When designing electronic products, we need to use circuit boards. Circuit boards can be divided into single-panel, double-layer and multi-layer boards according to the number of layers. Generally, double-layer boards are often used. Components can be placed on both sides, and the price is also very cheap. I think ordinary electronic products, industrial control electronics, sensors, etc. all use double-layer boards. However, for many miniaturized products and high-speed products, multi-layer boards will be used. Take mobile phones as an example. Many years ago, it was estimated that 40% boards or six-layer boards were enough for functional machines and old machines, but for intelligent machines with increasingly powerful functions, at least eight-layer boards started.
1. Why do you want to use multilayer boards?
Requirements for miniaturization of products. Nowadays, electronic products tend to be miniaturized, but there are quite a few chips and components used. On the premise that components can be placed, the PCB should be as small as possible, which leads to the fact that the PCB cannot be routed, and the area can only be changed by the number of layers.
High-speed signal integrity requirements. Now that the electronic technology is so developed, products such as routing, mobile phones, switches and base stations are all high-speed signals, which are susceptible to interference and crosstalk. Reasonable design of multilayer boards can effectively improve the integrity of signals and minimize the interference degree of signals.
2. What matters should be paid attention to when 2.layout designs multilayer boards?
When designing multilayer boards, the first problem to be paid attention to is the distribution of each layer, which is directly related to the product performance. For the two-layer board, the signal, power line and ground line cross together, but for the multi-layer board, this is a big concern.
How to allocate the layers. If there are four layers of boards, there are many distribution methods, such as 1 signal layer, 2 power layers, 3GND layer, 4 signal layers or 1 power layer, 2 signal layers, 3 signal layers and 4GND layers. The general distribution principles are as follows: the adjacent signal layer and GND layer play a role in shielding interference, the close coupling between power layer and GND layer is conducive to the stability of power supply, and high-speed signals are loaded between two copper-clad layers as much as possible to reduce interference.
It’s not a negative method. The so-called negative method means that the whole plane is a piece of copper skin, and taking a line means cutting the copper, which is very different from the usual line. Usually, we take the wire. This negative film method is commonly used in power supply layer and GND layer, which is often referred to as internal layer division.
