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Old 15th October 2012, 12:15 AM   #11
rsavas is offline rsavas  Canada
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Hi Marc,

Good stuff to read thanks for the links, take care

Rick
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Old 15th October 2012, 12:28 AM   #12
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Quote:
Originally Posted by marce View Post
What 3D PCB CAD packages are there out ther? There are 3D mechanical packages and some PCB software have in built pretty 3D sections where you can view your design in 3D, if you havn't got a real 3d modeling package or an IDF interface. But basic PCB layout is 2D.
Also as this is a DIY site one would expect DIY rates, say $0 per hour, lol
There are free cad packages that do good 3d renderings.

I prefer to do my own layouts as I know how I want a pcb laid out.
Someone else second guessing wouldnt work for me.
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Old 15th October 2012, 12:02 PM   #13
marce is offline marce  United Kingdom
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There is no second guesing in PCB layout, the circuit dictates how a design should be laid out, with the help odf data sheets etc.
Of course not all so called PCB designers achieve this, SMPS's being the main designs that get messed up, but not only by PCB designers, engineers as well.
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Old 15th October 2012, 01:04 PM   #14
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My 2 cents advice:
Try to make all moves / routes decisions based on some technical rationale.
Examples include minimizing; stray capacitance at high impedance nodes, proximity of low level signals to fast high level signals, effects of return currents, reducing inductance for high frequency bypassing, etc
To really do so you will have to know or have some good estimate of what is acceptable, this requires knowing the circuit requirements as well how the layout effects these.
I often see many hours spent in making the circuit "look good", and although this may be nice it is in my opinion incidental.
Analog signal flow and its optimization isn't too hard to implement, whereas getting good low to high frequency current return path (where induced voltages do not effect low level signals) is often more difficult to do.

In the end if you have rationale for why everything was done a certain way and it doesn't work well, you'll figure out why and simply add the lesson learned to your rationale for future work.

Note: The above strategy even works with present high speed digital autorouters, with most of the design time taken to properly set-up design rules and methods to be able to achieve them.


Thanks
-Antonio

Last edited by magnoman; 15th October 2012 at 01:12 PM.
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Old 15th October 2012, 02:44 PM   #15
marce is offline marce  United Kingdom
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Good PCB layout is 75% placement, and that cant be achieved without the schematic open. We use dual screens all the time, as you have to have the schematicopen as it is your guide to the layout.
Autorouters is the biggest misnomer and causes more grief between design and management than any other tool. Interactive use of automatic routing functions is more appropiate (such as BGA break out, length matching,provided you leave enough room when manually routing say your DDR interface). As I said there is no second guesing or rules of thumb these days for layout, it has to be exact, and as said adding the rules (skew groups, routing topography etc) is somthing that has to be done at the outset. Dont forget working out the stack up as a lot of boards are controlled impedancefor high speed stuff.
As Dr Eric Bogatin says, No Myths allowed.
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