Hi -
I am starting a project that will use small 1.3" displays that require a small flex tape to be soldered to the board. There will be no connector used in my situation.
My main question, the flex tape will be folded under the display, then soldered. The display will sit on top of the folded flex tape, insulated with foam tape. So there is a great deal of room for error in alignment. Does anyone have experience with this sort of footprint and how to design an accurate footprint.
Any advice you can offer would be appreciated.
Thanks
Jim
Soldering the Flex to the PCB is a bad idea. True, this TFT is low cost but, a poor connection/trouble will require Un-soldering - Never fun and never clean enough to satisfy me. You’ll end up trashing the PCB, too - that’s okay if PCB cost is very low - you decide…
I’d use a Flex Compatible connector mounted to PCB.
Yes, I do understand your point. Thanks.
However, I have a no headroom on the top of the board nor do I have the real estate on the bottom of the board to accommodate a connector. I certainly would like to use one but soldering the raw panel to the top of the PCB will be the way to go for my situation. This is a one-off project anyway, so I am not concerned with damage to the PCB, I will have several extras to use in case I damage one.
Jim
In that case, I would use a TFT footprint (or, make one) having only the TFT. Could include the Flex if desired but that’s not needed because it’s fllexible enough to accomodate Millimeters of Lateral (sideways) and Vertical positioning such as to enable soldering it onto a PCB (that has PAD’s (like SMD Pads). The PADs will be on the PCB, not the TFT Footprint.
ADDED: Use/make a Symbol indicating a Flex and Label the Connections. Label matching connections on the PCB’s PADs… Example Symbol below showing one label (Vcc)…
Crude cartoon below… You can mount the TFT to Standoff’s or spacers (grey in the cartoon)…
Yes, this is essentially what I was originally asking. What I plan on doing is to pre-fold the flex tape under the raw display panel, hold the flex down against the back of the display with tape. Then make careful measurements of the solder pads relative to the display housing. I have the mechanical details of the flex tape solder connections (pitch, etc). I was just hoping to find someone that has already done this and give me guidance as to what issues I may encounter.
I’ve done this before in Medical products and it’s not complex (as I inferred…)
Since the Flex is, well, Flexible - there shouldn’t be a problem positioning its Pad/Traces over the TFT’s Pads (that are on the PCB)… Plenty of movement flexibility of several Milimeters.
I locked the Flex down to the PCB the same way shown below (even though I actually used a Flex-Card Connector type for connections)…
I threw this together as a example so, did Not fuss with accuracy, details or positioning… You’ll get the idea, though.
I did Not bother hiding the Pins/housing in Kicad but I did hide it in FreeCAD (which I used to create the Folded Flex)… I also added a screw, holding strip…
If you buy the TFT/flex as in your posted link, you’ll have hardware to assess flexibility, positionig design choices/details…
Also, though I did Not do this here, Exporting a STEP file (of what you see as the beginnings of a real effort)… Having an Exported STEP then, adding/linking it to Footprint would make it easier to position/design though, the back and forth between software/etc is lack-luster busy work…
good luck
Left-side is FreeCAD with Transparency…, Right-side is Kicad
Any depth available on the back side of the pcb? Have you considered putting a flex connector on the back and passing the flex section through a slot or cutaway? Have you tried soldering a bit of flex to some proto board as a feasibility test?
My real estate on the rear of the board is at a critical minimum and there will not be any room for a connector. This was my initial desire when planning the project.
Thanks for the input -
Jim
Yes, soldering flexi is a bad idea, but some displays come like that, so choice unless you find a different model.
Those which come to be soldered are not made for FFC connectors and in most cases you won’t find any suitable connector for it.
It says clearly in the spec on Aliexpress “solder type”. Don’t re-invent the wheel and just solder it.
These small hole in the FFC visible below:
are for hot solder to make a better contact with the pads on the board.
Soldering is easy. Un-soldering is not, unless you have a very wide tip to heat all contacts at the same time. Otherwise is very easy to damage the FFC with heat.
I used small OLED displays in a past with similar connection type.
I made a footprint for it, but mine is 0.65mm pitch 15 pins, yours is 0.7mm and 12 pins.
The space behind the FFC (bottom of the footprint) allows some space for FFC to bend nicely.
Please find my footprint as attached. Modify it to your display dimensions and that’s it. Job done.
This is commonly done with hot bar soldering. IIRC you can use a footprint with pads about the same size as the exposed contacts on the flex circuit. You will just need to design (or have your manufacturer design) a jig for the assembly process, to hold the FFC and the board in the right relative positions during the hot bar soldering process.
