Intro: How to Remove and Re-attach LCD Ribbon From a PCB With a Fine Pitch
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.
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.
Step 1: Before You Start, Make an Assessment of LCD Ribbon and Module
Before you can even begin to think about removing the ribbon you must make an assessment of what you have and what may or may not be possible.
So Before you start:
Have you tried reworking ribbon? There are already some good techniques for small repairs such as the hot air gun technique.
Other favorites of reworking the LCD connection that i have read here are the tinfoil on a heat gun. This has good temperature management but not so good in tight spaces. The solder iron with flat blade and tin foil is more precise but a 25 Watt iron can be too brutal on the ribbon.
If you have tried re-working the ribbon with no more improvement then these are my next steps of LCD assessment.
1. Do you have enough spare ribbon to detach and re-attach? The more ribbon you have the more goes you may get but watch out for the mechanical caveat below.
2. Will you be mechanically constrained if you cut the ribbon. This is a tough one as some shortening of the ribbon may make it impossible to re-assemble the device!!
3. Is the Ribbon continuity visibly good, by that i mean the carbon connection lines are continuous and unbroken - Do check otherwise you may be wasting your time.
4. Is it really the ribbon causing the problem? The driver chip could be failing.
5. Finally the easiest call is made by the item is going to be trash and you got nothing to lose.
In the photos below you can see the available ribbon length was generous enough but do watch for mechanical constraints. In some cases you could find yourself not being able to lay down the LCD back down as it is too tight a radius to sit down.
The photo with the pencil pointing indicates how much ribbon was available.
Step 2: Remove Old Ribbon Connection
Ok so you got nothing to lose by re-attaching the ribbon.....Lets get going.
The ribbon removal needs careful thought depending on your device. It would be difficult to write a complete panacea solution for every device so please use some careful judgement on your device.
You do not want to pull at the ribbon as you will most likely damage what you already have. In my instance it was best to cut the ribbon free as close to the PCB pads as possible.I used a scalpel to slice parallel to the PCB board to remove the ribbon. Do make a good job of this as you may need to preserve as much extra ribbon to re-attach the LCD module.
Look carefully at what you have to detach and thing of what could improve your chances to make a good clean removal.
These were my observations and experiences:
Do not slice across the top! You will slice into the PCB tracks.
Do not pull the ribbon! It is likely to de-form, could tear OR break carbon connection as a result.
From my photos you can the LCD ribbon being cut. I should of used a rounded head blade and not a pointed blade as shown.
The LCD assembly was lifted off and put in safe place to avoid damage. The ribbon was then gently lifted and peeled back with tweezers to remove the bulk. You must not use force to remove the remainder ribbon especially if your PCB is off a cheap quality OR single sided cardboard type variety. The PCB pads can come off with the ribbon! If you have a double sided PCB of FR4
quality then LCD PCB pads should have better adhesion to the laminate but in fine pitch devices they still can come off so beware.
Step 3: Clean the PCB Pads
Having removed the ribbon, the PCB pads will need some attention to remove leftover ribbon material.
If you have a half decent PCB the connecting pads may be gold flashed (actually called Electroless Plated gold). This gold flashing is good as it provides a very good flatness to the PCB pads but they are not as mechanically strong as gold edge connectors (like you see on old PC adapter cards) which is a hard gold . The gold plate here is soft and also micrometer thin on the surface.
If you have just tin solder pads the surface may be a bit rough. You can re-touch solder pads to improve flatness and hence the connection.
For either connection style you need to remove any old glue from the ribbon and remaining carbon debris from the pads. I used isopropanol on a cotton wool bud. Do not flood the PCB with cleaning fluid as you may effect electro-mechanical elements in close proximity such as switches and other items on the PCB which are not sealed against cleaning!
The PCB pads must be thoroughly cleaned and no debris must exist. Use you X10 OR x20 eyepiece here to check how clean the pads are. The PCB pads need to be pristine and nothing less.
From the photos you can see the PCB pads before cleaning through the eyepiece and the final photo shows the clean PCB pads with leftover cotton wool buds.
Step 4: Trimming and Preparing the LCD Ribbon for Re-attachment
The ribbon was then laid flat with a ruler and a scalpel was used to trim up the ribbon.
I found it was best to use a plastic ruler to view through to the ribbon so i could see how much i should cut off.
A metal ruler can be used and may have straighter edge to work against but a plastic ruler was sufficient.
Do use a rounded scalpel blade to prevent dragging the LCD ribbon while cutting.
Do use a flat cutting board or a cutting mat.
Do check the ruler is as perpendicular to the sides as much as possible.
Remember you may only have one chance at re-trimming so getting right first time is essential.
From the photos you can see that ribbon was trimmed with a rounded scalpel blade. The ribbon also had extra green tape which adhered to the original heel of the PCB pad connection. This gave extra mechanical stability for the ribbon but has to be peeled off to allow for re-connection. Later in this instructable i will mention about putting back extra mechanical stability for ribbon support.
Step 5: Pre-Assembley and Registration of LCD Ribbon
After cleaning the PCB pads thoroughly and trimming the ribbon the re-registration of the LCD ribbon was the hardest.
If you have a fine pitch ribbon like i had this will cause you the most trouble. I needed an extra steady pair of hands to help and some patience before i got the the ribbon aligned. It took twenty minutes of nudging the PCB and ribbon to get a precise alignment. Our alignment was actually better than the original which was slightly skewed to one side.
If you do not have an extra pair of hands then i did think of using a large ball of Blu-tak to hold things in place but a second pair of hands is much better!
The trick to get good alignment is to allow some the gold pad fingers toes of the PCB to be visible just beyond the carbon lines of the ribbon. You then get the pads toes to line up with the carbon lines of the LCD ribbon.
Do not continue until you have excellent alignment of the black carbon lines of the ribbon to the PCB pads. The finer the pitch of the ribbon the better registration is required.
Do use your X10 or X20 eyepiece to check registration continually
The photos below show how i handled the PCB and LCD and clamped the ribbon in place. The LCD display is being held by a plastic clamp above the PCB assembly. The PCB below which has components both sides is laying on some foam (try polystyrene). This allowed me to nudge the PCB under the ribbon into position. The plastic ruler acts as a LCD ribbon clamp. When you have got the registration get a steady handed friend to hold the ruler as a ribbon clamp in place so you can then apply the heat to stick the ribbon back down.
The photos actually do not show the good alignment but just poor alignment but you can see what nudging should happen to get alignment.
Check out the third photo and you can see what fine pitch means. There are two carbons tracks with a gap in every 1mm (25.4 thou). Now you see why it took twenty minutes to align!
You may want to skip forward to the next step to see the re-attached picture of the ribbon and to see how the alignment was achieved. You should see the gold PCB pad finger toes in line with the carbon of the ribbon
The best result is found on the right hand of the ribbon in the picture after alignment and heating. The left hand side had too much heat applied.
Step 6: Apply the Heat to Re-attach Ribbon
So you now have your pristine PCB pads and the ribbon is clamped in place we are ready to apply heat.
Some tips to applying heat:
1. Do not apply so much heat you obliterate the ribbon. Yes it sounds stupid but i over cooked one side of my ribbon and got away with it. You may want to test on the bit you trimmed off elsewhere to get correct amount of heat.
2. Only tack the ribbon down my pressing the heated tip down vertically and stroking from the heel to the toe. That is to say in the same line that the carbon lines flows.
3. Do not be tempted to apply heat with a broad swiping action! - The LCD ribbon with heat will drag or tear especially on fine pitch ribbons.
4. Avoid applying heat to other components you do not want to! If the work space is tight shield other components.
Tools for apply heating are up to you but i used a 25W Soldering iron with a wide flat tip covered in tin foil. Warning, the solder iron is too hot with tin foil so i cool it a little by dipping it into a wet sponge just before applying the heat. I used the solder iron tip method because i have more fine control but it did not have a regulated heat. If you have a good soldering iron with temperature control start low and work up to get the right heat.
You can also use a hot glue gun tip covered in tin foil which has a milder heat but the glue gun tip can be too large in confined spaces.
Applying the heat
The steps to apply your heat are as follows:
1. Do one final check of registration before heating
2. Tack down one end of the ribbon and re-check the registration.
3. If all good then tack down other end and again check registration.
4. With the LCD ribbon now tacked and registration is still maintained you can apply the Heat to the remaining ribbon.
Again Do not apply heat to the ribbon in one broad stroke. Work from the heel of the ribbon to the toe Or work by dabbing. By dabbing I mean hitting one spot on the ribbon with the heated tip and then lifted vertically again cooling the tip with the wet sponge before each dab.
You will know that the ribbon is attached as the glue in the ribbon changes its appearance on the PCB.
The first photo in this step is for demonstration purposes to show a solder iron with tinfoil attached.
The second photo in this step is the actual ribbon re-attached. You can see that the left hand side of the ribbon has not worked out as well as the right. I had too much heat in the solder iron. This is how i ended up cooling the solder iron with the wet sponge before applying heat.
Ideally i would like the whole ribbon to look more like the right hand side of the photo.
You can also see how the PCB gold pad toe is just visible. This is how the good registration is achieved.
Step 7: Optional Post Ribbon Attachment - Adding Extra Mechanical Support
This bit is optional but could help with mechanical stability of the LCD ribbon.
In our case the LCD ribbon was not only glued to the PCB pads but there was some additional tape at the heel of the ribbon to hold the ribbon in place. By holding at the heel the ribbon you get some good extra mechanical support.
I did not replace the heel taped to the ribbon so we added some mylar sticky tape across the ribbon pads to add some extra support.
You may want to consider some extra support depending on your LCD environment such as vibration.
I would not advocate hot gluing for obvious reason and do not know whether an epoxy glue would be advisable.
You would only apply LCD ribbon supplementary support after successful testing otherwise any re-work after attachment may be impossible.
Step 8: Re-Assemble Your Device and Test
In our LCD module we partially assembled the device as best as possible so we could test it its operation.
From the photo you can see the LCD operation is much better than the couple of lines we had but is not ideal.
Step 9: Results and Lessons Learned
Our result was a partial success and not 100%,more like high 90's%.
From the photo some lines were still not functional but considered against the two lines that we had it was a very good result.
I did not go further with more re-work as the VW LCD module was considered a good enough result and some other time pressures intervened. It was concluded that we could read the display well enough and operate items from the controller. It was also considered as one of those quit while your ahead things!
For some people this may not be good enough but i hope that some of the steps i have listed will get people going in the correct direction when considering this. I do believe with a little more time a 100% is achievable. I took two hours to dismantle and remove the ribbon, Most of this was thinking things through... and another two hours to re-register and re-attach ribbon.
On the Lessons learned from this there are many :
1. Most important was that you may only get one go.
2. The ribbon and PCB need the utmost respect to not introduce other problems.
3. Registration of the ribbon is difficult with fine pitch but not impossible.
4. You need a good set of eyes, an eyepiece, steady hands and patience.
5. Ideally you would like a temperature controlled heat application. (A compact heated metal roller to apply heat to the ribbon)
The technique for LCD ribbon removal and re-attachment are achievable certainly on simpler ribbons and fine pitch ribbons with careful preparation and thought. I hope this instructable is comprehensive enough for people to get some good results.
Thanks for following.
UPDATE 12-10-2012 - Background and Reference Material
The ribbon is know as a "Heat Seal Connection" OR "HSC". In the industry heat and pressure are used to make this type of connection. The material comes from a family of "Anisotropic Conductive Films" OR "ACF".
The material bonds at 180 DegreeC. Direct Ribbon connection is used for economy (i.e. no fancy connectors) and for the number of connections its offers in a small footprint which would not be possible through traditional connectors.
The other end of the ribbon that joins to the LCD is terminated on the glass on Indium tin oxide (ITO) which is one of the most widely used transparent conducting oxides.
If you want more information there are many different types of LCM assemby (LCD Display plus it driving chips) to look at but these are the main ones (increasing in density):
1. Elastomeric Connection
2. Heat Seal Connection - What was fixed in the instructable!
3. FPC - Flexible Printed Circuit as used on phones. Can be many layers and expensive.
3. Tab Connection
4. Chip on Glass
5. Chip on Films
In manufacture of these modules a machine is used for assembly which would compress HSC to the LCD Or the PCB and then apply the correct amount of heat.