Abstract:
A method of forming a key comprising the steps of: depositing an electroless metallic layer on an upper surface of a substrate; removing the metallic layer from selected portions to expose the substrate, said exposed portions of the substrate defining the image of an indicia; depositing a second metallic layer on the remaining portions of the first metallic layer by electrolysis; and coupling a lower surface of the substrate to an element for actuating a switch. A device for tactile actuation by a user, having an element, for activating a switch, coupled to a body supporting a metallic layer for tactile actuation by a user, wherein the metallic layer extends over an upper surface of the body and wherein at least one aperture extends through the metallic layer to said upper surface thereby defining at least one visible indicia.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a device for tactile actuation or keying by a user and the method of forming such a device. It particularly relates to a device having a metal finish with images particularly indicia defined therein. The device may be a key in a keyboard. 
     It is often desirable to give devices a metallic or metallic looking finish. Such a finish generally has high lustre and is aesthetically pleasing to the user. 
     In the portable radio telephone market phones with a metallic finish and with keys with a metallic finish are known. 
     One problem with keys having a metallic finish is that it is difficult to indelibly put images of indicia onto the keys such as letters, numbers or characters which indicate the key&#39;s function. 
     Another problem is that it is difficult to define fine characters on metal keys. Consequently it is difficult to put more complex characters, in particular Chinese and/or Japanese Characters, or more than one character on small keys. 
     Another problem is arranging for the indicia defined onto the metal keys to be visible to a user in a range of ambient lighting environments. 
     It would be desirable to provide improved keys with a metallic finish. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention there is provided a device for tactile actuation by a user, having an element, for activating a switch, coupled to a body supporting a metallic layer for tactile actuation by a user, wherein the metallic layer extends over an upper surface of the body and wherein at least one aperture extends through the metallic layer to said upper surface thereby defining at least one visible indicia. 
     The indicia defined by the aperture or apertures can be particularly fine. Furthermore, the keys can be effectively back-lit, have aesthetic appeal, are hard-wearing, and can be formed from a simple manufacturing process. 
     According to another aspect of the present invention there is provided a method of forming a key for tactile activation by a user comprising the steps of: depositing a first metallic layer on an upper surface of a substrate; removing the metallic layer from selected portions to expose the substrate, said exposed portions of the substrate defining the image of an indicia; depositing a second metallic layer on the remaining portions of the first metallic layer; and coupling a lower surface of the substrate to an element for actuating a switch such that, in use, tactile actuation of the key through the second metallic layer activates the switch. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention and to understand how the same may be brought into effect reference will now be made by way of example only to the following drawings in which: 
     FIG. 1 illustrates a mobile phone in an exploded view; 
     FIG. 2 illustrates a cross-section of the keypad and switching assemblies; 
     FIGS. 3 a  and  3   b  illustrates an assembled keymat; 
     FIGS. 4 a  and  4   b  illustrate the assembly of a keymat; and 
     FIGS. 5 a  to  5   h  illustrate the creation of a key  110  with a metal finish. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a mobile phone  2  is shown in an exploded view and some of the various components which make up a portable radiotelephone can be identified. These include a front cover (also known as the A-cover)  4 , keypad  100 , retaining screws  6 , display clamp  8  for retaining the display  12 , speaker  10 , a layer  30  of key dome switch elements  32 , microphone  18 , printed circuit board (PCB)  16 , retaining clip  20  for fastening the front cover  4 , and a rear cover (also known as B-cover)  22 . The battery (not shown) clips onto the rear of the telephone forming an integral part of the rear cover  22 . 
     The keypad  100  has keys  110  arranged in an array. The front cover  4  has a corresponding array of apertures  5 . When the phone is assembled, each key  110  of the keypad  110  protrudes through a corresponding aperture  5  in the front cover  4  and overlies a corresponding key dome switch element  32  of the layer  30 . When a user depresses one of the keys  110  the corresponding switching element  32  completes a circuit on the PCB  16  and controls the phones functionality. Each of the keys  110  carries on the upper surface protruding from the front cover  4  indicia, such as numeral(s), character(s) and/or letter(s), indicating the function of the key. 
     One design of keypad  100  is shown in cross-section in FIG.  2 . The keypad comprises a flexible rubber keymat  102  to which keys  110  are attached by adhesive  116 . Each key  110  has a body or substrate  112  which projects through a corresponding hole  5  in the front cover  4  and which has, extending over its upper surface, a metal layer  114 . The metal layer  114  has a metal finish which has a high luster and is hard wearing. Indicia are defined on the upper surface of the keys  110  by apertures  116  in the metal layer which expose the underlying body  112 . 
     The portions of the keymat  102  to which the keys are attached on an upper surface  104  are surrounded and joined to the main web of the keymat by resilient deformation zones  104 , and have on a lower surface  106 , directly underlying each of the attached keys  110 , a projection  108 . 
     A switch assembly  40  underlies but is separated from each projection  108 . Each switch assembly  40  comprises a key dome switch element  32  overlying two lower switch elements  17 . Each key dome switch element  32  is formed from a flexible dome  34  of resilient material protruding upwards from a layer  30  of sheet material. The underside of each flexible dome  30  has a conductive portion  36 . The lower switch elements  17  are connected to the PCB  16 . 
     When a user presses the metal layer  114  of the key  110 , the resilience of the deformation zone surrounding the key allows the key to travel towards the switch assembly  40  associated with the key so that the projection  108  can activate the switch assembly. The projection  108  urges the dome  34  to deform suddenly to a configuration in which the conductive portion  36  on its underside bridges the lower switch elements  17  and connects them together electrically. When the key portion is released the deformation zone  104  urges it to return to its original position as illustrated in FIG. 2, thereby disconnecting the switch elements  17  from each other. 
     The PCB  16  has on its upper surface an array of light sources such as light emitting diodes (LEDs)  50 . The domes  34  are made from a translucent resiliently flexible material. Preferably, the layer  30  and the domes  34  are formed from a silicone rubber mat. The keymat  102  is made from a translucent resiliently flexible material such as silicone rubber. The layer of adhesive  116  joining the body  116  of the key  110  to the keymat  102  is also translucent. The body  112  of the key is translucent. It is preferably made from a translucent plastics material. The layer  114 , which has a metal finish, is opaque. The light from the light source  50  can therefore travel through the intervening structures into the body  112  of the key. In a poorly lit environment, the light source is activated and the aperture  116  on the upper surface of the key  110  defining indicia is illuminated and can be clearly discerned in contrast to the opaque metal layer  114 . In a well-lit environment, the layer  114  reflects the ambient light, whereas the light falling on the aperture  116  passes into the body  112 . Consequently, the indicia defined by the aperture can be clearly discerned in contrast to the reflecting metallic layer  114 . Preferably, the aperture has a breadth which is great enough for the indicia to be resolved by the naked eye but narrow enough to accurately define complex indicia. Typically the breadth is between 0.15 and 0.45 mm. 
     The keypad  100  is illustrated in FIGS. 3 a  and  3   b.  FIG. 3 a  shows a front view of a keypad  100  intended for the Japanese market. It is shown to scale. FIG. 3 b  is a perspective rear view of the keypad  100 . 
     The process of making a keypad is illustrated in FIGS. 4 a  and  4   b.  Referring to FIG. 4 a  there is illustrated a frame  60  of keys  110 . The keys  110  are fully formed and include the body  112  and metal layer  114  as a finish. The keys  110  are held as an array by interconnects  62 . The array corresponds to the array of projections  108  on the underside of the keymat  102 , the array of apertures  5  in the front cover  4 , the array of domes  34  on the layer  30  and the array of switch elements  17  on the PCB  16 . The keys  110  are adhered to the keymat  102  to form the keypad  100  as shown in FIG. 4 b.  For the sake of clarity, the interconnects  62  are not shown. 
     A process for forming the metal layer  114  on the keys  110  will now be described. Although this process would occur to each key forming part of a frame  60 , for the sake of clarity it will be describe with relation to one key only. 
     The inventors have made the surprising innovation that a process known from the art of conductive interconnects which is used to form thin tracks of interconnect on circuit boards can be used in a new method to form the extensive metal layer  114  while simultaneously creating narrow apertures which define fine indicia. The process has previously been used to form Moulded Interconnect Devices (MID) and further information on the process is published by “Moulded Interconnect Device International Association”. 
     One process of forming the layer  114  is illustrated in FIGS. 5 a  to  5   h.  The use of photoresists and etchants is well document in the art of Very Large Scale Integration (VLSI). 
     FIG. 5 a  illustrates the body  112  of a key  110  which acts as a substrate for the metal layer  114 . The body  112  is made of plastics material, preferably translucent plastics. It has been found that polytherimide (PEI) or acrylic-butadiene-styrene (ABS) are suitable. 
     A first metallic layer  118  of electroless copper is formed on the upper surface of the body  112 . The body  112  has a catalyst such as palladium added to its upper surface and is placed into a bath of chemicals containing copper salt and a reducing agent such as formaldehyde. The copper salt is reduced in the presence of the catalyst to metallic copper and is thereby deposited on the surface of the body  112 . The layer  118  of electroless copper typically has a thickness of 1-1.5 microns. 
     A photoresist layer  120  is then applied to the upper surface of the first metallic layer  118  as illustrated in FIG. 5 c.    
     An opaque mask  122  is then placed over the photoresist layer  120 . The mask  122  has apertures  124  defined in it. These apertures  124  have the shape of the indicia which will be defined by the apertures  116  in the metal layer  114 . The mask is then illuminated with UV light. The photoresist  120  exposed through the aperture  124  becomes soluble and is removed to form an aperture  126  in the photoresist layer  120 . The remaining photoresist acts as a mask while the first metallic layer  118  is etched through the aperture  126  as illustrated in FIG. 5 e.    
     The structure formed at the end of the etch step is illustrated in FIG. 5 f.  The first metallic layer  118  has been completely removed in the aperture  126  to expose the upper surface of the body  112 . The remaining photoresist layer  120  is then removed exposing the first metallic layer  118  with an aperture  116  therein exposing the upper surface of the body  112 . 
     A second layer  128  containing metal is then deposited on the first metal layer  118  using electrolytic plating techniques. The first and second metallic layers in combination form the layer  114  previously described. An aperture  116  extends through both layers to exposed the upper surface of the body  112 . 
     A layer formed by electroless deposition may contain impurities from the chemical bath in which the copper deposited was reduced. In particular the reducing agent such as formaldehyde may be present. 
     Although in the forgoing description a particular method of forming the metal layer on the keys has been described and a particular application described it should be appreciated that the scope of the invention is not so limited.