Abstract
The requirement of electroless Au plating solution has been increased with miniaturization of printed circuit boards and downsizing of electronic devices and the solutions are expected to be cyanide-free from the viewpoint of worldwide environmental protection. We have developed a cyanide-free immersion type electroless gold plating solution using alkylphosphine as a complexing agent. Tris(3-Hydroxypropyl) phosphine(T3HPP) was used as a complexing agent and thiourea was added in the solution. The optimum bath composition of cyanide-free immersion type Au plating solution was 0.01mol/l Au, 0.015mol/l T3HPP, 0.20mol/l thiourea and 0.07mol/l potassium dihydrogenphosphate. The addition of some additive such compounds as 1,2,3-benzotriazole, mercaptobenzothiazole, and catechol was also effective to stabilize the solution and to prevent dissolution of Cu from substrates. Deposition rate of gold was 0.06μm/30min from the immersion type solution at the bath temperature of 80°C and pH value of 7.0. The solution provides so good stability and the gold films obtained from above solutions showed high performance of pull strength of solder ball.
