This tutorial is to introduce the different methods of routing.  There are two different methods: 1. Interactive 2. Auto Route



For those of you who would like to follow along with my examples, download this zip file.  The following image shows how all of the chips are placed:



All of the thin white lines that you see show connections between chips that will need to be made.  If a surface mount component has a thin white X on a pad, that means that the pad must connect to another plane through the use of a thermal.

The Auto Route feature of Expedition PCB is very powerful.  The example I have above is quite simple, however, the Auto Router will be able to figure out how to connect very complex designs so that you will not have to.  To open up the Auto Route window, click the menu Route -> Auto Route.


The following image is the Auto Route window:




When you first run the auto route all passes will be enabled.  Each pass is designed to do one task to your entire board before performing another specific task.  This time, leave all of the passes enabled so that you will be able to see what the auto router can do.  Click the Route button on the bottom right and watch.  Your board should look something close to the following after running the Auto Router:




As you can see the auto router will not always produce perfect routing.  Several wires can be shortened from what was drawn and there are 2 thermals with connections purelly underneath the chip.  Having no access to a wire is very bad because if that connection needs to be severed because of a mistake in connecting the chip, you will need to remove the chip before you can change the wiring.  If you have access to every single wire at some point, you will not need to remove any chips in order to change the wiring of your board.

Though the connection is correct, the wire between U100 and C1 uses a via to connect to the bottom layer.  That via is not needed and all we will need to do is move the routing around to remove that layer change.  First delete the routing between C1 and U100 and then we can move the connection between U100 and CR1 above C1.  To move routes, simply left-mouse click on the routing and then drag to the new location you wish it to be.  If you are following along, try and get your board to look like the following:


The ability to move already routed connections is the most powerful aspect of the routing tools.  In addition to moving them, you can draw in your own routes, like we will in a second, and the routing tools will attempt to maintain previous connections while accomodating you while you draw in your route.

Click the menu Route -> Interactive -> Plow and your cursor will turn into a pair of crosshairs.  While your cursor looks like crosshairs, you will be able to manually route the connections indicated by the thin white lines mentioned earlier.  Left-mouse click and drag from the through hole on C1 to pin 11 of U100 and watch how the routing moves around your cursor.  When you reach pin 11, the route will automatically complete itself and it should look something like the following:


Now the issue of routing completely under a chip needs to be addressed.  Pin 15 of U100 and pin 16 of U101 both are routed 100% under the chip.  To change that, simply left-mouse click on the thermal and drag it to the outside of the chip like in the following image:


Now lets look at the routing for U101 and J2:


As you can see, the routing between the connector J2 and the chip U101 is mediocre at best.  Sometimes you can make the routing better by simply rotating one of the chips/connectors so that the routes overlap less.  Lets try rotating the connector J2 180 degrees.  In order to do that you will need to get back into place mode, then you will be able to select the connector and rotate it.  Watch as the routes maintain connectivity, though not optimally.


The previous image shows even worse connections, however that was just because the routing tools tried to maintain the connections previously made.  Try deleting all of the connections like in the following:


Now open up the auto routing window again and click only the last routing option like in the following:


The reason for only enabling the last route pass is so that all of your other connections will be maintained.  Using the other routing options will change another other manual routing you have performed.  Click the route button and look at the new connections:


As you can see the new routes are actually worse than before we started moving the connector's orientation, but do not be fooled into thinking that the first orientation of J2 was the better orientation.  By deleting the 4 routes again and by manually routing, you can obtain the following:


Everyone can agree that the above routing is better than the other ways that the connector has been routed to the chip U101.

As fair warning you should always doublecheck the routing of your chips after running the auto router because some times you can draw better connections by hand.

Routing Advice:


Run the auto router first.

Often the auto router will not get the most optimum connections but at least it will give you an idea of how things can be connected


Always double check the auto router.

Some people may find that the auto routing will look good enough for them, however I will warn those people right now that you should always double check the auto router because you should try and make your wires as short as possible, which is not something the auto router is always good at.


Always have access to wire. (I.E. a connection is not completely underneath a chip)

The auto router will make some connections this way and that is very bad.  If you accidently wire two things together that were not supposed to be wired together, you will need to be able to cut the wire.  If the connection is entirely under chips you will need to remove the chip before you can cut the wire, which will more than likely damage the chip in the removal process.


Try to use 45 degree corners, not 90 degree corners

If you imagine the routes on your board as water canals, you would agree that having a 90 degree corner will limit the flow of water that can go through that particular canal.  This same principle applies to electricity so try not to have 90 degree corners in your routing.