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386 Appendix A — Soldering and Safety Basics

critical, but the 0.031˝ variety as shown in Figure A-2 seems to work quite well for most work.
A one-pound spool of it costs about $13, and it never seems to run out. The particular type
of lead solder is usually 60/40: 60% tin and 40% lead. The combination of these two metals in
those percentages creates a low-melting-point alloy that acts almost like a totally different
metal. In the figure, the 66/44 represents the type of rosin flux in the solder and not the ratio
of metals.

FIGURE A-2: Lead solder, 60/40 .031˝ rosin flux core

If you were to dissect solder, you’d find that it’s hollow and filled with flux. This flux core is a
reducing agent that cleans the metal parts to be soldered of oxidation and other impurities. For
electronics rosin flux is used because acid flux would eat away at the parts. Rosin flux is a sticky
organic brown substance that you’ll see on your circuit boards when you solder. You can use
alcohol or specially formulated flux remover to get rid of it if you want.
With the recent Restriction of Hazardous Substances (RoHS) directive issued by the European
Union in 2003, lead-based solder will no longer be used for commercial electronics production.
Instead, new lead-free solder is substituted. This is good because lead is poisonous if ingested
and if handled for long durations. However, these lead-free solders haven’t been completely