Varied-thickness heat sink for integrated circuit (IC) packages and method of fabricating IC packages

An assembly method for an integrated circuit package having an integrated circuit die having a plurality of bond pads, having a lead frame having a plurality of leads, the plurality of leads having an enclosable portion for enclosure within the integrated circuit package, and having a heat sink having a portion thereof enclosable within the integrated circuit package, the method comprising:

• locating the heat sink enclosable at least partially within the integrated circuit package having a surface of a first portion of the heat sink facing the lead frame in close proximity to a substantial part of the enclosable portion of each of the plurality of leads of the lead frame, with a die-attach area on the surface of the first portion of the heat sink attachable to the integrated circuit die, and with a second portion of the heat sink projecting away from the first portion of the heat sink under the die-attach area;
• bonding the lead frame to the heat sink using a heat conductive material for transferring heat from the integrated circuit die to the heat sink, the heat sink positioned having the die-attach area on the surface of the first portion of the heat sink, the first portion of the heat sink extending beneath a substantial part of the enclosable portion of said plurality of leads of the lead frame in close proximity to the enclosable portion of the plurality of leads, the first portion of the heat sink extending beneath at least eighty percent of an area formed by the enclosable portion of the lead frame having a plurality of leads;
• bonding the integrated circuit die to the die-attach area on the surface of the first portion of the heat sink;
• reducing the inductance of the plurality of leads of the lead frame by varying at least one of the distance between the heat sink from the plurality of leads of the lead frame, the size of the first portion of the heat sink, the thickness of the heat sink, and the width of the heat sink resulting in a reduction of inductance of about 18 percent over a heat sink of essentially uniform thickness;
• electrically connecting the plurality of bond pads of the integrated circuit die to the plurality of the leads of the lead frame using a plurality of bond wires;
• and
• electrically connecting the heat sink to the lead frame.

An assembly method for a Leads-Over-Chip integrated circuit package having an integrated circuit die having a plurality of bond pads, having a lead frame that includes a plurality of leads, the plurality of leads having an enclosable portion for enclosure within the integrated circuit package, and having a heat sink having a portion thereof enclosed within the integrated circuit package, the method comprising:

• locating a heat sink enclosable at least partially within the integrated circuit package having a surface of a first portion of the heat sink facing the lead frame in close proximity to a substantial part of the enclosable portion of the plurality of leads of the lead frame, with a die-attach area on the surface of the first portion of the heat sink attachable to the integrated circuit die, and with a second portion of the heat sink projecting away from the first portion of the heat sink under the die-attach area;
• attaching the integrated circuit die to the lead frame;
• reducing the inductance of the plurality of leads of the lead frame by varying at least one of the distance between the heat sink from the plurality of leads of the lead frame, the size of the first portion of the heat sink, the thickness of the heat sink, and the width of the heat sink resulting in a reduction of inductance of about 18 percent over a heat sink of essentially uniform thickness;
• bonding the integrated circuit die to the die-attach area on the surface of the first portion of the heat sink, the heat sink positioned having the die-attach area on the surface of the first portion of the heat sink, the first portion of the heat sink extending beneath a substantial part of the enclosable portion of the plurality of leads of the lead frame in close proximity to the enclosable portion of the plurality of leads, the first portion of the heat sink extending beneath at least eighty percent of an area formed by the enclosable portion of the lead frame having a plurality of leads;
• and
• electrically connecting the plurality of bond pads of the integrated circuit die to the plurality of leads of the lead frame using a plurality of bond wires.

An assembly method for a Leads-Under-Chip integrated circuit package having an integrated circuit die having a plurality of bond pads, having a lead frame that includes a plurality of leads, the plurality of leads having an enclosable portion for enclosure within the integrated circuit package, and having a heat sink, the method comprising:

• locating a heat sink enclosable at least partially within the integrated circuit package with a surface of a first portion of the heat sink facing the lead frame in close proximity to a substantial part of the enclosable portion of the plurality of leads of the lead frame, with a die-attach area on the surface of the first portion of the heat sink attachable to the integrated circuit, and with a second portion of the heat sink projecting away from the first portion of the heat sink under the die-attach area;
• attaching the integrated circuit die to the lead frame;
• reducing the inductance of the plurality of leads of the lead frame by varying at least one of the distance between the heat sink from the plurality of leads of the lead frame, the width of the heat sink, the size of the first portion of the heat sink, and the thickness of the heat sink resulting in a reduction of inductance of about 18 percent over a heat sink of essentially uniform thickness;
• bonding the integrated circuit die to the die-attach area on the surface of the first portion of the heat sink, the heat sink positioned having the die-attach area on the surface of the first portion of the heat sink, the first portion of the heat sink extending beneath a substantial part of the enclosable portion of the plurality of leads of the lead frame in close proximity to the enclosable portion of the plurality of leads, the first portion of the heat sink extending beneath at least eighty percent of an area formed by the enclosable portion of the lead frame having a plurality of leads;
• and
• electrically connecting the plurality of bond pads of the integrated circuit die to the plurality of leads of the lead frame using a plurality of bond wires.