Radiant energy – Photocells; circuits and apparatus – Housings
Reexamination Certificate
2000-11-16
2003-07-22
Kim, Robert H. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
Housings
C250S551000
Reexamination Certificate
active
06596986
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a reflection sensor used for detecting presence of a detection object. More specifically, the present invention relates to a reflection sensor surface-mounted on a substrate.
BACKGROUND ART
As a sensor for detecting presence of a detection object, a contact sensor incorporating a micro-switch and a non-contact sensor such as a photo-interrupter are used conventionally. Generally, the photo-interrupter includes so-called transmission photo-interrupters and reflection photo-interrupters. The transmission photo-interrupter comprises a light emitting element and a light receiving element faced to each other. On the other hand, the reflection photo-interrupter comprises the light emitting element and the light receiving element faced in a same direction.
Recently, demand for the reflection photo-interrupter is greater than for the transmission photo-interrupter. A reason for this is that the reflection photo-interrupter has a construction which allows mounting on a greater variety of locations than does the transmission photo-interrupter.
Now, a conventional reflection sensor (photo-interrupter) will be described with reference to
FIG. 9
to
FIG. 21. A
reflection sensor
1
shown in the figures has a generally rectangular parallelepiped protective package
2
(FIG.
19
), in which a light emitting element
31
and a light receiving element
32
are buried (FIGS.
20
and
21
).
The protective package
2
includes a first resin body
21
enclosing the light emitting element
31
, a second resin body
22
enclosing the light receiving element
32
, and a third resin body
25
for holding these two resin bodies
21
,
22
. As shown in
FIG. 19
, the first and the second resin bodies
21
,
22
have respective upper surfaces exposed to outside, but the other surfaces are covered by the third resin body
25
.
The first and the second resin bodies
21
,
22
are transparent, allowing light to pass through. The first and the second resin bodies
21
,
22
are formed of an epoxy resin for example. On the other hand, the third resin body
25
is non-transparent and therefore does not allow the light to pass through. The third resin body
25
is formed of a black PPS (polyphenylene sulfide) for example.
The epoxy resin has a linear expansion coefficient of 11~12×10
−5
/° C. for example, whereas the PPS has a linear expansion coefficient of 6~7×10
−5
/° C. for example. Therefore, when heated, the first and the second resin bodies
21
,
22
made of the epoxy resin expand at a greater rate than does the third resin body
25
which is made of the PPS.
As shown in
FIG. 20
, the light emitting element
31
is electrically bonded to a lead
5
a
, and electrically connected to another lead
5
b
via a wire
4
a
. Likewise, the light receiving element
32
is electrically bonded to a lead
5
c
, and electrically connected to another lead
5
d
via a wire
4
b
. The leads
5
a
~
5
d
have free end portions soldered to electrode pads P provided on a substrate S respectively. The soldering can be achieved by using a solder re-flow method to be described here below.
First, solder paste H is applied to each of the electrode pads P. Next, the reflection sensor
1
is placed on the substrate S so that the free end portions of the leads
5
a
~
5
d
are located on the corresponding electrode pads P. The substrate S and the reflection sensor
1
in this state is brought in a heating furnace and heated. The temperature in the heating furnace at this time is not lower than 200° C. for example. Thus, the applied solder paste melts thereby wetting the free end portions of the leads
5
a
~
5
d
and the electrode pads P. Then, the substrate S and the reflection sensor
1
is taken out of the heating furnace and allowed to cool, so that the solder paste sets to fix the reflection sensor
1
onto the substrate S.
The conventional reflection sensor
1
with the above described construction is known to have the following problems.
Specifically, as has been described earlier, the first and the second resin bodies
21
,
22
thermally expand at a greater rate than does the third resin body
25
. However, the first and the second resin bodies
21
,
22
are surrounded by the third resin body
25
except for the respective upper surfaces. Therefore, when the reflection sensor
1
is heated, the first and the second resin bodies
21
,
22
expand only in an upward direction as indicated by a dashed line in FIG.
20
. When the resin bodies
21
,
22
expand only in one direction as in the above, the wire
4
a
,
4
b
can be pulled off the lead
5
b
,
5
d
respectively.
Further, the conventional reflection sensor
1
has the following problem. Specifically, as has been described earlier, the reflection sensor
1
is heated to the temperature not lower than 200° C. in the heating furnace, and then cooled. During the cooling, the molten solder paste H becomes solid at a temperature of about 180° C. for example, fixing the leads
5
a
~
5
d
onto the electrically conductive pads P. However, at this particular point (at the temperature of 180° C.), the protective package
2
(especially the first and the second resin bodies
21
,
22
) is still in a thermally expanded state in a course of thermal shrinkage with ongoing decrease in temperature.
If the protective package shrinks while the leads
5
a
~
5
d
have been fixed onto the conductive pads P, a force to pull the leads
5
a
~
5
d
off the protective package
2
is exerted. This generate excessive stress on the wires
4
a
,
4
b
, and can pull the wires
4
a
,
4
b
off the leads
5
a
~
5
d.
DISCLOSURE OF THE INVENTION
It is therefore an object of the present invention to provide a reflection sensor capable of solving the above described problem.
A reflection sensor provided by a first aspect of the present invention comprises:
a light emitting element;
a light receiving element cooperative with the light emitting element;
a first resin body enclosing the light emitting element and including a first surface and a second surface away from the first surface;
a second resin body enclosing the light receiving element and including a third surface and a fourth surface away from the third surface;
a third resin body holding the first and the second resin bodies;
a first pair of leads electrically connected to the light emitting element;
a second pair of leads electrically connected to the light receiving element;
wherein the first surface and the second surface of the first resin body and the third surface and the fourth surface of the second resin body are respectively exposed to outside.
According to the arrangement as described above, each of the first resin body and the second resin body can thermally expand uniformly in upward and downward directions. Therefore, it becomes possible to effectively prevent unwanted stress from developing within the first resin body and the second resin body.
According to a preferred embodiment of the present invention, the first and the second resin bodies are transparent whereas the third resin body is non-transparent. Here, the term “transparent” is used for a case in which the resin body allows a predetermined light to pass through. Therefore, if a resin body which looks black to human eyes allows an infrared ray for example, the resin body is described as “transparent” to the infrared ray.
According to the above preferred embodiment, the first and the second resin bodies have a thermal expansion coefficient larger than that of the third resin body.
Preferably, the first and the second resin bodies are formed of an epoxy resin whereas the third resin body is formed of a heat resistant resin.
Preferably, the second surface of the first resin body provides a bottom surface of the first resin body whereas the fourth surface of the second resin body provides a bottom surface of the second resin body.
Preferably, the bottom surface of the first resin body and the bottom surface of the second resin body are covered only partially by the third resin body.
The leads of the
Sano Masashi
Suzuki Nobuaki
Suzuki Shin'ichi
Bednarek Michael D.
Kim Robert H.
Rohm & Co., Ltd.
Shaw Pittman LLP
Song Hoon K.
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