U.S. patent application number 11/759417 was filed with the patent office on 2007-12-13 for method for silver plating.
Invention is credited to Toshifumi Kadokawa, Shingo Kitamura, Seiji Omori, Masakazu Yoshimoto.
Application Number | 20070284258 11/759417 |
Document ID | / |
Family ID | 38820792 |
Filed Date | 2007-12-13 |
United States Patent
Application |
20070284258 |
Kind Code |
A1 |
Yoshimoto; Masakazu ; et
al. |
December 13, 2007 |
Method For Silver Plating
Abstract
The invention provides a method for silver plating using a
non-cyanide acid silver plating bath to form a silver plating film
exhibiting good adhesiveness while suppressing dissolution of
resist in pattern plating. The method includes conducting strike
plating using a non-cyanide acid strike plating bath prior to the
silver plating.
Inventors: |
Yoshimoto; Masakazu;
(Kyogo-Ken, JP) ; Kitamura; Shingo; (Hyogo-Ken,
JP) ; Omori; Seiji; (Hyogo-Ken, JP) ;
Kadokawa; Toshifumi; (Hyogo-Ken, JP) |
Correspondence
Address: |
MARSHALL, GERSTEIN & BORUN LLP
233 S. WACKER DRIVE, SUITE 6300, SEARS TOWER
CHICAGO
IL
60606
US
|
Family ID: |
38820792 |
Appl. No.: |
11/759417 |
Filed: |
June 7, 2007 |
Current U.S.
Class: |
205/263 |
Current CPC
Class: |
C25D 5/022 20130101;
H05K 3/244 20130101; C25D 5/34 20130101; C25D 17/002 20130101; C25D
3/46 20130101; C25D 3/38 20130101; C25D 5/10 20130101 |
Class at
Publication: |
205/263 |
International
Class: |
C25D 3/46 20060101
C25D003/46 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 9, 2006 |
JP |
2006-161049 |
Claims
1. A method for silver plating onto a substrate, comprising
conducting strike plating onto a substrate using a non-cyanide acid
strike plating bath and subsequently conducting silver plating onto
the substrate using a non-cyanide acid silver plating bath.
2. The method according to claim 1, wherein both the non-cyanide
acid silver plating bath and the non-cyanide acid strike plating
bath have a pH of less than 3.
3. The method according to claim 1, wherein the non-cyanide acid
strike plating bath is an acid silver strike plating bath or an
acid copper strike plating bath.
4. The method according to claim 1, wherein either or both of the
non-cyanide acid silver plating bath and the non-cyanide acid
strike plating bath contain at least a sulfonate ion.
5. The method according to claim 1, wherein either or both of the
non-cyanide acid silver plating bath and the non-cyanide acid
strike plating bath contain at least an aliphatic phosphine.
6. The method according to claim 3, wherein the acid copper strike
plating bath is used and contains at least a sulfate ion.
7. The method according to claim 4, wherein either or both of the
non-cyanide acid silver plating bath and the non-cyanide acid
strike plating bath further contain an azole compound and/or a
thiophene compound.
8. The method according to claim 5, wherein either or both of the
non-cyanide acid silver plating bath and the non-cyanide acid
strike plating bath further contain an azole compound and/or a
thiophene compound.
9. The method according to claim 6, wherein either or both of the
non-cyanide acid silver plating bath and the non-cyanide acid
strike plating bath further contain an azole compound and/or a
thiophene compound.
10. The method according to claim 4, wherein either or both of the
non-cyanide acid silver plating bath and the non-cyanide acid
strike plating bath further contain a surfactant or a
surface-active polymer compound.
11. The method according to claim 5, wherein either or both of the
non-cyanide acid silver plating bath and the non-cyanide acid
strike plating bath further contain a surfactant or a
surface-active polymer compound.
12. The method according to claim 6, wherein either or both of the
non-cyanide acid silver plating bath and the non-cyanide acid
strike plating bath further contain a surfactant or a
surface-active polymer compound.
13. The method according to claim 3, wherein the method further
comprises the step of conducting displacement deposition prevention
treatment to the substrate between the strike plating and the
silver plating and wherein the strike plating is conducted using
the acid copper strike plating bath.
14. The method according to claim 1, wherein the method further
comprises the step of conducting pretreatment using an acid
degreasing bath prior to the strike plating.
15. The method according to claim 1, wherein either or both of the
non-cyanide acid silver plating bath and the non-cyanide acid
strike plating bath comprises an ion-exchange membrane therein to
separate an anode and a cathode.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for silver
electroplating with a non-cyanide bath, and in particular to a
method for forming a silver plating film using an acid plating
bath, exhibiting good adhesiveness while suppressing dissolution of
resist in pattern plating.
BACKGROUND OF THE INVENTION
[0002] Silver is widely used not only for functional plating as it
is excellent in properties such as electric conductivity and
solderability, but also for decorative plating as it is also
excellent in aesthetic appearance. In the current industrial
practices, almost all the silver plating processes are operated
with a cyanide bath.
[0003] Much research has been reported on a non-cyanide bath for
silver plating. Some of the reports include the development of an
acid silver-plating bath. It has been known since a long time ago
that silver plating may be also conducted from an acid bath. For
example, "Electroplating Baths for Silver A Review of Cyanide-Free
Formulations: S. R. Natarajan & R. Krishnan, Metal Finishing,
February 1971, P51", which was published about 30 years ago,
discloses acid silver-plating baths. However, the baths disclosed
in the literature were not suitable for industrial applications in
terms of adhesiveness and film properties, etc.
[0004] Studies have been continued over the years for the
improvement of the acid silver-plating baths. Examples of
silver-plating baths that can be reportedly used under acid
condition include those described in the following literatures.
[0005] JP H02-290993A discloses a bath using potassium iodide as a
complexing agent and teaches that the pH is in the range of 1 to
11, preferably 3 to 6. JP H07-166391A discloses a silver-plating
solution using succinimide as a complexing agent at a pH of 4 to
10.
[0006] Plating solutions using hydantoin as a complexing agent are
also disclosed. Though hydantoin is generally used in alkaline
baths at a pH of 7 or more as disclosed in JP H08-104993A,
hydantoin-containing silver-plating solutions and strike plating
solutions used at a pH of 3.0 to 10.0 are described in JP
H07-180085A. JP2000-34593A discloses "a phosphine-containing
aqueous solution for reduction-deposition of metal". In the
Example, a silver electroplating solution at a pH of 0.98 is
disclosed in the same. JP Patent No. 3365866 discloses a
silver-plating solution containing at least one of alkane sulfonic
acid ion and alkanol sulfonic acid ion, and a non-ionic surfactant.
Though there is no description about pH, it is deemed to be a
strong acid bath judging from the disclosed composition.
[0007] Acid baths are more suitable to partial plating and pattern
plating than alkaline baths as the former are less likely to attack
resist than the latter. In particular, among the acid baths, strong
acid silver-plating baths made with simple salt at pH of less than
3 are advantageous as they can be stable without using a complexing
agent and thereby can be formed and operated at lower cost.
[0008] Silver exhibits noble potential and thus has a problem of
readily causing displacement deposition. Though some literature
references have disclosed baths that can reduce or prevent
deposition by adding additives or using other methods, such baths
cannot prevent it in an industrially applicable way.
SUMMARY OF THE INVENTION
[0009] Accordingly, it is an object of the present invention to
provide a method for acid silver plating to form a dense silver
plating film exhibiting good adhesiveness while suppressing
dissolution of resist in pattern plating.
[0010] Accordingly, the subject matter of the present invention is
a method for silver plating onto a substrate using a non-cyanide
acid silver plating bath (A), comprising conducting strike plating
onto the substrate using a non-cyanide acid strike plating bath (B)
prior to the silver plating.
[0011] In one embodiment of the method according to the present
invention, both the non-cyanide acid silver plating bath (A) and
the non-cyanide acid strike plating bath (B) have a pH of less than
3.
[0012] In another embodiment of the method according to the present
invention, the non-cyanide acid strike plating bath (B) is an acid
silver strike plating bath (B1) or an acid copper strike plating
bath (B2).
[0013] In a further embodiment of the method according to the
present invention, either or both of the non-cyanide acid silver
plating bath (A) and the non-cyanide acid strike plating bath (B)
contain at least a sulfonate ion.
[0014] In a further embodiment of the method according to the
present invention, either or both of the non-cyanide acid silver
plating bath (A) and the non-cyanide acid strike plating bath (B)
contain at least an aliphatic phosphine.
[0015] In a further embodiment of the method according to the
present invention, the acid copper strike plating bath (B2)
contains at least a sulfate ion.
[0016] In a further embodiment of the method according to the
present invention, either or both of the non-cyanide acid silver
plating bath (A) and the non-cyanide acid strike plating bath (B)
further contain an azole compound and/or a thiophene compound.
[0017] In a further embodiment of the method according to the
present invention, either or both of the non-cyanide acid silver
plating bath (A) and the non-cyanide acid strike plating bath (B)
further contain a surfactant and/or a surface-active polymer
compound.
[0018] In a further embodiment of the method according to the
present invention, the method further comprises the step of
conducting displacement deposition prevention treatment to the
substrate between the strike plating and the silver plating and
wherein the strike plating is conducted using the acid copper
strike plating bath (B2).
[0019] In a further embodiment of the method according to the
present invention, the method further comprises the step of
conducting pretreatment using an acid degreasing bath prior to the
strike plating.
[0020] In a further embodiment of the method according to the
present invention, either or both of the non-cyanide acid silver
plating bath (A) and the non-cyanide acid strike plating bath (B)
comprise an ion-exchange membrane therein to separate an anode and
a cathode.
[0021] Since the method for non-cyanide silver plating according to
the present invention uses an acid bath for both the strike plating
step and the main silver plating step, it can solve the following
two problems: [0022] (1) decrease in adhesiveness of a plating film
due to alkaline components remaining on the substrate (e.g. metal
surface) to be plated in the main silver plating step, and [0023]
(2) dissolution of resist due to an alkaline strike plating
bath.
[0024] Therefore, the present invention can provide a method for
forming a silver plating film exhibiting good adhesiveness suitable
for partial or pattern plating using resist.
[0025] In addition, since the method according to the present
invention uses a strong acid silver-plating bath made with simple
salt at a pH of less than 3, the present invention can provide a
method that can be carried out at lower cost despite using a
non-cyanide bath. The method can be applied not only to functional
plating to form a plating film excellent in properties such as
solderability but also to decorative plating.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] Since a stronger acid generally dissolves base metal more
easily, strike plating is necessary prior to silver plating for
good adhesiveness. However, unlike other metal plating processes,
no study has been done for using an acid strike plating bath in
case of a silver plating process using an acid plating bath because
the acid strike plating bath is deemed to cause displacement
deposition easily.
[0027] However, even when an acid silver plating bath is used to
avoid dissolution of resist, dissolution of resist may occur if an
alkaline strike plating bath is used in the previous step. In
addition, if an alkaline strike plating bath is used before an acid
silver plating bath, since alkaline components in the alkaline
strike plating bath may remain on the metal surface to be plated
after completion of the strike plating, good plating film may not
be formed in the subsequent silver plating process. The present
inventors have determined that one or more improvements can be made
by strike plating using a strong acid bath prior to silver plating
using a strong acid silver plating bath.
[0028] The present invention, in various embodiments, may have one
or more advantages including, but not limited to, suppressing
dissolution of resist in pattern plating, preventing alkaline
components from remaining on the metal surface to be plated, and
forming a dense plating film with good adhesiveness.
[0029] The silver plating method of this invention will be
described in further detail below.
[0030] One embodiment of the invention provides a method for silver
plating onto a substrate using a non-cyanide acid silver plating
bath (A), comprising conducting strike plating onto the substrate
using a non-cyanide acid strike plating bath (B) prior to the
silver plating.
[0031] Both the silver plating bath (A) and the strike plating bath
(B) are required to be acidic. Preferably, both baths have a pH of
less than 3. As for the main silver plating bath (A), it goes
without saying that the bath should be acidic for the purpose of
preventing resist dissolution. The bath (A) having a pH of less
than 3 eliminates the need for a complexing agent for stability,
allowing the plating process to be operated at lower cost.
Accordingly, in one type of embodiment of the invention, the silver
plating bath is essentially free of or completely free of a
complexing agent. Further, by adjusting the acidity of the both
baths to the pH of less than 3, adhesion of alkaline components
onto the substrate possibly occurring in the previous strike
plating step, which may affect the adhesiveness, can be
avoided.
[0032] The pH is preferably less than 3 and more preferably less
than 2.
[0033] Silver strike plating is preferably adopted as the strike
plating step. Copper strike plating is also adopted as the strike
plating bath. In such case, depending on the desired properties of
the plating film, displacement prevention treatment or silver
strike plating may be preferably conducted between the copper
strike plating step and the silver plating step.
[0034] Any or all of the silver plating bath (A), the copper strike
plating bath (B1) and the silver strike plating bath (B2) may
contain any known acid alone or in combination as the acid
component for keeping the bath acidic. Sulfonic acids are
preferably used in terms of appearance of the plating film and
electric properties such as surface resistivity of the plating
film, etc. Among the sulfonic acids, aliphatic and aromatic
sulfonic acids may be preferably used and aliphatic sulfonic acids
may be more preferably used.
[0035] Preferable aliphatic sulfonic acids include alkane sulfonic
acids and alkanol sulfonic acids. Examples of alkane sulfonic acids
include methanesulfonic acid, ethanesulfonic acid,
1-propanesulfonic acid, 2-propanesulfonic acid, 1-butanesulfonic
acid, 2-butanesulfonic acid and pentanesulfonic acid, etc. Examples
of alkanol sulfonic acids include 2-hydroxyethane-1-sulfonic acid
(isethionic acid), 2-hydroxypropane-1-sulfonic acid
(2-propanolsulfonic acid), 2-hydroxybutane-1-sulfonic acid and
2-hydroxypentane-1-sulfonic acid, as well as
1-hydroxypropane-2-sulfonic acid, 3-hydroxypropane-1-sulfonic acid,
4-hydroxybutane-1-sulfonic acid and 2-hydroxyhexane-1-sulfonic
acid, etc.
[0036] In a preferred embodiment of the invention, either or both
of the silver plating bath (A) and the strike plating bath (B) may
at least contain one or more aliphatic or aromatic phosphines
represented by the Formula (1):
##STR00001##
wherein X.sub.1, X.sub.2 and X.sub.3, which may be the same or
different, each represent a hydrogen atom, a substituted or
unsubstituted C.sub.1 to C.sub.10 alkyl group, or a substituted or
unsubstituted benzene ring, one or more substituents for the
substituted alkyl or the substituted benzene ring being selected
from the group consisting of a hydroxyl group, a carboxyl group, a
sulfonic group and an amino group, provided that all of X.sub.1,
X.sub.2 and X.sub.3 are not hydrogen atoms at the same time.
[0037] Among the phosphines, lower alkyl phosphines represented by
the Formula (2):
##STR00002##
wherein Y.sub.1, Y.sub.2 and Y.sub.3, which may be the same or
different, each represent an unsubstituted C.sub.1 to C.sub.3 alkyl
group or a C.sub.1 to C.sub.3 alkyl group substituted with one or
more substituents selected from the group consisting of a hydroxyl
group, a carboxyl group, a sulfonic group and an amino group,
[0038] may be more preferably used.
[0039] Preferable examples of the phosphines include unsubstituted
alkyl phophines in which each alkyl group is a methyl group, an
ethyl group or a propyl group; and substituted alkyl phosphines in
which each alkyl group is substituted by one or more substituents
selected from the group consisting of a hydroxyl group, a carboxyl
group, a sulfonic group and an amino group. The substituted alkyl
phosphines include hydroxy lower alkyl phophines having a
hydroxymethyl group, a hydroxyethyl group or a hydroxypropyl group;
carboxy lower alkyl phophines having a carboxymethyl group, a
carboxyethyl group or a carboxypropyl group; sulfo lower alkyl
phophines having a sulfomethyl group, a sulfoethyl group or a
sulfopropyl group; and amino lower alkyl phophines having an
aminomethyl group, an aminoethyl group or an aminopropyl group.
[0040] Tris(hydroxy lower alkyl)phophines, in which one hydrogen
atom on each lower alkyl group is substituted by a hydroxyl group
to form each hydroxy lower alkyl selected from the group consisting
of a hydroxymethyl group, a hydroxyethyl group and a hydroxypropyl
group, may be more preferably used among these phosphines from the
viewpoints of cost and stability. Tris(3-hydroxypropyl)phophine may
be most preferably used.
[0041] The copper strike plating bath (B1) of the present invention
preferably contains at least a sulfate ion as one of the bath
components.
[0042] Any or all of the silver plating bath (A), the copper strike
plating bath (B1) and the silver strike plating bath (B2) of the
present invention may further contain an azole and/or thiophene
compound.
[0043] As the azole compounds, tetrazoles, imidazoles,
benzimidazoles, pyrazoles, indazoles, thiazoles, benzothiazoles,
oxazoles, benzoxazoles, triazoles and derivatives thereof may be
preferably used.
[0044] Among these compounds, imidazoles, pyrazoles, indazoles and
triazoles may be more preferably used, and triazoles may be most
preferably used. Examples of these compounds are listed below.
[0045] Preferred imidazoles include imidazole, 1-methylimidazole,
1-phenylimidazole, 2-methylimidazole, 2-ethylimidazole,
2-propylimidazole, 2-butylimidazole, 2-phenylimidazole,
4-methylimidazole, 4-phenylimidazole, 2-aminoimidazole,
2-mercaptoimidazole, imidazole-4-carboxylic acid, benzimidazole,
1-methylbenzimidazole, 2-methylbenzimidazole, 2-ethylbenzimidazole,
2-butylbenzimidazole, 2-octylbenzimidazole, 2-phenylbenzimidazole,
2-trifluoromethylbenzimidazole, 4-methylbenzimidazole,
2-chlorobenzimidazole, 2-hydroxybenzimidazole,
2-aminobenzimidazole, 2-mercaptobenzimidazole,
2-methylthiobenzimidazole, 5-nitrobenzimidazole,
benzimidazole5-carboxylic acid, tris(2-benzimidazolylmethyl)amine
and 2,2'-tetra (or octa) methylene-dibenzimidazole, etc. More
preferred imidazoles include imidazole, benzimidazole,
tris(2-benzimidazolylmethyl)amine and 2,2'-tetra (or octa)
methylene-dibenzimidazole.
[0046] Preferred pyrazoles or indazoles include pyrazole,
3-methylpyrazole, 4-methylpyrazole, 3,5-dimethylpyrazole,
3-trifluoromethylpyrazole, 3-aminopyrazole, pyrazole-4-carboxylic
acid, 4-bromopyrazole, 4-iodopyrazole, indazole, 5-aminoindazole,
6-aminoindazole, 5-nitroindazole, 6-nitroindazole, etc. More
preferred pyrazoles include pyrazole and 3-aminopyrazole.
[0047] Examples of compounds other than imidazoles, pyrazoles and
indazoles include tetrazoles, thiazoles, benzothiazoles, oxazoles,
benzoxazoles and triazoles. Preferred tetrazoles and derivatives
thereof include tetrazole, 5-aminotetrazole,
5-mercapto-1-methyltetrazole and 5-mercapto-1-phenyltetrazole, etc.
Preferred thiazoles or benzothiazoles and derivatives thereof
include thiazole, 4-methylthiazole, 5-methylthiazole,
4,5-dimethylthiazole, 2,4,5-trimethylthiazole, 2-bromothiazole,
2-aminothiazole, benzothiazole, 2-methylbenzothiazole,
2,5-dimethylbenzothiazole, 2-phenylbenzothiazole,
2-chlorobenzothiazole, 2-hydroxybenzothiazole,
2-aminobenzothiazole, 2-mercaptobenzothiazole and
2-methylthiobenzothiazole, etc. Preferred oxazoles or benzoxazoles
and derivatives thereof include isoxazole, anthranil, benzoxazole,
2-methylbenzoxazole, 2-phenylbenzoxazole, 2-chlorobenzoxazole,
2-benzooxazolinone and 2-mercaptobenzoxazole, etc. Preferred
triazoles and derivatives thereof include
2H-1,2,3-triazole-2-ethanol, N-trimethylsilyl-1,2,4-triazole,
3-amino-5-methyl-1,2,4-triazole,
5,5'-diamino-3,3'-bis-1,2,4-triazole, 4H-1,2,4-triazole-4-propanol,
1,2-dihydroxy-5-(phenylmethyl)-3H-1,2,4-triazole-3-thione,
1,2,4-triazole-1-acetic acid, 1,2,3-triazole, 1,2,4-triazole,
1H-1,2,4-triazole-1-ethanol,
1,5-dimethyl-1H-1,2,3-triazole-4-carboxylic acids,
5-amino-1,2,4-triazole-3-carboxylic acids,
2H-1,2,3-triazole-2-acetic acid, 1,2,4-triazole-3-carboxylic acids,
1-methyl-1,2,4-triazole-3-carboxylate esters,
3-amino-1,2,4-triazole, 4-amino-1,2,4-triazole,
1H-1,2,3-triazole-1-ethanol, 1,2,4-triazole-3-ethylcarboxylates,
3-amino-5-mercapto-1,2,4-triazole,
4-amino-3-hydrazino-5-mercapto-1,2,4-triazole,
4-methyl-3-(methylthio)-5-phenyl-4H-1,2,4-triazole,
3-mercapto-1,2,4-triazole,
1,2-dihydroxy-5-(3-pyridinyl)-3H-1,2,4-triazole-3-thione,
1,2,4-triazole sodium salt, 1H-1,2,3-triazole-1-ethylacetate,
1H-1,2,3-triazole-1-acetic acid, 2H-1,2,3-triazole-1-ethylacetate,
2H-1,2,3-triazole-1-acetic acid,
1-(3-aminopropyl)-1H-1,2,3-triazole dihydrochloride,
3-amino-5-methylmercapto-1,2,4-triazole,
5-methylmercapto-1,2,3-triazole, ethyl-2-(1H-1,2,4-triazole-1-yl)
acetic acid, 5-mercapto-1,2,3-triazole sodium salt,
4-(2-hydroxyethyl)-1,2,4-triazole, 5-methyl-1,2,4-triazole-3-thiol,
1-hydroxybenzotriazole, 5-methyl-1H-benzotriazole, benzotriazole
sodium salt, benzotriazole-5-carboxylic acids,
2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 6H,12H-benzotriazolo
[2,1-a]benzotriazole, 4-methylbenzotriazole,
2(2'-hydroxy-5'-octylphenyl)benzotriazole,
2-(2'-hydroxy-3',5'-di-t-butylphenyl)benzotriazole,
2-(3',5'-di-tert-butyl-2'-hydroxyphenyl)chloro-2H-benzotriazole,
tolyltriazole sodium salt, tolyltriazole potassium salt,
1,2,3-benzotriazole and 2-(2'-hydroxy-5'-methacryloxy
ethylphenyl)-2H-benzotriazole, etc.
[0048] Preferred thiophenes and derivatives thereof include
thiophene, 2-bromothiophene, 2-thiophenenitrile,
3-dodecylthiophene, 4-dibenzothiophene-4-boric acid,
tetrahydrothiophene, benzothiophene-3-boric acid,
tetrahydrothiophene-1,1-dioxide, 2-(acetylamino)thiophene,
2-benzoylthiophene, 3-thiopheneacetonitrile,
2-amino-5-methylthiophene-3-nitrile, 4-methyl-2-thiophenecarboxylic
acids, 2-chloro3-methylthiophene,
3-[(chloroacetyl)amino]-2-thiophenemethylcarboxylates,
3-acetylthiophene, 5-chlorothiophene-2-boric acid,
5-methylthiophene-2-boric acid, 2-thiophenesulfonylchloride,
4-bromo-2-thiophenecarboxylic acids,
3-chloromethyl-2-methylbenzothiophene, 3-formylthiophene-2-boric
acid, 3-formyl-2-thiopheneboric acid,
3-chloro4-methylthiophenemethylcarboxylates, 3-methoxythiophene,
3-aminothiophene, 4-bromothiophene-2-carbaldehyde,
2-thiopheneacetic acid, 5-methyl-2-thiophenecarboxylic acids,
2-amino-3,5-dinitrothiophene, 5-acetyl-2-thiopheneboric acid,
2-thiopheneacetonitrile,
2-(acetylamino)-3-thiophenemethylcarboxylates,
2-thiophenecarboxylic acid hydrazides,
3-methyl-2-thiophenecarboxylic acids,
5-chlorothiophene-2-carboxylic acids,
2,5-dimethyl-3-formylthiophene,
4-bromo-3-methyl-2-thiophenecarbonylchloride,
5-chlorothiophene-2-sulfonylchloride, 2-thiophenemethylamine,
thiophene-2-methylamine, 3-chloro-6-methoxybenzothiophenecarboxylic
acids, 3-methylbenzothiophene-2-carboxylic acids,
2,4-dibromothiophene, 2,3,5-tribromothiophene,
2,5-dibromothiophene, 2,5-dichlorothiophene, 2-iodothiophene,
4-bromo-2-propionylthiophene, 4-bromo-2-propylthiophene,
3-bromo-5-methyl-2-thiophenecarbaldehyde,
2,5-dichloro-3-acetylthiophene,
.alpha.-(phenylmethylene)-2-thiopheneacetonitrile,
thiophene-2-acetylchloride, 3-bromo-2-chlorothiophene,
4-bromo-5-(1,1-dimethylethyl)-2-thiophenecarboxylic acid,
5-acetyl-2-thiophenecarboxylic acids, 2,5-carboxythiophene,
2,5-thiophenedicarboxylic acids, 2,5-bis(methoxycarbonyl)thiophene,
2-formylthiophene-3-boric acid, 3-formyl-4-thiopheneboric acid,
5-bromothiophene-2-carbaldehyde, 2,5-diacetylthiophene,
thiophene-3-carbaldehyde, 3-hydroxy-3-thiophene methylcarboxylates,
thiophene-2-carboxylic acids, 2-thiophenecarbonylchloride,
5-bromo-4-methyl-2-thiophenecarboxylic acids,
2,5-dichlorothiophene-3-sulfonylchloride, 2-thiopheneethylacetate,
thiophene-2-carboxamide, 3-methyl-2-thiophenecarbaldehyde,
3-thiophene methyl acetate, 2-iodomethylthiophene,
4-chlorothiophene-2-carboxylic acid, 2-nitrothiophene,
3-methyl-2-thiophenecarbonylchloride, etc.
[0049] The above-stated compounds may be used preferably in the
range of 0.01 to 50 g/L and more preferably in the range of 0.05 to
10 g/L.
[0050] Any or all of the silver plating bath (A) and the strike
plating bath (B) may further contain a surfactant and/or
surface-active polymer compound. The addition of the surfactant
and/or surface-active polymer compound may improve one or more
properties including throwing power, refinement and uniformity in
grain size, and adhesiveness, etc.
[0051] Preferred surfactants include known cationic surfactants,
anionic surfactants, nonionic surfactants and amphoteric
surfactants, which may be used alone or in combination as
necessary.
[0052] Preferred cationic surfactants include tetra(lower
alkyl)ammonium halides, alkyl trimethylammonium halides,
hydroxyethylalkylimidazolines, polyoxyethylenealkylmethylammonium
halides, alkylbenzalkonium halides, dialkyldimethylammonium
halides, alkyldimethyl benzilammonium halides, alkylamine
hydrochlorides, alkylamine acetates, alkylamine oleates,
alkylaminoethylglycins, alkylpyridinium halides, etc.
[0053] Preferred anionic surfactants include alkyl(or formalin
condensate)-.beta.-naphthalene sulfonic acid(or salt thereof),
fatty acid soaps, alkylsulfonates, .alpha.-olefinsulfonates, alkyl
benzene sulfonates, alkyl(or alkoxy)naphthalenesulfonates,
alkyldiphenylether disulfonates, alkylethersulfonates, alkylsulfate
salts, polyoxyethylenealkylethersulfate salts, polyoxyethylene
alkylphenol ether sulfate salts, higher-alcohol monophosphate
salts, polyoxyalkylene alkylether phosphates,
polyoxyalkylenealkylphenylether phosphates, polyoxyalkylene
phenylether phosphates, polyoxyethylene alkylether acetates,
alkyloyl sarcosines, alkyloyl sarcosinates, alkyloylmethyl alanine
salts, N-acylsulfocarboxylates, alkyl sulfoacetates, acyl methyl
sodium taurate, alkyl fatty acid glycerine sulfates, hardened
coconut oil fatty acid glyceryl sodium sulfates, alkyl
sulfocarboxylates, alkyl sulfosuccinates, dialkyl sulfosuccinates,
alkyl polyoxyethylene sulfosuccinic acids, monooleylamide
sulfosuccinate (sodium salt, ammonium salt, and TEA salt), etc.
[0054] Preferred nonionic surfactants or surface-active polymer
compounds include polyoxyalkylene alkyl ethers(or esters),
polyoxyalkylene phenyl(or alkyl phenyl)ethers, polyoxyalkylene
naphthyl(or alkyl naphthyl)ethers, polyoxyalkylene styrenated
phenyl ethers(or derivatives thereof having a polyoxyalkylene chain
added to the phenyl group), polyoxyalkylene bisphenol ethers,
polyoxyethylene polyoxypropylene block polymers, polyoxyalkylene
sorbitan fatty acid esters, polyoxyalkylene sorbitan fatty acid
esters, polyethylene glycol fatty acid esters, polyoxyalkylene
glycerine fatty acid esters, polyoxyalkylene alkyl amines,
condensation adducts of ethylenediamine and polyoxyalkylene,
polyoxyalkylene fatty acid amides, polyoxyalkylene castor (or/and
hardened castor) oils, polyoxyalkylene alkyl phenyl formalin
condensates, glycerin (or polyglycerin) fatty acid esters,
pentaerythritol fatty acid esters, sorbitan mono-(and sesqui- and
tri-)fatty acid esters, higher fatty acid mono-(and di-)ethanol
amides, alkyl alkylode amides, oxyethylene alkyl amines,
polyalkylene glycols, polyalkylene diamine, polyvinyl pyrrolidone
and polyethylene-imine, etc.
[0055] Preferred amphoteric surfactants include
2-alkyl-N-carboxymethyl (or ethyl)-N-hydroxyethyl(or
methyl)imidazolinium betaines, 2-alkyl-N-carboxymethyl(or
ethyl)-N-carboxymethyloxyethylimidazolinium betaines, dimethyl
alkyl betaines, N-alkyl-.beta.-aminopropionic acids (or salts
thereof), alkyl(poly)aminoethyl glycines,
N-alkyl-N-methyl-.beta.-alanines (or salts thereof), fatty acid
amido propyldimethyl aminoacetic acid betaines, etc.
[0056] The content of these surfactants, which may be chosen as
appropriate, is generally in the range of 0.001 g/L to 50 g/L and
preferably in the range of 0.01 g/L to 50 g/L.
[0057] The acid strike plating bath and the silver plating bath
used in the silver plating method of the invention may contain a
grain refiner, a smoother and a brightener, etc., alone or in
combination, in addition to the above-stated surfactants. The
content thereof is generally in the range of 0.01 to 50 g/L and
preferably in the range of 0.1 to 30 g/L.
[0058] Any or all of the silver plating bath (A) and the strike
plating bath (B) used in the invention may further contain a
displacement deposition prevention agent. Any known displacement
deposition prevention agents may be used. Examples of the agent
include heterocyclic thione compounds, amide or imide compounds,
amino acids, open chain secondary amines having a sulfur atom and a
double bond, cyclic thiol compounds having a sulfur atom with a
double bond, amino or thiol compounds having a pyridine,
pyrimidine, piperidine, piperazine or triazine skelton, etc.
Specific examples of the agent include 3-amino rhodanine,
3-thiourazole, 2-thiouramil, 4-thiouramil,
2,5-dioxo-4-thio-hexahydropyrimidine,
4,6-dioxo-2-thio-hexahydropyrimidine,
2,6-dioxo-4-thio-hexahydropyrimidine, glutamic acid imide,
succinimide, glutamic acid, arginine, valine, diethylthiourea,
dimethylthiourea, thioacetamide, allylthiourea, thiosemicarbazide,
dimercaptothiadiazole, thiosalicylic acid, benzoxazole,
thiobenzamide, 2-aminopyridine, 3-aminopyridine, 4-aminopyridine,
aminopyrimidine, N-aminopyrrolidine, N-aminomethylpyrrolidine,
N-aminoethylpyrrolidine, N-aminopiperidine,
N-aminomethylpiperidine, N-aminoethylpiperidine, N-aminopiperazine,
N-aminomethylpiperazine, N-aminoethylpiperazine, triazinethiol,
etc. The agent may be added as appropriate in the range of 0.001
g/L to 50 g/L.
[0059] The invention may further comprise a displacement deposition
prevention treatment step after the strike plating in case where
the copper strike plating bath (B2) is used for the strike
plating.
[0060] The displacement deposition prevention agents as mentioned
above that may be contained in the silver plating bath (A) and/or
the strike plating bath (B) may be contained in the solution used
for this step.
[0061] According to the invention, an acid degreasing bath may be
preferably used in the degreasing step, which is conducted prior to
the silver or copper strike plating. In the degreasing step, though
it is not limited to using the acid bath and an alkaline bath may
be also used, it is recommendable to use the acid degreasing bath
in the degreasing step if the resist or masking agent used for
patterning has a weak resistance to alkali.
[0062] According to the invention, either or both of the silver
plating bath (A) and the strike plating bath (B) include an
ion-exchange membrane to conduct the silver plating and/or the
silver strike plating with an anode being separated from a cathode.
Though the ion-exchange membrane may be preferably applied to any
of the silver plating bath (A) and the strike plating bath (B), it
may be more preferably applied to the strike plating bath (B).
Furthermore, it may be still more preferably applied to the strike
plating bath that is stabilized by a complexing agent. It can bring
a remarkable effect to the strike plating bath using a phosphine
compound as the complexing agent. Though either of a
cation-exchange membrane or an anion-exchange membrane may be used,
the anion-exchange membrane may be preferably used. By separating
the cathode and the anode with the ion-exchange membrane, the
disintegration of the complexing agent, smoother, and brightener,
etc., added in the plating bath or the strike plating bath may be
prevented. The adverse effect on the plating film of compounds
generated by consumption or disintegration of these additives may
be also prevented. The ion-exchange membrane may also prevent an
increase in silver concentration in the bath when a silver anode is
used, facilitating the control of metal concentration in the
bath.
[0063] By separating the cathode and the anode, accordingly the
cathode chamber and the anode chamber (i.e. catholyte and anolyte),
an insoluble anode may be used. As the insoluble anode, that made
of any known materials such as a carbon anode, a platinum anode, a
platinum-coated titanium anode, a ruthenium oxide-coated electrode
and iridium oxide-coated electrode, etc. may be used. Accordingly,
the silver anode and the insoluble anode as stated above may be
used alone or in combination as the anode.
[0064] The method of silver plating using the acid bath according
to the invention generally comprises the successive steps of, but
not limited to, degreasing, acid activation, strike plating and
silver plating. Water washing is usually conducted between each
step.
[0065] The acid silver strike plating is generally conducted under
the following conditions. The bath temperature is preferably 10 to
50 degrees C. and more preferably 20 to 35 degrees C. The electric
current density is preferably 0.5 to 5 A/dm.sup.2 and more
preferably 2 to 3 A/dm.sup.2. The plating time is preferably 10 to
300 seconds and more preferably 20 to 100 seconds.
[0066] The acid copper strike plating is generally conducted under
the following conditions. The bath temperature is preferably 20 to
40 degrees C. and more preferably 25 to 35 degrees C. The electric
current density is preferably 0.2 to 10 A/dm.sup.2 and more
preferably 1 to 5 A/dm.sup.2. The plating time is preferably 10 to
300 seconds and more preferably 20 to 100 seconds.
[0067] The silver plating is generally conducted under the
following conditions. The bath temperature is preferably 10 to 50
degrees C. and more preferably 15 to 40 degrees C. The electric
current density is preferably 0.1 to 10 A/dm.sup.2 and more
preferably 0.5 to 5 A/dm.sup.2. The plating time changes as
appropriate in accordance with the desired thickness of plating
film.
EXAMPLES
[0068] The invention will be explained in more detail based on the
following Examples. However, it is to be understood that the
invention is not intended to be limited to these examples. The
invention may be variously modified within the scope of the
technical idea of the present invention.
[0069] Each plating process was evaluated from the aspects of both
adhesiveness of plating film and existence of dissolution of
resist. Adhesiveness of plating film was evaluated by a bending
test. In the bending test, each test piece was bent 90 degrees
twice in accordance with JIS-H8504 standards before checking
whether peeling of plating film occurred or not. The dissolution of
resist was checked during or after conducting each plating process
onto a test piece having a simulated pattern formed with a plating
resist. As for the plating resist, developer and resist stripper,
PHOTO FINER PER-2000 series (Taiyo Ink MFG, Co., Ltd) was applied
for the formation of the simulated pattern under the standard
conditions.
[0070] Since the dissolution of resist was observed when employing
a commonly-used alkaline-type degreasing agent, acid CLEANER AC-100
(Daiwa Fine Chemical Co., Ltd.) for general purpose use was used
instead as the degreasing agent so as to evaluate the process.
Comparative Example 1
[0071] Acid degreasing, silver cyanide strike plating, acid silver
plating and drying were applied to a copper substrate in this
order. Washing was conducted between each step. The composition of
the treatment bath used in each step is as follows.
TABLE-US-00001 Silver cyanide strike plating silver cyanide(as
silver) 3.6 g/L potassium cyanide 80 g/L temperature 25 degrees C.
electric current density 2 A/dm.sup.2 plating time 60 sec
TABLE-US-00002 Silver plating bath silver methanesulfonate (as
silver) 30 g/L methanesulfonic acid 80 g/L 3-amino-1,2,4-triazole 5
g/L 1,2,4-triazole 3 g/L 2-mercaptobenzimidazole 0.1 g/L
temperature 25 degrees C. electric current density 1 A/dm.sup.2
plating time 5 min
[0072] In the test piece having a simulated pattern, resist
dissolution was observed during the silver cyanide strike
plating.
[0073] In case where washing was conducted extremely cautiously and
carefully between the silver cyanide striking plating and the acid
silver plating, neither cracking nor peeling of the plating film
was observed in the bending test, showing a good flexibility and
adhesiveness. However, in case where the washing was conducted in a
common way with water, peeling of the plating film was
observed.
Comparative Example 2
[0074] Acid degreasing, alkaline pyrophosphate copper strike
plating, displacement prevention treatment, 5% methanesulfonic acid
dipping, acid silver plating, and drying were applied to a 42 alloy
substrate in this order. Washing was conducted between each step.
The composition of the treatment bath used in each step is as
follows.
TABLE-US-00003 Alkaline copper pyrophosphate strike plating bath
copper pyrophosphate (as copper) 25 g/L pyrophosphoric acid 200 g/L
ammonium nitrate 7 g/L temperature 55 degrees C. electric current
density 4 A/dm.sup.2 plating time 60 sec
TABLE-US-00004 Silver plating bath silver methanesulfonate (as
silver) 30 g/L methanesulfonic acid 80 g/L 3-amino-1,2,4-triazole 5
g/L 1,2,4-triazole 3 g/L 2-mercaptobenzimidazole 0.1 g/L
temperature 25 degrees C. electric current density 1 A/dm.sup.2
plating time 5 min
[0075] In the test piece having a simulated pattern, resist
dissolution was observed during the alkaline copper strike plating.
Exfoliation of the plating film was observed in the bending
test.
Example 1
[0076] Acid degreasing, acid silver strike plating, acid silver
plating and drying were applied to a copper substrate in this
order. Washing was conducted between each step. The composition of
the treatment bath used in each step is as follows.
TABLE-US-00005 Silver strike plating bath silver methanesulfonate
(as silver) 3 g/L tris(3-hydroxypropyl)phosphine 15 g/L
methanesulfonic acid 40 g/L temperature 25 degrees C. electric
current density 2.5 A/dm.sup.2 plating time 60 sec
TABLE-US-00006 Silver plating bath silver methanesulfonate (as
silver) 30 g/L methanesulfonic acid 80 g/L 3-amino-1,2,4-triazole 5
g/L 1,2,4-triazole 3 g/L 2-mercaptobenzimidazole 0.1 g/L
temperature 25 degrees C. electric current density 1 A/dm.sup.2
plating time 5 min
[0077] Neither cracking nor peeling of the plating film was
observed in the bending test, showing a good flexibility and
adhesiveness. No sign of resist dissolution and peeling was
observed in the test piece having a simulated pattern.
Example 2
[0078] Acid degreasing, acid activation, silver strike plating,
silver plating and drying were applied to a copper substrate in
this order. Washing was conducted between each step. The
composition of the treatment bath used in each step is as follows.
In Example 2, the anode and the cathode were separated by an
anionic exchange membrane in the silver strike plating bath.
Iridium oxide was used as the anode. 5% methanesulfonic acid
solution was used as anolyte.
TABLE-US-00007 Silver strike plating bath silver methanesulfonate
(as silver) 3 g/L tris(3-hydroxypropyl)phosphine 15 g/L
methanesulfonic acid 40 g/L temperature 25 degrees C. electric
current density 2.5 A/dm.sup.2 plating time 60 sec
TABLE-US-00008 Silver plating bath silver methanesulfonate (as
silver) 30 g/L methanesulfonic acid 80 g/L polyvinyl pyrrolidone 1
g/L 2-(2'-hydroxy-5'-methylphenyl) 0.1 g/L benzotriazole
2-aminothiazole 0.5 g/L temperature 25 degrees C. electric current
density 1 A/dm.sup.2 plating time 5 min
[0079] Neither cracking nor peeling of the plating film was
observed in the bending test, showing a good flexibility and
adhesiveness. No sign of resist dissolution and peeling was
observed in the test piece having a simulated pattern. In case
where the ionic exchange membrane was not used, 10% or more of the
complexing agent for silver, tris(3-hydroxypropyl)phosphine, added
to the silver strike plating bath was consumed by the electrolysis
at 5 AHr/L. On the other hand, in case where the ionic exchange
membrane was used, only about 1% of the complexing agent was
consumed.
Example 3
[0080] Acid degreasing, silver strike plating, silver plating and
drying were applied to a 42 alloy substrate in this order. Washing
was conducted between each step. The composition of the treatment
bath used in each step is as follows.
TABLE-US-00009 Silver strike plating bath silver isethionate (as
silver) 3 g/L tris(3-hydroxypropyl)phosphine 15 g/L isethionic acid
40 g/L temperature 25 degrees C. electric current density 2.5
A/dm.sup.2 plating time 60 sec
TABLE-US-00010 Silver plating bath silver isethionate (as silver)
30 g/L isethionic acid 80 g/L polyethylene-imine 0.1 g/L 3-amino
pyrazole 1 g/L 5-amino-1,2,4-triazole-3-carboxylic acid 0.05 g/L
temperature 25 degrees C. electric current density 1 A/dm.sup.2
plating time 5 min
[0081] Neither cracking nor peeling of the plating film was
observed in the bending test, showing a good flexibility and
adhesiveness. No sign of resist dissolution and peeling was
observed in the test piece having a simulated pattern.
Example 4
[0082] Acid degreasing, silver strike plating, silver plating and
drying were applied to a 42 alloy substrate in this order. Washing
was conducted between each step. The silver plating bath contained
displacement prevention agent. The composition of the treatment
bath used in each step is as follows.
TABLE-US-00011 Silver strike plating bath silver methanesulfonate
(as silver) 3 g/L tris(3-hydroxypropyl)phosphine 15 g/L
methanesulfonic acid 40 g/L 3-amino rhodanine 0.05 g/L temperature
25 degrees C. electric current density 2.5 A/dm.sup.2 plating time
60 sec
TABLE-US-00012 Silver plating bath silver methanesulfonate (as
silver) 30 g/L methanesulfonic acid 80 g/L alkylamineoxide-based
surfactant 0.1 g/L thiophene-2-carboxylic acid 0.5 g/L temperature
25 degrees C. electric current density 1 A/dm.sup.2 plating time 5
min
[0083] Neither cracking nor peeling of the plating film was
observed in the bending test, showing a good flexibility and
adhesiveness. No sign of resist dissolution and peeling was
observed in the test piece having a simulated pattern.
Example 5
[0084] Acid degreasing, copper strike plating, displacement
prevention treatment, acid dipping, silver plating and drying were
applied to a 42 alloy substrate in this order. Washing was
conducted between each step. The composition of the treatment bath
used in each step is as follows.
TABLE-US-00013 Copper strike plating bath copper methanesulfonate
(as copper) 10 g/L tris(3-hydroxypropyl)phosphine 15 g/L
methanesulfonic acid 10 g/L sulfuric acid 50 g/L temperature 50
degrees C. electric current density 5 A/dm.sup.2 plating time 10
sec
TABLE-US-00014 Displacement prevention treatment bath dipotassium
hydrogenphosphate 5 g/L 2-mercaptobenzimidazole 0.03 g/L amino
piperazine 1 ml/L temperature 20 degrees C. dipping time 10 sec
TABLE-US-00015 Acid dipping Methansulfonic acid 50 g/L
TABLE-US-00016 Silver plating bath silver methanesulfonate (as
silver) 30 g/L methanesulfonic acid 80 g/L
tris(3-hydroxypropyl)phosphine 150 g/L 1,2,4-triazole 4 g/L
2-mercapto-benzothiazole 0.05 g/L 4-amino-1,2,4-triazole 3 g/L
temperature 25 degrees C. electric current density 1 A/dm.sup.2
plating time 5 min
[0085] Neither cracking nor peeling of the plating film was
observed in the bending test, showing a good flexibility and
adhesiveness. No sign of resist dissolution and peeling was
observed in the test piece having a simulated pattern.
Example 6
[0086] Acid degreasing, copper strike plating, silver strike
plating, silver plating and drying were applied to a 42 alloy
substrate in this order. Washing was conducted between each step.
The composition of the treatment bath used in each step is as
follows.
TABLE-US-00017 Copper strike plating bath copper methanesulfonate
(as copper) 10 g/L tris(3-hydroxypropyl)phosphine 15 g/L
methanesulfonic acid 10 g/L sulfuric acid 50 g/L temperature 50
degrees C. electric current density 5 A/dm.sup.2 plating time 10
sec
TABLE-US-00018 Silver strike plating bath silver methanesulfonate
(as silver) 3 g/L tris(3-hydroxypropyl)phosphine 15 g/L
methanesulfonic acid 40 g/L aminopiperazine 1 ml/L temperature 25
degrees C. electric current density 2.5 A/dm.sup.2 plating time 60
sec
TABLE-US-00019 Silver plating bath silver methanesulfonate (as
silver) 30 g/L methanesulfonic acid 80 g/L
3-mercapto-1,2,4-triazole 10 g/L 1,2,4-triazole 1 g/L
2-mercapto-benzothiazole 0.05 g/L temperature 25 degrees C.
electric current density 1 A/dm.sup.2 plating time 5 min
[0087] Neither cracking nor peeling of the plating film was
observed in the bending test, showing a good flexibility and
adhesiveness. No sign of resist dissolution and peeling was
observed in the test piece having a simulated pattern.
* * * * *