Method of making electronic module with multiple solder dams in

Abstract

The present method employs a first plating resist for forming circuit lines on a carrier substrate. While the plating resist is still in place a metal, such as nickel, is deposited on top of the circuit lines. A second plating resist is employed for plating solder on the circuit lines at solder sites. At this stage additional solder can be deposited at each solder site to provide or supplement the necessary low melt solder required for forming a solder joint. The first and second resists along with solder thereon are then stripped and copper foil on the carrier substrate is etched away around the circuit lines. A soldermask is then formed on the carrier substrate over the circuit lines except for circuit lines in the chip sites. The soldermask has a single large opening at each chip site which has lateral dimensions which are slightly larger than the lateral dimensions of the chip to be connected at the chip site. During curing of the soldermask, which involves heat, the nickel layer on top of the circuit lines within the chip site opening quickly oxidizes to provide solder dams which extend along the lengths of the lines within the chip site openings immediately adjacent the solder sites. The chips are then placed within the soldermask windows and electrically connected by solder joints to the solder sites of the circuit lines by a flip chip attach method. The chip sites are then encapsulated with an underfill encapsulant to protect the solder joints.