PCB proofing of high precision Multilayer PCB, four major pr
As the "core force" in the fields of communication, medical treatment, industrial control, security, automobile, electric power, aviation, military industry, computer peripheral and other fields, multi-layer PCB is becoming more and more powerful, and PCB is more and more precise, so it is more and more difficult to produce. 1. It is difficult to make inner layer circuit. Multi layer board circuit has special requirements of high speed, thick copper, high frequency and high Tg value. For example, there are many impedance signal lines in the inner layer of ARM development board. To ensure the integrity of impedance, it is more difficult to produce the inner circuit. There are many signal lines in the inner layer, and the width and spacing of the lines are basically about 4mil or less; the thin multi-core plate is easy to wrinkle, which will increase the production cost of the inner layer. Suggestion: the design of line width and distance should be above 3.5/3.5mil (most factories have no difficulty in production). For example, a six layer board is suggested to be designed with a pseudo eight layer structure, which can meet the impedance requirements of 50ohm, 90ohm and 100ohm with 4-6mil inner layer. 2. There are more and more layers of multi-layer plate, and the requirement of inner layer alignment is higher and higher. Due to the influence of the workshop environment temperature and humidity, the film will have the same rise and contraction when the core board is produced, which makes the alignment accuracy between the inner layers more difficult to control. Suggestion: this can be handed over to reliable PCB manufacturing plants. 3. The difficulty of the pressing process is the superposition of the core plate and the PP (plate curing sheet), which is prone to delamination, slide plate and drum residue. In the process of structural design of the inner layer, the factors such as dielectric thickness between layers, flow glue flow and heat resistance of plate should be considered to reasonably design the corresponding laminated structure. Suggestion: keep the copper layer evenly laid in the inner layer, and lay copper evenly in large area without the same area as pad. 4. High Tg or other special plates are used in multi-layer board production. The roughness of drilling holes with different materials is different, which increases the difficulty of removing glue residue in the hole. High density multilayer board has high hole density, low production efficiency and is easy to break the cutter. The hole edge is too close between the vias of different networks, which will lead to CAF effect problem. Suggestion: the hole edge spacing of different networks should be no less than 0.3mm