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PCB board design by Protel
Date:2014-6-30 15:00:16

 

Altium Protel is introduced circuit-aided design system, is the first all-in-one design tools integrated board-level design system. On the basis of the schematic has been completed on the use Protel PCB design in general should follow to determine the shape, placement, routing, rules, checks and several other steps. This paper analyzes the basic principles of placement, routing, and explore some of the experience and skills throughout the PCB design process. 
 
With the popularity of computers, electronic CAD technology has not only high-level professionals to design special tools LSI's, especially the emergence of Protel software makes general engineering and technical personnel can also use it to handle the daily work of circuit design problems and improve work efficiency. Protel is the circuit-aided design (EDA) industry in the most convenient and operate the most efficient, user-friendly interface, the best aids, but also with the most EDA tools in China. In this paper, Protel99 SE design tools, analysis and discussion of the basic principles of PCB design skills and experience. 
First, quickly determine PCB shape 
PCB circuit board design should first determine the shape, is usually prohibited to draw electrical wiring layer wiring range. Unless otherwise specified, have the general shape of a rectangular board, an aspect ratio of 3:2 or 4:3 is generally preferable. Before any painting can draw two horizontal and two vertical lines, then use the "Place toolbar" in the "Settings origin" tool to set the endpoint of a line segment that is the origin of the coordinate (0,0), then Double-click on each line, make the appropriate changes to their starting point and end point coordinate values​​, so that four segments end to end to form a closed rectangular box, the board determines is finished appearance. If you need to adjust the size of the circuit board in the drawing process, as long as the modification of each segment corresponding coordinate values. From a cost and wrap wire length, noise immunity considerations, board size as small as possible, but the board size is too small, poor heat dissipation, and adjacent wires can cause interference. However, when the circuit board is larger than the size of 200mm × 150mm, the mechanical strength of the circuit board should be considered, the installation of a suitable mounting holes to play a supporting role. 
Second, component placement 
 
First, before beginning to load the layout of the table through the network components, this process is often not fully loaded network table encounter errors, mainly grouped into two categories: one component is not found, the solution is confirmed schematics package has been defined components, and confirm to add the corresponding PCB component libraries, if still can not find elements necessary to create a component that encapsulates its own; the other is missing pin, the most common is the diodes, transistors cited foot loss, which is due to the pin generally schematic letters a, K, E, B, C, and the pin element is PCB number 1,2,3, the solution is to change the definition of the principle diagram, or Changing the definition of PCB components to make it consistent. Experienced designers usually create a library based on its own PCB components package outline practical, easy to use and less error-prone. 
When the layout, we must follow some basic rules: 
(1) special components special consideration. Between the high-frequency components to be as close as possible, shorter is better; has a high potential difference between the distance of elements try to increase; components should have a large weight bracket; heating element away from sensitive components and to install appropriate heat sink or placed off-board; layout potentiometer, adjustable inductors, variable capacitors, micro-switches and other adjustable components should be considered structural requirements of the machine, in order to facilitate the adjustment shall prevail. In short, some of the special characteristics of components from the component itself, the chassis structure, ease of maintenance, debugging and other aspects into account in the layout, in order to ensure to make a stable and easy to use PCB board. 
 
(2) according to the layout of the circuit function. If there are no special requirements, as far as possible in accordance with the elements of the schematic layout elements, usually the case the input signal from the left and right output, input from the upper, lower output. The circuit according to the process, the arrangement position of each functional circuit unit, the signal flow more smoothly and consistent direction. Further, the digital circuit must be separated analog circuit layout and to reduce interference. 
Text (3) silkscreen label. To facilitate the installation and maintenance of the circuit, generally on the upper and lower surface of the printing plate is required for printing logo design and text code, such as labels and the nominal value element, the element outline shape, factory signs, etc., a lot of beginners silkscreen designs often omitted, or only pay attention to the text symbol placed neat appearance, but the actual manufacture of the PCB board, the character panel is not being blocked elements invaded flux area is erased, there's the element label playing on the adjacent components, assembly and maintenance of the inconvenience caused. Correct character layout silkscreen principle should be no ambiguity, they must attack, nice. 
 
Third, wiring 
This is the PCB design is a very important aspect, PCB layout has sided wiring, double-sided and multilayer wiring wiring. Wiring in two ways: automatic routing and interactive routing. In the wiring process should pay attention to the following questions: 
(1) length. Deposited copper wire as short as possible, in high-frequency circuits and even more so. Deposited copper bend should be rounded or beveled, right angle or sharp corners at high frequency circuits and wiring density will affect the electrical properties. Further, when the double-sided wiring conductors on both sides should be mutually perpendicular, oblique or curved traces to avoid parallel to reduce parasitic capacitance. 
 
(2) width. The width of the deposited copper electrical characteristics should be able to meet the requirements but to facilitate production as a criterion, its minimum value depends on the current flowing through it, but generally not less than 0.2mm, if the board size is large enough, the width of the best copper deposition not less than 0. 3mm. The relationship between ground and power lines are: a ground> Power cable> signal line, the normal power supply line width of 1.2-2.5mm, the width of the signal line 0.2-0.3mm. 
(3) line spacing. Apply spacing between adjacent copper electrical safety requirements should be met, and in order to facilitate the production, the spacing should be as wide as possible. Able to withstand at least the minimum spacing voltage peak, generally require deposition of copper from the potential difference between 2000V should be greater than 2mm. In the case of low wiring density, the pitch should be as large as possible. Line spacing is usually best not less than 0.3 mm. 
(4) shielding and grounding. Deposited copper ground wire should be as common on the edge of the circuit board. The board should do as much as possible to retain copper ground wire, so you can make the shield capacity enhancement. 
 
IV Conclusion 
PCB board design is a complex and simple process. For a circuit with the same instrument or even the same circuit elements and parameters, the device design and the type of electrical wiring directions will produce different results, there may be significant differences in the results. Thus, how to properly structure must be designed and printed circuit board component layout and the overall direction of the correct choice of cabling technology structure of the instrument together three aspects to consider reasonable process structure, can help eliminate noise interference arising due to improper wiring, while ease of production, such as installation, commissioning and maintenance.

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