Multi-layer PCB is used as the “core force” in the fields of communication, medical treatment, industrial control, security, automobile, electric power, aviation, military industry, computer periphery, etc. With more and more product functions and denser lines, it is relatively difficult to produce.
At present, domestic PCB manufacturers that can mass-produce multilayer circuit boards often come from foreign-funded enterprises, and only a few domestic-funded enterprises have the strength to mass-produce. The production of multilayer PCB requires not only high investment in technology and equipment, but also experienced production technicians. At the same time, obtaining the customer certification of multilayer PCB requires strict and complicated procedures. Therefore, the entry threshold of multilayer PCB is high, and it takes a long time to realize industrial production. Specifically, the processing difficulties encountered in the production of multilayer circuit boards are mainly in the following four aspects.
Four Difficulties in Production and Processing of Multilayer PCB
1. Difficulties in making inner circuit
Multilayer circuit has various special requirements of high speed, thick copper, high frequency and high Tg value, so the requirements of inner wiring and graphic size control are getting higher and higher. For example, the ARM development board has a lot of impedance signal lines in its inner layer, so it is more difficult to ensure the integrity of impedance.
There are many signal lines in the inner layer, and the width and spacing of the lines are basically about 4mil or less; It is easy to wrinkle in the thin production of multi-core board, and these factors will increase the production cost of inner layer.
2. Difficulties in alignment between inner layers
With more and more layers of multilayer boards, the alignment requirements of inner layers are higher and higher. Film will expand and contract under the influence of the temperature and humidity of the workshop environment, and the core board will expand and contract the same when it is produced, which makes the alignment accuracy between inner layers more difficult to control.
3. Difficulties in pressing process
The superposition of multi-Melanie sheet and PP (prepreg) is prone to problems such as delamination, sliding plate and drum residue during pressing. There are too many layers, and the control of expansion and contraction and the compensation of size coefficient can’t keep the consistency; Thin interlayer insulation will easily lead to failure of interlayer reliability test.
4. Difficulties in drilling production
Multilayer boards are made of high Tg or other special plates, and the roughness of holes made of different materials is different, which increases the difficulty of removing the glue residue in the holes. High-density multilayer board has high hole density, low production efficiency, and easy tool breakage. Between different network vias, too close hole edges will lead to CAF effect.
Therefore, in order to ensure the high reliability of the final product, it is necessary for the manufacturer of multilayer board to carry out corresponding control in the production process.