How to connect Flat Flex Cable 0.5mm pitch directly to a PCB? - Page 1
Forum section: electronics / projects

author: quarks
author_rank: Frequent Contributor
timestamp: June 21, 2014, 01:52:20 pm
content: Hello all,I just had a look to a faulty display connection and expected to see something like a ZIF connector for the Flexible Flat Cable (FFC). But the FFC is directly connected (maybe soldered) to the PCB. So far I have never seen this before and wonder if anyone has experience with FFC 0.5mm connected this way and can give me a hint how to handle this?My first idea to try to use a ZIF connector does not seem to work, because of the required additional space for the connector.Thanksquarks

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 21, 2014, 02:10:17 pm
content: Flat cable soldered directly to the PC board is not uncommon. Sure a connection can break after the fact just as with any other surface-mount "component". Often this technique is used just to save money (and actually increase reliability). Sometimes higher-end equipment uses connectors, but they are EXTRAORDINARILY fiddly IME. You are much better off simply re-soldering the bad joint and getting on with your life. Adding a connector after the fact just isn't worth the grief, IMHO.

author: rob77
author_rank: Super Contributor
timestamp: June 21, 2014, 02:13:39 pm
content: i was never in the situation when i needed to repair such a joint, i was only disassembling units with such a flex cables. it's actually quite easy to unsolder them with hot-air . and i ASSUME it will work the opposite way as well using solder paste.

author: quarks
author_rank: Frequent Contributor
timestamp: June 21, 2014, 03:15:53 pm
content: Richard Crowley and rob77,thanks for the quick replies.Because the connection is inside a DMM there is very little work room. Therefore I am a bit concerned a heatgun might damage/melt the plastic of the housing.Nevertheless what solder paste would you recommend and what temp do you suggest to heat up the FFC from the insulatetd top side to be sure to make a good solder joint and how can shorts be avoided when trying this?byequarks

author: rob77
author_rank: Super Contributor
timestamp: June 21, 2014, 03:58:29 pm
content: first of all i would suggest to practice on some other boards first - for example many CD/DVD computer drives have such a flat cables soldered to boards and it's quite easy to find one for this purpose.i would suggest to wrap the flat cable in alufoil - to avoid warping and damage to the flat cable.use smaller diameter nozzle for the hot-air - 3mm or 5mmremove all solder from the pads/cable before soldering back - use the solder sucking wire and gel-type soldering flux.when soldering back - use a 63/37 (60/40) solder paste - it has lower melting point than the Pb-freeto avoid shorts - dispense the solder paste to the pads only (fine needle and microscope/good magnifying glass for 0.5mm pitch) and use a gel-type soldering flux (noclean one).and of course the cable must be secured in place when soldering back

author: zapta
author_rank: Super Contributor
timestamp: June 21, 2014, 04:21:49 pm
content: These inexpensive Chinese OLED displays use a flex that is soldered directly to the PCB. I took apart one of them and then manually soldered it back. Not too difficult, you anchor a few key points and then drag soldering it.

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 21, 2014, 08:37:20 pm
content: Quote from: quarks on June 21, 2014, 03:15:53 pmthen there is very little hope. working with the casing intact is not a good idea after the fact. its not uncommon to try to dismantle the casing first. other than heat gun, another hope is the flux and good sweeping skill. as we have discussed, after the fact direct connection doesnt necessarily means cheap cost, but space constraint, you try open the almighty canon lenses you see alot of this stuff, err i mean to the motor. fwiw.