U.S. patent application number 14/552478 was filed with the patent office on 2016-05-26 for formaldehyde-free electroless metal plating compositions and methods.
The applicant listed for this patent is Rohm and Haas Electronic Materials LLC. Invention is credited to Crystal P. L. LI, Zhixiong LIANG, Weigang WU.
Application Number | 20160145745 14/552478 |
Document ID | / |
Family ID | 54834611 |
Filed Date | 2016-05-26 |
United States Patent
Application |
20160145745 |
Kind Code |
A1 |
WU; Weigang ; et
al. |
May 26, 2016 |
FORMALDEHYDE-FREE ELECTROLESS METAL PLATING COMPOSITIONS AND
METHODS
Abstract
Formaldehyde-free electroless metal plating solutions include
glyoxylic acid or salts thereof in combination with tertiary amines
which stabilize the glyoxylic acid and salts. The electroless metal
plating solutions are environmentally friendly, stable and deposit
bright metal deposits on substrates.
Inventors: |
WU; Weigang; (Fanling,
HK) ; LI; Crystal P. L.; (Tin Shui Wai, HK) ;
LIANG; Zhixiong; (Fanling, N.T., HK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rohm and Haas Electronic Materials LLC |
Marlborough |
MA |
US |
|
|
Family ID: |
54834611 |
Appl. No.: |
14/552478 |
Filed: |
November 24, 2014 |
Current U.S.
Class: |
427/443.1 ;
106/1.05; 106/1.25; 106/1.26; 106/1.27 |
Current CPC
Class: |
C23C 18/34 20130101;
C23C 18/40 20130101; C23C 18/31 20130101; C23C 30/00 20130101; C23C
18/1893 20130101; C23C 18/52 20130101; C23C 18/48 20130101; H05K
3/187 20130101; C23C 18/50 20130101; C23C 18/44 20130101 |
International
Class: |
C23C 18/31 20060101
C23C018/31; C23C 18/44 20060101 C23C018/44; C23C 18/34 20060101
C23C018/34; C23C 30/00 20060101 C23C030/00; C23C 18/40 20060101
C23C018/40 |
Claims
1. A composition comprising one or more sources of metal ions, one
or more sources of glyoxylic acid, salts or mixtures thereof and
one or more tertiary amine compounds, salts, halides or mixtures
thereof having a formula: ##STR00013## wherein R.sub.1, R.sub.2 and
R.sub.3 may be the same or different and are linear or branched,
substituted or unsubstituted hydroxy(C.sub.1-C.sub.10)alkyl, linear
or branched, substituted or unsubstituted
carboxy(C.sub.1-C.sub.10)alkyl, linear or branched, substituted or
unsubstituted (C.sub.1-C.sub.10)alkylamine, linear or branched,
substituted or unsubstituted (C.sub.1-C.sub.10)alkyl phosphonic
acid, a moiety having a formula: ##STR00014## wherein R.sub.4 and
R.sub.5 may be the same or different and are linear or branched,
substituted or unsubstituted hydroxy(C.sub.1-C.sub.10)alkyl, linear
or branched, substituted or unsubstituted
carboxy(C.sub.1-C.sub.10)alkyl, linear or branched, substituted or
unsubstituted (C.sub.1-C.sub.10)alkylamine, linear or branched,
substituted or unsubstituted (C.sub.1-C.sub.10)alkyl phosphonic
acid, or moiety
--(CH.sub.2).sub.a--N--((CH.sub.2).sub.b).sub.2--(P(O)(OH).sub.2)
(IIa) where a and b may be the same or different and are integers
of 1 to 6, m is an integer from 1 to 6, B is a moiety having a
formula: ##STR00015## wherein R.sub.6 and R.sub.7 may be the same
or different and are hydrogen, hydroxyl, carboxyl,
hydroxy(C.sub.1-C.sub.3)alkyl, carboxy(C.sub.1-C.sub.3)alkyl,
(C.sub.1-C.sub.3)alkyl, or B may be a substituted or unsubstituted
(C.sub.5-C.sub.6)cycloalkyl ring and m=1, A is a chemical bond with
the nitrogen of formula (I) or a moiety having a formula:
##STR00016## wherein R.sub.8, R.sub.9, R.sub.10 and R.sub.11 are
the same or different and are hydrogen, hydroxyl,
(C.sub.1-C.sub.3)alkyl, n, p, q may be the same or different and
are integers of 1 to 6, with the proviso that when any two of
R.sub.1, R.sub.2 and R.sub.3 are carboxymethyl moieties or salts
thereof the third cannot be formula (II) where A is a chemical
bond, m is 2, R.sub.6 and R.sub.7 are hydrogen and R.sub.4 and
R.sub.5 are carboxymethyl moieties or salts thereof; and a molar
ratio of the one or more tertiary amine compounds to the glyoxylic
acid or salts thereof is 0.05:1 to 15:1, the compositions are
formaldehyde-free.
2. The composition of claim 1, wherein the one or more sources of
glyoxylic acid is chosen from non-dissociated glyoxylic acid,
dihydroxy acetic acid, a dihaloacetic acid and the bisulphite
adduct of glyoxylic acid.
3. The composition of claim 1, wherein the salts of glyoxylic acid
are chosen from alkali metal salts and ammonium salt of glyoxylic
acid.
4. The composition of claim 1, wherein the one or more tertiary
amines are chosen from triethanolamine,
2-[bis(2-hydroxyethyl)amino]acetic acid and its salts,
N-(2-hydroxyethyl)iminodiacetic acid and its salts,
nitrilotriacetic acid, nitrilo(3-propionic)diacetic acid and its
salts, nitrilotripropionic acid and its salts,
N,N-bis(2-hydroxypropyl)ethanolamine,
1-[bis(2-hydroxyethyl)amino]-2-propanol,
2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)-1,3-propanediol,
N,N-Bis(carboxymethyl)-DL-alanine and its salts,
triisopropanolamine, L-glutamic acid N,N'-diacetic acid and its
salts, N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine,
N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine,
1,3-Diamino-2-hydroxypropane-N,N,N',N'-tetraacetic acid and its
salts, ethylenediaminetetrapropionic acid and its salts,
propylenediaminetetraacetic acid and its salts,
N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid and its
salts, diethylenetriamine pentaacetic acid and its salts,
triethylenetetramine-N,N,N',N'',N''',N'''-hexaacetic acid and its
salts, methyl diethanolamine, methyliminodiacetic acid and its
salts, tris(carboxymethyl)ethylenediamine,
1,2-diaminocyclohexanetetraacetic acid and its salts,
N-(2-aminoethyl)-trans-1,2-diaminocyclohexane-N,N,N-pentaacetic
acid and its salts, ethylene glycol tetraacetic acid and its salts,
diethylene triamine pentamethylene phosphonic acid and its salts,
(ethylenedinitrilo)-tetramethylenephosphonic acid and its salts,
(nitrilotrimethylene)triphosphonic acid and its salts.
5. The composition of claim 1, wherein metal ions are chosen from
copper ions, tin ions, nickel ions, silver ions, gold ions and
mixtures thereof.
6. The composition of claim 1, further comprising accelerators,
uniformity enhancers, stabilizers, grain-refiners, complexing
agents, chelating agents, additional reducing agents, pH adjusting
agents, antioxidants and surfactants.
7. A method comprising: a) providing a substrate; b) applying the
composition of claim 1 to the substrate; and c) electroless plating
metal on the substrate.
8. The method of claim 7, wherein the substrate comprises a
plurality of through-holes and further comprising: d) desmearing
the through-holes; and e) plating metal on walls of the
through-holes.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to environmentally
friendly, formaldehyde-free electroless metal plating compositions
and methods containing glyoxylic acid and salts thereof and
tertiary amines. More specifically, the present invention is
directed to environmentally friendly, formaldehyde-free electroless
metal plating compositions and methods containing glyoxylic acid
and salts thereof and tertiary amines to inhibit decomposition of
the glyoxylic acid and salts thereof.
BACKGROUND OF THE INVENTION
[0002] Electroless metal plating compositions such as electroless
copper plating compositions are in widespread use in metallization
industries for depositing copper and other metals on various types
of substrates. In the manufacture of printed wiring boards, for
example, the electroless copper baths are used to deposit copper
into through-holes and circuit paths as a base for subsequent
electrolytic copper plating. Electroless copper and other
electroless metal plating compositions also are used in the
decorative plastics industry for deposition of metals onto
non-conductive surfaces as a base for further plating of copper,
nickel, gold, silver and other metals as required. Typical
electroless copper plating baths which are in commercial use today
contain divalent copper compounds, chelating agents or complexing
agents for the divalent copper ions, formaldehyde reducing agents
and various addition agents to make the bath more stable, adjust
the plating rate and brighten the copper deposit. Although many of
such baths are successful and are widely used, the metallization
industry has been searching for alternative electroless copper
plating baths that do not contain formaldehyde due to its toxic
nature.
[0003] Formaldehyde is known as an eye, nose and upper respiratory
tract irritant. Animal studies have shown that formaldehyde is an
in vitro mutagen. According to a WATCH committee report
(WATCH/2005/06--Working group on Action to Control Chemicals--sub
committee with UK Health and Safety Commission) over fifty
epidemiological studies have been conducted prior to 2000 suggested
a link between formaldehyde and nasopharyngeal/nasal cancer but
were not conclusive. However, more recent studies conducted by IARC
(International Agency for Research on Cancer) in the U.S.A. showed
that there was sufficient epidemiological evidence that
formaldehyde causes nasopharyngeal cancer in humans. As a result
the INRS, a French agency, has submitted a proposal to the European
Community Classification and Labelling Work Group to reclassify
formaldehyde from a category 3 to a category 1 carcinogen. This
would make usage and handling of it more restricted, including in
electroless copper formulations. Accordingly, there is a need in
the metallization industry for a comparable or improved reducing
agent to replace formaldehyde. Such a reducing agent must be
compatible with existing electroless copper processes; provide
desired capability and reliability and meet cost targets.
[0004] To address the problems of formaldehyde, researchers have
attempted to use glyoxylic acid or its salts as a formaldehyde
replacement; however, glyoxylic acid and its salts have a high
decomposition rate which compromises its performance as an
acceptable substitute for formaldehyde. One of the most likely
decomposition pathways is the Cannizzaro reaction:
2CHOCOO.sup.-+OH.sup.-.fwdarw.C.sub.2O.sub.4.sup.2-+HOCH.sub.2COO.sup.-
[0005] Similar to formaldehyde, glyoxylic acid disproportionates to
form oxalate and glycolate under strong basic conditions. The
Cannizzaro effect of glyoxylic acid is more serious than that of
formaldehyde. Thus it can be seen that glyoxylic acid concentration
drops sharply in the bath solution, and results in termination of
electroless copper plating unless replenished with more of the
reducing agent. Accordingly, the operating cost is very high.
Examples of attempts to arrest the decompositions of glyoxylic acid
via the Cannizzaro reaction are disclosed in U.S. 2003/0054094 to
Itabashi et al. and U.S. 2003/0183120 also to Itabashi et al. U.S.
2003/0054094 alleges that Cannizzaro reaction may be inhibited by
including certain molar amounts of methanol, primary amines,
secondary amines, metasilicic acid and its salts, phosphoric acid
and its salts, germanium dioxide, vanadic acid and its salts in the
electroless copper plating solution. U.S. 2003/0183120 alleges that
including succinic acid in the electroless copper plating solution
may inhibit the Cannizzaro reaction.
[0006] Although there are methods which may inhibit the Cannizzaro
reaction and inhibit the decomposition of glyoxylic acid in
electroless metal plating solutions, there is still a need to
provide an electroless metal plating solution which prevents or
reduces the decomposition of glyoxylic acid, is environmentally
friendly and provides uniform, bright metal deposits on
substrates.
SUMMARY OF THE INVENTION
[0007] Compositions include one or more sources of metal ions, one
or more sources of glyoxylic acid, salts or mixtures thereof and
one or more tertiary amine compounds, salts or halides thereof
having a formula:
##STR00001##
where R.sub.1, R.sub.2 and R.sub.3 may be the same or different and
are linear or branched, substituted or unsubstituted
hydroxy(C.sub.1-C.sub.10)alkyl, linear or branched, substituted or
unsubstituted carboxy(C.sub.1-C.sub.10)alkyl, linear or branched,
substituted or unsubstituted (C.sub.1-C.sub.10)alkylamine, linear
or branched, substituted or unsubstituted (C.sub.1-C.sub.10)alkyl
phosphonic acid or a moiety having a formula:
##STR00002##
where R.sub.4 and R.sub.5 may be the same or different and are
linear or branched, substituted or unsubstituted
hydroxy(C.sub.1-C.sub.10)alkyl, linear or branched, substituted or
unsubstituted carboxy(C.sub.1-C.sub.10)alkyl, linear or branched,
substituted or unsubstituted (C.sub.1-C.sub.10)alkylamine, linear
or branched, substituted or unsubstituted (C.sub.1-C.sub.10)alkyl
phosphonic acid, or moiety
--(CH.sub.2).sub.a--N--((CH.sub.2).sub.b).sub.2--(P(O)(OH).sub.2)
(IIa) where a and b may be the same or different and are integers
of 1 to 6, m is an integer from 1 to 6, B is a moiety having a
formula:
##STR00003##
where R.sub.6 and R.sub.7 may be the same or different and are
hydrogen, hydroxyl, carboxyl, hydroxy(C.sub.1-C.sub.3)alkyl,
carboxy(C.sub.1-C.sub.3)alkyl, (C.sub.1-C.sub.3)alkyl, or B may be
a substituted or unsubstituted (C.sub.5-C.sub.6)cycloalkyl ring and
m=1, A is a chemical bond with the nitrogen of formula (I) or a
moiety having a formula:
##STR00004##
wherein R.sub.8, R.sub.9, R.sub.10 and R.sub.11 are the same or
different and are hydrogen, hydroxyl or (C.sub.1-C.sub.3)alkyl, n,
p, q may be the same or different and are integers of 1 to 6, with
the proviso that when any two of R.sub.1, R.sub.2 and R.sub.3 are
carboxymethyl moieties or salts thereof the third cannot be formula
(II) where A is a chemical bond, B is formula (IIb), m is 2,
R.sub.6 and R.sub.7 are hydrogen and R.sub.4 and R.sub.5 are
carboxymethyl moieties or salts thereof; and a molar ratio of the
one or more tertiary amine compounds to the glyoxylic acid or salts
thereof is 0.05:1 to 15:1, the compositions are
formaldehyde-free.
[0008] Methods include providing a substrate and applying the
composition including the one or more sources of metal ions,
glyoxylic acid, salts or mixtures thereof and one or more of the
tertiary amines, salts, halides or mixtures thereof to the
substrate; and electroless plating copper on the substrate.
[0009] The combination of the one or more tertiary amines and
glyoxylic acid, salts or mixtures thereof provide a stable
electroless metal plating composition which is formaldehyde-free
and environmentally friendly. The tertiary amines inhibit the
decomposition of glyoxylic acids and its salts, thus prolonging the
life of the plating composition and reducing the cost of the
operation of the plating composition as replacement with glyoxylic
acid or its salts is reduced or eliminated. The combination of the
one or more tertiary amines, salts, halides or mixtures thereof and
the glyoxylic acid, salts or mixtures thereof at the molar ratios
provides for a more efficient electroless metal plating process
than many conventional electroless metal compositions and plating
processes. In addition, the plating compositions may provide for
substantially uniform, bright metal deposits on substrates and
reduced skip plating.
BRIEF DESCRIPTION OF THE DRAWING
[0010] FIGURE illustrates the European Backlight Reference Plates
for determining metal plating coverage performance of through-holes
of printed circuit boards for electroless copper plating.
DETAILED DESCRIPTION OF THE INVENTION
[0011] As used throughout this specification, the abbreviations
given below have the following meanings, unless the context clearly
indicates otherwise: g=gram; mg=milligram; mL=milliliter; L=liter;
cm=centimeter; m=meter; mm=millimeter; .mu.m=micron; ppm=parts per
million; .degree. C.=degrees Centigrade; M=molar; g/L=grams per
liter; v=volume; wt %=percent by weight; RO=reverse osmosis;
DI=deionized; T.sub.g=glass transition temperature;
EDTA=ethylenediaminetetraacetic acid; K=potassium; Na=sodium;
Fe=iron; and CN=cyanide.
[0012] The terms "printed circuit board" and "printed wiring board"
are synonymous. The terms "plating" and "deposition" are used
interchangeably throughout this specification. The term "moiety"
means a part of a molecule or polymer that may include either whole
functional groups or parts of functional groups as substructures.
The term "halide" means chloride, bromide, fluoride or iodide. All
amounts are percent by weight, unless otherwise noted. All
numerical ranges are inclusive and combinable in any order except
where it is logical that such numerical ranges are constrained to
add up to 100%.
[0013] Aqueous based electroless metal plating compositions include
one or more sources of metal ions, glyoxylic acid, salts of
glyoxylic acid or mixtures thereof as reducing agents for the metal
ions and one or more tertiary amine compounds, salts and halides
thereof having a formula:
##STR00005##
where R.sub.1, R.sub.2 and R.sub.3 may be the same or different and
are linear or branched, substituted or unsubstituted
hydroxy(C.sub.1-C.sub.10)alkyl, linear or branched, substituted or
unsubstituted carboxy(C.sub.1-C.sub.10)alkyl, linear or branched,
substituted or unsubstituted (C.sub.1-C.sub.10)alkylamine, linear
or branched, substituted or unsubstituted (C.sub.1-C.sub.10)alkyl
phosphonic acid or a moiety having a formula:
##STR00006##
where R.sub.4 and R.sub.5 may be the same or different and are
linear or branched, substituted or unsubstituted
hydroxy(C.sub.1-C.sub.10)alkyl, linear or branched, substituted or
unsubstituted carboxy(C.sub.1-C.sub.10)alkyl, linear or branched,
substituted or unsubstituted (C.sub.1-C.sub.10)alkylamine, linear
or branched, substituted or unsubstituted (C.sub.1-C.sub.10)alkyl
phosphonic acid, or moiety
--(CH.sub.2).sub.a--N--((CH.sub.2).sub.b).sub.2--(P(O)(OH).sub.2)
(IIa) where a and b may be the same or different and are integers
of 1 to 6, m is an integer from 1 to 6, B is a moiety having
formula:
##STR00007##
R.sub.6 and R.sub.7 may be the same or different and are hydrogen,
hydroxyl, carboxyl, hydroxy(C.sub.1-C.sub.3)alkyl,
carboxy(C.sub.1-C.sub.3)alkyl, (C.sub.1-C.sub.3)alkyl, or B may be
a substituted or unsubstituted (C.sub.5-C.sub.6)cycloalkyl ring and
m=1, A is a chemical bond with the nitrogen of formula (I) or a
moiety having a formula:
##STR00008##
wherein R.sub.8, R.sub.9, R.sub.10 and R.sub.11 are the same or
different and are hydrogen, hydroxyl or (C.sub.1-C.sub.3)alkyl, n,
p and q may be the same or different and are integers of 1 to 6,
with the proviso that when any two of R.sub.1, R.sub.2 and R.sub.3
are carboxymethyl moieties or salts thereof the third cannot be
formula (II) where A is a chemical bond, B is formula (IIb), m is
2, R.sub.6 and R.sub.7 are hydrogen and R.sub.4 and R.sub.5 are
carboxymethyl moieties or salts thereof; and a molar ratio of the
one or more tertiary amine compounds to the glyoxylic acid or salts
thereof is 0.05:1 to 15:1.
[0014] Preferably R.sub.1, R.sub.2 and R.sub.3 may be the same or
different and are linear or branched, substituted or unsubstituted
hydroxy(C.sub.1-C.sub.6)alkyl, linear or branched, substituted or
unsubstituted carboxy(C.sub.1-C.sub.6)alkyl, linear or branched,
substituted or unsubstituted (C.sub.1-C.sub.6)alkylamine, linear or
branched, substituted or unsubstituted (C.sub.1-C.sub.6)alkyl
phosphonic acid or a moiety having a formula:
##STR00009##
where R.sub.4 and R.sub.5 may be the same or different and are
linear or branched, substituted or unsubstituted
hydroxy(C.sub.1-C.sub.6)alkyl, linear or branched, substituted or
unsubstituted carboxy(C.sub.1-C.sub.6)alkyl, linear or branched,
substituted or unsubstituted (C.sub.1-C.sub.6)alkylamine, linear or
branched, substituted or unsubstituted (C.sub.1-C.sub.6)alkyl
phosphonic acid, or moiety
--(CH.sub.2).sub.a--N--((CH.sub.2).sub.b).sub.2--P(O)(OH).sub.2)
(IIa) where a and b may be the same or different and are integers
of 1 to 3, m is an integer from 1 to 3, R.sub.6 and R.sub.7 may be
the same or different and are hydrogen, hydroxyl, carboxyl,
hydroxy(C.sub.1-C.sub.2)alkyl, carboxy(C.sub.1-C.sub.2)alkyl,
(C.sub.1-C.sub.2)alkyl, A is a chemical bond with the nitrogen of
formula (I) or a moiety having a formula:
##STR00010##
wherein R.sub.8, R.sub.9, R.sub.10 and R.sub.11 are the same or
different and are hydrogen, hydroxyl or (C.sub.1-C.sub.2)alkyl, n,
p, q may be the same or different and are integers of 1 to 3.
[0015] More preferably, R.sub.1, R.sub.2 and R.sub.3 may be the
same or different and are linear or branched, substituted or
unsubstituted hydroxy(C.sub.1-C.sub.4)alkyl, linear or branched,
substituted or unsubstituted carboxy(C.sub.1-C.sub.4)alkyl, linear
or branched, substituted or unsubstituted
(C.sub.1-C.sub.4)alkylamine, linear or branched, substituted or
unsubstituted (C.sub.1-C.sub.4)alkyl phosphonic acid or a moiety
having a formula:
##STR00011##
where R.sub.4 and R.sub.5 may be the same or different and are
hydroxy(C.sub.1-C.sub.3)alkyl, carboxy(C.sub.1-C.sub.3)alkyl, m is
an integer from 2 to 3, R.sub.6 and R.sub.7 may be the same or
different and are hydrogen, hydroxyl, carboxyl,
(C.sub.1-C.sub.2)alkyl, and A is a chemical bond with the nitrogen
of formula (I).
[0016] Salts of the foregoing tertiary amine compounds include, but
are not limited to alkali metal salts, such as potassium, sodium
and lithium salts and ammonium salts. Preferably the salts are
alkali metal salts such as potassium and sodium, more preferably
the salt is sodium.
[0017] Halides are Cl.sup.-, F.sup.-, Br.sup.- and I.sup.-. Sources
of halides include, but are not limited to hydrogen chloride,
hydrogen bromide, hydrogen fluoride and hydrogen iodide. Preferably
the source of halides is hydrogen chloride.
[0018] Substituent groups include, but are not limited to hydroxyl,
linear or branched hydroxy(C.sub.1-C.sub.4)alkyl, carboxyl, linear
or branched carboxy(C.sub.1-C.sub.4)alkyl, linear or branched
(C.sub.1-C.sub.4)alkyl or an amine moiety having formula:
##STR00012##
where R.sub.12 and R.sub.13 may be the same or different and are
hydrogen or linear or branched (C.sub.1-C.sub.4)alkyl,
hydroxy(C.sub.1-C.sub.3)alkyl, carboxy(C.sub.1-C.sub.3)alkyl and d
is an integer of 1 to 3. Preferably substituent groups are
hydroxyl, carboxyl or (C.sub.1-C.sub.3)alkyl.
[0019] Examples of the foregoing tertiary amines are
triethanolamine, 2-[bis(2-hydroxyethyl)amino]acetic acid and its
salts, N-(2-hydroxyethyl)iminodiacetic acid and its salts,
nitrilotriacetic acid, nitrile(3-propionic)diacetic acid and its
salts, nitriltripropionic acid and its salts,
N,N-bis(2-hydroxypropyl)ethanolamine,
1-[bis(2-hydroxyethyl)amino]-2-propanol,
2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)-1,3-propanediol,
N,N-Bis(carboxymethyl)-DL-alanine and its salts,
triisopropanolamine, L-glutamic acid N,N'-diacetic acid and its
salts, N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine,
N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine,
1,3-Diamino-2-hydroxypropane-N,N,N',N'-tetraacetic acid and its
salts, ethylenediaminetetrapropionic acid and its salts,
propylenediaminetetraacetic acid and its salts,
N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid and its
salts, diethylenetriamine pentaacetic acid and its salts,
triethylenetetramine-N,N,N',N'',N''',N'''-hexaacetic acid and its
salts, methyl diethanolamine, methyliminodiacetic acid and its
salts, tris(carboxymethyl)ethylenediamine,
1,2-diaminocyclohexanetetraacetic acid and its salts,
N-(2-aminoethyl)-trans-1,2-diaminocyclohexane-N,N,N-pentaacetic
acid and its salts, ethylene glycol tetraacetic acid and its salts,
diethylene triamine pentamethylene phosphonic acid and its salts,
(ethylenedinitrilo)-tetramethylenephosphonic acid and its salts,
(nitrilotrimethylene)triphosphonic acid and its salts.
[0020] The electroless plating compositions are formaldehyde-free,
thus enabling environmentally friendly electroless metal plating
compositions. The tertiary amines suppress unwanted decomposition
of glyoxylic acid and its salts to provide a more efficient and
reliable electroless plating composition. The compositions are also
free of ethylenediamine tetraacetic acid and its salts.
[0021] Sources of glyoxylic acid include non-dissociated glyoxylic
acid, salts of glyoxylic acid such as alkali metal salts of
glyoxylic acid, such as sodium and potassium salts, and those
reducing agents that can provide glyoxylate ions in an alkaline
solution such as dihydroxy acetic acid, a dihaloacetic acid and the
bisulphite adduct of glyoxylic acid. Preferably the source of the
reducing agent is glyoxylic acid. The concentration range may be
from 0.1 g/L to 100 g/L, preferably from 1 g/L to 50 g/L.
[0022] The amount of the tertiary amine included in the electroless
compositions is based on a molar ratio of tertiary amine to
glyoxylic acid. The molar ratio of the tertiary amine suppressor to
glyoxylic acid in the electroless composition is in a range of
0.05:1 to 15:1. When the molar ratio is lower than 0.05:1, the
suppressor does not effectively suppress glyoxylic acid
decomposition. When the molar ratio is greater than 15:1, the
suppressor substantially hinders plating performance. Preferably
the molar ratio of tertiary amine to glyoxylic acid is 0.2:1 to
10:1, more preferably 0.4:1 to 10:1.
[0023] Metals which may be plated include, but are not limited to
copper, gold, silver, nickel and tin. Preferably the metals are
copper, tin and nickel, more preferably the metals are copper and
nickel. Most preferably the metal is copper. Alloys which may be
plated include but are not limited to binary alloys such as
copper/tin and copper nickel alloys and ternary alloys such as
copper/tin/silver. Conventional sources of metal ions which are
soluble in an aqueous medium may be used. Conventional amounts of
metal ions for electroless plating may be used.
[0024] Sources of copper ions include, but are not limited to water
soluble halides, nitrates, acetates, sulfates and other organic and
inorganic salts of copper. Mixtures of one or more of such copper
salts may be used to provide copper ions. Examples include copper
sulfate, such as copper sulfate pentahydrate, copper chloride,
copper nitrate, copper sulfamate, copper hydroxide, and copper
methane sulfonate ((CH.sub.3O.sub.3S).sub.2Cu). Copper ion
concentrations in the composition may range from 0.25 g/L to 30 g/L
or such as from 0.5 g/L to 20 g/L or such as from 1 g/L to 10
g/L.
[0025] Sources of nickel ions include, but are not limited to
nickel sulfate, nickel chloride, nickel sulfamate, and nickel
phosphate. Mixtures of nickel compounds may be used in the plating
compositions. The nickel compounds may be added to the plating
compositions in amounts sufficient to provide a nickel ion
concentration in the plating composition of 0.1 g/L to 50 g/L, or
such as 0.5 g/L to 30 g/L, or such as 1 g/L to 20 g/L.
[0026] Sources of tin ions include, but are not limited to salts,
such as tin halides, tin sulfates, tin alkane sulfonates, tin
alkanol sulfonates, and acids. When tin halide is used, it is
typical that the halide is chloride. The tin compound is typically
tin sulfate, tin chloride or a tin alkane sulfonate, and more
typically tin sulfate or tin methane sulfonate. Sufficient amounts
of tin salts are added to the electroless composition to provide
tin (II) ions in amounts of 0.5 g/L to 80 g/L, typically from 5 g/L
to 50 g/L.
[0027] Sources of silver ions may be provided by silver salts such
as, but are not limited to silver halides, silver gluconate, silver
citrate, silver lactate, silver nitrate, silver sulfates, silver
alkane sulfonates and silver alkanol sulfonates. When a silver
halide is used, it is typical that the halide is chloride.
Typically the silver salts are silver sulfate, a silver alkane
sulfonate or mixtures thereof, and more typically silver sulfate,
silver methane sulfonate or mixtures thereof. Sufficient amounts of
silver salts are added to the electroless plating composition to
provide silver ions in amounts of 0.01 g/L to 60 g/L, typically
from 0.02 g/L to 30 g/L.
[0028] Sources of gold ions include, but are not limited to one or
more gold salts which provide gold (I) ions. Such sources of gold
(I) ions include, but are not limited to alkali gold cyanide
compounds such as potassium gold cyanide, sodium gold cyanide, and
ammonium gold cyanide, alkali gold thiosulfate compounds such as
trisodium gold thiosulfate and tripotassium gold thiosulfate,
alkali gold sulfite compounds such as sodium gold sulfite and
potassium gold sulfite, ammonium gold sulfite, and gold (I) and
gold (III) halides such as gold (I) chloride and gold (III)
trichloride. Sufficient amounts of gold sources are added to the
electroless plating compositions to provide gold ion concentrations
of 0.5 g/L to 50 g/L, or such as from 5 g/L to 30 g/L, or such as
from 10 g/L to 20 g/L.
[0029] In addition to the foregoing components, the electroless
metal plating composition may include one or more optional
additives to tailor the compositions to a desired plating
performance for a given application. Such optional additives
include, but are not limited to accelerators, uniformity enhancers,
stabilizers, grain-refiners, complexing agents, chelating agents,
additional reducing agents, pH adjusting agents, antioxidants and
surfactants.
[0030] Uniformity enhancers with an ability to enhance the
initiation of electroless plating include but are not limited to
aldehydes such as glyoxal, succindialdehyde, glucose and
acetaldehyde. Such aldehydes may be included in the electroless
metal plating compositions in amounts of 0.01 g/L to 10 g/L,
preferably from 0.5 g/l to 5 g/L.
[0031] Except for formaldehyde, one or more additional reducing
agents may include, but are not limited to hypophosphite, glycolic
acid, glyoxal, ascorbic acid, formic acid and glycine. The
additional reducing agents may be used in their conventional
amounts.
[0032] Complexing agents include, but are not limited to
ethylenediamine-N,N'-disuccinic acid (EDDS) and its salts, Rochelle
salts, potassium tartrate, citric acid and its salts,
ethanoldiamine, Iminodiacetic acid and its salts, pyrophosphoric
acid and its salts, salicylic acid and its salts, hydroxyethylidene
diphosphonic acid and its salts, xylitol and D-sorbitol. The molar
ratio of complexing agents to metal ions may range from 0.5:1 to
50:1 or such as from 1:1 to 15:1 or such as from 1.2:1 to 8:1.
[0033] Stabilizers include, but are not limited to sulfur
containing compounds such as 2-mercaptopyridine,
2-mercaptobenzothiazole, 2-mercaptothiazoline,
mercaptobenzothiazole, thiourea and its derivatives; cyanides such
as KCN, NaCN, K.sub.4[Fe(CN).sub.6], thiocyanates; dipyridyls and
its derivatives such as 2,2'-dipyridyl, methylpiperidine,
1,2-di-(2-pyridyl)ethylene, 2,2'-dipyridylamine, pyridazine,
6,6'-dimethyl-2,2'dipyridyl, di-2-pyrylketone and
2,2'-bipyrimidine. Such stabilizers may be included in amounts of 1
ppm to 10 g/L.
[0034] Optional grain-refining additives include, but are not
limited to high molecular weight polymer compounds such as
polyalkylene glycols, polyacrylamides, poly acrylates,
polypropylene glycols, polyethylene glycols (PEG). Some are
available in various molecular weights such as PEG which may be
available as PEG 600, PEG 2000, PEG 4000, PEG 6000 and PEG 10000.
The grain-refining additives are included in amounts of 0.1 ppm to
300 ppm, preferably 1 ppm to 100 ppm.
[0035] Rate-accelerating additives include, but are not limited to
sulfur-based organic molecules such as bis(sodium
sulfopropyl)disulfide, sodium
3-(benzothiazol-2-ylthio)-1-propanesulfonate and other disulfides.
Such compounds are included in amounts of 0.1 ppm to 30 ppm,
preferably from 0.5 ppm to 10 ppm. Other rate accelerating
additives include, but are not limited to ammonia, ethylenediamine
and mannitol. Such rate-accelerating compounds may be included in
amounts of 0.01 g/L to 5 g/L.
[0036] Typically, the pH of the composition is adjusted by one or
more alkaline compounds chosen from lithium hydroxide, sodium
hydroxide, potassium hydroxide and ammonium hydroxide to provide a
pH greater than 7, typically 8 and greater. In the field of ultra
large scale integrated (ULSI), organic alkalis such as tetramethyl
ammonium hydroxide (TMAH) are used for pH adjustment to avoid the
introduction of alkaline metal ions onto the surface or into the
plated copper coating. More typically, sodium hydroxide, potassium
hydroxide and TMAH or mixtures thereof are used. Preferably
potassium hydroxide is used because potassium oxalate has a higher
solubility than that of sodium oxalate. Preferably the potassium
hydroxide concentration is from 3 g/L to 100 g/L, more preferably
from 10 g/L to 80 g/L. A preferred pH range of the electroless
metal compositions is from 10 to 14, more preferably from 11.5 to
13.5, most preferably from 12.5 to 13.5.
[0037] Conventional surfactants may be included in the
compositions. Such surfactants include ionic, such as cationic and
anionic surfactants, non-ionic and amphoteric surfactants. Mixtures
of the surfactants may be used. In general, surfactants may be
included in conventional amounts for electroless copper plating
compositions. Surfactants may be included in the compositions in
amounts of 0.001 g/L to 50 g/L.
[0038] Cationic surfactants include, but are not limited to
tetra-alkylammonium halides, alkyltrimethylammonium halides,
hydroxyethyl alkyl imidazoline, alkylbenzalkonium halides,
alkylamine acetates, alkylamine oleates and alkylaminoethyl
glycine.
[0039] Anionic surfactants include, but are not limited to
alkylbenzenesulfonates, alkyl or alkoxy naphthalene sulfonates,
alkyldiphenyl ether sulfonates, alkyl ether sulfonates,
alkylsulfuric esters, polyoxyethylene alkyl ether sulfuric esters,
polyoxyethylene alkyl phenol ether sulfuric esters, higher alcohol
phosphoric monoesters, polyoxyalkylene alkyl ether phosphoric acids
(phosphates) and alkyl sulfosuccinates.
[0040] Amphoteric surfactants include, but are not limited to
2-alkyl-N-carboxymethyl or ethyl-N-hydroxyethyl or methyl
imidazolium betaines, 2-alkyl-N-carboxymethyl or
ethyl-N-carboxymethyloxyethyl imidazolium betaines, dimethylalkyl
betains, N-alkyl-.beta.-aminopropionic acids or salts thereof and
fatty acid amidopropyl dimethylaminoacetic acid betaines.
[0041] Preferably the surfactants are non-ionic. Non-ionic
surfactants include, but are not limitted to are alkyl phenoxy
polyethoxyethanols, polyoxyethylene polymers having from 20 to 150
repeating units and block and random copolymers of polyoxyethylene
and polyoxypropylene.
[0042] Antioxidants include, but are not limited to monohydric,
dihydric and trihydric phenols in which a hydrogen atom or atoms
may be unsubstituted or substituted by --COOH, --SO.sub.3H, lower
alkyl or lower alkoxy groups, hydroquinone, catechol, resorcinol,
quinol, pyrogallol, hydroxyquinol, phloroglucinol, guaiacol, gallic
acid, 3,4-dihydroxybenzoic acid, phenolsulfonic acid,
cresolsulfonic acid, hydroquinonsulfonic acid, catecholsulfonic
acid and salts thereof. Antioxidants may be included in the
compositions in conventional amounts typically used for electroless
copper compositions such as from 1 ppm to 1000 ppm.
[0043] The electroless metal compositions may be used to deposit a
metal on both conductive and non-conductive substrates. The
electroless compositions may be used in many conventional methods
known in the art. Typically copper deposition is done at
temperatures of 20.degree. C. to 80.degree. C. Preferably the
electroless compositions deposit copper at temperatures of
20.degree. C. to 60.degree. C. The substrate to be plated with
copper is immersed in the electroless composition or the
electroless composition is sprayed onto the substrate. Conventional
plating times may be used to deposit the copper onto the substrate.
Deposition may be done for 5 seconds to 30 minutes; however,
plating times may vary depending on the thickness of the metal
desired on the substrate and the plating bath temperature. Metal
plating rates may range from 0.15 .mu.m/5 minutes to 0.5 .mu.m/5
minutes, preferably from 0.25 .mu.m/5 minutes to 0.45 .mu.m/5
minutes.
[0044] Substrates include, but are not limited to materials
including inorganic and organic substances such as glass, ceramics,
porcelain, resins, paper, cloth and combinations thereof.
Metal-clad and unclad materials also are substrates which may be
plated with the electroless copper compositions.
[0045] Substrates also include printed circuit boards. Such printed
circuit boards include metal-clad and unclad with thermosetting
resins, thermoplastic resins and combinations thereof, including
fiber, such as fiberglass, and impregnated embodiments of the
foregoing.
[0046] Thermoplastic resins include, but are not limited to acetal
resins, acrylics, such as methyl acrylate, cellulosic resins, such
as ethyl acetate, cellulose propionate, cellulose acetate butyrate
and cellulose nitrate, polyethers, nylon, polyethylene,
polystyrene, styrene blends, such as acrylonitrile styrene and
copolymers and acrylonitrile-butadiene styrene copolymers,
polycarbonates, polychlorotrifluoroethylene, and vinylpolymers and
copolymers, such as vinyl acetate, vinyl alcohol, vinyl butyral,
vinyl chloride, vinyl chloride-acetate copolymer, vinylidene
chloride and vinyl formal.
[0047] Thermosetting resins include, but are not limited to allyl
phthalate, furane, melamine-formaldehyde, phenol-formaldehyde and
phenol-furfural copolymers, alone or compounded with butadiene
acrylonitrile copolymers or acrylonitrile-butadiene-styrene
copolymers, polyacrylic esters, silicones, urea formaldehydes,
epoxy resins, allyl resins, glyceryl phthalates and polyesters.
[0048] Porous materials include, but are not limited to paper,
wood, fiberglass, cloth and fibers, such as natural and synthetic
fibers, such as cotton fibers and polyester fibers.
[0049] The electroless copper compositions may be used to plate
both low and high T.sub.g resins. Low T.sub.g resins have a T.sub.g
below 160.degree. C. and high T.sub.g resins have a T.sub.g of
160.degree. C. and above. Typically high T.sub.g resins have a
T.sub.g of 160.degree. C. to 280.degree. C. or such as from
170.degree. C. to 240.degree. C. High T.sub.g polymer resins
include, but are not limited to polytetrafluoroethylene (PTFE) and
polytetrafluoroethylene blends. Such blends include, for example,
PTFE with polypheneylene oxides and cyanate esters. Other classes
of polymer resins which include resins with a high T.sub.g include,
but are not limited to: epoxy resins, such as difunctional and
multifunctional epoxy resins, bimaleimide/triazine and epoxy resins
(BT epoxy), epoxy/polyphenylene oxide resins, acrylonitrile
butadienestyrene, polycarbonates (PC), polyphenylene oxides (PPO),
polypheneylene ethers (PPE), polyphenylene sulfides (PPS),
polysulfones (PS), polyamides, polyesters such as
polyethyleneterephthalate (PET) and polybutyleneterephthalate
(PBT), polyetherketones (PEEK), liquid crystal polymers,
polyurethanes, polyetherimides, epoxies and composites thereof.
[0050] The electroless compositions may be used to deposit copper
on walls of through-holes or vias of printed circuit board
substrates as well as other parts of the boards. The electroless
compositions may be used in both horizontal and vertical processes
of manufacturing printed circuit boards.
[0051] In general, the boards may be rinsed with water and cleaned
and degreased followed by desmearing the through-hole walls.
Typically prepping or softening the dielectric or desmearing of the
through-holes begins with application of a solvent swell. Any
conventional solvent swell may be used. The specific type may vary
depending on the type of dielectric material. Minor experimentation
may be done to determine which solvent swell is suitable for a
particular dielectric material. Solvent swells include, but are not
limited to glycol ethers and their associated ether acetates.
Examples of commercially available solvent swells are
CIRCUPOSIT.TM. Conditioner 3302A, CIRCUPOSIT.TM. MLB Conditioner
211, CIRCUPOSIT.TM. Hole Prep 3303 and CIRCUPOSIT.TM. Hole Prep
4120 solutions (available from Dow Electronic Materials).
[0052] After the solvent swell, a promoter may be applied.
Conventional promoters may be used. Such promoters include sulfuric
acid, chromic acid, alkaline permanganate or plasma etching.
Typically alkaline permanganate is used as the promoter. Examples
of commercially available promoters are CIRCUPOSIT.TM. Promoter
4130, CIRCUPOSIT.TM. MLB Promoter 213-A and CIRCUPOSIT.TM. MLB
Promoter 3308 solutions (available from Dow Electronic Materials).
Optionally, the substrate and through-holes are rinsed with
water.
[0053] A neutralizer may then be applied to neutralize any residues
left by the promoter. Conventional neutralizers may be used.
Typically the neutralizer is an aqueous acidic solution containing
one or more amines or a solution of 3 wt % hydrogen peroxide and 3
wt % sulfuric acid. An example of a commercially available
neutralizer is CIRCUPOSIT.TM. MLB Neutralizer 216-5. Optionally,
the substrate and through-holes are rinsed with water and then
dried.
[0054] After neutralizing an acid or alkaline conditioner is
applied. Conventional conditioners may be used. Such conditioners
may include one or more cationic surfactants, non-ionic
surfactants, complexing agents and pH adjusters or buffers.
Examples of commercially available acid conditioners are
CIRCUPOSIT.TM. Conditioners 3320A and 3327 solutions (available
from Dow Electronic Materials). Suitable alkaline conditioners
include, but are not limited to: aqueous alkaline surfactant
solutions containing one or more quaternary amines and polyamines
Examples of commercially available alkaline surfactants are
CIRCUPOSIT.TM. Conditioner 231, 3325, 3323A, 813 and 860
formulations. Optionally, the substrate and through-holes are
rinsed with water.
[0055] Conditioning may be followed by micro-etching. Conventional
micro-etching compositions may be used. Micro-etching is designed
to provide a micro-roughened metal surface on exposed metal (e.g.
innerlayers and surface etch) to enhance subsequent adhesion of
plated electroless metal and later electroplate. Micro-etches
include, but are not limited to 60 g/L to 120 g/L sodium persulfate
or sodium or potassium oxymonopersulfate and sulfuric acid (2%)
mixture, or generic sulfuric acid/hydrogen peroxide. Examples of
commercially available micro-etching compositions are
CIRCUPOSIT.TM. Microetch 3330 Etch solution and PREPOSIT.TM. 748
Etch solution (available from Dow Electronic Materials).
Optionally, the substrate is rinsed with water.
[0056] Optionally, a pre-dip may then applied to the micro-etched
substrate and through-holes. Pre-dips include, but are not limited
to organic salts such as sodium potassium tartrate or sodium
citrate, 0.5% to 3% sulfuric acid or an acidic solution of 25 g/L
to 75 g/L sodium chloride.
[0057] A catalyst may then be applied to the substrate.
Conventional catalysts may be used such as conventional
tin/palladium colloidal catalysts. Commercially available catalysts
include, but are not limited to CATAPOSIT.TM. 44 and CATAPOSIT.TM.
404 catalyst formulations (available from Dow Electronic
Materials). Application may be done by conventional methods used in
the art, such as immersing the substrate in a solution of the
catalyst or by spraying or by atomization using conventional
apparatus. Catalyst dwell time may range from 1 minute to 10
minutes, typically from 2 minutes to 8 minutes for vertical
equipment and for 25 seconds to 120 seconds for horizontal
equipment. The catalysts may be applied at temperatures from room
temperature to 80.degree. C., typically from 30.degree. C. to
60.degree. C. The substrate and through-holes optionally may be
rinsed with water after application of the catalyst.
[0058] The substrate and walls of the through-holes are then
electrolessly plated with metal using the electroless metal
composition. Plating times and temperatures may be conventional.
Typically metal deposition may be done at temperatures of
20.degree. C. to 80.degree. C., more typically from 30.degree. C.
to 60.degree. C. The substrate may be immersed in the electroless
plating composition or the electroless composition may be sprayed
onto the substrate. Typically, electroless plating may be done for
5 seconds to 30 minutes; however, plating times may vary depending
on the thickness of the metal desired.
[0059] Optionally anti-tarnish may be applied to the metal.
Conventional anti-tarnish compositions may be used. An example of
anti-tarnish is ANTI TARNISH.TM. 7130 solution (available from Dow
Electronic Materials). The substrate may optionally be rinsed with
water and then the boards may be dried.
[0060] After the substrate is plated with copper, the substrates
may undergo further processing. Further processing may include
conventional processing by photoimaging and further metal
deposition on the substrates such as electrolytic metal deposition
of, for example, copper, copper alloys, tin and tin alloys.
[0061] The combination of the one or more tertiary amines and
glyoxylic acid, salts or mixtures thereof provide a stable
electroless metal plating composition which is formaldehyde-free
and environmentally friendly. The tertiary amines inhibit the
decomposition of glyoxylic acids and its salts, thus prolonging the
life of the plating composition and reducing the cost of the
operation of the plating composition as replacement with glyoxylic
acid or its salts is reduced or eliminated. The combination of the
one or more tertiary amines, salts, halides or mixtures thereof and
the glyoxylic acid, salts or mixtures thereof at the molar ratios
provides for a more efficient electroless metal plating process
than many conventional electroless metal compositions and plating
processes. In addition, the plating compositions may provide for
substantially uniform, bright metal deposits on substrates and
reduced skip plating.
[0062] The following examples are not intended to limit the scope
of the invention but to further illustrate it.
Example 1
[0063] Glyoxylic acid-reduced electroless copper plating
compositions were prepared as shown below. The compositions
included copper ions, glyoxylic acid as reducing agent, potassium
tartrate as copper complexing agent, potassium hydroxide as pH
adjusting agent, suppressors of glyoxylic acid decomposition, and
2,2'-dipyridyl as stabilizer. The electroless copper compositions
were free of formaldehyde. They were tested for the quality of
their copper deposits and the stability of the glyoxylic acid.
TABLE-US-00001 TABLE 1 AMOUNT COMPONENT Formulation 1 Formulation 2
Formulation 3 Formulation 4 Copper ions from copper chloride 2 g 2
g 2 g 2 g Glyoxylic acid 7 g 7 g 7 g 7 g Potassium tartrate 30 g 30
g 30 g 30 g Potassium hydroxide 15 g 15 g 15 g 15 g Triethanolamine
12 g \ \ \ (0.08M) Nitrilotriacetic acid \ 20 g \ \ (0.1M)
Triisopropanolamine \ \ 16 g \ (0.08M) N,N,N',N'-tetrakis(2- \ \ \
15 g hydroxypropyl) ethylenediamine (0.05M) 2,2'-dipyridyl 10 ppm
10 ppm 10 ppm 10 ppm Water To one liter To one liter To one liter
To one liter
Example 2
[0064] The temperature of the composition of Formulation 1 of Table
1 was maintained at 40.degree. C. and the pH of the composition was
13 during electroless copper deposition. Copper was deposited on
substrates for 5 minutes. The substrates used were unclad S1141
epoxy/glass laminates with dimensions 5 cm.times.5 cm and
copper-clad S1141 epoxy/glass multi-laminate boards (six layers)
with dimensions 2 cm.times.3.5 cm obtained from Shengyi Technology
Co., Ltd. The former were used for measuring the deposition rate,
and the latter were used for evaluating the backlight performance
of the through-holes. The drill smear and other impurities of the
through-holes in each board were then removed in a vertical desmear
line process as follows:
1. The boards were treated with solvent swell composed of 12.5%
CIRCUPOSIT.TM. MLB CONDITIONER 211 solution for 5 minutes at
75.degree. C. 2. Each board was then rinsed with cold water for 3
minutes. 3. The boards were then treated with an alkaline promoter
of aqueous alkaline permanganate composed of 10% CIRCUPOSIT.TM. MLB
PROMOTER 213-A solution for 10 minutes at 80.degree. C. 4. Each
board was then rinsed with cold water for 3 minutes. 5. The boards
were then treated with an aqueous neutralizer composed of 5%
CIRCUPOSIT.TM. MLB NEUTRALIZER 216-5 solution for 5 minutes at
40.degree. C. 6. Each board was then rinsed with cold water for 3
minutes. 7. The surface of each board/laminate was immersed in an
aqueous bath containing 3% CIRCUPOSIT.TM. CONDITIONER 3323A
solution for 5 minutes at 40.degree. C. 8. Each board/laminate was
then rinsed with cold water for 4 minutes. 9. The through-holes of
each board were then microetched with an aqueous acidic solution of
100 g/L sodium persulfate and 2% v/v sulfuric acid at room
temperature for 1 minute. 10. Each board was then rinsed with cold
water for 3 minutes. 11. A pre-dip was then applied to each
board/laminate for 1 minute at room temperature. The pre-dip was
CATAPREP.TM. 404 solution obtained from Rohm and Haas Electronic
Materials. 12. The boards/laminates were then primed for 5 minutes
at 40.degree. C. with a catalyst bath for electroless copper
metallization. The catalyst bath contained 2% CATAPOSIT.TM. 44
solution, which was obtained from Rohm and Haas Electronic
Materials. 13. The boards/laminates were then rinsed with cold
water for 2 minutes. 14. The boards/laminates were then activated
with 2.5% ACCELERATOR.TM. 19E solution at room temperature for 2
minutes. 15. The boards/laminates were then rinsed with cold water
for 2 minutes. 16. Each board/laminate was then immersed in the
electroless copper plating composition of Formulation 1 for
electroless copper deposition. The copper deposition was done for 5
minutes at 40.degree. C. at a pH of 13. 17. Each copper plated
board/laminate was then rinsed with cold water for 2 minutes. 18.
Each copper plated board/laminate was then rinsed with deionised
water for 1 minute. 19. After blow-drying, each laminates was
observed for the quality of copper deposits, and the deposition
rate was then measured by a wet titration method. 20. Each board
was then sectioned laterally to expose the copper plated walls of
the through-holes. Multiple lateral sections 1 mm thick were taken
from the walls of the sectioned through-holes of each board to
determine the through-hole wall coverage for the boards using the
conventional European Backlight Grading Scale from 0 to 5, where 0
means the worst results and 5 the best results. Reference samples
showing results from 0 to 5 are shown in the FIGURE. Each lateral
section was placed under a conventional optical microscope of
50.times. magnification with a light source. The light was applied
to the backside of the sample. If no light was observed, the sample
was completely copper plated and the image under the microscope was
black as shown in reference sample marked 5.0 of the FIGURE. If
some light was observed, the lateral section was compared to the
reference samples marked 0.0 to 4.5. The more light which passed
through the sample the lower the backlight rating and the poorer
the plating quality. The S1141 copper plated boards had average
backlight values of 4.0 which was an acceptable value for
commercial backlight values.
[0065] To evaluate the stability of the reducing agent, glyoxylic
acid concentrations were determined by a wet titration method. The
bath solution mentioned above was idled at 40.degree. C. with air
agitation. The glyoxylic acid concentrations were then measured
after 6 hours and the percentage of remaining glyoxylic acid in the
bath was calculated. The following method was used to calculate the
glyoxylic acid concentrations: [0066] a) Pipetted 5 mL testing
solution into 250 ml beaker and added approximately 50 mL RO water.
[0067] b) Titrated to pH=10.0 with standardized 0.1 N HCl and added
15 mL 0.1 M sodium sulfite or 1-2 g sodium sulfite solid using a
conventional pH meter. [0068] c) Stirred for 3-5 minutes to ensure
complete reaction between the glyoxylic acid and sodium sulfite.
[0069] d) Titrated the generated sodium hydroxide with 0.1 N HCl to
pH=10.0 and recorded mLs delivered. This titrant represented the
glyoxylic acid concentration. CHOCOOH (g/L)=mL of
HCl.times.0.1.times.74/sample size (5 mL).
[0070] After 6 hours idling, there was still 54% glyoxylic acid
left, and no copper oxide was observed. Thus the electroless copper
composition was stable.
21. The copper deposits obtained from the bath composition of
Formulation 1 were salmon pink. Minor amounts of skip plating were
observed. The deposition rate measured was 0.19 .mu.m/5 minutes.
The amount of copper plated was determined by the following wet
titration procedure: First, the copper deposit on the laminate was
completely dissolved, and then a buffer solution containing
ammonium chloride pH=10 was added to the solution followed by
titrating with 0.05 M EDTA standard solution. Thus, the total mass
of copper deposit was calculated.
Example 3
[0071] Formulations 2 to 4 of Table 1 were processed in the same
way as Example 1. The temperature of the compositions was
maintained at 40.degree. C. and a pH of 13 during electroless
copper deposition. Copper was deposited on substrates for 5
minutes.
[0072] When nitrilotriacetic acid, Formulation 2, was employed as
suppressor of glyoxylic acid decomposition, it was found that the
copper deposits were salmon pink, smooth and there was no
observable skip plating. The highest deposition rate achieved was
0.21 .mu.m/5 minutes. The S1141 copper plated boards had average
backlight values of 4.25. After 6 hours idling, there was still 41%
glyoxylic acid left, and no copper oxide was observed. Thus the
electroless copper composition was stable.
[0073] When triisopropanolamine, Formulation 3, was used as
suppressor of glyoxylic acid decomposition, it was found that the
copper deposits were red and smooth. No skip plating was observed.
The deposition rate was 0.33 .mu.m/5 minutes. The S1141 copper
plated boards had average backlight values of 4.25. After 6 hours
idling, there was still 56% glyoxylic acid left. No copper oxide
was observed. Thus the electroless copper composition was
stable.
[0074] In Formulation 4,
N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine was used to
suppress the glyoxylic acid decomposition. The results showed that
the copper deposits were red and smooth and no skip plating was
observed. The deposition rate was 0.32 .mu.m/5 min. The S1141
copper plated boards had average backlight values of 3.5. After 6
hours idling, there was still 65% glyoxylic acid left, and no
copper oxide was observed. Thus the electroless copper composition
was stable.
[0075] Although there was some variation in the parameters tested
for Formulations 2-4, they all showed many positive attributes. All
of the formulations appeared free of copper oxide, the copper
deposits were smooth and no skip plating was observed. With the
exception of Formulation 2, the plating rates were on the upper
range desired for electroless plating; however, Formulation 2 had a
bright, salmon pink deposit. Formulations 2 and 3 showed good
backlight performance and were in the acceptable commercial range.
After 6 hours idling tine both Formulations 3 and 4 retained over
50% of the original glyoxylic acid added.
Example 4 (Comparative)
[0076] The following electroless copper plating solution was
prepared:
TABLE-US-00002 TABLE 2 AMOUNT COMPONENT Formulation 5 Formulation 6
Copper ions 2 g 2 g Formaldehyde 3 g / Glyoxylic acid / 7 g
Potassium tartrate 30 g 30 g Potassium hydroxide 15 g 15 g Water To
one liter To one liter
[0077] Formulations 5 and 6 of Table 2 were blank controls of
formaldehyde and glyoxylic acid as reducing agents for copper. No
reducing agent decomposition suppressors were added into the bath
solutions. The temperature of the solutions was maintained at
40.degree. C. and a pH of 13 during the idling test with air
agitation. After 6 hours about 69% of the formaldehyde remained,
and no copper oxide was observed. This suggested the electroless
copper composition was stable, and decomposition of formaldehyde by
the Cannizzaro reaction was not a serious issue.
[0078] In contrast, Formulation 6 which included glyoxylic acid
only had 20% glyoxylic acid left after 6 hours idling. The
decomposition rate of glyoxylic acid was very rapid such that from
a practical production point of view, glyoxylic acid would not be a
suitable substitute for formaldehyde. The rapid decomposition of
glyoxylic acid would result in sudden termination of electroless
plating and high cost for replenishing the reducing agent. This is
one of the main barriers for application of glyoxylic acid as a
reducing agent in electroless copper plating solutions.
Example 5 (Comparative)
[0079] Three electroless copper plating solutions were prepared as
shown in Table 3 below.
TABLE-US-00003 TABLE 3 AMOUNT COMPONENT Formulation 7 Formulation 8
Formulation 9 Copper ions 2 g 2 g 2 g Glyoxylic acid 7 g 7 g 7 g
Potassium tartrate 30 g 30 g 30 g Potassium hydroxide 15 g 15 g 15
g Potassium stannate 6 g / / Hexamethyl- / 2.5 g / enediamine
Succinic acid / / 100 ppm Water To one liter To one liter To one
liter
[0080] Formulations 7 and 8 included two conventional Cannizzaro
reaction-suppressing agents, potassium stannate and
hexamethylenediamine, respectively. Their molar concentrations were
around 0.02 M. The temperature of the solutions was maintained at
40.degree. C. and a pH of 13 during the idling test with air
agitation. After 6 hours of idling, only about 20% glyoxylic acid
remained in each solution. This is substantially the same as the
electroless copper plating solution of Formulation 6 where no
Cannizzaro reaction-suppressing agent was added. The conventional
Cannizzaro reaction-suppressing agents, potassium stannate and
hexamethylenediamine, did not effectively suppress glyoxylic acid
decomposition.
[0081] In Formulation 9, succinic acid, another conventional
Cannizzaro reaction-suppressing agent was tested. The temperature
of the composition was maintained at 40.degree. C. with a pH of 13
during the idling test with air agitation. After 6 hours, only
around 20% glyoxylic acid remained. As with Formulations 7 and 8
the succinic acid did not effectively suppress the Cannizzaro
reaction.
Example 6 (Comparative)
[0082] Two electroless copper plating formulations were prepared as
shown in Table 4 below.
TABLE-US-00004 TABLE 4 AMOUNT COMPONENT Formulation 10 Formulation
11 Copper ions 2 g 2 g Formaldehyde 3 g / Glyoxylic acid / 7 g
Potassium tartrate 30 g 30 g Potassium hydroxide 15 g 15 g
Triethylamine 8.1 g / (0.08M) N,N,N',N'-Tetramethylethylenediamine
/ 9.3 g (0.08M) Water To one liter To one liter
[0083] Formulations 10 and 11 included triethylamine and
N,N,N',N'-tetramethylethylenediamine, respectively, as suppressors
of glyoxylic acid decomposition. Both are tertiary amines; however,
none of the alkyl groups was substituted by functional groups, such
as carboxylic acid, carboxylate, hydroxyl or phosphonic acid. The
temperature of the composition was maintained at 40.degree. C. with
a pH of 13 during the idling test with air agitation. After 6 hours
idling time only around 21% glyoxylic acid remained. This was
substantially the same as the control solution of Formulation 6 in
Example 4 which had 20% remaining. The two unsubstituted tertiary
amines did not show acceptable glyoxylic acid decomposition
suppression.
Example 7
[0084] A plurality of electroless copper plating solutions was
prepared as shown in Table 5 below. The glyoxylic acid
decomposition suppressor was triisopropanolamine. The molar ratio
of the triisopropanolamine to glyoxylic acid was varied with the
remainder of the components kept at the same concentration in the
eleven formulations.
TABLE-US-00005 TABLE 5 Molar Glyoxylic ratio Triisopropanolamine
acid Copper Potassium Potassium 2,2'- Formulation TIPA:GA (TIPA)
(GA) ions tartrate hydroxide dipyridyl 12-1 0:1 0 g/L 7 g/L 2 g/L
30 g/L 15 g/L 10 ppm (0.1M) 12-2 0.05:1 0.96 g/L 7 g/L 2 g/L 30 g/L
15 g/L 10 ppm (0.005M) (0.1M) 12-3 0.2:1 3.83 g/L 7 g/L 2 g/L 30
g/L 15 g/L 10 ppm (0.02M) (0.1M) 12-4 0.8:1 15.3 g/L 7 g/L 2 g/L 30
g/L 15 g/L 10 ppm (0.08M) (0.1M) 12-5 1.6:1 30.6 g/L 7 g/L 2 g/L 30
g/L 15 g/L 10 ppm (0.16M) (0.1M) 12-6 3:1 57.4 g/L 7 g/L 2 g/L 30
g/L 15 g/L 10 ppm (0.3M) (0.1M) 12-7 5:1 95.6 g/L 7 g/L 2 g/L 30
g/L 15 g/L 10 ppm (0.5M) (0.1M) 12-8 10:1 191.3 g/L 7 g/L 2 g/L 30
g/L 15 g/L 10 ppm (1M) (0.1M) 12-9 15:1 286.9 g/L 7 g/L 2 g/L 30
g/L 15 g/L 10 ppm (1.5M) (0.1M) 12-10 20:1 382.6 g/L 7 g/L 2 g/L 30
g/L 15 g/L 10 ppm (2.0M) (0.1M) 12-11 30:1 573.9 g/L 7 g/L 2 g/L 30
g/L 15 g/L 10 ppm (3.0M) (0.1M)
Example 8
[0085] The electroless copper plating solutions of Example 7 were
tested for their plating performance and stability. The substrates
used were of the same type as in Example 2 above. The substrates
were treated and electroless plated as described in Example 2. The
temperature of the plating solutions was maintained at 40.degree.
C. with a pH of 13 during electroless copper deposition. Copper was
deposited on the substrates for 5 minutes. The results are shown in
Table 9.
TABLE-US-00006 TABLE 9 Molar Deposition ratio rate Appearance/ Bath
Formulation TIPA:GA (.mu.m/5 min) Coverage Bath solution stability
12-1 0:1 0.31 Salmon pink; Dark blue, Good complete transparent
deposit 12-2 0.05:1 0.3 Salmon pink; Dark blue with Good complete a
slightly of deposit purple, transparent 12-3 0.2:1 0.27 Salmon
pink; Dark blue with Good complete a slightly of deposit purple,
transparent 12-4 0.8:1 0.33 Salmon pink; Dark blue with Good
complete a slightly of deposit purple, transparent 12-5 1.6:1 0.32
Salmon pink; Dark blue with Good complete a slightly of deposit
purple, transparent 12-6 3:1 0.35 Salmon pink; Dark blue with Good
complete a slightly of deposit purple, transparent 12-7 5:1 0.41
Salmon pink; Dark blue with Good complete a slightly of deposit
purple, transparent 12-8 10:1 0.42 Salmon pink; Dark blue with Good
complete a slightly of deposit purple, transparent 12-9 15:1 0.33
Red and dark, Dark blue with Good complete a slightly of deposit
purple, transparent 12-10 20:1 0.26 Red and dark, Dark blue, a Good
complete slightly deposit viscous and turbid 12-11 30:1 0.21 Red
and dark, Dark blue, Partly complete viscous and plated out deposit
turbid after plating
[0086] When the molar ratio of TIPA:GA was varied from 0:1 to 10:1,
all of the plating solutions were transparent, dark blue and with a
slight of purple color. The deposits were salmon pink without any
observable skip plating. As the molar ratio of TIPA:GA increased
from 15:1 and greater, the deposits' appearance became darker. This
indicated that the deposits' morphology became rougher. When the
molar ratio reached 30:1, complete coverage of the substrate was
achieved but the deposit was dark and red and the solution was
viscous and turbid. What was worse was that the plating solution
started to partly plate out after plating. The deposition rate
gradually increased with increasing the triisopropanolamine
concentration; however, beyond the molar ratio of 10:1, the
deposition rate decreased with the increasing concentration.
Example 9
[0087] A plurality of electroless copper plating solutions was
prepared as shown in Table 10 below. The glyoxylic acid
decomposition suppressor was triisopropanolamine. The molar ratio
of the triisopropanolamine to glyoxylic acid was varied with the
remainder of the components kept at the same concentration in the
nine formulations.
TABLE-US-00007 TABLE 10 Molar Glyoxylic ratio Triisopropanolamine
acid Copper Potassium Potassium Formulation TIPA:GA (TIPA) (GA)
ions tartrate hydroxide 13-1 0:1 0 g/L 7 g/L 2 g/L 30 g/L 15 g/L
(0.1M) 13-2 0.05:1 0.96 g/L 7 g/L 2 g/L 30 g/L 15 g/L (0.005M)
(0.1M) 13-3 0.1:1 1.82 g/L 7 g/L 2 g/L 30 g/L 15 g/L (0.01M) (0.1M)
13-4 0.2:1 3.83 g/L 7 g/L 2 g/L 30 g/L 15 g/L (0.02M) (0.1M) 13-5
0.4:1 7.66 g/L 7 g/L 2 g/L 30 g/L 15 g/L (0.04M) (0.1M) 13-6 0.8:1
15.3 g/L 7 g/L 2 g/L 30 g/L 15 g/L (0.08M) (0.1M) 13-7 1.6:1 30.6
g/L 7 g/L 2 g/L 30 g/L 15 g/L (0.16M) (0.1M) 13-8 5:1 95.6 g/L 7
g/L 2 g/L 30 g/L 15 g/L (0.5M) (0.1M) 13-9 10:1 191.3 g/L 7 g/L 2
g/L 30 g/L 15 g/L (1M) (0.1M)
Example 10
[0088] The temperature of the plating solutions was maintained at
40.degree. C. with a pH of 13 and air agitation. The remaining
glyoxylic acid was measured after 6 hours idling. The results are
shown in Table 11.
TABLE-US-00008 TABLE 11 Molar The remaining ratio glyoxylic acid
Formulations TIPA:GA (%) 13-1 0:1 19 13-2 0.05:1 25 13-3 0.1:1 27
13-4 0.2:1 36 13-5 0.4:1 44 13-6 0.8:1 56 13-7 1.6:1 61 13-8 5:1 59
13-9 10:1 58
[0089] The plating solutions with a molar ratio of TIPA:GA as low
as 0.05:1 started showing a suppressing effect on the decomposition
of glyoxylic acid. By increasing the concentration of the
suppressor, remaining glyoxylic acid gradually increased from 19%
where there was no triisopropanolamine in the plating solution to
61% where the ratio of TIPA:GA was 1.6:1. Beyond the molar ratio of
1.6:1, the suppressing capability of the triisopropanolamine tended
to stability as shown by the results obtained in Formulations 13-8
and 13-9.
* * * * *