Types & Methods of Soldering

Computers rely on soldered joints to function.

Without soldering, today's day-to-day life would be very different. Most types of consumer gadgets, including televisions, mobile phones, MP3 players and computers, contain electronic circuit boards that rely on soldered joints to function. The origins of soldering date from about 3000 B.C. when metalworkers in Mesopotamia melted lead to join pieces of copper. Since then, jewelers, artists, scientists and tradespeople have adopted the techniques in pursuit of their crafts.

Types of Soldering

Solder provides both mechanical support and electrical connectivity, and is widely associated with the manufacture of electrical and electronic circuits. Preferred soldering methods in these industries include hand soldering and machine soldering. Plumbers and automotive engineers use solder to join and seal pipes and radiators, generally using manual methods including gas soldering. Solder also plays a significant role in the creation of art and jewelry, where manual soldering techniques join precious metals, including gold and silver.

Gas Soldering

Jewelers use gas soldering for delicate work.

Larger materials like gas pipes or car radiators require sustained heating to reach the melting point of solder. A gas torch can deliver controlled local heating and is generally the preferred soldering tool for plumbers and auto mechanics. The parts to be soldered must be clean, and coating the joint with flux helps the solder flow readily. Jewelers and artists also use gas soldering as it is a highly accurate way of applying heat to a delicate item.

Hand Soldering

Although machine soldering is widespread in electronics assembly, hand soldering skills still apply when repairing either through-hole or surface mount circuit boards. The electric soldering iron is an indispensable tool for small-scale repairs to electronic equipment, and various styles of soldering tip are available to suit different sizes and shapes of component. Surface mount packages generally require the finest soldering tips and you may need a magnifier when working with fine-pitch components.

Wave Soldering

Wave soldering machines can process batches of circuit boards.

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.

Reflow Soldering

Reflow soldering, a machine soldering process, is the preferred technique for surface mount circuit boards. Reflow requires that solder is applied at the start of the process, generally by stencil printing solder paste onto required areas of the board. Automated pick-and-place machines then place the components directly onto the solder paste, which retains them in position temporarily. The board then passes through a reflow oven where the solder paste melts to form the permanent joint.

References

• ASM International; Principles of Soldering; Giles Humpston, et al.; April 2004
• New Mexico State University; A Primer on Hand Soldering Electrical Connections; D.L. Pippen; 1997
• Copper Development Association: Soldering School
• Swarthmore College; Surface Mount Technology Lab Tutorial; Aron Dobos; May 2006
• Indiana University-Purdue University Indianapolis: Wave Soldering
• Research International: Solder Reflow Technology Handbook: Solder Reflow Basics