Current trends for portable electronics devices, such as notebook computers, PDAs, cell phones, etc., are towards smaller, thinner, and lighter weight elements and devices. Furthermore, there is a desire to have larger area displays and often multiple active color displays within this shrinking electronics package. The data entry pad, or keypad, represents an opportunity for improved functionality in terms of thinness, weight, visual appeal, and multi-functional use of space. Several general types of keypads are briefly described below.
Thin keypads are typically molded, thermoformed, die cut or stamped from thin polymeric or metal sheet material or composite laminates of these materials. Indicia are typically printed on the surface of the keypad. In some cases, the keypads are transparent or translucent so that they may be backlit. However, while thin and lightweight, these keypads appear generally flat.
Thick keypads, also commonly referred to as “Chicklet” style key pads, are typically injection molded from flexible polymers or compression molded from polymer or metal powders. Indicia may be incorporated into the keys during the injection molding process using multiple-shot molding, formed into the surface of the key during the molding, or printed on the surface of the keys after molding. Again, transparent or translucent keypad keys may be lit from behind. However, these thick keypads are often difficult to fit into thin electronics packages.
Keyboard with touch sensing technology includes varieties that monitor the resistive contact between conducting electrodes and varieties that detect of the capacitive coupling between a user's finger and the keypad electrode. An illustrative example of the capacitance technique is embodied in the capacitive touch screen detection board made by 3M Touch Systems (e.g., 3M's touch screens that are commercially available under the name ClearTek). This detection board energizes the keypad button electrodes with an AC electrical signal. When a finger or other conducting object approaches the electrode, capacitive coupling shunts current from the electrode through the conducting object to ground. A very sensitive detection circuit on the detection board measures this current and delivers an output signal to the electronic device. One advantage of the touch sensing system is that only a single electrode is required at each keypad button location. Button switches based on electrical resistance may require two sets of electrodes for each button or alternatively a conductive layer disposed on another film located adjacent to the button electrodes.
A keyboard having a thin transparent pressure sensitive display panel is disclosed in Nakagawa U.S. Pat. No. 7,034,806 titled Virtual Keyboard. Touch sensitive detection devices such as those from 3M Touch Systems described above can provide similar functionality when mounted on an active display. The keypad on the display panel permits dynamic reallocation of key designations. However, the keypad generally appears flat. An improved keypad is desirable.