Coatings solder powders

Solder powders coated with a thin layer of Parylene exhibit a high degree of resistance to oxidation and to reaction with the flux contained in the solder paste without substantially interfering with the reflow characteristics of the solder. The powders are used as such or as solder paste. The preferred Parylene type is Parylene E, made from 4-ethyl[2.2]paracylophane since it melts below the melting point of the solder, i.e., about 180°C." The formulation of a typical solder pastes are shown in Table 2.4. 

Metal powder can also be coated onto the workpiece. The 3M Company has developed a cold welding technique in which the workpiece, the metal powder, water, glass shot and additives are tumbled together in a barrel. Coatings are limited to ductile metals such as Cd, An, Sn, Pb, In, Ag, Cu, brass, and tin/lead solder the method is generally suitable only for small parts, and it doesn t produce a fine surfaced, cosmetic coating. Costs are comparable to those for electroplating with afterbake (Kirk-Othmer 1981). 

---