Note: Descriptions are shown in the official language in which they were submitted.
2 ~ ~~6~~2
PALLADIUM COLLOID SOLUTION AND ITS UTILISATION
The invention relates to a palladium colloid solution,
a utilisation of the solution for coating electrically
non-conductive substrate surfaces with metallic
coverings, and a printed circuit board produced by
using the solution.
Metallisation of electrically non-conductive substrate
surfaces is known per se. Electrolytic processes are
used for metallising printed circuit boards, plastics
parts for decorative applications and also for
functional purposes. To this end the substrate
surfaces, after an appropriate pre-treatment, are
activated with a solution normally containing noble
metal, and then metallised in a currentless manner. If
necessary, further metal layers may be applied to this
first metal layer by means of an electrolytic coating
process.
The currentless metallisation process however has
considerable disadvantages (difficulty of monitoring
the process in currentless metallising baths, use of
formaldehyde as a reducing agent, which is suspected of
being carcinogenic , utilisation of complex formers
which are difficult to handle in terms of waste water
3
past to develop better processes. In some processes,
the process step of currentless metallisation needed to
generate the electrical surface conductivity, is no
longer necessary.
The electrical surface conductivity necessary for
electrolytic metallisation is in this case for example
generated by means of intrinsically conductive organic
polymers, these being applied as a thin layer to the
surfaces. In DE 38 06 884 C1, DE 39 28 832 A1, DE 39
31 003 A1, EP 0 206 133 A1 and EP 0 413 109 A2, there
are described methods which use such polymer layers and
subsequent metallisation. In these methods the
conductive form of the polymer is generated by an
acidic or oxidising subsequent treatment of the monomer
adsorbed on the substrate surface, in which the monomer
is polymerised. A disadvantage however is that the
conductive polymer layer is applied not only to the
non-conductive substrate surfaces, but is also
deposited on metallic surfaces such for example as the
copper surfaces on printed circuit boards, so that
subsequently deposited metal layers do not adhere
sufficiently securely on these metal surfaces.
In another variant of the method, the surfaces with the
conductive organic polymer layer are coated after
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4
treatment with an activator containing noble metal (DE
42 11 152 C1) .
In another alternative method, disclosed in the
documents DE 39 39 676 C1, DE 41 12 462 A1, DE 42 27
836 A1 and GB 22 43 833A, the conductive polymer layer
is formed only on the non-conductive surfaces, the non-
conductive monomer reacting in an acidic solution
directly with the oxidation agent adsorbed on the non-
conductive substrate surfaces. However, the monomer
compounds used, from which the conductive polymer film
is generated, is, as in the preceding variant of the
method, relatively volatile, so that special
precautionary measures have to be taken in order to
protect working personnel.
Furthermore, as disclosed in US-PS 46 31 117, US-PS 48
74 477, DE 41 41 416 A1 and WO 92/19092, thin carbon
layers may be applied to the substrate surfaces in
order to generate the surface conductivity. In this
case also the conductive layers form not only on the
non-conductive areas of the substrate surfaces, but on
metallic surface areas. Therefore the carbon layers
must be removed from these areas before metallisation.
This requires an additional process step.
CA 02186482 2004-09-02
In a further alternative method, the first conductive
layer required for electrolytic metallisation is
generated by treatment in solutions containing noble
metal. Various alternative methods are described f_or
5 this purpose.
According to US-PS 30 99 608, the substrate surfaces
are firstly treated with a palladium/tin oxide-colloid
solution and then with a solution by means of which the
adsorbed tin compounds are again removed from the
surfaces. The surfaces can then be metallised with a
copper solution containing pyrophosphate.
According to DE 33 04 004 A1, the surfaces are likewise
treated with a palladium/tin oxide-colloid solution and
then with a solution for removing the tin compounds.
Thereafter electrolytic metallisation can take place.
According to DE 33 23 476 C2 the surfaces are also
treated with a palladium/tin oxide-colloid solution and
then with a solution by means of which adsorbed tin
compounds are removed from the surfaces. The surfaces
are metallised with copper baths with special organic
compounds which enable the preferred separation of the
surface areas coated with palladium colloid.
CA 02186482 2004-09-02
6
According to DE 37 41 459 C1 the substrate surfaces,
after a catalytic activation, for example with a
palladium/tin oxide-colloid solution. are treated with
a solution containing nitrogenous compounds, for
example polyvinylpyrrolidone,and are thereafter
electrolytically metallised.
According to US-PS 47 90 913 and US-PS 48 91 069 the
surfaces are treated with a palladium/tin oxide-colloid
solution which additionally contains a stabiliser and a
promoter, the hydrogen occurring during the
electrolytic deposition being taken up by the adsorbed
palladium colloid and reinforcing the electrolytic
metallisation. Salts of aluminium, titanium, zirconium
and hafnium and as promoter materials such as organic
hydroxy, thiourea compounds, surface-active compounds,
amino acids, polycarboxylic acids, and water-soluble
polymers are used. Thereafter electrolytic
metallisation can take place.
According to US-PS 50 71 517, the surfaces are treated
with a palladium/tin oxide-colloid solution and then
with a weakly alkaline solution for removing the tin
compounds. Thereafter electrolytic metallisation can
take place.
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According to EP 0 398 019 A1 the substrate surfaces,
before treatment with a solution containing metal, such
for example as a palladium/tin oxide-colloid solution,
are treated with a solution which contains a surface-
s active compound and which reinforces the adsorption of
metal.
The abovenamed methods have the disadvantage that a
sufficiently dense and pore-free metal coating can only
be deposited, and a sufficiently high degree of
adhesion of the deposited metal film on the metallic
areas, for example on the copper surfaces of a printed
circuit board, can only be achieved which can scarcely
be maintained during industrial application of the
methods.
According to US-PS 39 84 290, in a further alternative
method, there is deposited on the entire surface of the
substrate a more electropositive (nobler) metal than
the metal present on the substrate in specific areas.
During metallisation of printed circuit boards, for
example, palladium or silver is applied to the copper
surfaces and the non-conductive areas. Then the metal
coating formed is treated with an etching solution,
which attacks only the original metal surfaces
(copper), so that the nobler metal film formed is again
removed from the original metal surfaces. Thereafter
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8
electrolytic metallisation can take place. According
to a variant of the method the substrate surfaces are
treated, in conjunction with coating with the nobler
metal, with a solution containing chalcogen compounds.
In a further variant of the method, the substrate
surfaces are firstly treated with a colloid solution
containing a noble metal, and then with a solution
containing chalcogenide compounds. In~this way the
adsorbed noble metal is converted into a highly
conductive noble metal-chalcogenide compound which is
stable against chemical influences. More typically, a
palladium/tin oxide-colloid solution is used as an
activator and sodium sulphide as a chalcogenide
compound (US-PS 48 95 739, US-PS 49 52 286, US-PS 50 07
990, US-PS 50 17 742).
According to US-PS 48 10 333, the substrate surfaces
are first treated with an alkaline permanganate
solution. There then forms on the substrate surfaces a
manganese dioxide layer to a reaction of the
permanganate with the organic material of the
substrate. This layer is subsequently treated with a
chalcogenide solution and then with a noble metal
solution. Thereafter electrolytic metallisation is
carried out.
.. 2186~8~
9
The treatment with the chalcogenide solution however
leads, on metallic areas of the substrate surfaces, to
a formation of metallic chalcogenides, so that these
metallic chalcogenide layers must be removed before the
subsequent electrolytic metallisation by an etching
process, from the metal surfaces, in order to obtain
sufficient adhesion of the deposited metal on the metal
substrate. The etching process must be carried out
within narrow parameter limits, in order on the one
hand not to damage the formed conductive layer, and on
the other hand to remove the entire metallic
chalcogenide layer from the metal surfaces.
According to US-PS 49 19 768, the surfaces to be coated
are firstly treated with a solution containing tin (II)
ions, then with a chalcogenide solution and thereafter
with a solution of a noble metal, for example with
palladium chloride. Then the pre-treated substrate
surfaces can be electrolytically metallised. In this
case also the metallic chalcogenide layer formed must
be removed from the metallic areas of the substrate in
an etching process. The same problems arise as in the
first case mentioned.
In all processes in which colloidal noble metal
solutions and in particular palladium/tin oxide-colloid
solutions are used, there exists the problem that the
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colloidal solutions are oxidation-sensitive. This is
due above all to the easy oxidation of the tin (II)
compounds into tin (IV) compounds. Due to oxidation of
the tin compounds, the stabilising effect on the
5 colloid solution of the tin (II) ions is lost, as tin
(IV) ions do not have a stabilising effect. In this
way the colloid coagulates, and palladium is
precipitated.
10 In addition, only a limited palladium concentration can
be adsorbed on the substrate surfaces from
palladium/tin oxide-colloid solutions. Therefore the
capacity for metallisation of palladium layers, which
are adsorbed from these colloids, is less than that of
colloid solutions stabilised with organic protective
colloids.
Another noble metal colloid solution is described in DE
42 03 577 A1. In this case there are involved colloids
of the noble metal oxides which, after adsorption on
the non-conductive substrate surfaces, must be reduced
by a further treatment step to the corresponding
metals.
Noble metal solutions stabilised with organic
protective colloids are less sensitive to oxidation
than the palladium/tin oxide-colloid solutions
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11
mentioned above. In US-PS 40 04 051, US-PS 46 34 468,
US-PS 46, 52 311 and US-PS 47 25 314, such noble metal
solutions are described for processes with currentless
metallisation baths, preferably with alkaline copper
baths.
In a further alternative method for direct electrolytic
metallisation, the substrate surfaces according to DE
42 06 680 C2 are treated with noble metal colloid
solutions stabilised with organic protective colloids
instead of with tin compounds. In addition, in order
to remove the adsorbed protective colloid compounds
from the substrate surfaces, a solution is used which
contains sulphur compounds with sulphur in the
oxidation stage of +1 to +5. This method has the
advantage that coating of the non-conductive surface
areas with the noble metal colloid is successful
without deposition of a disturbing layer on the
metallic areas of the surfaces to be coated.
However, the noble metal colloid solutions stabilised
with organic protective colloids are also oxidation-
sensitive, as the colloidal noble metal reacts with
atmospheric oxygen, which is carried into the solution.
In an acidic solution, the colloidal palladium is
transferred by oxidation into soluble palladium salts,
so that the noble metal colloid is destroyed. The
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12
colloid solutions react particularly in the use of
continuous installations used for manufacturing printed
circuit boards and in which the treatment solutions are
sprayed or splashed on to the horizontally guided
printed circuit boards, with oxygen, as the solutions
in this case are intensively moved, and they therefore
come more intensively into contact with air than when a
dipping process is used.
Therefore the problem underlying the present invention
is to avoid the disadvantages of prior art and to find
a palladium colloid solution with low oxidation
sensitivity and a method enabling electrically non-
conductive substrate surfaces to be coated with metal
by a direct electrolytic deposition of metal.
According to one aspect of the invention, there is
provided a palladium colloid solution with low
oxidation sensitivity, containing at least one tin-free
reducing agent and at least one organic protective
colloid for stabilising the colloid solution, and in
addition at least one noble metal selected from the
group rhodium, iridium and platinum, or at least one
compound of these noble metals or a mixture of these
noble metals and of these compounds.
According to one aspect of the invention, there is
provided utilisation characterised by electroytic
metallisation.
~ CA 02186482 2004-09-02
12a
According to yet another aspect of the invention, there
is provided utilisation of a palladium colloid solution
characterised by individual or all new features or
combinations of the disclosed features.
According to one aspect of the invention, there is
provided a method of manufacturing a palladium colloid
solution with low oxidation sensitivity, containing
palladium, at least one tin-free reducing agent and at
least one organic protective colloid for stabilising
the colloid solution, and at least one second noble
metal selected from the group consisting of rhodium,
iridium, platinum, compounds thereof and mixtures
thereof, characterised by the following process steps:
producing a parent solution from a palladium compound,
the organic protective colloid and the reducing agent
in diluted aqueous hydrochloric acid; heating the
solution to a temperature of 50°C. to 70°C., and
maintaining the temperature of the solution for
approximately 24 hours; and cooling the solution to a
temperature of 20°C. to 40°C., and adding at least one
of the second noble metal selected from the group
consisting of rhodium, iridium, platinum, compounds
thereof and mixtures thereof.
According to another aspect of the invention, there is
provided a method for coating electrically non-
conductive substrate surfaces with metallic layers by
direct metallisation of said surfaces with a palladium
CA 02186482 2004-09-02
12b
colloid solution with low oxidation sensitivity
consisting of palladium, at least one tin-free reducing
agent and at least one organic protective colloid for
stabilising the colloid solution, and at least one
second noble metal selected from the group consisting
of rhodium, iridium, platinum, compounds thereof and
mixtures thereof, wherein the weight ratio of the
second noble metal to palladium is from about 0.01:10
to 1.0:10, comprising the process steps of treating the
substrate surfaces with the palladium colloid solution;
rinsing off disturbing colloidal residues of the
palladium colloid solution from the substrate surfaces;
and metallising the substrate surfaces with a
metallising solution electrolytically and without a
currentless metal layer being previously applied.
According to yet another aspect of the invention, there
is provided a method of manufacturing a palladium
colloid solution with low oxidation sensitivity,
containing palladium, at least one fin-free reducing
agent and at least one organic protective colloid for
stabilising the colloid solution, and at least one
noble metal selected from the group consisting of
rhodium, iridium, platinum, compounds thereof and
mixtures thereof, wherein compounds of the noble metals
are selected from the group consisting of trivalent
rhodium, iridium, and bivalent platinum compounds,
characterised by the following process steps: producing
a parent solution containing the palladium, the organic
protective colloid and the reducing agent in diluted
CA 02186482 2004-09-02
12c
aqueous hydrochloric acid; heating the parent solution
to a temperature of 50°C. to 70°C., and maintaining the
temperature of the solution for approximately 24 hours;
and cooling the solution to a temperature of 20°C. to
40°C., and adding at least one of said noble metal.
According to a further aspect of the invention, there
is provided a method for coating electrically non-
conductive substrate surfaces with metallic layers by
direct metallisation of said surfaces with a palladium
colloid solution with low oxidation sensitivity
consisting of palladium, at least one tin-free reducing
agent and at least one organic protective colloid for
stabilising the colloid solution, and at least one
second noble metal selected from the group consisting
of rhodium, iridium, platinum, compounds thereof and
mixtures thereof, wherein the weight ratio of the
second noble metal to palladium is from about 0.01:10
to 1.0:10, comprising the process steps of (a) treating
said substrate surfaces by spraying or splashing onto
said substrate surfaces, the palladium colloid
solution; (b) removing colloidal residues of the
palladium colloid solution from the substrate surfaces
after treatment in step (a); and (c) metallising the
substrate surfaces with a metallising solution
electrolytically and without a currentless metal layer
being previously applied.
CA 02186482 2004-09-02
12d
According to yet another aspect of the invention, there
is provided a method of coating electrically non-
conductive substrate surfaces with metallic coatings,
having the following method steps: treating the
substrate surfaces with a palladium colloid solution,
having a low sensitivity to oxidation and containing at
least one tin-free reducing agent and at least one
organic protective colloid for stabilising the colloid
solution and additionally at least one noble metal,
selected from the group including rhodium, iridium and
platinum, or at least one compound of these noble
metals, or a mixture of these noble metals and these
compounds; rinsing, if necesary, undesirable residues
of the palladium colloid solution from the substrate
surfaces; and metallising the substrate surfaces with a
metallising solution.
According to a further aspect of the invention, there
is provided a method of producing a palladium colloid
solution having a low sensitivity to oxidation and
containing at least one tin-free reducing agent and at
least one organic protective colloid for stabilising
the colloid solution and additionally at least one
noble metal, selected from the group including rhodium,
iridium and platinum, or at least one compound of these
noble metals, or a mixture of these noble metals and
these compounds, characterised by the following method
steps: producing a prefabricated stock solution from a
' CA 02186482 2004-09-02
12e
palladium compound, from at least one organic
protective colloid and from at least one reducing agent
in dilute aqueous hydrochloric acid; heating the
solution to between 50°C and 70°C, possibly
additionally adding reducing agent to the solution and
maintaining the temperature of the solution for
substantially 24 hours; and after cooling the solution
to between 20°C and 40°C, adding at least one of the
additional noble metal compounds.
According to another aspect, there is provided a method
of directly depositing a metal to electrically non-
conductive substrate surfaces comprising the steps of:
(a) treating the substrate surfaces with a palladium
colloid solution with low oxidation sensitivity,
containing at least one tin-free reducing agent and at
least one organic protective colloid for stabilising
the colloid solution, and in addition at least one
noble metal selected from the group rhodium, iridium
and platinum, or at least one compound of these noble
metals or a mixture of these noble metals and of these
compounds and (b) electrolytically m etallising the
substrate surfaces with a metal plating solution.
According to yet another aspect, there is provided the
method wherein palladium colloid solution is
characterised by protective colloids selected from the
group of compounds: polyvinylpyrrolidon,
polyvinylpyridine, polyvinylmethylketone, polyvinyl
alcohol, polyvinyl acetate, polyacrylic acid and its
CA 02186482 2004-09-02
12f
derivatives, polyethylene glycol, polyimine, alkyl and
hydroxyalkylcellulose, and its copolymers.
According to yet another aspect, there is provided the
method further comprising the step of rinsing off the
solution containing at least one compound selected from
the group consisting of quaternary and polyquaternary
compounds after the solution is brought into a pH value
of 1 to 3.
According to a further aspect, there is provided a
method characterised in that protective colloids are
used, selected from the group comprising
polyvinylpyrrolidone, polyvinylpyridine,
polyvinylmethylketone, polyvinylalcohol,
polyvinylacetate, polyacrylic acid and its derivatives,
polyethylene glycol, polyimine, and alkyl and
hydroxyalkyl cellulose and its copolymers.
The palladium colloid solution according to the
invention is characterised by additional contents of
noble metals, selected from the group rhodium, iridium
and platinum or compounds of these metals or their
mixtures. By means of these additionally contained
noble metals, the problem of oxidation sensitivity of
such noble metal colloid solutions is avoided. These
21$64$2
13
solutions may without difficulty be brought intensely
into contact with atmospheric oxygen even over a
lengthy period without their effectiveness being
thereby impaired. For example in continuously-
operating plants used in the manufacture of printed
circuit boards, these solutions come intensively into
contact with oxygen, as the solutions are applied to
the material to be coated through spray or splash
nozzles, the oxygen being taken up by the solution in
the spray or splash jet. In the same installations,
these solutions are also returned from the printed
circuit boards again into the liquid reservoir which is
usually disposed underneath, the liquid, depending on
the construction of the treatment device, passing back
for example in free fall or over guide planes into the
liquid reservoir. Here also there is an intimate
contact of the solution with atmospheric oxygen.
As the solutions are less oxidation-sensitive than the
known colloid solutions, far less reducing agent is
necessary in the use and supplementation of the colloid
solutions containing additional noble metal, without
the electrochemical reduction/oxidation potential in
the solution, necessary for the function of the colloid
solution, being displaced from a negative operating
value to a positive value. From this there arises the
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14
further advantage that during use of the solutions,
fewer chemicals are consumed.
Moreover, the proportion of copper ions in these
solutions, which arises through slow dissolution of
copper substrates in contact with the solution, for
example of printed circuit boards, is less critical
than in the case of known palladium colloid solutions.
In these colloid solutions, the consumption of
reduction agent increases in the solutions, in order to
obtain their efficiency, as soon as a critical upper
limit of the copper concentration is exceeded.
Therefore the consumption of reducing agents in over
solutions, in which a large printed circuit board
surface has been processed, is considerable. As soon
as the critical upper limit of the copper concentration
in these solutions has been reached, a negative
electrochemical reduction/oxidation potential can no
longer be maintained in the colloid solution, even by
further addition of reducing agents, so that the
colloid solution becomes ineffective for substrate
treatment.
The critical upper limit of copper concentration
therefore lies very much higher for the solutions
according to the invention than for colloid solutions
without additional noble metals. A large printed
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circuit board surface can be treated in the colloid
solution before this concentration limit is reached.
Therefore fewer of the chemicals, which are expensive
particularly because of the noble metal content in the
5 colloid solution, is necessary for the reconstitution
of such baths.
In colloid solutions containing hypophosphite as a
reducing agent, phosphate, in addition to
10 hypophosphite, is also active, which forms in these
colloid solutions from hypophosphite as a reducing
agent, when the additional noble metals are added to
the palladium colloid solution. In this way the degree
of effectiveness of the added hypophosphite as a
15 reducing agent is appreciably increased.
The advantages obtained by the addition of the
additional noble metals to the palladium colloid
solution are extraordinarily surprising as it is not
possible successfully to metallise electrically non-
conductive substrate surfaces in a directly
electrolytic manner, as, for the pre-treatment of these
substrate surfaces, colloid solutions produced only
with the noble metals rhodium, iridium or platinum are
used. In addition, colloid solutions of the additional
noble metals cannot be produced without palladium under
°~
16
the conditions preferred for formation of palladium
colloid.
In order to produce the novel colloid solution, firstly
a palladium colloid parent solution is prepared
according to known methods. For this purpose for
example a solution of a palladium compound is combined
with an organic protective colloid and then mixed with
a solution of a reducing agent. In this case the
organic protective colloid serves to stabilise the
palladium colloid solution against undesirable
palladium flocculation. Aqueous solutions are
preferably used, which can in addition contain organic
solvents, for example in order to enable the solubility
of specific compounds in the colloid solution or the
initial materials required for manufacture of the
colloid solution to be achieved in their initial
solutions. Such colloid solutions are described also
in the publications US-PS 40 04 051, US-PS 46 34 468,
US-PS 46 52 311 and US-PS 47 25 314. Therefore the
procedure for manufacturing the palladium colloid
parent solution can be seen in these documents.
There may be used as palladium compounds all materials
which are reducible to metallic palladium by reducing
agents, which. are easy to handle and which dissolve
sufficiently well in the initial solution or by
~ ~ ~~~~2
dissolution in the initial solution into soluble
compounds. Suitable materials are inorganic salts such
for~example as chlorides, sulphates, nitrates,
phosphates, pyrophosphates, cyanides and fluoroborates,
organic salts, for example of carboxylic acids, such as
formic, ethanoic, succinic, malic, lactic, citric,
ascorbic, oxalic, benzoic and vanillic acids, and
complex compounds such for example as ammin, halogen
complexes and complexes with organic complex formers.
Palladium (II) chloride and palladium (II) sulphate in
an aqueous hydrochloric solution have proved
particularly suitable.
Palladium compounds can be dissolved in an aqueous
solution, if necessary with proportions of organic
solvents. Water is preferred for economic reasons as a
solvent in the colloid solution.
The palladium concentration in the colloid solution
lies in the range from 50 mg/1 to 1000 mg/1 solution,
preferably from 1000 mg/1 to 5000 mg/1 solution. It is
advantageous to set as small a palladium concentration
as possible, approximately from 250 mg/1 solution, in
order to minimise the loss of expensive palladium by
carry-over of the solution when dipping and retrieving
the substrates to be coated. On the other hand, the
concentration selected must be of such a height that
218b482
18
sufficient absorption of the palladium is obtained on
the substrate surfaces in order to enable the surfaces
to be metallised subsequently without difficulty.
In order to stabilise the colloid solution to be
manufactured, organic compounds are used as protective
colloids. For this purpose either ionic or non-ionic,
preferably water-soluble polymers are used. On the one
hand, natural polymers such for example as proteins,
peptides, polysaccharides, gelatines, agar-agar, gum
arabic, tannin, and on the other hand synthetic
polymers such for example as alkyl or
hydroxyalkylcellulose, polyvinyl pyridine, pyroladon,
methylketone, alcohol, acetate, polyamine, polyacrylic
acid, polya~rylamide, polyacrylates and their other
derivates, polyethylene glycol, its derivates and its
copolymers, and the mixtures of these compounds with
one another are suitable. Polyvinylpyrrolidon and in
particular poly(4-vinylpyrrolidon) is particularly
suitable. The molecular weight of these materials
should be within a range of 1.000 g/mol to 10.000.000
g/mol, preferably however within the range of 2.000
g/mol to 2.000.000 g/mol and particularly preferably
within a range of 3.000 g/mol to 1000.000 g/mol. The
weight ratio of these materials to palladium in the
colloid solution should be set within a range of 1 . 1
i
~1~64~2
19
to 100 . 1 and preferably within a range of 3 . 1 to 10
. 1.
There are used as reducing agents compounds which are
capable of reducing the palladium compounds to metallic
palladium. The function of the reduction agents
however consists in maintaining the electrochemical
reduction/oxidation potential in the colloid solution
within a specific negative range, while preventing
undesired side reactions, for example oxidation of the
colloid, by means of the reducing agent. The
concentration of the reducing agent is therefore so
selected that a sufficiently negative
reduction/oxidation potential value in the solution is
obtained.
Among others, suitable reducing agents are compounds
from the compound classes of the low alkylaminboric
hydrides (mono-, di-, trialklyaminboric hydrydes), such
for example as dimethalaminboric hydride, alkali metal
boric hydrydes such as lithium, sodium, potassium boric
hydrides and in particular sodium boric hydryde,
ascorbic acid, isoascorbic acid, metal hypophosphite,
preferably alkali metal hypophospite, such for example
as sodium hypophosphite, hypophosphorous acid, metal
phosphite, preferably alkali metal phosphite, such for
example as sodium phosphite, phosphorous acid, formic
i
2186482
acid, formaldehyde, hydrazine and its derivates, such
for example as hydrazine hydrate and its salts
hydrazine sulphate, formiate, dichloride, mononitrate,
monochloride, oxalate, hypophosphite, phosphate,
5 orthophosphate, and tartrate and its derivates 1, 1-
dimethylhydrazine, 1, 2- dimethylhydrazine, methyl
hydrazine, ethylhydrazine, phenylhydrazine, iso-
propylhydrazine and its hydrochlorides and
hydrazoethanic acid, further hydroxylamine and its
10 derivates such for example as alpha- and beta-
hydroxylamines. Among the latter there belong the
compounds of the alpha and beta alkylhydroxylamines
with 1 to 5 carbon atoms in the either linear or
branched alkyl group, such for example as alpha- and
15 beta- methylhydroxylamine, alpha, and beta,
ethylchydroxylamine, and further alpha- and beta-
arylhydroxylamine, aryl being phenyl, benzyl or
naphthyl, and substituted with one or a plurality of
low alkyl groups, such for example as alpha- and beta-
20 phenylhydroxylamine.
The colloid solution can further contain halogenide
ions, for example chloride ions, in a concentration of
0.1 to 50 g/1 solution, their proportion arising via
the stoichiometric ratio to palladium in the palladium
compound. In this way the stability of the colloid
solution is increased and the electrolytic metal
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21
deposition carried out after treatment with the colloid
solution is simplified. It has become apparent that an
increased proportion of halogenide ions in the colloid
solution leads to an accelerated metal coating. If,
based on the stoichiometric ratio in the palladium
compound, halogenised ions are contained in the
palladium solution required for producing the colloid
solution, these also stabilise the solution against
undesired precipitation of palladium compounds.
The pH value of the colloid solution likewise has an
influence on the subsequent electrolytic metallisation.
The solution should preferably be set in the acidic
range, preferably in the pH range from 1 to 3 and
particularly in the pH range from 1.2 to 2Ø As soon
as the colloid solution has been set at acidic, the
palladium colloid becomes more effectively adsorbed on
the substrate surfaces. Moreover, the colloid
stability against flocculation of palladium is
increased.
In order to produce the palladium colloid parent
solution, the initial solution containing palladium is
mixed with the preferably aqueous solution of the
reducing agent. After mixing, the solution is heated
to an increased temperature, for example to a
temperature of 50 to 70°C, and if necessary further
'~
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22
reducing agent is added. During mixing, a presented
solution is intensively agitated/stirred, in order to
favour the formation of smaller colloid particles. It
is assumed that colloid particles will form in a range
of magnitude from 50 Angstrom to approximately 2000
Angstrom. The precise size is not known. Presumably
particles which attain a size of approximately 10 ~,m,
no longer adhere securely to the substrate surfaces.
Therefore a colloid with particle sizes in this order
of magnitude may no longer be effective. On the other
hand, smaller particles are particularly oxidation-
sensitive, as their specific surface is greater than
that of larger particles.
The particle size in the colloid solutions depends on
various external influences and is controlled by the
competition between nuclear formation and nuclear
growth speed. It is generally known that the particles
are smaller the more rapidly the solutions are mixed,
and the higher the temperature during mixture of the
solutions and the higher the concentration of reducing
agents and palladium in the solutions. Further, no
colloid particles arise particularly when strong
reducing agents are used.
After mixture of the individual ingredients of the
colloid solution, the increased temperature is
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23
maintained for several hours longer, for example for a
further 24 hours. Thereafter the additional noble
metals are added, preferably after the solution has
been cooled to a temperature of 20 to 54oC. Rhodium,
iridium and platinum are used as additional noble
metals. Preferably the trivalent rhodium iridium and
the bivalent platinum compounds, basically however also
other compounds of these metals, may be used. The
noble metals may be added to the solution for example
as salts. More typically there are used for this
purpose halogenide salts, sulphates, hydroxides,
cyanides, phosphates, pyrophosphates, phosphites,
hypophosphites, fluoroborates, carboxylic acid salts,
such for example as the salts of formic, ethanoic,
succinic, malic, lactic, citric, ascorbic, oxalyic,
benzoic or vanillic acid, and complex compounds such
for example as ammin, halogen complexes and complexes
with organic complex formers.
The concentration of the additional noble metals in the
colloid solution is set in dependence on the palladium
content. Preferred weight ratios of additional noble
metal to palladium are 0.01 . 10 to 1.0 . 10.
Specific surface structures of the additional noble
metal on the colloid particles are possibly responsible
for achieving the resistance of the colloid solution to
2186482
24
oxidation. In order to understand the effect of these
structures, the possible reactions are represented in a
hypocolloid solution containing hypophosphite as a
reducing agent. In this respect reference is made to
the reaction diagram given below (the following
meanings are indicated: (ads): adsorbed compound (gel):
compound dissolved in solution, (gas): compound in the
gas phase):
Reaction (1) describes the de-activating effect of the
dissolved oxygen for the colloid solution, in which
palladium is oxidised into palladium (II) ions.
According to reaction (5) hypophosphite is oxidised
catalytically into phosphate, forming hydrogen.
Reactions (2) and (3) illustrate possible consumption
reactions for dissolved oxygen. It should be noted in
this respect that according to reaction (4) hydrogen
probably desorbs very quickly from the palladium
colloid particle surface, so that the surface-catalysed
oxidation of the hydrogen by means of oxygen to water
according to reaction (3) is only possible to a
secondary degree. On the other hand, according to
reaction (2) phosphate is only very slowly oxidised to
orthophosphate. Therefore, in the stationary
condition, a high content of dissolved hydrogen occurs.
This reinforces reaction (1).
' CA 02186482 2004-09-02
Reaction diagram:
Pd° + 1/202 (ads) + 2H' \_------_\ Pd2 + Hz0 (1)
H3P03 (ads) + 1/2 02 (ads) \_------_\ H3P04 (2)
HZ ( ads ) + 1 / 202 ( ads ) \ _------_\ HZO ( 3 )
rapid rapid
H2(ads) _-_\_-_ --\HZ(gel) -__\__- --\Hz(gas) (4)
H3 POz ( ads ) + H20 \ _------_ \ HZ ( ads ) + H3P03 ( ads ) ( 5 )
10 Copper ions in the colloid solution, which for example
can increase in the presence of hydrogen by dissolution
of copper from the surfaces of the printed circuit
boards in the solution, clearly reinforce reaction (1)
and inhibit reactions (2) and (3).
One effect of the surface structures of the additional
metal on the colloid particles could for example
consist in catalysing the oxidation of the phosphate to
orthophosphate with oxygen according to reaction (2),
in order to accelerate the consumption of dissolved
oxygen. In this way the stationary concentration of
dissolved oxygen would be clearly reduced. In fact a
negative electrochemical reduction/oxidation potential
can be maintained by the addition of phosphate to the
colloid solution even during the action of atmospheric
oxygen. This effect on the other hand is not observed
-- 2186482
26
without additional noble metals in the colloid
solution.
After addition of the additional noble metals, the
colloid solution may be used in a metallisation
process.
i
It has proved advantageous to monitor the colloid
solution by measuring the electrochemical
reduction/oxidation potential. This is particularly
necessary when using reducing agents which decompose
catalytically in the colloid solution, such for example
as with borohydride and hypophosphite compounds, in
order to achieve the required process reliability. In
order to measure the electrochemical
reduction/oxidation potential, the voltage between a
metal electrode submerged in the colloid solution, for
example a gold or platinum electrode, and a second
electrode which adopts a predetermined potential in the
solution, is measured. Any electrochemical standard
electrode such for example as a silver/ silver chloride
or calomel electrode may be used as a second electrode.
The potential which occurs after production of the
colloid solution at the measurement electrode, measured
against a silver/silver chloride standard electrode,
should lie in the range between approximately -170 mV
to approximately -300mV. Under this measurement; the
'~- 2186482
27
colloid solution can be monitored. If necessary, the
reducing agent can be automatically supplemented, as
soon as the potential becomes more positive for example
than -170 mV.
In order to provide metal coating on substrate
surfaces, the latter are pre-treated according to known
methods. For example, resin impurities of copper
surfaces on printed circuit boards are removed by resin
etching methods (for example by a permanganate process
with the process steps pre-swelling/etching in alkaline
permanganate solution/reducing the formed manganese
dioxide (and oxide layers from the copper surfaces by
copper-etching (for example with hydrogenperoxide/
sulphuric acid solutions). Further, a solution
containing a wetting agent may be used to wet the resin
surfaces. Suitable for this among other things are'
non-ionic wetting agents such for example as
ethoxylised alkyphenol ether and polyethylene glycol
(Handbook of Printed Circuit Technology, 1993, Volume
3, Pages 61 to 69) .
After this pre-treatment, in which the surfaces achieve
hydrophilic properties, the latter are conditioned in
order to reinforce the subsequent adsorption of the
palladium colloid. Complex forming and/or cationic
surface active compounds are used as conditioning
i
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28
agents. Typical cationic surface active compounds are
quoted in US-PS 43 59 537. These involve emulsion
copolymers which are converted by generally known
methods into positively=charged ion exchanger resins by
chemical reaction.
There may be used as complex-forming compounds which
have a conditioning action, those compounds which for
example are quoted in Kirk-Other, Encyclopaedia of
Chemical Technology, Third Edition, Volume 5, Pages 339
to 368.
Compounds containing nitrogen and with a chemical
affinity to noble metal are preferably used as
conditioning compounds. These involve in particular
cationic wetting agents, such for example as trimethyl-
alkyl-ammonium halogenides with a short chain length of
the alkyl residue, polyelectrolytes, for example
quaternary compounds (for example the polyquaternary
compounds named in DE 37 43 740 A1, DE 37 43 741 A1, DE
37 43 742 A1, DE 37 43 743 Al, DE 37 43 744 A1, and DE
35 30 617 A1), and in particular the polyquaternary
polyvinylimidazoles, and complex formers containing
nitrogen such for example as the lower alkanolamines,
the alkyl group containing 1 to 5 carbon atoms and
being linear or branched. Further low alkanolamines,
which may be used as conditioning agents, include
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29
diethanolamine, triethanolamine, monoisopropanolamine,
disopropanolamine, trisopropanolamine, mono-sec-
butanolamine, di-sec-butanolamine, 2-amino-2-methyl-1-
propandiol, 2-amino-2-ethyl-1,3-propandiol, 2-
dimethylamino-2-methyl-1-propanol, tris
(hydroxylmethyl)- amino methane, and various mixtures
of the alkanolamines.
During substrate treatment, a temperature of 35oC to
60oC is preferably set in the conditioning solution.
However, a higher temperature, up to the boiling point
of the solution, or a lower temperature, may be
selected. The treatment time can be extraordinarily
short; basically, a few seconds are sufficient for
conditioning the substrate surfaces. An upper
threshold arises only from economic considerations.
Treatment times of about 5 minutes are advantageous.
After conditioning and the subsequent rinsing of the
substrate surfaces, the latter are preferably treated
in a solution which substantially contains reducing
agents. In this way the loss of reducing agent in the
colloid solution by carry-over upon dipping and
removing the substrate is minimised. The temperature
of this solution can likewise be at room temperature.
However, a higher temperature up to the boiling point
of the solution can be selected.
2186482
Thereafter the substrate is brought into contact
directly with the colloid solution without further
rinsing processes. In this case the palladium colloid
particles are adsorbed on to the conditioned
5 electrically non-conductive substrate surfaces and
prepare these for metallisation. The colloid solution
is heated to a temperature increased in comparison to
room temperature, for example 40°C; the treatment time
should not be considerably less than 20 seconds. An
10 advantageous treatment time lies between 2 and 7
minutes.
If necessary, the substrate surfaces are then again
rinsed and thereafter brought into contact with a
15 treatment solution, in which there is a chalcogen
compound with chalcogen in the oxidation stages +1 to
+5. Preferably suitable are sulphur compounds and in
particular the compounds from the substance classes of
the sulphinic acids, particularly with l to 5 carbon
20 atoms with a linear or branched alkyl chain, sulphites,
thiosulphates, sulphides, sulphones, dithionite,
dithionate and other compounds. In this respect,
particularly suitable materials have proved to be the
compounds hydroxymethansulphinic acid, alkalisulphite
25 and alkalithiosulphate. Mixtures of these compounds
may also be advantageously used. Basically, the
corresponding selenium and tellurium compounds are
2186482
31
suitable. A particularly suitable solution for after
treatment of substrate surfaces contains basically in
addition to sodium thiosulphate, also sodium citrate.
A temperature of this solution increased above room
temperature (25°C) is not necessary. The treatment
time can be selected within wide ranges, without any
influence on the result of treatment. Therefore times
of at least a few seconds are sufficient. A favourable
treatment time lies between 1 and 2 minutes.
Probably, the organic protective colloid layer, which
has been adsorbed by the treatment with the colloid
solution on the substrate surfaces, is removed
therefrom by treatment with this solution, so that the
palladium colloid particles are released and thus can
develop their action for the subsequent metallisation.
After this treatment and the subsequent rinsing of the
substrate surfaces, the latter can be metallised. The
metal layer may be deposited electrolytically, without
a currentless metal layer being previously applied.
Basically all electrically depositable metals, such for
example as the metals copper, nickel, silver, gold,
palladium, cobalt, tin, lead, zinc, chromium, cadmium,
iron and their alloys and their mixtures with one
another and with other elements, for example phosphorus
2186482
32
and boron, can be considered as metals. For deposition
of copper, for example a sulphuric acid copper sulphate
solution (for example electrolytic copper bath
CUPRACID~ of the firm Atotech Deutschland GmbH, Berlin,
Germany) is used. Naturally, further metals may also
be deposited on the first metal layer.
Furthermore, the colloid solution containing the
additional noble metals may also be used as an
activator for the previously known currentless
metallisation. Such methods are described for example
in the US Patent 46 34 468. An additional variant of
the method, which is not disclosed in the above
document, consists in treating the substrate according
to the above statements after treatment with the
colloid solution with the chalcogen solution described
above.
For metallisation, the substrate surfaces may be
treated in a dipping process. The advantages of the
colloid solution containing the additional noble metals
become apparent in particular however when using spray
and splash jets, as the oxidation-sensitivity of the
known palladium colloid solutions has a particularly
disadvantageous effect above all in these treatment
methods.
i
''.
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33
By means of the advantageous effect of the additional
noble metals in the colloid solution, the new palladium
colloid solutions are clearly more stable against
oxidation than the known colloid solutions.
In order to metallise drilled, stamped holes or holes
produced in any other way in printed circuit boards,
these are treated both in the conventional dipping
process and also in continuous processes with the
colloid solutions according to the invention. In
continuous-flow installations, the printed circuit
boards are moved horizontally in the treatment plant,
and brought into contact with the treatment solutions
by means of splash or spray nozzles. therefore the
novel colloid solution is particularly suitable for
this application. With treatment of the printed
circuit boards in continuous-flow installations without
addition of the additional noble metals to the
palladium colloid solution is industrially and
economically impossible.
The palladium colloid solution containing the
additional noble metals can be used to metalise various
substrates. In addition to metallising holes in
printed circuit boards, other substrates for
electronics, such for example as hybrid carriers or
integrated circuits and multi-chip modules, as well as
2186482
34
plastics for the range of decorative applications, such
for example as in automobile trimming, in sanitary
technology, for furniture fittings, costume jewellery,
and in the functional regions such for example as for
casings shielded against electromagnetic radiation and
reflectors, can be coated with this solution for
subsequent metallisation.
The following examples are intended to~explain the
invention in more detail:
EXAMPLE 1:
A palladium colloid solution was produced by mixing two
solutions:
Solution 1: dissolution of 4g palladium (II) chloride
in 27 ml aqueous concentrated hydrochloric acid (37% by
weight),
Supplementation of the solution with de-ionised water
to 1 litre solution,
Dissolution of 20 g poly (4-vinylpyrrolidon) in the
solution.
Solution 2: provision of 1 litre de-ionised water
'- 2186482
Dissolution of 50 g sodium hyphosphite, NaH2P02H20.
Firstly 800 ml de-ionised water was placed in a
container, then 100 ml of solution 1 ovas added to the
5 water and thereafter 30 ml of solution 2 was added.
Then the solution was heated to 70°C. During heating,
a further 70 ml of solution 2 was added slowly and with
continuous stirring. Then the solution became slowly
dark in colour.
Solution 3: dissolution of 1.5 g rhodium (III)
chloride or 1.0 g rhodium (III) oxide hydrate in 25 ml
aqueous concentrated hydrochloric acid (37% by weight),
supplementation of the solution with de-ionised water
to a final volume of 1 litre.
Thereafter the solution was left for a further 24 hours
at the temperature of 70oC. After cooling the solution
to approximately 40oC, 10 ml of solution 3 and then a
further 2 ml of solution 2 were added. Thereafter the
solution was ready for use.
EXAMPLE 2:
Solution 4: placing of 1 litre de-ionised water,
addition of 50 ml hypophosphorous acid (50o by weight).
2186482
36
Solution 5: dissolution of 1.5 g platinum (II)
chloride in 25 ml aqueous concentrated hydrochloric
acid (37% by weight), filling of the solution with de-
ionised water to a final volume of 1 litre.
A colloidal solution as in example 1 was produced, yet
instead of solution 2 solution 4, and instead of
solution 3, solution 5 were used.
EXAMPLE 3:
Solution 6: dissolution of 2.5 g iridium (III)
chloride in 25 ml aqueous concentrated hydrochloric
acid (37% by weight),
filling of the solution with de-ionised water to a
final volume of 1 litre.
A colloidal solution as in example 1 was produced, yet
instead of solution 3, solution 6 was used.
EXAMPLE 4:
Solution 7: dissolution of 0.05 g rhodium (III) oxide
hydrate and 0.08 g platinum (II) chloride in 25 ml
aqueous concentrated hydrochloric acid (37o by weight),
2186482
37
filling of the solution with de-ionised water to a
final volume of 1 litre.
A colloid solution as in example 1 was produced, yet
instead of solution 3, solution 7 was used.
The colloid solution obtained has a slightly higher
oxidation sensitivity than the solutions obtained in
examples 1 to 3.
EXAMPLE 5:
Solution 8: dissolution of 0.08 g rhodium (III)
chloride and 0.13 g iridium (III) chloride in 25 ml
aqueous concentrated hydrochloric acid (37% by weight),
filling of the solution with de-ionised water to a
final volume of litre.
A colloidal solution as in example 1 was produced, yet
instead of solution 3, solution 8 was used.
The colloid solution obtained has a slightly higher
oxidation sensitivity than the solutions obtained in
examples 1 to 3.
EXAMPLE 6:
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38
A perforated printed circuit board was metallised in a
dipping process according to the following procedure:
Treatment time Temp.
1. Pre-treatment with a solution
containing a wetting agent 2-5 min. 50C
Rinsing 1-2 min.
2. Etching of copper surfaces
in a hydrogen peroxide/
sulphuric acid solution 2 min. 25C
Rinsing 2 min.
3. Conditioning with quaternary
polyelectrolyte (e. g. polyvinyl-
imidazol (pH value:8-9) 5 min. C
35-60
Rinsing
4.Treatment
with
a hydrochloric
sodium
hypophosphite solution 1 min. 25C
5. Treatment with the solution
in Example 1 4-7 min. 30-50C
Rinsing
6. Treatment in an aqueous sodium
thiosulphate/sodium
citrate solution 1-2 min. C
25
7. Cleaning of copper surfaces with
diluted sulphuric acid 1 min.
Rinsing
8. Electrolytic coppering
e.g. with sulphuric copper sulphate
electrolyte)
A dense and pore-free copper layer was obtained on the
bore hole walls, which was enclosed after a few minutes
of electrolysis time.
EXAMPLES 7 AND 8:
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39
A perforated printed circuit board was metallised in
the dipping process according to example 6. In process
stage 5, instead of the palladium colloid solution from
example 1, the palladium colloid solutions from
examples 2 and 3 were used.
A dense and pore-free copper layer was obtained on the
bore hole walls, which was closed after a few minutes
of electrolysis time.
EXAMPLES 9 TO 11:
100 ml of the palladium colloid solutions, produced in
accordance with examples 1 to 3, were respectively
stirred in a beaker at 600 rpm on a magnetic stirrer
and in this way exposed to a reinforced action of air.
The electrochemical reduction/oxidation potential of
the solutions was measured with a platinum electrode
with reference to a silver/silver chloride reference
electrode. The potential at the platinum electrode
after a few minutes came to values between -170 and -
250 mV and remained constant within this range.
EXAMPLE 12:
Example 6 was repeated in a continuous-flow
installation, in which the printed circuit board is
'' 2186482
guided continuously in a horizontal position between
rollers, and is transported from one treatment station
to the next. The treatment solutions were sprayed on
to the printed circuit board and into the bore holes
5 through nozzles. The treatment times were shorter than
in example 6; they came to only 20% of the times there
given. Although the palladium colloid solution in the
continuous-flow installation came more intensively into
contact with air due to the intensive movement of the
10 solution, it remained stable over a long period. Even
after a continuous execution of the method over a
period of several days the electric chemical
reduction/oxidation potential measured in the palladium
colloid solution at approximately - 250 mV, measured
15 against a silver/silver chloride standard electrode,
was kept approximately constant. After passing through
all the stations, a dense and pore-free copper layer
was obtained on the bore hole walls, which was closed
after a few minutes of treatment time in the coppering
20 solution. This result could be obtained even when the
test was carried on for several days operation.
EXAMPLE 13 (COMPAR.ATIVE EXAMPLE):
25 A previously known palladium colloid, not additionally
stabilised with noble metals, was produced from 870 ml
de-ionised water, 100 ml of the solution 1 obtained
2 i 8~~82
41
according to example 1, and 30 ml of the solution 2
obtained according to example 2. This colloid was
exposed, as in examples 9 to 11, to a reinforced action
of air, and the electrochemical reduction/oxidation
potential in the solution was measured. Within a few
minutes after the start of the action of air, the
potential changed from originally approximately -300 mV
to positive values. After a short action time values
of approximately +400 mV were measured~at the platinum
electrode.
20
