PCB Manufacturing

Your Guide to PCB Layout Design Basics & Steps

PCB Layout Design

What is PCB

Before diving into PCB design and layout, we need to know what a PCB is first. PCB (printed circuit board) is an electronics assembly board used to create the electric connection between the components using copper traces. Copper layers, base laminate, solder mask, silkscreen and surface finishes are contained in one PCB board. And usually we classify PCBs according to their layer counts: single layer PCB, double layer PCBs and multilayer PCBs.

PCB Design and Layout

What is PCB Layout Design

PCB layout design means the process of converting an ideal into files which can be used to produce printed circuit boards. Starting from ideals and functional intentions, PCB design engineers need to generate schematic, PCB Gerber files and BOM files finally.

This article mainly contains from PCB schematic to Gerber generation. Which contain the step by step process of how to design the schematic, layout design and also how to generate the Gerber file for PCB fabrication.

The Basics about PCB Design and Layout

After knowing what is PCB and PCB design, we will talk about the PCB design basics and main steps. PCB design mainly involved three steps as shown below.

  1. Schematic Design.
  2. PCB Layout Design.
  3. Gerber Generation.

Nowadays there is a number of software available that we can use for PCB design like Cadence allegro, Altium, Kicad, mentor graphics..etc. and a user manual will be provided by the software owner on how to use the software.

In this article, we will talk about layout PCB design with Allegro, in the Allegro software there are three part as following:

  • Capture CIS:which is used for schematic creation.
  • Pad Creation: which is used for creating the components pad.
  • PCB Editor:which is used for layout design for PCB.

Details Steps of PCB Layout Design

Now that we know the basics about PCB and the main steps of PCB design, it is time to talk about the details of the three main steps: schematic design, PCB layout design and Gerber generation.

Schematic Design

figure show the schematic

Figure 1: The above figure show the schematic page

Steps making the schematic

Go to capture CIS double click on that and you can see the black page.

Once the page will open you have to go to the file >new >project after selecting the project you will get one folder in that folder you have to enter the name of the project and also you have to select the project location where you need to create the project file.

Once you created the project directory,you will get the new page in that only you have to start to making the circuit,there will be a different types of circuit (normal or high speed ). but the making the schematic it should be neat and clearly you have to make like package,part number,signal direction,different types of ground and also different types of supply.

In the schematic page there are icons at the right side of the page which you can use for part creation and also import the part from the library. Also there is icon wire which will be used to connect between the two components please refer to the above image.

Even you have the option that you can edit the existing part:

Click on part>right click>edit option

Once you complete the schematic you have to assign the foot print for each components. after assigning the foot print you need to generate the netlist.

Netlist: which will provide all the information like (connection,package,part number..etec) in the time of layout design.

PAD CREATION: This is one of the very important rules in the PCB design,for creating the pad you have to use the padstack editor.

figure show the Pad Editor page

Figure 2:The above figure show the Pad Editor page

As per the above image you can create the different shapes of pad example(circle,oval square,rectangle etc..) either in SMD or THRU hole also you can create the different types of vias (blind/buried and micro via)

Steps For making the Pad Creation: Double click on pad stack editor the page will open as per the above image and you have to select below units left corner of the page (mm or mils). Next go to the file>new and it will open with a new folder in that you have added the pad stack name(ex:resistor,capacitor etc…) as per the IPC standard IPC 2221A.

Before creating the pad you have to refer to the Data sheet of particular components. In that data sheet they will mention the dimension of the pad even though that datasheet will help to create the complete package of the components in the time of footprint creation.

After reading the datasheet you have to select the pad either thru hole or SMD shown in the above image once you selected the pad stack usage, if it is thru hole you have to mention the size of the drill hole or if it is SMD no need to mention.

Next you have to add the value in the begin layer and end layer (silkscreen top, silkscreen bottom and past mask top, past mask bottom), pad size should be as per the IPC standard. After completing the process you have to save in the project directory. This is the complete process of creating the pad stack for the components.

PCB Layout Design

FOOTPRINT CREATION: After completing the pad stack you have to open the PCB EDITOR for making the complete footprint. Once you double click on the PCB editor you will get the page as shown in the below image.

The above figure show the PCB Editor page

Figure 3:The above figure show the PCB Editor page

Once it will open you have to do the setting. For grid setting setup>grid and also you have choose the unit(mm or mils). after that go to the file>new in that you will get the new folder in that you have to mentioned the Drawing name for example (resistor,capacitor…etc.). In the below drawing type will be available so that you have to select the package symbol or package wizard. After that you have entered the value as per the datasheet. Once you add all the value you will get the finish option. There are two types which you can create the footprint one is manually (package symbol wizard) and another is (package symbol).

Before creating any footprint you have to make sure that the proper path should be given. If you will not provide them then you will not be able to create the footprint. To add the path you have to go to the setup>user preference>library>pad path>psm path. So this is the step to create the complete footprint.

PCB LAYOUT DESIGN: Once you complete the foot print you have to assign the all footprint in the schematic symbol and run the netlist. Once you run the netlist the PCB editor page will open and you have to import the components. There is two option to import the components one is you have to go file>import>logic similarly another option is place>quick place you can use the any option for importing the components.as I said that you can work with mils standard or mm and 95% PCB designer work with mils slandered only. After that you have to take the size of the board for that you have to click on the shape of the any icon which shape you want to create once you clicked at the right side you can see the one folder which contain the option, find, visibility in the option select the board geometry below that select the board outline. And add the board size dimension. Place the board outline and move the drawing origin edge of the board. So next you have to place all the components according to the schematic flow or circuit flow.

Once you place the components, the next option is constraint manager setting this is very important role in the PCB layout side because very thing you have to add here for example (track thickness, via size, grouping, impedance, Daly time..etc ) also when you are working with high speed design the grouping need to make in the constraint setting only.so this will play very important role in the PCB design side.

To add all the values go to constraint setting>electric constraint set. Once you completed the setting another important setting you have do that is stackup in this option you have to do layer stackup for example single layer double layer if the PCB is contain high speed signals for that you have to go for multilayer PCB.once completion of the PCB stackup you have to start the working on board routing, and while routing time you have taken care for the spacing, track width length of the track… etc.

Once you complete the routing. Next step is text alignment. Like adding the company name on the board, the text should be in the silkscreen top (if components on top side of the PCB) and silkscreen bottom (if components in the bottom side of the PCB). After completion of the board you have to generate the Gerber file which you can fabricate the PCB. Then our PCB design and layout is finished.

Gerber Generation

Figure 4:The above figure show the PCB Gerber files

Gerber Generation

When you have finished PCB layout design, the circuit board design is completely finished. But we need to generate the files to Gerber files which are widely accepted by PCB manufacturers.

To generate the gerber file.you have to the manufacture option in that manufacture>artwork click on art work the page will open in that select the all the file click on ok button so in this you will get the all the file like (layer file, NC file, design file..etc) that gerber file you have to send the PCB fabrication person so that using that gerber file he can make the PCB. This is the complete process of making the PCB design from schematic to the gerber file.

In this article, we talked about the main steps about printed circuit board layout services in detail, and hope it is helpful to you to understand PCB design and layout. Please contact us freely if you have any doubts or any requirements for PCB design layout.

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