How do novices learn PCB layout

2018-11-23 21:08Writer: qyadminReading:

 

    PCB design Printed circuit board PCB LayoutPrinted circuit board (PCB) layout is as much art as science, and the only way to learn is through experience and practice. Starting with simple projects will help you learn how to use your design software. Each software package is different, but there are a few basic design principles that will apply no matter what. As long as you work slowly and carefully you'll be able to design a clear, logical circuit board that's easy to assemble.

  Instructions

  1 Download and install the PCB design software of your choice. There is a wide range of PCB design software packages available, from high-end commercial products to freeware tools. Some offer a wider range of features than others, but they each function essentially the same way.

  2 Examine your schematic and make a list of all the components in the circuit. Starting from a clear, logical schematic will make your life a lot easier. Your first PCB should be a fairly simple circuit. You'll be learning how to use your software as you lay out your board, so don't get in over your head on the first try.

  3 Split up as much of your list of components as you can into distinct functional groups. Any section of the circuit that performs a distinct task and has its own input and output could be a group. Oscillator circuits, the power supply and filters are all examples of possible functional groups.

  4 Open your software, and follow the instructions in your software's documentation to set the size of the board and the number of layers. Boards can have many different layers of copper traces which are connected together with holes in the board called "vias." Multilayer boards can get very complex, but single layer boards are difficult to lay out without using wire jumpers. For your first simple project, use a two-layer board. Most of the components will go on the top layer, and most of the traces will go on the bottom.

  5 Turn on the "snap to grid" feature in your software, and set the units to imperial measurements (inches) rather than metric. Because of the variety of software it's impossible to give exact instructions for how to turn on "snap to grid," but all PCb design software will have this feature. It locks the mouse onto a grid, helping keep your design clear and organized. The standard unit of measurement in PCB design is a thousandth of an inch, also called a "thou" or a "mil," not to be confused with millimeter ("mm".) Your PCB manufacturer can give you their tolerances for minimum trace width and spacing between traces in thousandths of an inch. You can also set the size of the grid. Start with a grid spacing of 50 thousandths of an inch, and switch to a smaller grid when you need to do more detailed work.

  6 Select your components in the software and place them all on the board. Don't worry about organizing them for now, just get everything on the board.

  7 Split up your components into the functional groups you decided on, and lay out each group separately. Don't worry yet about where on the board each group is, but get the groups themselves well organized. Components connected to each other should be close together, and similar components should be arranged similarly. For example, lay out all diodes and other polarized parts with the cathode facing the same way, and all ICs with the number one pin in the same position. Lay out resistors in neat rows.

  8 Arrange all of your groups logically on the board once the groups themselves are set. Groups which connect to each other should be close by. Keep any analog and digital sections separate from each other. Make sure you also place pads for any off the board components such as potentiometers and switches.

  9 Lay down the circuit traces, following your schematic. Use fairly wide traces, and be sure that you're within your manufacturer's tolerance. There will be some error in manufacturing, so traces that are too close may get shorted together. Only use 45 degree angles for turns, and never 90 degrees. Sharp corners are difficult to manufacture. If you need a right angle, use a pair of 45 degree turns. Your software should have a feature that will automatically keep each turn to 45 degrees. The more current that a trace will carry, the wider it needs to be. Keep your traces as short as possible, especially on high-frequency lines. Follow the link in the Resources section to a calculator that can give you the minimum trace width in mils given the current and copper thickness of the board in ounces per square foot. Use one ounce copper unless your circuit will carry a lot of current. Keep your power and ground traces nice and wide to minimize resistance.

  10 Carefully check your layout against your schematic, following every trace. When you're satisfied, contact your circuit board manufacturer. They'll tell you what files they need, and give you an estimate on cost and turnaround time.

  11 Send your layout files to the manufacturer, and wait for your finished boards to come back.


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