What technology to use? - Page 1
Forum section: electronics / general

author: Jane
author_rank: Frequent Contributor
timestamp: August 09, 2014, 06:03:47 am
content: We need to desolder old ( faulty) Flexible Printed Circuit( FPC) that was soldered by Anisotropic conductive film(ACF) and solder a new Flexible Printed Circuit.What device is best for that work?Thank you for your replies.

author: Precipice
author_rank: Frequent Contributor
timestamp: August 09, 2014, 07:33:54 am
content: Hot air to soften the old glue, then clean the remainder off the pads with more heat and solvent, would be my plan.Are you sure you want to solder the replacement cable on, rather than use more Z-tape? It's easy to get small quantities on ebay, or sparkfun sell it, no need to buy a full reel and keep it refrigerated...If you really do want to solder it, then take great care, it's often tricky, especially on fine pitch FFCs. I eventually bought a proper hot bar soldering machine, which does the right thing, with a short pulse of heat, while applying pressure, as hand soldering was too hard and unreliable.

author: Jane
author_rank: Frequent Contributor
timestamp: August 09, 2014, 07:59:25 am
content: Thanks for the reply.What kind of hot bar soldering machine do you use? I am also thinking about buying hot bar soldering machine. Which one would you recommend?

author: Precipice
author_rank: Frequent Contributor
timestamp: August 09, 2014, 08:14:37 am
content: Mine's a "Unitek Miyachi Pulse Thermode welding transformer (model 1-291-02-03) with ‘Thin-line’ 180 pedal operated head with a selection of thermodes and compressed air valve."Looks a lot like this (not got a photo of mine, it spends most of its time in storage, as it takes up a lot of bench space)http://www.labx.com/v2/spiderdealer2/vistasearchdetails.cfm?lvid=29897426They're quite expensive normally, I was very lucky to get mine off ebay. It's been great, but I couldn't possibly justify full price - I'd probably try to sub the work out, or build something not as good...If you can do what you want with just pressure-activated Z-tape, and this is a one-off repair, then I wouldn't really recommend anything more complex!

author: Jane
author_rank: Frequent Contributor
timestamp: August 09, 2014, 10:24:45 am
content: Thank you for the replyAnd how much easier is it to desolder and solder Flexible Printed Circuit by using your kind of device?

author: Precipice
author_rank: Frequent Contributor
timestamp: August 09, 2014, 11:06:37 am
content: If you have to do lots, then it's a great help.If you only need to do one connector, then the setup time means it's probably quicker to do things manually, especially if you can just use Z-tape to attach the new FFC.The results from the machine, though - they're perfect once it's set up right (and bear in mind, you may need to buy suitable thermodes for every job, so there's a lead time. It depens how much space there is around your connector as to whether you can use a too-big thermode).I got mine from a company that had been using it to rework failing LCD monitors. They were very pleased with it, but the contract had come to an end.Are you sure your replacement FFC wants to be soldered? Not all of them have suitable materials, and can just melt...At the moment, I'm using FFCs with stripped back plastic, so the only thing for the final 5mm are the conductors, but I have also soldered more normal cables. You do need to avoid stiffeners, though!If you can put up a photo of your job, I'll have a look...

author: Jane
author_rank: Frequent Contributor
timestamp: August 09, 2014, 01:50:29 pm
content: Thank you for your replyI am sending the pictures. Can you please check and let me know what technology is useful?Thanks

author: Precipice
author_rank: Frequent Contributor
timestamp: August 09, 2014, 02:07:43 pm
content: Definitely not soldering!Z-tape will do what you need, cheaply and easily, and without needing heat or careful pressure, fingers will be fine. You will need to clean all the old tape off with heat and a solvent, and you need to be careful not to damage the conductive ink on the LCD.https://www.sparkfun.com/products/12042if you want small quantities. There's a datasheet, which shows the differences between tapes. You may want narrower tape, though, it's difficult to cut cleanly.If you have many of these to repair, then yes, you may want to get a proper thermal bonder - but for small numbers, I would stick (ha!) with the tape.

author: Jane
author_rank: Frequent Contributor
timestamp: August 09, 2014, 02:25:17 pm
content: Thank you for the reply.You say:Z-tape will do what you need,cheaply and easily, and without needing heat or careful pressure, fingers will be fine.But laterIf you have many of these to repair, then yes, you may want to get a proper thermal bonderCan thermal bonder be used both for Flexible Printed Circuit that is soldered and Flexible Printed Circuit that uses Z-tape?What are advantages of using (proper )thermal bonder?Speed, accuracy?