Patent Publication Number: US-8525794-B2

Title: Device and technique for assigning different inputs to keys on a keypad

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/114,908, filed Apr. 25, 2005 now U.S. Pat. No. 7,511,700, entitled “Device and Technique for Assigning Different Inputs to Keys on a Keypad;” which is a continuation-in-part of U.S. patent application Ser. No. 11/080,375, filed Mar. 14, 2005, entitled “Stack Assembly For Implementing Keypads On Mobile Computing Devices.” The aforementioned priority applications are hereby incorporated by reference for all purposes. 
    
    
     TECHNICAL FIELD 
     The disclosed embodiments relate generally to the field of keypads for mobile computing devices. In particular, the disclosed embodiments relate to a device and technique for assigning different inputs to keys on a keypad. 
     BACKGROUND 
     Over the last several years, the growth of cell phones and messaging devices has increased the need for keypads that are small and tightly spaced. In particular, QWERTY keypads have become smaller with greater key switch density. With decreasing overall size, there has been greater focus on efforts to make individual keys more usable to a user. For example, keyboard design considers how readily the user can select or click (“clickability”) individual key structures of keyboard. The clickability may be affected by various factors, such as the individual key structure size and shape, as well as the spacing between key structures and the tactile response of individual key structures. 
     Other features that may affect usability include illumination of the keypad. Smaller keyboards tend to have smaller print patterns, and thus are more difficult to see. Some of the solutions provided for illuminating key pads includes using incandescent light sources and lighting areas surrounding individual key structures. The need for illumination becomes more important with small and/or tightly spaced key structures, because the smaller keys are more difficult to see. Furthermore, the smaller keyboards tend to be more unfamiliar to users who may be use to full-size keyboards, and many users have difficulty typing without seeing the individual key structures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a small-form factor keyboard for use with a mobile computing device, according to an embodiment of the invention. 
         FIG. 2A  is a side cross-sectional view along lines A-A of  FIG. 1 , according to an embodiment. 
         FIG. 2B  is a side cross-sectional view along lines B-B of  FIG. 1 , according to an embodiment. 
         FIG. 2C  illustrates an implementation of the groove (or scallop) at the juncture of the lateral edges and the exterior surface of a key. 
         FIG. 3B  is an illustrative isometric view of an isolated key structure with a sub-layer ornamentation, according to an embodiment of the invention. 
         FIG. 3A  is an illustrative isometric view of an isolated key structure with a sub-layer ornamentation, according to an embodiment of the invention. 
         FIG. 4A  illustrates an alternative keyboard layout with non-abutting key structures, according to an embodiment. 
         FIG. 4B  illustrates adjacent key structures from a horizontal set of key structures in the keyboard shown with  FIG. 4A . 
         FIG. 5A-5G  illustrate a manufacturing process for producing a keyboard having nearly abutting key structures, as described with  FIG. 1  and  FIG. 2A-2B , under an embodiment of the invention. 
         FIGS. 6A-6D  illustrate a different manufacturing process for forming a keyboard comprised of key structures, according to an embodiment of the invention. 
         FIGS. 7A-7E  illustrate another technique for forming a keypad or keyboard, under an embodiment of the invention. 
         FIG. 8A  is an isometric view of a keyboard separated from a mobile computing housing, according to an embodiment of the invention. 
         FIG. 8B  is an isometric view of a mobile device housing for a keyboard, under an embodiment of the invention. 
         FIG. 9  is a frontal view of a mobile computing device, configured according to an embodiment of the invention. 
         FIG. 10  illustrates a frontal and bottom isometric view of the mobile computing device  900 , according to an embodiment of the invention. 
         FIG. 11  illustrates basic components of a stack assembly for use with a keypad or keyboard of a mobile computing device. 
         FIG. 12A  illustrates an actuation member for use with a stack, under an embodiment of the invention. 
         FIG. 12B  illustrates a design for a electrical contact layer, under an embodiment of the invention. 
         FIGS. 13A and 13B  illustrate a stack formation, under an embodiment of the invention. 
         FIGS. 14A and 14B  illustrate an alternative design for a stack, under an embodiment of the invention. 
         FIGS. 15A and 15B  illustrate an alternative construction in which a mask is combined with an illumination layer  410  as part of a stack formation, under an embodiment of the invention. 
         FIG. 16  is a frontal view of the different layers and elements that can be used to integrally form a modular stack, under an embodiment. 
         FIGS. 17A-17E  illustrate another technique for forming an actuation member layer, under another embodiment of the invention. 
         FIG. 18  illustrates an embodiment of the invention implemented within a mobile computing device having a first keyboard design. 
         FIG. 19  illustrates an embodiment of the invention implemented within a mobile computing device having a second keyboard design. 
         FIG. 20  illustrates a keyboard configured for implementation with a number assignment technique, according to an embodiment of the invention. 
         FIG. 21  illustrates a system in which keys or key structures can be paired (or clustered) to provide a single numeric value, or separate non-numeric values. 
         FIG. 22  illustrates a mobile computing device, configured with a key assignment scheme in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Overview 
     Embodiments of the invention provide an effective keypad assembly and keypad layout for mobile computing devices. In particular, embodiments of the invention provide keyboard layouts and designs. Additionally, embodiments described herein provide for stack components to make keyboards operable on small-form factor devices. 
     According to one embodiment, a small form-factor keypad is provided that prioritizes available housing real-estate for the area occupied by individual keys. The result is larger keys and/or smaller sized mobile computing devices, at least compared to past approaches for placing keypads and keyboards on such devices. 
     In another embodiment, a modular stack assembly is provided for making small-form factor keyboards operable on mobile computing devices. 
     In still another embodiment, a technique and design is provided to facilitate users in making number entries on small form-factor keyboards. 
     While numerous embodiments and implementations are provided in this application, the embodiments described herein do not necessarily depend on one another. For example, under an embodiment, a mobile computing device may implement a keyboard design such as described with  FIG. 1 , but omit use of a stack assembly such as described by other embodiments of the invention. Numerous variations and implementations for embodiments of the invention are described in this application. 
     Keypad Design 
     Embodiments described herein provide a keyboard having keys that are tightly spaced in at least one direction (e.g. the horizontal direction). This promotes a small overall form factor for the mobile computing device and/or larger keys on the device. Several features and considerations are implemented with a keyboard design of one or more embodiments of the invention. These features and considerations include (i) a shape or footprint of individual keys that form the keypad, (ii) a spacing between adjacent and neighboring keys in the keypad (e.g. a horizontal spacing between adjacent keys of a row), and/or (iii) a spacing between adjacent sets of keys (e.g. a vertical spacing between rows of a keyboard). One result achieved by an embodiment of the invention is that a larger percentage of a housing surface can be used for the individual keys that comprise a keyboard of the mobile computing device. This enhances the usability of the keypad, particularly in the user&#39;s ability to see and select keys using finger tips and pointed objects. 
     According to an embodiment, a mobile computing device is provided having a housing on which a keypad is provided. The keypad may be formed from a plurality of key structures that extend from a surface or region of the housing. Individual key structures that form the keypad are moveable inward, so to move from an original position into an engaged position. When moved into the engaged position, processor(s) contained within the housing register an input, depending on the particular key structure that is engaged. A majority of the key structures have a footprint that is oblong in shape to define a length and a width of that key structure. The footprint is also symmetrical about at least its length. Each key structure in the majority includes an outer surface that is provided with an outward curvature relative to the region of the housing. 
     In an embodiment, the keypad is a keyboard, with each key structure being assignable to a particular letter and/or character. In one embodiment, key structures that form the keyboard that are most proximate to one another in a first direction (e.g. the horizontal direction) nearly abut one another. The key structures may also be distributed linearly in the first direction, so that a dimension of the keyboard in the first direction corresponds substantially to a sum of a dimension of the individual key structures in the first direction. 
     As used herein, the term “substantially” means nearly equal, or at least 80% of a stated quantity or expression. Similar relational expressions, such as “about” or “approximately” should be considered to be 90% or more of a stated quantity. 
     The expression “nearly abuts” means almost or nearly in contact. In the context of key structures of a mobile computing device, the expression “nearly abuts” means (i) two key structures are sufficiently separated to move independently; and (ii) the two key structures are proximate enough so that they appear to be in contact or abutting. Additional description and variations to the expression “nearly abutting” are provided below in this application. 
     In another embodiment, a keypad is provided for a mobile computing device. The keypad includes a plurality of key structures that are distributed to extend in a horizontal direction and in a vertical direction on a face of the mobile computing device. For at least a majority of the plurality of key structures, individual key structures that are most proximate to one another in the horizontal direction nearly abut one another, while key structures that are most proximate to one another in the vertical direction are spaced apart. Additionally, individual key structures in the majority of key structures have a footprint that is oblong. 
     In one variation, the lengthwise direction of the footprint for the majority of key structures corresponds to the vertical direction. Alternatively, the lengthwise direction of the footprint for the majority of key structures may be tilted about the vertical direction. 
     The expression “spaced-apart” means a spacing that is greater than what would appear to be abutting. Two key structures that are spaced apart may be separated by a visible underlying surface or layer. 
     Among other features provided by keyboard embodiments described herein, the individual key size of a keyboard on a mobile computing device is maximized, or at least enhanced relative to the form factor of the mobile computing device. In some embodiments, the key structures are elongated to have length in a vertical direction, while a limiting dimension (e.g. the width) of the mobile computing device is in the horizontal direction. The use of elongated keys having lengths in the non-limiting dimension of the mobile computing device enables the individual key structures to be made larger, without need to increase the dimensions of the mobile computing device. The larger key size enables larger graphics and tactile feedback for the user. For example, the user has more key area to locate and select keys using fingertips. 
     The use of elongated key structures that are aligned with the non-limiting dimension of the mobile computing device also permit for the key structures to be shaped in a manner that is conducive to the user&#39;s touch and use. For example, one embodiment provides for individual key structures that are barrel shaped, so as to contour outward in symmetrical fashion. The contoured shape and dimension of individual keys hinders inadvertent finger movements by the user that may result in inadvertent strikes to neighboring keys. Specifically, the contour shape provided enables the user to avoid finger slippage and to have a better feel for the key when making a key strike. 
       FIG. 1  illustrates a small-form factor keyboard for use with a mobile computing device, according to an embodiment of the invention. The keyboard  100  is provided on a surface  102  of housing  110  for a mobile computing device. An example of a mobile computing device for use with embodiments of the invention includes cell phones, messaging devices and/or cell phone combination devices(e.g. a HANDSPRING TREO device, manufactured by PALMONE, INC.), and personal digital assistants. The keyboard  100  includes a plurality of key structures  120  that are distributed to span in a horizontal direction (X) and a vertical direction (Y). In an example provided, the key structures  120  are provided in a QWERTY layout on the surface  102 . As such, most (if not all) key structures  120  may be assigned a letter and possibly one or more alphanumeric characters, although some key structures may be assigned functions (e.g. Enter). The assignment of letters, functions (e.g. “Enter”) and other alphanumeric characters, may be displayed with the key structure  120  through artwork or print. In an example provided by  FIG. 1 , 30 key structures  120  are provided to accommodate 26 letters and 4 special keys or functions, although more or fewer can be included in the keyboard  100 . To accommodate a general QWERTY layout, an embodiment provides that the key structures  120  are distributed in at least three horizontal sets  122 . In the example provided, the horizontal sets  122  are rows, or substantially linear in the horizontal direction (X). However, as described with other embodiments, the horizontal sets  122  may extend in the horizontal direction, while being staggered or arcuate (such as to form a “smile”). 
     According to an embodiment, an overall horizontal dimension of each horizontal set  122  consists primarily of a sum of the horizontal dimensions of the individual key structures in that horizontal set. With reference to  FIG. 1 , an embodiment provides that a dimension of any horizontal set  122  represented by TW is substantially or approximately equal (e.g. within 90%) to a sum of a maximum width W of each key structure  120  in that horizontal set  122 . 
     In  FIG. 1 , adjacent key structures  120  in each horizontal set  122  nearly abut one another. In an embodiment, the adjacent keys are nearly abutting if adjacent keys have the appearance of being abutting, when in fact individual each key structure  120  are separated from adjacent key structure that appear to be abutting. Adjacent key structures may appear to be abutting if no space or structure appears to separate the key structures. However, while the key structures may appear to be abutting, sufficient separation does exist between abutting key structures which enables any key structure to be moved inward independently and freely of adjacent key structures that appear to be abutting. Thus, inward movement by one key structure  120  key does not translate to the nearly abutting key structure. In an implementation where individual key structures are aligned to make contact with and direct actuation members into electrical contacts, a distance of separation for nearly abutting key structures corresponds to a distance that is of the order of a tolerance level for assembling the housing and interconnecting components or layers (excluding the actual keypad)) to make the keyboard effective. For example, in implementations described with  FIGS. 11 ,  13 A,  13 B,  14 A,  14 B,  15 A, and  15 B, the tolerance level may be tied to individual tolerances for assembling a stack assembly comprising an actuation member layer, illumination layer, electrical contact layer and/or any other layer or element for the assembled and integrated stack. The tolerance level of the stack may comprise the sum tolerances provided by placement of each layer that forms the stack. According to embodiments, a separation distance between nearly abutting key structures is less than 0.6 mm, and more preferably, less than or equal to about 0.1 mm. In one implementation, a separation distance between nearly abutting key structures is about 0.05 mm. 
     While an embodiment such as described by  FIG. 1  provides for nearly abutting key structures  120 , it should be notes that other embodiments may provide for a greater separation between the adjacent key structures  120  of the horizontal sets  122 . For example, the separation between adjacent key structures  120  of the horizontal sets  122  may range to about 0.60 mm to 0.75 mm, so that the key structures  120  are tightly spaced, but not necessarily nearly abutting. An example of such an embodiment is shown with  FIGS. 4A and 4B . 
     In an embodiment of  FIG. 1 , adjacent horizontal sets  122  are separated from one another by strips  112  of housing  110 , forming regions of the surface  102 . As such, key structures  120  that are nearest or most proximate to one another in the vertical direction (Y) are spaced-apart. As described in  FIG. 2B , individual key structures  120  may extend or be supported underneath the housing  110  in the vertical direction (Y), as the horizontal sets  122  are sufficiently spaced apart to provide for the housing strips  112 . As described with an embodiment of  FIG. 2B , sub-layer extensions may extend from each key structure  120 , underneath the surface  108  and just under a top visible edge  127  and bottom visible edge  129  of that key structure. The sub-layer extensions hold in place on the housing the individual key structures and/or the keyboard (or portions thereof, depending on whether the key structures are provided on a carrier or carrier segments). 
     The layout of keyboard  100  as its spans the horizontal (X) and vertical (Y) directions may have several variations and alternatives. For example, while  FIG. 1  illustrates each horizontal set  122  being aligned in the vertical direction, other implementations may stagger each horizontal set. Likewise, the horizontal sets  122  may be provided with less linearity, such as in a curved or “smiley face” configuration, or staggered at one or more locations. 
     In an embodiment shown by  FIG. 1 , individual key structures  120  are shaped to occupy a greater amount of area on surface  108  of housing  110 . In one embodiment, a majority of the key structures  120  are each provided a footprint  128  that is oblong, and an exterior surface that has at least one outward curvature (see  FIG. 2A  and  FIG. 2B ). The footprint  128  corresponds to the two-dimensional space occupied by the key structure on the surface  108  of the housing  110 . By being oblong, the footprint  128  of a particular key structure  120  (e.g. the letter “I”) has a maximum length L that is greater than its maximum width W. In one embodiment, the footprint  128  is symmetrical about the lengthwise axis. For example, the particular shape of key structures on the interior of the keyboard is rectangular. Other oblong shapes for footprints of key structures are possible, such as elliptical or a rectangular/ellipse combination. In an embodiment shown, a lengthwise direction  126  of the footprint  128  for the majority of key structures  120  coincides with the vertical axis (Y) and the non-limiting dimension of the mobile computing device. In another embodiment, the lengthwise direction  120  of the footprint  128  for the key structures  120  may be tilted with reference to the vertical axis (Y). 
     Not all key structures may be provided with the oblong and/or symmetrical key structures. In an example provided by  FIG. 1 , boundary key structures  121 , which are provided at the boundary of each horizontal set  122 , may have a different shape than the other key structures in the keyboard. In one implementation, the boundary key structures  121  have the same length dimension, or shaped to be oblong, but are non-symmetrical. For example, a boundary side  123  of each boundary key structure  121  may be curved, rather than linear, so as to provide that key structure the non-symmetrical footprint. Furthermore, the keyboard  100  may include numerous other key structures, such as application keys, number keys, a space bar etc. Many of these key structures may have different shapes and orientations. According to an embodiment, a majority of the key structures of the keyboard are shaped to include the oblong footprint and the symmetry about the lengthwise axis  126 . In an implementation shown, these key structures  120  are non-boundary key structures that are assigned letter values and more likely to be heavily used. 
     In addition to the footprint design, individual key structures  120  may be provided with an outward curvature on an exterior surface  144  (see  FIG. 2A  and  FIG. 2B ). When the thickness or height of the individual key structure is viewed, the exterior surface may be convex. As will be described, the outward curvature facilitates the user in making better key strikes, in part by providing a surface that hinders inadvertent finger slippage and movements. In one embodiment, individual key structures  120  (specifically, at least those with symmetrical and oblong footprints) are provided a curvature about one axis. In an embodiment, the curvature is provided about the lengthwise direction  126  of the individual keys, which in the example provided by  FIG. 1 , corresponds to the vertical axis (Y). As will be described, the curvature may be symmetrical, so as to coincide with a centerline of an individual key structure  120 . A result is that the individual key structure  120  is “barrel shaped” so as to extend from surface  108  in the form of a partial cylinder. 
       FIGS. 2A and 2B  are side cross-sectional views along respective lines A-A and B-B of  FIG. 1 , according to an embodiment. The cross-section of  FIG. 2A  illustrates adjacent key structures  120  of one of the horizontal sets  122 . Each key structure  120  may extend a height h above the surface  108 . In one embodiment, a key structure portion  141  extending from surface  108  is includes a rectangular base  143  and the exterior surface  144  having an outward curvature (e.g. convex), so as to form a cylindrical area over the surface  108 . The curvature of key structures in  FIG. 2A  is about the vertical axis (Y). In another implementation, the portion  141  extending from surface  108  may omit the rectangular base and provide only the outward curvature. The user may make contact with a finger or stylus to the exterior surface  144  to direct the individual key structure inward into the housing  110 , causing actuation of that key. 
     In one implementation, the exterior surface  144  has a peak  146  at a centerline of the key structure, with a symmetrical inward curvature  147  that extends from peak  146  towards the lateral edges  148 ,  148  of the individual key structure  120 . A horizontal distance between lateral sides  148 ,  148  represents the width W of the key structure  120 . 
     In an embodiment, a separation t between adjacent key structures  120  in the horizontal sets  122  may be reduced or minimized, so that the key structures are nearly abutting. In one embodiment, the separation represented by t is less than 0.1 mm, and preferably between 0.04 mm and 0.06 mm. In one implementation, this distance is about 0.05 mm. Other embodiments enable greater separation between key structures, while maintaining the nearly abutting relationship between adjacent horizontal key structures. For example, the key structures may be up to 0.7 mm spaced apart. 
     A bottom portion  149  of the key structure  120  may extend underneath the surface  108  of the housing. In an embodiment, the bottom portion  149  may be aligned with and/or connected to a corresponding actuation member  152  that move inward with insertion of the key structure  120 . When the key structure  120  is struck and moved inward, the corresponding actuation member  152  makes contact with an aligned electrical contact, thereby actuating an electrical signal to processing resources of the computing device. The alignment of each key structure, its corresponding actuation member  152 , and the aligned electrical element enable processing resources of the mobile computing device to correlate key strikes to a particular value, such as a particular letter of the alphabet. In one embodiment, the actuation members  152  are joined or integrated with the corresponding key structures  120 . For example, each actuation member may be molded or otherwise formed into a bottom surface of the corresponding key structure. In another embodiment, the actuation members  152  may be separately formed from the key structures  120 . With embodiments described with  FIG. 11  and elsewhere in this application, the actuation members  152  may form part of a stack assembly that is inserted underneath the keyboard  100 . Such a stack assembly may also include the aligned electrical contacts, as well as an illumination layer. In an embodiment, the distance t may be less than or equal to the tolerance level for assembling the stack for the keyboard  100 . 
     The cross-section of  FIG. 2B  illustrates adjacent key structures  120  in different horizontal sets  122 . From a perspective shown by  FIG. 2B , each key structure  120  extends the height h from the surface  108  with no curvature. The length L of the key structure  120  may be defined as a distance between a top edge and a bottom edge  127 ,  129  of the key structure  120 . The key structures  120  may extend from openings  154  formed in surface  108  of the housing  1110 . In one implementation, each opening  154  is extends lengthwise in the horizontal direction (X) to accommodate an entire horizontal set  122 . Alternatively, each opening  154  may accommodate only an individual key structure  120 , or some other combination of key structures. 
     Below the housing  110 , the key structure  120  may include extensions  155  that extend underneath an interior formation  156  of the housing  110 . The interior formation  156  may provide additional space to accommodate lateral extensions  155  of the key structure  120 . At the same time, the interior formation  156  overlays the lateral extensions  155  to prevent the key structure from falling out of the housing  110 . In this way, an embodiment provides that individual key structures  120  have housing support on their respective vertical edges, but not their lateral edges  148 ,  148 . In  FIG. 2B , lateral extensions  155  of the key structures  120  extend underneath the housing  110  at edges  151 ,  153 . 
     In an embodiment, a distance T separates proximate key structures  120  in the vertical direction (Y). According to an embodiment shown by  FIG. 1 , the distance T separates adjacent horizontal key sets  122 . The housing strip  112 , occupying an area extending the distance T, may be visible to the user. In one implementation, the distance T measures between 1.0 and 5.0 mm, and more preferably between 2.0 and 4.0 mm. 
     From the perspective shown in  FIG. 2B , insertion of the key structure  120  causes actuation member  120  to move inward and trigger an electrical contact. Mechanisms such as described in  FIG. 2A  (e.g. integrated actuation member  152 ) or elsewhere in this application (e.g. modular mechanical stack) may be used to correlate insertion of the key structure  120  and actuation of a corresponding electrical signal. 
     With reference to  FIGS. 2A and 2B , individual key structures  120  may be provided on one or more carriers or carrier strips. In one implementation, for example, the key structures  120  may be molded, joined or otherwise connected or integrated to a single carrier  159 . The single carrier  159  may extend underneath the housing  110  in both the X and Y direction. Alternatively, the carrier for the key structures  120  may be in the form of a strip that extends to provide key structures for individual horizontal sets  122 . 
     In one embodiment, a spacing structure or formation may be provided at the juncture of the curved exterior surface  145  and the lateral edges  108 . The spacing formation may be in the form of a groove or scallop.  FIG. 2C  illustrates an implementation of the groove  160  (or scallop) at the juncture of each of the lateral edges  148 ,  148  and the exterior surface  144 . The formation enables the user to see and/or feel (through fingers) further separation between adjacent key structures  120  in the horizontal set  122 . 
     Key Structure Design 
       FIG. 3A  is an illustrative isometric view of an isolated key structure  220 , according to an embodiment of the invention. The key structure  220  has a base  210  that extends at least partially into the housing  110  (see  FIGS. 2A and 2B ). An exterior surface  244  extends over the base  210 , forming a cylindrical or barrel shaped surface to meet the user&#39;s finger tip or stylus. The key structure  210  is provided with an ornamentation  212  that is printed or otherwise formed on the exterior surface  245 . In one embodiment, an up-down orientation of the ornamentation  212  coincides with the vertical direction (Y) (SEE  FIG. 1 ). As a result of the key structure being elongated, ornamentation  212  may also be elongated, making the letter and/or characters assigned to the individual keys larger and more viewable to the user. The key structure&#39;s lengthwise direction  242  also coincides with the vertical direction (Y). A curvature of the exterior surface  244  is provided about the lengthwise direction  242 , with the peak of the curvature appearing at the centerline of the exterior surface  244 . 
     In one embodiment, lateral grooves  248 ,  248  may be provided to facilitate the user&#39;s ability to separate and select adjacent key structures in the horizontal direction (Y). The lateral grooves  248 ,  248  may extend the length of the key structure  120 . The particular type of space formation may vary. 
       FIG. 3B  is an illustrative isometric view of a key structure  220 , with an alternative outward appearance. In  FIG. 3B , the ornamentation  212  is provided within or underneath a body  268  of the key structure  220 . In an embodiment shown, the body  268  of the key structure  220  may be formed from a clear or translucent material, such as a clear plastic. The ornamentation  212  may be formed on a surface  214  or region underneath the body  268 , such as on a film layer (see e.g.  FIGS. 5A-5G ). 
     Non-Abutting Keyboard Design 
       FIG. 4A  illustrates an alternative keyboard layout that does not employ use of nearly abutting key structures, according to another embodiment of the invention. With reference to  FIG. 4A , a keyboard  300  may incorporate horizontal key sets  322  similar to a configuration such as shown in  FIG. 1 , except that adjacent key structures  320  in the horizontal key sets  322  are not nearly abutting one another. Rather, a spacing R may exist between adjacent key structures  320  in the horizontal sets  322 . The spacing may be sufficient in dimension to allow users to view into a gap formed by the adjacent key structures  320 . A housing structure in the spacing R, or a space interior to the housing may be readily viewable to the user. For an implementation that employs a stack assembly, the adjacent key structures  320  in each horizontal key set  322  may be closely spaced, but still separated by a distance that is non-abutting. Even if the key structures  320  are considered non-abutting, a relationship where TW is substantially or approximately equal (within 80% or 90%) of the sum of the individual maximum widths W may still hold true. 
     According to an embodiment, the adjacent key structures  320  in each horizontal key set  322  are spaced by a distance that exceeds 0.75 mm. In one implementation, the range of separation between adjacent key structures  320  is between 0.75 and 1.5 mm, and more preferably of the range of 1.0 mm. The separated distance between the key structures  320  may refer to a minimum distance between the two structures as they extend above the surface of the housing. 
       FIG. 4B  illustrates adjacent key structures  320  of one of the horizontal key sets  322  in the keyboard  300 . In contrast to an embodiment such as shown by  FIG. 2A , the adjacent key structures  320  are separated by the distance R, which is sufficient in dimension to not provide the appearance of being abutting. As such, this distance permits the user to view an underlying space or region between the key structures  320 . In an embodiment, the distance R is still sufficiently small to avoid the need for providing the housing surface  108  in between the key structures in the horizontal sets  322 . In another embodiment, the dimensions of the key structures  320  may be made more narrow in the horizontal direction to make extension of the housing surface  108  in between the key structures of the horizontal sets  122  practical. 
     Keypad Manufacturing Processes 
       FIG. 5A-5G  illustrate a manufacturing process for producing a keyboard having nearly abutting key structures, as described with  FIG. 1  and  FIG. 2A-2B , under an embodiment of the invention. A process such as described in  FIG. 5A-5G  allows for individual key structures to be placed sufficiently close to one another so as to qualify as being “nearly abutting”. As will be described, a process illustrated by  FIG. 5A-5G  creates separated sets of key structures that are interwoven together as part of the assembly process to form a keyboard  100  such as described in  FIG. 1 . Such a manufacturing technique provides an alternative to using standard molding techniques for forming the individual key structures of the keyboard  100 , as standard molding techniques are difficult to implement in a manner that allows key structures to be spaced by a distance that is nearly abutting to another key structure. In contrast to the standard molding techniques, the use of interweaving patterns to assembly separate key structure groups into one keyboard enables adjacent key structures  120  in the horizontal sets  122  of keyboard  100  to be placed sufficiently close to one another to be nearly abutting. As such, any reference to a numeral of  FIG. 1  is intended to illustrate a suitable or descriptive element for a particular step or process. 
     As shown in  FIG. 5A , a thin film  510  formed from polycarbonate or other flexible material is used as a base for individual key structures. A print or silkscreen image is created on the film to provide the ornamentations  512  that are to be placed on the individual key structures. In an example provided by  FIG. 5A , the ornamentations  512  are in the form of letters, although other ornamentations such as numbers and alternative characters may be printed on the film  510 . The placement of the ornamentations  512  coincides with where individual key structures are to be formed that carry those ornamentations. As will be described, the individual key structures will be formed in separate groups or sets that are subsequently interwoven together. The location where each key structure is to be formed is dictated by an interwoven pattern used, and not necessarily by the relative position of that key structure relative to other key structures in the keyboard layout (e.g. QWERTY layout). 
     In  FIG. 5B , a manufacturing step is shown where individual key structures  520  are formed on the film  510  at locations where corresponding ornamentations are provided. Each key structure  520  is formed over one of the ornamentations, so that is carries that particular ornamentation. 
     In  FIG. 5C , film  510  is cut to form separate key structure groups  515 ,  525 . In an example provided, each key structure group  515 ,  525  includes three key structures  520 . The particular interweaving pattern used in the example provided is one where each key structure group  515 ,  525  includes at (i) at least two keys from a given horizontal set  122  in the keyboard  100 ; (ii) the two key structures are in the given horizontal set are not adjacent to one another in the keyboard layout, but rather separated by at least one other key; and (iii) at least one key structure from another one of the horizontal sets  122 . As such, a void  523  exists between two key structures  520  of the same horizontal set  122 . A dimension D of void  523  may be equal to a sum of the width of an individual key structure and the separation distances between that key structure and each adjacent key structure in its particular horizontal set (with reference to  FIG. 2A , D=W+2t). A cut-out strip  513  of film  510  is used to join the key structures  520  of each group  515 ,  525 . In each group  515 ,  525 , the strip  513  extends a length to join the key structures  520  from the different horizontal sets. This length is about equal to the vertical separation between the horizontal sets  122  when the keyboard is formed. It should also be noted that the particular interweaving pattern used to form each key structure group is one of design choice. For example, other patterns may provide for key structure groups to include only key sets from a single row or horizontal set of keyboard  100 . 
       FIG. 5D  is a side cross-sectional views cut along lines C-C of  FIG. 5C , showing a cross-section of key structure group  515 . The strip  513  extends between and join key structures  520  from different horizontal sets  122 . The strip  513  is formed to include an upward bend  514  and plateaus  518  on opposite sides of the upward bend  514 . A differential t 2  represents the differential between the upward bend  514  and the plateaus  518 . The upward bend  514  separates the key structures  520 , with individual key structures  520  provided on each plateau  518 . 
       FIG. 5E  illustrates another one of the key structure groups  525  with strip  513  joining key structures  520 . This key structure group  525  is to be interlaced or weaved with the key structure group  515  of  FIG. 5D . In order to provide an accommodating interwoven structure, key structure group  525  is provided with a downward bend  524  to adjoin key structures  520  on different horizontal sets  122 . Each key structure  520  is provided on a corresponding plateau  518  that is raised with respect to the downward bend  524  by the differential t 2 . 
       FIG. 5F  illustrates a midframe  540  to hold two or more key structure groups  515 . The midframe  540  includes openings  542  to hold key structures that eventually hold key structures of a common horizontal set  122 . 
       FIG. 5G  illustrates that key structure groups  515 ,  525  are assembled in an interwoven fashion about the midframe  540 . In one implementation, the strip  513  of one of the key structure groups  515  may be attached to a topside  544  of the midframe  540 , with the key structures  520  of the group hovering in the openings  542  of the midframe. At the same time, the strip  513  of the key structure group  525  may be attached to an underside (not shown) of the midframe  540 , with its key structures  520  extending out of the respective openings  542 . The upward bend  514  and downward bend  524  enable the key structures  520  of the respective groups  515 ,  525  to be assembled in the interwoven manner about the midframe  540 , without the strip  513  of one key structure group being in conflict with the strip of another key structure group. Rather, in the example provided, the strip  513  of the key structure group  515  is provided above the midframe  540 , while the strip of the key structure group  525  is provided below the midframe  540 . Once the strips  513  of each respective key structure group  515 ,  525  are connected to the midframe  540 , the key structures  520  of the respective key structure groups float in the space provided by the openings  542 , enabling each of those structures to move inward. 
     A manufacturing process for forming a keyboard such as described in  FIG. 5A-5G  enables a separation distance between adjacent key structures to be tighter than what would normally be allowed should key structures be formed through standard molding techniques. Thus, for example, a process such as described in  FIG. 5A-5G  may be used to place key structures  520  within 0.05 mm of one another, while a traditional molding technique would require the key structures to be separated by a distance no less than 0.5 mm. 
       FIGS. 6A-6D  illustrate a different manufacturing process for forming a keyboard comprised of key structures, according to an embodiment of the invention. 
     In  FIG. 6A , a film of polycarbonate or similar material  610  is provided holes  612  where corresponding key structures  620  are to be formed. The holes  612  are used to provide material for molding the individual key structures  620 .  FIG. 6B  illustrates the formation of the key structures  620  over the corresponding holes  612 . 
       FIG. 6C  illustrates how individual key structures  620  are formed over the film  610  using a molding process. A material for forming the key structures  620  is passed from the underside  616  of the film  610  through each of the respective holes  612 . This may be accomplished by positioning gates for shooting the material against each hole  612  on the underside  616 . The material is then passed through the individual hole  612  and used to form the key structure  620  on a topside  618  of the film  610 . In one embodiment, the material pushed through the film  610  to form the individual key structures  620  is a resin material. The material may be made translucent or milky in order to make the ornamentations provided by the key structure  620  more noticeable, as well as to enable illumination from under the film  610  to illuminate the key structure  620 . An ornamentation  622  on each key structure may be made through a surface printing of the corresponding key structure after that structure is formed. Alternatively, the ornamentation may be formed on the film  610  before the formation of the key structure  620 . For example, the ornamentation  622  for each key structure  620  may be formed on the film at the region where each hole  612  is provided. The material used to form the key structure  620  may be translucent (e.g. clear resin), so that the ornamentation  622  underneath the key structure is visible, particularly with illumination from underneath the key structure  620 . 
     A manufacturing process such as shown by  FIG. 6A-6D  enables more precise formation of key structures  620  than would otherwise be possible using more traditional or common molding techniques. A process such as shown by  FIGS. 6A-6D  may yield spacing between key structures as described with, for example, embodiments of  FIG. 1  and  FIG. 4A . 
     Various other manufacturing processes and techniques exist for forming a keyboard or keypad, such as described with embodiments of the invention.  FIG. 7A-7E  illustrate another technique, in which a molding process can be used to form the individual key structures  720 , with ornamentation provided through an underlying film  710 . 
     In  FIG. 7A , a film  710  (e.g. polycarbonate material) is formed to include ornamentations  712 . The ornamentations  712  are printed on an underside  716  (or backside) of the film  710 . The film  710  may be formed from translucent material to enable the ornamentations to be visible from the topside  718  of the film  710 . 
       FIGS. 7B and 7C  illustrate that key structures  720  are formed using gates  730  on the topside  718  of the film  710 . The resulting key structures  720  may be formed through the gates to include a key structure shape. Thus, in contrast to an embodiment such as described with  FIG. 5 , the gates may be provided on the same side of the film  710  as the key structures that result from the molding process. Each key structure  720  may include a base region  722  over film  710  to stabilize the key structure on the film. 
       FIG. 7D  shows an optional step where film  710  is cut or slit. A resulting slit patter  732  is provided. In an embodiment shown, the slit patter  732  consists of slits that extend in the horizontal direction, so as to separate horizontal sets  122 . The slit pattern  732  may improve the clickability of the individual key structures  720 . 
       FIG. 7E  shows the completed keyboard, with key structures  720  molded on the topside  718  of the film  710 , and ornamentation  712  provided on the underside  716  of the film  710 . Separate rows  750  (or horizontal sets) of key structures  720  are provided. The spacing between adjacent key structures in a given row  750  may vary. In one embodiment, the spacing is of the range of 0.3-1.0 mm, so that the individual key structures are close, albeit not nearly abutting. 
     Keyboard Implementation on Mobile Computing Devices 
       FIG. 8A  is an isometric view of a keyboard separated from a mobile computing housing, according to an embodiment of the invention. The keyboard  800  includes key structure rows  812 ,  814 ,  816  and  818 , where key structures  820  that comprise the rows are arranged in a QWERTY layout. The perspective shown in  FIG. 8A  provides the first row  812  containing the “QWERTY” keys as being the most proximate. 
     Each key structure  820  includes a base  822  and an exterior surface  824 . The base  822  may at least partially reside within a housing of the mobile computing device. In one embodiment, the key structures  820  may be provided on a carrier  815 , or a combination of carrier strips that interconnect two or more of the key structures. The exterior surface  824  may include an outward contour along the vertical axis Y. As a result, each key structure  820  is provided a barrel or cylindrical shape on its exterior. A minimum horizontal distance  825  between the base  822  of adjacent key structures  820  of each row  812 - 818  is sufficiently small (e.g. 0.05 mm) to give each key structure  820  the appearance that adjacent key structures are abutting. As such dimension of horizontal distance  825  may be sufficiently small to preclude users from seeing between the bases  822  of the adjacent key structures  820 . In contrast, a minimum vertical distance  835  between key structures  820  adjacent rows does not give the appearance that the key structures are abutting. For example, a housing section, or an underlying surface of the keyboard extending the vertical distance  835  of proximate key structures, may be plainly visible to sight. 
     To distinguish adjacent key structures  820 , an embodiment such as shown by  FIG. 8A  provides for formation of a groove  840  or scallop on lateral edges of each key structure. Each groove  840  may separate the key structure  820  from an adjacent key structure in the row-wise direction. 
       FIG. 8B  illustrates a mobile computing device housing  870 , for use with an embodiment of the invention. The housing  870  may include a plurality of openings  860  to accommodate horizontal sets of key structures (e.g. horizontal sets  122  in  FIG. 1 ). As shown by  FIG. 8B , the openings  860  may extend in the X direction to accommodate the entire width (TW in  FIG. 1 ) of the horizontal set. As such, the openings  860  contain no intersecting housing structure to separate or laterally support adjacent key structures. The keyboard  800 , for example, may be coupled with the housing  870  so that the individual key structures  820  extend from a surface  862  of the housing. No horizontal support is provided between key structures  820  (other than the carrier  815 ). The absence of horizontal support and intersecting housing structures within openings  860  provide one mechanism by which key structures can be made nearly abutting. In contrast, the openings are spaced by the housing surface  162 , which provides a clearly visible separation between key structures in the vertical direction. 
       FIG. 9  is a frontal view of a mobile computing device, configured according to an embodiment of the invention. A device  900  such as shown in  FIG. 9  may have both text-messaging capabilities (e.g. email, instant message, etc.) and cellular-voice capabilities. As such, the device  900  requires both keyboard  910  and cellular phone functionality. Despite the dual functionality of the device  900 , the device is provided dimensions that are more in accordance with traditional cellular phones. A width (along axis X′) of the computing device  900  is the limiting dimension. As such, features of the mobile computing device that require the most area are elongated. In embodiment shown, the display  930  and individual key structures  920  of keyboard  910  are elongated in alignment with a length of the device  900  (along axis Y′). The keyboard  910  may be configured similar to embodiments such as described with  FIG. 1  and  FIG. 4A . 
     In addition to having elongated key structures, a dimension of the keyboard  910  may extend almost all of the width of a front panel  915  of the device  900 . As such, the width of the keyboard  910  is substantially equal to the width of the mobile device  900 . Furthermore, individual key structures  920  may be tightly spaced (either to be abutting or non-abutting), so that each key structure can have a maximum individual width. The result is a combination of relatively large key structures  920  on mobile computing device, having dimensions (specifically width) that is substantially that of a traditional cell phone. In one embodiment, the size of the computing device, in combination with the dimensions of the keyboard  910  and individual key structures  920 , allows for the user to hold the mobile computing device in one hand while readily operating the keyboard with that same hand. 
       FIG. 10  illustrates a frontal and bottom isometric view of the mobile computing device  900 , according to an embodiment of the invention. As shown, the individual key structures are tightly spaced together in the row-wise direction, either in abutting or non-abutting fashion. Each key structure  920  is provided a barrel shaped exterior, having an outward curve. This facilitates the user&#39;s selection of keys when operating the keyboard  910 . 
     Stack Assembly Overview 
     Embodiments described herein provide for a modular or integrally assembled stack that can be used to make keypads of mobile computing devices operable. Embodiments such as described with  FIG. 11  may be implemented in conjunction with a keyboard layout embodiment such as described with  FIG. 1  and  FIG. 4A . However, a stack such as described by embodiments of the invention may also be used with numerous other types of keypads or keyboards, including keyboards or keypads that are not included with embodiments of the invention. 
     According to one embodiment, a stack assembly is provided for use with a keyboard or keypad of a mobile computing device. In one embodiment, the stack assembly includes an electrical contact layer, and actuation member layer, and an illumination layer. The electrical contact layer includes a plurality of contact elements. The actuation member layer includes a plurality of actuation members are, wherein each actuation member is aligned so that an axial movement of that member causes a corresponding one of the plurality of contact elements to actuate. The illumination layer is configured to emit light to the keypad. 
     As used herein, the term “axial” movement also means vertical movement, or movement in a direction that is inward with respect to a housing of the mobile computing device. 
     The term “layer” refers to an occupied thickness. A layer may include more than one type of material, including sub-layers (e.g. underlying film). 
     In another embodiment, a mobile computing device is provided having a housing, one or more processors contained within the housing, and a keyboard comprising a plurality of key structures provided on a surface of the housing. Additionally, a modular stack assembly may be contained within the housing and operatively engaged with the keyboard to enable each of the plurality of key structures to be operated to register input with the one or more processors. 
     The terms “integral” or “integrally combined” mean that elements or components are combined to form a single or modular unit. For example, different materials and fabrication processes may be used to integrally form a stack, but after its formation, the stack may be treated as a single or modular unit. 
     The term “operatively engaged” means that two elements are coupled in a manner that is operative, assuming electrical power is provided if needed for operation of the coupled elements. 
     Throughout this application, numerous references are made to measurements, such as distances and positions. The use of language, such as “about” or “approximately”, is used to define or quantify such measurements should be assumed to have some margin of variation (e.g. plus/minus 5%) as deemed practical given the context of the usage. 
     Components of Modular Stack Assembly 
       FIG. 11  illustrates basic components of a stack assembly for use with a keypad or keyboard of a mobile computing device. A stack  100  includes an illumination layer  1110 , an actuation member  1120 , and an electrical contact layer  1130 .  FIG. 11  illustrates one simplified arrangement for the layers, with illumination layer  1110  provided most proximate a surface of a housing  1103  on which key structures  1108  of a keyboard  1105  (or other type of keypad set) are provided. The key structures  1108  may be extended from the housing  1103  through corresponding openings or apertures formed in the housing. The stack  1100  electronically interconnects or interfaces the keypad  1105  with a processor  1150  or processing resources of the mobile computing device. 
     The illumination layer  110  includes lighting resources that illuminate the keyboard  1105 , or at least individual key structures  1108  in the keyboard  105 . The electrical contact layer  1130  provides individual contact elements  1132  that are electrically interconnected via a printed circuit board, flex circuit, or other mechanism, to processing resources of the mobile computing device. Each contact element  1132  may be assigned to one of the key structures  1108 . The actuation member layer  1120  includes individual actuation members  1122  that are aligned with a corresponding contact element  1132  and key structure  1105 . Each individual actuation member  1122  travels with insertion of the corresponding key structure  1105  into the corresponding contact element  1132 , causing that contact element to be switched or otherwise actuated. The result is that the processing resources of the mobile computing device are provided a signal corresponding to insertion of the particular key structure  1108 . 
     While  FIG. 11  illustrates a particular order of placement of the layers in the stack  100 , other arrangements and ordering of the different layers of the stack are possible. In addition, other components may comprise the stack  100 . Some of these arrangements are described below. 
     In an embodiment shown by  FIG. 11 , each layer may be fixed, joined or statically placed to an adjacent layer, so that the layers that form the stack assembly or integrally combined. The integral formation of the stack  1100  means that the stack assembly can be treated as single unit, or as a module. As such, it is possible for the stack  1100  to be assembled separately from other components of a mobile computing device. For example, stack  1100  may be assembled as part of an original equipment manufacture (OEM) process. Subsequently, stack  1100  may be inserted as a modular component into the housing of the mobile computing device during a separate manufacturing or assembly process. 
     Numerous mechanisms and means may be employed in order to affix or statically interconnect the different layers of the stack  1100 . For example, embodiments described below employ adhesives to affix one layer of the stack  1100  to another layer. Other mechanisms, such as mechanical fasteners (e.g. screws, clips, snap-on couplings) may also be employed to secure one layer with another. 
     The placement of each layer that forms the stack  1100  may align to enable each key structure  1108  to be insertable and cause the corresponding element  1132  on the electrical contact layer  1130  to actuate. The actuation members  1122  enable key structure insertion and/or travel to translate into actuation of the corresponding electrical element  1132 . The electrical contact layer  1130  and the actuation member layer  1120  may be aligned so that each key structure  1108  of the mobile computing device is insertable to effectuate an input with processor  1150 . The processor  1150  may correlate the electrical contact element  1132  switched with the corresponding input. The illumination layer  1110  may also be aligned with the key structure  1108  so that light-emitting sources align with corresponding key structures  1108 . According to an embodiment, alignment structures and mechanisms may be used to align the layers of the stack  100  during its formation. For example, alignment pins and pin holes, ridges, and/or optical markers may be used to align one of the layers in the stack assembly  1150  with an adjoining layer. 
     Illumination Layer 
     The illumination layer  1110  illuminates the keyboard  1105  from within the housing  1103  of the mobile computing device. The illumination layer  1110  provides a medium on which light-emitting material or elements are provided. In one implementation, at least some of the key structures  1108  forming the keyboard  1105  may be made of translucent materials so that illumination from within the housing  1103  results in the key structures being illuminated to the user. In another implementation, regions in the keyboard  1105 , such as around perimeters of individual key structures, may be illuminated. 
     According to one embodiment, the illumination layer  1110  is formed from electroluminescent (EL) material. The EL material illuminates may uniformly (or substantially thereof) illuminate across at least one or more regions of the illumination layer  1110 . One result that can be achieved is that the keyboard  1105  may be sufficiently uniformly lit to avoid dark spots or darkened key structures  1105 . 
     In another embodiment, the illumination layer  1110  may be formed from another type of lighting source. In one embodiment, the illumination layer  1110  may comprise a carrier that is provided discrete light sources, such as light-emitting diodes (LEDs). The carrier of the illumination layer  1110  may be formed from any material capable of carrying the light sources and the electrical conductivity to those sources. The LEDs may be patterned on the surface of the illumination layer  1105  to illuminate the individual key structures  1105  from underneath. Various patterns may be used to distribute the LEDs on the illumination layer  1110 . Furthermore, other types of illumination sources may be used, such as incandescent light sources. 
     Actuation Member Layer 
       FIG. 12A  illustrates a general design for the actuation member layer  1120 , according to an embodiment of the invention. Reference is made to elements of  FIG. 11  for context. The actuation member layer  1120  includes a carrier  1124  from which the plurality of actuation members  1122  are provided. As illustrated by  FIG. 11 , each actuation member  1122  is aligned with a corresponding key structure  1108  and a corresponding contact element  1132  of the electrical contact layer  1130 . When a given key structure  1108  travels inward, that key structure  1108  may direct the corresponding actuation member  1122  into the contact element. In one implementation, the actuation members  122  extend inward from the carrier  1124  towards corresponding contact elements  1132  of the electrical contact layer  1130 . However, it is also possible for a portion of the overall length of each member  1122  to extend upward towards the key structure  1108 . 
     In an embodiment such as shown by  FIG. 12 , the carrier  1124  may extend under the keypad  1105  to provide individual actuation members for each key structure  1108 . The carrier  1124  enables the actuation members  1122  to be separately formed from the key structures  1108  and the electrical contact layer  1130 . This is in contrast to some past approaches, where actuation members are formed as part of the key structure  1108 , such as through extensions formed off of the bottom surfaces of the key structures. The carrier  1124  may be aligned and affixed to the electrical contact layer  1130  as part of an assembly process for the overall stack  1100 . Subsequently, the carrier  1124  may be aligned with the keyboard  1105  of the mobile computing device in a separate assembly process. 
     According to an embodiment, the individual actuation members  1122  may be formed to be substantially more rigid than the carrier  1124 . In one embodiment, the carrier  1124  is made from an elastomer or other flexible or compliant membrane to reduce resistance to inward travel by the actuation members  1122 , and the actuation members  1122  are made rigid to be responsive to a user inserting the corresponding key structure. An example of a construction for the carrier  1124  is a thin sheet of silicon-rubber. 
     As described in  FIG. 16 , slits or cuts may be formed onto the carrier  1124  in order to enhance the flexibility of the carrier  1124 . For example, three cuts may partially surround each member  1122 . The cuts lessen the overall resistance provided by the carrier  1124  when the key structure  1108  directs the member  1122  inward. 
     As will be described in greater detail with  FIGS. 17A-17E , different techniques for forming the actuation member layer  1120  may be employed. In one embodiment, the actuation member  1122  and the carrier  1124  are formed from an elastomer such as silicon-rubber or polycarbonate materials. In another embodiment, the carrier  1124  and the individual actuation members  1122  are formed from different materials that may be combined or otherwise joined, such as the silicon-rubber and hard plastic respectively. As further described by  FIGS. 17A-17E , various techniques may be used to form the actuation member layer  1120  independent of the other layers in the stack  1100 . For example, a co-molding process may be used to mold the hard or rigid material of the actuation member  1122  with the flexible material of the carrier. As another example, the actuation members  1122  may be separately joined to the carrier  1124  using adhesives or other forms of chemical bonds. 
     In one embodiment, an overall area of the actuation members  1122  is smaller than a footprint of the corresponding contact element  1132 . In one implementation, the ratio of a diameter of the actuation member  1122  to a diameter of the corresponding contact element  1132  is less than 1:2, and preferably of the range of 1:4. An overall length of the actuation member  1122  is sufficient to actuate the corresponding contact element  1132 . In one implementation, this length is about 0.5 mm. In an implementation such as described with  FIG. 12B , where contact elements  1132  are snap-domes, the overall height needed is about 0.3 mm, corresponding to the separation of the outer contact surface  1135  ( FIG. 12B ) from the inner surface  1136  ( FIG. 12B ). 
     Electrical Contact Layer 
     In an embodiment, the electrical contact layer  1130  includes a substrate  1134 , such as a printed circuit board or a flex circuit, on which the electrical contact elements  1132  are provided. Circuitry provided by the substrate  1134  may interconnect the electrical contact elements  1132  with the processor of the mobile computing device. 
       FIG. 12B  illustrates one of the electrical contact elements  1132  provided on the substrate  1134 . In an embodiment such as shown by  FIG. 11 , the electrical contact elements  1132  is snap-dome contact, having an outer contact surface  1135  and an interior contact  1136 . The outer contact surface  1135  may bend or curve outward over the interior contact  1136 . The outer contact surface  1135  and the interior contact  1136  may form a switch that can be actuated. In the absence of an external force, the switch is in an open state. Contact by the corresponding actuation member  1122  causes the outer contact surface  1135  to collapse inward, thereby making contact with the interior contact  1136 . When the stack is powered, this contact closes the switch formed by the outer contact surface and the interior contact  1136 . The result is that the processor is signaled a “key-down” event that indicates insertion of the corresponding key structure  1108 . 
     One advantage provided by the snap-dome construction is that the user is provided a tactile sensation when actuation occurs. This sensation is in the form of a “snap”, felt with the collapse of the outer contact surface  1135 . In the context of a mini-keyboard, the sensation informs the user that a key-down event was registered, so that the user can concentrate on viewing the key structures, and not the display of the mobile computing device. 
       FIG. 12B  illustrates the contact element  1132  partially covered with a sheath layer  1138 . The sheath layer  1138  is commonly used to enhance the tactile response that would otherwise be generated from the collapse of the outer contact surface  1135 . Typically, the sheath layer  1138  is formed from a material such as MYLAR, which is semi-rigid but collapsible. The sheath layer  1138  is normally affixed over an entire surface of the outer contact area  1135 . The actuation member  1122  may make contact with the sheath layer  1138  to cause the collapse of both the sheath layer and the outer contact surface  1135 , thereby enhancing the snap response for the user. 
     In an embodiment shown by  FIG. 12B , the sheath layer  1138  may include an opening  1139  to receive the corresponding actuation member  1122 . In this way, the actuation member  1122  makes direct contact with the outer surface  1135 , rather than with the sheath layer  1138 . Less resistance is thus provided to the actuation member  1122  in making the snap-dome contact snap. However, the sheath layer  1138  may be affixed to the outer contact surface  1135  so that inward movement of that surface causes the sheath layer  1138  to further enhance the snap-sensation. Thus, the enhanced tactile sensation provided by the sheath layer  1138  may be preserved, while less resistance is given to the user inserting the corresponding key structures. 
     With regard to a stack assembly, each layer that forms the stack  1100  may be integrated into the stack at a specific tolerance level or margin of error. The tolerance of each layer in the stack assembly is tied together. Thus, the actuation members  1122  are always aligned to make contact and actuate the corresponding electrical contact  132 . This is a direct result of assembling the stack as an independent unit. In embodiments in which the electrical contacts correspond to snap domes, the result of the tolerances in the layer of the stack being tied together is that the actuation members and domes remain perfectly aligned, ensuring both good electrical contact and tactile feedback. 
     Additionally, the tolerance for the integration of each layer in the stack may be cumulative, so that the overall tolerance of the stack  1100  is the sum, or at least the accumulation of the different tolerances. Furthermore, with regard to keyboard embodiments such as shown and described with  FIGS. 1 ,  2 A and  2 B, the tolerance level of the stack as a whole may correspond to the order of the separation between key structures  120  in the horizontal sets  122 . 
     Modular Stack Implementations 
       FIGS. 13A and 13B  illustrate a stack formation, under an embodiment of the invention. In  FIG. 13A  an exploded view of a stack  1200  is illustrated. The exploded view illustrates the different elements that can be used to form an assembled and modular stack  1200 . The stack  1200  may be placed underneath a keyboard  1205  comprising a plurality of key structures  1208 . In the example provided, ten key structures  1208  are shown to simulate a row of a QWERTY keyboard. 
     In an embodiment shown by  FIG. 13A , stack  1200  includes an illumination layer  1210  positioned proximate to the keyboard  1205 , an actuation member layer  1220  provided underneath the illumination layer  1210 , and an electrical contact layer  1230  provided underneath the actuation member layer  1220 .  FIGS. 11 ,  12 A and  12 B illustrate suitable constructions and implementations of the illumination layer  1210 , actuation member layer  1220 , and electrical contact layer  1230 , under an embodiment. More specifically, actuation member layer  1220  may include a carrier  1224  on which a plurality of actuation members  1222  are provided. The electrical contact layer  1230  may include a substrate  1234  having a plurality of electrical contact elements  1232 . As with previous embodiments, one type of electrical contact elements  1232  that can be employed are “snap-dome” contact elements. Additional information for construction and formation of the actuation member layer  1220  is provided with  FIG. 16  and  FIG. 17A-17E . 
     In an embodiment, the illumination layer  1210 , the actuation member layer  1220 , and the electrical contact layer  1230  are aligned and affixed to one another. According to an embodiment, a thin adhesive layer  1215  affixes the actuation member layer  1220  to the illumination layer  1210 , and a thick adhesive layer  1225  affixes the actuation member layer  1220  to the electrical contact layer  1230 . In one implementation, the thin adhesive layer  1215  is adhesive tape or film, such as VHB type adhesives manufactured by 3M. A thickness of the thin adhesive layer may range between 0.025 mm and 0.2 mm, and more preferably between 0.05 mm and 0.1 mm. In an embodiment, the thick adhesive layer  1225  may be positioned on the perimeter of the substrate  1134  and/or actuation member layer  1220 , so as to not contact any of the contact elements  1232  or actuation members  1222 . A suitable thickness for the thick adhesive layer  1225  may range between 0.3 mm and 1.0 mm, and more preferably at about 0.8 mm. A suitable type of adhesive for this layer may be open cell foam adhesive, such as high-density open cell urethane foam with acrylic adhesive manufactured by 3M. 
     In one embodiment, the illumination layer  1210  is formed from EL material. Placement of the illumination layer  1210  directly underneath the key structures  1208  permits maximum light output through the keypad  1205  and individual key structures  1208 . In one implementation, the key structures  1208  may be formed from translucent or clear material, so as to act as light pipes that emit light from the illumination layer  1210 . 
       FIG. 13B  is a side cross-sectional view that illustrates the placement of the assembled stack  1200  within a housing  1203  of a mobile computing device. Each layer that forms the stack  1200  is affixed to the adjacent layers. The thick adhesive layer  1225  may circumvent an interior region where the actuation members  1222  are positioned in contact or just above the electrical contact elements  1232 . The alignment of layers that comprise the stack  1200  may be rigidly maintained, while the key structures  1208  have limited lateral movement over the stack  1200 . In one embodiment, stack  1200  is employed with the keypad  1205  floating over it. The keypad may include a carrier formed from a flexible membrane, such as an elastomer (e.g. silicon rubber). The key structures  1208  may be molded onto the carrier of the key structures, and positioned within the housing to float over the stack  1200 . The floating keypad  1205  means that individual key structures  1208  have ability to move laterally, such as when contact by the finger or stylus of the user is received. The carrier of the key structures may extend just under the housing  1203 , and each key structure  1208  may extend from the housing through a corresponding opening or aperture, so that insertion of the key structure into the aperture causes the corresponding actuation member  1222  to inwardly travel and actuate the corresponding electrical contact element  1232 . 
       FIGS. 14A and 14B  illustrate an alternative design for a stack  1300 , under an embodiment of the invention. As with previous embodiments, stack  1300  includes an illumination layer  1310 , an actuation member layer  1320 , and an electrical contact layer  1330 . However, the respective layers are ordered differently than compared to some of the other embodiments described herein. In an embodiment such as shown by  FIG. 14A , the illumination layer  1310  is positioned to overlay the electrical contact layer  1330 . The illumination layer  1310  and the electrical contact layer  1330  may be separately attached using adhesives. The actuation member layer  1320  is positioned over the illumination layer  1310  and proximate to the housing  1203 . In order to enable keypad  1305  to be illuminated from the illumination layer  1310 , an embodiment forms at least a carrier  1324  of the actuation member layer  1320  from translucent, clear, or semi-clear (e.g. white translucent) material that illuminates with light. A thick adhesive layer  1325  may affix the actuation member layer  1320  to the combined illumination layer  1310  and electrical contact layer  1330 . 
     In one embodiment, the illumination layer  1310  is formed from EL material. By overlaying the electrical contact layer  1330 , the illumination layer  1310  may make contact with discrete points on a substrate  1334  of the electrical contact layer  1330 , as well as with portions of at least some of the contact elements  1332 . In an embodiment such as shown with  FIG. 12B , where the contact-elements  1332  are snap-domes, the illumination layer  1310  may overlay and contact the sheath layer  1138  ( FIG. 12B ). The actuation members  1322  may push against the illumination layer  1310  in order to cause the snap-dome contact element to switch. It is possible for an opening in the illumination layer  1330  to be provided in alignment with the opening  1139  ( FIG. 12B ) of the sheath layer  1138  in order to accommodate the corresponding actuation member  1222 . 
       FIG. 14B  illustrates the assembled stack  1300 , placed within a housing  1303  of a mobile computing device. The stack  1300  may be tightly aligned and formed as a separate component for the mobile computing device. As with an embodiment of  FIGS. 13A and 13B , a keypad  1305  may be formed from its own combination of a carrier and key structures  1308 . The carrier of the key structures may extend under the housing  1303  of the mobile computing device. The key structures  1308  may be molded, joined or otherwise formed on the carrier and extended over the housing  1303 . The keypad  1305  may float over the stack  1300 , with the openings in the housing  1303  acting as insertion guides for each key structure  1308  when it is inserted. As described elsewhere, each key structure  1308  may align with a corresponding actuation member  1322  and a corresponding contact element  1332 . 
     Even with use of a translucent material for the carrier  1324  of the actuation member layer  1320 , the placement of the illumination layer  1310  directly over the contact element layer  1230  reduces the amount of lighting emitted for the keypad  1305 , when compared to an embodiment such as shown by  FIGS. 13A and 13B . However, combining the illumination layer  1310  with the electrical contact layer  1330  enables the combined layers to be readily integrated with the actuation member layer  320 . Precise alignment and assembly is required only for the combined layer, the adhesive layer  1325 , and the actuation member layer  1320 . Assembly requirements are thus reduced, enabling the stack  1300  to be made with less expense and effort. 
       FIGS. 15A and 15B  illustrate an alternative construction in which a mask  440  is combined with an illumination layer  1410  within a stack  1400 .  FIG. 15A  is an exploded view of a stack design similar to an embodiment shown with  FIGS. 13A and 13B . The stack  1400  includes an illumination layer  1410  placed over an actuation member layer  1420 . The actuation member layer  1420  may be placed over the electrical contact layer  1430 . However, in contrast to an embodiment such as described with  FIGS. 13A and 13B , the mask  440  is superimposed on the illumination layer  1410  just underneath a housing  1403  of the mobile computing device. An example of how mask  1440  can be constructed is shown with  FIG. 16 . The mask  1440  serves to shade or block light from being emitted from diffusing. Rather, light may be focused to emit only from translucent key structures  1408 , or from space in the opening of the hosing where that key structure is provided. The result is that the lighting provides better contrast for regions that are desired to be lit, and less light to regions where the lighting is a distraction. 
     It is possible for an embodiment to use mask  1440  with an illumination layer that is combined or overlaid with the electrical contact layer, as described with embodiments of  FIGS. 14A and 14B . However, in an embodiment where there is an intervening layer (e.g. actuation member layer  1320  in  FIG. 14A  and  FIG. 14B ), the effectiveness of using the mask  1440  is reduced. 
       FIG. 16  is a frontal view of the different layers and elements that can be used to integrally form a modular stack  1500 , under an embodiment. An embodiment shown assumes the stack  1500  is for use with a thirty key keypad, such as found with many small-form factor computing devices using QWERTY keyboard layouts. More or fewer keys, and different keyboard configurations may be used to take advantage of the modular stack  1500 . For example, the stack  1500  may accommodate 9-12 keys for a standard numerical keypad found on the typical cell phone. For purpose of description, an order or arrangement as shown and described by an embodiment of  FIGS. 15A and 15B  is assumed when describing embodiments of  FIG. 16 . 
     In an embodiment shown, a stack may be assembled to include an illumination layer  1510 , an actuation member  1520 , a thick adhesive layer  1525 , an electrical contact layer  1530 , and a mask  1540 . As described with other embodiments, the illumination layer  1510  may be formed from EL material. Alternatively, the illumination layer  1510  may be formed from discrete light sources, such as LEDs or other forms of light emitting mechanisms. 
     The actuation member layer  1520  may comprise the carrier  1524  and a plurality of actuation members  1522  that extend away from the key structures in use. The carrier  1524  may be designed for maximum flexibility, while the actuation members  1522  may be structured to be rigid. To this end, the carrier  1524  may be formed from a flexible material and be provided slits  526  about individual actuation members  1522  in order to facilitate those actuation members to travel inward more freely. The particular slit configuration shown in  FIG. 16  is of design choice, and alternative slit patterns may be employed. For example, L-shaped corner slits about each action member  1522  may be used about rather than connected lines that partially circumvent each actuation member. 
     The adhesive layer  1525  may correspond to a perimeter layer that surface mounts to the electrical contact layer  1530  and/or the actuation member layer  1520 . The electrical contact layer  1530  may employ snap-dome contact elements for tactile response, as described above. However, other forms of contact elements may also be used, including contact diaphragms and tabs. 
     In one embodiment, mask layer  1540  is formed from a material that blocks the transmission of light. When placed over the illumination layer, light focuses and escapes from cut-outs  1542  formed in the mask layer  1540 . The cut-outs  1542  may be shaped to accommodate the shape of the desired illumination. In the case where translucent key structures are employed so that the key structures themselves are illuminated, the shape of the cut-outs may correspond to the shape of the key structures. For example, in  FIG. 16 , the cut-outs  1542  are rectangular in shape to accommodate similarly shaped key structures. 
     Actuation Member Layer Design and Formation 
     Various actuation member layers designs and formation techniques may be used to create a carrier on which actuation members may extend. In one embodiment, the carrier of the actuation member may be formed from a film (using polycarbonate or similar material) that is overlaid with silicon-rubber. The silicon-rubber may be shaped to have protrusions in the form of actuation members. The silicon rubber may be molded onto the film and designed to have a minimal thickness in regions other than where the actuation members are formed. The actuation members may extend a length (0.5 mm in one implementation) from the carrier so as to be able to actuate a corresponding contact element with insertion of the key structure. Once the actuation members are formed, the carrier may be die or laser-cut to have a slit pattern that makes the carrier less resistant to movement of the actuation members. 
       FIGS. 17A-17E  illustrate another technique for forming an actuation member layer, under another embodiment of the invention. In  FIG. 17A , a film  1702  is created of a desired dimension and shape. The film  1702  may be translucent, and/or colored, white, milky white (via print or ink) or clear. The film  1702  may be formed from a flexible material, such as silicon-rubber. In  FIG. 17B , holes  1712  or fie cut or otherwise formed in the film  1702 . The holes  1712  are positioned where the actuation members are to subsequently be formed. The holes  1712  subsequently act as gates for an injection mold that will form the actuation members. 
     In  FIG. 17C , a plurality of actuator members  1716  are molded through the film  1702 . The material used to form the actuation member  1716  is formed from a semi-rigid or rigid material, such as hard plastic. Due to the small dimension of the actuation member  1716 , conventional molding techniques may be unreliable for securely forming and maintaining the actuation member on the film.  FIG. 17D  illustrates a molding technique for forming the actuation members  1716  more securely and reliably. The actuation member  1716  may extend out of the underside  1722  of the film  1702 , while the actuation member is gated from the topside  1724  of the film. Thus, material used to form the actuation member  1716  is injected through the holes  1712 , using a molding medium angled with the topside  1724 .  FIG. 17D  illustrates two possible gate positions for the injection mold. A vertical gate  1736  may use a runner oriented vertically with the hole  1714  to pass the injection mold onto the underside  1722 . An edge gate  1738  may use a runner oriented at an angle to an edge of the hole  1714 . 
       FIG. 17E  shows that the film  1702  may be cut using, for example, die or laser-cutting, in a pattern that partially circumvents the individual actuation members  1716 . A resulting slit-pattern  1732  enhances the flexibility of the film  1702  and reduces the resistance of the actuation members  1716  to movement. 
     In an alternative embodiment, the actuator member  1716  may be formed from a material such as hard plastic that is molded on the underside  1722  of the film  1702 . As shown by  FIG. 17F , the actuation member  1716  may be provided a gate on the underside that results in the actuation member  1716  being molded to have a base  1742  and an extension  1744 . The base  1742  stabilizes the mold of the plastic, while the extension provides the narrow dimension needed for the contact element. Temperature-sensitive adhesive may be spot-placed on the film at locations where the actuation members are to be extended to assist adhesion of the molding onto the film. The adhesion of the adhesive may be triggered when hot mold for the plastic is placed on the film. 
     Mobile Computing Device Implementation 
       FIG. 18  illustrates an embodiment of the invention implemented within a mobile computing device  1800 . The mobile computing device  1800  includes a housing  1810  from which a keyboard  1805  is provided. Individual key structures  1808  comprising the keyboard  1805  may be arranged on a front panel  1812  of the housing  1810 . The mobile computing device  1800  may employ a QWERTY style keyboard, having at least one key structure for every letter in the alphabet, with additional key structures for spacing and special characters. As such, the keyboard  1805  may include over thirty key structures  1808 , including three rows of key structures having ten keys each. 
     A stack  1820  (shown in phantom) may be maintained within the housing. The stack  1820  may be formed according to an embodiment such as described above. As described, stack  1820  may include individual actuation members  1808  separately formed from the key structures that are responsive to a particular key structure traveling inward into the housing  810 . In one embodiment, the stack  1800  is integrally combined using techniques such as described with  FIGS. 13A ,  13 B,  14 A,  14 B,  15 A, and  15 B. The formation of the stack  1820  may occur before the mobile computing device  1800  or its keyboard  1805  are assembled. As such, the stack  1820  may be a modular component that can be inserted into the housing  1810  and made to operatively engage the key structures  1808 . 
     In  FIG. 18 , the keyboard design is to closely space key structures  1808  that extend in the row-wise direction.  FIG. 19  illustrates a different implementation of a mobile computing device  1900  in which a stack  1920  is provided, according to an embodiment of the invention. A keyboard layout of the mobile computing device  1900  provides individual key structures that are spaced both row-wise and vertically. Despite the variation in key structure spacing, stack  1920  may have similar design and dimensions as the stack  1820  shown in  FIG. 18 . The modularity of the stack design enables the use of similar designs in different keyboard layouts, as the case may be. 
     Number Assignment Technique 
     Mobile computing devices that incorporate cellular phone functionality and keyboards for entering text (e.g. for use in messaging applications) generally have a need to assign both numeric and character values to individual keys. Both types of characters need to be readily available to the user. For example, if the user wishes to make a phone call, the user will want to have key strikes recognized as numbers, not character entries. 
     With keyboards becoming small, the size of individual keys has also become smaller. For applications that require numeric entry (e.g. phone application), small key size leads to larger entry errors. This problem is particularly apparent with numeric keys since users typically operate mobile computing devices as cell phones using one hand. 
     Embodiments of the invention provide a number assignment technique to enhance the user&#39;s ability to enter numbers, particularly in the context of using a phone application on a smart phone or other mobile computing device. In an embodiment, a mobile computing device includes a keypad that is operatively connected to processing resources of the device. The mobile computing device may be equipped with a keyboard (e.g. with a QWERTY layout) having a plurality of keys or key structures. The keys provided may be identified in two sets: (i) a first includes keys that are individually actuatable to register a corresponding non-numeric character entry, (ii) a second set of the plurality of key structures are individually actuatable to register with the one or more processors a corresponding numerical entry. While it is possible for the first or second set of keys to have complete overlap with the other set, an embodiment contemplates that some, but not all of the keys in the first set and the second set have overlap. The second set of keys includes a plurality of key pairs, and each key pair each includes a first key and a second structure. According to an embodiment, the mobile computing device registers either of (i) actuation of the first key structure in a given key structure pair of the second set, (ii) actuation of the second key structure of the given key structure pair, and (iii) actuation of first key structure and the second key structure of the given key structure pair, to be of a single numerical value. 
       FIG. 20  illustrates a keyboard configured for implementation with a number assignment technique, according to an embodiment of the invention. A keyboard  2000  includes a plurality of key structures  2020  having both numeric marking  2004  and non-numeric markings  2006 . A first set of key structures  2015  includes all of the key structures displayed. A second set of key structures  2025  is delineated by shading. Each key structure  2020  in the second set  2025  is paired with another key structure of that set to form a key structure pair  2030 . According to one embodiment, a pair marking  2008  circumvents each key structure pair  2030  in the second set  2025 . 
     The keyboard  2000  may be operated in either numeric or non-numeric mode. In numeric mode, each key structure pair  2030  in the second set  2025  is assigned to a single number. If either key structure in any given key structure pair  2030  is struck, the mobile computing device interprets the key strike as the single number. Furthermore, an embodiment provides that if both key structures in the same key structure pair  2030  are struck at the same time, then the mobile device also recognizes that same single input. For example, with reference to  FIG. 20 , the following key strikes (identified by non-numeric markings  2006 ) result in the following input being registered when the mobile computing device is operated in numeric mode: 
                                             Key Strike   Input Registered                          D R G   4 1 5           G H H   5 5 5           E (TY) R T   1 2 1 2                        
The use of parenthesis in the above example are intended to illustrate the case of a simultaneous key strike.
 
     An embodiment such as described in  FIG. 20  recognizes that when a mobile computing device is operated in a numeric mode, fewer key structures will be required. The designation of key structures for use in key structure pairs  2030  provides a mechanism to increase the amount of key space needed by a user to register a single numeric input. In this way, the keyboard is more number friendly when used with the phone application or other numeric applications. 
     The marking pattern used on a mobile computing device facilitate usage of the mobile computing device in alternating numeric and non-numeric modes. As typical with small keyboards, the individual key structures are generally provided the non-numeric marking  2006  to indicate the value that will be registered by the mobile computing device when that key is struck, unless a mode is entered where the key structure is to correspond to another value. According to an embodiment, the numeric markings  2004  are treated differently. In one embodiment, the numeric markings  2004  are not provided on every key structure  2020  that can be struck to enter a numeric value. Rather, each numeric marking  2004  is assigned to an individual key structure pair  230  of the second set  225 . Additionally, the pair marking  2008  identifies the key pairs  2030  to the user. In embodiment shown by  FIG. 20 , the pair markings  2008  form a perimeter about both the numeric marking  2004  and the non-numeric marking  2006 . However, other forms of marking arrangements are possible to delineate key pairs, as well as their numeric and non-numeric values. For example, each key pair  230  may be provided a different color for the numeric marking  2004  or non-numeric marking  2006 . 
     An embodiment such as described in  FIG. 20  may be implemented with a keyboard such as described with  FIGS. 1 ,  4 A or elsewhere in this application. In particular, an embodiment may utilize tightly spaced keys to enhance the user&#39;s perception of key pair set  230 . For example, in  FIG. 20 , pair markings  2008  are interrupted by separation lines  2035  of the key structures  230 . However, since the separation lines  2035  are thin (such as the case where adjacent key structures are nearly abutting as described with  FIG. 1 ), pair marking  2008  may, relatively speaking, be visually uninterrupted by the separation lines. 
     As shown in  FIG. 20 , not all number values require separate key structure pairs  230 . For example, the number “0” requires just one individual key structure  2020  (see  FIG. 22 ). 
       FIG. 21  illustrates a system in which keys or key structures can be paired (or clustered) to provide a single numeric value, or separate non-numeric values. A system includes one or more processors  2110  and a keyboard  2140 , implemented within, for example, the confines of the housing of a mobile computing device. The processors  2110  may execute one or more numeric applications  2120  and one or more text-based applications  2130 . An example of a numeric application  2120  includes a phone application or a calendar application. An example of a text-based application includes an email or document editing application. 
     The processor(s)  2110  may execute each of the applications with different sets of rules. Specifically, the numeric application A user may operate keyboard  2140  to enter a key strike sequence  2142 . The rules for each application may govern how that application interprets the input. For example, if the numeric application  2120  is operating (the user opens phone application), a set of rules  2122  cause the processor  2110  to interpret the key strike sequence according to pair sets: designated pairs of keys have a single value. Key strikes that correspond to keys not in the set containing key strike pairs may be handled differently (e.g. they may be ignored). If the text-based application is operating (the user opens email application), a set of rules  2132  cause the processor  2110  to interpret the key strike sequence  2142  according to a rule where each key strike has an alphanumeric value. 
       FIG. 21  illustrates one mechanism for establishing the key structures having dual character/number assignments are to be interpreted for their numerical values. An embodiment such as described above provides that the numeric mode is established with the operation or execution of a numeric application (e.g. Phone or Calculator application). Other mechanisms may also be employed to establish a “number lock” on the set of keys that have number assignments. For example, the user may be able to enter an input that establishes a number lock, so that characters having dual assignments of numbers and characters are interpreted only as numbers. The number lock may even be established in a text-based application. For example, the user may enter the number lock when drafting an email for purpose of writing a phone number out. 
       FIG. 22  illustrates a mobile computing device, configured with a key assignment scheme in accordance with an embodiment of the invention. In  FIG. 22 , a mobile computing device  2210  includes capabilities for messaging, cellular phone and voice and other applications. A keyboard  2215  includes key structures  2220  that are each assigned to a letter or character when text mode is employed. For numeric mode, the key pairs  2230  are identified using markings  2208 . Each key pair  2230  includes its own number value. A key strike in a given key pair  2230  results in (i) a letter or character assigned to that specific key structure if the device  2210  is in text mode, or (ii) a number assigned to the key structure pair of that key structure if the device is in number mode. 
     Alternative Key Pair/Group Assignment Schemes 
     While an embodiment shown uses two key structures to form key structure pairs having one numerical assignment, other embodiments may utilize three or more key structures for single numeric assignments. For example, three key structures  220  may be assigned to one another. 
     Furthermore, the assignment of number values is just one application for pairing or grouping key structures. For example, a device may have a keyboard that can be operated to enter text and to enter input for gaming applications. Gaming applications normally require just a few buttons. In such an application, a cluster of keys (e.g. four) may be delineated to correspond to one gaming function (e.g. “Action”). The delineation may include use of markings that visually separate the cluster for the user, while also providing markings to show letters. 
     Conclusion 
     Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments. As such, many modifications and variations will be apparent to practitioners skilled in this art. Accordingly, it is intended that the scope of the invention be defined by the following claims and their equivalents. Furthermore, it is contemplated that a particular feature described either individually or as part of an embodiment can be combined with other individually described features, or parts of other embodiments, even if the other features and embodiments make no mentioned of the particular feature. This, the absence of describing combinations should not preclude the inventor from claiming rights to such combinations.