【 Weak current College 】 PCB design considerations 】

As an electronic engineer to design the circuit is a prerequisite of tough, but the principle design and perfect, if the circuit board design not reasonable performance will be greatly diminished, serious or even does not work properly. In my experience, I summarize here some PCB design should pay attention to an Apocalypse to you.
No matter what software, PCB design has a general procedure, in order to save time and effort, so I will be making processes to introduce. (Because windows Windows protel interface style and close to the action also similar, and powerful simulation capabilities, using more of the people, will draw software for instructions. ）

Schematic design is the preparatory work, often to the beginner to easy draw directly to the PCB, this will outweigh the simple Board, if skilled process, may wish to skip. But for a beginner to follow process that, on the one hand can develop good habits, on the other hand on the complex circuit is the only way to avoid mistakes.

In drawing schematics, hierarchical design should pay attention to individual files last to connect as a whole, this also on the future work is significant. Due to differences in some of the software will appear seemingly connected software actually not even (electrical performance). If you do not have correlation detection tools detect, in the event of a problem, and the Board has found that late. Therefore repeatedly emphasized in order to make the importance of hope drew attention.

Schematic diagram is based on the design of the project, as long as the electrical connection is nothing to say correctly. Here we focus on a specific panel within the program.

L, making physical borders

Closed physical borders on subsequent component layout, alignment is a basic platform for the automatic layout constraints for role play, otherwise, come from a schematic diagram of the components will be lost. But here it is important to note that accurately, otherwise after an install issue creekif. There is a corner where best to use ARC, on the one hand, you can avoid sharp scratches workers, while at the same time can reduce stress. Before a product is always in the transport process in individual machines appears bottom PCB fracture, after using the arc.

2, the introduction of components and network

The components and network people draw good border should be very simple, but often the problem here, be sure to carefully follow the prompts to resolve the error, otherwise individually later charges greater strength. Here's the problem in General with some of the following:

Components of the package is not found, the components of a network problem, unused symbols or PIN, control prompts these problems can quickly fix.

3, the layout of the component

Elements of layout and alignment of product life, stability, electromagnetic compatibility has a great effect, should pay special attention to the place. In general you should have the following principles:

Place order 3.l

First place and the structure of the fixed components, such as the power outlet, led, switch, connections, and the like, these devices are placed after the LOCK function with software lock it so that it will not be mistaken. Then place the line of special elements and large components, such as heating elements, power transformer, IC, etc. Last place small devices.

3.2 note thermal

Components layout but also pay special attention to the heat issues. For high power circuit, you should put those heating elements such as the power tubes, transformer, as far as possible, pull over scattered layout placement, easy to heat not concentrated in one place, and not too close to high capacitance prevent premature aging of the electrolyte.

4. wiring

Cabling principles

Alignment of learning is very advanced, each person will have their own experiences, but some common principles.

◆ Highfrequency digital circuit alignment fine some short, some good

¡Ô high-current signals, high-voltage signals and small signal should note the isolation distance and isolation (to withstand pressure, typically to 2KV the distance when onboard to 2mm, on top of this to scale as more, e.g. to withstand the pressure testing 3KV, high-voltage line between 3.5mm above should, in many cases to avoid Creepage, also in the printed circuit board on the high-voltage between slot. ）

¡Ô two panel wiring, both sides of the wire should be perpendicular, skew, or bend the alignment, avoid parallel to reduce parasitic coupling; as circuit transmission and output printed conductors used should as far as possible avoid adjacent parallel rabbits to avoid ECHO, the best among those with Earth wire conductors.

◆ Alignment greater than 90 ° corner, to the extent possible, eliminate 90 ° corner, also use a 90-degree corner

◆ The address line or cable length difference, the alignment is not too big, otherwise the short-term part to people-go bend line for compensation

◆ Alignment as far as possible, walk in the welding surface, in particular through-hole PCB technology

◆ Use the hole, jumper

¡Ô single-panel pad must be large, the pads are connected to the line must be bold, be placed on the tears tears, general quality of single panel manufacturers would not be very good, otherwise on welding and RE-WORK will have problems

¡Ô large-area deposited copper to use grid to prevent wave bubble and when the Board due to thermal stress and bending, but in special occasions to consider the size of the flows, GND, not simple foil populated, but need to go to alignment

◆ Components and alignment can not be too near the place, the average single-panel for paper plates, stress fracture, if after an edge connection or drop components would be affected

◆ Must consider production, ease of debugging, maintenance

On analog circuit for processing in question is very important, the noise generated by ground is often notIt is expected, but once you produce will bring great trouble, and should not rain silk. For amplifier circuit, very slight and noise is because after the level of zoom in on the impact of significant sound quality; high-precision A/D conversion circuit, if ground wire on the high frequency components exist will have the effect of temperature drift, the amplifier. At this point you can Board of 4 corners plus retreat a foot Lotus in capacitors, and the Board of the diaphragm, a foot attached to the mounting holes up (by screws and the enclosure link) so that you can apply this component into account, the amplifier and the AD is stable.

In addition, electromagnetic compatibility issues in current awareness of environmentally friendly products extremely concerned at the situation all the more important. Generally speaking, the source of the electromagnetic signal 3: signals, radiation, transmission lines. Crystal is a common form of high frequency signal source, in the power spectrum of harmonics on Crystal energy value significantly higher than the average. Viable approach is to control the signal amplitude, Crystal shell grounding, on the interference signals are masks, using special filter circuits and devices, etc.

To note is that snake alignment, as different it applications are different, the computer's motherboard is used in some of the clock signal, such as PCIClk, AGP-Clk, its role in two points: 1, 2, impedance matching filter inductance.

On some important signals, such as INTELHUB schema HUBLink to a total of 13 root, frequency up to 233MHZ, requirements must be strictly equal length, to eliminate the delay caused by the vulnerability, in this case, the snake alignment is the only solution.

In General, snake-like the alignment of line from > = 2 x line width; if in normal PCB Board, in addition to the role of a filter inductance, can also serve as a radio antenna inductance coils, etc.

5. adjust the sound

Complete wiring, you want to do is text, individual components, alignment to do some adjustments and deposited copper (which should not be too long, otherwise it will affect the speed, but also to the routing trouble), also in order to facilitate production, commissioning and maintenance.

Deposited copper usually refers to large areas of copper foil to fill the void left after routing, you can shop and GND of copper foil, or you can shop the copper foil VCC (but this short easy burning devices once, with the best grounding, unless forced to increase the power of open area, stand heavy current VCC received only). Package and then usually refers to two root ground wire (TRAC) to wrap a special signal cable to prevent it being to interfere or interfere with others.

If you replace with deposited copper ground wire must be taken to the entire land is connected, the current size, flow and there are no special requirements to ensure that unnecessary mistakes.

6. check the check network

Sometimes due to misuse or negligence resulting in the art of the Board of the network relations and schematic diagram, then Procurator check is necessary. So picture after must not anxious to plate manufacturers, you should first do checks for follow-up.

7. use the simulation function

After completing these tasks, if time allows also for software emulation. Especially high frequency digital circuits, so that you can find some problems ahead of time, significantly reducing the workload of debugging in the future.