US 3902908 A
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United States Patent [191 Rantell et al.
[4 1 Sept. 2, 1975 CATALYST SYSTEM FOR ACTIVATING SURFACES PRIOR TO ELECTROLESS DEPOSITION  Inventors: Alan Rantell, London, England; Abraham Holtzman, Bat-Yam,
Israel  Assignee: MacDermid Incorporated,
22 Filed: Oct. 4, 1973 21 Appl.No.:403,502
 Foreign Application Priority Data Mar. 21, 1973 United Kingdom 13545/73  US. Cl. 106/1; 1 17/47 A; 204/30  Int. Cl. C23C 3/00  Field of Search 106/1; 204/30; 117/47 A;
 References Cited UNITED STATES PATENTS 3,532,518 lO/l97O DOttavio 204/30 X 3,650,913 3/1972 DOttavio 204/30 3,698,919 10/1972 Kuzmik ..204/3OX Primary ExaminerLewis T. Jacobs Attorney, Agent, or FirmSteward & Steward 57 ABSTRACT compound when contacted with conventional alkali or acid accelerators in the plating process.
8 Claims, No Drawings CATALYST SYSTEM FOR ACTIVATING SURFACES PRIOR TO ELECTROLESS DEPOSITION CROSS REFERENCE TO PRIOR RELATED APPLICATIONS This application corresponds to British Provisional Specification No. 13545/73, filed Mar. 21, 1973.
FIELD OF THE INVENTION The present invention relates to the preparation and use of a catalyst composition for activating nonconductive surfaces prior to electroless deposition of metals.
For the purpose of electroless or chemical plating of non-conductive substrates, small quantities of activator or catalyst must first be placed on the surface of the substrate. Palladium is found to be the most satisfactory catalyst but any metal selected from palladium, gold, silver or the platinum group of metals is suitable.
The activating or catalyzing process is often carried out by consecutive immersion of the substrate in solutions containing PdCl and SnCl respectively. More recently the use of single step activators comprising colloidal mixtures of PdCl and SnCl has been proposed. Typical working strength catalyst solutions contain:
PdCI. 300- lUUOmg/I SnCL |s SOg/l wt sno smo 1 7 g/l HCl 250- 3(J0ml/l However, these PdCl- /sncl mixtures are more effective when used in conjunction with an additional treatment solution known as an accelerator. Accelerators are generally solutions of strong acids or strong alkalis and are employed between the catalyst treatment and electroless deposition.
The method and conditions of preparation of PdCIg/SIICI- mixtures is critical. Further, the high con ccntration of PdCIg employed makes the catalyst solutions very expensive. Less critical yet cheaper solutions would be an advantage.
SUMMARY OF THE INVENTION The principle of the invention involves the formation of a highly active compound by reaction at high temperature between a stannous salt, usually the chloride, and low concentrations of palladous or other similar catalytic ions; e.g. Au(l), Au( III), Pt(II), Pt(IV), Rh(IIl), Ru(IlI), Ru(IV), Os(III), Os(IV), Ir(III), Ir- (IV) or Ag(l). The choice of booster compound is determined by the nature of the accelerator solution employed in the processing cycle. It is essential that the 5 booster compound should form a sparingly soluble compound when contacted with the accelerator; i.e. if a NaOH accelerator is employed, the booster com pound should be an acid salt of metal ion-forming insoluble hydroxides at alkaline pH values; e.g. compounds containing Mg, Fe, Fe, Mn, Cu, Ni, Co or Cr.
In one method of implementing the present invention, the catalyst is formed by heating the component supplying the catalytic ion and the booster compound in strong acid solution at temperatures in excess of 75C, and then adding an excess of stannous ion. The temperature of the mixture is maintained above 75C until the reaction is completed. During the reaction, the color of the mixture changes from light amber to dark brown, returning to light amber. Finally the completion of the reaction is indicated when the color of the mixture becomes dark brown for the second time.
This may take from 1 to 20 minutes.
Alternatively the stannous ion may be added in two stages. Sufficient stannous salt to carry out the reaction is first added to the mixture of catalytic ion and booster compound at temperatures in excess of C. The quantity required may be between 2 and 50 g/l as SnCl depending on temperature and concentration of catalytic ion. When the reaction is complete after 1-20 minutes, a vast excess of an acid stannous salt is added. Small quantities of sodium stannate are found useful for stabilizing the compound formed between Sn(II) and the catalytic ion, e.g. (Pd(II)).
The preheating of the reactants to temperatures in excess of 75C prior to admixing them in the preparation step is an important part of the invention. The catalytic activity of the reaction product formed between Sn(II) and the catalytic ion, e.g. Pd(II), increases with increase of reaction temperature during manufacture, allowing relatively low concentrations of catalytic ion to be used. At temperatures below 75C much greater concentrations of catalytic ion are required in order to maintain catalytic activity; viz. greater than 150 mg/l of PdCl The reaction between Sn(II) and Pd(II), i.e. the catalytic ion, may take two routes. The preferred reac tion yields a Sn(II)/Pd(ll) addition compound whereas a secondary reaction causes formation of metallic palladium. The latter reaction is generally undesirable. The use of high manufacturing temperatures and excess stannous salt encourages the preferred reaction and inhibits the secondary reaction. V
The invention is illustrated by the following examples for the preparation and use of the catalyst.
EXAMPLE I For 1 liter of working strength catalyst a mixture containing:
PdCl 45 mg. MnCl. 15 g.
HCl (37% w/v) 200 ml. H. ,O 400 ml.
is heated to.90C and reacted with a solution containing:
SnCI 2H O 150 g. Na- SnO 3H- 4 g. HCl (3771 w/v) 300 ml.
The temperature is maintained at C for 15 minutes and then allowed to cool prior to use.
The catalyst may be used to activate plastic surfaces or copper clad printed circuit boards prior to electroless deposition. For the plating of ABS plastics the following processing cycle is preferred:
ABS plastic is etched in a mixture containing 200-400 g/l CrO and 300600 g/l H 50 at 4070C for 2l0 minutes. After thorough rinsing, the plastic is immersed in the catalyst solution for l-5 minutes at 5 room temperature. For increased activation it is perg/l NaOH for lminutes at 20-60C. The preferred temperature of the accelerator is 40C. The activated plastic is then immersed in any electroless nickel or copper plating solution. A preferred composition is:
pH adjusted to 8.0 8.5 with NH.
The electroless nickel solution is employed at 20-30C for 5-l0 minutes.
EXAMPLE 2 For 1 liter of working strength catalyst a mixture containing:
Pd(l 45 mg. FeCl 40 g.
HCl (37% w/v) 200 ml. H. 400 ml.
is heated to 90C and then reacted with 20g SnCl .2H-,O. After the reaction has continued for a period of minutes, a mixture containing:
The time allowed for the reaction of the first addition is not critical and may be for any period greater than 1 minute, but 15 minutes is preferred. The reaction temperature again is important, as it must be greater than 75C, 90-95C being preferred.
The catalyst solution may be used to activate plastic surfaces in the manner described in Example 1.
EXAMPLE 3 The catalyst is prepared and used-as in Example 1 except that in this instance the PdCl is replaced by 75 mg of HAu Cl EXAMPLE 4 For 1 liter of working strength catalyst a mixture containing:
Pdcl 40 mg. AICL, g.
HCI (37% w/ 200 ml. up 400 ml.
is heated to 90C and reacted with a solution containing:
The temperature of the mixture is maintained at 90C for IS minutes and then cooled to room temperature for use. The electroless plating procedure then proceeds in a similar manner to that described in Example I, except that in this instance the accelerator solution should be l0500 ml/] of ammonia solution (28% w/v).
In this example AICL, acts as a booster compound when used in conjunction with an ammonium hydrox- LII idc accelerator since Al(OH) is not soluble in ammonia solution.
EXAMPLE 5 For 1 liter of working strength catalyst a mixture containing:
PdCl- 45 mg. BaCl 40 g.
HCl (37% w/v) 200 ml. H 0 400 ml.
is heated to 90C and reacted with a solution containing:
The temperature of the mixture is maintained at 90C for 15 minutes and then the catalyst is cooled at room temperature for use.
The catalyst solution may be used to activate plastic Surfaces in a similar manner to that described in Example 1, except that in this instance the accelerator solution should be 10-200 g/l H 50 The activated catalysts referred to in the invention are not colloidal in nature. Tyndall effect measurements taken on the undiluted catalyst solutions and electron microscopy of the adsorbed catalyst fail to show any colloidal particles. The active component of the snCl /Pdcl catalyst is an acid soluble complex formed between Sn(ll) and Pd(ll). On contact with the accelerator solution, a slow redox reaction occurs:
Sn(-ll) Pd(lll) Sn(lV) Pd(O).
The elemental palladium formed can then initiate electroless deposition. The presence of the booster enables a concentration of catalytic metal ion in solution equivalent to about 10 mg/l of Pd as PdCl to be effective. For economic reasons a concentration equivalent to about 500 mg/] of PdCl represents a practical maximum.
Booster compounds such as MnCl and FeCl;, produce a voluminous surface precipitate when the adsorbed catalyst contacts the sodium hydroxide accelerator. The precipitated metal hydroxides help to retain the Pd(ll) on the plastic surface until the redox reaction has occurred. If no booster compound is used the Pd(ll) may leach into the accelerator before any reaction has occurred.
What is claimed is:
l. A method for preparing a catalyst solution by heating an acid solution of a Pd(ll) catalytic ion wherein said catalytic ion is present in amount sufficient to provide in the working strength catalyst solution a concentration equivalent to about 10500 mg/l of Pd as PdCI- with a solution containing a stochiometric excess of stannous salt wherein at least one of said catalytic ion and stannous salt solutions is first heated to a temperature in excess of C before the other is added to it, and wherein a booster compound consisting of a soluble metal salt, of which the cation is capable of forming a precipitate when contacted with the accelerator solution used in an electroless plating process, is added to the catalyst mixture during preparation, said booster compound being present in amount of about 0.] mol/l up to 5 mol/l in the working strength solution.
2. A method for preparing a catalyst as in claim 1, for use in an electroless plating process employing as the accelerator a strong alkali, wherein the booster compound is a salt containing a cation selected from the group consisting of Mg, Fe, Fe. Mn, Mn, Cu, Ni, Co, Cr.
3. A method for preparing a catalyst as in claim 1, for use in an electroless plating process employing as the accelerator an alkaline ammonia solution, wherein the booster compound is a salt containing a cation selected from the group consisting of Mg, Fe. Mn'. Mn, zu: Pb2+ AliH 4. A method for preparing a catalyst as in claim 1, for use in an electroless plating process employing as the accelerator sulphuric acid or a soluble acid sulphate, wherein the booster compound is a salt containing a cation selected from the group consisting of Ca Ba, Sr, Pb.
5. A method for preparing a catalyst as in claim 1, for use in an electroless plating process employing as the accelerator a soluble carbonate or phosphate, wherein the booster compound is a salt containing a cation selected from the group consisting of Ca Ba, Sr, Pb'l't', Mgl-i" F ll+q 11 3+g M 2+, M 3+ C 2+, bJiZ-i-q CO2+, c 3+q Cd2+s 2 2+g l)b.l-l-s Alli-F 6. A method for preparing a catalyst as in claim 1, for use in an electroless plating process employing as the accelerator a soluble fluoride, wherein the booster compound is salt containing a cation selected from the group consisting of Mg, Ca, Ba, Sr, Zn, Cd, Al3+ Pb2+ M l-F, M 3+ 7. An aqueous acid catalyst solution comprising a Pd(ll) catalytic ion wherein said catalytic ion is present in amount sufficient to provide in the working strength catalyst solution a concentration equivalent to about l()5()0 mg/l of Pd as PdCl a stochiometric excess of stannous salt, and a booster compound consisting of a soluble metal salt of which the cation is capable of forming a precipitate when contacted with the accelerator solution used in an electroless plating process employing a substrate which has been catalyzed in said catalyst solution, said booster compound being present in amount of about 0.1 mol/l up to 5 mol/l in the working strength solution.
8. An aqueous catalytic solution composition as defined in claim 7, wherein the booster compound is selected from the group consisting of Ca Ba, Fr, 2+ 2+ 2+ m -1+ :i+ 2+ 2+ C 3+ 2+ 2+ 2+ a+