Stress-free socketed optical display package with die...

Details Stress-free socketed optical display package with die... Stress-free socketed optical display package with die...

1999-07-19

2002-11-05

Ton, Toan (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Holder, support, frame, or housing

C349S150000

Reexamination Certificate

active

06476885

ABSTRACT:

TECHNICAL FIELD
The present invention relates, generally, to liquid crystal display assemblies and, more particularly, relates to miniature liquid crystal display assemblies constructed to reduce residual stresses.
BACKGROUND ART
In the recent past, substantial research and development resources have been directed toward small scale Liquid Crystal Display (LCD) and light valve technologies. These high information content, miniature LCD assemblies enable enhanced availability of graphics, data and video information for employment in high resolution projection displays, such as a reflective LCD projectors, SXGA formats (1,280×1,024 pixel resolution) and even HDTV formats (above 1,000 line resolution), or the like.
Reflective LCD projectors, in particular, are highly desirable since they offer the brightness of traditional three-lamp front-projection systems in combination with the high resolution of an LCD panel. At the heart of these optical engines is reflective liquid crystal on crystalline silicon light valve technology which, when combined with sophisticated optical architecture and the appropriate electronic interface, enables very high resolution, high brightness, large screen displays.
Briefly, as shown in
FIGS. 1 and 2
, these light valves or small scale LCD assemblies
20
include a die
21
having a pixel array
22
which is generally composed of rows and columns of electrically conductive pathways each forming an individual pixel (not shown). Each pixel can be individually changed to an “on” condition by selecting the appropriate row and column of pixel array
22
. Positioned around or concentrated on one end of the pixel array are a plurality of die bond pads
23
which are internally connected to the pixel array
22
to enable operational control thereof. Selection of the appropriate pixel is controlled by control circuitry, either included within the die
21
or external to the die
21
. In either configuration, external control signals may be used to control the functions of the die
21
.
A transparent glass plate
24
is typically placed over the die
21
and the pixel array
22
, such that a portion of the glass plate
24
overhangs the die
21
. The glass plate
24
is usually affixed to die
21
through an adhesive seal
25
which together cooperate to define a sealed volume encompassing the pixel array
22
. This sealed volume is then commonly filled with a solution
26
of Twisted Nematic Liquid Crystals (TNLC). The LCD package is completed by rigidly or semi-rigidly mounting the die
21
to a substrate material
27
(e.g., ceramic, metal, plastic, silicon, polyamide, or other substrate materials) for mounting support and heat conductive dissipation for the die.
One problem associated with these LCD panels assemblies is bowing or warpage of individual panels caused by residual stresses acting upon the components during operation. This is particularly noticeable in reflective-type LCD panels which have increased flatness requirements due to the nature of the reflective surface of the die. For example, thermal expansion characteristics, as well as lattice mismatching, can generate significant stresses in the underlying substrate material, therein causing significant bowing of the mirrored surface. The bowing, which translates to a non-planarity of the surface, causes both (1) a non-uniform thickness of the liquid crystal layer between the bowed reflective surface and the planar transmissive top layer, and (2) variations in the path length of the reflected light from different parts of the element, and of the array. These effects compromise the electro-optic properties of the elements and/or array.
Some of these problems have been recently addressed by minimizing or isolating the coupling between the die
21
, the transparent plate
24
and the underlying substrate material
27
. In effect, the panels are sufficiently isolated from one another so that the transfer of residual stresses therebetween are minimized. Typical of these application may be found in our U.S. patent application Ser. Nos.: 09/130,631, filed Aug. 6, 1998; 09/256,702, filed Feb. 24, 1999; and 09/281,758, filed Mar. 30, 1999, each herein incorporated by reference in their entirety.
Another problem associated with these small scale LCD or light valve assemblies
20
is the formation of an electrical connection with an electrical interface (not shown) for operation thereof. Typically, direct electrical connections to the die bond pads
23
of the die
21
are unacceptable since a significant amount of mechanical stress would be imparted upon its display unit by the electrical connector of the electronic interface. To address this situation, the electrical interconnection is performed through a flex circuit
29
mounted to the substrate, and which functions as an isolatory buffer. As viewed in
FIGS. 1 and 2
, the flex circuit
29
includes a plurality of flex circuit bond pads
30
which are typically wire bonded to the die bond pads
23
through bonding wires
31
. More recently, a distal ringed coupling portion
32
of flex circuit
29
is adhesively or fixedly mounted to the top surface of substrate
27
for support thereof. Finally, a glob coating
33
is applied to die
21
, substrate
27
and the distal end of flex circuit
29
. The glob coating
33
(
FIG. 2
) further normally encapsulates the bonding wires
31
and the die and flex circuit bond pads
23
and
30
without obscuring a view of the pixel array
22
through the glass plate
24
.
While this approach is advantageous in several respects, namely, providing a relatively stress-free electrical connection between the die
21
and the electrical interface, the flex circuit
29
poses numerous manufacturing challenges. For instance, the flex circuit
29
is often mounted to the substrate
27
in the early stage of the component assembly. Although one end of the flex circuit is secured to the LCD package, the other end is free to move and is often in excess of five inches. Handling of this combination, thus, becomes substantially more cumbersome and difficult to control during subsequent manufacture. Specially designed palates and assembly fixtures have been developed, which are longer than standard automated fixtures, to secure the package and flex circuit tail for automated manufacture. Accordingly, the tooling costs are increased due to their specific use, while at the same time requiring a larger amount of manufacture space.
Moreover, the flex circuit
29
itself is relatively costly to implement, and difficult to handle. During manufacture, several additional assembly steps are required to adhere the flex circuit
29
to the substrate
27
.
Accordingly, there is a need to electrically connect an small scale LCD assembly to an electrical interface which minimizes residual stress induced upon the cell, as well as reduce the complexity and costs of assembly.
DISCLOSURE OF INVENTION
The present invention provides a liquid crystal display package including a liquid crystal cell having a die with a pixel array, and a transparent plate attached to the die. A liquid crystal material is disposed in a gap region between the die and the transparent plate. The display assembly further includes a containment structure adapted to couple to and at least partially receive liquid crystal cell therein, and an electrical connector portion integrated with the containment structure. A plurality of conductive contacts are positioned in the containment structure for secured support thereof, and in substantially stress-free electrical connection with the pixel array. The conductive contacts further are configured to releasably couple to mating conductive contacts of an opposed electrical connector.
In one embodiment, the die includes a plurality of die bond pads in electrical communication with the pixel array, and the substrate includes a plurality of substrate bond pads in electrical communication with the conductive contacts. The substrate includes a plurality of integrally formed circuits electrically coupling respective substrate bond pads

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