U.S. patent application number 15/797277 was filed with the patent office on 2018-03-08 for optical coupling device, manufacturing method thereof, and power conversion system.
The applicant listed for this patent is Renesas Electronics Corporation. Invention is credited to Yukio NOMURA.
Application Number | 20180068990 15/797277 |
Document ID | / |
Family ID | 56693035 |
Filed Date | 2018-03-08 |
United States Patent
Application |
20180068990 |
Kind Code |
A1 |
NOMURA; Yukio |
March 8, 2018 |
OPTICAL COUPLING DEVICE, MANUFACTURING METHOD THEREOF, AND POWER
CONVERSION SYSTEM
Abstract
In order to improve properties, an optical coupling device has a
potting resin and an internal mold resin between a light emitting
element and a light receiving element. The internal mold resin is a
cured product of a composition having an epoxy resin and a curing
agent, and is a resin having a light transmission property.
Additionally, the internal mold resin MRI contains an aromatic ring
and an alicyclic compound. By thus lowering the ratio of an
aromatic ring in the epoxy resin, deterioration of the resin can be
suppressed. Thereby, a decrease in the light transmission property
of the epoxy resin cured product can be suppressed, and degradation
of the transmission performance for an optical signal can be
reduced.
Inventors: |
NOMURA; Yukio; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Renesas Electronics Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
56693035 |
Appl. No.: |
15/797277 |
Filed: |
October 30, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14941719 |
Nov 16, 2015 |
9831226 |
|
|
15797277 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 2224/48247
20130101; H01L 25/167 20130101; H01L 33/54 20130101; H01L 2924/181
20130101; H01L 31/167 20130101; H01L 2924/181 20130101; H01L
2924/00012 20130101 |
International
Class: |
H01L 25/16 20060101
H01L025/16 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 25, 2015 |
JP |
2015-035604 |
Claims
1. A manufacturing method of an optical coupling device, comprising
the steps of: (a) providing both a first lead frame having a first
mounting part and a first lead and a second lead frame having a
second mounting part and a second lead; (b) mounting a first
element over the first mounting part; (c) forming a first resin
over the first element; (d) mounting a second element over the
second mounting part; and (e) facing the first resin over the first
element and the second element with each other so as to form a
second resin between the second element and the first resin,
wherein the second resin is a cured product of a composition having
an epoxy resin and a curing agent, and has a light transmission
property, wherein the epoxy resin contains an aromatic ring and an
alicyclic compound, wherein the cured product of the second resin
includes silica in a ratio of 60 to 90 wt % based on the weight of
the epoxy resin composition, and wherein the cured product is a
compound represented by the formula: ##STR00005##
2. The manufacturing method of an optical coupling device according
to claim 1, wherein the (e) step is a step of forming the second
resin by thermally curing the epoxy resin with the curing
agent.
3. The manufacturing method of an optical coupling device according
to claim 1, wherein the epoxy resin excludes an aromatic ring.
4. The manufacturing method of an optical coupling device according
to claim 1, wherein the epoxy resin is an epoxy resin represented
by the formula (1): ##STR00006##
5. The manufacturing method of an optical coupling device according
to claim 4, wherein the curing agent excludes an aromatic ring.
6. The manufacturing method of an optical coupling device according
to claim 1, wherein the first resin is a silicone resin cured
product.
7. The manufacturing method of an optical coupling device according
to claim 1, wherein a transmittance per mm of a thickness of the
second resin is 10% or more for light having a wavelength within a
range of 700 nm to 1000 nm.
8. The manufacturing method of an optical coupling device according
to claim 1, wherein a reflectance per mm of the thickness of the
second resin is 90% or less for light having a wavelength within a
range of 700 nm to 1000 nm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S.
application Ser. No. 14/941,719, filed Nov. 16, 2015 which is the
disclosure of Japanese Patent Application No. 2015-035604 filed on
Feb. 25, 2015 including the specification, drawings and abstract is
incorporated herein by reference in its entirety.
BACKGROUND
[0002] The present invention relates to an optical coupling device,
a manufacturing method thereof, and a power conversion system.
[0003] A photocoupler has a light emitting element, such as a light
emitting diode, and a light receiving element, such as a
phototransistor, and transmits an electrical signal by converting
an inputted electrical signal into light with the light emitting
element and by returning the light to the electrical signal with
the light receiving element.
[0004] A photocoupler is disclosed, for example, in Japanese
Unexamined Patent Application Publication No. 2008-189833 (Patent
Document 1), in which a light emitting element and a light
receiving element are sealed by a cured product of a thermosetting
epoxy resin composition.
[0005] Also, a photocoupler using a primary sealing resin and a
secondary sealing resin is disclosed in Japanese Unexamined Patent
Application Publication No. 2014-33124 (Patent Document 2). The
primary sealing resin contains an epoxy resin for primary sealing,
a phenolic resin curing agent for primary sealing, an inorganic
filler for primary sealing, and fatty acid wax for primary sealing;
and the secondary sealing resin contains an epoxy resin for
secondary sealing, a phenolic resin curing agent for secondary
sealing, an inorganic filler for secondary sealing, and fatty acid
wax for secondary sealing. At least one of the resin for primary
sealing and the resin for secondary sealing contains fatty acid
amide wax.
[0006] Also, an optical semiconductor device sealed by a cured
product of an epoxy resin composition is disclosed in Japanese
Unexamined Patent Application Publication No. 2005-239901 (Patent
Document 3). The epoxy resin composition is one whose main
components are an epoxy resin (A) having two or more epoxy groups
in one molecule, a phenolic resin curing agent (B), a curing
accelerator (C), and fused crushed silica (D). The epoxy resin
composition further contains a phenolic antioxidant (E) as an
essential component. Additionally, the light transmittance of a
cured product of the epoxy resin composition, the product having a
thickness of 1 mm, is 15% or more for the light having a wavelength
of from 700 nm to 1000 nm, and the light transmittance retention
rate thereof after being subjected to 125.degree. C. for 1000 hrs
is 50% or more for the light having a wavelength of 720 nm.
PRIOR ART DOCUMENT
[0007] Patent Document
[0008] [Patent Document 1] Japanese Unexamined Patent Application
Publication No. 2008-189833
[0009] [Patent Document 2] Japanese Unexamined Patent Application
Publication No. 2014-33124
[0010] [Patent Document 3] Japanese Unexamined Patent Application
Publication No. 2005-239901
SUMMARY
[0011] As described above, a photocoupler has a light emitting
element, such as a light emitting diode, and a light receiving
element, such as a phototransistor, and transmits an electrical
signal by converting an inputted electrical signal into light with
the light emitting element and by returning the light into the
electrical signal with the light receiving element.
[0012] According to such a signal transmission technology using
light, signal transmission paths can be electrically separated from
each other. That is, a signal can be transmitted, via light,
between a primary electrical circuit and a secondary electrical
circuit that are electrically insulated from each other.
[0013] It is necessary that a light emitting element on the side of
the primary electrical circuit and that on the side of the
secondary electrical circuit are insulated from each other by a
resin having a light transmission property.
[0014] However, according to the study by the present inventors, it
has been confirmed in a photocoupler that the light transmission
property of a resin is decreased due to discoloration of the resin,
and hence there is a need for the improvement thereof.
[0015] Other problems and new characteristics will become clear
from the description and accompanying drawings of the present
specification.
[0016] Of the preferred embodiments disclosed in the present
application, outlines of the typical ones will be briefly described
as follows.
[0017] An optical coupling device described in one embodiment
disclosed in the present application has a first resin and a second
resin between a first element and a second element. The second
resin is a cured product of a composition having an epoxy resin and
a curing agent, and has a light transmission property.
Additionally, the second resin contains an aromatic ring and an
alicyclic compound.
[0018] A manufacturing method of an optical coupling device
described in one embodiment disclosed in the present application
includes the steps of: forming a first resin over a first element;
and forming a second resin between a second element and the first
resin after facing the first resin over the first element and the
second element each other. The second resin is a cured product of a
composition having an epoxy resin and a curing agent, and has a
light transmission property. Additionally, the epoxy resin contains
an aromatic ring and an alicyclic compound.
[0019] A power conversion system described in one embodiment
disclosed in the present application is one including an amplifier
circuit part, and an optical coupling part to be coupled to the
amplifier circuit part. The optical coupling part has a first resin
and a second resin between a first element and a second element.
The second resin is a cured product of a composition having an
epoxy resin and a curing agent, and has a light transmission
property. Additionally, the second resin contains an aromatic ring
and an alicyclic compound.
Advantage of the Invention
[0020] According to an optical coupling device described in the
typical embodiments that are disclosed in the present application
and described below, discoloration of a resin in the device can be
suppressed and the properties of the device can be improved.
[0021] According to a manufacturing method of an optical coupling
device, described in the typical embodiments that are disclosed in
the present application and described below, an optical coupling
device, in which discoloration of a resin in the device is
suppressed and good properties are achieved, can be
manufactured.
[0022] According to a power conversion system described in the
typical embodiments that are disclosed in the present application
and described below, discoloration of a resin in a device that
forms the power conversion system can be suppressed and the
properties of the system can be improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a sectional view illustrating a configuration of
an optical coupling device according to First Embodiment;
[0024] FIG. 2 is a sectional view illustrating a manufacturing step
of the optical coupling device according to First Embodiment;
[0025] FIG. 3 is a plan view illustrating a manufacturing step of
the optical coupling device according to First Embodiment;
[0026] FIG. 4 is a sectional view illustrating a manufacturing step
of the optical coupling device according to First Embodiment, the
step following that of FIG. 2;
[0027] FIG. 5 is a plan view illustrating a manufacturing step of
the optical coupling device according to First Embodiment, the step
following that of FIG. 3;
[0028] FIG. 6 is a sectional view illustrating a manufacturing step
of the optical coupling device according to First Embodiment, the
step following that of FIG. 4;
[0029] FIG. 7 is a sectional view illustrating a manufacturing step
of the optical coupling device according to First Embodiment, the
step following that of FIG. 6;
[0030] FIG. 8 is a sectional view illustrating a manufacturing step
of the optical coupling device according to First Embodiment, the
step following that of FIG. 7;
[0031] FIG. 9 is a sectional view illustrating a manufacturing step
of the optical coupling device according to First Embodiment, the
step following that of FIG. 8;
[0032] FIG. 10 is a sectional view illustrating a manufacturing
step of the optical coupling device according to First Embodiment,
the step following that of FIG. 9;
[0033] FIG. 11 is a sectional view illustrating a configuration of
an optical coupling device of First Comparative Example;
[0034] FIGS. 12(A) to 12(C) are schematic views illustrating a
mechanism by which a void is produced in a resin interface;
[0035] FIGS. 13(A) to 13(C) are schematic views illustrating a
mechanism by which a resin is discolored;
[0036] FIG. 14 is a view schematically illustrating a reaction in
which an aromatic ring undergoes oxidation discoloration;
[0037] FIG. 15 is a sectional view illustrating a configuration of
an optical coupling device of Second Comparative Example;
[0038] FIGS. 16(A) to 16(C) are schematic views illustrating a
mechanism by which discoloration of a resin is suppressed;
[0039] FIGS. 17(A) to 17(C) are schematic views illustrating states
of voids, when a silicone resin cured product having a low hardness
is used;
[0040] FIGS. 18(A) to 18(C) are schematic views illustrating states
of a void, when a silicone resin cured product according to Second
Embodiment is used; and
[0041] FIG. 19 is an illustrative view illustrating one example of
a power conversion system according to Third Embodiment.
DETAILED DESCRIPTION
[0042] If needed for convenience, the following embodiments will be
described by dividing each of them into multiple sections or
embodiments; however, the multiple sections or embodiments are not
irrelevant to each other, but they are in a relationship in which
one is a variation, application example, detailed description, or
supplementary description of part or the whole of the others,
unless otherwise indicated. When the numbers of elements, etc.
(including numbers of pieces, numerical values, amounts, ranges,
etc.) are referred to in the following embodiments, the numbers are
not limited to the specific ones but may be more or less than the
specific numbers, unless otherwise indicated or except when the
numbers are obviously limited to the specific numbers in
principle.
[0043] Further, in the following embodiments, the constituents
(also including element steps, etc.) are not necessarily essential,
unless otherwise indicated or clearly essential in principle.
Similarly, when the shapes and positional relations, etc., of the
constituents, etc., are referred to in the following embodiments,
those substantially the same or similar to the shapes, etc., should
also be included, unless otherwise indicated or except when
considered to be clearly otherwise in principle. The same is true
with the aforementioned numbers, etc., (including the numbers of
pieces, numerical values, amounts, and ranges, etc.).
[0044] Hereinafter, preferred embodiments will be described in
detail with reference to the accompanying views. In the whole views
for explaining the embodiments, members having the same function as
each other will be denoted with the same or relevant reference
numeral and duplicative description will be omitted. When a
plurality of similar members (parts) are present, an individual or
specific part may be represented by adding a sign to the collective
reference numeral. In the following embodiments, description of the
same or similar parts will not be repeated in principle, unless
particularly necessary.
[0045] In the views used in the embodiments, hatching may be
omitted even in sectional views in order to make them easier to
see. Alternatively, hatching may be added even in plan views in
order to make them easier to see.
[0046] In a sectional view or a plan view, the size of each part
does not correspond to that of an actual device, and a specific
part may be displayed to be relatively large in order to make the
view easier to understand. The same is true with the case where a
sectional view and a plan view correspond to each other.
First Embodiment
[0047] Hereinafter, an optical coupling device according to the
present embodiment will be described in detail with reference to
the accompanying drawings.
[0048] [Structure Description]
[0049] FIG. 1 is a sectional view illustrating a configuration of
an optical coupling device according to the present embodiment. The
optical coupling device according to the embodiment is a
photocoupler. The optical coupling device according to the
embodiment illustrated in FIG. 1 has a light emitting element LED,
a light receiving element PD, and two types of resins (PR, MRI)
arranged between them. An electrical signal can be transmitted by
converting an inputted electrical signal into light with the light
emitting element LED and by returning the light to the electrical
signal with the light receiving element PD.
[0050] The light emitting element (light emitting chip) LED is a
photoelectric conversion element that receives an electrical signal
to output an optical signal. A light emitting diode using, for
example, GaAs, AlGaAs, or the like, can be used as the light
emitting element LED. The light emitting element LED is mounted
over a chip mounting part DP1. The chip mounting part DP1 is a
plate-shaped member including a metal, such as, for example, copper
(Cu). The light emitting element LED is fixated (adhered, fixed)
over the chip mounting part (die pad) DP1 via a die bond material.
The die bond material (mounting material) is a conductive adhesive
(conductive paste). Two leads LD1 are arranged around the chip
mounting part DP1. One of the two leads LD1 is coupled to the chip
mounting part DP1 (see FIG. 3). The surface electrode of the light
emitting element LED and the other lead LD1 are electrically
coupled together via a wire W1. The wire W1 is a linear member
(thin metal wire) including a metal material, such as, for example,
gold (Au).
[0051] A potting resin PR is formed over the light emitting element
LED. In other words, the light emitting element LED over the chip
mounting part DP1 is covered with the potting resin PR. It is
necessary that the potting resin PR has an insulation property and
has a light transmission property for the light having the
wavelength of an optical signal. For example, a silicone resin
cured product, or the like, can be used as the potting resin PR. In
the present embodiment, a mixture of various compounds to be used
as materials for resins (PR and later-described MRI) is referred to
as a "resin composition", and a cured product of this composition
is referred to as a "resin cured product".
[0052] A silicone resin cured product is a high molecular compound
having, as amain chain, an organopolysiloxane (structure having
both an --Si--O--Si--O-- chain as a main chain and an organic group
over Si).
[0053] The silicone resin cured product has a light transmission
property for the light having the wavelength of an optical signal.
For example, the transmittance per mm of the thickness of the
silicone resin cured product is 10% or more for the light having a
wavelength within a range of 700 nm to 1000 nm. Further, the
reflectance per mm of the thickness of the silicone resin cured
product is 90% or less for the light having a wavelength within a
range of 700 nm to 1000 nm.
[0054] In order to improve the strength of the silicone resin cured
product, a filler, such as silica, may be mixed into a silicone
resin composition. The content of a filler (e.g., silica) is
preferably 20 wt % or less, and more preferably 0 wt %. When being
coated, i.e., before being cured, the silicone resin composition
has a liquid state. If the content of a filler is more than 20 wt
%, the flowability of the silicone resin is decreased. Accordingly,
the circumference of the light emitting element LED cannot be
uniformly filled with the resin, causing the covering of the light
emitting element LED to be decreased. If the content of a filler is
more than 20 wt %, the hardness of the silicone resin, after being
cured, becomes too large, and it becomes difficult to fully relieve
the stress applied to the light emitting element LED.
[0055] The light receiving element PD is a photoelectric conversion
element that receives an optical signal to output an electrical
signal. For example, a photodiode, a phototransistor, a light
receiving IC, or the like, can be used as the light receiving
element PD. The light receiving element PD is mounted over a chip
mounting part (die pad) DP2. The chip mounting part DP2 is a
plate-shaped member including a metal, such as, for example, copper
(Cu). The light receiving element PD is fixated (adhered, fixed)
over the chip mounting part DP2 via a die bond material. The die
bond material (mounting material) is a conductive adhesive
(conductive paste). A plurality of leads LD2 are arranged around
the chip mounting part DP2. One of the leads LD2 is coupled to the
chip mounting part DP2. The surface electrodes of the light
receiving element PD and the other leads LD2 are electrically
coupled together via a wire W2, respectively. The wire W2 is a
linear member (thin metal wire) including a metal material, such
as, for example, gold (Au).
[0056] The light receiving element PD and the light emitting
element LED are arranged to face each other. That is, the chip
mounting parts DP1 and DP2 are arranged up and down so as to be
spaced apart from each other by a certain distance, and the light
emitting element LED is arranged below the chip mounting part DP1,
and the light receiving element PD above the chip mounting part
DP2, as illustrated in FIG. 1. Herein, the light emitting element
LED is covered with the potting resin PR. The potting resin PR is a
translucent resin.
[0057] The space between the potting resin PR and the light
receiving element PD and the outer periphery of them are sealed by
an internal mold resin (translucent mold resin) MRI. The outer
periphery of the internal mold resin MRI is sealed by an external
mold resin (light-shielding mold resin) MRO.
[0058] An epoxy resin cured product (cured product of an epoxy
resin composition) can be used as the internal mold resin MRI. The
epoxy resin cured product does not contain a reflecting agent, such
as titanium oxide, and has a light transmission property for the
light having the wavelength of an optical signal. For example, the
transmittance per mm of the thickness of the silicone resin cured
product is 10% or more for the light having a wavelength within a
range of 700 nm to 1000 nm. Further, the reflectance per mm of the
thickness of the silicone resin cured product is 90% or less for
the light having a wavelength within a range of 700 nm to 1000
nm.
[0059] The epoxy resin cured product is formed by a reaction
between the main agent and the curing agent in the epoxy resin
composition. The epoxy resin composition can be cured and highly
polymerized by crosslinking the epoxy groups in the main agent
(epoxy resin) via the curing agent. Each of the main agent and the
curing agent may be any of a monomer, from a dimer to a pentamer,
an oligomer (below icosamer) and a prepolymer.
[0060] A compound, in which the ratio of an aromatic ring is small,
is used as the main agent. For example, cycloaliphatic epoxy resins
(e.g., dicyclopentadiene-based epoxy resin, etc.), epoxy resins
having a nitrogen-containing ring (e.g., triazine ring-based epoxy
resin, etc.), and the like, can be used as the main agent in which
the ratio of an aromatic ring is small. A compound represented by
the following formula (1) can be used as the
dicyclopentadiene-based epoxy resin. Alternatively, a compound
excluding an aromatic ring may be used as the main agent.
##STR00001##
[0061] A compound, in which the ratio of an aromatic ring is small,
is used as the curing agent. More preferably, a compound excluding
an aromatic ring is used. For example, an acid anhydride curing
agent, etc., can be used as the curing agent excluding an aromatic
ring. A compound represented by the following formula (2) can be
used as the acid anhydride curing agent.
##STR00002##
[0062] By thus using a compound, in which the ratio of an aromatic
ring is small, as the main agent, the ratio of an aromatic ring in
the epoxy resin cured product becomes small, thereby allowing
deterioration of the resin to be suppressed.
[0063] Further, by using a compound, in which the ratio of an
aromatic ring is small, as the curing agent, the ratio of an
aromatic ring in the epoxy resin cured product becomes small,
thereby allowing deterioration of the resin to be suppressed.
[0064] Hereinafter, a reaction between a main agent, in which the
ratio of an aromatic ring is large, and a curing agent, in which
the ratio of an aromatic ring is large, will be described. With a
reaction of a composition having: a compound represented by the
following formula (3) as the main agent; and a compound represented
by the following formula (4) as the curing agent, a compound
represented by the following formula (5), which is an epoxy resin
cured product, can be produced. That is, an epoxy group in the
compound represented by the formula (3) reacts with an OH group in
the compound represented by the formula (4), so that a
polymerization reaction progresses (see the portions enclosed by
the dashed lines in the formulae (3), (4), and (5)).
##STR00003##
[0065] If such a main agent, in which the ratio of an aromatic ring
is large, and such a curing agent, in which the ratio of an
aromatic ring is large, are used, the ratio of an aromatic ring in
an epoxy resin cured product becomes large.
[0066] On the other hand, by using a main agent, in which the ratio
of an aromatic ring is small, and a curing agent, in which the
ratio of an aromatic ring is small, the ratio of an aromatic ring
in an epoxy resin cured product can be made small, thereby allowing
deterioration of the resin to be suppressed. Details will be
described later.
[0067] In an epoxy resin cured product to be used as the internal
mold resin MRI, a filler, such as silica, may be mixed into an
epoxy resin composition in order to improve the strength of the
product. Further, by mixing a filler, such as silica, the
difference between the coefficient of thermal expansion of the lead
LD1 or LD2 including a metal and that of the internal mold resin
MRI can be reduced. A filler, such as silica, is mixed, for
example, in a ratio of approximately 60 to 90 wt % based on the
weight of the epoxy resin composition (main agent, curing
agent).
[0068] Additionally, it is preferable not to add a reflecting
agent, such as titanium oxide, and a colorant, such as carbon, to
an epoxy resin composition to be used as the internal mold resin
MRI, in order to secure a light transmission property.
[0069] An external mold resin MRO is provided to cover the internal
mold resin MRI, so that entry of light from the outside is
prevented. Accordingly, the external mold resin MRO has a
light-shielding property. For example, a black epoxy resin cured
product, etc., can be used as the external mold resin MRO.
[0070] In the optical coupling device according to the present
embodiment, an electrical signal is supplied to the light emitting
element LED via the lead LD1, and the light emitting element LED
emits light in response to the electrical signal. The light emitted
by the light emitting element LED enters the light receiving
element PD via the potting resin (silicone resin cured product) PR
and the internal mold resin (epoxy resin cured product) MRI. Then,
the light is converted into the electrical signal in the light
receiving element PD, which is transmitted, via the lead LD2, to a
device (not illustrated) to which the lead LD2 is coupled.
[0071] [Description of Manufacturing Method]
[0072] FIGS. 2 to 10 are sectional views or plan views each
illustrating a manufacturing step of the optical coupling device
according to the present embodiment.
[0073] As illustrated in FIG. 2, the light emitting element LED is
mounted over the chip mounting part DP1 of a lead frame LF. For
example, a die bond material (not illustrated) is coated over the
chip mounting part DP1 of the lead frame LF, and the light emitting
element LED is mounted thereover and fixed. The lead frame LF has a
structure in which a plurality of combinations of the chip mounting
part DP1 and the leads LD1 arranged at the outer periphery of the
part DP1 are interlinked by a frame F. The light emitting element
LED is mounted over the chip mounting part DP1 of the lead frame
LF. The shape of the lead frame LF is not limited, but for example,
the lead frame LF as illustrated in FIG. 3 can be used. As
illustrated in FIG. 3, two leads LD1 are arranged around the chip
mounting part DP1, and one of them is coupled to the chip mounting
part DP1.
[0074] Subsequently, the surface electrode of the light emitting
element LED and the lead LD1 are coupled together by the wire W1
(wire bonding step), as illustrated in FIGS. 4 and 5. In FIG. 5,
the surface electrode of light emitting element LED is indicated by
a round shape.
[0075] Subsequently, the potting resin PR having a liquid or paste
form is dropped (coated) over the light emitting element LED over
the chip mounting part DP1, so that the light emitting element LED
is covered with the potting resin PR, as illustrated in FIG. 6. For
example, a silicone resin cured product, or the like, is used as
the potting resin PR. For example, a liquid silicone resin
composition is coated and then cured by being subjected to a heat
treatment. Heating temperature is, for example, approximately
160.degree. C. to 200.degree. C. Thereafter, the silicone resin
cured product is cooled to room temperature (normal
temperature).
[0076] The light emitting element LED can be protected by thus
covering it with the potting resin (silicone resin cured product)
PR. In particular, a so-called compound semiconductor, such as
GaAs, AlGaAs, or the like, is mostly used for the light emitting
element LED. Such a compound semiconductor is harder and more
brittle as compared to a semiconductor, such as, for example,
silicon. Accordingly, the stress applied to the light emitting
element LED using such a material can be relieved by covering the
light emitting element LED with a soft silicone resin cured
product. A silicone resin cured product has a flexibility higher
than that of an epoxy resin cured product. In particular, the
light-emitting property of the light emitting element LED may be
degraded due to application of stress, but degradation of the
light-emitting property can be suppressed by covering the element
LED with a soft silicone resin cured product. Further, the
distortion, occurring due to the thermal expansion difference with
the internal resin, can be suppressed by covering only the vicinity
of the light emitting element LED.
[0077] Subsequently, the light receiving element PD is mounted over
the chip mounting part DP2. For example, a die bond material (not
illustrated) is coated over the chip mounting part DP2 of the lead
frame LF, and the light receiving element PD is mounted thereover
and fixed, as illustrated in FIG. 7. The lead frame LF for the
light receiving element PD has a structure in which a plurality of
combinations of the chip mounting part DP2 and the leads LD2
arranged at the outer periphery of the part DP2 are interlinked by
a frame F. Subsequently, a plurality of the surface electrodes of
the light receiving element PD and the leads LD2 are coupled
together by the wire W2, respectively (wire bonding step).
[0078] Herein, after the light emitting element LED is mounted over
the chip mounting part DP1, the light receiving element PD is
mounted over the chip mounting part DP2, but the order of these
steps is not limited. Additionally, the potting resin PR is not
formed over the light receiving element PD in FIG. 7, but the
potting resin PR may be formed thereover. However, when a
semiconductor, such as, for example, silicon, is used as the light
receiving element PD, it is not likely to undergo stress
deformation. Accordingly, the potting resin (silicone resin cured
product) PR can be omitted.
[0079] Subsequently, the lead frame LF over which the light
emitting element LED is mounted and the lead frame LF over which
the light receiving element PD is mounted are faced with each
other, so that both the lead frames LF are sandwiched by a forming
mold M1, as illustrated in FIG. 8. Herein, the leads LD1 and LD2 of
the two lead frames LF may be processed into a desired shape by
press working, etc., if necessary.
[0080] An epoxy resin composition is injected (put) into the space
(cavity) between the forming mold M1 in the state where the two
lead frames LF are being sandwiched by the forming mold M1, and the
resin composition is subjected to a heat treatment so as to form
the internal mold resin MRI. A sealing method, in which a sealing
resin is supplied to a space formed in the forming mold M1 and then
cured as stated above, is referred to as a transfer mold
method.
[0081] Herein, an epoxy resin cured product is used as the internal
mold resin MRI in the present embodiment. In particular, an epoxy
resin cured product is used, the cured product being formed by the
reaction (thermal curing, polymerization, crosslinking, high
polymerization) between the aforementioned main agent and curing
agent in each of which the ratio of an aromatic ring is small. Also
in the present embodiment, polymerization progresses with an epoxy
group in the main agent reacting with the curing agent. This
reaction progresses by heating. By thus making the ratio of an
aromatic ring in the epoxy resin cured product small, deterioration
of the resin can be suppressed as described later. Thereby,
degradation of the light transmission property of the epoxy resin
cured product can be suppressed, and degradation of the
transmission performance for an optical signal can be reduced.
Heating temperature is, for example, approximately 160.degree. C.
to 200.degree. C. Thereafter, the aforementioned epoxy resin is
cooled to room temperature.
[0082] In this step, the light emitting element LED and the light
receiving element PD are integrated with each other by the internal
mold resin MRI. Specifically, the internal mold resin MRI is formed
between the potting resin PR and the light receiving element PD.
Also, the internal mold resin MRI is formed to surround the potting
resin PR, the light receiving element PD, and the region between
them. The potting resin PR and the internal mold resin MRI are
arranged between the light emitting element LED and the light
receiving element PD, but these resins have a light transmission
property, as described above, and hence there is no obstacle to the
transmission of an optical signal. For example, the transmittance
per mm of the thickness of each of the potting resin PR and the
internal mold resin MRI is 10% or more for the light having a
wavelength within a range of 700 nm to 1000 nm. Further, the
reflectance per mm of the thickness thereof is 90% or less for the
light having a wavelength within a range of 700 nm to 1000 nm.
[0083] A withstand voltage can be improved by adopting such a
double mold structure (sealing body structure by the potting resin
PR and the internal mold resin MRI). The withstand voltage of the
optical coupling device according to the present embodiment, the
device adopting the double mold structure, is, for example, 10 kV
or more.
[0084] Further, an epoxy resin composition, in which the ratio of
an aromatic ring is small, is used as described above, and hence
deterioration of the resin can be suppressed. Even when the device
is used particularly under a hot environment, as the case of an
in-car optical coupling device, deterioration of the resin can be
suppressed, and a decrease in the light transmission property can
be suppressed.
[0085] Thereby, the life of the device can be extended.
Specifically, in a high temperature-long term storage test, the
properties can be maintained at 150.degree. C. for 10000 hours or
longer, as described later.
[0086] Subsequently, the lead frames LF protruding from the
internal mold resin MRI are sandwiched by the forming mold M2, as
illustrated in FIG. 9. In this state, the epoxy resin composition
is injected into the space (cavity) between the forming mold M2 and
to the outer periphery of the internal mold resin MR, and then
subjected to a heat treatment. Thereby, the external mold resin MRO
covering the internal mold resin MRI is formed. For example, a
black epoxy resin cured product, or the like, can be used as the
external mold resin MRO. In the external mold resin MRO, the ratio
of an aromatic ring may be larger than that of the internal mold
resin MRI. A cured product of a composition in which, for example,
the compound represented by the above formula (3) is used as a main
agent and the compound represented by the above formula (4) is used
as a curing agent and a colorant, such as carbon, is added to them,
can be used as the external mold resin MRO. For example, the
aforementioned composition is injected into the space (cavity)
between the forming mold M2, and then subjected to a heat
treatment. Heating temperature is, for example, approximately
160.degree. C. to 200.degree. C. Thereafter, the aforementioned
epoxy resin cured product is cooled to room temperature.
[0087] Subsequently, the leads LD1 and LD2 are cut off from the
lead frames LF, and the leads (outer lead parts) LD1 and LD2 each
protruding from the external mold resin MRO are bent, as
illustrated in FIG. 10. Herein, the leads LD1 and LD2 may be bent
simultaneously with the cutting thereof.
[0088] The optical coupling device according to the present
embodiment can be formed by the aforementioned steps.
[0089] As described above, an epoxy resin cured product, in which
the ratio of an aromatic ring is small, is used as the internal
mold resin MRI in the present embodiment, and hence deterioration
of the internal mold resin MRI can be suppressed.
[0090] FIG. 11 is a sectional view illustrating a configuration of
an optical coupling device of First Comparative Example. In the
optical coupling device in FIG. 11, for example, an epoxy resin
composition, in which the ratio of an aromatic ring is large, is
used as the internal mold resin MRI.
[0091] Examples of the epoxy resin cured product in which the ratio
of an aromatic ring is large include: a cured product using an
epoxy resin containing a benzene ring in a main agent (e.g.,
o-cresol novolac-based epoxy resin, etc.); a cured product using a
phenol-based curing agent as a curing agent; a cured product of the
compound represented by the aforementioned formula (5); and the
like. If such an epoxy resin cured product is used, a void is
produced between the potting resin PR and the internal mold resin
MRI.
[0092] Occurrence of such a void will be described with reference
to FIG. 12. FIGS. 12(A) to 12(C) are schematic views illustrating a
mechanism by which a void is produced in a resin interface. There
is no chemical bond in the surface of the potting resin (silicone
resin cured product) PR covering the light emitting element LED
illustrated in FIG. 12(A), and hence the potting resin (silicone
resin cured product) PR and the internal mold resin (epoxy resin
cured product) MRI are not chemically bonded. Additionally, these
resins are materials different from each other, and hence the
coefficients of thermal expansion thereof are different from each
other. For example, the coefficients of thermal expansion of a
silicone resin (400 ppm) and an epoxy resin (22 ppm) are different
from each other by one order or more. Accordingly, when the
internal mold resin (epoxy resin cured product) MRI is heated and
then cooled to room temperature during the formation thereof, the
interface between the potting resin (silicone resin cured product)
PR and the internal mold resin (epoxy resin cured product) MRI is
exfoliated as illustrated in FIG. 12(B), thereby causing a void S
(FIG. 12(C)).
[0093] Further, if the void S is produced between the resins, the
internal mold resin (epoxy resin cured product) MRI is discolored
due to an influence by the air (oxygen) in the void S. This
discoloration will be described with reference to FIGS. 13(A) to
14. FIGS. 13(A) to 13(C) are schematic views illustrating a
mechanism by which the resin is discolored. FIG. 14 is a view
schematically illustrating a reaction in which an aromatic ring
undergoes oxidation discoloration. When the void S is produced in
the interface between the potting resin (silicone resin cured
product) PR and the internal mold resin (epoxy resin cured product)
MRI, as illustrated in 13(A), air (oxygen) enters the inside of the
void (FIG. 13(B)). The epoxy resin undergoes oxidation
discoloration due to this oxygen. In particular, an aromatic ring
has high reactivity and a carbon compound radical (free radical)
produced by oxidation combines with an aromatic ring (benzene
ring), so that a C.dbd.C bond, C--C bond, C--R bond, and the like,
are cut (FIG. 14). A benzene ring has a high electron density due
to IC electrons, and hence it is likely to be attacked by a free
radical. With this reaction, a new carbon compound radical (free
radical) is produced such that the reaction, in which the epoxy
resin cured product undergoes oxidation discoloration, progresses
in a chain reaction (FIG. 13(C)). The oxidation discoloration
reaction is likely to progress particularly in a hot
environment.
[0094] With such oxidation discoloration of the epoxy resin cured
product, the light transmission property of the epoxy resin cured
product is decreased, and the transmission performance for an
optical signal is degraded.
[0095] FIG. 15 is a sectional view illustrating a configuration of
an optical coupling device of Second Comparative Example. As the
optical coupling device of the Second Comparative Example
illustrated in FIG. 15, when the potting resin (silicone resin
cured product) PR is arranged, for example, between the light
emitting element LED and the light receiving element PD, the
interfaces between the potting resin (silicone resin cured product)
PR and the internal mold resin (epoxy resin cured product) MRI are
produced on both the sides of the light emitting element LED, and
hence the epoxy resin cured product is little influenced by an
oxidation discoloration reaction. In other words, discoloration of
the epoxy resin cured product, the discoloration intersecting the
transmission path of an optical signal between the light emitting
element LED and the light receiving element PD, is never generated.
However, in the structure of the Second Comparative Example in
which the potting resin (silicone resin cured product) PR is
arranged between the light emitting element LED and the light
receiving element PD, a spark is generated between the light
emission side and the light receiving side via the void S, thereby
decreasing the withstand voltage.
[0096] On the other hand, by adopting a double molding structure
(sealing body structure by the potting resin PR and the internal
mold resin MRI), as in the present embodiment, the withstand
voltage can be improved. Further, when an epoxy resin cured
product, in which the ratio of an aromatic ring is small, is used,
the progress of the aforementioned oxidation discoloration reaction
can be suppressed. Thereby, degradation of the transmission
performance for an optical signal can be suppressed. Furthermore,
degradation of the transmission performance for an optical signal
can be suppressed even under a hot environment, thereby allowing
the life at high temperature to be extended. For example, in a high
temperature-long term storage test, the properties can be
maintained at 150.degree. C. for 10000 hours or longer.
[0097] FIGS. 16(A) to 16(C) are schematic views illustrating a
mechanism by which discoloration of the resin is suppressed. Even
if the void S is produced as illustrated in FIG. 16 (A), the
reaction, in which an epoxy resin cured product undergoes oxidation
discoloration, is not likely to progress by using the epoxy resin
cured product in which the ratio of an aromatic ring is small,
thereby allowing the oxidation discoloration of the epoxy resin
cured product to be suppressed.
[0098] In order to make the ratio of an aromatic ring in an epoxy
resin cured product small, an aromatic ring in a main agent is
replaced by a cycloaliphatic compound, as illustrated in FIG.
16(B). For example, a benzene ring is replaced by
dicyclopentadiene. Additionally, in order to make the ratio of an
aromatic ring in an epoxy resin cured product small, a curing agent
is changed from a compound having an aromatic ring to a compound
excluding it, as illustrated in FIG. 16(C). For example, phenol is
changed to an acid anhydride.
Example
[0099] The results of oxidation discoloration tests for epoxy resin
cured products in which the ratio of an aromatic ring is small are
shown in Table 1. Three types of an epoxy resin composition A, an
epoxy resin composition B, and an epoxy resin composition C were
used as the epoxy resin compositions. Each of the epoxy resin
compositions has a main agent, in which the ratio of an aromatic
ring is lowered, and a curing agent, in which the ratio thereof is
lowered. An epoxy resin composition in which the ratio of an
aromatic ring is large, specifically, an epoxy resin composition,
having a main agent containing o-cresol novolac and a curing agent
containing phenol, was also tested in the same way, as a
comparative example (Ref).
[0100] Each of the epoxy resin compositions was cured, and a sample
thereof, having a thickness of 1 mm, was left in a thermostatic
oven (in the air) at 150.degree. C. for 500 hours. In this test,
the surface of the epoxy resin cured product is exposed to the air,
and hence the test is a more accelerated test than a test performed
in a manufactured product state. In a manufactured product state,
the internal mold resin (epoxy resin cured product) MRI is covered
with the external mold resin MRO and the paths through which air
(oxygen) is supplied are few, and hence the progress of
discoloration is slower than the values shown in Table 1. For
example, the degree of the discoloration of the epoxy resin cured
product after 150.degree. C. for 10000 hours in a manufactured
product state can be matched with the color of the epoxy resin
cured product in the sample after 150.degree. C. for 500 hours in
the present test.
TABLE-US-00001 TABLE 1 initial state 24 H 48 H 168 H 300 H 500 H
Rev. white light cream orange drown dark cream brown A white white
white white white white B white white white white white white C
white white white white white white
[0101] In the case of Comparative Example (Ref), the discoloration
of the sample that was white in the initial state progresses with
elapsed time of 24 hours, 48 hours, 168 hours, 300 hours, and 500
hours, and the sample becomes dark brown after 500 hours, as
illustrated in Table 1.
[0102] On the other hand, with respect to the epoxy resin
compositions in which the ratio of an aromatic ring is lowered, the
discoloration of the sample (epoxy resin cured product) using any
of the compositions A to C is not confirmed after 500 hours. It has
been revealed that the properties can be maintained at 150.degree.
C. for 10000 hours or longer in a manufactured product state by
using an epoxy resin cured product in which the ratio of an
aromatic ring is lowered.
CONCLUSION
[0103] Thus, by using, as a main agent (epoxy resin), a compound in
which the ratio of an aromatic ring is small, the ratio of an
aromatic ring in the epoxy resin cured product becomes small, and
hence deterioration of the resin can be suppressed.
[0104] An example of the epoxy resin in which the ratio of an
aromatic ring is small includes one containing an aromatic ring and
an alicyclic compound. An epoxy resin cured product formed by
curing the epoxy resin contains the aromatic ring and the alicyclic
compound. The ratio of an alicyclic compound in the epoxy resin or
the cured product is preferably 20% or more. The ratio of an
alicyclic compound is calculated by (the number of alicyclic
compounds/the total of the number of aromatic rings and the number
of alicyclic compounds in an epoxy resin or a cured
product).times.100%.
[0105] Alternatively, an epoxy resin or a cured product excluding
an aromatic ring may be used.
[0106] The aforementioned o-cresol novolac-type epoxy resin (main
agent) is represented by the following formula (6):
##STR00004##
[0107] In order to reduce the ratio of an aromatic ring, the
compound represented by the aforementioned formula (1)
(dicyclopentadiene-type epoxy resin (main agent)) is used in place
of the compound represented by the formula (6). That is, the
portion of a benzene ring is replaced by dicyclopentadiene (see
FIG. 16(B)).
[0108] In this case, the ratio of an aromatic ring to an alicyclic
compound is 1:1 in the repeating unit structure (structure in the
parenthesis) in the main agent. For example, when an aromatic ring
is indicated by A and an alicyclic compound by B, the structure is
represented by -(A-B)n-. In this case, the ratio of an alicyclic
compound becomes approximately 50%.
[0109] Alternatively, an epoxy resin using a nitrogen-containing
ring (e.g., triazine ring) may be used in place of an aromatic
ring. Also in this case, the ratio of an aromatic ring becomes
small. An example of an epoxy resin in which the ratio of an
aromatic ring is small includes one containing an aromatic ring and
a nitrogen-containing ring. An epoxy resin cured product formed by
curing the epoxy resin also contains the aromatic ring and the
nitrogen-containing ring. The ratio of a nitrogen-containing ring
in the epoxy resin or the cured product is preferably 20% or more.
Alternatively, an epoxy resin or a cured product excluding an
aromatic ring may be used.
[0110] Also, a compound excluding an aromatic ring (e.g., acid
anhydride), or the like, is used as the curing agent.
[0111] An epoxy resin cured product is used as the internal mold
resin MRI in the present embodiment, but a silicone resin cured
product may be used as that. A silicone resin cured product
excludes a reflecting agent, such as titanium oxide, and has a
light transmission property for the light having the wavelength of
an optical signal. For example, the transmittance per mm of the
thickness of the silicone resin cured product is 10% or more for
the light having a wavelength within a range of 700 nm to 1000 nm.
Further, the reflectance per mm of the thickness of the silicone
resin cured product is 90% or less for the light having a
wavelength within a range of 700 nm to 1000 nm. The binding energy
between atoms of a silicone resin cured product is larger than that
of an epoxy resin cured product, and hence a silicone resin cured
product is less likely to be decomposed than an epoxy resin cured
product. Further, if a silicone resin cured product is decomposed
(oxidized), it becomes a compound having a high light transmission
property, such as SiO.sub.2, and hence discoloration is not likely
to be generated. Accordingly, degradation of the transmission
performance for an optical signal can be reduced.
Second Embodiment
[0112] In the present embodiment, examples of the applications of
the optical coupling device according to First Embodiment will be
described.
[0113] A silicone resin cured product is used as the potting resin
PR in First Embodiment; however, of silicone resin cured products,
a rubber-like silicone resin cured product having a Shore A
hardness of 15 to 30 may be used as the potting resin PR.
[0114] By using such a silicone resin cured product, the
transmission property for an optical signal can be further
stabilized, in addition to the advantages of First Embodiment
(improvement in a withstand voltage, extended life at high
temperature).
[0115] It can also be considered that, for example, a gel-like,
soft silicone resin cured product having a low hardness (a Shore A
hardness of less than 20) is used. By using such a gel-like, soft
silicone resin cured product having a low hardness, the potting
resin (silicone resin cured product) PR can be deformed to follow
the concavities and convexities of the surface of the internal mold
resin (epoxy resin cured product) MRI. In such a case, a void
between the resins, which has been described in First Embodiment,
can be filled (resins can be closely adhered together), and hence
entry of oxygen can be reduced, and discoloration of the internal
mold resin (epoxy resin cured product) MRI can be reduced.
[0116] However, a gel-like, soft silicone resin cured product
having a low hardness has a tackiness, and hence the position of
the joint surface between resins is likely to change due to a
change in temperature (vertical change in temperature, reflow,
temperature cycle, etc.). For example, when a temperature is
changed (e.g., normal temperature (25.degree. C.).fwdarw.reflow
temperature (260.degree. C.).fwdarw.cooling (25.degree. C.)), the
position and size of the void S, located in the transmission path
of an optical signal, are changed as illustrated in FIGS. 17(A) to
17(C). In this case, the transmission property for an optical
signal is changed. A cohesive failure may also be caused. FIGS.
17(A) to 17(C) are schematic views illustrating the states of
voids, when a silicone resin cured product having a low hardness is
used.
[0117] On the other hand, when a rubber-like silicone resin cured
product having a certain hardness, for example, a Shore A hardness
of 15 to 30 is used, the void S may be caused and an influence by
oxygen may be caused, but changes in the position and size of the
void S becomes less than when a silicone resin cured product having
a low hardness is used, as illustrated in FIGS. 18(A) to 18(C).
Herein, with respect to an influence by oxygen, the problem of
discoloration of the resin can be avoided by lowering the ratio of
an aromatic ring in the epoxy resin cured product described in
First Embodiment. FIGS. 18(A) to 18(C) are schematic views
illustrating the states of a void, when the silicone resin cured
product according to the present embodiment is used.
[0118] Thus, with a combination of a rubber-like silicone resin
cured product having, for example, a Shore A hardness of 15 to 30
and an epoxy resin cured product in which the ratio of an aromatic
ring is small, the transmission property for an optical signal can
be stabilized, in addition to the advantages of First
Embodiment.
Third Embodiment
[0119] In the present embodiment, application examples of the
optical coupling device described in First Embodiment or Second
Embodiment will be described. The places, to which the optical
coupling device described in First Embodiment or Second Embodiment
can be applied, are not limited, and for example, the device can be
used in the power conversion system described below.
[0120] FIG. 19 is an illustrative view (circuit block view)
illustrating one example of a power conversion system (power
conversion apparatus) according to the present embodiment.
[0121] The power conversion system illustrated in FIG. 19 has a
load, such as a motor MOT, an inverter (amplifier circuit part)
INV, a power supply BAT, a controller (control circuit) CTC, and
photocouplers (optical coupling devices, optical coupling parts)
PC. Herein, a three-phase motor is used as the motor MOT. A
three-phase motor is configured to be driven by a voltage having
three phases different from each other. The photocoupler PC is an
optical coupling part to be inserted between an electrical circuit
that forms the inverter INV and an electrical circuit that forms
the controller CTC. The photocoupler PC has a function to
electrically insulate the inverter INV and the controller CTC from
each other and to transmit a signal from the controller CTC toward
the inverter INV.
[0122] In the power conversion system in FIG. 19, the power supply
BAT is to be coupled to the inverter INV such that a voltage
(power) of the power supply BAT is supplied to the inverter
INV.
[0123] Alternatively, a voltage to be supplied to the inverter INV
may be converted, or the coupling state between the power supply
BAT and the inverter INV may be switched by interposing a
non-illustrated converter or relay between the power supply BAT and
the inverter INV. The motor MOT is coupled to the inverter INV, so
that a DC voltage (DC power) supplied from the power supply BAT to
the inverter INV is converted into an AC voltage (AC power) by the
inverter INV so as to be supplied to the motor MOT. The motor MOT
is driven by the AC voltage (AC power) supplied from the inverter
INV.
[0124] The controller CTC is also coupled to the inverter INV, so
that the inverter INV is controlled by the controller CTC. That is,
a DC voltage (DC power) is supplied from the power supply BAT to
the inverter INV, which is converted into an AC voltage (AC power)
by the inverter INV controlled by the controller CTC and then
supplied to the motor MOT, thereby allowing the motor MOT to be
driven. The controller CTC is formed, for example, by an ECU
(Electronic Control Unit), and has a built-in controlling
semiconductor chip, such as an MCU (Micro Controller Unit).
[0125] The inverter INV has six IGBTs (Insulated Gate Bipolar
Transistors) 10, corresponding to three phase. That is, in each of
the three phase, the IGBTs 10 are coupled between a power supply
potential (VCC) supplied from the power supply BAT to the inverter
INV and an input potential of the motor MOT, and between the input
potential of the motor MOT and a ground potential (GND),
respectively.
[0126] The motor MOT is to be driven (rotated) by controlling a
current flowing through the IGBT 10 with the controller CTC. That
is, the motor MOT can be driven by controlling ON/OFF of the IGBT
10 with the controller CTC.
[0127] In this case, if the inverter INV, through which a
relatively large current for driving the motor MOT flows, and the
controller CTC, through which a relatively small current, such as a
control signal, flows, are electrically coupled together, there is
the concern that noise may be caused on the controller CTC
side.
[0128] So, by inserting the photocoupler PC, having a function to
electrically insulate the inverter INV and the controller CTC from
each other and to transmit a signal from the controller CTC toward
the inverter INV, as illustrated in FIG. 19, the reliability of the
power conversion system can be improved.
[0129] Further, by using the optical coupling device described in
First Embodiment or Second Embodiment as the photocoupler PC to be
used in the aforementioned power conversion system, the reliability
of the power conversion system to be improved.
[0130] The invention made by the present inventors has been
specifically described above based on preferred embodiments;
however, it is needless to say that the invention should not be
limited to the preferred embodiments and various modifications may
be made to the invention within a range not departing from the gist
of the invention. For example, a photocoupler is exemplarily
described as an optical coupling device in First Embodiment;
however, the resin described in First Embodiment may be applied to
an optical MOSFET.
* * * * *