Abstract
This paper describes a selective wet-etching method of Ni thin film under solder (Pb/Sn) bumps for electroplating cathode metals. The etching rate (VM) of Pb and that of Sn were measured by the weight change of the metal sheet. The etching rate of Ni was measured by the change of the film thickness. The optimum ratio of HCl/HNO.sub.3/CH.sub.3 COOH was determined from the triangular coordinate of VM and the selective etching ratio (γ), calculated from VM. That ratio was CH.sub.3 COOH>HNO.sub.3>HCl and it realizes a selective etching ratio (γ) higher than 1 with minimum solder dissolution.
