Preliminary work

1. Use the schematic design tool to draw the schematic diagram and generate the corresponding network table. Of course, in some special cases, such as the circuit board is relatively simple, and there is already a network table, you can directly enter the PCB design system without schematic design. In the PCB design system, you can directly use parts to package and manually generate the network table.

2. Manually change the network table to define the pads that are not on the schematic diagram such as the fixed pins of some components to the network connected with them, and the pads that are not physically connected can be defined to the ground or protected ground. The pin names of some devices whose pin names are inconsistent with those in PCB package library are changed to be consistent with those in PCB package library, especially diodes and triodes.

What preliminary work should be done in PCB schematic design

 

2、 Draw the package library of non-standard device defined by yourself

It is suggested that all the devices you draw should be put into a special PCB library design file.

3、 Setting up PCB design environment and drawing PCB frame with hollowing out in the middle, etc

1. The first step after entering the PCB system is to set the PCB design environment, including setting the size and type of grid point, cursor type, board layer parameters, wiring parameters and so on. Most of the parameters can use the system default value, and these parameters after setting, in line with personal habits, later do not need to modify.

2. Planning circuit board, mainly to determine the circuit board frame, including the size of the circuit board, and so on. Place a pad of appropriate size where the fixing hole needs to be placed. For 3mm screws, the pad with 6.5~8mm outer diameter and 3.2~3.5mm inner diameter can be transferred from other boards or PCB Izard to the standard plate.

Note: before drawing the circuit board border, make sure that the current layer is set as the keep out layer, that is, the wiring layer is prohibited.

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. Network table is the soul of PCB automatic wiring, and it is also the interface between schematic design and impression circuit board design. Only after the network table is loaded, can circuit board wiring be carried out.

In the process of schematic design, ERC inspection does not involve the packaging of parts. Therefore, in schematic design, the package of parts may be forgotten. When introducing network table, the package of parts can be modified or supplemented according to the design situation. Of course, the network table can be generated manually in PCB directly, and the part packaging can be specified.

5、 The location of the part package is also called part layout

Protel99 can layout automatically or manually. If automatic layout, run “auto place” under “tools”, with this command, you need to have enough patience. The key of wiring is layout, most designers use the form of manual layout. Select a component with the mouse, hold down the left mouse button, drag the component to the destination, release the left mouse button, and fix the component. Protel99 has added some new techniques in layout. New interactive layout options include automatic selection and automatic alignment. Using the automatic selection method, you can quickly collect components with similar packages, then rotate, expand and organize them into groups, and then move them to the desired position on the board. When the simple layout is completed, a group of components with similar package can be expanded or shrunk neatly by using automatic alignment.

Tip: during automatic selection, use shift + X or Y and Ctrl + X or y to expand and contract the X and Y directions of the selected components.

Note: the layout of parts should be comprehensively considered from the aspects of heat dissipation of mechanical structure, electromagnetic interference and convenience of wiring in the future. First, the devices related to the mechanical size are arranged and locked, then the large position occupying devices and the core components of the circuit, and then the small peripheral components.

6、 Make appropriate adjustment according to the situation, and then lock all devices

If the space on the board allows, some wiring areas similar to the experimental board can be placed on the board. For large boards, more fixing screw holes should be added in the middle. If there are heavy devices or large connectors on the board, the fixing screw holes should also be added on the side of the stressed devices. If necessary, some test pads can be placed at appropriate positions, preferably in the schematic diagram. The network of all fixed screw hole pads is defined to ground or protection ground. After placing it, use the view3d function to check the actual effect and save it.

7、 Routing rule settings

The routing rule is to set the rules of each routing specification (such as the usage level, line width of each group, via spacing, topological structure of routing, etc., which can be exported from other boards through the menu of design rules, and then imported into this board). This step does not need to be set every time. It can be set once according to the habit of individual. When selecting design rules, you need to reset the following points:

1. Clearance constraint of routing label

It specifies the distance that must be kept between the routing pad vias of different networks on the board. The general plate can be set as 0.254mm, the empty plate can be set as 0.3mm, and the dense plate can be set as 0.2-0.22mm. The production capacity of a few printing plate processing manufacturers is 0.1-0.15mm. If you can obtain their consent, you can set this value. Less than 0.1 mm is absolutely forbidden.

2. Routing layers and directions

Here you can set the used routing layer and the main routing direction of each layer. Please note that the veneer only uses the top layer, and the plug-in veneer only uses the bottom layer, but the power layer of the multilayer board is not set here (you can click the top layer or bottom layer in the design layer stack manager, add it with add plane, double-click it with the left mouse button, and delete it after clicking this layer) Delete), and the mechanical layer is not set here (you can select the mechanical layer to be used in the design mechanical layer, and select whether it is visible and whether it is displayed in single-layer display mode at the same time).

Mechanical layer 1 is generally used to draw the border of the board;

The mechanical layer 3 is generally used to draw the mechanical structural parts such as the stop strip on the drawing board;

Mechanical layer 4 is generally used for drawing ruler and notes. You can use PCB wizard to export a PCAT structure board to have a look.

3. Via shape (routing via style of routing label)

It specifies the inner and outer diameters of vias automatically generated during manual and automatic wiring, which are divided into minimum, maximum and preferred values, among which the preferred value is the most important, the same below.

4. Routing label width constraint

It specifies the routing width for manual and automatic routing. The preferred option for the whole board range is generally 0.2-0.6mm, and some network or network class line width settings are added, such as ground wire, + 5V power line, AC power input line, power output line and power pack. The network group can be defined in design netlist manager in advance. The width of ground wire can be 1 mm in general, and that of various power wires can be 0.5-1 mm in general. The relationship between line width and current of printed board is about 1 ampere per mm line width. Please refer to relevant information for details. When the preferred value of wire diameter is too large for SMD pad to run through in automatic routing, it will automatically shrink to a section of wire between the minimum width and the width of pad when entering SMD pad. Board is the line width constraint of the whole board, and its priority is the lowest, that is, the line width constraints of network and network group are satisfied first.

5. Setting of copper clad connection shape (polygon connect style of manufacturing label)

It is recommended to use the relief connect mode, and the conductor width should be 0.3-0.5mm, 4 wires 45 or 90 degrees.

The other items can be set according to their original default values, such as the topological structure of wiring, the distance between power layers and the length of network matching the connection shape.

Select tools preferences, in the interactive routing section of the options column, select push object (push other routes when encountering different network routes, ignore object is to pass through, and avoid object is to block) mode, and select automatically remove. Track and via in the defaults column can also be changed. Generally, it is not necessary to move them.

Place fill layer in the area where there is no wiring, such as the wiring layer under the radiator and the horizontal two pin crystal oscillator, and place fill layer in the corresponding place of top or bottom solver where tin is to be applied. Wiring rule setting is also one of the key points of PCB design, which needs rich practical experience.

8、 Automatic routing and manual adjustment

1. Click the menu command auto route / setup to set the automatic routing function

Select all items except add testpoints, especially the lock all pre route option and the routing grid option. Before automatic wiring starts, PROTEL will give you a recommended value, which can be ignored or changed to its recommended value. The smaller the value is, the easier it is for the board to be 100% routed, but the more difficult and time it takes for wiring.

2. Click the menu command auto route / all to start automatic routing

If it can not be fully distributed, it can be manually completed or UNDO once. (do not use all the wiring function to cancel, it will delete all the pre wiring and free pads, through the hole) after adjusting the layout or wiring rules, and then re wiring. Do DRC once after completion, and correct any mistakes. In the process of layout and wiring, if any error is found in the schematic diagram, the schematic diagram and network table should be updated in time, the network table should be changed manually (the same as the first step), and the network table should be re installed before routing.

3. Preliminary manual adjustment of wiring

The ground wire, power line and power output line that need to be thickened should be thickened. A few wires with too much winding should be re arranged to eliminate some unnecessary vias. Use view3d function again to check the actual effect. In manual adjustment, you can select tools density map to check the wiring density. Red is the densest, followed by yellow, and green is loose. After reading, you can press the end key on the keyboard to refresh the screen. The red part should be adjusted loosely until it turns yellow or green.

9、 Switch to single layer display mode (click the menu command tools / preferences and select single layer mode in the display bar of the dialog box)

Pull the wires of each wiring layer neatly and aesthetically. When adjusting by hand, you should always do DRC, because sometimes some lines will be broken, and you may walk several lines from the middle of the broken line. When it is almost finished, you can print out each wiring layer separately, so as to facilitate reference when changing the line. In the meantime, you should often use 3D display and density map function to check. Finally, cancel the single layer display mode and save.

10、 If the device needs to be re labeled, click the menu command tools / re annotate and select the direction, then press OK.

Return to the schematic diagram, select tools back annotate and select the newly generated *. Was file, then press OK. Some labels in the schematic diagram should be drag and drop again to make it beautiful. After all the labels have been adjusted and passed the DRC, drag and drop all the characters in the silk screen layer to the appropriate position.

Note that characters should not be placed under components or above via pads. If the character is too large, it can be reduced appropriately. The drilldrawing layer can put some place coordinate and place dimension as needed.

Finally, put on the printing plate name, design plate number, company name, document first processing date, printing plate file name, document processing number and other information (see the figure in step 5). The program provided by the third party can be used to add graphics and Chinese annotation, such as BMP 2 PCB.EXE Design of Chinese character input package for rotel99 and Protel99SE PCB FONT.EXE And so on.

11、 Repair all vias and pads

Tear filling can increase their fastness, but it will make the line on the board look worse. Press s and a keys (select all) on the keyboard in sequence, then select tools teardrops, select the first three in the general column, and select Add and track modes. If you don’t need to convert the final file to Protel DOS format file, you can also use other modes, and then press OK. When finished, press the X and a keys of the keyboard in sequence (none selected). For the patch and single panel must be added.

12、 Place copper clad area

The safety distance in the design rules is temporarily changed to 0.5-1 mm, and the error mark is cleared. Place polygon plane is selected to place the copper covering of ground wire network in each wiring layer (try to use octagonal shape instead of arc to wrap the pad). Finally, if you want to convert to DOS format file, you must choose octagonal. After setting, press OK button again to draw the border of the area to be covered with copper. The last edge can be left blank. Press the right mouse button directly to start covering with copper. By default, it thinks that your starting point and ending point are always connected by a straight line. When the circuit frequency is high, you can choose grid size larger than track width to overlay the grid line.

Place the copper cladding of the other wiring layers. Observe the place where there is no copper cladding on a large area of one layer. Place a through hole at the place where there is copper cladding on other layers. Double click any point in the copper cladding 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 safety distance in the design rules back to the original value.

13、 Do it again for the last time

Select the clearance constraints max / min width constraints short circuit constraints and UN routed nets constraints, and press the run DRC button to correct any errors. Save after all correct.

14、 For manufacturers supporting Protel99SE format (pcb4.0) processing, the file can be exported as a *. PCB file when viewing the document directory; for manufacturers supporting Protel99 format (pcb3.0) processing, the file can be saved as PCB 3.0 binary file for DRC. Exit without saving after passing. When viewing the document directory, export this file as a *. PCB file. At present, most manufacturers can only make boards drawn by Protel autotrax under DOS, so the following steps are essential to generate a DOS PCB file:

1. Change all mechanical layer contents to mechanical layer 1, export network table as *. Net file when viewing document directory, and export PCB as *. PCB file in program PCB 2.8 ASCII file format when opening this PCB file.

2. Open PCB file with Protel for windows PCB 2.8, select Save as in the file menu, and select autotrax format to save a file that can be opened in DOS.

3. Use Protel autotrax under DOS to open this file. Individual strings may need to be drag and drop again or resized. The size of pad X-Y may be interchanged when all the two pin patch elements are up and down. Adjust them one by one. The big four column chip IC will also swap all the pads X-Y. it can only be adjusted half automatically and manually one by one. Please save it at any time. In this process, it is easy to make human errors. Protel DOS board has no undo function. If you used to cover copper and choose to use arc to wrap the pad, then all the networks are basically connected now. It’s very tiring to delete and modify these arcs one by one manually, so it’s recommended that you use octagonal to wrap the pad. After all these are completed, use the network table exported above as the separation setup in the DRC route. The values should be smaller than those under the windows board. If there are errors, correct them until all DRC passes.

You can also directly generate Gerber and drilling files to the manufacturer, select File cam manager and press “next” button to get six options: BOM is the list of components, DRC is the design rule inspection report, Gerber is the light drawing file, NC drill is the drilling file, pick place is the automatic pick and place file, and test points is the test point report. After selecting Gerber, follow the prompts step by step. Some of the parameters related to the production capacity need to be provided by the printing plate manufacturer. Until you press finish. Right click on the generated Gerber output 1, select Insert NC drill to add the drilling file, and then right click to select generate cam files to generate the real output file. The photo file can be exported and opened with CAM350 for verification. Note that the power layer is negative output.

15、 E-mail or copy the plate to the manufacturer, indicating the material and thickness of the plate (1.6 mm for general plate, 2 mm for super large plate, 0.8-1 mm for radio frequency microstrip plate, etc.), quantity, special attention during processing, etc. Call the manufacturer within two hours after sending the email to confirm whether it is received or not.

16、 The BOM file is generated and exported, and then edited into a format conforming to the company’s internal regulations.

17、 The frame screw hole connector and other parts related to the chassis machining (i.e. select and delete other irrelevant parts) are exported to AutoCAD R14 DWG format file of metric size for mechanical designers.

18、 Organize and print all kinds of documents. Such as component list, component assembly drawing (with printing scale), installation and wiring instructions, etc.

Source: EEPW

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