AMLCD Resizing

AMLCD Resizing

LAWRENCE E. TANNAS, JR.
TANNAS ELECTRONICS
ORANGE, CALIFORNIA

As published in PROCEEDINGS OF SPIE, 17-19 April 2001, Vol. 4362, P288

ABSTRACT

The resizing of commercial off-the-shelf (COTS) Liquid Crystal Displays (LCDs) for custom sizes as required in avionics has been successfully demonstrated. There are two key points about resizing; it works and it is cost effective. The AMLCD is definitely more suitable for avionics than CRTs and electromechanical displays. LCDs can be more sunlight readable and more dimmable than CRTs for avionics. However, the COTS LCD, resized or not, custom or not, needs to be ruggedized with suitable back light, packaging, etc., and successfully tested before it is qualified for avionics applications.

1. RESIZING

The modern COTS AMLCD is easily resized. The resizing is relatively easy because of the microsphere spacer technology and improved LC material stability. When the cell is cut and reopened, the plates can expand or contract, depending upon the forces constraining the cell thickness and dissolved gases. The microspheres keep the plates apart and the atmospheric pressure keeps the plates together. When the cell is opened during resizing, the atmospheric pressure is neutralized and the pressure keeps the plates together. When the cell is opened during resizing, the atmospheric pressure is neutralized and the cell may expand, changing the cell thickness and its optical performance. Internally dissolved gases will expand and fill the volume or atmospheric air will enter the cell. Controlling the cell thickness and preserving the LC is as critical in resizing as it is in the original cell filling. After sealing, the cell is again stable. Resealing is very similar to the original cell sealing, except instead of having one or two ports for filling, an entire side of the display is opened up. If done properly, the cell thickness can end up the same as it was when originally sealed.

The economic viability of resizing display glass depends on how much of the COTS display can be retained. Obviously, the part cut off is of little value, Figures 1 & 2. The exception is in spare parts, such as drivers, and as an archival test sample. The resizing operation, Reference 1, using tooling as developed by Tannas Electronics takes less than two hours in labor using custom-designed tooling costing less than $25,000.00. All of the original display glass, TAB circuits and LC material, except for the parts cut off, are preserved. Additionally, the process preserves the original performance. The polarizers, compensation film, LC material and/or drivers could be changed but at a significant additional cost. The back light no longer fits but its parts may be *L.Tannas@IEEE.Org; tel/714/633-7874; fax/714/633-4174; http://www.Tannas.com; Tannas Electronics, 1426 E. Dana Place, Orange, California, USA, 92688-1737 used in a custom back light. Since avionics usually require a much higher performing custom back light, a new custom back light is required.

o make the display suitable for avionics it must be ruggedized, Reference 2, and enhanced in the same manner as a COTS or custom LCD and for the same reasons. A higher intensity back light with dimming capability and an anti-reflective front treatment must be incorporated, Reference 3. Additionally, a heater on the back light and on the display may be desirable. NVG compatibility may be required. The display may need special cooling for high temperature operation. The display must be mounted in a custom bezel to protect the peripheral Tape Automated Bonding (TAB) circuits and anisotropic adhesive bonding of TAB circuits to the glass. More details on adapting LCDs to avionics are given in References 4 & 5. The TAB circuits connecting to the display glass for electrical interconnection often need to be bent back to minimize the peripheral area. In avionics, a high priority is placed upon maximizing the display imaging area to aircraft panel area. Fortunately, this is also a priority in most commercial products such as in notebook and palm computers. In older COTS displays and non-computer displays, the row and column TAB circuits may not be bendable and need to be re-mounted with ribbon cable extenders that are bendable so that the original circuit boards, chips and TAB circuits can be routed to the back of the display. Chip-on-glass drivers, when used, are usually on narrow glass edges of acceptable size, Figure 3.

2. COTS AVAILABILITY

There are large numbers of commercial display sizes and models. Many of the displays have multiple manufacturers and are interchangeable. Multiple choices for resizing and candidates for unique products exist. To date, only AMLCDs have been found to be suitable for avionics. There are large numbers of displays available in the “after market”, Figures 4, 5, 6 & 7. These are new displays that are either excess production or surplus from products that did not evolve. The prices of these COTS displays out of production are a fraction of the prices of COTS displays in production which are a fraction of the price of custom-made avionics displays. A very large volume of displays in avionics is a very, very small volume in the commercial world. Using out-of-production displays may be a good tactic in avionics. A product life supply of displays can be purchased at a very low cost. The cost of resizing can be delayed until the display is actually needed. This may be a better product strategy than depending upon the continuous production of any display for the lifetime of an avionics product. Avionics are typically designed for a 20-year product life.

3. WARRANTY

Many LCD manufacturers take exception to the implied warranty of fitness for aircraft cockpit and so-called hazardous applications. A typical notice given with the display data sheet may be as follows: “The intended purpose of this product does not include military vehicles or civilian aircraft cockpit applications. Should any product be used in these applications no warranty or representation is made that the product is free from claims of patent infringement and no indemnification against such claims will be provided.” This notice is not necessarily applicable because a resized display glass is a component characterized with component properties. Only a part of the COTS display module is used in resizing. The resized display glass is a component that in itself cannot be judged as being or not being suitable in a hazardous application. Only after the resized display glass is repackaged, ruggedized and installed in its ultimate product and then successfully tested to the performance and environmental requirements of the system can it be qualified for hazardous or avionics applications. This principle applies to all components. A microprocessor chip may not be ruled suitable for an avionics application until after it is packaged and tested to the performance and environmental requirements of the system.

4. PROTOTYPES

Several prototype COTS displays from several different manufacturers have been disassembled and resized to square formats by the Tannas resizing process. Examples are shown herein, Figures 4, 5, 6 & 7. The photographs show the glass, driver and interconnection TABs. An outline drawing gives the critical dimension. Cutting off more of the display glass, cutting off corners, remounting the TABs, etc., can reduce the outlines further. If the TAB driver chips are mounted on only two sides, then the shape can be changed as shown in the picture of a 13.3-inch display with a large corner cut off, Figure 8. To minimize the impact on the TAB driver chips, the display is cut at or near the juncture of column driver TAB chips. The circuit board supplying the signal to the row drivers can usually be cut at the same juncture, Figures 1 & 2. The signal to the column drivers is shifted into the first driver chip, which is then relayed to the next driver, etc., and then applied in parallel to the display lines. Cutting off the end of the shift register at a driver chip junction typically has no impact on the performance of the display. The display signals and input electronics continue to operate as if the ends of the multi-chip shift register are still attached. The input image can remain the same. However, only the part of the image corresponding to the remaining display will be shown.

5. PERFORMANCE

The major performance parameters are summarized in the figures of resized prototype dimensioned diagrams of actual COTS resized displays, Figures 4, 5, 6 & 7. The COTS performance specifications are for the display module that is greatly influenced by the module packaging and back light. The backlights in computer modules are tightly packaged with minimal lamp cooling. The fluorescent lamp temperature, when operating at peak efficiency, is 110 degrees C near the cathode ends and 65 degrees C in the center. In avionics, the backlight can be mounted farther away from the display. Wider temperature ranges can be achieved after repackaging with custom heating and cooling techniques as developed for avionics, References 4 & 5. A complete discussion of the COTS display performance as applied to avionics can be found in Reference 4. Antialiasing software is used in avionics primary flight instruments to smooth pixel noise. The high RGB dot density in the column lines using sub-pixel dot addressing can be used for antialiasing. The dot density in the columns is typically 240 dots per inch.

6. TEST STAND

In the last photograph, Figure 9, several notebook computer displays are shown in operation. The displays were removed from the computers and approximately 25% of the display was removed. The cut was made at the juncture of an integral number of column driver chips and the drivers and supporting circuit board was also removed. No changes were made to the computer, software or image. The displayed image is unaltered except for the part of the image that would have been displayed on the removed part of the display. The resealed seal is tested and considered adequate if it survives boiling (100 degrees C) and freezing (-20 degrees C) in water for 60 minutes per cycle for ten cycles. The polarizers, electronics and anisotropic adhesive bonding of the electronics to the glass fail during the first boil cycle and must be protected in a ruggedized design. For product qualification, further testing of a resized display is required after ruggedizing and packaging. The test stand will be used to correlate short-term temperature cycling with long-term performance.

7. SUMMARY

AMLCDs are the ultimate displays for avionics, Reference 6. Resizing removes the availability issue for special sizes and shapes. Resized COTS LCDs are considered suitable for primary avionics in aviation applications. Resizing LCDs is a cost-effective way of making small lots of LCDs for custom applications at a fraction of the cost of custom-made LCDs. The LCD technology is still evolving and improving in materials, electronics and technology. Resizing COTS displays is the Tannas way for custom applications to have access to and to keep up with the improvements in the state of the art. Resizing is not only applicable to avionics but to the electronics industry at large where unique sizes and shapes are required.

REFERENCES

1. Tannas, Jr., Lawrence E., Patent No.: US 6,204,906 B1, March 20, 2001.

2. Multichip Assembly, Inc., San Jose, CA, 408/721-2740, dmm@multichipassy.com

3. Pacific Aerospace & Electronics, Inc., Display Division, Vancouver, WA, 360/574-5000, mlengyel@pcth.com.

4. Tannas, Jr., L.E., “Application of backlit AMLCDs to Avionics,” SID ’98, Anaheim, California, May 18-21, 1998

5. McCartney, R.I.; Haim, E.; and Kucera, C., “Performance testing of the primary flight instruments for the Boeing 777 airplane,” SPIE cockpit displays III, Vol. 2734, April 10-11, 1996, Orlando, Florida, pp 86-93.

6. Tannas, Jr., L. E., “Opinion: The AMLCD is the ultimate avionics display”, SID Information Display“, Vol. 17, No. 1, Jan. 2001, pp 22-24.

FIGURES

 


Figure 1: 6.4-inch COTS AMLCD resized to 4 by 4-inch display (Note circuitboard with tab also cut).

\>Figure 2: 10.4-inch COTS AMLCD resized to 6.25 by 6.25-inch display (note dimensions given in TED6-1/4 by 6-1/4).

 

Figure 3: 5.1-inch COTS AMLCD before resizing to TED3 by 3PI (note COG cutting to be done at first column chip from lower right.

 

Figure 4: TED3 by 3PI resized display.

 


Figure 5: TED6-1/4 by 6-1/4PI resized display before mounting row circuitboard to rear.

 

Figure 6: TED5 by 5PI resized display before remounting row circuit to rear.

 

Figure 7: TED8 by 8PI resized with flex cables for row and column circuits.

 

Figure 8: 13.3-inch COTS AMLCD resized to special shape (note cut can be made anywhere so long as it does not interrupt a row or column line continuity between driver and remaining pixels.

 

Figure 9: Test Stand showing notebook PCs driving their displays after resizing.