Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-10-08
2004-08-24
Chang, Richard (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S854000, C029S827000, C029S855000, C174S050510, C174S050510, C257S676000, C257S692000, C257S693000, C257S696000, C361S773000
Reexamination Certificate
active
06779264
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin-sealed surface mount electronic device.
2. Description of the Prior Art
With reductions in the size of electronic equipment, there has been an increase in the use of surface mount semiconductor devices, such as diodes and transistors, and the size of these devices also is being reduced.
FIG. 3
shows the general construction of a surface mount diode of the past, FIG.
3
(A) being a plan view thereof, and FIG.
3
(B) being a cross-section view as seen from the direction indicated by the arrows along the line II—II in FIG.
3
(A).
The electronic device
100
of
FIG. 3
has a first external lead
110
, which has a electronic element placement pad (die pad)
111
for placement of an electronic element, and a second external lead
120
, which is disposed at a distance from the element placement pad
111
. A semiconductor element
130
is placed on the element placement pad
111
. A bonding wire
150
makes a connection between an external connection terminal of the semiconductor element
130
and the second external lead
120
. The semiconductor element
130
, the electronic element placement pad
111
, the inner lead part of the first external lead
110
, the inner lead part of the second external lead
120
, and the bonding wire
150
are sealed by a sealing resin
140
. As shown in this drawing, the first external lead
110
and the second external lead
120
are bent in an S shape, with one end of the leads
110
and
120
exposed to the outside of the sealing resin
140
, so as to form outer lead parts. The lower surfaces of the outer leads extend in a direction that is substantially parallel to the bottom surface
141
of the sealing resin
140
, and are substantially on the same plane as the bottom surface
141
of the sealing resin
140
.
The above-noted electronic device is manufactured by first punching out and bending a thin metal sheet to the appropriate shape to form a lead frame, onto which the semiconductor device is placed. Then, after making the prescribed connections, the device is sealed using sealing resin. The sealing with the sealing resin
140
is done within a die of the prescribed shape, so as to include the electronic element placement pad
111
, the inner lead part of the first external lead
110
, and the inner lead part of the second external lead
120
, resin being injected via a resin injection port
190
, indicated by the double-dot-dash line, on one of the shorter sides of the device.
The dimensions of a usual resin sealed electronic device of the past were approximately a vertical dimension (X-axis dimension L
X
in
FIG. 3
) of 1.3 mm, a horizontal dimension (Y-axis dimension L
Y
in
FIG. 3
) of 0.8 mm, and a height (Z-axis dimension H in
FIG. 3
) of 0.7 mm.
Because the thickness of the lead frame used in an electronic device of the past was 0.1 mm or greater, however, it was difficult to achieve a surface mount electronic device with a resin package having all of the vertical, horizontal, and height dimensions smaller than approximately 1 mm, including resin-sealed semiconductor devices making use of a semiconductor substrate.
Because the thickness of the lead frame is 0.1 mm or greater, the spacing between the element placement pad
111
of the first external lead
110
and the second external lead
120
grows to over 0.2 mm by the formation of the lead. Because of the relationship between such parameters as the lead bending depth, the associated thickness of the resin at the bottom of the element placement pad
111
that is required therefor, the lead length required for bending, and the establishment of a flat surface for placement of an element, in the case of diodes in particular, it was not possible to achieve a vertical length of less than 1.0 mm.
As electronic devices became smaller, because of the delicate bending shape of the bent parts
112
and
122
near the bottom surface of the sealing resin of the external leads, there was a tendency toward such problems as insufficiencies in the adhesion and filling in of sealing resin, the strength of the lead itself, and the adhesive strength between the lead and the sealing resin, and poor adhesion and filling in of solder used for mounting, and it was difficult to achieve an electronic component that provided improvements in these deficiencies.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an electronic device that solves the problems of the limitation in size reduction of surface mount resin sealed electronic devices in the past, and to enable the achievement of an electronic device having a resin package with vertical, horizontal, and height dimensions that are all below 1 mm.
It is another object of the present invention to provide a resin sealed surface mount electronic device that, even with a reduction in size of the electronic device, provides good filling in of sealing resin to the bent parts near the bottom surface of the sealing resin of the external leads, good adhesion strength between the leads and the sealing resin, and good strength in the leads themselves, and further providing good adhesion and filling in of solder when the device is mounted.
To achieve the above-noted object, the present invention has the following constitution.
Specifically, a first aspect of an electronic device according to the present invention has an electronic element, a first external lead with an element placement pad having a thickness t of less than 0.1 mm, and a second external lead that is disposed at a distance from the above-noted element placement pad, wherein the electronic element, the element placement pad, part of the first external lead, and part of the second external lead are sealed with a sealing resin, the first external lead being bent in an S shape, the bending depth d thereof being at least as large as the thickness t of the first external lead, and the thickness T of the resin on the non-device side of the element placement pad being smaller than the bending depth d.
In the first aspect of an electronic device of the present invention, the first external lead thickness t, the relationship of this thickness t to the bending depth d, and the relationship between the sealing resin thickness T at the bottom of the element placement pad and the bending depth d are established. By doing this, it is possible to limit the height of the electronic device, and to achieve the flat area required in the element placement pad. Additionally, because the spacing between the element placement pad and the second external lead can be made short, it is possible to reduce the dimension in the vertical direction.
In the configuration of the above-noted first aspect of the present invention, it is preferable that the spacing between the element placement pad and the second external lead be made no greater than 0.12 mm. Using this preferable configuration, it is possible to make a further reduction in the vertical-direction dimension of the electronic device.
In the above-noted configuration, it is preferable that the outer vertical, horizontal, and height dimensions of the sealing resin all be no greater than 1.0 mm. Using this preferable configuration, it is possible to achieve a compact electronic device that was not possible to achieve in the past, thereby contributing to the reduction in size of electronic equipment.
In the first aspect of the present invention, it is preferable that the width of the inner lead parts of the first and second external leads within the sealing resin be of a substantially uniform width and not broaden beyond the exposed part. Using this preferable configuration, it is possible to obtain a compact electronic device having a width (Y-direction dimension) that does not become large. The effect of reducing the package size is particularly significant in the case in of an electronic device having three or more terminals.
In the above-noted configuration, it is preferable that the thickness of the electronic element be substantially th
Fukazawa Hideki
Kobayashi Takeshi
Utsunomiya Satoshi
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