Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With contact or lead
Reexamination Certificate
1997-09-08
2001-01-30
Picard, Leo P. (Department: 2835)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With contact or lead
C257S690000, C257S692000, C257S696000, C257S695000
Reexamination Certificate
active
06181003
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an improvement applicable to a semiconductor device packaged in a plastic package and to a method for producing a semiconductor device packaged in a plastic package. More specifically, this invention relates to an improvement applicable to a semiconductor device packaged in a plastic package and a method for production thereof, the improvement being developed to increase the reliability thereof by reducing possibilities in which a solder layer connecting a lead and a foot print of a printed board is cracked, resulting in an incomplete mechanical and electrical connection between a lead and a printed board.
BACKGROUND OF THE INVENTION
In the wake of the quick development in the technical field of an
C, a memory card and the like, requirement to make them thinner and smaller in size is increasingly more severe. Such a requirement is directed also to a semiconductor device employable for an
C and/or a memory card.
Referring to
FIG. 1
illustrating a cross section of a semiconductor device packaged in a plastic package available in the prior art, a plurality of leads
603
(The leads
603
are arranged on a semiconductor device chip in parallel to one another.) are adhered to the top surface
601
a
(the surface under which monolithic electronic components are produced and actually the bottom surface in
FIG. 1
) of a semiconductor device chip
601
by employing an adhesive tape e.g. polyimide resin type
602
. Each of the leads
603
is bonded with each of bonding pads
104
a
produced on the top surface of the semiconductor device chip
601
, by an Au wire
604
. The semiconductor device chip
601
provided the leads
603
is molded in a plastic mold e.g. a mold of polyimide resin
605
, remaining the top surface of the ends
603
a
of the leads
603
and the bottom surface
601
b
of the semiconductor device chip
601
unmolded. Although the thickness of the plastic mold
605
is in the range of 0.3-0.4 mm in the vertical direction, it is marginal on the side surface of the semiconductor device chip
601
. This is for the purpose to make the thickness of a finished semiconductor device packaged in a plastic package thin and to make the horizontal area thereof small.
After turning the finished semiconductor device packaged in a plastic package upside down, the ends
603
a
of the leads
603
are soldered with foot prints
610
arranged on a printed board
610
a.
In this manner, electric connection is secured between the end
603
a
of the lead
603
and the foot prints
610
by means of a solder lump
611
.
Since a semiconductor device chip
601
is mounted on a printed board in an upside-down position, and since the bottom surface thereof is not covered by a plastic mold e.g. a mold of polyimide resin
605
in the prior art, the thickness of a finished semiconductor device packaged in a plastic package is sizably reduced.
The foregoing semiconductor device packaged in a plastic package available in the prior art is, however, involved with a drawback wherein the solder lumps
611
connecting the end
603
a
of the leads
603
and the foot print
610
arranged on the printed board
610
a
is inclined to be cracked, resulting in unsatisfactory mechanical and electric connection between the end
603
a
and the foot print
610
. This is of course a parameter to degrade the reliability of a semiconductor device packaged in a plastic package from electrical and mechanical viewpoints.
This adverse phenomenon is assumed to be caused by large difference in coefficient of thermal expansion between a semiconductor device chip and a printed board and by weak connection between a lead
603
and a foot print
610
. In other words, the length of a lead
603
is designed to be short for the purpose to reduce the horizontal area of a semiconductor device packaged in a plastic package. Therefore, it is difficult for the lead
603
to absorb a stress derived from a difference in coefficient of thermal expansion between a semiconductor device chip and a printed board. In addition, a small area of the end
603
a
of a lead
603
which is caused by the design in which the length of the lead
603
is made short, causes to make the connection strength weak between the end
603
a
of a lead
603
and the foot print
610
.
In the foregoing environments, development of a semiconductor device packaged in a plastic package, wherein the connection between a lead and a printed board is strong, thereby the semiconductor device packaged in a plastic package is reliable from electrical and mechanical viewpoints is strongly required.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, an object of this invention is to provide a semiconductor device packaged in a plastic package, wherein the connection between a lead and a printed board is strong, thereby the semiconductor device packaged in a plastic package is reliable from electrical and mechanical viewpoints.
The other object of this invention is to provide a method employable for producing the foregoing semiconductor device packaged in a plastic package.
To achieve the first one of the foregoing objects, a semiconductor device packaged in a plastic package in accordance with a first embodiment of this invention comprising:
a semiconductor device chip,
a plurality of leads arranged along the top surface of the semiconductor device chip in parallel to one another from the central part of the semiconductor device chip toward the edge of the semiconductor device chip,
a plastic mold covering the top and side surfaces of the semiconductor device chip,
wherein each of the leads is bent at location close to the edge of the semiconductor device chip or at location which is not so remote from the edge of the semiconductor device chip, to make the shape of the lead a J-shape and to cause the end of the lead to cover the top surface of the plastic mold.
To achieve the first one of the foregoing object, a semiconductor device packaged in a plastic package in accordance with a second embodiment of this invention comprising:
a semiconductor device chip,
a plurality of leads arranged along the top surface of the semiconductor device chip in parallel to one another from the central part of the semiconductor device chip toward the edge of the semiconductor device chip,
a plastic mold covering the top and side surfaces of the semiconductor device chip,
wherein the plastic mold produced on the top surface of the semiconductor device chip is limited to the central part of the semiconductor device chip and each of the leads is bent at the edge of the plastic mold produced on the central part of the top surface of the semiconductor device chip, to make the shape of the lead a U-shape and to cause the end of the lead to cover the top surface of the plastic mold.
To achieve the first one of the foregoing object, a semiconductor device packaged in a plastic package in accordance with a third embodiment of this invention comprising:
a semiconductor device chip,
a plurality of leads arranged along the top surface of the semiconductor device chip in parallel to one another from the central part of the semiconductor device chip toward the edge of the semiconductor device chip,
a plastic mold covering the top and side surfaces of the semiconductor device chip,
wherein the plastic mold produced on the top surface of the semiconductor device chip is limited to the central part of the semiconductor device chip and each of the leads is bent at location close to the edge of the semiconductor device chip or at location slightly remote from the edge toward the central part of the semiconductor device chip, not to cover the top surface of the plastic mold.
In any of the semiconductor devices packaged in a plastic package in accordance with the first through third embodiments of this invention, it is practical to use epoxy resin for the plastic mold.
In any of the semiconductor devices packaged in a plastic package in accordance with the first through third embodiments of this invention, it is practical to adhere the leads to the semiconductor de
Duong Hung Van
Jones Volentine, L.L.P.
OKI Electric Industry Co., Ltd.
Picard Leo P.
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