Process for producing a layer composite consisting of a luminescence conversion layer and a scattering layer

A process of producing a layer composite includes a luminescence conversion layer and a scattering layer, wherein a press having a first pressing tool with a cavity and a second pressing tool is used including introducing a first polymer including a luminescence conversion substance into the cavity, inserting a film between the first and second tools, closing the press and carrying out a first pressing, hardening the first polymer to form a luminescence conversion layer in the press, opening the press, wherein the luminescence conversion layer adhering to the film remains in the press, introducing a second polymer including scattering particles into the cavity, closing the press and carrying out a second pressing, hardening the second polymer to form a scattering layer disposed on the luminescence conversion layer, opening the press, and removing the support film with the layer composite including the luminescence conversion layer and the scattering layer.

RELATED APPLICATIONS

This is a §371 of International Application No. PCT/EP2011/062470, with an international filing date of Jul. 20, 2011 (WO 2012/022576 A1, published Feb. 23, 2012), which is based on German Patent Application No. 10 2010 034 923.2, filed Aug. 20, 2010, the subject matter of which is incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to a process of producing a layer composite which has a luminescence conversion layer and a scattering layer, wherein the layer composite is provided in particular for use in a radiation-emitting optoelectronic component.

BACKGROUND

WO 97/50132 discloses a radiation-emitting optoelectronic component in which at least some of the radiation emitted by an active layer of the optoelectronic component is converted by a luminescence conversion layer to longer wavelengths. In this manner, mixed-color or white light can be produced, e.g., with a radiation-emitting active zone which emits ultraviolet or blue light. By the luminescence conversion layer, ultraviolet or blue light is thereby generally converted into light of a longer wavelength, in particular into light of a complementary color such as yellow, for example, to generate white light.

In the case of that type of generation of white light by luminescence conversion, the visual impression of the optoelectronic component in the switched-off state is often unsatisfactory. The reason for this is that in a bright environment even when the optoelectronic component is in the switched-off state the luminescence conversion layer is excited to emit yellow light which, however, in contrast to the operating state is not mixed with emitted ultraviolet or blue light to produce white light. As a consequence, the surface of the optoelectronic component in the switched-off state has, in the regions provided with the luminescence conversion layer, the color of the longer wavelength generated by luminescence conversion, e.g., yellow, which is often perceived by observers as unattractive. This is the case in particular with comparatively large-scale illumination units which are based, e.g., upon organic light-emitting diodes (OLEDs), but also with LEDs or LED modules having one or a plurality of radiation-emitting semiconductor chips.

To reduce the yellow color impression of the luminescence conversion layer when a radiation-emitting, optoelectronic semiconductor chip is in the switched-off state, it is proposed in DE 10 2006 051 746 A1 to dispose a light-scattering layer, which contains, e.g., scattering particles, above the luminescence conversion layer.

In the case of radiation-emitting, optoelectronic components which have that type of layer sequence consisting of a luminescence conversion layer and a scattering layer, the resulting color impression in the switched-on and/or switched-off state depends in particular upon the thicknesses of the luminescence conversion layer and the scattering layer and upon the properties of the boundary surfaces of these layers. In particular, deviations in the layer thicknesses of the luminescence conversion layer and/or the scattering layer can lead to a deviation in the color impression of the optoelectronic component from a desired reference value.

It could therefore be helpful to provide a process of producing a layer composite having a luminescence conversion layer and a scattering layer, which renders it possible to produce the layers of the layer composite with a high degree of precision in relation to the layer thicknesses and dimensions thereof, wherein the production outlay is relatively small.

SUMMARY

We provide a process of producing a layer composite including a luminescence conversion layer and a scattering layer in which a molding press having a first pressing tool with a cavity and a second pressing tool is used including introducing a first polymer including a luminescence conversion substance into the cavity, inserting a support film between the first and the second pressing tool, closing the molding press and carrying out a first pressing procedure, hardening the first polymer to form a luminescence conversion layer in the molding press, opening the molding press wherein the luminescence conversion layer adhering to the support film remains in the molding press, introducing a second polymer including scattering particles into the cavity, closing the molding press and carrying out a second pressing procedure, hardening the second polymer to form a scattering layer disposed on the luminescence conversion layer in the molding press, opening the molding press, and removing the support film with the layer composite including the luminescence conversion layer and the scattering layer.

DETAILED DESCRIPTION

In the case of the process of producing a layer composite having a luminescence conversion layer and a scattering layer, a compression molding process is employed. A molding press is used which has a first pressing tool and a second pressing tool. The first pressing tool is, e.g., the lower pressing tool and the second pressing tool is the upper pressing tool of the molding press. During the pressing procedure, the first pressing tool and the second pressing tool can be compressed at high pressure to press a material, in particular a polymer, located in the press to form a shape defined by the shape of the pressing tools.

Preferably, the first pressing tool, in particular the lower pressing tool of the molding press, has a cavity into which a preferably liquid polymer can be introduced.

In the process, a first polymer which contains a luminescence conversion substance is introduced into the cavity of the first pressing tool. The thickness of the luminescence conversion layer produced by the process can be advantageously adjusted very precisely by the fill quantity of the first polymer introduced into the cavity of the first pressing tool.

Furthermore, a support film is inserted in the process between the first pressing tool and the second pressing tool. The support film is used for the purpose of being able to remove the layer composite in a convenient manner from the molding press after the process has been carried out. The support film used is preferably a particularly temperature-stable film, e.g., consisting of PI (polyimide) or ETFE (ethylene tetrafluoroethylene).

The molding press is then closed and a first pressing procedure is carried out. The first polymer is then hardened in the preferably still closed moulding press to form a luminescence conversion layer.

The molding press is then opened, wherein the produced luminescence conversion layer adheres to the support film. At this point in time, the support film having the luminescence conversion layer adhering thereto is still not removed from the molding press, but rather continues to remain in the molding press. In particular, the support film having the luminescence conversion layer adhering thereto can be held on the second pressing tool.

A second polymer which contains scattering particles is then introduced into the cavity of the first pressing tool. As in the case of the luminescence conversion layer, the thickness of the scattering layer produced by the process can be adjusted very precisely by the fill quantity of the second polymer introduced into the cavity of the first pressing tool.

The molding press is then reclosed and a second pressing procedure is carried out in which the second polymer is pressed onto the luminescence conversion layer still present in the molding press.

The second polymer is then hardened in the preferably still closed molding press to form a scattering layer disposed on the luminescence conversion layer. The molding press is then opened and the support film together with the layer composite consisting of luminescence conversion layer and the scattering layer is removed.

The layer composite consisting of the luminescence conversion layer and the scattering layer which adheres to the support film can then be removed from the support film and applied in particular to a radiation-emitting, optoelectronic semiconductor chip.

The described process of producing a layer composite consisting of the luminescence conversion layer and the scattering layer renders it possible in an advantageous manner to achieve a high level of precision in relation to planarity, plane parallelism, layer thickness and roughness of the luminescence conversion layer and the scattering layer. Upon application of the layer composite to a radiation-emitting semiconductor chip, good homogeneity is advantageously achieved with regard to white impression, chromaticity coordinate and brightness. In particular, these variables can be effectively reproduced in series production.

Preferably, the first polymer and the second polymer have the same base material. “Base material” is understood to be the material into which, in the case of the luminescence conversion layer, the luminescence conversion substance is embedded and, in the case of the scattering layer, the scattering particles are embedded. In an advantageous manner, the base material of the luminescence conversion layer and scattering layer is therefore the same apart from these embedded additives. On the one hand, this has the advantage that the luminescence conversion layer and the scattering layer adhere well to one another. Furthermore, reflection losses at the boundary surface between the luminescence conversion layer and the scattering layer are reduced in this manner.

Advantageously, the base material of the luminescence conversion layer and/or scattering layer is a silicone. Silicones are characterized by high long-term stability, in particular low sensitivity to UV-radiation.

Preferably, the support film is fixed onto a support frame. The support film can conveniently be inserted into the molding press with the support frame and then be removed after the pressing procedures.

Prior to introduction of the first and/or second polymer, a film is preferably inserted into the cavity of the first pressing tool. In this manner, the cavity and the material introduced into the cavity are advantageously protected against contamination. Preferably, a film is used to which the first and/or second polymer introduced into the cavity adhere(s) only slightly. This ensures that the luminescence conversion layer produced in the pressing procedure continues to adhere to the support film, but not to the film in the cavity.

The film inserted into the cavity is preferably fixed in the cavity by a negative pressure. For example, the cavity can have intake openings which can be connected to a vacuum pump. By virtue of the fact that the film is fixed in the cavity by a negative pressure, it adapts in an advantageous manner to the contour of the cavity.

The cavity in the first pressing tool is advantageously evacuated after closure of the molding press, before the pressing procedure is carried out. This prevents, in the luminescence conversion layer and/or scattering layer produced in the pressing procedure, the occurrence of air inclusions or inhomogeneities in thickness which could result in color inhomogeneities in an optoelectronic component.

The luminescence conversion layer preferably has a thickness of 10 μm to 200 μm. Like the luminescence conversion layer, the scattering layer produced in the second pressing procedure also preferably has a thickness of 10 μm to 200 μm. In particular, the luminescence conversion layer and the scattering layer can have the same thickness.

Suitable luminescence conversion substances contained in the luminescence conversion layer are described, e.g., in WO 98/12757, the subject matter of which is hereby incorporated herein by reference. The scattering particles contained in the scattering layer can be in particular particles consisting of TiO2. However, other particles can also be used, whose refractive index differs from the refractive index of the base material of the scattering layer such as, e.g., particles consisting of Al2O3or particles consisting glass or synthetic material which are, e.g., spherical or in the form of hollow spheres. The scattering particles preferably have a radius of 50 nm to 1000 nm.

After production, the layer composite consisting of the luminescence conversion layer and the scattering layer can be cut to a desired size preferably by punching, cutting, water jet cutting or with a laser beam.

The layer composite consisting of the luminescence conversion layer and the scattering layer can be applied in particular to a radiation-emitting, optoelectronic semiconductor chip. In particular, the layer composite can be adhered to the semiconductor chip. The layer composite is applied to the optoelectronic semiconductor chip such that the luminescence conversion layer faces towards the semiconductor chip so that the scattering layer follows the luminescence conversion in the emission direction of the radiation which is emitted by the optoelectronic semiconductor chip.

Our processes will be explained in greater detail hereinafter with reference to examples in conjunction withFIGS. 1 to 9.

Like parts or parts acting in an identical manner are each provided with the same reference numerals in the Drawings. The illustrated parts and the size ratios of the parts with respect to each other are not to be regarded as being to scale.

In the case of the process described herein, the layer composite consisting of a luminescence conversion layer and a scattering layer is produced by compression molding.FIG. 1illustrates a first intermediate step of the process. In the process, a molding press10is used which is illustrated schematically in cross-section inFIG. 1. The molding press10has a first pressing tool11and a second pressing tool12. For example, the first pressing tool11is the lower pressing tool and the second pressing tool12is the upper pressing tool. The first pressing tool11has a cavity13into which a liquid polymer can be introduced prior to the pressing procedure.

The size of the cavity13can be adapted to the fill quantity, e.g., by a spring assembly15. Prior to filling the cavity13, a film14is preferably inserted into the cavity13and protects the cavity13against contamination and, after the pressing procedure, facilitates removal of the molded part produced in the pressing procedure. The film14can contain, e.g., ETFE (ethylene tetrafluoroethylene). The film14is drawn in an advantageous manner by a negative pressure such that it adapts to the contour of the cavity13. The lower pressing tool11can have intake openings (not shown) suitable for this purpose. Furthermore, prior to the pressing procedure, a support film8is preferably inserted between the first pressing tool11and the second pressing tool12. In the case of the example ofFIG. 1, the support film8is fixed onto a support frame9, wherein the support frame9is fixed on the second pressing tool12.

A liquid first polymer4is introduced into the cavity13. The first polymer4serves to produce the luminescence conversion layer and preferably has a silicone as the base material. The base material contains a luminescence conversion substance5. Suitable luminescence conversion substances are known, e.g., from WO 97/50132 and are therefore not explained in greater detail.

In the intermediate step illustrated inFIG. 2, the molding press10has been closed to carry out a first pressing procedure in which the first pressing tool11and the second pressing tool12are pressed against each other under high pressure. In an advantageous manner, the molding press10is evacuated after closure and before the pressing procedure is carried out to prevent air inclusions from forming in the layer produced in the pressing procedure. The polymer contained between the pressing tools11,12is pressed in this manner to form a luminescence conversion layer1which is advantageously planar and uniformly thick. The luminescence conversion layer1preferably has a thickness of 10 μm to 200 μm, which can be adjusted by the quantity of the previously introduced first polymer. The luminescence conversion layer1is hardened preferably in the still closed molding press10such that it is dimensionally stable.

In the intermediate step illustrated inFIG. 3, the molding press10has been opened. The luminescence conversion layer1produced in the first pressing procedure advantageously adheres to the support film8which is attached to the second pressing tool12by the support frame9. To ensure that, after opening of the molding press10, the luminescence conversion layer1adheres to the support film8and not to the film14in the first pressing tool11, the material used for the support film8is preferably one to which the polymer of the luminescence conversion layer1adheres more strongly than to the material of the film14. In particular, an ethylene tetrafluoroethylene (ETFE) or a polyimide (PI) can be used as the material for the support film8.

In the intermediate step illustrated inFIG. 4, a second polymer6has been introduced into the cavity13of the first pressing tool11. The second polymer6serves to produce the scattering layer and preferably contains a silicone as the base material to which scattering particles7are added. The scattering particles7are, e.g., TiO2particles. However, other materials whose refractive index differs from the refractive index of the base material of the second polymer6can also be used as the scattering particles7.

The previously produced luminescence conversion layer1is still located in the molding press10and is attached to the second pressing tool12by the support frame9of the support film8above the cavity13.

In the intermediate step illustrated inFIG. 5, a second pressing procedure is carried out in which the previously introduced second polymer which contains the scattering particles is pressed to form a scattering layer2. In an advantageous manner, the molding press10is evacuated once again prior to the pressing procedure. During the pressing procedure, the scattering layer2is pressed onto the previously produced luminescence conversion layer1. The scattering layer2produced in the second pressing procedure preferably has a thickness of 10 μm to 200 μm. By pressing the scattering layer2onto the luminescence conversion layer1, a layer composite is produced which is advantageously characterized by very planar boundary surfaces and good homogeneity in the thicknesses of the two layers. In an advantageous manner, the scattering layer2is still hardened in the closed molding press10.

In the intermediate step illustrated inFIG. 6, the molding press10is opened. The layer composite3which consists of the luminescence conversion layer1and the scattering layer2applied thereto adheres to the support film8which is attached to the second pressing tool12by the support frame9. The luminescence conversion layer1and the scattering layer2adhere particularly well to one another if they are produced from the same base material. Apart from the embedded luminescence conversion substances and the scattering particles, the luminescence conversion layer1and the scattering layer2are advantageously formed from the same polymer, in particular a silicone.

The support film8with the layer composite3adhering thereto and consisting of the luminescence conversion layer1and the scattering layer2can then be removed from the molding press10by the support frame9, as illustrated inFIG. 7.

The layer composite3can then be removed from the support film8, as illustrated inFIG. 8. If necessary, the layer composite3can then be cut to a size required for the application, e.g., by punching, cutting, water jet cutting and laser beam cutting.

The layer composite3produced in this manner consists of the luminescence conversion layer1and the scattering layer2and can be applied in particular to an optoelectronic semiconductor chip, in particular an LED.FIG. 9illustrates an example of an optoelectronic semiconductor chip20in which the layer composite3consisting of the luminescence conversion layer1and the scattering layer2is applied to the semiconductor layer sequence15of the semiconductor chip20.

The semiconductor layer sequence15applied, e.g., to a support substrate16has an active layer17which emits electromagnetic radiation. In particular, the active layer17can emit ultraviolet or blue radiation. In particular, a semiconductor layer sequence15based upon a nitride compound semiconductor material is suitable for this purpose.

With the luminescence conversion layer1, some of the radiation emitted by the active layer17is converted into a longer wavelength, e.g., yellow light. Therefore, a mixed light18which comprises the primary radiation emitted by the active layer and the radiation converted in the luminescence conversion layer1is emitted by the semiconductor chip20. The mixed light18can be in particular white light. The scattering layer2on the luminescence conversion layer1has the advantage that it reduces a yellowish color impression of the luminescence conversion layer1when the semiconductor chip20is in the switched-off state.

An optical element such as, e.g., a lens21, can be disposed downstream of the semiconductor chip20in the emission direction. In this case, the undesired effect can occur, namely that some of the radiation impinging upon the inner side of the lens21facing towards the semiconductor chip20is reflected back in the direction of the semiconductor chip20. This radiation which is reflected back in the direction of the semiconductor chip20is advantageously reflected back by the scattering layer2in the emission direction.

Our processes are not limited by the description using the examples. Rather, this disclosure includes any new feature and any combination of features included in particular in any combination of features in the appended claims, even if the feature or combination itself is not explicitly stated in the claims or examples.