Homologous temperature

Homologous temperature expresses the temperature of a material as a fraction of its melting point temperature using the Kelvin scale. For example, the homologous temperature of lead at room temperature is approximately 0.50 (T_H = T/T_mp = 298K/601K = 0.50).

Solder (T_mp: 183°C = 456K) at 0.85T_mp or 115°C (= 388K), would thus be expected to have comparable properties to copper (T_mp: 1085°C = 1358K) at 0.85T_mp or 881°C (= 1154K).

In electronics applications, where circuits typically operate over a –55°C to +125°C range, eutectic tin-lead (Sn63) solder is working at 0.48T_mp to 0.87T_mp. The upper temperature is high relative to the melting point; from this we can deduce that solder will have limited mechanical strength (as a bulk material) and significant creep under stress. This is borne out by its comparatively low values for tensile strength, shear strength and modulus of elasticity.^{[citation needed]}

Copper, on the other hand, has a much higher melting point, so foils are working at only 0.16T_mp to 0.29T_mp, and their properties are little affected by temperature.