Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame
Reexamination Certificate
1998-11-09
2001-10-23
Williams, Alexander O. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
C257S696000, C257S698000, C257S673000, C257S775000, C257S797000, C257S670000, C257S672000, C257S692000, C257S690000, C029S827000
Reexamination Certificate
active
06307253
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a lead frame used for making semiconductor devices such as a diode and a transistor for example. The present invention also relates to a semiconductor device using the lead frame.
BACKGROUND ART
A conventional type of semiconductor device may have the following arrangement. Specifically, the semiconductor device includes partially overlapped lead terminals extending in the opposite directions, a semiconductor element (chip) interposed between the partially overlapped lead terminals, and a mold member made of synthetic resin for packaging the semiconductor element together with the members around the semiconductor element. The applicant of the present invention disclosed a lead frame used for making the semiconductor device of the above type in Japanese Patent Publication Nos. 6-36422 and 6-71015. The conventional lead frame is shown in
FIGS. 27-29
of the accompanying drawings of this application.
The conventional lead frame
20
includes at least two elongated side frames
21
,
22
extending in parallel to each other, and section bars
23
connecting the side frames
21
,
22
at predetermined intervals. Each section bar
23
has two joint portions
23
a
having a relatively small width. Thus, the side frames
21
,
22
can be shifted longitudinally with respect to each other. The side frame
21
is formed with a plurality of first lead terminals
24
, while the side frame
22
is formed with a corresponding number of second lead terminals
25
. The free end portions of the paired first and second lead terminals
24
,
25
are arranged close to each other. The side frames
21
,
22
are provided with engaging holes
26
at predetermined intervals. These holes are brought into engagement with sprockets (not shown) used to move the side frames
21
,
22
longitudinally thereof.
The semiconductor device D is made through the following steps:
{circle around (1)} A semiconductor element T is bonded to the free end portion
24
a
of the first lead terminal
24
;
{circle around (2)} By moving the side frames
21
,
22
at different rates, the free end portion
25
a
of the second lead terminal
25
is put on the semiconductor element T which is bonded to the first lead terminal
24
;
{circle around (3)} The free end portion
25
a
of the second lead terminal
25
is bonded to the semiconductor element T by soldering, conductive adhesive, or pressure welding for example;
{circle around (4)} With their free end portions
24
a
,
25
a
overlapped, the lead terminals
24
,
25
are moved to a synthetic resin molding section, at which the semiconductor element T together with other members around the semiconductor element is enclosed by a mold member M of synthetic resin, as indicated by single-dot chain lines in
FIG. 29
; and
{circle around (5)} The lead terminals
24
,
25
are cut off at their joint portions after continuity across the terminals is inspected.
According to the prior art, a plurality of semiconductor devices D can be made using a single lead frame
20
. Thus, the manufacturing efficiency of the semiconductor devices D is remarkably improved.
In accordance with the above prior art, the section bars
23
are deformed when the side frames
21
,
22
are shifted longitudinally. However, the joint portions
23
a
of each section bar
23
do not entirely undergo plastic deformation but are subjected to elastic deformation to some extent. Thus, due to restoring force from the spring-back action of each section bar
23
, the side frames
21
,
22
are urged toward the initial positions the frames were held in before the shifting operation. Consequently, the lead terminals
24
,
25
are slightly bent. As a result, the elastic force of these terminals
24
,
25
may work to cause the lead terminals to be detached from the semiconductor element T, which leads to defective products with improper electrical continuity.
One way to deal with the above problems may be to move the side frames
21
,
22
without providing any play between the sprocket and the engaging holes
26
. In this way, the spring-back action of the section bars
23
may be completely restrained. In practice however, it is difficult to eliminate the play between the sprocket and the engaging holes
26
. Thus, conventionally the defective connection due to the spring-back of the section bars
23
was not completely prevented.
The above problems become more serious in an instance where more than one second lead terminals (corresponding to a single first lead terminal) are bonded to a semiconductor element. Specifically, when use is made of a lead frame provided with a single first lead terminal and more than one second lead terminals to be bonded to a single semiconductor element, the rigidity of the lead terminals put together is increased. Thus, the strength of the detaching force to act on the bonding region between the lead terminals and the semiconductor element is increased. As a result, more lead terminals may be unduly detached from semiconductor elements, thereby increasing the number of defective products.
DISCLOSURE OF THE INVENTION
It is, therefore, an object of the present invention to overcome the problems described above.
According to a first aspect of the present invention, there is provided a lead frame including at least one pair of elongated side frames extending in parallel to each other, and section bars connecting the side frames at predetermined intervals.
One of the side frames is formed with a plurality of first lead terminals which are arranged at predetermined intervals and extend toward another side frame. Each first lead terminal has a free end portion and a base portion. Said another side frame is formed with second lead terminals corresponding to the first lead terminals. Each second lead terminal has a free end portion and a base portion. The first and the second lead terminals are arranged so that the free end portions of the first and the second lead terminals are overlapped when the side frames are shifted longitudinally.
Further, at least one of the first and the second lead terminals includes a predetermined area formed with a weaker portion having a relatively small bending strength.
The weaker portion may be provided in various ways. For instance, the entire free end portion of a lead terminal may have a relatively small width. The free end portion or base portion of a lead terminal may have a constricted portion. Or a hole may be formed at the free end portion or base portion of a lead terminal. It is also possible to cause the free end portion or base portion of a lead terminal to have a smaller thickness in a limited area. A cutout may be formed at the free end portion or base portion of a lead terminal.
Further, for purposes of providing a weaker portion, some of the above arrangements (namely, a narrowed portion, a constricted portion, a hole and the like) may be utilized in combination. Still further, the first and the second lead terminals may be provided with weaker portions of different arrangements, or more than one weaker portions may be formed in a single lead terminal.
Preferably, each of the first lead terminal and the second lead terminal is provided with a weaker portion.
Preferably, a weaker portion formed in a lead terminal is arranged either at a free end region which will be enclosed by a package of synthetic resin or at an area which will remain to be connected to the side frame after the cutting operation. This is because if a product semiconductor device includes a weaker portion at the exposed part of a lead terminal projecting from the package, the bonding operation of the semiconductor device onto a circuit board may not be properly performed. However, if a semiconductor device functions properly, it is possible to form a weaker portion at the exposed part of a lead terminal projecting from the package.
A single first lead terminal may be arranged to correspond to a single second lead terminal. Alternatively, a single first lead terminal may be arranged to correspond to more than one second lead term
Imai Hiroshi
Yamamoto Masao
Merchant & Gould P.C.
Rohm & Co., Ltd.
Williams Alexander O.
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