Find a pcb design company to do PCB Layout design, and prepare the documents as follows. At least the circuit diagram, structure diagram and parts list (BOM) should be provided as the quotation basis.
1. Circuit diagram: circuit diagram, wiring diagram (Schematic) & Nets List.
The format of the circuit diagram can be ORCAD or Protel, but if it is Autocad file, it will incur additional cost for drawing the circuit diagram.
2. Parts specification sheet & BOM: record the types, models, packages and feet of each part.
3. Structural drawing (DXF or DWG file): the size, overlapping structure, tool hole, part surface, joint, finger or IC pin position sequence of each part.
4. Layout guideline: requirements and restrictions of special signal lines (line width, line spacing, impedance, equal length, ground covering, copper net cloth, ……) requirements and restrictions of special components (spacing, height, heat flow, forbidden area).
In the process of transferring schematic diagram to layout environment through netlist file, PCB Layout design outsourcing engineer will also transfer device information, netlist, layout information and initial trace width setting.
Here are some recommended steps for the layout design stage:
1. Set the grid and units to appropriate values. In order to achieve finer layout control of components and traces, the device grid, copper-plated grid, via grid and SMD grid can be designed to be 1mil.
2. Set the blank area and the via hole of the circuit board frame to the required values. PCB manufacturers may have specific minimum or nominal recommended values for blind holes and buried holes.
3. Set the corresponding pad/via parameters according to the PCB manufacturer’s capability. Most PCB manufacturers can support smaller vias with a hole diameter of 10mil and a pad diameter of 20mil.
4. Set design rules as required.
5. Set customized shortcut keys for common layers, so that you can quickly switch layers (and create vias) during wiring.
Handling errors in schematic diagram transmission
A common error in schematic diagram transmission is the non-existent or incorrect package assignment. Note that:
If a device in the schematic diagram is not packaged, an alarm message will pop up, indicating that the virtual component cannot be exported. In this case, no default packaging information will be transferred to the layout, and the components will simply be deleted from the layout.
If the package is passed, but it can’t match the valid package shape correctly, an alarm message indicating the mismatch will also be generated during the delivery process.
Correct the package allocation in the schematic diagram, or create a valid package for any device. After correction, the forward labeling step is performed to update and synchronize the design information.
Layout design outsourcing engineer updates the design through annotation
Annotation is the process of transferring design changes from schematic to layout or from layout to schematic.Backward labeling (layout to schematic) and forward labeling (schematic to layout) are the key to keep the design accurate.
In order to protect the completed work, it is necessary to back up and archive the current version of schematic and layout files before any important forward or backward labeling steps.
Do not attempt to make changes in both schematic and layout.Either the design steps are synchronized or only one part of the design is synchronized.
Renumbering devices
Device renumbering is a function of renumbering components on PCB in a specific order.The reference labels should be sorted from top to bottom and from left to right on the PCB.This makes it easier to locate the device position on the board during assembly, testing and error checking.
Handle last-minute device or netlist changes
Last-minute PCB device or netlist changes by Layout outsourcing engineers are not advisable, but sometimes they have to be done because of device availability problems or detection of last-minute design errors. If the component or netlist needs to be changed, it should be done in the schematic diagram, and then marked forward to the layout tool. Here are some tips:
1. If a new device is added after the layout design starts (such as a pull-up resistor on the open-drain output), then add resistors and networks to the design from the schematic diagram. After marking in the forward direction, the resistor will be displayed outside the outer frame of the circuit board as an un-laid component, and the flying line will be displayed to indicate the connection network. Next, move the components into the outer frame of the circuit board and conduct normal wiring.
2. Backward labeling and reference label change can work well together, such as renumbering the rear layout.
Select positioning device by highlighting.
In the process of PCB layout, one way to browse specific components or traces in the schematic diagram is to use the’ highlight selection’ function. This function allows you to select a component or a trace (or multiple objects) and then check their positions in the schematic diagram.
This function is especially useful when matching bypass capacitors and their corresponding IC connections. Conversely, you can also locate specific components or traces in the layout when browsing the schematic diagram.
