Resistive Touch Screen – Deployment

In the following, you will be guided to the notes of AMT resistive touch screen design and also your LCD front bezel design, in order to reach the reliability of the end product.

Terms

Touch Screen Drawing

1. Outside Dimension: The overall external size of the touch screen, which is usually the size of the glass substrate of the touch screen. The overall size tolerance is specified in the drawing of the touch screen.
2. View Area: This dimension is for mechanical engineers to design the size of LCD front bezel opening.
3. Active Area: Touch screen’s function area.
4. Tail: Touch screen’s circuit connecting line, there are 4-, 5-, and 8-wire variations.
5. Touch Screen Surface: The front side of touch screen is the touch function side. The material is a film, and the surface of this film could be made antiglare, clear or glare hardcoated. The touch screen surface should be facing outward.

LCD Display Module Drawing

1. Outside Dimension: The overall external size of the LCD module, i.e. size of the metal casing that houses the LCD panel and the PCB.
2. Bezel Opening Area: Also known as LCD’s View Area. This is exactly LCD metal frame’s cutout opening area. LCD’s metal frame has to be fully covered off by system’s front bezel.
3. Active Area: LCD’s function area.

Design Notes

1. For LCD Active Area (function area) to be completely covered under touch screen, LCD Active Area must at least equal to touch screen’s Active Area. And further giving consideration to the tolerance, it is therefore suggested that LCD Active Area should be smaller than touch screen’s Active Area by approximately 1mm each horizontally and vertically.
2. Attentions to be paid for LCD front bezel design:
   • AMT suggests that LCD Bezel Opening Area (or View Area) should be smaller or at least equal to Touch Screen View Area, so that the area not intended for viewing is fully covered off by LCD’s bezel.
   • In order to maintain the linearity along the boundary of touch screen’s Active Area. Be sure to note the following:
     • System’s or LCD’s front bezel must be designed with its opening cutout edge falling between touch screen’s View Area and Active Area tending closer to the Active Area.

     

     • With AMT’s resistive touch screens, there is an Isolation Ink Area between the Active Area and View Area, which might be a fully transparent area or might not. This area should also be covered off by system’s or LCD’s front bezel.
3. In case your LCD has narrow borders, AMT may need to enlarge the touch screen designed in order to make the touch screen lastingly reliable.
4. AMT suggests that LCD tail should go out by the wide border side.
5. Bezel/Surface Gap:
   A gap of approximate 0.5 mm is recommended between the bezel and the top ITO PET. This will prevent undesired contact reception.



6. Front Gaskets:
   The front gasket provides buffer to the touch screen when it is being squeezed tight to the front bezel; a single-side adhesive front gasket is recommended, do not use very high bond double-sided tape (VHB type adhesive). It is suggested that the front gasket be bonded to the touch screen perimeter. Please ensure that the view area of the touch screen are not enclosed/encased by the front gasket.

   

   The gasket expands when compressed thus make sure it does not overlap into the viewing area of the touch screen. Compression force around the perimeter of the touch screen should be even. It must also be ensured that the front bezel itself does not come into contact with the view area of the touch screen. The thickness of the gasket is suggested to be less than 1.0 mm, except for special considerations or designs. See the following illustration.

   

7. Tail:
   The prescribed bend radius of the t ail must not be exceeded, as poor conduction or even breakage can result. Integral tail types can tolerate a bend radius of 5.0mm minimum, HSC types up to 1.5mm, and 1.0mm for FPC tails.



8. Mounting:
   The touch screen must be secured from below by the application of double-sided adhesive to the display. If the screen is affixed to the bezel by using very high bond double side adhesive, the top ITO PET may separate form the screen. Contact us for more information.



9. Non-Input Area:
   A zone near the edge insulation is particularly susceptible to damage by contact, especially from stylus use. This area must be covered by the bezel and protected form contact. If you have special requirements of the application, please contact us for more information.



10. Venting:
    Note: Venting is generally not recommended unless the touch screen is to be applied in an extra high / low altitudes. AMT’s standard touch screens feature no air vent. Few types of the touch screen will design with the inclusion of an air vent to equalize atmospheric conditions with the outside. The vent must be clear, and contact with foreign matter, particularly liquids, must be avoided.

Reiteration of Design Notes

1. LCD Active Area should equal to or be smaller than Touch Screen Active Area (by approximately 1mm each horizontally and vertically).
2. LCD Bezel Opening Area should equal to or be smaller than Touch Screen View Area.
3. System’s or LCD’s front bezel opening cutout edge to fall between touch screen’s View Area and Active Area and tend closer to the Active Area.
4. Isolation Ink Area to be covered off by LCD’s front bezel.
5. Tail to go out by the wider border side of LCD.