Power transistor with heat dissipation and method therefor
A device comprising a substrate, an integrated circuit (IC) die attached to the substrate on one side, a plurality of contact pads on an active side of the IC die, a plurality of thermally and electrically conductive legs, each of the legs attached to a respective one of the contact pads, and an encapsulating material formed around the substrate, the IC die, and a portion of the legs. A contact end of each of the legs is exposed, and one of the contact ends conducts a signal from a transistor in the IC die.
1. A method comprising:
attaching a power die to a leadframe;
attaching a heat spreader to an active surface of the power die, wherein
the heat spreader is thermally and electrically conductive;
the active surface includes bond pads that are electrically conductive; and
the heat spreader includes a flat surface and a plurality of legs attached to one side of the flat surface, each of the legs are attached to a corresponding one of the bond pads;
molding an encapsulating material to surround the power die, the leadframe, and the legs of the heat spreader, wherein a top side of the flat surface is exposed through the encapsulating material; and
cutting through the flat surface between the legs to form external contacts that are electrically independent of one another.
2. The method of claim 1 wherein:
the attaching the heat spreader to the leadframe includes using at least one of: a conductive adhesive and a conductive bond.
3. The method of claim 1 further comprising:
the cutting through the flat surface includes using one of a group consisting of: a mechanical saw and a laser.
4. The method of claim 1 further comprising:
forming the legs on the heat spreader by using at least one of the group consisting of: chemical etching, a laser, a punch press, and a mechanical saw.
5. The method of claim 1 wherein the top side of the flat surface is coplanar with a top surface ( 48 ) of the encapsulating material.
6. The method of claim 1 further comprising:
attaching a control die to the leadframe; and
forming a wire bond between the control die and the power die.
7. The method of claim 1 further comprising:
attaching the external contacts to corresponding electrical contacts on a circuit board.
8. The method of claim 7 wherein:
one of the external contacts conducts a signal from a power transistor in the power die.
9. The method of claim 7 wherein:
the attaching the heat spreader to the circuit board includes using at least one of: an electrically conductive adhesive and an electrically conductive bond.
10. A method comprising:
attaching a die to a substrate;
attaching a first end of each of a plurality of legs to an active surface of the die, wherein:
each of the plurality of legs is thermally and electrically conductive; and
the active surface includes a plurality of electrically conductive bond pads, each first end of the legs is attached to a corresponding one of the bond pads; and
encapsulating the die and at least part of the legs in a mold compound, wherein each of the legs form at least part of a corresponding one of a plurality of external contacts that are exposed through the mold compound;
wherein
a second end of each of the legs is attached to a surface,
the attaching the first end of the legs to the bond pads is performed while each of the second end of the legs is attached to the surface, and
one side of the surface is exposed after the encapsulating,
the method further comprising:
after the encapsulating, removing at least a portion of the surface between the legs to form the external contacts, wherein the external contacts are electrically independent of one another.
11. The method of claim 10 wherein:
the first end of the legs has an exposed surface area that is between 50 and 100 percent of a contact area of the corresponding bond pads.
12. The method of claim 10 wherein:
the legs retain the same shape before and after the legs are attached to the bond pads of the die.
13. The method of claim 10 wherein:
the attaching the legs to the substrate includes using at least one of: a conductive adhesive and a conductive bond.
14. The method of claim 10 further comprising:
the removing at least a portion of the surface between the legs to form the external contacts includes using one of a group consisting of: a mechanical saw and a laser.
15. The method of claim 10 wherein:
the die is a power die and one of the external contacts conducts a signal from a transistor in the die.