First: preparation. This includes the preparation and schematic library components. "Make bricks without straw his tools", to make a good board, in addition to good design principles, we should also paint it. During PCB design, first we have prepared schematic and PCB SCH component library components library. Component library can peotel own library, but generally very difficult to find suitable, preferably their own standards based on the selected device size information to do their own cell library. PCB do first principle component library, component library do SCH. Require higher PCB component library, which directly affect the board's installation; SCH component libraries required is relatively loose, as long as the definition of a good note and PCB component pin attributes and the corresponding relationship on the line. PS: Note that the standard library in the hidden pin. Following is the schematic design, PCB ready to start after good design.
       Second: PCB Design. This step has been determined according to the circuit board size and the mechanical positioning, in the PCB design environment, drawing PCB board, according to positioning requirements place the necessary connectors, buttons / switches, screw holes, mounting holes and so on. And fully consider and determine the layout of regional and non-routing areas (such as screw holes around the extent to a non-routing area).
       No. 3: PCB layout. Layout that the white put the device on the board. Then, if the preparations mentioned above are good, then it can be generated in the schematic netlist (Design-> Create Netlist), after the PCB map into the network table (Design-> Load Nets). To see the devices crashed the whole pile up, and the pin connection between the still fly line tips. Then the layout of the device can. General layout follows the principle:
       ①, according to a reasonable partition electrical properties, are generally divided into: digital circuit area (that is afraid of interference, but also interference), analog circuit area (fear of interference), power-driven areas (the source of interference);
       ②, to complete the circuit the same function should be placed as close as possible, and adjust the connection of all components to ensure that the most simple; the same time, adjusting the relative position between the function block to function block connection between the most simple;
       ③, the quality of major components for the installation location and installation should be considered strength; heating element and temperature-sensitive components should be separated, if necessary, measures should also be considered thermal convection;
       ④, I / O-driven device as close to the printing plate's edge, close to the connector leads;
       ⑤, clock generator (such as: crystal or Restructure) used to be as close as possible to the clock of the device;
       ⑥, each integrated circuit in the power input pin and ground between the need to add a decoupling capacitor (usually a good high frequency performance of multilayer ceramic capacitor); circuit board space than the dense, they can be around in a few integrated circuits Add a tantalum capacitor.
       ⑦, relay coil Department to increase discharge diode (1N4148 can be);
       ⑧, layout requirements to balance density and orderly, not top-heavy or a Shen
       - Require special attention to the placement of components, we must consider the components of the actual size (share of area and height), the relative position of parts to ensure electrical performance and circuit board production and installation of Ke Xingxing and convenience at the same time, ensure that the above principles should be reflected appropriately to modify the device's display, so neat appearance, such as the device to be placed neatly and direction can not be placed too "patchwork."
This step relates to the overall image and the next step wiring board level of difficulty, so they do take great efforts to consider. Layout, and not sure where you can first make a preliminary layout, full consideration.
       Fourth: wiring. PCB design layout is the most important processes. This will directly affect the performance of the PCB board good or bad. In the PCB design process, three types of wiring such a general division of state: first, Bouton, then the basic        PCB design requirements. If no cloth lines pass, and made fly lines everywhere, it would be a failure of the board, it can be said yet started. Followed by the electrical properties of the meet. This is a measure of a printed circuit board eligibility criteria. This is the fabric through, the careful adjustment of wiring, so that it can achieve the best electrical performance. Followed by appearance. If your wiring through the cloth, and no place to affect electrical properties, but a glance chaotic, with colorful, colorful, and that even if the electrical properties of how good you are, the eyes of others, or a piece of garbage. This testing and maintenance to great inconvenience. Wiring should be uniform, not criss-cross clueless. These must ensure the electrical performance and to meet the individual requirements of the other under the situation, otherwise, it is bartering the. Wiring, the main by the following principles:
       ①, under normal circumstances, the first power line and ground should be wiring to ensure that the electrical properties of the circuit board. In the conditions permit as far as widening the power, ground width, it is better than the power supply ground line width, their relationship is: ground> Power Line> signal line, usually the signal line width: 0.2 ~ 0. 3mm, the smallest width of up to 0. 05 ~ 0. 07mm, the power cord is generally 1. 2 ~ 2. 5mm. PCB can be used for digital circuits to wire to form a wide loop that constitutes a ground network to use (analog circuit ground can not be used this way)
       ②, more stringent requirements in advance of the line (such as high-frequency line) for routing, input and output side of the adjacent parallel edges should be avoided to avoid reflection interference. Necessary, add ground isolation between two adjacent layers of wiring to be perpendicular to each other, parallel prone to parasitic coupling.
       ③, oscillator shell ground, the clock line is to be as short as possible, and can not be attracted everywhere. Clock oscillator circuit following the special high-speed logic circuit part to increase the land area should not take the other signal line, so that the surrounding electric field close to zero;
       ④, as far as possible the line wiring by 45 º, 90 º line can not be used to reduce high-frequency signal radiation; (the line is also used for high double-arc)
       ⑤, any signal lines are not formed loop, such as inevitable, the loop should be as small as possible; signal line vias to as little as possible;
       ⑥, key lines as short and thick, and add protection to both sides.
       ⑦, transmitted through the flat cable signal and noise field with a sensitive signal, use the "ground - signal - ground" approach leads.
       ⑧, the key signal test points should be set aside to facilitate the detection of the production and maintenance
       ⑨, after the completion of schematic wiring, wiring should be optimized; the same time, preliminary check, the network checks and DRC, the wiring region on earth is not populated, with large area ground copper layer for use in the PCB on the not the place to be to spend all connected with the land use as a ground. Or made of multilayer, power, ground layer of the occupation.

       PCB layout process requirements:
       ①, line
       In general, the signal line width is 0. 3mm (12mil), power line width of 0. 77mm (30mil), or 1. 27mm (50mil); between the lines and lines and the pad is greater than equal to the distance between 0. 33mm (13mil), practical application, should be considered when conditions permit greater distance;
       Higher wiring density can be considered (but not recommended) using IC pin to go between the two lines, line width of 0. 254mm (10mil), line spacing no less than 0. 254mm (10mil). Special circumstances, when the device pin dense, narrow the width of the time, can reduce the line width and spacing appropriate.
       ②, pad (PAD)
       Pad (PAD) and the transition pore (VIA) of the basic requirements are: disk diameter than the hole diameter is greater than 0. 6mm; for example, common pin-type resistors, capacitors and integrated circuits, etc., using plate / hole size 1. 6mm / 0. 8mm (63mil/32mil), sockets, pins and diodes such as 1N4007, using 1. 8mm / 1. 0mm (71mil/39mil). Practical application, should be based on the actual component size to decide when conditions would be appropriate to increase pad size;
PCB board design of the component installation pin aperture components should be higher than the actual size of a large 0. 2 ~ 0. 4mm or so.
       ③, Via (VIA)
       Usually 1. 27mm / 0. 7mm (50mil/28mil);
       When the wiring density is high, through the appropriate hole size can be reduced, but not too small, can be considered 1. 0mm / 0. 6mm (40mil/24mil).
       ④, pads, lines, vias spacing requirements
       PAD and VIA: ≥ 0. 3mm (12mil)
       PAD and PAD: ≥ 0. 3mm (12mil)
       PAD and TRACK: ≥ 0. 3mm (12mil)
       TRACK and TRACK: ≥ 0. 3mm (12mil)
       Density is high:
       PAD and VIA: ≥ 0. 254mm (10mil)
       PAD and PAD: ≥ 0. 254mm (10mil)
       PAD and TRACK: ≥ 0. 254mm (10mil)
       TRACK and TRACK: ≥ 0. 254mm (10mil)
       Fifth: Route Optimization and screen printing. "There is no best, only better!" No matter how you rack their brains to work out, so after you finish the painting, go see, or feel that a lot of places can be amended. General design experience is: optimize routing time is twice the initial wiring of the time. After feeling no need to modify the place, you can shop copper a (Place-> polygon Plane). General shop shop copper ground wire (note that analog ground and digital ground of separation), multiply the power and might be required shop. When the screen, pay attention to the device can not be blocked or removed through hole and the pad. Meanwhile, the design elements face to face, the bottom of the mirror should be done word processing, to avoid confusion level.
       Sixth: Network and DRC checking and structural inspection. First, in determining the schematic design of the premise is correct, the network file generated PCB schematic network file with the physical connection of a network check (NETCHECK), results in a timely manner in accordance with the output file to amend the design to ensure that wiring the connection of the correctness; network right after the passage of inspection, the design of the PCB DRC check the output file results in a timely manner in accordance with the design be amended to ensure that the electrical properties of PCB layout. Finally for further installation of structures on the PCB mechanical inspection and verification.
       Seventh: plate. Prior to this, the best also have a review process.
       PCB design is a work of mind test, whose secret thoughts, experience high out of the board like design. So, very carefully designed to give full consideration to all aspects of the factor (such as ease of maintenance and inspection that a lot of people not to think), keep improving, we will be able to design a good board.