Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame
Reexamination Certificate
1998-06-05
2001-05-08
Whitehead, Jr., Carl (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
C257S669000, C257S690000, C257S784000
Reexamination Certificate
active
06229199
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a packaged semiconductor device of the type which provides proper electrical conduction between bondwires and lead terminals within a resin package. The present invention also relates to a bonding structure concerning bondwires and leads used for such a packaged semiconductor device.
2. Description of the Related Art
An example of a conventional packaged semiconductor device is shown in
FIGS. 7A and 7B
. Of these figures,
FIG. 7A
is a sectional view showing the conventional semiconductor device, while
FIG. 7B
is an enlarged view of the encircled portion S in FIG.
7
A.
The conventional packaged semiconductor device generally designated by reference
1
includes a semiconductor chip
10
, a die pad
11
for mounting the chip
10
, and a plurality of leads
13
electrically connected to the chip
10
via bondwires
12
. Each bondwire
12
, which may be made of gold for example, has a first end
12
a
attached to a bonding pad (not shown) formed on the upper surface of the chip
10
, and a second end
12
b
attached to the upper surface of the inner portion
13
a
of a corresponding lead
13
. The attaching of the bondwire
12
may be performed by a well-known thermocompression bonding method.
The semiconductor device
1
also includes a resin package
14
made of a thermosetting resin material such as epoxy. As shown in
FIG. 7A
, the resin package entirely encloses the chip
10
and the bondwires
12
, while partially enclosing the leads
13
. In this arrangement, each lead
13
has an inner portion
13
a
located within the package
14
, and an outer portion
13
b
extended out of the package. As can be seen, the outer portion
13
b
first extends obliquely downward, and then bends to extend horizontally in its free end. The horizontal free end is in alignment with the bottom surface of the package
14
, so that the semiconductor device
1
is easily mounted onto a printed circuit board (not shown).
As shown in
FIG. 7B
, the second end
12
b
of the bondwire
12
is reduced in thickness. This is because the above end is subject to compression by a presser member of a bonding machine used for the above-mentioned thermocompression bonding method. From the compressed second end
12
b
, a non-compressed portion
12
c
having a uniform diameter d extends obliquely upward. Conventionally, the angle &agr; between the non-compressed portion
12
c
and the upper surface of the inner portion
13
a
is substantially equal to or greater than 30 degrees. There is a bending portion
12
d
between the compressed second end
12
b
and the non-compressed portion
12
c.
The packaged semiconductor device
1
having the above arrangement is conveniently fixed to a printed circuit board by reflow soldering, as described below.
First, the semiconductor device
1
is placed on a printed circuit board in a manner such that the horizontal free ends of the respective leads
13
overlap solder paste which is applied beforehand to the circuit board. Then, the semiconductor device
1
, together with the printed circuit board, is brought into a suitable furnace to be heated. At this stage, the solder paste arranged at each free end is liquidized due to heat, immersing the corresponding free end. Finally, by cooling the semiconductor device
1
and the printed circuit board, the melted solder material is solidified to fix the respective leads
13
to the circuit board.
However, the above semiconductor device
1
has been found to have the following disadvantage.
Specifically, when the semiconductor device
1
is heated in the furnace for melting the solder paste, the resin package
14
and bondwires
12
of the device
1
will expand due to the heat. Here, it should be noted that the expansion of the resin package
14
tends to be greater than that of the bondwires
12
. Because of this, the resin package
14
, as expanding, will give additional tension to the bondwire
12
. When this happens, undesired stress due to the additional tension is concentrated at the bending portion
12
d
of the bondwire
12
. Consequently, a crack or even larger break may be formed in a certain area of the compressed second end
12
b
of the bondwire
12
, so that the product semiconductor device
1
may fail to provide intended function.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a packaged semiconductor device capable of overcoming the problem described above.
Another object of the present invention is to provide a bonding structure concerning a bondwire and a lead, wherein the bondwire is reliably fixed to the lead without forming a crack in a compressed portion of the bondwire.
According to a first aspect of the present invention, there is provided a packaged semiconductor device comprising:
a semiconductor chip;
a die pad for mounting the semiconductor chip;
at least one bondwire having a first end connected to the semiconductor chip, a second end opposite to the first end, and a transitional portion extending from the second end;
at least one lead having an inner portion connected to the second end of the bondwire and an outer portion; and
a resin package for enclosing the semiconductor chip, the die pad, the bondwire and the inner portion of the lead;
wherein an angle defined between the inner portion of the lead and the transitional portion of the bondwire is no greater than 15 degrees.
With such an arrangement, since the angle between the inner portion of the lead and the transitional portion of the bondwire is rendered sufficiently small, stress concentration at a bent portion between the second end and transitional portion of the bondwire is remarkably reduced. Thus, occurrence of a crack at the second end of the bondwire is prevented to a great extent.
According to a preferred embodiment, a length of the transitional portion is at least twice as great as a diameter of the transitional portion. More preferably, the above angle may be no greater than 10 degrees, or even 5 degrees
According to a second aspect of the present invention, there is provided a packaged semiconductor device comprising:
a semiconductor chip;
a die pad for mounting the semiconductor chip;
at least one bondwire having a first end connected to the semiconductor chip, a second end opposite to the first end, and a transitional portion extending from the second end, the second end having a contact surface;
at least one lead having an inner portion attached to the contact surface of the second end of the bondwire, and an outer portion; and
a resin package for enclosing the semiconductor chip, the die pad, the bondwire and the inner portion of the lead;
wherein an angle defined between the contact surface of the second end of the bondwire and the transitional portion of the bondwire is no greater than 15 degrees.
The second end of the bondwire may be smaller in thickness than the transitional portion of the bondwire.
According to a third aspect of the present invention, there is provided a packaged semiconductor device comprising:
a semiconductor chip;
a die pad for mounting the semiconductor chip;
at least one bondwire having a first end connected to the semiconductor chip, a second end opposite to the first end, and a transitional portion extending from the second end, the transitional portion including a first section directly continuous with the second end of the bondwire and a second section continuous with the first section;
at least one lead having an inner portion connected to the second end of the bondwire and an outer portion; and
a resin package for enclosing the semiconductor chip, the die pad, the bondwire and the inner portion of the lead;
wherein the first section of the transitional portion extends in parallel to the inner portion of the lead in close contact therewith.
According to a fourth aspect of the present invention, there is provided a bonding structure comprising:
a bondwire including a connection end and a transitional portion extending from the connection end; and
a lead attached to the conne
Davis Jamie L.
Jr. Carl Whitehead
Merchant & Gould P.C.
Rohm & Co., Ltd.
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