Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – Encapsulated
Reexamination Certificate
2003-01-23
2004-05-04
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
Encapsulated
C257S788000, C313S512000
Reexamination Certificate
active
06730942
ABSTRACT:
The present application is based on Japanese Patent Applications No. 2002-016181 and No. 2002-016182, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a light emitting apparatus. More particularly, the invention relates to an improvement in a sealing member for a light emitting apparatus using a group III nitride compound semiconductor light emitting element (hereinafter referred to simply as “light emitting element,” such as LED, as a light source.
2. Related Art
In conventional light emitting apparatuses, an LED is mounted on a cup part in a mount lead, and the LED is connected to an inner lead through an electrically conductive wire. The LED is covered, together with the electrically conductive wire, a part of the mount lead, and a part of the inner lead, with a sealing member formed of a light transparent resin.
In the light emitting apparatuses having the above construction, it is common practice to form the sealing member using a transparent epoxy resin. When light emitting elements, which emit short-wavelength light, are used with the epoxy resin as the sealing member, a change in color (discoloration) of the sealing member occurs. This color change has been estimated to be attributable to a double bond in the epoxy resin, and, to solve this problem, the use of an alicyclic epoxy resin has been proposed in Japanese Patent Laid-Open No. 274571/1999.
The use of the alicyclic epoxy resin can certainly improve the resistance to discoloration of the sealing member. The alicyclic epoxy resin, however, causes a deterioration in mechanical and physical properties of the sealing member, for example, due to very high curing speed and the occurrence of distortion after curing, resulting in increased susceptibility to cracking of the sealing member.
In view of these points, the present applicant has proposed in Japanese Patent Laid-Open No. 196642/2001 the use, as the sealing member, of a hydrogenated epoxy resin produced by hydrogenating an aromatic epoxy resin. This hydrogenated epoxy resin has a hydrogenation ratio in an aromatic ring of not less than 85%, a loss ratio of epoxy groups of not more than 20%, and a total chlorine content of not more than 0.3% by weight.
It is an object of the invention to provide a sealing member which, while ensuring resistance to discoloration and resistance to cracking comparable to those in the invention described in Japanese Patent Laid-Open No. 196642/2001, has a novel composition provided by improving the technique described in the prior application.
Further, in view of the fact that the discoloration of the sealing member is considered attributable to short-wavelength light emitted from the light emitting element, as well as to heat generated from the light emitting element, it is another object of the invention to provide a sealing member which possesses excellent heat resistance in addition to the resistance to discoloration and the resistance to cracking.
SUMMARY OF THE INVENTION
The present inventors have made extensive and intensive studies on the relationship between a light emitting element of a group III nitride compound semiconductor and an epoxy resin. As a result, they have found that a mixture of an alicyclic epoxy produced by hydrogenating an aromatic epoxy and an alicyclic epoxy having a lower molecular weight than the alicyclic epoxy described just above in a given mixing ratio can provide a sealing member which has high resistance to light and heat and is less likely to be deteriorated. The invention has been made based on such finding and has the following construction.
Specifically, according to the invention, there is provided a light emitting apparatus comprising:
a group III nitride compound semiconductor light emitting element; and
a sealing member for covering the light emitting element on its light emission side,
said sealing member comprising:
a main agent comprising a first component of an alicyclic epoxy produced by hydrogenating an aromatic epoxy and a second component of an alicyclic epoxy having a lower molecular weight than the first component, the mixing amount of the second component being not less than 10% by weight and less than 30% by weight based on the main agent, and
a curing agent.
According to the light emitting apparatus having the above construction, when a mixture of the first component and the second component in a predetermined ratio is used as the main agent of the sealing member, excellent mechanical and physical properties can be ensured while maintaining the resistance to discoloration of the sealing member.
In carrying out our invention in one preferred mode, when the acid anhydride is selected as the curing agent, the sealing member can be of two-component type before curing. This can improve working properties particularly at the time of molding of the sealing member. Consequently, the light emitting apparatus can be provided at low price.
Further, in another preferred mode, when the cationic polymerization catalyst is selected as the curing agent, the sealing member can be of one-component type before curing. This is suitable for use of the epoxy resin as an adhesive (a, paste) for bonding the light emitting element, for example, to, a lead frame.
REFERENCES:
patent: 6060611 (2000-05-01), Hara et al.
patent: 6617787 (2003-09-01), Kato et al.
patent: 2001/0008484 (2001-07-01), Kato et al.
patent: 11-199645 (1999-07-01), None
patent: 11-274571 (1999-10-01), None
patent: 2001-196642 (2001-07-01), None
patent: 2003-13001 (2003-01-01), None
Kawamura Masato
Mabuchi Akira
Matsumura Kanae
Yasukawa Takemasa
Crane Sara
McGinn & Gibb PLLC
Toyoda Gosei Co,., Ltd.
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