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I have an LED strip that I need to solder to a flexible PCB (designed in Eagle).

enter image description here

What is the easiest way to solder the LED strip to the flexible PCB? Also, what can be changed in Eagle to make it easier to solder to the LED strip?

How do they accomplish the connection on the image below?

enter image description here

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    \$\begingroup\$ For a one-off I'd probably lightly tin both (or use some SMD paste), only partially overlap them and then heat the exposed part of the real PCB pad with an iron, one pad at a time. A better solution would be to dispense with the joint entirely by making the LEDs part of your custom board... Also beware documented quality issues and package sealing failures with LEDs "pixels" and modules of that type when bought on the grey market. \$\endgroup\$ May 15 '20 at 21:14
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The bottom image has the flexible part only extending half way in to the pad, and then soldered like a PCB jumper

enter image description here

This however does make it risk being levered off from the board, as there is generally nothing binding it on the bottom of the flex, only the narrow interface

There are other ways you can approach it to make the joint stronger, a simple one being to make the pads on the flex end closer to a crescent shape, this way the stress of flexing is spread out over a wider area,

Even better is to flip the ribbon over, and use the longer pads of what your joining to flow some solder between them, for the maximum surface area in common, makes rework more painful though.

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  • \$\begingroup\$ This is definitely not the case. If you look carefully (above pad 26 and between the pads) you'd see that flexible circuit definitely extends almost all the way to the end of the PCB pad, not to half of it. Solderable FPC usually have pads on both sides and holes in them, so the connection is quite strong. \$\endgroup\$
    – Maple
    May 16 '20 at 2:47
  • \$\begingroup\$ hi @Maple, so do you suggest to have pads on the FPC? with holes, and double sided, that matches the PCB? thanks \$\endgroup\$ May 16 '20 at 5:40
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do you suggest to have pads on the FPC? with holes, and double sided, that matches the PCB?

Technically, they are VIAs (PTH or Plated Through Holes), not just holes. They look like this (image by Amada):

enter image description here

What I am suggesting is treating LED strip as FPC. Then your task becomes a typical FPC-to-FPC soldering, which is usually done with reflow process, as far as I know.

The most common example of it is connection between backlight and touch panel leads to larger LCD FPC board, as seen below (image by Newhaven Display)

enter image description here

If you have one lying around take a look and do something similar. Also, couple interesting recommendations on designing FPC pads here.

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