Seeed Studio XIAO Plus, More Castellation IOs for SMD Soldering
Update — August 2026: The XIAO Plus family has grown from the three original models to five. We’ve added the new XIAO SAMD21 Plus and XIAO RP2040 Plus to the lineup. Scroll down to see what’s new.
The beloved Seeed Studio XIAO boards, with their surface-mount device (SMD) design and Castellated Mounting Holes, have become popular integrated system modules in countless creative designs, projects, and even commercial products. Their board-to-board soldering capability allows XIAO boards to be easily integrated into carrier boards, enabling faster assembly and scalable production.
Since launching our first XIAO SAMD21 (formerly Seeeduino XIAO) in 2019, we’ve received countless community requests for more than the standard 14 castellated mounting holes on two edges, as these weren’t sufficient for complex projects requiring additional IOs. Now, please meet Seeed Studio XIAO Plus – our response to this community feedback.
Inspired by the cool SMD pins design of the RICK TNY, Seeed Studio XIAO Plus represents a new iteration of our regular XIAO Boards, featuring redesigned 23 castellation pins (20 GPIOs, 3 power pins) and back solder points specifically for projects needing expanded IOs. We’re launching XIAO Plus versions for five models: XIAO ESP32S3 Plus, XIAO nRF52840 Plus, XIAO nRF52840 Sense Plus, XIAO SAMD21 Plus, and XIAO RP2040 Plus, which are all available for instant order at our webstore.
Why More XIAO Plus Boards?
When XIAO Plus was first introduced, we started with three boards based on community demand and the available I/O resources of each MCU. Since then, we’ve continued working to bring the expanded-castellation design to more members of the XIAO family.
Today, we’re adding two more:
- XIAO SAMD21 Plus brings the Plus design to the original XIAO MCU family, adding 16 extra GPIOs through the redesigned SMD castellations. It also integrates Li-ion battery management, dedicated Reset and Boot buttons, and a programmable WS2812 RGB LED.
- XIAO RP2040 Plus brings the same expanded-I/O concept to the RP2040 platform, adding 15 extra GPIOs, onboard Li-ion battery management, and battery-voltage monitoring while retaining the RP2040’s familiar dual-core Cortex-M0+ architecture.
This means the XIAO Plus family now spans five boards, giving developers more MCU choices while keeping the same compact XIAO form factor and SMD-oriented design philosophy.
What's new with the back solder points?
Previously, XIAO boards lacked uniformity in their back-side solder points and layouts, hampering our ability to develop universal expansion boards. Our latest XIAO boards (RP2350, RA4M1, MG24 and MG24 Sense) share nearly identical back layouts. The XIAO Plus boards follow suit, with aligned battery and debugger pads.
This standardization means our upcoming expansion boards (such as the XIAO Clip Board) will work with all seven boards (3 XIAO Plus models, XIAO RP2350, RA4M1, and MG24/Sense). We’re actively working on compatibility solutions for other XIAO boards and will share updates once available.
Is XIAO Plus harder to solder?
The through-holes for 7-pin headers remain unchanged, but the castellated mounting holes are slightly smaller and closer together (13 on the left, 10 on the right). While this does make board-to-board soldering more challenging, our 11-person product team successfully tested it with early samples.
We’ll be honest – it requires more precision, but proper tools make a significant difference. Essential items include a brass sponge, water-soluble flux pen, tweezers, acid brush, and rubbing alcohol. For detailed guidance, check out SparkFun’s excellent tutorial on How to Solder: Castellated Mounting Holes.
Join Seeed Studio XIAO Adopter Program
Ready to showcase your soldering skills? Share your XIAO Plus project ideas in the comments! I’ll select three winners to receive their chosen XIAO Plus board (via coupon). Winners will be announced on January 10, 2025. Share now! To assist developers in adapting their projects to the XIAO Plus quickly, we’re adding all the XIAO Plus Boards to the Seeed Studio XIAO Adopter Program. If you’re an author or maintainer of a popular open-source project on GitHub, or an influencer on platforms like YouTube or Tiktok or Instagram, make sure your users can run your code on the XIAO Plus. Join to receive 2 free boards and technical support to make your code compatible with these exciting new boards.
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