Information on the clear connection film to an LCD display

Question

I have recently been asked by a friend andriu011 how to improve the connection of the clear film ribbon between a glass LCD display and a circuit board. Frankly I do not even know the technical name of this type of connection cable. I have seen them and been frustrated by them when they have lost their connection. Usually pressure is applied to the back of the film against the glass to make the connection to the LCD circuits in the glass. If anyone knows what to call this technology so I can google it and learn more it would be appreciated. Also if you have any suggestions for cleaning the connections or improving them please tell me.

John

andriu011 · Answer

Thank you John for putting this post up, also thank you everyone for any help and great recommendations, the display looses the segments of the numbers and within time all the segments go away, i have tried heating the ribbon cable with hair dryer and pressed down to somehow glue the connections back, got lucky sometime and got some segments back but not completely. Wondering if there is something in the world that will replace, or any glue to apply or any ideas how to make this work. Thank you everyone. Have attached a picture to Dave and John conversation above.

andriu011 · Answer

Yes, the end attached to the glass seem attached strongly, i am heating and press pressure to the end cable that is attached to PCB. Here is another picture with same remote but something black stuff added but still has the same issues. Have also attached a picture of what the company came up with and fixed the display issue for good ( the pins are metal ).

andriu011 · Answer

Hi John, Here is the picture of the remote.

beacon_dave · Answer

Are the 5 solder pins to the left the only obstructions under the board in the area of the ribbon ? i.e. could you slide a thin spring clip onto that lower edge of the PCB such that it pressed the ribbon firmly against the PCB. By this stage, there may be some oxidisation of the contacts, which is making conductivity poor with the adhesive alone. May need to lift it, clean it and try some of that conductive tape Shabaz mentioned, then fit a clip.

shabaz · Answer

Hi John,

I've never tried it, but Adafruit sell 'Z-axis conductive tape', it's quite expensive for a short length. That might work. If the actual ribbon needs replacing, then that may need to be something custom (e.g. a flexible PCB can be designed in CAD and manufactured, many of the PCB manufacturers in China offer this service in single or low-volume). I don't know if it would be appropriate for the LCD or not though, I've never tried repairing an LCD, so this is just guesswork that it might work! : )

dougw · Answer

Are you referring to elastomeric connectors? Sometimes called Zebra connectors.

jw0752 · Answer

Hi Doug, I haven't seen ty unit yet so I am not sure but I got the impression it was more like clear plastic ribbon. John

shabaz · Answer

If the flexible plastic comes off, then the special tape could be attempted. Otherwise, merely glueing it won't work I think, since there is nothing to apply pressure to each contact along the plastic. Maybe something can be retrofitted to apply pressure in the enclosure, but might need some custom surround created perhaps 3D printed, and screwed down maybe. It would be experimental though, and might not work. If the lead frame pins have solved the problem for good then replacing the entire LCD and the interface PCB could be easier than trying to maintain the older ones with the flexible plastic.

beacon_dave · Answer

3M Electrically Conductive Adhesive Transfer Tape 9703 https://multimedia.3m.com/mws/media/66235O/3m-electrically-conductive-adhesive-transfer-tape-9703.pdf

beacon_dave · Answer

Some more info on 3Ms anisotropic product range. Get Connected with 3M Anisotropic Conductive Film (ACF) https://multimedia.3m.com/mws/media/296669O/3mtm-anisotropic-conductive-film-adhesive-get-connected.pdf

beacon_dave · Answer

Is it the ribbon to PCB end that is causing the problem ? I've seen some designs which have a shaped spring clip that applies a downward force to keep the ribbon in contact with the PCB. Looks like you could do something similar here.

shabaz · Answer

Hi Andrei, The black material is likely epoxy resin glue. The metal pins are called 'lead frame pins' and are quite common on LCDs, but usually come pre-attached (and often glued, sometimes with a transparent glue and sometimes with opaque) as part of the display, from the LCD manufacturer. Converting an LCD from the flat flex to the lead frame pins might be manually possible, but you'd need a PCB with the holes in it. I think if the lead frame pins is the option you're aiming toward, then it would be better to purchase the LCD with the lead frame pins pre-attached if this is an option (assuming that the interface board with the holes is also available), otherwise there is the difficulty in trying to source the correct lead frame pins for the thickness of the glass on the LCD, and finding a suitable adhesive etc.

Jan Cumps · Answer

Aw Andrei, I have had LCDs with flat flex issues too. I have been able to temporarily fix issues by bending them in a position where they made the LCD work, then taping everyting with normal bureau tape. But that never lasts. Otherwise, merely glueing it won't work I think, since there is nothing to apply pressure to each contact along the plastic. You're supposed to use a hot bar (a very very broad soldering iron, a s long as the flat flex and a s broad as the solder-down contacts). Tricky. The display looks like the Nokia one used on the older TI MSP320 LCD boosterpack (used it in the first design of the eLoad here on e14). I believe there is no stock left of the source LCD - one of the reasons that the boosterpack is obsolete now.

jw0752 · Answer

Hi Shabaz,

Thanks for the info. I think we are heading in the right direction. Andrei is sending a unit to me to check out and I am just trying to get a head start on things. It looks like Adafruit has several different options.

John

beacon_dave · Answer

Adafruit supplies it as a 50mm x 150mm patch (see Shabaz's link). 3M appear to supply it in 32.9m rolls of varying widths. You wouldn't have to cut it line by line as it is 'anisotropic', otherwise you could just use conductive tape. You just need a single strip that covers the area of the ribbon that is in contact with the PCB. It will depend a lot on how cleanly you can separate the existing join. It is an adhesive solution so you are basically replicating what you already have. You may still want to investigate some mechanical method over and above the adhesive. 3M recommend using it in conjunction with this tape. Does the display start working with manual pressure applied in its current configuration ? If so it may be worth looking at a mechanical clip solution first.

beacon_dave · Answer

With generic heat seal connector ribbon cable I presume that the anisotropic conductive glue is manufactured into the length of the cable, so that it can be cut to length and attached as required, so perhaps it is more a case of trimming off the used end and then reapplying heat to a fresh bit of cable. This assumes that you have plenty spare to have another go which doesn't look likely in this case. With production run cables however, the glue may only be applied sparingly to the very end sections, especially if the bonding mechanisms are different at each end e.g. to glass and to PCB. This problem of failing heat seal connections appears to be quite common in the automotive industry. Some repair attempts describe the conductive tracks in the ribbon disintegrating when attempting to expose them, which could be an issue here if attempting to use the conductive tape approach for repair. I see that you can get special tips for soldering irons 'T-iron' / 'T-tip' which basically look like an oversized DIL package desoldering bit with some silicone rubber facing to prevent overheating of the ribbon. https://www.amazon.co.uk/CITALL-Soldering-T-iron-Ribbon-Repair/dp/B07BBMD8DW Perhaps with such a tool it may be possible to reheat the connection more successfully with less risk of damage.

Information on the clear connection film to an LCD display

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