SOLDER BUMP STRETCHING METHOD

1 . A method, comprising:

heating a solder bump above a melting temperature of the solder bump;

stretching the solder bump to increase a height of the solder bump; and

cooling down the solder bump.

2 . The method of claim 1 , further comprising bonding a top holder to a top die above the solder bump.

3 . The method of claim 2 , wherein bonding the top holder is achieved by vacuum suction.

4 . The method of claim 2 , wherein heating the solder bump is performed by using a heat element in the top holder.

5 . The method of claim 4 , wherein the heat element comprises an electrical wire.

6 . The method of claim 1 , further comprising bonding a bottom holder to a substrate below the solder bump.

7 . The method of claim 1 , wherein stretching the solder bump increases a grain orientation angle between a short crystal axis of a main element of the solder bump and a normal axis of a substrate below the solder bump.

8 . The method of claim 7 , wherein the main element is Sn.

9 . The method of claim 7 , wherein the angle is above 50°.

10 . The method of claim 1 , wherein the heating is above 300° C.

11 . The method of claim 1 , wherein a ratio of a center width of the solder bump over a top contact width of the solder bump is from 0.6 to 1.0 after the stretching.

12 . The method of claim 1 , wherein the solder bump has an increased portion of a lamellar structure after the stretching.

13 . A method, comprising:

bonding a top holder to a top die having a solder bump;

heating a solder bump above a melting temperature of the solder bump;

stretching the solder bump to increase a height of the solder bump in order to increases a grain orientation angle between a short crystal axis of a main element of the solder bump and a normal axis of a substrate below the solder bump; and

cooling down the solder bump.

14 . The method of claim 13 , wherein the bonding is achieved by vacuum suction.

15 . The method of claim 13 , wherein heating the solder bump is performed by using a heat element in the top holder.

16 . The method of claim 15 , wherein the heat element comprises an electrical wire.

17 . The method of claim 13 , further comprising bonding a bottom holder to a substrate below the solder bump.

18 . The method of claim 13 , wherein the angle is above 50°.

19 . The method of claim 13 , wherein a ratio of a center width of the solder bump over a top contact width of the solder bump is from 0.6 to 1.0 after the stretching.

20 . A method, comprising:

bonding a top holder to a top die having a solder bump, wherein the solder bump includes Sn;

heating a solder bump above a melting temperature of the solder bump using a heat element in the top holder;

stretching the solder bump to increase a height of the solder bump in order to increases a grain orientation angle between a short crystal axis of Sn in the solder bump and a normal axis of a substrate below the solder bump, wherein a ratio of a center width of the solder bump over a top contact width of the solder bump is from 0.6 to 1.0 and the solder bump has an increased portion of a lamellar structure after the stretching; and

cooling down the solder bump.