Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With housing or contact structure
Reexamination Certificate
2002-04-09
2004-03-23
Flynn, Nathan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With housing or contact structure
C257S100000, C257S081000, C257S684000, C257S788000, C257S791000
Reexamination Certificate
active
06710377
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-110675, filed on Apr. 9, 2001; the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
This invention relates to a light emitting device, in particular, having a structure where a semiconductor light emitting element is sealed by a resin element.
Light emitting devices including LEDs (light emitting diodes) or other semiconductor light emitting have been widely used as various kinds of indicators, light sources, flat-type display devices, backlight of liquid crystal displays, and so forth.
The typical light emitting devices have a structure where a light emitting element is sealed by a resin in order to protect the element against a outer atmosphere or mechanical shocks.
FIG. 10
shows such a typical conventional light emitting device. The light emitting device shown here is of a so-called “surface mounting” type, including a package (resin stem)
800
, semiconductor light emitting element
802
and sealing element
804
of a resin.
The resin stem
800
has a structure molding a pair of leads
805
,
806
shaped from lead frames with a resin portion
803
of a thermoplastic resin. The resin portion
803
has an opening
801
, and the semiconductor light emitting element
802
is place therein. Then the semiconductor light emitting element
802
is sealed with an epoxy resin
804
.
The semiconductor light emitting element
802
is mounted on the lead
806
. An electrode (not shown) of the semiconductor light emitting element
802
and the lead
805
are connected to each other by a wire
809
. When en electric power is supplied to the semiconductor light emitting element
802
through those two leads
805
,
806
, the semiconductor light emitting element
802
emits light, and the light is extracted from an emission surface
812
via the epoxy resin
804
.
The Inventor, however, made researches and has found that conventional light emitting devices of this type have still room for improvement from the viewpoint of reliability and long-time stability.
That is, through temperature cycle tests of 700 cycles under temperatures in the range from −40° C. to 110° C., various undesirable phenomena were observed, such as cracks C in the epoxy resin
804
as shown in
FIG. 11
, or exfoliation of the epoxy resin
804
at the interface I with the resin stem
800
. In some cases, the semiconductor light emitting element
802
broke, or exfoliated from the mount surface, and the wire
809
cut down.
The light emitting device shown in
FIG. 10
certainly meets the requirements currently in force, i.e., 100 cycles as the current level of temperature cycle tests requested for ordinary civilian uses, and 300 cycles for car-borne uses. However, for further improvement of the reliability toward the future uses, essential review is required.
The same circumstances commonly exist in all structures sealing semiconductor elements with epoxy resin, without being limited to that shown in FIG.
10
.
As a result of a careful review of malfunctioning mechanisms, the inventor has realized that the epoxy resin
804
is physically hard and fragile and produces a large stress upon hardening and that there still exists room for improvement in the quality of close contact with the resin portion
803
of a thermoplastic resin that surrounds it.
SUMMARY OF THE INVENTION
The invention has been made upon recognition of those problems. It is therefore an object of the invention to provide a light emitting device of a type sealing a semiconductor light emitting element with a resin, which can improve the reliability and long-time stability, and can compactly mount a plurality of chips.
According to an embodiment of the invention, there is provided a light emitting device comprising: a semiconductor light emitting element; and a silicone resin provided to embed the semiconductor light emitting element, the silicone resin having a hardness not lower than 50 in JISA value.
The present application contemplates, with the term “silicone resin”, any resin having as its skeleton a structure in which silicon atoms having organic radicals such as alkyl radicals or aryl radicals are alternately connected to oxygen atoms. Needless to say, those containing additive elements added to such skeletons are also included in “silicone resins”.
REFERENCES:
patent: 5430330 (1995-07-01), Takahama et al.
patent: 5832600 (1998-11-01), Hashimoto
patent: 5861680 (1999-01-01), Yamanaka
patent: 62054974 (1987-03-01), None
Flynn Nathan
Greene Pershelle
Hogan & Hartson LLP
Kabushiki Kaisha Toshiba
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