U.S. patent application number 09/134041 was filed with the patent office on 2001-08-30 for method of making an electronic device.
Invention is credited to HAMATANI, JUNICHI, TSURUHARA, SATOSHI.
Application Number | 20010016978 09/134041 |
Document ID | / |
Family ID | 17265384 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010016978 |
Kind Code |
A1 |
HAMATANI, JUNICHI ; et
al. |
August 30, 2001 |
METHOD OF MAKING AN ELECTRONIC DEVICE
Abstract
An electronic device containing an electronic element such as a
thermistor element is produced first by providing the element with
electrodes formed on its two main surfaces facing outward away from
each other, at least two terminals and a casing. Each terminal has
a contact part for contacting one of the electrodes and an extended
part extending from the contact part. The contact part of at least
one of the terminals is elastic and bendable. The terminals and the
electronic element are inserted into the casing either sequentially
or simultaneously as an assembly in any of the ways such that the
electrodes on the electronic element are not rubbed directly
against the contact parts of the terminals. This may be done by
disposing flexible guide plates over the contact parts such that
the electrodes will glide over these guide plates as the electronic
element is inserted after the terminals are installed inside the
casing. Alternatively, the contact parts may be contacted to the
electrodes to form an assembly outside the casing which is made
divisible into two parts, and the assembly is placed into one of
the divided parts and the two parts of the casing are joined
together.
Inventors: |
HAMATANI, JUNICHI; (SHIGA,
JP) ; TSURUHARA, SATOSHI; (SHIGA, JP) |
Correspondence
Address: |
MAJESTIC PARSONS SIEBERT & HSUE
SUITE 1100
FOUR EMBARCADERO CENTER
SAN FRANCISCO
CA
94111-4106
US
|
Family ID: |
17265384 |
Appl. No.: |
09/134041 |
Filed: |
August 14, 1998 |
Current U.S.
Class: |
29/612 ; 29/613;
439/267; 439/637 |
Current CPC
Class: |
H01C 1/148 20130101;
Y10T 29/49133 20150115; Y10T 29/49098 20150115; Y10T 29/49169
20150115; H01G 2/106 20130101; H01C 17/28 20130101; Y10T 29/49087
20150115; Y10T 29/49139 20150115; Y10T 29/49217 20150115; Y10T
29/49085 20150115 |
Class at
Publication: |
29/612 ; 29/613;
439/637; 439/267 |
International
Class: |
H01C 007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 19, 1997 |
JP |
9-254463 |
Claims
What is claimed is:
1. A method of making an electronic device, said method comprising
the steps of: providing an electronic element having two main
surfaces which face outward away from each other and electrodes
formed individually on said main surfaces; providing at least two
terminals each having a contact part for contacting one of said
electrodes and an extended part extending from said contact part,
the contact part of at least one of said terminals being an elastic
contact part for elastically contacting a corresponding one of said
electrodes; providing a casing for containing therein said
electronic element and the contact parts while said electronic
element is sandwiched between said terminals with each of said
contact parts contacting the corresponding electrode and the
extended parts extending out of said casing; inserting said
electronic element into said casing; and inserting said terminals
into said casing, wherein said steps of inserting said electronic
element and said terminals are carried out without having either of
said electrodes rubbed by said elastic contact part.
2. The method of claim 1 wherein each of said electrodes has a
first layer and a second layer which is formed on said first layer
with an peripheral part of said first layer exposed, and wherein
the steps of inserting said electronic element and said terminals
are carried out without having said exposed peripheral part of said
first layer rubbed by said elastic contact part.
3. The method of claim 2 wherein said first layer is made of a
first metal and said second layer is made of a second metal, said
first metal being less likely to generate migration than said
second metal.
4. The method of claim 3 wherein said electronic element is a
heat-generating element which generates heat when in operation.
5. The method of claim 4 wherein said heat-generating element is a
thermistor element.
6. The method of claim 1 wherein the step of inserting said
electronic element is carried out after the step of inserting said
terminals and comprises the steps of: disposing a flexible planar
guide plate between said elastic contact part inside said casing
and the corresponding electrode of said electronic element before
said electronic element is inserted into said casing; inserting
said electronic element into said casing until said electrodes
reach positions each facing a corresponding one of the contact
parts; and thereafter pulling out said guide plate.
7. The method of claim 1 wherein the steps of inserting said
electronic element and said terminals include the steps of: setting
said electronic element and said terminals in an assembled
condition by causing each of said electrodes to be contacted by a
corresponding one of the contact parts of said terminals, said
terminals having a gap therebetween; and thereafter inserting said
electronic element and said terminals into said casing together
while maintaining said electronic element and the corresponding
contact parts in said assembled condition and elastically deforming
said elastic contact part so as to narrow said gap between said
terminals.
8. The method of claim 7 wherein said casing includes a main part
and a lid, said main part having at least one open surface and
serving to surround said electronic element and the contact parts,
said lid having throughholes, serving to allow the extended parts
of said terminals to pass therethrough and to support said
electronic element and said terminals, and being engageable to said
main part to thereby close said open surface of said main part;
wherein the step of setting said electronic element and said
terminals in said assembled condition includes the steps, while
said terminals are supported by said lid, of: increasing a distance
of separation between the contact parts; thereafter positioning
said electronic element between said contact parts; and thereafter
decreasing said distance of separation between said contact parts;
and wherein the steps of inserting said electronic element and said
terminals are carried out while said terminals are supported by
said lid and include the step of attaching said lid to said main
part.
9. The method of claim 8 wherein at least one of said throughholes
has a clearance which is sufficiently large to allow one of said
terminals passing therethrough and being supported by said lid to
vary the angle of the one terminal passing therethrough with
respect to said lid; and wherein the step of increasing said
distance of separation between said contact parts includes varying
said angle of said one terminal inside said clearance.
10. The method of claim 9 wherein the one throughhole having said
clearance has a sloped inner wall for allowing said angle of said
inserted one terminal to be varied more than if said clearance had
not said sloped inner wall.
11. The method of claim 1 wherein said casing is divisible into a
first half and a second half across a dividing plane which is
parallel to said main surfaces of said electronic element; and
wherein the steps of inserting said electronic elements and said
terminals into said casing include the steps of: disposing said
electronic element and one of said two terminals inside said first
half such that the contact part of said one terminal is in contact
with one of said electrodes of said electronic element; thereafter
disposing the other of said two terminals such that the contact
part of said other terminal contacts the other of said electrodes;
and thereafter joining said first half and said second half to form
said casing.
12. The method of claim 11 wherein the step of disposing the other
terminal is carried out while said second half supports said other
terminal.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a method of making an electronic
device of the type having its electronic element contained inside a
casing such that it makes electrical contacts through terminals
having an elastic spring-like contact part. In particular, this
invention relates to a method of inserting such an electronic
element and its terminals into a casing.
[0002] One of the examples of such an electronic device that is of
interest from the point of view of this invention is a device
having a thermistor with a positive temperature coefficient (PTC)
as its electronic element contained inside a casing. FIGS. 8A and
8B show an example of prior art thermistor element 1 characterized
as having two main surfaces facing outward away from each other and
electrodes 2 and 3 formed thereon. Silver used to be the material
for forming such electrodes, but silver tends to cause the
phenomenon of migration, especially when used under a dewing
condition which is likely to cause migration and a short circuit,
damaging the thermistor element 1. For this reason, it has been
known to form the electrodes 2 and 3, as shown in FIGS. 8A and 8B,
by first providing a first electrode layer 4 and then a second
electrode layer 5 thereon such that peripheral areas of the first
electrode layer 4 remain exposed, the first electrode 4 layer
comprising a metallic material such as nickel that can provide an
ohmic contact but is not likely to cause a migration and the second
electrode layer 5 comprising silver. Since the first and second
electrode layers 4 and 5 thus formed remain nearly at the same
potential, even if the silver of the second electrode layer 5 is
ionized, the electrostatic force on the ionized silver is extremely
weak, not significantly contributing to the migration of the silver
ions.
[0003] FIG. 9 shows a prior art thermistor device 6 obtained by
putting a thermistor element 1 as shown in FIGS. 8A and 8B inside a
casing 7 made, for example, of a resin, glass, ceramic or metal
material. Since the thermistor element 1 is a heat-producing
element and reaches a high temperature when in operation, it is
commonly made and sold in the form of such a device 6. The device 6
also includes two terminals 8 and 9 made of stainless steel or a
copper alloy, each having a contact part 10 contacting a
corresponding one of the electrodes 2 and 3 of the thermistor
element 1 and an extended part 11 extending from the corresponding
contact part 10. The contact parts 10 are each formed so as to
serve as a spring, adapted to elastically contact the electrodes 2
and 3.
[0004] The casing 7 has throughholes 12 formed therethrough, and
the thermistor element 1 and the contact parts 10 of the terminals
8 and 9 are contained inside the casing 7 such that the thermistor
element 1 is sandwiched and supported between and by the contact
parts 10 of the terminals 8 and 9 which pass through the
throughholes 12 through the casing 7, leaving the extended parts 11
extending outside.
[0005] According to common methods of producing a thermistor device
thus structured, the terminals 8 and 9 are first set at specified
positions inside the casing 7 and the thermistor element 1 is then
inserted between the contact parts 10 of the two terminals 8 and 9.
When the thermistor element 1 is thus inserted between the contact
parts 10, the contact parts 10 are deformed against its elastic
spring force such that the gap therebetween is increased and that
they can admit the thermistor element 1 therebetween while they
remain in contact with the thermistor element 1. In other words,
the electrodes 2 and 3 are rubbed against the contact parts 10 as
the thermistor element 1 is inserted into the casing 7 inside which
the terminals 8 and 9 are already installed. This tends to scratch
and damage the electrodes 2 and 3, as shown schematically at 13 in
FIG. 10.
[0006] One of the factors contributing to the scratches on the
electrode surface is the shape of the contact parts 10. In order to
minimize the heat conduction from the thermistor element 1 to the
terminals 8 and 9, the width of the terminals 8 and 9 is reduced at
their contact parts 10 as shown in FIG. 11 so as to reduce as much
as possible the area through which the contact parts 10 contact the
electrodes 2 and 3. These contact areas are much smaller than the
surface area of the electrodes 2 and 3 and hence the pressure
applied by the contact parts 10 on (or the force on a unit area of)
the electrodes 2 and 3 is relatively large, or large enough to
scratch the electrodes 2 and 3. Such scratches (as shown at 13)
usually affect the quality and/or the function of the electronic
element (such as the thermistor element 1). In the case of the
thermistor element 1 with a particular structure as described
above, the scratches 13 may extend beyond the second electrode
layer 5 and may reach the exposed part of the first electrode layer
4 surrounding the second electrode layer 5. This has the
undesirable effect of effectively causing the second electrode
layer 5 to come closer through the scratch 13 to the main surface
of the thermistor element 1. If the thermistor device 6 having such
scratches 13 is used under a dewing condition, the silver of the
second electrode layer 5 may begin to migrate around the scratch
13.
[0007] Worse still, since a relatively large force is applied to
the outer periphery of the thermistor element 1 when it is being
inserted into the casing 7, the outer periphery of the thermistor
element 1 may develop cracks.
SUMMARY OF THE INVENTION
[0008] It is therefore an object of this invention to provide a
method of making an electronic device of the type described above
with which the problems as described above can be overcome.
[0009] Methods embodying this invention, with which the above and
other objects can be accomplished, may be characterized broadly as
comprising the steps of providing an electronic element such as a
thermistor element with electrodes formed on its two mutually
parallel outwardly facing main surfaces, at least two terminals and
a casing as described above, and inserting the electronic element
and the terminals into the casing either simultaneously or
sequentially such that the electrodes are not rubbed by the contact
part of either of the terminals. There are many ways to prevent
such rubbing of the electrodes by the contact parts of the
terminals. One of the ways is to insert the terminals first and
then cover their contact parts with flexible planar guide plates
such that the electrodes will glide over them as the electronic
element is inserted. Another method is to sandwich the electronic
element between the terminals with the contact parts of the latter
contacting the electrodes on the main surfaces of the former to
thereby preliminarily form an assembly consisting of the electronic
element and the contacting terminals and then to insert this
assembly into the casing. For this purpose, the casing may be made
divisible into halves such that the pre-formed assembly is inserted
into one of them and then the two halves are joined together.
Alternatively, the casing may be made divisible into a tubular main
body with one open surface and a lid with throughholes for closing
this open surface. The terminals are preliminarily passed through
these throughholes and supported by the lid. With one or both of
these throughholes appropriated configured, one or both of the
terminals passing therethrough can be tilted such that they can be
opened as the electronic element is inserted and then closed to
form an assembly which is then inserted as a whole into the main
body. These methods are also applicable for making an electronic
device containing two or more electronic elements inside a casing.
The electrodes on the electronic element may be of a layered
structure with the inner layer made of a metal less likely to
general migration than the metal material of the outer layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The accompanying drawings, which are incorporated in and
form a part of this specification, illustrate embodiments of the
invention and, together with the description, serve to explain the
principles of the invention. In the drawings:
[0011] FIG. 1 is a sectional view of a thermistor device being
produced by a method according to a first embodiment of this
invention;
[0012] FIG. 2 is a front view of a portion of FIG. 1 to show how a
guide plate overlaps a corresponding one of the electrodes;
[0013] FIG. 3 is a sectional view of a thermistor device being
produced by another method according to a second embodiment of the
invention;
[0014] FIG. 4 is a sectional view of a thermistor device being
produced by still another method according to a third embodiment of
the invention;
[0015] FIGS. 5A and 5B are sectional views of a thermistor device
at two different times while it is being produced by still another
method according to a fourth embodiment of the invention;
[0016] FIG. 6 is a sectional view of a portion of a thermistor
device being produced by still another method according to a fifth
embodiment of the invention;
[0017] FIG. 7 is a sectional view of a thermistor device being
produced by still another method according to a sixth embodiment of
the invention;
[0018] FIG. 8A is a front view of a prior art thermistor element,
and FIG. 8B is its side view;
[0019] FIG. 9 is a sectional view of a prior art thermistor device
having the thermistor element of FIGS. 8A and 8B contained inside a
casing;
[0020] FIG. 10 is a front view of the prior art thermistor element
of FIGS. 8A and 8B with an electrode surface scratched as it was
inserted into a casing; and
[0021] FIG. 11 is a front view of one of the terminals shown in
FIG. 9.
[0022] Throughout herein, like components are indicated by the same
numerals even where they are components of different devices and
may not necessarily be described repetitiously.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The invention is described next by way of examples of a
method for making a thermistor device (as an example of an
electronic device) as shown at 6 in FIG. 9. For its production, a
thermistor element 1 (as an example of an electronic element), two
terminals 8 and 9 and a casing 7 are prepared. These components
have already been described above and their description will not be
repeated.
[0024] The method of production includes the step of inserting the
thermistor element 1 into the casing 7 and the step of inserting
the terminals 8 and 9 into the casing 7, but each of these steps
can be carried out in different ways, as will be described
below.
[0025] According to a first embodiment of the invention shown in
FIG. 1, the terminals 8 and 9 are inserted into the casing 7 first
and then the thermistor element 1 is inserted. When the thermistor
element 1 is inserted into the casing 7, guide plates 14 are each
placed between one of the electrodes 2 and 3 of the thermistor
element 1 and corresponding one of the contact parts 10 of the
terminals 8 and 9. As shown in FIG. 2, the area of each guide plate
14 is greater than the area of each contact part 10 which contacts
the electrode 2 or 3, and, in particular, the width of the guide
plate 14 is made greater than the width of the contact area of each
contact part 10 through which it contacts the electrode 2 or 3. The
material and the shape of the guide plates 14 are not intended to
limit the scope of this invention. Any thin plate with a smooth
surface can serve the purpose of this invention. Thin plates of
stainless steel which can be easily bent in the direction of the
thickness may be utilized advantageously.
[0026] With the guide plates 14 positioned as shown in FIG. 1, the
thermistor element 1 is inserted into the casing 7 as indicated by
arrow 15 until the electrodes 2 and 3 reach the positions opposite
to and facing the contact parts 10 of the terminals 8 and 9. After
the thermistor element 1 and the terminals 8 and 9 are properly
positioned, the guide plates 14 are pulled out.
[0027] According to this method, the guide plates 14 serve to
prevent direct contacts between the contact parts 10 of the
terminals 8 and 9 with the electrodes 2 and 3 while the thermistor
element 1 is inserted into the casing 7. Because the contact parts
10 of the terminals 8 and 9 are already positioned opposite to the
second electrode layers 5 of the electrodes 2 and 3 when the guide
plates 14 are pulled out, the thermistor device 6 can be assembled
without causing any scratches as shown at 13 in FIG. 10.
[0028] The electrodes 2 and 3 are rubbed against the guide plates
14 when the electronic element 1 is inserted and when the guide
plates 14 are pulled out, but since the area of the guide plates 14
is greater than the contact areas of the contact parts 10 with the
electrodes 2 and 3, as explained above, the pressure (force per
unit area) applied on the contact surface between the electrodes 2
and 3 and the guide plates 14 is much smaller than that between the
electrodes 2 and 3 and the contact parts 10 in the case of a prior
art method. Thus, the guide plates 14 do not cause any scratches
although they rub against the electrodes 2 and 3.
[0029] Since the guide plates 14 also serve to allow the thermistor
element 1 to be inserted smoothly, no large external force is
applied to the peripheral parts of the thermistor element 1. Thus,
the possibility of developing cracks along the periphery of the
thermistor element 1 can also be reduced.
[0030] In order to measure the effect of the method of the present
invention described above, a dewing cycle test was carried out by
producing both test thermistor devices by the method described
above and comparison devices with scratched electrodes by a prior
art method of production. These thermistor devices of both kinds
were cooled at a low temperature of 0.degree. C. for a few minutes
and then brought under a high-temperature, high-humidity condition
of 40.degree. C. and 95% RH for forming dews thereon. The test was
carried out such that a current would be passed only when dews were
formed. Table 1 shows the frequency of occurrence of migration per
sample as the cycle number was increased from 1 to 20 to 100 to
1000.
1 TABLE 1 Cycle Number 1 20 100 1000 Test Samples 0/5 0/5 0/5 0/5
Comparison Samples 0/5 5/5 5/5 5/5
[0031] Table 1 shows that no migration was observed on any of the
comparison samples if the cycle number was 1 but that migration was
observed on all of the comparison samples if the cycle number was
20 or over. By comparison, generation of migration was not observed
on any of the test samples although the cycle number reached 1000.
This indicates that the method of present invention as described
above can prevent migrations very effectively.
[0032] FIG. 3 shows a thermistor device as shown at 6 in FIG. 9 in
the course of being produced by another method according to a
second embodiment of this invention. By this method, the step of
inserting the thermistor element 1 into the casing 7 and that of
inserting the terminals 8 and 9 into the casing 7 are carried out
at the same time. This is done by first contacting the contact
parts 10 of the terminals 8 and 9 respectively against the
electrodes 2 and 3 of the thermistor element 1 and then inserting
the assembly of the thermistor element 1 and the terminals 8 and 9
together into the casing 7 as shown by the black arrow 17 while
elastically deforming the contact parts 10 as shown by white arrows
16 so as to reduce the separation between the two terminals 8 and
9. It is important, when using this method, to be careful to cause
the contact parts 10 of the terminals 8 and 9 to contact the
electrodes 2 and 3 of the thermistor element 1 such that the
contact parts 10 will not touch the exposed peripheral parts of the
first electrode layers 5. It is also important to be careful not to
adversely affect the elastic property of the contact parts 10 when
the contact parts 10 of the terminals 8 and 9 are elastically
deformed.
[0033] By this method, too, the electrodes 2 and 3 are not rubbed
against the contact parts 10 of the terminals 8 and 9 as the
thermistor element 1 is inserted into the casing 7 because the
thermistor element 1 and the terminals 8 and 9 are in a fixed
positional relationship, and hence a thermistor device as shown in
FIG. 9 can be assembled without causing any scratches as shown at
13 in FIG. 10. Moreover, since no external force is applied on the
peripheral parts of the thermistor element 1 as the latter is being
inserted into the casing 7, no cracks are generated along the
periphery of the thermistor element 1.
[0034] FIG. 4 shows a thermistor device as shown at 6 in FIG. 9 in
the course of being produced by still another method according to a
third embodiment of this invention. By this method, the casing 7 is
divisible into a first half 7a and a second half 7b across a
dividing plane parallel to the main surfaces of the thermistor
element 1 which is inserted thereinto. The two halves 7a and 7b of
the casing 7 are respectively provided with a V-shaped protrusion
19 and a similarly V-shaped groove 18 which are mutually engageable
such that the two halves 7a and 7b can be tightly joined
together.
[0035] When the thermistor element 1 and the two terminals 8 and 9
are inserted into the casing 7 thus divisible, one of the terminals
(say, the terminal 8) and the thermistor element 1 are firstly
inserted into either half of the casing 7 (say, the first half 7a)
such that contact part 10 of the terminal 8 is already in contact
with the electrode 2 of the thermistor element 1, as shown in FIG.
4. Thereafter, the other terminal 9 is positioned such that its
contact part 10 will contact the other electrode 3 of the
thermistor element 1 and the second half 7b is joined to the first
half 7a as shown by arrow 20. In this method, the terminal 9 may
preferably be supported preliminarily by the second half 7b of the
casing 7.
[0036] Neither by this method do the contact parts 10 rub against
the electrodes 2 and 3 as the thermistor element 1 is inserted into
the casing 7. Since one of the terminals 8, the thermistor element
1 and the other terminal 9 are sequentially assembled while the
exposed parts of the first electrode layers 5 are kept away from
the contact parts 10 of the terminals 8 and 9, scratches as shown
at 13 in FIG. 10 are not made on the electrodes 2 and 3. Since no
external force is applied on the peripheral parts of the thermistor
element 1 throughout the process, no cracks are generated along the
periphery of the thermistor element 1.
[0037] FIGS. 5A and 5B show a thermistor device as shown at 6 in
FIG. 9 at two points in time in the course of being produced by
still another method according to a fourth embodiment of this
invention. By this method, the casing 7 is made divisible into a
main part 7c and a lid 7d. The main part 7c is for surrounding and
containing therein the thermistor element 1 and the two terminals 8
and 9 and has at least one open surface 21. The lid 7d is for
closing this open surface 21 of the main part 7c and has
throughholes 12 for admitting therethrough the extended parts 11 of
the terminals 8 and 9 to thereby support the terminals 8 and 9. The
thermistor element 1 and the two electrodes 8 and 9 are inserted
into the casing 7 at the same time, as by the method according to
the second embodiment of this invention.
[0038] Firstly, the contact parts 10 of the terminals 8 and 9 are
brought into contact with the electrodes 2 and 3 of the thermistor
element 1. This is done by increasing the gap between the contact
parts 10 while the terminals 8 and 9 are supported by the lid 7d
and then positioning the thermistor element 1 between the two
contact parts 10, as shown in FIG. 5A. Thereafter, the elastic
contact parts 10 are elastically deformed, as shown in FIG. 5B, as
the gap between the contact parts 10 is narrowed such that the
electrodes 2 and 3 come into contact with the contact parts 10.
[0039] The throughholes 12 through the lid 7d are preferably
provided with a sufficient clearance such that the tilting angles
of the terminals 8 and 9 supported by the lid 7d can be varied as
the gap between the contact parts 10 is changed gradually. Such a
clearance may be provided to only one of the throughholes 12.
Alternatively, the extended parts 11 of the terminals 8 and 9 may
be made flexible such that the gap between the two contact parts 10
can be increased by bending their flexible extended parts 11.
[0040] The main part 7c and the lid 7d of the casing 7 are brought
together, as indicated by arrow 22 in FIG. 5B, while the terminals
8 and 9 remain supported by the lid 7d and the gap between the
terminals 8 and 9 is made narrower by bending their contact parts
10 such that the thermistor 1 and the terminals 8 and 9 are
inserted together inside the main part 7c until and main part 7c
and the lid 7d are engaged together. The main part 7c and the lid
7d of the casing 7 are respectively provided with a V-shaped
protrusion 24 and a similarly V-shaped groove 23 which are mutually
engageable such that they can be tightly joined together.
[0041] By this method, too, as by the method according to the
second embodiment of the invention, the thermistor element 1 and
the two terminals 8 and 9 are already in a fixed positional
relationship when they are inserted into the main part 7c of the
casing 7, and hence the contact parts 10 do not rub the electrodes
2 and 3 during the insertion process. Thus, a thermistor device as
shown at 6 in FIG. 9 can be assembled without producing any
scratches as shown at 13 in FIG. 10 on the electrodes 2 and 3.
Since no external force is applied on the peripheral parts of the
thermistor element 1 throughout the process, no cracks are
generated along the periphery of the thermistor element 1.
[0042] FIG. 6 shows a variation on the fourth embodiment ("the
fifth embodiment") of the invention described above with reference
to FIGS. 5A and 5B characterized by an improved shape of the
throughholes 12 through the lid 7d of the casing 7. As shown
enlarged in FIG. 6, the throughholes 12 are formed so as to have
not only an extra clearance but also sloped surfaces 25 and 26 such
that the terminals 8 and 9 supported by the lid 7d can be tilted by
an even larger angle, as indicated by a broken line. This means
that the gap between the two contact parts 10 can be increased even
more without causing any unreasonable deformation such that even a
thicker thermistor element can be sandwiched therebetween without
having its electrodes scratched by the contact parts 10. The
ability to increase the gap between the contact parts 10 also means
that the thermistor element 1 can be more easily positioned
therebetween and hence that the overall efficiency of the
production process is thereby improved.
[0043] The sloped surfaces 25 and 26 may be provided to only one of
the throughholes 12.
[0044] FIG. 7 shows another thermistor device in the course of
being produced by still another method according to a sixth
embodiment of this invention. This method is similar to the first
embodiment described above with reference to FIG. 1, but the
thermistor device to be produced is characterized as having a
plurality of thermistor elements. For the convenience of
illustration, FIG. 7 shows a method of making a thermistor device
with only two thermistor elements 1a and 1b and one extra terminal
28 with a planar contact part 27 supported by the casing 7, in
addition to the terminals 7 and 8 shown in FIG. 1.
[0045] According to the sixth embodiment, as according to the first
embodiment, the terminals 8, 9 and 28 are inserted into the casing
7 first and then the thermistor elements 1a and 1b are inserted.
FIG. 7 shows a point in time where one of the thermistor elements
1a has already been inserted and the other thermistor element 1b is
about to be inserted. Since the thermistor elements 1a and 1b are
inserted in similar manners, only the insertion of the second
thermistor element 1b will be described next.
[0046] As shown in FIG. 7, before the thermistor element 1b is
inserted into the casing 7, a guide plate 14 is disposed between
the electrode 3 thereon and the contact part 10 of the terminal 9
which has already been inserted into the casing 7. The thermistor
element 1b is then inserted into the casing 7, as shown by arrow
29, until its electrodes 2 and 3 reach positions opposite
respectively to the contact parts 27 and 10 of the terminals 28 and
9. After the thermistor element 1b and the terminals 28 and 9 are
properly positioned, the guide plate 14 is pulled out. The method
according to the sixth embodiment of the invention also has the
same effects as the method according to the first embodiment
described above but is particularly of interest because the present
invention is hereby shown to be equally applicable to the
production of a device wherein only one of the two terminals
sandwiching an electronic element has an elastically bendable
contact part, the other terminal having a non-elastic contact
part.
[0047] The invention has been described above with reference to
only a limited number of examples but these examples are not
intended to limit the scope of the invention. Although not
described separately, any of the methods according to the second
through fifth embodiments of the invention can be applied to the
production of an electronic device containing two or more
electronic elements such as the subject matter of the sixth
embodiment. It also goes without saying that the invention is not
limited to thermistor devices encapsulating PTC thermistor
elements. The encapsulated electronic element may be a negative
temperature coefficient thermistor, or a heat-generating element of
any other kind. Furthermore, it can be any electronic element as
long as it has electrodes formed on its main surfaces which are
substantially parallel to each other and facing outward oppositely
away from each other. Neither are the physical properties of the
two electrode layers 4 and 5 intended to limit the scope of the
invention. The invention is equally applicable to the production of
an electronic device with an electronic element having electrodes
of a single-layer structure.
[0048] In summary, the present invention introduces a method of
assembling an electronic device by inserting an electronic element
and terminals into a casing without having the electrodes scratched
by the elastic contact parts of the terminals.
* * * * *