Wave soldering is a bulk soldering process used for the manufacturing of printed circuit boards. The circuit board is passed over a pan of molten solder in which a pump produces an upwelling of solder that looks like a standing wave. As the circuit board makes contact with this wave, the components become soldered to the board. Wave soldering is used for both through-hole printed circuit assemblies, and surface mount. In the latter case, the components are glued onto the surface of a printed circuit board (PCB) by placement equipment, before being run through the molten solder wave. Wave soldering is mainly used in soldering of through hole components. As through-hole components have been largely replaced by surface mount components, wave soldering has been supplanted by reflow soldering methods in many large-scale electronics applications. However, there is still significant wave soldering where surface-mount technology (SMT) is not suitable (e.g., large power devices and high pin count connectors), or where simple through-hole technology prevails (certain major appliances). Wave solder process There are many types of wave solder machines; however, the basic components and principles of these machines are the same. The basic equipment used during the process is a conveyor that moves the PCB through the different zones, a pan of solder used in the soldering process, a pump that produces the actual wave, the sprayer for the flux and the preheating pad. The solder is usually a mixture of metals. A typical leaded solder is composed of 50% tin, 49.5% lead, and 0.5% antimony. The Restriction of Hazardous Substances Directive (RoHS) has led to an ongoing transition away from 'traditional' leaded solder in modern manufacturing in favor of lead-free alternatives. Both tin-silver-copper and tin-copper-nickel alloys are commonly used, with one common alloy (SN100C) being 99.25% tin, 0.7% copper, 0.05% nickel and <0.01% germanium. Fluxing Flux in the wave soldering process has a primary and a secondary objective. The primary objective is to clean the components that are to be soldered, principally any oxide layers that may have formed. There are two types of flux, corrosive and noncorrosive. Noncorrosive flux requires precleaning and is used when low acidity is required. Corrosive flux is quick and requires little precleaning, but has a higher acidity. Preheating Preheating helps to accelerate the soldering process and to prevent thermal shock. Cleaning Some types of flux, called "no-clean" fluxes, do not require cleaning; their residues are