WO2011040937A1

WO2011040937A1 - Semiconductor light source and method for producing a semiconductor light source

Info

Publication number: WO2011040937A1
Application number: PCT/US2009/067523
Authority: WO
Inventors: Christopher Eichelberger; Michael Godwin
Original assignee: Osram Opto Semiconductors GmbH
Current assignee: Ams Osram International GmbH
Priority date: 2009-09-30
Filing date: 2009-12-10
Publication date: 2011-04-07
Anticipated expiration: 2012-03-30

Abstract

In at least one aspect, the semiconductor light source (1) comprises a carrier (2) having a main area (20) and an optoelectronic semiconductor chip (3). The semiconductor chip (3) is suited to emit visible and/or ultraviolet radiation. Further, a reflector (4) is mounted on the main area (20). The reflector surrounds the semiconductor chip in a lateral direction. A light pipe (5) is arranged downstream the semiconductor chip seen in a direction (M) of main emittance of the semiconductor chip. Furthermore, the light pipe is spaced apart from the semiconductor chip. A fixture of the light pipe is realized by means of the reflector. Moreover, an average width (W) of a core (51 ) of the light pipe at a side (40) of the reflector remote from the semiconductor chip matches an average inner diameter (D) of the reflector at this side with a tolerance of at most 25%.

Description

Semiconductor light source and method for producing a semiconductor light source

Related Applications

The present application claims the benefit of U.S. Provisional Patent Application No. 61/247,369, filed September 30, 2009, which is incorporated herein by reference in its entirety.

Description of Related Art

In the document US 6,769,799 B2, an apparatus, methods and articles of manufacture for a co-extruded light pipe are disclosed. Summary of Invention

It is an object to provide a semiconductor light source with a light pipe wherein radiation emitted by a semiconductor chip is efficiently coupled into the light pipe. It is another object to provide a method for producing such a semiconductor light source.

According to at least one aspect, the semiconductor light source comprises a carrier having a main area. The function of the carrier is to provide mechanical stability for the light source. Preferably, the carrier can serve as an electrical connection means. As an example, the carrier can be a printed circuit board, a circuit board, a metal core board, or a ceramic board with conductor paths on it. Preferably, the carrier has a low thermal resistance. For example, an average thermal conductivity of the carrier is equal to or exceeds 40 W/ (m K) , especially 100 W/ (m K) .

According to at least one aspect, the semiconductor light source comprises at least one optoelectronic semiconductor chip. The semiconductor chip is mounted on the main area of the carrier and is capable of emitting ultraviolet or visible radiation during operation of the light source. For example, the semiconductor chip is a thin-film chip with a thickness of at most 200 urn, especially of at most 20 μπι with regard to epitaxially grown layers. The semiconductor chip could be formed as described in the documents WO 2005/081319 Al or DE 10 2007 004 304 Al, of which the disclosure content relating to the semiconductor chip is hereby incorporated by back-reference. Especially, the semiconductor chip could be a light-emitting diode, a laser diode or a super-luminescence diode.

According to at least one aspect, the semiconductor light source comprises a reflector that is arranged on the main area of the carrier. Preferably, the reflector partially or completely surrounds the semiconductor chip in a lateral direction. The reflector is fashioned to reflect radiation emitted by the semiconductor chip. A material of the carrier preferably differs from a material of the reflector. Especially, the carrier and the reflector are manufactured separately.

According to at least one aspect of the semiconductor light source, a light pipe is arranged downstream the semiconductor chip seen in a direction of main emittance of the semiconductor chip. Via the light pipe, the radiation generated by the semiconductor can be led to various places of, for instance, a dashboard of a car. It is preferred that the light guide is a multi-mode light guide. In other words, an effective light guiding area of the light pipe is comparably big, for example exceeding 3000 μπι² or 5000 um^, and supports the guidance of a large number of transversal modes.

According to at least one aspect, the light pipe is spaced apart from the semiconductor chip. Thus, the light pipe is not in direct contact with the semiconductor chip. Especially, there are at least two steps in the refractive index between the semiconductor chip and the light pipe. There can be an air gap between a light entrance surface of the light pipe and the semiconductor chip.

According to at least one aspect, the light pipe is fixed relative to the semiconductor chip by means of the reflector. In other words, the light pipe and the reflector are directly mechanically connected with each other. Thus, it is possible that the light pipe is only attached to the carrier by means of the reflector. The fixture in between the light pipe and the reflector can be reversible or irreversible.

According to at least one aspect of the light source, an average width of a core of the light pipe at the side of the reflector remote from the semiconductor chip matches an average inner diameter of the reflector at this side with a tolerance of at most 25%. Preferably, the tolerance is at most 15%, especially at most 10%, particularly preferable at most 5%. In other words, an average width of the core of the light pipe is essentially equal to the average inner diameter of the reflector, on a side of the reflector remote from the semiconductor chip. The core can be a part of the light pipe that is capable of transmitting and guiding light.

In at least one aspect, the semiconductor light source comprises a carrier having a main area and an optoelectronic semiconductor chip arranged on the main area of the carrier. The semiconductor chip is suited, to emit visible and/or ultraviolet radiation in operation of the light source. Further, a reflector of the light source is mounted on the main area. The reflector partially or completely surrounds the semiconductor chip in a lateral direction. A light pipe of the light source is arranged downstream the semiconductor chip seen in a direction of main emittance of the semiconductor chip. Furthermore, the light pipe is spaced apart from the semiconductor chip. A fixture of the light pipe to the other parts of the light source like the carrier is realized by means of the reflector. Moreover, an average width of a core of the light pipe at a side of the reflector remote from the semiconductor chip matches an average inner diameter of the reflector at this side with a tolerance of at most 25%.

According to at least one aspect, the reflector, especially the inner surfaces of the reflector, are shaped parabolic, elliptic and/or hyperbolic. Thus, the reflector can be a compound parabolic reflector, in short CPC, a compound elliptical concentrator, in short CEC, or a compound hyperbolic concentrator, in short CHC. In this case, an average inner diameter of the reflector can increase with increasing distance from the semiconductor chip until the light entrance surface of the light pipe. With regard to the distance to the carrier, the inner diameter of the reflector can be monotonxcally increasing or strictly increasing.

According to at least one aspect, the core of the light pipe is composed of or comprises a homogenously distributed transparent material. In this case, a refractive index of the core can be constant, at least in a lateral direction perpendicular to a direction of main guidance. For example, the core consists of a plastic or of a glass. Preferably, an average width of the core exceeds an average diameter of the semiconductor chip.

According to at least one aspect, the reflector has inner surfaces that are reflective for the generation emitted by the semiconductor chip. An average reflectance of the inner surfaces can exceed 75%, preferably 90%.

According to at least one aspect, the core of the light pipe is in direct contact with a coating. The coating can consist of or can comprise a reflective light-proof material. By way of example, the coating is realized by a thin metallic film with a thickness in the range between 1 um and 50 um, inclusive. A reflectance of the coating with regard to the radiation emitted by the semiconductor is at least 70%, preferably at least 80%, particularly preferably at least 95%.

According to at least one aspect, the light pipe is no fiber optics. Thus, a guiding of the radiation in the light pipe is not based on total reflection but on normal reflection. Hence, a real part of the refractive index of the coating preferably exceeds a real part of the refractive index of the core.

According to at least one aspect of the light source, the reflector further comprises protrusions, wherein the protrusions completely or partially penetrate through the carrier. By means of the protrusions, the reflector can be fastened to the carrier. Especially, the protrusions extend into recesses of the carrier.

According to one aspect of the semiconductor light source, lateral surfaces of the semiconductor chip are partially or completely covered by a material of the reflector. Thus, a semiconductor material of the semiconductor chip can be in direct physical contact with a material of the reflector, especially with a plastic .

According to at least one aspect of the light source, a cavity is formed by the carrier, the reflector and the light pipe. Especially, the cavity is defined exclusively by these elements of the light source. The at least one semiconductor chip is preferably completely arranged within this cavity. The cavity can be fashioned in an air-tight manner. In this case, the semiconductor chip and the light entrance surface of the light pipe can be sealed against the environment by the carrier, the reflector and the light pipe.

According to at least one aspect, the reflector of the light source is formed by a two-component injection molding. Then, the reflector preferably consists of or comprises two or more then two different plastics . By two-component injection molding, physical properties of a reflecting part of the reflector and of fastening parts of the reflector can be adjusted independently from each other to a large extent. Hence, optical and mechanical properties of the reflector can be improved nearly independently from each other. According to at least one aspect, the semiconductor light source further comprises a surface-mountable chip housing. The at least one semiconductor chip is arranged and mounted in the chip housing. The chip housing further can be directly mounted on the main area of the carrier by means of a surface mount technology such as a soldering. Especially, no parts of the chip housing protrude through the main area of the carrier. Moreover, the chip housing can be completely surrounded by the reflector in a lateral direction. It is also possible that the chip housing is spaced apart from a material of the reflector, especially in a lateral direction. The chip housing can contain one or more semiconductor chips . Furthermore, a method for producing a semiconductor light source is provided. With this method, especially a - -

semiconductor light source as described in connection with at least one of the preceding aspects can be manufactured. Thus, the subject matter disclosed for the semiconductor light source is also disclosed for the method and vice-versa.

In at least one aspect, the method for producing the semiconductor light source comprises the steps:

molding a parabolic shaped part of a reflector in a mold;

providing an optoelectronic semiconductor chip arranged on a main area of the carrier and inserting it into the mold, the main area being temporarily part of the mold;

molding a base part of the reflector, the base part being in direct contact with lateral surfaces of the semiconductor chip; and

attaching a light pipe to the reflector.

Preferably, the steps of the method are performed in the sequence given above, although deviations there from can be possible.

Brief Description of the Figures Advantageous embodiments and developments of the semiconductor light source and a method for producing the semiconductor light source will become apparent from the exemplary embodiments described below in association with the figures.

In the figures : FIGs. 1 to 3, 6 and 7 show schematic sectional illustrations of semiconductor light sources of exemplary embodiments and FIGs. 4 and 5 show schematic steps of methods for producing exemplary embodiments of semiconductor light sources.

Detailed Description of the Drawings

In the exemplary embodiments and figures, similar or similarly acting constituent parts are provided with the same reference symbols. The elements illustrated in the figures and their size relationships among one another should not be regarded as true to scale. Rather, individual elements may be represented with an exaggerated size for the sake of better representability and/or for the sake of better understanding. An exemplary embodiment of a semiconductor light source 1 is illustrated in FIG. 1. In FIG. 1A, a sectional view of a reflector 4 of the light source 1 is drafted, in FIG. IB, a sectional view of the whole light source 1 can be seen.

The reflector 4 comprises an inner surface 45 of a parabolic shaped part 43. Moreover, the reflector 4 comprises fastening means 41 and protrusions 44. By means of the fastening means 41, that as an example can be a screw thread or a snap fit, a light pipe 5 is affixed to the reflector 4. Further, by means of the protrusions 44, the reflector 4 is fastened to a carrier 2 of the light source 1. For this purpose, the protrusions 44 can extend into recesses of the carrier 2, not drawn in FIG. 1. On a main area 20 of the carrier 2, an optoelectronic semiconductor chip 3 is mounted. Radiation that is emitted during operation by the semiconductor 3, is led to a light entrance surface 50 of the light pipe 5. Light that does not directly travel to the light entrance surface 50 from a radiation exist surface 30 of the semiconductor chip 3 is reflected by the inner surface 43 of the reflector 4 to the light entrance surface 50. In order to ensure a high coupling efficiency from the radiation into the light pipe 5, the parabolic shaped part 43 of the reflector 4 shows a high reflectance. Preferably, a diffuse reflectance contributes to an overall reflectance of the inner surface 45 only to a minor extent, for example to at most 40%, preferably to at most 20%. In other words, most of the light reflected on the inner surface 45 is reflected in such a way that an angle of incident is equal to an emergent angle. In order to achieve high reflectance, the reflector 4 can consist of or can comprise a bright and/or white plastic material. Especially, the inner surface 45 of the reflector 4 is formed from white plastic. In other words, the inner surface 45 can be free from a reflective coating. Hence, the reflector 4 can be one- pieced and thus can be manufactured cost-effectively. Although the inner surface 45 is declared as parabolic shaped, besides being a compound parabolic concentrator, in short CPC, the reflector can also be a compound elliptical concentrator, in short CEC, or a compound hyperbolic concentrator, in short CHC . To efficiently couple the radiation into the light pipe 5, a distance L between the radiation exit surface 30 of the semiconductor chip 3 and the light entrance surface 50 of the light pipe is at least three times and at most eight times, inclusive, an average edge length E of the semiconductor chip. Thus, the semiconductor chip 3 is considerably spaced apart from the light pipe 5.

Furthermore, an average diameter D of the reflector at a side 40 remote from the semiconductor chip 3 resembles an average width W of the light pipe 5 at this side 40. In other words, essentially the whole reflector 4 is filled by the light pipe 5 on the side 40 remote from the semiconductor chip 3.

As in all other embodiments, the semiconductor chip 3 can be directly mounted on the main area 20 of the carrier 2 by means of a surface mount technology, especially by means of a soldering. In this case, the semiconductor chip 3 can be free of a housing. Then, for instance, the radiation exit surface 30 is not followed by a lens or an encapsulant material. It is possible that the semiconductor chip 3 includes a luminescence conversion material. - -

The light pipe 5 can be screwed to the reflector 4. In order to achieve, for example, an air tight sealing of a cavity 6 formed by the light pipe 5, the carrier 2 and the reflector 4, the light source 1 can comprise a gasket, not shown in the figures.

Another exemplary embodiment of the light source 1 is depicted in FIG. 2. In FIG . 2A, a sectional view of the light source 1 is shown whereas in FIG. 2B, a sectional view of the light pipe 5 only is illustrated.

According to FIG. 2, deviating from the exemplary embodiment in FIG. 1, the protrusions 44 penetrate completely through the carrier 2 and are expanded headlike on a side of the carrier 2 remote from the semiconductor chip 3. As in FIG, 1, the parabolic shaped part 43 of the reflector 4 begins immediately at the main area 20 of the carrier 2. Thus, also radiation emitted, for example, on lateral surfaces 35 of the semiconductor chip 3 can be efficiently reflected by the reflector 4 into a direction to the light pipe 5.

The light pipe 5 can comprise a core 51 that consists of a homogenously distributed material that is transparent for the radiation emitted by the semiconductor chip 3. For instance, the core 51 can consist of at least one transparent plastic or of at least one glass.

The core 51 can be coated with a reflective coating 52, for example made of a metal. Lateral surfaces of the light pipe 5 near the light entrance surface 50 are provided with fastening means 53 by which the light pipe 5 can be fastened to the fastening means 41 of the reflector 4 reversibly or irreversibly. Optionally, the light entrance surface 50 is coated by an anti- reflection coating 54. For the production of a solid light pipe 5 the light pipe is for example molded or extruded in an acrylic material, e.g. Polymethylmethacrylate, in short PM A, with or without a coating or cladding. Other materials which are transparent in the visible radiation spectrum like glass or other plastics can also be used. PMMA is, however, preferred due to excellent optical properties and low cost. For the production of a flexible light pipe 5, e.g. a silicone can be used. Suitable materials for the coating of the light pipe and/or the reflector are metals, e.g. aluminum. The coating can be applied via vacuum metallization, for example. It is also possible to use white plastic for the coating and/or the reflector.

The carrier 2 has for example the following dimensions:

- length between at least 20 mm and at most 30 mm, inclusive, e.g. 25.4 mm;

- width between at least 20 mm and at most 30 mm, inclusive, e.g. 25.4 mm;

- thickness between at least 1 mm and at most 2 mm, inclusive, e.g. 1.5 mm.

The chip 3 has an area for example between at least 500 μιη² and at most 6000 μπι², inclusive, preferably between at least 1000 urn² and at most 4000 μιη², inclusive. In the figures, for the sake of simplicity, the reflector 4 and the light pipe 5 are drawn rotationally symmetric with regard to a direction M of main emittance of the semiconductor chip 3. As in all other embodiments, the reflector 4 and/or the light pipe 5 can be shaped non-rotationally symmetric with regard to the direction M of main emittance. For example, a part of the light guide 51 that is located in the reflector 4 can be shaped rotationally symmetric as well as the reflector 4 itself whereas an end of the light pipe 5 remote from the reflector 4 can be shaped line-like in order to illuminate, for example, a display or a panel.

The light guide 51 has for example a diameter between at least 5 mm and at most 20 mm, inclusive, preferably between at least 8 mm and at most 13 mm, inclusive. The dimensions of the reflector 4 can be the same as the dimensions of the light guide 51. Deviating from the figures, the semiconductor light source 1 can comprise more than one semiconductor chip 3. Especially, a plurality of semiconductor chips 3 can be arranged symmetrically with regard to a symmetry axis of the reflector 4 in a direction perpendicular to the carrier 2.

In the embodiment of FIG. 3, the reflector 4 of the semiconductor light source 1 comprises a base part 42 and a parabolic shaped part 43. In the base part 42, the inner surface 45 is oriented essentially perpendicular with regard to the main area 20 of the carrier 2. It is possible that lateral surfaces of the carrier 2 are flush with lateral surfaces of the reflector 4. The parabolic shaped part 43 begins at a distance from the main area 20, being at least the distance from the radiation exit surface 30 to the main area 20 of the carrier 2. For the sake of simplification, the light pipe 5 is not drawn in FIG. 3.

A method for producing the semiconductor _. light source 1 is schematically illustrated in FIG. 4. According to FIG. 4A, the parabolic shaped part 43 of the reflector 4 is injection molded in a mold 8a-c. The mold 8a corresponds to an outer geometry of the reflector 4 to be molded. The inner part 8b of the mold has the same form as the parabolic shaped part 43 and the inner surfaces 45 of the reflector 4, respectively. By a third part 8c of the mold, the molding cavity is closed.

According to FIG. 4B, the mold part 8c is removed and replaced by the carrier 2 with the semiconductor chip 3 mounted on the main area 20. Thus, the carrier 2 forms a part of the mold during the molding. The radiation exit surface 30 of the semiconductor chip 3 can be in direct contact with the inner mold 8b. Also, there can be a foil of, for instance, a silicone between the semiconductor chip 3 and the mold 8b. Then, the base part 42 of the reflector 4 is molded. In a direction perpendicular to the main area 20, a height of the base part 42 preferably is equal to or exceeds a thickness of the semiconductor chip 3. The reflector 4 can be molded by a two-component injection molding. Then, the plastics of the base part

42 and the parabolic shaped part 43 can be different from each other. According to FIG. 4C, the light source 1 is finished by attaching the light pipe 5 to the reflector 4. This can be performed, for example, by means of pressing the light pipe 5 into the reflector 4. According to FIG. 5, the reflector 4 is molded first. Subsequently, the light pipe 5 is attached to the reflector 4. Preferably afterwards, the reflector 4 is attached to the carrier 2 by plastically deforming the protrusions 44.

In FIG. 6, single rays R of the radiation emitted by the semiconductor chip 3 are illustrated. Furthermore, according to FIG. 6, the semiconductor chip 3 is housed in a chip housing 7 that is spaced apart from the inner surface 45 of the reflector 4. The radiation emitted by the semiconductor chip 3 can be pre-focused by the housing 7.

In FIG. 7, another exemplary embodiment of the semiconductor light source 1 is shown in sectional three-dimensional views, compare FIGs . 7A and 7B. Only the reflector 4 is depicted in FIG. 7C, also in a sectional three-dimensional view. The invention is not restricted to the exemplary embodiments by the description on the basis of the -

exemplary embodiments. Rather, the invention encompasses any new feature and also any combination of features, which in particular comprises any combination of features in the patent claims and any combination of features in the exemplary embodiments, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments .

Claims

Claims:

1. Semiconductor light source (1) comprising:

a carrier (2) having a main area (20);

an optoelectronic semiconductor chip (3) arranged on the main area (20) of the carrier (2) and suited to emit visible and/or ultraviolet radiation;

a reflector (4} that is mounted on the main area (20) and that partially or completely surrounds the semiconductor chip (3) in a lateral direction; and a light pipe (5) arranged downstream the semiconductor chip (3) seen in a direction (M) of main emittance of the semiconductor chip (3),

wherein the light pipe (5) is spaced apart from the semiconductor chip (3);

the light pipe (5) is fixed relative to the semiconductor chip (3) by means of the reflector

( ) ; and

an average width (W) of a core (51) of the light pipe

(5) at a side (40) of the reflector (4) remote from the semiconductor chip (3) matches an average inner diameter (D) of the reflector (4) at this side (40), with a tolerance of at most 25 %.

2. Semiconductor light source (1) according the preceding claim, wherein the reflector (4) is a compound parabolic reflector, and wherein the average inner diameter (D) of the reflector (4) increases with increasing distance from the semiconductor chip (3) until a light entrance surface (50) of the light pipe (5} . Semiconductor light source (1) according to one of the preceding claims, wherein the core (51) of the light pipe (5) is composed of or comprises a homogeneously distributed transparent material, and wherein the core (51) of the light pipe (5) is in direct contact with a coating (52) , the coating consists of or comprises a reflective light-proof tight material.

Semiconductor light source (1) according to one of the preceding claims, wherein the reflector (4) consists of or comprises a white plastic and wherein inner surfaces (45) of the reflector (4} are formed from the white plastic, and wherein the inner surfaces (45) are free of a reflective coating, and wherein a diffuse reflectance contributes to an overall reflectance of the surfaces (45) to at most 40%.

Semiconductor light source (1) according to one of the preceding claims, wherein the at least one of the reflector (4) and the light pipe (5) are not formed rotationally symmetric.

Semiconductor light source (1) according to one of the preceding claims, the reflector (4) further comprising protrusions (44), wherein the protrusions (44) completely penetrate through the carrier (2) .

Semiconductor light source (1} according to one of the preceding claims, wherein the semiconductor chip (3) is directly mounted onto the main area (20) of the carrier (2) by means of a surface mount technology, and wherein the semiconductor chip (3) is free of a housing. Semiconductor light source (1) according to one of the preceding claims, wherein lateral surfaces (35) of the semiconductor chip (3) are partially or completely covered by a material of the reflector (4) .

Semiconductor light source (1) according to one of the preceding claims, wherein a cavity (6} in which the semiconductor chip (3) is located is completely surrounded by the carrier (2), the reflector (4) and the light pipe (5) .

Semiconductor light source (1} according to one of the preceding claims, wherein the light pipe (5) is fixed with the reflector (4) by means of a screw fastening .

Semiconductor light source (1) according to one of the preceding claims, wherein the reflector (4) is formed by a two-component injection moulding, and wherein the reflector (4) consists of or comprises two different plastics.

Semiconductor light source (1) according to one of the preceding claims, wherein a distance (L) between the semiconductor chip (3) and the light pipe (5) is at least three times and at most eight times, inclusive, an average edge length (E) of the semiconductor chip (3) .

Semiconductor light source (1) according to one of the preceding claims, further comprising a surface mountable chip housing { 7 ) in which the semiconductor chip (3) is arranged, the chip housing ( 7 ) is directly mounted onto the main area (20} of the carrier (2) and is completely surrounded by the reflector (4) in a lateral direction, the chip housing (7) further being spaced apart from a material of the reflector (4) . 14. Method for producing a semiconductor light source (1) comprising the steps:

moulding a parabolic shaped part (43) of a reflector (4) in a mould (8);

providing an optoelectronic semiconductor chip

(3) mounted on a main area (20) of a carrier (2) and inserting it into the mould (8), the main area (2) temporarily being a part of the mould (8);

moulding a base part of the reflector (4), the base part (42) being in direct contact with lateral surfaces (35) of the semiconductor chip (4); and

attaching a light pipe (5) to the reflector

(4) , wherein

the light pipe (5) is spaced apart from the semiconductor chip (3) ;

the light pipe (5) is fixed relative to the semiconductor chip (3} by means of the reflector ( 4 ) ; and

an average width (W) of a core (51) of the light pipe (5} at a side (40) of the reflector (4) remote from the semiconductor chip (3) matches an average inner diameter (D) of the reflector (4) at this side (40), with a tolerance of at most 25 %.