Process Encyclopaedia

Soldering and brazing

Overview

Soldering and brazing differ from welding because only the filler melts, not the materials that are joined. Soldering differs from brazing by the melting temperature of the filler alloy - this is usually below 450oC for soldering and above 450oC for brazing. Soldering using lead-tin alloys was the first hot joining process, used as far back as 4000BC.

Materials and shapes

Brazing is usually used for joining metals, and especially where the parts are not of the same material. Most geometries are possible; however, good join alignment is essential to achieving a strong joint. Mechanical cleaning or the use of flux is needed to give good joint strength. The strength of the joint is also dependent on good design. Because of the low melting point of the filler, soldered joints have limited use at high temperatures. Also, the joints are usually not strong and therefore not used in load-bearing situations. Soldering aluminium and stainless steel is difficult because of their strong oxide layers.

Economics

Equipment is generally low cost, except where automation is used. The need for good joint alignment usually means fixtures are required, adding to the cost. Wave soldering is the most economic means of soldering large batches of printed circuit boards.

Typical products

Plumbing, electrical circuits