how to remove and re-attach lcd ribbon from a pcb with a fine pitch

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How to remove and re-attach LCD Ribbon from a PCB with a Fine Pitch http://www.instructables.com/id/How-to-remove-and-re-attach-LCD-Ribbon-from-a-PCB-/

1 of 18 24/12/2013 10:49 μμ

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This instructable came about from a broken LCD control module out of amodern VW Camper Van. The LCD module is part of a control unit which wasvirtually unreadable and a replacement for a new unit was £400+. It really was ano 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 theLCD. The symptoms are caused by poor location of the LCD ribbon inmanufacture and also the poor position of the whole module in the vehicle whichexposes it to heat and is subject to vibration within the vehicle. This causes theribbon to fail eventually and is a known common fault.

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3 of 18 24/12/2013 10:49 μμ

The ribbon in this display actually controls the Rows of the LCD matrix and theColumns were handled by a rubber standoff connection on the longest side ofthe LCD. There were no problems with the rubberized connection.

Some re-work on the LCD ribbon had already been tried with a littleimprovement but the poor registration of the ribbon pushed me to try a newattachment.

From the photos below you can see the LCD control unit and the state of theLCD ribbon before repair. You can just make out the offset placement and poorregistration of the ribbon before repair.The marks on the ribbon are my mistake of applying too much heat duringre-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 andnimble work is required and i cannot stress how important it is to take your timeand 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 myfriend 20 minutes just to line up the ribbon for re-attachment. The ribbon in thiscase is sub 1mm pitch OR less than 25.4 thousands of an inch. You may want totry a simpler ribbon repair on an old LCD clock for example before jumping inhead first with fine pitch.

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

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

Essential Tools:


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4 of 18 24/12/2013 10:49 μμ

1. Eyepiece - X10 minimum, X20 Preferred - For Viewing/Cleaning PCB padsand registration of ribbon2. Scalpel with rounded blades - For ribbon removal and trimming.3. Small Ruler - plastic or metal - For trimming and clamping of LCD ribbon4. Solder Iron Or Hot glue gun - For applying heat, adjustable temperaturesolder iron would be preferred.5. Small amount of Tinfoil - For wrapping over solder iron or glue gun nozzle6. Cotton Wool Ear Buds - For cleaning PCB pads7. Isopropanol Or Methylated Spirit - For cleaning PCB pads8. Another pair of steady hands - For clamping the LCD ribbon in place9. Tweezers - For removing leftover ribbon.

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

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5 of 18 24/12/2013 10:49 μμ

Next » (/id/How-to-remove-and-re-attach-LCD-Ribbon-from-a-PCB-/step1/Before-you-start-make-an-assessment-of-LCD-Ribbon-/)

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DIVYA GARG (/member/DIVYA+GARG/) says:

I think........you are a good electronics engineer ...........but I am not as you......rather I have damaged my 3 calculator by thisaction.....................!..........................................but you have written verygood............!

billbbc (/member/billbbc/) says:

Saw this and used the nozzle of a hot glue gun to reglue a display tape. Workedfirst time without retrimming the tape.

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


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6 of 18 24/12/2013 10:49 μμ

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Unit I repaired with missing segments was a Honeywell CM907 controller. £65 UKsaved. Thank you for posting this.

bwelkin (/member/bwelkin/) says:

This step surprised me! I am very unclear what that thing is that is heating thesolder pads.

My recommendation is to use a T-iron (see eBay .. about $35USD) which has theadded advantage of having a heat shield that protects the insulation leading up tothe solder pads.

chaoticandrandom (/member/chaoticandrandom/) (author) in reply to bwelkin

In the photo i am only using asoldering iron covered in tin foil toheat the plastic ribbon. There is nosolder used in this setup. The tin foilis there only to provide a bettersurface to apply heat to the ribbon(does not stick to the ribbon!!).When heat is applied to the ribbon itmelts like a glue which in turn bondsitself to the PCB and the ribbonbecomes attached to the PCB as itcools.Actual Electrical connectivity isprovided by carbon lines which areprinted in the ribbon. The carbonlines only make contact via theadhesion of the ribbon.

The solder iron method technique isactually too hot and so i dip the


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7 of 18 24/12/2013 10:49 μμ

(/member/detinu77/)

1 year ago Reply (CIQW9NAH7430UZF)

solder iron in a sponge to cool it down before pressing down on theribbon. If you have a temperature controlled soldering iron it would bemuch 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 LCDribbon.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 isalmost 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 Itdoes look very useful. Thanks.

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

detinu77 (/member/detinu77/) says:

Is that an actual scalpel you're using? I haven't seen one of those in a while.


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8 of 18 24/12/2013 10:49 μμ

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elias.alberto (/member/elias.alberto/) says:

i have an alarm clock which doesn't have a ribbon, but instead some sort ofrubbery contact strip against which the display should be pressed. You can findpics of it on google images for "lcd rubber contact strip", it seems to be called azebra rubber. Any idea on how to glue/solder the display to that rubbery contactstrip?

artemff (/member/artemff/) in reply to elias.alberto

you just have to position theconductive rubber properly - this typeof LCD is very popular and it's mucheasier to repair compared to what theauthor has described. If some of thebars/elements are still not working,you may try cleaning the contactsusing the eraser. But

dasjeetu (/member/dasjeetu/) says:

Thanks for the idea, perfect.

Thanks for sharing...

paddyart (/member/paddyart/) says:

Great Instructable... It's fantastic to see people giving a fix a go, before buying anew one.I'll be giving this one a try one day.


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a2e (/member/a2e/) says:

There's always a guy who goes where everybody says "it cannot be done"...My admiration and respect fellow.

Treknology (/member/Treknology/) in reply to a2e

Ditto. One day someone will come outwith a "needle-point" soldering iron, sothat it becomes possible to individuallyre-solder SMD connections.

snayl (/member/snayl/) says:

Very thorough, a pleasure to read. I haven't had the need for a repair like this asof yet, but I shall definitely bookmark/download/etc. this instructable for futurereference!

artemff (/member/artemff/) says:

very detailed instructable, thanks for sharing.

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

Returning to your instructable - in principle, I can imagine using the sameapproach in your case. One can avoid soldering to sub-mm spaced contacts bytracing the board and connecting to different parts of it. This gives more freedomsince the wires can be checked individually. LCDs are far less expensivecompared to the control module you named so one can worry a bit less :)


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10 of 18 24/12/2013 10:49 μμ

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f5mando (/member/f5mando/) says:

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 alifetime warranty. I got it back fast, with 100% readout, and it continues to functionperfectly 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 linkhere, so I won't until I hear otherwise.

maxhuey (/member/maxhuey/) says:

I have seen this done by a kid (about 15 y/o) right on the sidewalk in theelectronic district street of HK. He brush some kind of liquid on the ribbon and asmall 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 goldentouch! You are one of them... Cheers

bahi (/member/bahi/) says:

Impressive and accurate work, never thought it could be possible to repair suchkind of connections.

Thanks for sharing.

chaoticandrandom (/member/chaoticandrandom/) (author) in reply to bahi

Thanks, these connections aredefinitely repairable but the fine pitchon this ribbon is the hardest part. Isuggest anyone having a go trysomething simpler before going with


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the more difficult projects. I had actually repaired an MP3 FM transmitterdisplay before doing this one. That was easy only just about 10 or soconnections and much larger pitch between them. It was good practise.

DrNerdington (/member/DrNerdington/) says:

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 haveactual foil+Kapton cables, which can actually be soldered) so I know how hardthis can be. Excellent work describing the process and pitfalls.

wa7jos (/member/wa7jos/) in reply to DrNerdington

I have done a lot of SMD rework, andone item that REALLY helps is a fluxpen. It will cost you about $7, and isabout the size of a small felt tipmarker, but it dispenses liquid flux. Alittle of this makes the solder flowmuch better, helps to avoid bridging,and lets you use the minimum soldernecessary.Along with the magnification yourecommend, get PLENTY of light onthe project.I use a magnifying visor when I don'thave access to a stereo microscope.Get the smallest soldering tip you can.Sometimes in a pinch, you can wrapsome small wire around a larger tipand extend the wire to form a new tip.


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chaoticandrandom (/member/chaoticandrandom/) (author) in reply to wa7jos

Experienced SMD Re-work definitelyhelps with fine pitch but No need forflux here on this type of connection.There is no solder here just the plasticstrip and carbon lines which bond withthe gold pads. You are just softeningthe plastic strip to bond with the PCB.

chaoticandrandom (/member/chaoticandrandom/) (author) in reply to DrNerdington

Your right, i seem to have got myconversion wrong. Thinking too hardabout everything else trying to getthe info down. I will update andcorrect later. Thanks.

guischall (/member/guischall/) says:

Great job!!

I'm wondering if it wouldn't be easier, more accurate and reliable to place a realSMT 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 intothe connector. Maybe you are interested in reworking that to get all lines back.

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i would not rule out aconnector fix totally butits nice if you can fix forzero cost if possible.Also you then have tomanage themechanical constraintsas well as choosing asuitable connector.Usually only the semiflexi PCB circuitsribbons go intoconnectors not thecarbon screen printedsort so may not be sodesirable.

guischall (/member/guischall/) in reply to guischall

Sorry, the connector on the linkdoesn't match the board design... youmust search for FFC, FPC connectorswith the number of vias of your cableand look for the real dimensions onthe datasheet.

maybe this one is a closer match:http://www.digikey.com/product-detail/en/5027906491/WM1449TR-ND/2356633

Spokehedz (/member/Spokehedz/) says:

Wow, I would say that for spending zero dollars that is a darn fine job!


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chaoticandrandom (/member/chaoticandrandom/) (author) in reply to Spokehedz

Yep,always good to fix things for zerodollars.Judging by today's exchange rate isave my friend 600 bucks...

mario59 (/member/mario59/) says:

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!

tacticalninja (/member/tacticalninja/) says:

I do have questions regarding the ribbon cable. Did your ribbon cable haveinsulation on both sides? If it has, did you strip or scrape a bit of insulation prior toconnecting it on the board?


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tacticalninja (/member/tacticalninja/) in reply to tacticalninja

Oops okay I read the comment belowand it seems that yours dont haveinsulation on the connecting side.

thearchitect (/member/thearchitect/) says:

Fantastic instructable! This is one of the things that I've always wondered about. Ithought some sort of conducting glue was in charge here, never thought it waseven pressure and heat.

Great job there, thanks for sharing!

Koray

amandaghassaei (/member/amandaghassaei/) says:

a lot of great info here! I've never worked withthis type of ribbon before, does it haveexposed leads on one side?

chaoticandrandom (/member/chaoticandrandom/) (author) in reply toamandaghassaei

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 printedon and thats the delicate part. Its easy to scratch off.The other side is shiny but it is not the side you connect.


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how to remove and re-attach lcd ribbon from a pcb with a fine pitch

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