What is Line Space
Line space is the measurement of the width of a line and the distance between adjacent lines on a printed circuit board for achieving fine lines and spaces on PCBs.
Fine lines in PCBs are generally defined as boards with 2 through 5 mil line and spacing. The term “mil” represents a unit of measurement commonly used in the PCB industry, where 1 mil is equal to 0.001 inches. Therefore, a line space of 2 mils would refer to a line width and spacing of 0.002 inches.
Line space is particularly important in the context of high-density interconnect (HDI) PCB technology. HDI technology offers advantages such as reducing circuit board size, increasing routing capabilities, and lowering fabrication costs. Achieving these benefits relies on the ability to create fine lines and spaces, making line space a critical factor in HDI PCB design and manufacturing.
Manufacturing processes such as laser direct imaging (LDI) and cupric chloride etching are often employed to achieve fine line spaces. LDI, a technology that uses lasers to directly expose the photoresist on PCBs, is considered the best option for HDI boards with line spaces less than 4 mils. On the other hand, cupric chloride etching is a controllable chemical process used to remove unwanted copper from the PCB, enabling line and space sizes down to 2 mils.
Precise registration in the drilling process is also essential for achieving fine lines and spaces. Laser drilling, which offers automatic registration of the drilling pattern to optical targets, ensures accurate alignment and drilling of the PCB.