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Plated-through Slots

Plated-through slot means the slot is plated with copper and can be used for electrical connections. It is the way of the through-plating realized in the circuit board, which is called plated-through slots, and the through-plating on the outline of the board is called side plating or edge plating.


Slots can be defined as plated through-holes (PTH) or non-plated through-holes (NPTH). Every milling with copper connections on TOP and BOTTOM will be produced as a plated hole (PTH). PTH slots are most commonly used for component packaging. But both the plated slots and non-plated through-slots are available for a PCB. Multi-layers PCB always includes the plated-through slots.

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The importance of plated-through slots

In most PCB manufacturers, there are a lot of different footprints and component types for PCB assembly. Most through-hole part outlines are designed with round holes to accommodate round or square leads. This configuration is ideal for most through-hole assemblies, but many parts use rectangular or “blade” style leads and do not fit well into round or square holes. Therefore, using a plated slot package is a better choice.


As the size of the pins increases, large blade-style connectors should use plated-through slots instead of round holes from the design and production perspectives. When parts are relatively small, we can still use round holes with rectangular pins. But round holes also take up more space on the board itself, and the use of plated slots often helps with size-constrained designs.


How to show the plated-holes/ slots on the Gerber?

First, place copper pads on the top and bottom solder mask layers.

Second, place the milling slot in the mechanical/contour layer.

l Plated holes/slots

The holes are with copper in the circuit layer, and holes have openings in the solder mask layer.

l Non-plated holes/slots

The holes are without copper in the circuit layer, and the openings don’t matter in the solder mask layer.

Some applications for PTH/NPTH

l Plated-through slots are suitable for the parts with rectangular or square (rather than round) leads or pins, such as DC jacks.

l Milling slots are to form air gaps for voltage isolation on the PCBs.


NextPCB' s capability of plated through slots

NextPCB can provide 0.5mm for the min size of the plated slot and 0.8mm for the min size of the non-plated slot. The plated-through slots are laser machined into the boards and then specially cleaned to remove the laser slags. There are some concerns to pay attention to the design of plated-through slots. A proper aspect ratio of the hole diameter to the board thickness helps to fully metalize the hole barrels and maintain enough annular ring width.


Most PCB layout software provides in their footprint editor to define the round hole or oval hole. But it is more reliable to indicate slot holes on a fabrication layer in the Gerber file when customers do PCB assembly prototype or mass production. Please do not hesitate to contact us if you have any questions about the slots or hole shapes in PCB design at any time, and the engineers in NextPCB will offer professional suggestions for you!


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