Abstract: A solder preform for hermetically sealing a cover to a container for a semiconductor package comprises a relatively thick flat ring of an alloy consisting of substantially 95% lead, 2.5% tin, and 2.5% silver, which alloy has the characteristic that it solidifies from the fluid state as a homogeneous mixture without substantial separation of the minority element crystals. The solder preform further comprises a relatively thin coating clad on each surface of the flat ring of an oxidation-resistant alloy, preferably an alloy consisting of substantially 96.5% tin and 3.5% silver.