PCB layout Beginners must be knowledge summary

The PCB is the abbreviation of the printed circuit board (i.e. printed circuit Board). The printed circuit board is a substrate for assembling electronic parts, and a printed circuit board which forms the connection between the points and the printed components on a general base material according to the predetermined design. The main function of the product is to make a variety of electronic 0 components to form a predetermined circuit connection, the role of relay transmission, electronic products are the key electronic interconnection, there is "the mother of electronic products," said.

This content for the PCB layout beginner finishing the relevant technical points and design experience, skills and other knowledge, convenient for beginners to get started quickly.

First, PCB layout is what

The PCB is the abbreviation of the printed circuit board (i.e. printed circuit Board). The printed circuit board is a substrate for assembling electronic parts, and a printed circuit board which forms the connection between the points and the printed components on a general base material according to the predetermined design. The main function of the product is to make a variety of electronic 0 components to form a predetermined circuit connection, the role of relay transmission, electronic products are the key electronic interconnection, there is "the mother of electronic products," said. Printed circuit boards are used as substrates and key interconnects for electronic parts, and any electronic device or product is required. Its downstream industries cover a wide range of areas, including general consumer electronics, information, communications, medical care, and even aerospace technology (Information Market forum) products. With the development of science and technology, the demand for electronic information processing of various kinds of products is gradually enhanced, and emerging electronic products are constantly springing up, which makes the use and market of PCB products expand continuously. The new 3G mobile phones, automotive electronics, LCD, IPTV, digital TV, computer replacement will also bring more than today's traditional market larger PCB market.

Layout is the meaning of planning.

Combined: PCB layout is the printed circuit board arrangement of the Chinese meaning.

Second, the basic PCB layout of the common electronic components in English

Especially in the use of PADS9.3 or allegro16.3 drawing schematic diagram, to understand the common electronic components English is an indispensable link. Often we use the first three letters of a part in place of a part, PCB design training for example: Resistance with res, cap for capacitance, inductor with IND, ... Wait a minute. Here are some of the things that I believe will help you.

Voltage Voltage

Current

Ohm Ohm

Volt Volt

Ampere ampere

Watt Watt

Circuit circuit

Circuit element circuit element,

Resistor resistance

Resistor resistor

Inductance inductance

Inductor inductor

Capacitance capacitance

capacitor capacitor

Ohm s Law

Kirchhoff's Law Kirchhoff ' s laws

Kirchhoff's Law of voltage Kirchhoff ' s voltage (KVL)

Kirchhoff's Law of current Kirchhoff ' s (KCL)

Loop loop

Networking Network

Passive two-terminal networks passive two-terminal network

Active Two-terminal network with two end networks

Three, PCB layout must consider the problem

PCB Design Draw circuit frame, border line and component pin pad the shortest distance can not be less than 2MM, (generally take 5MM more reasonable) otherwise the material is difficult. In the same circuit board, the power cord. The ground is thicker than the signal line.

Component Layout Principles

General principle: In the PCB design, if the circuit system has both digital circuit and analog circuit. Pcblayout training and high-current circuit, you must separate the layout, so that the coupling between the system to achieve the smallest in the same type of circuit, according to signal flow and function, sub-block, Partition place components.

Input signal Processing unit, the output signal driving element should be near the PCB design training circuit board edge, so that the input and output signal line as short as possible to reduce the input and output interference.

Component Placement Direction: components can only be arranged in two directions horizontally and vertically. When the potential difference between the components is large, the component spacing should be large enough to prevent the occurrence of discharge phenomenon.

Component spacing. For medium-density boards, small components, such as small power resistors, capacitors, diodes, and other discrete elements of the spacing with the plug-in, welding process, wave soldering, component spacing can take 50-100mil (1.27–2.54mm) manual can be larger, such as Take 100MIL, IC chip, Component spacing is generally 100–150mil in the IC to the capacitor to close to the chip power fall ground pin. Otherwise the filtering effect will be worse. In digital circuit, in order to ensure the reliable operation of digital circuit system,

IC decoupling capacitors are placed between the power supply and the ground of each digital integrated circuit chip. Decoupling capacitor is generally used porcelain capacitor, capacity of 0.01~0.1uf to the choice of capacitance capacity is generally based on the system operating frequency of the reciprocal choice F. In addition, A 10UF capacitor is also required between the power cord and the ground wire at the entrance of the circuit power supply, as well as a 0.01UF ceramic capacitor.

The clock circuit element is as close as possible to the clock signal pin of the microcontroller chip to reduce the line length of the clock circuit. And the following is better not to go. Just printed wire resistance is large, the voltage drop on the line is also large, affecting the performance of the circuit, the line width is too wide, the wiring density is not high, the board area increases,

If the current load is calculated in 20a/square millimeters, when the copper foil thickness is 0.5MM, (generally so many,) 1MM (about 40MIL) line width of the current load of 1 A, therefore, the line width of 1–2.54mm (40–100mil) can meet the general application requirements, High-power equipment board on the ground and power, according to the power size, can appropriately increase the line width, and in small power digital circuit, in order to improve the wiring density, the minimum line width take 0.254–1.27mm (10–15mil) can meet.

Iv. several modules that the PCB layout engineer should be familiar with

Here are a few modules that are often encountered in PCB design, as a PCB layout engineer should be familiar with these.

I-mode and CHTML

I-mode is a subsidiary of Japan Telecom (NTT) DoCoMo wireless communication Services in the Japanese market. is currently the world's largest number of users (all in Japan) wireless internet services. I-mode and WAP

The main difference is: I-mode content is written in cHTML, so the majority of the current network content as long as a slight modification can be used, and WAP is using the WML,PCB

Layout training Existing Web content must be converted to WML to be used by WAP.

A variant of the CHTML (Compact html) HTML. Most compatible with HTML.

-----------

bluetooth® (Bluetooth)

Bluetooth is a radio technology that supports short-range communication (typically within 10m) of a device. Pcb

Layout design training enables wireless information exchange between many devices including mobile phones, PDAs, wireless headsets, laptops, and related peripherals. Its standard is IEEE802.15. Working in 2.4HGz

Frequency band. Bandwidth of 1MB/S

(Note: Bluetooth is a very interesting name, from the 10th century unification of Denmark and Sweden, the name of the Scandinavian kings.) )

-----------

Wireless LAN

Wireless LAN, is the development of the local area network, the standard is IEEE802.11, IEEE802.11b and ieee802.11a. where 802.11b

Working in the 2.4GHz band, bandwidth up to 11Mbps. While 802.11a is defined in the 5GHz band, bandwidth is expected to reach 54mb/s. But correspondingly, Wireless

HomeRF

HomeRF is a combination of IEEE802.11 and DECT, designed primarily for home networking, designed to reduce costs. HomeRF also uses spread spectrum technology, working in the 2.4GHz band, the current homerf bandwidth of 1~2mb/s, the future will be increased to 10mb/s.

-----------

SyncML

SyncML is a common mobile data synchronization protocol for the industry. Use SYNCML to keep data on mobile devices in sync with remote data. by Ericsson, IBM, Lotus,

Matsushita, Motorola, Nokia, Palm, Psion and starfish Software are developed by the Association of Companies.

Five, PCB layout basis of the power supply, ground treatment

For each engaged in electronic product design engineering personnel understand the ground and the power line noise between the cause, pcblayout both in the entire PCB board wiring is done well, but due to the power, grounding the consideration of the interference caused by, will make the performance of the product decline, Sometimes it even affects the success rate of the product. Therefore, the wiring of electricity, grounding wire to be taken seriously, the electricity, ground noise caused by the interference to a minimum to ensure product quality. Now only the reduced noise suppression is expressed as:

A, with a large area of copper layer for ground use, on the printed circuit board is not used on the place are connected with the ground as ground. PCB design training or made of multilayer board, power, ground each occupy a layer.

B, it is well known that a decoupling capacitor is added between the power supply and ground.

C, as far as possible to widen the power supply, ground width, preferably ground than power lines, their relationship is: Ground > Power lines > Signal lines, PCB design usually signal line width is: 0.2~0.3mm, the most fine width up to 0.05~0.07mm, power cord for 1.2~2.5mm

The PCB of the digital circuit can be made up of a circuit with a wide ground wire, that is, a ground network to use (analog circuit can not be used in this way).

VI, PCB layout must understand the three elements of EMI

It is possible to avoid it only if you understand it first, and reduce its harm in the circuit. EMC electromagnetic compatibility is a necessary lesson in PCB layout. Do not know how to reduce EMI, so the PCB layout is not a great value

Three elements of electromagnetic interference:

Harassment source

Coupling pathways

Sensitive equipment

In order to realize the electromagnetic compatibility, we must start with the above three basic elements and apply the two measures of technology and organization.

The so-called technical measures, from the analysis of electromagnetic disturbance sources, coupling pathways and sensitive equipment, to take effective technical means to suppress the harassment source, eliminate or weaken the disturbance of the coupling, reduce the sensitive equipment response to harassment or increase the level of electromagnetic sensitivity;

In order to limit human harassment and verify the effectiveness of the technical measures used, organizational measures must be taken to develop and follow a set of complete standards and norms for reasonable spectral distribution, control and management of the use of the spectrum, based on frequency, working time, antenna directionality and other prescribed working methods, Analysis of electromagnetic environment and selection of geographical location, electromagnetic compatibility management and so on.

Electromagnetic disturbance Source: the electromagnetic energy emitted by any kind of natural or electric energy device can cause harm to people or other organisms sharing the same environment, or cause electromagnetic hazard to other equipment, sub-systems or systems, resulting in performance degradation or failure, which is called electromagnetic disturbance source.

Coupling pathway: a pathway or medium that transmits electromagnetic harassment.

Sensitive equipment (victim): refers to the electromagnetic interference from the source of the electromagnetic emissions emitted by the role of the person or other organisms will be harmed, as well as electromagnetic hazards, resulting in performance degradation or failure of the device, equipment, sub-system or system. Many devices, devices, sub-systems or systems can be both a source of electromagnetic interference and a sensitive device.

Seven, PCB layout beginners How to understand the differential signal

What is a differential signal? In layman's terms, the driver sends two equivalent, inverting signals, and the receiver can judge the logic state "0" or "1" by comparing the difference between the two voltages. The pair of lines that carry the differential signal is called the differential line. How is the differential line impedance calculated? The impedance of various differential signals are different, such as USB d+ D, the difference line impedance is 90ohm,1394 difference line is 110ohm, it is best to first look at the specification or related information. There are now many computational impedance tools, such as Polar's si9000, which affect the difference impedance of the cable width, differential line spacing, dielectric permittivity, the thickness of the media (the difference line to the reference plane between the media thickness), is generally adjusted differential line spacing and line width to control the differential impedance. Do the board when also to tell the manufacturers which lines to control the impedance. A differential signal is a numeric value that represents the difference between two physical quantities. In a strict sense, all voltage signals are differential, because one voltage can only be relative to another. In some systems, the system ' ground ' is used as a voltage reference point. When ' ground ' is used as a voltage measurement reference, this signal planning is called a single-ended. We use this term because the signal is represented by a voltage on a single conductor.

For PCB layout engineers, the most important thing is how to ensure that the advantages of differential traces can be fully played in the actual traces. Perhaps as long as the people who have contacted Layout will understand the general requirements of differential traces, PCB design that is "equal length, equidistant." The equal length is to ensure that two differential signals remain opposite polarity at all times, reducing common-mode components, and the offset is mainly to ensure that the difference impedance is consistent and reduce the reflection. "As close as possible to the principle" is sometimes one of the requirements for a differential route. Differential lines can also walk in different signal layers, but generally do not recommend this approach, because different layers such as impedance, over-hole differences will destroy the differential mode transmission effect, the introduction of common mode noise. In addition, if the adjacent two-layer coupling is not tight enough, it will reduce the ability of the differential line to resist noise, but if you can maintain the proper spacing between the surrounding lines, crosstalk is not a problem. In general frequency (under GHz), EMI will not be a serious problem, the experiment shows that the difference between 500Mils distance, 3 meters away from the radiation energy attenuation has reached 60dB, enough to meet the FCC electromagnetic radiation standards, So designers do not have to worry too much about the differential line coupling is not enough to cause the problem of electromagnetic incompatibility. But all these rules are not meant to be mechanically, and many engineers seem to have no idea of the nature of high-speed differential signal transmission. The following focus on the PCB differential signal design of several common pitfalls.

It is considered that the differential route must be very close. The proximity of the differential line is to enhance their coupling, both to improve immunity to noise and to make full use of the opposite polarity of the magnetic field to counteract electromagnetic interference from the outside world. Although this practice is very advantageous in most cases, but not absolute, if they can be guaranteed to be adequately shielded from outside interference, then we do not need to let the strong coupling of each other to achieve anti-jamming and suppression of EMI. How can we ensure that the differential track has good isolation and shielding? Increasing the distance from other signals is one of the most basic ways, the energy of electromagnetic field decreases with the square relation of distance, the interference between them is very faint when the line spacing exceeds 4 times times the line width, and the disturbance between them is very weak and can be neglected basically. In addition, through the ground plane isolation can also play a very good shielding role, this structure in high frequency (10G or more) IC package PCB design is often used, known as CPW structure, can guarantee strict differential impedance control (2z0).

The experience of my actual work:

, the high-current module to close to the power supply, weak to strong electricity; digital, analog ground a point of co-location; high-frequency device power line, ground to avoid long-term; between each digital IC power foot and grounding pin, welding high-frequency filter capacitance with shortest path, such as CC1 high-frequency porcelain capacitor, important parts and tantalum capacitor filter. Interference with large parts with an oscilloscope can be seen clearly.

PCB layout Beginners will be knowledge summary (Turn)