LED PACKAGE

Abstract

A solid state die such as an LED (or OLED) die that is fitted in a hole such as a through hole in a carrier substrate such as a PCB. The die is to be connected to the PCB e.g. to tracks on the PCB. The electrical contacts on the die are arranged to be (e.g. substantially) in the same plane as the contacts on the carrier substrate such as the PCB. This is achieved by the holes in the substrate such as the PCB being adapted so that the dies fit into the holes or openings, i.e. are each taken up into an opening before electrical contacts are made.

Claims

1-32. (canceled)

33. A light emitting die connected to a carrier substrate, the light emitting die comprising: a light emitting element, wherein the light emitting die is located in a hole or opening made in the carrier substrate, the carrier substrate having a first major surface or side and a second major surface or side, the light emitting die having a third major surface or side and a fourth major surface or side, the light emitting element being positioned on the third major surface, first contact elements being positioned in or on the fourth major surface of the light emitting die, the first contact elements being electrically connected to an anode and a cathode of the light emitting element, respectively the first contact elements on the fourth major surface of the light emitting die having an electrical connection to second contact elements on the second major surface of the carrier substrate by means of a conductive connection.

34. The light emitting die connected to a carrier substrate according to claim 33, wherein the light emitting die is encapsulated on the carrier substrate, or wherein the light emitting die is encapsulated on the carrier substrate with an encapsulant which is silicone or silicone based glue, or wherein the light emitting die is attached to removable foil or sheet.

35. The light emitting die connected to a carrier substrate according to claim 33, wherein the hole is a through hole.

36. The light emitting die connected to a carrier substrate according to claim 33, wherein the carrier substrate is a printed circuit board, or wherein the carrier substrate is flexible.

37. The light emitting die connected to a carrier substrate according to claim 33, wherein the electrical connection comprises conductive adhesive beads.

38. The light emitting die connected to a carrier substrate according to claim 33, wherein the fourth major surface of the light emitting die and the second major surface of the carrier substrate are substantially flush or co-planar, or wherein the fourth major surface of the light emitting die and the second major surface of the carrier substrate are offset between the fourth major surface and the second major surface, or wherein the fourth major surface of the light emitting die and the second major surface of the carrier substrate are offset by a distance smaller than the thickness of the carrier substrate, preferably less than 30%, more preferably less than 10% of the thickness of the carrier substrate.

39. The light emitting die connected to a carrier substrate according to claim 33, wherein an enclosure encloses the hole on three or four sides thereof, or wherein a layer is attached to the carrier substrate wherein an enclosure is formed in the layer, or further comprising an enclosure on the carrier substrate which encloses the hole, or further comprising an enclosure on the carrier substrate which encloses the hole on four sides thereof.

40. The method of repairing the light emitting die connected to a carrier substrate according to claim 34, wherein if any of the first contact elements on the fourth major surface of the light emitting die which are electrically connected to second contact elements on the second major surface of the carrier substrate is damaged, a damaged connection is repaired without having to remove the encapsulating material.

41. A method of connecting a light emitting die to a carrier substrate, the light emitting die having a light emitting element, the method comprising: locating the light emitting die in a hole or opening made in the carrier substrate, the carrier substrate having a first major surface or side and a second major surface or side, the light emitting die having a third major surface or side and a fourth major surface or side, positioning the light emitting element on the third major surface, positioning first contact elements in or on the fourth major surface of the light emitting die, electrically connecting the first contact elements to an anode and a cathode of the light emitting element, and electrically connecting the first contact elements on the fourth major surface of the light emitting die to second contact elements on the second major surface of the carrier substrate.

42. The method according to claim 41, comprising encapsulating the light emitting die on the carrier substrate, or comprising encapsulating the light emitting die on the carrier substrate with an encapsulant which is silicone or silicone based glue.

43. The method according to claim 41, wherein the hole is a through hole.

44. The method according to claim 41, wherein the carrier substrate is a printed circuit board, or wherein the carrier substrate is flexible.

45. The method according to claim 41, wherein the electrical connecting step comprises using conductive adhesive beads.

46. The method according to claim 41, wherein the fourth major surface of the light emitting die and the second major surface of the carrier substrate are arranged to be substantially flush or co-planar, or wherein the fourth major surface of the light emitting die and the second major surface of the carrier substrate are arranged to be substantially flush or co-planar with an offset between the fourth major surface and the second major surface, or wherein the fourth major surface of the light emitting die and the second major surface of the carrier substrate are arranged to be substantially flush or co-planar with an offset between the fourth major surface and the second major surface that is smaller than a thickness of the carrier substrate, preferably less than 30%, more preferably less than 10% of the thickness of the carrier substrate.

47. The method according to claim 41, further comprising forming an enclosure which encloses the hole.

48. The method according to claim 41, further comprising attaching a layer to the carrier substrate, the enclosure being formed in the layer.

49. The method according to claim 41, wherein locating the light emitting die in a hole or opening comprises attaching the light emitting die to a foil or sheet and inserting the light emitting die in the carrier substrate using the foil or sheet.

50. The method according to claim 49, further comprising removing the foil or sheet to expose the first and/or the second electrical contact elements.

51. The method according to claim 41, wherein the enclosure is formed self-aligning with the hole or opening.

52. A kit of parts comprising: a plurality of light emitting dies attached to a foil, and a carrier substrate; the light emitting dies having light emitting elements, the carrier substrate having periodically distanced holes or openings, the foil and the carrier substrate being adapted so that when the foil is offered up to the carrier substrate, each of the plurality of light emitting dies being aligned with one of the holes or openings for placement of each of the plurality of light emitting dies in the one of the holes or openings.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0058] FIG. 1 shows an example of naked die LED that is connected to conductors on a carrier substrate according to the prior art.

[0059] FIG. 2 shows an example of naked die LEDs connected to a printed circuit board and encapsulated according to the invention.

[0060] FIG. 3 shows how the naked die fits in an opening or through hole in the printed circuit board.

[0061] FIGS. 4A and 4B show example of footprints for the opening or through hole in the printed circuit board.

[0062] FIG. 5 is a cross section of an array of naked dies on a carrier substrate.

[0063] FIG. 6 is a perspective view of an array of naked dies on a carrier substrate

[0064] FIG. 7 shows a perspective view of a printed circuit board with openings and the corresponding enclosures according to the invention.

[0065] FIG. 8 shows a cross section of a printed circuit board with openings and the corresponding enclosures.

[0066] FIG. 9A shows a cross section of a printed circuit board topped by a film or layer used to form enclosures.

[0067] FIG. 9B shows a cross section of a printed circuit board topped by a film or layer once they have been punched or drilled to form openings for naked dies.

[0068] FIG. 10 shows a cross section of a carrier membrane with naked dies aligned with openings in the printed circuit board and the corresponding enclosures.

[0069] FIG. 11 shows a cross section of the naked dies fitting in the openings and the enclosure once encapsulating material has been dispensed in the enclosures.

[0070] FIG. 12 shows a cross section of the naked dies fitting in the openings and the enclosure once encapsulating material has been dispensed in the enclosures and between enclosures.

[0071] FIG. 13 shows a cross section of the naked dies fitting in the openings while allowing access to electrical contacts on the second surface of the naked dies and the electrical contact on the second surface of the printed circuit board.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0072] The present invention will be described with respect to particular embodiments but the invention is not limited thereto but only by the claims. Any reference signs in the claims shall not be construed as limiting the scope.

[0073] Where the term “comprising” is used in the present description and claims, it does not exclude other elements or steps. Where an indefinite or definite article is used when referring to a singular noun e.g. “a” or “an”, “the”, this includes a plural of that noun unless something else is specifically stated.

[0074] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order, unless specified. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. The terms or definitions used herein are provided solely to aid in the understanding of the invention.

[0075] Embodiments of the present invention relate to displays having solid state light sources in the form of dies. An LED or OLED can include a number of layers, e.g. semiconductor layers and an active layer. Generally a solid state light source such as an LED or OLED will have two electrical contacts. An LED or OLED can include a substrate, a first semiconductor layer, an active layer, a second semiconductor layer, a reflector layer, a first electrode and a second electrode.

[0076] FIG. 2 shows a cross section of an example of a solid state die such as an LED (or OLED) die 20 connected to a carrier substrate 23 such as a printed circuit board and encapsulated on the carrier substrate 23 such as the printed circuit board according to embodiments of the present invention. A naked die 20 has a first main surface or side 20A and a second side or main surface 20B. A light emitting diode (or OLED) element 20C is positioned on the first main surface 20A. Contact elements 21A and 21B are positioned in or on the second main surface 20B of the naked die 20. For example, the contact elements 21A and 21B are electrically connected to an anode and a cathode of the light emitting diode (LED or OLED) element 20C. The anode and cathode are signal conductors and at least two or more signal conductors (e.g. anode and cathode) from a solid state light source such as an LED or OLED die are provided per hole or opening in the carrier substrate. This reduces the number of holes required by 50% compared to conventional through hole technology.

[0077] The naked die 20 fits in a through hole or opening 22 made in a carrier substrate 23 like for example, a printed circuit board. The carrier substrate 23 such as a printed circuit board can be flexible. The carrier substrate 23 has a first main surface or side 23A and a second side or main surface 23B.

[0078] The contacts 21A and 21B on the second main surface 20B of the naked die 20 are electrically connected to contacts 24A and 24B on the second main surface 23B of the carrier substrate 23 such as a printed circuit board, by means of a connector. The connector may be e.g. conductive adhesive beads 25 and 26. The second main surface 20B of the naked die 20 and the second main surface 23B of the carrier substrate 23 can be substantially flush or co-planar. There may be an offset such as a small offset OFF between the second main surface 20B and the second main surface 23B. The offset OFF can be caused by tolerances of e.g. the equipment used to position the die 20 into the opening 22. The offset OFF is preferably smaller than the thickness of the carrier substrate 23. The offset (OFF) may be provided (i.e. tolerated) between the fourth major surface and the second main surface. This offset OFF is preferably smaller than the thickness of the carrier substrate, preferably less than 30%, more preferably less than 10% of the thickness of the carrier substrate. The offset for example, can be at most 30% or more preferably at most 10%. In these case the offset has little effect. For example the offset can be at most 30 micron or more preferably at most 10 micron. For example the carrier substrate may be a PCB which may have a thickness between 0.1 and 10 mm.

[0079] The light emitting naked die 20 is then preferably encapsulated in an encapsulant e.g. a silicone or silicone based glue 27.

[0080] If the electrical connection between an electrode (like e.g. 21A) on the naked die 20 and an electrode (like e.g. 24A) on the carrier substrate 23 is damaged, repair is possible without having to remove the encapsulating material 27.

[0081] FIG. 3 shows a top view of a solid state die such as the LED (or OLED) 20 fitting in the opening 22 made in the carrier substrate 23 such as the printed circuit board.

[0082] As illustrated on FIG. 4A, if the footprint of the light emitting die 20 is e.g. a square with a side of length L1, the opening 22 can be delimited by e.g. a square 40A with a side of length L2>L1. As illustrated on FIG. 4B, if the footprint of the light emitting die 20 is e.g. a square with a side of length L1, the opening 22 can be delimited by e.g. a circle 40B with a radius R>√2*L1 (L2 is 2R). More generally, the opening 22 has lateral dimensions (side of square, radius of a disk, width and length of a rectangle . . . ) larger than the lateral dimensions of the footprint of the light emitting die 20. The light emitting die 20 can then fit in, and can be taken up into the opening 22. Once inserted, the second surface 20B will be substantially co-planar with second surface 23B.

[0083] The difference in size between L2 and L1 or R (=L2/2) and L1 (i.e. in the x and y plane) is preferably larger than a tolerance ε that affects the alignment of the naked light emitting die 20 and the opening 22 in the z plane. Hence, this offset is preferably smaller than the thickness of the carrier substrate. The offset (OFF) may be provided (i.e. tolerated) between the fourth major surface and the second main surface. This offset OFF is preferably smaller than the thickness of the carrier substrate, preferably less than 30%, more preferably less than 10% of the thickness of the carrier substrate. The offset for example, can be at most 30% or more preferably at most 10%. In these case the offset has little effect. For example the offset can be at most 30 micron or more preferably at most 10 micron. For example the carrier substrate may be a PCB which may have a thickness between 0.1 and 10 mm.

[0084] A method to assemble a display with solid state light sources such as an LED (or OLED) display according to an embodiment of the present invention, will be described with reference to the drawings.

[0085] Light emitting naked dies 200, 201, . . . are pre-positioned on a carrier membrane 50 as illustrated on FIG. 5 and FIG. 6. The membrane 50 is used as a disposable tool for offering up and for allowing attaching of the naked dies to the carrier substrate 23. FIG. 5 illustrates a cross section through the carrier membrane 50 while FIG. 6 gives a perspective view of the light emitting naked dies distributed over the carrier membrane 50, e.g. in a periodical array. In FIG. 6, the solid state light sources can be LEDs (or OLED's) are shown as RGB triplets forming an array of regularly spaced RGB pixels. The carrier membrane 50 can be made of a plastic e.g. PVC, polyolefin, or polyethylene sheet or foil.

[0086] The carrier membrane 50 can for instance be a tape such as a dicing tape, a backing tape or a blue tape known from the art. The distances (Dx in FIG. 5 and Dx′ and Dy′ in FIG. 6) between adjacent light emitting dies can be the same distance between adjacent light emitting dies in a conventional LED (or OLED) display. Other configurations are included within the scope of the present invention.

[0087] For instance, the LEDs (or OLEDs) can be used to build a LED (or OLED) display and the LEDs (or OLEDs) can be clustered in groups of three or four of such LEDs (or OLEDs). Each LED (or OLED) of a cluster can correspond to a sub-pixel of a given primary color (e.g. RGB or RGBW with R=Red, G=Green, B=Blue and W=White).

[0088] FIG. 6 shows a perspective view of solid state light sources such as LEDs grouped in RGB triplets. A first triplet 200 comprises a red LED 200A, a green LED 200B and a blue LED 200C. A second triplet 201 comprises a red LED 201A, a green LED 201B and a blue LED 201C. The distance between the two adjacent triplets like e.g. a first triplet (200A, 200B, 200C) and a second triplet (201A, 201B, 201C) along a first direction is Dx′. The distance between two adjacent triplets like e.g. a first triplet (200A, 200B, 200C) and a third triplet (202A, 202B, 202C) along a second direction is Dy′.

[0089] FIG. 8 shows openings 220, 221, . . . made in substrate such as a printed circuit board 70. These can be through holes. Conductive tracks and contact pads can be made on a back side. This is typically the case with a PCB. The printed circuit board 70 can be a flexible circuit board made of a material like polyimide, PEEK, polyester . . . .

[0090] The openings 220, 221, . . . can be formed by any suitable techniques such as those of subtractive machining, e.g. by punching, cutting, drilling or laser ablation or drilling. But the carrier substrate may also be moulded with holes therein.

[0091] FIGS. 7 and/or 8 shows a cross section of the printed circuit board 70 with openings 220, 221 and the corresponding enclosures 230, 231. Enclosures 230, 231, . . . are formed or positioned around each of the holes or openings 220, 221, . . . . An enclosure 230, 231, . . . surrounds each hole or opening. The enclosures 230, 231 can be cylindrical and are open at both ends. For instance, the enclosures 230, 231 can have a circular cross section, a hexagonal cross section or a square cross section. If the enclosures 230, 231 have a circular cross section with an inner diameter DE and the openings 220, 221, . . . are delimited by a circle with a diameter DO, then DE is preferably larger than DO (DE>DO).

[0092] FIG. 7 shows a perspective view of the printed circuit board 70 with holes or openings 220, 221, 222, and the corresponding enclosures made in a thick layer or film 71 formed on the printed circuit board 70. The layer or film 71 may be 100 to 300 micron thick for example 200 micron thick.

[0093] The enclosures can, for example, be printed on the printed circuit board (e.g. inkjet printing or silk screen printing or any other form of 3D printing).

[0094] Alternatively, the enclosure can be drilled or punched in a thick film 71 which can be deposited on or fixed to the printed circuit board 70. In that case, the enclosures are formed at the same time as the openings in a self-aligning fashion as illustrated on FIG. 9A and FIG. 9B. The layer or film 71 may be 100 to 300 micron thick for example 200 micron thick. Layer or film 71 can be applied by roll lamination, roll to roll processing, squeegee coating, etc.

[0095] FIG. 9A shows a cross section of the printed circuit board 70 topped by a film or layer 71. Both the PCB 70 and layer 71 are fixed or fastened to each other. The layer 71 can e.g. be a resin that is cured after having been dispensed and spread on the printed circuit board 70, thereby adhering to the printed circuit board 70. The layer or film 71 may be 100 to 300 micron thick for example 200 micron thick. Layer or film 71 can be applied by roll lamination, roll to roll processing, squeegee coating, etc.

[0096] As shown in FIG. 9B holes 220, 221 are made in both the PCB 70 and layer 71 by a subtractive machining process, e.g. they are punched, ground, milled, laser oblated, drilled or laser drilled. They can be formed by subtractive machining e.g. punched, ground, milled, shaped, drilled or laser drilled or oblated at the same time. A cross section of the result can be seen on FIG. 9B. The enclosures can be connected with each other or be standalone.

[0097] The electrical contacts 72, 73, 74, 76 . . . on the printed circuit board 70 will be electrically connected to the contact pads of the solid state light sources such as LEDs (or OLEDS) on the naked dies which are on the side of the printed circuit board opposite to the side in contact with the layer 71.

[0098] When formed e.g. by printing on the printed circuit board 70, the enclosures 230, 231, . . . are distinct from each other as seen on FIGS. 7 and 8.

[0099] The openings or holes 220, 221, . . . form a lattice on the printed circuit board that has the same periodicity as the lattice formed by the naked dies on carrier 50 membrane. The openings or holes 220, 221, . . . in the printed circuit board 70 can be aligned with the light emitting naked dies 200 on the carrier membrane 50. This is illustrated on FIG. 10 which shows a cross section of both the carrier membrane 50 with light emitting naked dies 200, 201 . . . aligned with the openings 220, 221 in the printed circuit board 70 and the corresponding enclosures 230, 231 . . . made in the thick film 71 . . . . The layer or film 71 may be 100 to 300 micron thick for example 200 micron thick. This can be applied by roll lamination, roll to roll processing, squeegee coating, etc.

[0100] When the light emitting naked dies 200, 201 . . . are positioned in the corresponding holes or openings 220 and 221 having enclosures 230, 231 . . . an encapsulating material 270 can be dispensed in the enclosures 230, 231 . . . . This is illustrated in FIG. 11. The enclosures need not be connected with each other (i.e. when they are individually printed instead of being punched in a thick film). The encapsulating material can also be dispensed around the enclosures 230, 231 . . . as well as in the enclosures 230, 231 . . . . This is illustrated in FIG. 12. The encapsulating material 270 can be e.g. cured or cross-linked. This can be by chemical crosslinking, room temperature vulcanizing, ebeam, UV or infrared crosslinking for example. For example, the encapsulating material can be silicone or silicone based glue.

[0101] The carrier membrane 50 is then removed (e.g. peeled off), thereby giving access to electrical contacts on the second surface of the naked dies 200, 201 and the electrical contacts on the second surface of the printed circuit board 70. Connections between the electrical contacts can be done e.g. by dispensing electrically conducting adhesive to make the connections. This is illustrated on FIG. 13. A first electrical contact is formed by an electrically conducting adhesive bead 240 between an electrode 72 on the printed circuit board and a first contact on the die 200. A second electrical contact is formed by an electrically conducting adhesive bead 241 between an electrode 73 on the printed circuit board and a second contact on the die 200 . . . .

[0102] The backside of the completed product according to any or all of the embodiments is preferably covered with an insulating layer applied over all of the contacts. This insulating layer may be an insulating adhesive tape for example or a coating of an insulting varnish or any other suitable insulating material. This may be done by spraying, for example.

[0103] While the invention has been described hereinabove with reference to specific embodiments, this was done to clarify and not to limit the invention. The skilled person will appreciate that various modifications and different combinations of disclosed features are possible without departing from the scope of the invention.