5. How to solder

5.1. Resources

While this section is a work in progress, visitors are referred to the following useful resources:

• Video based instructions for soldering

• Text based instructions for soldering

• Safety guidelines for soldering

5.2. Outline

NOTE Since this course is geared towards chemists, a discussion of soldering should include chemical compositions

• Soldering is the act of joining two metals together with a fusible metal alloy called solder.

• The composition of early solders was 60/40 tin/lead, which melts at 188 C (370F)

• With the push to remove lead from consumer electronics, lead-free solder may contain many other elements such as copper, silver, bismuth, indium, zinc and antimony. The result is an alloy with a higher melting point, upwards of 200 C higher. A lead free solder commonly in use is tin-silver-copper with a melting point of 217/423

• Solders also contain a flux, which is a chemical cleaning agent designed to eliminate/remove metal oxides, often by a chemical reduction reaction. Compositions vary greatly (and are confidential intellectual property) but fall into three basic categories: rosin, organic and inorganic. Only the first two are typically found in electronics soldering and consist of various acids ranging from hydrochloric and ammonium chloride to citric and abietic.

• Practical standpoint - typically soldering components that have been designed to be easily soldered, so just do it.

• Through hole connections: insert the piece into the circuit board, prepare to solder from the opposite side of insertion, use soldering iron at 450F (220 C) to heat the components for ~ 2 seconds, touch solder to the heated components. Remove solder wire then remove the soldering iron. The components we use are reasonably tolerant to heat, which means you can go a bit slower to start with, but keep the heating to under 10 seconds.

• Check the solder joint for a peaked shape. Round indicates that there is too much solder and too little will result in the through hole not being filled. Also check for bridging, which is excess solder connecting pads that should not be connected.

Warning

See a problem? Have a suggestion? Please raise an issue and share your thoughts there.