Homebrew PCBs

On 6/20/2014 5:17 AM, Clement Quinson clement.quinson@... 
[Homebrew_PCBs] wrote:
> Well as I said, I am very interested by that kind of equipment, and 
> will meet in approx one week those guys during a OSHW conference. 
> Hopefully we'll chat, and I would like to contribute to their project, 
> by reproducing their experiments, and also helping with documentation.
> That could be a neat thing to push forward an efficient, "unified" 
> OSHW project like that !
> C
Hello--

I recall seeing a description of a "direct laser projection" PC-board 
exposure system that
uses an inexpensive ($300) laser engraver. You cover the copperclad 
board with several
coats of flat-black spray paint and then use the engraver to vaporize 
the pain and expose the
copperclad for etching.

I couldn't find the exact reference, but here's one that's similar:

http://www.youtube.com/watch?v=OTGZcY7WyYI


While we're on the topic, I wonder whether anyone has experimented
with using a 3D printer to deposit plastic resist on copperclad? I did
get a few comments, but to my knowledge,  so far no one has tried it.
You'll find my e-mail description of the process appended below.

73--

Brad  AA1IP

*****************
Hello--

I'm posting John's thoughtful comments (which I very much appreciate) below
and inserting my responses. My original posting is appended.


On 5/6/2014 11:39 AM, John D'Ausilio wrote:
> Responses inline (since there are so many questions
>
>
> Questions and caveats:
>
> --Component pads' shapes may not translate well from Gerber code--
> i.e., several overlapping passes would be needed to make large pads.
> In general, printers which extrude ABS or PLA use a tip with a 0.4mm
> hole. The resulting "noodle" is generally around 0.5mm wide and
> roughly circular in cross-section.

Hello, John and the groups--

Depending on the "squishdown" factor, a 0.5 mm wide noodle might produce
a 0.020 inch wide trace. If the noodle doesn't become a semicircle upon
contact with the copperclad surface, the trace width would be narrower.
> --Extruded plastic may not adhere well to copper.
>
> --Unetched copperclad board may need to be heated for best trace 
> adhesion.
> Getting the plastic to adhere to the build platform is challenging.
> ABS is usually printed on a heated metal plate covered with Kapton, or
> lately on a heated glass plate sprayed with cheap hairspray.
> I can try clipping some copperclad to my build plate and see what 
> happens ..
Copper's higher thermal conductivity might be our friend. Imagine
using a couple of Dale RH-50 chassis-mounted wirewound resistors
clipped to opposite sides on top of the copperclad board. The resistors
could provide auxiliary heating.

> --Dimensional issues: how accurately can a 3-D printer locate coordinates
> at distant extents of a large layout?
> Machines with orthogonal mechanics have the same accuracy at all
> points on the build plate. Machines with delta mechanics lose
> resolution towards the edges. The vast majority of hobbyist printers
> are orthogonal.
Excellent!
>> --What's the narrowest (or widest) trace that can be extruded?
>>
>> For general object printing the goal is to squash the first layer into
>> the build plate, reducing it's diameter and spreading it out.
>> Realistically you could probably achieve around 0.55 or so with a .4mm
>> nozzle
Converting 0.55 mm to inches would produce traces a whisker under .022 
inches in width.
> --How accurate can the copperclad board be leveled on the printing stage?
>
> We already level our platforms, assuming the copperclad is
> dimensionally stable over 20C-100C range (we usually heat to 100C for
> ABS) then leveling shouldn't present a problem.
One online source lists "...G-10 and FR-4 are rated at 285 degree F 
continuous operating
temperature..." but I didn't locate a value for horizontal coefficient 
of expansion.
>> --How well do various types of  extruded plastic resist commonly-used 
>> copper
>> etching solutions?
>>
> That's the $1000 question .. almost all printers in hobbyist use will
> print ABS or Polylactic Acid (PLA). I don't etch boards so I have no
> chemicals here, but I'd be happy to send you some samples.
The "go to" source for chemical resistance is apparently Cole-Parmer:

http://www.coleparmer.com/Chemical-Resistance?referred_id=11033&mkwid=sJFDnHw4J&pcrid=12430988319&kw=%2Bchemical%20%2Bresistance%20chart&mt=b&pdv=c&gclid=CLC49vnUl74CFe99OgodbF4A_w 


...Or TinyURL...

*http://tinyurl.com/jwnnbk2

Commonly-used etchants include ferric chloride, hydrochloric acid, 
ammonium persulfate
and vinegar.

ABS resistance:

Vinegar    A-- Excellent
*
Ferric Chloride A-- Excellent

Hydrochloric Acid 20% A-Excellent

Ammonium Persulfate A^2 -Excellent (2 = satisfactory to +120 F (+48 C)

I couldn't locate a reference for polylactic acid's chemical resistance,
but I'm pressed for time.


-Could you use different colored extrusion plastics to mark, say, power 
and ground traces?
> Not easily .. it's very challenging to print more than one color at
> the same height (you would need more than one nozzle, and a way to
> move them away from the piece so the unused one didn't plow into
> existing plastic)
Okay-- variously-colored resist would be a bonus.
> --Could you leave the extruded plastic traces in place as a solder mask
> and clean the plastic away only from component pads requiring soldering?
> All of our plastics melt at 220C or less .. not compatible with 
> soldering temps.
That might not be a problem if the plastic melts short of contaminating 
the solder
joint. Careful removal (mechanical abrasion?)  of the resist on the pads 
would
be necessary.

Further comments from all are welcome!


73--
Brad  AA1IP
********************************

Original posting follows:

Excuse the somewhat off-topic nature of this posting, but
I'm picturing the Glowbug application (i.e., custom component-terminal
boards) along with QRP and general circuit-design applications.

Has anyone in the group used a 3-D printer to create one-off PC boards?
Consider this as the inverse process of removing copper via a
CNC milling machine.

***********
Here's how the process might work; unfortunately, I don't own a
3-D printer, and thus the following description is theoretical and
riddled with caveats.

1.) Create a PC-board layout using any of several available tools.

2.) Translate the layout program's output into an X versus Y format
understood by the 3-D printer.

3.) Extrude plastic to "draw" the layout's traces on a sheet of copperclad
board.

4.) Etch the board.

5.) Remove the plastic traces and drill holes in pads to accommodate
through-hole components' leads; tin-plate the board if desired.
******



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