Multilayer circuit boards refer to circuit boards with three or more layers, two of which are on the outer surface, and the remaining layers are combined in the insulating board. The electrical connection between them is usually achieved through holes on the cross section of the circuit board. Multilayer printed circuit boards are most complicated than others, and are generally considered to be the most sophisticated PCB product due to their construction methods and design complexities.

Multilayer printed circuit boards and double-sided PCB boards are similar in appearance. Ordinary people can’t see the difference between them without paying attention, or you can’t tell whether it is a double-sided PCB board or multilayer PCB board. So, how to distinguish between ordinary double-sided PCB boards and multi-layer PCB boards?

First of all, we must have an understanding of the number of layers of the circuit board. The number of layers of the PCB board is the inner layer. 1 layer is referred to as single layer PCB, and 2 layers is referred to as double sided PCB. Multilayer PCB board refers to 4-48 layers; the higher the number of layers, the higher the unit price. Because the inner layer of the circuit is to be pressed, the technical content is high, and the machine cost is relatively high.

Generally speaking, you can identify multilayer pcb by following:
The more layers, the larger the shadow in the sheet;
Dim shadows can be seen in the multi-layer PCB circuit board, if the shadow is light then you can see a little dim, and if the shadow is deep you can see the circuit clearly;
Multilayer PCB circuit boards generally have a smooth surface, especially when they are cleaned after forming and processing;
If you want to know how many layers of the PCB board are, and the precise data, you can only check through the IM inspection of the manufacturer or the PCB drawing of the development engineer.

1. Suitable for complex design
Complex devices with a large number of components and circuits benefit from the use of multilayer PCBs. Devices with multiple uses and advanced features require this complexity. Many multi-layer PCB boards also have functions such as impedance control and electromagnetic interference shielding, which further improve the quality of PCB boards and equipment.

2. High power
Due to the high circuit density, the circuit board is also more powerful. This means that they provide high operating capacity and speed, making them particularly suitable for advanced equipment.

3. Highly durable
As the number of layers increases, thicker boards are more durable. Therefore, it can withstand more severe conditions.

4. Small size and light-weighted
Small size and light weight are additional features of multilayer boards. This makes them ideal for device miniaturization.

5. Single connection point
In terms of design simplicity and weight, the fact that multilayer pcb board work with a single connection point is an additional advantage.

These are a few of the applications using multilayer printed circuit boards:
Communications
Industrial controls
GPS technology
Aerospace
Computers
Military
Medical
Satellite systems

3-30 layers
Board finished thickness: 0.3mm-7.6mm
Material: FR-4,  High TG, FR4 halogen Free, Rogers, Telfon.
Max. Finished board size: 21*24(533*610mm)
Min. Drilled hole size: 6mil(0.15mm)
Min. Line width: 3mil(0.075mm), Min. Line spacing: 3mil(0.075mm)
Surface finish/treatment: HASL/HASL lead free, Chemical tin, ENIG,Immersion Silver, OSP, etc.
Copper thickness: 0.5-8 oz
Solder mask color: Green/yellow/black/white/red/blue
Copper thickness in hole: >20 um(>0.8mil)