Tips on soldering CRAZY small FFC cables & connectors

Discussion in 'The Projects Forum' started by joshzstuff, Sep 24, 2010.

  1. joshzstuff

    Thread Starter Member

    Sep 22, 2010
    After searching around the web I found that my problem was a common one:
    The "FFC Issue"
    That is, how to extend a FFC cable.

    I've contacted some specialty cable makers, however you need to buy a gazillion of them to make it worth their while.

    I'm doing an especially difficult cable .5mm/ 24position!

    Here's my poor subjects 'before' picture:


    I will post the "after" pictures using what ever technique you recommend.

    Some pointers I'm giving myself:
    - I'm going to use a FFC cable in the connector as a heat sync
    - I may try to only tin the connector and try to then attach it to the cable

    Difficulties I foresee:
    - extremely fine pitch makes bridging pins a hazard.
    - heat will damage the traces on the cable/ melt the plastic connector

    Tools I'm using:
    - I have a fine tip for my iron (1/32")
    - Silver bearing solder (62/36/2 .015dia.) [lower melting temp]

    . . . pictured above (they look huge next to the tiny connector don't they!)

    Any direction you can give me such as:
    - technique
    - tools
    - materials to use

    Will be greatly appreciated!
  2. bertus


    Apr 5, 2008

    The cable is NOT intended to be soldered.
    Normaly there is a clamp connector that can be soldered.

  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    I was not aware that a silver bearing solder existed that possessed a lower melting point than Eutectic tin/lead. Do you have the spec sheet for that solder?

    If you ARE going to try this might I suggest using a solder masking compound, which you can then scrape off the intended area where you want the solder to stick? Also, wrapping the plastic cable in wet paper towels might help prevent the heat damage that could occur. The plastic itself looks to be a form of heat resistant plastic. Note that is heat resistant- NOT heat proof.
  4. joshzstuff

    Thread Starter Member

    Sep 22, 2010
    Thank you for your reply, let me be clear about my intentions:
    My main objective is to make my own "extension cable" (or acquire one if it were possible in low quantity)
    I'm willing to attempt this if I MUST, however if you know of a better way, please let me know of this solution.
    Bertus, can you give me any information on this "clamp conector"
    Are you saying there is a better selection for both clamp AND connector?
    If so, where can I find it?

    Kermit2, perhaps you are right about the melting point.
    I was basing my comment on empirical observation rather than a data sheet.
    The silver bearing seems to whet better and melt quicker as compaired to 60/40 .038mm that is rated:
    -Melting Temperature:190°C
    -Peak Reflow Compatible (260 C):No

    Radio Shack is not always known for providing data on their products, here is the page for it:

    This sounds like a good idea, but I'm not familiar with this compound that you mentioned, can you provide an example?

    Another good idea Kermit2, heat is my friend/enemy on this project, so I will do whatever I can to keep it in the right spot.

    If you know of a better FFC I will buy it OR,
    Do you know of any FPC in .5mm 24position?

    What to you think about this idea . . .
    If the cable is the biggest problem, than I could attempt to solder 2 female connectors together . . . ?

    Thank you for your help, can you be more specific with your recommendations?
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    After looking closely at that picture, the connector you show DOES NOT appear to line up exactly with the ribbon cable. The outer most pins are noticeably inset from each of the outer most pads on the cable. This WILL not work if directly soldered, but will result in overlaps and shorts between lines.

    Please re-examine the connector you are picturing and re-think this procedure.
  6. prb22786

    New Member

    Sep 19, 2010
    FPC, and any sort of fine pitch ribbon are just a pain in general. You may want to research it a bit, see if you can find a connector thats press-fit. Unfortunately a lot of times these connectors require special tooling. If you are looking at a one time deal, here's some suggestions.

    First, use leaded solder. Lead-free solder has a tendency to grow "tin whiskers", which in a fine pitch high-frequency environment can lead to troubles down the road.

    Control your heat, whether this is by using heat sinks, or cooling with alcohol, or a combination of methods. You can build a strong, reliable solder joint by flowing it in steps, and immediately cooling with a q-tip soaked in isopropyl. Obviously, safety glasses.

    Flux is your friend. You're going to need it for this type of soldering. You'll need a reliable way to clean your connector afterwards, either in an alcohol bath or if you have one, an ultrasonic cleaner.

    Most important, strain relief. With this type of patching, strain relief is absolutely key to keeping everything together after the patch. Meter out all your connections, and when you're sure its been done properly, add strain relief. This can be done in a few ways, but basically you want to brace the cable for at least 10-20mm away from the connector, depending on how much room you have where the connector mates. Epoxy is the strongest way to do this, but you won't be able to take it apart again.

    If you want to research some similar connectors and see if you can find one to suit your needs, I'd look into Hirose, JST, and maybe Molex.
  7. beenthere

    Retired Moderator

    Apr 20, 2004
  8. joshzstuff

    Thread Starter Member

    Sep 22, 2010
    You scared me there for a second Kermit2, the implications of that problem would have meant that I had a non-standard pitch.
    As it turns out, it seems to be an optical illusion (probably because I took the picture off center)

    Here are some better shots of both the connector & the cable lined up with my target cable (a tiny camera module)


    Agreed, I do think it's "crazy" so I'm researching alternatives right now. Searching "press fit" took me to Arrow which turns out to be a dead end at the moment, but I'm going to try some of the suggestions from "beenthere"

    That's good to know, I'd like to fine some solder that is even smaller.
    I believe the silver bearing solder is 36% lead.

    Yes, good advice. I will need to make this a tedious process if it has any chance of success.

    I have liquid flux

    Understood, you've given me the idea of possibly gluing them together first to make sure everything lines up.

    I tried ALL of those guys, I emailed their tech support. Perhaps it's because I'm not some big company, but if there was a viable solution they did not lead me on to it.

    (Molex even told me they didn't carry the spec'd cable I described to them, but I later found it on their site!)

    beenthere, you bring up a good point.
    I have been searcing "FFC" or "FPC" all the while. As soon as I searched "flexible cable connectors" it took me to Tyco's site.

    Another question for you,
    I'm looking through Tyco's catalog and I have a few possible ideas, but the connector you chose seems to be for attaching to a board.
    (although MUCH easier to solder than what I currently have)
    Did you have a specific idea for using this connector?
    -I though about possibly mating 2 females together with something like this.
    This idea produces more bulk than I'd like, but it may be much easier than the route I started in.
  9. wayneh


    Sep 9, 2010
    Gasp, I'm amazed anyone would try to tackle this! Kudos to you if you succeed.

    Anyway, I just wanted to add something that seems obvious but no one has mentioned: A well lit workspace with a big magnifying glass. Maybe your eyes are younger than mine, but for something this small, just SEEing what you're doing can be challenging. I use a big handheld magnifier even working on breadboards, which are quite a bit bigger than your project. Yes I can see without it, but it DRAMATICALLY improves many chores like reading resistor color codes, seeing which row of holes a wire is in, etc.

    For lighting, make sure you have light from several angles so that shadows from your hands and tools don't obscure your vision.

    Good luck! If you succeed, I've got several ribbon repair projects for you. ;)
  10. beenthere

    Retired Moderator

    Apr 20, 2004
    Not to be discouraging, but I would not ever use one. Stranded flat cable is much easier, as well as using individual wires - if much more bulky. Mating connectors are common for wires at least.

    The only flat cable connectors I have seen were for attachment to a PCB.
  11. joshzstuff

    Thread Starter Member

    Sep 22, 2010
    I agree, but that is what the manufacturer of the camera chose so I have to find a way to work with it or find a completely new device.

    The problem is that the only way to get something to do 'exactly" what you want in the way that you want, is to design and manufacture yourself.
    Because of the cost implications and profit margins involved . . .
    manufacturers produce, not necessarily the 'best' product, or the most useful, but what the average Joe will buy.

    I find most of my 'hacking' projects to stem from this trend. But on the upside it has given me a window into learning more about devices and techniques, that sometimes have yet more benefit down the road.

    I have some nice magnifier lights on my bench and I use a small one when I'm ringing out the circuits and a 'helping hands' with the actual soldering.
    Your right about getting in your own way, it's a fight between magnification/ light/ room to work!

    I do think I am in need of better magnification though.
    I saw a magnifying kit on a while back, but my recent searches haven't turned anything up.

    Anyone recommend a good high power magnification set up?
    I'm currently using I believe a 4X lamp with a 5X(maybe) bubble.
    (Not certain about the power)


    Basically I tin both parts (with the least amount of solder possible) and then join them together one by one.

    tools made for the job:

    -some find tip probes made from alligator clips and sewing needles

    - cut away a small alligator clip to hold the connector whilst tinning.

    - I found a thin metal plate with a slot cut into it which was nearly perfect for holding the cable during soldering.

    Here is the results of my first attempt . . .


    It's not pretty . . . but it was a success!
    Well, eventually it was.
    The first cable had 2 shorts and 4 opens.
    Send them!
    My goal is to develop my technique so that I won't have to do any repairs after I make the cable.
    (I think an improvement in the connector tinning process will help)
    However, in the current process of making these cables, FFC repair is a must.

    You probably noticed right away that the connector is turned around backwards . . .
    This is because of an undersight on my part when ordering the cable/connectors. In order to maintain the same pin order, I needed cables with the 'opposite' terminal ends with bottom terminating connectors OR 'Same' side with top terminating.

    One other way to orient the cable requires a much more difficult process, but with the first cable under my belt, I got a little cocky I guess and went ahead and attempted a 'butt' style connection . . .


    Perhaps I'm getting better in some ways on the second attempt, because there were no shorts. However there were about 4 opens and one pin was particularly problematic with the trace detached from the board and floating behind the cable :mad:.

    I don't think this technique is worth the aggravation so I'm going to wait until I get the proper parts or practice the 1st gen style with what I have on hand.

    That compound idea might be an option, do you know of anything that might work like this Kermit2?

    Maybe it's just the way I used them, but it seems that water & flux & solder don't mix. You probably meant this suggestion for the anti-solder compound though, but I just wanted to report that I did try it;)

    I'm going to test the 1st one out to see how durable it is

    Strain Relief:

    I need to do this with the successful cable before I stress test it.
    Do you recommend a particular epoxy for this?

    I have a "plastic" glue, but I'm pretty sure this is out of the question because it might melt away the insulation during application.
    I'm not going to ever miss these parts, so It doesn't need to come apart . . . or do you mean to glue the connected piece inside the connector?

    Other items that I think might help if anyone has information on:

    -smaller solder? [than .015dia.] (would be a big help on tinning the connector!) It seems that the silver bearing is working for me, but if I could find some regular Tin/lead in a smaller gauge, I think it would make a "big" difference (I couldn't help the pun:D)

    -liquid solder?

    -other SMT techniques & tools?

    - ffc "type c"
    (apparently there is a ffc cable that comes stripped at one end . . .) I'm going to search around for this cable.

    Thanks for all your help!
    Keep the suggestions coming!
  12. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    You have struck a nerve.

    This is one of my favorite subjects. Soldering of difficult items is such great fun.

    You have chosen the right solder SN62 is probably the best you can pick. The only thing I can recommend is FLUX and heap of it.

    PS. If you, and anyone else, can avoid it NEVER use lead free solder. It is an absolute pain in the A. Greenies paranoia. The amount of lead in electronics is insignificant. (Eco arguments welcome)
  13. joshzstuff

    Thread Starter Member

    Sep 22, 2010
    Hear that Wayneh, send you FFC repairs to windoze first!

    Is there anything smaller? (than .015)
    (It's hard to avoid bridging when the solder you use is larger than the contact pitch!)
    Check, I use liquid flux.
    Are you sure you can't recommend anything else?
  14. sceadwian

    New Member

    Jun 1, 2009
    You could try solder paste, it's meant for SMD work. Basically you get a thin layer of this on there and drag your iron across it, or use a hot air gun to reflow it, you might have to practice with the thickness of the paste but allows you precise control of where the solder goes. Digikey has a 5cc syringe for 12 dollars, not cheap but it's really nifty stuff. I've seen Youtube videos of people using it it's really great stuff.
  15. PackratKing

    Well-Known Member

    Jul 13, 2008
    First off, what you are trying to do is not impossible, tho' it can be way up there in difficulty, from my pov, it's a routine piece of cake. Absolutely not kidding.

    Modern quasi-automatic major mfgr. 35mm SLR film cameras circa 1980 to present, { digitals included } are loaded with this type of connecter, on a mylar substrate, loosely termed "flex-circuits" far more delicate than what you have pictured. Some are soldered, others are clamp-connected.

    Your biggest concern, is a soldering tip small enuf to carry sufficient heat to the task, tho' more a concern, is the geometry of the tip, that will allow tiny amounts of solder to flow, as opposed to globs, which will drive you mad with bridging.

    I constructed a soldering tip, out of the rigid copper signal conductor in coaxial cable. This required drilling an adequate hole into a larger [15 - 30 watt ] tip, and swaging the co-ax wire into the other. Heat requirements will dictate the length of the add-in tip.

    With 3/8 - 1/2 ± " of coax protruding, squash the last 1/16" of co-ax into a roundish shape, then file it to look like an arrowhead............the sides of this "tip" once tinned, will carry enough solder to complete one land on your flex-ribbon....

    You mentioned .015 dia. solder....63/37 eutectic is best for this purpose.... I know it sounds weird, cut your solder into 1/32 inch lengths, or as your judgment will show, lengths that will comprise one connection. This, with paste flux wiped across all connects before you start, will allow you to pick up one piece of solder which will flow off the tip making the connect, and then move on down the line in the same manner.....bridging becomes next to impossible, and heat damage to the ribbon will be minimal - to - none.

    You will be amazed at how tiny a pitch you can solder with the Packrats' invention. :D Or on the other hand, I will be happy to do these for you, and guarantee integrity [ for a small fee :p]
    Last edited: Jan 14, 2014
  16. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    You mentioned it is hard to do without bridging. This can be true depending on how you do it. First suggestion is tin all your connections LIGHTLY. Next and probably the most important is FLUX (flux is a technicians best friend). Apply it liberally. When you then place your two components together all you have to is apply a CLEAN soldering iron. Just prior to applying the tip wipe it dry with a tissue (or if you must) a wet sponge. If you have done the first 2 steps correctly you should have a nice joint without too much solder. Also using this method if you manage to solder the first and last pins you can just run your iron across the rest and reflow all the joints at once. Last step, load your iron up with solder to protect it but don't forget to wipe it dry again before the next joint. You 1/32 tip should be ok so long as you don't try to add more solder. A smaller tip would be good if you had one. If you had a spare 1/32 you could file it down a little and RETIN it.

    With regards to solder as I said earlier SN62 is the easiest and coolest to work with. 63/37 (eutectic) is good also IF you have the temperature set right. Eutectic solder doesn't have a plastic state. It goes straight from a solid to a liquid as it heats up. The good thing about it is when it cools it also goes straight from a liquid to a solid state which means there is very little time for joint movement so the joint will "set" quicker and avoid "dry" joints. I feel though on joints this size the plastic period of SN62 wil be very minimal especially if you have your iron temp set correctly.

    By the way did I mention that you should use flux??????;)

    Another hint. If you are going to be doing a lot of this sort of work I suggest you get a stereo microscope. Especially if you have yes like mine.
  17. joshzstuff

    Thread Starter Member

    Sep 22, 2010
    EDIT: windoze, the order is now PackratKing, 1st for FFC repair

    Well, you've got my tools beat already!

    You make a good pitch PackratKing, name your price.
    I'm using a Weller WES51 with a PES51 Iron
    Or you can PM me if you like.

    Can anyone make any recommendations as to the solder paste I should buy?

    I might be getting a smaller one soon.
    I will say though that the size of the solder seems to be more of an issue than the iron thus far, but maybe with these new techniques I may be able do better.

    You mentioned the correct temp setting, I take it this will vary with application. What are some indicators that I may need to adjust my heat?
    currently I'm using ~750°

    I might need one in the future, thanks.
    You gave me an idea though, I looked up digital scopes and I got the idea of using my camera that accepts a macro lens.
    I'm going to try it out, the upshot of this type of solution is that I can use manual focus and record images at the same time!
  18. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    AAAAAHHHHHHHHHH way too hot. The melting point of 60/40 solder is about 525°F. At 750° you will probably be melting the FFC cable before acheiving what you want. Try adjusting the temp to about 550°F. This will allow for the drop in temp when you put the tip on the work. Also at the higher temps you will "cook" the solder and cause a dry/brittle joint. This causes the tin and lead to seperate.

    Good idea. Great for inspection.

    Stereo scopes are better because you get a 3D view and you can judge the position of the tip in relation to the work.
    joshzstuff likes this.
  19. joshzstuff

    Thread Starter Member

    Sep 22, 2010
    Ahh, that sounds like a pretty good explanation of some of my difficulties.
    I read that commercial shops keep their irons at that temp, but perhaps this is more for thru-hole work.
    I'll crank the iron down, thanks.

    Oh yeah, now that you say that, I can identify. I've been using the small magnifier of my lens (read: one eye!) and yes, I could definitely use some better depth perception!
  20. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    Through hole and also SMD with tracks hanging them. The PCB also conducts heat away as well but even so if the tip is selected correctly for the work being done the temp should still be set to the lower temp. I have no idea why they would have it at 750.

    You would be totally surprised at the difference it makes.