PCB Technical - Analysis of wiring skills and essentials when drawing PCB

In the arrangement process, the method is the finest and the limit is the highest. Although the PCB engineers who have been laying the line for more than ten years often think that they will not, because they have seen various problems, they know that this line will cause it to be laid out. What evil result, therefore, I don’t know how

In the arrangement process, the technique is the finest and the limit is the highest. Although engineers who have been laying the line for more than ten years often think that they will not, because they have seen various problems, they know what the thread will cause if it is laid out. As a result, I don’t know how to distribute it. But there are still good hands, they have a very rational common sense, and at the same time with a little self-creation mood.

At the beginning, let’s make a basic introduction. The number of PCB layers may be divided into single-layer, double-layer and multi-layer. Single-layer is now fundamentally abandoned. Double-layer boards are currently used in sound systems. They are usually rough-type boards for mobile power amplifiers. Multi-layer boards refer to boards with 4 or more layers. The density of components is usually not high. Talking about 4 layers is enough. From the perspective of vias, it may be divided into vias, blind vias, and buried vias. A through hole is a hole that directly connects to the truth layer from the top layer; a blind hole is passed from the top or bottom hole to the central layer, and then it is not connected.

The advantage is that the reputation of the via is not re-blocked to the end. Yes, other layers may still be routed on the reputation of this via; the buried via is the via from the central layer to the central layer, which is buried, and the surface is invisible. The complete situation is shown in the figure below.

Before voluntary wiring, use interactive wiring to control the high line in advance. The edges of the input end and the output end should not be adjacent and parallel to avoid reflections. When necessary, you can add a ground wire to block, and the wiring of two adjacent layers should be straight to each other, because the parallel control is prone to parasitic coupling. The deployment rate of voluntary wiring depends on a sophisticated organization. Wiring criteria can be set in advance, such as the number of wire bends, the number of vias, and the number of steps. Normally, it’s a walking research-style wiring, quickly connecting short lines, and then using labyrinth wiring to optimize all the wiring routes. It may disconnect the laid lines as necessary and try to rewire them to correct them. Overall wiring benefit.

For organizations, a rule is to isolate numbers and imitations as much as possible, so that a rule is that low speeds should not approach high speeds. The most basic rule is to isolate the digital ground from the analog ground. Because the digital ground is a switching device, the current is very large when it is switched on and off, and the time of immobility is very small. Therefore, the digital ground cannot be used and imitated. The ground is mixed together. A recommended organization might look like the picture below.

1. Wiring between the power supply and the ground wire) A decoupling capacitor should be added between the power supply and the ground wire. The power supply must be connected to the pin of the chip after decoupling capacitors. The following figure lists several faulty connection methods and a precise connection method. Most of them are against the reference. Is there any such fault? ? Decoupling capacitors usually have two effects. One is to supply the large current of the chip during braking, and the other is to remove power supply noise. Affect the power supply.

(2) Widen the power and ground wires as much as possible, preferably the ground wire is wider than the power wire, and its closed connection is: ground wire, power wire, signal wire) A large area of copper layer may be used as the ground wire. Places that are not used are connected to the ground, used as ground wire, or made into a multilayer board, power supply, ground wire, digital circuit and imitation circuit when assimilated

Because of the high frequency of the digital circuit, the sensitivity of the analog circuit is strong. For the signal line, the high-frequency signal line should be as far away as possible from the sensitive analog circuit device, but for all PCBs, the PCB ground wire is on the surface. There can only be one node, so it is necessary to deal with the problem of the common ground of the digital circuit and the analog circuit inside the PCB. In the circuit board, the ground of the digital circuit and the ground of the analog circuit are essentially isolated. Yes, it's just at the interface where the PCB and the watch are connected (such as inserting the first). There is a short connection between the ground of the digital circuit and the ground of the imitation circuit. Please pay attention. There is only one connection point, and there are also different grounds on the PCB. This is determined by the system arrangement.