DEVICE COMPRISING A LEAD FRAME AND METHOD FOR PRODUCING A PLURALITY OF DEVICES

Abstract

A device includes a carrier and a plurality of semiconductor chips configured to generate radiation. The carrier includes a lead frame. The lead frame includes two connecting parts for external electrical contacting of the device. The semiconductor chips are arranged on the carrier. The carrier is surrounded by a casing at least in places along its entire circumference. The casing forms a side face of the device at least in places. The side face includes traces of material removal.

Claims

1. A device comprising a carrier and a plurality of semiconductor chips configured to generate radiation, wherein the carrier comprises a lead frame, and the lead frame comprises two connecting parts for external electrical contacting of the device; the semiconductor chips are arranged on the carrier; the carrier is surrounded by a casing at least in places along its entire circumference; the casing forms a side face of the device at least in places; and the side face comprises traces of material removal.

2. The device according to claim 1, wherein the side face of the casing is perpendicular to a front side of the carrier at least in a partial area.

3. The device according to claim 1, wherein the casing is formed in one piece.

4. The device according to claim 1, wherein the carrier comprises at least one web which extends to the side face of the device and which is flush with the casing at the side face.

5. The device according to claim 1, wherein a cross-section of the casing perpendicular to a main extension direction of the device is quadrangular.

6. The device according claim 1, wherein a cross-section of the casing perpendicular to a main extension direction of the device tapers with increasing distance from the main extension direction.

7. The device according to claim 1, wherein a recess is formed in the carrier at least between two adjacent semiconductor chips and wherein the recess is filled with the casing.

8. The device according to claim 1, wherein the carrier consists of the lead frame.

9. The device according to claim 1, wherein the carrier comprises a molded body formed on the lead frame.

10. The device according to claim 9, wherein the semiconductor chips overlap with the molded body in a plan view on the device.

11. The device according to claim 1, wherein only the semiconductor chips closest to the ends of the device are directly connected to the lead frame in an electrically conductive manner.

12. The device according to claim 1, wherein the device is an LED filament.

13. The device according to claim 1, wherein the lead frame is self-supporting.

14. A method for producing a plurality of devices comprising the steps of: a) providing a carrier composite comprising a plurality of device regions, said carrier composite comprising a lead frame; b) arranging a plurality of semiconductor chips configured to generate radiation on the carrier composite; c) establishing an electrically conductive connection between the semiconductor chips and the lead frame; d) forming a casing by means of a molding process so that the casing extends continuously over a plurality of device regions and the device regions are surrounded by the casing at least in places along their entire circumference; and e) singulating the casing between adjacent device regions into the plurality of devices, the devices each comprising a portion of the carrier composite as a carrier, a portion of the casing and a portion of the plurality of semiconductor chips arranged on the carrier.

15. The method according to claim 14, wherein the carrier composite and the casing are cut through in a common step in step e).

16. The method according to claim 14, wherein adjacent device regions are each connected to one another via at least one web in step a) and wherein a casting mold, into which the carrier composite is inserted in step d), mechanically supports the carrier composite in the area of the webs.

17. The method according to claim 14, wherein the singulating causes each device of the plurality of devices to: include a portion of the lead frame forming two connecting parts for external electrical contacting of the device, with the carrier being surrounded by the portion of the casing at least in places along its entire circumference and the portion of the casing forming a side face of the device at least in places; and have traces of material removal on the side face.

18. The method according to claim 14, wherein the lead frame is self-supporting.

Description

[0063] Further features, designs and functionalities will become apparent from the following description of the exemplary embodiments in connection with the figures,

in which:

[0064] FIGS. 1A and 1B show an exemplary embodiment of a device in a perspective view (FIG. 1A) and in a schematic sectional view (FIG. 1B);

[0065] FIGS. 2A and 2B show an exemplary embodiment of a device in a schematic sectional view (FIG. 2A) and a corresponding plan view (FIG. 2B);

[0066] FIGS. 3A to 3D show an exemplary embodiment of a method of producing devices by means of intermediate steps each shown in a perspective view;

[0067] FIGS. 4A and 4B show an exemplary embodiment of a method by means of intermediate steps each shown in a perspective view, FIG. 4B showing a finished device; and

[0068] FIGS. 5A, 5B and 5C show an exemplary embodiment of a method of producing a device by means of intermediate steps each shown in a perspective view, FIGS. 5B and 5C showing a finished device in which, for better understanding, the casing is shown transparent in FIG. 5B and opaque in FIG. 5C.

[0069] Equal or similar elements as well as elements of equal function are designated with the same reference signs in the figures.

[0070] The figures and the mutual proportions of the elements depicted in the figures are not to be regarded as true to scale. Rather, individual elements and in particular layer thicknesses may be shown in exaggerated sizes for better representability and/or understanding.

[0071] FIG. 1 shows an exemplary embodiment of a device 1 having a carrier 3 and a plurality of semiconductor chips 2, the semiconductor chips being configured to generate radiation. Along a main extension direction 10, the device 1 extends between two ends 15 of the device.

[0072] The carrier 3 comprises a lead frame 30 with two connecting parts 31. The connecting parts are intended for external electrical contacting of the device 1 and form the opposite ends 15 of the device.

[0073] The semiconductor chips 2 are arranged on the carrier 3, in particular on a front side 33 of the carrier, and are attached to the carrier, for example, via a connection layer (not shown in the figures). The device also comprises a casing 4. The casing surrounds the carrier along its entire circumference, in particular in a section perpendicular to the main extension direction 10. In particular, the casing covers a side face 36 of the carrier 3. The side face 36 is parallel to the main extension direction of the device 1 and perpendicular to the front side 33 of the carrier 3.

[0074] The casing 4 forms a side face 11 of the device 1 in places. At the side face 11, the casing 4 comprises traces 12 of material removal. These are the result of a singulation process during production. The traces 12 typically extend over the entire main extension direction 10 on the side face 11. It is merely for the sake of simplicity that the traces 12 in FIG. 1A are only indicated in a partial area of the side face 11. The side face 11 of the casing is perpendicular to the front side 33 of the carrier.

[0075] A radiation conversion material 6 is arranged in the casing 4, said radiation conversion material converting primary radiation generated by the semiconductor chips 2 during operation of the device 1 at least partially into secondary radiation, so that the device emits light which appears white to the human eye, for example. The radiation conversion material 6 is expediently distributed throughout the casing 4 and is only indicated in a partial area in FIG. 1A merely for better representability.

[0076] The casing 4 contains a polymer material, such as a silicone, an epoxy or a hybrid material with a silicone or an epoxy, for example. This material can be a matrix material for the embedded radiation conversion material 6.

[0077] Along the main extension direction 10, the connecting parts 31 of the lead frame 30 are spaced apart from each other, so that the connecting parts are not directly connected to each other in an electrically conductive manner. A space 305 between the connecting parts is filled with the casing 4. The semiconductor chips 2 are each electrically conductively connected to their adjacent semiconductor chip 2 via connecting lines 7, such as wire bond connections. In each case only the semiconductor chips 2 closest to the ends 15 of the device are directly connected to the lead frame 30 in an electrically conductive manner. The semiconductor chips each have two contacts on their front side facing away from the carrier for electrical contacting by means of the connecting lines. The remaining semiconductor chips 2 are not directly electrically connected to the lead frame, but only via their respective adjacent semiconductor chips. However, the semiconductor chips 2 are thermally connected to the lead frame, so that heat loss occurring during operation of the device 1 can be efficiently dissipated from the semiconductor chips via the lead frame.

[0078] All semiconductor chips 2 of the device 1 can be energized by applying an external electrical voltage between the two connecting parts 31 so that they emit radiation during operation. For example, all semiconductor chips 2 are electrically interconnected in series.

[0079] The carrier 3, in particular the lead frame 30, has a plurality of recesses 39. The recesses 39 can be arranged between adjacent semiconductor chips 2. During operation of the device, radiation generated by the semiconductor chips 2 can pass through the recesses 39 after scattering in the casing 4, for example. The recesses 39 are filled with the casing. In this way, an emission of radiation at a rear side 34 of the carrier 3 opposite the front side 33 can be increased.

[0080] The casing 4 is formed in one piece, for example by a molding process. In a sectional view perpendicular to the main extension direction 10, the casing 4 has a quadrangular, in particular a rectangular basic shape. At the ends 15 of the device, the connecting parts 31 protrude from the casing 4.

[0081] In the exemplary embodiment shown, the carrier 3 consists of the lead frame 30. This means that the carrier 3 does not comprise any other elements. All semiconductor chips 2 of the device are arranged on the lead frame 30, in particular on exactly one connecting part 31 of the lead frame. However, it is also conceivable that one part of the semiconductor chips 2 is arranged on each one of the connecting parts 31.

[0082] The device is in particular designed as an LED filament. Along the main extension direction 10, the spatial expansion of the device is large compared to the spatial expansion perpendicular to this direction, for example at least five times as large or at least ten times as large. At the ends 15 of the device, the latter is preferably spot-weldable, so that the device can be mounted in a conventional glass bulb of a light bulb by means of spot welding and can be electrically contacted externally via the connecting parts.

[0083] Perpendicular to the main extension direction 10, the device 1 has an expansion along at least one direction, in particular along two directions perpendicular to each other, for example of between 0.5 mm and 5 mm inclusive, in particular between 1 mm and 3 mm inclusive.

[0084] For example, the semiconductor chips 2 have, along at least one direction, an edge length which is between 0.05 mm and 2 mm inclusive, in particular between 0.1 mm and 1 mm inclusive. For example, in a plan view on the front side 33 of the carrier, the semiconductor chips 2 may be rectangular or square. In the case of rectangular semiconductor chips 2, the direction along which the longest edge runs is, for example, parallel or substantially parallel, approximately with a deviation of not more than 10°, to the main extension direction 10.

[0085] For example, the carrier 3 and/or the lead frame 30 has a thickness, i.e. an expansion perpendicular to the front side 33 of the carrier, of between 50 μm and 300 μm inclusive.

[0086] The exemplary embodiment shown in FIGS. 2A and 2B essentially corresponds to the exemplary embodiment described in connection with FIGS. 1A and 1B. In contrast to the latter, the carrier 3 comprises a molded body 35 in addition to the lead frame 30. The molded body 35 is molded onto the lead frame 30 and connects the connecting parts 31 in a mechanically stable manner to each other. The connecting parts 31 can each have an interlocking structure 37. The interlocking structure 37 serves to increase the mechanical stability of the connection between the connecting parts 31 and the molded body 35.

[0087] In this exemplary embodiment, the semiconductor chips 2 are thus arranged without overlapping with the lead frame 30. The molded body 35 is suitably formed from a material that is transparent to the radiation generated by the semiconductor chips 2. The coupling out of radiation through the rear side 34 of the carrier 3 is increased by means of the molded body 35. In particular, any of the molding processes listed in the general part of the description is suitable for the production of the molded body.

[0088] The side faces 36 of the carrier are covered by the casing 4 as described in connection with FIGS. 1A and 1B. Radiation emerging from the side face 36 of the carrier, in particular radiation emerging laterally from the molded body 35, must therefore also pass through the casing 4 before it can exit from the side face 11 of the device 1. In this way, an excessive proportion of unconverted primary radiation due to radiation emerging laterally from the molded body 35 can be easily avoided or at least reduced.

[0089] FIGS. 3A to 3D schematically show an exemplary embodiment of a method of producing devices, the devices being designed as described in connection with FIGS. 1A and 1B.

[0090] As shown in FIG. 3A, a carrier composite 300 is provided, the carrier composite 300 comprising a lead frame 30. In the exemplary embodiment shown, the carrier composite consists of the lead frame 30. As described in connection with FIGS. 2A and 2B, the carrier composite 300, from which the carriers of the devices to be produced result during production, may also comprise a molded body.

[0091] The carrier composite 300 comprises a plurality of device regions 32, with the device regions being interconnected at this point. Between adjacent device regions 32, openings 301 are formed in the carrier composite 300. Adjacent device regions of the carrier composite 300 are therefore spaced apart from one another in places.

[0092] As described in connection with FIGS. 1A and 1B, the carrier composite 300 can optionally have recesses 39.

[0093] Subsequently, the semiconductor chips 2 are arranged on and attached to the carrier composite 300 (FIG. 3B). An electrical contacting of the semiconductor chips 2 is established via connecting lines 7, so that all semiconductor chips 2 of a device region 32 are electrically connected to each other and in particular also to the lead frame 30, in particular electrically in series.

[0094] A casing 4 is then formed as shown in FIG. 3C. The casing 4 directly adjoins the semiconductor chips 2 and in particular also the connecting lines 7. Furthermore, the casing 4 fills the openings 301 between adjacent device regions 32. In addition, the casing 4 fills a space 305 between the connecting parts 31 of a device region 32. The connecting parts 31 of a device region 32 are thus connected to each other in a mechanically stable manner by the casing.

[0095] A molding process in which the molding compound used is in liquid or viscous form is particularly suitable for forming the casing 4. The molding compound can be inserted into a closed or still open mold. For example, an injection molding process or an injection compression molding process such as liquid transfer molding is suitable.

[0096] The casing 4 extends continuously over a plurality of device regions 32 and can be planar on its front side as well as on its rear side opposite the front side. Hence, the casting mold used for the molding process can have a particularly simple geometry.

[0097] During the subsequent singulation process, shown in FIG. 3D, the casing 4 is cut through. This cutting produces the side faces 11 of the device 1 produced by the singulation process, which can be carried out using, for example, a sawing process or any other process mentioned in the general part of the description. Singulation produces traces characteristic of the particular singulation process, such as saw marks or other traces of material removal. The resulting casing 4 of the singulated devices 1 has a cuboid basic shape. A cross-section of the casing perpendicular to the main extension direction is quadrangular, for example rectangular.

[0098] FIGS. 4A and 4B show another exemplary embodiment of a method, FIG. 4B representing a finished device. The method and device differ from the previous description in that the casing 4 is not planar. This can be achieved, for example, by an appropriately designed casting mold. Also in this design, the casing 4 initially extends continuously over several device regions 32.

[0099] After singulation, the casing has a cross-section perpendicular to the main extension direction 10, as shown in FIG. 4B, in which the vertical expansion of the casing 4 tapers from the center of the carrier 3 towards the side faces 11. This results in a rounded cross-section of the device thus produced, in particular in the form of an LED filament. This can lead to a higher homogeneity of the radiation characteristic.

[0100] In the singulation step, the casing 4 is cut through as described in the previous exemplary embodiment. Due to the tapering cross-section, however, only a thinner layer of the casing needs to be cut through during the singulation step. The partial area of the side face 11 of the casing 4 which is created during separation again comprises traces 12 of material removal and runs perpendicular to the front side 33 of the carrier 3.

[0101] FIGS. 5A and 5B as well as 5C show another exemplary embodiment of a method and a device. In contrast to the description of FIGS. 4A and 4B, the carrier composite 300 comprises a plurality of webs 38 which connect adjacent device regions 32. This increases the mechanical stability of the carrier composite 300. In the singulation step, the webs 38 can be cut through together with the casing 4. On the side face 11 of the device, the webs 38 are surrounded by the casing 4 along their entire circumference in a side view of the device. At the side of the webs 38, the carrier 3 is surrounded by the casing 4 along its entire circumference. This is shown in FIG. 5C, where the casing 4 is shown opaque. The side face 11 of the device is thus formed by the casing 4, apart from the webs, which account for only a very small portion, typically less than 10%, less than 5% or less than 1%, of their area.

[0102] At the side face 11 of the device, in particular the casing 4 and the webs 38 are flush. To produce the casing, a casting mold 40 can be used in which the webs 38 are mechanically supported by the casting mold 40. This is shown schematically in FIG. 5A for a partial area. This simplifies a reliable positioning of the carrier composite 300 within the casting mold 40. This can also be done from opposite sides of the carrier composite, so that the carrier composite is clamped in the area of the webs when forming the casing.

[0103] A uniform overmolding of the carrier 3 is simplified. In particular, the casting mold 40 can be in direct contact with the webs 38.

[0104] As described above, in particular devices in the form of LED filaments or other omnidirectionally emitting devices can be produced in a simple and reliable manner by a method that essentially uses process steps that are also used in the production of other lead-frame-based designs of light-emitting devices.

[0105] In particular, all production steps can be carried out in a composite. In contrast to conventional LED filaments, the semiconductor chips are not placed on individual, prefabricated strip-shaped carriers. After the final singulation step, no further processing steps are required for the device.

[0106] The invention is not limited by the description based on the exemplary embodiments. Rather, the invention comprises any new feature as well as any combination of features, which in particular includes any combination of features in the claims, even if this feature or combination itself is not explicitly specified in the claims or the exemplary embodiments.

[0107] The present patent application claims the priority of German patent application DE 10 2017 127 621.1, the disclosure content of which is hereby included by way of reference.

LIST OF REFERENCE SIGNS

[0108] 1 device [0109] 10 main extension direction [0110] 11 side face [0111] 12 traces [0112] 2 semiconductor chip [0113] 3 carrier [0114] 30 lead frame [0115] 300 carrier composite [0116] 301 opening [0117] 305 space [0118] 31 connecting part [0119] 32 device region [0120] 33 front side of the carrier [0121] 34 rear side of the carrier [0122] 35 molded body [0123] 36 side face of the carrier [0124] 37 interlocking structure [0125] 38 web [0126] 39 recess [0127] 4 casing [0128] 40 casting mold [0129] 6 radiation conversion material [0130] 7 connecting line