Tin plating: high chemical stability, almost insoluble in dilute solutions of sulfuric acid, nitric acid and hydrochloric acid, and good solderability.
Copper-nickel plating: a method of plating a layer of nickel on metals or some nonmetals by electrolytic or chemical methods, which is called nickel plating. Nickel plating is divided into electrolytic nickel plating and chemical nickel plating. Electroless nickel plating is to deposit a uniform and compact nickel coating on the cathode (plated part) in an electrolyte composed of nickel salt (called main salt), conductive salt, pH buffer and wetting agent, with metal nickel as anode and direct current as cathode. Bright nickel is obtained from plating solution containing brightener, while dark nickel is obtained from electrolyte without brightener.
Electroless plating is also called electroless plating and autocatalytic plating [1]. The specific process refers to the process that metal ions in aqueous solution are reduced by reducing agent and precipitated on the surface of solid matrix under certain conditions. TM B374 (American Institute of Materials and Testing) is defined as "depositing a metal coating by controlled chemical reduction, which is catalyzed by the deposited metal or alloy". This process is different from displacement electroplating, the coating can be continuously thickened [2], and the plated metal itself has catalytic ability.
Tin plating is a kind of coating with good solderability and certain corrosion resistance, which is widely used in electronic components and printed circuit boards. In addition to physical methods such as hot dip plating and spraying, electroplating, dip plating and electroless plating are widely used in industry because of their simplicity. Immersion plating is to immerse the workpiece in the solution containing the metal salt to be plated, and deposit a metal coating on the surface of the workpiece according to the principle of chemical replacement. This is different from the general principle of electroless plating, because the plating solution does not contain reducing agent. Different from contact plating, contact plating means that when the workpiece is immersed in the metal salt solution to be plated, it must be closely connected with an active metal. Active metal enters the solution as anode to release electrons, and metal ions with higher potential in the solution get electrons and deposit on the surface of the workpiece. Tin dipping is only carried out on iron, copper, aluminum and their respective alloys.