Sodium Reduction Electroless Copper Plating

Electroless copper plating is widely used in electronics, aerospace, mechanical engineering, etc. For that traditional formaldehyde electroless copper plating technique not only pollutes the environment but also does harm to body, it is particularly urgent to develop a new non-polluted electroless copper plating technology. Electroless copper plating system uses hypophosphite as reducing agent overcomes many defects of the system which uses formaldehyde as reducing agent, and the former is most likely to replace the later one. Therefore, on account of hypophosphite electroless copper plating technique, this paper carried out series of study.At first, the thesis starts with pretreatment technique of electroless copper plating, oil removing chosen a new technique that combined oil removing solution with ultrasonic technology. The operation was simple and effective. Technological parameters of alkaline potassium permanganate roughtening system was optimized as KMnO4 50 g·L^-1, NaOH 30 g·L^-1, temperature 70℃, roughtening time10 minutes. Moreover, a new roughtening system which used peroxides as main component was invented and the roughtening effect of the new roughtening system was better than potassium permanganate roughtening system, but their mechanisms were different.Next, the hypophosphite electroless copper plating technique was optimized, and the parameters were CuSO4·5H2O 8.0 g·L^-1, NiSO4 0.8 g·L^-1, K4Fe(CN)6 2.0 mg·L^-1, NaH₂PO₂ 30 g·L^-1, sodium citrate 20 g·L^-1, H3BO3 30 g·L^-1, PEG 600 100 mg·L^-1, pH = 9, temperature 75℃. Square resistance of plating from this formula was less than 0.01 ?/□. Later on, the plating deposition rate which affected hypophosphite electroless copper plating system was discussed, and the range of every parameter of hypophosphite electroless copper plating system was determined. Then hypophosphite system and formaldehyde system were compared, the result was that grains from which hypophosphite system obtained was bigger but mechanical strength was higher, grains from which formaldehyde system obtained was smaller but mechanical strength was lower. At last, the effects which addition agent brought to hypophosphite electroless copper plating system were investigated. The result showed that the deposition rate was reduced when added K4Fe(CN)6 and 2, 2ˊ-Dipyridyl, but it came down after up when added maleic acid. The reducing degree which maleic acid led to was lower than K₄Fe(CN)₆ and 2, 2ˊ-Dipyridyl. The morphology of plating was improved obviously when added K₄Fe(CN)₆ and 2, 2ˊ-Dipyridyl into hypophosphite electroless copper plating system and the plating was changed from rough and brown black into fine and bright. The porosity was reduced by adding these addition agents. K₄F_e(CN)₆, maleic acid and 2, 2ˊ-Dipyridyl could reduce resistivity of the plating, however, when the concentration of addition agents increased to a certain degree, the affect of plating resistivity tended to subdued.