Author Topic: PCB CNC Milling/Isolation Routing  (Read 21697 times)

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Offline jaxbird

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PCB CNC Milling/Isolation Routing
« on: January 25, 2014, 03:02:23 pm »
Hello, I believe there must be quite a few members here who use this method for prototype PCB manufacturing.

I have been using this method myself for quite some time, I find it much preferable to traditional etching and manual drilling.

It would be nice to hear about others experience and setup.

First I wonder what software you are using?

I use a combination, Eagle PCB for schematic and layout, then the PCB-GCODE plug-in for Eagle to generate gcode files for the routing and drilling. And finally I control my CNC machine from an old stand alone box running Linux CNC (EMC2).

This combination is affordable (only Eagle might require a licence) and it works, but it does leave room for improvements.

IMO the weakest link is the PCB-GCODE plugin, while it does get the job done, it could be improved.

Anyway, would be nice to have a discussion on the pros and cons on the various solutions out there.

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Offline jaxbird

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Re: PCB CNC Milling/Isolation Routing
« Reply #1 on: January 26, 2014, 06:45:20 pm »
Based on the response, I might have overestimated the number of members using this approach :) Or maybe the subject just needs a bit more time and exposure.

Anyway, I'd also be interested in discussing preferred choice of tools and bits. For isolation, I prefer using flat V shaped ones, they are fairly cheap and come in many different angles (10 to 90 degrees), but I prefer something between 20 and 45 depending on how fine pitch I need.

Picture:




And here a test (QFP64 0.5mm pitch with a few 805 and 603), this is probably the smallest I can do with my latest machine:




Traces are 10 mil and spacing probably around 6-8 mil. (Normally I would remove more copper to make the soldering easier)


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Offline WarSim

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PCB CNC Milling/Isolation Routing
« Reply #2 on: January 26, 2014, 07:46:23 pm »
I also use isolation milling for my home lab. 
Which I am in the process of moving so my responses will be seldom. 
I started with the 90deg then the 60deg but I quickly realized that almost everything I need finer that 0.2mm isolation I tend to have a board house make it.  For this reason I have switched to .25mm and .5mm end mills.  With the 90deg I was getting .05mm variance and with the 60deg I was getting .03mm variance.  About .002mm is runout, supported by the fact my .25mm bit cuts .252mm isolation. 

I use Eagle export straight to my layout editor for my mill.  One thing I don't like is eagle exports metric board layouts in imperial.  If there is a way to work entirely in metric I haven't found it yet. 




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Offline Skimask

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Re: PCB CNC Milling/Isolation Routing
« Reply #3 on: January 26, 2014, 07:47:08 pm »
Seeing that tight routing about makes me want to break open my Sable2015, buy some decent bits, and give it another shot.
Bought m Sable2015 a few years ago.  Ended up making a vacuum table out of MDF, drilled a bunch of holes thru it, milled it flat, using a shop vac for vac source.  Z axis felt pretty good but never could decide what bits I should be using to get good cuts.
Using the same software setup you are, Eagle, PCB-Gcode plug in, LinuxEMC2.
Great more things to play with...
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

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Offline djsb

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Re: PCB CNC Milling/Isolation Routing
« Reply #4 on: January 26, 2014, 10:51:35 pm »
We use an LPKF Protomat S62 at work. Very good for prototyping simple 1 or 2 layer boards for our students. Wouldn't use it for a final commercial product though. That's not an issue in a university environment.

David.
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Offline WarSim

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PCB CNC Milling/Isolation Routing
« Reply #5 on: January 27, 2014, 04:53:30 am »
I guess I should have mentioned.  I am currently using a MITS Eleven Lab.  When I bought MITS understood they had competition and gave me a deal.  Back then lPFK thought price matching was beneath them.  I have no idea if LPFK has smartened up over the years, I have never had a reason to consider them again. 


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Offline Ealin

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Re: PCB CNC Milling/Isolation Routing
« Reply #6 on: January 27, 2014, 05:20:11 am »
Apologies in advance for a long post, I’m simply unable to write short comments.  :P

I have been doing isolation milling for about a year. Results have been reasonable successful, both in making single and double sided PCB’s.

End mills:
Depending on the pitch I need to achieve, I usually use 0.3mm or 0.2 endmills. 
The reason for not always using the smallest possible bit, is simply that I can reach higher feed rates with a 0.3mm.
Sadly I tend to break the 0.2 mm endmills, this gets rather annoying, not to mention expensive.


I haven’t tried the V shape bits yet. I have no idea what angle is or tip size is needed.
I have an (probably misplaced) idea that steeper angles are better, and tip size around 0.1 mm would be correct for 0.5 pitch IC’s ?
My hope is that these bits are sturdier than the end mills?
For via drilling, I find myself using a 0.5mm endmill, connectors are drilled using 0.8-1.0mm drill bits.

I have been experimenting with a modified a 3mm drill shaped  into a V type tool. This works quite well, but also tends to break from time to them. However that isn’t a problem, as I can just grind it into shape again.


Does anyone know a good place to buy 3-3.125 mm shank 0.2 endmills/vbits for pcbmilling?
Preferably somewhere within the EU as I really don’t fancy paying silly import taxes from the US or China.
Any recommendations are very welcome.

CNC Setup.
I actually have two CNC mills, both of them diy types. 
The first one is an Aluminum gantry on steel frame. This has a working area of 80cmx60cm.


The other one (just finished building) is much smaller, made specifically to do light work engraving. 


I aim to use this smaller CNC for PCB milling. I haven’t really tested it yet, but I have high hopes.  ::)
Everything on this machine is made with the large CNC mill, this ofc includes the motor control PCB.
Both cnc machines cost around 500€ to make, and ofc a lot of time. On that note I better mention that most aluminum parts I cast myself in a backyard foundry.

Tool chain.
So far I have been using Eagle along with PCB-Gcode. Machine control is handled by MACH3.
I have been looking at Coppercam, wanting to try it out at some point.

Quality.
On the large CNC machine I can manage 0.65 pitch, and 0.3 traces without too many issues. However migrating to 0.5mm pitch is probably pushing it atm.
I’m hoping that my new engraver will be able to do this.
While precision isn’t too much of at issue, milling quality isn’t quite as good as I hoped. 
I tend to get a lot of burring; this is only a minor annoyance, and goes away with some light sanding.

After sanding they look excatly like the picture posted by OP.
Nearly everything I do is SMD components, so far it hasen't let me down.
Timeframe from layout is done, until I have a finished board, is usually anywhere from 20 to 60 minutes. This includes light surface sanding.
Quality is ofc nowhere near manufacture grade. You obviously end up without soldermask or silkscreen, but for a hobbyist like me it’s good enough. 

Feeds&Speeds.
I usually run the spindle as fast as it will go, that would be around 20000 rpm.
With 0.3 endmills I seem to avoid breakage at 150 mm/min with 0.15 milling depth.
I haven’t pushed it further In regard to speed, as I’m happy with both speed and result.

Regards Ealin.
« Last Edit: January 28, 2014, 06:51:32 am by Ealin »
 

Offline djsb

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Re: PCB CNC Milling/Isolation Routing
« Reply #7 on: January 27, 2014, 06:28:16 am »
Hi,
Mega electronics in the UK can supply router bits sourced from india (made by a subsiduary of a swiss company-http://indsphinx.com/). They may work for you but I've found that the Genine LPKF universal 0.2mm bits work better on our machine and last longer. This may have something to do with the angle of the V shape of the router tip. The bit is spun at 60000 RPM (100000 on the newer models I think).
Also Midwest circuit technology (http://mctinfo.net/router-bitscat_20.html) in the USA is another source.

HTH.

David
David
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Offline jaxbird

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Re: PCB CNC Milling/Isolation Routing
« Reply #8 on: January 27, 2014, 06:40:21 pm »
When you are machining fiberglass panels (including PCB materials), there is a waste product (the "chaff") that is created.  This material is very fine (especially when you are milling), and is known to cause lung cancer. 
...

It is indeed a good warning  :-+ some nasty particles are generated when machining these materials.

Electronics is an occupation/hobby where many precautions must be taken when dealing with dangers like electrocution, carcinogens and various poisonous materials.

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Offline jaxbird

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Re: PCB CNC Milling/Isolation Routing
« Reply #9 on: January 27, 2014, 06:56:58 pm »
I have a few 0.5mm milling bits, but while they do a nice job, they do seem very fragile. I'm afraid they are going to break by just looking at them :)

In my experience, the disadvantage of V shaped bits is that the board must be very level and flat. I use a depth of around 50-80um for good results.

A vacuum table would be nice, but to keep my PCBs in place I just use a piece of wood secured to the bed that I plane occasionally to make sure it's level, just a few 10th of a mm each time.

And to secure the PCB I simply use some thin double sided tape.

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Offline poorchava

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Re: PCB CNC Milling/Isolation Routing
« Reply #10 on: January 27, 2014, 07:39:50 pm »
When I was very much into CNC machining, I simply covered the machine with a plastic hood (made of shopping bags...) that was hooked to a shop vacuum cleaner. Worked well enough.

Btw, the problem with V-bits is that you need pcb surface to be extremely flat with X-Y plane or otherwise you will end up with varying slot widths and possible breaks in traces. On the other hand straight endmills under 0.8mm or so are very very brittle (assuming you will use carbide type, HSS ones get dull very quickly against fiberglass laminate)
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Offline djsb

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Re: PCB CNC Milling/Isolation Routing
« Reply #11 on: January 27, 2014, 11:41:29 pm »
Hi Guys,

You probably already know this, but because it has to do with safety and there are young players that read this blog, I'm going to mention this anyway.

When you are machining fiberglass panels (including PCB materials), there is a waste product (the "chaff") that is created.  This material is very fine (especially when you are milling), and is known to cause lung cancer.  Here in the USA, our government's EPA has declared this as a hazardous waste, and it must be handled as such.  You need to have a vacuum system attached to your mill/drill machine-- and to meet EPA regulations, the vacuum must be one that was originally designed for an HEPA filter [i.e., *not* "retrofitted"].  The waste must be clearly labeled as "Hazardous Waste", and must be disposed of properly (usually through a company that does this for a living).

Even if you don't live in the USA and have no EPA-like government agency to contend with, that is still no excuse, and you should still deal with this hazardous waste properly.  If you just throw it in the trash, there are many people that could [unknowingly] be exposed to this hazard, and that is just the wrong thing to do.

Honestly, you should wear at least a dust mask while working around the machine while it is in operation, and later when you are cleaning the room with your HEPA vacuum.  I would also recommend rubber gloves and a "throw away" suit if there was a large spill that you are dealing with.

I wouldn't want you [or someone else exposed to your hazardous waste] to get lung cancer 10 years later because you failed to take precautions today, so please be extra careful working with your PCB mill/drill machine.

--Ken

The LPKF machine we use has a vacuum extraction system and it's placed underneath a large forced air extractor hood. Even then I wear an FFP3 rated dust mask, keep the window open in the room and only visit the machine occasionally to keep an eye on it. I still prefer it to the chemical etching tank we've been using upto now.

David.
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Offline WarSim

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PCB CNC Milling/Isolation Routing
« Reply #12 on: January 28, 2014, 01:34:45 am »
I personally have never broken an end mill 0.25mm nor 0.5mm.  Only bit I have ever broken was a .4mm drill and that wasn't during milling.  No idea why others are having issues.  I'll offer the fact that I have profiles for each mill entered into software.  Calculating RPM and process speed for each mill and depth range.  My bits are nothing special just 2 flute cutters. 

So no snorting lines of epoxy dust, check. 



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Offline Rerouter

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Re: PCB CNC Milling/Isolation Routing
« Reply #13 on: January 28, 2014, 07:01:34 am »
If you wanted to do that a line-scanner type laser range finder would probably be best (shoots the beam at an angle and calculates based upon how far up the pixel array cell the return beam hits, this is then averaged to find a quite precise distance depending on the beam angle,)
 

Offline Ealin

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Re: PCB CNC Milling/Isolation Routing
« Reply #14 on: January 28, 2014, 07:51:53 am »
I wonder if there is some kind of way to measure [while the machine is operating] the distance from the spindle to the PCB-- some kind of sensor, or...?  If you had this and it was sufficiently accurate [and fast, and high enough resolution], then your controller could compensate by controlling the height of the spindle.  I'm not a mechanical engineer, does anyone have any idea how this might be done?

hmmm interesting idea. Basically a feedback system that measures the elevation of the PCB.
A couple of nutty ideas spring to mind but none very useful.
« Last Edit: April 05, 2014, 05:48:10 am by Ealin »
 

Offline johansen

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Re: PCB CNC Milling/Isolation Routing
« Reply #15 on: January 28, 2014, 08:40:40 am »
I usually run the spindle as fast as it will go, that would be around 20000 rpm.
With 0.3 endmills I seem to avoid breakage at 150 mm/min with 0.15 milling depth.
I haven’t pushed it further In regard to speed, as I’m happy with both speed and result.

Regards Ealin.
you're going too fast it appears.
also, the photos you post seem to show a lot of chatter or something, the rpm you're dealing with three times the speed i'm running (6700)
here's a photo after assembly and light sanding.
http://johansense.com/bulk/boost/4phase_v1.JPG
http://johansense.com/bulk/crackpotidea_scalableboost_2.JPG

I'm using a diy spade bit.
Take a broken carbide end mill and grind two flats in it, tapered to a point at the center of rotation (this is the critical part)

then grind two flats at an 80 degree angle relative to the others (in the correct direction), such that you have a tapered parallogram coming to a point at the center of rotation. This gets you two flute engraving bit with relief cuts.
You will need a diamond file to get it razor sharp and a fine grit stone on a bench grinder running at rather high velocity to grind the carbide to the rough geometry (8 inch at 3500 rpm is what i use) Making it from a HSS drill bit should be easy.

the tip angle is relative, i think i've got about 60 degrees on mine.
cutting depth is critical.
the best i can do is cutting 15 mill isolation, simply because the runout on my diy cutting tool is on the order of .01"
« Last Edit: January 28, 2014, 08:43:20 am by johansen »
 

Offline jaxbird

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Re: PCB CNC Milling/Isolation Routing
« Reply #16 on: February 01, 2014, 02:29:37 am »
The LPKF machine we use has a vacuum extraction system and it's placed underneath a large forced air extractor hood. Even then I wear an FFP3 rated dust mask, keep the window open in the room and only visit the machine occasionally to keep an eye on it. I still prefer it to the chemical etching tank we've been using upto now.

David.

The LPKF machines are really nice, but also expensive. I used to etch quite a few boards, but it really takes a lot of effort, care and attention to get consistently good results. Plus I really hate doing manual drilling for through hole stuff.

I much prefer milling, it does not take much effort to get consistent results once you know the limitations and got everything dialed in.

I run mine in a box with a door and an acrylic window, then I have a vacuum attached that goes through first a cyclone, to collect the large shavings and dust (I also use it for acrylic and wood) then 2 levels of filtering.

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Offline jaxbird

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Re: PCB CNC Milling/Isolation Routing
« Reply #17 on: February 01, 2014, 02:48:47 am »
here's a photo after assembly and light sanding.
http://johansense.com/bulk/boost/4phase_v1.JPG
http://johansense.com/bulk/crackpotidea_scalableboost_2.JPG

...

Nice results with DIY bits  :-+ I might have a go at your method to resharpen some of my dull ones (sometimes it's really hard to tell as it's only something like 100um of the tip that is used)

Agree on the spindle RPM. In my experience, it takes some experimenting to find a good combination of RPM and machine speed. With some experience it's possible to just listen to the sound and know if it's doing well.

With dull bits, I have to use light wet sanding, but mostly I can get away with the rough side of a kitchen sponge, good for cleaning the surface anyway.

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Offline jaxbird

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Re: PCB CNC Milling/Isolation Routing
« Reply #18 on: February 01, 2014, 03:10:11 am »
One of the things lacking in the Eagle/PCB-GCode combinations is an easy way to make stencils. While it is possible to do it by exporting - manipulating - re-importing bitmaps, it is a bit tedious. So I spent a few evenings building a tool that allows easy generation of G-Code for stencil milling, still work in progress, but currently it looks something like this:




I am considering just writing a complete tool for all the milling and drilling operations, as I feel there is some room for improvement over the pcb-gcode plugin, especially things like optimization of movements and setup options etc. (but hey, not a complaint, it's a free tool and it does get the job done most of the time :))

« Last Edit: February 01, 2014, 03:20:49 am by jaxbird »
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Offline ConKbot

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Re: PCB CNC Milling/Isolation Routing
« Reply #19 on: February 01, 2014, 03:19:57 am »
-- I wonder if there is some kind of way to measure [while the machine is operating] the distance from the spindle to the PCB-- some kind of sensor, or...?  If you had this and it was sufficiently accurate [and fast, and high enough resolution], then your controller could compensate by controlling the height of the spindle.  I'm not a mechanical engineer, does anyone have any idea how this might be done?


http://www.rolanddga.com/products/engravers/egx20/features.asp

They have a magnet on the shoe and a hall effect sensor on the z axis carriage.  I dont know what kind of response it has, but it does pretty consistent work on 1/2 oz copper boards with a carbide V bit.  Not ideal and the machine can certainly be improved on. But the concept is good. 
 

Offline jaxbird

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Re: PCB CNC Milling/Isolation Routing
« Reply #20 on: February 01, 2014, 03:41:53 am »

http://www.rolanddga.com/products/engravers/egx20/features.asp

They have a magnet on the shoe and a hall effect sensor on the z axis carriage.  I dont know what kind of response it has, but it does pretty consistent work on 1/2 oz copper boards with a carbide V bit.  Not ideal and the machine can certainly be improved on. But the concept is good.

Guess they must be using it for some kind of relative measurements as the response must be exponential with the magnet and hall sensor so not easy to get a reliable absolute distance measurement.

I have considered doing some kind of rough grid pre-leveling by moving in a grid and reading the height when the tool touch the surface, then compensate the G-Code with the interpolated readings.

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Offline scientist

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Re: PCB CNC Milling/Isolation Routing
« Reply #21 on: February 08, 2014, 07:44:57 am »
Not sure if you know this, but there are copperclad boards used for PCBs that aren't FR4, i.e. they don't contain fiberglass.
 

Offline jaxbird

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Re: PCB CNC Milling/Isolation Routing
« Reply #22 on: February 08, 2014, 07:58:35 am »
Not sure if you know this, but there are copperclad boards used for PCBs that aren't FR4, i.e. they don't contain fiberglass.

It's a good point  :-+ I have tried these "cardboard" based boards and they can be used if you don't need fine pitch. The copper doesn't stick very well on them, so there is a high risk of lifting pads/traces both during engraving and soldering.

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Offline WarSim

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PCB CNC Milling/Isolation Routing
« Reply #23 on: February 08, 2014, 03:23:32 pm »

Not sure if you know this, but there are copperclad boards used for PCBs that aren't FR4, i.e. they don't contain fiberglass.

Yes of course there have been over 8 types of substrates used for coper clad.  I say over 8 because I have direct experience with 8 and I know there are others I have not used yet. 

This thread just assumes that FR4 is the only substrate in use, because it is the most common in current commercial products.  It is not a bad assumption because it is relatively cheeper based on its strengths.  Other better options for milling exist but at a performance cost, or financial cost. 

Not to detract from the slightly exaggerated cautions of fibreglass dust.  Any particularized fibrous substance in the lungs is bad.  Inhaling any thing into the lungs that the lungs can't expel or absorb is bad.  This includes any fibrous material, acidic material, basic material or bio-reactive material.  I causing against fou using on the dangers of the sensationalized danger and ignoring the mundane materials. 
 


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Offline scientist

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Re: PCB CNC Milling/Isolation Routing
« Reply #24 on: February 08, 2014, 04:08:24 pm »
Oh of course, don't mean to take away from your warning.
 


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