How can I design plated slots in my Gerber files?

design plated slots in gerber file

For Seeed Studio Fusion, the way in which plated milling slots are communicated in the manufacturing files is similar to plated through holes (PTH). That is, there must be some sort of hole, copper plating and an opening to expose the copper. The following simple steps show you how to do this:

1. In your chosen design software, draw the slot outline in the Mechanical layer (GML or GKO), this will be the final size of the hole after plating. To preserve the exact dimensions, the outline should be drawn using a zero width line, the same as the board outline (so it looks like a small cut-out). Only the area inside the shape will be cut out.

Mechanical layer

2. In both Copper layers (GTL, GBL and any other copper layers), draw the same slots but at least 0.1 mm (about 4 mil) larger than the slots in the mechanical layer. The amount of copper exposed is up to you,

Copper layers

3. Finally, draw the slot openings in the Solder Mask layers (top and bottom), at least 0.16mm (about 6 mil) larger than the copper pads.

Solder Mask layers

4. Remember to do this for the other copper and solder mask layers. And now you have designed a plated slot.

designed a plated slot

design plated slot

The only real difference between a plated slot and a plated through hole is the shape of the cut-out. For PTH, we usually illustrate this in the NC drill layer with a drill hit. For plated milling slots, we design this by drawing the opening as a cut-out. Some component libraries will generate plated milling slots in a separate milling NC layer, but we do not recommend this since it can be difficult to import NC milling layers Into CAM software correctly. They may also be designed as filled shapes – but our engineers may not follow the exact dimensions of the shape, which is why we recommend using a zero width outline.
Please note that our smallest milling tool is 0.8mm in diameter, so if you require milling slots smaller than this, we suggest you design them as a row of overlapping drill holes and include them in the NC drill layer.
Good luck,

plated slots

output metal-slot

How to output metal-slot correctly?

PTH (Plated-Through-Hole) technology


First, To design a slot shape outline in GML layer, and to make sure drawing closed, and marked Plated-Through-Hole process needed(Slot drills with copper). PTH NPTH
Second, To design a slot shape pad in circuit layer (GTL&GBL), and to make sure slot pad filled and enlarged 4 mil than slot shape outline of GML layer.
Third, To design solder masker opening of slot shape in solder masker layer. (GTS&GBS), and enlarged 0.16mm than pad size of GTL& GBL .

design solder masker

design solder maskers

1. GML layer for slot design

GML layer for slot design

2. GTL&GTS , GBL&GTS layer for pad design
GTL layer for slot

GTL layer for slot

GTS for slot

GTS for slot



GBL, GBS layer for slot design

GBL, GBS layer for slot design

GBL, GBS layer


1. To avoid board damage, please make sure pads next to pads in inner, outside or neighbouring up to 10mil. Solder mask
2. Since the slot need copper covering, you should be considerable copper thickness influence for slot dimension.
3. The stand CNC milling cutter is 0.8, 1.0, 1.6, 2.0, 2.4mm.We will use 2.0mm norms by default if it’s no specified. (minimum hole size is 0.8)
4. For penalized required, to make sure direction parallel between slot length and penalized length.