U.S. patent application number 16/400381 was filed with the patent office on 2019-12-19 for electroless copper plating compositions and methods for electroless plating copper on substrates.
The applicant listed for this patent is Rohm and Haas Electronic Materials LLC. Invention is credited to Patricia Gumbley, Alejo M. Lifschitz Arribio, Michael Lipschutz, Feng Liu, Catherine Mulzer, Sarah Wen.
Application Number | 20190382901 16/400381 |
Document ID | / |
Family ID | 66793923 |
Filed Date | 2019-12-19 |
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United States Patent
Application |
20190382901 |
Kind Code |
A1 |
Lifschitz Arribio; Alejo M. ;
et al. |
December 19, 2019 |
ELECTROLESS COPPER PLATING COMPOSITIONS AND METHODS FOR ELECTROLESS
PLATING COPPER ON SUBSTRATES
Abstract
Stable electroless copper plating baths include pyridinium
compounds to improve rate of copper deposition on substrates. The
copper from the electroless plating baths can be plated at low
temperatures and at high plating rates.
Inventors: |
Lifschitz Arribio; Alejo M.;
(Wallham, MA) ; Gumbley; Patricia; (Sudbury,
MA) ; Lipschutz; Michael; (Natick, MA) ; Liu;
Feng; (Ashland, MA) ; Mulzer; Catherine;
(Grafton, MA) ; Wen; Sarah; (Marlborough,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rohm and Haas Electronic Materials LLC |
Marlborough |
MA |
US |
|
|
Family ID: |
66793923 |
Appl. No.: |
16/400381 |
Filed: |
May 1, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62685353 |
Jun 15, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 18/40 20130101;
C23C 18/405 20130101 |
International
Class: |
C23C 18/40 20060101
C23C018/40 |
Claims
1. An electroless copper plating composition comprising one or more
sources of copper ions, one or more pyridinium compounds, one or
more complexing agents, one or more reducing agents, and,
optionally, one or more pH adjusting agents, wherein a pH of the
electroless copper plating composition is greater than 7.
2. The electroless copper plating composition of claim 1, wherein
the one or more pyridinium compounds or salts thereof are in
amounts of at least 0.5 ppm.
3. The electroless copper plating composition of claim 1, wherein
the one or more pyridinium compounds have a formula: ##STR00002##
wherein R.sub.1 is selected from the group consisting of linear or
branched, substituted or unsubstituted (C.sub.1-C.sub.10)alkyl,
substituted or unsubstituted (C.sub.6-C.sub.10)aryl, substituted or
unsubstituted (C.sub.6-C.sub.10) heterocyclic aromatic group and
substituted or unsubstituted benzyl; and R.sub.2 is selected from
the group consisting of hydrogen, hydroxyl, sulfate, amino,
carbonyl, carboxyl, vinyl and amide.
4. The electroless copper plating composition of claim 1, wherein
the one or more complexing agents are chosen from sodium potassium
tartrate, sodium tartrate, sodium salicylate, sodium salts of
ethylenediamine tetraacetic acid, nitriloacetic acid and its alkali
metal salts, gluconic acid, gluconates, triethanolamine, modified
ethylene diamine tetraacetic acids, S,S-ethylene diamine disuccinic
acid, hydantoin and hydantoin derivatives.
5. The electroless copper plating composition of claim 1, wherein
the one or more reducing agents are chosen from aldehydes,
borohydrides, substituted borohydrides, boranes, saccharides, and
hypophosphite.
6. The electroless copper plating composition of claim 1, further
comprising one or more compounds chosen from secondary
accelerators, grain refiners and stabilizers.
7. A method of electroless copper plating comprising: a) providing
a substrate comprising a dielectric; b) applying a catalyst to the
substrate comprising the dielectric; c) applying an electroless
copper plating composition to the substrate comprising the
dielectric, wherein the electroless copper plating composition
comprises one or more sources of copper ions, one or more
pyridinium compounds, one or more complexing agents, one or more
reducing agents, and, optionally, one or more pH adjusting agents,
wherein a pH of the electroless copper plating composition is
greater than 7; and d) electroless plating copper on the substrate
comprising the dielectric with the electroless copper plating
composition.
8. The method of claim 7, wherein the one or more pyridinium
compounds or salts thereof are in amounts of at least 0.5 ppm.
9. The method of claim 7, wherein the electroless copper plating
composition further comprises one or more compounds chosen from
stabilizers and secondary accelerators.
10. The method of claim 7, wherein the electroless copper plating
composition is at 40.degree. C. or less.
11. The method of claim 7, wherein the catalyst is a palladium
catalyst.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to electroless copper
plating compositions and methods for electroless plating copper on
substrates, wherein electroless copper plating has a high
electroless copper plating rate at low temperatures and the
electroless copper plating compositions are stable. More
specifically, the present invention is directed to electroless
copper plating compositions and methods for electroless plating
copper on substrates, wherein electroless copper plating has a high
electroless copper plating rate at low temperatures and the
electroless copper plating compositions are stable, wherein the
electroless copper plating compositions include pyridinium
compounds or salts thereof.
BACKGROUND OF THE INVENTION
[0002] Electroless copper plating baths are in widespread use in
metallization industries for depositing copper on various types of
substrates. In the manufacture of printed circuit boards, for
example, the electroless copper baths are used to deposit copper on
walls of through-holes and circuit paths as a base for subsequent
electrolytic copper plating. Electroless copper plating also is
used in the decorative plastics industry for deposition of copper
on non-conductive surfaces as a base for further plating of copper,
nickel, gold, silver and other metals, as required. Electroless
copper baths which are in commercial use today contain water
soluble divalent copper compounds, chelating agents or complexing
agents, for example, Rochelle salts and sodium salts of
ethylenediamine tetraacetic acid, for chelating the divalent copper
ions, reducing agents, for example, formaldehyde, and formaldehyde
precursors or derivatives, and various addition agents to make the
bath more stable, adjust the plating rate and brighten the copper
deposit.
[0003] It should be understood, however, that every component in
the electroless copper bath has an effect on plating potential, and
therefore, must be regulated in concentration to maintain the most
desirable plating potential for particular ingredients and
conditions of operation. Other factors which affect internal
plating voltage, deposition quality and rate include temperature,
degree of agitation, type and concentration of basic ingredients
mentioned above.
[0004] In electroless copper plating baths, the components are
continuously consumed such that the baths are in a constant state
of change, thus consumed components must be periodically
replenished. Control of the baths to maintain high plating rates
with substantially uniform copper deposits over long periods of
time is exceedingly difficult. In general, electroless copper
plating rates of equal to or greater than 0.6 .mu.m/5 min. are
highly desirable (preferably desired for current horizontal plating
applications) but rarely achieved, especially at low electroless
plating temperatures, such as below 40.degree. C. Consumption and
replenishment of bath components over several metal turnovers (MTO)
can also contribute to bath instability, for example, through the
buildup of side products. Therefore, such baths, and particularly
those having a high plating potential, i.e. highly active baths,
tend to become unstable and to spontaneously decompose with use.
Such electroless copper bath instability can result in non-uniform
or discontinuous copper plating along a surface. For example, in
the manufacture of printed circuit boards, it is important to plate
electroless copper on the walls of through-holes such that the
copper deposit on the walls is substantially continuous and uniform
with minimal, preferably, no break or gaps in the copper deposit.
Such discontinuity of the copper deposit can ultimately lead to
mal-functioning of any electrical device in which the defective
printed circuit board is included.
[0005] To address the foregoing stability issues, various chemical
compounds categorized under the label "stabilizers" have been
introduced to electroless copper plating baths. Examples of
stabilizers which have been used in electroless copper plating
baths are sulfur containing compounds, such as disulfides and
thiols. However, many stabilizers lower electroless copper plating
rates, and, also, at high concentrations can be catalyst poisons,
thus reducing plating rates or inhibiting plating and compromising
the performance of the plating bath. Low plating rates are
detrimental to electroless copper plating performance. Electroless
copper plating rate is also temperature dependent, thus when high
stabilizer concentrations lower the rate, increasing the plating
temperature can increase the rate. However, increasing the
operating temperatures can decrease the stability of the
electroless copper bath by increasing the buildup of byproducts as
well as increasing the rate of generation of byproducts by side
reactions, thus negating some of the effects of increasing the
stabilizer concentration. As a result, in most cases the amount of
stabilizer used must be a careful compromise between maintaining a
high plating rate and achieving an electroless bath that is stable
over a long period of time.
[0006] Alternatively, an "accelerator" additive can be incorporated
into the electroless bath formulation. Ideally, the accelerator
additive does not impact the stability of the electroless bath,
such that higher plating rates can be achieved while keeping bath
stability in check; or such that the same plating rate is now
achieved at lower temperatures which typically also results in a
more stable bath. The lower electroless bath temperatures reduce
cost of the electroless bath, for example, by decreasing the rate
of passive consumption of plating chemicals. Furthermore, a more
stable formulation, which is afforded by lowering the working
temperature, results in lower maintenance requirements. Finally,
lower plating temperatures can lower the build-up of internal
stress in the electroless deposit, making the metallization process
better suited for high-adhesion applications. Thus, rate
acceleration in electroless copper plating is a key strategy for
lowering working temperatures, lowering internal stress of copper
deposits such as on flexible substrates and decreasing overall
running costs of metallization.
[0007] Therefore, there is a need for an additive for electroless
copper plating baths which enables a high rate of electroless
copper plating at low temperatures to provide bright and uniform
copper deposits on substrates.
SUMMARY OF THE INVENTION
[0008] The present invention is directed to an electroless copper
plating composition including one or more sources of copper ions,
one or more pyridinium compounds, one or more complexing agents,
one or more reducing agents, and, optionally, one or more pH
adjusting agents, wherein a pH of the electroless copper plating
composition is greater than 7.
[0009] The present invention is also directed to a method of
electroless copper plating including: [0010] a) providing a
substrate comprising a dielectric; [0011] b) applying a catalyst to
the substrate comprising the dielectric; [0012] c) applying an
electroless copper plating composition to the substrate comprising
the dielectric, wherein the electroless copper plating composition
comprises one or more sources of copper ions, one or more
pyridinium compounds, one or more complexing agents, one or more
reducing agents, and, optionally, one or more pH adjusting agents,
wherein a pH of the electroless copper plating composition is
greater than 7; and [0013] d) electroless plating copper on the
substrate comprising the dielectric with the electroless copper
plating composition.
[0014] The pyridinium compounds enable increased electroless copper
plating rates at low plating temperatures of less than or equal to
40.degree. C. The electroless copper plating compositions and
methods of the present invention further enable good through-hole
wall coverage, even at low plating temperatures. Low plating
temperatures reduce consumption of electroless copper plating
composition additives which occur by undesired side reactions or by
decomposition, thus providing a more stable electroless copper
plating composition, and lower the cost of operating the
electroless copper plating process.
[0015] The electroless copper plating compositions of the present
invention are stable over wide concentration ranges of the
pyridinium compounds. A broad operating window for the pyridinium
compounds concentration means that the pyridinium compounds
concentrations do not need to be carefully monitored such that the
performance of the electroless copper plating compositions do not
substantially change regardless of how the composition components
are being replenished and consumed.
DETAILED DESCRIPTION OF THE INVENTION
[0016] 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; mm=millimeter; .mu.m=micron; ppm=parts per
million=mg/L; .degree. C.=degrees Centigrade; g/L=grams per liter;
DI=deionized; C=the element carbon; Pd=palladium; Pd(II)=palladium
ions with a +2 oxidation state; Pd.degree.=palladium reduced to its
metal state vs. its ionic state; wt %=percent by weight; and
T.sub.g=glass transition temperature.
[0017] 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%.
[0018] The terms "plating" and "deposition" are used
interchangeably throughout this specification. The terms
"composition" and "bath" are used interchangeably throughout this
specification. The term "alkyl", unless otherwise described in the
specification as having substituent groups, means an organic
chemical group composed of only carbon and hydrogen and having a
general formula: C.sub.nH.sub.2n+1. The term "average" is
equivalent to the mean value of a sample. 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%.
[0019] The electroless copper plating compositions of the present
invention include one or more sources of copper ions, one or more
pyridinium compounds, one or more complexing agents; one or more
reducing agents; water; and, optionally, one or more pH adjusting
agents, wherein a pH of the electroless copper plating composition
is greater than 7.
[0020] Preferably, the one or more pyridinium compounds have a
formula:
##STR00001##
wherein R.sub.1 is selected from the group consisting of linear or
branched, substituted or unsubstituted (C.sub.1-C.sub.10)alkyl,
substituted or unsubstituted (C.sub.6-C.sub.10)aryl, substituted or
unsubstituted (C.sub.6-C.sub.10) heterocyclic aromatic groups and
substituted or unsubstituted benzyl, wherein substituent groups are
selected from the group consisting of hydroxyl, sulfate, amino,
amide, carbonyl and carboxyl; and R.sub.2 is selected from the
group consisting of hydrogen, hydroxyl, sulfate, carbonyl,
carboxyl, vinyl, amino and amide. More preferably, R.sub.1 is
selected from the group consisting of linear or branched,
substituted and unsubstituted (C.sub.2-C.sub.4)alkyl and
substituted or unsubstituted C.sub.6-heterocyclic aromatic group,
wherein the substituent groups are selected from the group
consisting of hydroxyl and sulfate; and, more preferably, R.sub.2
is selected from the group consisting of hydrogen, hydroxyl and
sulfate; and, most preferably, R.sub.1 is selected from the groups
consisting of linear, substituted or unsubstituted
(C.sub.2-C.sub.4)alkyl, wherein a preferred substituent is sulfate;
and, most preferably, R.sub.2 is hydrogen. Preferably, the
pyridinium compound of formula (I) includes a counter anion to
neutralize the positive charge of the pyridinium compound.
[0021] Preferably, the foregoing pyridinium compounds are hydroxide
salts, sulfate, tetrafluoroborate, hexafluorophosphate, nitrate,
formate, acetate, tartrate or halogen salts, wherein the halogen is
selected from the group consisting of chloride, bromide, fluoride
and iodide. More preferably, the salts are halogens selected from
the group consisting of chloride and bromide, most preferably, the
halogen is chloride. Examples of three preferred pyridinium
compounds of the present invention are the salts 1-butylpyridinium
chloride, and 1-(3-sulfopropyl) pyridinium hydroxide inner salt
(also known as 1-(3-sulfopropyl) pyridinium) and 1-(4-pyridyl)
pyridinium chloride.
[0022] The pyridinium compounds of the present invention are
included in amounts of 0.5 ppm or greater, preferably, from 1 ppm
to 50 ppm, more preferably, from 2 ppm to 30 ppm, even more
preferably, from 2.5 ppm to 20 ppm, most preferably, from 5 ppm to
20 ppm.
[0023] Sources of copper ions and counter anions 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 can be used to provide copper ions.
Examples are copper sulfate, such as copper sulfate pentahydrate,
copper chloride, copper nitrate, copper hydroxide and copper
sulfamate. Preferably, the one or more sources of copper ions in
the electroless copper plating composition of the present invention
range from 0.5 g/L to 30 g/L, more preferably, from 1 g/L to 25
g/L, even more preferably, from 5 g/L to 20 g/L, further
preferably, from 5 g/L to 15 g/L, and most preferably, from 10 g/L
to 15 g/L.
[0024] Complexing agents include, but are not limited to, sodium
potassium tartrate, sodium tartrate, sodium salicylate, sodium
salts of ethylenediamine tetraacetic acid (EDTA), nitriloacetic
acid and its alkali metal salts, gluconic acid, gluconates,
triethanolamine, modified ethylene diamine tetraacetic acids,
S,S-ethylene diamine disuccinic acid, hydantoin and hydantoin
derivatives. Hydantoin derivatives include, but are not limited to,
1-methylhydantoin, 1,3-dimethylhydantoin and 5,5-dimethylhydantoin.
Preferably, the complexing agents are chosen from one or more of
sodium potassium tartrate, sodium tartrate, nitriloacetic acid and
its alkali metal salts, such as sodium and potassium salts of
nitirloacetic acid, hydantoin and hydantoin derivatives.
Preferably, EDTA and its salts are excluded from the electroless
copper plating compositions of the present invention. More
preferably, the complexing agents are chosen from sodium potassium
tartrate, sodium tartrate, nitriloacetic acid, nitriloacetic acid
sodium salt, and hydantoin derivates. Even more preferably, the
complexing agents are chosen from sodium potassium tartrate, sodium
tartrate, 1-methylhydantoin, 1,3-dimethylhydantoin and
5,5-dimethylhydantoin. Further preferably, the complexing agents
are chosen from sodium potassium tartrate and sodium tartrate. Most
preferably, the complexing agent is sodium potassium tartrate
(Rochelle salts).
[0025] Complexing agents are included in the electroless copper
plating compositions of the present invention in amounts of 10 g/l
to 150 g/L, preferably, from 20 g/L to 150 g/L, more preferably,
from 30 g/L to 100 g/L, even more preferably, from 35 g/L to 80
g/L, and, most preferably, from 35 g/l to 55 g/L.
[0026] Reducing agents include, but are not limited to, aldehydes,
such as, formaldehyde, formaldehyde precursors, formaldehyde
derivatives, such as paraformaldehyde, borohydrides, such sodium
borohydride, substituted borohydrides, boranes, such as
dimethylamine borane (DMAB), saccharides, such as grape sugar
(glucose), glucose, sorbitol, cellulose, cane sugar, mannitol and
gluconolactone, hypophosphite and salts thereof, such as sodium
hypophosphite, hydroquinone, catechol, resorcinol, quinol,
pyrogallol, hydroxyquinol, phloroglucinol, guaiacol, gallic acid,
glyoxylic acid, 3,4-dihydroxybenzoic acid, phenolsulfonic acid,
cresolsulfonic acid, hydroquinonsulfonic acid, catecholsulfonic
acid, tiron and salts of all of the foregoing reducing agents.
Preferably, the reducing agents are chosen from formaldehyde,
formaldehyde derivatives, formaldehyde precursors, borohydrides and
hypophosphite and salts thereof, hydroquinone, catechol,
resorcinol, and gallic acid. More preferably, the reducing agents
are chosen from formaldehyde, formaldehyde derivatives,
formaldehyde precursors, and sodium hypophosphite. Most preferably,
the reducing agent is formaldehyde.
[0027] Reducing agents are included in the electroless copper
plating compositions of the present invention in amounts of 0.5 g/L
to 100 g/L, preferably, from 0.5 g/L to 60 g/L, more preferably,
from 1 g/L to 50 g/L, even more preferably, from 1 g/L to 20 g/L,
further preferably, from 1 g/L to 10 g/L, most preferably, from 1
g/L to 5 g/L.
[0028] A pH of the electroless copper plating composition of the
present invention is greater than 7. Preferably, the pH of the
electroless copper plating compositions of the present invention is
greater than 7.5. More preferably, the pH of the electroless copper
plating compositions range from 8 to 14, even more preferably, from
10 to 14, further preferably, from 11 to 13, and most preferably,
from 12 to 13.
[0029] Optionally, but preferably, one or more pH adjusting agents
can be included in the electroless copper plating compositions of
the present invention to adjust the pH of the electroless copper
plating compositions to an alkaline pH. Acids and bases can be used
to adjust the pH, including organic and inorganic acids and bases.
Preferably, inorganic acids or inorganic bases, or mixtures thereof
are used to adjust the pH of the electroless copper plating
compositions of the present invention. Inorganic acids suitable for
use of adjusting the pH of the electroless copper plating
compositions include, for example, phosphoric acid, nitric acid,
sulfuric acid and hydrochloric acid. Inorganic bases suitable for
use of adjusting the pH of the electroless copper plating
compositions include, for example, ammonium hydroxide, sodium
hydroxide, potassium hydroxide and lithium hyddroxide. Preferably,
sodium hydroxide, potassium hydroxide or mixtures thereof are used
to adjust the pH of the electroless copper plating compositions,
most preferably, sodium hydroxide is used to adjust the pH of the
electroless copper plating compositions of the present
invention.
[0030] Optionally, but preferably, one or more stabilizers can be
included in the electroless copper plating compositions of the
present invention. Stabilizers include, but are not limited to
2,2'-dipyridyl and derivatives, 4,4'-dipyridyl, phenanthroline and
phenanthroline derivatives, thiomalic acid, 2,2' dithiodisuccinic
acid, mercaptosuccinic acid, cysteine, methionine, thionine,
thiourea, benzothiazole, mercaptobenzothiazole, 2,2'-thiodiacetic
acid, 3,3'-thiodipropionic acid, 3,3'-dithiodipropionic acid,
thiosulfate, and glycols such as polypropylene glycol and
polyethylene glycol.
[0031] Such optional stabilizers are included in the electroless
copper plating compositions of the present invention in amounts of
0.1 ppm to 20 ppm, preferably, from 0.5 ppm to 10 ppm, more
preferably, from 0.5 ppm to 5 ppm, most preferably from 0.5 ppm to
2 ppm.
[0032] Optionally, but preferably, one or more secondary
accelerators can be included in the electroless copper plating
compositions of the present invention. Such accelerators include,
but are not limited to, several free nitrogen bases such as
guanidine, guanidine derivatives, such as guanidine hydrochloride,
pyridine and pyridine derivatives such as aminopyridine, di- and
trialkylamines, such as trimethylamine and triethylamine,
N,N,N',N'-Tetrakis(2-Hydroxypropyl)ethylenediamine, and
ethylenediaminetetraacetic acid, and nickel(II) salts such as
Nickel(II) sulfate. An example of a preferred secondary accelerator
is guanidine hydrochloride.
[0033] Such accelerators can be included in amounts of 0.1 ppm to
500 ppm, preferably, from 0.2 to 15 ppm, more preferably from, 0.3
ppm to 10 ppm, most preferably from 0.3 ppm to 5 ppm.
[0034] Optionally, one or more surfactants can be included in the
electroless copper plating compositions of the present invention.
Such surfactants include ionic, such as cationic and anionic
surfactants, non-ionic and amphoteric surfactants. Mixtures of the
surfactants can be used. Surfactants can be included in the
compositions in amounts of 0.001 g/L to 50 g/L, preferably in
amounts of 0.01 g/L to 50 g/L.
[0035] Cationic surfactants include, but are not limited to,
tetra-alkylammonium halides, alkyltrimethylammonium halides,
hydroxyethyl alkyl imidazoline, alkyl imidazolium,
alkylbenzalkonium halides, alkylamine acetates, alkylamine oleates
and alkylaminoethyl glycine.
[0036] 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.
[0037] 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.
[0038] Preferably, the surfactants are non-ionic. Non-ionic
surfactants include, but are not limited to, alkyl phenoxy
polyethoxyethanols, polyoxyethylene polymers having from 20 to 150
repeating units and random and block copolymers of polyoxyethylene
and polyoxypropylene, and polyamines, such as polyallylamine.
[0039] Optionally, one or more grain refiner can be included in the
electroless copper plating compositions of the present invention.
Grain refiners include, but are not limited to, cyanide and cyanide
containing inorganic salts such as potassium hexacyanoferrate,
2-mercaptobenthiazole, 2,2'-bipyridine and 2,2'-bipyridine
derivatives, 1,10-phenanthroline and 1,10-phenanthroline
derivatives, vanadium oxides such as sodium Metavanadate, and
nickel salts such as nickel(II) sulfate. Grain refiners are
included in amounts well known to those of ordinary skill in the
art.
[0040] Preferably, the electroless copper plating composition of
the present invention consists of one or more sources of copper
ions, including corresponding anions, one or more pyridinium
compounds or salts thereof having formula (I), one or more
complexing agents, one or more reducing agents, water, optionally,
one or more pH adjusting agents, optionally, one or more
stabilizers, optionally, one or more secondary accelerators,
optionally, one or more surfactants, and optionally, one or more
grain refiners, wherein a pH of the electroless copper plating
composition is 10-14.
[0041] More preferably, the electroless copper plating composition
of the present invention consists of one or more sources of copper
ions, including corresponding anions, one or more pyridinium
compounds or salts thereof having formula (I), wherein the salts
are selected from the group consisting of hydroxide, chloride and
bromide salts, one or more complexing agents, one or more reducing
agents, water, one or more pH adjusting agents, one or more
stabilizers, optionally, one or more secondary accelerators,
optionally, one or more surfactants, and, optionally, one or more
grain refiners, wherein a pH of the electroless copper plating
composition is 11-13.
[0042] Most preferably, the electroless copper plating compositions
of the present invention consist of one or more sources of copper
ions, including corresponding anions, one or more pyridinium
compounds selected from the group consisting of 1-butyl pyridinium
chloride, 1-(3-sulfopropyl) pyridinium hydroxide and 1-(4-pyridyl)
pyridinium chloride, one or more complexing agents, one or more
reducing agents, water, one or more pH adjusting agents, one or
more stabilizers, optionally, one or more secondary accelerators,
optionally, one or more surfactants, and, optionally, one or more
grain refiners, wherein a pH of the electroless copper plating
composition is 12-13.
[0043] The electroless copper compositions and methods of the
present invention can be used to electroless plate copper on
various substrates such as dielectrics, semiconductors, metal-clad
and unclad substrates such as printed circuit boards. Such
metal-clad and unclad printed circuit boards can include
thermosetting resins, thermoplastic resins and combinations
thereof, including fibers, such as fiberglass, impregnated
embodiments of the foregoing. Preferably the substrate is a
metal-clad printed circuit or wiring board with a plurality of
through-holes, vias, or combinations thereof. The electroless
copper plating compositions and methods of the present invention
can be used in both horizontal and vertical processes of
manufacturing printed circuit boards, preferably, the electroless
copper plating compositions methods of the present invention are
used in horizontal processes.
[0044] 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.
[0045] 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.
[0046] The electroless copper plating compositions and methods of
the present invention can be used to electroless copper plate
substrates with 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 polyphenylene 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.
[0047] In the method of electroless copper plating with the
electroless copper compositions of the present invention,
optionally, the substrates are cleaned or degreased, optionally,
roughened or micro-roughened, optionally, the substrates are etched
or micro-etched, optionally, a solvent swell is applied to the
substrates, through-holes are desmeared, and various rinse and
anti-tarnish treatments can, optionally, be used.
[0048] Preferably, the substrates to be electroless copper plated
with the electroless copper plating compositions and methods of the
present invention are metal-clad substrates with dielectric
material and a plurality of through-holes such as printed circuit
boards. Optionally, the boards are rinsed with water and cleaned
and degreased followed by desmearing the through-hole walls.
Prepping or softening the dielectric or desmearing of the
through-holes can begin with application of a solvent swell.
Although, it is preferred, that the method of electroless copper
plating is for plating through-hole walls, it is envisioned that
the method of electroless copper plating can also be used to
electroless copper plate walls of vias.
[0049] Conventional solvent swells can be used. The specific type
can vary depending on the type of dielectric material. Minor
experimentation can be done to determine which solvent swell is
suitable for a particular dielectric material. The T.sub.g of the
dielectric often determines the type of solvent swell to be used.
Solvent swells include, but are not limited to, glycol ethers and
their associated ether acetates. Conventional amounts of glycol
ethers and their associated ether acetates well known to those of
skill in the art can be used. Examples of commercially available
solvent swells are CIRCUPOSIT.TM. Conditioner 3302A, CIRCUPOSIT.TM.
Hole Prep 3303 and CIRCUPOSIT.TM. Hole Prep 4120 solutions
(available from Dow Electronic Materials).
[0050] After the solvent swell, optionally, a promoter can be
applied. Conventional promoters can be used. Such promoters include
sulfuric acid, chromic acid, alkaline permanganate or plasma
etching. Preferably, alkaline permanganate is used as the promoter.
Examples of commercially available promoters are CIRCUPOSIT.TM.
Promoter 4130 and CIRCUPOSIT.TM. MLB Promoter 3308 solutions
(available from Dow Electronic Materials). Optionally, the
substrate and through-holes are rinsed with water.
[0051] If a promoter is used, a neutralizer is then applied to
neutralize any residues left by the promoter. Conventional
neutralizers can be used. Preferably, 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.
[0052] After neutralizing an acid or alkaline conditioner is
applied. Conventional conditioners can be used. Such conditioners
can 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 Advanced 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, 813 and 860 formulations
(available from Dow Electronic Materials). Optionally, the
substrate and through-holes are rinsed with water.
[0053] Optionally, conditioning can be followed by micro-etching.
Conventional micro-etching compositions can be used. Micro-etching
is designed to clean and provide a micro-roughened metal surface on
exposed metal (e.g. innerlayers and surface etch) to enhance
subsequent adhesion of plated electroless copper 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 (both available from
Dow Electronic Materials). Optionally, the substrate is rinsed with
water.
[0054] Optionally, a pre-dip can then be applied to the
micro-etched substrate and through-holes. Examples of pre-dips
include, but are not limited to, organic salts such as sodium
potassium tartrate or sodium citrate, 0.5% to 3% sulfuric acid,
nitric acid, or an acidic solution of 25 g/L to 75 g/L sodium
chloride. An example of a commercially available pre-dip is acidic
Pre-Dip CIRCUPOSIT.TM. 6520 solution.
[0055] A catalyst is then applied to the substrate. While it is
envisioned that any conventional catalyst suitable for electroless
metal plating which includes a catalytic metal can be used,
preferably, a palladium catalyst is used in the methods of the
present invention. The catalyst can be a non-ionic palladium
catalyst, such as a colloidal palladium-tin catalyst, or the
catalyst can be an ionic palladium. If the catalyst is a colloidal
palladium-tin catalyst, an acceleration step is done to strip tin
from the catalyst and to expose the palladium metal for electroless
copper plating. If the catalyst is a colloidal palladium-tin
catalyst, an acceleration step is applied after catalyst
adsorption, for example, by using hydrochloric acid, sulfuric acid
or tetrafluoroboric acid as the accelerator at 0.5-10% in water to
strip tin from the catalyst and to expose the palladium metal for
electroless copper plating. If the catalyst is an ionic catalyst,
the acceleration step is excluded from the method and, instead, a
reducing agent is applied to the substrate subsequent to
application of the ionic catalyst to reduce the metal ions of the
ionic catalyst to their metallic state, such as Pd (II) ions to
Pd.degree. metal. Examples of suitable commercially available
colloidal palladium-tin catalysts are CIRCUPOSIT.TM. 3340 catalyst
and CATAPOSIT.TM. 44 catalyst (available from Dow Electronic
Materials). An example of a commercially available palladium ionic
catalyst is CIRCUPOSIT.TM. 6530 Catalyst. The catalyst can be
applied by immersing the substrate in a solution of the catalyst,
or by spraying the catalyst solution on the substrate, or by
atomization of the catalyst solution on the substrate using
conventional apparatus. The catalysts can be applied at
temperatures from room temperature to 80.degree. C., preferably,
from 30.degree. C. to 60.degree. C. The substrate and through-holes
are optionally rinsed with water after application of the
catalyst.
[0056] Conventional reducing agents known to reduce metal ions to
metal can be used to reduce the metal ions of the catalysts to
their metallic state. Such reducing agents include, but are not
limited to, dimethylamine borane (DMAB), sodium borohydride,
ascorbic acid, iso-ascorbic acid, sodium hypophosphite, hydrazine
hydrate, formic acid and formaldehyde. Reducing agents are included
in amounts to reduce substantially all of the metal ions to metal.
Such amounts are well known by those of skill in the art. If the
catalyst is an ionic catalyst, the reducing agents are applied
subsequent to the catalyst being applied to the substrate and prior
to metallization.
[0057] The substrate and walls of the through-holes are then plated
with copper using an electroless copper plating composition of the
present invention. Methods of electroless copper plating of the
present invention can be done at temperatures of 40.degree. C. or
less. Preferably, methods of electroless copper plating of the
present invention are done at temperatures from room temperature to
40.degree. C., more preferably, electroless copper plating is done
from room temperature to 35.degree. C., even more preferably, from
30.degree. C. to 35.degree. C., most preferably, from 30.degree. C.
to 34.degree. C. The substrate can be immersed in the electroless
copper plating composition of the present invention or the
electroless copper plating composition can be sprayed on the
substrate. Methods of electroless copper plating of the present
invention using electroless copper plating compositions of the
present invention are done in an alkaline environment of pH greater
than 7. Preferably, methods of electroless copper plating of the
present invention are done at a pH of greater than 7.5, more
preferably, electroless copper plating is done at a pH of 8 to 14,
even more preferably, from 10 to 14, further preferably, from 11 to
13, and most preferably, from 12 to 13.
[0058] Preferably, the electroless copper plating rates of the
present invention are equal to or greater than 0.6 .mu.m/5 min. at
temperatures of less than or equal to 40.degree. C., more
preferably, the electroless copper plating rates of the present
invention are equal to or greater than 0.65 .mu.m/5 min., such as
from 0.65 .mu.m/5 min. to 1 .mu.m/5 min., even more preferably,
equal to or greater than 0.7 .mu.m/5 min., such as from 0.75
.mu.m/5 min. to 1 .mu.m/5 min., or such as from 0.75 .mu.m/5 min.
to 0.8 .mu.m/5 min., at temperatures of less than or equal to
35.degree. C., most preferably, electroless plating is done at
temperatures from 30.degree. C. to 34.degree. C.
[0059] The methods of electroless copper plating using the
electroless copper plating compositions of the present invention
enable good average backlight values for electroless copper plating
of through-holes of printed circuit boards. Such average backlight
values are preferably greater than or equal to 4.5, more preferably
from 4.6 to 5, even more preferably from 4.7 to 5, most preferably
from 4.8 to 5. Such high average backlight values enable the
methods of electroless copper plating of the present invention
using the electroless copper plating compositions of the present
invention to be used for commercial electroless copper plating,
wherein the printed circuit board industry substantially requires
backlight values of 4.5 and greater. The electroless copper metal
plating compositions and methods of the present invention enable
uniform, bright copper deposits over broad concentration ranges of
pyridinium compounds or salts thereof, even at high plating
rates.
[0060] The following examples are not intended to limit the scope
of the invention but to further illustrate the invention.
Example 1
Electroless Copper Plating Rates of an Electroless Copper Plating
Baths Containing Pyridinium Compounds
[0061] Ten (10) electroless copper plating baths are prepared. All
ten baths include the following components:
[0062] 1. 10 g/L Copper sulfate pentahydrate
[0063] 2. 40 g/L Rochelle salts
[0064] 3. 8 g/L Sodium hydroxide
[0065] 4. 4 g/L Formaldehyde
[0066] 5. 0.5 ppm 2,2'-dithiodisuccinic acid
[0067] 6. Water (balance)
The pH of each bath is 13. To nine (9) of the electroless plating
compositions one of the following pyridinium compounds is added in
the amount specified in Table 1. Bath 10 is a control where no
pyridinium compounded is added.
TABLE-US-00001 TABLE 1 1-(3-sulfopropyl) 1-butylpyridinium
pyridinium 1-(4-pyridyl) Bath chloride hydroxide pyridinium
chloride 1 2.5 ppm -- -- 2 10 ppm -- -- 3 20 ppm -- -- 4 -- 2.5 ppm
-- 5 -- 10 ppm -- 6 -- 20 ppm -- 7 -- -- 2.5 ppm 8 -- -- 10 ppm 9
-- -- 20 ppm
Each bath is used to plate copper on bare epoxy substrates of NP140
material (Nanya, Taiwan). Each epoxy substrate is first treated
according to the following process prior to electroless copper
plating:
[0068] (1) Conditioner 231 applied for 1.5 min. at 40.degree.
C.;
[0069] (2) Rinse with DI water for 2 min. at room temperature;
[0070] (3) Nitric acid pre-dip, pH=2, for 0.5 min. at room
temperature;
[0071] (4) Rinse with DI water for 2 min. at room temperature;
[0072] (5) 100 ppm of CIRCUPOSIT.TM. 6530 Catalyst for 1 min. at
40.degree. C.;
[0073] (6) Rinse with DI water for 1 min. at room temperature;
[0074] (7) 5 g/L boric acid and 0.6 g/L dimethylamine borane
aqueous solution for 1 min. at 32.degree. C.; and,
[0075] (8) Rinse with DI water for 1 min. at room temperature.
Electroless copper plating is done at 34.degree. C. for 5 minutes.
The plating rate is determined by weighing each substrate using a
conventional laboratory analytical balance prior to electroless
copper plating and then weighing each substrate subsequent to
plating. The difference in the weight of each substrate is then
used to calculate the deposit thickness using the laminate surface
area, which is 25 cm.sup.2 and the density of the copper deposit,
8.92 g/cm.sup.3 and the value is converted to plating rate by
dividing over the plating time length. The plating rate for each
bath is shown in Table 2.
TABLE-US-00002 TABLE 2 Bath Plating Rate 1 0.72 .mu.m/5 min. 2 0.77
.mu.m/5 min. 3 0.74 .mu.m/5 min. 4 0.75 .mu.m/5 min. 5 0.67 .mu.m/5
min. 6 0.61 .mu.m/5 min. 7 0.69 .mu.m/5 min. 8 0.59 .mu.m/5 min. 9
0.61 .mu.m/5 min. 10 (Control) 0.49 .mu.m/5 min.
Including 1-butylpyridinium chloride, 1-(3-sulfopropyl) pyridinium
hydroxide or 1-(4-pyridyl) pyridinium chloride in the electroless
copper plating bath increases plating rate. The copper deposits
from the baths containing 1-butylpyridinium chloride and
1-(3-sulfopropyl) pyridinium hydroxide appear bright and uniform
over substantially all of the epoxy substrates over the
concentrations of 2.5 ppm, 10 ppm and 20 ppm. The copper deposits
plated from the baths containing 1-(4-pyridyl) pyridinium chloride
show bright and uniform areas with minor patches of rough deposits.
The copper deposit plated from the control bath shows large areas
of irregular, rough and dark deposits with minor regions of bright
deposits.
Example 2 (Comparative)
Electroless Copper Plating Rates of an Electroless Copper Plating
Baths Containing Pyridine (Free Nitrogen Base)
[0076] Three (3) electroless copper plating baths are prepared. All
three baths include the following components:
[0077] 1. 10 g/L Copper sulfate pentahydrate
[0078] 2. 40 g/L Rochelle salts
[0079] 3. 8 g/L Sodium hydroxide
[0080] 4. 4 g/L Formaldehyde
[0081] 5. 0.5 ppm 2,2'-dithiodisuccinic acid
[0082] 6. Water (balance)
The pH of each bath is 13. Pyridine is added to the baths in
amounts of 2.5 ppm (Comparative Bath 1), 10 ppm (Comparative Bath
2) or 20 ppm (Comparative Bath 3).
[0083] Each bath is used to plate copper on epoxy substrates. The
epoxy substrates are treated as described in Example 1 in
preparation for electroless copper plating. Electroless copper
plating is done at 34.degree. C. for 5 minutes. The plating rate is
then determined as described in Example 1. The plating rate for
each bath is shown in Table 3.
TABLE-US-00003 TABLE 3 Comparative Bath Plating Rate 1 0.65 .mu.m/5
min. 2 0.48 .mu.m/5 min. 3 0.42 .mu.m/5 min.
Although the plating rate of pyridine at 2.5 ppm is higher than in
the Control in Example 1, at higher concentrations of 10 ppm and 20
ppm the plating rates decline to below the plating rate of the
control. The plating rate of pyridine is less than the Control
electroless copper bath in Example 1. The copper deposits have a
mixture of bright and uniform areas and rough and dull areas.
Example 3
Electroless Copper Plating Rates of an Electroless Copper Plating
Baths Containing Pyridinium Compounds and Guanidine
Hydrochloride
[0084] Fourteen (14) electroless copper plating baths are prepared.
All fourteen baths include the following components:
[0085] 1. 10 g/L Copper sulfate pentahydrate
[0086] 2. 40 g/L Rochelle salts
[0087] 3. 8 g/L Sodium hydroxide
[0088] 4. 4 g/L Formaldehyde
[0089] 5. 0.5 ppm 2,2'-dithiodisuccinic acid
[0090] 6. 0.36 ppm Guanidine Hydrochloride
[0091] 7. Water (balance)
The pH of each bath is 13. To thirteen (13) of the electroless
plating compositions one of the following pyridinium compounds is
added in the amount specified in Table 4. Bath 24 is a control
where no pyridinium compounded is added.
TABLE-US-00004 TABLE 4 1-(3-sulfopropyl) 1-butylpyridinium
pyridinium 1-(4-pyridyl) Bath chloride hydroxide pyridinium
chloride 11 2.5 ppm -- -- 12 5 ppm -- -- 13 10 ppm -- -- 14 15 ppm
-- -- 15 20 ppm -- -- 16 -- 2.5 ppm -- 17 -- 5 ppm -- 18 -- 10 ppm
-- 19 -- 15 ppm -- 20 -- 20 ppm -- 21 -- -- 2.5 ppm 22 -- -- 5 ppm
23 -- -- 10 ppm
Each bath is used to plate copper on bare epoxy substrates. Each
epoxy substrate is treated prior to electroless copper plating as
described in Example 1. Electroless copper plating is done at
34.degree. C. for 5 minutes. The plating rate is determined as
described above in Example 1. The plating rate for each bath is
shown in Table 5.
TABLE-US-00005 TABLE 5 Bath Plating Rate 11 0.46 .mu.m/5 min. 12
0.75 .mu.m/5 min. 13 0.78 .mu.m/5 min. 14 0.74 .mu.m/5 min. 15 0.83
.mu.m/5 min. 16 0.69 .mu.m/5 min. 17 0.65 .mu.m/5 min. 18 0.74
.mu.m/5 min. 19 0.78 .mu.m/5 min. 20 0.66 .mu.m/5 min. 21 0.98
.mu.m/5 min. 22 0.67 .mu.m/5 min. 23 0.81 .mu.m/5 min. 24 (Control)
0.5 .mu.m/5 min.
Including 1-butylpyridinium chloride, 1-(3-sulfopropyl) pyridinium
hydroxide or 1-(4-pyridyl) pyridinium chloride in the electroless
copper plating bath increases plating rate over the control which
included guanidine hydrochloride. The copper deposits from the
baths containing 1-butylpyridinium chloride and 1-(3-sulfopropyl)
pyridinium hydroxide appear bright and uniform over substantially
all of the epoxy substrates. The copper deposits plated from the
baths containing 1-(4-pyridyl) pyridinium chloride show bright and
uniform areas with minor patches of rough deposits. The copper
deposit plated from the control bath shows minor regions of bright
deposits intermingled with large areas of irregular and rough
deposits.
Example 4 (Comparative)
Electroless Copper Plating Rates of an Electroless Copper Plating
Baths Containing Pyridine (Free Nitrogen Base) and Guanidine
Hydrochloride
[0092] Five (5) electroless copper plating baths are prepared. All
five baths include the following components:
[0093] 1. 10 g/L Copper sulfate pentahydrate
[0094] 2. 40 g/L Rochelle salts
[0095] 3. 8 g/L Sodium hydroxide
[0096] 4. 4 g/L Formaldehyde
[0097] 5. 0.5 ppm 2,2'-dithiodisuccinic acid
[0098] 6. 0.36 ppm Guanidine hydrochloride
[0099] 7. Water (balance)
The pH of each bath is 13. Pyridine is added to the baths in
amounts of 2.5 ppm (Comparative Bath 4), 5 ppm (Comparative Bath
5), 10 ppm (Comparative Bath 6), 15 ppm (Comparative Bath 7) or 20
ppm (Comparative Bath 8).
[0100] Each bath is used to plate copper on epoxy substrates. The
epoxy substrates are treated as described in Example 1 prior to
electroless copper plating. Electroless copper plating is done at
34.degree. C. for 5 minutes. The plating rate is determined as
described above in Example 1. The plating rate for each bath is
shown in Table 6.
TABLE-US-00006 TABLE 6 Comparative Bath Plating Rate 4 0.61 .mu.m/5
min. 5 0.62 .mu.m/5 min. 6 0.57 .mu.m/5 min. 7 0.52 .mu.m/5 min. 8
0.48 .mu.m/5 min.
Even in combination with the accelerator guanidine hydrochloride,
the highest plating rates for the electroless copper baths
containing the base pyridine are just above 0.60 .mu.m/5 min. In
general, increasing the concentration of pyridine in the
electroless bath shows a tendency toward a decrease in electroless
copper plating rate. The copper deposits have bright and uniform
areas intermixed with rough and dull areas.
Example 5
Backlight Experiment with Aqueous Alkaline Electroless Cooper
Compositions of the Present Invention Containing Pyridinium
Compounds
[0101] The following aqueous alkaline electroless copper
compositions of the invention are prepared having the components
and amounts disclosed in Table 7 below.
TABLE-US-00007 TABLE 7 Component Bath 25 Bath 26 Copper sulfate
pentahydrate 10 g/L 10 g/L Rochelle salts 40 g/L 40 g/L Sodium
hydroxide 8 g/L 8 g/L Formaldehyde 4 g/L 4 g/L 2,2'-Dithiosuccinic
acid 0.5 ppm 0.5 ppm Guanidine hydrochloride 0.36 ppm 0.36 ppm
1-butylpyridinium chloride 10 ppm -- 1-(3-sulfopropyl) -- 10 ppm
pyridinium hydroxide Water To one liter To one liter
The pH of the aqueous alkaline electroless copper compositions have
a pH=13 at room temperature as measured using a conventional pH
meter available from Fisher Scientific.
[0102] Six (6) different FR/4 glass epoxy panels with a plurality
of through-holes are provided: TUC-662, SY-1141, IT-180, 370HR,
EM825 and NPGN. The panels are eight-layer copper-clad panels.
TUC-662 is obtained from Taiwan Union Technology, and SY-1141 is
obtained from Shengyi. IT-180 is obtained from ITEQ Corp., NPGN is
obtained from NanYa and 370HR from Isola and EM825 are obtained
from Elite Materials Corporation. The T.sub.g values of the panels
range from 140.degree. C. to 180.degree. C. Each panel is 5
cm.times.10 cm.
The through-holes of each panel are treated as follows: [0103] 1.
The through-holes of each panel are desmeared with CIRCUPOSIT.TM.
Hole Prep 3303 solution for 6 min. at 80.degree. C.; [0104] 2. The
through-holes of each panel are then rinsed with flowing tap water
for 2 min.; [0105] 3. The through-holes are then treated with
CIRCUPOSIT.TM. MLB Promoter 3308 aqueous permanganate solution at
80.degree. C. for 8 min.; [0106] 4. The through-holes are then
rinsed for 4 min. in flowing tap water; [0107] 5. The through-holes
are then treated with a 3 wt % sulfuric acid/3 wt % hydrogen
peroxide neutralizer at room temperature for 2 min.; [0108] 6. The
through-holes of each panel are then rinsed with flowing tap water
for 2 min.; [0109] 7. The through-holes of each panel are then
treated with CIRCUPOSIT.TM. Conditioner 231 alkaline solution for
1.5 min. at 60.degree. C.; [0110] 8. The through-holes are then
rinsed with flowing tap water for 2 min.; [0111] 9. The
through-holes are then treated with a sodium persulfate/sulfuric
acid etch solution for 1 min. at room temperature; [0112] 10. The
through-holes of each panel are then rinsed with flowing DI water
for 1 min.; [0113] 11. The panels are then immersed into acidic
Pre-Dip CIRCUPOSIT.TM. 6520 for 0.5 min. at room temperature and
then immersed into CIRCUPOSIT.TM. 6530 Catalyst which is an ionic
aqueous alkaline palladium catalyst concentrate (available from Dow
Electronic Materials) for 1 min. at 40.degree. C., wherein the
catalyst is buffered with sufficient amounts of sodium carbonate,
sodium hydroxide or nitric acid to achieve a catalyst pH of 9-9.5;
[0114] 12. The through-holes of each panel are then rinsed with
flowing DI water for 1 min. at room temperature; [0115] 13. The
panels are then immersed into a 0.6 g/L dimethylamine borane and 5
g/L boric acid solution at 32.degree. C. for 1 min. to reduce the
palladium ions to palladium metal; [0116] 14. The through-holes of
each panel are then rinsed with flowing DI water for 1 min.; [0117]
15. The panels are then immersed in the electroless copper plating
composition of Table 7 and copper is plated at 34.degree. C., at a
pH of 13 and copper is deposited on the walls of the through-holes
for 5 min.; [0118] 16. The copper plated panels are then rinsed
with flowing tap water for 4 min.; [0119] 17. Each copper plated
panel is then dried with compressed air; and [0120] 18. The walls
of the through-holes of the panels are examined for copper plating
coverage using the backlight process described below.
[0121] Each panel is cross-sectioned nearest to the centers of the
through-holes as possible to expose the copper plated walls. The
cross-sections, no more than 3 mm thick from the center of the
through-holes, are taken from each panel are placed under a
conventional optical microscope of 50.times. magnification with a
light source behind the samples. The quality of the copper deposits
are determined by the amount of light visible under the microscope
that is transmitted through the sample. Inside the plated
through-holes, transmitted light is only visible in areas where
there is incomplete electroless coverage. If no light is
transmitted and the section appears completely black, it is rated a
5 on the backlight scale indicating complete copper coverage of the
through-hole wall. If light passes through the entire section
without any dark areas, this indicates that there is very little to
no copper metal deposition on the walls of the through-holes and
the section is rated 0. If sections have some dark regions as well
as light regions, they are rated between 0 and 5. A minimum of ten
through-holes are inspected and rated for each board. Backlight
values of 4.5 and greater are indicative of commercially acceptable
catalysts in the plating industry.
[0122] The average backlight value for each type of FR/4 glass
epoxy panel is disclosed in the table below.
TABLE-US-00008 TABLE 8 Panel Bath 25 Bath 26 370HR 4.8 4.4 EM825
4.8 4.6 IT-180 4.8 4.7 NPGN 4.7 4.8 SY-1141 4.4 4.4 TU-662 4.6
4.7
Overall both baths show very good backlight values.
* * * * *