A method and structure for forming an electronic package with an interconnect structure that comprises lead-free solders. The method first forms a module by initially providing a chip carrier, a first joiner solder that is lead-free, and a core interconnect (e.g., solder ball, solder column) that includes a lead-free core solder. The liquidus temperature T1L of the first joiner solder is less than a solidus temperature TCS of the core solder. A first end of the core interconnect is soldered to the chip carrier with the first joiner solder, which includes reflowing the first joiner solder at a reflow temperature that is above T1L and below TCS, followed by cooling the first joiner solder to a temperature that is below a solidus temperature of the first joiner solder. Thus, the module with the soldered core interconnect has been formed. The method then provides a circuit card and a second joiner solder that is lead-free. The liquidus temperature T2L of the second joiner solder is less than TCS. A second end of the core interconnect is soldered to the circuit card with the second joiner solder, which includes reflowing the second joiner solder at a reflow temperature that is above T2L and below TCS, followed by cooling the second joiner solder to a lower temperature that is below a solidus temperature of the second joiner solder.
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