PCB castellated holes or Edge Plating

Thread Starter

DJ_AA

Joined Aug 6, 2021
267
Hi

I am designing a PCB module, which is a DC-DC Step up, that will produce 12V 1A from a 3.7-4.2V Li-Poly Battery.

I need to make this as module so that I can use in on multiple designs.

For my design, does it make a difference if you design the module with castellated holes or edge plating?

Does it also make a difference where you place such a pad on board, for example, if I was to place it on the corners of each PCB, does it make any difference compared to the middle are of the edges?

And also the size of the pads, what size would be recommended for my current requirement?
 

MrChips

Joined Oct 2, 2009
30,448
I believe that you don't need castellated holes.
Ordinary connector or pin pads anywhere on the board will work.
1A is not a substantial current. Any thru-hole pad will do.
Typical 0.040 - 0.50" pad with 0.035" hole will be fine. For tracks, I would go minimum 0.025" width, wider is better.
 

Ya’akov

Joined Jan 27, 2019
8,973
Castellation is convenient for assembly, but as @MrChips said, there are alternatives such as a connector. You can make an edge connector just by laying out the connects on the PCB. You will need a mate on the other board, but you can find a variety of them.
Board-to-board pin headers are also a decent option. Particularly the high pitch low profile SMD type.

Current handling is no problem at all with an edge connector, but pin headers are usually rated at about 1A so to have some headroom you can just use two pins for 0V/V- and two for V+. The obvious and genuine advantage of connectors is fast replacement should you have a fault or revision. Castellated modules are not much fun to desolder.
 

Thread Starter

DJ_AA

Joined Aug 6, 2021
267
We have a small Pick and Place assembly, so we are not looking to do it manually,

But as we are doing our first module, we want to make sure our pad size and hole are just correct for the power module.
 

Ya’akov

Joined Jan 27, 2019
8,973
Well, if you are targeting P&P, castellation actually makes a lot of sense.

For connectors, I’d probably consider something like this HiRose series. Note the current capacity of one pin is only 300mA so you’d probably want to do four, but the high pitch means you will have plenty of space for lots of pins.
 

Ya’akov

Joined Jan 27, 2019
8,973
Yes, we are trying to keep the PCB small as possible, therefore module with no connector is the option I need to take,
Sounds reasonable but just for the record, the stacking height of the connector is just 1.5mm, so it probably wouldn’t add enough to matter.
 

Thread Starter

DJ_AA

Joined Aug 6, 2021
267
What is a rectilinear profile?

The pads are projecting outside the board, as I believe the PCB manufacture will cut them to the edge of the PCB.
 

Ya’akov

Joined Jan 27, 2019
8,973
What is a rectilinear profile?

The pads are projecting outside the board, as I believe the PCB manufacture will cut them to the edge of the PCB.
Meaning straight lines without the projection. If you don’t want the PCB cut that way, why draw it that way? In any case. if you cut along the edge of the PCB, it’s pretty much what I was talking about. It certainly looks like it would work.
 

Thread Starter

DJ_AA

Joined Aug 6, 2021
267
This is what I believe is used so manufacturers know which PAD is protruding out of the edge of the PCB for the castellated holes process.
 

Jon Chandler

Joined Jun 12, 2008
980
Making castellated holes is a special process that most fab houses will charge extra for. If they route the board normally and cut off the tabs across the center of the holes, chances are high that the hole plating will tear out.
 
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