PCB Technical - PCB design depth answers

1. What is the meaning of each layer in PCB?

Mechanical mechanical layer: defines the appearance of the entire PCB board, that is, the overall structure of the PCB board.

Keepoutlayer prohibited wiring layer: defined on the copper side of the boundary of the electrical characteristics of the cloth. That is to say, after the forbidden wiring layer is defined first, in the subsequent layout process, the wires with electrical characteristics cannot exceed the boundary of the forbidden wiring layer.

Topoverlay Top screen printing layer & Bottomoverlay bottom screen printing layer: Define the top and bottom screen printing characters, which are the component numbers and some characters generally seen on the PCB board.

Toppaste top pad layer & Bottompaste bottom pad layer: refers to the copper platinum that we can see exposed to the outside.

Topsolder Top Solder Mask & Bottomsolder Bottom Solder Mask: Contrary to toppaste and bottompaste, it is a layer to be covered with green oil.

Drillguide via guide layer:

Drilldrawing via drilling layer:

Multiplayer: Refers to all layers of the PCB board.

2. How to set the layers of a 4-layer board with powerPCB?

You can set the layer definition to

1:no plane+ component (top route)

2:cam plane or split/mixed (GND)

3:cam plane or split/mixed (power)

4: no plane+component (if a single-sided component can be defined as no plane+route)

Notice:

The power and ground layer generated by the cam plane is negative and cannot be routed on this layer, while split/mixed generates a positive film, and this layer can be used as a power supply or ground, or it can be routed on this layer (the part recommended in the power layer and ground layer Route, because this will destroy the integrity of this layer and may cause EMI problems). Add the power network (such as 3.3V, 5V, etc.) in the assign of layer 2 from the list on the left to the list on the right, thus completing the layer definition

3. "Conduct signal integrity analysis, formulate corresponding wiring rules, and perform wiring according to these rules." How do you understand this sentence?

Pre-simulation analysis can obtain a series of layout and routing strategies to achieve signal integrity. Usually these strategies will be transformed into some physical rules to constrain the layout and routing of the PCB. The usual rules include topology rules, length rules, impedance rules, parallel spacing and parallel length rules and so on. PCB tools can complete routing under these constraints. Of course, the effect of the completion needs to be verified after post-simulation.

4. Assuming a 4-layer board, the middle two layers are VCC and GND, the wiring goes from top to bottom, and the return path from BOTTOM SIDE to TOP SIDE is VIA or POWER through this signal?

There is no clear statement about the return path of the signal on the via. It is generally believed that the return signal will return from the nearest ground or power-connected via. Generally, EDA tools treat vias as an RLC network with fixed lumped parameters during simulation. In fact, it takes a worst-case estimate.

5. When using PROTEL to draw the schematic diagram, the net list generated during the board production is always wrong, and the PCB board cannot be automatically generated. What is the reason?

You can manually edit the generated netlist according to the schematic diagram, and you can automatically route after passing the check. The board surface of automatic layout and wiring with board-making software is not very ideal. The netlist error may be that the component package in the schematic is not specified; it may also be that the library of the layout circuit board does not contain all the component packages in the specified schematic. Do not use automatic wiring if it is a single-sided board, but can use automatic wiring for a double-sided board. It can also be used for power supply and important signal lines manually, and others are automatic.

6. How to choose PCB software?

Choose PCB software according to your needs. There are many advanced softwares available in the market. The key is to see if it suits your design capabilities, design scale and design constraints. The knife is fast and easy to use, too fast will hurt your hands. Find an EDA manufacturer, please go over and make a product introduction, everyone sits down and talks, whether you buy or not, you will be rewarded.

7. How to draw and bind IC in PROTEL?

Specifically, the mechanical layer is used to draw the bonding drawing in the PCB, and the IC substrate liner is determined to be connected to vccgndfloat according to the IC SPEC. The mechanical layer print bonding drawing can be used.

8. How to understand the concept of broken copper and floating copper?

From the perspective of PCB processing, copper foil with an area smaller than a certain unit area is generally called broken copper. These copper foils with a too small area will cause problems due to etching errors during processing. From an electrical point of view, the copper foil that is not connected to any DC network is called floating copper. The floating copper will produce an antenna effect due to the influence of the surrounding signals. The floating copper may be broken copper, or it may be a large area of copper foil.

9. Is there any relationship between near-end crosstalk and far-end crosstalk with signal frequency and signal rise time? Will it change as they change? If there is a relationship, can there be a formula to explain the relationship between them?

It should be said that the crosstalk caused by the offending network to the victim network is related to the signal change edge. The faster the change, the greater the crosstalk caused (V=L*di/dt). The influence of crosstalk on the judgment of the digital signal on the victim network is related to the signal frequency. The faster the frequency, the greater the influence.

10. The connection between the PCB and the PCB is usually realized by inserting gold-plated or silver "fingers". What if the contact between the "fingers" and the socket is not good?

If it is a cleaning problem, use a special electrical contact cleaner to clean, or use an eraser for writing to clean the PCB circuit board. Also consider 1. Whether the gold finger is too thin, whether the pad does not match the socket; 2. Whether the socket has pine perfume or impurities; 3. Whether the quality of the socket is reliable.