U.S. patent application number 11/113011 was filed with the patent office on 2005-11-17 for electroless copper plating machine thereof, and multi-layer printed wiring board.
Invention is credited to Akahoshi, Haruo, Iida, Tadashi, Itabashi, Takeyiki, Nishimura, Naoki, Takai, Eiji, Ueda, Yoshinori.
Application Number | 20050252684 11/113011 |
Document ID | / |
Family ID | 17690052 |
Filed Date | 2005-11-17 |
United States Patent
Application |
20050252684 |
Kind Code |
A1 |
Itabashi, Takeyiki ; et
al. |
November 17, 2005 |
Electroless copper plating machine thereof, and multi-layer printed
wiring board
Abstract
A method is provided for removing plating blocking ions, such as
anions, in pairs with copper ions and oxidant ions of a copper ion
reducing agent from an electroless copper plating solution and
keeping a constant salt concentration in the electroless copper
plating solution during plating. The electroless copper plating
method uses a plating solution containing copper sulfate as copper
ion sources, and a copper ion complexing agent as copper ion
sources, glyoxylic acid as a copper ion reducing agent, and a pH
conditioner. The method is characterized by precipitating and
removing sulfuric and oxalic ions in said electroless copper
plating solution and keeping an optimum concentration of at least
one of sulfuric and oxalic ions in said electroless copper plating
solution during plating.
Inventors: |
Itabashi, Takeyiki;
(Hitachi, JP) ; Akahoshi, Haruo; (Hitachi, JP)
; Iida, Tadashi; (Atsugi, JP) ; Ueda,
Yoshinori; (Hadano, JP) ; Takai, Eiji;
(Yokohama, JP) ; Nishimura, Naoki; (Yokohama,
JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
17690052 |
Appl. No.: |
11/113011 |
Filed: |
April 25, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11113011 |
Apr 25, 2005 |
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09678800 |
Oct 4, 2000 |
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6900394 |
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Current U.S.
Class: |
174/262 |
Current CPC
Class: |
H05K 3/187 20130101;
C23C 18/40 20130101; C23C 18/1617 20130101 |
Class at
Publication: |
174/262 |
International
Class: |
H05K 001/11; H01R
012/04; B05D 003/04; B05D 003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 6, 1999 |
JP |
11-285322 |
Claims
What is claimed is:
1. An electroless copper plating method using a plating solution
containing copper sulfate as copper ion sources, and a copper ion
complex agent, a copper ion reducing agent and a pH conditioner,
wherein said method comprises steps of using the hydroxide of an
alkaline earth metal as said pH conditioner to react with sulfuric
ions in the electroless copper plating solution into a salt of said
alkaline earth metal, removing the precipitate from the plating
solution, measuring at least one of the concentration of sulfuric
ion and the concentration of oxalic ion in the plating solution and
keeping an optimum sulfuric ion or oxalic ion concentration during
an electroless copper plating.
2. An electroless copper plating method using a plating solution
containing copper sulfate as copper ion sources, and a copper ion
complex agent, glyoxylic acid or salt thereof as a copper ion
reducing agent, and pH conditioner, wherein said method comprises
steps of using alkaline earth metal hydroxide as said pH
conditioner, precipitating and removing sulfuric and oxalic ions as
salts of said alkaline earth metal in the electroless plating
solution during electroless copper plating.
3. An electroless copper plating method using a plating solution
containing copper sulfate as copper ion sources, and a copper ion
complex agent, a copper ion reducing agent, and a pH conditioner,
wherein said method comprises steps of adding at least one of
alkaline earth metal, alkaline earth metal oxide, alkaline earth
metal hydroxide, and alkaline earth metal salt (excluding sulfuric
salt) into said plating solution, reacting with and precipitating
sulfuric ions as an alkaline earth metal salt, measuring the
concentration of sulfuric ions in said plating solution, and
regulating the concentration thereof to a preset optimum
concentration during electroless copper plating.
4. An electroless copper plating method using a plating solution
containing copper sulfate as copper ion sources, and a copper ion
complex agent, glyoxylic acid or salt thereof as a copper ion
reducing agent, and a pH conditioner, wherein said method comprises
steps of adding at least one of alkaline earth metal, alkaline
earth metal oxide, alkaline earth metal hydroxide, and alkaline
earth metal salt (excluding sulfuric salt) into said plating
solution, and reacting with and precipitating sulfuric ions or
oxalic ion as an alkaline earth metal salt during electroless
copper plating.
5. An electroless copper plating machine using a plating solution
containing metallic ions, an agent for reducing said metallic ions,
and a pH conditioner, wherein said machine comprises an electroless
copper plating bath, a reaction bath adding a metal or a compound
containing a metal to said plating solution to precipitate ions, as
a metal salt precipitate, which suppress generation of said plating
metal as metal salts, and an ultra filtration unit for removing
said metal salt precipitate.
6. A multi-layer wiring board having insulating layers and circuit
layers accumulated and cemented alternately whose circuit layers
are electrically connected by copper-plated through-holes which
pass through the insulating layer between said circuit layers or by
copper-plated via-holes whose one end is closed, wherein said
plating is made by an electroless copper plating method in
accordance with claim 1.
7. A module having one or more semiconductor elements on said
multi-layer wiring board in accordance with claim 6.
8. A multi-layer wiring board having insulating layers and circuit
layers accumulated and cemented alternately whose circuit layers
are electrically connected by copper-plated through-holes which
pass through the insulating layer between said circuit layers or by
copper-plated via-holes whose one end is closed, wherein said
plating is made by an electroless copper plating method in
accordance with claim 2.
9. A module having one or more semiconductor elements on said
multi-layer wiring board in accordance with claim 8.
10. A multi-layer wiring board having insulating layers and circuit
layers accumulated and cemented alternately whose circuit layers
are electrically connected by copper-plated through-holes which
pass through the insulating layer between said circuit layers or by
copper-plated via-holes whose one end is closed, wherein said
plating is made by an electroless copper plating method in
accordance with claim 3.
11. A module having one or more semiconductor elements on said
multi-layer wiring board in accordance with claim 10.
12. A multi-layer wiring board having insulating layers and circuit
layers accumulated and cemented alternately whose circuit layers
are electrically connected by copper-plated through-holes which
pass through the insulating layer between said circuit layers or by
copper-plated via-holes whose one end is closed, wherein said
plating is made by an electroless copper plating method in
accordance with claim 4.
13. A module having one or more semiconductor elements on said
multi-layer wiring board in accordance with claim 12.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an electroless copper
plating method of reducing the concentration of byproduct ions and
deposition of byproducts in a plating solution, a device thereof,
and an application thereof.
[0002] The usual electroless copper plating solution contains
copper ions, a copper ion complex agent, a copper ion reducing
agent, and a pH conditioner, which must be supplied as the plating
advances. However, this supply increases anions in pairs with
copper ions, oxidant ions of the copper ion reducing agent, and
cations of the pH conditioner in the plating solution.
[0003] These ions increasing in the plating solution will
deteriorate the physical properties of the plated layer,
particularly the elongation ratio of the plated layer, reducing the
reliability of the plated layer. Further, it reduces the stability
of the plating solution and causes abnormal deposition and
autolysis.
[0004] Conventionally, to avoid such problems and to maintain a
constant salt concentration in the plating solution, various
plating techniques have been used, such as changing plating
solutions at short-time intervals, and continuously adding a new
plating liquid to the plating solution in use. However, these
approaches require a large quantity of expensive copper plating
solution and a lot of labor and money to dispose of liquid
wastes.
[0005] Japanese Non-examined Patent Publication No. 56-136967
(1981) has disclosed a method of continuously removing such
cumulative ions by an electro dialysis. This method requires
complicated operations to maintain the optimum pH for dialysis.
Further, the ion selecting membrane which allows plating blocking
ions only to penetrate the membrane is mechanically weak, difficult
to maintain, and too expensive.
[0006] Japanese Non-examined Patent Publication No. 7-268638 (1995)
has disclosed a plating method characterized by selecting the
metallic ion reducing agent and the pH conditioner in the
non-electro plating solution so that the oxidant ion of the
metallic ion reducing agent and the cation of the pH conditioner
may react into an insoluble salt to prevent oxidant ions of said
metallic ion reducing agent from increasing in said plating
solution.
[0007] However, this method is not effective to prevent an increase
of anions in pairs with metallic ions. The increase of the anions
will deteriorate the plating characteristics. This method also
suggests that the use of copper oxide or copper hydroxide in copper
plating will suppress characteristic deterioration of the plating
solution. In this case, however, the solubility of the copper oxide
or copper hydroxide has a great influence.
[0008] Solid copper oxide or copper hydroxide is usually added to
the plating solution. If the solid is not dissolved completely into
the plating solution, the particles left undissolved are plated as
the cores. This causes abnormal deposition or autolysis. Further,
copper oxide and copper hydroxide are more expensive than copper
sulfate as copper ion sources, which is conventionally used for
copper plating. That's the reason why copper oxide and copper
hydroxide have not been put in practical use.
[0009] Japanese Non-examined Patent Publication No. 7-286279 (1995)
has disclosed a method of adding barium hydroxide to the
non-electro plating solution and removing excessive sulfuric ions
as barium sulfate from the plating solution. However, this method
using formalin (35% aqueous formaldehyde solution) cannot avoid a
consequent increase of oxidant ions of the copper ion reducing
agent in the copper plating solution. The oxidant ions of the
copper ion reducing agent in this method are formic ions and cannot
be removed because barium formate has too great a solubility to be
precipitated.
[0010] Further, this method does not blow air into the solution
while adding barium hydroxide into the plating solution. When
alkaline barium hydroxide is added to the plating solution, the pH
value of the plating solution becomes higher. In electroless copper
plating, the plating solution becomes unstable when its pH goes too
high. Consequently, copper may deposit on unwanted places. This
abnormal deposition on printed circuits and the like may cause
short-circuits, reducing the yield of the products. Deposition on
the walls of the plating bath may drastically deteriorate the
workability.
[0011] The conventional plating equipment is usually designed to
directly add copper ions, the copper-ion reducing agent, and the pH
conditioner into the plating bath. However, this equipment cannot
be free from the floating of solid particles of insoluble salt in
the plating solution. The floating solid particles when deposited
on wiring boards may cause abnormal deposition on the boards.
[0012] If such a solid particle is caught in a through-hole on a
printed wiring board, it prevents part of the through-hole from
being plated, causing a discontinuity of the wiring (which is
termed "through-hole void").
[0013] In continuous electroless copper plating, byproduct ions
such as anions in pairs with copper ions and oxidant ions of the
copper ion reducing agent increase in the plating solution. This
increasing of the byproduct ions prevent the electroless copper
plating reaction from forming normal plating layers and reduces the
quality of the plated layer. This not only reduces the mechanical
properties of the plated layer, but also causes abnormal deposition
of metal on unwanted locations. Up to now, there have been
disclosed no effective electroless copper plating method of
preventing the increase of plating blocking ions or removing the
increased plating blocking ions and refreshing the plating
solution.
SUMMARY OF THE INVENTION
[0014] The main purpose of the present invention is to provide a
method of removing plating blocking ions such as anions in pairs
with copper ions and oxidant ions of the copper ion reducing agent
from the electroless copper plating solution and keeping a constant
salt concentration in the electroless copper plating solution
during plating, a device to realize said method, and applications
thereof.
[0015] A summary of the present invention is as follows:
[0016] [1] An electroless copper plating method using a plating
solution containing copper sulfate as copper ion sources, and a
copper ion complex agent, a copper ion reducing agent or glyoxylic
acid as a copper ion reducing agent, and pH conditioner, wherein
said method comprises steps of using the hydroxide of an alkaline
earth metal as said pH conditioner to react with sulfuric ions in
the electroless copper plating solution into a salt of said
alkaline earth metal, removing the precipitate from the plating
solution, measuring at least one of the concentration of sulfuric
ion in the plating solution (when the copper ion reducing agent is
used) and the concentration of oxalic ion in the plating solution
(when glyoxylic acid is used) and keeping an optimum sulfuric ion
or oxalic ion concentration or preferentially 0.1 mol per liter or
less of sulfuric ion and 0.2 mol per liter or less of oxalic ion
during plating.
[0017] [2] An electroless copper plating method using a plating
solution containing copper sulfate as copper ion sources, and
copper ion complex agent, a copper ion reducing agent or glyoxylic
acid as the copper ion reducing agent, and pH conditioner, wherein
said method comprises steps of adding at least one of alkaline
earth metal, alkaline earth metal oxide, alkaline earth metal
hydroxide, and alkaline earth metal salt (excluding sulfuric salt)
to the plating solution to react with sulfuric ions in the
electroless copper plating solution into a salt of said alkaline
earth metal, removing the precipitate from the plating solution,
measuring at least one of the concentration of sulfuric ion in the
plating solution (when the copper ion reducing agent is used) and
the concentration of oxalic ion in the plating solution (when
glyoxylic acid is used) and keeping an optimum sulfuric ion or
oxalic ion concentration or preferentially 0.1 mol per liter or
less of sulfuric ion and 0.2 mol per liter or less of oxalic ion
during plating.
[0018] [3] An electroless copper plating machine using a plating
solution containing copper sulfate as copper ion sources, and
copper ion complex, a copper ion reducing agent or glyoxylic acid
as a copper ion reducing agent, and pH conditioner, wherein said
device comprises an electroless copper plating bath, a reaction
bath which adds at least one of alkaline earth metal, alkaline
earth metal hydroxide, alkaline earth metal oxide, and alkaline
earth metal salt (excluding sulfuric salt) to said copper plating
solution therein to react with and precipitate sulfuric ions or
oxalic ion (when glyoxylic acid is used) as an alkaline earth metal
salt in said plating solution, a filter unit which separates said
metallic salt precipitate, means for measuring at least one of the
concentration of sulfuric ion (when the copper ion reducing agent
is used) and the concentration of oxalic ion in the plating
solution (when glyoxylic acid is used), and means for comparing at
least one of said measured concentrations by a preset reference
concentration and controlling the quantity of said alkaline earth
metal, alkaline earth metal hydroxide, alkaline earth metal oxide,
or alkaline earth metal salt (excluding sulfuric salt) to be
added.
[0019] [4] An electroless copper plating machine using a plating
solution containing metallic ions, an agent for reducing said
metallic ions, and a pH conditioner, wherein said machine comprises
An electroless copper plating bath, a reaction bath adding at least
a metal or a compound containing a metal to said plating solution
to precipitate ions which suppress generation of said plating
metal, and a ultrafiltration unit.
[0020] [5] Said filtration unit is preferably a cross-flow type
ultrafiltration unit or a filter press type ultrafiltration
unit.
[0021] [6] A multi-layer wiring board having insulating layers and
circuit layers accumulated and cemented alternately wherein the
circuit layers are electrically connected by copper-plated
through-holes which pass through the insulating layer between said
circuit layers or by copper-plated via-holes whose one end is
closed and wherein the copper plating of said multi-layer wiring
board is made by said electroless copper plating method.
[0022] [7] A module having one or more semiconductor elements on
said multi-layer wiring board.
[0023] The method of the present invention removes said insoluble
salt by saturating it at a temperature lower than the plating
temperature to cause it to precipitate and then removing the
precipitate. A method of concentrating the plating solution can
also be used to cause the insoluble salt to precipitate.
[0024] Removal of said insoluble salt can be done by circulating
the plating solution while plating is in progress or in a batch
manner when plating is not in progress after sulfuric ions and
oxidant ions of the copper ion reducing agent in the non-electro
plating solution exceed the preset quantities.
[0025] Below will be briefly explained a copper plating using
copper sulfate as copper ion sources, as a copper ion source and
glyoxylic acid as the copper ion reducing agent.
[0026] When copper sulfate, as copper ion sources, is used as a
copper ion source, the sulfuric ions increase in the plating
solution. When glyoxylic acid is used as a copper ion reducing
agent, the glyoxylic acid behaves as glyoxalate ions in the plating
solution and is reacted into oxalic ions which are the oxidant
ions. This reaction is
2CHOCOO.sup.-+4OH.sup.-.fwdarw.2C.sub.2O.sub.4.sup.2-+2e.sup.-+2H.sub.2O+H-
.sub.2 (Reaction formula 1)
[0027] When the concentration of the byproduct ions exceeds a limit
(0.1 mol per liter of sulfuric ions or 0.2 mol per liter of oxalic
ions), the plating solution will lose its characteristics quickly.
Experimentally, the concentration of the byproduct ions exceeds the
limit when a plating layer of 30 to 60 .mu.m thick is formed under
conditions of a plating bath load of 1 dm.sup.2 per liter.
[0028] When calcium hydroxide is added as a pH conditioner, the
sulfuric ions in the plating solution are precipitated as calcium
sulfate and the concentration of remaining sulfuric ions will
become very low (about 0.01 mol per liter or less), same the
solubility of calcium sulfate is about 0.15 gram solute per 100
grams water at 60.degree. C.
[0029] Similarly, the oxalic ions in the plating solution are
precipitated as calcium oxalate and the concentration of remaining
oxalic ions will become extremely low (about 7.times.10.sup.-6 mol
per liter or less), since the solubility of calcium oxalate is
about 0.001 gram solute per 100 grams water at 60.degree. C. When
the plating solution contains sulfuric ions of 0.01 mol per liter
or less and the oxalic ions of 7.times.10.sup.-6 mol per liter or
less, the plating characteristic is excellent and the plated layer
is very ductile.
[0030] Under this condition, no abnormal copper deposition is found
on non-plating locations and the plating solution is also very
stable. To add calcium ions into the plating solution, use a
calcium pH conditioner, calcium powder, calcium acetate, calcium
carbonate, calcium chloride, calcium oxide, and the like.
[0031] A similar result can be obtained when calcium is replaced by
barium. When one of the above barium compounds is used, almost all
sulfuric ions in the plating solution are precipitated as barium
sulfate and the concentration of remaining sulfuric ions will
become very low (about 1.5.times.10.sup.-4 mol per liter or less),
since the solubility of barium sulfate is about 0.0036 gram solute
per 100 grams water at 50.degree. C.
[0032] Similarly, the oxalic ions in the plating solution are
precipitated as barium oxalate and the concentration of remaining
oxalic ions will become extremely low (about 7.9.times.10.sup.-5
mol per liter or less), since the solubility of barium oxalate is
about 0.00175 gram solute per 100 grams water at 60.degree. C.
[0033] Air must be blown into the plating solution while said
compounds are added into the plating solution to remove the
precipitate of sulfuric and oxalic ions. For addition of a
substance which shows alkalinity in an aqueous solution and
increases the pH value of the plating solution such as calcium
hydroxide, barium hydroxide, calcium powder, barium powder, and the
like, blowing air into the solution is always required while the
substance is added to the plating solution.
[0034] A plating method and a plating machine in accordance with
the present invention do not limit the choice of a complexing agent
for the electroless copper plating solution (hereinafter
abbreviated as a copper plating solution). In other words, it can
be any as far as it can form a stable complex with copper ions such
as ethylenediaminetetraacetic acid (EDTA),
[0035] Rochelle salt, nitrilotriacetic acid (NTA),
[0036] nitrilotripropionic acid (NTP),
[0037] ethylenediaminediacetic acid (EDDA),
[0038] ethylenediaminepropionicdihydrochloride (EDDP),
[0039] iminodiacetic acid (IDA),
[0040] trans-1.2-diaminocyclohexane-N,N,N'N'-tetraacetic acid
(CyDTA),
[0041] diaminopropanoltetraacetic acid (DPTA-OH),
[0042] ethylenediaminediacetic acid (EDDA),
[0043] triethylenetetraaminehexaacetic acid (TTHA),
[0044] diethylenetriamine-N,N,N',N",N"-pentaacetic acid (DTPA),
[0045] dihydroxyethyl glycine (DHEG),
[0046] hydroxyethylenediaminetriacetic acid (EDTA-OH),
[0047] glycoletherdiaminetetraacetic acid (GEDTA),
[0048] nitrilotriporpionic acid (NTP),
[0049] diaminopropanetetraacetic acid (Methyl-EDTA)
[0050] hydroxyethyliminodiacetic acid (HIDA),
[0051] ethylenediaminetetraquis (methylenesulfonic acid) (EDTPO),
etc. As stated above, the sulfuric ions and the oxalic ions are
precipitated and separated as insoluble salts from the plating
solution and consequently the plating solution can maintain optimum
plating characteristics for a long time. The diagram of a machine
which can offer such effects is illustrated in FIG. 1.
[0052] The plating bath 1 performs electroless copper plating
(hereinafter abbreviated as copper plating). The copper plating
solution is circulated along a circulation route 2 which passes
through a filter column 3 (for separating floating objects such as
dust or solid barium sulfate, barium oxalate, etc.). Part of the
copper plating solution is sent to a reaction bath 4 and receives
copper ions, a copper ion reducing agent and a pH conditioner,
which are lost in plating there to recover the optimum
concentrations. FIG. 1 shows a heat exchanger 13 for heating the
plating solution, a copper sulfate as copper ion sources, a supply
tank 21, a pH conditioner supply tank 22, a copper ion reducing
agent supply tank 23, and circulation pumps 24, 25, and 27.
[0053] In the reaction bath, the concentrations of copper ions,
copper ion reducing agent, and pH conditioner to be added are
necessarily higher than the concentrations of those in the plating
bath so as to recover the optimum concentrations of the plating
solution in the plating bath with the fed-back copper plating
solution. If calcium hydroxide or barium hydroxide is used as a pH
conditioner, sulfuric ions and oxalic ions to be removed are
precipitated as insoluble salts first in the reaction bath.
Further, it sometimes happens that the concentrations of
ingredients of the solution in the reaction bath are high enough to
make the solution unstable.
[0054] In such a case, to prevent the copper plating solution from
decomposing, a gas containing oxygen, such as air, must be blown
into the reaction bath through the gas supply pipe 5. If the
solubilities of sulfuric salts and oxalic salts go lower as the
liquid temperature falls, it is recommended to cool the copper
plating solution in the reaction bath to increase the efficiency of
precipitation.
[0055] In this case, the copper plating solution passing through a
pre-cooling heat exchange 6 can be supplied to the reaction bath or
the reaction bath itself can be cooled. Since it is desirable to
heat the cooled copper plating solution to a desired solution
temperature before feeding it back to the plating bath, the copper
plating solution coming from the reaction bath is fed back to the
plating bath through a heating heat exchanger 7.
[0056] A concentration analyzer 8 measures the concentration of
copper ions, the concentration of the reducing agent, and the pH of
the plating solution in the reaction tank. The quantities of
ingredients to be supplied are controlled by pumps 9, 10, and 11 so
that the measured concentrations may be predetermined
concentrations. The concentrations of sulfuric ions and oxalic ions
can be measured by chromatography. Part of the plating solution is
taken out from the reaction bath for measurement. Besides
chromatography, the measurement can be done by a capillary
electrophoresis analyzer.
[0057] The copper plating solution supplied with copper ions,
copper ion reducing agent, and pH conditioner from the reaction
bath is fed to a ultra filtration unit 12. The ultra filtration
unit 12 contains an ultra filtration membrane which separates the
inner copper plating solution coming from the reaction bath from
the outer copper plating solution coming from the plating bath.
This is a cross-flow type ultra filtration unit. FIG. 2 is a
diagrammatic illustration of the ultra filtration unit illustrating
the principle thereof. FIG. 2 shows fine particles of crystals 29,
a cross-flow type ultra filtration unit 12, an ultra filtration
membrane 31, a flow of plating solution 32, and a filtrate 33.
[0058] Using the characteristics of the ultra filtration unit that
lets ions and low molecular organic compounds penetrate the
membrane, but blocks fine particles, the solid precipitate produced
in the reaction bath is separated and removed out from the system.
In other words, only ions passing through the ultra filtration
membrane can be fed back to the plating bath and solid components
can be continuously removed from the system.
[0059] In the cross-flow filtration, the copper plating solution
flows along the surface of the membrane. This prevents the membrane
from being blocked quickly. Only the filtrate which passes through
the membrane is fed back to the plating bath. This prevents the
crystallized fine particles from returning to the plating solution.
The pore size of the membrane is 0.5 microns or less,
preferentially 0.1 microns or less.
[0060] The filtration provided in accordance with the present
invention can be any type, so long as sulfuric and oxalic salts
produced in the reaction bath are not fed back to the plating bath.
Preferable filtration methods are a filter pressing method, a
cross-flow method, etc.
[0061] This method enables a long stable electroless copper plating
(hereinafter abbreviated as copper plating) with sulfuric and
oxalic ion concentrations low in the copper plating solution.
[0062] The purpose of the present invention can be realized with
the use of a similar method and device even when a compound which
will not produce any insoluble salt, such as potassium hydroxide,
etc., is used as a pH conditioner, when calcium or barium is added
singly in the reaction bath or when calcium or barium carbonate,
acetate, oxide, or chloride is added to the copper plating
solution.
[0063] However, when calcium carbonate and/or barium carbonate are
used, carbonic ions increase in the copper plating solution. When
calcium acetate and/or barium acetate are used, acetic ions
increase in the copper plating solution. Similarly, when calcium
chloride and/or barium chloride are used, chloric ions increase in
the copper plating solution.
[0064] Therefore, for the use of a calcium salt and/or a barium
salt, the quantity of the salt should be such that its salt
precipitate may not exert any influence upon the plating
characteristics. It is required to estimate the influence of the
salt in advance.
[0065] On the contrary, calcium hydroxide, barium hydroxide,
calcium, barium, calcium oxide, and barium oxide (when added to the
copper plating solution) will not increase ions in the copper
plating solution and are preferable since they can make the plating
characteristics stable for a long time period.
[0066] Potassium hydroxide can be used as a pH conditioner even
when calcium hydroxide and/or barium hydroxide are used to produce
oxalic or sulfuric salt precipitate. Also, in this case, the
purpose of the present invention can be realized.
[0067] In the above explanation, if the solubility of a compound
(e.g. calcium hydroxide) to be added is low, a slurry of the
compound is sometimes preferable to an aqueous solution of the
compound. In this case, a slurry pump is usually used to feed the
slurry compound to the reaction bath.
[0068] According to the present invention, byproduct ions, which
increase as a non-electro plating reaction advances, can be
eliminated, and consequentially, the electroless copper plating
solution can have a longer working life, drastically reducing the
plating cost.
BRIEF DESCRIPTION OF DRAWINGS
[0069] FIG. 1 is a diagram illustrating the configuration of a
plating machine in accordance with the present invention.
[0070] FIG. 2 is a schematic diagram of the ultra filtration unit
used in the plating machine in accordance with the present
invention.
[0071] FIG. 3 is a diagram illustrating the configuration of a
plating machine according to a preferred embodiment of the present
invention.
[0072] FIG. 4 is a diagram illustrating the configuration of a
plating machine according to another preferred embodiment of the
present invention.
[0073] FIG. 5 is a diagram illustrating the configuration of a
plating machine according to another preferred embodiment of the
present invention.
[0074] FIG. 6 is a schematic sectional diagram of a module having
semiconductor elements on a multi-layer board plated in accordance
with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment 1
[0075] A first embodiment of the present invention uses copper
sulfate as copper ion sources, as a copper ion source, glyoxylic
acid as a copper ion reducing agent and barium hydroxide as a pH
conditioner. This embodiment uses EDTA pentasodium as a complexing
agent because the solubility of barium hydroxide is not so
great.
[0076] Below are listed the ingredients of the plating solution and
the plating condition.
[0077] (Ingredients)
1 Copper (II) sulfate pentahydrate 0.04 mol per liter EDTA
pentasodium 0.1 mol per liter Glyoxylic acid 0.03 mol per liter
Barium hydroxide 0.01 mol per liter 2,2' bipyridyl 0.0002 mol per
liter Polyethylene glycol 0.03 mol per liter (mean molecular weight
= 600)
[0078] The concentration of barium hydroxide is controlled to keep
the pH of the plating solution at 12.3.
[0079] (Plating Condition)
2 pH 12.3 plating solution temperature 70.degree. C.
[0080] A copper wiring pattern was plated on a test board in said
copper plating solution. The stability of the plating solution and
the quality of the plated layer were evaluated from the existence
of an abnormal deposition of copper. The test board was prepared as
stated below. The physical property of the plated layer was also
evaluated.
[0081] (Preparation of a Test Board)
[0082] A test board was prepared by coating both surfaces of a 0.6
mm-thick glass-sheet reinforced resin laminated board with an
adhesive containing acrylonitrilebutadiene rubber modified phenol
resin as the main ingredient, and hardening the test board of at
160.degree. C. for ten minutes. The hardened test board has an
adhesive layer of about 30 microns thick on each surface. Then, the
test board was drilled at preset locations and dipped in a
coarsening liquid containing chromic anhydride and hydrochloric
acid to coarsen the adhesive surfaces.
[0083] Next, the board was dipped for ten minutes in a
single-liquid palladium colloidal catalyst solution (fabricated by
Hitachi Kasei Co., Ltd. acid aqueous solution containing
intensifier HS101B) as a copper plating catalyst, washed clean with
water, and dried up at 120.degree. C. for 20 minutes.
[0084] Both surfaces of the board were coated with a dry-film
photo-resist layer 35 microns thick (SR-3000 fabricated by Hitachi
Kasei Co., Ltd). A mask of a test pattern comprising lines 60
microns thick was placed on the photo resist surface of the board.
The board was exposed to light and developed. As the result, the
non-pattern parts on the surface of the board are all covered with
the photo-resist.
[0085] The test board prepared above and a stainless steel plate
were both dipped in the plating solution at a liquid temperature of
70.degree. C. and plated with a load of 1 dm.sup.2 per liter.
[0086] The stainless steel plate was prepared by dipping the plate
in 17% hydrochloric aqueous solution for 2 minutes, dipping it in
the above palladium collidal solution for 10 minutes, and washing
it thoroughly. While plating is in progress, air was blown into the
plating solution to stir up the solution. A prepared liquid (listed
below) was supplied to the plating solution to make the
concentration of copper ions, the concentration of glyoxylic acid
(copper ion reducing agent), and the pH constant.
[0087] (1) Copper ion supplement (CuSO.sub.4 5H.sub.2O) 200
grams
[0088] Water Quantity required to make one liter of the
solution
[0089] (2) Glyoxylic acid (copper ion reducing agent) supplement
40% glyoxylic acid solution
[0090] (3) pH conditioner (Ba(OH).sub.2) 40 grams
[0091] Water Quantity required to make one liter of the
solution
[0092] One plating cycle comprises a plating step to form a 30
.mu.m-thick copper layer on the stainless steel plate and the
pattern area of the test board. At the end of each plating cycle,
the plated copper layer was peeled off from the stainless steel
plate, cut into a piece of 1.25 cm by 10 cm. The mechanical
strength of the piece was measured by an ordinary tensile
tester.
[0093] The precipitates (barium sulfate, barium oxalate, and
others) which were formed during plating were filtered and removed
by circulation and filtration of the plating solution. After each
plating cycle is completed, the plating solution is cooled down to
room temperature (25.degree. C.) and filtered to remove the
precipitates (barium sulfate, barium oxalate, and others) before
the succeeding plating cycle. The concentrations of the sulfuric
and oxalic ions in this clean plating solution were measured by
chromatography. Table 1 shows the result of the measurement.
3 TABLE 1 Number of plating cycles Unit 1 2 3 4 5 6 7 Embodiment 1
Conc. of sulfuric ions mol/l 8 .times. 10.sup.-3 9 .times.
10.sup.-3 9 .times. 10.sup.-3 8 .times. 10.sup.-3 8 .times.
10.sup.-3 8 .times. 10.sup.-3 8 .times. 10.sup.-3 Conc. of oxalic
ions mol/l 7 .times. 10.sup.-6 7 .times. 10.sup.-6 7 .times.
10.sup.-6 6 .times. 10.sup.-6 7 .times. 10.sup.-6 6 .times.
10.sup.-6 6 .times. 10.sup.-6 Ductility of plate film % 9.8 10.5
9.7 10.1 7.8 10.3 6.8 Abnormal deposition -- None None None None
None None None Embodiment 2 Conc. of sulfuric ions mol/l 1 .times.
10.sup.-4 1 .times. 10.sup.-4 1 .times. 10.sup.-4 1 .times.
10.sup.-4 1 .times. 10.sup.-4 1 .times. 10.sup.-4 1 .times.
10.sup.-4 Conc. of oxalic ions mol/l 7 .times. 10.sup.-5 7 .times.
10.sup.-5 6 .times. 10.sup.-5 7 .times. 10.sup.-5 7 .times.
10.sup.-5 6 .times. 10.sup.-5 5 .times. 10.sup.-5 Ductility of
plate film % 10.1 8.5 9.6 7.1 6.8 10.2 7.2 Abnormal deposition --
None None None None None None None Embodiment 3 Conc. of sulfuric
ions mol/l 9 .times. 10.sup.-3 9 .times. 10.sup.-3 8 .times.
10.sup.-3 8 .times. 10.sup.-3 9 .times. 10.sup.-3 8 .times.
10.sup.-3 8 .times. 10.sup.-3 Conc. of formic ions mol/l 0.12 0.28
0.42 0.62 0.78 0.92 1.12 Ductility of plate film % 10.5 8.8 7.5 6.8
5.2 4.6 3.5 Abnormal deposition -- None None None None None Little
Little Embodiment 4 Conc. of sulfuric ions mol/l 1 .times.
10.sup.-4 1 .times. 10.sup.-4 1 .times. 10.sup.-4 1 .times.
10.sup.-4 1 .times. 10.sup.-4 1 .times. 10.sup.-4 1 .times.
10.sup.-4 Conc. of formic ions mol/l 0.11 0.26 0.43 0.62 0.77 0.95
1.18 Ductility of plate film % 11.0 10.2 7.6 7.3 5.5 4.3 3.4
Abnormal deposition -- None None None None None Little Little
Embodiment 6 Conc. of sulfuric ions mol/l 9 .times. 10.sup.-3 9
.times. 10.sup.-3 9 .times. 10.sup.-3 8 .times. 10.sup.-3 8 .times.
10.sup.-3 8 .times. 10.sup.-3 8 .times. 10.sup.-3 Conc. of oxalic
ions mol/l 7 .times. 10.sup.-6 7 .times. 10.sup.-6 7 .times.
10.sup.-6 7 .times. 10.sup.-6 7 .times. 10.sup.-6 7 .times.
10.sup.-6 7 .times. 10.sup.-6 Ductility of plate film % 10.2 8.7
9.6 8.8 8.5 9.8 7.5 Abnormal deposition -- None None None None None
None None Comparative Conc. of sulfuric ions mol/l 0.08 0.12 0.19
0.35 0.55 -- -- embodiment 1 Conc. of formic ions mol/l 0.12 0.24
0.38 0.67 0.98 -- -- Ductility of plate film % 9.8 7.5 5.4 3.2 1.2
-- -- Abnormal deposition -- None Little Some Some Deposition -- --
Comparative Conc. of sulfuric ions mol/l 0.08 0.13 0.18 0.33 0.56
-- -- embodiment 2 Conc. of oxalic ions mol/l 0.12 0.24 0.37 0.77
1.02 -- -- Ductility of plate film % 9.7 7.7 5.2 2.8 1.0 -- --
Abnormal deposition -- None Little Some Some Deposition -- --
[0094] The concentrations of sulfuric and oxalic ions in the
plating solution were measured after the plating solution was
filtered at the end of each plating cycle.
[0095] Even after seven plating cycles, the sulfuric ion
concentration was 1.5.times.10.sup.-4 mol per liter or less and the
oxalic ion concentration was 7.9.times.10.sup.-5 mol per liter or
less. The ductility of the obtained plated layer was 6% or more and
was not deteriorated so much as the number of plating cycles
increased. Further, no abnormal deposition was visually detected on
the test board, in the plating bath, pipings, and so on. The
plating solution was extremely steady even after seven plating
cycles were completed.
[0096] As stated above, the method in accordance with the present
invention was found to suppress an increase of sulfuric and oxalic
ions in the plating solution. This is due to the use of barium
hydroxide as a pH conditioner which causes the sulfuric and oxalic
ions to precipitate as insoluble barium salts. This precipitate is
separated from the plating solution, and so the plating solution
can be almost free from sulfuric and oxalic ions.
[0097] The long excellent plating characteristics can be obtained
by plating under conditions of the sulfuric ion concentration of
0.1 mol per liter or less and the oxalic ion concentration of 0.2
mol per liter or less in the plating solution.
Embodiment 2
[0098] A second embodiment of the present invention was carried out
under the same conditions as the first embodiment, but barium
hydroxide as a pH conditioner was substituted by calcium hydroxide.
As the solubility of calcium hydroxide is very low (approx. 1.7
gram solute per 1 liter water), its aqueous solution is not
available. Therefore calcium hydroxide in slurry (obtained by
powering calcium hydroxide and adding pure water thereto) was
used.
[0099] Powdered calcium hydroxide has greater surfaces in contact
with the plating solution and can easily react with sulfuric and
oxalic ions into insoluble precipitates in the plating solution
although the solubility of calcium hydroxide is very low. In this
case, however, the efficiency of removal of sulfuric and oxalic
ions from the plating solution is dependent upon the granule sizes
of the calcium hydroxide powder, the rate of solution stirring, and
so on. They must be optimized in advance.
[0100] To prevent a lot of crystals including undissolved calcium
hydroxide from existing in the plating solution, this embodiment
employs a method of adding a slurry of calcium hydroxide into the
reaction bath, which is provided separately from the plating bath,
instead of adding a slurry of calcium hydroxide directly into the
plating bath, mixing the slurry and the plating solution in the
plating bath, removing the precipitate by the ultra filtration
unit, and feeding back the filtered plating solution to the plating
bath.
[0101] Table 1 shows the result of an evaluation of the plating
characteristics. This method can keep the sulfuric and oxalic
concentrations very low (0.01 mol per liter or less of sulfuric ion
and 7.times.10.sup.-6 mol per liter or less of oxalic ion) even
after seven plating cycles.
[0102] The ductility of the obtained copper layer (foil) was 6% or
more and remained almost unchanged even after many plating cycles.
Further, no abnormal deposition was visually detected on the test
board, in the plating bath, pipings, and so on. The plating
solution was extremely steady even after seven plating cycles were
completed.
Embodiment 3
[0103] A third embodiment of the present invention uses copper
sulfate as copper ion sources, as a copper ion source, formaldehyde
as a copper ion reducing agent and barium hydroxide as a pH
conditioner. In this case, the oxidant ion of the formaldehyde is
formic acid. This embodiment assumes that formic acid cannot be
removed as a precipitate. Below are listed the ingredients of the
plating solution and the plating condition.
[0104] (Ingredients)
4 Copper (II) sulfate pentahydrate 0.04 mol per liter EDTA
pentasodium 0.1 mol per liter Formaldehyde 0.03 mol per liter
Barium hydroxide 0.01 mol per liter 2,2' bipyridyl 0.0002 mol per
liter Polyethylene glycol 0.03 mol per liter (mean molecular weight
= 600)
[0105] The concentration of barium hydroxide is controlled to keep
the pH of the plating solution at 12.3.
[0106] (Plating Condition)
5 pH 12.3 Liquid temperature 70.degree. C.
[0107] This embodiment plated the same test board using the same
method as Embodiment 1 in the above copper plating solution. The
physical property of the obtained plated layer (foil), abnormal
deposition, and concentrations of salts in the plating solution
were tested and measured in the same manner as Embodiment 1. 37%
formaldehyde aqueous solution is used to supply the copper ion
reducing agent.
[0108] Table 1 shows the result of an evaluation of the plating
characteristics. The concentration of sulfuric ions in the plating
solution was measured after the plating solution was filtered at
the end of each plating cycle. This method can keep the sulfuric
concentration very low (1.5.times.10.sup.-4 mol per liter or less)
even after seven plating cycles.
[0109] The ductility of the plated layer (foil) formed in the
seventh plating cycle was under half as much as that of the plated
layer (foil) formed in the first plating cycle, but it was strong
enough to assure the reliability. Further, within five plating
cycles, no abnormal deposition was visually detected on the test
board, in the plating bath, pipings, and so on. The plating
solution was extremely steady. After the sixth and seventh plating
cycles, a little abnormal deposition was found on the test board
and in the plating bath, but it was not significant enough to cause
short-circuiting of a wiring pattern on the test board.
Embodiment 4
[0110] A fourth embodiment of the present invention was carried out
under the same conditions as the third embodiment, but the pH
conditioner for the plating solution and the supplement was calcium
hydroxide. As the solubility of calcium hydroxide is very low, its
aqueous solution is not available. Therefore calcium hydroxide (in
slurry) was used as in the second embodiment.
[0111] The result of measurement is listed in Table 1. This method
can keep the sulfuric concentration very low (0.01 mol per liter or
less) after the seven plating cycles. The ductility of the plated
layer (foil) formed in the seventh plating cycle was under half as
much as that of the plated layer (foil) formed in the first plating
cycle, but it was strong enough to assure the required
reliability.
[0112] Further, within five plating cycles, no abnormal deposition
was visually detected on the test board, in the plating bath,
pipings, and so on. The plating solution was extremely steady.
After the sixth and seventh plating cycles, a little abnormal
deposition was found on the test board and in the plating bath, but
it was not significant enough to cause short-circuiting of a wiring
pattern on the test board.
Embodiment 5
[0113] A copper plating solution of a fifth embodiment of the
present invention was prepared using copper sulfate as copper ion
sources, as a copper ion source, glyoxylic acid as a copper ion
reducing agent and potassium hydroxide as a pH conditioner in
preparation of a plating solution.
[0114] (Ingredients)
6 Copper (II) sulfate pentahydrate 0.04 mol per liter EDTA
pentasodium 0.1 mol per liter Glyoxylic acid 0.03 mol per liter
Potassium hydroxide 0.03 mol per liter 2,2' bipyridyl 0.0002 mol
per liter Polyethylene glycol 0.03 mol per liter (mean molecular
weight = 600)
[0115] The concentration of potassium hydroxide is controlled to
keep the pH of the plating solution at 12.3.
[0116] (Plating Condition)
7 pH 12.3 Liquid temperature 70.degree. C.
[0117] A prepared liquid (listed below) was supplied to the plating
solution to make the concentration of copper ions, the
concentration of glyoxylic acid (a copper ion reducing agent), and
the pH constant, although they decrease as the plating
advances.
[0118] (1) Copper ion supplement (CuSO.sub.4 5H.sub.2O) 200
grams
[0119] Water Quantity required to make one liter of the
solution
[0120] (2) Glyoxylic acid (copper ion reducing agent) supplement
40% glyoxylic acid solution
[0121] (3) pH conditioner (Ba(OH).sub.2) 40 grams
[0122] Water Quantity required to make one liter of the
solution
[0123] As seen from the above, an aqueous solution of barium
hydroxide is used to keep the pH of the plating solution constant,
although potassium hydroxide is used as a pH conditioner when the
plating solution is prepared.
[0124] Even after seven plating cycles, the sulfuric ion
concentration was 1.5.times.10.sup.-4 mol per liter or less and the
oxalic ion concentration was 7.9.times.10.sup.-5 mol per liter or
less. The ductility of the obtained plated layer was 6% or more and
was not deteriorated so much as the number of plating cycles
increased. Further, no abnormal deposition was visually detected on
the test board, in the plating bath, pipings, and so on. The
plating solution was extremely steady even after seven plating
cycles were completed.
Embodiment 6
[0125] A sixth embodiment of the present invention uses a plating
solution containing copper sulfate as copper ion sources, as a
copper ion source, glyoxylic acid as a copper ion reducing agent
and potassium hydroxide as a pH conditioner. Below are listed the
ingredients of the plating solution and the plating condition.
[0126] (Ingredients)
8 Copper (II) sulfate pentahydrate 0.04 mol per liter EDTA
pentasodium 0.1 mol per liter Glyoxylic acid 0.03 mol per liter
Potassium hydroxide 0.03 mol per liter 2,2' bipyridyl 0.0002 mol
per liter Polyethylene glycol 0.03 mol per liter (mean molecular
weight = 600)
[0127] The concentration of potassium hydroxide is controlled to
keep the pH of the plating solution at 12.3.
[0128] (Plating Condition)
9 pH 12.3 Liquid temperature 70.degree. C.
[0129] This embodiment carried out plating according to the
processing flow illustrated in FIG. 1 using the above plating
solution. In other words, the copper plating was carried out in the
plating bath 1. The plating solution is circulated through a
filtration column 3 along the circulation path 2.
[0130] Part of the copper plating solution is sent to a reaction
bath 4 and receives copper ions, a copper ion reducing agent, and a
pH conditioner to supplement the lost quantities of ingredients.
The composition of the supplemental solution is listed below.
[0131] (1) Copper ion supplement (CuSO.sub.4.5H.sub.2O) 200
grams
[0132] Water Quantity required to make one liter of the
solution
[0133] (2) Glyoxylic acid (copper ion reducing agent) supplement
40% glyoxylic acid solution
[0134] (3) pH conditioner (KOH) 200 grams
[0135] Water Quantity required to make one liter of the
solution
[0136] Calcium powder was added to the plating solution in the
reaction bath to react with sulfuric and oxalic ions into insoluble
salts. As the pH of the plating solution increases when the calcium
powder is added, the pH conditioner is added to the plating
solution to decrease the pH. Further, the calcium powder generates
heat of dissolution when it dissolves into the plating solution.
Thus, care must be taken when dissolving the powder.
[0137] Therefore, the reaction bath was cooled for efficient
separation of the precipitate of oxalic salt.
[0138] When the calcium powder is added, the plating solution has
lots of precipitates (calcium sulfate, calcium oxalate, and calcium
particles which remain un-dissolved). Embodiment 6 removed these
precipitates from the plating solution by means of the ultra
filtration unit, regulated the concentration of copper ions, the
concentration of glyoxylic acid and the pH to predetermined values,
and then fed back the plating solution to the plating bath 1.
[0139] Table 1 shows the result of an evaluation of the plating
characteristics (the concentration of sulfuric ions, the
concentration of oxalic ions, the ductility of the plated layer,
and detection of abnormal deposition) of each plating cycle.
[0140] The concentration of sulfuric ions and the concentration of
oxalic ions in the table are the result of measurement after each
plating cycle is completed. This embodiment can keep the sulfuric
and oxalic concentrations very low (0.01 mol per liter or less of
sulfuric ion and 7.times.10.sup.-6 mol per liter or less of oxalic
ion) even after seven plating cycles.
[0141] The ductility of the obtained copper layer (foil) was 6% or
more and remained almost unchanged even after many plating cycles.
Further, no abnormal deposition was visually detected on the test
board, in the plating bath, pipings, and so on. The plating
solution was extremely steady even after seven plating cycles were
completed.
Embodiment 7
[0142] A seventh embodiment of the present invention was carried
out under the same conditions as Embodiment 6, but calcium powder
was replaced by barium oxide to react with sulfuric and oxalic ions
into precipitates. The testing method of this embodiment is the
same as Embodiment 6.
[0143] This embodiment can keep the sulfuric and oxalic
concentrations very low (1.5.times.10.sup.-4 mol per liter or less
of sulfuric ion and 7.9.times.10.sup.-5 mol per liter or less of
oxalic ion) even after seven plating cycles. The ductility of the
obtained copper layer (foil) was 6% or more and remained almost
unchanged even after many plating cycles. Further, no abnormal
deposition was visually detected on the test board, in the plating
bath, pipings, and so on. The plating solution was extremely steady
even after seven plating cycles were completed.
Embodiment 8
[0144] An eighth embodiment of the present invention was carried
out under the same conditions as Embodiment 6, but calcium powder
was replaced by barium carbonate to react with sulfuric and oxalic
ions into precipitates. The testing method of this embodiment is
the same as Embodiment 6.
[0145] This embodiment can keep the sulfuric and oxalic
concentrations very low (1.5.times.10.sup.-4 mol per liter or less
of sulfuric ion and 7.9 ? 10-5 mol per liter or less of oxalic ion)
even after seven plating cycles. The ductility of the obtained
copper layer (foil) was 6% or more and remained almost unchanged
even after many plating cycles.
[0146] However, it was found that the plating rate was reduced as
the carbonate increased in the plating solution. As a result of
visual checks, the plating solution was extremely steady even after
seven plating cycles were completed, but a little abnormal
deposition was found on the test board.
[0147] As stated above, the most excellent barium compound to be
added to the plating solution to react with sulfuric and oxalic
ions into precipitates is barium oxide, barium hydroxide, or a
simple substance of barium, since they will not increase ions in
the plating solution.
[0148] Although barium carbonate added to the plating solution as
in this embodiment can suppress an increase of sulfuric and oxalic
ions in the plating solution, an increase of carbonate ions was
recognized. However, the plating characteristic of this embodiment
is better than that of a method which does not use this embodiment.
By plating with a concentration of sulfuric ions of 0.1 mol per
liter and a concentration of oxalic ions of 0.2 mol per liter in
the plating solution, an excellent plating characteristic can be
maintained for a long time. This is the effect of this
embodiment.
Embodiment 9
[0149] A ninth embodiment of the present invention was carried out
under the same conditions as Embodiment 6, but calcium powder was
replaced by barium acetate to react with sulfuric and oxalic ions
into precipitates. The testing method of this embodiment is the
same as Embodiment 6.
[0150] This embodiment can keep the sulfuric and oxalic
concentrations very low (1.5.times.10.sup.-4 mol per liter or less
of sulfuric ion and 7.9.times.10.sup.-5 mol per liter or less of
oxalic ion) even after seven plating cycles. The ductility of the
obtained copper layer (foil) was 3% or more and a little inferior
to that of the embodiment using barium hydroxide. As a result of
visual checks, the plating solution was extremely steady even after
seven plating cycles were completed, but a little abnormal
deposition was found on the test board. It is assumed that this is
caused by the increase of acetic ions in the plating solution.
[0151] Although barium acetate added to the plating solution as in
this embodiment can suppress an increase of sulfuric and oxalic
ions in the plating solution, an increase of acetate ions was
recognized. However, the plating characteristic of this embodiment
is better than that of a method which does not use this embodiment.
By plating with a concentration of sulfuric ions of 0.1 mol per
liter and a concentration of oxalic ions of 0.2 mol per liter in
the plating solution, an excellent plating characteristic can be
maintained for a long time.
Embodiment 10
[0152] A tenth embodiment of the present invention was carried out
under the same conditions as Embodiment 6, but calcium powder was
replaced by barium chloride to react with sulfuric and oxalic ions
into precipitates. The testing method of this embodiment is the
same as Embodiment 6.
[0153] This embodiment can keep the sulfuric and oxalic
concentrations very low (1.5.times.10.sup.-4 mol per liter or less
of sulfuric ion and 7.9.times.10.sup.-5 mol per liter or less of
oxalic ion) even after seven plating cycles. The ductility of the
obtained copper layer (foil) was 3% or more and a little inferior
to that of the embodiment using barium hydroxide. As a result of
visual checks, the plating solution was extremely steady even after
seven plating cycles were completed, but a little abnormal
deposition was found on the test board. It is assumed that this is
caused by the increase of chloric ions in the plating solution.
[0154] As stated above, the most excellent barium compound to be
added to the plating solution to react with sulfuric and oxalic
ions into precipitates is barium hydroxide, barium oxide, or a
simple substance of barium, since they will not increase ions in
the plating solution.
[0155] Although barium chloride added to the plating solution as in
this embodiment can suppress an increase of sulfuric and oxalic
ions in the plating solution, an increase of chloride ions was
recognized. However, the plating characteristic of this embodiment
is better than that of a method which does not use this embodiment.
By plating with a concentration of sulfuric ions of 0.1 mol per
liter and a concentration of oxalic ions of 0.2 mol per liter in
the plating solution, an excellent plating characteristic can be
maintained for a long time. This is the effect of this
embodiment.
Embodiment 11
[0156] This embodiment of the present invention was carried out
under the same conditions as Embodiment 6, but calcium to be added
to the plating solution was replaced by barium to react with
sulfuric and oxalic ions into precipitates.
[0157] This embodiment can keep the sulfuric and oxalic
concentrations very low (1.5.times.10.sup.-4 mol per liter or less
of sulfuric ion and 7.9.times.10.sup.-5 mol per liter or less of
oxalic ion) even after seven plating cycles. The ductility of the
obtained copper layer (foil) was 6% or more and remained almost
unchanged even after many plating cycles. Further, no abnormal
deposition was visually detected on the test board, in the plating
bath, pipings, and so on. The plating solution was extremely steady
even after seven plating cycles were completed.
Embodiment 12
[0158] A twelfth embodiment of the present invention uses copper
sulfate as copper ion sources, as a copper ion source, formaldehyde
as a copper ion reducing agent and potassium hydroxide as a pH
conditioner. In this case, the oxidant ion of the formaldehyde is
formic acid. This embodiment assumes that formic acid cannot be
removed as a precipitate. Below are listed the ingredients of the
plating solution and the plating condition.
[0159] (Ingredients)
10 Copper (II) sulfate pentahydrate 0.04 mol per liter EDTA
pentasodium 0.1 mol per liter Formaldehyde 0.03 mol per liter
Potassium hydroxide 0.03 mol per liter 2,2' bipyridyl 0.0002 mol
per liter Polyethylene glycol 0.03 mol per liter (mean molecular
weight = 600)
[0160] The concentration of potassium hydroxide is controlled to
keep the pH of the plating solution at 12.3.
[0161] (Plating Condition)
11 pH 12.3 Liquid temperature 70.degree. C.
[0162] This embodiment plated the same test board using the same
method as Embodiment 1 in the above copper plating solution in the
plating flow illustrated in FIG. 1.
[0163] The copper plating solution is circulated along a
circulation route 2 which passes through a filter column 3.
[0164] Part of the copper plating solution is sent to a reaction
bath 4 and receives copper ions, a copper ion reducing agent, and a
pH conditioner, which are lost in plating there, to recover the
optimum concentrations. The composition of the supplemental
solution is listed below.
[0165] (1) Copper ion supplement (CuSO.sub.4.5H.sub.2O) 200
grams
[0166] Water Quantity required to make one liter of the
solution
[0167] (2) Formaldehyde (copper ion reducing agent) supplement 37%
glyoxylic acid solution.
[0168] (3) pH conditioner (KOH) 200 grams
[0169] Water Quantity required to make one liter of the
solution.
[0170] Calcium powder was added to the plating solution in the
reaction bath to react with sulfuric ions into insoluble salt. As
the pH of the plating solution increases when the calcium powder is
added, the pH conditioner was added to the plating solution to
decrease the pH. Further, the calcium powder generates a lot of
heat of dissolution when it dissolves into the plating solution.
Thus, care must be taken when dissolving the powder. Therefore, the
reaction bath was cooled for efficient separation of the
precipitate of oxalic salt.
[0171] When the calcium powder is added, the plating solution has
lots of precipitates (calcium sulfate and calcium particles which
remain undissolved). This embodiment removed these precipitates
from the plating solution by means of the ultra filtration unit,
regulated the concentration of copper ions, the concentration of
formaldehyde and the pH to predetermined values, and then fed back
the plating solution to the plating bath 1.
[0172] This embodiment can keep the sulfuric concentration very low
(1.5.times.10.sup.-4 mol per liter or less) even after seven
plating cycles. The ductility of the plated layer (foil) formed in
the seventh plating cycle was 3% which is under half as much as
that of the plated layer (foil) formed in the first plating cycle,
but it was strong enough to assure the reliability.
[0173] Further, within five plating cycles, no abnormal deposition
was visually detected on the test board, in the plating bath,
pipings, and so on. The plating solution was extremely steady.
After the sixth and seventh plating cycles, a little abnormal
deposition was found on the test board and in the plating bath, but
it was not significant enough to cause short-circuiting of a wiring
pattern on the test board.
Comparative Embodiment 1
[0174] This embodiment performed copper plating using a
conventional copper plating solution which contained formaldehyde
as a copper ion reducing agent and sodium hydroxide as a pH
conditioner.
[0175] The pH and the temperature of the plating solution were
respectively 12.5 and 70.degree. C. In this case, the oxidant ion
of the formaldehyde is formic acid and the solubility of sodium
formate is extremely high (99.6 grams solute per 100 grams water at
25.degree. C.). Further, the solubility of sodium sulfate is also
high (21.9 grams solute per 100 grams water at 25.degree. C.).
Therefore, sodium formate and sodium sulfate will never precipitate
even after the copper plating solution is cooled, and so these ions
(byproduct ions) cannot be removed.
[0176] The concentration of sulfuric ions, the concentration of
formic ions, and the physical quantity of the plated layer (foil)
in repetitive plating are illustrated in Table 1.
[0177] Table 1 shows that, as the repetitive plating advances, the
sulfuric and formic ions increase in the plating solution and the
ductility of the plated layer (foil) decreases. Further, the copper
plating solution became unstable as the plating advanced. The
plating solution started autolysis halfway in the fifth plating and
was unable to plate.
Comparative Embodiment 2
[0178] This embodiment performed copper plating using the same
copper plating solution as Comparative Embodiment 2 but calcium
hydroxide as the pH conditioner was replaced by potassium
hydroxide. The pH and the temperature of the plating solution were
respectively 12.5 and 70.degree. C.
[0179] In this case, the solubility of potassium sulfate is high
(10.8 grams solute per 100 grams water at 25.degree. C.).
Therefore, sodium sulfate will never precipitate, and so the
sulfuric ions cannot be removed.
[0180] Similarly, the solubility of potassium oxalate is also high
(35.9 grams solute per 100 grams water at 25.degree. C.).
Therefore, potassium oxalate did not precipitate even after the
copper plating solution was cooled, and so the oxalic ions could
not be removed.
[0181] The concentration of sulfuric ions, the concentration of
oxalic ions, and the physical quantity of the plated layer (foil)
in repetitive plating are illustrated in Table 1.
[0182] Table 1 shows that, as the repetitive plating advances, the
amount of sulfuric and oxalic ions increases in the plating
solution and the ductility of the plated layer (foil) decreases.
Further, the copper plating solution became unstable as the plating
advanced. The plating solution started autolysis halfway in the
fifth plating and was unable to plate.
[0183] As seen from the above, it is apparatus that use methods
which are not in accordance with the present invention that cause
blocking ions to increase in the plating solution, with the result
that the plating characteristics are deteriorated. This has proven
that the present invention has an advantage.
Embodiment 13
[0184] Below will be explained a plating machine which is one
embodiment in accordance with the present invention. FIG. 3 is a
diagram showing the configuration of a plating machine in
accordance with the present invention.
[0185] The copper plating was carried out in the plating bath 1.
The copper plating solution is circulated through a filtration
column 3 along a circulation path 2 to remove solids floating in
the copper plating solution. The device has another circulation
path passing through a heat exchanger 13 to heat up the copper
plating solution to a predetermined temperature.
[0186] Part of the copper plating solution is sent to a reaction
bath 4 and receives copper ions, a copper ion reducing agent, and a
pH conditioner to supplement the lost quantities of
ingredients.
[0187] In the reaction bath 4, the concentrations of copper ions,
copper ion reducing agent, and pH conditioner to be added are
necessarily higher than the concentrations of those in the plating
bath to recover the optimum concentrations of the plating solution
in the plating bath 1 with the fed-back copper plating
solution.
[0188] To prevent the copper plating solution from decomposing in
the reaction bath 4, a gas containing oxygen, such as air, is blown
into the copper plating solution in the reaction bath through a gas
supply valve 5 to stir up the solution with the gas. A
concentration analyzer 8 measures the concentration of copper ions,
the concentration of the reducing agent, and the pH of the plating
solution in the reaction tank. The quantities of ingredients to be
supplied are controlled by pumps 9, 10, and 11 so that the measured
concentrations may be predetermined concentrations.
[0189] Pumps 9, 10, and 11 respectively supply copper sulfate as
copper ion sources, aqueous solution, glyoxylic acid aqueous
solution, and barium hydroxide aqueous solution in that order.
[0190] The concentrations of copper ions, the copper ion reducing
agent, and the pH conditioner of the copper plating solution in the
reaction bath are higher than those of the plating solution in the
plating bath. Barium sulfate and barium oxalate are saturated and
precipitated first in the reaction bath 4 as the copper plating
solution is cooled by the heat exchanger 6 before entering the
reaction bath 4.
[0191] These precipitates (fine crystallized particles) are
separated from the copper plating solution by the cross-flow type
ultra filtration unit 12. The filtered clean copper plating
solution is fed back to the plating bath through the heating heat
exchanger 7.
[0192] The copper plating solution containing a lot of precipitate
is sent to the settling bath 14 in the upstream side of the
reaction bath 4. Only the supernatant plating solution overflows a
weir which is provided between the settling bath 14 and the
reaction bath 4 back into the reaction bath 4.
[0193] 70% or more of the solid precipitate in the copper plating
solution sent to the settling bath 14 remains settled and is taken
out of the system.
[0194] As stated above, the device in accordance with the present
invention can remove sulfuric and oxalic ions which deteriorate the
plating characteristics as barium salts and maintain an excellent
plating characteristic for a long time.
Embodiment 14
[0195] FIG. 4 is a flow diagram of a plating machine using a filter
press type ultra filtration unit. This embodiment uses almost the
same units as those of Embodiment 13 and performs similar
operations. An explanation thereof is omitted here. Unit 17 is a
recovery tank.
[0196] This embodiment is characterized in that the whole reaction
bath 4 is cooled further by water sent from the cooling unit 15
after part of the copper plating solution is supplied to the
reaction bath 4.
[0197] The concentrations of copper ions, the copper ion reducing
agent, and the pH conditioner of the copper plating solution in the
reaction bath 4 are higher than those of the plating solution in
the plating bath 1, and the reaction bath 4 is cooled by water from
the cooling unit 15. Therefore, barium sulfate and barium oxalate
are first saturated and easily precipitated in the reaction
bath.
[0198] These precipitates (fine crystallized particles) are
separated from the copper plating solution by the filter press type
ultra filtration unit 16. The filtered clean copper plating
solution is fed back to the plating bath 1 through the heating heat
exchanger 7.
[0199] The precipitate caught by the filter press type ultra
filtration unit 16 is scaled off from the filter membrane into the
recovery tank 17 through a funnel-shaped collecting means, and
taken out from the system.
[0200] As stated above, the device in accordance with the present
invention can remove sulfuric and oxalic ions which deteriorate the
plating characteristics as barium salts and maintain an excellent
plating characteristic for a long time.
Embodiment 15
[0201] This embodiment uses a copper plating solution containing
barium hydroxide or calcium hydroxide as a pH conditioner. FIG. 5
is a flow diagram of a plating machine using alkaline metal
hydroxide such as sodium hydroxide or potassium hydroxide as a pH
conditioner. FIG. 5 contains a delivery pump 26 and an alkali earth
metal salt supply tank 28.
[0202] The reaction bath 4 is equipped with a supply pump 18 for
supplying aqueous solution containing at least one of calcium
hydroxide, barium hydroxide, calcium carbonate, barium carbonate,
calcium acetate, barium acetate, calcium oxide, barium oxide,
calcium, and barium to react with sulfuric and oxalic ions into
precipitates.
[0203] The quantities of chemicals to precipitate the ions are
regulated by a pump 9 for supplying copper sulfate as copper ion
sources, aqueous solution, a pump 10 for supplying glyoxylic acid
aqueous solution, and an analyzing unit 8.
[0204] The quantity of sulfuric ions in the copper plating solution
can be calculated from the quantity of copper sulfate as copper ion
sources, solution supplied by pump 9. The quantity of oxalic ions
in the copper plating solution is calculated as the difference
between the quantity of oxalic acid solution measured by the
analyzing unit 8 and the quantity of the existing glyoxylic acid.
The copper plating solution control unit 19 performs these
calculations and controls the pump 18 according to the result of
calculation. The other configuration of this embodiment is the same
as that of Embodiment 13 and Embodiment 14.
[0205] As stated above, the device in accordance with the present
invention can remove sulfuric and oxalic ions which deteriorate the
plating characteristics as barium salts and maintain an excellent
plating characteristic for a long time.
Embodiment 16
[0206] FIG. 6 is a diagrammatic sectional view of a module
comprising a multi-layer wiring board 54 produced by a copper
plating method in accordance with the present invention and
semiconductor elements thereon. A number 45 indicates an insulating
layer.
[0207] The multi-layer wiring board 54 is prepared by forming a
wiring pattern on each board with a known photo-resist, plating a
conductor wiring 34 on the board by a method stated in said
embodiments, and piling a preset number of said plated boards with
an insulating layer 37 therebetween.
[0208] The conductor wirings on the plated boards are electrically
connected by via-holes 36 and through-holes 35 which are drilled in
advance and plated by a copper plating method of the present
invention.
[0209] Semiconductor elements 46 are mounted on predetermined
locations of said multi-layer wiring board 54 by a method using
solder balls 44. With this, a highly reliable module can be
obtained.
* * * * *