Method and apparatus for flip chip attachment by post collapse re-melt and re-solidification of bumps

1. 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.

2. The solder bump reflow process of claim 1 , wherein the first cooling temperature ranges between the solidus temperature and about 50° C. less than the solidus temperature.

3. The solder bump reflow process of claim 1 , wherein the material of the solder bumps includes lead solder.

4. The solder bump reflow process of claim 1 , wherein the material of the solder bumps includes lead free solder.

5. The solder bump reflow process of claim 1 , wherein the material of the solder bumps includes tin-lead solder.

6. The solder bump reflow process of claim 1 , wherein the solder bump material is 63% tin and 37% lead eutectic.

7. The solder bump reflow process of claim 6 , wherein the first heating temperature is above 183°°C. and the first cooling temperature is between 183° C. and 133° C.

8. 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; and

passing the die-substrate assembly through an oven operating with a plurality of temperature zones in a non-oxidizing atmosphere, 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, and holding the first heating temperature above the liquidus temperature 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, and holding the first cooling temperature below the solidus temperature to a first re-solidification of the solder bumps,

(c) in a third temperature zone of the oven, raising the die-substrate assembly to a second heating temperature above the liguidus temperature of the solder bumps, and holding the second heating temperature above the liguidus temperature 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 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.

9. The solder bump reflow process of claim 8 , wherein the first cooling temperature ranges between the solidus temperature and about 50° C. less than the solidus temperature.

10. The solder bump reflow process of claim 8 , wherein the material of the solder bumps includes lead solder.

11. The solder bump reflow process of claim 8 , wherein the material of the solder bumps includes lead-free solder.

12. The solder bump reflow process of claim 8 , wherein the material of the solder bumps includes tin-lead solder.

13. The solder bump reflow process of claim 8 , wherein the solder bump material is 63% tin and 37% lead eutectic.

14. The solder bump reflow process of claim 8 , wherein the first heating temperature is above 183° C. and the first cooling temperature is between 183° C. and 133° C.

15. The solder bump reflow process of claim 8 , wherein a number of the solder bumps on the die fail to metallurgically connect to the mating surfaces of the interconnect sites on the substrate during the first reflow and first re-solidification.

16. The solder bump reflow process of claim 15 , 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.

17. 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; and

passing the die-substrate assembly through an oven operating in a non-oxidizing atmosphere, including the steps of,

(a) raising the die-substrate assembly to a first heating temperature above the liquidus temperature of the solder bumps, and holding the first heating temperature above the liquidus temperature to cause a first reflow of the solder bumps onto the mating surfaces of rhe substrate,

(b) decreasing the die-substrate assembly to a first cooling temperature below the solidus temperature of the solder bumps, and holding the first cooling temperature below the solidus temperature to a first re-solidification of the solder bumps,

(c) raising the die-substrate assembly to a second heating temperature above the liquidus temperature of the solder bumps, and holding the second heating temperature above the liquidus temperature to cause a second reflow of the solder bumps onto the mating surfaces of the substrate, and

(d) 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 first and second reflow and the first and second re-solidification steps are conducted without exposing the assembly to an oxidizing atmosphere.

18. The solder bump reflow process of claim 17 , wherein a number of the solder bumps on the die fail to metallurgically connect to the mating surfaces of the interconnect sites on the substrate during the first reflow and first re-solidification.

19. The sdlder bump reflow process of claim 18 , 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.

20. The solder bump reflow process of claim 17 , wherein the first cooling temperature ranges between the solidus temperature and about 50° C. less than the solidus temperature.

21. The solder bump reflow process of claim 17 , wherein the material of the solder bumps includes lead solder.

22. The solder bump reflow process of claim 17 , wherein the material of the solder bumps includes leadfree solder.

23. The solder bump reflow process of claim 17 , wherein the material of the solder bumps includes tin-lead solder.

24. The solder bump reflow process of claim 17 , wherein the solder bump material is 63% tin and 37% lead eutectic.

25. The solder bump reflow process of claim 17 , wherein the first heating temperature is above 183° C. and the first cooling temperature is between 183° C. and 133° C.