U.S. patent application number 10/849820 was filed with the patent office on 2004-11-25 for printed circuit boards and the methods of their production.
Invention is credited to Murao, Kenji.
Application Number | 20040231995 10/849820 |
Document ID | / |
Family ID | 33447560 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040231995 |
Kind Code |
A1 |
Murao, Kenji |
November 25, 2004 |
Printed circuit boards and the methods of their production
Abstract
It is an object of the present invention to provide a copper
electroplating method for a printed circuit board having via-holes,
which can reproducibly secure good plated film quality and via-hole
filling capacity even when the board includes a resist or the like.
The electroplating bath for electroplating of a printed circuit
board, containing at least one compound selected from the group
consisting of pyridinium, bipyridinium, phenanthrolinium,
quinolinium and phenazinium salts in the form of onium with an
N-alkyl, N-aralkyl, N-aryl, N-alkylene or N-aralkylene moiety.
Inventors: |
Murao, Kenji; (Hitachi,
JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-9889
US
|
Family ID: |
33447560 |
Appl. No.: |
10/849820 |
Filed: |
May 21, 2004 |
Current U.S.
Class: |
205/125 ;
205/291 |
Current CPC
Class: |
C25D 7/12 20130101; H05K
2201/09563 20130101; H05K 3/423 20130101; C25D 3/38 20130101; C25D
7/123 20130101 |
Class at
Publication: |
205/125 ;
205/291 |
International
Class: |
C25D 005/02; C25D
003/38 |
Foreign Application Data
Date |
Code |
Application Number |
May 23, 2003 |
JP |
2003-145580 |
Claims
What is claimed is:
1. A printed circuit board having via-holes plated by a copper
electroplating, wherein the via-holes are substantially filled with
a copper electroplating using a copper electroplating bath
containing at least one compound selected from the group consisting
of pyridinium, bipyridinium, phenanthrolinium, quinolinium and
phenazinium salts in the form of onium with an N-alkyl, N-aralkyl,
N-aryl, N-alkylene or N-aralkylene moiety.
2. A method for producing a printed circuit board having via-holes
plated by a copper electroplating, wherein an electroplating bath
used in the copper electroplating contains at least one compound
selected from the group consisting of pyridinium, bipyridinium,
phenanthrolinium, quinolinium and phenazinium salts in the form of
onium with an N-alkyl, N-aralkyl, N-aryl, N-alkylene or
N-aralkylene moiety.
3. An electroplating method which conducts a copper electroplating
using an electroplating bath containing at least one compound
selected from the group consisting of pyridinium, bipyridinium,
phenanthrolinium, quinolinium and phenazinium salts in the form of
onium with an N-alkyl, N-aralkyl, N-aryl, N-alkylene or
N-aralkylene moiety.
4. The electroplating method according to claim 3, wherein the
N-alkyl, N-aralkyl, N-aryl, N-alkylene or N-aralkylene moiety
contains sulfonic acid moiety.
5. The electroplating method according to claim 3, wherein the
salts have a low molar extinction coefficient of 5000
M.sup.-1cm.sup.-1 (M: moles/litter) in a wavelength region of 400
to 700 nm.
6. A copper electroplating bath used in a copper electroplating
which contains at least one compound selected from the group
consisting of pyridinium, bipyridinium, phenanthrolinium,
quinolinium and phenazinium salts in the form of onium with an
N-alkyl, N-aralkyl, N-aryl, N-alkylene or N-aralkylene moiety.
7. The copper electroplating bath according to claim 6, wherein the
N-alkyl, N-aralkyl, N-aryl, N-alkylene or N-aralkylene moiety
contains sulfonic acid moiety.
8. The copper electroplating bath according to claim 6, wherein the
salts have a low molar extinction coefficient of 5000
M.sup.-1cm.sup.-1 (M: moles/litter) in a wavelength region of 400
to 700 nm.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a printed circuit board in
which a circuit board is subjected to a copper electroplating to
form a desired electrical circuit, more particularly to a printed
circuit board in which via-holes of a printed circuit board having
blind via-holes are filled with a copper electroplating, and a
method for producing the same. Further, the present invention
relates to a copper electroplating method for electroplating
via-holes of a printed circuit board having blind via-holes with
copper, and a copper electroplating bath for electroplating a
varying board with copper.
BACKGROUND OF THE INVENTION
[0002] Recently, electronic devices are increasingly required to be
compacter and more functional. The printed circuit board on which a
varying electronic device is mounted is increasingly required to
have a denser wiring, higher degree of integration and higher
contact reliability, in order to cope with the above trends. In
order to satisfy these requirements, the so-called build-up
process, in which conductive layer and insulating layer are
alternately laminated on a base substrate after undergoing a
full-additive process or semi-additive process to form a fine and
three-dimensional circuit, has been widely employed.
[0003] One example of the methods widely used for forming these
fine wirings comprises deposition of a thin copper film on a
surface of an insulating resin layer by sputtering or the like,
forming a desired resist pattern on the thin film and copper
electroplating the laminate. It is a common practice in this method
to secure an electrical contact between a conductive layer present
below an insulating layer and a conductive layer provided above it
by means of connecting holes by the name of via-holes, where each
via-hole is plated with a conductive material on the wall or
totally filled with a conductive material.
[0004] More specifically, an insulating layer is irradiated with
carbon dioxide gas or bored by a mechanical means (e.g., drill) on
the connecting or conducting passage area, and each hole is plated
with a conductive material on the wall or totally filled with a
conductive material. This procedure can secure electrical contact
between the conducting layers with the insulating layer in-between,
and is widely employed by the industry concerned.
SUMMARY OF THE INVENTION
[0005] However, it is more preferable to fill each via-hole totally
with a conductive material by electroplating than to plate the
via-hole wall only with a conductive material, because of much
improved reliability of the electrical contact.
[0006] Filling via-holes by electroplating carries another
advantage when 3 or more conductive layers are laminated via an
insulating layer, because the via-holes between the first and
second conductive layers can be arranged immediately above those
between the second and third conductive layers.
[0007] In result, this structure reduces a space for the via-holes
as a whole, thereby allowing the devices to be mounted at a higher
density. Via-holes generally have a diameter of several tens
microns in consideration of the trends to finer wirings.
[0008] When via-holes are filled with a conductive material by
electroplating, it is necessary to form a thin film of conductive
material beforehand by electroless copper plating or the like on
the surface to be electroplated. At the same time, special
considerations are required for the subsequent electroplating by
which via-holes are filled with copper.
[0009] More specifically, the surface, on which a conductive
circuit is formed, has a flat surface other than via-holes and a
concave portion of via-hole, with the result that it may be
excessively coated with a plated conductive film when the via-holes
are completely filled with a conductive material by electroplating.
Conversely, when the surface is to be coated with a conductive
layer of adequate thickness by electroplating, the via-holes may be
filled insufficiently.
[0010] In order to avoid these difficulties, copper electroplating
baths incorporated with several types of additives have been widely
used to fill the via-holes with a conductive material by
electroplating and, at the same time, to coat the surface with a
conductive layer of adequate thickness by copper
electroplating.
[0011] The copper electroplating bath prepared to adequately fill
via-holes is incorporated with three types of additives (polymer
component, leveler component and brightener component). The
procedure for filling via-holes with the above bath has been widely
recognized.
[0012] Of these three types of additives, the leveler component is
normally of an organic dye. The mechanisms by which these three
additive components work for filling via-holes by copper
electroplating are not fully understood. However, it is widely
accepted that the leveler component as one of the three additive
components works to control copper separation rate both inside and
outside of each via-hole. This is described below.
[0013] That is, the molecules constituting the leveler component
are adsorbed on the boar surface to be electroplated to retard
copper electroplating, but are depleted on the electrode (board
surface to be electroplated) by being electrochemically decomposed
or included in the plated film.
[0014] This depletion is accompanied by the leveler component
molecules diffusing towards the board surfaces from the bulk bath,
whose concentration remains essentially constant. Diffusion rate of
the leveler component molecules is one of the factors that
determine plating rate. The substance used as the leveler component
generally has a relatively high molecular weight, and produces a
gradient of its concentration in the passage (diffusion layer)
between the bulk plating bath to the board surface at a plating
rate beyond a certain level. On the other hand, the concave portion
of the via-hole requires a longer diffusion path than the flat
portion free of the via-holes to have a smaller quantity of the
diffused leveler component at the bottom than the upper flat
surface free of the via-holes. Therefore, the leveler component is
present always at a lower concentration on the via-hole bottom
surface than on the flat surface, with the result that the plated
copper film grows faster on the via-hole bottom surface than on the
flat surface. It is understood that the via-hole is filled with
copper by electroplating by the above effect.
[0015] The leveler component having the above characteristics may
cause undesirable effect of inhomogeneity of plated film thickness,
when it is unevenly distributed on the board surface.
[0016] The uneven concentration distribution of the leveler
component is more noted in the areas where it diffuses unevenly,
e.g., in the vicinity of the resist wall, or the plating bath tends
to flow unevenly, with the above-described via-hole insides and
outsides set aside.
[0017] Therefore, electroplating to fill via-holes needs a plating
bath completely free of leveler component or containing it at a low
concentration. It is an object of the present invention to provide
a plating method which fills via-holes while substantially removing
the problems caused by a leveler component and, at the same time,
secures a good plated film of uniform thickness on the other
portion.
[0018] An organic dye used as the leveler is generally expensive,
and use of a plating bath completely free of leveler component or
containing it at a low concentration brings another advantage of
reducing cost of the copper electroplating to fill the
via-holes.
[0019] The problems resulting from use of a leveler are described
taking a printed circuit board as an example, the similar problems
should occur with a semiconductor board which are provided with
finer via-holes.
[0020] Therefore, it is another object of the present invention to
provide a printed circuit board electroplated with copper on the
circuit board to form a desired electrical circuit thereon, wherein
the via-holes in the printed circuit board are filled with copper
by electroplating. It is still another object of the present
invention to provide a copper electroplating method for a printed
circuit board with blind via-holes to electroplate the via-holes.
It is still another object of the present invention to provide a
copper electroplating bath for electroplating a varying board with
copper.
[0021] The inventors of the present invention have concluded, after
having extensively studied to solve the above problems, that it is
necessary to find out a method for filling via-holes by
electroplating without depending on a leveler component.
[0022] They have also extensively studied functions of each of the
above-described additives in searching for plating baths completely
free of leveler component or containing it in trace quantities, to
find that a leveler component has two functions.
[0023] One of the functions is to form assemblies of the molecules
in the interface by stacking them, a property which many organic
dye exhibit. Formation of these assemblies tends to occur in
defects, e.g., dislocation or steps, in which addition of the
copper atoms progresses most notably. As a result, it retards
progress of plating in the cathodic interface.
[0024] The other function, which a leveler component exhibits, is
to break an adsorption film of polymer covering the electrode
surface, which is coated and blocked with the polymer component,
e.g., polyethylene glycol, thereby facilitating access of the
copper ion or brightener component to the board surface. It is a
property of organic, ionic compounds on which leveler component
charges are highly delocalized.
[0025] In other words, a leveler component represented by an
organic dye is found to have two functions contradictory to each
other, one is retarding the plating reaction and the other
accelerating the reaction. For the latter function, a leveler is
not necessarily of an associative dye. At the same time, it is
meant that even an organic, ionic compound of relatively low
molecular weight can exhibit the function, when filling of
via-holes is achieved mainly by a brightener component
function.
[0026] When a brightener approaches the electrode surface, the
surface area in the via-hole is reduced as the plating reaction
proceeds, with the result that the brightener component is
concentrated on the surface, and the reaction proceeds faster in
the via-hole inside than in the outside. The via-hole filling
process by the brightener concentration on the surface is based on
its property of being depleted at a lower rate in the plating
reaction process.
[0027] Based on the above concept, the inventors of the present
invention have searched for alternative via-hole filling additives
having a lower molecular weight than the conventional leveler
component, not associative at least at around a plating potential,
soluble in water and active in the interface.
[0028] The associative property of the conventional leveler
component is closely related to the fact that it is of an organic
dye. Therefore, it is an important condition for the additive
component that replaces the conventional leveler component not to
substantially exhibit strong light absorption in the visible
region.
[0029] The new leveler component will exhibit a high via-hole
filling capacity when used in combination with the brightener
component, as discussed above. It is found that the new additive
for the present invention can fill the via-holes and, at the same
time, give the plated film of high homogeneity on the portion other
than the via-holes.
[0030] It is also found, in the case of a board with a plated
resist pattern, that the new additive can give a highly flat and
excellent plated film even in the vicinity of the wall. It is well
known that the conventional leveler frequently deteriorates plated
film flatness significantly in the vicinity of the plated resist
wall.
[0031] The good results demonstrated by the method of the present
invention results from its independence on a compound of very low
diffusibility used for the conventional leveler for via-hole
filling.
[0032] In the method of the present invention, which uses no
component of low diffusibility, problems resulting from diffusion
of the copper ion itself, which are concealed in the presence of
the leveler component of strong functions, tend to be more
noted.
[0033] These problems sometimes observed in the vicinity of the
plated resist wall. They result from retarded diffusion of the
copper ion across the resist wall. The effect of retarded symmetry
of the copper ion diffusion is much smaller than that of a leveler,
but exactly opposite in direction.
[0034] In other words, the copper ion is more used for plating as
it diffuses more, unlike the case with a leveler. It is possible to
improve homogeneity of the plated film thickness to a still higher
extent by utilizing the functions of the cooper ion and leveler
component working in the opposite direction under the same
geometric conditions which limit diffusion of the solute.
[0035] The above can be achieved by only incorporating a trace
quantity of a leveler component in the electroplating bath, in
addition to the above-described polymer component, brightener
component and organic ionic compound. A leveler is incorporated
only in a quantity sufficient for canceling out small fluctuations
of film thickness resulting from asymmetry of the copper ion
diffusion.
[0036] The inventors of the present invention have noted a specific
quaternary, nitrogen-containing heterocyclic compound as the copper
plating promoter which satisfies the above requirements, achieving
the present invention.
[0037] Thus, the first aspect of the present invention relates to a
printed circuit board, the second aspect relates to a method for
producing the same, the third aspect relates to an electroplating
method, and the fourth aspect relates to a copper electroplating
bath. The copper electroplating bath is incorporated with at least
one compound selected from the group consisting of pyridinium,
bipyridinium, phenanthrolinium, quinolinium and phenazinium salts
in the form of onium with an N-alkyl, N-aralkyl, N-aryl, N-alkylene
or N-aralkylene moiety as a copper plating promoter.
[0038] In the present invention, the pyridinium, bipyridinium,
phenanthrolinium, quinolinium and phenazinium salts in the form of
onium with an N-alkyl, N-aralkyl or N-aryl moiety etc. mean an
organic pyridinium cation represented by the general formula: 1
[0039] (wherein, R.sub.1 is an organic moiety selected from the
group consisting of alkyl, phenyl and aralkyl moiety), an organic
bipyridinium cation represented by the general formula: 2
[0040] (wherein, R.sub.2 and R.sub.3 are each an organic moiety
selected from the group consisting of alkyl, phenyl and aralkyl
moiety),
[0041] an organic phenanthrolinium cation represented by the
general formula: 3
[0042] (wherein, R.sub.4 is an organic moiety selected from the
group consisting of alkylene and aralkylene moiety), an organic
quinolinium cation represented by the general formula: 4
[0043] (wherein, R.sub.5 is an organic moiety selected from the
group consisting of alkyl, phenyl and aralkyl moiety), and
[0044] an organic phenazinium cation represented by the general
formula: 5
[0045] (wherein, R.sub.6 is an organic moiety selected from the
group consisting of alkyl, phenyl and aralkyl moiety),
[0046] Of these five types of the cationic salts, the organic
bipyridinium salt is particularly preferable for its excellent
via-hole filling capacity and availability in the markets.
[0047] The N-alkyl, N-phenyl and N-aralkyl moieties etc.
represented by one of R.sub.1 to R.sub.5 may be substituted with a
varying substituent or unsubstituted. Sulfonic acid moiety is a
preferable substituent, because these moieties substituted
therewith can be more compatible with the sulfonic acid anion
normally present in the copper electroplating bath.
[0048] The pyridinium, bipyridinium, phenanthrolinium, quinolinium
and phenazinium salts in the form of onium with an N-alkyl,
N-aralkyl or N-aryl moiety etc. are clearly distinguished from an
organic dye which has been traditionally used as the leveler
component. These cationic salts are characterized by a low molar
extinction coefficient of only 5000 M.sup.-1cm.sup.-1 (M:
moles/litter) in a wavelength region of 400 to 700 nm.
[0049] Other objects, features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] FIG. 1 is a cross-sectional view of the printed circuit
board electroplated with copper, prepared in EXAMPLE 1, for the
portion containing via-holes, drawn based on the microgram.
[0051] FIG. 2 is a cross-sectional view of the printed circuit
board electroplated with copper, prepared in COMPARATIVE EXAMPLE 1,
for the portion containing via-holes, drawn based on the
microgram.
[0052] FIG. 3 is a cross-sectional view of the printed circuit
board electroplated with copper, prepared in COMPARATIVE EXAMPLE 5,
for the portion containing via-holes, drawn based on the
microgram.
DESCRIPTION OF THE REFERENCE NUMERALS AND SIGNS
[0053] 1: Base substrate
[0054] 2: Copper foil layer
[0055] 3: Resist
[0056] 4: Epoxy resin layer
[0057] 5: Copper-plated film
DETAILED DESCRIPTION OF THE INVENTION
[0058] The via-holes for the present invention are generally 10 to
600 .mu.m deep and 5 to 800 .mu.m in diameter for printed circuit
boards. These via-holes can be produced by boring an insulating
resin layer put between two conductive layers with laser beams. It
is needless to say that the via-holes are finer when the copper
plating of the present invention is applied to a semi-conducting
board.
[0059] Each via-hole can be electroplated, when its bottom and
sides are made conductive beforehand by electroless plating or
sputtering. It is also possible to make a desired portion outside
of the via-hole conductive by a similar means.
[0060] The representative composition of a copper electroplating
bath for filling via-holes by the copper electroplating method of
the present invention is copper sulfate pentahydrate: 55 to 240
g/L, concentrated sulfuric acid: 60 to 260 g/L and chlorine ion
content: 60 to 100 ppm. It should be noted that implementation of
the present invention does not become immediately difficult when
the composition is out of the above range.
[0061] The base composition prepared above for the copper
electroplating bath is incorporated with polyethylene glycol as a
polymer component at 20 to 300 mg/L and sodium salt of
bis-(3-sulfopropyl) disulfide (hereinafter referred to as SPS),
represented by (NaO.sub.3S--CH.sub.2--C- H.sub.2--CH.sub.2--S--)
.sub.2, as a brightener component at 1 to 30 mg/L. The above
solution is further incorporated with at least one selected from
the group consisting of the above-described five types of cationic
salts, i.e., pyridinium, bipyridinium, phenanthrolinium,
quinolinium and phenazinium salts in the form of onium with an
N-alkyl, N-aralkyl or N-aryl moiety etc. at 2 to 2000 .mu.mols/L
for the electroplating.
[0062] It is preferable, depending on circumstances, to incorporate
a trace quantity of an organic dye or the like as a leveler in the
electroplating bath composition prepared above to still improve
flatness of the plated film. The anions which can be suitably used
as the counter ion of the above-described organic cation include a
halide ion, e.g., chloride ion, and sulfonate ion. The ionic
compound is incorporated as the counter ion at a much lower content
than any other component of the base plating bath, and cannot
greatly affect the ionic concentration of the bath. No trouble is
anticipated when the chloride or sulfonate ion originally present
in the base composition of the plating bath is used as the counter
ion, unless its concentration is out of the originally intended
suitable ion concentration range.
[0063] For energizing the cathode and anode for electroplating,
either a potentiostatic or galvanostatic method can satisfy the
object of the present invention. Galvanostatic copper
electroplating is preferably carried out at a current density
applied of 2.5A dm.sup.-2, but the effect of the present invention
can be realized at 0.5 to 6.0A dm.sup.-2.
EXAMPLES
[0064] The present invention is described by EXAMPLES.
Examples 1
[0065] A base substrate having a copper foil coated on a surface
thereof was coated with a 15 .mu.m thick insulating layer of known
epoxy resin normally used for the build-up process, and then the
surface was irradiated with carbon dioxide gas laser beams to form
via-holes, 60 .mu.m in diameter at the opening, 50 .mu.m in
diameter at the bottom and 15 .mu.m deep. The coated base substrate
was immersed in a permanganic acid solution for desmearing, and
then provided with a catalyst by a known treatment method, to form
a 0.6 .mu.m thick electroless, copper-plated film. The treated base
substrate was cut into 60 mm by 60 mm specimens in such a way that
each had via-holes. Each specimen was electroplated at a current
density of 2.5A dm.sup.-2 for 26 minutes in a plating bath of the
composition given in Table 1 while it was kept upright. During the
plating, the bath was stirred by airing in the electroplating tank
having inner dimensions of width: 250 mm, depth: 200 mm and height:
200 mm.
[0066] The electroplated base substrate having via-holes was cut
and ground, to observe the via-hole cross-section. FIG. 1 presents
a microscopic cross-sectional view which schematically shows the
base substrate electroplated with copper, prepared in EXAMPLE 1. As
shown, the via-hole was filled with copper by electroplating. The
surface was good in flatness, with irregularities of only around
.+-.2 .mu.m even in the vicinity of the resist.
1TABLE 1 Composition of the plating bath used in EXAMPLE 1 Plating
bath components Concentration Copper sulfate pentahydrate 200 g/L
Concentrated sulfuric acid 60 g/L Hydrochloric acid (0.1 mol/L) 17
mL/L Polyethylene glycol 4000 100 mg/L SPS 5 mg/L Benzyl biologen
chloride 25 .mu.mol/L
Comparative Example 1
[0067] A base substrate was electroplated in the same manner as in
EXAMPLE 1, except that the electroplating bath composition given in
Table 1 contained no benzyl biologen chloride. The electroplated
base substrate having via-holes was cut and ground to observe the
via-hole cross-section. FIG. 2 presents a microscopic
cross-sectional view which schematically shows the base substrate
electroplated with copper, prepared in COMPARATIVE EXAMPLE 1. As
shown, the via-hole was not filled sufficiently with copper by
electroplating. The plated film surface was found to have
irregularities of .+-.5 .mu.m or more.
Example 2
[0068] A base substrate was electroplated in the same manner as in
EXAMPLE 1, except that the plating bath composition was replaced by
the one given in Table 2. The electroplated base substrate having
via-holes was cut and ground to microscopically observe the
via-hole cross-section. It was observed that the via-hole was
filled with copper by electroplating, and the copper-plated film
surface was good in flatness in the vicinity of the resist.
2TABLE 2 Composition of the plating bath used in EXAMPLE 2 Plating
bath components Concentration Copper sulfate pentahydrate 200 g/L
Concentrated sulfuric acid 80 g/L Hydrochloric acid (0.1 mol/L) 17
mL/L Polyethylene glycol 4000 200 mg/L SPS 8 mg/L Hexylpyridinium
chloride 35 .mu.mol/L
Compapative Example 2
[0069] A base substrate was electroplated in the same manner as in
EXAMPLE 2, except that the electroplating bath composition given in
Table 2 contained no hexylpyridinium chloride. The electroplated
base substrate having via-holes was cut and ground to
microscopically observe the via-hole cross-section. It was observed
that the via-hole was not filled sufficiently with copper by
electroplating, and the plated film surface had irregularities of
.+-.5 .mu.m or more.
Example 3
[0070] A base substrate was electroplated in the same manner as in
EXAMPLE 1, except that the plating bath composition was replaced by
the one given in Table 3. The electroplated base substrate having
via-holes was cut and ground to microscopically observe the
via-hole cross-section. It was observed that the via-hole was
filled with copper by electroplating, and the copper-plated film
surface was high in flatness showing no phenomenon of growth of
film thickness in the vicinity of the resist.
3TABLE 3 Composition of the plating bath used in EXAMPLE 3 Plating
bath components Concentration Copper sulfate pentahydrate 200 g/L
Concentrated sulfuric acid 100 g/L Hydrochloric acid (0.1 mol/L) 17
mL/L Polyethylene glycol 4000 100 mg/L SPS 6 mg/L Hexylquinolinium
chloride 30 .mu.mol/L
Compapative Example 3
[0071] A base substrate was electroplated in the same manner as in
EXAMPLE 3, except that the electroplating bath composition given in
Table 3 contained no hexylquinolinium chloride. The electroplated
base substrate having via-holes was cut and ground to
microscopically observe the via-hole cross-section. It was observed
that the via-hole was not filled sufficiently with copper by
electroplating, and the plated film surface had irregularities of
.+-.5 .mu.m or more.
Example 4
[0072] A base substrate was electroplated in the same manner as in
EXAMPLE 1, except that the plating bath composition was replaced by
the one given in Table 4. The electroplated base substrate having
via-holes was cut and ground to microscopically observe the
via-hole cross-section. It was observed that the via-hole was
filled with copper by electroplating, and the copper-plated film
surface was high in flatness showing no phenomenon of growth of
film thickness in the vicinity of the resist.
4TABLE 4 Composition of the plating bath used in EXAMPLE 4 Plating
bath components Concentration Copper sulfate pentahydrate 200 g/L
Concentrated sulfuric acid 70 g/L Hydrochloric acid (0.1 mol/L) 17
mL/L Polyethylene glycol 4000 150 mg/L SPS 7 mg/L Ethylphenazinium
chloride 30 .mu.mol/L
Comparative Example 4
[0073] A base substrate was electroplated in the same manner as in
EXAMPLE 4, except that the electroplating bath composition given in
Table 4 contained no ethylphenazinium chloride. The electroplated
base substrate having via-holes was cut and ground to
microscopically observe the via-hole cross-section and the via-hole
periphery in contact with the resist wall. It was observed that the
via-hole was not filled sufficiently with copper by electroplating,
and the plated film surface had irregularities of .+-.5 .mu.m or
more.
Comparative Example 5
[0074] A base substrate was electroplated in the same manner as in
EXAMPLE 1, except that the electroplating bath composition
contained Janus Green B as a leveler in place of benzyl biologen
chloride for the present invention (Table 5). The electroplated
base substrate having via-holes was cut and ground to
microscopically observe the via-hole cross-section and the via-hole
periphery in contact with the resist wall. FIG. 3 presents a
microscopic cross-sectional view which schematically shows the base
substrate electroplated with copper, prepared in COMPARATIVE
EXAMPLE 5. As shown, the via-hole was filled with copper to some
extent by the electroplating, but thickness of the plated film
increased to 5 .mu.m or more in the area in contact with the resist
wall. It was therefore found that flatness of the plated film as
one of the objects of the present invention could not be
secured.
5TABLE 5 Composition of the plating bath used in COMPARATIVE
EXAMPLE 5 Plating bath components Concentration Copper sulfate
pentahydrate 210 g/L Concentrated sulfuric acid 80 g/L Hydrochloric
acid (0.1 mol/L) 17 mL/L Polyethylene glycol 4000 120 mg/L SPS 5
mg/L Janus Green B 20 .mu.mol/L
[0075] It should be further understood by those skilled in the art
that although the foregoing description has been made on
embodiments of the invention, the invention is not limited thereto
and various changes and modifications may be made without departing
from the spirit of the invention and the scope of the appended
claims.
Effects of the Present Invention
[0076] As described above, the method of the present invention for
electroplating a board with via-holes can well fill the holes with
copper and realize high flatness of the plated film.
* * * * *