Conductive composites
View Patent ↗A conductive composite material formed from an organic polymer base, a highly conductive metal interlayer, and an electroless nickel top layer is described. The composite material may be electrically conductive and resistant to corrosion. The highly conductive metal interlayer may be silver or copper. An electroless nickel plating process is described that efficiently deposits the nickel top layer without the use of, surfactants, and stabilizers at low temperatures. The method enables reduction of substantially all of a nickel salt onto the silver surface leaving a spent bath solution free of nickel that can be recycled.
1. A method for preparing a conductive composite by forming a nickel phosphorus alloy electrolessly, comprising:
providing a metallic coated polymer base;
cleaning the metallic coated polymer base;
contacting the metallic coated polymer base with an aqueous solution of a tin salt;
washing the metallic coated polymer base after exposure to the aqueous solution of a tin salt to remove excess tin salt;
contacting the metallic coated polymer base with an aqueous solution of a palladium salt;
washing the metallic coated polymer base after exposure to the aqueous solution of a palladium salt to yield a palladium activated metallic coated polymer base; and
contacting the metallic coated polymer base with an aqueous solution comprising nickel sulfate, sodium hypophosphite, ammonium sulfate and ammonia.
2. The method of claim 1 , wherein a metal forming the metallic coated polymer base is silver.
3. The method of claim 1 , wherein a metal forming the metallic coated polymer base is copper.
4. The method of claim 1 , wherein a metal forming the metallic coated polymer base is between about 12.5 percent and about 37.5 percent by weight of the metallic coated polymer base.
5. The method of claim 1 , wherein the tin salt is stannous chloride.
6. The method of claim 1 , wherein the palladium salt is palladium (II) chloride.
7. The method of claim 1 , wherein a weight ratio of nickel sulfate to sodium hypophosphite is between about 0.6 and about 0.9.
8. The method of claim 1 , wherein a pH of the aqueous solution comprising nickel sulfate, sodium hypophosphite, animonium sulfate and ammonia is between about 8.5 and about 10.0.
9. The method of claim 1 , wherein a temperature of the aqueous solution comprising nickel sulfate, sodium hypophosphite, animonium sulfate and ammonia is between about 35° C. and about 90° C.