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PCB Tech

PCB Tech

PCB Tech

PowerPCB design specification of PCB design software
2021-08-19
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Author:IPCB

I. Overview


The purpose of this document is to explain the process and some precautions for printed board design using PADS's printed board design software PowerPCB, and to provide design specifications for designers in a working group to facilitate communication and mutual inspection between designers.


two. Design Flow


The PCB design process is divided into six steps: netlist input, rule setting, component layout, wiring, inspection, review, and output.


2.1 Netlist input


There are two ways to enter the netlist. One is to use PowerLogic's OLE PowerPCB Connection function, select Send Netlist, and use the OLE function to keep the schematic diagram and PCB diagram consistent at any time to minimize the possibility of errors. Another method is to load the netlist directly in PowerPCB, select File->Import, and input the netlist generated by the schematic diagram.


2.2 Rule settings


If the PCB design rules have been set in the schematic design stage, there is no need to set these rules, because when the netlist is input, the design rules have been imported into PowerPCB along with the netlist. If the design rules are modified, the schematic diagram must be synchronized to ensure that the schematic diagram is consistent with the PCB. In addition to the design rules and layer definitions, there are also some rules that need to be set, such as Pad Stacks, which need to modify the size of the standard vias. If the designer creates a new pad or via, layer 25 must be added.


Notice:


PCB design rules, layer definitions, via settings, and CAM output settings have been made into the default startup file, named Default.stp. After the netlist is input, according to the actual situation of the design, assign the power network and ground to the power layer and ground layer , And set up other advanced rules. After all the rules are set, in PowerLogic, use the Rules From PCB function of OLE PowerPCB Connection to update the rule settings in the schematic to ensure that the rules of the schematic and PCB are consistent.


2.3 Component layout


After the netlist is entered, all components will be placed at the zero point of the work area and overlapped together. The next step is to separate these components and arrange them neatly according to some rules, that is, component layout. PowerPCB provides two methods, manual layout and automatic layout.


2.3.1 Manual layout


a. Draw the board outline for the structural dimensions of the printed board of the tool

b. Disperse the components (Disperse Components), the components will be arranged around the edge of the board.

c. Move and rotate the components one by one, put them inside the edge of the board, and place them neatly according to certain rules.


2.3.2 Auto Layout


PowerPCB provides automatic layout and automatic local cluster layout, but for most designs, the effect is not ideal and it is not recommended.


2.3.3 Matters needing attention


a. The first principle of the layout is to ensure the wiring rate, pay attention to the connection of the flying leads when moving the device, and put the connected devices together


b. Separate digital devices from analog devices and keep them as far away as possible

c. The decoupling capacitor is as close as possible to the VCC of the device

d. When placing the device, consider future soldering, not too dense

e. Use the Array and Union functions provided by the software more to improve layout efficiency


2.4 Wiring


There are also two ways of wiring, manual wiring and automatic wiring. The manual wiring function provided by PowerPCB is very powerful, including automatic pushing and online design rule checking (DRC). Automatic wiring is performed by Specctra's wiring engine. Usually these two methods are used together. The common steps are manual-automatic-manual.


2.4.1 Manual wiring


a. Before automatic wiring, first hand-lay some important networks, such as high-frequency clocks, main power supplies, etc. These networks often have special requirements for wiring distance, line width, line spacing, shielding, etc.; in addition, some special packaging, Such as BGA,


It is difficult to arrange automatic wiring regularly, and manual wiring must be used.


b. After the automatic routing, the PCB routing should be adjusted by manual routing.


2.4.2 Automatic wiring


After the manual wiring is over, the remaining network is handed over to the automatic router for cloth. Select Tools->SPECCTRA, start the interface of the Specctra router, set the DO file, and press Continue to start the automatic wiring of the Specctra router. After the completion, if the wiring rate is 100%, then you can manually adjust the wiring; if not If it reaches 100%, it indicates that there is a problem with the layout or manual wiring, and the layout or manual wiring needs to be adjusted until all the connections are made.


2.4.3 Matters needing attention


a. Make the power cord and ground wire as thick as possible

b. Try to connect the decoupling capacitor directly to VCC

c. When setting the DO file of Specctra, first add the Protectall wires command to protect the manually clothed wires from being redistributed by the automatic router

d. If there is a mixed power layer, you should define the layer as Split/mixed Plane, divide it before wiring, and after wiring, use Pour Manager's Plane Connect for copper pour

e. Set all device pins to thermal pad mode by setting Filter to Pins, select all pins, modify properties, and tick the Thermal option

f. When manually routing, turn on the DRC option and use dynamic routing (DynamicRoute)


2.5 Inspection


The items to be checked include Clearance, Connectivity, High Speed and Plane. These items can be selected by Tools->Verify Design. If the high-speed rule is set, it must be checked, otherwise you can skip this item. If errors are detected, the layout and wiring must be modified.

ATL

Notice:


Some errors can be ignored. For example, a part of the outline of some connectors is placed outside the board frame, and errors will occur when checking the spacing; in addition, each time the traces and vias are modified, the copper must be re-plated.


2.6 Review


The review is based on the "PCB checklist", which includes design rules, layer definitions, line widths, spacing, pads, and via settings; also focus on reviewing the rationality of the device layout, the routing of power and ground networks, and high-speed clock networks. The wiring and shielding, the placement and connection of decoupling capacitors, etc. If the recheck is unqualified, the designer shall modify the layout and wiring. After passing, the rechecker and the designer shall sign separately.


2.7 Design output


The PCB design can be exported to a printer or a gerber file. The printer can print the PCB in layers, which is convenient for designers and reviewers to check; the gerber file is handed over to the board manufacturer to produce the printed board. The output of the gerber file is very important. It is related to the success or failure of this design. The following will focus on the matters needing attention when outputting the gerber file.


a. The layers that need to be output are wiring layer (including top layer, bottom layer, middle wiring layer), power layer (including VCC layer and GND layer), silk screen layer (including top silk screen, bottom silk screen), solder mask (including top solder mask) And bottom layer solder mask), and also generate a drilling file (NC Drill)


b. If the power layer is set to Split/Mixed, then select Routing in the Document item of the Add Document window, and before each gerber file output, you must use PourManager's Plane Connect for copper pour on the PCB diagram; if it is set to CAM Plane , Select Plane. When setting the Layer item, add Layer25, and select Pads and Vias in Layer25


c. In the device setup window (press Device Setup), change the value of Aperture to 199

d. When setting the Layer of each layer, select BoardOutline

e. When setting the Layer of the silk screen layer, do not select Part Type, select the top layer (bottom layer) and Outline, Text, Line of the silk screen layer

f. When setting the layer of the solder mask layer, select vias to indicate that no solder mask is added to the vias, and not to select vias to indicate solder masks, depending on the specific situation.

g. When generating drilling files, use the default settings of PowerPCB and do not make any changes

h. After all gerbera files are output, open and print them with CAM350, and check them according to the "PCB checklist" by the designer and reviewer

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3. Classic Q&A:


Question: Is the mil of Protel 99 imperial? How small is it in centimeters?


Answer: It can be changed to metric system: 1/1000inch, 0.00254CM


Question: The package can be found in the library file, but I don’t know the specifications of the components corresponding to each package, like resistors. I just wrote axial0.3--axial1.0 but I don’t know what kind of resistance the resistor corresponds to each package. what to do?


A: The footprint is the package, and the attributes closely related to the component size, pins, etc., must be set in advance when making a pcb board.: Generally, 1/8 resistors use axial_0.3 (related to the version of Protel, different versions may be different, You can check the relevant pcb: library files): small capacitor: rad_0.1, rad_0.2: large capacitor: rb_.2/.4: integrated circuit: dip_n (n is the number of pins): other details will not be repeated.



Question: What is the difference between the versions of Protel


Answer: There is no essential difference in the operation mode of PROTEL98/99/99SE, but the management mode of interface and project files has changed. Just take a book about PT98/99/99SE and flip through it. In fact, PT98/99/99SE is very easy to learn. If you only make schematics and printed boards, you will be familiar with it after using it several times.


Question: Is the success rate of automatic wiring 100%?


Answer: How should I say, unless it is a very simple board, in general, automatic wiring is only the first wiring, which requires manual optimization, and it must be necessary. There is still a lot of artificial intelligence in this area of software that needs to be improved. The place. Personally, I usually lay out first, then automatically deploy, then adjust the layout, and then automatically deploy. Finally, the "big battle" --- manual wiring.


Question: Draw the schematic diagram in sch, close it after saving it, and open the schematic diagram again, there is nothing in it. What the hell is going on, it seems like it can't be saved.


Answer: Is the Protel demo version you use? I have seen a demo version of Protel98 that cannot be saved. Maybe your problem is the same. It is recommended to install a Crack version.


Question: How to specify the package form of components in Protelfor Win?


Answer: 1. Specify in Advanced Schematic


Modify the footprint of the component in the schematic to the required PCB library package name. Then generate the netlist, add the required package library to the PCB, and load the components at the same time when the netlist is loaded.


  2, specified in Advanced PCB


Place the required component package directly in the PCB, set the designator to be consistent with the schematic, and then re-load the netlist.