Soldering the antenna back on to a Xiao ESP32 S3 sense board

Hi @slamer,

  That is a very small area, so I don't know if you have the kit, etc, to solder to it, and luckily for me, I have never had to try doing such microsurgery.

I just did a Google and found a discussion 

https://forum.kicad.info/t/is-the-footprint-for-a-u-fl-antenna-connector-supposed-to-look-like-this/61181

Comparing with your photo, I guess the two parallel horizontal pads in the middle of the photo are outer 'screen' connections (ie essentially just ground), and the small square, to the right of the horizontal pads, and in line with the space between the horizontal is the 'core' connection. 

First check, is that square, actually a metal pad connected to the RF output, or just the glue left behind when the pad came off?

If the pad is 'real' metal, then you might be able to solder a new socket on. If not, then you have currently no 'live' signal point to connect an antenna to. The feed will start under the rectangular metal screening box, but I have no clue if it is accessible.

In 'electrical' principle, a wire of the correct length, connected directly to the square pad, should work, but mechanically, that will just tear the pad off, so I would start with the socket replacement approach, if the square pad in intact.

Good luck!!!

Hi Dave, that's a good find. it gives me a sense of where the trace on the board might be.
I'm pretty sure the pad it self is gone so I am hoping I can scratch a bit of the coating on the board off to expose the lead then direct solder the antenna. I've watched some videos on doing this, but high probability I will let it go and get another sense board. Unfortunately the standard S3 board does not include the connector for the camera connector, so I need to buy the full assembly.

Hi @slamer,

Finding the track to the pad might be possible, but as a lifelong pessimist, I wouldn't be surprised to find it is a 4 layer board, and the track is on an inner layer. It might also be on the bottom layer?

Subject to any local trade limitations in your area, I think you should be able to buy the UFL socket if you attempt this feat ..

eg https://www.aliexpress.com/item/1005012081109232.html  

(I didn't choose that one in particular ... it was just the first one on my screen look more carefully before ordering.)

If you can figure out how to connect to the 'core' track, then having a connector means it can use the larger shield connection as an anchor, and you can probably reinforce with a tiny dab of glue.

Good luck ... 

Looking at your picture I couldn't really tell if you've lost your pad. Solder wick and a little flux to clean up the area might reveal you could just replace the connector. The small size is definitely a pain in the behind. When I solder them to Lora Boards I have found a method that seems to work well for my soldering technique. I clean up the pads really well with alcohol and then tin a single pad with a small blob of solder. I place the connector close and remelt the solder and gently push the connector into it with sharp nose tweezers. Once it is held in place i solder the other pads and come back to the first if I don't like the connection. I use a really sharp soldering tip for these little buggers.

Hi @Slamer,

There may still be a repair option if an accessible section of the antenna feed trace survived. Before scraping anything, check the schematic and KiCad files in Seeed’s XIAO ESP32-S3 resources, matching your board revision. Those should help establish where the signal track actually goes.

With USB and any battery disconnected, I’d clean the area with IPA and inspect it under magnification first. Be gentle with solder wick—dragging it across already damaged copper could lift more of the trace.

PCBWay’s soldering-problems article has a section on lifted pads and reconnecting to surviving copper. However, the long jumper-wire approach used for ordinary connections needs particular caution here: this is a 2.4 GHz antenna feed.

If you solder the existing antenna cable directly, its centre conductor goes to the confirmed RF feed and its shield to nearby ground. Keep the exposed portion extremely short and secure the cable mechanically so a tug cannot pull on the repair. A correctly matched replacement socket is another option, but its centre contact still needs that missing electrical connection restored.

The controlled-impedance section of high-frequency PCB article gives some background on why the trace geometry and ground return matter. A continuity check alone won’t establish that the repaired antenna connection performs properly.

If no accessible signal copper remains, replacing the board is a reasonable choice. I’d avoid digging into the board without knowing exactly what lies underneath.