Where are the microscope photos located on your page
http://research.microsoft.com/en-us/projects/papercutterpcbs ? I could not
spot them.
Jeff
_____
From:
Homebrew_PCBs@yahoogroups.com [mailto:
Homebrew_PCBs@yahoogroups.com]
On Behalf Of MIKE DURKIN
Sent: Friday, June 15, 2012 7:23 PM
To:
Homebrew_PCBs@yahoogroups.comSubject: RE: [Homebrew_PCBs] More Data - Produce Quick & Cheap PCBs with a
CNC paper cutter
I think Silhouette makes the best, low cost hobbyist cutter ... no
cartridges!!!
-----Original Message-----
From: Mike Sinclair
Sent: 15 Jun 2012 21:43:11 GMT
To:
Homebrew_PCBs@yahoogroups.com <mailto:Homebrew_PCBs%40yahoogroups.com>
Subject: [Homebrew_PCBs] More Data - Produce Quick & Cheap PCBs with a CNC
paper cutter
Sorry for the lag.....gainful employment comes first.
Believe me, I am not in any way casting dispersions towards those of you who
might see too many "warts" to this method or would rather deal with paint-on
or vinyl masks and etchant but I believe this way shows a lot of promise, is
quicker than any other way, not messy, fairly low-cost and still has some
more improvements to come. More expensive cutters may do a better job but,
for now, I'm focusing on the ones that target the cost-sensitive
scrapbooking hobby market - it's just too good a tool to pass up for
re-purposing.
As requested, I have uploaded a movie "cutting" a simple PCB.
http://www.youtube.com/watch?v=sQEncvJLrro<
http://www.youtube.com/watch?v=sQEncvJLrro&feature=youtube_gdata>
&feature=youtube_gdata
I also posted some microscope photos on my web page
http://research.microsoft.com/en-us/projects/papercutterpcbs/.<
http://research.microsoft.com/en-us/projects/papercutterpcbs/> So you can
see (or verify for yourself if you have one of these machines) that this
does, indeed, cut through copper clad. I continuity-checked this board and,
before checking and correcting under a microscope, found 100% continuity and
one short that was easily fixed.
Now for some nitty gritty:
I have posted (and will continue to post) the methods and equipment I
use(d). As you can see by the zoomed-out picture of the board, the lines are
somewhat wavy. I'm not sure what causes this or if it can be improved. It
may be due to the mechanical integrity of the cutting head (or lack of) and
drive belt (too much compliance?) or that additional cutter compensation is
required. This problem limits the minimum trace width to something larger
than a well-executed, chemically etched PCB can do.
I used 1/32" 0.5 oz copper clad PCB material available from wwww.digikey.com
(and elsewhere). I will experiment later with the more common 1.0 oz but for
now, the 0.5 oz will cut with a single pass of a not-new blade.
Note that if you get a clean mechanical and electrically isolated etch,
there is no need to "weed" or remove the unwanted copper unless it's for
high voltage or special RF work. Many times, extra ground plane can lower
noise. You just have to remember to ground those islands.
Something I've been working on is front-to-back registration for double
sided PCBs. The cutter I'm using has the ability to lay down registration
marks which can be read by the cutter head. More later....
The knife can leave behind tiny shards of copper that will have to be
removed with fine tweezers under an eye-loupe or cheap microscope. This is
also generally required in the workflow of the desktop milling machine
approach to mechanically etched PCBs. These shards will either cause
immediate shorts or, worse, cause a short later on so you need to look at
the etched PCB under magnification and remove these or correct any obvious
problems with a knife or tweezers. If you still detect a short with an
ohmmeter or an audible continuity tester (best) that you can't see, I use a
~10 uF capacitor charged up to around 30 volts and discharge across the
offending circuit traces that will usually zap the offending shard while
leaving the trace(s) alone. Experiment. I would suggest NOT scrubbing with
ScotchBrite as you do with mill-etched PCBs as it may fold over the raised
copper back into the cut trough, shorting the traces.
Some have asked about the life of the blade. My answer to that is to use 3rd
party 45 degree, carbide blades (the vendor is also listed on my website).
They're about $8.50 ea but are worth it. Consider the same material (single
crystal carbide) that is in the "V" shaped milling bits used in the
expensive mechanical etchers (TTech, LPKF, Accurate360) and spin at
~60,000rpm while the XY direction moves relatively slowly. The tip touches
and is abraded by the glass in the FR-4 substrate in both methods. If you
think about it, those spinning bits have a tangential contact length on the
PCB material many orders of magnitude more than a single pass of the carbide
blade in a CNC paper cutter. I do notice that the fine tip on my blade get
broken off early in the cutting process but the blade still works and lasts
quite long.
Something else I've noticed that may be a positive (but the jury's still
out) is the "cup" formed by the furrowing blade that piles up copper on the
edges of the cut. This cupping around pads to be soldered tends to reduce
solder bridges as the solder wants to pool in the cup.
More to come if there's any interest.
Mike
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