Care & Handling of LCDs

HOW TO SAFELY DISASSEMBLE AN LCD

The LCD (Liquid Crystal Display) is assembled in a frame that contains and protects the LCD, its backlight and electronics.  There are connectors to electrically interface with the backlight and LCD.

The resized LCD is typically reassembled in the original non-resized frame and backlight for shipping and acceptance testing purposes after resizing.  The frame and backlight, in this case, are used to house the resized LCD for testing and shipping and not intended for installation.

The LCD assembly should be disassembled in a clean and electro-statically free environment at nominally 50% relative humidity, and 23°C.  To prevent contamination, fingerprints and scratches on the display, the operator needs to wear industrial grade protective gloves.

At the laboratory of the customer, the frame needs to be disassembled to extract the resized LCD for its final installation in the customer’s product.  Typically, there are screws used to secure the assembled frame.  If present, the screws are first removed, as shown in the picture, and the frame is disassembled by gently prying it open as shown in the second picture.  After removal of the frame, the resized LCD can be gently lifted free of the backlight.  Parts of the frame and backlight may be resized by the customer for reuse in the customer’s final assembly.  These parts are ideally made for holding the glass, electronics and backlight assembly.  The sequence and orientation of the backlight films must be preserved as they are optimized  for best performance.

The Kapton (yellow-orange polyimide) flexible TAB circuits with driver chips and flexible circuit boards need to be handled with extreme care.  Neither should be bent in the reverse direction to factory curvature further than the flat shape.  Conductive traces on the inside of the curvature of the flexible circuit TAB or board may break if bent excessively in the direction opposite to when mounted in the original frame.  To minimize the possibility of tearing loose from the attachment to the LCD glass, the flexible circuit board should be heated as it is bent, as shown in the picture below.  If the circuit on the flexible material is injured, it will be ramified as a missing display line or entire section of missing display lines running the full length of the display with uniform intensity.  This type of failure is not easily remedied.  The repair requires replacement of the entire polyimide circuit, done by a vendor with appropriate machinery using a new flexible TAB or circuit applied by a trained technician.

Display line failures may occur from disturbances at the cut edge made during the resizing process.  This type of line failure is exhibited by a tapered intensity with maximum intensity at the cut edge where the LCD has been resized.  This type of failure is easily repairable. It should be returned to the supplier for repair.  It can be repaired by the technique described in Patent No.: US8,259,282 B2 awarded in the US or similar patents awarded in other countries. It is very important to be aware that this type of failure is easily induced while handling the resized LCD.  To minimize this type of failure the customer should not rub, clean, scratch or sand the cut edge seal.

HOW TO CLEAN AN LCD POLARIZER

One common problem with LCDs  is the occurrence of scratches on the polarizers.  Scratches of some type are nearly inevitable.  Scratches should be minimized so they are not easily noticeable by the user.  They often occur while cleaning the LCD or when moving the LCD across a surface with particle contamination.  The sliding action of the polarizer will cause scratches induced by the particles on the surface.  Any sharp object can easily scratch a polarizer.  Commercially available scratch removal compounds are not useful in removing scratches from an LCD polarizer.  The only remedy for a scratched polarizer is to replace it.  Vendors that specialize in polarizer replacement are available.  From a practical standpoint such polarizers are only replaced if the scratch is easily noticed and annoying to the user.

The polarizer should be cleaned with a soft, clean tissue without additives, moistened with 90% isopropyl alcohol or other approved cleaning agent and then dried with a dry tissue, rubbing in one direction until the surface is clean of any contaminant.  It may be necessary to replace the tissue with another dry tissue several times. The cleaning process should be done quickly without excessive pressure.  The isopropyl alcohol must be wicked up from the surface.  If the isopropyl alcohol is allowed to dry on the surface it will cause water condensation from the cooling action of the evaporating alcohol that will leave water marks.  Thus, the cleaning action of the alcohol can be counterproductive if is not wicked up from the surface with a clean dry tissue, carrying away the contaminant.

The theory of cleaning by this method is that the alcohol or cleaning agent dissolves the contaminant and must by wicked off the surface, carrying away the dissolved contaminant.  If left to dry on the surface the contaminant will be re-deposited on the surface and further contamination will occur from condensation of water from the atmosphere caused by the evaporating cleaning agent.

Acetone and other strong solvents will damage the polarizer beyond repair.  Acetone should never be allowed to be in the same laboratory with polarizers.

To disassemble, remove screws if any:

Remove Screws

Use a prying means to open the clam shell type of assembly:

Partial

Separate the frame parts and remove the LCD:

Disassembled

Use a heat gun to assist in bending the flexible circuit board:

Heat FlexCircuit