Electroless Ni-Sn-P Alloy Plating And Application In Microelectronics

This is a effect method that tin will be introduced to the electroless Ni-P alloy platings forming Ni-Sn-P alloy coatings. Ni-Sn-P coatings will have good properties in the corrosion resistance, heat resistance and weldability, etc. This paper mainly discussed the effect of process conditions and elements on the deposition rate, composition and surface morphology, and the effects of tin concentration in bath on corrosion resistance and weldability of the coatings. Then the rare earth elements were introduced to Ni-Sn-P alloy. The effect of rare earth on corrosion resistance and composition of the plating layer were discussed. The mechanism of electroless Ni-Sn-P were analysed.Firstly, the effect of concentrations of reducing agent, coordination agent and tin in bath on deposition rate, composition of plating layer and surface morphology, and the effects of tin concentration in bath on corrosion resistance and weldability of the coatings were studied on the four valence tin and bivalent tin of electroless Ni-Sn-P. The results showed that:the tin content in the deposit decreased with an increase in reducing agent concentration in the bath, the phosphorus content in the deposit increased with an increase in reducing agent concentration in the bath, when the reducing agent concentration was 35 g/L,the surface appearance is best in the four valence tin electroless Ni-Sn-P. when the reducing agent concentration was 20 g/L, the surface appearance is best in the bivalent tin electroless Ni-Sn-P. The tin content and phosphorus content in the deposit increased with an increase in coordination agent concentration in bath, when the coordination agent concentration was 30 g/L, the surface appearance is best in the four valence tin electroless Ni-Sn-P. when the coordination agent concentration was 40 g/L, the surface appearance is best in the bivalent tin electroless Ni-Sn-P. The tin content in the deposit increased with an increase in tin concentration in the bath, the phosphorus content in the deposit decreased with an increase in tin concentration in the bath, when the in concentration was 5 g/L, the deposition rate is best. The deposition rate increased with an increase in pH value, the four valence tin of electroless Ni-Sn-P, the phosphorus content in the deposit increased with an increase in pH value, the tin content in the deposit decreased at first and then increased.The bivalent tin of electroless Ni-Sn-P, when the pH value is 9-10, the surface morphology is best.When the pH value is 4.5, the surface morphology is best.The phosphorus content and the tin content in the deposit is mutual inhibition. Electroless Ni-Sn-P plating has better corrosion resistance than electroless Ni-P plating.The fifth chapter electroless Ni-Sn-P alloy platings of application in microelectronics were studied and succsessfully applied in leadframe with good weldbility,the the tin content in the deposit is 1-2%,the phosphorus content in the deposit is 11-13%.The sixth chapter discussed the difference of bivalent tin and four valence of electroless Ni-Sn-P depositional mechanism.The seventh chapter discussed that the rare earth elements were introduced into Ni-Sn-P alloy by electroless deposition to obtain Ni-Sn-P-RE composite coatings. The effect of rare earth on the deposition rate, composition of the platings, surface morphology and the corrosion resistance were discussed. The results showed that theNi-Sn-P-Ce coatings have better corrosion resistance than Ni-Sn-P coatings, when the Carbonated cerium concentration is 0.03g/L, the corrosion resistance is best and the tin content in Ni-Sn-P-RE coatings is higher than in Ni-Sn-P coatings, the phosphorus content in Ni-Sn-P-RE coatings is lower than in Ni-Sn-P coatings.The rate of deoposition decreased with the increase of lanthanide oxide and Carbonated cerium concentration in bath. The rate of deoposition increased at first and then decreased with the increase of Neodymium oxide concentration, when Neodymium oxide concentration in bath is 0.03 g/L, the rate of deoposition is fastest. The surface morphology of Ni-Sn-P-RE coating is flater, smoother than Ni-Sn-P coatings and cellular structures tend to disappear.