Multilayer PCB is used as the "core force" in the fields of communication, medical treatment, industrial control, security, automobile, electric power, aviation, military industry, and computer peripherals. The product functions are getting higher and higher, the PCB is getting more and more precise, and the production difficulty is getting more and more difficult. Larger, the higher the corresponding number of layers, the higher the cost of PCB proofing for multilayer circuit boards. So what are the difficulties in the production of multi-layer circuit boards? Next, Shenzhen PCBA manufacturers will introduce.
1. Difficulties in making the inner layer circuit of multi-layer PCB proofing
Multilayer circuit boards have various special requirements for high speed, thick copper, high frequency, and high Tg value, and the requirements for inner layer wiring and pattern size control are getting higher and higher. For example, the ARM development board. There are many impedance signal lines in the inner layer. 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; the width and spacing of the lines are basically around 4mil or less; the multi-core board with thin layers is easy to wrinkle, and these factors will increase the production cost of the inner layer.
Suggestion: The line width and line spacing should be designed above 3.5/3.5mil (most factories have no difficulty in production).
For example, for a six-layer board, it is recommended to use a fake eight-layer structure design, which can meet the impedance requirements of the inner layer 4-6mil line width 50ohm, 90ohm, and 100ohm.
2. Difficulties in alignment between inner layers of multi-layer PCB proofing
The number of layers of multi-layer boards is increasing, and the alignment requirements of the inner layers are also getting higher and higher. The film will expand and shrink due to the temperature and humidity of the workshop environment, and the core board will have the same expansion and contraction after production, which makes it more difficult to control the alignment accuracy between inner layers.
3. Difficulties in the lamination process of multi-layer PCB proofing
The superposition of multiple core boards and PP (prepreg) is prone to problems such as delamination, slippery boards and steam drum residues during lamination. In the structural design process of the inner layer, various factors such as the dielectric thickness between the layers, the glue flow, and the heat resistance of the sheet should be considered, and the corresponding lamination structure should be reasonably designed.
Suggestion: Keep the inner layer of copper evenly, and spread copper in different areas of a large area to balance the same PAD.
4. Difficulties in the production of multi-layer PCB proofing and drilling
The multi-layer board adopts high Tg or other special boards, and the roughness of the holes drilled by 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 tool breakage. Between different network vias, if the edge of the hole is too close, it will cause the CAF effect problem. Suggestion: The hole edge spacing of different networks is ≥0.3mm.
