FIELD OF THE INVENTION

The present invention relates to a flex foil having conductive contact regions on both major surfaces of the flex foil.

The present invention further relates to an LED assembly having an LED chip bonded to such a flex foil.

The present invention yet further relates to a lighting device comprising such an LED assembly.

The present invention still further relates to a method of bonding such flex foil to an LED chip.

BACKGROUND OF THE INVENTION

Nowadays, the interconnection between an LED chip and the outer world is typically provided by a rectangular or frame-shaped printed circuit board (PCB) or flex foil. A typical rectangular LED chip 10 is schematically depicted in FIG. 1. The rectangular LED chip 10 in FIG. 1 is a square chip in which opposite sides L have the same dimension as opposite sides W, i.e. the length and width of the chip is identical. The edge regions along the sides of the major surface of the LED chip 10 typically comprise one or more anode contacts 11 and one or more cathode contacts 12 for contacting the LED chip to the outside world. A central region 13 delimited by these edge contact regions may comprise a thin film

encapsulation layer to protect the LEDs in the substrate of the LED chip, which thin film encapsulation layer may be covered by a heat transfer material to facilitate effective cooling of the LEDs in the LED chip during operation.

In the case of a rectangular PCB or flex foil, the whole area of a rectangular LED chip is typically covered by a matching PCB or flex foil, whereas in the case of a frame- shaped PCB or flex foil, only the edge regions of the LED chip containing the anode and diode contacts are covered by the PCB or flex foil. However, in both scenarios a large amount of PCB or flex foil material is wasted; in the case of a rectangular PCB or flex foil, the central area of the LED chip is unnecessarily covered with redundant PCB or flex foil material, whereas in the case of a frame-shaped PCB or flex foil, such a frame shaped is typically achieved by milling or cutting out and disposing of the central region of a rectangular PCB or flex foil.

FIG. 2 depicts the typical losses in terms of PCB or flex foil material for a frame-shaped PCB or flex foil as a function of the edge dimensions of a square LED chip. The various curves CI depict the contact ledge width in mm of the contact regions of the LED chip. The same losses apply in terms of redundant area over the central region of the LED chip for a rectangular PCB or flex foil. Such losses are undesirable as it increases the production cost of an LED assembly containing the LED chip and PCB or flex foil.

Moreover, in case of a rectangular PCB or flex foil, the thickness of the heat transfer material over the thin film encapsulation layer may need to be increased to achieve effective cooling of the LEDs during operation, which undesirably adds to the thickness of the LED chip and can cause thermal expansion issues. Additionally, the interconnection of the LED assembly to a driver circuit can be less than straightforward.

SUMMARY OF THE INVENTION

The present invention seeks to provide a flex foil that reduces material losses and facilitates an LED assembly having improved characteristics.

The present invention further seeks to provide an LED assembly comprising such a flex foil.

The present invention yet further seeks to provide a lighting device including such an LED assembly.

The present invention still further seeks to provide a method of assembling such an LED assembly.

According to an aspect, there is provided a flex foil for providing an electrical connection to a plurality of electrical contacts disposed on at least two edge regions along a major surface of an electrical component, wherein the flex foil is a flex foil strip having a first major surface and a second major surface opposite the first major surface, the flex foil strip comprising a first strip portion at a first terminal end of the flex foil strip, the first strip portion separated from a second strip portion by a first diagonal fold line, the first strip portion comprising a first conductive contact region on the first major surface, the second strip portion comprising a second conductive contact region of the second major surface; and a terminal strip portion at a second terminal end of the flex foil strip opposite the first terminal end, the terminal strip portion comprising a terminal connector conductively coupled to the first conductive contact region and the second conductive contact region. The provision of a strip-shaped flex foil having diagonal folding lines allows for the flex foil to be folded along the edge regions of a major surface of a rectangular chip such as a rectangular LED chip. Such a strip-shaped flex foil can be made to size without having to discard substantial amounts of the flex foil material. Moreover, because the strip- shaped flex foil has a flexible terminal portion that may extend beyond the boundaries of the chip onto which the flex foil is mounted, a connection between the terminal connector of the flex foil and a further terminal connector, for example of a driver circuit mounted on a carrier comprising such a further terminal connector can be achieved in a straightforward manner, e.g. without the need to solder additional cables to a PCB or flex foil.

The flex foil strip may have any suitable number of strip portions. In an embodiment, the flex foil strip further comprises a third strip portion separated from the second strip portion by a second diagonal fold line, the third strip portion comprising a third conductive contact region on the first major surface, and a fourth strip portion separated from the third strip portion by a third diagonal fold line, the fourth strip portion comprising a fourth conductive contact region on the second major surface, wherein the connection strip portion abuts the fourth strip portion and the terminal connector is further conductively coupled to the third conductive contact region and the fourth conductive contact region. In this embodiment, the flex foil strip may cover all edge regions of a major surface of a rectangular chip such as a rectangular LED chip.

The terminal connector may be a surface mount design (SMD) terminal connector. Such connectors are commonly used in LED assembly technologies.

Each conductive region of the flex foil strip may comprise any suitable conductive material to make the region electrically conductive. Preferably, each conductive region comprises a metal conductive contact. More preferably, each metal conductive contact is a copper contact.

The flex foil strip in some embodiments may comprise a polymer layer stack including a first polymer layer carrying the first major surface and a second polymer layer carrying the second major surface; and a plurality of conductive tracks in between the first polymer layer and the second polymer layer electrically connecting the terminal connector to the respective conductive contact regions. This for instance protects the conductive tracks from external damage. The conductive tracks may be made of any suitable electrically conductive material, e.g. a metal. The conductive tracks may be copper tracks.

According to another aspect, there is provided a LED assembly comprising a rectangular LED chip having a further major surface comprising a first further contact region along a first edge region of the further major surface and a second further contact region along a second edge region of the further major surface perpendicular to the first edge region; and the flex foil of any of the above embodiments, wherein the first strip portion is bonded to the first further contact region such that the first conductive contact region on the first major surface is conductively coupled to the first further contact region; the second strip portion is folded relative to the first strip portion along the first diagonal fold line; and the second strip portion is bonded to the second further contact region such that the second conductive contact region on the second major surface is conductively coupled to the second further contact region.

In this manner, an LED assembly is provided that benefits from a reduced thickness due to the fact that the terminal connector of the LED chip does not need to be provided at the chip level but instead is provided as an extension lead in the form of the terminal strip portion. Moreover, the overall cost of the LED assembly is reduced due to the avoidance of substantial wastage of flex foil material.

A subset of the contract regions adjacent to the edges of the LED chip may be covered by respective strip portions of the flex foil strip, i.e. some edge regions of the LED chip may remain uncovered if not all edge regions contain contacts. Alternatively, the further major surface of the rectangular LED chip further comprises a third further contact region along a third edge region of the further major surface perpendicular to the second edge region; and a fourth further contact region along a fourth edge region of the further major surface perpendicular to the third edge region, wherein the flex foil strip comprises the third strip portion folded relative to the second strip portion along the second diagonal fold line; the third strip portion bonded to the third further contact region such that the third conductive contact region on the first major surface is conductively coupled to the third further contact region; the fourth strip portion folded relative to the third strip portion along the third diagonal fold line; and the fourth strip portion is bonded to the fourth further contact region such that the fourth conductive contact region on the second major surface is conductively coupled to the fourth further contact region. In this embodiment, all contact regions, i.e. all edge regions of the major surface of the rectangular LED chip are covered by (bonded to) respective flex foil strip portions.

The LED assembly may further comprise a driver circuit assembly having a further terminal connector mating with the terminal connector of the flex foil strip.

The respective further contact regions of the rectangular LED chip may be indium tin oxide regions, which is a transparent electrically conductive material commonly used in LED chip manufacturing techniques. Other suitable electrically conductive materials may be contemplated for the respective further contact regions.

The rectangular LED chip may comprise a substrate in which at least one organic LED is formed although other types of LEDs are equally feasible.

According to yet another aspect, there is provided a solid state lighting device comprising a housing including the LED assembly of any of the above embodiments. Such a solid state lighting device benefits from the particularly compact LED assembly, which therefore allows for a more compact solid state lighting device. This is for instance particularly advantageous where the solid state lighting device is a light bulb, as it is a well- known design challenge to provide a solid state lighting-based light bulb that can be used to replace incandescent or halogen light bulbs, as often the solid state lighting-based light bulb has a somewhat larger form factor such that the solid state lighting-based light bulb cannot be retrofitted in existing bulb holders such as ceiling-mounted luminaires, which may be designed to snugly fit an incandescent or halogen light bulb.

According to still another aspect, there is provided a method of assembling a

LED assembly, comprising providing a rectangular LED chip having a further major surface comprising a first further contact region along a first edge region of the further major surface and a second further contact region along a second edge region of the further major surface perpendicular to the first edge region; providing the flex foil of any of the above

embodiments; bonding the first strip portion to the first further contact region such that the first conductive contact region on the first major surface is conductively coupled to the first further contact region; folding the second strip portion relative to the bonded first strip portion along the first diagonal fold line; and bonding the second strip portion to the second further contact region such that the second conductive contact region on the second major surface is conductively coupled to the second further contact region. This facilitates a particularly cost-effective assembly as explained above. The assembly method may be extended to cover all four edge regions of the further major surface of the LED chip with flex foil strip portions in this manner. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described in more detail and by way of non- limiting examples with reference to the accompanying drawings, wherein

FIG. 1 schematically depicts a typical LED chip; FIG. 2 is a graph depicting typical losses of flex foil or PCB material when assembling such a flex foil or PCB on the LED chip of FIG. 1 in a known manner;

FIG. 3 schematically depicts a flex foil strip according to an embodiment; FIG. 4 schematically depicts an LED assembly according to an embodiment; and

FIG. 5 schematically depicts an assembly method of the LED assembly of

FIG. 4.

DETAILED DESCRIPTION OF THE EMBODIMENTS

It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

FIG. 3 schematically depicts a flex foil strip 100 according to an embodiment of the present invention. The flex foil strip 100 is typically made of a flexible electrically insulating material such as a flexible electrically insulating polymer, e.g. an electrically insulating organic polymer such as polyimide or the like. The flex foil strip 100 typically comprises a first major surface and a second major surface opposite the first major surface, i.e. opposing major surfaces, e.g. the front side and back side of the flex foil strip 100.

The first major surface and the second major surface each carry a plurality of electrically conductive contacts for contacting the further electrically conductive contacts of a chip onto which the flex foil strip 100 may be mounted. The plurality of electrically conductive contacts may be made of any suitable electrically conductive material, preferably a metal or metal alloy. Suitable metals include but are not limited to gold, silver, nickel and copper. Copper is particularly suitable because of its ease of processing and compatibility with many electrically insulating polymer materials such as polyimide.

The flex foil strip 100 is partitioned into a plurality of strip portions that each carry one or more conductive contacts that are alternatingly located on the first major surface and the second major surface of the flex foil strip 100 respectively. In an embodiment, the flex foil strip 100 has up to four strip portions, with each strip portion to be bonded to an edge region of a major surface of a rectangular chip as will be explained in more detail below. In an embodiment, the flex foil strip 100 may contain two, three or four of such strip portions.

In FIG. 3, the flex foil strip 100 is shown to have a first strip portion 101 at a first terminal end of the flex foil strip 100, which first strip portion 101 carries one or more first conductive contact regions 111 on the lower major surface of the flex foil strip 100 in the view of FIG. 3. The flex foil strip 100 is further shown to have a second strip portion 102 adjacent to the first strip portion 101 which second strip portion 102 carries one or more second conductive contact regions 112 on the upper major surface of the flex foil strip 100 in the view of FIG. 3.

The first strip portion 101 is separated from the second strip portion 102 by a first diagonal fold line 121, i.e. a fold line that extends diagonally across the width of the flex foil strip 100. The first diagonal fold line in some embodiments may comprise an indentation or the like substantially across the full width of the fold line 121 to assist the folding of the second strip portion 102 relative to the first strip portion 101. By folding over the second strip portion 102 relative to the first strip portion 101 along the first diagonal fold line 121, the folded-over second strip portion 102 becomes oriented under a 90° angle relative to the first strip portion 101 with the one or more second conductive contact regions 112 facing in the same direction as the one or more first conductive contact regions 111. In this manner, the first strip portion 101 and the second strip portion 102 may be aligned with perpendicular edge regions of the major surface of a rectangular chip such as a rectangular LED chip, with the first conductive contact regions 111 and the second conductive contact regions 112 aligned for bonding to further contact regions in the perpendicular edge regions of the rectangular chip.

A diagonal fold line may be located in a square portion of the flex foil strip

100 in between adjacent strip portions carrying one or more conductive contact regions, with the diagonal fold line forming a diagonal of this square. However, in order to limit the size of such a fold region in between contact regions, a conductive contact region proximal to the fold line may have a diagonal side proximal to and parallel with the fold line, such as the first conductive contact region 111 ' of the first strip portion 101, which first conductive contact region 111 ' is located adjacent to the first fold line 121. The opposing strip portion, here the second strip portion 102 may comprise a substantially triangular void region 102' opposite the diagonal side of the first conductive contact region 111 ' proximal to the first fold line 121. Alternatively, the second conductive contact region of the second strip portion 102 located proximal to the first fold line 121 may have a diagonal side proximal to and parallel with the first fold line 121 to further reduce the size of the fold region in between the adjacent strip regions carrying conductive contact regions.

In some embodiments, each of the strip portions has the same dimensions or at least the same length in order to cover the respective edge regions of a square chip. However, it is equally feasible to for instance have a first strip portion 101 and a second strip portion 102 (and optionally a third strip portion and a fourth strip portion) in which the first strip portion 101 and the optional third strip portion have a first length, whilst the second strip portion 102 and the optional fourth strip portion have a second length different to the first length, the first and second lengths corresponding to the respective lengths of the sides of a rectangular chip such as a rectangular LED chip. For the avoidance of doubt, in the context of the present application, a square chip is considered a special case of a rectangular chip.

In addition to the aforementioned strip portions, the flex foil strip 100 further comprises a terminal strip portion 105 at a second terminal end of the flex foil strip opposite the first terminal end, the terminal strip portion comprising a terminal connector conductively coupled to the first conductive contact region and the second conductive contact region. Contrary to the adjoining strip portions of the flex foil strip 100 that carry conductive contact regions, the terminal strip portion 105 is typically not separated from its adjoining strip portion but rather extends in the same direction of its adjoining strip portion with conductive contact regions. Consequently, when the respective strip portions of the flex foil strip 100 are bonded to a rectangular chip as previously explained, the terminal strip portion 105 will extend beyond the boundary of the rectangular chip.

The terminal strip portion 105 comprises a terminal connector 115 conductively coupled to the respective conductive contact regions of the flex foil strip 100, e.g. the one or more first conductive contact regions 111 of the first strip portion 101 and the one or more second conductive contact regions 112 of the second strip portion 102 shown in FIG. 1.. The terminal connector 150 may be any suitable type of terminal connector, such as by way of non-limiting example a surface mount design terminal. Other types of terminals are of course equally feasible. The terminal strip portion 105 including terminal connector 115 acts as a ribbon cable or the like for the rectangular chip onto which the flex foil strip 100 is bonded, such that the terminal connector 115 can be easily connected to a further terminal connector, such as the terminal connector of a driver circuit assembly due to the flexibility of the terminal strip portion 105.

In an embodiment, the terminal connector 115 may be conductively coupled to the respective conductive contact regions of the flex foil strip 100 by conductive tracks, which may be embedded in the flex foil strip 100. The flex foil strip 100 may be a multi-layer flex foil strip in which the conductive tracks are located in between layers of the multi-layer flex foil strip to protect the conductive tracks from external damage. The multi-layer flex foil strip 100 may comprise a polymer layer stack including a first polymer layer carrying the first major surface and a second polymer layer carrying the second major surface. The conductive tracks may be made of any suitable conductive material, such as one of the previously mentioned metals or metal alloys. In an embodiment, the conductive tracks are copper conductive tracks.

FIG. 4 schematically depicts an LED chip assembly including a rectangular

LED chip 10 having bonded thereto a flex foil strip 100 according to an embodiment. This may be any suitable type of LED chip 10, e.g. may contain any suitable type and number of LEDs, such as one or more OLEDs by way of non-limiting example. FIG. 5 schematically depicts an example embodiment of an assembly method for assembling such an LED chip assembly. The LED chip assembly of FIG. 4 will now be explained in further detail with the aid of FIG. 5. Where reference is made to bonding, it should be understood that is may be achieved by any suitable electrically conductive bonding material, for example of an electrically conductive adhesive or a solder.

The assembly process commences in the top left pane of FIG. 5 (labeled (1)) in which the first strip portion 101 is bonded onto a first edge region of the shown major surface of the rectangular LED chip 10, which first edge region contains first further conductive contact regions CL1. The first strip portion 101 is bonded onto the first edge region such that the first conductive contact regions 111 are conductively coupled to the first further conductive contact regions CL1.

Next, the flex foil strip 100 is folded along first folding line 121 such that the second strip portion 102 is folded over relative to the bonded first strip portion 101. This folding process alters the orientation of the initially upward facing second conductive contact regions 112 of the second strip portion 102 to downward facing contact regions, i.e. contact regions facing the second further contact regions CL2 along the second edge region of the rectangular LED chip 10, as shown in the right top pane of FIG. 5 (labeled (2). The second strip portion 102 is subsequently bonded onto the second edge region such that the second conductive contact regions 112 are conductively coupled to the second further conductive contact regions CL2 of the rectangular LED chip 10.

This process is repeated by folding flex foil strip 100 along second folding line 122 such that the third strip portion 103 is folded over relative to the bonded second strip portion 102. This folding process alters the orientation of the initially upward facing third conductive contact regions 113 of the third strip portion 103 to downward facing contact regions, i.e. contact regions facing the third further contact regions CL3 along the third edge region (opposite the first edge region) of the rectangular LED chip 10, as shown in the right bottom pane of FIG. 5 (labeled (3). The third strip portion 103 is subsequently bonded onto the third edge region such that the third conductive contact regions 113 are conductively coupled to the third further conductive contact regions CL3 of the rectangular LED chip 10.

The bonding process may be completed by folding flex foil strip 100 along third folding line 123 such that the fourth strip portion 104 is folded over relative to the bonded third strip portion 103. This folding process alters the orientation of the initially upward facing fourth conductive contact regions 114 of the fourth strip portion 104 to downward facing contact regions, i.e. contact regions facing the fourth further contact regions CL4 along the fourth edge region (opposite the second edge region) of the rectangular LED chip 10, as shown in the left bottom pane of FIG. 5 (labeled (4). The fourth strip portion 104 is subsequently bonded onto the fourth edge region such that the fourth conductive contact regions 114 are conductively coupled to the fourth further conductive contact regions CL4 of the rectangular LED chip 10.

The resulting LED chip assembly is shown in FIG. 4. As can be seen, the terminal portion 105 of the flex foil strip 100 extends beyond the boundary of the rectangular LED chip 10 by a length L' with the terminal connector 115 distal to the rectangular LED chip 10. The flexibility provided by the terminal portion 105 of length L' facilitates the straightforward connection of the terminal connector 115 to a further terminal connector, e.g. of a driver circuit assembly, by bending or otherwise flexing the terminal portion one of 5 to align the terminal connector 115 with the further terminal connector of this assembly. In an embodiment (not shown), the LED chip assembly may further comprise such a further assembly, for example a driver circuit assembly including a further terminal connector mating with the terminal connector 115.

In an embodiment, the terminal portion 105 linearly extends from its adjacent strip portion, here fourth strip portion 104. In other words, the terminal portion 105 is not folded over relative to its adjacent strip portion. However, embodiments in which a further diagonal fold line in between the terminal portion 105 and its adjacent strip portion of the flex foil strip 100 is present to facilitate the folding over of the terminal portion 105 relative to its adjacent strip portion may also be contemplated.

It is noted that in FIG. 4 and 5, all four edge regions of the major surface of the rectangular LED chip 10 are bonded to a corresponding strip portion of the flex foil strip 100 by way of non- limiting example. As previously explained, it is equally feasible to have only two or three of such edge regions bonded to a corresponding strip portion of the flex foil strip 100, in which case the flex foil strip 100 may comprise two or three strip regions carrying one or more conductive contact regions separated by one or two diagonal fold lines respectively, as also explained above.

The LED chip assembly according to embodiments of the present invention may be housed in the housing a lighting device to provide a lighting device including the LED chip assembly. This may facilitate the provision of a particularly compact lighting device, which is particularly advantageous if the lighting device is a light bulb. The lighting device may be any suitable type of light bulb, for example MRU, MR16, GU4, GU5.3, GU6.35, GU10, AR111, Par20, Par30, Par38, BR30, BR40, R20, R50 light bulbs and so on. It should be understood that these sizes are given by way of non-limiting example only and that any suitable size light bulb may include the LED chip assembly according to an embodiment of the present invention. It is furthermore noted for the avoidance of doubt that the lighting device may take any suitable shape and is not limited to light bulbs only.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several distinct elements. In the device claim enumerating several means, several of these means can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.