Browse Prior Art Database

Defect Measurement of Liquid Crystal Displays

IP.com Disclosure Number: IPCOM000105803D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 4 page(s) / 115K

Publishing Venue

IBM

Related People

Archibald, C: AUTHOR [+3]

Abstract

Disclosed is a manufacturing test procedure enhancement for the detection of flaws in Liquid Crystal Display (LCD) units.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 30% of the total text.

Defect Measurement of Liquid Crystal Displays

      Disclosed is a manufacturing test procedure enhancement for the
detection of flaws in Liquid Crystal Display (LCD) units.

      During manufacture and assembly of LCDs, contamination can
become trapped between glass panels that make up the LCD.  LCDs of
the backlit variety suffer from contamination trapped between the
glass panel and backlight diffuser.  In either case a defect may
appear on the display.  The most common of these defects are Sharp
and Dull Dots.  Sharp Dots are light or dark dots which appear in any
contrast setting.  Dull Dots are light or dark dots which appear in
only particular contrast settings.  The contrast between a Dull Dot
and the display background is not so marked as is the case for Sharp
Dots.  As with voids on a CRT, there is a tolerance in the
specification which limits the size and number of these defects.
Typically, Sharp Dots of up to 0.3mm and Dull Dots of upto 1.0mm are
allowable.  Measurements of these defects in a manufacturing
environment is a laborious task which can lead to inaccuracies.

      Conventional manufacturing test departments use slip gauges.  A
slip gauge is a transparent film with accurately printed black dots
of various diameters ranging from 0.05mm - 1.0mm.  A Sharp Dot is
assessed by placing the 0.3mm printed dot of the gauge adjacent to
the defect and determining if the defect is larger or smaller than
the dot, thereby determing if the defect is in or out of spec.  A
Dull Dot is assessed in the same way but using the 0.1mm printed dot.
Microscopes (x30) with in-built graticules are used.

The pixel dimensions of a particular LCD used as an example are shown
below.

                              0.03mm 0.28mm
               0.28mm  | |       | |      | |          |
                       | |       | |      | |          |
               0.03mm
                         |       | |      |
                         |       | |      |

The 0.28mm squares are the addressable pixels with a 0.03mm gap
between each.  If one pixel is off (i.e., black) and all other pixels
are on (i.e., white), the user sees a 0.34mm black dot on a white
background.  The size of the black dot is almost identical in size to
the spec limit for a Sharp Dot (0.3mm).  This dot can be moved
anywhere on the display area, very quickly using a mouse.  The
proposed method does exactly that.  The dot can be moved adjacent to
a Sharp Dot defect, and the decision as to whether the defect is in
or out of spec can be made very rapidly.  The borderline cases can
then be assessed off-line using the X30 microscope.

      If a three-by-three array of pixels is off and all other pixels
are on, the user sees a 0.96mm black square on a white background.
This is alm...