Leadless leadframe package design that provides a greater...

Details Leadless leadframe package design that provides a greater... Leadless leadframe package design that provides a greater...

2003-08-11

2004-11-16

Lee, Eddie (Department: 2811)

Active solid-state devices (e.g., transistors, solid-state diode

Lead frame

C257S672000, C257S684000

Reexamination Certificate

active

06818970

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to the packaging of small-scale integrated circuits. More particularly, the invention relates to leadless leadframe package designs.
BACKGROUND
A leadless leadframe package (LLP) is a relatively new integrated circuit package design that contemplates the use of a metal (typically copper) substrate in the formation of a chip scale package (CSP). As illustrated in
FIGS. 1A and 1B
, in typical leadless leadframe packages, a copper leadframe strip or panel
10
is patterned to define a plurality of arrays or matrixes
11
of semiconductor device areas
12
. Each device area
12
includes a die attach pad
13
and a plurality of contacts
15
disposed about their associated die attach pad
13
. Very fine tie bars
16
are used to support the die attach pads
13
and contacts
15
.
FIG. 2
illustrates a cross-sectional view of a typical resulting leadless leadframe package
14
. The die attach pad
13
supports a die
17
which is electrically connected to its associated contacts
15
by bonding wires
18
. A molded cap
20
encapsulates the die
17
and bonding wires
18
, and fills the gaps between the die attach pad
13
and the contacts
15
thereby serving to hold the contacts
15
in place. It should be appreciated that during singulation of the individual packages
14
, the tie bars
16
are cut and therefore the only materials holding the contacts
15
in place is the molding material. The resulting packaged chip can then be surface mounted on a printed circuit board or other substrate using conventional techniques.
FIG. 3A
illustrates a bottom plan, perspective view of an improved leadless leadframe package
14
′, while
FIG. 3B
illustrates a fragmentary and enlarged view of one of the contacts
15
and the molding material immediately surrounding the contact
15
. In this improved design, an edge portion of each contact
15
has been removed to define a stem
26
, which extends from an interior surface
25
of the contact
15
toward a respective peripheral surface
24
. The molding material surrounds the stems
26
while leaving a peripheral surface
27
of the stems
26
exposed on the peripheral surfaces
24
of the package
14
′. The portion of the molded cap
20
that covers the bottom surface
28
of the stem
26
is indicated by the phantom lines
29
, and is referred to as the bar portion
30
. These bar portions
30
, integrally formed into the molded cap
20
, function to lock the contact
15
into the molded cap
20
so that they are not pulled out by the singulating saw blade during the singulation process. Furthermore, the thinned peripheral edges of the contacts
15
reduce stress on the singulating saw blade since it is only required to cut through a smaller amount of metal during the singulation process. For further details, refer to U.S. patent application Ser. No. 09/470,826.
Although the contacts
15
of this package design
14
′ provide the above-mentioned advantages, the bar portions
30
have been found to occasionally break-away from the molded cap
20
by the frictional forces introduced during singulation. This results in structurally damaged leadless leadframe packages. Consequently, it would be desirable to further improve leadless leadframe package designs to have a greater degree of structural integrity.
SUMMARY
The present invention is directed towards a leadless leadframe package that has a greater degree of structural integrity such that portions of the molded cap do not break off during singulation processes. One aspect of the invention pertains to a leadless leadframe package that has a plurality of contacts, which have contact surfaces on the bottom surface of the package. At least some of the contacts have integrally formed stems that extend outward to the peripheral surface of the package. These stems have heights and widths less than the heights and widths of their corresponding contacts. An integrated circuit die is electrically coupled to at least some of the contacts. A molded cap encapsulates at least a portion of the die, the stems and the contacts. The molded cap leaves the contact surfaces of the contacts exposed on the bottom surface of the package, leaves a peripheral surface of the stems exposed on the peripheral surface of the package, and covers a bottom surface of each of the stems.
Another aspect of the invention pertains to a leadless leadframe panel assembly having a conductive substrate panel that has at least one array of device areas, each array of device areas having a plurality of tie bars and a plurality of contacts. The contacts have contact surfaces on the bottom surface of the leadless leadframe panel assembly. The contacts also have integrally formed stems that extend towards and connect to one of the tie bars. The stems have widths and heights that are less than the widths and heights of their corresponding contacts. A plurality of dice are mounted on the leadframe panel and each die is electrically connected to contacts within an associated device area A molded cap encapsulates at least a portion of each die, the tie bars, the stems and the contacts while leaving the contact surfaces of the contacts exposed and covering a bottom surface of each of the stems.
These and other features and advantages of the present invention will be presented in more detail in the following specification of the invention and the accompanying figures that illustrate by way of example the principles of the invention.


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