Package structure having tapering support bars and leads

Details Package structure having tapering support bars and leads Package structure having tapering support bars and leads

2000-09-25

2004-02-24

Lee, Eddie (Department: 2811)

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

Lead frame

With stress relief

C257S666000, C257S670000, C257S676000, C257S690000, C257S784000

Reexamination Certificate

active

06696749

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a package structure having tapering support bars and leads. More particularly, the present invention relates to a type of tapering support bar and lead used in the common lead frame of a quad flat non-leaded package.
2. Description of Related Art
Methods of manufacturing integrated circuits have developed quite rapidly. Besides the miniaturization of semiconductor devices, compact packages also have been developed. Nowadays, chip scale package (CSP) is one of the most common types of structures for housing a semiconductor chip. A chip scale package is only slightly larger than the semiconductor chip so that its volume occupation is relatively small and its signaling routes are relatively short. The carrier inside a chip scale package includes a lead frame, a flexible substrate and a rigid substrate. Because material cost of lead frames is low and easy to process, most chip scale packages use a lead frame. Quad flat non-leaded package (QFN) is one such lead frame based chip scale package. In general, a leadless chip scale package is used to encapsulate a low pin count semiconductor chip due to its short signaling route and small signal attenuation.
FIG. 1
is a schematic cross-sectional view of a conventional quad flat non-leaded package.
FIG. 2
is a bottom view of the quad flat non-leaded package shown in FIG.
1
.
As shown in
FIGS. 1 and 2
, structure and technique for fabricating a quad flat non-leaded package (QFN) is disclosed in U.S. Pat. No. 5,942,794 (Matsushita, 1999). The QFN structure is built around a lead frame. The lead frame has a die pad
100
in the middle surrounded by a plurality of leads
102
. The QFN structure also includes a die
104
having an active surface
106
and a backside
108
. The active surface
106
has a plurality of bonding pads
110
thereon serving as connection points from the die
104
to devices outside the package. The backside
108
of the die
104
is bonded to the die pad
100
using an adhesive material
112
. The bonding pads
110
are electrically connected to the leads
102
using conductive wires
114
. In general, the die
104
, the die pad
100
, the conductive wire
114
and the upper surface
118
a
of the leads
102
are enclosed by plastic material
116
. Therefore, only the lower surface
118
b
and side surface
118
c
of the leads are exposed as external contacts.
In the fabrication of a leadless package, the interconnected packages must be separated into individual packages in a singulation process after the lead frame is encapsulated by a plastic material. However, sudden stress on the leads
102
or support bar section hardly can be avoided regardless if the singulation is conducted by sawing or punching. This type of impact often leads to a slight parting between the lead or support bar and the packaging material and results in delamination. Hence, moisture sensitivity level (MSL) of the product will be decreased, and reliability of the product is compromised.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a lead frame having tapering support bars and leads capable of reducing delamination of the plastic material in an integrated circuit package and hence increasing reliability of the package.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a package having tapering support bars and leads. The package includes at least a lead frame, a die, a plurality of conductive wires and a plastic housing. The lead frame has a first surface and includes at least a package unit. The package unit includes a die pad, a plurality of leads and a plurality of support bars. The die pad is positioned in the middle. The leads and support bars are distributed around the periphery of the package unit. In addition, the width of the leads and support bars decreases gradually from a location close to the die pad towards the peripheral region. The leads and support bars have a rectangular or trapezoidal cross-section. A die is bonded on the surface of the die pad, and the die is electrically connected to the leads on the lead frame via a plurality of conductive wires. Plastic material such as epoxy resin encloses the die, the conductive wires and the first surface of the lead frame.
The gradual reduction of the width of the leads and support bars from a region close to the die pad towards the peripheral region of the package unit can reduce some of the pulling stress in a punch-shearing operation. Consequently, bonding strength between the leads and support bars on one hand and the encapsulating material on another is increased, and delamination of the plastic body of the package is prevented.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.


REFERENCES:
patent: 5521428 (1996-05-01), Hollingsworth et al.
patent: 5594234 (1997-01-01), Carter, Jr. et al.
patent: 5654585 (1997-08-01), Nishikawa
patent: 5821610 (1998-10-01), Nishikawa
patent: 6008528 (1999-12-01), Go et al.
patent: 6211462 (2001-04-01), Carter, Jr. et al.
patent: 6307755 (2001-10-01), Williams et al.
patent: 6392295 (2002-05-01), Iwaya et al.
patent: 404014250 (1992-01-01), None
IBM Technical Disclosure Bulletin, vol. 35, Issue 6, pp. 361 and 361, Fig. 1a-f, Nov. 1992.

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