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Custom LCD Solutions

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Custom LCD Solutions

Custom LCD Solutions

A complete custom LCD design service for Monochrome, and TFT displays

Benefits


Allows a more creative approach to the display design
  • Differentiates the end product by enhancing the display
  • Allows a display to be used where front panel space could be a premium
  • Reduce costs by integration of control panel features
  • Increase reliability of the end product
  • Can be designed for extreme operating conditions.

As technologies evolve and tooling charges reduce the option to design a complete custom display solution to handle the HMI functions becomes more viable. By choosing this approach product designers can be more creative in the overall product design helping to give the end product an edge over the competition.

Custom LCD panels and modules

Our design team can help you design a custom LCD panel, our expertise will help you define the layout and design to achieve maximum effect for minimum unit cost. By understanding the options available from a range of suppliers we can help select the technology that most suits the application saving time and expense.

Custom LCD solutions can vary in complexity from a simple two digit display though to a multi line, multi enunciator’s solution with integral drive components together with perhaps even some of the systems electronics. The design team at RDS can offer in depth technical design support on all elements of a project.


The LCD Panel



The passive LCD technologies have been available for a while and have their restrictions and advantages depending on the display requirement.
TN (Twisted Nematic) is the oldest and most simple technology. This is used in displays with few segments/icons. Contrast and viewing angles are very good at low multiplex rates, hence the few segments. Typical applications are limited numeric information and customized icons. Positive or negative mode is achievable both with and without backlight. Connection methods are solder pins, zebra connector, heat seal and FPC.
STN (Super Twisted Nematic) is a later development and is widely used in character modules. The STN technology has the advantage of good contrast and viewing angles at higher multiplex rates and is therefore suitable for dot matrix types of displays, alpha numeric, full graphic or in combination with special icons.
One limit to STN is that it’s naturally coloured, dark-blue segments on a yellow green back ground, or deep purple segments on a grey-green background, or finally a negative mode which is very crisp using a white backlight on a clear blue background. None of these can be inversed positive/negative mode like the TN technology. So the demand for more colour neutral displays with a high content of segment has prompted the development of the FSTN (Film Compensated Super Twisted Nematic). This is basically the STN technology but with an added colour compensation film which then makes the FSTN display colour neutral and easy to use in positive or negative mode. The high content of segments in STN/FSTN makes solder pins difficult, so most connections are made with zebra connectors and/or heat seal.

The Driver Electronics



The LCD needs an AC square wave 50-60HZ to turn the Liquid Crystal. Some micro controllers have this available as “built in LCD driver” However this is limited to very few segment lines and mainly suitable for the TN displays with limited segments/icons. When it comes to more complex displays with high content of segments i.e. high pixel resolution, then it is necessary to add a display driver IC. This could then be a combined driver and controller function so the system micro controller and LCD controller/driver can communicate on a data line.

The Backlight



Today nearly all backlights use LED’s in a typical small custom LCD module. The development in LED technology has also prompted new ideas in the mono chrome LCD market. The top end is an RGB LED backlight solution which basically makes any backlight colour possible i.e. red for a warning and green for normal operation. The backlight colour can be seen for quite a distance so even if the display content is not readable you can display the visible information by colour alone. Single or dual coloured backlights can do the same with less flexibility. Flashing backlights are also an option for alert. More advanced backlights can illuminate the LCD in small rectangular areas using different backlight colour in different areas, all depending on the application.
One important detail regarding the backlight design is the light guide which is a moulded acrylic type of clear plastic. There is no reason why the backlight guide should be a simple rectangular unit. There is no extra cost involved in using the same part and tool to add mounting holes, locating pips etc.

The Module



The module is the assembly of the LCD panel, controller/driver electronics and backlight unit. Most character modules use a base PCB with the IC’s bonded directly to the PCB, COB (Chip On Board).The LCD panel is held in place by a metal bezel and zebra connectors. In this case the backlight unit is then automatically positioned under the LCD panel between the zebra connectors. This is a fairly cost efficient and flexible method for medium volumes when more than one IC is needed to drive the LCD.
When it comes to small graphic and alpha numeric modules and a single IC is used then the module assembly can be done as COG (Chip On Glass) This construction method eliminates the need for a PCB and the connection to a main PCB is then done by an FPC and a mating ZIF connector. The general cost is reduced with fewer components. However the setup of a COG production line takes time and the process is 100% automated, so volume requirement is higher. Multiple COG is possible, but the production yield is less and this brings the total cost up.
When several drivers are needed for larger size panels and typical higher number of pixels then TAB/TCP (Tape Carrier Package) are used. They can be reworked where the COG module will be wasted if any failures are found. Using TCP IC’s brings the need for a collecting PCB where all IC’s are connected to bring the interface out in a cable or connector.
As for the backlight unit, there is no added cost to extend the PCB to carry other components relevant to the display mounting in a casing. So for instance switches and LED indicators around the display could be part of the customized module.

The Options



The full custom LCD module is the most flexible, but each component has a tooling cost so the total tooling cost could be an issue for lower volumes. Simple changes to standard modules, adding a connector or a different interface cable, is usually free of tooling costs, but could also save assembly costs at a later stage in the customer’s final assembly line.
Using a standard LCD panel and only tooling up a new backlight unit is also an opportunity to customize the display for a better match to a new design. A positive or negative mode display is a simple way of varying on design parameters. Change of backlight colour (LED) is only limited by available LED’s and a reasonable order volume.


Customized TFT.



A full custom TFT display is usually out of reach for most customers because of the required high production order volumes, and the actual tooling cost for the TFT substrate and colour filters is expensive. There are a few customizations possible around the small sized TFT’s which can make them easier to design into mechanical restrictions.
The actual TFT substrate and COG is the area that can not be altered. Backlight unit and bezel parts are possible to change for ease of assembly.
In many cases the FPC tail comes as standard and is very short and may not be set to the required corner. Tooling up a new FPC tail, shape, length etc can change the use of the small TFT making what was once an awkward display now easy to fit.

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