A Study On The Technology Of Electroless Copper Plating With Sodium Hypophosphite As Reductant

With the development of science and technology, more and more electronic products have been significant part in our daily life. And both the production and electromagnetic interference of them have close link with the electroless copper plating. Because of good conductivity and special shape, conductive fabrics coated with copper and nickel can be used for shielding electromagnetic radiation and interference. The electroless copper plating using formaldehyde as reducing agent is the main method for prepare copper-coated industry recently. However, formaldehyde is volatile and toxic, which is forbidden to use by many countries. So, this paper aims to study the electroless copper plating process using hypophosphite as reducing agent and improve the structure and properties of copper deposits, and apply it for solving problems such as plating structure disadvantage, high resistivity, big consumption of hypophosphite and badly response persistence and the K4Fe(CN)6 is first applied in the solution.The process of pretreatment for different base material like PET fabrics and epoxide resin before electroless copper plating was also investigated. The process is etching, sensitization, activation, electroless nickel plating, electroless copper plating and electroless nickel plating. The properties of conductive PET fabrics such as surface resistance, shielding effectiveness and adhesion of metal deposit to PET fabrics were investigated deeply.The best etching condition of PET fabrics is NaOH 200g/L, 70℃and 10min。At this condition, the weight loss of PET fabrics after etching is about 9.8% and the adhesion of metal deposit to fabric is most strong. In the epoxide resin ,because of ths harmful influence to the environment of potassium bichromate-sulphuric acid system, we prefer the alternative system- potassium permanganate with longer etching time. The most proper process before electroless copper plating is sensitization(SnCl₂ 8¹0 g/L) , activation(PdCl₂ 0.05 ⁰.06 g/L)and electroless nickel plating with alkaline bath.The electroless copper plating process using hypophosphite as reducing agent was investigated by orthogonal test. According to influencing sequence, the factors affecting the surface resistance and deposition rate are as followed: the concentration of nickel sulphate>pH value> the concentration of citrate > the concentration of hypophosphite >temperature. The best basic process of electroless copper plating is 8g/L CuSO₄, 0.9g/L NiSO₄, 40g/L NaH₂PO₂, 20g/L C₆H₈O₇, 30g/L H₃BO₃, pH 9.5 and 65℃.The deposition rate of electroless copper plating at different concentration of Cu²⁺, Ni²⁺, NaH₂PO₂, C₆H₈O₇, pH and temperature respectively, were measured when maintaining other factors as constant. The kinetic equation of electroless copper plating is obtained by regression analysis:The trace of H₂ emission was removed by adding polyethylene glycol. However, the deposition rate increased obviously and the copper deposits became loose and porous, which resulted in higher surface resistance of copper-coated fabrics.And with the increasing nickel sulphate concentration in certain range, the non-crystal of Cu-Ni-P do not appear as expect.The deposition rate on the 210T PET fabric decreased from 2.56 to 1.95 g/(min·m²) when adding 2⁴ mg/L K₄Fe(CN)₆ to the electroless copper plating bath. The copper deposit became compact and the color became copper-bright at the presence of 2⁴ mg/L K₄Fe(CN)₆ in the bath. The copper deposits have enhanced orientation of (111) crystal plane after adding 2⁴ mg/L K₄Fe(CN)₆ and the grain size increased from 30.8nm to 43.5nm.The surface resistance of 210T PET fabrics with 30g/m² copper deposit decreased from 79 to 19 mΩ/sq after adding 2⁴ mg/L K4Fe(CN)6.According to the recent research and experiment of the technology of electroless copper plating on PET fabrics and epoxide resin with sodium hypophosphite as reductant, this article supply a certain attempt to find good method on the industry area of conductive PET fabrics and PCB.