PCB Engineer's Design Points For Layout

The best design method of PCB: six things to be considered when the PCB schematic is passed to the design of the layout (layout). All of the examples mentioned in this article are developed in the MulTIsim design environment, but the same concept applies when using different EDA tools.


Initial schematic diagram transfer


In the process of transferring the schematic map to the layout environment, the device information, the net table, the layout information and the initial line width are also passed in the process of transferring the schematic map to the layout environment.


The following are some of the recommended steps for the layout design phase:


1. set the grid and unit as the appropriate value. In order to achieve more detailed layout control for components and lines, the device grid, copper grid, over hole grid and SMD grid can be designed to be 1mil.

The 2. circuit board frame blank area and vias Shecheng required value. The PCB manufacturer may have a specific minimum value or nominal recommendation for the blind holes and the burial holes.

3. set corresponding pads / hole parameters according to the PCB manufacturer's ability. Most PCB manufacturers can support a smaller hole with a diameter of 10mil and a disk with a diameter of 20MIL.

4. the design rules are set up according to the requirements.

5. set custom shortcuts for common layers to quickly switch layers (and create holes) during wiring.


A common error in the process of schematic transfer is a non - or incorrect packaging. It is important to note that:


If a device is not encapsulated in the schematic, a warning message will be popped, indicating that the virtual element can not be exported. In this case, no default encapsulation information is passed to the layout, and the component is simply deleted from the layout.


If the package passes through the past, but does not match the effective package shape correctly, then the mismatch warning message will be produced during the transfer process. In the schematic, the encapsulation distribution is corrected, or an effective package is created for any device. After correction, the forward step is performed to update and synchronize the design of information.


Annotation is the process of transferring the design changes from the schematic map to the layout or from the layout to the schematic diagram. Backdirection tagging (layout to schematic) and forward annotation (schematic map to layout) are the key to keeping the design accurate. In order to protect the completed work, we need to backup and archive the current version schematic and layout files before any important forward or reverse annotation steps. Do not try to make changes at the same time in the schematic and layout. Only one part of the design is changed (either a schematic or a layout), and then the correct annotation step is performed to synchronize the design of the data.



The device renumbering refers to the function of renumbering the components on the PCB in a particular order. The reference number should be sorted in the direction of PCB from top to bottom, from left to right. This makes it easier to locate the device position on the board in the process of assembly, testing and error checking.



The last minute change of PCB device or netlist is not advisable, but sometimes it has to be done because of device usability or the last design error. If you need to change the element or the net table, it should be done in the schematic and then annotated to the layout tool forward. Here are some tips:


1., if a new device is added after the layout starts, such as adding a pull-up resistor on the open drain output, then increase the resistor and network from the schematic diagram. After the forward annotation, the resistance will be displayed as an element that is not laid out in the outer frame of the circuit board, and the flight line indicates the connection network. Then the component is moved to the outer frame of the circuit board, and the normal wiring is carried out.


2. the post tagging and reference number changes can work well together, such as the renumbered of the post. In the PCB layout process, one way to browse a particular element or line in a schematic is to use a 'bright selection' function. This function allows you to select a component or a walk line (or a number of objects), and then look at their position in the schematic. This function is particularly useful when matching bypass capacitors and their corresponding IC connections. In turn, you can also locate a particular element or line in the layout when you browse the schematic.


 

(Source: internal information)

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