Palladium plating solution

A palladium plating solution consisting essentially of:

• a germanium compound consisting of a soluble germanium salt having a concentration ranging from 1 mg/l to 1000 mg/l in terms of a reduced value of palladium metal;
• a soluble palladium salt comprising one or more of dichloroethylenediamine palladium (II), palladium chloride, dichlorodiamine palladium (II), dinitrodiamine palladium (II), tetraamine palladium (II) nitrate, tetraamine palladium (II) sulfate, oxalatodiamine palladium (II), tetraamine palladium (II) oxalate and tetraamine palladium (II) chloride, said soluble palladium salt having a concentration ranging from 0.1 g/l to 50 g/l in terms of a reduced value of palladium metal;
• and
• an electrically conductive salt which is at least one selected from the group consisting of an ammonium salt, a sodium salt, and a potassium salt of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and citric acid, said electrically conductive salt having a concentration ranging from 10 g/l to 400 g/l.