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A die attach method for a semiconductor chip with a back metal layer located at the back surface of the semiconductor chip comprises the steps of forming a bonding ball array including a plurality of bonding balls with a same height on a die attach area at a top surface of a die paddle; depositing a

A die attach method for a semiconductor chip with a back metal layer located at the back surface of the semiconductor chip comprises the steps of forming a bonding ball array including a plurality of bonding balls with a same height on a die attach area at a top surface of a die paddle; depositing a die attach material in the bonding ball array area with a thickness of the die attach material equal or slightly larger than the height of the bonding ball; attaching the semiconductor chip to the die attach area at the top surface of the die paddle by the die attach material, wherein the bonding ball array controls the bond line thickness of the die attach material between the back metal layer and the top surface of the die paddle and prevents the semiconductor chip from rotating on the die attach material when it is melted.

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1. A die attach method for a semiconductor chip including a back metal layer located at the back surface of the semiconductor chip comprising: forming a bonding bump array including a plurality of bonding bumps with a same height on a die attach area at a top surface of a die paddle;depositing a die

1. A die attach method for a semiconductor chip including a back metal layer located at the back surface of the semiconductor chip comprising: forming a bonding bump array including a plurality of bonding bumps with a same height on a die attach area at a top surface of a die paddle;depositing a die attach material in the bonding bump array area with a thickness of the die attach material equal or slightly larger than the height of the bonding bump;attaching the semiconductor chip to the bonding bump array at the top surface of the die paddle by the die attach material, wherein the die attach material and the bonding bump array are located between the back metal layer of the semiconductor chip and the top surface of the die paddlewherein the bonding bump array controls a bond line thickness of the die attach material between the back metal layer and the top surface of the die paddle and prevents the semiconductor chip from rotating on the die attach material when the die attach material is melted. 2. The method of claim 1, wherein the bonding bump array has a shape of a rectangle, triangle, quadrangle, round, ellipse, sector or any polygon. 3. The method of claim 1, wherein the shape and an area of the bonding bump array are the same as those of the back metal layer. 4. The method of claim 1, wherein a melting point of the bonding bump is higher than a melting point of the die attach material. 5. The method of claim 1, wherein the bonding bump comprises a conductor, an insulator or a semiconductor. 6. The method of claim 1, wherein the bonding bump is made of copper, gold, silver, aluminum or their alloy. 7. The method of claim 1, wherein the bonding bump has a shape of sphere, ellipse, cube, cylinder or wedge. 8. The method of claim 1, wherein the die attach material comprises a conductive silver paste, a soft solder or a soldering paste. 9. The method of claim 1, wherein a metal coating is formed in the die attach area at the top surface of the die paddle before forming the bonding bumps, the metal coating is made of gold, silver, nickel or nickel-palladium-gold. 10. A die attach method for a semiconductor chip including a back metal layer located at the back surface of the semiconductor chip comprising: forming a bonding bump array including a plurality of bonding bumps with a same height on a die attach area at a top surface of a die paddle;depositing a die attach material in the bonding bump array area with a thickness of the die attach material equal or slightly larger than the height of the bonding bump;attaching the semiconductor chip to the bonding bump array at the top surface of the die paddle by the die attach material, wherein the die attach material and the bonding bump array are located between the back metal layer of the semiconductor chip and the top surface of the die paddlewherein the bonding bump array controls a bond line thickness of the die attach material between the back metal layer and the top surface of the die paddle and prevents the semiconductor chip from rotating on the die attach material when the die attach material is melted; andwherein the step of forming the bonding ball array comprises:a) forming a metal sphere by heating an end part of a metal wire and depositing the metal sphere in the die attach area;b) separating the metal sphere from the metal wire forming a bonding ball in the die attach area; andrepeating steps a) and b) to generate a plurality of bonding balls in the die attach area forming the bonding ball arraywherein the diameter of the bonding ball is adjusted by changing the diameter of the metal wire, as such the thickness of the die attach material between the back metal layer of the semiconductor chip and the top surface of the metal substrate can be controlled. 11. The method of claim 1, wherein the back metal layer covers the whole back surface of the semiconductor chip. 12. The method claim 1, the back metal layer covers a center portion of the back surface of the semiconductor chip. 13. The method of claim 12, wherein the bonding balls in the bonding ball array are only formed within an area at the top surface of the die paddle overlapped by the back metal layer. 14. A die attach method for a semiconductor chip including a back metal layer located at the back surface of the semiconductor chip comprising: providing a lead frame having a bonding bump array including a plurality of bonding bumps with a same height formed on a die attach area at a top surface of a die paddle;depositing a die attach material in the bonding bump array area with a thickness of the die attach material equal or slightly larger than the height of the bonding bump;attaching the semiconductor chip to the bonding bump array at the top surface of the die paddle by the die attach material, wherein the die attach material and the bonding bump array are located between the back metal layer of the semiconductor chip and the top surface of the die paddlewherein the bonding bump array controls a bond line thickness of the die attach material between the back metal layer and the top surface of the die paddle and prevents the semiconductor chip from rotating on the die attach material when the die attach material is melted. 15. The method of claim 14, wherein the bonding bump array has a shape of a rectangle, triangle, quadrangle, round, ellipse, sector or any polygon. 16. The method of claim 14, wherein the shape and an area of the bonding bump array are the same as those of the back metal layer. 17. The method of claim 14, wherein a melting point of the bonding bump is higher than a melting point of the die attach material. 18. The method of claim 14, wherein the bonding bump comprises a conductor, an insulator or a semiconductor. 19. The method of claim 14, wherein the bonding bump is made of copper, gold, silver, aluminum or their alloy. 20. The method of claim 14, wherein the bonding bump has a shape of sphere, ellipse, cube, cylinder or wedge.