Plating bath composition and method for electroless plating of palladium

Abstract

The present invention relates to an aqueous plating bath composition and a method for depositing a palladium layer by electroless plating onto a substrate. The aqueous plating bath composition according to the present invention comprises a source for palladium ions, a reducing agent for palladium ions and an aldehyde compound. The aqueous plating bath composition has an increased deposition rate for palladium while maintaining bath stability. The aqueous plating bath composition has also a prolonged life time. The aldehyde compounds of the present invention allow for adjusting the deposition rate to a constant range over the bath life time and for electrolessly depositing palladium layers at lower temperatures. The aldehyde compounds of the present invention activate electroless palladium plating baths having a low deposition rate and reactivate aged electroless palladium plating baths.

1 . An aqueous plating bath composition for electroless deposition of palladium, comprising
 (i) at least one source for palladium ions,   (ii) at least one reducing agent for palladium ions, wherein the at least one reducing agent for palladium ions is selected from the group consisting of hydrazine, formic acid, derivatives of the aforementioned and salts thereof, and   (iii) at least one aldehyde compound according to Formula (I)   
       
         
           
           
               
               
           
         
         wherein R is selected from the group consisting of —H; unsubstituted or substituted, linear alkyl groups comprising 1 to 10 carbon atoms; and unsubstituted or substituted, branched alkyl groups comprising 3 to 10 carbon atoms; and substituted or unsubstituted aryl groups; and 
         wherein the at least one aldehyde compound according to Formula (I) has a concentration ranging from 0.01 to 25 mg/l. 
       
     
     
         2 . The aqueous plating bath composition according to  claim 1 , wherein the unsubstituted or substituted, linear alkyl groups are selected from n pentyl group, n-butyl group, n-propyl group, ethyl group and methyl group. 
     
     
         3 . The aqueous plating bath composition according to  claim 1 , wherein the unsubstituted or substituted, branched alkyl groups are selected from 2 pentyl group, 3-pentyl group, 2-methylbutyl group, 3-methylbutyl group, 3-methylbut-2-yl group, 2-methylbut-2-yl group; 2,2-dimethylpropyl group, iso-butyl group, sec-butyl group, tert-butyl group, and iso-propyl group. 
     
     
         4 . The aqueous plating bath composition according to  claim 1 , wherein the unsubstituted or substituted aryl groups are selected from unsubstituted or substituted phenyl groups and unsubstituted or substituted naphthyl groups. 
     
     
         5 . The aqueous plating bath composition according to  claim 1 , wherein the linear alkyl groups, the branched alkyl groups, or the aryl groups are substituted and the substituents are selected independently from each other from amino, carboxyl, ester, mercapto, hydroxyl, methoxy, ethoxy, methyl, ethyl, halogen, allyl, vinyl, and aryl groups. 
     
     
         6 . The aqueous plating bath composition according to  claim 1 , wherein the at least one aldehyde compound according to Formula (I) is selected from hexanal, pentanal, butanal, propanal, ethanal, methanal, phenylmethanal, and 2-phenylacetaldehyde. 
     
     
         7 . The aqueous plating bath composition according to  claim 1 , wherein the at least one source for palladium ions is selected from palladium chloride, palladium acetate, palladium sulfate, palladium perchlorate, dichloro ethane-1,2-diamine palladium, diacetato ethane-1,2-diamine palladium; dichloro N 1 -methylethane-1,2-diamine palladium; diacetato N 1 -methylethane-1,2-diamine; dichloro N 1 ,N 2 -dimethylethane-1,2-diamine; diacetato N 1 ,N 2 -dimethylethane-1,2-diamine; dichloro N 1 -ethylethane-1,2-diamine; diacetato N 1 -ethylethane-1,2-diamine, dichloro N 1 ,N 2 -diethylethane-1,2-diamine; and diacetato N 1 ,N 2 -diethylethane-1,2-diamine. 
     
     
         8 . The aqueous plating bath composition according to  claim 1 , further comprising at least one complexing agent for palladium ions selected from the group consisting of primary amines, secondary amines and tertiary amines. 
     
     
         9 . (canceled) 
     
     
         10 . The aqueous plating bath composition according to  claim 1 , wherein the formic acid derivatives are selected from esters of formic acid. 
     
     
         11 . The aqueous plating bath composition according to  claim 1 , wherein the concentration of the at least one reducing agent ranges from 10 to 1000 mmol/l. 
     
     
         12 . A method for electroless palladium plating comprising the steps of
 (a) providing a substrate,   (b) contacting the substrate with the aqueous plating bath composition according to  claim 1  and thereby depositing a layer of palladium onto at least a portion of the substrate.   
     
     
         13 . The method for electroless palladium plating according to  claim 12  wherein the substrate is contacted with the aqueous plating bath composition at a temperature of 30 to 65° C. in step (b). 
     
     
         14 . A method for adjusting the deposition rate to a constant range over the life time of any electroless palladium deposition bath, the method comprises the steps of
 c) providing any electroless palladium deposition bath, and   d) adding at least one aldehyde compound according to Formula (I) as defined by  claim 1  to the electroless palladium deposition bath, and wherein the at least one aldehyde compound according to Formula (I) has a concentration in the bath ranging from 0.01 to 25 mg/l.   
     
     
         15 . A method for reactivating an aqueous electroless palladium deposition bath, the method comprises the steps of
 e) providing an already used aqueous electroless palladium deposition bath, wherein deposition rate of the bath has dropped in relation to an initial deposition rate of the bath, and   f) adding at least one aldehyde compound according to Formula (I) as defined by  claim 1 , and thereby increasing its deposition rate, and wherein the at least one aldehyde compound according to Formula (I) has a concentration in the bath ranging from 0.01 to 25 mg/l.