IoT#32 RPTC-Q - Soldering Flat Flex to PCB: LCD Initial Power Up and Rework

In today’s video, we investigate strange I2C SDA and SCL waveforms from our ESP32 to our NHD-C160100Diz LCD with ST7528i I2C Controller. We verify the Sitronix LCD controller is not responding to our I2C commands and investigate why. When we discover the issue, we perform the repair and test; will it work?
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[@Big74Mike2012]

I see that you are in possession of flux because you used some when soldering the FFC onto the board, so I'm wondering why you didn't use any when cleaning the old solder from the PCB pads?! That would've made the task much MUCH easier!

[@muxallopeniot9194]

You are correct, we have to use flux to clean the solder off of the pads.

[@MatthRrrr]

Hey, I may sound pedantic, but what you are soldering is a FPC (Flexible Printed Circuit); not a FFC. I mention this because I was looking into FFC soldering technique, and I don't know if the technique is different or not.

[@muxallopeniot9194]

Thanks for pointing that out. I tend to call everything a cable if it goes into a connector.

[@andyeash1730]

What is that red tape that's placed on the 14 pin FFC right before soldering?

[@muxallopeniot9194]

That's just the back of the FFC. The only tape I put on is the electrical tape to hold is in place while I soldered.

[@andyeash1730]

Interesting, the back of mine don't have anything on the back of the pins like that. Thanks!

[@jacksoncroyce6063]

It's solder braid/wick. It's fine braided copper wire with flux in it and you use it with your soldering iron to 'mop up' unwanted solder. It absorbs the solder and leaves pads clean. Very handy stuff. Google 'solder wick' to get a better idea.

[@gindevgin9298]

Hi! Thank you! Which product did you apply to clean the contacts?

[@muxallopeniot9194]

Alcohol pads

[@tonycstech]

That didnt work for me. Cable simply refused to stick, not sure why.

[@muxallopeniot9194]

Yeah, they can be a real PITA. My only thought is to try and clean everything really good, add liquid flux to the pads, and try to pre-tin (add solder to) the pads. That may help the solder flow better. Be very careful pre-tinning the pads that you don't tear them from the PCB.

[@ryszardkula2601]

nice

[@davecc0000]

What PCB layout software package are you using?

[@muxallopeniot9194]

I use Diptrace

[@norleonor5733]

hi therez whats the proper temperature when soldering film/flex things? i tried soldering one of my cymbal triggers and it melted the whole thing... :(

[@muxallopeniot9194]

Wow! Sorry to hear that. I thought I mentioned the soldering iron temp in the video but I don't remember. If you have an older flat flex, it may have been designed to be soldered with lead based solder that has a lower melting temp than lead-free solder. But any plastic will melt if you keep the iron on it too long.

[@NandhiniNandhini-jo6uf]

Flexible flat cable 3 light red color Hp deskjet 2131

[@giorgostexnikos6976]

nice jub

[@bskull3232]

Don't know what flux are you using, but most of the time liquid flux are water soluble ion-based ones, and they corrode PCB. Since they will be trapped under the FFC forever, it's not the best idea to use those. I'd rather use paste RMA no clean flux despite they leave a mess. At least I know the mess is not going to f* my board in the future. If you use NC flux, leave it there. If you use WS flux, congratulations, they are easy to clean, but if you failed to clean them, then good luck.