Patent Publication Number: US-2009231857-A1

Title: Illuminating device

Description:
CLAIM OF PRIORITY 
     This application claims benefit of the Japanese Patent Application No. 2006-315765 filed on Nov. 22, 2006 and Japanese Unexamined Patent Application Publication No. 2007-090741 filed on Mar. 30, 2007, which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to illuminating devices that illuminate operation units of various electronic appliances. In particular, it relates to a thin illuminating device with a low failure rate under application of external force. 
     2. Description of the Related Art 
     Electronic appliances such as audio appliances and portable electronic appliances have light-guiding members that guide light emitted from light-emitting devices such as light-emitting diodes (LEDs) to operation surfaces. Operation buttons formed on the operation surfaces and indicators of fixed characters and numerals engraved in the operation surfaces are illuminated with light that has been guided into the light-guiding members. 
     In a typical illuminating device, a light-guiding member formed of a resin plate such as an acryl plate is attached on the back of the operation surface of an electronic apparatus, and a light-emitting device is disposed to face a side of the light-guiding member. Light emitted from the light-emitting device enters the light-guiding member from an edge of the light-guiding member, and the light that has passed through the light-guiding member is applied to the operation buttons, indicators, and the like. 
     A light-emitting device including a semiconductor bare chip having a light-emitting function packaged in a light-guiding casing and conducting terminals protruding from the package has been used as the light-emitting device (refer to Japanese Unexamined Patent Application Publication No. 2001-167655). 
     According to an existing illuminating device equipped with a light-emitting device that includes a packaged semiconductor, the light-emitting device is thick and a light-guiding member such as an acryl plate needs to be thick to suit the thick light-emitting device. Thus the illuminating device also becomes thick. 
     Since light emitted from the light-emitting device passes through air and enters the light-guiding member such as an acrylic plate from an edge of the light-guiding member, only a small portion of light emitted from the light-emitting device enters the light-guiding member. Thus, the light use efficiency is low. 
     According to the existing art, a light-emitting device that emits light of a single color is provided, and light emitted from this light-emitting device is guided to individual portions to be illuminated through the light-guiding member. Thus, the electronic appliances could be illuminated in one color only. 
     SUMMARY OF THE INVENTION 
     The present invention provides an illuminating device that has a thickness smaller than that of the existing art and offers a high light use efficiency. 
     One aspect of the present invention provides an illuminating device including a substrate, a light-emitting element mounted on the substrate, a light-guiding layer disposed on a surface of the substrate and configured to guide light emitted from the light-emitting element along the surface of the substrate, a cover layer disposed at a position distanced from the surface of the substrate, and a boundary layer disposed between the substrate and the cover layer and configured to divide the surface of the substrate into a plurality of regions. The light-emitting element is a bare chip mounted on the substrate. The light-guiding layer includes a light-guiding elastomer disposed between the substrate and the cover layer. The bare chip is provided inside the elastomer. The elastomer is present in all regions surrounded by the substrate, the cover layer, and the boundary layer. 
     In this illuminating device, the light-emitting element in a bare chip form is mounted on the substrate, and the light emitted from the bare chip travels inside the elastomer that protects and covers the bare chip is guided to the substrate surface, and is applied to the illumination portion. Thus, compared to existing art in which an illuminating device with a bare chip accommodated in a package is mounted on a substrate, the thickness can be reduced. Moreover, since the light-guiding layer is a light-guiding elastomer, the bare chip enclosed in the light-guiding layer can be protected from external force. 
     Since light emitted from the bare chip enters the elastomer covering the bare chip, the light use efficiency can be improved compared to the case in which an illuminating device with a bare chip accommodated in a package is mounted on a substrate. 
     Preferably, the substrate has a recess, and the bare chip is installed in the recess so that the thickness of the illuminating device can be reduced. 
     Preferably, the bare chip is connected to a conductive member on the substrate with a lead, and the lead is provided inside the elastomer. 
     Since the lead is buried in the elastomer, application of excessively large stresses to the lead can be prevented even when external force works against the illuminating device. Thus, conduction failures caused by disconnection of the lead and separation of connecting portions between the lead and the bare chip and connecting portions between the lead and the substrate can be prevented. 
     The elastomer may contain a silicone rubber. Silicone rubbers have high transparency throughout the entire visible light wavelength band (380 nm to 800 nm). Compared to other light-guiding resins, silicone rubbers are less likely to undergo deterioration caused by yellowing, clouding, and discoloration under application of near ultraviolet light (300 nm to 400 nm). 
     Preferably, at least part of the boundary layer is light-guiding, the cover layer is also light-guiding, and light that has been guided inside the elastomer passes through the light-guiding boundary layer and the cover layer and is emitted outside. In such a case, the boundary layer is composed of a material having a refractive index higher than that of the elastomer constituting the light-guiding layer. 
     Preferably, a mechanism region surrounded by the light-guiding boundary layer is provided and a switch mechanism configured to operate when pressed through the cover layer is disposed inside the mechanism region. According to this structure, light is emitted outside from the boundary layer surrounding the switch mechanism and the periphery of the switch mechanism can be effectively illuminated. 
     Preferably, at least part of the boundary layer is non-light-guiding, the bare chip and the elastomer are present in each of the plurality of regions defined by the boundary layer, and the bare chips configured to emit light with different hues are respectively provided in the different regions. In such a case, the non-light-guiding boundary layer is composed of a material having a refractive index lower than that of the elastomer constituting the light-guiding layer. 
     With the above-described structure, the operation surface of an electronic appliance can be illuminated in different hues depending on the position. A plurality of the bare chips that emit light in different hues may be provided within one area defined by the boundary layer and which bare chips are to emit light may be selected so that the hue of light illuminating the region can be switched. 
     The elastomer may include a core layer having a high refractive index and cladding layers sandwiching the core layer and having a refractive index lower than that of the core layer, and light emitted from the bare chip may pass through the core layer and may be applied to the light-guiding boundary layer. 
     When the core layer and the cladding layers are composed of the elastomer, light can be propagated in a wider range in the core layer having a high refractive index. 
     The illuminating device may further include a light-guiding sealant layer configured to seal the bare chip. The sealant layer may be in contact with the elastomer. Alternatively, the bare chip and the lead may be buried in a light-guiding sealant layer and the sealant layer may be in contact with the elastomer. 
     According to the above-described structure, the bare chip or the bare chip and the lead are protected with a sealant layer composed of a resin material or the like. Since the sealant layer is further covered with the elastomer that serves as a light-guiding layer, protection of the bare chip and the lead is highly ensured. 
     According to the present invention, since the bare chip is directly mounted on an illuminating device, the illuminating device can be made thin. Since the bare chip is directly buried in a light-guiding elastomer or the bare chip sealed in a sealant layer is buried in the elastomer, the elastomer alleviates stresses applied when external force is applied. Thus, application of excessively large load on the bare chip and the wiring can be prevented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a front view of an operation unit equipped with an illuminating device of a first embodiment of the present invention; 
         FIG. 2  is an enlarged cross-sectional view of the operation unit shown in  FIG. 1  taken along line II-II; 
         FIG. 3  is an enlarged cross-sectional view showing a part of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view of an illuminating device according to a second embodiment of the present invention; 
         FIG. 5  is a cross-sectional view of an illuminating device according to a third embodiment of the present invention; 
         FIG. 6  is a cross-sectional view of an illuminating device according to a fourth embodiment of the present invention; 
         FIG. 7  is a cross-sectional view of an illuminating device according to a fifth embodiment of the present invention; 
         FIG. 8  is a cross-sectional view of an illuminating device according to a sixth embodiment of the present invention; and 
         FIG. 9  is a cross-sectional view of an illuminating device according to a seventh embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a plan view showing an operation unit  1  that uses an illuminating device according to a first embodiment of the present invention.  FIG. 2  is a partial cross-sectional view of the operation unit  1  taken along line II-II of  FIG. 1 .  FIG. 3  is a partial enlarged view of  FIG. 2 . 
     The operation unit  1  shown in  FIG. 1  is provided to the operation surface of a small electronic apparatus such as a cellular phone. In the operation unit  1 , an illumination portion occupying part of the area of the operation unit  1  is lighted up. The apparatus can be operated through a plurality of operation buttons in the operation unit  1 . 
     For the purposes of this specification, the phrase “light-guiding” used in “light-guiding layer”, “light-guiding property”, etc., refers to the function of an object that allows light to pass through inside. A “light-guiding layer” or a “light-guiding material” means not only a layer or material that is transparent and has a light transmittance of 100% or near, but also a layer or material that is translucent and has a light transmittance of less than 100% and a layer or material that has a milky or cloudy interior that scatters light while allowing light to pass through. 
     For the purposes of this specification, an “illumination portion” refers to a portion from which light applied from a light source constituted by a bare chip is emitted outside. When the operation unit  1  is viewed from outside, the illumination portion appears brighter than other portions. The “illumination portion” refers to, for example, a portion where a scattering surface is formed outside the light-guiding layer, the interior of the “light-guiding layer” or “another light-guiding material” in contact with the “light-guiding layer” that has been made milky or cloudy, or the interior of the “light-guiding layer” or “another light-guiding material” that has been made fluorescent by incorporation of a fluorescent material instead of being made milky or cloudy. 
     As shown in the cross-sectional view of  FIG. 2 , the operation unit  1  includes an illuminating device  10  and an operation mechanism unit  2  on a surface of the illuminating device  10 . 
     Referring to  FIG. 2 , the illuminating device  10  includes a substrate  11 . As shown in  FIG. 3 , the substrate  11  is a multilayer substrate having a high stiffness including a plurality of sectional layers  11   a,    11   b,  and  11   c  that are stacked. Conductive members are formed at interfaces of the sectional layers and at the top of the uppermost sectional layer  11   c.  A recess  12  is formed in part of the substrate  11 . A bare chip  30  of a light-emitting diode serving as a light source is installed in the recess  12 . 
     As shown in  FIG. 1 , the illuminating device  10  has the recesses  12  formed at a plurality of positions of the substrate  11 , and one bare chip  30  is mounted in every recess  12 . The bare chip  30  is a light-emitting diode that emits light when supplied with a forward current and includes compound semiconductors with a PN junction. Light with different hues is emitted depending on selection of the materials for the individual compound semiconductor layers. Each bare chip  30  is the semiconductor of an unpackaged light-emitting diode, and, as shown in  FIG. 3 , is fixed on the bottom of the recess  12  with an adhesive  31 . 
     The light-emitting diodes come in a variety of types including those having Al.Ga.N luminescent layers, Ga.N luminescent layers, and In.Ga.N luminescent layers. The bare chip  30  may be a laser diode instead of the light-emitting diode. In such a case, a phosphor may be incorporated into the illumination portion so that the illumination portion emits light when a laser beam is applied to the illumination portion. 
     As shown in  FIG. 3 , conductive members  32  are formed on the surface of the substrate  11 . An electrode layer of the bare chip  30  is wire-bonded to the conductive members  32  with leads  33 . The conductive members  32  are extended along a wiring pattern formed in the surface of the substrate  11  and connected to another wiring pattern disposed inside the layer via through hole conductive members  11   d  formed in the substrate  11 . 
     As shown in  FIG. 2 , the illuminating device  10  has a cover layer  13  at a position distant from the surface of the substrate  11 . The cover layer  13  is flexible and has light-guiding property. In this embodiment, the cover layer  13  is a transparent resin sheet composed of polyethylene terephthalate (PET) or the like. 
     As shown in the cross-sectional view of  FIG. 2 , a first sectional boundary layer  14   a  is disposed between the substrate  11  and the cover layer  13 . The first sectional boundary layer  14   a  has no light-guiding property. In other words, the first sectional boundary layer  14   a  is neither transparent nor translucent and its interior is configured not to transmit light. The first sectional boundary layer  14   a  is composed of an epoxy resin or the like. Alternatively, the first sectional boundary layer  14   a  may be formed by making part of the substrate  11  composed of a non-light-guiding material to protrude. Alternatively, the first sectional boundary layer  14   a  may be composed of a light-guiding material having a refractive index lower than that of an elastomer  18  constituting the light-guiding layer described below. When the first sectional boundary layer  14   a  is composed of a light-guiding material having a low refractive index, the conduction of light propagating in the elastomer  18  is obstructed by the first sectional boundary layer  14   a.    
     As shown in  FIG. 1 , the first sectional boundary layer  14   a  is patterned to surround a particular area. The portion surrounded by the first sectional boundary layer  14   a  is a first region A. Two second sectional boundary layers  14   b  are respectively formed on the left and right sides of the first sectional boundary layer  14   a.  Two second regions B surrounded by the first sectional boundary layer  14   a  and the second sectional boundary layers  14   b  are respectively formed on the left and right sides of the first region A. A third sectional boundary layer  14   c  having a letter-U-shaped pattern is formed under the first region A and the second regions B. A portion with a relatively large area surrounded by part of the first sectional boundary layer  14   a,  part of the second sectional boundary layers  14   b,  and the third sectional boundary layer  14   c  is a third region C. 
     As described above, the illuminating device  10  has the first sectional boundary layer  14   a,  the second sectional boundary layers  14   b,  and the third sectional boundary layer  14   c  formed between the substrate  11  and the cover layer  13 . The sectional boundary layers  14   a,    14   b,  and  14   c  define the regions A, B, and C. 
     The second sectional boundary layers  14   b  and the third sectional boundary layer  14   c  have the same structure as the first sectional boundary layer  14   a,  and, for example, are formed by patterning a non-light-guiding epoxy resin or the like. Four bare chips  30  are provided in the first region A, one bare chip  30  is provided in each of the second regions B, and four bare chips  30  are provided in the third region C. 
     As shown in  FIGS. 1 and 2 , first light-guiding boundary layers  15   a  are provided between the substrate  11  and the cover layer  13  in the first region A. Each first light-guiding boundary layer  15   a  surrounds a circular region and five first light-guiding boundary layers  15   a  are disposed at five places in the first region A. The circular region surrounded by the first light-guiding boundary layer  15   a  is a mechanism region  16   a.  As shown in  FIG. 2 , a switch mechanism  40  is provided inside the mechanism region  16   a.    
     As shown in  FIG. 1 , each second region B is provided with two circularly patterned second light-guiding boundary layers  15   b.  Regions respectively surrounded by the second light-guiding boundary layers  15   b  are mechanism regions  16   b,  and a switch mechanism  40  is provided in each mechanism region  16   b.  The third region C is provided with nine elliptically patterned third light-guiding boundary layers  15   c.  Regions respectively surrounded by the third light-guiding boundary layers  15   c  are mechanism regions  16   c.  A switch mechanism is also provided in each mechanism region  16   c.    
     The first light-guiding boundary layers  15   a,  the second light-guiding boundary layers  15   b,  and the third light-guiding boundary layers  15   c  are composed of a transparent or translucent epoxy resin or the like. In order to guide light propagating in the elastomer  18  constituting the light-guiding layer described below into the interiors of the first light-guiding boundary layers  15   a,  the second light-guiding boundary layers  15   b,  and the third light-guiding boundary layers  15   c,  the refractive indices of the first light-guiding boundary layers  15   a,  the second light-guiding boundary layers  15   b,  and the third light-guiding boundary layers  15   c  are preferably equal to or higher than the refractive index of the elastomer  18 . 
     As shown in  FIG. 2 , in the first region A, the elastomer  18  that constitutes a light-guiding layer fills the region sandwiched between the upper surface of the substrate  11  and the lower surface of the cover layer  13  and between the inner surface of the first sectional boundary layer  14   a  and the outer surfaces of the first light-guiding boundary layers  15   a.  The elastomer  18  is a light-guiding synthetic rubber which is transparent or translucent and contains a filler that scatters light. The light-guiding elastomer  18  is, for example, a silicone rubber. A silicone rubber is a polymer having a main chain formed of siloxane bonds (Si—O—Si) and an organic substituent, such as a methyl group, a phenyl group, or a vinyl group, in a side chain. 
     Silicone rubbers have high transparency throughout the entire visible light wavelength band (380 nm to 800 nm) used for illumination. Compared to other light-guiding resins, silicone rubbers are less likely to undergo deterioration caused by yellowing, clouding, and discoloration under application of near ultraviolet light (300 nm to 400 nm). Thus, silicone rubbers are suitable for use in illuminating devices. 
     As shown in  FIG. 3 , the elastomer  18  covers the surface of the substrate  11  and preferably completely fills the gap between the substrate  11  and the cover layer  13 . The elastomer  18  also fills the interior of each recess  12  in the substrate  11 . Accordingly, the bare chips  30  are embedded in the elastomer  18 , and the leads  33  are also embedded in the elastomer  18 . That is, the bare chips  30  and the leads  33  are in direct contact with the elastomer  18  and covered with the elastomer  18 . Since the bare chips  30  are embedded in the elastomer  18 , application of excessively large stresses onto the bare chips  30  can be prevented even when external force works against the illuminating device  10 . Although the leads  33  that connect the bare chips  30  to the conductive members  32  are located between the substrate  11  and the cover layer  13 , disconnections of the connecting parts between the leads  33  and the bare chips  30  and connecting parts between the leads  33  and the conductive members  32  can be easily prevented even when external force is applied to the illuminating device  10 . This is because the leads  33  are embedded in the elastomer  18 . 
     In the second region B, the elastomer  18  fills the region sandwiched between the upper surface of the substrate  11  and the lower surface of the cover layer  13  and between the outer surface of the first sectional boundary layer  14   a,  inner surfaces of the second sectional boundary layers  14   b,  and the outer surfaces of the second light-guiding boundary layers  15   b.  The bare chips  30  and the leads  33  connected to the bare chips  30  located in the second region B are embedded in the elastomer  18 . Similarly, the light-guiding elastomer  18  fills the region sandwiched between the upper surface of the substrate  11  and the lower surface of the cover layer  13  and surrounded by the outer surface of the first sectional boundary layer  14   a,  the outer surfaces of the second sectional boundary layers  14   b,  the inner surface of the third sectional boundary layer  14   c,  and the outer surfaces of the third light-guiding boundary layers  15   c.  The bare chips  30  and the leads  33  for wiring in the third region C are embedded in the elastomer  18 . 
     The method for making the illuminating device  10  is as follows. The bare chips  30  are respectively fixed, with the adhesive  31 , in the recesses  12  formed in the substrate  11 , and the electrode layers of the bare chips  30  are connected to the conductive members  32  on the surface of the substrate  11  with the leads  33  by wire bonding. In a step before or after the bare chip  30  mounting step, the first sectional boundary layer  14   a,  the second sectional boundary layers  14   b,  and the third sectional boundary layer  14   c  are formed on the upper surface of the substrate  11  by patterning. This is done by placing a mask with open patterns for forming the sectional boundary layers  14   a,    14   b,  and  14   c  on the surface of the substrate  11 , applying a curable epoxy resin or the like with a squeegee or the like, and thermally curing the applied resin. 
     Alternatively, a thin hollow needle may be attached to a syringe (injector), a curable epoxy resin or the like may be charged in the syringe, and the sectional boundary layers  14   a,    14   b,  and  14   c  may be drawn while pushing out the resin from the tip of the needle by increasing the pressure inside the syringe, followed by heating to cure the resin. 
     The first light-guiding boundary layers  15   a,  the second light-guiding boundary layers  15   b,  and the third light-guiding boundary layers  15   c  are formed at the same time as, before, or after the sectional boundary layers  14   a,    14   b,  and  14   c  are formed. As with the sectional boundary layers  14   a,    14   b,  and  14   c,  the light-guiding boundary layers  15   a,    15   b,  and  15   c  are formed by patterning a resin layer through a mask or direct drawing, and curing the resin. 
     After the sectional boundary layers  14   a,    14   b,  and  14   c  and the light-guiding boundary layers  15   a,    15   b,  and  15   c  are formed on the substrate  11 , a liquid resin material is charged in the first region A, the second regions B, and the third region C. The upper surface of the charged resin is made flat and smooth so that the upper surface of the resin substantially levels with the upper surfaces of the sectional boundary layers  14   a,    14   b,  and  14   c  and the light-guiding boundary layers  15   a,    15   b,  and  15   c.  Subsequently, the charged resin is heated or irradiated with light energy such as ultraviolet light to be cured and to thereby form a layer of the elastomer  18 . 
     Then reversing plates  41  are disposed in the mechanism regions  16   a,    16   b,  and  16   c  surrounded by the light-guiding boundary layers  15   a,    15   b,  and  15   c.  All of the first region A, the second regions B, and the third region C are covered with the same cover layer  13 . As shown in  FIG. 3 , an adhesive layer  19  is formed on the lower surface of the cover layer  13  in advance, so that when the first region A, the second regions B, and the third region C are covered with the cover layer  13 , the upper surfaces of the sectional boundary layers  14   a,    14   b,  and  14   c  and the upper surfaces of the light-guiding layers  15   a,    15   b,  and  15   c  are bonded to the lower surface of the cover layer  13  through the adhesive layer  19 . The adhesive layer  19  is a pressure-sensitive adhesive layer that exhibits adhesiveness or a curable adhesive layer that is cured by application of heat or ultraviolet light. 
     Alternatively, the reversing plates  41  may be bonded on the cover layer  13  with an adhesive in advance so that when the first region A, the second regions B, and the third region C are covered with this cover layer  13 , the reversing plates  41  are also placed in the mechanism regions  16   a,    16   b,  and  16   c.    
     The elastomer  18  easily deforms under external force. Thus, it is difficult to assuredly bond the upper surface of the elastomer  18  to the lower surface of the cover layer  13  through the adhesive layer  19 . However, since the sectional boundary layers  14   a,    14   b,  and  14   c  and the light-guiding boundary layers  15   a,    15   b,  and  15   c  are relatively hard, it is possible to firmly bond the upper surfaces of the sectional boundary layers  14   a,    14   b,  and  14   c  and the upper surfaces of the light-guiding boundary layers  15   a,    15   b,  and  15   c  to the lower surface of the cover layer  13  through the adhesive layer  19 . Thus, unintentional separation of the cover layer  13  after assembly can be prevented. 
     As shown in  FIG. 2 , in the first region A, a reflective layer  21  is disposed on the lower surface of the cover layer  13  in a portion not overlapping the first light-guiding boundary layers  15   a  or the mechanism region  16   a.  The reflective layer  21  is a metal film vapor-deposited on the lower surface of the cover layer  13  or a metal-colored or white coating film coating the lower surface of the cover layer  13 . The adhesive layer  19  is formed under the reflective layer  21  (on the surface of the reflective layer  21 ). Also in the first region A, a reflective layer  22  is formed on the upper surface of the substrate  11  in a portion not overlapping the first light-guiding boundary layers  15   a  or the mechanism region  16   a.  As shown in  FIG. 3 , the reflective layer  22  is formed in regions that do not overlap the recesses  12  where the bare chips  30  are mounted or the conductive members  32  connected to the leads  33 . The reflective layer  22  is also formed by vapor-depositing a metal or coating with a metal-colored or white coating film. 
     In the first region A, light emitted from the bare chips  30  directly reaches inside the light-guiding elastomer  18  without passing through air layers and is guided through the elastomer  18  by being reflected by the reflective layer  21  and the reflective layer  22 . Since the reflective layer  21  exists above the elastomer  18 , light cannot directly escape upward. Moreover, since the first sectional boundary layer  14   a  is non-light-guiding or since the first sectional boundary layer  14   a  is composed of a light-guiding material having a refractive index lower than that of the elastomer  18 , light does not pass through the interior of the first sectional boundary layer  14   a.  Light emitted from the bare chips  30  is mainly applied to the first light-guiding boundary layers  15   a.    
     The same applies for the second regions B and the third region C. Light emitted from the bare chips  30  in the second regions B is mainly applied to the second light-guiding boundary layers  15   b,  and light emitted from the bare chips  30  in the third region C is mainly applied to the third light-guiding boundary layers  15   c.    
     Light emitted from the bare chips  30  in the first region A is blocked with the first sectional boundary layer  14   a  and is not guided to the second regions B or the third region C. The same applies to light emitted from the bare chips  30  in the second regions B and to light emitted from the bare chips  30  in the third region C. 
     Bare chips  30  that emit light of different hues may be disposed in the regions A, B, and C, respectively. In this manner, the first light-guiding boundary layers  15   a,  the second light-guiding boundary layers  15   b,  and the third light-guiding boundary layers  15   c  respectively disposed in the regions A, B, and C can be illuminated with light of hues different from one another. For example, if red light-emitting diodes are used as the bare chips  30  in the first region A, the first light-guiding boundary layer  15   a  is illuminated in red. If green light-emitting diodes are used as the bare chips  30  in the second regions B, the second light-guiding boundary layers  15   b  are illuminated in green. If blue light-emitting diodes are used as the bare chips  30  in the third region C, the third light-guiding boundary layers  15   c  are illuminated in blue. 
     As shown in  FIG. 2 , the mechanism region  16   a  surrounded by the circularly patterned first light-guiding boundary layer  15   a  has no elastomer  18  charged therein, and the mechanism region  16   a  remains void. The switch mechanism  40  is provided in the mechanism region  16   a.  The switch mechanism  40  is provided with the reversing plate  41 , which is a dome-shaped metal plate having a springing property and electrical conductivity. The reversing plate  41  is bonded onto the lower surface of the cover layer  13  through the adhesive layer  19 . In the mechanism region  16   a,  an outer electrode  42  and an inner electrode  43  composed of conductive layers are formed on the surface of the substrate  11 , and the edge of the reversing plate  41  is disposed on the outer electrode  42 . When the cover layer  13  is pressed on the mechanism region  16   a,  the cover layer  13  deforms, the reversing plate  41  becomes reversed due to the pressure, and the reversing plate  41  contacts both the outer electrode  42  and the inner electrode  43 . As a result, the electrical current flows in the outer electrode  42  and the inner electrode  43 , and the switch circuit is turned ON. 
     In the second regions B, the switch mechanisms  40  are provided in the mechanism regions  16   b  surrounded by the second light-guiding boundary layers  15   b.  Similarly, in the third region C, switch mechanisms are provided in the mechanism regions  16   c  surrounded by the third light-guiding boundary layers  15   c.  The switch mechanisms in the mechanism regions  16   c  are reversing plates having an elliptical shape. 
     As shown in  FIG. 2 , in the operation unit  1 , the operation mechanism unit  2  is superimposed on the illuminating device  10 . The operation mechanism unit  2  is provided with a panel plate  51  which functions as a protective cover covering the surface of the illuminating device  10 . The panel plate  51  is rigid and does not deflect easily. A spacer  52  is interposed between the panel plate  51  and the cover layer  13  of the illuminating device  10 . The spacer  52  is a light-guiding film or a light-guiding plastic plate. The panel plate  51  is fixed to the spacer  52  with an adhesive, and the spacer  52  is fixed to the cover layer  13  with an adhesive. 
     The panel plate  51  has an operation hole  51   a.  An operation button  53  is provided in the operation hole  51   a.  A flange  53   a  is formed at the outer periphery of an end of the operation button  53  and faces the back surface of the panel plate  51 . The flange  53   a  prevents the operation button  53  from coming off from inside the operation hole  51   a  in the forward direction. The operation button  53  can also move in a downward direction in the figure within the operation hole  51   a.  A depressing protrusion  53   b  for depressing the reversing plate  41  is integrally formed on the back surface of the operation button  53 . 
     Operation holes  51   a  are formed in the panel plate  51  in all portions facing the mechanism regions  16   a  in the first region A, all portions facing the mechanism regions  16   b  in the second regions B, and all portions facing the mechanism regions  16   c  in the third region C. An operation button equivalent to the operation button  53  shown in  FIG. 2  is provided in every one of the operation hole  51   a.  The switch mechanisms in the mechanism regions  16   a,    16   b,  and  16   c  can be operated with the corresponding operation buttons. 
     As shown in  FIG. 2 , a coating film  54  having a hue such as black or brown is formed on the outer surface of the panel plate  51  composed of a light-guiding material. An illumination portion  54   a  with no coating film  54  is provided at the outer surface of the panel plate  51  in the outer peripheral region of the operation button  53 . The illumination portion  54   a  is ring-shaped, has a particular width, and is provided at the outer periphery of the operation button  53 . The illumination portion  54   a  is formed at every outer peripheral regions of the operation buttons in all regions A, B, and C. 
     When bare chips  30  are turned ON, light emitted from the bare chips  30  is guided into the elastomer  18  that functions as a light-guiding layer and applied to the first light-guiding boundary layers  15   a,  the second light-guiding boundary layers  15   b,  and the third light-guiding boundary layers  15   c.  As shown in  FIG. 2 , because the light-guiding cover layer  13 , the light-guiding spacer  52 , and the light-guiding panel plate  51  are provided on the first light-guiding boundary layers  15   a,  the light applied to the first light-guiding boundary layers  15   a  passes through these components and emitted in the forward direction from the illumination portion  54   a.  As a result, the outer periphery of the operation button  53  is illuminated. 
     In other words, because the adhesive layer  19  and the cover layer  13  are composed of a material having a refractive index higher than that of the first light-guiding boundary layer  15   a,  light applied to the interior of the first light-guiding boundary layer  15   a  from the elastomer  18  is transmitted into the cover layer  13  through the adhesive layer  19 . Then light emitted from the cover layer  13  into an air layer thereabove enters the interior of the panel plate  51  and illuminates the illumination portion  54   a.    
     As described above, when the bare chips  30  in the first region A, the bare chips  30  in the second regions B, and the bare chips  30  in the third region C respectively emit light of different hues, the outer peripheries of the operation buttons  53  in the first region A, the outer peripheries of the operation buttons  53  in the second regions B, and the outer peripheries of the operation buttons  53  in the third region C are illuminated in hues different from one another. 
     The operation buttons  53  may be non-light-guiding or may be composed of a transparent or translucent light-guiding material having a relatively high refractive index. In the case where the operation buttons  53  are composed of a light-guiding material, the outer peripheries of the operation buttons  53  can be illuminated with light of a particular hue due to the light emitted from the first light-guiding boundary layer  15   a.  In the case where coating films are formed on the surfaces of the operation buttons  53  composed of a light-guiding material and the coating films are partly removed to form patterns such as characters, figures, symbols, and designs, these removed parts indicating characters, figures, symbols, and designs can be illuminated. 
     In the embodiment shown in  FIGS. 1 to 3 , the reflective layer  21  on the elastomer  18  may instead be provided on the surface that faces the substrate  11  rather than the adhesive layer  19  or on the surface of the cover layer  13  facing the spacer  52 . 
     Other embodiments of the present invention will now be described. In these embodiments, the constitutional elements equivalent to those of the first embodiment shown in  FIGS. 1 to 3  are represented by the same reference symbols and detailed descriptions therefor are omitted. 
       FIG. 4  is a cross-sectional view showing an illuminating device  110  according to a second embodiment of the present invention. 
     The illuminating device  110  also has the first sectional boundary layer  14   a,  the second sectional boundary layers  14   b,  and the third sectional boundary layer  14   c  between the substrate  11  and the cover layer  13  to define a plurality of regions A, B, and C. Thus, bare chips  30  that emit light of different hues for different regions can be mounted. 
     As shown in  FIG. 4 , a boundary layer  115  surrounding the mechanism region  16   a  equipped with the switch mechanism  40  has no light-guiding property and is composed of a non-light-guiding epoxy resin or the like as with the sectional boundary layers  14   a,    14   b,  and  14   c.  Alternatively, the boundary layer  115  may be composed of a material having a refractive index lower than that of the elastomer  18  so that light propagating in the elastomer  18  can be easily reflected at the interface between the elastomer  18  and the boundary layer  115 . The cover layer  13  is not provided with the reflective layer  21 . 
     According to the illuminating device  110  shown in  FIG. 4 , light emitted from the bare chips  30  propagates in the elastomer  18  covering the bare chips  30 , passes through the light-guiding cover layer  13 , and emitted forward. Thus, the regions A, B, and C can be respectively illuminated with light of particular hues. In such a case, as shown in  FIG. 4 , a coating film  154  should be formed on the outer surface of the cover layer  13  to cover the front part of the bare chips  30  so that the portions with the bare chips  30  can be prevented from being illuminated excessively brightly compared to other portions. Moreover, illumination portions  154   a,    154   b,  and  154   c  having no coating film  154  and patterned into characters, figures, symbols, or designs can be formed so that the illumination portions  154   a,    154   b,  and  154   c  are partially illuminated with light having particular hues. 
     In such a case, when the refractive index of the cover layer  13  is higher than that of the elastomer  18 , light can easily enter the interior of the cover layer  13  from the elastomer  18 . Alternatively, a filler may be mixed into the interior of the entire cover layer  13  to render the cover layer  13  milky or cloudy so that the regions A, B, and C are illuminated bright when viewed from outside due to scattering of light inside the cover layer  13 . Particles of a phosphor may be incorporated in the cover layer  13  so that when light is guided from the interior of the elastomer  18  to the interior of the cover layer  13 , the regions A, B, and C emit fluorescent light. Alternatively, in the cover layer  13 , the illumination portions  154   a,    154   b,  and  154   c  may be partly made milky or cloudy or may partly include a phosphor. 
     Examples of the phosphor include an oxynitride or oxysulfide (liquid color phosphor) containing at least one element selected from Ti, Zr, Hf, Ta, W, and Mo, other green phosphors, blue phosphors, and any combination of these. 
     According to the illuminating device  110  shown in  FIG. 4 , the outer surface of the cover layer  13  can be used as an operation surface which is directly touched with fingers without forming the operation mechanism unit  2 . Optionally, the operation mechanism unit  2  shown in  FIG. 2  may be provided on the outer surface of the illuminating device  110  shown in  FIG. 4 . In such a case, no coating film  154  may be formed on the outer surface of the cover layer  13  and the spacer  52 , the panel plate  51 , and the operation buttons  53  constituting the operation mechanism unit  2  may be illuminated with light that has passed through the cover layer  13 . Alternatively, the coating film  54  may be provided on the surface of the panel plate  51  and part of the coating film  54  may be removed to form an illumination portion having a particular pattern. 
       FIG. 5  is a cross-sectional view showing an illuminating device  210  according to a third embodiment of the present invention. 
     In this illuminating device  210 , a reflector  221  is provided at the lower surface of the cover layer  13  in a portion facing the bare chip  30 . The lower surface of the reflector  221  is a reflecting surface  221   a  sloped with respect to the upper surface of the substrate  11 . For example, the reflecting surface  221   a  is a tapered surface sloped in respective directions. In the cross-sectional view of  FIG. 5 , the section line of the reflecting surface  221   a  is straight; however, the section line may be curved outward or curved inward. 
     According to the illuminating device  210 , light emitted from the bare chips  30  is reflected at the sloped reflecting surface  221   a  and scattered around within the elastomer  18 . A boundary layer  215  surrounding the mechanism region  16   a  has a higher refractive index than the elastomer  18  and a light-guiding property so that light can be easily guided inside. Alternatively, the boundary layer  215  may have no light-guiding property or a have a refractive index lower than the elastomer  18  so that light is not easily guided inside. When the boundary layer  215  has light-guiding property and a high refractive index, the boundary layer  215  is illuminated with light scattered inside the elastomer  18 . When the boundary layer  215  has no light-guiding property and a low refractive index, the light applied to the interior of the elastomer  18  passes through the cover layer  13  in the region where no reflector  221  is provided and readily emitted in the forward direction. 
     In the illuminating device  210  shown in  FIG. 5  also, the surface of the cover layer  13  can be used as an operation surface fingers can directly touch. Alternatively, the operation mechanism unit  2  shown in  FIG. 2  may be superimposed. 
       FIG. 6  shows an illuminating device  310  according to a fourth embodiment of the present invention. 
     An elastomer  318  provided in this illuminating device  310  has a light-guiding property and a three-layer structure including a center, which is a core layer  318   a,  a lower cladding layer  318   b  thereunder, and an upper cladding layer  318   c  on the core layer  318   a.  The core layer  318   a  is composed of a material having an absolute refractive index larger than those of the lower cladding layer  318   b  and the upper cladding layer  318   c.    
     The recess  12  in the substrate  11  is filled with the core layer  318   a.  At least part of the bare chip  30  in the recess  12  is located inside the core layer  318   a.  The reflector  221  formed as in  FIG. 5  has the reflecting surface  221   a  exposed in the core layer  318   a.    
     The core layer  318   a,  the lower cladding layer  318   b,  and the upper cladding layer  318   c  are all composed of a silicone rubber or the like and their refractive indices are made different by changing the substituents or dispersing microparticles of a metal or semiconductor oxide having a diameter of about several ten nanometers in the layers. 
     In  FIG. 6 , the upper end of the bare chip  30  is located in the core layer  318   a.  Since part of the bare chip  30  is located in the core layer  318   a,  light emitted from the bare chip  30  can be guided to the core layer  318   a  with little loss. 
     In other words, according to the illuminating device  310 , light emitted from the bare chip  30  propagates in the core layer  318   a  while being reflected at the interfaces between the core layer  318   a  and the upper and lower cladding layers  318   b  and  318   c,  is applied to the first light-guiding boundary layer  15   a,  and illuminates the first light-guiding boundary layer  15   a.  When part of the upper cladding layer  318   c  is removed, light is applied to the cover layer  13  from the removed portion, and the cover layer  13  is illuminated through that portion. 
     For the illuminating device  310  shown in  FIG. 6  also, the outer surface of the cover layer  13  may be used as an operation surface or the operation mechanism unit  2  shown in  FIG. 2  may be superimposed. 
       FIG. 7  shows an illuminating device  410  according to a fifth embodiment of the present invention. 
     The illuminating device  410  has a core layer  318   a  composed of an elastomer having a high refractive index on the surface of the substrate  11 , and a lower cladding layer  318   b  composed of an elastomer having a low refractive index is disposed between the substrate  11  and the core layer  318   a.  A hole is formed in the lower cladding layer  318   b  and serves as a recess. The bare chip  30  is mounted in the recess and is connected to the conductive members on the surface of the substrate  11  with the leads  33 . 
     The bare chip  30  and the leads  33  are covered with a sealant layer  411 , and the outer side of the sealant layer  411  is covered with the core layer  318   a  serving as a light-guiding layer. In other words, the bare chip  30  and the leads  33  are in direct contact with the sealant layer  411 , and the sealant layer  411  is in direct contact with the core layer  318   a.    
     The refractive index of the sealant layer  411  is preferably higher than that of the bare chip  30  but equal to or lower than that of the core layer  318   a.  After the bare chip  30  is mounted on the surface of the substrate  11  and connected to the conductive members on the surface of the substrate  11  via the leads  33 , the bare chip  30  is sealed with the sealant layer  411 . In this manner, the bare chip  30  and the leads  33  can be protected in the subsequent process. In a further subsequent process, the sealant layer  411  is covered with the core layer  318   a  composed of an elastomer so that the bare chip  30  and the leads  33  can be protected against pressures from outside during use or the like. 
     The sealant layer  411  is composed of a synthetic resin or a synthetic rubber. The sealing resin used in the sealant layer  411  is preferably the same compound as the elastomer forming the core layer  318   a  from the viewpoint of adhesiveness or the like. The sealant layer  411  may be integrally formed with the core layer  318   a.  Alternatively, other resins may be used. Examples of the resin typically include thermoplastic resins, thermosetting resins, and photocurable resins. Specific examples of the resin include methacrylic resins such as polymethyl methacrylate; styrene resins such as polystyrene and styrene-acrylonitrile copolymers; polycarbonate resins; polyester resins; phenoxy resins; butyral resins; polyvinyl alcohol; cellulose resins such as ethyl cellulose, cellulose acetate, and cellulose acetate butyrate; epoxy resins; phenol resins; and silicone resins. Furthermore, inorganic materials may also be used. For example, an inorganic material obtained by curing one or a combination of solutions obtained by hydrolytic polymerization of a metal alkoxide, a ceramic precursor polymer, and a solution containing metal alkoxide by the sol gel method. For example, an inorganic material containing a siloxane bond may be used. Sealing resins may be used either as a single kind of them or as a mixture of more than one kind in any combination and in any ratio. 
     The sealant layer  411  may contain a phosphor so that the wavelength of the light source can be converted to a desired wavelength and light can be propagated through the high-refractive-index layer. The amount of the phosphor used is not particularly limited but is typically 0.01 parts by weight or more, preferably 0.1 parts by weight or more, and more preferably 1 part by weight or more, and 100 parts by weight or less, preferably 80 parts by weight or less, and more preferably 60 parts by weight or less per 100 parts by weight of the sealing resin. 
     The sealant layer  411  may contain components other than the phosphor and the inorganic particles. For example, a stabilizer against processing, oxidation, or heat such as a coloring material for correcting color tone, an antioxidant, or a phosphor process stabilizer, a lightfast stabilizer such as a UV absorber, and a silane coupling agent may be contained. These components may be used alone or in any desired combination of two or more at a desired ratio. 
     The illuminating device  410  shown in  FIG. 7  has boundary layers  415   a,    415   b,  and  415   c  that penetrate the core layer  318   a  in a vertical direction. The boundary layers  415   a,    415   b,  and  415   c  are formed by the same patterns as or different patterns from those of the boundary layers  14   a,    14   b,  and  14   c  and boundary layers  15   a,    15   b,  and  15   c  shown in  FIG. 1 . The boundary layers  415   a,    415   b,  and  415   c  shown in  FIG. 7  are composed of a light-guiding material having a refractive index lower or higher than that of the core layer  318   a.  When the boundary layers are formed of a material having a lower refractive index, light propagating in the core layer  318   a  is reflected at the boundary layers. When the boundary layers are formed of a material having a higher refractive index, light propagating in the core layer  318   a  easily enters the boundary layers. 
     By selecting the refractive index of the boundary layers as such, the boundary layers can be used as either light-blocking layers or light-guiding paths, and propagation of light can thus be controlled. 
     According to the illuminating device  410  shown in  FIG. 7 , the boundary layer  415   a  and the boundary layer  415   b  are composed of a material having a low refractive index so that the boundary layers  415   a  and  415   b  have a light-blocking function. A cover layer  412  that forms an illumination section is provided on the core layer  318   a  at the right side of the boundary layer  415   b  in the drawing. The cover layer  412  is a light-scattering layer containing a filler that scatters light or a phosphor layer containing a phosphor. 
     The boundary layer  415   c  having a high refractive index can function as a light-guiding path at the left side of the boundary layer  415   b.  Upper cladding layers  318   c  having a low refractive index are formed on the core layer  318   a.    
       FIG. 8  shows a sixth embodiment of the present invention and  FIG. 9  shows a seventh embodiment of the present invention. The sixth embodiment and the seventh embodiment are each a partly modified illuminating device  10  of the first embodiment shown in  FIG. 1 . 
     According to the sixth embodiment shown in  FIG. 8 , a light-absorbing substance is substantially homogeneously dispersed in the first sectional boundary layer  14   a  and other sectional boundary layers, and a reflective layer  14   e  is provided at the border between the sectional boundary layer and the elastomer  18 . The reflective layer  14   e  is a layer having a light-reflecting function or a layer having a light-scattering property. When the light-absorbing substance is dispersed in the sectional boundary layer and the reflective layer  14   e  is provided, light that has reached the sectional boundary layer can be returned to the elastomer  18  functioning as the light-guiding layer so that light can be effectively used. 
     According to the seventh embodiment shown in  FIG. 9 , a light-absorbing layer  14   f  and the reflective layer  14   e  are provided at the borders between the first sectional boundary layer  14   a  and other sectional boundary layers and the elastomer  18  so that light can be readily returned to the elastomer  18 . The light-absorbing layer  14   f  is in either a paste form or an ink form in which a light-absorbing substance is dispersed in a binder resin and is gray or black in color.