Basic Routing

Routing is also known as “tracking”. Routing is the process of laying down tracks to connect components on your board. An electrical connection between two or more pads is known as a “net”.

• Keep nets as short as possible. The longer your total track length, the greater it’s resistance, capacitance and inductance. All of which can be undesirable factors.

• Tracks should only have angles of 45 degrees. Avoid the use of right angles, and under no circumstances use an angle greater than 90 degrees. This is important to give a professional and neat appearance to your board. PCB packages will have a mode to enforce 45 degree movements, make use of it. There should never be a need to turn it off. Contrary to popular belief, sharp right angle corners on tracks don’t produce measurable EMI or other problems. The reasons to avoid right angles are much simpler - it just doesn’t look good, and it may have some manufacturing implications.

• Forget nice rounded track corners, they are harder and slower to place and have no real advantage.Stick to 45 degree increments. Rounded track bends belong to the pre-CAD taped artwork era. 

• “Snake” your tracks around the board, don’t just go “point to point”. Point to point tracking may look more efficient to a beginner at first, but there are a few reasons you shouldn’t use it. The first is that it’s ugly, always an important factor in PCB design! The second is that it is not very space efficient when you want to run more tracks on other layers.

• Enable your Electrical grid, which is sometimes referred to as a “snap to center” or “snap to nearest” option. Let the software find the centers of pads and ends of tracks automatically for you. This is great for when you have pads and tracks which aren’t lined up to your current snap grid. If you don’t have these options enabled then you may have to keep reducing your snap grid until you find one that fits. Far more trouble than it’s worth. There is almost never a reason to have these options disabled.

• Always take your track to the center of the pad, don’t make your track and pad “just touch”. There are few reasons for this. The first is that it’s sloppy and unprofessional. The second is that your program may not think that the track is making electrical connection to the pad. Proper use of a snap grid and electrical grid will avoid problems here.

• Use a single track, not multiple tracks tacked together end to end. It may make no difference to the look of your final board, but it can be a pain for future editing. Often you’ll have to extend a track a bit. In this case it’s best to delete the old one and place a new one. It may take a few extra seconds, but it’s worth it. People looking at your finished board may not know, but YOU’LL know! It’s the little touches like this that set good PCB designers apart.

• Make sure your tracks go right through the exact center of pads and components, and not off to one side. Use of the correct snap grid will ensure that you get this right every time. If your track doesn’t go through the exact center then you are using the wrong snap grid. Why do you need to do this? It makes your board neater and more symmetrical, and it gives you the most clearance.

• Only take one track between 100 thou pads unless absolutely necessary. Only on large and very dense designs should you consider two tracks between pads. Three tracks between pads is not unheard of, but we are talking seriously fine tolerances here.

• For high currents, use multiple vias when going between layers. This will reduce your track impedance and improve the reliability. This is a general rule whenever you need to decrease the impedance of your track or power plane.

• Don’t “drag” tracks to angles other than 45 degrees

•  “Neck down” between pads where possible. Eg, a 10 thou track through two 60 thou pads gives a generous 15 thou clearance between track and pad.

• If your power and ground tracks are deemed to be critical, then lay them down first. Also, make your power tracks as BIG as possible.

•  Keep power and ground tracks running in close proximity to each other if possible, don’t send them in opposite directions around the board. This lowers the loop inductance of your power system, and allows for effective bypassing.

• Keep things symmetrical. Symmetry in tracking and component placement is really nice from a professional aesthetics point of view.

• Don’t leave any unconnected copper fills (also called “dead copper”), ground them or take them out.

• If you are laying out a non-plated through double sided board, then there are some additional things to watch out for. Non-plate through holes require you to solder a link through the board on both the top and bottom layer.

• Do not place vias under components. Once the component is soldered in place you won’t be able to access the joint to solder a feed through. The solder joint for the feed through can also interfere with the component.

• Try and use through hole component legs to connect top tracks to bottom tracks. This minimizes the number of vias. Remember that each via adds two solder joints to your board. 

• The more solder joints you have, the less reliable your board becomes. Not to mention that that it takes a lot longer to assemble.