Patent ID: 7367489

Claim:
A solder bump reflow process, comprising: providing a die having a plurality of solder bumps and a substrate having a plurality of mating surfaces on interconnect sites, the solder bumps being made with a material having a liquidus temperature and a solidus temperature; contacting the solder bumps of the die and the mating surfaces of the substrate to form a die-substrate assembly; placing the die-substrate assembly on a transport mechanism which passes through an oven having a non-oxidizing atmosphere, the oven operating with a plurality of physically separate temperature zones; passing the die-substrate assembly through the plurality of physically separate temperature zones of the oven, including the steps of, (a) in a first temperature zone of the oven, raising the die-substrate assembly to a first heating temperature above the liquidus temperature of the solder bumps as the die-substrate assembly passes through the first temperature zone of the oven, and holding the first heating temperature above the liquidus temperature for a time sufficient to cause a first reflow of the solder bumps onto the mating surfaces of the substrate, (b) in a second temperature zone of the oven, decreasing the die-substrate assembly to a first cooling temperature below the solidus temperature of the solder bumps as the die-substrate assembly passes through the second temperature zone of the oven, and holding the first cooling temperature below the solidus temperature to a first re-solidification of the solder bumps, wherein a number of the solder bumps fail to metallurgically connect to the mating surfaces of the interconnect sites on the substrate during the first reflow and first re-solidification, (c) in a third temperature zone of the oven, raising the die-substrate assembly to a second heating temperature above the liquidus temperature of the solder bumps as the die-substrate assembly passes through the third temperature zone of the oven, and holding the second heating temperature above the liquidus temperature for a time sufficient to cause a second reflow of the solder bumps onto the mating surfaces of the substrate, and (d) in a fourth temperature zone of the oven, decreasing the die-substrate assembly to a second cooling temperature below the solidus temperature to a second re-solidification of the solder bumps; wherein the number of the solder bumps which failed to metallurgically connect to the mating surfaces of the interconnect sites on the substrate during the first reflow and first re-solidification are metallurgically connected during the second reflow and second re-solidification; and wherein the first and second reflow and the first and second re-solidification steps are conducted as a continuous process in the oven without exposing the die-substrate assembly to an oxidizing atmosphere to avoid contamination of the die-substrate assembly during the solder bump reflow process.