Soldering is a process in which two metals are enjoined by a filler metal (solder), effectively promoting electrical conductivity. This method has been used for a long time, with high reliability, low risk of failure and ease of use. Soldering is mainly used for manufacturing integrated circuits that we can find in every electronic device. Embedded in the IC is the PCB, or Printed Circuit Board, where different electrical components of electrical devices are bound together.
To be able to be soldered into the PCB, an electrical component (e.g. Wires) have to be coated with the soldering material, in order to adhere to the board. Solder plating, or Tin-Lead plating is the process in which the material to be soldered, in this case, the wire, is plated with Tin-Lead solder before soldering it to the PCB, so as to assure complete adhesion to the PCB, and eliminate crevices that will later encapsulate heat in the solder and increase the chances of material failure.
The main function of this process, aside from complete adhesion is to protect the electrical contact from oxidizing, which further leads to corrosion. Tin plating has been used widespread; however, whiskers, or small tendrils or flashes of Tin become present in the solder that is one of the causes of short-circuiting in electronic devices. Tin-Lead has been introduced in order to avoid this phenomenon, where Lead is used to control the splatter of Tin in the solder.
There are different types of Tin-Lead coatings, according to ratio, but only 3 ratios are being considered: 60/40, 90/10 and 95/5. The ratio of Tin-Lead only depends on how much stress electrical components are experiencing, so, the higher the thermal and electrical stress, the higher amount of Lead is needed.
One can also distinguish the amount of Lead present, as 95/5 Tin-plate coats have matte finish, while higher Lead contents develop a bright and shiny finish.
Tin-Lead thin film deposition is also widely used because of its ability to be deposited to both ferrous (compounds that contain Iron) and non-ferrous (compounds not containing Iron), which makes it more economical for IC manufacturers.
Plating processes include Vapor Deposition, ion sputtering and Metallization. Vapor deposition deals with the atom by atom application of coats, under sub-atmospheric conditions (i.e. Vacuum). Thickness of application range from 1 atom so millimeters, depending on exposure to vacuum, and it can also be used to apply different layers at a time. Sputtering involves a target and a source, where ions from the source are bombarded to the material substrate, generating adhesion by immense pressure and elevated temperatures.
Metallization is the general term encompassing the different processes in material plating. Some of its processes are Vacuum Metalizing, where metal coat is heated to its boiling point, and letting condensation deposit the metal to the substrate surface, and Thermal Spraying, where metal coating is put to elevated temperature before application. Vacuum metalizing produces thicker and better yields than thermal spraying because of the presence of vacuum, that prevents outside contamination and complete adhesion.