Method for electroless nickel deposition onto copper without activation with palladium

Abstract

The invention relates to selective deposition of a nickel layer on a copper surface. The invention may be used in the production of electrically conductive areas for electronic circuits. Method for nickel deposition on the surface of copper comprises immersing an item, which surface is to be deposited with the nickel layer, into one or more baths, of which at least one contains a reducing agent and of which at least one is adapted for (electroless) plating of nickel. In order to extend the field of application and to obtain practically pure nickel coatings, said reducing agent comprises boronic or phosphoric compounds, comprising morpholine borane (C4H9BNO), or dimethylamine borane (C2H7BN), or sodium tetrahydroborate (NaBH4), or sodium hypophosphite (NaH2PO2) and said reducing agent directly or indirectly reduces insoluble copper (I) or copper (II) compounds on the copper surface. At least one of the mention baths comprises a ligand or mixture thereof.

1 . A method for nickel deposition on a surface of an item which is produced from copper or has a copper layer on the item comprising:
 immersing said item into an electroless nickel plating bath comprising:   a reducing agent and a ligand or mixture of ligands;   wherein: said reducing agent directly or indirectly reduces insoluble copper (I) or copper (II) compounds on the surface of the item or on the copper layer of the item; and at least one of said ligand in the bath facilitates dissolution of incompletely reduced insoluble copper compounds by binding the incompletely reduced insoluble copper compounds to soluble complexes, such that a substantially pure copper surface is present where nickel is deposited.   
     
     
         2 . The method of  claim 1 , wherein at least one of said ligand in the bath or mixture thereof consists of any water-soluble chemical compound capable of forming sufficiently stable complexes with copper ions selected from a group consisting of: ethylenediamine (C 2 H 8 N 2 ), diethylenetriamine (C 4 H 13 N 3 ), and N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine(C 14 H 32 N 2 O 4 ). 
     
     
         3 . The method of  claim 1 , wherein said method further comprises:
 initially immersing said item in an activation bath, which comprises said reducer and said ligand or the mixture therefor and subsequently immersing said item into the electroless nickel plating bath in which nickel is electrolessly deposited on the copper surface;   wherein in the activation bath, an electron which appears after an anodic oxidation reaction of said reducing agent from the activation bath activates the copper surface by reducing Cu(I) and Cu(II) oxides and/or oxy-hydroxy compounds on the surface, and at a same time, anodic catalytic or thermal decomposition reactions occur, releasing hydrogen, and the hydrogen is reacting as an active reducing agent with the Cu(I) and Cu (II) compounds on the copper surface, leaving the substantially pure copper surface and where nickel is then deposited without any intermediate step in the electroless nickel bath.   
     
     
         4 . The method of  claim 1 , wherein said reducing agent contains boronic or phosphoric compounds to reduce the insoluble copper (I) and copper (II) compounds present on the surface of the item produced from copper or has a copper layer; and the at least one ligand or a ligand from the mixture of ligands is selected from a group of chemical compounds of: ethylenediamine (C 2 H 8 N 2 ), diethylenetriamine (C 4 H 13 N 3 ), and N,N,N′,N′-tetrakis(2-hydroxypropyl) ethylenediamine(C 14 H 32 N 2 O 4 ), selecting concentrations of said chemical compounds of said ligand, such that said chemical compounds dissolves the incompletely reduced insoluble copper compounds by binding the incompletely reduced insoluble copper compounds to the soluble complexes so that substantially pure copper surface is produced on which the nickel is deposited. 
     
     
         5 . The method of  claim 3 , wherein said activation bath consists of a sodium hypophosphite (NaH 2 PO 2 ) solution with a concentration from 0.5 M up to the limit of solubility and said at least one ligand of: N,N,N′,N′-tetrakis (2-hydroxypropyl) ethylenediamine(C 14 H 32 N 2 O 4 ) in a concentration from 0.001 M to the solubility limit and an immersion time ranges from 1 to 15 min at a temperature of 80-96° C. 
     
     
         6 . The method of  claim 3 , wherein said activation bath consists of a morpholine borane (C 4 H 9 BNO) solution with a concentration from 0.01 M up to the limit of solubility and said mixture of ligands of: N,N,N′,N′-tetrakis(2-hydroxypropyl) ethylenediamine (C 14 H 32 N 2 O 4 ) and amino acetic acid (C 2 H 5 NO 2 ) in a concentration from 0.001 M to the solubility limit and an immersion time ranges from 1 to 15 min at a temperature of 18-50° C. 
     
     
         7 . The method of  claim 3 , wherein said activation bath consists of a dimethylamine borane (C 2 H 7 BN) solution with a concentration from 0.01 M up to the limit of solubility and said mixtures of ligands: nitrilotriacetic acid (C 6 H 9 NO 6 ) and ethylenediamine (C 2 H 8 N 2 ) in a concentration from 0.001 M to the solubility limit and an immersion time ranges from 1 to 15 min at a temperature of 18-50° C. 
     
     
         8 . The method of  claim 3 , wherein said activation bath consists of a sodium tetrahydroborate (NaBH 4 ) solution with a concentration from 0.01 M up to the limit of solubility and said mixtures of ligands of: diethylenetriamine (C 4 H 13 N 3 ) and ethylenediaminetetraacetic acid (C 10 H 16 N 2 O 8 ) in a concentration from 0.001 M to the solubility limit and an immersion time ranges from 1 to 15 min at a temperature of 18-50° C. 
     
     
         9 . The method of  claim 1 , wherein said electroless plating bath of nickel consists of nickel sulphate (NiSO 4 ) at a concentration of 0.05-0.5 M; reducing agent of sodium hypophosphite (NaH 2 PO 2 ) at a concentration of 0.25-3 M; N,N,N′, N′-tetrakis (2-hydroxypropyl) ethylenediamine (C 14 H 32 N 2 O 4 ) at a concentration of 0.25-1 M; and sodium hydroxide (NaOH) at a concentration sufficient for required pH adjustment. 
     
     
         10 . The method of  claim 1 , wherein said surface of said item which is produced by copper is plated by nickel using a sequence of two different nickel plating baths, a first nickel plating bath containing sodium hypophosphite (NaH 2 PO 2 ) as the reducing agent, metalizing the first nickel plating bath which is an alkaline electroless nickel plating bath with pH in a range of 8.5-10.0, and later said item is immersed in a second nickel plating bath which is an acidic electroless nickel plating bath with pH in a range of 4.0-6.0. 
     
     
         11 . The method of  claim 1 , wherein said bath is adapted for electroless plating of nickel consists of nickel sulphate (NiSO 4 ) at a concentration of 0.05-0.5 M; a reducing agent of morpholine borane (C 4 H 9 BNO) at a concentration of 0.01-1 M; a mixture of ligands of diethylenetriamine (C 4 H 13 N 3 ) at a concentration of 0.001-0.5 M; and N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine (C 14 H 32 N 2 O 4 ) at a concentration of 0.001-0.2 M: sodium hydroxide (NaOH) at a concentration sufficient for pH adjustment to pH 5.0-7.8; and plating at a temperature of 18-35° C. 
     
     
         12 . The method of  claim 1 , wherein said bath is adapted for electroless plating of nickel consists of nickel sulphate (NiSO 4 ) at a concentration of 0.05-0.5 M; a reducing agent of dimethylamine borane (C 2 H 7 BN) at a concentration of 0.01-1 M; ligands of: diethylenetriamine (C 4 H 13 N 3 ) at a concentration of 0.001-0.5 M; and N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine(C 14 H 32 N 2 O 4 ) at a concentration of 0.001-0.2 M: sodium hydroxide (NaOH) at a concentration sufficient for pH adjustment to pH 5.0-7.8; and plating at a temperature 18-35° C. 
     
     
         13 . The method of  claim 1 , wherein said bath is adapted for electroless plating of nickel consists of nickel sulphate (NiSO 4 ) at a concentration of 0.05-0.5 M; a reducing agent of sodium tetrahydroborane (NaBH 4 ) at a concentration of 0.01-0.5 M; a ligand of N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine (C 14 H 32 N 2 O 4 ) at a concentration of 0.001-0.2 M; a ligand of potassium sodium tartrate (KNaC 4 H 4 O 6 ) at a concentration of 0.05-0.2 M; disodium thiosulphate (Na 2 S 2 O 3 ) at a concentration of 0.001-0.01 M; sodium hydroxide (NaOH) at a concentration sufficient for pH adjustment to pH 12.0-13.0; and plating at a temperature of 18-35° C. 
     
     
         14 . The method of  claim 4 , wherein said bath is adapted for electroless plating of nickel consists of nickel sulphate (NiSO 4 ); sodium hydroxide (NaOH); a ligand of amino acetic acid (C 2 H 5 NO 2 ), and a ligand of N,N,N′,N′-tetrakis (2-hydroxypropyl) ethylenediamine (C 14 H 32 N 2 O 4 ) at a concentration of 0.001-0.2 M; and a reducing agent of sodium hypophosphite (NaH 2 PO 2 ) at a concentration exceeding 0.8 M. 
     
     
         15 . The method of  claim 14 , wherein said bath is adapted for electroless plating of nickel consists of nickel sulphate (NiSO 4 ) at a concentration of 0.05-0.5 M; the reducing agent of sodium hypophosphite (NaH 2 PO 2 ) at a concentration of 0.8-3 M; the ligand of amino acetic acid (C 2 H 5 NO 2 ) at a concentration of 0.25-1 M; and a ligand of N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine (C 14 H 32 N 2 O 4 ) at a concentration of 0.001-0.2 M; sodium hydroxide (NaOH) at a concentration sufficient for pH adjustment to pH 4.0-6.0; and plating at a temperature of 80-96° C. 
     
     
         16 . The method of  claim 4 , wherein said bath is adapted for electroless plating of nickel consists of nickel sulphate (NiSO 4 ) at a concentration of 0.05-0.5 M; a reducing agent of morpholine borane (C 4 H 9 BNO) at a concentration of 0.1-1 M; a ligand of diethylenetriamine (C 4 H 13 N 3 ) at a concentration of 0.001-0.5 M; and a ligand of N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine(C 14 H 32 N 2 O 4 ) at a concentration of 0.001-0.2 M: sodium hydroxide (NaOH) at a concentration sufficient for pH adjustment to pH 5.0-7.8; and plating at a temperature of 18-35° C. 
     
     
         17 . The method of  claim 4 , wherein said bath is adapted for electroless plating of nickel consists of nickel sulphate (NiSO 4 ) at a concentration of 0.05-0.5 M; a reducing agent of dimethylamine borane (C 2 H 7 BN) at a concentration of 0.1-1 M; a ligand of diethylenetriamine (C 4 H 13 N 3 ) at a concentration of 0.001-02 M and a ligand of N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine (C 14 H 32 N 2 O 4 ) at a concentration of 0.001-0.2 M; sodium hydroxide (NaOH) at a concentration sufficient for pH adjustment to pH 5.0-7.8; and plating at a temperature of 18-35° C. 
     
     
         18 . The method of  claim 4 , wherein said bath is adapted for electroless plating of nickel consists of nickel sulphate (NiSO 4 ) at a concentration of 0.05-0.5 M; a reducing agent of sodium tetrahydroborane (NaBH 4 ) at a concentration of 0.02-0.5 M; a ligand of ethylenediamine (C 2 H 8 N 2 ) at a concentration of 0.001-0.5 M; a ligand of potassium sodium tartrate (KNaC 4 H 4 O 6 ) at a concentration of 0.05-0.2 M; and a ligand of N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine(C 14 H 32 N 2 O 4 ) at a concentration of 0.001-0.2 M; disodium thiosulphate (Na 2 S 2 O 3 ) at a concentration of 0.001-0.01 M; sodium hydroxide (NaOH) at a concentration sufficient for pH adjustment to pH 12.0-13.0; and plating at a temperature of 18-35° C. 
     
     
         19 . (canceled) 
     
     
         20 . The method of  claim 3 , further comprising immersing said item with the activated copper surface into a second electroless nickel plating bath, in which nickel is electrolessly deposited on the copper surface, wherein the immersing said item into the second electroless nickel plating bath occurs after immersing said item in the activation bath without any intermediate step.