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I have a module with tiny Castellations (Half-Vias) at 1.5mm pitch. They are 0.8mm wide and 0.6mm deep. I am designing a breakout board for this - intended for hand soldering (not paste + pick n place).

I've seen breakouts for other castellated devices and soldered some myself.

What I am not really sure about is how long to make those pads - to make it (relatively) easy to solder.

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    \$\begingroup\$ "Pitch" is not a dimensionless quantity. \$\endgroup\$ – Olin Lathrop Jan 12 '17 at 14:13
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    \$\begingroup\$ If you have used breakouts that you soldered yourself (and found it workable), why don't you measure the pads on those breakout boards and replicate the dimensions? \$\endgroup\$ – dim Jan 12 '17 at 14:13
  • \$\begingroup\$ Woops missed mm - well spotted Olin. \$\endgroup\$ – Danny Staple Jan 12 '17 at 15:32
  • \$\begingroup\$ @dim actually - that may be the right answer. Even if the pad width/pitch is smaller - the length was workable. \$\endgroup\$ – Danny Staple Jan 12 '17 at 15:33
  • \$\begingroup\$ Consider investing in a cheap hot air station. Especially if you have a typical temperature controlled soldering iron rather than one of the extremely responsive sort, you may find that ground connections get fairly hard to solder (even with proper attention to thermal relief). Hot air can both let you use a paste solder without needing any pad outside the outline (though it's still nice to have if you have room), but you can also use the air tool to "assist" iron soldering of any pad you aren't getting enough heat into. And of course it's the only way you'll ever get one of these back off. \$\endgroup\$ – Chris Stratton Sep 13 '17 at 2:59
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I've been using a tried and tested footprint for a mini nRF24L01+ that has edge castellations at 1.27mm pitch. The pads extend 0.9mm (though rounding up to 1mm wouldn't hurt) and it is very manageable to solder by hand with a small tip.

Mini nRF24L01+ footprint

(Grid = 1mm.) Here's how it looks in real-life:

Mini nRF24L01+ in action

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I haven't had to do this myself but my gut feeling would be to make your pad cover the pad on the device you are soldering down and stick out by about a millimetre on each side.

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    \$\begingroup\$ Even more than a millimeter can be useful if you have the space. On the other hand, with better process, you don't need anything beyond the outline at all. \$\endgroup\$ – Chris Stratton Sep 13 '17 at 2:56

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