Wave soldering machines use a submersible pump to generate a wave of molten solder. They process populated circuit boards, generally in batches. A conveyor initially carries the boards over a fluxing station where liquid flux coats the underside of the board. Electrical heaters activate the flux and heat the boards progressively to prevent thermal shock occurring with the application of solder. Boards then pass over the solder with the underside of the board just contacting the wave, which coats all the joints..