Leadframe designs for plastic overmold packages

Abstract

The specification describes a plastic overmolded package for high power devices that has a very low lead count, typically fewer than eight, and in a preferred embodiment, only two. The leads occupy essentially the same linear space as the multiple leads in a conventional package and thus have a wide-blade configuration. To improve mechanical integrity, the leads in the package are provided with retention slots to add back the equivalent of the plastic joints in the spaces that were eliminated due to the wide-blade design. The retention slots extend in the width dimension of the leads.

1 . A plastic overmolded package comprising: 
 a. a leadframe, the leadframe comprising: 
 i. a center die attachment portion,  
 ii. at least two tab leads extending from the center die attachment portion, the tab leads having a width W and a thickness T,  
 iii. at least one slot formed in each of the tab leads, the slot extending through the thickness T of the tab leads and having an inboard edge E i  nearest to the device and an outboard edge furthest from the device,  
   b. a semiconductor device attached to the leadframe,    c. a plastic overmold having a top, a bottom and sidewalls encapsulating: 
 the semiconductor device,  
 the center die attachment portion of the leadframe, and  
 the inboard edge E 1  of the slot in the tab leads,  
   while leaving a substantial portion of the tab leads exposed, the exposed portions of the tab leads extending away from the sidewalls of the overmold.    
   
   
       2 . The package of  claim 1  wherein the inboard edge is essentially straight.  
   
   
       3 . The package of  claim 2  wherein the leadframe comprises two tab leads.  
   
   
       4 . The package of  claim 1  wherein the leadframe comprises two to six tab leads.  
   
   
       5 . The package of  claim 3  wherein the inboard edge has length L P  and L P  is greater than 0.3×W.  
   
   
       6 . The package of  claim 1  wherein the slot has width w s  and the tab lead has thickness t l  and w s /t l  is at least 1.  
   
   
       7 . The package of  claim 4  wherein the leadframe comprises 4 to 6 leads, with 2 or 3 leads per side, and the leads separated by distance s, wherein:  
       L p >0.3 [( N×w   l )+( N− 1) s]   
     where L p  is the sum of the inboard edges on a side of the plastic overmolded package, N is the number of leads on a side, and w l  is the width of the leads.