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Posted on 10/19/2014 11:17:31 PM
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1. Preliminary preparation for circuit board design
1. Draw the schematic diagram and generate the corresponding network table. If there is a network table, you can also directly enter the PCB design system without schematic design.
2. Manually change the network table Define the pads that are not on the schematic such as the fixed feet of some components to the network that communicates with it. Change the pin names of some devices with inconsistent pin names in the schematic and PCB package library to be consistent with the PCB package library, especially the two, triode, etc.
2. Draw the package library of non-standard devices that you define
It is recommended to put all the devices you draw into a design file for the PCB library that you have created.
3. Set up the PCB design environment and draw the board frame of the printed circuit with the hollow in the middle.
1. The first step after entering the PCB system is to set up the PCB design environment, including setting the grid size and type, cursor type, board layer parameters, wiring parameters, etc. Most parameters can be used by system defaults, and these parameters are set to meet personal habits and do not need to be modified in the future.
2. Planning the circuit board is mainly to determine the frame of the circuit board, including the size of the circuit board, etc. Place the pad of the appropriate size where the fixing holes need to be placed. For 3mm screws, 6.5~8mm OD and 3.2~3.5mm OD pads are available.
4. After opening all the PCB library files to be used, call in the network table file and modify the part package
This step is a very important link, the network table is the soul of PCB automatic wiring, but also the interface between the schematic design and the circuit board design, only after the network table is installed, the circuit board can be wired.
The footprint of the part may be forgotten during schematic design, but the package of the part can be modified or supplemented according to the design when the netsheet is introduced.
5. Arrange the position of the part package, also known as the part layout
Protel99 can be automatically laid out or manually laid out. If you want to auto layout, run "Auto Place" under "Tools", with this command, you need to be patient. The key to routing is layout, and most designers use manual layout. Select a component with the mouse, hold down the left mouse button, drag the component to the destination, release the left button, and fix the component. Protel99 has added some new tricks in terms of layout. New interactive layout options include auto-select and auto-align. Using automatic selection, components of similar packages can be quickly collected, then rotated, unfolded, and grouped to move to the desired location on the board. When a simple layout is complete, use auto-alignment to neatly unfold or contract a set of components that encapsulate similarly.
Note: The layout of parts should be comprehensively considered from the aspects of mechanical structure heat dissipation, electromagnetic interference, and convenience of future wiring. First, the mechanical dimension-related devices are arranged and locked, followed by the large space-occupying devices and the core components of the circuit, and then the small peripheral components.
6. Make appropriate adjustments according to the situation, and then lock all devices
If space on the board allows, some wiring areas similar to experimental boards can be placed on the board. For large boards, more fixing screw holes should be added in the middle. Fixing screw holes should also be added to the side of stressed devices such as heavy devices or large connectors on the board, and some test pads can be placed in appropriate positions if necessary, preferably added in the schematic. Change the small pad vias to larger, define the network of all fixed screw hole pads to the ground or protect the ground, etc.
After putting it down, use the VIEW3D function to check the actual effect and save it.
7. Wiring rule setting
Routing rules are to set the specifications of wiring (such as the use level, the width of each group, the spacing of vias, the topology of the routing, etc., which can be exported from other boards through the Menu of Design-Rules and then imported into this board).
Design-Rules generally requires the following settings:
1. Safety spacing (Clearance Constraint of Routing label)
It specifies the distance that must be maintained between traces, pad vias, etc. for different networks on the board. Generally, the board can be set to 0.254mm, the empty board can be set to 0.3mm, the denser patch board can be set to 0.2-0.22mm, and the production capacity of a very small number of printing plate processing manufacturers is 0.1-0.15mm, if you can ask for their consent, you can set this value. Below 0.1mm is absolutely prohibited.
2. Routing Layers of Routing Labels
Here you can set the trace layer used and the main trace direction for each layer. Please note that the single panel of the patch only uses the top layer, and the in-line single panel only uses the bottom layer, but the power layer of the multilayer board is not set here (you can add it with Add Plane after clicking on the top layer or bottom layer in the Design-Layer Stack Manager, double-click on the left mouse button to set it, and click on the main layer and use Delete to delete it), and the mechanical layer is not set here (you can set it in the Design-Mechanical Layer). and choose whether to display both visual and simultaneous display in single-layer display mode).
Mechanical layer 1 is generally used for drawing the border of the board;
Mechanical layer 3 is generally used for mechanical structural parts such as brakes on the drawing board;
Mechanical layer 4 is generally used for drawing rulers and annotations, etc., you can use the PCB Wizard to export a PCAT structure board to take a look
3. Via Shape (Routing Via Style of Routing Label)
It specifies the inner and outer diameters of the vias automatically generated during manual and automatic wiring, which are divided into minimum, maximum and preferred values, of which the preferred value is the most important, the same below.
4. Trace Line Width (Width Constraint of Routing Label)
It specifies the width of the trace when routing both manually and automatically. The preference for the entire board range is generally 0.2-0.6mm, and some network or network class line width settings are added, such as ground, +5 volt power cable, AC power input line, power output line, and power pack. The network group can be defined in advance in the Design-Netlist Manager, the ground wire is generally 1mm wide, and the various power cables are generally 0.5-1mm wide, and the relationship between the line width and current on the printing board is about 1 ampere of current allowed per millimeter of line width, please refer to the relevant information for details. When the wire diameter preference value is too large to allow the SMD pad to be routed automatically, it will automatically shrink to a section of trace between the minimum width and the width of the pad at the entrance to the SMD pad, where the Board is the line width constraint for the entire board, and its priority is the lowest, that is, the line width constraints of the network and network group are first met when routing. The following figure is an example
5. Copper connection shape setting (Polygon Connect Style for Manufacturing label)
It is recommended to use the Relief Connect method, the conductor width is 0.3-0.5mm, 4 wires, 45 or 90 degrees.
The rest of the items can generally be set according to its original default values, such as the topology of the cabling, the spacing of the power layers, and the length of the network to match the connection shape.
Select Tools-Preferences, and select the Push Obstacle mode in the Interactive Routing section of the Options bar, and select Automatically Remove (automatically delete redundant traces). You can also change the Track and Via in the Defaults column, and you don't need to touch them.
Place the FILL filling layer in the area where you don't want to have traces, such as the wiring layer under the radiator and the two pins of the horizontal oscillator, and put the FILL on the top or bottom solder if you want to tin it.
Wiring rule setting is also one of the keys to printed circuit board design, which requires rich practical experience.
8. Automatic wiring and manual adjustment
1. Click the menu command Auto Route/Setup to set the automatic wiring function
Check everything except Add Testpoints, especially the Lock All Pre-Route option, Routing Grid optional 1mil, etc. Before the automatic wiring starts, PROTEL will give you a recommended value that you can ignore it or change to its recommended value, the smaller the board, the easier it is to deploy 100%, but the more difficult and time-consuming the wiring.
2. Click the menu command Auto Route/All to start automatic wiring
If it cannot be fully routed, it can be done manually or UNDO once (do not undo all routing functions, it will delete all pre-routing and free pads and vias), adjust the layout or routing rules, and then reroute the routes. After completion, do a DRC and correct any mistakes. During the layout and wiring process, if the schematic is found to be wrong, the schematic and network table should be updated in time, the network table should be changed manually (same as the first step), and the network table should be reinstalled before deployment.
3. Make manual preliminary adjustments to the wiring
The ground wire, power cable, power output line, etc. that need to be thickened should be thickened, and a few wires that have been wound too much should be rearranged to eliminate some unnecessary vias, and the actual effect can be checked again with the VIEW3D function. In manual adjustment, you can select Tools-Density Map to view the wiring density, red is the densest, yellow is second, and green is looser. The red part should generally be loosely adjusted until it turns yellow or green.
9. Switch to single-layer display mode (click the menu command Tools/Preferences, select Single Layer Mode in the Display bar in the dialog box)
Pull the wires of each wiring layer neatly and beautifully. When adjusting manually, you should do DRC often, because sometimes some wires will break and you may walk several wires from the middle of it, and when you are almost finished, you can print out each wiring layer separately for easy reference when changing the line, and you should also check it frequently with the 3D display and density map function.
Finally, cancel the single-layer display mode and save the disk.
10. If the device needs to be re-annotated, click the menu command Tools/Re-Annotate and select the direction, then press the OK button.
And go back to the schematic and select Tools-Back Annotate and select the newly generated one*. WAS file, press the OK button. Some designations in the schematic should be dragged and dropped again for aesthetics, and after all of them have been adjusted and DRC passed, drag and drop the characters of all the silkscreen layers to the appropriate positions.
Note: Characters should not be placed under the component or on top of the via pad. For oversized characters, the DrillDrawing layer can be appropriately scaled down, and the DrillDrawing layer can be equipped with some coordinates (Place-Coordinate) and dimensions (Place-Dimension) as needed.
Finally, put the design version number, the date of the first processing of the document, the file name of the printing plate, the processing number of the document and other information.
11. Teardrops on all vias and pads
Teardrops increase their fastness, but they can make the lines on the board more unsightly. Press the S and A keys of the keyboard (select all), then select Tools-Teardrops, select the first three of the General column, and select the Add and Track modes, if you don't need to convert the final file to PROTEL's DOS version of the format file, you can also use other modes, and then press the OK button. When you're done, press the X and A keys on your keyboard (all unchecked). For patches and single panels, it must be added.
12. Place the copper-clad area
Temporarily change the safety spacing in the design rules to 0.5-1mm and remove the error marks, and choose Place-Polygon Plane to place the copper clad of the ground wire network at each wiring layer (try to use octagonal shapes instead of arcs to wrap the pads).
After the setting is completed, press OK and twist to draw the border of the area that needs to be copper-cladded, and the last edge can not be drawn, just press the right mouse button to start copper cladding. By default, it assumes that your start and end points are always connected by a straight line, and when the circuit frequency is high, you can choose to set the Grid Size larger than the Track Width to cover the grid lines.
Place the copper cladding of the remaining wiring layers accordingly, observe the place where there is no copper cladding in a large area on a certain layer, put a via where there is copper cladding on other layers, double-click any point in the copper clad area and select a copper cladding, click OK directly, and then click Yes to update the copper cladding. Several copper clad layers are repeated several times until each copper clad layer is full. Change the safe spacing in the design rule back to its original value.
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