PCB Engraving Notes

[Fish4Fun]

One of the reasons I wanted a small CNC router was PCB prototyping. I purchased one of Microcarve's A4 machines back in the Spring, but it wasn't until the past few weeks that I actually successfully routed a PCB. This post is simply a "how I did it" post. It is my hope that others might share the details of their experiences, and that this sharing might help make it easier for others to route a PCB.

I have read about the plug-in for Eagle Cad, and I considered this route, but I am not a big fan of Eagle; I prefer Altium's DXP. Once the schematic and PCB designs were finished in DXP, I "printed" the PCB to a PDF file. Using Adobe I then saved the pdf document to a jpg file. Using Vectric's Aspire I imported the jpg file in as a "bitmap", and then used the "trace bitmap tool" to create the primitives. At this stage I separated the "drill holes" to a "new layer", and created the drill tool path.

The creation of the trace vector's tool path turned out to be critical to "success". I was using a 0.1mm, 45 degree 0.125" engraving bit, and in theory the cut depth should be between 0.0007in and 0.0028in (1/2oz to 2oz copper). What I actually found was that single pass profile cutting even as deep as .010in was problematic, instead, setting the cutting depth to ~0.005in with a pass depth of 0.002in created clean crisp trace profiles. By placing the traces within ~0.030in of each other, no "slivers" or "islands" were left between the traces.

I had several failed attempts using "thin" (.010in to .020in) PCB material; I had my best results so far with 1/16th (0.0625) inch PCB material. I have ordered some 0.032in PCB material, but I haven't tried it yet.

So far I have not attempted a double sided PCB, but I plan to. My thought is to attempt double sided boards by making two ~0.032in single sided PCB's and then placing them "back to back" and using the "via holes" to connect the PCBs. Using a variation of this approach, a 0.007in double sided PCB could be placed between the two single sided 0.032in PCBs for "power planes". For now I am going to stick with perfecting a double sided PCB process.

If any are interested I will post pictures of some PCBs I have routed.

Fish

[microcarve]

Originally Posted by Fish4Fun If any are interested I will post pictures of some PCBs I have routed.

I'm certainly interested!


John

[louieatienza]

Originally Posted by Fish4Fun One of the reasons I wanted a small CNC router was PCB prototyping. I purchased one of Microcarve's A4 machines back in the Spring, but it wasn't until the past few weeks that I actually successfully routed a PCB. This post is simply a "how I did it" post. It is my hope that others might share the details of their experiences, and that this sharing might help make it easier for others to route a PCB. I have read about the plug-in for Eagle Cad, and I considered this route, but I am not a big fan of Eagle; I prefer Altium's DXP. Once the schematic and PCB designs were finished in DXP, I "printed" the PCB to a PDF file. Using Adobe I then saved the pdf document to a jpg file. Using Vectric's Aspire I imported the jpg file in as a "bitmap", and then used the "trace bitmap tool" to create the primitives. At this stage I separated the "drill holes" to a "new layer", and created the drill tool path. The creation of the trace vector's tool path turned out to be critical to "success". I was using a 0.1mm, 45 degree 0.125" engraving bit, and in theory the cut depth should be between 0.0007in and 0.0028in (1/2oz to 2oz copper). What I actually found was that single pass profile cutting even as deep as .010in was problematic, instead, setting the cutting depth to ~0.005in with a pass depth of 0.002in created clean crisp trace profiles. By placing the traces within ~0.030in of each other, no "slivers" or "islands" were left between the traces. I had several failed attempts using "thin" (.010in to .020in) PCB material; I had my best results so far with 1/16th (0.0625) inch PCB material. I have ordered some 0.032in PCB material, but I haven't tried it yet. So far I have not attempted a double sided PCB, but I plan to. My thought is to attempt double sided boards by making two ~0.032in single sided PCB's and then placing them "back to back" and using the "via holes" to connect the PCBs. Using a variation of this approach, a 0.007in double sided PCB could be placed between the two single sided 0.032in PCBs for "power planes". For now I am going to stick with perfecting a double sided PCB process. If any are interested I will post pictures of some PCBs I have routed. Fish

I've wanted to try some pcb milling... pics would be cool... I think if the pdf has vector info you could open it in Inkscape and then resave it as an eps file or other... instead of turning the geometry to a bitmap and then tracing it?

[doorknob]

I'm interested, too.

I do have a question - in your description you mentioned:

I "printed" the PCB to a PDF file. Using Adobe I then saved the pdf document to a jpg file. Using Vectric's Aspire I imported the jpg file in as a "bitmap", and then used the "trace bitmap tool" to create the primitives.

Did you save the pdf document to a jpg file because that was the only image format that Adobe permitted, or because that's the only format that Aspire will import as a bitmap, or for some other reason? The reason why I ask is because with jpeg being a lossy format, I was wondering whether it was possible that you might lose some fine trace features or line width in the process, such that the bitmap trace process could miss something. I suppose that you could have chosen a minimum-compression jpeg conversion such that it would not be an issue. But I could also be totally off base with this question...

[Yello]

I used to own a Bungard CCD which is mainly used for PCB drilling/routing/iso-milling.

My thoughts:

If you do iso milling you should consider a software that converts Gerber to Iso data. IsoCam is such a software. Not sure about the pricing though. There is a free demo version, not sure what that can do nowadays.

Controlling how deep you mill is very critical. FR4 laminate has about 10% thickness variation. On top of that, often laminate (specially single sided) is very often not flat and it's not too easy to fix it really flat on the table.

A better way is to build something that controls the entry relative to the PCB surface. The CCD uses some sort of guide that is fixed to the spindle and the Z-axis is then totally released.

If you want to do double sided PCBs it's a good idea to have 2 holes outside your PCB for fixation. Then it's easy to just turn the PCB over and do the other side.

[Fish4Fun]

@John, LOL, You are a picture hound ;-)



@louieatienza, I am still very much in the learning stages of the Vectric software, and I don't always do things the way that is "best". My attempts at importing vector files were NOT successful, I am not certain if the problem was the source files (from DXP) or the settings in Aspire, but several hours worth of attempts failed and left me frustrated, the bitmap tracing does loose detail, but it works ;-)

@Yello, NOW THAT"S A COOL MACHINE! Wow! Yes, having a "floating Z" makes A LOT of sense! I have found the PCB flatness is somewhere between bad and awful.

I downloaded the "GerbMagic" demo. It worked, but the resulting vector file had to be re-sized, and the results were mediocre at best. I honestly got much better results from the method I described. It is highly probable that my lack of success with GerbMagic was my own fault and not the fault of the various applications.

Yes, registration holes are always a good idea on PCBs, especially in a "production setting", but my approach of "laminating" PCBs has more to do with one-off prototyping where it may take me a couple attempts to get each side "right" with my milling process. By using two discrete PCBs the "pressure is off" to get two perfect mill paths onto the same PCB. In the past I have used both toner transfer and photo-sensitive etching processes for both single sided and double sided PCBs with fair success, but the routing process seems to offer the quickest turnaround time for prototyping.

@ALL, I started this thread because in researching this process mostly what I found was information about dedicated/specialty machines and software. Eagle has a supposedly very good plugin for exactly what I am trying to do, and for many that is likely the best way to go, but several of the "key features" of Eagle are counter-intuitive to me, so my efforts were focused on making my A4 produce suitable prototype PCBs with familiar software, and I thought/hoped others might be interested. I am glad this has been the case.

When I ordered my engraving bits I ordered 10 * 60 degree 0.1mm bits and 5 * 45 degree 0.1mm bits. I am now very curious to try smaller angle bits (5 degree to 30 degree). They are fairly cheap on ebay from China, but the lead time is pretty long, lol. My thought is that with the smaller angle bits higher detail might be possible while still ensuring the traces are "isolated". If I am doing the math right a 30 degree bit with a 0.1mm tip 0.005" "into" the PCB should have a cutting width of ~0.007 inches, while a 45 degree bit has a cutting width of ~0.015 inches (at the "top). I think to do SMD work, a 30 degree bit will be the maximum my system will tolerate. I would love some feedback on this if anyone has any....

I will update this thread as I attempt SMD and Multi-layer PCBs. I would hope that others continue to share their experiences, and that the thoughts here help people looking to attempt PCBs with their routers/mills.

Fish

[Drools]

I'm not sure if Altium's DXP produces gerber files but if it does you can use a freeware program called linegrinder. Of Itself So - Line Grinder, Gerber to GCode Isolation Milling
It will take the gerber files and produce gcode for mach3.
There are lots of goodies like this in the PCB routing forum.

[RomanLini]

I would suggest you keep trying with Eagle and the free PCB plugin (that produces gcode), I know Eagle can be a real mongrel to get over that steep learning curve but it is actually fairly simple to use once you know what does what. It's just counter-intuitive.

There are some tutorials you can get to make learning Eagle a bit easier.

[Fish4Fun]

@Drools....

There are lots of goodies like this in the PCB routing forum.

DOH, why didn't I think of looking THERE? LOL. I did do a bunch of searching here @ the zone, (and quite a lot of reading), but it seems I missed the VERY OBVIOUS "PCB Milling" Sub-Forum. I generally enter the zone directly to the DIY-CNC router table machines forum, and tend to ignore the others; I should REALLY take some time and read through the sub-forums list on the main page....thanks for pointing that out to me... I will give line grinder a try!

@Romanlini....

I have dabbled with Eagle for ~10 years or so; it is not that I am unfamiliar with it, I just don't "like" it. I can think of lots of good reasons to use Eagle, not the least of which is their huge support base, but it drives me batty to use it. Don't get me wrong DXP has it's own set of idiosyncrasies, (I frequently think DXP was a downgrade from Altium's earlier "Protel" generations of software, but I have been using it long enough they don't bother me so much.) About a million years ago there was a DOS PCB program, I don't even remember what it was called, that got me "started" in the world of computer aided PCB design. Compared to Eagle or anything else from this millennium it was very crude, but it was also very simple to use.

I usually start with pencil and paper, then I do a more formal schematic in DXP. I then do an "auto route" to a double sided PCB. Then I study the auto route output and begin moving parts and changing pin assignments based on how convoluted the routing is. Most of the time I can work out the PCB so it is single-sided with few or no "jumpers". This works for me because everything I have done in the past 10 years has been a fairly low density uC-based project. At the end of the day 60% of the pin assignments to the uC can be re-assigned to facilitate the PCB layout, and then it is just a matter of making the firmware match the pin assignments.

***WAY OFF TOPIC*** RomanLini, you haven't come across a simple/cheap AC line voltage to 5Vdc-12Vdc circuit in the 100mA to 500mA range have you? Something that would prevent the proliferation of wall worts? I search the net every now and again in the hopes that someone has come up with a small footprint solution that doesn't require proprietary magnetics, but thus far I haven't really found anything. I have considered picking a cheap wall wort or charger and ordering a box full of them and de-packaging them, but I would really love to find an IC with a low external parts count that I could simply "add" to my various low-power schematics....Just thought you might have run across something.

****BACK ON TOPIC****

Thank you both for your input!

Fish

[RomanLini]

Hi, sorry I don't think you will get a single IC package for isolated off-line SMPS conversion due to the requirements for certification, isolation etc that always needs some magnetics (transformer).

It's not really hard to build one, apart from it's always going to take quite a few parts and many of the parts need to be rated for AC mains. You can buy Asian wall-warts for a few dollars each in quantity.

I think you are on to something with the wall-wart idea, maybe you could contact Asia and try to purchase a quantity of the assembled PCBs for off-line SMPS wall warts but without the packaging or mains plug etc.

[Fish4Fun]

@ RomanLini, I don't think they can sell them much cheaper w/o packaging than they are already selling them, lol. I bought some 5V 1000mA AC to "USB" supplies for ~ $2 delivered. I just hate to take them apart....but that is likely the best answer. I am constantly doing small projects that simply need 5V from mains, but it feels like I am "cheating" using a $2 wall wort....doesn't mean it isn't the best answer. Thanks for the reply, I was just hoping I had "missed" something ;-)

Fish

[msimpson99]

While my machine is pretty large, I built it with precision in mind because I wanted to make some of my own boards for various projects.

Here is a quick little video of my first board.
KRMx01 Isolation Routing - YouTube

You have to keep many things in mind when designing a board for isolation routing. This project was a dual layer board and since I wanted to use a socket for the PIC24, I had to make sure the auto router did not use any of the top chip pads.



This board is a PIC24, 4 channel Wave player.

I use a Festool MFK700 router for my CNC because it has practically no measurable run out.

I am about to make a mini vacuum table for PCB routing because I found the clamps are just not good enough for good routing. A vacuum table will hold the PCB flat in the middle.