Uploaded March 2026 | Updated September 2026, 1 week ago
Thanks to PCBWay.com/?from=atomic for the fantastic PCBs and SMT assembly.
A few ESP32 Rainbow boards started failing QA, and at first I assumed it was assembly. Tombstoning? Paste volume? Pick and place alignment?
Nope. It was the footprint.
Specifically, a SOT666 package that I thought was a safe, boring, standard choice. Turns out “SOT666” doesn’t mean what I thought it meant.
KiCad’s default footprint matches one manufacturer’s definition. The datasheet for the actual part I was using recommends something noticeably different. Pad length, spacing, the works. On screen they both say SOT666. On the bench, they behave differently.
The result? The chip didn’t self-align properly during reflow. A tiny part, slightly off, just enough to cause intermittent QA headaches.
In this video I walk through:
• The microscope footage from the failing boards
• The KiCad footprint versus the datasheet layout
• Where the dimensions don’t match
• Why solder surface tension couldn’t “save” it
• And how I’m fixing it for the next production run
I’ll admit it: I assumed the package name was the standard. Fortunately, that assumption only impacted a couple of boards.
If you design PCBs for real production, double-check the recommended land pattern. Even when the package name looks familiar. Especially when it looks familiar.
---
If you'd like to help support the channel and help me buy more nonsense - I have a Patreon page: patreon.com/atomic14
We've also got a shop now! shop.atomic14.com
And if you're shopping on AliExpress or Amazon then if you click on these links I will get a little bit of affiliate money:
Aliexpress - https://s.click.aliexpress.com/e/_Ac05mF
Amazon - amazon.com/?tag=atomic14-20
You can also join us on Discord here: discord.gg/h2DDnDdjD2
There's also the Atomic14 newsletter here: atomic14.substack.com
And don't forget about the MakerNews newsletter - makernews.substack.com
Thanks to PCBWay.com/?from=atomic for the fantastic PCBs and SMT assembly.
A few ESP32 Rainbow boards started failing QA, and at first I assumed it was assembly. Tombstoning? Paste volume? Pick and place alignment?
Nope. It was the footprint.
Specifically, a SOT666 package that I thought was a safe, boring, standard choice. Turns out “SOT666” doesn’t mean what I thought it meant.
KiCad’s default footprint matches one manufacturer’s definition. The datasheet for the actual part I was using recommends something noticeably different. Pad length, spacing, the works. On screen they both say SOT666. On the bench, they behave differently.
The result? The chip didn’t self-align properly during reflow. A tiny part, slightly off, just enough to cause intermittent QA headaches.
In this video I walk through:
• The microscope footage from the failing boards
• The KiCad footprint versus the datasheet layout
• Where the dimensions don’t match
• Why solder surface tension couldn’t “save” it
• And how I’m fixing it for the next production run
I’ll admit it: I assumed the package name was the standard. Fortunately, that assumption only impacted a couple of boards.
If you design PCBs for real production, double-check the recommended land pattern. Even when the package name looks familiar. Especially when it looks familiar.
---
If you'd like to help support the channel and help me buy more nonsense - I have a Patreon page: patreon.com/atomic14
We've also got a shop now! shop.atomic14.com
And if you're shopping on AliExpress or Amazon then if you click on these links I will get a little bit of affiliate money:
Aliexpress - https://s.click.aliexpress.com/e/_Ac05mF
Amazon - amazon.com/?tag=atomic14-20
You can also join us on Discord here: discord.gg/h2DDnDdjD2
There's also the Atomic14 newsletter here: atomic14.substack.com
And don't forget about the MakerNews newsletter - makernews.substack.com
