WO2004044877A2

WO2004044877A2 - A display device and method for making same

Info

Publication number: WO2004044877A2
Application number: PCT/IB2003/005069
Authority: WO
Inventors: Hung Tao Suen; Zhu Qinghang Yi; Chuan Hang Yang
Original assignee: Cotco International Limited; Davies, Paul, Richard
Priority date: 2002-11-11
Filing date: 2003-11-11
Publication date: 2004-05-27
Also published as: WO2004044877A3

Abstract

A display device including a reflector body and a base member mounted with a plurality of light emitting components, wherein the reflector body includes a front surface, a back surface and a peripheral wall interconnecting the front surface and the back surface, the reflector also includes a plurality of through apertures extending from the back surface to the front surface, and the reflector body and the substrate member are held and tightened together by fastening means so that the light emitting device being disposed within the through aperture.

Description

A DISPLAY DEVICE AND METHOD FOR MAKING SAME

FIELD OF THE INVENTION

The present invention relates to display modules, devices, sub-assemblies, apparatus and methods for making same. More particularly, this invention relates to light emitting components, modules, sub-assemblies, devices, apparatus and methods for making same. More specifically, although of course not limiting thereto, this invention relates to light emitting display components, modules, sub- assemblies, devices and apparatus with light emitting electronic components. Yet more specifically, this invention relates to a multi-segment surface mountable light emitting components or modules.

BACKGROUND OF THE INVENTION

Display components, modules, sub-assemblies, devices and apparatus are pivotal in providing information by way of visual communication in the modern world. In this specification, "display device" means and includes, whether jointly, severally or collectively, display components, modules, devices and apparatus for succintiveness and wherever appropriate for the context. Many display devices, especially devices with electronic controlled display devices, include light emitting display devices. For example, multi-segment light emitting displays such as the well known seven-segment display devices with light emitting diodes arranged in segments disposed in the shape of a rectangular "8" are widely used in many electronic devices for providing visual information since many numeric or alpha numeric characters can be formed conveniently by selectively lighting up different combinations of the light emitting diodes of the seven-segment displays. Some seven-segment displays also include a small circular segment adjacent to one of the corners of the generally rectangular "8" segments to provide a decimal point or a foil-stop sign.

Conventional seven-segment displays are available as a module or a sub- assembly including a reflector housing mounted on a printed circuit board (PCB). A plurality of through apertures corresponding to the seven-segments are formed between the front surface and the back surface of the reflector. The PCB provides a substrate member for mounting the light emitting diodes as well as providing electrical connection between the light emitting diodes and the external driving and controlling circuitry. The through apertures on the reflected body forming the segments are usually filled with epoxy resin for diffusing light from the light emitting diodes and the surrounding peripheral walls of the through apertures are usually utilized as a reflector of the light emitting from the light emitting diodes. The epoxy resin also serves to seal the gaps along the junctions between the through apertures of the reflector body and the PCB.

Conventional seven-segment displays are usually quite thick, bulky and are provided with leads for insertion mounting. With the ever increasing demand for electronic devices and apparatus with a low-profile or slim design, the conventionally packaged seven-segment displays are no longer satisfactory or adequate. As a result, seven-segment displays with a slimmer, thinner or lower- profile are highly desirable and beneficial.

To fulfil the afore-said demand and requirements, surface mountable seven- segment displays with a lower-profile reflector body mounted on a back substrate member of PCB are desirable. However, it has been noted that the yield rate of surface mountable seven-segment displays are relatively low because of high reject rates due to unevenness of the filled level of the epoxy resin and also due to air bubbles in the hardened epoxy resins.

Uneven levels of epoxy resins among the different lighting segments are undesirable as the quality of the display can be adversely affected. Air bubbles in the hardened epoxy-resin filled in the through aperture of the reflector body may be detrimental since they may cause cracking of the device when undergoing reflow soldering which requires the device to be passed through a solder flow of a high temperature of up to, for example, 260°C.

Hence, it will be highly desirable if the shortcomings associated with conventional seven-segment displays can be alleviated by providing a surface mountable seven-segment display while overcoming at least some of the known problems which have hindered or obstructed the availability of low-cost and high reliability surface mountable seven-segment displays. Of course, it can be expected that such improved surface mountable seven-segment displays will be widely used to provide improved display devices once they are available at low- costs and with a high reliability. OBJECT OF THE INVENTION

Hence, it is an object of the present invention to provide improved surface mountable seven-segment displays which alleviate at least some of the problems or shortcomings associated with, for example, the development and production of, surface mountable seven-segment displays and methods for making same. It is also an object of this invention to improve display devices by providing improved surface mountable seven-segment displays with a lower-profile packaging and with a higher reliability. At a minimum, it is an object of this invention to provide the public with a useful choice of a new surface mountable seven-segment display, methods for making same and display devices incorporating same.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a display device including a reflector body and a base member mounted with a plurality of light emitting diodes, wherein said reflector body and said base member being held and tightened by fastening means.

According to another aspect of the present invention, there is provided a display device including a reflector body and a base member mounted with a plurality of light emitting diodes, wherein said through aperture is filled with at least two layers of transparent or translucent material. According to another aspect of the present invention, there is provided a display device a display device including a reflector body and a base member mounted with a plurality of light emitting devices, wherein

said reflector body includes a front surface, a back surface and a peripheral wall interconnecting said front surface and said back surface, said reflector also includes a plurality of through apertures extending from said back surface to said front surface, and

said reflector body and said substrate member are held and tightened together by fastening means so that said light emitting devices are disposed within said through apertures.

According to yet another aspect, there is provided in the present invention a method of forming a light emitting device having a reflector body and a substrate member which are fastened together, said device includes a plurality of segment apertures filled with a transparent or translucent material, including the steps of:-

- forming a substrate member with a plurality of through holes, a pattern of conductive tracks, and a plurality of conductive pads for making external connections,

mounting a plurality of light emitting diodes on said substrate member,

forming a reflector body with a plurality of through apertures, fastening and tightening said reflector and said substrate member together with fastening means,

filling said through apertures of said reflector with a filing material.

According to yet another aspect, there is provided in the present invention method for assembling a light emitting device having a reflector body and a substrate member, said reflector body includes a front surface, a back surface and a peripheral wall interconnecting said front surface and said back surface, said reflector body also includes a plurality of through apertures extending from said back surface to said front surface, including the sequential steps of:-

- partially filling said segment apertures with a filling material,

curing said filling material,

further filling said segment apertures with additional filling material, and

curing said additional filling material.

Preferably, said base member includes a substrate member with a pattern of conductive tracks and with a plurality of conductive pads for making external connections, said plurality of light emitting devices including light emitting diodes mounted on said base member and connected to said pattern of conductive tracks. Preferably, wherein said reflector body is substantially plastic and said fastening means are integrally formed with said reflector body.

Preferably, said fastening means include a plurality of studs extending from said back surface of said reflector body and away from said reflector body.

Preferably, wherein said substrate member includes a plurality of through apertures disposed in spatial correlation with said studs of said reflector body.

Preferably, said substrate member and said reflector body being fastened together by deformation of the free ends of said studs.

Preferably, the free ends of said studs protrude above said substrate member when said substrate member and said reflector are temporary held together before being permanently fastened by said fastening means.

Preferably, said studs being distributed on said back surface of said reflector body.

Preferably, four studs are distributed on said back surface of said reflector body.

Preferably, guiding means for guiding said substrate member to spatially align with said reflector member are provided on said back surface.

Preferably, said studs and said guiding means are integrally formed with said reflector. Preferably, wherein the junction between said through hole of said reflector body and said substrate member is sealed.

Preferably, said junction being sealed by a sealing agent applied around the periphery of said through aperture, said sealing agent preferably includes an epoxy resin surrounding said aperture.

Preferably, said through apertures of said reflector being filled with a transparent or translucent material or a combination of transparent or translucent materials, said transparent or translucent materials preferably include the same epoxy resin of said sealing agent.

Preferably, said substrate member includes a printed circuit board with through apertures disposed thereon for co-operatively receiving said fastening means.

Preferably, said same transparent or translucent filling material includes an opaque, light diffusing epoxy resin.

Preferably, said filling material includes an epoxy resin or a mixture of epoxy resins, the filling of said through apertures by said filling material being accomplished in at least two steps, the filling material filled in the first step being hardened before the next filling step.

Preferably, said additional filling material is cured at a higher temperature and for a longer duration than the curing of said filling material. Preferably, the depth of the epoxy resin filled in the segment apertures in the first filling step does not exceed half of the depth of the respective segment apertures.

Preferably, said filling material and said additional filling material contain the same epoxy resin.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be explained in further detail below by way of examples and with reference to the accompanying drawings, in which: -

Fig. 1 is a perspective view showing generally the back surface of a preferred reflector body for illustrating the example of a seven-segment display of the present invention,

Fig. 2 is a perspective view showing, in particular, the back surface of the reflector and the PCB in spatial correlation before assembling,

Fig. 3 is a perspective view showing the device of Fig. 2 before the reflector body and the PCB are tightened together,

Fig. 4 illustrates the reflector body of Fig. 1 indicating the appropriate locations for application of sealing agents,

Fig. 5 shows the device of Fig. 3 after the reflector body and the PCB have been tightened and held together, Fig. 6 is a schematic view illustrating the fastening of the reflector body and the PCB,

Fig. 6a is an enlarged view showing the circled portion of the PCB of Fig.

6,

Fig. 6b is an enlarged view showing the protrusion of a stud extending from the reflector body above the aperture of the PCB of Fig. 6a,

Fig. 6c shows the relation of the reflector body and the PCB after the reflected body and the PCB have been tightened and the stud deformed to provide fastening,

Fig. 7 is a schematic view showing a general cross-section of the semifinished device before epoxy resin is filled,

Fig. 8 is similar to Fig. 7 by showing the imperfection or defects present in the junctions between the reflector body and the PCB,

Fig. 9 illustrates the first stage of a preferred method of the present invention showing the first step for filling the segment apertures with epoxy resin, and

Fig. 10 shows the second stage of the preferred method by showing, for illustration only, a second or subsequent steps for filling the through apertures with further epoxy resins. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be explained in further detail below by reference, for illustration only, to an example of a seven-digit display 1 including a reflector body 10 and a base member 20. In this specific example, the base member 20 includes a printed circuit board (PCB) 21 mounted with a plurality of light emitting diodes 30. The reflector body 10 includes a rigid housing 11 with a plurality of through apertures or segment apertures 12 forming the light emitting segments. The reflector body 10 is preferably made of hard plastics with a fine or smooth surface so that the surrounding peripheral walls of the through apertures 12 of the reflector body 10 can be sufficiently reflective without further processing. In the present example, the reflector body 10 and the PCB 21 are held and tightened together by fastening means.

Referring firstly to Fig. 1, the reflector body 10 includes a main housing 11, a plurality of through apertures 12 corresponding to the locations of the lighting segments, a plurality of pillars or studs 13 extending from the back surface of the reflector body 11 and a plurality of guiding pins 14. The reflector body 10 includes a front surface 15, a back surface 16 and a peripheral wall 17 interconnecting the front surface 15 and the back surface 16. The pillars or studs 13 are distributed on the back surface of the reflector body and extend generally perpendicularly away from the back surface to form part of the fastening means for holding and tightening the substrate member 20 and the reflector body 10 together. The guiding pins 14 are provided as guiding means to assist spatial alignment between the substrate member 21 and the reflector body 10 so that the light emitting components 22, which are light emitting diodes for the present example, can be properly placed with respect to the reflective surfaces through apertures or segment apertures 12 of the reflector body 10.

Referring also to Fig. 2, the base member 20 and the PCB 21 are shown in more detail. The PCB 21 includes a top surface 22 and a bottom surface 23. A plurality of conductive pads 24 for making electrical connection with external devices or circuitry are provided near the periphery of the top surface of the PCB. In order to provide electrical connection between the conductive pads 24 and the light emitting diodes 30, a circuit or circuits are provided on the PCB. The circuit or circuits may be provided in the form of a pattern of conductive tracks interconnecting the conductive pads 24 and the light emitting diodes 30. Of course, the pattern of conductive tracks may be printed or formed on the PCB by appropriate methods. In the finished form of the device 1, the device 1 can be surface mounted on other devices or PCBs with the contact pads 24 providing the connection interface.

A plurality of apertures 25 for forming part of the fastening arrangement are distributed on the PCB with spatial correlation to the studs 13 on the reflector body 10. A plurality of apertures 26 are also formed on the bottom surface of the PCB for co-operatively receiving the guiding pins 14 to facilitate easy and convenient spatial alignment between the reflector body 10 and the PCB 21. The through apertures 25 on the PCB may have the general cross-section of that shown in Fig. 6a with a hollow channel extending between the top 22 and bottom surfaces of the PCB and with the aperture being wider near the top surface 22 of the PCB.

After the PCB has been mounted with a plurality of light emitting diodes 30, the PCB 21 and the reflector body 10 are placed together with the assistance of the guiding pins 14, as shown in Fig. 3. A general relation between the reflector body 10, the PCB 21 and the diodes 30 in this semi-finished module is shown in Fig. 7. At this stage, the studs 13 protrude above the top surface 22 of the PCB, as shown in Fig 6b.

This semi-assembled module comprising the reflector body 11 and the substrate member 21 are then held tightly together and fastened by the studs by deforming the free ends of the studs, for example, by heat-press deforming. In this example, the free ends of the studs 13 are deformed into bosses conforming to the shape of the wider aperture adjacent the top surface 22 of the PCB, as shown in Fig. 6 and Fig. 6c, while the reflector body 10 and the PCB 21 are being tightly held together, for example, by the assistance of appropriate tools. The spread or deformation of the top ends of the studs in the wider aperture holds the reflector body 10 and the PCB 21 tightly together even after the removal of the external force. The general relation between the reflector body 10 and the PCB 21 at this stage is shown in Fig. 6.

To reduce or alleviate the risk of epoxy leakage from the junction between the base of the through apertures 12 of the reflector body and the PCB 21 which have been found to be the major cause of unevenness of the levels of epoxy in the different lighting segments, the junctions are sealed before the reflector body 10 and the PCB are more permanently held together. For example, the junctions can be sealed by applying an epoxy mix around the peripheries or edges surrounding the through apertures 12 at the back surface of the reflector housing 11, as illustrated in Fig. 4. This semi-finished module comprising the reflector body 10 and the PCB 21 with the junctions between the through apertures 12 surrounded by the sealing agent is then subject to heating, for example, oven heating, in order to cure, settle or harden the sealing agent. This junction sealing has been noted to alleviate or prevent leakage of epoxy from the through apertures 12 to the PCB 21.

The next stage is to fill the through apertures 12 with appropriate translucent or transparent filling materials in order to diffuse light emanating from the light emitting diodes and to prevent the light emitting diodes from direct contamination, for example, by dust, grease or other adverse contaminants. It has been observed that air bubbles are present in the hardened epoxy in the through apertures 12 notwithstanding very carefol dispensing of same. Upon a more microscopic examination, it is noted that imperfect junctions 40 present at the interface between the reflector body and the PCB, as illustrated with emphasis in Fig. 8, are the primary culprits. These imperfect junctions 40 may result in "hidden caves" and cause the "bridging" phenomenon which may prevent complete filling up of the bottom of the through apertures with epoxy resin.

As the viscosity of the epoxy will be lowered initially on being heated up, the air being trapped at the imperfect junctions would be released as small bubbles and trapped within the through apertures while emerging from the imperfect junctions 40 to the top surface.

To alleviate the problems associated with the imperfect junctions 40 and in order to eliminate, or at least reduce, undesirable air bubbles, the filling material 50, which is epoxy resin for the present example, is filled in two stages in this present invention. In the first stage, epoxy is slowly dispensed into the segment apertures so that the segment apertures 12 are only partially filled with epoxy resin. Then, the epoxy resin is cured or settled by heating, for example, at a relatively low temperature for a relatively long duration, for example, at 115°C for five hours. As a convenient example, the initial partial filling of the filling material does not exceed half of the depth of the respective segment apertures. An example of a suitable rate and pressure for dispensing the sealing agent is at 5 mg/s and 0.4- 0.5 MPa.

As the segment apertures 12 are only partially filled, shorter time is required for the air bubbles to transit through the aperture 12 and the bubbles can generally escape before the epoxy is hardened. The curing of the epoxy resin at a relatively low curing temperature for an extended period of time also assists effective escape of the air bubbles.

After the epoxy resin in the partially filled segment apertures have been cured or hardened, the segment apertures 12 can be filled up slowly with additional filling materials 50 to the desirable levels. After the segment apertures 12 have been filled to appropriate levels, the epoxy filled module can be transferred to the oven again for heat curing in order to settle or harden the epoxy. For this stage, the heating can be at a higher temperature, for example, at or about 150°C and with a shortened duration, for example, two hours.

In general, the filling material is dispensed with an accurately controlled dispensing apparatus with a fine nozzle 60 as shown in Fig.9. An example of a suitable rate for dispensing the sealing agent is at 15 mg/s.

By adopting this two-stage epoxy filling and hardening procedure, the problems associated with trapped bubbles can be greatly alleviated.

While the present invention has been explained by reference to the preferred embodiments described above, it will be appreciated that the embodiments are only examples provided to illustrate the present invention and are not meant to be restrictive on the scope and spirit of the present invention. This invention should be determined from the general principles and spirit of the invention as described above. In particular, variations or modifications which are obvious or trivial to persons skilled in the art, as well as improvements made on the basis of the present invention, should be considered as falling within the scope and boundary of the present invention. Furthermore, while the present invention has been explained by reference to a seven-segment display with light emitting diodes, it should be appreciated that the invention can apply, whether with or without modification, to other light emitting devices without loss of generality.

Claims

1. A display device including a reflector body and a base member mounted with a plurality of light emitting devices, wherein

- said reflector body and said substrate member are held and tightened together by fastening means so that said light emitting devices are disposed within said through apertures.

2. A display device according to claim 1, wherein said base member includes a substrate member with a pattern of conductive tracks and with a plurality of conductive pads for making external connections, said plurality of light emitting devices including light emitting diodes mounted on said base member and connected to said pattern of conductive tracks.

3. A display device according to claim 1, wherein said reflector body is made substantially of plastics and said fastening means are integrally formed with said reflector body.

4. A display device according to claim 3, wherein said fastening means include a plurality of studs extending from said back surface of said reflector body and away from said reflector body.

5. A display device according to claim 4, wherein said substrate member includes a plurality of through apertures disposed in spatial correlation with said studs of said reflector body.

6. A display emitting device according to claim 5, wherein said substrate member and said reflector body being fastened together by deformation of the free ends of said studs.

7. A display device according to claim 6, wherein the free ends of said studs protrude above said substrate member when said substrate member and said reflector are temporary held together before being permanently fastened by said fastening means.

8. A display device according to claim 4, wherein said studs being distributed on said back surface of said reflector body.

9. A display device according to claim 8, wherein four studs are distributed on said back surface of said reflector body.

10. A display device according to claim 8, wherein guiding means for guiding said substrate member to spatially align with said reflector member are provided on said back surface.

11. A display device according to claim 10, wherein said studs and said guiding means are integrally formed with said reflector.

12. A display device according to claim 1, wherein the junction between said through hole of said reflector body and said substrate member is sealed.

13. A display device according to claim 12, wherein said junction being sealed by an epoxy sealing agent applied around the periphery of said through aperture.

14. A display device according to claim 13, wherein said through apertures of said reflector being filled with a transparent or translucent material including the same epoxy resin of said sealing agent.

15. A display device according to claim 14, wherein said subsfrate member includes a printed circuit board with through apertures disposed thereon for co-operatively receiving said fastening means.

16. A display means including a display device of claim 1.

17. A display means including a display device of claim 12.

18. A display means including a display device of claim 15.

19. An electronic device including a display of claim 16.

20. An electronic device including a display of claim 17.

21. An electronic device including a display of claim 18.

22. A display device including a reflector body and a base member mounted with a plurality of light emitting diodes, wherein said through aperture is filled with at least two layers of transparent or translucent material.

23. A display device according to claim 21, wherein said same transparent or translucent material includes an epoxy resin.

24. A method for forming a light emitting device having a reflector body and a substrate member which are fastened together, said device includes a plurality of segment apertures filled with a transparent or translucent material, including the steps of:-

mounting a plurality of light emitting diodes on said substrate member,

forming a reflector body with a plurality of through apertures,

- fastening and tightening said reflector and said substrate member together with fastening means,

filling said through apertures of said reflector with a filing material.

25. A method according to claim 24, wherein said filing agent being non- opaque and light diffusing.

26. A method according to claim 24, further including the following step:- applying sealing agents around through apertures of said reflector body on said back surface before fastening saidτeflector and said substrate member together.

27. A method according to claim 24, wherein said filling material includes an epoxy resin or a mixture of epoxy resins, the filling of said through apertures by said filling material being accomplished in at least two steps, the filling material filled in the first step being hardened before the next filling step.

28. A method for assembling a light emitting device having a reflector body and a substrate member, said reflector body includes a front surface, a back surface and a peripheral wall interconnecting said front surface and said back surface, said reflector body also includes a plurality of through apertures extending from said back surface to said front surface, including the sequential steps of:-

- partially filling said segment apertures with a filling material,

curing said filling material,

further filling said segment apertures with additional filling material, and

curing said additional filling material.

29. A method according to claim 28, wherein said addition filling material is cured at a liigher temperature and for a longer duration than the curing of said filling material.

30. A method according to claim 28, wherein said filling material and said additional filling material contain a light diffusing opaque epoxy resin.

31. A method according to claim 28, wherein said filling material and said additional filling material contain the same epoxy resin.

32. A method according to claim 28, wherein the depth of the epoxy resin filled in the segment apertures in the first filling step does not exceed half of the depth of the respective segment apertures.