Castellated Edges

Castellations are small plated edges, typically used for making circuit boards into small PCB modules. These are often seen on wireless modules, such as the ESP8266-12E.

While we don’t offer full support for castellations, they can be fabricated if you don’t mind a few minutes of rework and verification of the PCBs.

Design Considerations

It’s helpful to include a fallback hole near the edge. The ESP8266-12E boards, are a great example here. The extra via allows easy connecting of wires for rework, and makes it easy to salvage a module if the fabricated PCB doesn’t turn out perfectly.

ESP2866-12E, available at

Indicating in the design file

Castellations are simple to call out in most design tools. Simply include a via on the PCB, so the board outline goes through it.

However, due to our panelization process, the castellated vias must be indicated with round pads for copper and stop mask. The pads must also not extend more than 40 mil from the board edge. Square pads or pads that extend far beyond the edge will be trimmed, and the via will not be plated.

It’s also helpful to use a 10 mil wide line for the board outline. With our milling tolerance of 5 mil, this provides a good visual indicator of where the physical board edge might be. The fabricated edge can be anywhere within that line. This is very helpful for fine-pitch castellations with smaller holes.

Callout as seen in a design tool
Callout as seen in a design tool

Rectangular castellations can be made by using vias with round pads as noted above, and adding overlapping rectangular SMD pads. Since these pads are inside the board outline, they will not be trimmed, and will provide additional area for soldering (see below for example).

Cleaning up the final boards

We make a best-effort to minimize support tabs on castellated edges, but it sometimes happens. In these cases, you’ll need to file the tab off of your edge.

Additionally, the via plating may not be fully removed during the milling process. In some cases it’s smashed next to the edge, where it can cause unwanted connectivity between vias. In others, it’s smashed inside the via, where it will prevent good solder flow. A fine point file or hobby knife will help remove excess plating.

An unreworked castellated PCB, with visible plating stubs
An unreworked castellated PCB, with visible plating stubs
Another version, with tabs on castellated edge and modifications for rectangular pads
Another version, with tabs on castellated edge and modifications for rectangular pads
Castellated Edges

Teensy 3.6 DIY Reference Board

Shared project from Teensy creator Paul Stoffregen on OSH Park:


Teensy 3.6 DIY Reference Board

A known good reference board for testing the MKL04 chip when building a DIY Teensy 3.6. Refer to this table for the differences between Teensy 3.6 and other models. The soldering friendly LQFP package (at least more friendly than BGA) is used on this board.

Order from OSH Park

Parts Placement Diagram

Bill Of Materials

1   MK66FX1M0VLQ18
1   IC_MKL04Z32_TQFP32
1   USB A Connector
1   USB Mini B Connector
1   Micro SD Socket
1   MCP1825S Voltage Regulator
1   TPD3S014 USB Power Switch
1   Crystal, 16 MHz
1   Crystal, 32.768 kHz
3   Diode, Schottky, B120
1   Capacitor, 100uF, 6.3V
4   Capacitor, 4.7uF
10  Capacitor, 0.1uF
1   Resistor, 100K
2   Resistor, 470
2   Resistor, 220
2   Resistor, 33
1   Pushbutton
2   Test Point, Black
Teensy 3.6 DIY Reference Board

Resurrecting a Psion Series 5 PDA

RasmusB on is resurrecting a Psion Series 5 PDA:



Bringing a Psion Series 5 into this decade by replacing all the important bits.

The completed result will (hopefully) be a portable modern Linux system with all the connectivity options expected in a modern device.

The keyboard adapter board is available on Tindie:


USB keyboard adapter for Psion Series 5 keyboards

This is an USB interface for Psion series 5 PDA keyboards. Plug in a keyboard and a USB cable, and use it with any modern computer!

The design files and source code are available on GitHub:


Resurrecting a Psion Series 5 PDA

EEPROM Programmer Arduino Shield

From the The Oddbloke Geek Blog, an EEPROM programmer shield designed for Arduino Mega:


Simple EEPROM Programmer … revisited

Some time ago, I wrote about my DIY EEPROM programmer driven by an Arduino Mega. It’s a very simple, low-tech project … but has attracted a consistently-high number of visitors to the site and is something I use several times a week.

EEPROM Programmer Arduino Shield