WO2008075277A1

WO2008075277A1 - Flexible substrate for display devices

Info

Publication number: WO2008075277A1
Application number: PCT/IB2007/055145
Authority: WO
Inventors: Rabin Bhattacharya; Antonius H. M. Holtslag
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2006-12-21
Filing date: 2007-12-17
Publication date: 2008-06-26
Also published as: TW200844925A

Abstract

A flexible substrate for electronic elements is provided. The substrate (102), comprises a plurality of through substrate openings (103), wherein at least one of said openings (103') is provided with a cover means (104) that at least partly covers said opening (103'). The substrate (101) is adapted to be bent in at least one direction, such as to form a line of curvature (Lc) which crosses said opening (103') provided with a cover means, and the cover means (104) is attached on said substrate (101) allowing mutual mobility between two positions (A, B) on said substrate (101) located on mutually opposite sides of said opening (103') provided with said cover means (104), counted along said line of curvature (Lc).

Description

Flexible substrate for display devices

FIELD OF THE INVENTION

The present invention relates to a flexible substrate for electronic elements, comprising a plurality of through substrate openings.

The present invention also relates to flexible display devices comprising such a flexible substrate on which at least one electro-optical switching element is arranged.

BACKGROUND OF THE INVENTION

The applications of flexible display devices are currently increasing. For example, flexible display devices have been integrated into textiles to form textile lighting systems, such as clothing and furniture with integrated displays.

One design of a flexible display device is described in US 2006/0007059 Al, comprising a flexible electrical circuit where a series of holes have been cut through the flexible circuit board to give it greater flexibility.

One problem however with display devices based on such perforated circuit boards is that the reduced circuit board area also imply that the circuit board area available for transporting heat away from the light-emitting devices is reduced. The heat transport is typically much higher within the circuit board material than from the circuit board material to the surrounding air. Hence, the temperature of the circuit board during operation will be higher for such a perforated circuit board than for a conventional non-perforated board. Further, another problem with display devices based on such perforated circuit board is that a notable amount of the light emitted by the light-emitting elements will escape thought the holes to the backside of the substrate, hence lowering the light utilization efficiency.

Thus, there is still a need in the art for providing improved flexible display devices.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partly overcome the above- mentioned problems, and to fulfill the need in the art. Especially, it is an object of the present invention to provide a display device, and components therefore, which is flexible, provides a good heat transport away from heat dissipating elements, and which reduces the amount of light that is lost due to escape to the back side of the display. The present inventors have found that it is possible to improve the heat transport away from the LEDs and to reduce the amount of light that is lost due to escape to the back side of the display in a substrate provided with through substrate openings without hampering the flexibility of the substrate. By providing the openings with cover means that at least partly cover the opening but that are attached to the substrate in such a way that it does not hamper the flexibility of the substrate, the objects of the invention are met.

Thus, in a first aspect, the present invention relates to a flexible substrate for electronic elements, comprising a plurality of through substrate openings. At least one of said openings is provided with a cover means that at least partly covers said opening.

The substrate is adapted to be bent in at least one direction, such that it, when bent in that direction forms a line of curvature that crosses at least the opening provided with a cover means.

The cover means is attached on said substrate allowing mutual mobility between two positions on said substrate located on mutually opposite sides of said opening provided with said cover means, counted along said line of curvature. The provision of a cover at least partly covering the opening has at least two major advantages:

(i) The substrate area available for heat transport is increased, yielding a better heat transport away from heat dissipating electronic elements, such as light-emitting diodes, and (ii) less light will escape through the openings to the back side of the substrate in case the electronic elements are light-emitting elements, such as light-emitting diodes. These two advantages are met while the flexible substrate retains its flexibility, when compared to the prior art substrate provided with openings.

In embodiments of the present invention, the cover means is attached to said substrate at one or more positions, such that all the positions are located along a single line, which is parallel to the surface of said substrate and perpendicular to said line of curvature.

One exemplary approach of providing the openings with covers is to have all the connection locations (if more than one) along a single line, which is perpendicular to the line of curvature formed when the substrate is bent in the preferred direction. In such case, the cover will not hamper the capability of being bent in this direction of bending.

In embodiments of the present invention, the cover means is attached to said substrate at only one local position. When the cover means is attached at only one local position, it does not hamper the flexibility in any direction of bending, since the attachment location does not have an essential extension along any line of curvature.

In embodiments of the present invention, the cover means has a reflective side

When the cover means has a reflective side facing the side of the substrate on which light-emitting electronic elements are accommodated, the light utilization efficiency will be improved since light emitted towards the cover means will be reflected thereon in a forward direction.

In embodiments, the cover means comprises a metallic material. Metallic materials have good thermal transport properties. Hence, the ability of the substrate to transport heat away from the electronic components, such as light-emitting diodes, is further improved.

In some embodiments, the metallic material may be connected to conductive lines arranged on said substrate.

Conductive lines are typically arranged on the substrate and connected to electronic components. Thus, when electronic components are arranged on the substrate and connected to these conductive lines, there will be a good heat transfer from the electronic components to the cover means via the conductive lines.

In embodiments of the present invention, the area of said cover means is smaller than the area of the corresponding opening. When the area of the cover means is smaller than the area of the corresponding opening, the cover means can pass through the opening such that the cover does not hamper the flexibility of the substrate, irrespective if the substrate is bended in a convex or concave shape.

In embodiments of the present application, the opening and the corresponding cover means are formed in the material of the substrate by the arrangement of a through substrate slit partially surrounding a surface portion of said substrate.

This provides a simple approach of providing both the opening and the corresponding cover means in a single operation, i.e. the arrangement of the through substrate slit. In embodiments of the present invention, at least one electro-optical switching element is accommodated by said substrate.

The substrate is especially advantageous for electro-optical switching elements, such as light-emitting diodes (LEDs), since both the advantages of heat transfer and light utilization efficiency are relevant for such elements.

In another aspect, the present invention relates to a display device, comprising a substrate of the present invention, and at least one electro-optical switching element arranged thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects of the present invention will now be described in more detail with reference to the appended drawings showing currently preferred embodiments of the invention.

Figure 1 illustrates a first embodiment of a light-emitting device of the present invention.

Figure 2 illustrates a second embodiment of a light-emitting device of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present application relates in one aspect to a display device and in another aspect to a substrate for use in such a display device.

A first embodiment of the present application relates to a flexible display device 100 comprising a substrate 101, which accommodates a plurality of electro-optical switching elements 102. The display device can for example be a display for displaying messages, images, or a light source.

The substrate 101 is made of a flexible material. The substrate 101 may for example comprise thin plastic sheets. Other materials suitable for flexible substrates are known to those skilled in the art. The electro-optical switching elements 102 may be transmissive, reflective or emissive. An emissive electro-optical switching element may for example be one or more light-emitting diodes (LEDs). The electro-optical switching elements 102 are driven by drive electronics 106 that, for example, may be arranged on a substrate separated from the flexible substrate 101. Electrical connection 107 connects the drive electronics to the electro-optical switching elements 102 via conducting lines 108 in and/or on the substrate 101. Alternatively, the drive electronics 106 may be positioned on the flexible substrate 101.

Further, there is provided a plurality of mutually spaced apart through substrate openings 103 in the substrate 101. In the embodiment shown in figure 1 , the openings are square shaped, but the openings can take any shape, for example a triangular or circular shape.

The openings 103 are arranged in a repetitive pattern across the substrate 101. Here, the openings 103 are arranged in a grid pattern, i.e. a network of uniformly spaced- apart horizontal and vertical columns and rows, respectively. The pattern of openings 103 results in a pattern of areas 109 between adjacent openings, which areas accommodates the electro -optical switching elements.

In one such area 109, one or more electro-optical switching elements may be accommodated. For example, three LEDs, one red, one green and one blue LED may be accommodated in such area 109 to form a RGB-pixel. Alternatively, one such area may accommodate one LED.

The areas 109 are connected to each other by connection areas 110 of the substrate. The connection areas 110 preferably contain no electro-optical switching elements. Conducting lines 108 connecting two electro-optical switching elements located in two separate areas 109 should preferably be guided via the connection areas 110. The openings 103 in the substrate 101 provide for increased flexibility of the substrate 101 and the display device 100. The bending and torsion action will be concentrated to the connection areas 110.

At least one of the openings 103', preferably all the openings 103, of the substrate is provided with a cover 104 that at least partly covers the opening 103'. The cover 104 is attached to the substrate 101 at one local connection position

105 located in one of the corners of the opening. Further, the area of the cover 104 is smaller than the area of the opening 103', such that the cover 104 can be accommodated within the opening.

The term "local connection position", as used herein, refers to that the cover is attached to the substrate at a position that has no substantial extension along the perimeter of the cover. Typically, the extension of the connection position along the perimeter is less than 10 %, such as less than 5 % of the perimeter.

For example, when the cover has the shape of a quadrangle, the extension of a "local connection position" is essentially less than one side of the quadrangle. When the cover has the shape of a circle, the extension of a "local position" is restricted to a sector forming an angle of less than about 36°, such as less than 18°.

When the substrate is bent, lines of curvature are formed in the substrate. One such line of curvature Lc crosses the opening 103' and the local connection position 105. Due to that the cover 104 is only attached to the substrate in only one position

105, which position has no substantial extension along the line of curvature Lc, the cover 104 does not essentially affect the mutual mobility between two positions A and B that are located on mutually opposite sides of the opening 103', counted along the above line of curvature Lc. When the substrate 101 is bended, the cover 104 will not to any substantial degree hamper the flexibility of the substrate.

Since the cover 104 is only attached to the substrate 101 in one single local position 105, the above holds for any direction of bending. Thus, the flexibility of the substrate 101 is retained despite the introduction of the cover 104. The introduction of the cover 104 involves several advantages. For example, the cover 104 prevents light emitted from the electro-optical switching elements 102 arranged close to the opening 103' from escaping through the opening 103' to the back side of the substrate.

In preferred embodiments, the cover 104 is at least partly reflective, such that light from an electro-optical switching element 102 incident on the cover 104 is reflected thereon.

Hence, at least part of the surface of the cover 104 that faces the electro- optical switching element 102 is reflective, such as for example coated with a reflective material or machined to form a reflective surface. This will increase the light utilization efficiency, especially when compared to a similar substrate lacking the cover, since a larger proportion of the light will exit the device in a forward direction, and since the leakage of light to the backside is reduced.

Further, the introduction of the cover 104 yields a larger surface area of in which heat dissipated by the electro-optical switching elements can be transported. Hence, by introducing the cover 104, the heat transfer away from the electro-optical switching elements 102 will be improved, especially when compared to a similar substrate lacking the cover.

Preferably, the cover 104 is provided with, or consists of, a material that has good heat transfer properties, such as a metallic material or a thermally conductive polymer. For example, it is preferred that a portion of the conductive lines 108, which typically are of a metallic material, and which thus typically has good heat transfer properties, is guided to the cover 104. Since the conductive lines 108 are in contact with the heat dissipating elements 102, good heat transfer to the covers can be accomplished with this approach. The cover 104 and the opening 103' may be formed in one piece, where the opening 103' and the cover 104 is formed by cutting a slit in the substrate 101, which slit essentially surround a portion of the substrate 101. The essentially surrounded portion will form the cover 104, which partially covers an opening 103' in the substrate 101. Alternatively, the cover 104 and the substrate 101 may be formed from separate surface elements that are joined together, for example by means of gluing, welding, etc.

For example, the cover 104 may be of a metallic material for high thermal transport and/or for high reflectance. The metallic material could preferably be connected to the conductive lines 108 for good heat transport

The present invention is not limited to cases where each cover is attached to the substrate in only one local position.

One alternative embodiment is shown in figure 2, illustrating a substrate 101 provided with a plurality of mutually spaced apart through substrate openings 103 at least partially covered by means of covers 104.

In this embodiment, the cover 104 is connected to the substrate 101 at two discrete local positions 105 and 105'. A straight line Lp crossing the opening 103' can be drawn parallel to the surface of the substrate and through both of the two local positions 105, 105'. In this case, the substrate is adapted to be bent in a direction such that a line of curvature Lc crossing the opening 104 is formed that is perpendicular to the straight line Lp.

Due to that the cover 104 is only attached to the substrate in two positions 105, 105', each having no substantial extension along the line of curvature 106, and since both the connection positions are located on the same line Lp perpendicular to the line of curvature, the cover 104 does not essentially affect the mutual stretchability between two positions A and B that are located on mutually opposite sides of the opening 103', counted along the above line of curvature Lc. Hence, when the substrate is bent in this direction, the cover 104 will not to any substantial degree hamper the bendability of the substrate in this direction.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the cover may be connected to the substrate at a location representing the essentially full extension of one side of a polygon, since this will not hamper the bendability in the direction such that the line of curvature is perpendicular to this extended connection location.

The openings and the cover may have the same or different general shape, and may for example be shaped as a polygon, such as a quadrangle or a hexagon, or a circle, or an irregular shape.

Typically, the area of the cover is smaller than the area of the opening, such that the cover can pass through its corresponding opening. However, the cover may alternatively have a larger area than the corresponding opening, such that the Optionally, one or both sides of the flexible substrate may be coated with a flexible and waterproof material (not shown), such as a silicone rubber, poly-urethane rubber or certain kinds of epoxy, This results in that the substrate and the display device becomes resistant to wear and tear, moisture and contamination, while it keeps the flexible character. Furthermore, the cover coating minimizes the mechanical stress in the flexible device during bending, and protects it from excessive bending. The coating can be either fully transparent or diffusive.

Areas of application for flexible display devices, in particular flexible display devices of the present invention, include but are not limited to textile products, such as for example, pillows, toys, such as cuddly toys, mats or carpets, garments, such as gloves, jackets, etc, curtains, furnishing fabrics, vehicle ceilings, bed textiles and backpacks.

Incorporating a flexible display device in such a textile product allows the textile product to become luminous and/or display information, such as messages.

Even though the substrate of the present invention is disclosed above for use in a display device, with electro -optical switching devices, such as LEDs accommodated on the substrate, the substrate as such is not limited to this. The substrate of the present invention may be used to accommodate any type of electronic elements to act as a flexible substrate for those electronic elements. For example, the substrate may be used in any general flexible circuit board, not limited to a flexible display device. The substrate is generally advantageous since essentially all electronic elements dissipate heat, and the present substrate has good heat transfer properties.

Claims

CLAIMS:

1. A flexible substrate (101) for electronic elements (102), comprising a plurality of through substrate openings (103), characterized in that at least one of said openings (103') is provided with a cover means (104) that at least partly covers said opening (103'); said substrate (101) is adapted to be bent in at least one direction, such as to form a line of curvature (Lc) which crosses said opening (103') provided with a cover means; and said cover means (104) is attached on said substrate (101) allowing mutual mobility between two positions (A, B) on said substrate (101) located on mutually opposite sides of said opening (103') provided with said cover means (104), counted along said line of curvature (Lc).

2. A substrate according to claim 1, wherein said cover means (104) is attached to said substrate (101) at one or more positions (105, 105') all located along a single line (Lp) which is parallel to the surface of said substrate (101) and perpendicular to said line of curvature (Lc).

3. A substrate according to claim 1 or 2, wherein said cover means (104) is attached to said substrate (101) at only one local position (105).

4. A substrate according to any of the preceding claims, wherein said cover means (104) has a reflective side.

5. A substrate according to any of the preceding claims, wherein said cover means (104) comprises a metallic material.

6. A substrate according to claim 5, wherein said metallic material is connected to conductive lines (108) arranged on said substrate.

7. A substrate according to any of the preceding claims, wherein the area of said cover means (104) is smaller than the area of said opening (103').

8. A substrate according to any of the preceding claims, wherein said opening (103') and said cover means (104) are formed in said substrate material by the arrangement of a through substrate slit partially surrounding a surface portion of said substrate.

9. A substrate according to any of the preceding claims, wherein at least one electro-optical switching element (102) is accommodated by said substrate (101).

10. A light-emitting device (100), comprising a substrate (101) according to any of the preceding claims and at least one electro -optical switching element (102) arranged thereon.