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How to remove and re-attach LCD Ribbon from a PCB with a Fine Pitch

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This instructable came about from a broken LCD control module out of a modern VW Camper Van. The LCD module is part of a control unit which was virtually unreadable and a replacement for a new unit was £400+. It really was a no lose option, either have a go at fixing it or end up buying a new unit.

The fault of the LCD was that it only displayed a couple lines of output on the LCD. The symptoms are caused by poor location of the LCD ribbon in manufacture and also the poor position of the whole module in the vehicle which exposes it to heat and is subject to vibration within the vehicle. This causes the ribbon to fail eventually and is a known common fault.
The ribbon in this display actually controls the Rows of the LCD matrix and the Columns were handled by a rubber standoff connection on the longest side of the LCD. There were no problems with the rubberized connection.

Some re-work on the LCD ribbon had already been tried with a little improvement but the poor registration of the ribbon pushed me to try a new attachment.

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.

Essential Tools:

1. Eyepiece - X10 minimum, X20 Preferred - For Viewing/Cleaning PCB pads and registration of ribbon
2. Scalpel with rounded blades - For ribbon removal and trimming.
3. Small Ruler - plastic or metal - For trimming and clamping of LCD ribbon
4. Solder Iron Or Hot glue gun - For applying heat, adjustable temperature solder iron would be preferred.
5. Small amount of Tinfoil - For wrapping over solder iron or glue gun nozzle
6. Cotton Wool Ear Buds - For cleaning PCB pads
7. Isopropanol Or Methylated Spirit - For cleaning PCB pads
8. Another pair of steady hands - For clamping the LCD ribbon in place
9. Tweezers - For removing leftover ribbon.

If you don't have X10 eyepiece to hand but you have an old scrap scanner you can pinch the lens out of it. The lens is close to X10 conversion.




 
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DIVYA GARG1 year ago
I think........you are a good electronics engineer ...........but I am not as you ......rather I have damaged my 3 calculator by this action.....................!..........................................but you have written very good............!
billbbc1 year ago
Saw this and used the nozzle of a hot glue gun to reglue a display tape. Worked first time without retrimming the tape.

I simply lifted the clear tape off from the top of the ribbon, then slowly stroked the ribbon contacts in turn a couple of times with the hot glue gun tip. Not hot enough to cause any damage.

Unit I repaired with missing segments was a Honeywell CM907 controller. £65 UK saved. Thank you for posting this.
bwelkin1 year ago
This step surprised me! I am very unclear what that thing is that is heating the solder pads.

My recommendation is to use a T-iron (see eBay .. about $35USD) which has the added advantage of having a heat shield that protects the insulation leading up to the solder pads.
chaoticandrandom (author)  bwelkin1 year ago
In the photo i am only using a soldering iron covered in tin foil to heat the plastic ribbon. There is no solder used in this setup. The tin foil is there only to provide a better surface to apply heat to the ribbon (does not stick to the ribbon!!).
When heat is applied to the ribbon it melts like a glue which in turn bonds itself to the PCB and the ribbon becomes attached to the PCB as it cools.
Actual Electrical connectivity is provided by carbon lines which are printed in the ribbon. The carbon lines only make contact via the adhesion of the ribbon.

The solder iron method technique is actually too hot and so i dip the solder iron in a sponge to cool it down before pressing down on the ribbon. If you have a temperature controlled soldering iron it would be much better.
You can control the heat.

Hope that was a bit clearer :)

The T-tip iron you mention is a specially adapted solder iron for LCD ribbon.
It has a wide metal bar tip and distributes heat across it.
The T-tip one i saw on eBay was 40 Watt unregulated so again that is almost double my 25 Watt iron i used and that was too hot.
I haven't used one of these before so I can't really comment on it BUT It does look very useful. Thanks.

Anyway I was trying to use tools that most people have at home and with little or no extra cost.




detinu771 year ago
Is that an actual scalpel you're using? I haven't seen one of those in a while.
i have an alarm clock which doesn't have a ribbon, but instead some sort of rubbery contact strip against which the display should be pressed. You can find pics of it on google images for "lcd rubber contact strip", it seems to be called a zebra rubber. Any idea on how to glue/solder the display to that rubbery contact strip?
you just have to position the conductive rubber properly - this type of LCD is very popular and it's much easier to repair compared to what the author has described. If some of the bars/elements are still not working, you may try cleaning the contacts using the eraser. But
dasjeetu1 year ago
Thanks for the idea, perfect.


Thanks for sharing...
paddyart1 year ago
Great Instructable... It's fantastic to see people giving a fix a go, before buying a new one.
I'll be giving this one a try one day.
a2e1 year ago
There's always a guy who goes where everybody says "it cannot be done"... My admiration and respect fellow.
Treknology a2e1 year ago
Ditto. One day someone will come out with a "needle-point" soldering iron, so that it becomes possible to individually re-solder SMD connections.
snayl1 year ago
Very thorough, a pleasure to read. I haven't had the need for a repair like this as of yet, but I shall definitely bookmark/download/etc. this instructable for future reference!
artemff1 year ago
very detailed instructable, thanks for sharing.

I recall that in the old days when I was younger and digital multimeters were expensive, I broke the LCD of the multimeter I borrowed.
To fix it, I purchased LCD, which could be soldered and I used extra thin copper wires to connect it to the main board since this was a different type LCD and one-to-one connection was out of the question.

Returning to your instructable - in principle, I can imagine using the same approach in your case. One can avoid soldering to sub-mm spaced contacts by tracing the board and connecting to different parts of it. This gives more freedom since the wires can be checked individually. LCDs are far less expensive compared to the control module you named so one can worry a bit less :)
f5mando1 year ago
I wouldn't ever attempt this again after ruining two SID displays from a (GM) Saab.
There is a company here in the USA that repairs these for reasonable cost, and a lifetime warranty. I got it back fast, with 100% readout, and it continues to function perfectly three years later.
*I also took advantage of their electronic throttle rebuild under the same terms, also with a perfect result. Not sure if it's acceptable to post their name or link here, so I won't until I hear otherwise.
maxhuey1 year ago
I have seen this done by a kid (about 15 y/o) right on the sidewalk in the electronic district street of HK. He brush some kind of liquid on the ribbon and a small butane torch for heat source - several quick passes did not melt the ribbon. I can imagine my hand would shake like mad but some people just got the golden touch! You are one of them... Cheers
bahi1 year ago
Impressive and accurate work, never thought it could be possible to repair such kind of connections.

Thanks for sharing.
chaoticandrandom (author)  bahi1 year ago
Thanks, these connections are definitely repairable but the fine pitch on this ribbon is the hardest part. I suggest anyone having a go try something simpler before going with the more difficult projects. I had actually repaired an MP3 FM transmitter display before doing this one. That was easy only just about 10 or so connections and much larger pitch between them. It was good practise.
Not to disparage you or your (otherwise excellent) I'ble, but by my calculations, 1mm is about 39.37 mils (thousandths of an inch), not 25.4.

I've done a similar repair on Virtual Boy video game systems (although they have actual foil+Kapton cables, which can actually be soldered) so I know how hard this can be. Excellent work describing the process and pitfalls.
I have done a lot of SMD rework, and one item that REALLY helps is a flux pen. It will cost you about $7, and is about the size of a small felt tip marker, but it dispenses liquid flux. A little of this makes the solder flow much better, helps to avoid bridging, and lets you use the minimum solder necessary.
Along with the magnification you recommend, get PLENTY of light on the project.
I use a magnifying visor when I don't have access to a stereo microscope.
Get the smallest soldering tip you can. Sometimes in a pinch, you can wrap some small wire around a larger tip and extend the wire to form a new tip.
chaoticandrandom (author)  wa7jos1 year ago
Experienced SMD Re-work definitely helps with fine pitch but No need for flux here on this type of connection. There is no solder here just the plastic strip and carbon lines which bond with the gold pads. You are just softening the plastic strip to bond with the PCB.
chaoticandrandom (author)  DrNerdington2 years ago
Your right, i seem to have got my conversion wrong. Thinking too hard about everything else trying to get the info down. I will update and correct later. Thanks.
guischall2 years ago
Great job!!

I'm wondering if it wouldn't be easier, more accurate and reliable to place a real SMT connector on the board?

something like this one: http://www.digikey.com/product-detail/en/FH40-64S-0.5SV/HFW64CT-ND/2295757

It's pretty cheap and easier to solder, then you just have to clamp the cable into the connector. Maybe you are interested in reworking that to get all lines back.
chaoticandrandom (author)  guischall2 years ago
i would not rule out a connector fix totally but its nice if you can fix for zero cost if possible. Also you then have to manage the mechanical constraints as well as choosing a suitable connector. Usually only the semi flexi PCB circuits ribbons go into connectors not the carbon screen printed sort so may not be so desirable.
Sorry, the connector on the link doesn't match the board design... you must search for FFC, FPC connectors with the number of vias of your cable and look for the real dimensions on the datasheet.

maybe this one is a closer match:
http://www.digikey.com/product-detail/en/5027906491/WM1449TR-ND/2356633
Spokehedz2 years ago
Wow, I would say that for spending zero dollars that is a darn fine job!
chaoticandrandom (author)  Spokehedz2 years ago
Yep,always good to fix things for zero dollars.
Judging by today's exchange rate i save my friend 600 bucks...
mario592 years ago
Ciao!

At least now, we have AN IDEA of what one needs to face such problems!
Each time I tried to repair, it failed mierabily.
Thanks for sharing!

I do have questions regarding the ribbon cable. Did your ribbon cable have insulation on both sides? If it has, did you strip or scrape a bit of insulation prior to connecting it on the board?
Oops okay I read the comment below and it seems that yours dont have insulation on the connecting side.
Fantastic instructable! This is one of the things that I've always wondered about. I thought some sort of conducting glue was in charge here, never thought it was even pressure and heat.

Great job there, thanks for sharing!

Koray
a lot of great info here! I've never worked with this type of ribbon before, does it have exposed leads on one side?
Thanks, glad you like, i really did want to get down everything i learned.
There are no exposed leads on the ribbon but it is not symmetrical.
The matt (non shiny) side has the carbon connection lines screen printed on and thats the delicate part. Its easy to scratch off.
The other side is shiny but it is not the side you connect.