What unit is mil in PCBA process?

Mil is translated as mil in Chinese. In PCBA processing, mil is often heard. So, what exactly is mil? Actually, mil is a very important length unit in PCBA process, generally referring to line width, line spacing, aperture, and also used to indicate the thickness of copper foil. Let's take a detailed look next!

Definition and Conversion of mil

Mil is an imperial unit of length defined as follows:

1 mil=1/1000 inch=0.0254 millimeters (mm)

In the field of PCB design and manufacturing, mil is widely used. For example, in wiring design, common line widths and spacing are generally measured in mil units, such as 6mil, 8mil, or 10mil. In terms of aperture representation, common via apertures may be 12mil, 16mil, or 24mil.

The Application of mil in PCB Design

1. Line width and line spacing

The wires in PCB are used to connect different electronic components, and their width (line width) and spacing between adjacent wires (line spacing) directly affect signal integrity and current carrying capacity. For example, high-speed signal lines may require wider line widths to reduce signal loss, while high-density circuit designs require smaller line spacing to save space.

2. Via

Via is a through-hole on PCB used to connect different layers, and its aperture is usually measured in mil. For example, standard vias may be 12mil, while microvias may be as small as 6mil or less to accommodate HDI (high-density interconnect) technology.

3. Copper foil thickness

The conductive layer of PCB is composed of copper foil, and the thickness of copper foil is usually expressed in ounces (oz), but can also be converted in mil. For example, the thickness of 1oz copper is about 1.4mil (35 μ m), and common copper thickness specifications include 1oz (1.4mil), 2oz (2.8mil), etc.