PCB layout software

[jorgen.bergfors at idg.se]

>>  Well, why don't you use a dedicated software ? You can still use a
>> manual routing, but you have back-annotation, electrical
>>  rule check, etc... that way, if you have a correct schematic, you're
>> sure to have a correct pcb (electricaly speaking).
>> 

>Shure.

>But one thing is also shure:

>It takes a hell lot of time to set up the system.  You have to define
>object bodys, schematic views, simulation code, pinouts and a footprint
>for EVERY single type of component you use.  Most probably you have to
>define a lot of resistor and capacitor types because of varying wire
>length (instead using wire bridges you often use resistors with long
>wires to get over some pcb trakcks, whenever possible etc.).

>Most software packages I know have lots of 74LSXXX in their librarys,
>and maybe a 741, but most of our analog stuff is not there.

>Not to mention all the debugging afterwards, because of wrong defined
>pinouts etc. etc. I do this all day long in my day job, every cell I
>design gets a schematic body, simulation code (hand coded if necessary)
>etc etc, and very often I get netlist problems at first, because I've
>forgotten something, or mixed it up.

>I estimated that setting up such a system with all the components you will >ever use will take the time of 3-4 complete modules alltogether. I think that >this is much to much for diy (but ok for professional use).

>So Jorgen has some reason for hand layout.

>Maybe I have just evaluated the wrong software package.
>Then I would be greatfull for any hint to a package which doesn't have all
>the disadvantages I've mentioned above.

A couple more reasons for not using PCB layout software:

1. Most software cost money. A general drawing program is useful for so many other things, that you want to have it in any case. But an extra program for PCB layout means extra cost.

2. When I design the board manually, I can do sneaky things like shaving off portions of pads to make room for a trace that would not otherwise fit. The boards I have seen other people do are not as compact and have more wire links than mine, that's a fact.

3. I can design the schematics symbols to look exactly like I want them. I have emulated the style in Elektor magazine, for nostalgic reasons.

4. I can have beautiful full color parts placement diagrams. My parts symbols look almost exactly like the real parts.

5. It is good brain gymnastics to keep the routing in the head. Occasionally I make a mistake, but it is necessary to build a prototype anyway. Board layout errors are usually easy to correct on the prototype.
Nowadays I make a prototype board before i try out the circuit at all. So I can test the board at the same time as I test the circuit itself. If I need to add say an IC, I make a small Veroboard "dongle". Then when everyting works as it should, I correct the board in Corel Draw and etch a new one. This is quick and easy because I print the films on transparencies and use pre-coated boards that give perfect results every time.

/Jorgen