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LCD TV Flex PCB application

LCD TV Flex PCB application
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LCD TV Flex PCB application

  • LCD TV Flex PCB application
    Re: LCD flex ribbon repare
    There are two severe problems with flat flex cables .You will need to replace this as repairs may not solve the issue.The guage of the wires being 44/45 swg may be solderable under a microscope .
    The other is the finger /comb connectors of the LCD glass .

    Each system has advantages and disadvantages, and the one that’s right for you depends on your needs. Edge-lit sets are typically much thinner and lighter than those that use a full array because the lighting source takes up less space. Full-array sets are somewhat thicker and heavier, but they make up for that with local dimming, which means one section of the LED panel can be dimmed while other sections remain bright.

    That improves blacks and contrast in the resulting picture.

    LED sets that use full-array backlighting tend to produce the best picture of all LCD TVs. Those that use edge lighting sacrifice picture quality but are the lightest and thinnest TVs on the market.

    Sorry to hear your repair didn't work out. But something has been nagging me in your picture of the cut piece 3M 9703 tape. You cut a 2mm wide strip right? From the way it looks, to me it looks like it's in the wrong direction. What I mean to say is, the direction of conductivity runs up and down along the WIDTH of the tape, not the LENGTH. You need to cut a piece the width of the cable, then cut it down to fit the space. I'm sure you just used the wrong axis as there shouldn't be wax tape on the ends, only on the top or bottom (unless you did that, then I have no clue what went wrong).

    It’s not uncommon in cheaper devices to find a ribbon cable soldered directly to the circuit board like the one pictured above. Using a connector would have been a much more resilient approach, but adding parts adds cost. If you take a close look you’ll see things aren’t looking so great anymore. [Chaotic and Random] pulled this board out of his VW Camper Van. Rather than buy an expensive replacement part, he shows us how to repair a soldered ribbon wire connection.

    With accurate design and automated production, flex circuits can also eliminate human errors from hand-built wire harnesses that show up in assembly. Flex systems also require less manual labor during assembly and can reduce production errors, therefore decreasing assembly time and costs. Durability is greater than wire harnesses as well; a flexible circuit can move and flex up to 500 million times without failure in designs that have moving parts. Plus, the exceptional thermal stability of polyimide also permits circuits to withstand applications with extreme heat.
    Before you run out and buy an LCD TV with LED backlighting, you should consider one important factor—price.

    LED-backlit TVs are impressive, but they’re more expensive than their fluorescent-lit peers. If picture quality is extremely important to you, then spending a little more money to enjoy the benefits of full-array LED backlighting may make sense for you. If you’re willing to pay a premium to have the thinnest TV on the block, edge-lit LED is the way to go. If you’re a bargain shopper, you will probably be able to satisfy yourself and your wallet with a well-made fluorescent-lit LCD TV—if you can find one.
    Figure 1 shows one of the common flex designs: a flex cable. A flex cable is a miniaturized form of a ribbon cable that is flat and flexible. The cable consists of a flat and plastic film base, with multiple metallic conductors bound to one surface. Often each end of the cable is reinforced with a stiffener for insertion of components and to provide stress relief.

    Another common form is rigid-flex. A rigid-flex design consists of multiple innerlayers of flexible circuits and rigid regions typical to everyday PCBs. These are often found in cellphones, LCD TVs, antennas, laptops, and more.

    An LED TV is a type of LCD TV that uses LEDs to backlight the display, rather than the cold cathode fluorescent lights (CCFLs) used in most LCD TVs.

    Vendors of LCD TVs include Aquos, LG, Samsung and Sony.

    Pros: Not prone to burn-in. Available in smaller sizes than plasma, so may be a better option depending on the available space.

    Cons: Can suffer from slower response, which can create a ghosting effect. Some models are also prone to the screen door effect, which means that a faint mesh pattern may be visible.

    Advanced flex is a single PCB design that incorporates multiple stackup changes, as well as components placed on the flexible substrate. A flex system is a combination of multiple flex types.
    There are several factors that make buying a new TV confusing, but few topics bewilder consumers as much as the use of LED terminology. LED TVs are simply a type of LCD TV. Baffled? Don’t be. Every LCD TV requires a source to illuminate its pixels, and in LED TVs, that source is a series of LEDs. Other LCD sets originally used a series of fluorescent tubes termed CCFL-backlit technology. In most modern LCD sets, those fluorescent tubes have been replaced with full array LEDs.

    Flex Design Challenges

    Quite a few challenges are specific to flex circuits. The most important ones are briefly discussed below.

    Stackup. Defining the flexible and rigid regions correctly within the stackup is absolutely essential. Three popular stackup configurations with flex design include:

    Once the LCD module is assembled, certain problems can arise. The first problem is missing segments. Barring any problems with the LCD glass, missing segments result from excessive resistance through a conductive path. This can be caused by buckling of the connector, which lifts the conductive traces from the PCB or the LCD. This problem can occur for connectors that have height-to-width ratios greater than 3 to 1, lack proper side constraint, or are over-compressed. If no segments are lit under compression, then oxidation of all the electrodes could be the problem.

    A related connector failure is indicated by a display with faded segments. High resistance is once again the problem – but only enough resistance to cause fading. If fading occurs, the connector resistance can be lowered by increasing the width of the connector’s conductive core, changing to a connector with a lower bulk resistivity, decreasing the assembly height, or increasing the electrode width. The contact resistance can be decreased by using gold-plated PCB traces.

    Elastomeric connectors offer a reliable method for connecting displays to PCBs. While the connectors themselves are inexpensive, assembly of the components involves some additional cost. Finally, elastomeric connectors are limited to post in which the display can be conveniently located directly above and parallel to the PCB.

    To overcome these assembly and component-placement requirements, a new type of connector was developed: the heat-seal connector (HSC).

    Heat-Seal Connectors

    A heat-seal connector consists of a polyester film approximately 0.001 in. (0.025 mm) thick that is printed with traces of conductive ink (Fig. 1). The ink contains particles of carbon or silver, depending on the application. The printing process is similar to screen printing, so variable pitches and other custom designs are quite common. A single custom FISC can even connect multiple components together in any number of configurations. The ink is typically left exposed, but in some post a layer of insulating material is placed over the ink to protect against shorts and to offer better abrasion resistance. The area where the connector will be bonded to the components is coated with a thin layer of electrically conductive thermosetting adhesive. (The adhesive is anisotropic, so bridging or shorting is not a problem.) The final assembly of the connector to the components is accomplished using heat and pressure. Once a bond is made it is long lived and very durable.

    A HSC can be bonded to most common PCB pads and other substrate materials. The adhesive bonds well to copper, gold, tin, and carbon-ink pads, as well as to the glass used for LCDs. The major requirements for the bonding surface are that it be clean, flat, and smooth to assure adequate bond strength.

    I need to do a permanent repair on an LCD panel, I don't mean a repair to the tv, but to the actual LCD panel itself. Here's the story:

    Manufacturers make a big deal out of LED backlighting because sets that use the technology are usually more energy efficient than CCFL LCD TVs. There are other benefits as well, but to understand them you have to take a closer look at the implementation of LED backlighting. Currently, LED-backlit LCD TVs use one of two systems.

    From the photos below you can see the LCD control unit and the state of the LCD ribbon before repair. You can just make out the offset placement and poor registration of the ribbon before repair.
    The marks on the ribbon are my mistake of applying too much heat during re-work attempt (see my tips for applying heat and lessons learned later).

    Do not under estimate the patience required for this repair as some delicate and nimble work is required and i cannot stress how important it is to take your time and not rush. You may only get one chance with this sort of repair.

    The registrations of the LCD ribbon in this repair was difficult. It took me and my friend 20 minutes just to line up the ribbon for re-attachment. The ribbon in this case is sub 1mm pitch OR less than 25.4 thousands of an inch. You may want to try a simpler ribbon repair on an old LCD clock for example before jumping in head first with fine pitch.

    Also the removal of the LCD ribbon is a delicate process as you do not want to tear what is a good ribbon or damage the carbon printed lines. Also the PCB must be respected to avoid introducing other faults and the the re-attachment may need an extra pair of hands.

    You may also want to review the last step for results and lessons learned from this instructable before jumping in head first but i believe this will give a you a good insight to some important factors of LCD ribbons and possible success.

    I've just bought A Funai LCD-B3206 32" LCD tv as faulty from ebay. The fault was 3 vertical lines down the screen.

    I've found the fault was a bad connection right inside part of the display panel. To find this I've probably dismantled it further than intended. I suspect most tv repairers would have declared the panel was faulty and needed replacing. But i'm not "most" repairers.

    After removing the chassis and the back metal cover of the display panel, it reveals the connections to the panel. There is a thin PCB running along the top of the panel, from there about 6 flat gold plated ribbon cables connect to the panel.

    Video processing and conversion is one of the drawbacks to picture quality, really the only drawback. There are motion artifacts present depending on the signal source and strength (if streaming). This is the one clear advantage to LED/LCD TVs in my mind; the best ones do smooth out images better than OLED TVs. It must be more difficult for the OLED technology to process images more similar to plasma TVs in this regard.


    Refresh rates of early devices were too slow to be useful for television. Portable televisions were a target application for LCDs. LCDs consumed far less battery power then even the miniature tubes used in portable televisions of the era. The earliest commercially made LCD TV was the Casio TV-10 made in 1983.[13] Resolutions were limited to standard definition, although a number of technologies were pushing displays towards the limits of that standard; Super VHS offered improved color saturation, and DVDs added higher resolutions as well. Even with these advances, screen sizes over 30" were rare as these formats would start to appear blocky at normal seating distances when viewed on larger screens. Projection systems were generally limited to situations where the image had to be viewed by a larger audience.

    Nevertheless, some experimentation with LCD televisions took place during this period. In 1988, Sharp Corporation introduced the first commercial LCD television, a 14" model with active matrix addressing using thin-film transistors (TFT). These were offered primarily as boutique items for discerning customers, and were not aimed at the general market. At the same time, plasma displays could easily offer the performance needed to make a high quality display, but suffered from low brightness and very high power consumption. However, a series of advances led to plasma displays outpacing LCDs in performance improvements, starting with Fujitsu's improved construction techniques in 1979, Hitachi's improved phosphors in 1984, and AT&T's elimination of the black areas between the sub-pixels in the mid-1980s. By the late 1980s, plasma displays were far in advance of LCDs.

    I can�t honestly say that the picture quality on the 4K UHD version of the TCL Roku TV looks appreciably better than the 1080p version. With good 1080p and 4K sources there is a bit more clarity and cleaner images edges. Picture quality including blacks, contrast, and color is not the standout feature of these TCLs...


    This lack of contrast is most noticeable in darker scenes. To display a color close to black, the LCD shutters have to be turned to almost full opacity, limiting the number of discrete colors they can display. This leads to "posterizing" effects and bands of discrete colors that become visible in shadows, which is why many reviews of LCD TVs mention the "shadow detail".[6] In comparison, the highest-end LED TVs offer regular contrast ratios of 5,000,000:1.

    OLED and LCD TV Conclusions:

    Testing both of these flagship high-end top-of-the-line OLED and LCD TVs side-by-side at the same time using simultaneous identical test patterns and picture content was incredibly interesting, and also incredibly revealing because they were side-by-side for all of the tests and comparisons.

    Some of the test results and conclusions summarized below are not that unexpected. OLED TVs have all of the same high performance picture quality advantages as Plasma TVs, which were overwhelmingly preferred by videophiles over traditional LCDs – and OLEDs now significantly outperform the Plasmas across the board in all categories – so the performance advantages are even greater for OLEDs. However, the latest high-end LCDs also outperform traditional LCDs…

    Below we list separately the OLED TV and LCD TV Conclusions together with their respective strengths, weaknesses, and future improvements. See the main Display Shoot-Out Comparison Table for all of the DisplayMate Lab measurements and test details, and see the Results Highlights section above for detailed explanations of the Conclusions presented below.

    Since the total amount of light reaching the viewer is a combination of the backlighting and shuttering, modern sets can use "dynamic backlighting" or local dimming to improve the contrast ratio and shadow detail. If a particular area of the screen is dark, a conventional set will have to set its shutters close to opaque to cut down the light. However, if the backlighting is reduced by half in that area, the shuttering can be reduced by half, and the number of available shuttering levels in the sub-pixels doubles. This is the main reason high-end sets offer dynamic lighting (as opposed to power savings, mentioned earlier), allowing the contrast ratio across the screen to be dramatically improved. While the LCD shutters are capable of producing about 1000:1 contrast ratio, by adding 30 levels of dynamic backlighting this is improved to 30,000:1.

    However, the area of the screen that can be dynamically adjusted is a function of the backlighting source. CCFLs are thin tubes that light up many rows (or columns) across the entire screen at once, and that light is spread out with diffusers. The CCFL must be driven with enough power to light the brightest area of the portion of the image in front of it, so if the image is light on one side and dark on the other, this technique cannot be used successfully. Displays backlit by full arrays of LEDs have an advantage, because each LED lights only a small patch of the screen. This allows the dynamic backlighting to be used on a much wider variety of images. Edge-lit displays do not enjoy this advantage. These displays have LEDs only along the edges and use a light guide plate covered with thousands of convex bumps that reflect light from the side-firing LEDs out through the LCD matrix and filters. LEDs on edge-lit displays can be dimmed only globally, not individually. For cost reasons, most of LCD TVs have edge-lit backlighting.

    One of the best performances we've seen in this area for a mid-priced 4K TV although this is still a weakness of all LED-backlit LCD TVs.Color saturation and contrast begin degrading at around 15 degrees, they do not degrade noticeably until around 20 degrees off center...

    One of these ribbon cables has a bad connection. If I press down on it the fault clears.

    For both TVs the display power used depends on the picture content. OLEDs are light emissive so the brighter the content the more power they use (and none for black). For standard LCDs the display power is independent of content (same for all white or all black). However, the Samsung LCD TV has Local Dimming so it uses less power on darker content because of the local dimming of the backlight.

    We measured the average display power for various programs of bright and dark picture content. The LG OLED TV used an average of 39 percent less power than the Samsung LCD TV for the Cinema/Movie modes, and an average of 17 percent less power for the Vivid/Dynamic modes for identical Brightness (Luminance) levels. This is an impressive achievement for OLEDS. See the Display Power section for measurements and details.

    I've made a temporary "repair" by inserting a foam pad between this interconnection and the metal casing of the panel so it presses down on the interconnection and it's now working fine.

    Liquid-crystal-display televisions (LCD TV) are television sets that use liquid-crystal displays to produce images. LCD televisions are thinner and lighter than cathode ray tube (CRTs) of similar display size, and are available in much larger sizes. When manufacturing costs fell, this combination of features made LCDs practical for television receivers.

    In 2007, LCD televisions surpassed sales of CRT-based televisions worldwide for the first time,[citation needed] and their sales figures relative to other technologies are accelerating. LCD TVs are quickly displacing the only major competitors in the large-screen market, the plasma display panel and rear-projection television. LCDs are, by far, the most widely produced and sold television display type.

    LCDs also have a variety of disadvantages. Other technologies address these weaknesses, including organic light-emitting diodes (OLED), FED and SED, but as of 2014 none of these have entered widespread production for TV displays.

    The ribbon cables are flat, gold plated, and they fix down onto gold plated PCB pads. But they are not soldered, and they do not plug into connectors. I can't actually figure out what does actually hold them in place, i'm thinking conductive adhesive perhaps?

    All high-end TVs include a number of user selectable Picture Modes, each with different intended viewing conditions and applications that provide different color, brightness, contrast and calibration settings, and selectable picture processing options. The LG OLED TV has 8 selectable modes and the Samsung LCD TV has 4 modes. We will analyze the two most important ones: the native display mode that delivers the highest brightness, contrast, and color saturation, called the Vivid mode on the LG OLED TV and the Dynamic mode on the Samsung LCD TV, and the mode that delivers the most accurate colors and picture quality that is preferred by videophiles, called the Cinema mode on the LG OLED TV and the Movie mode on the Samsung LCD TV. We include measurements and analysis for both modes on each TV. For all of the tests and measurements we used the manufacturer’s default factory settings for each of the modes and did not make any additional changes or adjustments.

    Looking on other forums, I see a few others with this problem, so it's not an isolated incident.

    The question is how to make a proper and permanent repair?

    There may still be a chance to fix it if you can expose the super thin contacts within the damaged cable and add a new bit of a FFC on the end act as an extension and create new contacts. Another idea is perhaps thin strips of copper tape? I wish I was there to help you!

    EDIT: A tip I learned is if you gently heat the tape when it's attached with the tip of a soldering iron, you can soften it enough to gently loose it off. Then use isopropyl alcohol (rubbing alcohol to those in the US) to clean up the residue along with gentle scraping with a blade.

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