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Classification method of printed circuit board PCB by hole type
2021-09-27
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Author:Aure

Classification method of printed circuit board PCB by hole type




Vias are an important part of multi-layer PCB circuit boards, and drilling costs usually account for 30% to 40% of PCB production costs. Therefore, via design has become an important part of PCB design. Simply put, every hole on the PCB can be called a via. From the point of view of function, vias can be divided into two categories: one is used as an electrical connection between layers; the other is used for fixing or positioning devices. From the process point of view, these vias are generally divided into three categories, namely blind vias (Blind Via), buried vias (Buried Via) and through holes (Through Via).



Classification method of printed circuit board PCB by hole type



Blind holes are located on the top and bottom surfaces of the printed circuit board and have a certain depth. They are used to connect the surface line and the underlying inner line. The depth of the hole usually does not exceed a certain ratio (aperture). Buried hole refers to the connection hole located in the inner layer of the printed circuit board, which does not extend to the surface of the circuit board. The buried hole is located in the inner layer of the circuit board, and is completed by a through-hole forming process before lamination, and several inner layers may be overlapped during the hole forming process. The third type of hole is a through hole, which penetrates the entire circuit board and can be used to realize internal interconnection or component installation positioning holes. Because the through hole is easier to implement in the process and the cost is lower, most of the printed circuit boards use it instead of the other two types of through holes. From a design point of view, a via is mainly composed of two parts, one is the drill hole (Drill Hole), and the other is the pad area around the drill hole. The size of these two parts determines the size of the via.


Obviously, when designing a high-speed and high-density PCB, the circuit board designer always hopes that the smaller the hole, the better, so that more wiring space can be left on the PCB; in addition, the smaller the via, the smaller its own parasitic capacitance. More suitable for high-speed circuits. However, the reduction of hole size also brings about an increase in cost, and the size of vias cannot be reduced indefinitely. It is limited by process technologies such as drilling (Drill) and electroplating (Plating). The smaller the hole, the longer it takes to drill, and the easier it is to deviate from the center position. According to the current level of PCB manufacturing technology, when the ratio of PCB substrate thickness to aperture (that is, the ratio of thickness to diameter) exceeds 10, the uniform copper plating of the hole wall cannot be guaranteed, and the thickness of the copper layer is uneven, especially in the middle of the plating layer. Loose and thin coatings will seriously affect the fatigue life of the holes.


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