Is this ribbon cable a custom job? - Page 1
Forum section: electronics / beginners

author: dazz
author_rank: Frequent Contributor
timestamp: February 19, 2024, 09:51:47 pm
content: I just managed to break the ribbon cable for the screen of my old tablet trying to pry off the dead battery. Do you guys think there's a way to source a replacement? I googled the markings on it but nothing came up.It's not a huge deal, it probably wasn't even worth replacing the battery in the first place, just curious. Thanks!

author: Benta
author_rank: Super Contributor
timestamp: February 19, 2024, 10:03:41 pm
content: First, that not a "ribbon cable".It's a flex-PCB, and yes, they're to 99% custom, just like normal PCBs.

author: Whales
author_rank: Super Contributor
timestamp: February 19, 2024, 10:33:50 pm
content: If it's a custom flex PCB: you can try and find the cracked traces, slowly soften the plastic with acetone, dig for the copper and solder tiny little bridging wires. You'll need a microscope, stupid amounts of patience and it might still be too thick to fit inside something like a tablet case. Went through hell trying to repair one of these once for my x260 thinkpad, I didn't have a microscope at the time and it was a disaster.If all of the wires are straight through: you can probably buy a standard (straight) ribbon cable to replace it. It will have to be longer (so that you can fold it and bend it for the offset) and again therefore might not fit the case.

author: tooki
author_rank: Super Contributor
timestamp: February 19, 2024, 11:32:37 pm
content: Quote from: Whales on February 19, 2024, 10:33:50 pmFlat flex PCBs are normally made of Kapton, which is highly resistant to acetone (and to most other solvents, including extremely aggressive ones like the dimethylformamide that has been the bane of one project I’ve been working on the past few months). Kapton’s chemical resistance is second only to Teflon (and maybe PEEK). But it’s not particularly abrasion resistant, so mechanical excavation will be a much more productive way to expose the traces.

author: dazz
author_rank: Frequent Contributor
timestamp: February 20, 2024, 12:48:26 am
content: Thanks, guys. The traces are far to thin for me to try to fix them. I will try, got nothing to lose anyway, but I'm not holding my breath.Quote from: Whales on February 19, 2024, 10:33:50 pmYes, I believe all the traces go straight from one side to the other end. What's the name of the connectors for those things, please? That might help me find a replacement.

author: dazz
author_rank: Frequent Contributor
timestamp: February 20, 2024, 01:30:34 am
content: OK, nevermind. It's not a straight through connector, so I won't be able to fix this. Thanks anyway everybody!

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 20, 2024, 03:06:46 am
content: Quote from: dazz on February 20, 2024, 01:30:34 amJLCPCB (and others!) can manufacture two-sided flex PCBs like this, and they're not too expensive. Right now, 100mm×100mm (3.94"×3.94") cost about 14€ + shipping for the minimum five, but the price does get up for anything larger. It isn't difficult to reproduce the flex PCB in say EasyEDA, either, if you just find out exactly how the pins are connected.I recommend you start by taking a picture of the existing flex PCB on top of graphing paper (or similar, with a rectangular grid), making sure the camera lens is perpendicular to the paper and centered, to minimise distortions. The size is the determining factor for the flex PCB size. Then, check the connectivity using a multimeter in diode or ohms mode. Make a simple schematic to document them, then convert the schematic to a two-sided board, and draw the traces and vias.

author: notsob
author_rank: Frequent Contributor
timestamp: February 20, 2024, 03:14:47 am
content: If you cannot find one, go with JLPCB - you will need to carefully measure and document what you are trying to replace.CAUTION: The shipping will probably cost more than the FFC (Flat Flex Cable) that you have

author: dazz
author_rank: Frequent Contributor
timestamp: February 20, 2024, 03:19:57 am
content: Quote from: Nominal Animal on February 20, 2024, 03:06:46 amI may consider doing this, yes. I'm not new to pcb design, even if my designs were all pretty simple stuff, this shouldn't be hard to do if I can figure out where the connections go. Problem is JLCPCB removed the affordable shipping options to where I live a while back and DHL or FEDEX are not an option since they will prety much extort you with their made up handling and import fees. I'll look into it though, thanks.

author: amyk
author_rank: Super Contributor
timestamp: February 20, 2024, 04:16:24 am
content: Use the surface tension of solder to your advantage. It won't stick to the plastic but it will to the traces, so once you've exposed them, a quick brush with a tinned iron may be all that's needed.

author: Whales
author_rank: Super Contributor
timestamp: February 20, 2024, 11:44:07 am
content: Quote from: tooki on February 19, 2024, 11:32:37 pmThat's what I thought too, but then I tried it. Initially the acetone did nothing, but after several applications of a few drops in over the span of a few minutes (it kept drying too fast) the kapton became softer and weaker, allowing me to slice and abrade through it much more easily.Sadly sometimes the opposite side also got too soft, causing even more injury to the FFC

author: BILLPOD
author_rank: Frequent Contributor
timestamp: February 21, 2024, 02:22:23 pm
content: Good Morning Dazz, look on Ebay for the same model tablet you have. There may be non working tablets for cheap that you could harvest the cable/PCB from. That is my suggestion.

author: dazz
author_rank: Frequent Contributor
timestamp: February 21, 2024, 08:54:32 pm
content: Quote from: BILLPOD on February 21, 2024, 02:22:23 pmGood idea, thank you. I'll see if I can find one. It's not a very popular model but who knows.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: February 22, 2024, 02:23:54 pm
content: Good idea, thank you. I'll see if I can find one. It's not a very popular model but who knows.Now that my curiosity has been piqued, would you share the make and model of the tablet? Thanks

author: tooki
author_rank: Super Contributor
timestamp: February 23, 2024, 10:34:18 am
content: Quote from: Whales on February 20, 2024, 11:44:07 amThen that one isn’t actually Kapton.I submerged a piece of Kapton tape in acetone yesterday for over an hour, and it didn’t affect it even the tiniest bit. (As a control, I put in a piece of PVC insulation and a piece of mPPE insulation. The PVC turned to mush within 15 minutes, the mPPE just softened a bit.)I’ve left the Kapton in it for the weekend. I’ll check it on Monday.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 23, 2024, 11:25:10 am
content: Quote from: Whales on February 20, 2024, 11:44:07 amPerhaps it wasn't polyimide (Kapton) but polyester (PET)?

author: dazz
author_rank: Frequent Contributor
timestamp: February 23, 2024, 02:45:41 pm
content: Quote from: BILLPOD on February 22, 2024, 02:23:54 pmIt's a very inexpensive Android 11 Teclast P85. I don't like to throw things away if I can fix them, but this one is going to the bin, because jlcpcb is quoting me 40€ for the minimum order of 5 flex pcb's of this size and that's more than this thing is worth by now. Also it's too much work to figure out all the connections and then design the pcb, and there's no guarantee it will work anyway.

author: Rerouter
author_rank: Super Contributor
timestamp: February 23, 2024, 02:49:37 pm
content: If its a straight ribbon, work from the connectors back, you can probably buy a straight ribbon that you can make work for those connectors,

author: dazz
author_rank: Frequent Contributor
timestamp: February 23, 2024, 03:26:26 pm
content: Quote from: Rerouter on February 23, 2024, 02:49:37 pmUnfortunately, it's not. Also one side of the connector has two rows of 23+22 tiny staggered connections that look pretty difficult to replicate in Kicad. I'm just going to pass on this one.

author: tooki
author_rank: Super Contributor
timestamp: February 23, 2024, 04:12:58 pm
content: Quote from: dazz on February 23, 2024, 03:26:26 pmWhy not go on AliExpress and see if any vendors just have that replacement flat flex? Even if you don’t find exactly the part you need, see if a vendor of similar parts for other models can source it for you. It won’t cost nearly as much as designing your own, which I agree is pointless.

author: Terry Bites
author_rank: Super Contributor
timestamp: February 24, 2024, 10:45:46 am
content: You've not provided any specifications (pitch, width length, connector type etc.) so who knows if it might be available as an off the shelf item.Check out Samtec Sudden Solutionshttps://www.samtec.com/