Tips on soldering CRAZY small FFC cables & connectors

sceadwian

Joined Jun 1, 2009
499
If you have parasitic heat draw from surrounding bits, or the device itself I can not stress enough pre-heating the board/site. I'm just talking about a hundred degrees over ambient, not even close to soldering temperatures. It decreases the peak thermal load on the iron by... more than a little, when the iron is removed if your in a cold room it will help prevent thermal shock from rapid cooling.

Study IR soldering profiles sometime, there's a forced air pre-heat followed by a peak in the pre-heat followed by the application of the actual IR heat source pulse for a period of time, then the IR source is removed and the pre-heat source is lowered to allow anealing of the joints followed by ambient air until the joints have cooled to room temperature. These profiles aren't used just because they're amusing and complicated, they result in nearly perfect solder joints.
 

Thread Starter

joshzstuff

Joined Sep 22, 2010
30
Study IR soldering profiles sometime, there's a forced air pre-heat followed by a peak in the pre-heat followed by the application of the actual IR heat source pulse for a period of time, then the IR source is removed and the pre-heat source is lowered to allow anealing of the joints followed by ambient air until the joints have cooled to room temperature. These profiles aren't used just because they're amusing and complicated, they result in nearly perfect solder joints.
I hear you sceadwian,
I watched a video just the other day that described this progression with hot air.

If you have parasitic heat draw from surrounding bits, or the device itself I can not stress enough pre-heating the board/site. . . .
It decreases the peak thermal load on the iron by... more than a little, when the iron is removed if your in a cold room it will help prevent thermal shock from rapid cooling.
I guess one good way to do this is is with hot air. I would say that I am a little more heat sensitive with a FFC cable than I would be with a board.

Preheat w/ flux?
I'm using liquid flux right now, It seems like it's application might negate any advantages I might gain with a preheated board?
Possibly might I be able to heat the flux after I apply it?
I am due to receive flux past, perhaps this might help in this regard?

Thanks to your suggestions in the thread, I've been able to produce my 1st 'perfect' cable! (That is one that did not need any 'fixing' due to shorts or opens.)

Here is a picture next to the 1st gen cable for comparison:


This time I used a more sane iron temp, resulting in much less damage to the cable!

Also, I used a little different strategy concerning bridging, I purposely bridged sets of the connector leads together, resulting in a better tin since I could span the leads with my solder & iron. Then when I reflowed the connector onto the cable, the bridged leads took care of them self with the surface tension of the terminals.

Next step, strain relief, probably with epoxy.

I will continue to practice this technique.
Thanks for all of your helpful advice!
 
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It is a bit hard to see the joints on the left hand connector but the right hand one doesn't look too bad. There appears to be a few that "seem" to not have fillets around the pins. Grab some isopropyl alcohol and give them a reall good clean. It is much easier to inspect when you haven't got all that flux residue everywhere.

You also said "less damage"....... with the right temps, flux and process you should have no damage to the cable or connector. You will notice in the picture the connector on the left appears to have a few pins that have a small excess of solder. If you re-flux the pins and wipe you tip clean then run it gently across all pins from one end to the other it should clean up very nicely.
 

thallmon

Joined Sep 27, 2010
5
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!
Use a heat sink from a proccesor to keep evert thin cool
 

Thread Starter

joshzstuff

Joined Sep 22, 2010
30
There appears to be a few that "seem" to not have fillets around the pins.
Ok, I looked for a proper definition of "fillet" without success. What part to you call the 'fillets'?
Can you describe a little about how the pins should look ideally?

Grab some isopropyl alcohol and give them a reall good clean. It is much easier to inspect when you haven't got all that flux residue everywhere.
Will do for the next one, this one now has an epoxy covering.

"less damage"....... with the right temps, flux and process you should have no damage to the cable or connector. You will notice in the picture the connector on the left appears to have a few pins that have a small excess of solder. If you re-flux the pins and wipe you tip clean then run it gently across all pins from one end to the other it should clean up very nicely.
That technique seems to work the best. The trick seems to be getting the right amount of solder on the pins: Enough to tin them, but not too much to cause bridging.
@"less damage" Yes, when my technique is perfected there will be no damage, but correcting for my mistakes has worn on the cable more than necessary.
Still, the 'damage' to this last cable is negligible, probably not perceptible from the photo.

Hot air rework tool and solder paste, a whole lot easier than trying it with an iron.
I just got my solder paste in yesterday, but I don't yet have a hot air tool.
Can you recommend a good one for this application?
Perhaps ideal settings & suggestions of some nozzles & tips?

In the mean time, I thought I might try to use the solder paste with my iron, any advice as to how to proceed?
 

windoze killa

Joined Feb 23, 2006
605
Ok, I looked for a proper definition of "fillet" without success. What part to you call the 'fillets'?
Can you describe a little about how the pins should look ideally?
A fillet is the solder shape. You should see the solder forming a nice concave shape between the pad and the pin. That is call a fillet. Same thing applies to welding as well. It SHOULD always be concave. If it was convex the departure/wetting angle of the solder could not be observed to actually see if the solder has wetted properly. Have a look at the PDF.

That technique seems to work the best. The trick seems to be getting the right amount of solder on the pins: Enough to tin them, but not too much to cause bridging.
BINGO. Exactly

@"less damage" Yes, when my technique is perfected there will be no damage, but correcting for my mistakes has worn on the cable more than necessary.
Still, the 'damage' to this last cable is negligible, probably not perceptible from the photo.
Practice makes perfect (or pretty close to it)

I just got my solder paste in yesterday, but I don't yet have a hot air tool.
Can you recommend a good one for this application?
Perhaps ideal settings & suggestions of some nozzles & tips?
Although a hot air tool is handy for these types of joints it is not mandatory. You can still use an iron with solder paste. All solder paste is is little balls of solder in a flux paste. When heated the flux melts and cleans the surfaces and then the solder melts to form the joint.


In the mean time, I thought I might try to use the solder paste with my iron, any advice as to how to proceed?
See above
 

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