Carried out using PADS PCB design process, the need to focus attention on the PCB design flow and related notes, so as to better provide design specifications for system designers working group, but also to facilitate designers mutual exchange and checks between.
02
Process design
PCB design flow into netlist input, rule setting, component placement, routing, inspection, review, six step output.
2.1 netlist input
Netlist inputted two ways, one is using the OLE PowerPCB ConnecTIon PowerLogic function, select Send Netlist, on OLE functions, can be maintained consistent with the principles and PCB map at any time, to minimize the possibility of error.
Another method is directly loadable in the netlist PowerPCB, select File-> Import, the netlist generated schematics input comes.
2.2 rule set
If you have already set a good PCB design rules, then in the schematic design phase, you will not need to set these rules, because when the input netlist, netlist design rules have been entered into with the PowerPCB. If you modify the design rules, it must be synchronized schematic, to ensure consistency of schematic and PCB. In addition to design rules and layer defines, to set some rules, such as Pad Stacks, need to modify the size of the standard via. If the designer built a pad or via, be sure to add Layer 25.
Precautions:
PCB design rules, layer defines vias provided, the output of the CAM has made the default startup file set, the name Default.stp, netlist input comes after, according to the actual situation of the design, the power distribution network and the power and ground to and set other advanced rules. After all the rules are set up, in PowerLogic using OLE PowerPCB ConnecTIon's Rules From PCB features, updates the rules set in the schematic, to ensure that the rules of schematic and PCB diagram of the same.
2.3 component layout
After the component layout netlist input, all the components are zero in the work area, overlaps with, the next step is to separate these components, according to some rules neatly, i.e., component layout. PowerPCB provides two methods, manual layout, and automatic layout.
2.3.1 manual layout
Structure size (1) to draw the tool PCB board edge (Board Outline).
(2) dispersing the components (Disperse Components), components will be arranged around the edge of the plate.
(3) a component to a moving, rotating, into the inner panel side, according to certain rules neatly.
2.3.2 Automatic Layout
PowerPCB provides automatic layout and automatic layout of the local cluster, but for most of the design, the effect is not ideal, is not recommended.
2.3.3 Notes
a. layout of the first principle is to ensure routability wiring connected to the attention of the fly line when moving the device, the device has a connection relationship together
b. digital devices and analog devices to separate, as far as possible away from the
c. VCC decoupling capacitor as close to the device
d. to consider when placing the device after welding, not too dense
e. multi-use function Array Union and software to improve the efficiency of the layout
2.4 wiring line manner
The wiring is divided into manual and automatic routing. PowerPCB provide manual routing function is very powerful, including automatic push, online design rule checking (DRC), automatic routing Specctra by the routing engine, usually with the use of these two methods commonly used procedure is manual - automatic - manual.
2.4.1 Manual Route
(1) before the automatic routing, first with handmade cloth some important networks, such as the high frequency clock, the main power supply, these networks tend to trace distance, width, line spacing, shielding and other special
Requirement; other special packages such as BGA, automatic routing rules too hard cloth, but also by hand wiring.
After (2) automatic routing, but also by hand wiring of PCB traces can be adjusted.
2.4.2 Automatic routing
After the end of the manual routing, and the rest of the network on to the Autorouter from cloth. Select Tools-> SPECCTRA, start Specctra router interface DO set file, press ConTInue started the Specctra router automatic routing, if the end of the cloth was 100% pass, then routing can be manually adjusted; if not to 100%, indicating a problem with the wiring layout or manually, or manually adjust the layout of the wiring, so far until all Bouton.
2.4.3 Notes
a. bold power line and ground as much as possible
b. possible decoupling capacitor directly connected to the VCC
c. In the DO file provided Specctra added first command Protect all wires, wire cloth hand protection is not discouraged cloth automatically routing
d. If there are hybrid power layer, the layer should be defined as Split / mixed Plane, the wiring before dividing it, after the completion of the cloth line, using the Pour Manager Plane
Connect conduct copper
e. Set all device pins to a thermal pad mode, the practice is to Pins Filter, select all the pins, modify the properties, options Thermal before tick
f. When the DRC routing option is turned manually using dynamic routing (Dynamic Route)
2.5 Inspection Check items
Includes spaced (Clearance), connectivity (ConnecTIvity), high speed rule (High Speed) and power planes (Plane), these items can be selected Tools-> Verify Design performed. If the high-speed rules must be checked, otherwise you can skip this one. Detect errors, you must modify the layout and routing. Note: Some errors can be ignored, such as the Outline of the part of some connectors on the outer plate and frame, check to be wrong pitch; revised alignment for each other and vias after copper must re once.
2.6 Review
The review "PCB check table", including design rules define layer, line width, pitch, pads, through holes are provided; also reasonable, power, ground network key device layout traces review, the high-speed clock network traces and the shield, placing decoupling capacitors and the like are connected. Review unqualified designers to modify the layout and routing, qualified after, review and designers were signed.
2.7 Design Output
PCB design can be output to a printer or output Gerber files. The printer can print layered PCB, designers and reviewers facilitate inspection; Gerber files to the system board manufacturers, PCB production. Painted light output very important documents related to the success of this design, the following will highlight considerations output gerber files.
a. need to output layer wiring layer (including the top, bottom, intermediate wiring layer), the power supply layer (layer comprises VCC and GND layer), silkscreen (including the top screen, and bottom screen), solder resist layer (a solder resist top layer comprises and the underlying solder resist), while also generating drill files (NC drill)
. B If the power supply layer is provided Split / Mixed, then carried out in the copper Routing Add Document Document item selection window, and before each file output light painting, have to use Pour Manager of Plane Connect to FIG PCB; if set to CAM Plane, select Plane, provided layer paragraph, should Layer25 together, select Pads and Vias layer in Layer25
c. In the apparatus arranged window (press Device Setup), the value is changed to 199 Aperture
D. On the setting of each layer Layer, selected from the Board Outline
e. Set Layer silkscreen, do not choose Part Type, select the top (bottom) and Outline of silkscreen, Text, Line
f. When the solder resist layer disposed Layer choose expressed via hole without solder resist is not selected via the home represented solder, as the case determination
g. When generating drill files, using the default settings PowerPCB, do not make any changes
H. After all of the light output Gerber files, and print CAM350 with open, by a designer and reviewers "PCB Checklist" The inspection.
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