Vias are an important part of PCB circuit boards, and the cost of drilling usually accounts for 30% to 40% of the cost of PCB board manufacturing. Simply put, every hole on the PCB can be called a via. So, what are the classification and composition of PCB circuit board vias?
1. Classification of vias
In terms of function, vias can be divided into two categories: one is used for electrical connection between layers; the other is used for fixing or positioning components. From the perspective of process, vias are divided into three categories, namely blind holes, buried holes and through holes.
Blind holes are located on the top and bottom surfaces of the circuit board, have a certain depth, and are used to connect the surface circuit and the inner circuit. The depth of the hole usually does not exceed a certain ratio (aperture). The buried hole is located in the connection hole of the inner layer of the circuit board, and it does not extend to the surface of the circuit board. The above two types of holes are located in the inner layer of the circuit board, and are completed by through-hole forming process before lamination. A through hole refers to a hole that passes through the entire circuit board and can be used to realize internal interconnection or as a mounting positioning hole for components. Because the through hole is easier to realize in the process and the cost is lower, it is used in most PCB proofing.
2. The composition of vias
From a design point of view, the via hole is mainly composed of two parts, one is the drill hole in the middle, and the other is the pad area around the drill hole. The size of these two parts determines the size of the via. When designing high-speed, high-density PCBs, designers always hope that the smaller the vias, the better, so that more wiring space can be left on the board. However, the reduction in the hole size brings about an increase in cost, and the size of the via hole is limited by the drilling and electroplating technology: the smaller the hole, the longer it takes to drill the hole, and the easier it is to deviate from the center position; and When the depth of the hole exceeds 6 times the diameter of the drilled hole, it is impossible to ensure that the hole wall can be evenly plated with copper.
