Professional pilots review the basics of flying every year, and recurrent training is good for just about any profession, including electronics assembly. So here’s a quick review of basic soldering steps and some best practices for each.
The quality of a soldered joint is measured by its appearance, strength, and reliability. Solder joint quality depends upon the condition of the materials and the soldering process used. The soldering process in turn depends upon solder composition, surface finish of the PWB, and environmental factors such as flux chemistry and thermal conditions. A high-quality solder joint not only joins materials together, but also provides a reliable electrical connection.
The primary soldering steps include:
- Tight solder contact with the materials being joined. A good point contact is more important than a large area contact.
- Slow heat application to all materials. Too rapid heating can result in cracks and poor electrical conduction.
- Using flux or paste to remove oxide from all surfaces and provide for smooth flow of the molten solder. Many manufacturers now use primarily “no-clean” fluxes.
- Sufficient heat to melt the solder so it flows across the surfaces and joins them with fillets that provide joint strength. Although the fillet size is an indicator of solder quality, too much fillet can result from excessive heating and lead to cracks and a loss of component lead flexibility.
- Proper cooling of the joint. Be sure that the solder freezes prior to handling the PWB. Moving the board can cause the joint to create an open or short circuit, or may result in poor reliability. Cooling time is just as important as heating time, as cooling too quickly can result in cracks or degraded electrical characteristics.