Direct die solder of gallium arsenide integrated circuit dies and methods of manufacturing gallium arsenide wafers

1. An electronic circuit device comprising:

a substrate;

a die attach pad located on the substrate;

a GaAs integrated circuit die having a copper backside contact pad and having a footprint of approximately the same size as the die attach pad, the GaAs integrated circuit die being connected to the die attach pad by a solder layer, the solder layer being disposed between the copper backside contact pad and the die attach pad on the substrate in a manner such that the GaAs integrated circuit die self-aligns with the die attach pad after reflow of the solder layer; and

a barrier layer formed from nickel and a palladium flash layer, said barrier layer being disposed between said copper backside contact pad and said solder layer.

2. The electronic circuit device of claim 1 wherein said substrate is a printed circuit board.

3. The electronic circuit device of claim 1 wherein thermal resistance of the solder layer is at least 40% lower than thermal resistance of an epoxy layer.

4. The electronic circuit device of claim 1 wherein the copper backside contact pad has a thermal conductivity of approximately 4 W/cmK.

5. A GaAs integrated circuit incorporating the electronic circuit device of claim 1 .

6. A method for manufacturing a GaAs wafer assembly, said method comprising:

fabricating a GaAs wafer having a copper layer over a backside of the wafer;

electroless plating a barrier layer over said copper layer;

forming a palladium flash layer over the copper layer;

forming at least one singulated die from said GaAs wafer; and

direct die soldering said at least one singulated die to a die attach pad on a substrate such that a solder layer is formed between the at least one singulated die and the die attach pad, the soldering performed in a manner such that the at least one singulated die self-aligns with the die attach pad after reflow of the solder layer.

7. The method of claim 6 wherein said substrate is a printed circuit board.

8. The method of claim 6 wherein a surface area of said singulated die is substantially equivalent to a surface area of said die attach pad.

9. A GaAs integrated circuit made in accordance with the method of claim 6 .

10. The GaAs integrated circuit of claim 9 wherein said GaAs integrated circuit comprises a through-wafer via at least partially filled with copper.

11. The GaAs integrated circuit of claim 10 wherein the electroless plating covers more than 40% of the through-wafer via.

12. An electronic circuit module comprising:

a singulated GaAs integrated circuit die having a copper contact pad;

a printed circuit board having a die attach pad, said die attach pad sized to receive the singulated GaAs integrated circuit die and having a footprint of approximately the same size as the singulated GaAs integrated circuit die;

a solder layer disposed between said copper contact pad of the die and said die attach pad of the printed circuit board, said copper contact pad of the singulated GaAs integrated circuit die attached to said die attach pad of the printed circuit board in a manner such that the singulated GaAs integrated circuit die self-aligns with the die attach pad after reflow of the solder layer;

a nickel layer, said nickel layer formed between said copper contact pad and said solder layer; and

a flash palladium layer, said flash palladium layer formed between said nickel layer and said copper contact pad and configured to act as a wetting layer for the solder layer.

13. The electronic circuit module of claim 12 wherein the size of said die attach pad does not exceed the size of said singulated GaAs integrated circuit die by more than 150 microns in at least one direction.

14. The electronic circuit module of claim 12 wherein said singulated GaAs integrated circuit die is a radio frequency integrated circuit die.