PCB PROTEL Encyclopedia of Science and Technology
SchematIC diagram of PCB board with common errors in 1:
(1) ERC pin has no access signal:
a. Define input/output content for pins when creating packages;
B. When creating or placing components, inconsistent grid contents are modified, and the pins and lines are not connected;
c. When you create a component, the pin direction is reversed and must be connected to a non pin name end.
(2) Component out of drawing boundary: The component is not created in the center of the sheet of the catalog.
(3.) The net list of the created project file can only be partially transferred to the PCB board: Global is not selected when generating the net list.
(4) Do not use annotations when using self created multi part components.
2. Common errors in PCB:
(1) Node not found while loading network:
a. Components in the schematic use packages not in the PCB library;
b. Components in the schematic use packages with inconsistent names in the PCB library;
c. Components in the schematic use packages with inconsistent pin numbers in the PCB library. For example, 3-pole tube: the pin numbers in sch are e, b, c, while the pin numbers in PCB board are 1, 2, 3.
(2) When printing, it cannot always be printed on one page:
a. When creating a PCB library, it is not at the origin;
b. The component has been moved and rotated for many times, and there are hidden characters outside the PCB board boundary. Select to display all hidden characters, shrink the PCB board, and move characters within the boundary.
(3) The DRC network is divided into several parts:
It indicates that the network is not connected. Please check the file, and then use the connected copper wire to find it.
In PCB design, wiring is an important step to complete product design. It can be said that all previous preparations have been completed. In the whole PCB, the wiring design process is limited, the skills are fine, and the workload is large. PCB board wiring includes single-sided wiring, double-sided wiring and multi-layer wiring. There are also two ways of routing: automatic routing and interactive routing. Before automatic routing, you can use interactive pre routing for more demanding lines. The edges of input end and output end shall avoid adjacent and parallel to avoid reflection interference. If necessary, add ground wire for isolation, and the wiring of two adjacent layers shall be perpendicular to each other, so parasitic coupling can easily occur in parallel. The routing rate of automatic routing depends on a good layout. You can preset routing rules, including the number of bends, vias, and steps for routing. Generally, exploratory wiring is carried out first, short wires are quickly connected, and then labyrinth wiring is carried out. Try rewiring to improve the overall effect.
3. Treatment of power supply and ground wire
Even if the wiring in the whole PCB board is well completed, the interference caused by insufficient consideration of the power supply and ground wire will reduce the efficiency of the product, and sometimes even affect the success rate of the product. In this regard, the wiring of power supply and ground wire shall be seriously treated, and the noise interference generated by power supply and ground wire shall be minimized to ensure the product quality. Every engineer engaged in electronic product design knows the cause of the noise between the ground wire and the power line, and now only expresses the reduced noise suppression: as we all know, the noise between the power supply and the ground wire coupling capacitor increases. Widen the width of power supply and ground wire as much as possible. The ground wire is wider than the power line. Mm, power cord 1.2 to 2.5 mm. For PCB boards of digital circuits, a wide ground wire can be used to form a loop, that is, a grounding grid can be used (the grounding of analog circuits cannot be used in this way). Use a large area of copper layer as the ground wire, and connect the unused place on the printed board to the ground as the ground wire. Or the Multilayer board, power supply and ground wire can occupy one layer respectively.
4. Common Grounding Treatment of Digital Circuit and Analog Circuit
Nowadays, many PCB boards are no longer single functional circuits (digital or analog circuits), but are composed of a mixture of digital and analog circuits. In this case, it is necessary to consider the mutual interference between them when wiring, especially the noise interference on the ground wire. The frequency of digital circuit is high, and the sensitivity of analog circuit is strong. For signal lines, high-frequency signal lines should be as far away from sensitive analog circuit equipment as possible. For the ground wire, the entire PCB has only one node to the outside world. Recall that the problem of digital and analog common grounding must be handLED inside the PCB board, while digital and analog grounding are actually separated inside the board. They are not connected to each other, but only at the interface between the PCB board and the outside world (such as the plug). Etc.). There is a short circuit between digital grounding and analog grounding. Please note that there is only one connection point. There are also different grounds on the PCB, depending on the system design.
The signal line is wired on the power (grounding) layer
In the wiring of multilayer printed boards, because there are not many lines left in the signal line layer, adding more layers will cause waste, increase production workload, and increase costs accordingly. In order to solve this conflict, we can consider wiring in the power (grounding) layer. The power plane should be considered first, then the ground plane. Because the integrity of the stratum is protected.
6. Treatment of connecting leg in large area conductor
A large area of grounding (electricity), the legs of co mm only used components are connected to it Welding requirements high power heaters 2) It is easy to cause virtual solder joints. Therefore, considering the power efficiency and process requirements, cross shaped pads are made. They are called heat insulation pads, which are usually called heat insulation pads With this kind of pipe, the possibility of virtual solder joint caused by excessive heat dissipation of cross section during welding can be greatly reduced The electrical (ground) leg of a multilayer PCB board is treated as the same pipe