Complexing agent for improving cyanide-free silver plating binding force and preparation method and preplating process thereof

The invention discloses a complexing agent for improving cyanide-free silver plating binding force and a preparation method and a preplating process thereof. The complexing agent comprises alanine and thiosemicarbazide; the alanine and the thiosemicarbazide are mixed; de-ionized water is added for dissolving; the heating and the evaporation are performed; then, KOH or NaOH solution is added to adjust the pH value as 9-10; and the filtration is performed to obtain the complexing agent; the preplating process comprises the following steps: the complexing agent and silver nitrate are added in purified water to adjust the pH value as 9-10 to obtain electrolyte solution; the electrolyte solution is added in an electrolysis tank; a preplating piece is connected to the cathode of an electrode, and is put in the electrolyte solution; and the electrolyte solution is stirred in air for preplating. The silver plating binding force requirement of copper in an electronic device with copper alloy, iron alloy and aluminum alloy parts is realized; and in particular, the special requirement of the silver plating binding force of special product structural parts is solved.