I have a friend who forgets that the rest of us can’t read his mind. He often starts a conversation without any sort of introduction or context. There have been many times where after several minutes of dialog I have had to hold up my hands and simply ask; “what are you talking about?” Once he backs up and gives me an overview, then I am ready for the details.
Although this had made for some amusing moments, it isn’t nearly so funny when it happens on the job. I must confess though, I have been guilty of doing the same thing when I talk about PCB design. Someone will ask me a question and I will launch into a detailed explanation until I notice that their eyes have glazed over. Once again I’ve made the mistake of assuming that my audience had the background for what I was explaining when they did not.
Because of this I thought that it would be a good idea to create an overview of the PCB development process. You may find it helpful to get the 10,000 foot view of PCB design so that you are better prepared to talk about the details when the need arises.
Nail it All Down with Schematic Capture
Let’s start with the assumption that the need for the printed circuit board has already been determined, and the specifications and requirements have been laid out for its function. We’ll start our overview then from the beginning of the actual circuit design phase of the PCB.
The design engineers will begin to create circuitry for the PCB in a schematic capture tool. By pulling in circuitry from previous schematics or drawing new circuitry, the foundation of the new circuit board will be started. Schematic capture involves placing logical components in the schematic and then connecting the pins of those components together with nets. At this point it is very important to connect with your part vendors to verify that new and existing components are available in the quantities that are needed as well as at a price that will fit within the project budget. Fortunately the best schematic capture tools today have options to connect through the cloud to your part vendors which makes the job of the design engineer much easier.
Next the new circuitry needs to be simulated and analyzed for correct functionality using schematic simulation tools. A lot of time can be saved with testing like this up front instead of waiting until the board is built to conduct a bench test. After the testing is concluded satisfactorily, the completed schematic circuitry will be ready to go into PCB layout.
Using a BOM application while editing your schematic can help you when choosing parts
Create Your Design in Printed Circuit Board Layout
PCB layout is where the actual physical design of the board will take place by taking the logical connectivity from the schematic and applying it to physical models. These models will create metal footprints to solder the leads of the components to on the finished board, and the nets will be connected together using metal strips called traces between the pads.
The first step in PCB layout is to build the component footprint models. Here again it is vital for the layout team to have the same cloud connection to part vendors in their CAD tools. This way they will be able to retrieve the most current part specifications for the components used in the design. In addition to building and verifying component footprints, the physical shape and configuration of the board must also be created. The layout team can pull in the physical board parameters from the mechanical engineering tools, or create the board shape themselves. Finally to complete this pre-layout process, different attributes in the PCB layout CAD tools will be created. These attributes will specify the circuit board layers, the design clearance rules, and other design constraints such as trace widths.
Now it is time for the layout team to design the board. They will place the component footprint models on the board outline shape observing design rules such as component clearances to each other and to the edge of the board. They also have to place these components for best functionality taking in thermal and signal integrity considerations. Once the components are placed, the designer will then connect the nets together by routing metal traces between their connecting pads. When the routing is complete, the design is ready to be checked using the CAD tool’s rule checking system to find design errors. Once any errors are corrected, the design is ready to be sent out for manufacturing.
Cloud connections to your part vendors in your CAD BOM tools can be very helpful
Manufacturing; the Final Step of the PCB Development Process
Several things need to happen to send the design out for manufacturing. Drawings need to be created that tell the manufacturing vendors exactly how to build the board. These drawings specify the thickness of the board, any mounting hardware that has to be attached, and other features that are important for the fabrication and assembly of the board. The layout team will also create additional data files for the manufacturer such as XY coordinate files to specify the location of the physical components that need to be soldered to the board.
Designers in charge of getting the circuit board through to PCB manufacturing will need to keep track of PCB assembly throughout the PCB design process. After all, circuits have nuanced needs for copper and copper foil that need to be understood prior to the point of PCB fabrication. The Gerber files should have all the information on copper that manufacturers need to create the boards that are necessary for your product.
One of the most important data files that will be sent to the manufacturer is the bill of materials, or “BOM”. This document will specify what each component is and what its unique identifying reference designator is on the board. The best CAD tools today often merge the creation of the PCB BOM with the same functionality used by design engineers for part availability, pricing, and logical & physical design specifications. This way the design engineers know exactly what kind of part they are getting and whether or not it is available and how much it costs when they are first creating their initial schematic. This same information is then available all the way through the design cycle for the layout engineers and the manufacturing team.
You can see how having the best PCB design tools makes the difference in how the PCB development process is accomplished. Altium Designer is the PCB design software that we use, partly because of the cloud connection to our part vendors in Active BOM. This tool not only connects us to our vendors giving our design engineers the information they need at their fingertips, but it will also create any style of formatted BOM that our manufacturers need.
If our PCB development process sounds like it would be a good fit for your company, find out more information by talking to an expert at Altium today.
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