Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package
Reexamination Certificate
1999-06-30
2001-04-03
Abraham, Fetsum (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
C257S666000, C257S667000, C257S668000, C257S669000, C257S670000, C257S671000, C257S672000, C257S673000, C257S674000, C257S675000, C257S676000
Reexamination Certificate
active
06211563
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor package, and more particularly, to a semiconductor package wherein the chip is attached to the leadframe.
2. Description of the Prior Art
While the size of periphery of semiconductor chip is decreased, the position of bonding pads must be taken care simultaneously to prevent the supporting bar from contacting with the leadframe, which results in the failure of electronic property. In general, the package with LOC (lead on chip) structure increases the package density and improves the performance. In past, the conventional package includes the leadframe having the die pad for supporting the chip. In the conventional package having the leadframe, as shown in FIG.
1
and
FIG. 3
, the chip is positioned onto the die pad whose size is larger than that of the chip. To describe the conventional package having leadframe more detail, the chip
20
is attached to the die pad
80
and then electrically coupled to the leadframe
10
by the bonding wires
30
for transmitting signal; the molding compound is used to encapsulate the above leadframe
10
and the chip
20
to form a complete package body that also protect the bonding wires
30
from break resulted from the external force. However, the package body may be broken due to the stress resulted from “the popcorn effect”, caused by the evaporated moisture during the under-filling process for injecting the molding compound. To explain “the popcorn effect” more detail, the delamination or gap is liable to form between the die pad and the molding compound due to the poor adhesion. Therefore, the moisture may be absorbed by the delamination or gap within the package body during the storage stage, and then the moisture will be evapored after the package body being moved into the furnace for heating. Thus, the cracks caused by the evaporated moisture will break the package body. One method for solving “the popcorn effect” that cause the cracks is to carry out the baking process, which is executed before the package body moved into the furnace, to remove the moisture. Another method is to form a plurality of through holes, such as heat exhausting holes, to drive out the moisture.
SUMMARY OF THE INVENTION
One of the objects of the present invention is using the materials having lower moisture absorption to prevent “the popcorn effect”. Such the material, such as polyimide tape, also serves as the adhesive material to attach the chip to the leadframe. Another object of the present invention is to reduce the influence of unmatched CTE (coefficient of thermal expansion) on the conjunction between the metal and the high polymer.
The present invention also provides an adhesive material, such as the polyimide tape, by which the chip is attached to the leadframe. The present invention also provides the supporting bar to replace the die pad for supporting the chip. The chip is attached to th e supporting bar by thermal compress or the silver epoxy.
The package body of the present invention concludes the leadframe and the chip on the surface of the leadframe. The chip may be formed on the leadframe by the flip-On-chip technology. The chip is electrically coupled to the leadframe by the bonding wire, to electrically transmit signal to external. A plurality of external leads are connected to the supporting bar, respectively. The terminals of the supporting bar are connected to the separating portion of the leadframe and the other terminals of the supporting bar are used to support the chip. The separating portion is used to separate the leadframe from the side rail not shown) in the separating procedure.
Each terminal of the inner leads is connected to external leads by the separating portion of the leadframe. An adhesive material is attached to the surface of the leadframe. The size of the chip is larger than that of tape. The chip is attached to the supporting bar by thermal compress or the silver epoxy, it is worthy noting that the size of the chip is smaller than that of die pad to prevent the excessive silver epoxy oozes. Then, the molding compound is used to encapsulate the chip and the leadframe to form a complete package body.
In the preferred embodiment of the present invention, the package body having the leadframe and the adhesive material are used to eliminate unmatch of CTE (coefficient of thermal expansion) of conjunction between the metal and the high polymer material. The present invention also provides the adhesive material to replace the die pad. Thus, the problem resulted from stress is eliminated while the chip and the leadframe is encapsulated with the molding compound.
REFERENCES:
patent: 5612569 (1997-03-01), Murakami et al.
Abraham Fetsum
Sampo Semiconductor Cooperation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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