Electrical connectors – Preformed panel circuit arrangement – e.g. – pcb – icm – dip,... – With provision to conduct electricity from panel circuit to...
Reexamination Certificate
1999-02-08
2001-09-25
Sircus, Brian (Department: 2839)
Electrical connectors
Preformed panel circuit arrangement, e.g., pcb, icm, dip,...
With provision to conduct electricity from panel circuit to...
C439S071000
Reexamination Certificate
active
06293804
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to liquid-crystal display (“LCD”) connectors, and in particular, to a mechanical self-aligning interconnect device used to connect an LCD with a base circuit.
BACKGROUND OF THE INVENTION
The number of cellular phones being used in the United States is growing at a rapid rate. This means that more and more people are carrying cellular phones with them from one location to another. As such, most cellular phone users desire a phone that is lightweight, compact, easy to carry and full of features. As a result of this demand, cellular phone designers are striving to develop smaller types of cellular phones that are still capable of incorporating all of the features that are available to cellular phone users.
Most cellular phones use an LCD to communicate information to the user while the phone is being used. A LCD uses strips or squares of liquid-crystal material to form digits or pixels that communicate information when energized. Some aspects of the manufacture of LCDs are extremely precise. For example, the tolerances for the location of the electrical traces or contacts on the LCD that are used to drive the LCD are on the order of ±0.025 mm. The electrical traces that interconnect the LCD with a second device are typically made from indium tin oxide (“ITO”) or some other conductive material. However, other aspects of the LCDs are not as precise due to the nature of the materials that are used or the methods in which they are manufactured.
LCDs have a very wide tolerance for the mechanical dimensions of the glass and the positioning of the electrical traces with respect to the edges of the glass. These tolerance ranges are much larger and are generally only required to be accurate within ±0.200 mm or even greater. This large tolerance is predominantly a result of the manufacturing process that necessitates scoring and breaking of a larger glass panel to create discrete LCDs.
Due to the number of parts and their associated tolerances, designing mechanical interconnects for the LCDs that are used in cellular phones is problematic. This is particularly true for LCDs that use chip-on-glass technology, in which an LCD driver chip is bonded directly to the LCD glass. These designs do not incorporate a secondary connection means, such as a flex film, which is used in chip-on-flex and chip-on-tab technologies. Flex film is an array of conductors bonded to a thin dielectric film. In these designs, one end of the flex film is bonded to the LCD driver chip while the other end, because the flex film is flexible, may be manipulated and bent around objects until being connected to a circuit which drives the LCD driver chip. However, using flex film is no longer appealing in cellular phone designs due to size constraints.
In prior cellular phone designs, the LCD is generally held in place with a light guide. The LCD is mounted in the lightguide and the edges of the lightguide are used to align and hold the LCD in position. Thus, the edges of the LCD, which have wide tolerances, are used to align the LCD in place. In these devices, an LCD connector is retained by the lightguide and used to electrically connect the LCD with the printed circuit board of the cellular phone.
Since all known prior art cellular phone designs align the LCD by using the edge of the LCD glass they suffer from the large tolerances associated with the LCD glass. To that end, this creates connection and quality problems that are difficult to deal with in the manufacture of a larger number of cellular phones.
Since the LCD driver chip must be electrically connected with the contacts on the printed circuit board of the cellular phone an optimization of the respective interconnection between the of the LCD contacts and the printed circuit board contacts is required to provide a reliable and repeatable mechanical design. Best engineering practice dictates that the system must function under all tolerance conditions. However, since the LCD is captured and aligned by the edges of the LCD glass, ultimately the large glass tolerances drive the design of these devices to incorporate a large connection pad size and pitch, often beyond the limits of practicality. This hinders efforts to miniaturize the size of cellular phones.
Another problem that must be dealt with is that the performance and functionality of the LCD may be negatively impacted due to the relatively high resistance of the indium-tin oxide which is used as the material to electrically connect the driver to the pixels within the LCD. The ITO traces therefore need to be minimized for low resistance and optimal performance. This is in direct conflict with the requirements of large ITO pads required for reliable design. To illustrate, the acknowledge pulse of the typical LCD may not work if the connection resistance approaches 90 m&OHgr;, which allows for very little ITO in the electrical path.
As cellular phones get smaller and more featured, space within the transceiver has become extremely important. The problem associated with interconnecting the LCD with the cellular phone's printed circuit board was not dealt with in prior devices because designs were either accommodating to the large tolerances or design principles were sacrificed to meet space requirements. To that end, a need exists for a way to optimally electrically interconnect the LCD to the printed circuit board in a cellular phone with precision.
BRIEF SUMMARY OF THE INVENTION
The present invention discloses an interconnection device for interconnecting a plurality of contacts accurately positioned on an LCD with a plurality of connections on an underlying base circuit which provides operating signals to the LCD. The interconnection device solves the problems associated with the large tolerances of the LCD glass used in cellular phone applications by taking advantage of the characteristics of chip-on-glass LCD design. Chip-on-glass LCD design mounts an LCD driver chip to the LCD with a high degree of accuracy. By reducing the alignment tolerances by one order of magnitude, the LCD and printed circuit board interconnection can be improved significantly, reducing size, increasing performance and reliability, and easing the manufacture of the LCD and associated hardware. In addition, the interconnection device allows tighter framing of the LCD in the cellular phone or device.
The interconnection device directly takes advantage of the precision location of the LCD contacts and the LCD driver chip as a means to align the interconnection device to the LCD. As a necessity to the proper operation of the LCD, the LCD driver chip is normally mounted to a tolerance of ±0.04 mm in the LCD design. Further, the LCD driver chip is bonded to the glass permanently because the bonding agent used is stronger than the LCD glass. The LCD contacts are also precisely located on the LCD in relation to the LCD driver chip. As previously mentioned, the LCD contacts are normally made from ITO or some other conductive material.
By aligning the interconnection device with the LCD driver chip instead of the LCD glass, the tolerance of the glass is eliminated from the design. This allows the size of the LCD contacts, which are in electrical connection with the LCD driver chip, to be reduced by essentially twice the tolerance that is associated with using the LCD glass as the alignment point. These features will ensure that the contacts of the interconnection device make electrical contact with the LCD contacts at a much tighter tolerance than previously possible. The precise make-up of the contacts used on the interconnection device are irrelevant and could be selected from the group including spring contacts, pogo pins, a discreet conductive elastomer, or conductive wires.
The interconnection device preferably comprises a non-conductive body having at least one surface located for self-aligning engagement with the LCD driver chip. At least one conductive lead is included in the non-conductive body that has a first contact and a second contact that
Ericsson Inc.
Hyeon Hae Moon
Myers Bigel & Sibley & Sajovec
Sircus Brian
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