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The design process of a PCB will essentially begin by creating a schematic. By Milan Yogendrappa. February 9, 0 Comments. The first step involved in PCB design is to draw your concept block diagram on a paper. This block diagram is then developed into schematic designs using CAD software. A schematic consists of component symbols and net connections between the symbols. These nets will become traces on the circuit board. The next stage of design is the pre-layout stage, in this stage, the BOM from the schematic is validated for long lead time components and obsolete components.
During the validation process, the manufacturing part numbers MPN and vendor part numbers are verified. During this stage, the stack-up design is also completed. The PCB layout stage is next. In this stage, the board parameter settings, board outline, component placement, routing, and production document generation are completed. The design process comprises various different stages. Each stage has its own defined processes and checklists. To design a successful PCB, it is essential to follow the processes and check through the design checklist at every milestone.
In this section, we will go through the different steps that are involved in designing a PCB using Altium Designer. A schematic diagram is a representation of the elements of a system using abstract and graphic symbols.
In this phase, the design is entered into the schematic tool Altium, Allegro, etc. A schematic shows the components that are used in the design and how they are connected together. If the design uses a hierarchical schematic, where numerous functional schematics are interrelated with each other, the schematic defines the relationships between groups of components in different schematics. An example of the schematic diagram is shown below.
If you want to learn more about the step-by-step approach to schematic generation, refer to our post on schematic and netlist checks to ensure error-free designs. Schematic generation is the process of creating a logical representation of the electronic circuit. When you generate a schematic, you are connecting a collection of symbols components together in a unique way, creating your unique electronic product. The symbol generation process involves drawing the body of the component, adding pins and pin numbers, defining the reference designators, and assigning a footprint.
The body of the symbol is created by placing graphical design objects in the schematic library editor workspace. Altium Designer includes a variety of closed symbol shapes including rectangle, pentagon, ellipse, and triangle as shown below. Pins define the connection points on the component for the incoming and outgoing signals. Pin numbering is made to ensure the connections shown in the schematic, end up connected properly by copper on the PCB.
It is the component pins that give the component its electrical properties and define connection points on the component for directing signals in and out. A pin is placed to represent each pin on the actual physical component. Reference designators mainly consist of category, value, manufacturer, manufacturer part number, and supplier.
It is recommended that every symbol on your circuit have its own unique designator so that every part is easily identifiable. For example, every resistor should follow a consistent naming sequence of R1, R2, R3, etc. Footprint gives an idea of the actual size of the component. For example, when we put a component on the sand, it will leave its impression there. This imprint is its actual physical size.
Some components come in standard packages and the footprints are easy to find. In some cases, we may have to create the footprint manually.
Below are the steps to be followed to create a footprint in Altium Designer. It is very important for a PCB designer to clearly show how the components are interconnected in the schematic. First, whenever you have two wires that form a junction and share an electrical connection, that intersection needs to have a junction dot.
This is standard practice in every schematic design. If you have a pair of intersecting wires that are not electrically connected and are just overlapping, then you will not need a dot. The important signals on the board should be marked once the components are connected. Also, the power traces need to be identified and marked. The footprints of components are shown on the schematic diagram when you transfer the schematic information to the PCB layout.
Netlist in any PCB designing software contains information of the component name as well as the pad of that component which is connected. Netlist also assigns numbers to the connections in serial order. The Netlist Manager dialog is used to control and manage the netlist of the board.
Nets can be edited, added, or deleted as the requirements. The pins or pads of the components in the nets can also be edited. Export Netlist option is used to export the netlist of the PCB to the current document. A net by net verification in the schematic should be carried out whether all the nets are connected as intended. The bill of materials BOM , is simply a list of required materials for manufacturing a printed circuit board.
In the pre-layout stage, we initiate the design of stack-up, ensure that the BOM is verified for all parts, and verify that the parts are active and not obsolete. The first step in the pre-layout stage is to ensure that all the materials required for your design are available. Designers need to have the details of the stack-up before starting the layout design.
Designers always design the stack-up but they are usually assisted by the fab house to get a right stack-up arrangement. They can get the required help from a PCB manufacturer or they can use stack-up tools, like our Stackup Planner.
The PCB layout stage includes setting up the design tool, board outline, import of netlist, component placement, routing, silkscreen cleanup, DRC check, and generation of documents for production Gerbers, netlist, etc. The board layout is started by setting the stack-up and design rules.
The stack-up is set up in the tool using the Layer Stackup Manage r tool. The stack-up design generated by the stack-up tool from the PCB manufacturer is used as a reference to set up the stack-up in the layout tool.
Design rules are a set of instructions for the PCB layout tool to follow. Each and every aspect of the design is covered in the PCB constraint settings. PCB design rules can be broadly classified as:. The shape of the PCB is referred to as the board outline and is essentially a closed contour. The board shape can be redefined in different ways:. Cross-select mode enables the corresponding selection of the object between PCB layout and schematic.
In other words, if you select an object on the layout, the corresponding object on the schematic is also selected. This ensures accurate component placement on your layout.
The below image shows the steps to activate cross-select mode in Altium Designer. The component placement process begins by placing the components which are at the fixed locations as per the design requirements.
These components normally include connectors and their associated components. The next step is to place the main components such as CPU, memory, and analog circuits. The third step is to place the auxiliary components to the main components such as crystals, decoupling capacitors , and series resistors. Routing is the process of laying the copper traces between the nodes.
This conductive path is defined by placing tracks, arcs, and vias on the copper layers to establish a connection between the two nodes. Interactive routing method is used to route the connection in the PCB designer. The below image shows the steps to access the interactive routing command.
Once the command is launched click on a pad that needs to be routed. The interactive router defines a route path from the selected pad to the cursor location. The size of the track is as per the PCB set design rules.
If your schematic has recurring circuits, you can auto-group the components to save time during the routing process. The sequence of routing is to complete the decoupling capacitors routing and the power vias.
Then route the critical traces such as impedance traces and high-speed traces. Then route non-critical traces. It is a good policy to route traces in an orthogonal way.
The power plane is a layer of copper to which the power supply is connected. The ground plane is a layer of copper to which a ground connection is made. To learn about capacitor placement read Decoupling capacitor placement guidelines for PCB design.
Design rule check DRC is a process of checking both the logical and physical integrity of a design. This feature can also be enabled online so that the checks are performed parallelly as we progress through the design process.
This step should be performed on every routed board to confirm that minimum clearance rules have been followed and there are no violations.
The below image shows the DRC dialog. Filling all the specific information on the fab notes is very important as it documents all the vital information of the PCB design for future reference.
If the board is being designed for a customer it is recommended to get approval from the customer after the above step. An example of fab notes is shown below.
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