Leadframe for semiconductor packages

Abstract

A leadframe for semiconductor packages. The leadframe includes a die pad, a side rail, a tie bar, and a plurality of leads. The side rail is around the die pad. The tie bar connects the die pad and the side rail. The leads extend from the side rail to close proximity to the die pad. Each lead has a corresponding lead relative to a predetermined center line. A predetermined pair of corresponding leads are substantial asymmetrical with each other in appearance relative to the predetermined center line.

1 . A leadframe for semiconductor packages, comprising:
 a die pad;   a side rail around the die pad;   a tie bar connecting the die pad and the side rail; and   a plurality of leads extending from the side rail to close proximity to the die pad, comprising a first lead and a second lead being at opposite locations of the leadframe relative to a center line through the die pad, and the first and second leads being substantially asymmetrical with each other relative to the center line.   
     
     
         2 . The leadframe as claimed in  claim 1 , wherein the first and second leads comprise substantially different lead lengths. 
     
     
         3 . The leadframe as claimed in  claim 1 , wherein the first and second leads comprise substantially different lead widths. 
     
     
         4 . The leadframe as claimed in  claim 1 , wherein the first and second leads comprise substantially asymmetrical extending traces. 
     
     
         5 . The leadframe as claimed in  claim 1 , wherein the plurality of leads further comprise a third lead adjacent to the first lead, and a fourth lead adjacent to the second lead. 
     
     
         6 . The leadframe as claimed in  claim 5 , wherein a space between the first and third leads is substantially different from that between the second and fourth leads. 
     
     
         7 . The leadframe as claimed in  claim 5 , wherein a pitch between the first and third leads is different from a pitch between the second and fourth leads. 
     
     
         8 . The leadframe as claimed in  claim 5 , wherein the space between the first and third leads is not uniform. 
     
     
         9 . The leadframe as claimed in  claim 8 , wherein at least one section of the space between the first and third leads increases and then decreases. 
     
     
         10 . The leadframe as claimed in  claim 5 , wherein the third lead and the fourth lead are at opposite locations of the leadframe relative to the center line. 
     
     
         11 . A method of achieving a desired impedance value for a leadframe for semiconductor packages, comprising:
 providing a leadframe comprising a die pad, a side rail around the die pad, a tie bar connecting the die pad and the side rail, and a plurality of leads extending from the side rail to close proximity to the die pad; and   designing a layout of the plurality of leads comprising a first lead and a second lead being at opposite locations of the leadframe relative to a center line through the die pad, wherein   the first and second leads are substantially asymmetrical with each other relative to the center line.   
     
     
         12 . The method as claimed in  claim 11 , wherein the first and second leads comprise substantially different lead lengths. 
     
     
         13 . The method as claimed in  claim 11 , wherein the first and second leads comprise substantially different lead widths. 
     
     
         14 . The method as claimed in  claim 11 , wherein the first and second leads comprise substantially asymmetrical extending traces. 
     
     
         15 . The method as claimed in  claim 11 , wherein the plurality of leads further comprise a third lead adjacent to the first lead, and a fourth lead adjacent to the second lead. 
     
     
         16 . The method as claimed in  claim 15 , wherein a space between the first and third leads is substantially different from that between the second and fourth leads. 
     
     
         17 . The method as claimed in  claim 15 , wherein a pitch between the first and third leads is different from a pitch between the second and fourth leads. 
     
     
         18 . The method as claimed in  claim 15 , wherein the space between the first and third leads is not uniform. 
     
     
         19 . The method as claimed in  claim 18 , wherein at least one section of the space between the first and third leads increases and then decreases. 
     
     
         20 . The method as claimed in  claim 15 , wherein the third lead and the fourth lead are at opposite locations of the leadframe relative to the center line.