ILLUMINATION ARRANGEMENT, ELECTRONIC DEVICE, AND MANUFACTURING METHOD

FIELD OF THE INVENTION

[0001] The invention relates to an illumination system arranged to illuminate at least one target to be illuminated, the illumination system comprising at least one light-emitting unit, at least one target to be illuminated, and at least one light channel which is operationally connected to the at least one light-emitting unit and to the at least one target to be illuminated and which is arranged to transfer light emitted from the at least one light-emitting unit to the at least one target to be illuminated.

[0002] The invention further relates to a method for illuminating at least one target to be illuminated, the method comprising emitting light, and conveying the emitted light through a light channel to the at least one target to be illuminated.

[0003] The invention still further relates to an electronic device comprising at least one light-emitting unit, at least one target to be illuminated, and at least one light channel which is operationally connected to the at least one light-emitting unit and to the at least one target to be illuminated and which is arranged to transfer light emitted from the at least one light-emitting unit to the at least one target to be illuminated.

BACKGROUND OF THE INVENTION

[0004] Typically, keypads for electronic devices are illuminated by connecting a light source to a relatively thick light guide plate provided on top of a printed circuit board, wherefrom the light is coupled out e.g. through a transparent keypad mat. However, such a solution increases the thickness of the electronic device by as much as a couple of millimetres, it has a poor efficiency and, due to its structure, incurs extra manufacturing costs.

[0005] According to prior art, keypads for electronic devices can be illuminated also by using a light channel solution wherein a light channel is arranged to transfer light emitted from a light source to a keypad. Typically, such a light channel is arranged on a planar plate, which increases the number of necessary components in the electronic device, thus increasing the thickness of the electronic device and making it more difficult to assemble during manufacture. Alternatively, the light channels may also be fused onto a printed circuit board, but in such a case, a portion of the surface area of the printed cir-

cuit board may have to be reserved for the light channels, which, in turn, makes the tasks of designing the printed circuit board and assembling the components even more challenging.

[0006] US 2003/0210780 discloses a solution in which at least one portion of the housing of a portable electronic device is composed of one or more optical fibers. The optical fibers are positioned into the housing either separately, which is very cumbersome, or by laminating the fibers between two films and thereafter forming the housing around the films, which requires many difficult process steps. Thus, using optical fibers for illuminating is quite difficult and cumbersome and therefore expensive.

BRIEF DESCRIPTION OF THE INVENTION

[0007] An object of the invention is thus to provide a novel and improved illumination system, a method for illuminating a target to be illuminated, and an electronic device.

[0008] The illumination system according to the invention is characterized in that the illumination system comprises a cover layer in connection with which the light channel is arranged.

[0009] The invention is based on the idea that the illumination system comprises at least one light-emitting unit, at least one target to be illuminated, and at least one light channel which is operationally connected to the at least one light-emitting unit and to the at least one target to be illuminated and which is arranged to transfer light emitted from the at least one light-emitting unit to the at least one target to be illuminated, the illumination system further comprising a cover layer in connection with which the light channel is arranged.

[0010] According to an embodiment of the invention, the light channel is arranged three-dimensionally in connection with the cover layer.

[0011] According to a second embodiment of the invention, the light channel is arranged at least partially inside the cover layer.

[0012] According to a third embodiment of the invention, the light channel is arranged at least partially on the surface of the cover layer.

[0013] According to a fourth embodiment of the invention, the light- emitting unit is arranged in the light channel.

[0014] According to a fifth embodiment of the invention, the light channel is arranged to provide a desired illumination area in response to determining the physical dimension of the light channel.

[0015] According to a sixth embodiment of the invention, the light channel is arranged to provide one or more colours in response to selecting the colour of the material at an outlet point of light.

[0016] According to a seventh embodiment of the invention, one or more light-emitting units are arranged in operational connection with the light channel and further to emit a total of two or more light components of different colour.

[0017] According to an eighth embodiment of the invention, the target to be illuminated is a keypad comprising one or more keys.

[0018] According to a ninth embodiment of the invention, the cover layer comprises a thermoplastic plastic.

[0019] In connection with the present invention, a light channel refers to a discrete structure in connection with a base structure for guiding light from a light source to a target to be illuminated. Light channels are easier to form into a cover layer than optical fibres. Typically, the width of the light channel is 50 to 200 μm but, depending on the application, it may be smaller or larger. The structure of the light channel is typically a multilayer one, and the fight channel may be branched or unbranched.

[0020] The different embodiments of the invention enable considerable advantages to be achieved over the prior art solutions. An advantage of an embodiment is that the illumination system decreases the number of necessary components in an electronic device, which enables a more integrated and thus thinner electronic device to be achieved. This is a substantial advantage in small electronic devices in particular, such as mobile equipment, PDA (Personal Digital Assistant) devices, portable computers, remote controls, wrist watches, and operation panels for various instruments. A further advantage of an embodiment is that the illumination system enables lower energy consumption on account of the smaller number of components and a simpler structure. Hence, the intensity of illumination can be significantly reduced e.g. by using fewer or lower power LED components. A further advantage is that a larger surface area of the printed circuit board becomes available to be used for other purposes. A further advantage of an embodiment is that the illumination system can be manufactured employing several different manufacturing proc-

esses and using different materials. A still further advantage of an embodiment is that the light channels also enable characteristics that can be utilized in different manners. For example, the shape and/or surface structure of the light channel may be designed so as to enable an electronic device to be provided with different patterns or text, or, by adjusting the width of the light channel, illumination areas of different sizes to be achieved. A yet further advantage of an embodiment is that e.g. some keys may be illuminated differently than others, for instance by means of different colours or different intensity of illumination, which can be utilized e.g. when using game applications. The illumination arrangement is easy to manufacture and the use of optical fibres for illuminating can be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The invention is now described in closer detail in connection with some embodiments and with reference to the accompanying drawings, in which

[0022] Figure 1 is a schematic cross-sectiona! view showing an illumination system according to an embodiment of the invention.

[0023] Figure 2 is a schematic perspective view showing an illumination system according to an embodiment of the invention.

[0024] Figure 3 is a schematic cross-sectional view showing an illumination system according to an embodiment of the invention.

[0025] Figure 4 is a flow diagram showing a manufacturing method according to an embodiment of the invention.

[0026] For the sake of clarity, the figures show the embodiments of the invention in a simplified manner. In the figures, like reference numerals identify like elements.

DETAILED DESCRIPTION OF THE INVENTION

[0027] Figure 1 is a simplified cross-sectional view showing an illumination system according to an embodiment of the invention. Herein, a target to be illuminated is a key 100 provided in a keypad for mobile equipment arranged in a substantial vicinity of a cover layer 106; in this embodiment, arranged in a key hole 108 provided in the cover layer 106. In this embodiment, a light-emitting unit is implemented as a LED component 102 arranged inside the cover layer 106. Alternatively, the light-emitting unit 102 may be any component or device suitable for a light source. The light-emitting unit 102 may be

arranged on the surface of the cover layer 106, or partly inside the cover layer 106 and partly on the surface thereof. The illumination system may comprise one or more light-emitting units 102, which may illuminate one or more targets 100 to be illuminated. The LED component 102 is arranged to emit light to a light channel 104 integrated inside the cover layer 106, the light channel 104, in turn, being operationally connected both to the LED component and to the key 100. The illumination system may also comprise several light channels 104, or a light channel 104 may be branched to illuminate several targets 100 to be illuminated. The emitted light is transferred along the light channel 104 from the LED component 102 towards the key 100, preferably illuminating the contact surface of the key and thus enabling the electronic device to be used also in poorer light. Herein, the printed circuit board of the electronic device is an element separate from the cover layer 106 in connection with which the light channel 104 is arranged.

[0028] Figure 2 is a simplified perspective view showing an illumination system according to an embodiment of the invention. Light emitting units 102, 102', 102" are arranged on the inner surface of a cover layer 106, and light channels 104, 104', 104" are provided from the light emitting units 102, 102', 102" towards keys 100, 100', 100" such that the path of each light channel 104, 104', 104" forms a three-dimensional form, in other words the path of the light channel 104, 104', 104" is non-planar. Such a three-dimensional path enables the space of the cover layer 106 to be used effectively and the entire structure of the electronic device to be made more uniform. In the disclosed embodiment, the light channels 104, 104', 104" are branched, so that they are arranged to convey light in a versatile manner between the light emitting units 102, 102", 102" and the keys 100, 100', 100".

[0029] Figure 3 shows an illumination system according to an embodiment of the invention, wherein a light-emitting unit 102 is arranged in a light channel 104 integrated inside a cover layer. Such a solution enables the amount of light to be coupled to the light channel 104 to be further increased and thus the performance to be improved.

[0030] Various structures to turn beams of fight may be used in the light channels and in the inlet or outlet couplings thereof. Preferably, a light channel has three layers such that an optically denser core layer resides between optically less dense bottom and surface layers. Typically, the layers are manufactured from the same material such that their optical densenesses have

been modified e.g. by a suitable additional agent. Thus, the different layers of the light channel are provided with different refractive indexes, which enables angular reflection of light along the light channel. Typically, the difference of the refractive indexes of the light channel is 1 to 2% but, depending on the application, it may also be smaller or larger. The greater the difference of the refractive indexes, the acuter the curves the light can be made to reflect.

[0031] According to an embodiment, the width of the light channel is 50 to 200 μm. A light channel may also be used for providing, even inside a single light channel, an electronic device with illumination areas of different sizes by selecting the dimension, such as the size or the shape, of the light channel appropriately in order to achieve a desired illumination area.

[0032] According to an embodiment, a light channel may also be used for providing an electronic device with specific areas, such as different patterns or texts, e.g. by determining the shape of the light channel and the outlet points of light appropriately. Further, the targets to be illuminated may be manufactured from materials of different colour, which enables lights of different colour to be achieved. For example, each side of a multipurpose key provided in mobile equipment may be illuminated differently, or a key may be provided with a pattern symbolizing a given function, which enhances the usability of the mobile equipment. Furthermore, the light channels may also be utilized in connection with different software applications e.g. such that some keys are illuminated differently than others, so that e.g. the telephone keypad in mobile equipment can be better applied to a keypad used for playing games.

[0033] According to a preferred embodiment, one or more light sources.are arranged in operational connection with a light channel, and further arranged to emit a total of two or more light components of different colour into the light channel. For example, a red, green, and blue light component may be emitted from one RGB component, and LED components of different colour may be coupled in parallel. In the light channel, the light components of different colour quickly become mixed together since several reflections take place in the narrow channel.

[0034] The illumination system may be manufactured by using known manufacturing methods. Figure 4 shows an embodiment according to which a cover layer is provided with a light channel by two or multicomponent injection moulding. Two-component injection moulding, also known as 2C injection moulding, is typically carried out by using two casting moulds or, alter-

natively, a two-phase changing mould. Firstly, a first component, such as molten thermoplastic plastic appropriate for producing a light channel, e.g. polycarbonate (PC) or polymethylmethacrylate (PMMA) ₁ is injected 400 into the casting mould. The first component is then left to cool down (402) after injecting. Next, the casting mould is changed 404, and a second component, such as molten thermoplastic plastic appropriate for producing a cover layer, e.g. PC/ABS or polyamide (PA) ₁ is injected 406 into it. After the second component has cooled down 408 sufficiently, the casting mould is opened and the produced piece is removed 410 from the mould. Alternatively, the cover layer and the light channel may also be cast in reverse order, or the structure may even be provided with several layers and mould inserts so as to achieve e.g. a better performance or a more efficient inlet coupling.

[0035] Techniques called IML (In Mould Labelling) and IMD (In Mould Decoration) may be applied to the two or more component injection moulding manufacturing method. In the IML technique, typically, a thin film is placed between the mould such that the thin film is moved, or a light channel is moved from the surface of the thin film, to the surface of the product to be injection moulded, while in the latter technique, typically, a thin cover preform that has been thermoformed in advance is placed on the bottom of the injection moulding mould, and a frame plastic is injected into this preform or outside thereof.

[0036] According to an embodiment, a cover layer is provided with a light channel by using injection moulding moulds of the above-described type such that a piece having grooves on its surface is formed. After injection moulding, the grooves are filled with a material appropriate for light channels.

[0037] According to an embodiment, a cover layer is provided with a light channel such that the grooves for the light channels are produced on the inner or outer surface of either a planar or an already formed thermoplastic cover layer by using a known method, such as embossing or machining. The formed grooves are filled e.g. by using a doctor bfade printing technique wherein preferably a viscous, such as liquid or gel-like, light channel material is spread onto the surface of a plate, after which a doctor blade or another spreading element suitable for spreading is used for drawing against and over the surface such that the light channel material fills the grooves. After the material has dried, typically, the planar piece is thermoformed.

[0038] According to an embodiment, a cover layer is provided with light channels by a lithography process in a manner similar to that used for printed circuit boards but, in this case, preferably on a thermoplastic substrate and preferably on a thin plate, e.g. a single-layer plate. In such a case, when the layer thickness is e.g. approximately 200 micrometres, thermoforming is simpler, which enables the plate to be used as that in the IML technique. This is a significant advantage for cover structures for mobile equipment in particular. In the lithography process, the light channels are formed by means of a known exposure process, such as a conventional exposer for printed circuit boards or by writing with a laser or ionic beam.

[0039] According to an embodiment, a cover layer is provided with light channels by using IMD or IML techniques. The common idea, as disclosed above, is to use a separate film which is placed inside the injection moulding mould. Such films, which may be either already thermoformed or not thermoformed, may be provided with different patterns using different techniques, such as printing by using e.g. screen printing, gravure printing, ink-jet printing or another known printing technique suitable for producing light channels, lithographically, by printing or embossing. Such films may also be laminated on top of one another between the layers e.g. for protecting the channels or for separating the manufacture of electric and optic layers from each other into separate processes. This laminating process may also be implemented within an injection moulding process, in which case e.g. the film containing the light channels is typically placed into the mould such that the channels remain within the frame plastic. After the channels have been completed, the injection moulding process may also be continued by injecting yet a third component onto the structure to bury the structure.

[0040] Preferably, the illumination system is manufactured from a flexible or elastic material, such as siloxanes or soft acrylic polymers. Siloxane polymers are usable, particularly when fusing active components, since siloxane polymers are typically easily modifiable and flexible materials. In injection moulding, the materials used are typically conventional transparent thermoplastic materials, such as polycarbonate or polymethylmethacrylate.

[0041] It is obvious to one skilled in the art that as technology advances, the basic idea of the invention may be implemented in many different ways. In some cases the features set forth in the present application may be used as such, irrespective of other features. On the other hand, if necessary,

the features set forth in the present application may be combined to form different combinations. The invention and its embodiments are thus not restricted to the above-described examples provided for the sake of illustration but the invention may vary within the scope of the claims.