Abstract:
An integrated circuit package lead frame, comprising a plurality of leads and a spine electrically connected to said plurality of leads, said spine comprising indentations between a pair of said leads. The indentations prevent the pair of leads from becoming electrically connected to each other after a singulation process.

Description:
BACKGROUND  
       [0001]     During a typical packaging process, an integrated circuit (“IC”) is mounted inside a plastic mold compound (“package”). Various points on the IC are electrically connected to lead frames circumscribing the package using bond wires. In turn, the lead frames circumscribing the package are electrically connected to an application board, such as a printed circuit board (“PCB”). In this way, multiple electrical connections are established between the IC and the PCB. For example,  FIG. 1  shows a side view of an exemplary IC  100  electrically connected to lead frames  102  of a package  104  using bond wires  106 . The lead frames  102  are electrically connected to a PCB  108 , thereby establishing multiple electrical connections between the IC  100  and the PCB  108 .  
         [0002]     Mold compounds (i.e., packages) generally are manufactured in mass quantities. More specifically, specially-shaped molds are used to fabricate sheets having multiple mold compounds. These sheets are subjected to a cutting process or singulation process, wherein the individual mold compounds that comprise each sheet are separated from each other. A top view of an exemplary mold sheet  200  is shown in  FIG. 2   a . The mold sheet  200  comprises a plurality of individual mold compounds (i.e., “unit packages”)  202 .  FIG. 2   b  shows a detailed top view of a unit package  202 . As previously mentioned, each package  202  is circumscribed by a lead frame  204 .  
         [0003]      FIG. 2   c  shows a detailed top view of a design  210  of the lead frame  204 . The lead frame design  210  comprises, among other things, multiple spines  212 . Each spine  212  is substantially straight (i.e., no considerable bends, curves, or other angles) as shown in the figure. However, various manufacturing process errors often cause the manufactured lead frame  204  spine of  FIG. 2   b  to differ in shape from the spine  212  of the lead frame design  210  in  FIG. 2   c .  FIGS. 3   a  and  3   b  illustrate this concept in greater detail than  FIGS. 2   b  and  2   c . In particular,  FIG. 3   a  shows a close-up view of the spine  212  of the lead frame design  210 . Each lead frame corner  214  of the spine  212  is shown to be at an angle of approximately 90 degrees. However, as illustrated in FIG.  3   b , due to manufacturing variations and errors, a manufactured lead frame  204  may result in a spine  300  having lead frame corners  302  that are rounded in shape.  
         [0004]     Referring to  FIG. 4   a , during a singulation process, the manufactured lead frame  204  is sawed or otherwise cut along singulation lines  401  to separate the unit packages  202  of the mold sheet  200  from each other. As shown in  FIG. 4   b , the singulation process may successfully separate the unit packages  202  by cutting along the singulation lines  401  of  FIG. 4   a , such that the spine  300  is removed. However, because the lead frame corners  302  are round in shape, many of the leads  304  may have one or more burrs  400 . Each burr  400  is simply a portion of the lead  304  to which the burr  400  is attached that was not removed during the singulation process because of the round shape of the lead frame corners  302 . In many cases, burrs  400  of adjacent leads  304  may be large enough to physically abut each other, thus forming short circuit pathways  402 . Each short circuit pathway  402  provides an electrical connection between adjacent leads  304 , thus short circuiting the leads  304  and rendering the unit package  202  comprising the leads  304  useless.  
       BRIEF SUMMARY  
       [0005]     The problems noted above are solved in large part by an integrated circuit package lead frame that prevents electrical short circuiting between leads due to burrs produced during the singulation process. One exemplary embodiment may comprise a plurality of leads and a spine electrically connected to said plurality of leads, said spine comprising indentations between a pair of said leads. The indentations prevent the pair of leads from becoming electrically connected to each other after a singulation process. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     For a detailed description of exemplary embodiments of the invention, reference will now be made to the accompanying drawings in which:  
         [0007]      FIG. 1  shows a side view of an IC embedded in a package electrically connected to a PCB;  
         [0008]      FIG. 2   a  shows a top view of a mold sheet comprising multiple unit packages;  
         [0009]      FIG. 2   b  shows a top view of an individual unit package having a lead frame;  
         [0010]      FIG. 2   c  shows a detailed, top view of a design of the lead frame and a lead frame spine;  
         [0011]      FIG. 3   a  shows a top view of lead frame corners of the lead frame design of  FIG. 2   c;    
         [0012]      FIG. 3   b  shows a top view of a manufactured lead frame having rounded corners;  
         [0013]      FIG. 4   a  shows a top view of singulation lines of the manufactured lead frame;  
         [0014]      FIG. 4   b  shows a top view of the manufactured lead frame after a singulation process, wherein adjacent leads are electrically connected to each other;  
         [0015]      FIG. 5   a  shows a top view of a design of a modified lead frame, in accordance with a preferred embodiment of the invention;  
         [0016]      FIG. 5   b  shows a top view of the modified lead frame, in accordance with a preferred embodiment of the invention;  
         [0017]      FIG. 5   c  shows a top view of the modified lead frame after a singulation process, in accordance with a preferred embodiment of the invention;  
         [0018]      FIG. 6  shows a flow diagram of an etching process implementing the modified lead frame; and  
         [0019]      FIG. 7  shows a flow diagram of a stamping process implementing the modified lead frame. 
     
    
     NOTATION AND NOMENCLATURE  
       [0020]     Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ” Also, the term “couple” or “couples” is intended to mean either an indirect or direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. The terms “etchings” and “indentations” are used interchangeably.  
       DETAILED DESCRIPTION  
       [0021]     The following discussion is directed to various embodiments of the invention. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment.  
         [0022]     Presented herein is a modified lead frame design that prevents the aforementioned problem of electrical short circuiting caused by burrs that are produced during the singulation (i.e., sawing) process.  FIG. 5   a  shows a modified lead frame design  500  comprising a spine  502  and multiple leads  504 . The modified lead frame design  500  comprises etchings (i.e, indentations)  506  along the spine  502  between the leads  504 . The etchings  506  may be substantially semicircular in shape and approximately 0.1 mm in diameter, although the scope of disclosure is not limited to this shape and/or size. The preferred embodiment of the design  500  comprises two etchings  506  between each pair of leads  504  as shown in the figure, although the scope of disclosure is not limited to any particular number of etchings.  
         [0023]     As previously discussed, because of various production errors, the lead frame  204  of  FIG. 3   b  has rounded corners  302  that were not present in the lead frame design  210  of  FIG. 3   a . The modified lead frame design  500  also may be subject to such a corner-rounding effect during production. However, the corner-rounding effect on the modified lead frame design  500  will not be substantial enough to produce burrs. More specifically,  FIG. 5   b  shows a modified lead frame  520  manufactured according to the modified lead frame design  500 . The modified lead frame  520  comprises lead frame corners  522 , leads  524 , a spine  526  and etchings  528  along the spine  526  between each pair of leads  524 .  
         [0024]     During the manufacturing process, lead frame corners  522  are subject to a rounding effect, thus producing corners  522  different from the corners  505  of the modified lead frame design  500 .  FIG. 5   c  shows the two separate portions of the manufactured, modified lead frame  520  after a singulation process is conducted along singulation lines  521  of  FIG. 5   b  such that the spine  526  is removed. Although the corners  522  are subject to a rounding effect, the etchings  528  of  FIG. 5   b  prevent the corners  522  from being rounded to a degree such that burrs are formed. Because no burrs are formed on any of the leads  524 , not one of the leads  524  is short circuited by coming into electrical contact with another lead  524 . Thus, the presence of the etchings  528  substantially reduces or eliminates the occurrence of short-circuited leads.  
         [0025]     The modified lead frame  520  of  FIG. 5   a  may be fabricated using any suitable technique. Two such techniques are etching and stamping, both of which will now be discussed in turn.  FIG. 6  shows an etching process that implements the modified lead frame  520 . The process may begin by obtaining flat, metal (e.g., copper) sheets, each side coated with photoresist film (block  600 ). The process is continued by performing surface cleaning and lamination (block  602 ). Next, the photoresist is exposed to a lead frame pattern (i.e., an etching mask) corresponding to the modified lead frame  520  with the aid of an ultraviolet light source and a precision pattern glass/film (block  604 ). Portions of the material that, are to be retained as metal are coated with resists. Conversely, portions of the material that are to be etched are kept free of resists (block  606 ). The material then is run through a series of nozzles spraying an etchant (block  608 ), after which the protective photoresist film is stripped from the finished lead frame (block  610 ). The etched portions subsequently are singulated (i.e., cut or sawed) into strips (block  612 ). The cut strips then are cleaned and plated (e.g., with silver) at the inner leads to facilitate wire bonding (block  614 ). Finally, the plated strips are taped with lead lock tape and downset (block  616 ).  
         [0026]      FIG. 7  shows a stamping process that implements the modified lead frame  520  of  FIG. 5   a . The process may begin by piercing sheet metal along the edges to create indexing holes that position the sheet during processing (block  700 ). The holes are used to advance the sheet metal strip through a stamping machine which uses die-and-punch sets (i.e., stamp designs) specific to the lead frame geometry of the modified lead frame  520  (block  702 ). The process is continued as a series of stamping operations that progressively approach the final lead frame geometry of the modified lead frame  520 , until the geometry of the modified lead frame  520  is obtained (block  704 ).  
         [0027]     The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.