Re: gEDA-user: Design changs required to mill PCBs?

[Bob Paddock <bob.paddock@xxxxxxxxx>]

On Sunday 01 October 2006 21:44, Dan McMahill wrote:

> > I had the opportunity to use a LPKF milling
> > machine to make a four layer board yesterday.
> 
> How do you stack things up? 

The two inter-layers are one double sided board.  The solder and component
sides are single layer copper.

> On the machine I used, for a 2 layer board  
> there were 2 pins which provided alignment. 

Yes.

> Plated holes were a pain,  
> you had to insert a small copper tube filled with solder into each hold 
> and then wick out the solder.   
> I found them to be somewhat unreliable. 

The plating is done with a silver paste that is 'sucked' into the holes
with the vacuum of the machine.  Prepreg is then used to 'glue'
the three sheets together.  It was then placed into a heated 15 Ton press.
As I was only helping out, and you had to leave it in the press over night,
I don't know how the end result came out yet.

> I didn't usually change my layouts but I did make one change to the 
> milling flow.  With the tool I had, it would first trace around all of 
> the traces and then go back and mill away all the remaining copper 
> islands.  I often times skipped the step where it milled away the copper 
> islands because it took a long time and wore out bits.

Yes, we were discussing that.  There is a 'mileage' counter on the bit travel.

What I always wonder about with these tools, or similar X/Y machines is why
no one ever optimizes the travel to save time.  Seems like it should be simple
mater of sorting the vectors?  Instead the machine goes at random from
place to place.

I always thought this  rotary table "X/Y" was cool, no ball screws etc.
http://freeandeasy.sourceforge.net/

> > My generally experience with the LPKF machine yesterday
> > was they seem to have their process well thought out, but the software
> > has usability issues which where minor, and
> > any meaningful documentation is nonexistent.
> 
> thats funny.  My memory of the software for the tool I used is about the 
> same.

I wish it was funny.  The industry should not be this way.  Usability
and documentation are important aspects of any project.  Especially
if your paying $50,000+ for the milling equipment.

> Here's a nifty trick. I once was going to do a spinoff of a board where 
> most of it was the same but I was going to totally replace about a 2x3 
> section of the board with a different circuit.  I used the milling 
> machine to make a board that was just the new part and also used the 
> milling machine to cutout the part which was going to be replaced on my 
> existing board.  

I'll keep that in mind, might come in handy.  Still learning the machine so
there have been many "oops" so far.  Mostly due to the lack of documentation.
Like is the Prepreg the  blue goo, or is the through hole plating paste the yellow
goo, or the other way around?  Is the bottle that says nothing but "Irritant" 
in three languages dangerous? 
[Myself I'd not let something like that on the premises without a MSDS sheet.]



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