This invention relates generally to devices comprising an electronic information display module, and in particular to the mounting of such a display module inside a housing of the device.

Electronic information displays are flat and emissive monochrome, multi-color or full color displays that can be used in various applications, such as mobile phones, personal organizers and in a great number of other domestic and professional electronic assemblies and devices comprising an information display. Examples of such displays include Small Molecule Organic Light Emitting Diode (SMOLED), Polymer Organic Light Emitting Diode (PLED) Field Emission Displays (FED) and Liquid Crystal Displays (LCD).

In general, the display or display module is arranged inside a cavity of a device housing. The housing typically comprises a transparent window, behind which the display is mounted. The window might serve different purposes, including aesthetic and protective purposes. Alternatively an exit substrate or a light emitting surface of the display module is functioning as the housing window.

Normally the display is mounted using some kind of mountings, such as clip- on brackets. In order to increase manufacturing tolerances, simplify assembly and possibly make room for additional circuitry the cavity is typically somewhat larger than the actual display module. Thus, there are in general distances or gaps between the display module and interior surfaces of the cavity. In devices having a separate housing window, there is typically a gap between the display exterior and the housing window as well. The dimensions of these gaps are most commonly ranging from 0.2 mm to 10 mm.

The device is typically assembled under normal atmospheric conditions, the housing thus being filled with air. Some devices however, in particular devices that are to be operated in humid conditions, are filled with specific gases, for example nitrogen. The gaps will naturally be filled with the same gas or air as the rest of the housing, thus making up air or gas gaps between the display module and the interior surfaces of the display cavity and/or housing window.

A SMOLED/PLED module comprises a substrate made of a transparent material, e. g. glass, on which a stack of structured layers is deposited. In general, this stack of structured layers comprises light emitting polymer layers, which are sandwiched between an anode and a cathode layer. When a high enough voltage is applied across the polymer stack, light is emitted from the polymer layer and can be observed through a transparent exit substrate of the display. Since the polymer layers are oxygen and water sensitive, the complete stack of layers is typically sealed off from its surroundings by a metal or glass coverlid or by an additional sealing cover layer. In the case of a so-called top-emissive display design, the emitted light can be viewed from the cover side by applying a transparent electrode (cathode) facing the cover side, in combination with a transparent coverlid or a transparent sealing layer. In this particular case the substrate and the counter electrode (anode) may be non transparent, e. g. metallic. The sealing off process of the polymer stack is generally performed under inert gas conditions.

When operating for example a SMOLED/PLED, the general idea is to transform electrical power into emitted light, to form a desired image. However, only a fraction of the inputted electrical power will effectively be converted to photons, i. e. light.

The remaining power is instead dissipated and converted into heat. Thus, a large fraction of the applied power actually has the effect of warming up the display. Since ageing of the polymer materials used in the display will become more rapid at elevated temperatures, resulting in decreased luminous output, heating of the display is highly unwanted. This problem is further accentuated by the fact that an ageing polymer is generally compensated for by increasing the driving current of the corresponding pixel, thus generating even more heat. Consequently, the degradation and the heating of the display module are two problems accelerating each other. Furthermore, in multi or full color displays the internal tuning of different colored pixels might be affected. For example, in an RGB display, having red (R), green (G) and blue (B) pixels the colorpoint of the RGB triplet might change, due to a varying ageing behavior per primary color. This will eventually result in a decay of the color perception.

Some types of displays, e. g. LCDs, does not in themselves generate light. In order to make such displays readable in dark environments, backlight configurations are employed.

In passive matrix addressing displays, the cathodes and anodes form a matrix structure of rows and columns. These cathodes/anodes (i. e. rows/columns) are connected via conductive leads to one or more foils that are connected to the substrate. In order to operate

the display module of a device, a driver IC (s) of the cathodes/anodes are supplied with a voltage or power input and data signal input from electronics and a battery in the device. If active matrix addressing is used, each electroluminescent display element or pixel contains its own current source and circuitry, which is fed via data lines, power lines and addressing rows.

Generally, the total power consumed by a display in operation can be split up in one part that is attributed to the display and another part that is attributed to the IC driver of the display. Effectively, both parts act as main heat contributors warming up the entire display module. In case the display has a backlight configuration, the backlight typically consumes a lot of power and contributes significantly to the total heat generation of the display module.

Electronic information displays mounted in device housings are experienced to have a number of inherent problems. One problem concerns the lifetime of the display. It is commonly known that polymers in polymer based displays degrade, thus loosing luminous power over time. Similar lifetime problems also affects other types of displays. Another problem concerns the readability of the display. It has been noted, that the use of an housing window, comprised in the housing, might reduce the readability of the display due to increased blurriness. A still further problem regards the robustness of the device. The mounting of the display inside the device might not be as shock resistant as desired, resulting in the display dislodging from the device housing and/or even breaking of the display.

It is realized, that the rate of temperature increase as well as the final temperature level reached during operation of the display module due to the power dissipation depends on the heat capacity and the heat conduction of the components within the module, and on the thermal interaction between these components and the ambient environment. Since there will not occur any significant convectional heat transfer in air or gas gaps of the limited size described above, these particular gaps act as excellent insulators.

Consequently, the major part of the heat produced within the display module is confined within the module, thus creating the unwanted temperature rise. Thus, one goal of the present invention is to provide for improved heat transfer from the display module to the surroundings of the device, thus reducing the degradation of the polymers and/or the ageing of the display.

It is further realized that the reduced readability for devices having a housing window, at least partly, is due the optical properties of the display assembly. In particular, the exit substrate of the display, the housing window and the air or gas gap in-between typically have different refractive indices. The refractive index of the gap is typically close to one, as for air, whereas the indices of the substrate and the window typically are substantially higher.

Consequently, the interface between the display and the gap as well as the interface between the gap and the window introduce reflective surfaces, between which some of the light emitted from the display is reflected, and thus ads to the blurriness and affect the readability of the display.

It is still further realized that the air or gas gaps are related to even more problems, as will be discussed below. The invention is thus based on the insight that intermediate air or gas gaps between the display module and the housing window and/or housing cavity inside a device housing gives rise to a range of problems regarding the operation of the device.

Consequently it is an object of the present invention is to provide for improved mountings of display modules inside device housings, eliminating at least partially the problems related to air or gas gaps. This object is achieved by an assembly according to claim 1. The appended sub-claims present advantageous embodiments of the invention.

Thus, according to the invention an assembly comprising an electronic information display module and a housing is provided. The housing has a display cavity in which the display module is arranged and the display cavity is at least partially defined by an internal surface of the housing. The assembly further comprises at least one non-gaseous padding substance, which is arranged between and in direct contact with the display module and said internal surface, such that the substance at least partially fills a gap between said internal surface and said display module.

The padding substance can provide for improved heat transport from the display module to the housing, improved robustness of the assembly and/or improved readability of the display.

The magnitude of the heat transport depends directly on the heat conductivity of the substance. Therefore, for the purpose of transporting heat it is advantageous to use a substance having the highest possible heat conductivity. Thus, according to one embodiment, the padding substance is comprised of a material promoting heat transport away from the display module. The general idea of applying a thermally conductive padding substance in cavities in and/or around the display is based on the recognition that heat generated inside the

display will effectively be transported towards the device housing and thus to the surroundings of the device, via the applied padding substance. Hence, the temperature increase of the display itself can be moderated, extending the lifetime of the display module.

According to one embodiment, at least one padding substance is electrically insulating. This is advantageous in that is enables the substance to be added directly onto electrical circuitry, e. g. the cathode structure and/or a driver circuitry of a display module, without interfering with the electrical functionality, i. e. causing shortcuts. The substance can thus provide for improved heat transportation not only from the actual display, but also from electrical circuitry.

According to one embodiment, at least one padding substance is mechanically shock or stress absorbing. Such a substance has the advantage of improving the robustness of the display mounting in the device.

According to one embodiment, at least one padding substance has a gel-like texture. Gel-like substances are advantageous in that they easily fill the intended region completely, while they at the same time are easy to seal off from ambient regions. In the context of the present invention, the term"gel-like substance"includes any substance being viscous enough to completely fill the intended cavity, possibly under pressure, but still rigid enough not to leak out from said cavity. The use of a gel-like substance is advantageous in that it provides for simple manufacturing and reliability of the device. A gel is thus a preferred material because of its good shaping properties.

According to one embodiment, at least one padding substance has curing properties. The padding substance can be curable through any suitable curing method, and the cured substance preferably has a very high viscosity (a gel) or might even be a solid. The padding substance can thus be applied to the intended region in an uncured or partly cured state and subsequently, when the substance is properly in place, it can be fully cured. Thus, according to these embodiments the advantages of a viscous substance is combined with the advantages of a less viscous or even solid material, i. e. it can easily be made to fill the intended region but does not easily leak into surrounding areas.

According to still another embodiment, at least one padding substance is adhesive. This embodiment can have the advantage of reducing or eliminating the need for prior art mountings of the display, resulting in easier and less expensive manufacturing of the device. The adhesiveness might furthermore have the advantage of providing for additional robustness of the device.

According to one embodiment, at least one padding substance is silicone- based.

According to one embodiment, the display module comprises a coverlid covering a display circuitry. The coverlid can for example be made out of glass or metal.

Between the coverlid and the backside a gap is formed. In order to promote heat transfer from the display, the gap is filled with a non-gaseous, heat conductive substance. In case the display is top emissive, the coverlid thus being transparent, the substance must of course be transparent as well. In this particular application, the substance has to be electrically insulating or an extra non-conductive layer between the substance and the cathodes has to be added in order to prevent any electrical shortcuts between different cathodes.

In case the housing comprises a housing window, an interior surface of that housing window forms part of the display cavity. If a substance is to be deposited between the display module and the window, the substance has to be transparent for visible light and must not cause any perception distortions of the displayed image. In the context of the invention, any material able to transmit enough visible light in order to admit a proper readability of the display is to be regarded as transparent.

Thus, according to one embodiment of the invention the housing comprises a housing window of which an internal surface at least partly defines the display cavity, and a transparent padding substance is arranged between and in direct contact with the display module and the internal surface housing window. The transparent padding substance can provide for many advantages, such as promoting heat transfer and/or improved robustness for the assembly. The transparent padding substance can furthermore have a refractive index which is matched to refractive indices of the light emitting surface of the display module and of the housing window. This is advantageous in that it improves the readability of the display. In the context of the present invention, a matched refractive index is an index that is close to the index of either the display exit surface or the window, to both of these indices, or to an average thereof. The transparent padding substance can for example have a refractive index that is essentially similar to the mean value of the refractive indices of the housing window and the light emitting surface of the display module. This is advantageous in that the distinctness of both refractive interfaces are reduced substantially and that the resulting interfaces are about equally accentuated. Alternatively, the transparent padding substance has about the same refractive index as one of the housing window and the light emitting surface of the display module. This is advantageous in that one of the reflective interfaces is effectively eliminated and the blurriness substantially reduced as compared with prior art.

It is to be noted, that the transparency requirement on the padding substance only applies to padding substances that are to be deposited between the display module a housing window, i. e. in the optical path of the display. The optical properties of padding substances deposited elsewhere are of course irrelevant. It is also to be noted, that it is possible to use different padding substances at different locations in the same device. For example, in a device having a housing window a first, transparent padding substance having an optimally matched refractive index can be deposited between the window and the display module whereas a second padding substance being highly thermal conductive might be deposited in the rest of the cavity.

According to one embodiment, a transparent padding substance serves as a sole mounting for the display module inside the housing. The transparent substance might for example be a glue. This embodiment is advantageous in that is provides a simplified and cost effective mounting for the display module. In addition, the substance can for example have the advantage of promoting heat transport, improving the readability or improving the robustness of the assembly.

According to one embodiment, the assembly comprises only one single padding substance. The single padding substance can for example be transparent and confined to a gap between the display module and a housing window. This embodiment is advantageous in that the readability of the display is enhanced without substantially increasing the total weight of the display, i. e. without adding more padding substance than needed. Of course, also the spatially confined substance promotes heat transfer from the display, even if not to the same extent as does a total encapsulation of the display module.

As an alternative, the single padding substance is filling up all thermally insulating gaps inside the assembly. Thus, the display as well as any additional circuitry placed inside the housing is encapsulated in the substance. This is advantageous in that it provides for even better heat transportation due to enlarged heat transporting surface and/or improved robustness for the assembly.

The non-gaseous substance might for example be a liquid, a gel or a solid. For the purpose of transporting heat, the substance preferably has good heat transporting properties. For the purpose of reducing the blurriness of the display when deposited between a display module and a housing window, the substance preferably has a refractive index that is matched (i. e. gives less accentuated refractive interfaces) to that of the exit surface of the display and of the housing window.

However, for the invention to provide advantages as compared to prior art, the heat conductance, the shock absorbing capabilities and/or the refractive index matching of the substance only need (s) to be better than air and other prior art gases used inside device housings. In principle, any non-gaseous substance provides better heat transport characteristics than air and gases do, and can thus be used to provide advantages as compared to prior art. Furthermore, a large range of non-gaseous substances is transparent and has a refractive index more closely matched to the housing window and to the exit surface of the display. Basically, every non-gaseous substance has a refractive index that is higher than air and other gases (which is close to one), but a few might however have a refractive index too high to provide better matching. However, the use of a substance having an unmatched (too high or too low) refractive index can still have the advantage of stimulating heat transportation and/or improve robustness. Consequently, a very large range of substances can be used in the invention in order to provide advantages as compared to prior art.

It is thus to be noted, that the important property for the substance is to be non- gaseous. There are a multitude of different substances fulfilling this requirement. In addition to this fundamental requirement, there are a number of desired properties for the substance, such as being particularly heat conducting, having a suitable refractive index, being shock absorbing etc. When compared to air however, a majority of the non-gaseous substances has at least some of the desired properties. It goes without saying, that the different advantages of the invention can be combined in every possible way. Thus, a substance having more than one of the above properties might be advantageously used, combining the advantages of each property. Consequently, a large number of substances can be used, even if each application typically has a few substances that are more preferred than others.

In summary, the substance can be chosen to provide for any combination of advantages listed in the following, non-exhaustive list: Improved heat transportation from the display (substance having high heat conductivity) Improved readability of the display (substance having a matched refractive index and placed between housing window and the display) Improved robustness (shock absorbing substance) Simplified mountings (adhesive and/or curable substance reduces the need for display mountings) Improved heat transport from display circuitry (electrically insulating substance)

Different devices are expected to require different priorities regarding the advantages. Even if it might be difficult to find a substance having exactly the right characteristics for every advantage to be maximized, the invention provides for priorities to be made for each device by choosing between different substances having different properties. For example, for some devices the heat transportation might be the most important issue, while the robustness or readability might be the most important issue for other devices.

As a basis for the invention is the insight that the mounting of displays inside device housing can be improved by depositing a non-gaseous substance between the display and the housing window, thus eliminating the air gap of prior art.

Embodiments of the invention will now be described in further detail, with reference to the accompanying drawings, on which: Figure 1 is a schematic view of a device having a housing and a display window; Figure 2 is a cross-sectional view of an inventive display assembly, along a section I-I indicated in Figure 1; Figure 3 is a cross-sectional view of an inventive display assembly, along a section I-I indicated in Figure 1; Figure 4 is a cross-sectional view of an inventive display assembly, along a section I-I indicated in Figure 1; and Figure 5 is a cross-sectional view of an inventive display assembly, along a section 1-1 indicated in Figure 1.

It is to be noted, that the drawings only serve as exemplifications and not as limitations for the invention.

The inventive assembly can be implemented on any device having a display module mounted inside a housing. One example of such a device 10 is illustrated in Figure 1, in form of a cellular phone. The device 10 thus has a housing 12 and a display window 11, behind which a display module is mounted.

Figure 2 illustrates a cross-sectional view of an assembly according to the present invention. The cross-section is shown along the axis I-I, which is the same axis as the one shown in Figure 1. The assembly comprises a housing 23 and a housing window 22. A display module 20 is mounted inside a cavity of the housing 23 and spaced from the housing window 22. A space gap between the window 22 and the display 20 is filled with a substance 21. Since the substance is deposited in the optical path of the display, it has to be transparent and optically clear not to disturb images transmitted from the display and perceived by a viewer. Preferably, the substance is more thermally conductive than air, and has a refractive index matched to those of the window and the display. In such case, the substance serves the double purposes of transporting heat and reducing internal reflections inside the assembly.

According to some embodiments, the substance furthermore has adhesive properties. In case the substance is adhesive, it can furthermore serve as mounting for the display module inside the device. It is also possible for the substance to have curing properties. In such case the substance might be added into the gap in an uncured condition, and cured when it is properly in place. For example, the substance might be transparent glue, such as epoxy. In such case, the glue might be added to housing window in an uncured condition, and subsequently cured once the display module is mounted thereon. Once the glue is cured, it might serve as a sole mounting for the display inside the housing.

According to other embodiments, the substance is a gel-like substance or a gel.

Preferably the gel has a high viscosity enough for it to stay in place, in the gap, without any further arrangements, i. e. without the substance needing to be further encapsulated.

Figure 3 shows another embodiment of the invention, along the same cross- sectional axis 1-1 shown in Figure 1 and 2. The assembly shown in Figure 3 is similar to the embodiment shown in Figure 2. Thus, the assembly comprises a housing 33 having a window 32 and a cavity. Inside the housing 33 a display module 30 is mounted, on a distance 31 from the window 32. On an opposite side, the display furthermore has a protecting layer 35, protecting cathode circuitry of the display. Preferably, the protecting layer is electrically insulating. Similar to the embodiment shown in Figure 2, the gap between the display and the window is filled with a substance. According to these embodiments however, the complete cavity, formed by the housing, the housing window and possibly additional walls inside the housing, is filled with a substance. The requirements and advantages using various substances is similar to those described with for the embodiments referring to Figure 2.

According to a still further embodiment, described with reference to Figure 4, the display module 40 comprises a coverlid 46, covering cathode circuitry of the display.

According to this embodiment, a cavity between the display 40 and the coverlid 46 is filled with a substance. According to one embodiment, the substance is electrically insulating, and can thus be applied directly to electrical circuitry of the display. According to another embodiment, the display 40 has a protecting layer, similar to layer 35, which serves as a protecting layer between cathode circuitry and the substance in the cavity 41. The assembly furthermore has a substance 41 deposited between a housing window 42 and the display 40.

According to a still further embodiment, described with reference to figure 5, an outer or exit surface 56 of the display 50 serves as a part of the housing 55. Thus, no housing window is present and consequently no gap between the display module and such a housing window. A substance 51 is instead confined to the back side of the display module.

Even though this embodiment does not provide for better readability, it still provides other advantages such as improved heat conduction and/or robustness.

Thus, the substance can be confined to a gap between a housing window and a display or to a gap between the inner surface of the display cavity and the backside of the display module or it might surround the display module entirely. The display cavity can be either a confined space surrounding the display module or include other members such as driver circuitry for the display. It is also possible for the display cavity to include the complete interior of the housing. The more viscous substance used, the less critical is the sealing of the cavity. When using a liquid substance, due care is needed not to have the substance leaking into the neighboring areas or out from the housing. On the other hand, when using a gel-like substance the gel might be stable enough not to need any additional casing or sealing. For example, a silicone gel can be used.

Presently, a number of substances usable for the invention is marketed by the company Dow Corning and disclosed at their Internet web site "http ://dowcorning. com/content/etronics/etronicstherm/default. asp". For example, the substance CY52-276, provided by Dow Coming, is usable. It is transparent, has 7 times the heat conductivity of air and provides shock absorption capacity.

It is to be noted, that different substances might be used in combination. For example, a substance having excellent optical properties might be used filling a gap between a display and a housing window, whereas the rest of the cavity surrounding the display is filled with a substance having optimal heat conductivity. Obviously, the optical properties have no importance for a substance that is not to be placed in the optical path of the display.

The non-gaseous substance can, for example, be added onto the housing window before the display module is mounted. This is particularly advantageously when

using substances that are easily deformable (e. g. a gel), in which case a suitable amount on of the substance is applied onto the window and automatically dispersed when mounting the display module. In case the substance is adhesive and is to function as a mounting for the display module, a suitable amount of adhesive substance is preferably add either onto the display or onto the window, and the display is subsequently applied to the window under pressure.

If the substance has curing properties, it is advantageously applied in an uncured state and subsequently cured once the display module is properly placed in the housing. Different curable substances are cured in different ways, some are cured by exposing them to heat, others are cured by exposing them to UV-radiation and still others are simply cured upon exposure for atmospheric conditions.

In case the substance is supposed fill the cavity in which the display module is to be mounted, and thus fully encapsulate the display module, it is preferably placed in the cavity before the display is mounted.

If the substance is a solid, it preferably is in the form of a sheet which is placed between the display module and the housing window when the display is mounted in the housing. To avoid any gas or air gap between the sheet and the display or the window, the display must exert a certain pressure towards the window. For some applications, it is preferred for the solid substance to be slightly elastic.

It is to be noted, that this description only serves as an instructive and exemplifying description for the invention. The skilled man can easily envisage several other embodiments which are within the scope of the invention.

In summary, the invention refers to devices having a display module mounted in a cavity of a housing and provides improved display assemblies for such devices. For the purpose of the invention, it is realized that the use of assemblies that gives rise to air gaps between the display module and the cavity is related to a range of problems, including poor heat transportation from the display, reduced readability of the display and possibly poor robustness of the assembly. Therefore, an assembly is provided that is characterized in that it comprises a non-gaseous padding substance deposited between and in direct contact with the display module and the cavity. The padding substance thus fills a gap between the display module and the cavity and consequently reduces the problems related to prior art air gaps.