PTH outline | plated slots | plated milling | PCBs | copper outlines and routings

Plated Outlines, -Milling, -Slots & Half-Opens

Sometimes, an application requires that PCBs not only have plated through-holes but also plated contours or slots. This allows either certain components to fit and be soldered more efficiently, or the entire PCB can be soldered along its edges.

The following five categories are commonly used to distinguish between plated contours and milling:

1. PTH slots
2. PTH routings
3. PTH outlines
4. Half-Opens
5. PTH milling

Plated slots in PCBs are often referred to as "long holes." These are either milled or nibbled during production. Nibbling refers to the drilling of many overlapping holes, resulting in a slot. For this process, a special nibbling drill with a specific grind is used. In both cases, the tool is subjected to higher stress—either from the horizontal movement during milling or from the continuous drilling along an edge, where the nibbling drill slides sideways along the hole's edge. Therefore, the smallest tool diameter that can be used for slots is 0.50 mm, as smaller tools would lack the necessary stability.

Plated Slots on PCB without Solder Mask and Type 7 Capped Vias

When preparing data, it is important to note that plated slots also require an annular ring. Standard annular rings are 0.20 mm all around. In special cases, this can be reduced to 0.15 mm.

PCB in CAM – Slots with Annular Ring

After the electroplating process, a 0.50 mm milled slot will typically become about 0.45 to 0.40 mm wide, as the copper buildup reduces the slot width. This is the smallest possible plated slot. Common standard slot widths are 1.0 mm and 1.6 mm. Thinner plated slots may experience tool deviation or slight misalignment due to the forces acting on the tools. Additionally, it is very difficult to remove milling dust from very narrow slots before plating, which can result in minor over-plated burrs.

2. Plated Milling Areas

Plated milling areas refer to a much larger region than just a slot that is milled out of the PCB and plated. Depending on the size of this area, production can face certain challenges. In specific plating processes (e.g., panel plating), the laminate must cover these large areas without tearing. Pattern plating is more advantageous in such cases. It is also important to note that a milled edge does not achieve the usual roughness that is desirable for optimal adhesion in plated-through processes. The copper adhesion in plated milling areas is weaker than in plated holes. In multilayer boards, it is therefore essential to connect the inner layer copper to the plated milling areas to stabilize them.

PCB with Plated Routing

In CAM processing, it is important to ensure that, as with plated contours, a sufficiently wide annular ring is provided.

Since these involve larger areas and the laminate adhesion can be critical depending on the process, we recommend 0.25 mm or significantly more if possible.

Plated contours on PCBs are usually created using a 2.00 mm or 2.40 mm milling tool. It is important to note that the PCB still requires connections to the manufacturing panel. Therefore, a fully plated contour around the entire edge is not possible. Corners are typically used for these connections. However, depending on the size and design, other connection points may also be necessary. Particularly when the PCBs are large and the plated milling cuts are long, additional hold points must be added to ensure that the panels do not become unstable during production. At these hold points, once the boards are separated, there will be no metallization on the PCB edge.

The aforementioned disadvantages regarding the adhesion of a plated contour also apply here, as milling leaves smoother edges compared to drilling. Therefore, it is also essential to connect any available inner layer copper to the plated contour wherever possible.

PCB with Edge Metallization

In CAM processing, it is important to ensure that an adequately wide annular ring is provided. This ring typically includes the entire 2.00 mm outer milling tool, meaning the copper must extend at least 2.25 mm beyond the future contour edge to ensure the plated contour milling tool runs entirely within the copper.

PCB in CAM – Slots and Edge Metallization

PCB with Edge Metallization (no solder mask)

4. Half-Opens

So-called half-opens represent a special type of plated outlines. Please refer to the dedicated section for more information.

PCB with Half-Opens

Through-plated depth milling should be treated like standard depth milling in the CAM process, but only on one side, as it does not go through the entire circuit board.

As with any depth milling, either the milling depth or the remaining material thickness must be explicitly specified. Common tolerances for depth milling are +/- 0.20 mm. In some cases, more precise tolerances are possible (more expensive).

Plated Depth-Milling (fully gold-plated PCB)

In multilayer boards with small layer spacing, it is important to ensure that the underlying inner layers have copper clearance within this depth tolerance, so that the through-plated depth milling does not cause a short circuit.