Is there a faster way to solder FPC ribbons together?

Thread Starter

strantor

Joined Oct 3, 2010
6,798
I have a bunch of RPi ribbons with the wide style on one end and the narrow style on the other. And I need to connect cameras with narrow style to boards with narrow style. I don't have any proper ribbons but I can solder together the ribbons I do have. I tried it last night, two out of two ribbons I made, miraculously had no opens or shorts. This what I think of as a "medieval method" of doing it:

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I put a very light coating of solder paste on each connector and melt it with the heat gun to tin the pads. Then arrange the two ribbons on top of each other on the (cold) hot plate with a masonry chisel to keep them in place and apply a bit of pressure. Then turn on the hot plate, wait for solder to melt, turn it off, wait an hour or so for it to cool.

This takes forever and I feel like my 100% success rate is an anomaly and I should probably quit while I'm ahead. I may or may not need to make 3 more of these tomorrow. Is there any less stupid way to do this stupid thing?
 

R!f@@

Joined Apr 2, 2009
9,918
WTH @strantor
I thought you were chiseling a ribbon cable :D
Still, your method is more effective in getting 100% connection. Soldering ribbons is sometimes a nightmare with an iron at times.
I would try the same but without a chisel I believe.
 

jiggermole

Joined Jul 29, 2016
161
well i bookmarked the method cause I ain't got a better idea.
The only method I can think of would be to hold things with capton tape and drag solder it. Maybe clean up any excess with braid.
 

Ya’akov

Joined Jan 27, 2019
9,167
Maybe something like this? Of course if this is a problem of working with what is on hand then that doesn’t help.

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The only time I ever had to do this, and it was with a single cable, I tinned both cables, put a layer of tacky flux on the up-facing one, taped them down in the finished positions with polyimide tape very close to the ends, and then used hot air.

It worked, but a sample of one doesn’t really say if it is consistent. If you have a lot of them to do, I would be inclined to make a jig that holds them in so they the top one is slightly flexed so it will want to apply a bit of pressure, then use the method above or a hot plate as you are.
 

MisterBill2

Joined Jan 23, 2018
18,535
Very interesting and rather timely. I have a video camera that has a similar ribbon cable that has broken, and a replacement does not seem to be available. Your success is very encouraging. Thanks.
 

Thread Starter

strantor

Joined Oct 3, 2010
6,798
Maybe something like this? Of course if this is a problem of working with what is on hand then that doesn’t help.
Yeah I did this because I didn't have proper ribbons and I needed them right away. I would have just ordered them if there were no rush. I thought I was done, emergency passed, so I still didn't order any; put it on the to-do list but hadn't got around to it yet. And now the same emergency threatens to make a follow-up visit.
 

MrSoftware

Joined Oct 29, 2013
2,201
You've got a working method, that's the most important part! Only for the sake of trying to make it faster; instead of using the hot plate for heat, slather the ribbons with thick flux (my favorite is the MG Chemicals in the syringe), then hold them together with your chisel and use hot air to heat them enough to flow the solder. Maybe keep the hot plate warm but heat the chisel with the hot air to get the heat into the ribbons? The ample flux will make it flow nice and hopefully prevent any shorts. Maybe bring in a small fan to cool the joint faster so you can remove the chisel sooner. That chisel must have a bazillian joules of heat capacity, if you could find something with less mass it would probably speed your process significantly. Great job creating a working solution though, that was creative.
 

Thread Starter

strantor

Joined Oct 3, 2010
6,798
Melting that ribbon material would be a concern as I see it.
Yes it requires adult supervision, one of the reasons I am not in love with it. The material is polyamide AFAIK so shouldn't melt below 350C. I only had the hot plate set for 220C, but it's not a very well made hot plate and the surface temperature is always way hotter than what is shown, unless it has been at setpoint for a good long while. So I just turned it on and watched it until I saw the solder flow, then turned it off. The solder should melt sooner than anything else.
 

MrSoftware

Joined Oct 29, 2013
2,201
Melting that ribbon material would be a concern as I see it.
If that stuff is the same as rigid-flex PCBs; I recently did some hot air rework of connectors on rigid-flex PCBs and the flex part took the heat just fine, the same as a regular PCB. It's the same material without the stiffener layer (typically FR4).
 
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