Re: gEDA-user: PCB paste layer, revisited.

[Dave N6NZ <n6nz@xxxxxxxx>]

Chris Albertson wrote:
> I think the "correct" way to do this is for the file to hold information 
> that exactly describes the solder paste.  You need the three dimensional 
> shape.  Plan view and thickness.
> 
> How to cut a stencil so as to get the above is not part of the layout 
> but part of the "process".
> 
> I see two steps.  (1) create the solder past specs based whatever 
> information may be available and helpful The abount oand shape of the 
> paste depends on the part and the
> size of the pad.  A user could specify some rules but reasonable default 
> rules should be built in.  Just using the pad size is a rather crude 
> rules but a decent start.

No, actually, starting with the pad size sucks, big time.  It's too crude.

>  (2) The sticil is made based on the shape and 
> volume of the paste.  There should be rules that translate past 
> size/volume to stencil shape and again the user can change some parameters

Sure.  I see where you are going, and it makes sense.  In fact, it would 
be very useful for driving the prototyping/low-volume processes that do 
not use a stencil, but instead use a syringe on an X/Y mechanism that 
deposits a controlled volume of solder at a specific coordinate.

What you are talking about, though, is a whole new output path and new 
tool chain.  pcb -> paste spec file -> "your tool here" -> "magic file"

Where "magic file" might be a gerber for a stencil, a vector file to cut 
a stencil, X/Y/volume to drive a paste application robot.

Which part of this system are you willing to write?  Which part can you 
test?

You have given me an idea for an alternate kludge, also.  I might simply 
export the pad geometry into a text file that I can post-process with a 
crude pattern matching system.  Dumb, but maybe quick.  Maybe too dumb 
-- need to think about it.

In any case, it's time to get down to brass tacks.  Who is willing to 
apply coding effort to the problem of getting better paste output?  I 
really need input from someone who understands the element data structures.

-dave


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