Abstract: This invention relates to a high performance copper alloy and its manufacturing methods for electrical and electronic parts which have good electrical conductivity, superior mechanical properties, and high thermal stability of tin-lead plating. The copper alloy consisting essentially of copper and from copper-nickel-silicon-phosphor-magnesium alloys for semiconductor leadframe alloys consisting essentially of copper and from 0.5 to 2.4% by weight nickel, from 0.1 to 0.5% by weight silicon, from 0.02 to 0.16% by weight phosphorus, and from 0.02 to 0.2% by weight magnesium.