I've been struggling to hand solder a 28 pin, 0.5mm pitch FFC connector to a board. I tried drag soldering and that was a disaster, producing numerous bridges that were difficult to remove. One pin at a time was hit or miss as to whether I'd get a good joint or a bridge. I've been using tons of flux. Maybe my soldering iron is too hot? Too cold? I don't know. I ended up using an exacto knife to fix a couple of bridges.
Is there a clever way to do this?
Use flux and desolder braid to remove all the spare solder you can, then you may be
able to lose the bridges with more flux. Absolute minimum of solder or solder
paste is the rule for fine parts.
0.5mm is definitely tricky, can be done with solder stencil and reflow oven OK,
which is what such parts are designed for. A 0.1mm thickness of solder paste
is about right for this sort of part.
Another technique is drag soldering the bare pads with only with a small amount
of solder, then pressing the legs to the wetted pads with a soldering iron without
dragging to remelt (extra flux).
I've had success drag soldering at that pitch. If you get lots of bridges, you're using too much solder, but you almost always get a few bridges that need to be cleaned up. Use your solder sucker (or a braid, if you prefer) to remove the extra solder. You need a lot less solder for drag soldering than you'd expect. It's not really much harder than 0.65 pitch (tssop)
The trick is to use a liquid flux. Remove bridges with braid but use it correctly. Place the iron on the braid about a quarter of an inch from the end. Then press down with the iron and bend the braid 180 degrees back on itself. Then move the iron and braid to the bridge and apply it for a second and then remove it.
The bending makes a stable structure and ensures that the braid is in good thermal contact and is at the right temperature to do its job.
Yes, apply flux to the braid first.
.
Thanks for suggestions.
When I tried to limit the amount of solder I didn't get very many solder joints. So I added more solder and then got bridges. I was using lots of liquid flux but it evaporates pretty quickly leaving only so much time to clean the tip, grab the solder, put on my magnifying glasses and try to hold my hands steady.
The one thing I wasn't doing was fully wetting the braid when trying to clear bridges. The solder sucker was totally ineffective. Those bridges in between the connector pins were very, very stubborn.
Maybe the key is practice. I've got several of these inexpensive breakout boards and connectors.
jboyton:
Thanks for suggestions.When I tried to limit the amount of solder I didn't get very many solder joints. So I added more solder and then got bridges. I was using lots of liquid flux but it evaporates pretty quickly leaving only so much time to clean the tip, grab the solder, put on my magnifying glasses and try to hold my hands steady.
The one thing I wasn't doing was fully wetting the braid when trying to clear bridges. The solder sucker was totally ineffective. Those bridges in between the connector pins were very, very stubborn.
Maybe the key is practice. I've got several of these inexpensive breakout boards and connectors.
do some research on ChipQwik rework solder pastes. They are low temperature alloys that are much easier to work with on SMT parts. The solder is mechanically weaker than 60/40 rosin core.
Chuck.
chucktodd:
do some research on ChipQwik rework solder pastes. They are low temperature alloys that are much easier to work with on SMT parts. The solder is mechanically weaker than 60/40 rosin core.
Are you suggesting I get an oven? Or that there is some way to use this lower temperature paste with a soldering iron?
using solder paste will still cause bridges if you apply too much. if solder has no place to go, it will bridge.
solder paste is not cheap. if you are going to do more smt soldering, you may want to check out hot air rework stations. you don't need to get the most expensive top of the line model. otherwise, just youtube search on how to solder smt using an iron if you have not done so yet.
There is no need to use an oven. This picture is of a chip of that pitch I soldered with just an iron and solder braid, no flux apart from that in the solder.
I've just built myself a custom hot plate for SMT soldering, but in the past, I've managed to get very good results with solder paste and a gas powered soldering iron that has an hot air attachment.
It works in the same way as a hot air rework station, but not generally as expensive, and takes up a lot less space.
As above though, you'll still get bridges if there's too much solder paste.
Ian.
I could go the toaster oven route. But I'm just doing one offs and probably won't be working at this fine a pitch very often. So I'm not sure it's worth it for me. Especially since there will also be a learning curve with using solder paste and an oven.
It looks like Grumpy_Mike has it figured out. My work looks like that when the pitch is 0.8mm. But at 0.5mm I just don't have the control. Is it simply a matter of practicing and developing the skill? Or is there something more, some important piece of information that would make a difference? I wonder if my cheap soldering iron is a factor.
yes there is something more
do you have a good magnifier? That I think is a must have if you work with smt. do a search here for magnifier recommendation.
No, I don't. Without my contacts or glasses I am myopic enough that I can more or less put my face right there. Then I add a pair of reading glasses and my eyes focus as close as 10cm from the board. So I have a pretty good view of things but not as good as with a quality magnifier.
That said I don't think it's the main problem.
I have really bad eyesight and the magnifier helps a lot.
once you use it, you'd wonder why you did not get one before. you can still wear your contacts/glasses while using the magnifier. Its only like $14.
The $14 one is sold out. This one is the same but $20
http://www.ebay.com/itm/Headband-Magnifier-Jewelry-Visor-4-Multi-Lens-Glasses-Head-Loupe-/151786443985?hash=item23572d54d1
Thanks for the link.
Those sure have a big GEEK appeal. Although me with my reading glasses on and nose practically touching the board probably isn't better.
Yes I use a head mounted visor like that. I can get two levels of magnification by either looking through the visor lense or adding my glasses into the mix as well. I have my glasses on the end of my nose so a tilt of the head will change the magnification factor.
The iron quality is vital I use a magnetic temperature controlled iron with a very fine conical tip from Wella.
jboyton:
Are you suggesting I get an oven? Or that there is some way to use this lower temperature paste with a soldering iron?
using a low temperature on your iron 500F or 600F and ChipQwik it is quite easy to solder fine pitch chips.
you sparingly spread the paste on the PCB, place the chip on the PCB, alignment is crucial, then drag the soldering iron tip across/along the pins of the chip.
I have used this method to successfully place Mega2560 (0.5mm pitch 100pin ) CPU's.
Chuck.
This is what I use, here just soldering a light sensor to strip board but it is the same as when there are many pins.
Thanks Chuck. I searched briefly for more information about this method but couldn't find anything. Do you know anywhere else this is discussed? Or videos of the technique?
Grumpy_Mike: Do you put the gum back in your mouth after soldering? 
