PCB Tech - PCB printed circuit board design technology process

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

1. Netlist input

There are two ways to input the netlist. One is to use PowerLogic's OLE PowerPCB Connection function, select Send netlist, and apply 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 import the netlist generated by the schematic diagram.

2. Rule setting

If the design rules of the PCB board 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 entered into the PowerPCB along with the netlist. If the design rules are modified, you must Synchronize the schematic diagram to ensure that the schematic diagram is consistent with the PCB board. 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, be sure to add Layer25. Note:

PCB design rules, layer definitions, via settings, and CAM output settings have been created as default startup files, named Default. $tp, after the netlist is input, according to the actual situation of the design, the power supply network and ground are allocated to the power supply layer and the ground layer, and other advanced rules are set. 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.

3. PCB Component layout

After the netlist is entered, all the 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, the component layout PowerPCB provides two methods. Manual layout and automatic layout. 2.3.1 Manual layout

A. Draw the board outline for the structure size of the printed board of the tool

B. 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

3.1 automatic 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 routing rate, pay attention to the connection of the flying lines when moving the device, and put the devices with the connection relationship together

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

C. The decoupling capacitor should be as close as possible to the CC of the device

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

E. Use the Aray and Union functions provided by the software to improve layout efficiency

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.

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 wiring, the PCB wiring needs to be adjusted by manual wiring.

4.2 Automatic wiring

After the manual wiring is completed, the remaining network is handed over to the automatic router for cloth. Select Tool-> SPECCTRA, start the Specctra router interface, set the DO file, and press Continue to start the Specctra router automatic wiring. After the end, if the distribution rate is 100%, then you can enter

It is OK to manually adjust the wiring; if it is less than 100%, 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.

Precautions

A. The power cord and ground wire should be as thick as possible

B. Try to connect the decoupling capacitor directly to ⅴCC

C. When setting the Spectra DO file, first add the Protect all wires command to protect the manually clothed wires from being rewired by the automatic router

D. If there is a mixed power layer, the layer should be defined as Split/mixed Plane, and it should be divided before wiring. 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 attributes, and tick the Thermal option

F. When manually routing, turn on the DRC option and use Dynamic routing

5. Check

The items to be checked include Clearance, Connectivity, HighSped 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.

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.

6. Review

The review is based on the "PCB board 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 The routing and shielding of the clock network, 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