Bright PCB is always here to fit customers’ PCB Layout need. We have specialist experienced for years to help client to layout their PCB, FPC and Rigid-Flex PCB. And already serviced hundreds of clients. Below are the Processes of the PCB Layout.
The purpose of this document is to describe the PCB design process using PowerPCB with PADS, and to provide design specifications for a team of designers to facilitate communication and cross-checking between designers.
2, the design process
PCB design process is divided into netlist input, rule set, component layout, wiring, inspection, review, output six steps.
2.1 Netlist Entry
Netlist input in two ways, one is to use PowerLogic OLE PowerPCB Connection function, select Send Netlist, application OLE function, you can always keep the schematic diagram and the PCB map of the same, to minimize the possibility of error. Another method is to directly load the netlist in PowerPCB, select File-> Import, the netlist generated by the schematic input.
2.2 Rule Settings
If the PCB design rules have been set up during the schematic design phase, you do not need to set these rules anymore, because when you enter the netlist, the design rules are entered into the PowerPCB with the netlist. If you modify the design rules, you must synchronize the schematic to ensure that the schematic and PCB are consistent. In addition to the design rules and layer definition, there are some rules need to set, such as Pad Stacks, the need to modify the size of standard vias. If the designer creates a new pad or via, be sure to add Layer 25.
PCB design rules, layer definition, through-hole settings, CAM output settings have been made into the default startup file, named Default.stp, netlist input came in accordance with the design of the actual situation, the power network and ground distribution to the power layer and the formation , And set other advanced rules. After all rules are set, in PowerLogic, use the Rules From PCB feature of OLE PowerPCB Connection to update the rule settings in the schematic to ensure that the rules of the schematic and the PCB map are consistent.
2.3 component layout
After the netlist input, all the components will be placed in the work area of zero, overlapping together, the next step is to separate these components, according to some rules neatly placed, that is, the layout of components. PowerPCB provides two methods, manual layout and automatic layout.
2.3.1 Manual Layout
A. Structural dimensions of the tool PCB Draw the Board Outline.
B. Disperse components, the components will be arranged around the edge of the board.
C. The components one by one to move, rotate, placed within the board edge, in accordance with certain rules placed neatly.
2.3.2 Automatic layout
PowerPCB provides automatic layout and automatic local cluster layout, but for most of the design, the effect is not ideal, not recommended.
A layout of the primary principle is to ensure the wiring rate of the cloth, pay attention to flying devices when the connection line, the wiring of the device together
B. Digital devices and analog devices to be separated, as far as possible away
C. Decouple the capacitor as close to the VCC of the device as possible
D. When placing the device to consider the subsequent welding, not too dense
E. Use the Array and Union functions provided by the software to improve the efficiency of the layout
There are two ways of wiring, manual routing and automatic routing. PowerPCB provides manual routing capabilities, including automatic push, on-line design rule checking (DRC), and automatic routing by Specctra’s routing engine, usually in conjunction with the two methods, commonly used manual-automatic-manual.
2.4.1 Manual wiring
A. Automatic routing, the first by hand cloth some important networks, such as high-frequency clock, the main power supply, these networks are often the alignment distance, line width, line spacing, shielding, etc. have special requirements; other special packaging, Such as BGA, automatic routing is difficult to cloth rules, but also with manual wiring.
B. After the automatic routing, but also with manual wiring to adjust the alignment of the PCB.
2.4.2 Automatic wiring
After the manual routing, the rest of the network to the automatic router from the cloth. Select Tools-> SPECCTRA, start Specctra router interface, set the DO file, press Continue to start the Specctra router automatically wiring, after the end if the cloth rate of 100%, then you can manually adjust the wiring; To 100%, indicating the layout or manual wiring problems, need to adjust the layout or manual wiring until all the cloth so far.
A. The power cord and ground wire should be as thick as possible
B. Decoupling capacitors should be connected directly to VCC as far as possible
C. Set Specctra DO file, first add the Protect all wires command to protect the manual cloth line is not automatically router
D. If you have a hybrid power plane, you should define the layer as a Split / mixed Plane, split it before wiring it, and then use Plour Connect from Pour Manager for copper
E. Set all device pins to the hot pad mode by setting Filter to Pins, selecting all pins,
Modify the properties and tick the Thermal option
F. Manual DRC option to open the wiring, the use of dynamic routing (Dynamic Route)
The items checked are Clearance, Connectivity, High Speed, and Plane. These items can be selected with Tools-> Verify Design. If a high speed rule is set, it must be checked, otherwise it can be skipped. To check for errors, you must modify the layout and routing.
Some errors can be ignored, for example, some of the Outline part of the connector on the board outside the box, check the spacing will be wrong; In addition to each modified traces and vias, have to re-copper once.
Review the layout of the device according to the “PCB checklist”, including design rules, layer definition, line width, pitch, pad, vias; also focus on review the rationality of the layout of the power supply, ground wire network, high-speed clock network Of the alignment and shielding, decoupling capacitors placed and connected. Review failed, the designer to modify the layout and wiring, qualified, the reviewers and designers were signed.
2.7 Design Output
The PCB design can be output to a printer or to output a light-painted file. The printer can be PCB layered printing, to facilitate the review of designers and reviewers; light painting documents to the system board manufacturers, the production of printed circuit boards. Light output of the document is very important, related to the success of this design, the following will focus on the output of the painted file attention.
(Including top layer, bottom layer, middle wiring layer), power layer (including VCC layer and GND layer), silk screen layer (including the top silk screen, bottom silk screen), solder mask (including the top solder mask And the bottom solder mask), but also to generate a drilling file (NC Drill)
B. If the power layer is set to Split / Mixed, select Routing in the Document field of the Add Document window and use Pour Manager’s Plane Connect for copper on the PCB map before each output of the paint file; if set to CAM Plane, then select Plane, Layer in the set of the time, we should add Layer25, in the Layer25 select Pads and Vias
C. In the Device Settings window (press Device Setup), change the Aperture value to 199
D. When setting the Layer for each layer, select Board Outline
E. Set the layer of the screen layer, do not select Part Type, select the top (bottom) and silk screen layer Outline, Text, Line
F. Set the layer of solder mask layer, select the vias on the hole without the solder mask, no vias that solder resistance, as the case may be
G. When creating the drilling file, use the default PowerPCB settings and do not make any changes
H. After the output of all the painted files, open and print with CAM350, by designers and reviewers according to “PCB checklist” check
Two: LAYOUT considerations
1: parts arranged when the part of the circuit as much as possible together, the alignment as short as possible.
2: IC decoupling capacitors should be as close as possible to the IC pin to increase the effect.
3: If the voltage difference between the two lines is large, pay attention to the safety clearance.
4: to consider the current size of each loop, that is, to determine the status of fever copper thickness.
5: line corner as far as possible to have an acute angle, right angle is best to use obtuse and arc.
6: For high-frequency circuits, the two lines is best not to go too long parallel to reduce the impact of distributed capacitance, the general approach to the top floor of the public.
7: Gaoping circuit to consider the high-frequency impedance of the ground, the general use of a large area of grounding, the nearest ground, reduce the inductance of the ground weight, so that the potential of the street close.
8: high-frequency circuit to the coarse and short circuit to reduce the length of the alignment is too long to produce the inductance and high-frequency impedance of the circuit.
9: parts arrangement, the general should the same kind of parts together, as neat, polar components as possible in the same direction, reducing the potential production costs.
10: For RF models, the power supply part of the parts away from the receiver board as far as possible to reduce interference.
11: For TF models, the transmitter should be as far away from the PIR as possible to reduce the PIR interference caused by the launch.
Components, working groups, precautions, components, working groups, precautions.
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