Note: Descriptions are shown in the official language in which they were submitted.
-2- i22~ 6
6 Field of Invention
8 This invention relates to metallizing nonconductor
9 I It also relates to manufacture of printed wiring boards with
plated- through-holes. In particular it concerns methods of
electro~latino insulating surfaces and the composition of
12i~ electroplating solutions used for this purpose.
13
141~ Background the Invention
~5jl ;
16l, Non-metallic surfaces are usually metallized by first
17l; making the respective surface catalytically receptive to
18', electroless metal deposition and subsequently exposing the
19~l thus catalyzed surface to a plating bath solution of the
kind operating without an external source of electricity
21 l and for a time sufficient for forming a metal, e.g., Cut or
22 j No layer of desired thickness. This initial layer is
23
24 I
26
2J
I
2g .. I
31
- 3 -
122~346
1 ¦ usually provided with additional metal deposits formed by
2 conventional electroplating. In well known methods for
3 making plated through hole printed circuit boards, this
4 metallizing concept end its variations ore employed for
metallizing the hole walls. In the version starting with
6 two-sided copper clad laminate as the base materiel, a panel
7 of suitable size is first provided with the required holes,
8 ! and rendered catalytically receptive by immersion in a known
ill catalyst solution. Subsequently a metal; usually copter,
101i deposit is formed by exposure to a bath solution which
11l produces metal deposits without en external source of
12l electricity, generally known as electroless plating baths,
131' and for a time sufficient for achieving a thickness of,
it microns
14, e.g., 0.5 to 2,51 This initial, conductive mottler
15l is further plated up by means of conventional
16ll electroplating.
17 Al The typical catalyst solutions employed in the
18!, aforedescribed methods have been used in this industry for
19l many years and have been developed to a relatively high
20!l degree of stability. Surfaces treated with such solutions
21 catalytically promote the generation of electroless metal
22' deposits by the oxidation of suitable components present in
23 the electroless plating bath with this mechanism acting as
24 an internal source of electrons to be used in the plating
reactor by reducing complexes metal ions to metal.
26 Operation of electroless posting solutions requires
27 rather careful monitoring of the different components and
28 replenishing of used up materials by controlled addition of
29
if ~2XÇ;8~6 1
--4--
1 chemicals. Furthermore, the said plating solutions have a .
Z tendency to indiscriminate deposition thus forming metal,
3 e.g., copper deposits on walls and the bottom of tanks used
4 for operating such plating baths. This necea6itate6 .
5 frequent interruption of the plating operation, removal of .
61 the plating solution from the tank and cleaning the tank
Al walls and bottom by means of an etching operation. .
81 Electroless metal plating is, therefore, rather .
9" expensive and complex and needs highly trained operators.
101' In spite of these substantial shortcomings, .
11¦ electroless deposition of an initial fever of metal has, up
12 I to no, been an integral part of all processes used for
13' metallizing non-metallic surfaces including such processes
14l; employed in the manufacture of printed circuit boards.
Radovsky et at, 1'.5. Patent 3,099.608 has described
161~ the use of palladium-tin-chloride killed to form an
17l essentially non-conductive film of colloidal or I
18l~ se~i-colloidal particles on the hole walls made in a l
19' laminate used to make printed circuits: undo of ,
20 I electroplating for copperizing said hole walls.
21 ¦ The process of Radovsky et at has, however, severe ,
22 shortcomings and was found to be not applicable for
23 practical use. The p~lladium-tin-chloride colloidal
24 su6pen6ion has an unacceptably short life span. It can only
be used for about nine days due to coagulation of the
26 su6pen6ion and, because of its high palladium content is
27 rather expensive. Furthermore, the ~adovsky et at method
28 deposits substantially more copper on the surface than on
29
If 1'26846
: :
1 the walls of through holes and is, therefore, unacceptable
2 for commercial use. .
3 Radovsky et at is based on the use of a "thin,
barely visible film of particles" of 'semi-colloidal
palladium" deposited on the surface to be plated, said film
6 having "substantial resistance" and on the teaching "that ,
7 the palladium being by nature both a catalytic metal and a .
8 Al conductive metal has potentialities for semitones and
9, combined activating and conductive functions" (column 4,
10 lines 53 to 56) and further, that "After the electroplating ,
11l is started at a conductor it is activated apparently by the
12 , catalytic properties of the palladium and the
13 Al electrode position process proceeds directly on the film. of
14; conductivator particles" (column 4, lines 62 to 66). hi ,
15; column 5, lines 2 to 7 Radovsky et so state: "Since the
16j colloidal palladium deposit in the through holes was an
I ! extremely poor conductor to serve as a base for the .
18 1 electroplating as compared with the deposited graphite i
19l, something else must have aided in the electrode position,
20 i.e., a catalyst must hue aided in the plating reaction". ,
21 j In spite of the fact that Radovsky et sluice observation dates
221j from 1959 and consequently is contemporary with the use of I
23 graphite for metallizing non-conductors and with the first
24 application of the "seeder-electroless plating-technologv"
for metallizing plastic ports and making plated-through-hole
26 (PITH) boards it did not result in a process of Any
27 practical use. Considering the substantial initial .
r Dick lies vim eke seeder-elec~roless chenille Ed ice
If 122~i. 16
l development, and further, the continuing complexity
21 characteristic of electroless plating bath operation,
31 control and maintenance, when compared to the comparatively
4 simple electroplating process, it is rather most surprising
S that Radovsky's observations were of no impact as for as the
6 I technological development of the lust two decades is
7 concerned. The reason is, that Rsdovsky's observations did
8, not result in a teaching which allows the sversge person
g skilled in the art to mike use of it. Lacking this
lo teaching, Rsdovsky's observation could only be duplicated l ,
if when using his "conductivator-solution" sod the corner I
12 pyrophosphate electroplating bath existing at the time. It
13 is believed that Rsdovsky did not recognize the importance
14 of the.comDosition of the copper electroplating both. For
example, of the known formulations for pvrophosphate
16 electroplating both employed at the time of Rsdovsky's !
17~ filing, the simplest one did not produce copper of sdequatt
18 quality for printed circuit boards; the more complex type of
lo both did produce adequate copper quality, but inhibits the
I working of Radovsky's suggested process. The industry ,
21 therefore found Rsdovsky's observations to be of no
22 prscticsl use. The "seeding-electroless copper,
231; followed or not followed by the electroplating was
isle consequently accepted as the only approach metsllizing
sly non-metallic surfaces available to the sot.
26 Rsdovsky therefore teaches sway from the present
27¦¦ invention claimed by applicant. To arrive at this invention
33 the misconception presented by Radovsky that the
332 1.
_ 7 _ 122~46
characteristics of the electroplating baths were not critical
had to be overcome and completely discarded.
Summary of the Invention
In accordance with an aspect of this invention there is
disclosed a method for metallizing a non-metallic surface, by
electroplating the non-metallic surface in a vessel provided
with a counter-electrode and containing an electroplating bath
solution comprising in ionic form a metal (B) to be electroplated,
the non-metallic surface being provided with a conductive
connector area, the connector area being located outside of
and abutting the non-metallic surface area to be electroplated,
the abutting connector area being employed as an electrode
during electroplating, characterized by the steps comprising:
(a forming a plurality of discrete metallic
sites on the non-metallic surface, each of the sites comprising
metal (A), the metal (A) being different from the metal (s);
(b) exposing the non-metallic surface including at
least a portion of the connector area to the electroplating
bath solution, the solution having a conductivity sufficient to
carry electroplating current to the metallic sites of the metal
(A) and further comprising at least one component (C) which when
an electroplating potential is applied allows deposition of
the metal (B) on the metallic sites comprising or consisting of
metal (A), at a rate which is faster compared to the deposition
rate of the metal (s) on surfaces consisting of, or formed by,
the species of the eletrodeposited metal (B), with the proviso
that component (C) does not contain pyrophosphate anion;
(c) applying a potential between the connector area
and the counter-electrode which is sufficient lo: initiate
electroplating of metal (s) on the exposed portion of -the
connector area and (2) allow electroplating of metal (B) on
neighboring metallic sites, the application of the potential
initiating electroplating of metal (B) on the connector area
and on the neighboring metallic sites, the electroplating of
metal (B) on the connector area covering the connector area with
metal (B);
dale
. .
- 8 - lo 2 I 6
(d) continuing the application of the potential
until all of the neighboring metallic sites are covered with
metal (B), the rate of forming metal (B) deposits on the
neighboring metallic sites being greater than the electron
deposition rate of metal (s) on surfaces consisting of or
formed by the species of metal (B), the greater rate of
electrode position of metal (s) on the neighboring metallic
sites continuing until all of the sites are covered with metal
(B); and
(e) continuously electroplating metal (B) on the
exposed portion of the connector area and on the electroplated
sites to produce an electrically conductive continuous film
of metal (B) having a thickness of at least 0.5 microns.
In one embodiment, the rate of deposition on the
metallic sites is at least one order of magnitude greater and
preferably two orders greater than the rate of deposition on
the plated-out metal.
In another embodiment, the metallic sites and the metal
to be deposited are comprised of metals selected from Groups It
or VIII of the Periodic Table of Elements provided that they are
note the same.
In still another embodiment, the component referred to
above is selected from dyes, surfactants, chelating agents,
brighteners or leveling agents.
In yet another embodiment, the substrate provided with
metallic sites is exposed to one or more of the following treat-
mints: heat treatment; treatment with a cleaner conditioner;
and/or treatment with a reducing agent.
Brief Description of the Drawings
Fig. 1 is a graphical presentation showing the current-
potential relationship defining the difference delta t = Eli-
Eli
Fig. 2 is a graphical presentation showing the current-
potential relationship defining the difference delta dip =
Eden - Eddy p
dale
"
I 6
it. 3 represents a series of photographs
allowing a chronological sequence of electrode position
according to the method of this invention.
Detailed description of the Invention
The method disclosed and claimed herein is
an improved, method of plating non-metallic surfaces
on a
- pa -
malt/ J
~2Z~ 6
l! l
595-213. I
l I,
1 substrate More particularly, it is a highly effective .
2 method for plating through hole walls in metal clad
laminates. I .
A special advantage obtained in the manufacture of :
plated-through-hole printed circuits is the integrity of the
6 copper hole wall. Since the copper is electroplated
. directly on the nonmetallic hole wall substrate without an
8' intervening electroless metal layer the physical properties
g and adhesion at the copper-plastic interface are greatly
10'l improved. This is particularly important in the manufacture
11; of high reliability printed circuits such US multilayerC.
2! In practice, the method of this invention for I
135 electroplating nonmetallic surfaces on a substrate involves l
Al the steps of forming discrete metallic sites on the surface I
to be pleated in which said metallic sites are of a metal
16; species different from the species of the metal to be
17 deposited, providing a connector are on said substrate and
18'' outside the nonmetallic surface area to be electroplated
19'; convecting said surface to be plated and at lest part of
20l the connector area with an electropletin?, bath which
21lj contains a platesble natal of the species to be
isle electrode posited end A component which allows preferential i
23 deposition of said metal to be deposited on said metallic .
24 sites over plated-out metal from said electrode positing
metal, providing e vessel containing the electroplating bath
26 with a counter-electrode, end applying potential between
27 the electrodes formed by said connector area and said
28 counter electrode sufficient to initiate and cause
29
30 l if .
31 I 1,
32~
if l :
:
Z6l346 1
1 preferential deposition on the reface provided with said
2 sites for A time sufficient to form a deposit of desired,
3 fiubstantially uniform thickness.
S Without intending to be bound by nay pnrelcular
err it is applicant's belief that the direct
6 ! electroplating process claimed herein it bused on the
7 following principle.
8 I. (1). Metallic sizes are provided on the nonmetallic
9 surfaces are connected to a "connector ares"
(connector-electrode) Also provided on Ned
11 surface by the plating both electrolyte forming a
12 "resistive pith" between the connector area and I
13 the neighboring sites similar paths ore formed
14 between rites.
to) The higher the conductivity of the electrolyte the
16 lower the resistance of the "resistive path " with
17 a theoretical electrolyte of infinite '
18 conductivity, all sites would be sty the same ,
19 potential US tint of the connector area.
Conversely, with a theoretical electrolyte of very
21 low conductivity, the resistance between sites and
22~ the connector area would for all prnctlcal
23 Al purposes be too high for developing a potential
24l~ for posting on the sites.
25~l to) With practical electrolytes, n voltage drop
26 develops on the resistive pith. Thus, based on
27~ the foregoing:
28l (a) m e poeentinl supplied by the power source to
29 the counter-electrode and the connection urea
30' l
31 i
32 1 l
.
lZZ6~6
I
1 ' ho to be selected A no to compensate not only ,
2 for the voltage drop between the electrode
3 including deposition overvoltage but Also for .
4 the voltage drop on the resistive path formed .
S by the electrolyte 80 that the adequate plating
6 I potential it supplied to the metallic sites:
7 (b) the higher the electrolyte conductivity, the
faster is the plating reaction on the sites t
g (end also the more uniform in thickness):
(c) the conductivity of the electrolyte should be ,
11 selected no high us acceptable with respect in t
12 plating parameters.
13
The term conductivity as used herein defined no a l
function of the concentration of the current carrying I
16 species
17 i.e., in an acidic bath, the hydrogen ions are assumed to
18 sat as the main current carrying species. .
19 ,
II. (1) For all practical purposes it is imperative tint
21 the deputy formed by electroplating it .
z substnntinlly uniform and that its thickness is
23' 6ubstantinlly not a function of the distance to the
24 I connector area. In the case of printed circuit
I , boards with hole with metnllized hole wanly, the
26 deposit on the surface nod the one on the hole
271 ' Jo
2811 ,
29ll !
30l, i
31j
32
:
1~26~46
1 wall should not be of substantial, inadmissible
2 difference in thickness.
(~) The problem of non-uniformity also exits for
4 electroplating in general. To overcome it, certain
S additives are used in the plating bath known eye.
6 as leveling agents.
Al' (3) Pyrophosphate electroplating baths comprising such
8 additives produce satisfactory results if used in
g' the standard "seeding, electroless-electroplating"
process.
11 (4) Copper pvrophosphate baths of thy additive
12 comprising type, available at the time, rendered
13 the process suggested by Radovsky inoperative. The
14 reason for this is that the additives commonly used
attach themselves equally on the metal of the
16 species plated out (copper) and the palladium o.
17 the metallic sites or even preferentially attach
18 themselves to the latter thus interfering with or
19; inhibiting the plating operation on said sites.
Pithier unexpectedly in the light of Radovsky.
21 l applicant obtained satisfactory results no far 25
æ I both uniform thickness and superior quality of the
23 deposit is concerned, by employing bath
24 formulations comprising one or more components
which preferentially attach themselves to the
261 species of the metal to be plated out thus reducing
27 I the plating action on said surfaces if compared to
28l~ the plating action on the metallic sites of a
29 11
3011
_ v ,
31 1!
if 12~46
-13-
1 different, suitable metal, e.g., palladium, or by
2 preferentially attaching themselves to the metal of ,3 the metallic sites and increasing the plating
4 action on said sites if compared to the surface of .
the species of the metal plated out.
7 The problems described above with respect to the
8 1 use of the seeding, electroless-electroplating process as
Al well as the inoperative procedure described in Radovsky's .
US. patent 3,099,608 are completely overcome by the
11l invention claimed by applicant and disclosed herein.
12l As is evident from the above theorized mechanist I
13, the potential applied must be sufficient to electrode posit i
14 said placeable metal at a rate faster on said discrete sites `
than on the plated-out metal. In practice, this potential
16 is determined by well-known, and accepted electrochemical it
17" techniques.
18l One such technique involves measurements of the
191 current-potential relationships for the electrode position of
a metal on various substrates in the absence and presence of
21 the component (C). In the potential range applicable in I ,
22 standard electrodeposieion solutions twig , for a copper
23 sulfate and sulfuric acid plating solution approximately 0 ` .
24 to -20n my us saturated calmly electrode, and for a copper
Z5 pyrophosphate plating solution approximately -300 to -1,0n(
26 my us saturated calmly electrode), it is found that the
27 rate of plating on various substrates (e g., those
eon o~prislne eke eta Swiss) is Ester Ben the plans if
32
,1
I! I ,
.
if 122~t~4c6
If ,
-14-
if .
1' solution contains component (C) compared to the rate of
21 plating on other 6ubstrstes, ego the metal which is to be
3 plated out. .
41 Adsorptive components (component (C)) of the
51 electroplating solution can be selected on the basis of the
Al current-potential curves obtained with an electrode made of i
I the electroplating metal (e.g., copper) and with the
8 electrode made OX metal employed for forming the metallic ,
9 sites (e.g., palladium). Current-potential curves are
recorded using the three-electrode system comprising the
11 test the counter and the reference electrodes. Electrode i
12 polarization con be performed either by applying the
13 linearly changing potential and recording the current
14 (Volta metric method), or by applying a constant current and
recording the potential (galvanostatic method). description
16 of the three-electrode system Volta metric, and ,
17 galvanostatic methods are given in the book entitled "Modern .
18 Electrochemistry", by JIMMY. Buckers and Aye. Rudy
19 published by Plenum Purl. Corp., New York, YO-YO., 1970, pages
891-~93~ 1019-10~6.
21 A rapid method for selecting the bath composition ,
22 for the process of this invention uses current-potential i
23!l curves to evaluate the difference, delta t, which is '.
24¦1 defined by:
25l1 delta t = E i E i
26 1
27lj where Eli and Eli are potentials, at thy current density j
28l i, of the electrode made of the electroplating metal and the
301l .
ill !
32, i
i
~-~ .
.' . ' .
1~6~346
-15- ,
ill metal employed for forming the metallic sites, respectively
21~ (Fig. 1). The current density i is in the range of 30-507~ .
3 I of the peek current it (Fig. 1). with the current density
4 I selected in this wry the electrode mode of the metal
51~ employed for forming the metallic sites is not substantially
6 ' covered by the posting metal sty the Hi potential. The ,
7 current density i in the galvsnostatic method is selected
8 also in a way such that there is non-subetsntisl covers of
9 the electrode mode of the metal employed for forming the
metallic sites with the plated metal.
11 The procedure for selection of the adsorptive .,
12 coronets consists of the following steps: ,
13 if) Record current-potentisl (i-v) curves for the
14 two types of test electrodes, the electroplating metal
(err,. Cut and the metal employed for forming metallic sites i
16 I Pod) ,
17 (2) Select current density i in the range of
18 30-50~ of the pest current ,
19 (3) Read potentials Eli and Eli for the
selected current from the current-potentiRl curves (it
21 (4) Calculate the difference in potentials
22 '
231 delta t = E i E i
251, (5) Adsorptive component causing the highest
26!~ delta value is the preferred component, i.e., the both
27l! with the highest value of the difference delta t is the
28 preferred both.
29 It if
32 l
.
. .1 .,
.... . . I .
1! 122~46 l
-16- .
1 ¦ The some method sod criterion it used to select the .
2 preferred concentration of the adsorptive component.
3 Another rapid method for selecting the bath
4 composition for the process of this invention also uses
current-potential curves, but in this case the function i
6 delta tE)dep is determined, and this is defined by
7 delta dip ' E' dip E dip
9' l
JO where Eden and Eden respectively, are the i
ill deposition potentials tire., the potentials extrapolated to i
12 zero current from the current/potential curves) for the
placeable metal on the substrate made of the electroplating
metal and for the metal employed for forming the metallic
sites (Fig. 2).
16~l The experimental method is the same for this
technique as for the previously described method. However,
181 Eden and Eden are calculated by extrapolating
I the current/potential curves to zero current and then
20~ reading the values of Eden and Eden In this
21 ¦ procedure for selection of bath composition for the process `
22 I of this invention, the bath with the highest delta I .
23 Eden value is the preferred bath. Adsorptive
24 component causing the highest delta Eden value is the
preferred concentration of the ad80rptive component.
26 Both of these quick methods for selecting bath
27 composition for plating at the constant current can be
Ed modified r the use id tber technique of Mel plains Jo
32 ,
i
i' I .
!
-17- 122~46
I .
1 such a pulse plating fast galvanoststic or potentiostatic i
2 plating. Besides the above described quick methods for , .
3 selecting bath composition for the process of this invention
4 other methods rough. given above, JIMMY. Buckers and AWOKE. ,
S Ruddy, pp. 1017 and seq.) used in the electrochemical l
6 scientific studies, can be used in the some way. .
7 Accordingly, any component which causes the plstin
8 rate lo be faster on the metallic sites than on eke
g placeable metal US described above is within the purview of .
this invention.
11 In one embodiment of the present invention, to
12 component (C) effects preferential deposition by 1,
13 preferentially attaching itself to a surface of the species !
14 of metal (B) if compared to the surface of the species of
metal (A) thus substsntiallv inhibiting or reducing the l
16!, plating reaction on surfaces formed by metal (B) without i
17 substantially interfering with the plating reaction on
I ; surfaces formed by the species of the site metal (A). In ,
19 soother embodiment, component (C) preferentially attaches
itself to the species of the site metal (A) with said
21, attached component (C) reducing the over potential and thus ,
22" increasing the plating reaction if compared to said resection .
23 on surfaces of the species of metal (B).
24 In accordance with a preferred embodiment of the
invention, the conductivity of the electroplating bath
26 solution and the potential applied to the, connector area and
271 the counter electrode are selected sufficiently high to !
z l achieve u rye of dupes OX rho Doris of the spew
32,1 1 ,'
.
.. ,~,............................................
.
1~1 of the site metal (A) 122~846
2 which it at least one order, and preferably two orders of
3 , magnitude higher than the deposition rote on the surface of
I the species of metal (B). It was found that the maximum
5 I conductivity suitable for the process of this invention is
6 ! for all practical purposes as high us permissible with
7, respect to other plating parameters.
8 It was also found that the potential applied to the
9 electrodes has to be selected to compensate for the
potential drop on the resistive path formed by the platoon
11 bath solution between the connector are and the metallic
12 sites consisting of, or comprising petal (A), and between,
13 such neighboring sites.
14 Moreover, it is preferred that this potential be
selected at the highest value permissible with respect to
16 the other plating parameters.
17 The metal (A) as well as metal (B) may be selected
18 from Groups It or VIII of the Periodic Table of Elements
19 provided that they are different.
Preferably metals PA) and (B) are selected if. such a
21 way that metal (A) displays a lower plating potential Thor;
22 , metal (B) under the conditions provided by the plating
23 operation.
24 Preferred metals for (A) are selected from
palladium platinum, silver and told with the most preferred
26i being palladium.
27 I Preferred metals (B) are selected from copper and
281l nickel.
29i,
31 !
12Z6~346
The preferred electroplating bath solutions are
acidic.
Component (C) may be selected from dyes,
surfactants, chelating agents, brighteners and leveling
agents which preferentially attach themselves to surfaces
comprising or
consisting of metal (B) and acting by reducing or inhibit-
in the plating reaction and/or form depolarizing agents
preferentially attaching themselves to surfaces consisting
lo of metal (A) and increasing the plating reaction on said
surface.
Suitable dyes are, e.g., the ones selected from
Victoria Pure Blue FOB (KIWI. 4259), ethylene blue
(KIWI. 52015), methyl violet (KIWI. 42535), acid blue 161
(KIWI. 15706), Aleutian blue 8GX (KIWI. 74240), and other
N-heterocyclic compounds, triphenylmethane type dyes and
aromatic amine, mines and dyes compounds including
fused ring amine, mines and dyes compounds. Suitable
surfactants include non ionic surfactants such as alkyd-
phonics polyethoxyethanols, e.g., octylphenoxy polyeth-
oxyethanol, and non ionic fluorocarbon surfactants such as
Zanily FUN, a commercial product of ELI. Dupont deNemours
and Co. (Inc.).
Among the many surfactants, including wetting agents
and water soluble organic compounds proposed for use in
electroplating solutions are surfactants and polymers
*trade mark
- 19 -
arc
i .
~5-21 A 20 1226846
I
1 containing polyoxyeehylene. Compounds containing as low as
2 four and 86 high as one million polyoxethylene groups hove
S been found Jo be effective. A preferred group of said
compounds includes polyoxyethylene polymers having as few as
twenty and as many as 150 polyoxyethylene groups. Also
6 referred are block copolymers of polyoxyethylene and
7 polyoxypropylene conic no 10 to 400 oxyethylene groups. Among these
Al' preferred block copolymers are those containing from seven to two hundred
g fifty oxyethylene groups. In general it has been found that these
10j polyoxyethylene compounds when added to an electroplating
11 bath, particularly an acidic electroplating bath, will
12' greatly enhance the growth of electroplated metal on the
13;j nonconductor surfaces provided with said metallic sites.
14-; Most frequently these polyoxyethylene compounds are used in
IS the electroplating solutions in a concentration range of 0.1
16 to 1 g/l. The optimum concentration depends on the
17~ composition of the electroplating solution and
18 !¦ polyoxyethylene compound selected. In some cases less than
lgi' Old or more than 1 g/l and up to 100 g/l may be preferred.
20l Representative chelating agents include riboflavin,
21 I 2,4,6-(2-pyridyl)-s-triazine and the pyrophosphate anion.
22'~' Suitable brighteners and leveling agents include
23 N-heterocyclic compounds, triphenylmethane type dyes,
24 Thor sod Thor derivatives. Among the Thor
derivatives which are suitable for use are
26 tetramethylthi~ram disulfide and ally Thor. Suitable
27 commercial examples are Electro-Brit~ PC-667 and Copper
28 Gleam PC
29 I
*A commercial product of Electrochemicals, A Division of
Dart Industries, Inc. (trade mark)
**A commercial product of LeaRonal Co. (trade mark)
32 ;
If
1 122~346
i~5-213~ -21-
1 Other suitable additives include saccharin, and
2 o-benzaldehyde sulfonic derivatives which are especially
3 useful in Writs nickel plating bath.
4 In the preferred embodiment of the invention,
metallic sites are formed by treating the respective surface
6 with a solution comprising the metal (A) as a compound or
71~ complex, e.g., as allied chloride as exemplified by
I palladium-tin chloride, a double metal halide. Reference to
g such double metal halides can be found in US. Patent Nos.
3,011,420, 3,532,518, 3,672,923 and 3,672,938.
11,
12 In forming metallic sites of motel (A) it has been
13; found advantageous, following treatment with the said
14 . solution to expose the surface to a reducing agent.
In the case of the site-formin~ compound comprising
I tin, it has further been found advantageous to remove the
17~, tin-compound from the surface provided with sites. this is
18 accomplished by a tin removing solvent such as a dilute
19 , aqueous fluoroboric acid solution or strongly basic
20l! solutions which allow formation of soluble alkali
21 , stunts.
Z2 !, In order to achieve improved shelf-life of the
Z3 surfaces provided with sites it has been found advantageous
24 to expose the surface treated with the site providing
26 solution to a heat process, e.g., at a temperature of
27
291~ , j
31
lZ2~346
~5-120C for 10 minutes or longer. It has been found
that surfaces thus treated inunediately after removal
from the site providing solution may be stored for
extended periods of, e.g., 9 months without dotter-
mental influence. It is advantageous after extended
storage to expose the sites to an acidic solution,
e.g., one molar sulfuric acid for 15 to 20 minutes.
Suitable reducing agents mentioned above
may be selected from sodium bordered, formaldehyde,
dimethylamine borne or hydroxylamine.
It has also been found advantageous to
pretreat the non-metallic surface prior to the site-
providing step by exposing it to a cleaner conditioner,
for example, an aqueous solution containing a blend
of non ionic and cat ionic wetting agents. Such
cleaner conditioners are widely used in printed
circuit and plating on plastics arts.
I,
Detailed Description of the Drawings
.
Figs. 1 and 2 are explained in detail on
pp. 13-16 of this specification.
- 22 -
mob
Lowe
it. pa is a photograph in the sequence (a)
to (f) taken after 1 minute of electrode position in
an electroplating bath. The substrate is a copper
clad laminate protruded with palladium metallic sites
on the walls of the through hole. Copper is the
metal being deposited.
Fig. 3b is a photograph of the same
substrate taken after 2 minutes electrode position.
Fig. 3c is a photograph of the same
substrate taken after 3 minutes electrode position.
Fig. Ed is a photograph of the same
substrate taken after 4 minutes electrode position.
Fig. ye is a photograph of the same
substrate taken after 5 minutes electrode position.
- 23 -
ma/ Jo
95 -21 PA -24- lZ26~34~
it
1 Fig. of it photograph of the same substrate
2 taken after 20 minutes electrode position.
4 This series of photographs show that the metal
deposition on the surface of the hole is uniform and
6 continuous.
7 l
8, Example 1
10'' This example describes metallizin~ the walls of
11l, holes drilled in copper clad insulating sheets of the type
12 used in the manufacture of printed circuits. Panels were
I cut from a 1.6 mm thick, copper clad, FRY epoxy-glass
14 ' sheet.
151, Holes were drilled in the copper clad epoxy-glass
16 FRY panels.
17 I! The panels provided with holes were then treated
18 ! with a solution which contains a cat ionic surfactant, a
l9j, non ionic surfactant and an alkanolamine, adjusted to a pi
20ll below 4; thus cleaning and conditioning the hole wall
21 Jo surfaces for subsequent treatment steps.
22! Subsequently the panels were dipped into a 1
23 aqueous sulfuric acid solution for 5 minutes, water rinsed,
24 treated with a dummy per sulfate solution (120 g/l at a pi
less than 2) for 45 seconds at 40C, to deoxidize the copter
26 surface, and again water rinsed.
27 ¦ The panels were then treated for S minutes in a
28¦I redip solution containing: stuns chloride, 5 g/l
29. 1.
TV
31 lo *trade mark
32l! 1
Lowe -us-
11 12Z~
1 sodium chloride. 225 g/l: and sufficient hydrochloric acid
2 to obtain pi of lets than 0.5. After the redip step the
3 panel was exposed for five minutes to a
4 palladium-tin-chloride solution at 55C. The panels were
continuously agitated in the palladium-tin-chloride
6 solution. The palladium-tin-chloride solution was
I formulated as follows: the 601ution of Example 3 of US.
8jj 3,682,671 is diluted to a
g palladium concentration of 210 Mel by mixing with a
solution 3.5 M sodium chloride and 0.0~ M stuns chloride.
11 After immersion in the palladium-tin-chloride solution the
12; panels were water rinsed, heat treated in an oven for 60
13 minutes at loo and then brushed.
14 Some of the panels were electroplated in an
electroplating solution consisting of: copper sulfate, 0.3
16 Mole; sulfuric acid, 1.8 Mole; and hydrogen chloride, 1.3
17l, millimole. The current density was 3.8 Ask. do. Before
18; electroplating, the copper surfaces were deoxidized by
19 dipping for five seconds in a solution of sodium per sulfate.
After electroplating for 5 minutes, only 10% of the hole
21 " walls was covered. After electroplating for one hour, the
22 I panels were removed end the holes examined. Copper was
23 ! electroplated partially down the walls of the holes, but
24 ¦ there was no plating at the mid-point which left a void in
25 ¦ the center of each hole.
26 I Additional panels were electroplated after S g/l
27 I of a non ionic surfactant, octlylpheno~ypolyethoxyethanol,
28 was added to the copper electroplating solution. The hole
29,1 1
.jjj_ 30 1
I 31.~
lZ2~346 1
AYE -26-
1 ¦ walls were completely covered with a continuous film of
2¦ copper petal, without voids, in less than 5 minutes.
lo i
Example II I
i
6 Additional panels prepared by the method of
7 Example I were electroplated in a copper electroplating
8 solution which was the same as Example I except that it
9 1! contained 5 g/l of methyl violet instead of the non ionic
10l surfactant. After five minutes of electroplating, the hole .
11 walls were covered with a complete, continuous film of l
12 ' copper metal. i
Example III
16 The procedure of Example II wins repeated except l
17 I that ethylene blue was substituted for methyl violet. .
Again, after five minutes of electroplating, the hole walls
19 if were covered with a complete, continuous film of copper.
20 I .
21¦1 Example IV t
æ Al l
23 The procedure of Example I was repented except
24 that a Watts nickel electroplating bath WAS substituted for
I the copper electroplating bath. The White nickel bath
Tao consisted of: nickel sulfate, 300 g/l nickel chloride 30
27 g/l; and boric acid, 30 g/l. There was only incomplete
28 plating on the hole walls. A saccharin brighter was added
29 to the Watts nickel bath, and another panel was plated A
31
l .,
.. ., ., ,. .. .. , , ... . , .. , .
AYE -27-
~22~;t346
i
1 complete continuous film of electroplated nickel quickly
2 covered the hole walls.
4 Example V
6 it The procedure of Example IV WAS repeated except
I' the Watts nickel plating path contained 20 ml/l of
8 ~ectro-Nic 10-0., a briar comprising an o-benzaldehyde
sulfonic acid (commercially available from Sel-Rex, Hooker
10,, Chemicals and Plastics Corp., Natalie, Jo 07110). A complete I,
11 continuous film of electroplated nickel was obtained on the
lo hole walls.
13
14 Example VI
16 The procedure of Example IV was repeated except
17, that Copper Gleam I a brighter used for copper
18 sulfate/sulfuric acid electroplating bath, comprising a
19 , triphenylmeth~ne dye was added to Watts nickel bath. A
complete continuous film of electroplated nickel was
21 obtained on the hole walls. '
22j~
23j~ E alluvia
24lj
25l~ This example describes the manufacture of a
26l' printed circuit utilizing the metallizing techniques of this
2~1i invention.
29 1'
30l *trade mark
31,
32''
owe PA ¦ -28- 122S~46
1 ¦ Copper clad insulating sheets of FRY or SUE
Z grades are cut into convenient size panels for the
manufacturing process. The holes required for plated
4 through hole connections are drilled, and the copper
surfaces of the panel are demurred. The panels are then
treated as in Example I in a cleaning and conditioning
it solution, sulfuric acid solution, rinse, sodium per sulfate
I solution, rinse, p-e-dip solution, and a
g palladium-tin-chloride solution. Subsequently the panels
lo are rinsed, heat treated in an oven for 20 minutes at l~GC.
11 and Russia. The panels ma be stored sty this sty or
12 processes immediately without process interruption.
13 7 At this stage the panels are provided with a
14 plating resist mask produced by well-known photo printing
I screen printing or other suitable processes.
16 The panels are then subjected to a reverse current
Al elctrocleaning procedure at 3 A/sq.dm in an alkaline clearer
18 for 45 seconds rinsed and sodium per sulfate treated (as
I above) for 5 seconds and rinsed again.
20" The panels are then electroplated for 5 minute at
21 3 A/sq.dm using a bath comprised of the following:
22 1,! Copper sulfite g/l
! Sulfuric Acadia g/l
23 Chloride ion * 70 Pam
Electro-Brite (PC-667) 5 ml/l
I
26 The resulting panels are then rinsed and copper
27 !! electroplated for 40 minutes at 3 A/sq.dm in 8 bath
I count 8 inning:
28,!
29'!
30!' *trade mark
I
31
32 if,
,95-213~ -29~ 6~46
l Copper sulfate 75 g/l
Sulfuric acid 190 g/l
2 Chloride Ion 50 Pam
3 Copper Gleam PC 5 ml/l
4 ! 1
Alternatively, the panels, instead of undergoing
the dual electroplating steps described above, are plated in
7 8 single step for approximately 45 minutes at 3 A/sq.dm in
8 ! the first electroplating bath described above.
' The panels are then rinsed, and then converted to
., printed circuit boards by the well known steps of solder
10 I:
if plating at 2 Ask do for lo minutes, rinsing, resist
12 stripping, etching with ammonia Cal copper chloride solution,
13i solder fusing, applying solder mask and trimming the circuit
14 board size.
16 Example VIII
I
181 A copper clad panel is processed in accordance
lo` with Example VII up to and including the step of exposing
20 it the panel to a palladium-tin-chloride solution. This step
21 , is followed by a rinse and then immersion in a 5%
22!i fluoroboric acid solution which it a solvent for the tin
231¦ component of the palladium-tin-chloride sites deposited on
241I the walls of the holes. Then the panel is plated at 3
A/sq.dm in a copper electroplating bath formulated in
26 accordance with the present invention and composed as
2~1 lot ow:
29 '
Jo!! ,
it *trade mark
31l! l
32,i
If .
59S~ 30_
122~346
1 ¦ Copper 5ul fate 75 I
Sulfuric acid 190 g/l
2 Chloride ion * 50 Pam
Copper Gleam PC 5 ml/l
3 After depositing a layer of copper 35 micrometers
trick, the panel is rinsed, dried and, by well-known
6 tuitions, a positive photo resist etch mask is applies
j, covering the desired circuit pattern including the plated
7 '
I, through holes. The copper is etched, and the resist
subsequently removed by standard processes, thus forming &
finished printed circuit board.
11 .
: Exar~le_IX
12
13 ;
. This example describes the reparation of a
14
Jo printed circuit board of the multi layer type. A well known
;; procedure is used to form a multi layer composite by
16
I, combining individual layers of circuit patterns on
17,
it insulating carriers and forming them into a laminate. Afterthe through holes are produced and the smear removed from
,' the copper layers forming port of the hole walls, the
21l! laminate is then processed as described in Example VII or
! VIII.
23 1 '
2 ¦¦ Example X
26 This example describes the preparation of a
27 printed circuit board on a bare or unclad laminate not
28 I provided with copper foil on its surfaces.
2911 ,
30;. '.
31¦! i
32, *trade mark
1, ,
5g5-~131 -31- 122~346
1 The surfaces of the panel are provided with on
2 adhesive layer by the method of Stahl et I US. 3.625,758,
3 and holes ore formed. The panel is attached to an
4 electroplating fixture to provide a suitable conductive
border forming a suitable connector area. The panel is
6 adhesion promoted by the procedures of Stahl et at. The
71i panel us then processed as described in Example VIII.
g Example XI
11 Copper clad, FRY epoxy lass panels were drilled
12 to form through holes, cleaned and treated with conditioning
1.3 solution, redip solution and palladium-tin-chloride
14. solution as in Example I. Following the
15I palladium-tin-chloride solution and rinse, the copper clad
16 panels were dried and immersed one in each of the following
I reducing agents (dissolved in aqueous lam sodium hydroxide I .
18 I solutions):
: Sodium bordered
I ~ydroxylamine.
21 Both panels were electroplated for two minutes in the copper
22 1! electroplating bath of Example VIII. Complete, continuous
23 I films of copper were obtained on the hole walls.
24
us
26 i
27'
trade mark
31
I '
2~i~346
2 Example XII
The procedure of Example XI was repeated except
S that an aqueous solution of potassium hexachloroplatinate
6 (IV) and stuns chloride, was substituted for the
711~ palladium-tin-chloride solution. The reducing agent used
Al was a 1 g/l solution of sodium bordered. The holes were
Al' covered with a continuous film of copper in less than 5
10 l minutes of electroplating.
11 .,
12 , Example
13
14 The procedure of Example VIII was repeated except
lo ! that a copper pyrophosphate electroplating bath was
16 substituted for the copper sulfate/sulfuric acid bath. The
17,l copper pyrophosphate bath had the following formulation:
I Copper 32 g/l
18l, Pyrophosphate anyone g/l
19 ,! Ammonia Z25 g/l
It Temperature 52C
2~j
21l The pyrophosphate anion performed the function of
22 component C. After 5 minutes plating sty 4.5 A/sq.dm there
23 was complete coverage of the hole wall with copper. When
24 another panel was plated in the same plating bath with the
addition of 1 ml/l of the conventional brighter for copper
26 pyrophosphate plating baths, a dimercaptothiQdiazole
I compound (commercially available as POW from M&T Chemicals
28
29
30 l
1 I
31 ¦ *trade mark
1226~34~
1¦ Inc., Roy, NJ 07065). After 5 minutes in the copper
pyrophosphate bath with the conventional Pow brighter,
3 the hole walls were not plated. The dimercaptothiodiazole
is strongly adsorbed on the palladium metallic sites and
prevents preferential deposition on the palladium metallic
6 , sites.
.,,
8 Example XIV
jig _
The procedure in Example VII was repeated except
11 the following the palladium-tin-chloride solution and
12 rlnse-step the copper clad panels were, without drying,
13 immersed in a solution containing fluoboric acid (100 ml/l)
14 and hydroxyethylene Damon rustic acid (4 g/l) for 0.5
minutes, rinsed and then electroplated according to this
16 invention in a copper electroplating solution which was the
17'l same as Example I except that the non-ionic surfactant was
18 Pluronic F-127, a block copolymer of propylene and ethylene
19 oxides (commercially available from BASF-Wyandotte Corps was
present in the solution as Component C in a concentration of
21 , 0.2 g/l. After 5 minutes of electroplating at a potential
Z l' providing a current density of 3.8 Adam the hole walls
23~1 were covered with a complete, continuous film of copper.
28 Al *trade mark
291,
30 1
ho 31 It
-34-
Example XV
2 11 122~i~346
3 1 In the following examples the procedure for
Al Example XIV was repeated with A being the save end Examples
I B to 0 using different surfactants as component C, and with
Al concentrations, current densities and plating times as shim
I hereinafter. The result after electroplating, in all cases,
8 was a complete void free continuous film of copper covering
9 the hole walls.
lo Example Compound Cone (g/l) CUD (A/dm)Plating Tip
if (Mix)
12 A Pluronic F-127 0.2 3.8 5
13 B Pluronic F-127 0.2 5.92 3
14 C Carbowax 1540 0.3 3.8 5
D Carbowax 1540 0.3 5.92 3
I E Pluronic F-6~ 1.0 3.8 5
17 , F PLuronic F-68 lo 5.92 3
18 G P:Luronic L-42 1.0 3.8 5
lo H Polyox WAR 80 lo 3.8 15
I I Carbowax 4000* 0.5 3.8 15
21 J Olin log 0.5 3.8 15
22, K Olin 6G 0.5 3.8 15
23l, L Carbowax 20M 0.5 I 15
24¦ M Pluronic L-64 0.5 3.8 15
251 N Tergitol Mix Foam lo 0.5 3.8 15
26;1 0 Carbowax 600 lo 3.8 15
27 11
28 , Pluronic is BASF-Wyandott~ Corp.'s trademark for a
29 1 series of block copolymers of polyoxyet~ylene and
polyoxypropylene. Pluronic F-127 has a polyoxypropylene
31~l base of about 70 oxypropylene units which are attached
32
Ii *trade mark
---35--
1%Z~1~46
I two polyethylene chains which contain in aggregate about 300
2 oxyethylene groups. In Pluronic F-~8, the polyoxypropylene
I portion contsin6 approximately 160 units. Pluronic Lo has
Al approximately 20 polyoxypropylene units and 15
polyoxyethylene units.
Jo Polyox WAR I is a polyoxyethylene compound with
ill an average molecular weight of 200,000 commercially
available from Union Carbide Corp.
Al Olin, Andy logger alkylphenyl polyoxyethylene
compounds with six and ten oxyethylene groups respectively.
11 They are commercially available from Olin Corp. Stamford,
12!i Ct.
13 Tergitol Mix Foam-lX is a polyoxy~propylene -
14 polyoxyethylene compound of a linear alcohol commercially
available from Union Carbide Corp.
I ,
17 Exa~E~e X~rI
-----
18
I' . .
The procedure in example XIV was repeated except
that the electroplating solution was a nickel bath comprised
21~ as follows:
22 Nazi 6H2 195 g/l
' Nikko 6H2 175 g/l
24i1 H3B03 40 g/l
251¦ pi 1.5
26~, Temp. 46~C
27j; The non ionic surfactant added to this solution as
28jl Component C was Carbowax inn a concentration of 0.1 g/l.
glue After electroplating at a potential providing 3.8 Adam
30~l, for 15 minutes the hole walls were covered with a complete
31 continuous film of nickel.
32
Jo *trade mark
. .
l 2 ~46
-36-
1 Exam ye VOW
3 ¦ In order to more fully demonstrate the usefulness
4 ¦ of polyoxyethylene groups in currying out the invention,
5 I sodium lsuryl sulfate, an anionic surfactant widely used in
Al the electroplating industry, and recommended for use in acid
7 I copper sulfate electroplating baths was tested as follows.
I The procedure of Example XIV was repeated except that in one
9" cop~er~electroplating bath I g/l sodium laurel sulfate
10,~ commercially available from ELI. Dupont de Numerous and Co.
11' as Duponol*C) was added as the surfactant instead of
12 ' Pluronic Phoned in a second and third electroplating bath
13 solution 1.0 g/l ammonium polyether sulfate and 1.0 g/l
14 ammonium laurel polyether sulfate (commercially available as
: .
Siphon E h from Alcoholic Inc. 3440 Fairfield Rod, Baltimore,
16 MD) were used respectively instead of Pluronic F-127. After
17, 5 minutes plating time both the puller sulfate and
18 puller laurel sulfate containing electroplating baths 1,
19 , produced complete continuous films of copper covering the
20" hole walls, while even after 15 minutes plating time
21 j electroplating in the laurel sulfate containing
221, electroplating did not over the hole walls. This
23~¦ experiment shows that a simple linear anionic surfactant,
24¦, laurel sulfate, was ineffective for purposes of this
2511 invention. When the surfactant is selected according to the
26l~, teachings of this invention such as when the laurel sulfate
Ill structure was modified by the polyether group, it became
joy effective as Component C.
29jl !
I 1! *trade mark
31 I
32',
^37-
I 2 I 6
2 Example YO-YO
3 The procedure of Example VIII was repeated except
4 that substituted Theresa were substituted for Copper Gleam
PC. In one copper electroplating solution, 5 Mel
6 I tetramethylthiuram disallowed, and in a second such solution,
Al 0.8 g/l of ally Thor were used respectively as
8 Component C. After electroplating for 15 minutes at a
9 potential providing 3.8 amp/sq.dm the hole walls of printer
circuit boards plated in either solution were covered with a
11 continuous film of copper.
12 It should be understood by those skilled in the
13 art that various modifications may be made in the present
14 invention without departing from the spirit and scope
thereof as described in the specification and defined in the
16 appended claims.
17 !
18
19
21
22
23
I
25 11
26
I
28 Al *trade mark
21 !
