Low temperature method for forming solder bump interconnections to a plated circuit trace

A method for forming a microelectronic component package comprising an integrated circuit component attached to a printed circuit board by a plurality of solder bump interconnections, said method comprising

• fabricating a printed circuit board comprising a solder-wettable metal trace affixed to a dielectric substrate, said trace comprising a plurality of terminals, each terminal comprising a bond pad and a runner section connected to the pad and comprising a solder plate overlying the bond pad and the runner section, said solder plate being formed of a tin-base metal having a first melting temperature,
• attaching a plurality of solder bumps to the component, said solder bumps being composed of an indium-base metal having a second melting temperature,
• superposing said component onto the board to form an assembly such that the solder plate at each said bond pad contacts the corresponding bump,
• heating the assembly to a temperature greater than the tin-indium eutectic melting temperature but less than the first melting temperature and the second melting temperature, whereupon at each bond pad the tin-base metal and the indium-base metal cooperate to form an interfacial liquid phase that wets the solder plate and the solder bump, and
• cooling the assembly to solidify the liquid phase to form solder bump interconnections that bond the component to the board.

A method for forming a microelectronic component package comprising an integrated circuit component attached to a printed circuit board by a plurality of solder bump interconnections, said method comprising

• fabricating a printed circuit board comprising a solder-wettable metal trace affixed to a dielectric substrate, said trace comprising a plurality of terminals, each terminal comprising a bond pad and a runner section connected to the pad and further including a solder plate overlying the the bond pad and the runner section, said solder plate being formed of an indium-containing alloy having a first melting temperature,
• attaching a plurality of solder bumps to the component, said bumps being composed of a bismuth-containing alloy having a second melting temperature,
• superposing said component onto the board to form an assembly such that a solder bump contacts the solder plate at each said bond pad,
• heating the assembly to a temperature greater than the indium-bismuth eutectic melting temperature but less than the first melting temperature and the second melting temperature, whereupon at each bond pad the indium-containing alloy and the bismuth-containing alloy cooperate to form an interfacial liquid phase that wets the solder plate and the solder bump, and
• cooling the assembly to solidify the liquid phase to form solder bump interconnections that bond the component to the board.