The limitations for width and separation between conductors depends on the based copper. The table below sums up the manufacturing options:

External layers

Copper base* Minimum width (Tw) Minimum gap (Ts)
18µ 0.125mm 0.150mm
35µ 0.200mm 0.200mm
70µ 0.250mm 0.250mm

Internal layers

Copper base Minimum width (Tw) Minimum gap (Ts)
18µ 0.125mm 0.150mm
35µ 0.150mm 0.180mm
70µ 0.250mm 0.250mm

The most important characteristics of the drills on the printed circuit board are: diameter, if they are plated or non plated and their depth. The last characteristic is determined by the thickness of the base material, and is key in determining the minimum drill possible as described in the calculation section.

Minimum diameters

Drilling type Minimum drilling diameter
Plated 0.250mm
Non plated 0.350mm
Blind via 0.500mm

Final diameter tolerances

Drilling type Tolerance
Plated +0.1mm/-0.05mm
Non plated +0.1mm/-0.05mm

Calculate Aspect Ratio:

The Aspect Ratio is the relationship between the minimum manufacturable drilling on the thickness of the circuit board, following the formula below:

Snap 2016-10-07 at 15.59.35

Aspect ratio ≤ 6.

The annular ring is the metal ring left around the drilling on a pad.

Minimum annular ring

Plated Minimum annular ring (Cm)
Cu Base+18µ 0.150mm
Cu Base+35µ 0.200mm

Internal layers

Plated Minimum annular ring (Cm)
18µ , 35µ , 70µ 0.200mm

The solder mask is a coating put on to protect the printed circuit board, so that it cannot be soldered on except in designated areas.

Colour Minimum margin (Mc) Minimum width (Mb)
Green 0.075mm 0.100mm
White, black, grey, blue, red 0.075mm 0.150mm

Note: except when otherwise specified, the mask will be adapted by eliminating traces smaller than the minimum trace and expanding it to the minimum margin.

Used to reference the components and indicate their position and dimensions on the printed circuit board, can also include logos, circuit board codes, quality marking and any images that comply with the minimum parameters for production capacity.

Colour Minimum width (Mi) Minimum trace margin/soldermask (Mt)
White 0.125mm 0.100mm
Black 0.180mm 0.100mm

Note: except when specified otherwise, all marking images coinciding with areas without solder mask will be eliminated.

CNC milling is an automatic cutting system that uses a rotating tool guided by a numerical control system. The mechanical options for milling done with this process are determined by the precision of the numerically controlled machine and the diameter of the tool used, the latter being the only variable the designer may change.

Mechanical options

Concepts Figures
Minimum tool diameter (Sm) 0.80mm
Minimum radius for internal windows (Rm) 0.40mm
Position tolerance +/-0.20mm
Minimum Copper-Edge gap (Cg) 0.20mm

Plated Edges/Castellated holes (half holes) Type of process used to connect circuit boards. It consists in putting a metallic cover on the sections at the edge of the circuit board to allow for lateral soldering and electric union between layers.

Plated Edges

Concepts Figures
Minimum legth (Pc) 1.50mm
Minimum separation between lengths (Nc) 0.80mm
Position tolerance +/-0.20mm
Size tolerance +/-0.10mm

Castellated holes (half holes)

Concepts Figures
Minimum drill (Dm) 0.80mm
Minimum annular ring (Ar) 0.20mm
Minimum separation between pads 0.20mm
Position tolerance drill/edge +/-0.20mm
Size tolerance +/-0.10mm

Bevelling Type of mechanisation used to facilitate insertion of circuit boards into card-type connectors (e.g. PCI, AGP, ISA, etc.). This reduces the edge of the circuit board where the connector is located to 30°.

Note: this process affects the whole length of the edge of the circuit board where the connector will be located, even if it doesn’t take up the whole length. This process should not be used on top of the metallic area of a circuit board, so it is recommended to apply the following formula:

Snap 2016-10-07 at 16.10.32

Conical Countersink Type of process used to embed the head of screws with a cone shape. It is a 45° groove drill on one of the sides of the circuit board.

Note: the maximum upper diameter (Da) is determined by the following formula:

Snap 2016-10-07 at 16.12.15

Flat Countersink Type of process used to embed the head of screws with a flat shape. It is a 90° groove drill on one of the sides of the circuit board


Grooves Process required to assemble certain types of components such as contactors, joysticks onto the PCB or for components that cannot stick out above the surface of the PCB, membrane keyboards for example.

Scoring or V-cut consists in creating two grooves in a V shape on either side of the circuit board coinciding with the axis that divides them. The hold force between the circuit boards is determined by the size of the core left between the two V-cuts.

Applicable figures

Concepts Figures
Minimum material thickness 0.50mm
Maximum material thickness 2.40mm
Position tolerance +/-0.10mm
Minimum separation between Copper – Edge (Cs) 0.40mm for base material thickness 0.8mm
0.50mm for base material thickness 1.6mm
0.70mm for base material thickness 2.4mm
Slot angle 30º

Note: Recommended use of V-cut depaneling machine. After separating the circuit boards, the absolute measurements of the circuit boards may vary +/- 0.30 mm.