Abstract:
The invention concerns an LCD connection for a communication unit to connect an LCD to PCB. The connection includes several parts to make the connection between the LCD and the PCB reliable, but still easy and cheap to assembly. It is also easy to dismantle since the connector is neither fixed mounted to the LCD nor to the PCB. The connector includes an LCD covered with an Indium Tin Oxide (ITO) pad, an Anisotropic Conductive Foil (ACF) layer on top of the ITO pad, at least one Double Flexible Printed Circuit (DFPC) located on the ACF layer, a spring connector and a PCB. The invention also includes a method for connecting an LCD to a PCB.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a Liquid Crystal Display (LCD) connection for connecting an LCD to a printed circuit board (PCB) in a communication unit. 
     2. Description of Prior Art 
     A connection between an LCD and a PCB in a communication unit is in many cases exposed to mechanical and other stresses, and specially when located in a communication unit that stress can be harmful to the connection between the LCD and the PCB. This is due to how a user handles his/her communication unit. It is not unusual that it is handled quite roughly and it might easily be dropped and thereby exposing the connection to stress. To reduce the of cost of assembling a communication unit it should be easy to assemble and also be possible to dismantle, which gives another set of demands on the connection between the LCD and the PCB. 
     In conventional solutions the LCD is provided with indium tin oxide (ITO) pads that electrically connects the LCD to a connector, and through that the connector connects to the PCB. The ITO pads are sensitive to contact with the surrounding and might easily react with the surroundings. One known way to avoid this is to attach the connector directly to the LCD, covering the ITO pads and thereby protecting them. Another solution is to cover the ITO pads with a metal film that protects the ITO pads. 
     U.S. Pat. No. 5,270,848 shows a liquid crystal apparatus that includes a laminated film made of an ITO film having a surface and a metal film on the surface. The connection electrode has been attached directly to the ITO film. 
     U.S. Pat. No. 6,025,644 shows a liquid crystal display device having input connection terminals connecting to output connection terminals using an Anisotropic conductive film (ACF) as binding. The output connection terminals are connected to a flexible printed circuit (FPC) using an elastic connector, i.e. a rubber connector. The FPC is connected to a PCB by inserting one end of the FPC into a connector on the PCB. 
     There are many ways to solve the connection problem between an LCD and a PCB, like having a fixed connection that can withstand any mechanical or other stress, but in most cases that will be avoided in the assembly of electronic products. The cost of assembling a fixed connection is too high. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an LCD connection for connecting an LCD to a PCB in a communication unit that allows the communication unit to be exposed to mechanical and other stresses while maintaining contact between the LCD and the PCB. 
     According to the claimed invention this objective is obtained by an LCD connection including an LCD provided with a plurality of connecting pads, a PCB is also provided with a plurality of connecting pads and a connector connecting said LCD to said PCB, where said connector includes springy metal parts between the connecting pads to establish contact with the LCD and the PCB. 
     Another object of the invention is to provide an LCD assembly for a communication unit that can easily be mounted and dismantled, but still remain reliable. 
     According to the claimed invention this objective is obtained by an LCD connection including an LCD having Indium Tin Oxide (ITO) pads covered by an Anisotropic Conductive Foil (ACF) layer, Double Flexible Printed Circuits (DFPC), a spring connector having springy metal ends and a PCB, where the spring connector is flexibly mounted on a lightguide that holds the LCD and the PCB together. 
     Yet another objective of the claimed invention is to provide a method for connecting an LCD to a PCB in a communication unit. 
     According to the claimed invention this objective is obtained by using a connector that is flexibly mounted between the LCD and the PCB and having conductive layer applied on the LCD to create a reliable connection. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will be explained more fully below, by way of example, in connection with preferred embodiments and with reference to drawing, in which: 
     FIGS. 1-2 shows in a perspective view a preferred embodiment of the communication unit according to the invention. 
     FIG. 3 schematically shows the essential parts of a telephone for communication with a cellular network. 
     FIG. 4 shows an exploded view of LCD assembly together with a PCB. 
     FIG. 5 shows a schematic cross section of an LCD connection according to the invention. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     According to a first aspect the LCD connection according to the invention will be described with reference to a hand portable phone, preferably a cellular/mobile phone. A preferred embodiment of this phone is shown in FIGS. 1 and 2, where a cellular/mobile phone is shown in perspective. As will be seen, the phone is provided with a front cover  2  having a window frame  3  encircling the protection window of the display assembly  1 . The cellular/mobile phone comprises a user interface having an on/off button  4 , a keypad  7 , a battery  14  (not shown), a display/LCD  1 , an earpiece  21  and a microphone  22  (not shown). In FIG. 2 the phone is shown from another perspective having back cover  13 . There is also shown in FIG. 2 a release device  23  for releasing the back cover  13  from the rest of the phone, and a horseshoe shaped edge  12 . The horseshoe shaped recess  12  aims to prevent the user from covering the internal antenna  24  (not shown) placed in the upper part of the phone with his fingers. Any covering of the antenna  24  by the user might disturb the function of the antenna  24 . The horseshoe shaped recess  12  is ergonomically designed to make the user place his fingers on it and not on the antenna part of the back cover  13 . 
     The keypad  7  has a first group of keys  8  as alphanumeric keys, by means of which the user can enter a telephone number, write a text message (SMS), write a name (associated with the phone number), etc. Each of the twelve alphanumeric keys  8  is provided with a FIGS. “ 0 - 9 ” or a sign “#” or “*”, respectively. In alpha mode each key is associated with a number of letters and special signs used in the text editing. 
     The keypad  7  additionally comprises a menu selection key  9 , a up/down key  10 , and a cancel key  11 . The functionality of the menu selection key or NaviKey™  9  depends on the state of the phone. The NaviKey™  9  is used together with the up/down key  10 , where the selection/navigation is made by the NaviKey™  9  and the scrolling in the menus is made by the up/down key  10 . The functionality of the NaviKey™  9  changes depending on the menus and its present functionality is shown in separate fields in the display  1  just above the NaviKey™  9 . The cancel key  11  is used to delete an input or cancel the last selection and jump to another menu level. 
     The menu selection key  9  is placed centrally on the front surface of the phone between the display  1  and the group of alphanumeric keys  8 . Hereby the user will be able to control this key with his thumb. This is the best site to place an input key requiring precise motor movements. Many experienced phone users are used to one-hand handling. They place the phone in the hand between the fingertips and the palm of the hand. Hereby the thumb is free for inputting information. 
     FIG. 3 schematically shows the most important parts of a preferred embodiment of the phone/terminal, said parts being essential to the understanding of the invention. The microphone  22  records the user&#39;s speech, and the analogue signals formed thereby are A/D converted in an A/D converter (not shown) before the speech is encoded in an audio part  20 . The encoded speech signal is transferred to the controller  18  (physical layer processor), which e.g. supports the GSM terminal software. The controller  18  also forms the interface to the peripheral units of the apparatus, including RAM and ROM memories  17   a  and  17   b,  a SIM card  16 , the display  1  and the keypad  7  (from FIG. 1) as well as data, power supply, etc. The controller  18  communicates with the transmitter/receiver circuit  19 . The audio part  20  speech-decodes the signal, which is transferred from the controller  18  to the earpiece  21  via a D/A converter (not shown). 
     The preferred embodiment of the phone of the invention is adapted for use in connection with the GSM network, but, of course, the invention may also be applied in connection with other phone networks. It could be cellular networks, various forms of cordless phone systems or in dual band phones accessing sets of these systems/networks. 
     The controller  18  is connected to the user interface. Thus, it is the controller  18 , which monitors the activity in the phone and controls the display  1  in response thereto. 
     Therefore, it is the controller  18 , which detects the occurrence of a state change event and changes the state of the phone and thus the display text. The user may cause a state change event, when he/she activates the keypad  7  including the menu selection key or keys  9 , and these type of events are called entry events or user events. However, the network communicating with the phone may also cause a state change event. These type of events and other events beyond the user&#39;s control are called non-user events. Non user events comprise status change during call set-up, change in battery voltage, change in antenna conditions, message on reception of SMS, etc. 
     An embodiment of the invention will be described with reference to FIGS. 4 to  5  showing the various features of an LCD connection. In the shown embodiment the LCD connection will be connecting an LCD to a PCB in a communication unit. 
     In FIG. 4 is an exploded view of an LCD assembly is shown together with a PCB including at least a display frame  25 , an LCD  30 , a connector  34 , a lightguide  26 , a reflector  27 , a speaker assembly  28 , a dome sheet  29  and a PCB  35 . The connector  34  that connects the LCD  30  and the PCB  35  to each other is flexibly located in a slot on the lightguide  26 . 
     FIG. 5 shows a cross section of an LCD connection for connecting an LCD  30  to a PCB  35 , where the LCD connection includes an LCD  30 , Indium Tin Oxide (ITO) pads  31 , an Anisotropic Conductive Foil (ACF) layer  32 , a Double Flexible Printed Circuits (DFPC)  33 , a spring connector  34  and a PCB  35 . The cross section showing the LCD connection is not proportional. Instead the included parts have been exaggerated in order to be easily described. 
     The LCD connection enables the LCD  30  to be electrically connected to the PCB  35  so that the output on the LCD  30  can be transferred from the PCB  35  to the LCD  30 . The LCD connection needs to be flexible to withstand stress, while it maintains contact between the LCD  30  and the PCB  35 . In the embodiment shown in FIG. 4 this been has achieved by having a connector  34  that is attached neither to the LCD  30  nor to the PCB  35 . The connector  34  can thereby move freely to minimise the effect of any stress affecting the communication unit. In FIG. 5 a spring connector  34  is shown having a spring part  38  that preferable is rather extended to keep the spring effect at a maximum. The spring connector has springy metal parts in both ends of the connector. In the shown embodiments the spring part  38  is also the conductive element of the spring connector  34 , which is made of gold or a gold-plated metal. Having gold in the conductive element gives a good connection. It is possible to use other types of connectors, e.g. elastic connectors, as shown in one of the prior art document. The spring connector  34  used gives an advantage over elastic connectors, because the spring connector  34  kept its springy characteristics better than an elastic connector does. A connector made of an elastic material will age and loose its springy characteristics over time. 
     On the LCD  30  the ITO pads  31  have been located with conventional methods, and it is the ITO pads  31  that connects to electrodes on the LCD  30 . The ITO pads  31  are sensitive to exposure and might therefore easily get into reaction with the environment. One way to solve this is to attach the connector directly to the ITO pads  31 . The ITO pads  31  will thereby be covered and protected by the connector. However this is not the best connection that has been created since it is rather difficult to attach the connector that in most cases are made of gold directly to the ITO pads  31 . A gold to gold contact is preferred. In the preferred embodiment therefore the ITO pads  31  have been covered by an ACF  32  that isolates the ITO pads  31 . The ACF  32  is also used to bond a DFPC  33  to the ACF  32 . It is further used to connect the ITO pads  31  to the DFPC  33  by including small gold balls or pieces in the ACF  32  that connects the ITO pads  31  to the DFPC  33 . 
     The DFPC  33  comprises two conductive layers  36  and a plastic layer  37 , where the plastic layer  37  is located between the two conductive layers  36  and holds the two conductive layers  36 . The two conductive layers  36 , which preferably is made of gold foil, are connected to each other through gold-plated holes  39  in the plastic layer  39 . The plastic layer  37  that serves as a holder of the two conductive layers  36  is made of polyimide resin or the like. 
     The spring connector  34  connects in one end to the DFPC  33  and the other end to the PCB  35  and to the electronic parts on the PCB  35 . 
     The connection between the LCD  30  and the PCB  35  is created by applying an ACF  32  on the ITO pads  31  and on the LCD  30 , and in the same step locating the DFPC  33  on the ACF  32 . The ACF  32  protects the ITO pads  31  from reaction with the surroundings and binds the DFPC  33 , establishing an electric connection between the ITO pads  31  and the DFPC  33 . The LCD  30  with the ITO pads  31 , the ACF  32  and the DFPC  33  is located in the lightguide  26 . Furthermore the spring connector  34  is mounted in a slot on the lightguide  26 . Finally the lightguide  26  together with the above mentioned parts are mounted on the PCB  35 , and a connection between the LCD and the PCB has been created, by compressing the springy ends of the spring connector  34  towards connecting pads on the LCD  30  and the PCB  35 . 
     The invention is not limited to the above-described examples or to the drawings showing examples of an embodiment, but can be varied within the scope of the appended claims.