A method includes forming regions of solder paste on a redistribution structure, wherein the solder paste has a first melting temperature; forming solder bumps on an interconnect structure, wherein the solder bumps have a second melting temperature that is greater than the first melting temperature; placing the solder bumps on the regions of solder paste; performing a first reflow process at a first reflow temperature for a first duration of time, wherein the first reflow temperature is less than the second melting temperature; and after performing the first reflow process, performing a second reflow process at a second reflow temperature for a second duration of time, wherein the second reflow temperature is greater than the second melting temperature.