Semiconductor device with thermal dissipation lead frame

Abstract

A lead frame for assembling a semiconductor device has a die pad surrounded by lead fingers. Each of the lead fingers has a proximal end close to but spaced from an edge of the die pad and a distal end farther from the die pad. A semiconductor die is attached to a surface of the die pad. The die has die bonding pads on its upper surface that are electrically connected to the proximal ends of the lead fingers with bond wires. An encapsulation material covers the bond wires, semiconductor die and the proximal ends of the lead fingers. Prior to assembly, hot spots of the die are determined and the lead fingers closest to the hot spots are selected to project closer to the die than the other lead fingers. These longer lead fingers assist in dissipating the heat at the die hot spot.

1 . A method of designing a lead frame for a semiconductor device, comprising:
 providing a lead frame having an initial structure including a die pad, a frame that at least partially surrounds the die pad, die pad support members coupling the die pad to the frame, and a plurality of lead fingers extending from the frame towards the die pad, each of the lead fingers having a distal end at the frame and proximal end close to but spaced from an edge of the die pad;   determining at least one thermal hot spot region of a semiconductor die to be attached to the die pad;   modifying the initial frame structure to have at least one thermal dissipating lead finger selected from the plurality of lead fingers, wherein the at least one thermal dissipating lead finger has a proximal end closer to the edge of the die pad than the proximal ends of the lead fingers adjacent to the at least one thermal dissipating lead finger; and   forming the lead frame, wherein the at least one thermal dissipating lead finger is the closest lead finger to the thermal hot spot region when the semiconductor die is attached to the die pad.   
     
     
         2 . The method of  claim 1 , wherein the at least one thermal dissipating lead finger is a single lead finger. 
     
     
         3 . The method of  claim 2 , wherein the single lead finger has a lateral projection extending from its proximal end. 
     
     
         4 . The method of  claim 3 , wherein the lateral projection has an edge parallel to a closest edge of the die pad. 
     
     
         5 . The method of  claim 3 , wherein the lateral projection extends in a gap between the edge of the die pad and at least one of the plurality of lead fingers. 
     
     
         6 . The method of  claim 1 , wherein the plurality of lead fingers comprise lead finger groups disposed between the die pad support members, and wherein the at least one thermal dissipating lead finger is located away from the die pad support members. 
     
     
         7 . The method of  claim 1 , wherein determining the at least one thermal hot spot region of the semiconductor die to be attached to the die pad comprises:
 testing the die under normal operating conditions and measuring power consumption values of regions of the semiconductor die, wherein the thermal hot spot region has a power output per square mm of functional die surface area that is greater than a mean power output per square mm of the total functional die surface area.   
     
     
         8 - 20 . (canceled)