Multilayer PCBis the "core main force" in communICation, medical treatment, industrial control, security, automobile, power, aviation, military industry, computer peripheral and other fields. With more and more product functions and more and more intensive lines, the production becomes more and more difficult.
At present, domestic PCB manufacturers that can mass produce multilayer circuit boards often come from foreign-funded enterprises, and only a few domestic enterprises have the strength of mass production. The production of multilayer circuit boards requires not only high input in PCB technology and equipment, but also experienced production technicians. At the same time, the procedures for obtaining Multilayer board customer certification are strict and cumbersome. Therefore, the threshold for access to multilayer circuit boards is high, and the period for realizing industrialized production is long. Specifically, the processing difficulties encountered in the production of multilayer circuit boards are mainly the following four aspects.
Four Difficulties in Processing multilayer PCB
1. Difficulties in making inner PCB circuit
Multilayer PCB circuit has various special requirements such as high speed, thick copper, high frequency and high Tg value. The requirements for inner PCB wiring and graphic size control are getting higher and higher. For example, there are many impedance signal lines in the inner layer of the ARM development board. To ensure the integrity of the impedance increases the difficulty of the inner layer circuit production.
There are many signal lines in the inner layer, and the width and spacing of lines are basically about 4mil or less; The production of thin multi-core plates is easy to wrinkle, and these factors will increase the production cost of the inner layer
2. Difficulties in alignment between inner layers
The number of layers of multilayer board is increasing, and the alignment requirements of the inner layer are also getting higher and higher. Film will expand and shrink due to the influence of workshop environment temperature and humidity, and the core board will expand and shrink the same after production, which makes the alignment accuracy between inner layers more difficult to control.
3. Difficulties in pressing process
The superposition of multiple core plates and PP (prepreg) is prone to delamination, slide plate and steam drum residue during pressing. The number of layers is large, and the control of expansion and contraction and the compensation of size coefficient cannot keep consistent; The thin interlayer insulation layer is easy to lead to the failure of interlayer reliability test.
4. Difficulties in drilling production
multilayer boards adopt high Tg or other special boards. The roughness of drilling holes made of different materials is different, which increases the difficulty of removing the glue residue in the holes. High density multilayer PCB board has high hole density, low production efficiency, and is easy to break the tool. Too close hole edges between holes of different networks will cause CAF effect problems.
Therefore, in order to ensure the high reliability of the final product, it is necessary for the multilayer board manufacturer to carry out corresponding control during the production process.