R4 WiFi "No device found" due to a bad solder joint

Official Hardware UNO Family UNO R4 WiFi
1

I thought I should share my experience having a seemingly somewhat common issue that other threads here advise solving through firmware updates, but actually turned out to be a hardware problem.

Recently I bought a R4 WiFi from what I believe is the official store on Amazon. Right out of the box I couldn't upload sketches to it from Windows or Linux with the known "no device" error from bossac (with the board led properly switching to flashing in the bootloader mode):

No device found on COM4
No device found on ttyACM0

I couldn't update the firmware from Windows either, but on Linux it worked and seemed to fix the problem.

Fast forward to yesterday, when I uploaded a sketch that flooded the serial output line due to a print in a too tight loop, making the TX led basically stay constantly on, like here.

This effectively killed the ability to upload either sketches or firmware from the IDE on either OS, just like in that thread.

Using the stand-alone ESP32 firmware update script it was possible to flash that chip firmware from linux just fine, but it didn't affect the problem. The bootloader flash procedure with 2400 baud and rfp-cli also wasn't working with

[Error] E3000105: The device is not responding.

I tried soldering the RA4M1 jumper and flashing the bootloader using the Minima procedure (and deleting that sketch from memory while at it), which worked perfectly fine, but didn't solve the problem after the jumper was removed.

Finally I broke out my oscilloscope to test the serial lines between the two chips, and found a bad solder joint on the A8 pin of the TXB level converter chip, which effectively cut the serial data line transmitting from RA4M1 to ESP32, so the upload software could not get any reply from the chip. The sketch putting high load on that serial line may have fried the already flaky joint.

While trying to directly test the pad on the side of the chip with a sharp probe I must have mechanically pinched the solder blob to the pad, because it actually started working; but it clearly needs a proper reflow.

I must say that under a strong magnifying glass the SMD solder joints on the board look quite grainy and bad, compared even to through-hole connector joints on the same board, so I think the manufacturing process for these boards may need a few tweaks.

2

Good Catch! Check if they will give you your money back. If it were mine I would simply touch it up with an iron and keep an eye on it for future problems. Not all SMD soldering gives shiny joints.

3

The problem isn't shiny, the problem is they look more or less like piles of half-melted balls, sort of like here (or the "graping" effect earlier - can't quite tell the difference).

I guess the main concern is what's going on under than ESP32 chip, because that's the only part that can't be touched up with an iron like you say.

4

You should contact Amazon, customers can return a product. Check Return Items You Ordered - Amazon Customer Service

6

First, do you think I didn't try something as simple as that? By the way, a failed attempt at sketch upload due to faulty serial leaves the device in the bootloader mode in any case.

Second, how is that going to fix a hardware issue?

8

Unfortunately the time for that has run out, so I'll just fix this joint and hope whatever is inaccessible under the ESP chip holds.

I mainly posted this to document a potential issue with soldering reliability on these boards that might be causing similar intermittent issues for other people, and is something someone maybe should look into.

P.S. I've actually managed to make a photo of the soldering on the resistor next to the power led using a phone through a magnifying glass. You can just about see how grainy the bit actually in focus is.

IMG_20240624_200928
IMG_20240624_2009281605×1235 419 KB

9

That is a manufacturing defect. The balls you see are solder balls that are part of the solder paste when doing SMD manufacturing. Considering what it is they should exchange it even if it is out of warranty, I am assuming you started to use this. Also contact the manufacturer and let them know. Also let them you have yet to review there product.