U.S. patent number 3,841,881 [Application Number 05/288,777] was granted by the patent office on 1974-10-15 for method for electroless deposition of metal using improved colloidal catalyzing solution.
This patent grant is currently assigned to RCA Corporation. Invention is credited to Nathan Feldstein, Thomas Stephen Lancsek.
United States Patent |
3,841,881 |
Feldstein , et al. |
October 15, 1974 |
METHOD FOR ELECTROLESS DEPOSITION OF METAL USING IMPROVED COLLOIDAL
CATALYZING SOLUTION
Abstract
A colloidal solution of a catalytic metal is prepared by
admixing an acid-soluble salt of the metal, hydrochloric acid, a
soluble stannous salt present in excess of the amount necessary to
reduce the metal salt to colloidal metal, and a quantity of stannic
chloride that has been separately aged. A substrate surface upon
which metal is to be deposited is treated with the catalytic
colloidal solution. The catalyzed surface is then subjected to an
electroless plating bath.
Inventors: |
Feldstein; Nathan (Kendall
Park, NJ), Lancsek; Thomas Stephen (Morrisville, PA) |
Assignee: |
RCA Corporation (New York,
NY)
|
Family
ID: |
23108602 |
Appl.
No.: |
05/288,777 |
Filed: |
September 13, 1972 |
Current U.S.
Class: |
106/1.11;
106/1.23; 106/1.24; 106/1.26; 106/1.28 |
Current CPC
Class: |
C23C
18/28 (20130101) |
Current International
Class: |
C23C
18/20 (20060101); C23C 18/28 (20060101); C23c
003/02 () |
Field of
Search: |
;106/1 ;204/30
;117/47A,13E |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hayes; Lorenzo B.
Attorney, Agent or Firm: Bruestle; G. H. Hill; W. S.
Claims
We claim:
1. A colloidal catalytic solution for catalyzing a substrate prior
to electroless metal deposition thereon, said catalyst comprising
the solution resulting from the admixture of an acid soluble salt
of a catalytic metal selected from the group consisting of gold,
and the platinum family of metals, hydrochloric acid, a stannous
salt soluble in aqueous solution, said stannous salt being in
excess of the amount necessary to reduce said metal salt to
colloidal metal, and a quantity of a solution of stannic chloride
which has been separately aged for the equivalent of at least 4
days at room temperature prior to admixture, said stannic compound
being present in a concentration of about 0.01 to 0.5 molar in said
catalytic solution.
2. A solution according to claim 1 in which said catalytic metal is
palladium.
3. A solution according to claim 1 in which said catalytic metal is
gold.
4. A solution according to claim 1 in which said catalytic metal is
platinum.
5. The method of making a colloidal catalyst solution for
application to a substrate surface prior to electroless metal
deposition thereon, comprising admixing an acid soluble salt of a
catalytic metal selected from the group consisting of gold, and the
platinum family of metals, hydrochloric acid, a stannous salt
soluble in aqueous solution, said stannous salt being in excess of
the amount necessary to reduce said metal salt to colloidal metal,
and a quantity of stannic chloride solution which has been
separately aged for a period which is the equivalent of at least 4
days at room temperature and said stannic compound being present in
a concentration of about 0.01 to 0.5 molar in said catalyst
solution.
6. The method of claim 1 in which said catalytic metal is
palladium.
7. The method of claim 5 in which said catalytic metal is gold.
8. The method of claim 5 in which said catalytic metal is platinum.
Description
BACKGROUND OF THE INVENTION
Various metals can be deposited on certain substrate surfaces by a
process known as autocatalytic electroless plating. Autocatalytic
electroless plating baths usually contain a salt of the metal being
deposited, a reducing agent for the metal salt, a complexing or
chelating agent and a pH adjustor.
Some metallic surfaces are inherently catalytic for initiating
deposition of certain metals from autocatalytic electroless plating
baths. However, non-metallic surfaces must be treated to render
them catalytic. One common method of rendering a non-metallic
surface catalytic for the autocatalytic electroless deposition of a
number of metals is to treat it, first, with a sensitizing solution
of stannous chloride. Then the sensitized surface is treated with
an activating solution of palladium chloride which deposits an
adherent film of palladium nuclei. These nuclei serve as catalyst
for initiating the reduction of the metal salt and its deposition
on the substrate. After an initial layer of the metal is thus
deposited, this initial layer catalyzes further deposition.
The above described method of autocatalytic electroless deposition
has been widely used. Another method that has been widely used
commercially for depositing a catalytic coating on a surface is the
so-called colloidal catalyst solution method, as described, for
example, in U.S. Pat. No. 3,011,920. In this method, the initial
step of sensitizing the surface with a stannous chloride solution
is omitted. Instead the surface is treated with a single solution
which comprises an acid soluble salt of a catalytic metal (usually,
a noble metal), hydrochloric acid, and a soluble stannous salt
which is present in excess of the amount necessary to reduce the
catalytic metal salt to colloidal metal. The excess amount of
stannous salt reacts to form a protective colloid which inhibits
flocculation that would normally occur when stannous ions and noble
metal ions are present in the same solution. After treatment of the
surface to be plated with the colloidal catalyst solution, the
surface is treated with the electroless plating bath in the usual
way.
The colloidal catalyst solution method has been found generally
satisfactory for deposition of metals such as nickel and copper, on
surfaces such as glass and hydrophilic dielectrics, especially
where the catalyzed surface is given a treatment with an
accelerator such as a solution of sodium hydroxide prior to contact
with the electroless plating bath. The accelerator dissolves the
protective colloid which is present on the catalyzed surface.
In the case of hydrophobic surfaces, such as Teflon, for example,
neither the colloidal catalyst solution method nor the two-step
method first described, has been satisfactory. On this type of
surface, coverage of the deposited metal has usually ranged between
zero and very poor.
The present invention is an improvement in the colloidal catalyst
solution method which enables it to be used on hydrophobic surfaces
and also provides improved reliability on other substrates. The
improvement consists in adding to the colloidal catalyst solution,
a solution of a stannic compound that has been separately aged. The
quantity of stannic ion added is enough to make the solution at
least 0.01 molar in this ingredient.
The addition of the aged stannic chloride introduces a hydrolyzed
compound containing stannic ions. The improvement appears to be due
to this compound.
DESCRIPTION OF PREFERRED EMBODIMENTS
Examples 1-3
In the examples which follow, the surface being coated was a plate
of Teflon plastic. The plating bath was one for autocatalytically
electrolessly plating copper and had the composition given
below.
Copper Plating Bath Compositions
______________________________________ CuSO.sub.4.5H.sub.2 O 15 g/l
Propylenediamine tetraacetic acid, 60 cc/l sodium salt (40% active
solution) NaOH 4.0 g/l H.sub.2 CO (37% solution) 40 cc/l NaCN 4
mg/l Temperature 40.degree.C
______________________________________
A plating cycle of 5 minutes was used.
Besides copper (from the above-described bath), nickel, cobalt,
gold and alloys of any two or more of these four metals, for
example, can be deposited from conventional electroless plating
baths using the colloidal catalyst solutions described herein.
The following are colloidal catalyst solutions for catalyzing the
surface to be plated. The surface is either dipped in or sprayed
with the solution. Treating time can be about 30 seconds or
more.
Colloidal Catalyst Solutions ______________________________________
Example 1 Example 2 Example 3
______________________________________ H.sub.2 O 600 cc/l 600 cc/l
600 cc/l HCl (Conc.) 300 cc/l 300 cc/l 300 cc/l SnCl.sub.2 50 g/l
37.5 g/l 37.5 g/l (Anhydrous) Aged SnCl.sub.4 3.2 .times.
10.sup.-.sup.2 1.6 .times. 10.sup.-.sup.2 2.4 .times.
10.sup.-.sup.2 (molar conc.) Na.sub.2 SnO.sub.3.3H.sub.2 0 None
None 1.5 g/l PdCl.sub.2 1 g/l None None HAuCl.sub.4.H.sub.2 O None
1 g/l None H.sub.2 PtCl.sub.6 None None 1 g/l
______________________________________
The pH of these solutions should be maintained below about 1.
The aged SnCl.sub.4 may be prepared as an aqueous 0.5 molar
solution aged for one week at room temperature. In the catalyst
solution, its concentration is preferably 0.01 to 0.5 molar. Aging
time varies with conditions. At elevated temperatures it can be as
little as a few hours. At ordinary room temperature it is
preferably at least 4 days to 1 week.
After treating the Teflon surface with the catalyst solution, the
surface is rinsed with water and then preferably treated with an
accelerator as described in U.S. Pat. No. 3,011,921. This may be a
5 percent solution of sodium hydroxide, for example, and treating
time is a few minutes.
It will be noted that the above described examples of colloidal
catalyst solutions may contain Na.sub.2 SnO.sub.3.sup.. 3H.sub.2 O
as an optional ingredient. If present, this ingredient functions as
a means of generating additional protective colloids for the
catalytic metal.
The surface is again rinsed with water after treatment with the
accelerator and it is then treated with the plating bath.
Platings on Teflon using the above-described materials and
procedures have produced about 95 percent plating coverage with all
three examples. For comparison purposes, another three Teflon
plates were treated with similar colloidal catalyst solutions
except that the aged SnCl.sub. 4 was omitted. The plating baths and
plating cycles were the same. However, in these comparison
examples, plating coverage was only about 5 percent on each
plate.
An example of a nickel autocatalytic electroless plating bath that
can be used in the present process is:
NiSO.sub.4.6H.sub.2 O 25 g/l Na.sub.4 P.sub.2 O.sub.7.10H.sub.2 O
50 g/l Dimethylamine borane 1.5 g/l NH.sub.4 OH (conc.) 50 cc/l
Temperature 40.degree.C
In the present method, the colloidal catalytic metal can be gold or
any one of the platinum group of metals. The platinum group of
metals consists of platinum, ruthenium, rhodium, palladium, osmium
and iridium.
* * * * *