NPTH - Non Plate Thru-Hole

Creating a NPTH requires proper soldermask expansion and copper pullback from the edge of the hole.

3D Color View

If the design calls for a NPTH as show above (P2) a circle arc can be used to create the ring around the un-plated hole.

Note that the soldermask was not pulled back from the edge of the hole for P1.

The designer of this NPTH will get a technical query from the PCB fabricator asking for permission to pull back the soldermask from the edge of the hole.

Shown in 2D the soldermask is correctly pulled back from the edge of the hole for P2.

Are we done Now ?

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Before answering that question, let's look at typical surface mount pad.

Note soldermask expansion, which is typically 4 mils.

The soldermask registration accuracy needs to be considered.

More work is needed to properly finish this NPTH.

Let's add a 5mil expansion to the arc (full circle)

Ok, now we are done. P2 is good to go.

There may be other factors to consider, like copper pours with same or different net than the ring around the hole.


That's It !