DESCRIPTION

Background of the Invention

The invention relates to a filament for a lamp comprising several light emitting semiconductor chips, a lamp with a filament and a method for producing a filament.

In the state of the art a substrate is provided and the light emitting semiconductor chips are arranged on the substrate to form a filament for a lamp.

It is an object of the invention to provide an improved fila ^¬ ment, an improved lamp and to provide an improved method for producing a filament.

The objects of the invention are attained by the independent claims. Further embodiments are disclosed in the dependent claims .

A filament for a lamp is proposed that can easily be pro ^¬ duced. The proposed filament comprises at least two light emitting semiconductor chips, wherein at least three lead frames are embedded in a carrier body. The light emitting semiconductor chips are arranged on the lead frames. Further ^¬ more, two electrical terminals are connected to the carrier body. Therefore, it is not necessary to provide a separate substrate for embodying the filament with the light emitting semiconductor chips. Since there is no separate substrate, the proposed filament has a small height and a small weight. Additionally, the costs for producing the filament and the material necessary for producing the filament are reduced. Furthermore, no further connecting layer is necessary to fix the semiconductor chips to the substrate. Therefore, the pro ^¬ posed filament has a higher long term stability. Depending on the used embodiment, there may be more than three lead frames embedded in the carrier body and more than two light emitting semiconductor chips arranged on the lead frames.

In an embodiment, the first light emitting semiconductor chip is arranged on the first lead frame, wherein the second light emitting semiconductor chip is arranged on the second lead frame .

In a further embodiment, the first light emitting semiconduc- tor chip is arranged on the first and on the second lead frame, and wherein the second light emitting semiconductor chip is arranged on the second and on the third lead frame.

Depending on the used embodiment, the light emitting semicon- ductor chips are electrical connected in series and/or in parallel .

In a further embodiment, at least a third lead frame is em ^¬ bedded in the carrier body. A first electrical contact of the first light emitting semiconductor chip is connected with the first lead frame. A second electrical contact of the first light emitting semiconductor chip is connected with the second lead frame. A first electrical contact of the second light emitting semiconductor chip is connected with the sec- ond lead frame. A second electrical contact of the second light emitting semiconductor chip is connected with the third lead frame. The first lead frame is electrically connected with the first electrical terminal. The third lead frame is electrically connected with the second electrical terminal.

In a further embodiment, the first lead frame and the second lead frame are identical, which means that they have the same shape. Additionally, also the third lead frame can have the same shape as the first lead frame and the second lead frame. Therefore only one shape of a lead frame is necessary to pro ^¬ duce the proposed filament. This reduces tool costs for pro ^¬ ducing the lead frames and simplifies the structure of the lead frames. In a further embodiment, the carrier body is made of moulding material. Therefore, the filament can be easily produced by moulding material as a carrier body. Furthermore, moulding material can be combined with light emitting semiconductor chip producing methods .

In a further embodiment, the lead frames comprise parts that project to a side face of the carrier body. This increases the stability of the carrier body. Therefore, the carrier body can be made of soft material, especially the carrier body can be made of moulding material.

In a further embodiment, the electrical terminals are fixed by a welding connection to a respective lead frame. The lead frames can be made of metal. A welding connection is robust and can easily be performed.

In a further embodiment, the electrical connection between the lead frames and the electrical contacts of the light emitting semiconductor chips are embodied as wire bonds.

In a further embodiment, the carrier body covers side faces of the lead frames, wherein upper faces of the lead frames are at least partially free of carrier body material, wherein the light emitting semiconductor chips are arranged on the upper free faces of the lead frames.

In a further embodiment, an electrical insulating layer is arranged between a light emitting semiconductor chip and a lead frame. Thus it is possible to insulate the lead frame electrically from the semiconductor chip. Therefore, a higher flexibility for guiding current on the lead frames is provid ^¬ ed .

In a further embodiment, the light emitting semiconductor chips are covered with a transparent cover layer. The cover layer protects the semiconductor chips against mechanical damage and chemical influence.

In a further embodiment, the light emitting semiconductor chip is covered with a transparent cover layer, wherein the cover layer comprises luminescent material for shifting a wavelength of a light that is emitted by the light emitting semiconductor chip. Therefore, the cover layer can provide two functions, firstly protecting the semiconductor chip and secondly converting the wave length to a desired wave length.

In a further embodiment, the lead frames are made of metal, especially of metal plates. Metal lead frames provide a suf ^¬ ficient stability for the filament especially in combination with a moulding material for the carrier body. Additionally, the lead frames can easily be produced by using a sheet of metal, wherein the lead frames are punched, etched or cut by a laser from the sheet of metal. The proposed filament can be used for any kind of lamp, especially for a bulb.

A method for producing a filament for a lamp is proposed, wherein at least three lead frames are embedded in a carrier body. A carrier body may be formed by a moulding material. A first and a second light emitting semiconductor chip are mounted on the lead frames. A first electrical terminal is connected to the carrier body and a second electrical termi ^¬ nal is connected to the carrier body. The first light emit ^¬ ting semiconductor chip and the second light emitting semiconductor chip are connected with the first and the second electrical terminal. Therefore, a simple and fast method for producing a filament is proposed.

In a further embodiment, a plate with a lead frame structure with more than two lead frames is provided. The plate is em- bedded in a moulding material forming a carrier plate body. A carrier body with at least two lead frames is separated from the carrier plate body. Then the electrical terminals are fixed to the carrier body. To use a plate for producing the filament increases the output of the production method. A lot of carrier bodies with different shapes and different numbers of lead frames can be produced by using a plate. In a further embodiment, a cover layer is deposited on the structured plate and the light emitting chips before separat ^¬ ing the light emitting chips in groups of lead frames which means in carrier bodies. Brief Description of the Drawings

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 is a cross-sectional illustration of a filament.

Fig. 2 is a schematic top view of the filament of Fig. 1.

Fig. 3 is a schematic top view of a further embodiment of a filament.

Fig. 4 shows a schematic top view of a further embodiment of a filament.

Fig. 5 shows a schematic side view of the filament of

Fig. 4.

Fig. 6 shows a part of the filament of Fig. 4 in more

tail . Fig. 7 shows a part of a metal sheet plate with several lead frames. Fig. 8 shows a filament with a rectangular shaped carrier body .

Fig. 9 shows a filament with a curved shaped carrier body.

Fig. 10 shows a filament with parallel arranged light emit ^¬ ting semiconductor chips.

Fig. 11 shows a further filament with parallel arranged

light emitting semiconductor chips.

Fig. 12 shows a schematic view of a lamp with a filament.

Fig. 1 depicts a schematic cross sectional view of a fila- ment 1. The filament 1 comprises three lead frames 2, 6, 7 that are embedded in a carrier body 3. Embedded in a carrier body means that at least a part of a side face of the lead frames is covered by carrier body 3. Therefore the carrier body and the lead frames form a stable filament. A first light emitting semiconductor chip 4 is arranged on the first lead frame 2. A second light emitting semiconductor chip 5 is arranged on the second lead frame 6. A third lead frame 7 is also embedded in the carrier body 3. The first, second and third lead frame 2, 6, 7 are arranged in a straight line. De- pending on the used embodiment, the first, the second and the third lead frames can also be arranged in a u-form or in an s-form. A first terminal 8 is connected with the first lead frame 2. A second terminal 9 is connected with the third lead frame 7. The connection between the terminals and the lead frames may for example be embodied as welding connections.

The first and the second terminal 8, 9 are electrical termi ^¬ nals that are provided for electrically connecting the fila ^¬ ment with corresponding electrical contacts of a lamp. The first and second light emitting semiconductor chips 4, 5 are embodied to generate light. The light can be visible for ex ^¬ ample blue, green or red light or invisible light. The semi ^¬ conductor chips 4, 5 may be embodied as light emitting diodes or as laser diodes for example. Depending on the used embodiment, more than three lead frames may be embedded in the carrier body 3. Furthermore, more than two light emitting semiconductor chips may be arranged, wherein at least one light emitting semiconductor chip is arranged on one lead frame. The light emitting semiconductor chips may be electrically connected in parallel and/or in se ^¬ ries. Furthermore the light emitting semiconductor chips may be electrically connected via the lead frames and/or direct- ly. In the shown embodiment, the light emitting semiconductor chips 4, 5 are electrically connected in series. Depending on the used embodiment, the light emitting semiconductor

chips 4, 5 may also be electrically connected in parallel. A first electrical contact 10 of the first light emitting semiconductor chip 4 is electrically connected by a conductor 11 with the first lead frame 2. The conductor 11 may be em ^¬ bodied as a wire bond. A second electrical contact 12 of the first light emitting semiconductor chip 4 is electrically connected by a second conductor 13 with the second lead frame 6. In the same way, the second light emitting semiconductor chip 5 comprises a first electrical contact 10 that is elec ^¬ trically connected by a first conductor 11 with the second lead frame 6. A second electrical contact 12 of the second light emitting semiconductor chip 5 is electrically connected by a second conductor 13 with the third lead frame 7. The first electrical terminal 8 is mechanically and electrically connected with the first lead frame 2. The second electrical terminal 9 is electrically and mechanically connected to the third lead frame 7. The mechanical stability of the filament 1 is attained by the carrier body 3 and the embedded lead frames 2, 6, 7. The carrier body 3 may be made of moulding material for example silicone, epoxy material and so on. As discussed above, the electrical contact between the light emitting semiconductor chips 4, 5 may be realized by a direct electrical connections between the electrical contacts 10, 12 of the light emitting semiconductor chips 4, 5. The first and the second and also further light emitting sem ^¬ iconductor chips may be embodied as identical chips. Further ^¬ more, the first, the second and/or the third lead frame may have the same shape and may be embodied as identical lead frames. Additionally, the third lead frame 7 may have a shape of a part of a first and/or a second lead frame. The conduc ^¬ tor lines 11, 13 may be embodied as wire bonds. The semicon ^¬ ductor chips may be arranged on an upper side 35 of the lead frames that is for example free of carrier body 3. This in- creases a thermal contact between the semiconductor chips 4, 5 and the lead frames 2, 6, 7. The lead frames 2, 6, 7 may be embodied as metal parts for example. The carrier body 3 may be electrical isolating. Depending on a further embodiment, an electrical insulating layer may be arranged between a light emitting semiconductor chip and the lead frame on which the light emitting semiconductor chip is arranged. Furthermore, a cover layer 14 may be arranged that covers at least the semiconductor chips 4, 5 or as shown in the embodi ^¬ ment the whole carrier body 3. The cover layer 14 is made of light-transparent material and may comprise luminescent mate ^¬ rial to convert the wavelength of the light. The cover layer 14 is for example made of silicone. A function of the cover layer 14 is to protect the semiconductor chips and if luminescent material is arranged, also to change a wavelength of the light that is emitted by the light emitting semiconductor chips 4, 5.

The carrier body 3 is arranged along a z-axis. The carrier body 3 has a height along a y-axis that is in the shown em ^¬ bodiment larger than a height of the lead frames 2, 6, 7. The z-axis and the y-axis are aligned in a rectangular position to each other. An x-axis is in a rectangular position to a plane that is defined by the y-axis and the z-axis. Depending on the used embodiment, the carrier body 3 may have a smaller height along the y-axis than the lead frames 2, 6, 7. The lead frames may have the same or different height. Depending on the used embodiment, the carrier body may only cover side faces of the lead frame for example if the height of the cov ^¬ er body is smaller than the height of the lead frames 2, 6, 7.

Fig. 2 shows a schematic top view on the filament 1 of

Fig. 1. In this view, the cover layer 14 is not shown. Additionally, side parts 15 of the lead frames 2, 6, 7 that are embodied as small stripes project from a main area of the lead frames 2, 6, 7 to a side face 16, 17 of the carrier body 3.

The filament can comprises several second lead frames 6 with second light emitting semiconductor chips 5 that are arranged in series. This is indicated by s shaped lines 36 that cross the filament 1. The carrier body 3 has a width along the x- axis that is in the shown embodiment larger than a width of the lead frames 2, 6, 7. Depending on the used embodiment, the carrier body 3 may have the same or a smaller width than the lead frames 2, 6, 7. The lead frames may have the same or different width. Depending on the used embodiment, the carri ^¬ er body may only cover areas between two lead frames for ex ^¬ ample if the width of the cover body is equal or smaller than the width of the lead frames 2, 6, 7.

Depending on the used embodiment, the first and second semi ^¬ conductor chips 4, 5 may also be embodied as flip chips that comprise at a bottom face the first and the second electrical contact.

Such a filament 1 is schematically depicted in Fig. 3. Fig. 3 shows a cross-sectional view of a filament 1 that comprises a carrier body 3 with embedded lead frames 2, 6, 7 as discussed above. The first terminal 8 is electrically and mechanically connected with the first lead frame 2. The second electrical terminal 9 is electrically and mechanically connected with the third lead frame 7. The first and the second light emit- ting semiconductor chip 4, 5 comprise at bottom faces a first and a second electrical contact 10, 12. The first and the second electrical contact 10, 12 are electrically connected with different lead frames. The first electrical contact 10 of the first light emitting semiconductor chip 4 is connected by a conductor 11 with the first lead frame 2. The second electrical contact 12 of the first light emitting semiconduc ^¬ tor chip 4 is connected with the second lead frame 6 by a second conductor 13. A first electrical contact 10 of the second light emitting semiconductor chip 5 is connected by a first conductor 11 with the second lead frame 6. A second electrical contact 12 of the second light emitting semicon ^¬ ductor chip 5 is connected by a second conductor 13 with the third lead frame 7. The first and second conductor 11, 13 may be embodied as solder balls. At least the light emitting sem ^¬ iconductor chips 4, 5 may be covered by a cover layer that is light transparent and that may comprise luminescent material. Depending on the used embodiment, there may also be embodied more than three lead frames and more than two light emitting semiconductor chips 4, 5 as discussed above. Depending on the used embodiment, there may also be arranged some light emit ^¬ ting semiconductor chips 4, 5 in parallel. Also in this embodiment a mechanical stability of the filament 1 is proposed by the carrier body 3 that is for example made of moulding material and the mechanical stability is provided by the lead frames 2, 6, 7. Depending on the used embodiment, there may also be more than two light emitting semiconductor chips 4, 5 that comprise electrical contacts at the bottom face and that are connected with separate lead frames 2, 6, 7.

Fig. 4 shows a top view on a further embodiment of a fila ^¬ ment 1 that comprises a similar structure as the filament 1 of Fig. 1. Compared to the embodiment of fig. 1, there are more than two light emitting semiconductor chips 4, 5. Fur- thermore, there are more than three lead frames that are em ^¬ bedded in the carrier body 3. The carrier body 3 may be made of the same material as in the above discussed embodiments of fig. 1 to 3. There are three types of lead frames 2, 6, 7. The lead frames 2, 6, 7 show different shapes compared to the lead frames of fig. 1. The proposed second lead frame 6 com ^¬ prises a main area 18, wherein the second light emitting sem ^¬ iconductor chips 5 are arranged on the main area 18. The main area 18 has nearly a square face wherein several side parts 15 project to side face 16, 17 of the carrier body 3. The main area 18 is connected with a first and a second project ^¬ ing arm 21, 22. The first and the second projecting arm 21, 22 are arranged along a longitudinal axis 23 of the filament 1 and at a front side of the main area 18. The main area 18 and the first and the second projecting arm 21, 22 comprise upper faces that are free of the carrier body 3. The first and the second projecting arm 21, 22 comprise contact areas 23, 24 that are used for electrically connecting the first and the second conductors that may be embodied as wire bonds. There are six second lead frames with six second light emit ^¬ ting semiconductor chips 5.

The first electrical terminal 8 is mechanically and electri- cally connected with a first lead frame 2. The first lead frame 2 is embodied as the main area 18 of a second lead frame 6, wherein front sections of the second lead frame i.e. front sections of the projecting arms 21,22 are cut off. The first terminal 8 is connected with the first and the second projecting arms 21, 22 of a first lead frame 5. The third lead frame 7 is embodied as a front section of the second lead frame 6 with front sections of the first and the second projecting arms 21, 22. The second electrical terminal 9 is electrically and mechanically connected with the front sec- tions of projecting arms 21, 22. The main area 18 of the sec ^¬ ond lead frame is cut off from the projecting arms 21, 22. Therefore, the third lead frame 7 for connecting the second terminal 9 is in this embodiment realised by a first and a second front part of the projecting arms 21, 22. The first projecting arm 21 is electrically connected with a wire bond of a second light emitting semiconductor chip 5. The first and the second lead frames 4, 5 max be embodied as different or identical light emitting semiconductor chips. Furthermore there might also be arranged more than two different types of light emitting semiconductor chips 4, 5 that may be different in the wavelength of the emitted light and/or in the light flux of the emitted light.

Fig. 5 depicts a schematic side view of the filament 1 of Fig. 4. The carrier body or at least the light emitting semiconductor chips 4, 5 may be covered by a transparent cover layer 14. The cover layer 14 may be made of silicone and may comprise luminescent material for a wavelength conversion.

Fig. 6 shows a section of the filament 1 of Fig. 5, wherein the cover layer 14 and the carrier body 3 are transparently illustrated. The section comprises a main area 18 of a second lead frame 6 and a first section of a further second lead frame 6. The section therefore shows the two parts of a sec ^¬ ond lead frame. The second lead frame 6 comprises different layers with different shapes 37, 38. In the shown embodiment the second lead frame 6 comprises an upper layer 37 and a lower layer 38. The lower layer 38 has a smaller face than the upper layer 37. Therefore less material is necessary for providing a second lead frame with a first and a second pro ^¬ jecting arm 21, 22 and with a main area 18 for a light emit ^¬ ting semiconductor chip and with a first and second contact area 23, 24 for electrically connecting the semiconductor chip with the further lead frames. The first and the second projecting arm 21, 22 are part of the upper layer 37. The first and the second projecting arm 21, 22 are connected by a connecting element 25 that is connected with bottom faces of the first and second projecting arm 21, 22. Depending on the used embodiment, the connecting element 25 and the first and the second projecting arm 21, 22 are made of the same materi ^¬ al and are embodied in one part. Fig. 7 shows in a schematic view a top view of a lead frame plate 28 with several lead frames 2. The lead frame plate 28 may be embodied as a metal plate. The lead frames 2 are ar ^¬ ranged in rows 30 and lines 26. The lead frames 2 may be cut, stamped or etched in the lead frame plate 28. The lead frames 2 of one line 26 are connected by projecting parts 27. The lead frames 2 of a row 30 are not electrically connected to each other. Therefore, it is possible to mount light emitting semiconductor chips 4 on the lead frames 2 and to embed the lead frame plate 28 in a carrier body plate 29. The lead frames 2 may be cut, stamped or etched in the lead frame plate 28 after the embedding in the carrier body plate 29. Then the carrier bodies 3 with a shape of a stripe 39 along the rows 30 can be cut out of the lead frame plate 28 and the carrier body plate 29 as indicated by a dashed line 40. Then electrical connections of the light emitting semiconductor chips are formed to generate a series and/or a parallel con ^¬ nection of the light emitting semiconductor chips 4. Then electrical terminals 8, 9 are fixed to the lead frames that are arranged at the opposite ends of the stripe 39 of the carrier body 3. Thus, it is easily possible to produce a fil ^¬ ament 1 as explained referring to the above figures. Fig, 7 shows a simplified lead frame plate 28. The lead frames of the lead frame plate may have the shapes of the preceding ex ^¬ amples .

Fig. 8 shows a filament 1 with a rectangular shaped carrier body 3. The lead frames and the electrical connections of the light emitting semiconductor chips 4, 5 are not shown.

Fig. 9 shows a filament 1 with a curved shaped carrier body 3. The lead frames and the electrical connections of the light emitting semiconductor chips are not shown.

Fig. 10 shows a filament 1 that is basically constructed as the filament 1 of fig. 2, whereby in this example two light emitting semiconductor chips 4, 5 are arranged in parallel on the first and on the second lead frame 2, 6.

Fig. 11 shows a filament 1 that is basically constructed as the filament 1 of fig. 3, whereby in this example two first light emitting semiconductor chips 4 are arranged in parallel on the first and on the second lead frame 2, 6 and two second light emitting semiconductor chips 5 are arranged in parallel on the second and the third lead frame 6, 7. Fig. 12 shows a schematic view of a lamp 41 with a design of a bulb. The lamp 41 may also have other designs. The lamp 41 has two electrical contacts 42, 43 that are connected with the terminals 8, 9 of the filament 1. The filament 1 may have the structure of one of the above explained embodiments of filament 1.

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 filament

2 lead frame

3 carrier body

4 first chip

5 second chip

6 second lead frame

7 third lead frame

8 first terminal

9 second terminal

10 first electrical contact

11 conductor

12 second electrical contact

13 second conductor

14 cover layer

15 side parts

16 first side face

17 second side face

18 main area

21 first projecting arm

22 second projecting arm

23 first contact area

24 second contact area

25 connecting element

26 line

27 projecting part

28 lead frame plate

29 carrier body plate

30 row

35 upper side face

36 s-shaped line

37 upper layer

38 lower layer

39 stripe

40 dashed line

41 1amp

42 electrical contact of lamp

43 further electrical contact of lamp