PCB Multilayer Board Design

1 Determination of the shape, size and number of layers of the board

Any printed board has the problem of coordinating with other structural parts. Therefore, the shape and size of the printed board must be based on the overall structure of the product 5. However, from the perspective of production technology, it should be as simple as possible, generally a rectangle with a less disparate aspect ratio, so as to facilitate assembly, improve production efficiency and reduce labor costs.

In terms of the number of layers, it must be determined according to the requirements of circuit performance, board size and circuit density. For multi-layer printed boards, four-layer boards and six-layer boards are the most widely used. Taking four-layer boards as an example, there are two conductor layers (component surface and welding surface), a power supply layer and a ground layer.

The layers of the multi-layer board should be kept symmetrical, and preferably even-numbered copper layers, that is, four, six, eight, etc. Because of the asymmetric lamination, the board surface is prone to warpage, especially for surface mount multilayer boards, which should be paid attention to. 6

2 The location and placement of components

The position and placement direction of components 5 should first be considered from the perspective of circuit principle and cater to the trend of the circuit. Whether the placement is reasonable or not will directly affect the performance of the printed board, especially for high-frequency analog circuits, which have stricter requirements on the location and placement of components. Reasonable placement of components, in a sense, has heralded the success of the printed board design. Therefore, when starting to arrange the layout of the printed board and deciding the overall layout, the circuit principle should be analyzed in detail, and the location of special components (such as large-scale ICs, high-power transistors, signal sources, etc.) should be determined first, and then Arrange other components to avoid possible interference factors.

On the other hand, the overall structure of the printed board should be considered to avoid uneven arrangement of components and disorder. This not only affects the appearance of the printed board, but also brings a lot of inconvenience to assembly and maintenance work. 6

3 Requirements for conductor layout and wiring area

In general, the wiring of multi-layer printed boards is carried out according to the circuit function. When wiring the outer layer, it is required to have more wiring on the welding surface and less wiring on the component surface, which is conducive to the maintenance and troubleshooting of the printed board. Thin, dense wires and signal lines that are susceptible to interference are usually arranged on the inner layer. A large area of copper foil should be distributed evenly in the inner and outer layers, which will help reduce the warpage of the board and also enable a more uniform coating on the surface during electroplating. In order to prevent damage to the printed wires and short circuits between layers during machining, the distance between the conductive patterns in the inner and outer wiring areas and the edge of the board should be greater than 50 mils.