CA1226846A - Method for electroplating non-metallic surfaces - Google Patents

Abstract

ABSTRACT

Method for electroplating non-metallic surfaces on a substrate, e.g. of plating holes in metal clad laminates, is disclosed. Metallic sites are formed on the surface and the resulting site-containing surface is electroplated with an electroplating bath comprising a component which causes the plating to preferentially occur at these sites as opposed to the plating on surfaces of the same metal as the one plated out; whereby a rate differential of the plating-reaction on site-surfaces is achieved with respect to the plating-reaction on a surface consisting of the metal to be plated out. The metal deposited is different from the metal existing at the deposition surface.

Description

-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.

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 I
2g .. I

- 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 if ~2XÇ;8~6 1 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 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 "

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 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.

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 :

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 _ v , 31 1!

if 12~46 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 ,1 I! I , .

if 122~t~4c6 If , 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 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 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

*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 291~ , j 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.

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.

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 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

l ., .. ., ., ,. .. .. , , ... . , .. , .

~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.

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

13 ;
. This example describes the reparation of a Jo printed circuit board of the multi layer type. A well known ;; procedure is used to form a multi layer composite by 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.

us 26 i 27' trade mark 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 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 30 l 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, ho 31 It 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 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 Ii *trade mark 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
-----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.

Jo *trade mark . .

l 2 ~46 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 32', ^37-2 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 !

I

I
28 Al *trade mark 21 !

Claims (37)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. 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, said non-metallic surface being provided with a conductive connector area, said connector area being located outside of and abutting the non-metallic surface area to be electroplated, said abutting connector area being employed as an electrode during electroplating, characterized by the steps comprising:
(a) forming a plurality of discrete metallic sites on said non-metallic surface, each of said sites comprising metal (A), said metal (A) being different from said metal (B);
(b) exposing said non-metallic surface including at least a portion of said connector area to the electro-plating bath solution, said solution having a conductivity sufficient to carry electroplating current to said metallic sites of said metal (A) and further comprising at least one component (C) which when an electroplating potential is applied allows deposition of said metal (B) on said metallic sites comprising or consisting of metal (A), at a rate which is faster compared to the deposition rate of said metal (B) on surfaces consisting of, or formed by, the species of the electrodeposited 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 to:
(1) initiate electroplating of metal (B) on the exposed
1. claim 1 continued...
   
   portion of the connector area and (2) allow electroplating of metal (B) on neighboring metallic sites, the application of said potential initiating electroplating of metal (B) on the connector area and on said neighboring metallic sites, the electroplating of metal (B) on the connector area covering the connector area with metal (B);
   (d) continuing the application of said potential until all of said neighboring metallic sites are covered with metal (B), the rate of forming metal (B) deposits on said neighboring metallic sites being greater than the electrodeposition rate of metal (B) on surfaces consisting of or formed by the species of metal (B), the greater rate of electrodeposition of metal (B) on said neighboring metallic sites continuing until all of said sites are covered with metal (B); and (e) continuously electroplating metal (B) on the exposed portion of said connector area and on said electroplated sites to produce an electrically conductive continuous film of metal (B) having a thickness of at least 0.5 microns.
2. 2. The method of claim 1 characterized in that said component (C) preferentially attaches itself to a surface of the species of metal (B) compared to the surface of the species of metal (A), thus substantially inhibiting or reducing the plating reaction on surfaces formed by metal (B) without substantially interfering with the plating reaction on surfaces formed by the species of the site metal (A).
3. 3. The method of claim 2, characterized in that said component (C) increases the over potential on surfaces formed by metal (B).
4. 4. The method of claim 1, characterized in that said component (C) preferentially attaches itself to the species of site metal (A), said attached component (C) substantially increasing the plating reaction on surfaces formed by site metal (A) compared to the plating reaction on surfaces of the species of metal (B).
5. 5. The method of claim 4 characterized in that said attached component (C) reduces the over potential thus increasing the plating reaction compared to the plating reaction on surfaces of the species of metal (B).
6. 6. The method of claim 1 characterized in that component (C) is selected from dyes, surfactants, chelating agents, brighteners and leveling agents.
7. 7. The method of claim 6 characterized in that component (C) is a dye selected from methylene blue and methyl violet.
8. 8. The method of claim 6 characterized in that component (C) is a surfactant selected from alkylphenoxy-polyethoxyethanols, nonionic fluorocarbon surfactants, polyoxyethylene compounds, block copolymers of polyoxyethylene and polyoxypropylene.
9. 9. The method of claim 8 characterized in that component (C) is selected from compounds containing 4 to 1,000,000 oxyethylene groups.
10. 10. The method of claim 9 characterized in the component (C) is selected from the compounds containing twenty to one hundred fifty oxyethylene groups.
11. 11. The method of claim 8 characterized in that component (C) is selected from ethylene oxide - propylene oxide copolymers containing 10 to 400 oxyethylene groups.
12. 12. The method of claim 6 characterized in that component (C) is the chelating agent 2,4,6-(2-pyridyl)-s-triazine.
13. 13. The method claim 6 characterized in that component (C) comprises a brightener and/or leveling agent selected from N-heterocyclic compounds, triphenyl methane dyes, thiourea, allyl thiourea, tetramethylthiuram disulfide, thiourea derivatives, saccharin and O-benzaldehyde sulfonic acid derivatives.
14. 14. The method of claim 1 characterized in that the conductivity of the electroplating bath solution and the potential applied to the connector area and the counter-electrode are selected sufficiently high to achieve a rate of deposition on the surface of the species of the site metal (A) which is at least one order of magnitude higher than the deposition rate on the surface of the species of metal (B).
15. 15. The method of claim 14 characterized in that the conductivity is adjusted to the highest value permissible with respect to the other plating paratmeters.
16. 16. The method of claim 14 characterized in that the potential is adjusted to compensate for the potential drop on the resistive path formed by the plating bath solution between the connector area and the metallic sites consisting of, or comprising metal (A), and between such neighboring sites.
17. 17. The method of claim 16 characterized in that the potential is adjusted to the highest value permissible with respect to the other plating parameters.
18. 18. The method of claim 1 characterized in that metal (A) and metal (B) are selected from Groups Ib and VIII of the Periodic Table of Elements, and that metal (A) differs from metal (B).
19. 19. The method of claim 18 characterized in that component (C) is selected from dyes, surfactants, chelating agents, brighteners and leveling agents.
20. 20. The method of claim 1 characterized in that metals (A) and (B) are selected so that potential for the deposition of metal (B) on metal (A) is less negative than the potential for the deposition of metal (B) on itself under the conditions provided by the plating operation.
21. 21. The method of claim 20 characterized in that component (C) is selected from dyes, surfactants, chelating agents, brighteners and leveling agents.
22. 22. The method of claim 18 characterized in that metal (A) is selected from palladium, platinum, silver or gold.
23. 23. The method of claim 18 characterized in that metal (B) is selected from copper and nickel.
24. 24. The method of claim 1 characterized in that the site formation step comprises employing metal (A) in solution as a compound or complex.
25. 25. The method of claim 24 characterized in that the compound is a metal halide or double metal halide.
26. 26. The method of claim 25 characterized in that the double metal halide is a palladium-tin-chloride.
27. 27. The method of claim 24 characterized in that the solution comprises metal (A) and a tin-halide and that the treated surface is subsequently exposed to a solvent for tin-compounds.
28. 28. The method of claim 25 characterized in that the plurality of metal sites of metal (A) is formed by treating the non-metallic surface with a solution comprising metal (A) and subsequently exposing said surface to heat or to a reducing agent.
29. 29. The method of claim 28 characterized in that said heat-treatment is effected at a temperature in the range of 65 to 120°C and for at least 10 minutes.
30. 30. The method of claim 28 characterized in that said reducing agent is selected from sodium borohydride, formaldehyde, dimethylamine borane and hydroxylamine.
31. 31. The method of claim 1 characterized it that in further comprises the steps of terminating the deposition of metal (B) after establishing a continuous film of metal (B) of desired thickness over the non-metallic surface; and by electrolytically depositing one or more metal layers on said film or part thereof.
32. 32. The method of claim 14 characterized in that the rate of deposition on the surface of the species of the site metal (A) is two orders of magnitude higher than the deposition rate on the surface of the species of metal (B).
33. 33. In a method for the manufacture of a printed circuit board which includes forming holes in a copper clad in-sulating sheet, or in a laminate formed by plurality of such sheets, and providing the non-metallic walls of said holes with a metal layer, the improvement which comprises:
    (a) providing a vessel containing a counter-electrode and an electroplating bath of conductivity sufficient to carry electroplating current comprising in dissolved form a metal (B) to be electroplated, said copper cladding being located outside of and abutting the non-metallic surface of said walls to be electroplated, said abutting copper cladding being employed as an electrode during electroplating;
    (b) forming a plurality of discrete metallic sites on the walls of said holes, each of said sites comprising or consisting of a metal (A) said metal (A) being different from metal (B);
    (c) at a subsequent step exposing said sheet or laminate including said copper cladding thereon to the electroplating bath solution which further comprises at least one component (C) which when an electroplating potential is applied allows preferential deposition of said metal (B) on said metallic sites comprising or con-sisting of metal (A), at a rate which is faster compared to the electrodeposition rate of metal (B) on surfaces consisting of or formed by the species of the electro-deposited metal (B), with the proviso that component (C) does not contain pyrophosphate anion;
    
    (d) applying a potential between the copper cladding and the counter-electrode which is sufficient to:
    
    (1) initiate electroplating of metal (B) on the exposed portion of the copper cladding and (2) allow the electro-plating of metal (B) on neighboring metallic sites, the application of said potential initiating electroplating of metal (B) on the copper cladding and on said neighbor-ing metallic sites, the electroplating of metal (B) on the copper cladding covering the copper cladding with metal (B);
    (e) continuing the application of said potential until all said neighboring metallic sites are covered with metal (B), the rate of forming metal (B) deposits on said neighboring metallic sites being greater than the electro-deposition rate of metal (B) on surfaces consisting of or formed by the species of metal (B) on said neighboring metallic sites continuing until all of said sites are covered with metal (B); and (f) continuously electroplating metal (B) on said sheet or laminate to produce an electrically conductive continuous film of metal (B) having a thickness of at least 0.5 microns.
34. 34. The method of claim 33 characterized in that it further comprises the steps of providing a negative image resist layer on the surface of said copper clad sheet or laminate, said layer leaving exposed the areas corresponding to a desired conductor pattern which includes said holes, the walls defining said holes provided with said sites of metal (A); and, after the electroplating step, removing said resist layer and etching away the metal in the areas which have been covered by said resist layer.
35. 35. The method of claim 33 characterized in that it further comprises the steps of providing a positive image resist layer on the surface of said copper clad sheet or laminate subsequent to the electroplating step, said resist layer covering the areas corresponding to the desired circuit pattern including the holes; and etching away the metal not covered by the positive image resist layer thus forming the printed circuit board pattern.
36. 36. In a method for the manufacture of printed circuit boards comprising forming holes in a non-metallic, insulat-ing sheet and metallizing, non-metallic areas of said sheet corresponding to a desired printed circuit conductor pattern with a metal layer having a desired thickness, the improvement which comprises:
    (a) providing a vessel containing a counter-electrode and containing an electroplating bath solution of conductivity sufficient to carry electroplating current to sites of a metal (A) to allow the deposition of a metal (B) comprising in ionic form metal (B), said non-metallic areas being provided with a conductive connector area, said connector area being located outside of and abutting the non-metallic surface area to be electroplated said abutting connector area being employed as an electrode during electroplating;
    (b) forming a plurality of discrete metallic sites on the walls of said holes and in said areas corresponding to said conductor patterns each of said sites comprising or consisting of a metal (A), said metal (A) being different from a metal (B) to be electroplated;
    (c) at a subsequent step exposing said sheet including said connector area to the electroplating bath solution which further comprises one or more component(s) (C) which allow deposition of said metal (B) on said metallic sites comprising or consisting of metal (A) when current is applied,at a rate which is faster compared to the electrodeposition rate of metal (B) on surfaces formed by the species of the electro-deposited metal (B), with the proviso that component (C) does not contain pyrophosphate anion;
    (d) applying a potential between the connector area and the counter-electrode which is sufficient to:
    (1) initiate electroplating of metal (B) on the exposed portion of the connector area and (2) allow elctroplating of metal (B) on neighboring metallic sites, the application of said potential initiating electroplating of metal (B) on the connector area and on said neighbor-ing metallic sites, the electroplating of metal (B) on the connector area covering the connector area with metal (B);
    (e) continuing the application of said potential until all said neighboring metallic sites are covered with metal (B), the rate of forming metal (B) deposits on said neighboring metallic sites being greater than the electro-deposition rate of metal (B) on surfaces consisting of or formed by the species of metal (B), the greater rate of electrodeposition of metal (B) on said neighboring metallic sites continuing until all of said sites are covered with metal (B); and (f) continuously electroplating metal (B) onto the exposed portion of the connector area and onto said electroplated sites to produce an electrically conductive continuous film of metal (B) having a thickness of at least 0.5 microns.
37. 37. The method of claim 36 characterized in that said connector area covers the surface of said insulating sheet in small areas along its edges, and is shaped like a window frame.