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Author Topic: broken FFC  (Read 7514 times)
Angrysunshine
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« on: April 05, 2010, 02:33:17 PM »

I started this topic as a reply in another blog, since I'm new and couldn't post a topic on my own. I think it's more appropriate to put it in on it's own, so I'll catch everyone up.

Me:
"I have a ffc that is/was soldered directly to the board. It was old and stale and it cracked (right where it is connected to the board). It's half off now. I have an image of it, but am not sure how to insert it.

Is it fixable? Since it attaches directly to the board, is it still possible to attach a new one? What kind? etc."

cellofaan:
"The only way to connect a new ffc cable is to solder it directly to the board.
You could try to vile down the broken connections, and just press the cable against them. If they make good contact, it will probably work, but it isn't easy to fix it in place and keeping the pressure on it."

Me (now, following up on that):
A new cable: I'm not sure how I'd connect the new cable. Some of the material on the board side is torn up. Can I solder that? Could I make it so it has some kind of door or other lock attached as well so this is less likely to happen like this again?

The broken cable: The cable part doesn't seem damaged, the board side does. It's just that the cable part cracked or snapped off. Would I need to sand the board side of the connection?

If I could show a picture perhaps it would help me describe:

* BrokenFFCFront.JPG (215.11 KB. 1428x561 - viewed 368 times.)
[ Attachment Invalid Or Does Not Exist ]
I claim no copyright for this image

« Last Edit: April 05, 2010, 05:09:28 PM by Angrysunshine » Logged
cellofaan
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« Reply #1 on: April 05, 2010, 04:29:40 PM »

That looks very broken indeed. You might be able to solder it, but it won't be easy. I'm not that knowledgeable on soldering. Maybe Bernard can tell you more.
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bernard
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« Reply #2 on: April 05, 2010, 09:27:16 PM »

The "cable" is actually not a cable but some kind of flex pcb -- it is made into a "cable" but the whole thing is really one piece. 

Could you post another picture of what does the other end of the cable look like? 

I can count 20 pins -- so I suspect we are talking about a LCD panel here? (this wasn't clear from your explanation). 

Could you measure the size of all this -- in particular, compute the distance between two pins (where soldering will be required) -- or more specifically the entire size divided by 20.  Also do the same on the other end of the cable.

Soldering is possible, but not the simplest and risky. I do not have much experience, but I know somebody that had quite a lot of experience in soldering dense SMT parts with simple "home" soldering tools.

One thing I also see here is that the PCB might be damaged -- I am not sure, but it looks like the pads peeled off the PCBs (probably yes) -- which raises the level of difficulty.

What is your expertise level in crafting electronics:  Have you soldered before? Do you have a multimeter?

BTW:  "PCB" is for "Printed Circuit Board" -- or the [typically] green hard board with the "traces" on it.  The traces are covered with some green translucent stuff so it does not "rust" (oxidize). If the pads are broken, you have to get the signal from elsewhere on the board.

On that note, also post the entire surrounding board to see more traces and where they go.

Since the LCD is obviously broken, the risk is somewhat low -- at worst, you break it more.   Roll Eyes 


To your question:  can you solder to that cable -- answer: it depends :S  it depends how that cable has been built.  I would suspect that you can solder this because it seems it has been soldered before.

Do you need to extend or replace that cable?  This might impact what solution you should opt for.
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Angrysunshine
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« Reply #3 on: April 07, 2010, 05:12:25 PM »

Can I keep calling it a FFC or "cable", or is there another name for it? You are right about it, it is an LCD and does have 20 pins, as I hope the images will show.

I do have some soldering experience, but with bigger things, not PCBs, though I do have the equipment. I also have a multimeter.

Pictures
Board Front:

* FFCBoardFrontAltered.jpg (266.56 KB. 1823x453 - viewed 359 times.)


Pins next to a ruler:

* FFCRuledPinsAltered.jpg (281.87 KB. 1325x1019 - viewed 378 times.)

It looks to me like 20 pins = 12 32nds? So the distance between two pins would be ((1/32) * 12)/20, that is 0.01875"?

Where the "cable" connects to the board:

* FFCRuledBoardConnectionAltered.jpg (268.87 KB. 1369x943 - viewed 353 times.)

This looks like the distance between all the connections (the only word I know to describe that) is 17 32nds? So the distance between two would be ((1/32) * 17)/20, 0.0265625"?

Board Back:

* FFCBoardBackAltered.jpg (361.57 KB. 1620x558 - viewed 354 times.)


Do I need more pictures? Should I be measuring in mm? The first number looks good for inches, but the second one looks a little crazy.

Also, in my original image at least, it looks like not all the pins lead somewhere. Could that be right?

I would rather replace, or if necessary extend, the cable. Would that make it more difficult or easier? How hard is this? Is it reasonable to believe I can fix this, or should I look into another screen?

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bernard
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« Reply #4 on: April 07, 2010, 05:51:26 PM »

yes, mm please.  I am lost with inches.  Beside most of the FFC I have seen are spec'd in mm.  Typical FFCs spacing are 0.5 mm and 1.0 mm. 

But we can make the math...   0.01875 inches = 0.47625 millimeters  -- so that looks close to 0.5 mm to me -- which is the standard FFC cable spacing -- that end is the one we extend so it should be 0.5 mm normally.   

for the other end, it looks "wider" than the "cable" (I do not have a word either for this). So in mm, it would be 0.0265625 inches = 0.6746875 millimeters.  Not much bigger than 0.5mm (I would have hoped 1 mm)  --  there are a bit of rounding errors here I would re-do the measurement in mm to be sure.

You say it is not all connected?  It is possible. If some are not connected, than that's less soldering to do!  Smiley

Since this is probably not 0.5 mm on the board, you cannot just put another FFC cable "on top" and solder it all at once since you will not find a FFC with the same spacing.  So it sounds you are stuck soldering every signal separately.  Some of the wires are still connected but not that much.   I think you could try to re-use that cable, and find ways to hook wires onto it. 

It will not be easy.  Also you will have to find another similar thing to practice soldering on -- open a defective electronic device to see if you can find a similar orange part.  I know most CD players have that.  (Like a internal CD drive in a PCs)

You will need Flux -- paste, liquid or "pen". This is the key to do this type of soldering. The flux will "channel" the soldering.  You do not need much solder, always put flux before soldering (can't have too much flux). You can put solder on both sides separately, just enough to "paint" the wire and the pads, no need for more.  Then, apply flux again put the wire on the pad apply heat on top, does not need much - barely enough to melt the "thin" solder. 

pads on PCBs are fragile, too much heat and the pad will peel off.

Some of the pads in your thing seems damaged (not sure, try with a multimeter to see if there is still metal there).  For those, you will have to find the signal elsewhere on the board.  Either cutting through the protective layer to get to a trace or find another exposed pad that connects to it.

In anyway, you HAVE to practice since errors might be difficult to fix.  Find similar junk PCBs and "orange" flex pcbs and try out the technique. There is no way you will succeed the first time. 

To hook to the wire itself, you might be able to melt the orange protective layer to get to the cable "metal".  It is 0.5 mm in there, not much space.   

You might also need "wick" too to remove solder. 

There is also "flux cleaner" -- but this is just to make a cleaner job (it really look super-clean afterwards Smiley ) -- But the idea here is that flux, with time, I think is not good for the metal, you might be able to clean with something else (alcohol? lighter fuel?). A bottle might be expensive for a single tiny project like yours.

So you will need: 
- a small roll of "wire wrap" (the thinnest gauge you can find)
- flux  (pen or liquid are best for this type of stuff, but "paste" tends to be easier to find)
- wick
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Angrysunshine
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« Reply #5 on: April 07, 2010, 07:46:45 PM »

Haven't done reading bernard's post, but I forgot to post picture of the other other side, so here they are for those who want them:

* FFCtoBoard1bAltered.jpg (492.47 KB. 3430x825 - viewed 386 times.)

* FFCtoBoard2a2Altered.jpg (495.59 KB. 1274x617 - viewed 398 times.)

I have closer ups of the middle and right end as well. If they are wanted, say so and I'll post them.


* FFCtoBoardBack1aAltered.jpg (427.98 KB. 3188x672 - viewed 364 times.)

* FFCtoBoardBack1bAltered.jpg (449.29 KB. 2897x887 - viewed 387 times.)


Ok, now to read bernard's post more closely.

« Last Edit: April 07, 2010, 10:19:47 PM by Angrysunshine » Logged
Angrysunshine
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« Reply #6 on: April 07, 2010, 09:50:52 PM »

bernard,
I remeasured:

* FFCtoBoardmmAltered.jpg (429.45 KB. 1540x1155 - viewed 366 times.)

I did my best to get as accurate a measurement as I could. Other pictures looked like connections line up to mm, but I think they were skewed. This was the most head-on, ruler-closest-to-the-connection picture I got.

To me it looks like this doesn't add up to a distance of 1 mm between each. Sad

That just means that all the great info you put down is even more useful. And lots of questions!

You said I'll have to connect each with it's own wire, which might be fragile. Perhaps I could glue some flexible material, maybe extra cable, as a bridge between the wires and the board, and glue the wires to that as well...

Two slightly different questions in another direction: I have conductive glue. Could I use that to glue a new cable on in place of wires? Or to form other connections, or fix the damaged pads so the signal comes through? Also, do you think I should take off the cable completely? It makes me nervous to leave it hanging half off.

I do have flux and wick and I can order the rest. Perhaps I will look up the soldering tutorial post to make sure I get the right kinds.

Whatever your answers are, you're right that I should find something to practice on. There's none of those treasures around the apartment, so I'll have to go farther afield.

If I am going to solder, I'm not sure what and where I would cut open. Should I get a new cable at least, with 0.5 mm on one end and something else on the other?

So many questions. Thank you for all you've done so far. If this becomes too much to deal with, just PM me.

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Angrysunshine
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« Reply #7 on: April 09, 2010, 05:52:43 PM »

I just spent more time than I'd like to admit searching (and finding, whew) my multimeter. I then found that something wasn't working. Found out the wires themselves were still working, so that's fine. Now I see the tips are way too huge to not cross connections, but I have some pre-tinned wire that I think will work.

On the other hand, if I understand correctly:

* FFCPowerPathAltered.jpg (417.93 KB. 1609x766 - viewed 354 times.)

I'm not sure I can get into that space and if I do, but the pads aren't connected to the cable, how is power going to get to them so I can check if they're still working...

Also, some of the pads may be laying on top of one another. Would that short circuit the connection? Does it matter?

I have soldering wire as thin as the pads, so perhaps I ought to order thinner stuff. The glue I have, I can put into a dispenser with a tiny tip so that it doesn't bridge the connections and short circuit stuff. That seems to imply that it would be just as likely to short circuit one way or another. Either way, I think I should find a huge magnifying glass if I plan to continue with this.

I think this is one I might have to let go. Though people solder this stuff every day so it must be possible.  Perhaps I should consider ordering a different screen. Or perhaps I am more dexterous than I think?

« Last Edit: April 09, 2010, 05:58:00 PM by Angrysunshine » Logged
bernard
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« Reply #8 on: April 09, 2010, 11:26:48 PM »

People solder this stuff everyday using specialized equipment yes. But using a bare soldering iron is tricky at best. I would go for it (if it was me) but the majority of people would not.

Do you know the LCD Panel specs -- in particular its size and native resolution? Or what is the brand/model number? (typically written on a sticker on the back)

Sure that if pads are touching (crossing), this is not good.

For your multimeter testing, the pads that looks "peeled off", my question was: is it really peeled off or is there still metal there?  (put the probe on the top pad and "under" and see if it "connects" (beep).

I do not understand your power question thingy. But at this stage, I would rather focus on the broken connection on that board and forget about the rest. 
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random-jimmy
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« Reply #9 on: April 10, 2010, 08:32:51 AM »

From the looks of it, it may be that the pads have not peeled off the PCB (which is good) - it should still be solderable either way, just with the pads gone it makes it harder.If the pads are actually torn off then all you have to do is scrape the green stuff off the trace and solder to that (the trace is the line going to the pad).

For wire, you are probably best finding a high-density IDE hard drive cable (i.e. the one with thinner wires) and using that to solder with. Because it will be in a big flat ribbon, you should just be able to glue it onto the board for mechanical strength.

I would stay away from conductive glue, as it is likely to have unwanted effects at the high frequencies that wire operates at (in the order of 50-150MHz).

My final word - make sure you have a temperature-regulated soldering iron with a fine tip. This is a MUST - otherwise you will only damage the LCD further.
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bernard
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« Reply #10 on: April 10, 2010, 03:56:59 PM »

hey random-jimmy -- what is the best iron temperature to do that type of work?
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Angrysunshine
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« Reply #11 on: April 11, 2010, 02:15:03 PM »

bernard,
The LCD is a samsung 171p (it's over sized for my A3 Intuos tablet, which is part of why I'm considering a different monitor). I found some good specs on http://www.gideontech.com/content/articles/96/1

It's 17" with a native resolution of 1280 x 1024

Also, "under" means the other side of the board, right?
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Angrysunshine
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« Reply #12 on: April 11, 2010, 02:22:48 PM »

random-jimmy,

I'm new to this stuff, so...high-density IDE cable - wouldn't I still have trouble with the unusual pitch? Also, I searched for the stuff and only see them with connectors, not bare. Does that mean I pull/cut the connectors off and scrape off/strip the wires?

I also like bernard's question - what temperature is best for this type of work (thanks bernard, not a question I'd have remembered to ask)?
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bernard
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« Reply #13 on: April 11, 2010, 08:30:48 PM »

Monitor case designed by F.A. Porsche?  Cool stuff!  Cool

It is a nice screen, maybe worth the trouble. It is a delicate balance of cost vs. energy.  If buying a temperature-controlled iron costs more than finding a new screen, then either you try with your bare soldering iron or give up right-away to hunt for a new screen (and maybe try to sell that one as "broken").

Of course, if you like soldering and getting into that stuff more or just like getting new toys tools then go for it Smiley
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bernard
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« Reply #14 on: April 11, 2010, 09:27:19 PM »

High-density IDE cables -- ah yeah! those do look thin indeed.  Yes, you can just keep (cut) a middle portion between 2 connectors (might not be very long thought).  For the pitch: with these flat cables you can easily "strip off" individual wires for a short distance.

random-jimmy: Are these typically stranded or solid?
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