Thermal compress bonding

1. A method comprising:

placing a first plurality of work pieces into work piece holders of a substrate carrier;

picking up and placing a second plurality of work pieces, with each of the second plurality of work pieces being placed on one of the first plurality of work pieces;

bringing the first plurality of work pieces in contact with a first heating tool, wherein the first heating tool is integral with the substrate carrier and heating the first plurality of work pieces with the first heating tool;

bringing the second plurality of work pieces in contact with a second heating tool and heating the second plurality of work pieces with the second heating tool, the second heating tool being configured to apply a force on the second plurality of work pieces and being different than the first heating tool; and

reflowing solder bumps between the first and the second plurality of work pieces to simultaneously bond the first and the second plurality of work pieces together.

2. The method of claim 1 , wherein the second heating tool comprises a plurality of heating heads, and wherein the plurality of heating heads are configured to heat the second plurality of work pieces simultaneously.

3. The method of claim 1 , wherein the second heating tool comprises a single heating head contacting all of the second plurality of work pieces, and wherein the single heating head is configured to heat the second plurality of work pieces simultaneously.

4. The method of claim 1 further comprising:

before the step of reflowing, applying a downward force to press the second plurality of work pieces against the first plurality of work pieces;

during the step of reflowing, holding the second plurality of work pieces at a fixed level; and

after the solder bumps are melted and before the solder bumps are solidified, applying an upward force to the second plurality of work pieces to increase heights of the solder bumps.

5. The method of claim 1 , wherein the first and the second plurality of work pieces are arranged as an array.

6. The method of claim 1 , wherein the first plurality of work pieces fills all work piece holders in the substrate carrier.

7. The method of claim 1 , wherein the first plurality of work pieces are package substrates, and the second plurality of work pieces are device dies.

8. A method comprising:

placing a first plurality of work pieces into work piece holders of a substrate carrier;

picking up and placing a second plurality of work pieces, with each of the second plurality of work pieces being vertically aligned to one of the first plurality of work pieces, wherein the each of the first plurality of work pieces comprises a first solder bump contacting a second solder bump of the each of the second plurality of work pieces;

placing a first heating tool in contact with the first plurality of work pieces simultaneously, the first heating tool being integral with the substrate carrier;

placing a second heating tool over and contacting the second plurality of work pieces simultaneously;

heating the first plurality of work pieces using the first heating tool and heating the second plurality of work pieces using the second heating tool to perform a reflow process, wherein the first solder bump and the second solder bump are melted to form a third solder bump; and

before the third solder bump is solidified, simultaneously applying an upward force to the second plurality of work pieces to increase a height of the third solder bump.

9. The method of claim 8 , wherein the second heating tool comprises a plurality of heating heads, and wherein the plurality of heating heads are configured to heat the second plurality of work pieces simultaneously.

10. The method of claim 8 , wherein the second heating tool comprises a single heating head contacting all of the second plurality of work pieces, and wherein the single heating head is configured to heat the second plurality of work pieces simultaneously.

11. The method of claim 8 further comprising, before and during the step of reflowing, applying a downward force to press the second plurality of work pieces against the first plurality of work pieces.

12. The method of claim 8 , wherein the first and the second plurality of work pieces are arranged as an array.

13. The method of claim 8 , wherein the first plurality of work pieces fills all work piece holders in the substrate carrier.

14. The method of claim 8 , wherein the first plurality of work pieces are package substrates, and the second plurality of work pieces are device dies.