Phase Diagrams

Design Issues

Eutectic solder
· Solder is a lead-tin alloy for which the phase diagram is shown. Pure lead, pure tin and the eutectic composition of the alloy all have unique melting points.
· When joining electrical conductors this unique melting temperature is an advantage, preventing component movement during the solidification and avoiding a high resistance joint.

After: Askland,
"The Science of Engineering Materials," PWS (1994)

· 60/40 radio solder has the eutectic composition of Pb-61.9 wt % Sn. The lamella structure of the solid formed is shown on the diagram.