Abstract:
A keypad of a portable wireless terminal includes a sheet having a plurality of holes, a plurality of keys inserted into respective ones of the holes, and a silicon adhesive layer on a lower surface of the sheet to fix the keys to the sheet. A protrusion at a lower surface thereof contacts a dome switch. The keys are firmly mounted at a precise position, and more beautiful design can be realized since a decoration line or a decoration shape can be easily formed to set an appearance of the keys.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to input devices, and more particularly to an input device for inputting information into an electronic system including but not limited to a portable wireless terminal. The present invention is also a method for a keypad of this type. 
   2. Background of the Related Art 
   Communication terminals generally include telephones commonly used in the home or office and portable wireless terminals. Portable wireless terminals have developed more functions as wireless communication techniques have evolved. These functions include voice transmission/reception, letter message transmission, data transmission, and image transmission/reception. 
   A keypad used as a switching device for generating input signals and setting various functions is used not only in general telephones but also in portable wireless terminals. Keypads of this type have keys on which numbers and letters are printed, and the keys are assembled in a front housing of the terminal in an operative state. The keypad is used to perform various functions, and is externally exposed thereby making its design, preference pattern, visual effect, and endurance very important. 
     FIG. 1  shows disassembled view of a portable wireless terminal. This terminal includes a folder  2  coupled to one side of a front case  1  by a hinge  3 . A rear case  4  is also coupled to the front case. A printed circuit board  5  has contact points  5   a  arranged at an inner space formed between the front and rear cases. A dome switch assembly  6  is located adjacent the printed circuit board and a keypad made of a hard material is arranged on the dome switch assembly. The keypad is formed of a thin-film sheet  11  and keys  12  are formed on an upper surface of the sheet. The keys are inserted into respective holes  1   a  in the front case in such a manner that a part of each key is exposed to an outer portion of the terminal through the holes  1   a.    
     FIG. 2  shows an isolated view of a related-art keypad which may be inserted into the portable wireless terminal shown in  FIG. 1 , and  FIG. 3  is a sectional view taken along line A-A of  FIG. 2 . In the keypad, a dome switch  6  having an elastic force and a restoration force is mounted on the printed board  5 , and keypad  10  having a key  12  formed on one part of sheet  11  is located adjacent the dome switch. A soft silicon material  13  is molded into the key. 
   The aforementioned keypad of the related art has a number of drawbacks. One drawback relates to the material from which keys of the keypad are made. As shown in  FIGS. 2 and 3 , each key of the keypad is made of a hard material, which makes its forming operation difficult and makes it difficult to change the key into various designs. That is, since a film of hard material is used to form each key, shapes of the keys are limited. For example, an edge part of each key is smashed which gives the key an ambiguous appearance. Also, since it is difficult to form a decoration line for beauty at the key surface, the appearance of the key is not beautiful. 
     FIG. 4  shows another related-art keypad for a portable wireless terminal, and  FIG. 5  is a sectional view taken along line B-B of  FIG. 4 . In these figures, dome switch  6  is mounted on a printed circuit board  5  and a supporting member  23  of silicon material and having a protrusion  23   a  is located on the dome switch. A keypad  20  is installed on an upper surface of the supporting member, and a plurality of keys  22  of plastic material are attached to predetermined positions on an upper surface of a pad sheet  21  of the keypad using an adhesive (not shown). 
   The aforementioned related-art keypad also has a number of drawbacks. For example, when appearance is processed by spray painting and ultraviolet coating, the painting and coating are applied to an adhesion part of the keys. As a result, the keys do not adhere to the keypad completely but are shaken, or an adhesion position of the keys becomes deteriorated or distorted. Also, since heights of the keys are different from one another based on the amount of adhesive applied to fix each key to the pad sheet, each key has a different feeling or touch which thereby degrades reliability of the product. Also, since the keys are not in precise alignment with the key holes in the front case, quality of appearance is deteriorated and the user has a degraded pressing feeling for the keys. 
   SUMMARY OF THE INVENTION 
   An object of the invention is to solve at least one the above problems and/or disadvantages of the related-art keypads discussed above. 
   Another object of the present invention is to provide a keypad of an electronic device such as but not limited to a portable wireless terminal, in which keys are easily and firmly fixed in precise positions of a keypad and relative to key holes in a front housing of the terminal. 
   Another object of the present invention is to provide a keypad of an electronic device, such as but not limited to a portable wireless terminal, which has keys of uniform height in order to improve key tactility during use. 
   Another object of the present invention is to provide a method of making any one or more of aforementioned keypads. 
   To achieve these and other objects or advantages, the present invention provides a keypad of a portable wireless terminal comprising: a sheet in which a plurality of holes are perforated; a plurality of keys inserted into respective holes of the sheet; and a silicon adhesive layer adhered to a lower surface of the sheet s to fix the keys to the sheet and having a protrusion at a lower surface thereof in order to touch a dome switch. A stopping portion, protruding outwardly by being inserted into the sheet holes, is formed at a lower circumferential surface of the keys in order to be inserted into the holes of the sheet. 
   The present invention is also a method for fabricating a keypad of a portable wireless terminal comprising the steps of: punching-processing a plurality of holes at a file material of a sheet; inserting the keys into respective holes of the sheet; and forming a silicon adhesive layer at a lower surface of the sheet and thus fixing the keys to the sheet. The keys are inserted into the holes of the sheet by an insert injection molding method. 
   Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a disassembled view showing parts of a portable wireless terminal; 
       FIG. 2  is a view showing a related-art keypad which may be adapted for use in the portable wireless terminal of  FIG. 1 ; 
       FIG. 3  is a sectional view taken along line A-A of  FIG. 2 ; 
       FIG. 4  is a view showing another related-art keypad which may be adapted for use in the portable wireless terminal of  FIG. 1 ; 
       FIG. 5  is a sectional view taken along line B-B of  FIG. 4 ; 
       FIG. 6(A)  is a perspective view showing a portable wireless terminal according to a preferred embodiment of the present invention, and  FIG. 6(B)  is an exploded sectional view showing one portion of the keypad in the terminal of  FIG. 6(A) ; 
       FIG. 7  is a longitudinal section view showing a keypad of the portable wireless terminal according to the present invention; 
       FIG. 8  is a view for explaining a pin-point gate method which may be used to form the keys of the keypad of the present invention; and 
       FIG. 9  is a flow chart showing steps included in a method for making a keypad of a portable wireless terminal according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 6(A)  is a view showing a portable wireless terminal according to a preferred embodiment of the present invention,  FIG. 6(B)  is an exploded sectional view of a portion of a keypad included in the terminal of  FIG. 6(A) , and  FIG. 7  is a cross-sectional view of one key in the keypad shown in  FIGS. 6(A) and 6(B) . As shown, the terminal includes a folder  111  coupled to one side of a front case  110  by a hinge  111   a , which allows the folder to be folded. A rear case  120  is coupled to the front case. 
   A printed circuit board  130  having a contact point  130   a  is located at an inner space formed between the front case and the rear case. A plurality of dome switches  140  are respectively arranged on the printed circuit board  130  and a keypad  150  includes keys  152  in alignment with respective ones of the dome switches. 
   A plurality of holes  151   a  are formed at an upper surface of a sheet  151  of the keypad. Keys  152 , preferably made of a plastic material, are inserted and assembled into respective ones of the holes  151   a  using, for example, an insert injection-molding process. A stopping portion  152   a  is preferably formed at a lower portion of the keys  152 . This stopping portion may be integrally formed with each key as a result of the injection-molding process. 
   For example, during injection molding a recess  180  may be formed in the key preferably along its outer surface. If desired, the recess may traverse a circumferential path around this. As shown in  FIG. 6B , inner surfaces  186  and  187  may be provided above and below the recess contact portions of the sheet near each hole. This contact and more specifically the stopping portion  152   a  formed at least in part by surface  187  operates to hold the key firmly within the hole. 
   A adhesion layer  153 , preferably made of silicon, is adhered to a lower surface of the sheet  151  and preferably to a periphery of stopping portion  152   a . The adhesive layer, thus, provides an additional force for fixing the keys  152  into the holes of the sheet. A protrusion  153   a  is formed at a lower surface of the adhesion layer in order to touch or at least be in close proximity to the dome switches  140 . 
   In the keypad of the portable wireless terminal of the present invention, if a user presses key  152  for generating a signal which, for example, corresponds to a dialed number or a specific terminal function, the protrusion  153   a  of the adhesion layer  153  presses against the dome switches  140 . The dome switch deflects in response to this force, thereby touching a contact point  130   a  on the printed circuit board to initiate a desired operation. 
   As previously discussed, each key  152  of the keypad is firmly held within a respective hole  151   a  of the sheet by stopping portion  152   a , which is preferably but not necessarily formed at a lower surface of the keys. The optional adhesive layer is adhered to a lower portion of the key and the sheet. In this position, the adhesive layer provides an additional force for fastening the keys to the holes in the sheet. Through the stopping portion and/or the adhesive layer, the keys in the keypad of the present invention are assured of being firmly fixed on the sheet and precisely located relative to the key holes in the terminal housing. 
     FIG. 8  is a view explaining a pin-point gate method which is preferably used to form the keypad of the present invention. In a state where keys  152  are inserted into holes  151   a  of the sheet, the sheet is turned over between a lower metallic pattern M 1  and an upper metallic pattern M 2 . An adhesive material (e.g., silicon)  153  is then injected into the lower portion of the keys through an injection opening H of the upper metallic pattern M 2  in accordance with the pin-point gate method, thereby simultaneously and very rapidly assembling the keys onto the sheet. 
     FIG. 9  is a flow chart showing steps included in a method of making a keypad of a portable wireless terminal according to a preferred embodiment of the present invention. This method includes forming a plurality of holes in a sheet of preferably hard film material using, for example, a punching machine. The holes will accommodate one or more keys of the keypad, S 210 . Next, keys of preferably a plastic or rubber material are inserted into the respective holes of the sheet. This may be accomplished by an insert injection molding method, S 220 . The sheet is then turned over to assume a state where the keys are inserted into respective holes between a lower metallic pattern and an upper metallic pattern. Adhesive material is then injected into the lower portion of each key using a pin-point gate method, which preferably involves injecting the adhesive through more than two injection openings, thereby firmly mounting each key to the sheet. 
   In the first step S 210 , by using a punching machine, the plurality of holes are formed at predetermined positions in the sheet. In the second step S 220 , the keys are inserted into the holes of the sheet preferably using an insert injection-molding method, which allows the keys to be molded within the holds of the sheet. At this time, because the material which is injected into the sheet holes overlaps onto both sides of the portion of the sheet forming the holes, the recess and stopping portion previously discussed will be formed. 
   For reference, in the insert injection-molding method, composite components may be fabricated by integrating a workpiece in with resin. This is accomplished by putting or inserting the workpiece in the metallic pattern and then injecting the resin. The sheet of the present invention corresponds to the work piece. 
   The stopping portion of the keys formed by the insert injection molding method is advantageous because it prevents each key from being released from a respective hole of the sheet. The keys can be formed of plastic (resin), rubber, or another suitable material to suit the user&#39;s taste. 
   Unlike related-art keypads, in the keypad of the portable wireless terminal of the present invention keys are inserted into and held within holes of a sheet using a key molding metallic pattern. As a result, all keys of the keypad are formed simultaneously, using the pin-point method which involves injecting injection material through more than two injection openings. Accordingly, it is easy to form a decoration line or a decoration shape at the appearance of the keys when the keys are formed and thus a beautiful keypad can be formed. 
   In the third step S 230 , the adhesive layer of soft material is formed at the lower portion of the sheet in order to provide additional force for fixing the keys within the holes of the sheet. This minimizes the impact applied to the dome switches and thus improves pressing tactility. The adhesive layer can be formed by bonding according to a general adhesive agent or by a rubber metallic pattern or by another known technique. Also, it is preferable to include a step for spray post-processing the appearance of the keys to thereby enhance tactility of the keys according to the user&#39;s taste. 
   As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.