WO2018014959A1

WO2018014959A1 - Optoelectronic light emitting unit

Info

Publication number: WO2018014959A1
Application number: PCT/EP2016/067361
Authority: WO
Inventors: Alias ASLIZA
Original assignee: Osram Opto Semiconductors GmbH
Current assignee: Ams Osram International GmbH
Priority date: 2016-07-21
Filing date: 2016-07-21
Publication date: 2018-01-25
Anticipated expiration: 2019-01-21

Abstract

The invention refers to an optoelectronic light emitting unit comprising a light emitting device (1), wherein the light emitting device (1) is at least partially covered with a layer (3), wherein the layer (3) has silicone rubber particles.

Description

OPTOELECTRONIC LIGHT EMITTING UNIT

DESCRIPTION The invention refers to an optoelectronic light emitting unit according to claim 1.

Optoelectronic light emitting units can be embodied as light emitting diodes that are at least partially covered with a light-transparent layer. The light-transparent layer has ma^¬ trix material and fillers and diffusors. The fillers and dif- fusors are made of fumed or fused silicon dioxide.

It is an object of the invention to provide an improved opto- electronic light emitting unit.

The object of the invention is attained by the optoelectronic light emitting unit according to claim 1. Further embodiments of the light emitting unit are disclosed in the dependant claims.

One advantage of the proposed light emitting unit is that the transparent layer has an improved crack resistance. The im^¬ proved crack resistance is caused by a lower rigidity of the layer. These improved features are attained by the silicone rubber particles that are in the transparent layer. Further^¬ more, the light emitting unit is less sensitive for tempera^¬ ture changes. Therefore, a long term stability of the light emitting unit is attained. Especially outdoor applications of the light emitting unit are improved since the light emitting unit is less sensitive and more robust for thermal cycles. Furthermore, the flexibility and toughness of the transparent layer is improved without reducing the mechanical strength of the layer and without reducing moisture resistance of the layer. The silicone rubber particles act as stress absorber and improve the impact resistance of the layer. Furthermore, the heat and ultraviolet light resistance of the layer is in^¬ creased . In an embodiment, the transparent layer comprises particles having a diameter between 1 and 100 ym, especially between 1 and 35 ym. Experiments have shown that this range of diameter provides good mechanical and chemical and physical properties for the layer.

In a further embodiment, the particles have a medium diameter between 0.7 ym and 15 ym, especially between 2 ym and lOym. This medium diameter range provides a good quality for the layer. In a further embodiment, the rubber particles have a spherical shape. The spherical shape provides an equal elas^¬ ticity in different directions of the layer. The provided improved light-transparent layer can be used for at least partially covering a light emitting diode.

In a further embodiment, the layer has epoxy resin as a ma^¬ trix material. The epoxy resin and the silicone rubber parti- cles provide a specific material system with a high function^¬ ality for the optoelectronic light emitting unit. The sili^¬ cone rubber particles can easily be mixed in a liquid or pasty epoxy resin material. The epoxy resin material is light-transparent and provides a suitable mechanical protec- tion of the light emitting unit.

In one embodiment, the silicone rubber particles represent at least 0.1 weight percent of the layer. Depending on the used embodiment, the silicone rubber particles may represent more than 0.1 weight percent of the layer. The silicone rubber particles may represent up to 50 weight percent of the layer or more. This range of mixture between the matrix material and the silicone rubber particles provides a sufficient transparency of the layer and a sufficient rigidity of the layer and a sufficient elasticity of the layer.

In one embodiment, the silicone rubber particles have a hard^¬ ness between 10 durometer A and 90 durometer A. This range of hardness can be used for different applications of the light emitting unit to provide a transparent layer with suitable properties . In a further embodiment, the silicone rubber particles have a tensile strength between 5 N/mm² and 15 N/mm². This range of tensile strength is sufficient for the silicone rubber mate^¬ rial in the provided transparent layer. In a further embodiment, the transparent layer may have fur^¬ ther particles and further material, for example luminescent material. The luminescent material is embodied to convert a wave length of light to another wave length. The luminescent material may be used to convert a blue light of a light emit- ting unit with a converted orange light to attain a white light .

In a further embodiment, the silicone rubber particles have a moisture of less than 0.5 % preferably less than 0.1 weight percent. Therefore, the transparent layer and the light emit^¬ ting unit are protected against moisture.

In a further embodiment, the silicone rubber particles are coated with a cover layer. The cover layer may be made of epoxy resin. The cover layer is used to improve a compatibil^¬ ity of the silicone rubber powder and the matrix material.

The above-described properties, features and advantages of this invention and the way in which they are achieved will become clearer and more clearly understood in association with the following description of the exemplary embodiments which are explained in greater detail in association with the drawings. Here in schematic illustration in each case: Fig. 1 shows a schematic cross-sectional view of a light emitting unit,

Fig. 2 shows a top view on the light emitting unit, Fig. 3 shows a schematic cross-sectional view of a fur^¬ ther embodiment of a light emitting unit, Fig. 4 shows a top view of the light emitting unit of

Fig. 3,

Fig. 5 shows a cross-sectional view of a further embodi^¬ ment of a light emitting unit,

Fig. 6 shows a top view on the light emitting unit of

Fig. 5,

Fig. 7 shows a schematic view of a silicone rubber par- ticle, and

Fig. 8 shows a cluster of silicone rubber particles.

Fig. 1 shows a schematic cross-sectional view of a light emitting unit 1 that may for example be embodied as light emitting diode. The light emitting unit may be embodied as an optoelectronic semiconductor chip that is embodied to gener^¬ ate electromagnetic radiation. The light emitting unit may be embodied as a semiconductor laser diode for example. The light emitting unit 1 comprises at least one emission face 2 that emits electromagnetic radiation for example visible light. The emission face 2 is in this embodiment arranged on an upper side of the light emitting unit 1. The emission face 2 is covered by a layer 3 that is at least transparent for the electromagnetic radiation that is generated by the light emitting unit 1. A layer is transparent if at least 30 % or at least 50% or more of incident electromagnetic radiation is transmitted. The transparent layer 3 comprises silicone rub^¬ ber particles 4. The layer 3 furthermore comprises matrix ma- terial 12. The matrix material 12 may be for example silicone or epoxy resin. The epoxy resin material may be based on a cycloaliphatic-based epoxy resin material. The silicone rubber particles 4 may be provided as powder and mixed with liquid matrix material and deposited on the emis^¬ sion face 2. The silicone rubber particles 4 may be homogene- ously mixed in the matrix material 12. The silicone rubber particles 4 have a distinctive property compared to inorganic filler or silicone resin particles. Unlike silicone resin powder which has a cage-like structure (polymethylsiloxane) , silicone rubber particles have a linear cross-linked struc- ture that provides a flexible and stress-relieving property. The silicone rubber particles may have a spherical shape. The silicone rubber particles will deform more easily under ex^¬ erted pressure in contrast to silicone resin powder and anor^¬ ganic filler that sustain their shapes.

Depending on the used embodiment, the layer 3 may comprise further material despite the matrix material and the silicone rubber particles. For example filler particles or diffusor particles or luminescent material 13 for converting a wave- length of an electromagnetic radiation may be arranged in the layer 3.

The silicone rubber particles are made of an elastomer (rub^¬ ber-like material) composed of silicone - itself a polymer - containing silicone together with carbon, hydrogen and oxygen. Silicone rubber particles may be embodied as one- or two-part polymers, and may contain fillers to improve proper^¬ ties. Silicone rubber particles may be made of polysiloxanes that consist of Si-O-Si units. Polysiloxane is very flexible due to large bond angles and bond length when compared to basic polymers such as polyethylene. The silicone rubber par^¬ ticles are generally non-reactive, stabile and resistant to extreme temperatures from -55 °C to +300 °C while still main^¬ taining its properties. Silicone rubber is in its uncured state a highly-adhesive gel or liquid. In order to convert it to a solid, it must be cured, vulcanized or catalysed. This is normally carried out in a two-stage process at a point of production and in a prolonged post-cure process. Silicone rubber may be cured with a platinum-catalysed cure system, a condensation cure system or a peroxide cure system.

A method for producing silicone rubber is disclosed in EP 0 796 883 Bl . Furthermore, the silicone rubber particles are produced by the company Shin-Etsu with the product names KMP- 594 for example. The silicone rubber particles are produced as a silicone rubber powder and are mixed with a matrix mate^¬ rial for example epoxy resin. Fig. 2 shows a schematic top view on the emission face 2 of the light emitting unit 1. The layer 3 covers in this embodi^¬ ment the whole emission face 2. The silicone rubber particles 4 are for example homogeneously distributed in the matrix ma^¬ terial 12 of the layer 3.

In a further embodiment that is shown in Fig. 3, side faces 7, 8 of the light emitting unit 1 are covered by the layer 3. The light emitting unit 1 is arranged on a carrier 6. The carrier 6 can be made of sapphire, metal, silicon, silicone, printed circuit board or any other suitable material. The side faces 7, 8 of the layer 3 are covered by the layer 3. The layer 3 comprises a matrix material and the silicone rub^¬ ber particles 4. Depending on the used embodiment, the side faces 7, 8 of the light emitting unit 1 may be embodied as emission faces that radiate electromagnetic radiation.

Fig. 4 shows a top view on the arrangement of Fig. 3. The layer 3 circumvents the light emitting unit 1 on the four side faces 7, 8, 9, 10.

Fig. 5 shows a further embodiment of a light emitting unit 1 that is covered with a layer 3, wherein the layer 3 comprises silicone rubber particles 4. In this embodiment, the light emitting unit 1 is arranged on a carrier 6. All side faces 7, 8 and the upper face 2 of the light emitting unit 1 are cov^¬ ered with the layer 3. Fig. 6 shows a schematic top view on the arrangement of Fig. 5.

Fig. 7 shows a schematic view of a silicone rubber particle 4. The silicone rubber particle 4 has in this embodiment a spherical shape. Depending on the used embodiment, the rubber particle may also have other shapes. In a further embodiment, the silicone rubber particle 4 may comprise a cover layer 5. The cover layer 5 may be made of a material that is different to the material of the silicone rubber particle. For example the cover layer 5 may be made of the same material as the ma^¬ trix material of the layer 3. In one embodiment, the cover layer 5 may be made of epoxy resin. Since the silicone rubber particle 4 has a spherical shape, it can deform its shape to- wards any direction. Therefore, an increased flexibility of the layer 3 is attained.

Fig. 8 shows a schematic illustration of a cluster 11 comprising several silicone rubber particles 4. In a further em- bodiment, the silicone rubber particles 4 of the layer 3 may be connected to clusters 11 comprising several single sili^¬ cone rubber particles 4 for example ten or more. Also the silicone rubber particles 4 of the cluster 11 may comprise a cover layer 5 as shown in Fig. 7.

The layers 3 of the above explained embodiments may addition^¬ ally comprise fillers, luminescent material or scattering ma^¬ terial. The layer 3 of the above discussed embodiments may provide a mechanical protection, a chemical protection and may provide an optical function. For example the layer 3 may be embodied as a scattering layer or as a conversion layer.

The layers 3 of the above explained embodiments may have sil^¬ icone rubber particles that have a diameter between 1 and 100 ym, especially between 1 ym and 30 ym. The layers 3 of the above explained embodiments may have silicone rubber parti^¬ cles with a medium diameter between 0,7 ym and 15 ym, especially between 2 ym and 10 ym. The layers 3 of the above explained embodiments comprise ma^¬ trix material and silicone rubber particles, wherein the sil^¬ icone rubber particles represent 0,1 % to 50% weight of the layer. The layers 3 of the above explained embodiments may have silicone rubber particles with a hardness between 10 and 90 durometer A, especially about 30 durometer A. The layers 3 of the above explained embodiments may have silicone rubber particles with a tensile strength between 5 N/mm2 and 15 N/mm2. The layers 3 of the above explained embodiments may have silicone rubber particles with a moisture of less than 0,5% of weight, preferably less than 0,2% of weight.

Depending on the used embodiment, additional layers may be arranged between the light emitting unit 1 and the layer 3. Therefore, it is not necessary for the advantageous proper^¬ ties of the discussed embodiments that the layer 3 is direct^¬ ly arranged on a face of the light emitting unit 1, for exam^¬ ple on a face of an optoelectronic semiconductor chip.

The invention has been illustrated and described in detail with the aid of the preferred exemplary embodiments. Never^¬ theless, the invention is not restricted to the examples dis^¬ closed. Rather, other variants may be derived therefrom by a person skilled in the art without departing from the protec^¬ tive scope of the invention.

REFERENCE SYMBOLS

1 light emitting unit

2 emission face

3 layer

4 silicone rubber particle

5 cover layer

6 carrier

7 side face

8 second side face

9 third side face

10 fourth side face

11 cluster

12 matrix material

13 luminescent material

Claims

1. Optoelectronic light emitting unit (1), wherein the light emitting unit (1) is at least partially covered with a layer (3) , wherein the layer (3) having silicone rubber particles ( 4 ) .

2. The light emitting unit of claim 1, wherein the layer is transparent for electromagnetic radiation, especially for the light that is emitted by the light emitting unit.

3. The unit of claim 1 or 2, wherein the silicone rubber

particles (4) have a diameter between 1 and 100 ym, espe^¬ cially between 1 ym and 30 ym.

4. The unit of any one of the preceding claims, wherein the silicone rubber particles (4) have a medium diameter be^¬ tween 0,7 ym and 15 ym, especially between 2 ym and 10 ym.

5. The unit of the preceding claims, wherein the light emit^¬ ting unit (1) is embodied as a light emitting diode.

6. The unit of any one of the preceding claims, wherein the layer (3) comprises epoxy resin as matrix material (12) .

7. The unit of any one of the preceding claims, wherein the layer (3) comprises matrix material (12) and the silicone rubber particles (4), wherein the silicone rubber parti^¬ cles (4) represent 0,1 % to 50% weight of the layer (3) .

8. The unit of any one of the preceding claims, wherein the silicone rubber particles (4) have a hardness between 10 and 90 durometer A, especially about 30 durometer A.

9. The unit of any one of the preceding claims, wherein the silicone rubber particles (4) have a tensile strength be^¬ tween 5 N/mm² and 15 N/mm².

10. he unit of any one of the preceding claims, wherein the layer (3) has luminescent material (13) that is embodied to convert a wavelength of an electromagnetic radiation to a different wavelength.

11. he unit of any one of the preceding claims, wherein the silicone rubber particles (4) have a moisture of less than 0,5% of weight, preferably less than 0,2% of weight.

12. The unit of any one of the preceding claims, wherein an emission face (2) of the light emitting unit (1) is at least partially covered by the layer (3) .

13. The unit of any one of the preceding claims, wherein at least a side face (7, 8, 9) of the light emitting unit is at least partially covered with the layer (3) .

14. The unit of any one of the preceding claims, wherein the silicon rubber particles (4) are covered with a cover layer (5) .

15. The unit of any one of the preceding claims, wherein the light emitting unit (1) is a semiconductor light emitting chip, wherein at least a part of the semiconductor light emitting chip is covered with the layer (3) , wherein preferably a light emitting face (2) of the semiconductor chip is covered with the layer (3) .