Deposition of electroless Ni on micro-sized acrylic spheres

In this work a thin film of electroless Ni was deposited on the surface of commercial acrylic spheres about 4 lm in size. After the acrylic spheres were cleaned, sensitized and activated successively, they were put into an acid plating bath containing sodium hypophosphite as reducing agent for the electroless Ni deposition. The acrylic spheres with a film of Ni deposit were molded into a cold set resin and ground and polished to form a cross section for observation. The thickness of the Ni film was measured and the state of the adhesion of Ni film to the surface of the acrylic sphere was observed by a scanning electron microscope. The results showed that the Ni film deposited in a plating bath with pH 4.2 can tightly adhere on the surface of the acrylic sphere due to the compressive stress of the Ni film. The thickness of the Ni film on the acrylic sphere can reach about 0.35 lm in 3 min of deposition time at 50–70 C of plating temperature. The activation energy of electroless Ni deposition in plating bath with pH 4.2 is about 28.50 kJ/mole. The acrylic spheres with a layer of electroless Ni film deposited by the method proposed in this work can be further applied to anisotropic conductive adhesives in flip chip package