m/minute or more
but 3 .mu.m/minute or less in the step (2) when a metal to be
etched is immersion-etched in the etchant (the above etching speed
will be referred to as "immersion-etching speed" hereinafter). That
is because when such an etchant is used, the top portion and bottom
portion of a conductor pattern are etched at equivalent speeds, so
that an etching form closer to a rectangular form can be obtained.
When the etching speed in the immersion etching is larger than 3
.mu.m/minute, the difference in the etching speed in the top
portion and that in the bottom portion becomes large, so that the
top space width 1f tends to be large and that the bottom space
width 1e tends to be small. When the etching speed in the immersion
etching is smaller than 0.3 .mu.m/minute, the improvement effect on
the roughness of side surfaces 1d of a conductor pattern may
decrease.
[0061] As an etchant having an etching speed of 0.3 .mu.m/minute or
more but 3 .mu.m/minute or less when a metal to be etched is
immersion-etched, there is used an etchant of which the etching
component concentration is adjusted as required. For example, when
the metal to be etched is copper or copper alloy, there is employed
an etchant containing 0.2 to 3 mass % of iron (III) chloride and
0.2 to 2 mass % of hydrogen chloride or an etchant containing 0.5
to 8 mass % of copper (II) chloride and 1 to 5 mass % of hydrogen
chloride.
[0062] In the first etching method, the etched portion after the
step (2) is carried out may sometimes have a narrowed portion
remaining. This problem is caused because a water-insoluble
reaction product in a narrowed portion is removed faster to make
the etching proceed non-uniformly in the initial stage of the
etching in the step (2), so that the function of removing the
narrowed portion is decreased. For getting around the above
problem, it is sufficient to take the step of removing the
water-insoluble reaction product prior to the step (2).
Specifically, the step (3) of removing a water-insoluble compound
with a liquid that dissolves the water-insoluble reaction product
is carried out between the step (1) and the step (2). As a liquid
in the step (3), an aqueous solution containing a chemical agent
that dissolves the water-insoluble reaction product can be used.
Naturally, when the metal to be etched is dissolved in the step
(3), the above effect is no longer obtained. Therefore, the liquid
that is used in the step (3) to dissolve the water-insoluble
reaction product is required to be a liquid that dissolves the
metal to be etched, at a slow speed of less than 0.3 .mu.m/minute
even if it dissolves the metal to be etched, and most preferably,
the liquid does not at all dissolve the metal to be etched.
[0063] The chemical agent that dissolves the water-insoluble
reaction product can be selected as required depending upon kinds
of the water-insoluble reaction product, while it is selected from
monovalent acids such as hydrochloric acid, amidosulfuric acid,
acetic acid, etc., hydroxy acids such as citric acid, gluconic
acid, etc., or chelating agents such as ethylenediamine tetraacetic
acid salt, etc. Preferably, these chemicals dissolve the
water-insoluble reaction product as rapidly as possible.
[0064] In the first etching method, when the metal to be etched is
copper or copper alloy, an aqueous solution containing hydrochloric
acid is particularly preferably used as a liquid in the step (3).
Further, the above liquid is preferably warmed before used, since
the dissolving speed of the water-insoluble reaction product is
increased. The method for applying the above liquid to a material
be etched can be selected from various methods such as a spray
method, an immersion method, a paddle method, etc. The spray method
is preferred owing to advantages that the movement of the liquid to
fine concave regions on the surface of the material to be etched is
rapidly carried out so that a water-insoluble reaction product can
be dissolved fastly and that the apparatus can be downsized.
[0065] As mentioned above, when the metal to be etched is copper or
copper alloy, particularly preferably, an etchant containing copper
(II) chloride as an etching component is used, since the side
surfaces of an etched portion become very smooth. However, when the
etchant containing copper (II) chloride as an etching component is
used, the solubility of the water-insoluble reaction product is
low, and in many cases, the step (2) takes a long time, or a
narrowed portion remains in the side surface of a conductor
pattern. When the metal to be etched is copper or copper alloy and
when an etchant containing copper (II) chloride as an etching
component is used in the step (2), it is particularly effective to
carry out the step (3) between the step (1) and the step (2).
[0066] The second etching method of this invention (to be referred
to as "second etching method" hereinafter) will be explained.
[0067] In the second etching method, the etching material refers to
a material obtained by stacking metal layers containing a metal to
be etched each on both surfaces of an insulating substrate and
forming resist patterns on the metal layers.
[0068] The substrate can be selected from various synthetic resins
such as an epoxy resin, a phenolic resin, a melamine resin, a
polyester resin, a polyimide resin, a polyamide resin, a
fluororesin, etc., fiber-reinforced resins obtained by impregnating
fibers such as paper and a glass fiber, etc., with these synthetic
resins, such as paper phenol, paper epoxy, glass epoxy, etc., and
various glasses, ceramics and metals. When a printed wiring board
is produced, a fiber-reinforced resin, heat-resistant resins such
as a polyimide, a fluororesin, etc., and ceramics are suitably used
from the viewpoint of insulating properties, mechanical properties,
heat resistance, etc. There can be also used a substrate obtained
by compounding or stacking two or more materials.
[0069] The metal to be etched refers to a metal material that is
removed by etching. The metal to be etched can be selected from
various metals such as copper, copper alloy, aluminum, tin, etc.
When a printed wiring board is produced, copper or copper alloy is
preferably used from the viewpoint of conductivity, mechanical
properties, soldering properties, etc.
[0070] The method for stacking the metal layers on the substrate is
not specially limited, and the substrate and metal foils can be
bonded with a phenol-, melamine-, epoxy-, urethane-, silicon- or
modified silicon-containing adhesive, any one of adhesives
containing various rubbers such as chloroprene, nitrile and acrylic
rubbers, or a vinyl-acetate-containing adhesive. Further, metal
foils can be also stacked on the substrate by a so-called heat-seal
method. There can be also employed a so-called casting method in
which a heat-melted product or solution of a material for forming a
substrate is applied onto a metal foil and the applied material is
cooled or dried to solidify to form a laminate. There can be also
used a laminate produced by forming a metal layer on each surface
of a substrate by electric plating, electroless plating or a vacuum
vapor deposition method such as sputtering, etc.
[0071] The method for forming a resist pattern is not specially
limited, and it can be selected from various methods such as a
photolithography method, a screen printing method, etc. Of these
methods, the photolithography method is preferably used, since a
fine pattern can be easily formed. As a resist for use in the
photolithography method, there can be used both a negative
photoresist in which a portion other than a portion insolubilized
by exposure to light is removed by dissolving it with an alkali
aqueous solution, etc., and a positive photoresist in which a
portion solubilized by exposure to light is removed by dissolving
it with an alkali aqueous solution, etc., while the positive
photoresist is particularly preferred since the bottom of a line
portion is hardly spread, so that a highly reliable printed wiring
board can be produced. In addition, in the second etching method,
the resist used on the surface A and the resist used on the surface
B may be the same or may be different.
[0072] In the second etching method, characteristically, the
surface A is etched in the step (4) first, then the material to be
etched is reversed in the step (5), and then the surface B is
etched in the step (6). The resist pattern on the surface B may be
formed at any time before the step (6) of etching the surface B,
while the surface B may be sometimes affected by an etchant that
moves around onto the surface B during the etching of the surface
A, and the adhesion of a resist material to the surface B may be
deteriorated, so that it is preferred to form the resist pattern on
the surface B before the etching of the surface A. The resist
pattern on the surface A may be removed after completion of the
etching of the surface B, or may be removed before the etching of
the surface B. However, when the resists on the surface A and the
resist on the surface B can be removed by the same method, it is
preferred to remove the resists on the two surfaces together after
completion of the etching of the surface B from the viewpoint of
efficiency. Further, in case that a resist pattern on the surface A
remains when the surface B is etched, advantageously, a microscopic
morphological change does not take place on the surface A.
[0073] In the second etching method, there is used an etchant that
reacts with the metal to be etched to form a water-insoluble
reaction product like the etchant used in the step (1) of the first
etching method.
[0074] Such an etchant has the property of dissolving the metal to
be etched when it flows at a relatively fast speed but dissolving
almost no metal to be etched when it stands still or flows at a
slow speed. When the lower surface is etched with a spray etching
apparatus, the etchant inevitably moves around on the upper surface
of a material to be etched, while the flow of the etchant on the
upper surface of the material to be etched is extremely slow as
compared with the flow of the etchant on the lower surface, so that
the etchant that moves around onto the upper surface hardly
dissolves the upper surface and changes the form of the upper
surface. When such an etchant is used, therefore, both surfaces of
the material to be etched can be spray-etched from below without
using any complicated apparatus or steps, and fine conductor
patterns can be formed on both surfaces by an etching method.
[0075] In the second etching method, when the metal to be etched is
copper or copper alloy, it is preferred to use an etchant
containing 1 to 20 mass % of iron (III) chloride as a main
effective component and 5 to 100 mass %, based on the iron (III)
chloride, of oxalic acid as a form improver. That is because the
above etchant has a great difference between the speed of
dissolving the metal to be etched in a flowing state and the speed
of dissolving the metal to be etched in a standing state and hence
make it possible to remarkably reduce the change of form of the
upper surface during the etching of the lower surface.
[0076] In the second etching method, it is the most preferred to
hold the material to be etched horizontally for reliably producing
a fine conductor pattern, while the effect of this invention can be
produced so long as it is held in a nearly horizontal state.
Specifically, all that is required of the angle that is to be
formed by the etching surface of the material to be etched and the
horizontal is 20.degree. or less, and it is more preferably
10.degree. or less, still more preferably 5.degree. or less.
[0077] In the second etching method, it is required to eject the
etchant to the material to be etched, from below with a spray
nozzle. FIGS. 3 and 4 are schematic cross-sectional views showing a
positional relationship of the material to be etched and the spray
nozzle. In FIG. 3, the material to be etched is conveyed from right
to left. In FIG. 4, the material to be etched is conveyed from
front to back. In FIG. 3, the angle x formed by a perpendicular
line P perpendicular to the direction in parallel with the carrying
direction and downward from the material 3a to be etched and the
center line C of the spray nozzle is preferably 45.degree. or less,
particularly preferably 20.degree. or less. In FIG. 4, further, the
angle .gamma. formed by a perpendicular line P' perpendicular to
the direction at right angles with the carrying direction and
downward from the material 3a to be etched and the center line C'
of the spray nozzle is preferably 30.degree. or less, more
preferably 10.degree. or less, still more preferably 5.degree. or
less. When the center axis of the spray nozzle is out of these
ranges, the etching may proceed non-uniformly, or a pattern formed
after the etching may not be a faithful reproduction of a resist
pattern.
[0078] In the second etching method, the pressure (gauge pressure)
for supplying a liquid to the spray nozzle is preferably adjusted
to 50 to 500 kPa. When the supply pressure is lower than the above,
the difference between the speed of dissolving the metal to be
etched by an etchant that moves around onto the upper surface
during the etching of the lower surface and the speed of dissolving
on the lower surface is small, and the form of the upper surface
may be sometimes changed during the etching of the lower
surface.
[0079] In the second etching method, a water-insoluble reaction
product may be sometimes formed on part or the whole of the surface
B by an etchant that moves around onto the surface B during the
etching of the surface A. As a result, the etching of the surface B
may take a long time, or there may be sometimes a difference in
etching completion between a region where the water-insoluble
reaction product is formed and a region where it is not formed. For
getting around the above problem, the step (7) of removing the
water-insoluble reaction product can be carried out between the
step (4) of etching the surface A and the step (6) of etching the
surface B. Specifically, it is sufficient to carry out the step of
washing with an aqueous solution containing a chemical agent that
dissolves the water-insoluble reaction product between the step (4)
and the step (6). The above chemical agent that dissolves the
water-insoluble reaction product can be selected from like chemical
agents which are used for the treatment to remove the
water-insoluble reaction product in the step (3) of the first
etching method. For example, it can be selected from monovalent
acids such as hydrochloric acid, amidosulfuric acid, acetic acid,
etc., hydroxy acids such as citric acid, gluconic acid, etc., or
chelating agents such as ethylenediamine tetraacetic acid salt,
etc.
[0080] Since the material that has been etched has a
water-insoluble reaction product adhering thereto, it is preferred
to carry out the procedure of removing the water-insoluble reaction
product from both surfaces after the etching of the surface B. For
this procedure, it is sufficient to carry out the step of washing
with an aqueous solution containing a chemical agent that dissolves
the water-insoluble reaction product like the step (7).
[0081] The second etching method is suitably applied to the
production of a double-sided printed wiring board, while it can be
also used as part of the steps of producing a printed wiring board
having three or more conductor layers.
EXAMPLES
[0082] Examples 1 to 11 are examples of the first etching
method.
Example 1
Preparation of Material to be Etched
[0083] A positive liquid resist was applied to a copper-clad
laminate obtained by stacking a 40 .mu.m thick polyimide insulating
substrate and a 18 .mu.m thick electro-deposited copper foil (metal
layer), and the positive liquid resist was dried such that a dried
resist layer had a thickness of 5 .mu.m. The resist was exposed
through an evaluation pattern having a line width/space width of 25
mm/25 .mu.m, followed by development and washing with water, to
form a resist pattern, whereby a material to be etched for etching
test was prepared.
<Preparation of Etchant for Step (1)>
[0084] Water was added to 6.0 kg (2.22 kg as iron chloride
anhydride) of a commercially available 40.degree. Be iron (III)
chloride aqueous solution (concentration 37 mass %) and 0.25 kg
(0.18 kg as oxalic acid anhydride) of oxalic acid dihydrate up to a
total of 30 kg to prepare 30 kg of an etchant containing 7.4 mass %
of iron (III) chloride and 0.60 mass % of oxalic acid.
<Step (1)>
[0085] The above etchant for the step (1) was ejected to the
material to be etched, with a spray-etching apparatus (trade name:
YCE-85III, supplied by YAMAGATA MACHINERY CO., LTD.) at a spray
pressure of 200 kPa until an etching depth of 16 .mu.m (89% of
electro-deposited copper foil thickness) was reached. The material
to be etched was washed with water immediately after being etched.
The time period for the above etching was 70 seconds. When the
material to be etched after it was washed with water was observed
through an optical microscope, there was observed a pale greenish
crystal (water-insoluble reaction product) that adhered to side
surfaces of the etched portion.
<Preparation of Etchant for Step (2)>
[0086] Water was added to 0.080 kg (0.030 kg as iron chloride
anhydride) of a commercially available 40.degree. Be iron (III)
chloride aqueous solution (concentration 37 mass %) and 0.60 kg
(0.21 kg as hydrogen chloride) of hydrochloric acid having a
concentration of 36 mass % up to a total of 30 kg to prepare 30 kg
of an etchant containing 0.10 mass % of iron (III) chloride and
0.72 mass % of hydrogen chloride. When the above copper-clad
laminate having no resist pattern was immersed in this etchant,
copper on the surface was dissolved in 90 minutes, and the
polyimide as the substrate was exposed. Therefore, the
immersion-etching speed of this etchant for the step (2) was 0.2
.mu.m/minute.
<Step 2>
[0087] The material to be etched, after the step (1), was etched
with the above etchant for the step (2) until the bottom space
width 1e of the etched portion became 25 .mu.m which was the same
as the space width of the resist pattern (etching time period 75
seconds). The etched material was washed with water immediately
after being etched. For conditions such as an etching apparatus, a
spray pressure, etc., the same conditions as those in the step (1)
were employed. When the etched material after it was washed with
water was observed through an optical microscope, there was
observed no water-insoluble reaction product that adhered to side
surfaces of the etched portion.
<Post Treatment>
[0088] The etched material after the end of the step (2) was
immersed in an aqueous sodium hydroxide solution having a
concentration of 3.0 mass % for 3 minutes to peel off the resist
pattern, and then hydrochloric acid having a hydrogen chloride
concentration of 3.6 mass % was ejected with a spray nozzle for 30
seconds to clean it, followed by washing with water and drying,
whereby a printed wiring board for evaluation was produced.
Examples 2-5
[0089] Printed wiring boards for evaluation were produced in the
same manner as in Example 1 except that the composition of the
etchant for the step (2) was changed as shown in Table 1. In
addition, when each of etched materials of these Examples was
observed through an optical microscope after the end of the step
(2), there was observed no water-insoluble reaction product that
adhered to side surfaces of the etched portion.
Examples 6-9
[0090] Printed wiring boards for evaluation were produced in the
same manner as in Example 1 except that the step (3) of cleaning
the material to be etched with hydrochloric acid having a hydrogen
chloride concentration of 3.6 mass % for 30 seconds by means of the
same spray-etching apparatus as that used in the step (1) was
carried out between the step (1) and the step (2) and that the
composition of the etchant for the step (2) was changed as shown in
Table 1. When each of etched materials of these Examples was
observed through an optical microscope after the end of the step
(2), there was observed no water-insoluble reaction product that
adhered to side surfaces of the etched portion.
Example 10
[0091] A printed wiring board for evaluation was produced in the
same manner as in Example 8 except that the step (1) was carried
out until an etching depth of 11 .mu.m (61% of thickness of an
electro-deposited copper foil) was reached.
Example 11
[0092] A printed wiring board for evaluation was produced in the
same manner as in Example 8 except that an aqueous sodium
persulfate solution having a concentration of 10 mass % was used as
an etchant for the step (2). When the etched material of this
Example was observed through an optical microscope after the end of
the step (2), there was observed no water-insoluble reaction
product that adhered to side surfaces of the etched portion.
Example 12
[0093] A printed wiring board was produced in the same manner as in
Example 8 except that the step (3) was not carried out.
Example 13
[0094] A printed wiring board was produced in the same manner as in
Example 8 except that the etchant for the step (1) was changed as
shown in Table 1. When the material to be etched in this Example
was observed through an optical microscope after the end of the
step (1), there was observed a pale greenish crystal
(water-insoluble reaction product) that adhered to side surfaces of
the etched portion.
Comparative Example 1
[0095] A printed wiring board for evaluation was produced in the
same manner as in Example 1 except that the step (1) was carried
out until a bottom space width of 25 .mu.m was reached and that the
step (2) was not carried out.
Comparative Example 2
[0096] A printed wiring board for evaluation was produced in the
same manner as in Example 8 except that the etching in the step (1)
was carried out until an etching depth of 9 .mu.m (50% of thickness
of an electro-deposited copper foil) was reached.
Comparative Example 3
[0097] An attempt was made to produce a printed wiring board in the
same manner as in Example 8 except that the etchant for the step
(1) contained no oxalic acid. However, the top space width 1f
became too wide before the etching depth reached 16 .mu.m, so that
the resist pattern was peeled off the material to be etched. Hence,
no printed wiring board for evaluation could be produced. When the
material to be etched in this Comparative Example was observed
through an optical microscope after the end of the step (1), there
was observed no water-insoluble reaction product that adhered to
side surfaces of the etched portion.
Comparative Example 4
[0098] A printed wiring board for evaluation was produced in the
same manner as in Example 8 except that an etchant having the same
composition as that of the etchant for the step (1) was used as an
etchant for the step (2).
<Evaluations>
[0099] Each of the printed wiring boards obtained in Examples and
Comparative Examples was embedded in an epoxy resin, and embedded
products were cut. Their cross sections were polished, and each of
the polished cross sections was observed through an optical
microscope to measure a top space width 1f of an etched portion.
Further, it was observed whether or not a narrowed portion 2a
existed. When the narrowed portion 2a existed, its depth d was
measured, and the results were classified on the basis of the
following three ratings. The depth d refers to a length from a
standard line of the upper end portion 2b to a deepest portion 2c
(FIG. 2). Table 2 shows the evaluation results.
[0100] (A) No narrowed portion 2a is found.
[0101] (B) Narrowed portion has a depth of less than 2 .mu.m.
[0102] (C) Narrowed portion has a depth of 2 .mu.m or more but less
than 3 .mu.m.
[0103] (D) Narrowed portion has a depth of 3 .mu.m or more.
[0104] Further, each printed wiring board for evaluation was
observed through a scanning electron microscope, and side surfaces
1d of a conductor pattern were observed for a state to classify the
state on the basis of the following five ratings. Table 2 shows the
evaluation results. [0105] (A) The state of side surfaces 1d of a
conductor pattern is very smooth. [0106] (B) Smooth. [0107] (C)
Slightly roughened. [0108] (D) Roughened. [0109] (E) Greatly
roughened.
TABLE-US-00001 [0109] TABLE 1 Adherence Time of water- period
insoluble for Etching reaction etching depth product Composition of
etchant in step in step after for step (1) (1) (1) step (1) Example
1 Iron (III) chloride 7.4 mass % 70 seconds 16 .mu.m Yes Oxalic
acid 0.60 mass % Example 2 Iron (III) chloride 7.4 mass % 70
seconds 16 .mu.m Yes Oxalic acid 0.60 mass % Example 3 Iron (III)
chloride 7.4 mass % 70 seconds 16 .mu.m Yes Oxalic acid 0.60 mass %
Example 4 Iron (III) chloride 7.4 mass % 70 seconds 16 .mu.m Yes
Oxalic acid 0.60 mass % Example 5 Iron (III) chloride 7.4 mass % 70
seconds 16 .mu.m Yes Oxalic acid 0.60 mass % Example 6 Iron (III)
chloride 7.4 mass % 70 seconds 16 .mu.m Yes Oxalic acid 0.60 mass %
Example 7 Iron (III) chloride 7.4 mass % 70 seconds 16 .mu.m Yes
Oxalic acid 0.60 mass % Example 8 Iron (III) chloride 7.4 mass % 70
seconds 16 .mu.m Yes Oxalic acid 0.60 mass % Example 9 Iron (III)
chloride 7.4 mass % 70 seconds 16 .mu.m Yes Oxalic acid 0.60 mass %
Example 10 Iron (III) chloride 7.4 mass % 45 seconds 11 .mu.m Yes
Oxalic acid 0.60 mass % Example 11 Iron (III) chloride 7.4 mass %
70 seconds 16 .mu.m Yes Oxalic acid 0.60 mass % Example 12 Iron
(III) chloride 7.4 mass % 70 seconds 16 .mu.m Yes Oxalic acid 0.60
mass % Example 13 Copper (II) chloride 10 mass % 210 seconds 16
.mu.m Yes Benzotriazole 0.20 mass % Comparative Iron (III) chloride
7.4 mass % 135 seconds *1 Yes Example 1 Oxalic acid 0.60 mass %
Comparative Iron (III) chloride 7.4 mass % 35 seconds 9 .mu.m Yes
Example 2 Oxalic acid 0.60 mass % Comparative Iron (III) chloride
7.4 mass % 40 seconds 16 .mu.m No Example 3 Comparative Iron (III)
chloride 7.4 mass % 70 seconds 16 .mu.m Yes Example 4 Oxalic acid
0.60 mass % Adherence of water- Immersion in- etching Time soluble
speed period reaction of for product etchant etching after
Composition of etchant in step in step step Step for step (2) (2)
(2) (2) (3) Example 1 Iron (III) chloride 0.10 mass % 0.2 .mu.m/min
75 No No Hydrogen chloride 0.72 mass % seconds Example 2 Iron (III)
chloride 0.20 mass % 0.3 .mu.m/min 60 No No Hydrogen chloride 0.72
mass % seconds Example 3 Iron (III) chloride 0.80 mass % 1
.mu.m/min 45 No No Hydrogen chloride 0.72 mass % seconds Example 4
Iron (III) chloride 3.0 mass % 3 .mu.m/min 15 No No Hydrogen
chloride 0.72 mass % seconds Example 5 Iron (III) chloride 5.0 mass
% 4 .mu.m/min 15 No No Hydrogen chloride 0.72 mass % seconds
Example 6 Iron (III) chloride 3.0 mass % 3 .mu.m/min 15 No Yes
Hydrogen chloride 0.72 mass % seconds Example 7 Copper (II)
chloride 0.50 mass % 0.3 .mu.m/min 50 No Yes Hydrogen chloride 3.0
mass % seconds Example 8 Copper (II) chloride 8.0 mass % 3
.mu.m/min 20 No Yes Hydrogen chloride 3.0 mass % seconds Example 9
Copper (II) chloride 15 mass % 5 .mu.m/min 20 No Yes Hydrogen
chloride 3.0 mass % seconds Example Copper (II) chloride 8.0 mass %
3 .mu.m/min 30 No Yes 10 Hydrogen chloride 3.0 mass % seconds
Example Sodium persulfate 10 mass % 1 .mu.m/min 60 No Yes 11
seconds Example Copper (II) chloride 8.0 mass % 3 .mu.m/min 45 No
No 12 Hydrogen chloride 3.0 mass % seconds Example Copper (II)
chloride 8.0 mass % 3 .mu.m/min 20 No Yes 13 Hydrogen chloride 3.0
mass % seconds Comparative -- -- -- -- -- Example 1 Comparative
Copper (II) chloride 8.0 mass % 3 .mu.m/min 40 No Yes Example 2
Hydrogen chloride 3.0 mass % seconds Comparative -- -- -- -- --
Example 3 Comparative Iron (III) chloride 7.4 mass % 0 .mu.m/min 60
Yes Yes Example 4 Oxalic acid 0.60 mass % seconds *1: See
Comparative Example 1 of the present specification.
TABLE-US-00002 TABLE 2 Narrowed portion of Roughening side of side
surfaces of surfaces of Top space conductor conductor width 1f
pattern pattern Example 1 27 .mu.m B C Example 2 27 .mu.m B B
Example 3 28 .mu.m B B Example 4 29 .mu.m B B Example 5 32 .mu.m B
B Example 6 30 .mu.m A B Example 7 27 .mu.m A A Example 8 28 .mu.m
A A Example 9 31 .mu.m A A Example 10 33 .mu.m A A Example 11 35
.mu.m B B Example 12 27 .mu.m C A Example 13 30 .mu.m A A
Comparative 27 .mu.m D D Example 1 Comparative 40 .mu.m A A Example
2 Comparative -- -- -- Example 3 Comparative 26 .mu.m D E Example
4
[0110] As is seen when Examples and Comparative Examples are
compared, there can be obtained cross-sectional forms close to a
rectangular form and conductor patterns free of a narrowed portion
and roughened surfaces. As is seen when Example 1 and Comparative
Example 1 are compared, in Comparative Example that does not carry
out the step (2) that is an essential requirement, side surfaces of
an etched portion have a narrowed portion and roughening. As is
seen when Example 8 and Comparative Example 2 are compared, in
Comparative Example 2 in which the etching depth in the step (1) is
less than 60% of a copper foil thickness, the top space width 1f is
broad, and the cross-sectional form of the conductor pattern is
finally trapezoidal. As is seen from Comparative Example 3,
further, when an etchant that does not form a water-insoluble
reaction product is used in the step (1), no fine pattern can be
formed. Further, also when an etchant that forms a water-insoluble
reaction product is used in the step (2) like Comparative Example
4, the side surfaces of a conductor pattern have a narrowed portion
and roughening.
[0111] As is seen when Examples 1 to 5 are compared, in Example 1
in which the immersion-etching speed is less than 0.3 .mu.m/minute,
it is found that the effect of suppressing the surface roughness of
sides of a conductor pattern tends to decrease. Further, in
Examples 5 and 9 in which the immersion-etching speed is faster
than 3 .mu.m/minute, it is found that the top space width 1f tends
to increase. Further, in comparison with the etching time period
(135 seconds) in Comparative Example 1 in which the etching in the
step (1) alone is carried out, the etching time periods in Examples
2 to 12 that are preferred embodiments of this invention are short
in spite of the step (1) using the same etchant as that in
Comparative Example 1. In particular, the etching time periods in
Examples 4 to 6 (total etching time period 85 seconds) and the
etching time periods in Examples 8 and 9 (total etching time period
90 seconds) are short.
[0112] As is seen when Example 8 and Example 13 are compared, it is
seen that in Example 8 in which the etchant used in the step (1) is
an etchant containing iron (III) chloride and oxalic acid, there
can be obtained a cross-sectional form closer to a rectangular
form.
[0113] As is seen when Examples 6, 8 and 11 are compared, there can
be obtained a cross-sectional form closer to a rectangular form
when an etchant containing iron (III) chloride or copper (II)
chloride is used as an etchant for use in the step (2). Further, in
Examples 7, 8, 9, 10, 12 and 13 that use etchants containing copper
(II) chloride as an etchant in the step (2), it is seen that smooth
surfaces are obtained.
[0114] As is seen in Example 12, when the metal to be etched is
copper or copper alloy and when the etchant component used in the
step (2) is copper (II) chloride, a narrowed portion 2a is liable
to remain on side surfaces of a conductor pattern. However, as is
seen in Example 8, when the step (3) is carried out, the narrowed
portion can be highly inhibited even in such a case.
[0115] In Examples 1 to 9, 11 and 12 where the etching conditions
in the step (1) are the same, the immersion-etching speed of the
etchant in the step (2) and the etching time period in the step (2)
are not in inverse proportion. That is because the ratio of the
immersion-etching speed and the etching speed by a spray method
differs depending upon the composition of the etchant. Further, the
etching speed in the depth direction changes toward a slower speed
as the etching proceeds, and the degree of this change differs
depending upon the composition of the etchant, which is also one of
reasons.
[0116] The following Examples 14 to 17 are examples of the second
etching method.
Example 14
Preparation of Etchant
[0117] Water was added to 11 kg (4.1 kg as an anhydride) of a
commercially available 40.degree. Be iron (III) chloride aqueous
solution (concentration 37 mass %) and 1.1 kg (0.79 kg as an
anhydride) of oxalic acid dihydrate up to a total of 100 kg to
prepare an etchant containing 4.1 mass % of iron (III) chloride and
0.79 mass % of oxalic acid.
<Preparation of Material to be Etched>
[0118] A positive photoresist was applied to both surfaces of a
copper-clad laminate obtained by bonding 12 .mu.m thick rolled
copper foils (metal layer) to both surfaces of a 160 .mu.m
thickness glass epoxy insulating substrate, and it was dried such
that a dried resist layer had a thickness of 5 .mu.m each.
Evaluation resist patterns having a line width/space width of 15
.mu.m/15 .mu.m each were formed thereon by exposure, development
and washing with water, to prepare a material to be etched for an
etching test.
<Step (4)>
[0119] The above material to be etched was held horizontally with
the surface A facing downward, and the above etchant controlled at
a temperature of 30.degree. C. was ejected to the material to be
etched to etch the surface A. As an etching apparatus, there was
used an etching apparatus having a full-cone spray nozzle (trade
name: ISJJX20PP, supplied by H. IKEUCHI Co., Ltd.) having a spray
nozzle top end 6 cm (z: FIG. 3) below the material to be etched,
having an ejection axis on a perpendicular line and having an
ejection angle of 65.degree.. The pressure for supplying the
etchant to the spray nozzle was set at 200 kPa, the ejection amount
was set at 2.0 L/minute (ejection amount per unit area 77
mL/cm.sup.2minute), and 90 seconds after the above etching was
started, the ejection of the etchant was stopped. When the material
to be etched was observed through an optical microscope after it
was washed with water, a pale greenish crystal (water-insoluble
reaction product) was observed adhering to side surfaces of the
etched portion.
<Step (5)>
[0120] The upper and lower sides of the material to be etched were
reversed.
<Step (6)>
[0121] It was held horizontally with the surface B facing downward,
and the surface B was etched for 90 seconds under the same
conditions as those in the step (4).
<Post Treatment>
[0122] The material of which the etching was completed was immersed
in an aqueous sodium hydroxide solution having a concentration of
3.0 mass % for 3 minutes to peel off the resist patterns. Then,
hydrochloric acid having a hydrogen chloride concentration of 3.6
mass % was spray-ejected to both sides for 30 seconds each,
followed by washing with water and drying, to prepare a printed
wiring board for evaluation.
<Evaluation>
[0123] The printed wiring board for evaluation was observed through
a digital microscope (trade name: VK-8500: supplied by KEYENCE
CORPORATION) to show that the line/space width on the entire
surface of each side was in the range of 15.+-.2 .mu.m and that no
opening of a line, etc., took place.
Example 15
[0124] An etchant containing 4.1 mass % of iron (III) chloride and
2.0 mass % of oxalic acid was prepared in the same manner as in
Example 14. Surfaces A and B were etched with the above etchant in
the same manner as in Example 14 for 20 minutes each. On each
surface, a rolled copper foil in a portion free of a resist pattern
was removed in 12 minutes after the ejection of the etchant was
started. In this printed wiring board for evaluation, the
line/space width on the entire surface of each sides was in the
range of 15.+-.2 .mu.m, and no opening of a line, etc., was not
observed. When the etched material was observed through an optical
microscope after washed with water, a pale greenish crystal was
observed adhering to side surfaces of the etched portion.
Example 16
[0125] A printed wiring board for evaluation was produced in the
same manner as in Example 14 except that the entire etching
apparatus was tilted at 10.degree. from the horizontal in the step
(4) and the step (6). In this case, the material to be etched, the
nozzle and the ejection axis thereof had the same positional
relationship as that in Example 14. On each surface, the line/space
width of a portion etched in the highest position was 15 .mu.m.+-.2
.mu.m/15 .mu.m.+-.2 .mu.n, and the line/space width of a portion
etched in the lowest position was 16 .mu.m.+-.2 .mu.m/14 .mu.m.+-.2
.mu.m.
Example 17
[0126] A printed wiring board for evaluation was prepared in the
same manner as in Example 16 except that the entire etching
apparatus was tilted at 20.degree. from the horizontal. On each
surface, the line/space width of a portion etched in the highest
position was 15 .mu.m.+-.2 .mu.m/15 .mu.m.+-.2 .mu.m, and the
line/space width of a portion etched in the lowest position was 18
.mu.m.+-.2 .mu.m/12 .mu.m.+-.2 .mu.m.
Comparative Example 5
[0127] A printed wiring board for evaluation was produced in the
same manner as in Example 14 except that the etchant contained no
oxalic acid and that the time period of the ejection of the etchant
on each surface was set for 45 seconds. In this printed wiring
board for evaluation, while the surface B was etched in the step
(6), the etching of the surface A proceeded to excess, and the
line/space width was in the range of 9 .mu.m.+-.3 .mu.m/21
.mu.m.+-.3 .mu.m although it differed depending upon where it was
measured. Further, a line/space width of approximately 15 .mu.m/15
.mu.m was obtained in a most part of the surface B. However, there
was observed the existence of some portions where the line width
was narrower than 6 .mu.m ( of the target value), or the line was
open due to overetch because of contact to the etchant during the
etching of the surface A. Further, when the etched material was
observed through an optical microscope after washed with water, no
water-insoluble substance was observed adhering to side surfaces of
an etched portion.
Comparative Example 6
[0128] A Printed wiring board was produced in the same manner as in
Comparative Example 5 except that the material to be etched was
washed with water between the step (4) and the step (6). This
printed wiring board for evaluation had a line/space width of
approximately 15 .mu.m/15 .mu.m on a surface on each side. However,
both surfaces were locally etched to excess, and the line width was
observed being partly smaller than 10 .mu.m (2/3 of the target
value), or lines were observed being opened in extreme sites.
Comparative Example 7
[0129] A printed wiring board for evaluation was produced in the
same manner as in Example 14 except that the composition of the
etchant was changed to a composition containing 4.1 mass % of iron
(III) chloride and 0.16 mass % of oxalic acid and that the time
periods for ejecting the etchants in the steps (4) and (6) were set
for 80 seconds each. Copper foil on a pattern-free area on each
surface was removed in 60 seconds after the ejection of the etchant
was started. In this printed wiring board for evaluation, the
etching on the surface A proceeded to excess while the surface B
was etched, and the line/space width was in the range of 12.+-.3
.mu.m/18.+-.3 .mu.m although it differs depending upon measurement
sites. Further, most part of the surface B had a line/space width
of 15 .mu.m.+-.3 .mu.m/15 .mu.m.+-.3 .mu.m, while the surface B was
etched to excess since the etchant contacted thereto during the
etching of the surface A, and it was observed that there were hence
partly portions having a line width of smaller than 6 .mu.m ( of
the target value). Further, when the etched material was observed
through an optical microscope after it was washed with water, no
water-insoluble reaction product was observed adhering to side
surfaces of an etched portion.
Comparative Example 8
[0130] A printed wiring board for evaluation was produced in the
same manner as in Example 16 except that the tilting angle of the
etching apparatus was set at 30.degree.. On each surface, the
line/space width of a portion etched in the highest position was 15
.mu.m.+-.3 .mu.m/15 .mu.m.+-.3 .mu.m in the highest position, while
a portion etched in the lowest position had copper still remaining
in a space portion.
Comparative Example 9
[0131] A printed wiring board for evaluation was produced in the
same manner as in Comparative Example 8 except that the time period
for ejection of the etchant was set for 300 seconds. On each
surface, the line/space width of a portion etched in the lowest
position was 15 .mu.m.+-.3 .mu.m/15 .mu.m.+-.3 .mu.m, while the
etching proceeded to excess in a portion etched in the highest
position, and the line/space width in that portion was 9 .mu.m.+-.3
.mu.m/21 .mu.m.+-.3 .mu.m.
[0132] By this invention, a printed wiring board having fine
conductor patterns on both surfaces thereof can be produced by a
simple method as shown in Examples 14 to 17. As shown in
Comparative Examples 5 to 7, when the etchant that does not form a
water-insoluble reaction product, which etchant is an essential
requirement for the second etching method, is not used, the etching
that is not intended proceeds locally due to the etchant that moves
around onto the upper surface, and hence there cannot be produced
any printed wiring board having a fine wiring pitch by such simple
steps as those which are used in this invention. As shown in
Comparative Examples 8 and 9, when the material to be etched is not
held at an angle of 20.degree. or less from the horizontal, an
in-plane variability takes place on the finish of etching, and
hence there cannot be produced any printed wiring board having a
fine wiring pitch by such simple steps as those which are used in
this invention.
INDUSTRIAL UTILITY
[0133] The etching method of this invention can be suitably used
not only in the production of printed wiring boards but also in
various other industrial fields where the highly controlled etching
of copper or copper alloy is required for the production of lead
frames, precision gears, precision flat springs, discs and stripes
for encoders, various stencils, etc.
* * * * *