Tin-bismuth solder connection having improved high temperature properties, and process for forming same

A process for solder bonding a first faying surface and a second faying surface, said process comprising

• applying to at least one faying surface a film composed of a metal selected from the group consisting of gold and silver,
• applying a solder paste onto the film to form a particulate deposit formed predominantly of solder particles of an alloy composed substantially of tin and bismuth,
• assembling the second faying surface in contact with the particulate deposit to form an assembly,
• heating the assembly to a temperature sufficient to melt and the particulate deposit to form a liquid that wets the faying surfaces, whereupon the metal from the film dissolves into the liquid, and
• cooling to solidify the liquid to form a solder connection bonded to the faying surfaces.

A process for solder bonding a first faying surface and a second faying surface, said process comprising:

• applying to the first faying surface a solder layer formed of an alloy composed substantially of tin and bismuth,
• coating the solder layer with a film composed of a metal selected from the group consisting of gold and silver,
• applying a solder paste onto the film to form a particulate deposit formed predominantly of solder particles of an alloy composed of substantially of tin and bismuth,
• assembling the second faying surface in contact with the particulate deposit to form an assembly,
• heating the assembly to a temperature sufficient to melt the solder layer and the particulate deposit to form a liquid that wets the faying surfaces, whereupon the metal from the film dissolves into the liquid, and
• cooling to solidify the liquid to form a solder connection bonding to the faying surfaces.

A process for mounting a component onto a printed circuit board, said component comprising a contact formed of a solder-wettable metal, said printed circuit board comprising a bond pad formed of a solder-wettable metal, said process comprising:

• electrodepositing a plate onto the bond pad, said plate being formed of a solder alloy composed of between about 30 and 70 weight percent bismuth and the balance substantially tin,
• electrodepositing a film onto the plate, said film being composed of a tertiary metal selected from the group consisting of gold and silver,
• applying a paste onto the film to form a deposit comprising solder particles formed of an alloy composed of between about 30 and 70 weight percent bismuth and the balance substantially tin,
• assembling the component and the substrate to form an assembly such that the contact of the component is in contact with said deposit,
• heating the assembly to a temperature sufficient to melt the plate and the deposit and to dissolve the coating to form a liquid that wets the bond pad and the contact and extends continuously therebetween, and
• cooling to solidify the liquid to form a solder connection bonding the contact and the bond pad and containing between about 1.0 and 2.2 weight percent tertiary metal to enhance high temperature properties.