What kind of adhesive for end of flat flex cable (FFC)? - Page 1
Forum section: electronics / projects

author: mosafet
author_rank: Contributor
timestamp: June 19, 2023, 11:47:37 pm
content: Most FFC that have a press friction fit have a thicker piece of plastic bonded to the end so it can be pushed in without damaging the cable.What kind of adhesive is used to bond those end pieces? I'm trying to repair some cables and I can't get anything to stick. I've tried cyanoacrylate, epoxy, toluene based glues, generic double sided tape. I have not tried polyurethane or two-part acrylic glue yet but I'm getting weary. Nothing sticks to whatever plastic they're using.I know there are some tape-like double-sided adhesives used in cell phones that are ridiculously strong. I'm also considering some sort of UV cured adhesive. Ideas?Anyone know what the factory uses? I haven't been able to find any information.Edit:Some other thoughts: Maybe a light coat of acetone then clamp them together? The way the plastic behaves when heated makes me think it's possibly some sort of vinyl, PVC? Maybe PVC pipe glue (is this stuff just acetone)?

author: thm_w
author_rank: Super Contributor
timestamp: June 20, 2023, 12:43:43 am
content: Its labeled as PET here:https://www.assmann-wsw.com/uploads/datasheets/ASS_7541_CA.pdfhttps://www.antala.uk/adhesive-for-bonding-pet-plastic/If this is just a one off repair you could also tape around the outside to try to hold it in place.

author: mosafet
author_rank: Contributor
timestamp: June 20, 2023, 04:54:01 am
content: Difficult to say if it's PET or not. I've looked at various cable datasheets and they use all sorts of different things. Most of the cables I'm fixing are from Japanese manufacturers like Fujikura, Tsujimoto, etc.There really isn't a way to use the cable without that stiff piece firmly bonded because the cable will deform from the spring fingers and you can get all sorts of problems. Not to mention the edges tend to get destroyed and the traces peel off when the backing is not stiff enough.The PVC/acetone "glue" didn't work so maybe it is PET or something.I'm trying PVA next which I'm 99% sure will do nothing.I wonder if at the factory they friction weld it together or something. I don't know. E6000 or T7000 glue?

author: Someone
author_rank: Super Contributor
timestamp: June 20, 2023, 07:51:36 am
content: If repair is too complex/costly/difficult, buy new cables? They tend to be pretty generic.

author: jpanhalt
author_rank: Super Contributor
timestamp: June 20, 2023, 09:18:59 am
content: When bonding plastics it is usually helpful to know what type of plastic. If it is PET, there are specialty adhesives and primers:https://www.permabond.com/materials_bonded/bond-pet/

author: mosafet
author_rank: Contributor
timestamp: June 20, 2023, 02:08:40 pm
content: Thanks. It seems likely to be PET or at least some similar polyester.Apparently that end piece is called "support tape" and is possibly heat bonded at the factory. Possibly with some sort of "treatment" to adjust the plastic's properties before heating. I found some of this tape and it's coated with "polyester resin", does that make it easier to bond? Not sure if I can buy it as an individual.There are primers made of heptane or isopropyl acetate that can be used with cyanoacrylate glue. Loctite 770 is one of those primers and seems easy but expensive to get. This doesn't seem like it makes a very strong bond even with primer. Edit: I just found Loctite "plastics" glue which seems to probably include this primer and it's not expensive.Interesting patent:https://patents.google.com/patent/US3950206A/enThe reason I haven't just bought new cables is because it's difficult to find them with the exact properties and size needed (or way too expensive), which tends to be important because the whole reason a FFC was used in the first place is because of special needs. These cables I'm working with are a little less than 1m long. I mean you can get custom manufactured cables but that seems a little crazy. I could make my own custom cables or repurpose cables for sure but then I'm back to the problem of needing to bond that support tape myself. I do have a few cables on order to test but it may be a long time before I get them.I do have a last ditch plan to simply rebuild parts of the circuit with regular cables/wire and appropriate modifications to the physical design but I'm not there yet.

author: jpanhalt
author_rank: Super Contributor
timestamp: June 20, 2023, 03:55:26 pm
content: Have you considered a simple laminator and thin laminator stock as your stiffener?

author: mosafet
author_rank: Contributor
timestamp: June 20, 2023, 06:24:02 pm
content: Quote from: jpanhalt on June 20, 2023, 03:55:26 pmNo I hadn't thought of that, thanks! I have a couple laminators that I use for making PCB's. I don't think the stock lamination stuff is thick and stiff enough but maybe multiple layers. I wonder if I could just laminate the original pieces back together. I'll try it. The only problem is I can't control the temperature very well. I have the parts and have been meaning to build a circuit to control the heat and show me the temperatures but this stuff is buried in a long list of projects.

author: jpanhalt
author_rank: Super Contributor
timestamp: June 20, 2023, 06:47:27 pm
content: Wikipedia says PET mels at 260°C. However, since it is a polymer, that is probably wide. The Tg (glass transition temperature) is probably more relevant, and that is about 65° to 80°C. I would see how something in the rage of its Tg works out so long as the laminating material will melt sufficiently to bond.Reference:https://omnexus.specialchem.com/selection-guide/polyethylene-terephthalate-pet-plastic#:~:text=The%20glass%20transition%20temperature%20of,Tg%20of%2065%C2%B0C.

author: jpanhalt
author_rank: Super Contributor
timestamp: June 20, 2023, 07:02:13 pm
content: As I think about that low Tg, Stitch Witchery (attachment), which works well at 100°C, and the stiffener you have may work.

author: mosafet
author_rank: Contributor
timestamp: June 20, 2023, 07:10:33 pm
content: IIRC, PET is a crystalline polymer so it doesn't really have a glass transition, it just melts at some point.Anyway, I put it in my biggest 1500 watt laminator on the highest temperature and it didn't work. Even using the laminator sheets they only stuck as well as their preexisting adhesive (ie. not well). Presumably this isn't hot enough for the PET and I verified the hottest temp is only 140C.Good idea though. I'll have to think about it.

author: mosafet
author_rank: Contributor
timestamp: June 20, 2023, 07:27:06 pm
content: I read somewhere, maybe in that patent, about using polystyrene based adhesives. I'm mixing up some ABS glue to try.I also just read that some laser toner is made of polyester resin. I wonder if I could sandwich some of that and run it through the laminator. I know that will melt because that's how I make PCB's.

author: artag
author_rank: Super Contributor
timestamp: June 20, 2023, 08:28:23 pm
content: Quote from: mosafet on June 20, 2023, 02:08:40 pmIf you have to do that, these transition PCBs may be useful :https://www.ebay.co.uk/itm/194402505682Use short generic FFCs to connect them to the PCB and then link them with PVC ribbon cable.

author: mosafet
author_rank: Contributor
timestamp: June 29, 2023, 02:43:34 pm
content: After testing, as far as I can tell the T7000 adhesive is just watered down Shoe Goo (ie. lots of toluene). So not any better and doesn't stick to PET at all as far as I can tell.Flame treating with make PET more receptive to adhesives but these cables are very thin so it's not really possible to just "flame the skin" because the cable IS the skin. I'm sure the adhesion promoters will work similar but I haven't tried this. Graphics are often attached to PET using these methods.Laser welding works but the irregularities of the cable make it infeasible. The varying thickness where the conductors are and any writing/ink or other color inconsistencies on the cable. Maybe if you could scan the surface down to the micron and adjust power on the fly or something, I don't know. I was using clear PET over the opaque cable and clamping with glass. There is an impossibly thin line between burning the plastic and melting it. Really really difficult.I found this 3M 467MP transfer adhesive and it actually seems to work well. It's pressure sensitive. It's really strong and resistant to chemicals which is good for example if using around Deoxit on your connector. This sent me down a rabbit hole looking for other potential 3M adhesives but there are so many I can't tell what is what. They do seem to have a number of things specifically for "low energy" (LSE) plastics like PET but it's difficult to find something specific. They have "adhesive finder" tools but there is no single interface and everything is scattered to suck.There is some sort of transfer tape used to hold the two plastic halves of PCMCIA cards together and that stuff is some of the strongest I have ever seen. I don't know what it is though.So I'm using the 467MP for now. It will take some real-world usage to determine if it holds up.

author: Weston
author_rank: Regular Contributor
timestamp: June 29, 2023, 06:54:31 pm
content: I would a bit worried about the added thickness of any adhesive tapes, but try any tape based off of 3M 300LSE , which is an adhesive for plastics with low surface energy.The variant 3M 9495LE is pretty widely available on amazon and such. I have not tested it on PET, but it works well to adhere items to SLS 3d printed parts where other adhesives have issues. Its 6.7mil thick, I am not sure if there are thinner variants you can easily buy.The 300LSE spec sheet specifically mentions PET, so it should workhttps://multimedia.3m.com/mws/media/1371388O/3m-high-strength-acrylic-adhesive-300lse.pdf

author: rounin
author_rank: Regular Contributor
timestamp: June 30, 2023, 01:54:53 am
content: Reltek B-45TH lists PET as a supported material. We use it to bond rubbers to metal. They have a couple different epoxies that are supposed to be good for plastics.Probably /way/ too messy for FFC though.