Solder plate reflow method for forming solder-bumped terminals

A method for manufacturing a printed circuit board comprising a copper circuit trace including a plurality of terminals adapted for attachment of an electronic component by solder bump interconnections, each terminal comprising an enlarged terminal pad and an adjacent linear runner section and having a solder bump bonded to the terminal pad, said method comprising

• applying a metallic copper plate having a uniform thickness onto a dielectric substrate, said plate including the circuit trace and an adjacent region about the trace,
• apply a removable mask onto the copper plate, said mask covering the adjacent plate region and having an opening exposing the copper plate in a pattern corresponding to the circuit trace including each said terminal,
• immersing the masked copper plate into an electroplating bath containing dissolved tin and lead ions, and cathodically biasing the plate to codeposit metallic tin and metallic lead onto the exposed copper to form an outer plate of tin-lead solder alloy, whereby said mask prevents deposition onto the adjacent plate region,
• removing the mask from the copper plate to expose the adjacent region,
• etching the copper plate to remove the adjacent copper region, whereby the solder plate protects the underlying copper from etching to define the circuit trace including said terminals having said enlarged terminal pads, and
• heating to reflow the electroplated solder alloy, whereupon solder alloy is drawn onto each terminal pad from the runner section to form a solder bump.

A method for manufacturing a printed circuit board comprising a copper circuit trace including a plurality of terminals adapted for attachment of an electronic component by solder bump interconnections, each terminal comprising a circular terminal pad adapted for carrying a solder bump and an adjacent linear runner section, said method comprising

• affixing a metallic copper plate having a uniform thickness onto a dielectric substrate such that the copper plate includes the trace and an adjacent region about the trace,
• apply an electrically insulative photoresist mask onto the copper plate to cover the adjacent region, said mask having an opening for exposing the copper plate in a pattern corresponding to the circuit trace and defining each terminal such that the linear runner section has a width of between about 50 and 150 microns and the pad has a diameter between about 1.2 and 2.0 times the runner section width,
• immersing the masked copper plate into an aqueous electroplating bath containing dissolved tin and lead ions, and cathodically biasing the plate to reduce said ions and codeposit metallic tin and metallic lead selectively onto the exposed copper trace to produce a solder plate thereon, said plate being deposited to a thickness between about 10 and 25 microns and being composed of a solder alloy consisting of between about 35 and 45 weight percent lead and the balance tin,
• removing the mask to expose the adjacent copper region about the solder-plated trace,
• immersing the copper plate including the solder-plated trace in an etching solution effective to dissolve copper but not reactable with the solder alloy, whereby copper is etched from the adjacent region and protected at the trace by said solder plate to thereby define the trace, said trace including said terminals and having said solder plate overlying said copper plate, and
• heating the solder-plated trace to reflow the electroplated solder alloy, whereupon solder alloy is drawn onto each terminal pad from the neighboring runner section to form a solder bump having a height between about 60 and 80 microns. e