Shenzhen City Lian xing Ye Electronics Co., Ltd

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2012-06-23
The basic concepts of high-speed design of Printed Circuit Board Design PCB board design circuit boaPrinted Circuit Board Design Technical Reference
     Profile PCB design, PCB design, the basic concept of the PCB design process high-speed PCB Design Process PCB Design Note special component layout
   The printed circuit board design is based on the circuit schematic picture shows the basis to achieve the functionality required by the circuit designer. The printed circuit board design refers to the layout, you need to consider the layout of the external connection. Optimize the layout of the internal electronic components. Optimize the layout of the metal lines and vias. Electromagnetic protection. Various factors such as heat dissipation. Good layout can save production costs, and achieve a good performance of the circuit and thermal performance. The simple layout by hand to achieve a complex layout with the computer-aided design (CAD).
  In the high-speed design, controlled impedance boards and line characteristic impedance is one of the most important and the most common problems. First look at the definition of the transmission line: the transmission line by two of a certain length of the conductor, a conductor used to send the signal, the other is used to receive signals (remember the "loop" to replace the concept of "land"). In a multilayer, each line, the transmission line part of the nearby reference plane can be used as second line or loop. A line become a "good" performance and the key to the transmission line so that its characteristic impedance remains constant throughout the line.

The circuit board as controlled impedance board "The key is to make the characteristic impedance of all lines to meet a specified value, usually between 25 ohms and 70 ohms. In the multi-layer circuit board, the key to a good performance of the transmission line so that its characteristic impedance remains constant in the whole line.

However, what is the characteristic impedance? Understanding of the characteristic impedance of the easiest way to see the signal transmission met. Have the same cross-section transmission line moves along a similar microwave transmission shown in Figure 1. Assume that wave and a volts ladder to the transmission line, such as the one-volt battery connected to the transmission line between the front end (it is located in the send line and loop) Once connected, the voltage wave signal along the line speed of light spread, its speed is usually about six inches / ns. Of course, this signal is indeed a voltage difference between the send line and loop, it can be sent on the wire at any point and loop adjacent points measured. Figure 2 is a schematic diagram of the voltage signal transmission.

The method of Zen is the first "signal is generated, then spread along this transmission line speed of six inches / ns. The first 0.01 ns forward 0.06 inches, then sent on the wire the excess positive charge, while the loop the excess negative charge, it is these two charge difference to maintain a 1 volt between the two conductors, while the two conductors form a capacitor.

The next 0.01 ns, but also a 0.06-inch transmission line voltage to be adjusted from 0 to 1 volt, which must be added to the positive charge to send line, plus some negative charge to the receiving line. Move 0.06 inches, must be more positively charged Hejia to send the line, while the more negative charge to the loop. Every 0.01 nanoseconds, another section of the transmission line to be charged, and then signal propagation along this section of Charge from the transmission line the front of the battery, move along this line, the continuous part of the give transmission line charge, and thus sent on the wire and loop formation volts. Forward 0.01 ns from the battery to get some charge (± Q), a constant time interval (± t) constant flow from the battery power (± Q) is a constant current. Negative current into the circuit is actually equal to the positive current outflow, just in the front end of the signal wave, alternating current through the capacitance of next line, the end of the entire cycle.

PCB (Printed Circuit Board) abbreviation of the printed circuit board

Edit the specific method of this paragraph (1) the purpose and role of the 1.1 specification, design jobs, increase productivity and improve the quality of the product.

(2) Scope of application 1.1 XXX developed by the Ministry of VCD Super VCDDVD audio and other products.

Responsibility attitude 3.1 Development Department all electronic engineers, technicians and computer graphics workers.

(4) the qualifications and training 4.1 Electronic Technology;

4.2 basic computer operation knowledge;

4.3 familiar with the use of computers PCB drawing software.

5 guidance (unit of length MM) and the minimum of the minimum line width of 5.1 copper foil: 0.1MM, panel 0.2MM edge of the copper foil 1.0MM

Minimum clearance of 5.2 copper foil: 0.1MM panel: 0.2MM.

Minimum distance of 5.3 copper foil side of the board 0.55MM, component and board edge minimum distance for 4.0MM 5.0MM, plate and plate edge minimum distance

5.4 General through-hole to install twice the aperture size (diameter) of the component pad, dual panel is minimized .. 5MM minimum, a single panel 2.0MM Kong (2.5MM) with a circular pad, waist round shaped pad, as shown below (if any standard cell libraries,

Zeyi standard cell libraries date)

Pad long side, short side of the hole:

5.5 electrolytic capacitor can not touch the heating element, high-power resistors, sensitive resistors, pressure, heat the solution capacitance and radiator interval minimum 10.0MM, which components to the radiator interval minimum 2.0MM.

5.6 large components (such as: transformer diameter 15.0MM above, electrolytic capacitors, high current socket) to increase the copper foil and soldering area as shown below; shaded area of fat minimum equal to the pad area.

5.7 screw hole radius 5.0MM can not foil (to the ground outside) components. Requirements) (according to the chart.

5.8 tin-bit can not be screen printing oil.

5.9 pad center distance is less than 2.5MM, have a silk screen of the pad surrounding oil adjacent parcels, ink width 0.2MM (Yee 0.5MM).

5.10 jumper is not on the IC below or motors, potentiometers, and other components of the bulk metal casing.

5.11 in the large area of PCB design (about more than 500CM2 above) to prevent the tin stove PCB board bent, stay in a 5 to 10MM wide gap in the middle of the PCB board to hold the components (alignment) is used in the tin stove coupled to prevent bending of the PCB layering, under the shadow of the map area ::

5.12 a transistor must be marked in the screen printing on e, c, b feet.

5.13 need tin furnace after welding components, disk to drive away the tin position, contrary to the direction of a tin, as the hole size is 0.5MM to 1.0MM as shown below:

5.14 Design of Double-Sided to note that the metal shell components, plug-ins when the shell and the printed circuit board contact pads of the top-level can not be opened, and must use a green oil, or screen printing oil cover (such as the feet of the crystal).

5.15 In order to reduce the solder joint short circuit, all the double-sided PCB, vias do not open the green oil window.

5.16 each piece of PCB must be marked with solid arrows the direction of the solder pot:

Minimum distance between the 5.17 holes 1.25MM (dual panel is invalid)

5.18 layout placed in the direction of the DIP package IC with tin stove direction at the vertical, not parallel, as shown; difficult layout that allows horizontal IC (IC placed in the direction of the OP package and DIP contrary ).

5.19 wiring direction is horizontal or vertical, transferred by the vertical level of 45 degrees to go into.

5.20 components placed horizontally or vertically.

Placed 5.21 silkscreen character level or right 90 degrees.

5.22 copper foil into a round pad width than the circular diameter of the pad hours, you need to add teardrop. Figure:

5.23 coding and design number on the board vacancy.

5.24 wiring for grounding or power.

5.25 as short as possible, paying particular attention to the clock line low signal line and all the high-frequency circuit wiring to be shorter.

5.26 analog circuits and digital circuits, ground and power supply system to be completely separate.

5.27 If the PCB has a large area of ground and power cord area (an area of more than 500 mm2), should the local open window. Figure:

5.28 Electric Bolt PCB positioning holes requirements as follows, the shaded area can not put the components, except hands components, L 50 330mm, H 50 250mm, the fruit is less than 50X50 will have to puzzle mold before electricity interpolation, if more than 330X250 then changed hands flapper. Positioning holes are required in the long side.

Edit this paragraph, PCB design concept used hole 1, as little as possible once the selection of the hole, be sure to handle it the gap with neighboring entities, in particular, is easy to overlook the intermediate layers and vias are not connected to the line via the gap, automatic routing, you can choose to automatically resolve the "on" sub-menu in the number of vias to minimize (Via Minimiz8tion). (2) carrying capacity the greater, the greater the required hole size, such as power and ground planes and other layers connected by vias is larger.

, Silk screen layer (Overlay) To facilitate circuit installation and maintenance, etc., logo and text code on the upper and lower surface of the printing of the printing plate, such as the component label and the nominal value of the components outside the profile shape and manufacturers logo, production date, and so on. Many beginners silkscreen, only pay attention to the text symbol placed a neat appearance, ignoring the actual system PCB. Their design printed on the board, the character is not component to block the invading flux area is wiped credit, and some component label to hit the adjacent components, so that all the design will give the assembly and maintenance inconvenience. Silkscreen character layout principles are: "no ambiguity, they must attack, nice".

3, a large number of library Protel package of the particularity of SMD SMD package, namely, surface welding device. The most prominent feature of such devices in addition to compact single-sided distribution of pin holes. Therefore, choose to use these devices you want to define where the surface of a good device to avoid "missing pin (the Missing Plns)". In addition, the relevant text of these components marked only with the components where the surface is placed.

4, the grid fills the grid-like filling (the External Plane) and recharge areas, (Fill)

As the name of both the network-like filling the area is deal with the large area of copper foil mesh, fill area only intact copper foil. Beginners design process on the computer is often less than the difference between the essence, as long as you zoom in the drawing after a glance the It is usually not easy to see the difference between the two, so use more pay no attention to the distinction between the two, to emphasize the strong suppression of high frequency interference on the circuit characteristics, the former applies to be done a large area populated places, particularly in certain areas as the shield area, is particularly appropriate when the partition or high-current power line. The latter used for the line end or transition zone filled by the small area.

5, the pad (Pad) pad is the most common exposure in the PCB design is the most important concepts, but beginners are easy to overlook the selection and correction in the design of size-fits-round pad. Pad type of select components to be considered the component shape, size, layout, vibration and heat of the force direction and other factors. Protel library in the package gives a range of different size and shape of the pad, such as round, square, octagonal, round side and positioning pads, but sometimes this is not enough, need to edit. For example, on heating by a larger force, current pad can design their own as the "teardrop" design of the familiar color TV PCB line output transformer pin pad, many manufacturers is the using this form. In general, self-editing pad addition to the above stresses, but also consider the following principles:

(1) the shape, length inconsistent when considered in connection width and specific pad side length of the size difference is not too large;

(2) requires the selection of the length asymmetry in the alignment between the components lead angle pads tend to do more with less;

(3) the size of each component pad holes according to the component pin thickness editor, respectively, to determine, in principle, is the hole size than the pin diameter of 0.2-0.4 mm.

6, various types of membrane (the Mask) film is not only essential the PcB production process, and is a necessary component welding conditions. Location and its role in the "film" and "film" can be divided into the component surface (or welding surface) flux membrane (TOp or the Bottom and the component side (or welding surface) Solder Mask (TOp or BottomPaste Mask) two class the name suggests, the flux membrane is applied to the pad to improve the solderability of a layer of film, light-colored round spots on the green board is slightly larger than the pad solder mask, the opposite is true, in order to The board made to adapt to the soldering form of wave soldering, the board pad at the copper foil can not stick to the tin, coated with a layer of paint in various parts of the outside pad should be used to prevent these parts on the tin. see, these two films is a complementary relationship between the resulting discussion, it is not difficult to determine the menu

Similar to the "solder the Mask En1argement and other project settings.

7, fly line - has a dual meaning automatic routing network for observation of a similar rubber band connection, the components transferred through the network table and do a preliminary layout, use the Show command you can see the layout cross-network connection status, to constantly adjust the location of the components to make this cross at least, to get the automatic routing routability. This step is very important, we can say that may quicken the power, spend more time value! In addition, automatic routing to the end of which the network has not yet Bouton, also available through this feature to find find out the cloth does not pass the network can be used hand-compensation, it is the compensation is not necessary to use "fly line" the meaning of the second floor, is the future of the printed board with a wire connectivity of these networks. to explain, if the board is a high-volume automated lines of production, this fly line can be regarded as European resistance, with a uniform pad spacing The resistive element to the design.

Printed circuit board (Printed "circuit board, PCB) are almost of them in every kind of electronic equipment. If a device has electronic components are, they are set in various sizes on the PCB. In addition to the fixed variety of small parts, PCB's main function is to provide top of the parts of mutual electrical connection. As electronic devices become increasingly complex, more and more parts needed, the PCB on top of the line parts more and more intensive. The standard PCB looks like this. Bare board (top parts) are often referred to as "printed circuit board Printed Wiring Board (PWB).

The board itself, the substrate is insulated, is not easy to bend the material produced. The fine line materials can be seen in the surface copper foil, the original copper foil covering the entire board in the manufacturing process was partially etched out to stay part of it becomes a mesh of tiny lines. These lines, known as the conductor (conductor pattern) or wiring, and is used to provide circuit connection of the parts on the PCB.

To the parts above the PCB, we will be directly soldered to their pins in the wiring. In the most basic PCB (single panel), the parts are concentrated in the side of the wire are concentrated on the other side. The way we need holes in the board, this pin to across the board to the other side, so parts of the pin was soldered on the other side. So, front and back of the PCB were called to the part surface (Component Side) and the welding surface (Solder Side).

If the PCB on top of some parts, finished can also be removed or put back, the parts will be used when installing the socket (Socket). Since the outlet is directly soldered on the board, the parts can be removable. See below is a ZIF (Zero the Insertion Force, zero pluggable power) receptacles, which allows parts (in this case is the CPU) can be easily inserted into the socket can also be removed. The lever next to the socket, you can after you insert parts fixed.

If you want two PCB interconnected, generally we will use the edge connector commonly known as "Goldfinger" (edge connector). Goldfinger contains many of the bare copper pad and copper pad in fact is also part of the PCB layout. Normally connected on a PCB golden finger inserted into the appropriate slot in another piece of PCB (usually called the Slot of the expansion slots). In the computer, such as display card, sound card or other similar interface cards, are by Goldfinger to connect with the motherboard.

Green or brown on the PCB, the color of the solder mask (solder mask). This layer is an insulating protective layer can protect the copper, can also prevent the parts are welded to the right place. Addition in the solder layer printing layer screen printing surface (silk screen). Usually in the above text and symbols printed on (mostly white), to mark out the location of the various parts on the board. Screen printing surface is also known as the icon surface (legend).

Edit this paragraph, the PCB design process in the PCB design, in fact, before the formal wiring to go through a very long step, the following is the PCB design major processes:

System specification first as planning the system specifications for the electronic equipment. Contains the system functions, cost constraints, the size of the operation situation, and so on.

The system functional block diagram for the next must be to create a functional block diagram of the system. The relationship between the box must be marked.

System partition several PCB split PCB can be reduced, not only in size, but also allows the ability to upgrade and exchange parts. The system functional block diagram on the basis of our segmentation. Like a computer can be divided into the motherboard, graphics card, sound card, floppy disk drive and power.

Decided to use the size of the package and PCB when the PCB use technology and circuit number decision, the next step is to determine the size of the board. PCB design is too large, then the packaging technology is necessary to change or re-partition action. In the choice of technology, but also the quality and speed of the circuit diagram considerations go.

Edit this paragraph, high-speed PCB design process traditional PCB design flow, the signal rate is getting higher and higher, even the GHZ above the field of high-speed PCB design is no longer applicable. High-speed PCB design must be the perfect combination of simulation and verification. The simulation is not the traditional sense of a simple design verification, but embedded throughout the design process before the simulation rules, rules-driven design, to the end of the post-simulation

PCB Design Considerations (1) to avoid signal lines, such as clock and reset signals arranged in the PCB edge.

(2) chassis ground and signal lines are separated by at least 4 mm; to keep the chassis ground of the aspect ratio less than 5:1 to reduce the inductance.

(3) has identified the location of the device and line LOCK function to lock it, so that does not malfunction.

(4) The minimum conductor width of not less than 0.2mm (8mil) in high-density high-precision printed circuit conductor width and spacing is generally preferable to 12mil.

(5) alignment between IC pin DIP package can be applied to the 10-10 and 12-12 principle, that is, when the feet by two lines, the pad diameter can be set to 50mil, line width and line distance are 10mil, when only by a line between the feet, the pad diameter can be set to 64mil, line width and line spacing for 12mil.

(6) In order to increase the pad when the pad diameter is 1.5mm, peel strength, can be long is not less than 1.5mm, width 1.5mm and long circular pad.

(7) Design encounter traces smaller pad connection, the connection between the design you want to pad alignment into a teardrop shape, so that the pad is not easy from the skin, lines and pads is not easy to disconnect.

(8) a large area of copper, copper design should be open window, plus cooling holes, and the window is designed to mesh.

(9) as short as possible to the connection between the high-frequency components, reducing their distribution parameters and the mutual electromagnetic interference. Susceptible to interference components can not endure each other too close to the input and output components should be kept away.

Edit this paragraph, component placement, the connection between the high-frequency components: high-frequency components, the shorter the better, try to reduce the connection of distributed parameter and the electromagnetic interference between the components susceptible to interference can not be too near. The distance between the part of input and output part of the components should be as large as possible.

2, has a high potential difference components: Increase the distance between the high potential difference components and connections to avoid accidental short circuit occurs, damage to components. 2000V potential difference between the copper film from the line in order to avoid the occurrence of creepage phenomenon, general requirements should be larger than 2mm, a higher potential difference, the distance should also increase. Devices with high voltage, you should try to layout of the reach of hand when debugging.

Much weight components: Such components should have a bracket, while the big, heavy, fat calories and more components, and should not be installed on the circuit board.

4, heat and thermal components: Note that the heating elements should be kept away from the thermal component.

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