Multi-layer PCB board in communications, medical, industrial control, security, automotive, electric power, aviation, military, computer peripherals and other fields as the “core of the main”, more and more functional products, more and more dense traces, then relatively, the production is increasingly difficult.
Multi-layer circuit board production not only requires high technology and equipment investment, but also requires experienced production technicians, at the same time, to obtain multi-layer board customer certification, strict and cumbersome procedures, therefore, multi-layer circuit board access threshold is high, the realization of industrial production cycle is long. Specifically, multi-layer circuit board in the production of processing difficulties encountered in the following four major areas.
Four major difficulties in the production and processing of multilayer circuit boards
1、The inner layer trace production difficulties
Multi-layer board circuit has high speed, thick copper, high frequency, high Tg value of various special requirements, the requirements for the inner layer wiring and graphics size control is increasingly high. For example, the ARM development board has a lot of impedance signal traces on the inner layer, which makes the production of inner layer traces more difficult to ensure the integrity of impedance.
The inner layer has many signal traces, and the width and spacing of the traces are basically around 4 mil or smaller; the board layer is easy to wrinkle with multiple cores and thin production, and these factors will increase the production cost of the inner layer.
2. Difficulties in alignment between inner layers
The number of multi-layer boards is increasing, and the alignment requirements of the inner layer are also getting higher and higher. The film will expand and shrink under the influence of the temperature and humidity of the workshop environment, and the core board will have the same expansion and contraction, which makes the alignment accuracy between the inner layers more difficult to control.
3. Difficulties in the pressing process
The stacking of multiple core boards and PP (semi-cured sheet) is prone to delamination, slip sheet and vapor pack residue problems when pressed together. With more layers, the control of rise and shrinkage and the compensation amount of size coefficient cannot be kept consistent; with thin insulation layer between layers, it will easily lead to the problem of inter-layer reliability test failure.
4. Difficulties in drilling production
The multi-layer board is made of high Tg or other special boards, and the roughness of the drilling holes of different materials is different, which increases the difficulty of removing the glue residue in the holes. High-density multi-layer boards have high hole density, low production efficiency, and easy to break the knife. Between different network vias, the edge of the hole is too close to cause the CAF effect problem.
Therefore, in order to ensure the high reliability of the final product, the multi-layer board manufacturer needs to carry out corresponding control in the production process.