kicad-developers team mailing list archive

["Simon Huwyler" <simon.huwyler@xxxxxxxxxx>]

Hi!

Only a quite short anwer for the moment - maybe I have more time this 
evening...

> a) in my opinion, this should not be tied to layers. Instead it should
> be part of a "net class" in the design rules. This would allow the user
> to keep separate inner/outer constraints per net class. When
> creating/modifying a net class, the user will be able to specify the
> applicable layers (eg. [2-4,7,12]). This approach is also cleaner, since
> all constraints will be in the same dialog window.

I'm not so sure about that, but maybe I just have to think again. The thing 
is that we're NOT talking about NET constraints. Let's suppose I have the 
following netclasses:

Power
50Ohm_Transmission_line
default

Now, in addition to the constraints based on these nets, we must apply 
constraints based on the layers. So, what should we do?


default_inner: 8 mils, applicable to layers 2 and 3
default_outer: 6 mils, applicable to layers 1 and 4

What about Power? Say, we have (unrealistically) set this to 6 mils. What 
now, if we place a power track on layer 3? What is the right constraint?
I still think, it's much more obvious to just say:

We have NET constraints.
We have LAYER constraints.

We must satisfy BOTH of them
The logical consequence is: They must be defined separately.

But as I said: Maybe I just have to think again.

> b) why don't you make a "blueprint" in launchpad for this? I'm no expert
> in how launchpad works, but it looks like the right tool for submitting
> ideas and technical details.

Neither am I! :-) but I try to do it this week-end!


> *) is the benefit of using the smallest clearance and spacing on the outer 
> copper layers
> worth the this trouble in general?  Are your boards really that busy on 
> these outer
> layers?  Seeqstudio is forcing you down a path that you do not have to 
> take.  You can use
> them by using the wider spacing in the inner layers, on all layers.  What 
> are you gaining
> really?  Or is it just one part with narrow pad spacing pushing you down 
> this path?

In fact, the idea rised upon an urge! Yes, it's definitively a HUGE issue. 
Not that I have such a dense design, but I have a fine pitch device! Nothing 
special, just a 0.5mm QFP. But it won't fit into the inner constraints for 
seeedstudio. So I could set the constraints to 8mils and live with the 
errors. And with the fact that I don't use what I pay for.
An what is the trouble? As in C++ vs C: You don't pay for what you don't 
need. Don't care about layer constrants? Leave them at 0. And, after all, 
that's in the tradition of Kicad: Don't care about individual solder paste 
clearance? Just leave it at 0.

> *) next question is, who else needs this?

everyone that places a QFP device on a 4 layer print produced by 
seeedstudio. :-)

> *) the documentation would need to be updated if we were to go down this 
> path.  Otherwise
> we might get bug reports when somebody sees a different spacing on a 
> different layer for
> the same net.

The beauty about my approach would be, that, if you don't acively insert a 
number, nothing changes.
But I agree, this would need an update of the documenation. But I could do 
this, too. And - after all - most additional features need to be documented, 
aren't they? :-) And

To finish this response, I just want to stress again, that this was not just 
an idea after thinking about what may bee a cool feature, but really the 
result of some frustration that my real problem could not be solved 
satisfactionally by the actual version of kicad.

Greets
Simon


-----Ursprüngliche Nachricht----- 
From: Dick Hollenbeck
Sent: Friday, April 26, 2013 3:22 PM
To: kicad-developers@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Kicad-developers] layer based constraints

On 04/26/2013 03:02 AM, Dimitris Lampridis wrote:
> On 04/25/2013 02:22 AM, Simon Huwyler wrote:
> > As some PCB manufacturers (i.e. seeedstudio) have different clearance-
> > an width constraints for outer- and inner layer, I had the idea to teach
> > Kicad to manage “layer based” constraints.
>  >
> > Ok, for the moment, I chatted enough. What do you think about it?
>
> Hi Simon,
>
> We use Kicad at work and we would like to get involved in the
> development process, not only as a means to return something to this
> excellent community, but also to actively improve the tools we are using.
>
> To this end, I've also just subscribed to this list (hi everyone!), and
> I'm keeping a list of features/fixes that I would like to start
> proposing for implementation. I'm responding to your idea because it was
> already on our list.
>
> Now, back to your suggestion, here's my two pennies' worth:
>
> a) in my opinion, this should not be tied to layers. Instead it should
> be part of a "net class" in the design rules. This would allow the user
> to keep separate inner/outer constraints per net class. When
> creating/modifying a net class, the user will be able to specify the
> applicable layers (eg. [2-4,7,12]). This approach is also cleaner, since
> all constraints will be in the same dialog window.
>
> b) why don't you make a "blueprint" in launchpad for this? I'm no expert
> in how launchpad works, but it looks like the right tool for submitting
> ideas and technical details.
>
> Cheers,
> Dimitris


Hi Simon,

I was thinking what Dimitris is thinking, before I read his post.  Clearly 
you took the
path that allowed you to get it working.  And usually that is the best path. 
But in this
case I think we can all see a certain discomfort in blurring what the layer 
setup dialog
is for.

The first question I have is this:

*) is the benefit of using the smallest clearance and spacing on the outer 
copper layers
worth the this trouble in general?  Are your boards really that busy on 
these outer
layers?  Seeqstudio is forcing you down a path that you do not have to take. 
You can use
them by using the wider spacing in the inner layers, on all layers.  What 
are you gaining
really?  Or is it just one part with narrow pad spacing pushing you down 
this path?


*) next question is, who else needs this?


*) the documentation would need to be updated if we were to go down this 
path.  Otherwise
we might get bug reports when somebody sees a different spacing on a 
different layer for
the same net.  Of course this happens on spin 2 of the board, after you have 
forgotten
about the layer specific override and cannot figure out why that layer is 
different.


As you can see, I am not taking a stand on need, only trying to see if it 
exists.


Dick



















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