My Hobbies - Circad Course - Lesson 7
Pcb Layout Creation

Parabola

Barra Colore


Once you've imported the components in TUTOR1.PCB, you'll move them near the work area center, using GC, avoiding components too near the one to the other.

Now, with NR create the pcb ratnest, to see the real wirings between components. The ratnest lines will be displayed using symbol lines, placed into Ratnest layer. With NU you can remove the ratnest lines.

These lines are very useful because they permit to see how is better to place the pcb components, to avoid or to reduce, wirings cross. Using GC+R you can move and rotate the components, and with GT you can move the text label CONN1, to have the result showed in the figure above.

With NS you can hilight the wirings pads to known the other points of the pcb is connected to. If you use the command over a partially wired track, you'll can view che remaining part of the track that must be wired.

When you use the option over a track completly and correctly wired, you'll see displayed, in the status line, the track name. Else, if some points of the track are not wired, then it will appears the message "Signal routing is not complete". If you wire togheter two or more pads that didn't get wired, with NS you'll obtain the message "Two or more signals are cross-linked".

The command NS check if the tracks wirings are been done correctly, comparing the netlist data with the pcb wirings. Then, it's important that the netlist electric scheme is correct. Else you should make a bad pcb with not well wired, or missed, tracks.

The autorouter, available in the Dos Circad versions, is not included in the Windows evaluation version. If you need it you must buy Circad.

Then, we have to manually place the circuit tracks one by one, using the "ratnest" line to check the wirings!

This is one of the removed features of Windows Circad version, like Gerber export.

Every time a track is entirely placed, with PL, use one more time NR to remove the ratnest of it. If a track is partially placed, using NR you'll also remove the ratnest for the tracks parts that are not been wired. Sometimes, it will appears that all the tracks are been placed, but this is not true. You can see the real situation using NS over a node of a partially wired track. The command, in fact, will redisplay the ratnest indication for the nodes not connected.

During the track placing phase, with NS, or at the end of this with N+, you can check if a track is too near to another electrical part of the circuit. The clearance distance between tracks, pads and other electrical elements must follow the parameters showed with SC. In the image above you can see a track that is too near to the pad C of Q1 (error "Spacing/clearance violation") and the same track connected, only for one single mils, at the same pad (error "Two or more signals are cross-linked").

This is the final result, manually obtained placing the tracks with the option PL, using a line thickness of 40 mils. There are also some symbol elements, like the LED label or the drill pcb reference. With GT"+R some labels are also been rotated. Also, with PL, using the Top Silk symbol layer (component side silk) a border are been added around the pcb.

At least, with PT, in the Bottom Copper (solder layer) signal layer are been placed some labels to identify the pads of CONN1. These label are mirrored because you look at them thru the component layer, but they will be look right once you've printed the master film and maked the fotogravure, observing the pcb from the solder layer.



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