CNC PCB milling

[executivul]

@NeverDie Here are my steppers I currently use on my 3040 cnc: https://www.ebay.co.uk/itm/Nema23-2Nm-Closed-Loop-Stepper-Motor-Driver-3phase-Hybrid-Easy-DC-Servo-Kit-CNC/254675291058?hash=item3b4bd48bb2:g:FcsAAOSwAuZX4lcl

[NeverDie]

@executivul I notice that closed looop ethercat is also starting to become popular:
https://www.aliexpress.com/item/33028892255.html?spm=a2g0o.productlist.0.0.4a3acc12R4bh4z&ad_pvid=202008201300179940172292214280005385422_2&s=p

Especially for LinuxCNC and Mach3/4 users. I don't know enough about either of those software packages to know what, if any, advantages they may have, but the downside seems clear enough: you need to worry about what kind of jitter and lag the PC you run it on may have.
Maybe that's where the closed loop helps out? The ethernet affords some noise immunity. Not sure to what degree, or not, that noise is even a problem with typical non-ethernet GRBL driven configurations.

I notice that the new TMC5160's have motion planning built into the chips themselves, though I haven't yet seen any configurations which take advantage of that. Sounds intriguing, as it would be able to capitalize on any feedback practically instantaneously. Maybe it will be a game changer? The TMC5160 datasheet makes some vague references to closed loop.

[Yveaux]

@NeverDie EtherCAT is simply awesome. Over the years I developed multiple EtherCAT masters and slaves, and used it in many industrial machine control solutions.
It has proven extremely useful for realtime distributed control and offers great flexibility.
Jitter on bus cycle deserves attention, but on the other hand even windows can run an EtherCAT master; it just all depends on your application and control requirements.
In the case of small CNC and 3D printers it may be slight overkill however.
Let me know if you would like to go deeper into the topic, or have specific questions!

[executivul]

@NeverDie These closed control loops have got really good traction lately, these days there is a sprawl of new/cheaper devices/clones. I've used mine without issue for 2 years now.
My problem was frequent binding of the machine. I have a 60,000rpm spindle and I normally use 1400mm/min speed and 300mm/s^2 acceleration. The machine itself is far from perfect, sometimes I can hear it knocking, and with older steppers and drivers I lost a few steps every time it jammed, resulting in 0.1-0.3mm of error at the end of a longer milling process.
The culprit is either some misalignment and lack of parallelism or some of the balls have flat spots. The binding does not occur in the same place or direction every single time, so I believe the balls are more likely to be the cause. The solution would be a complete rebuild using higher quality linear rails, but the the price and the time needed to do it makes me leave it as it is since I can mill 0.15mm isolation with 0.25mm traces for smd and also large 20cm x 30cm boards for through hole projects (mostly).

[NeverDie]

@executivul So even with the closed loop it's still off at the end? That's hard to wrap my head around.

I guess the ultimate solution would be DRO's then. Short of that, or the improvements you're talking about, maybe you could re-zero periodically during the job? You're getting great results, though, so I don't blame you for leaving it alone.

[NeverDie]

@Yveaux said in CNC PCB milling:

@NeverDie EtherCAT is simply awesome. Over the years I developed multiple EtherCAT masters and slaves, and used it in many industrial machine control solutions.
It has proven extremely useful for realtime distributed control and offers great flexibility.
Jitter on bus cycle deserves attention, but on the other hand even windows can run an EtherCAT master; it just all depends on your application and control requirements.
In the case of small CNC and 3D printers it may be slight overkill however.
Let me know if you would like to go deeper into the topic, or have specific questions!

That's great! Do you think there's much hope of seeing a greatly cost-reduced arduino version of ethercat anytime soon? I mean, by way of analogy, for a long while wi-fi seemed intractably expensive, and even the expensive wi-fi breakouts for arduino's seemed pretty dodgy. Then out of the blue ESP8266 suddenly made good arduino wi-fi possible for cheap.

[Yveaux]

@NeverDie EtherCAT requires a dedicated ASIC (e.g. Beckhoff ET1100) or FPGA IP Core.
There have been some developments where MPU & EtherCAT slave controller were integrated into a single piece of silicon (TI, Renesas, Microchip) but these are less popular than the ET1100.
For distributed IO it is an awesome technology, but when all IO and controller can be located onto a single board (like with most hobby CNCs) it is overkill, at least for the masses.
But again, you never know what nice lowcost EtherCAT solution could be coming our way.

[NeverDie]

@Yveaux That makes sense to me. If people are mainly doing it for noise immunity, I'm reasonably sure that differential op-amps (which are cheap) and twisted pair wiring (which is cheap) will do the business. That's how ethernet does it. If that's still not enough, then add shielding. Also, the more twisting the better. At least, I would think that it would be sufficient for a home environment.

I'll be testing this theory with the closed-loop stepper drivers that I'll be installing, since with those it will be the data coms between the GRBL board and the stepper drivers that will be running across long wires instead of power pulses to the steppers, where noise didn't really matter. I guess we'll see!

[Joerideman]

Hey, I have trouble understanding the last 10 posts.

It sounds like this go's beyond the PCB milling?

What are you aiming to achieve?

[NeverDie]

@Joerideman said in CNC PCB milling:

Hey, I have trouble understanding the last 10 posts.

It sounds like this go's beyond the PCB milling?

What are you aiming to achieve?

No, the aim is still pcb milling. More specifically: PCB milling at fine pitch and whatever might support that. Regular through-hole milling is something that just about any PCB mill can handle, so the discussion has shifted to milling for newer SMD parts, where the pitch between pads can be quite challenging for some mills, like mine for example. Then the question becomes: which are the best bang/buck upgrades (or even just calibrations) that will get you there.

[Joerideman]

So, I have seen that with a popular 3018 CNC a atmega328p-au can be milled.

0.2mm traces with 0.2mm clearance can be routed.

What specs are you going for?

[NeverDie]

@Joerideman said in CNC PCB milling:

So, I have seen that with a popular 3018 CNC a atmega328p-au can be milled.

0.2mm traces with 0.2mm clearance can be routed.

What specs are you going for?

I thought the atmega328p had wider pitch than that, as I have etched those before. Nonethmeless, where did you see a 3018 that could do those specs? I think for now, if I'm understanding you correctly, that would be good enough, at least for me. That would effectively be a 0.4mm pitch, right? Measured center to center from one pad to the next.

I don't think my rig is any worse than a 3018. Most low-end CNC's seem pretty similar, with aluminum extrusion frames, acme screws, round rods and inexpensive linear bearings for glides, and dubious spindles, dodgy collets, and questionable z-axis reinforcement against twisting. I guess one could look at bantam tools or wegstr for differences, as they seem to be hitting it. I doubt there's any one thing but probably a range of things done right. Perhaps being companies allows them to source parts reliably with the right tolerances, thus avoiding aliexpress roulette.

Anyhow, I think I'll get there if I keep chipping away at it. With PCB deliveries slowing down due to covid19, it's worth the effort to figure it out. ;-)

I see working with PCB's as an advantage, because the machine itself doesn't need to be big, and in theory even (some) premium parts become affordable because the travel distances are relatively short.

[Joerideman]

@NeverDie

I shared a link to this channel before.

CNC PCB - high quality with the budget 3018 CNC – 05:20
— DIY TECH BROS

I am waiting for their next video. I am told it will show us a bit more about the limits of the machine.

It doesn't actually show an atmege328 I am not sure where or if have actually seen this.

The Wegstr, has only a Z axis for the spindle. And from what I read they use a brushless motor for this. I guess that by only moving it up and down, this part becomes very rigid.

[NeverDie]

@Joerideman said in CNC PCB milling:

@NeverDie

I shared a link to this channel before.

CNC PCB - high quality with the budget 3018 CNC – 05:20
— DIY TECH BROS

I'm pretty sure the pitch on the given example in that video is wider than 0.4mm.

The Wegstr, has only a Z axis for the spindle. And from what I read they use a brushless motor for this. I guess that by only moving it up and down, this part becomes very rigid.

Good observation. The fixed z-axis is closer to a classic mill configuration. I like that approach because it makes it easier to build rigidity into the z-axis.

[NeverDie]

@Joerideman said in CNC PCB milling:

So, I have seen that with a popular 3018 CNC a atmega328p-au can be milled.

0.2mm traces with 0.2mm clearance can be routed.

What specs are you going for?

I looked up the atmega328p datasheet here: http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-7810-Automotive-Microcontrollers-ATmega328P_Datasheet.pdf

The pitch on the DIP package is obviously 2.540mm.

The pitch on the TQFP package is 0.8mm. That's the one I tend to favor because it's easy to handle, and I have a clamshell chip programmer for it.

The ptich on the VQFN package is 0.5mm.

On the other hand, looking at the "other' datasheet for the atmega328p: https://ww1.microchip.com/downloads/en/DeviceDoc/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061A.pdf
it does appear to also make reference to a 28M1 package, which has only 28 pins and a lead pitch of 0.45mm. As far as the atmega328p is concerned, that appears to be the lowest pitch package. Pad width is a nominal 0.22mm, so of the various packages it's the closest to the one you said. The entire package is just 4mmx4mm in size.

I'd be reluctant to attempt a chip that small without solder mask, but with an appropriate solder mask it would be possible I suppose. Hence, getting the solder mask part of pcb milling right is definitely important as the line pitch gets smaller and smaller, and that certainly is the trend.

In any case, the lead pitch on the nRF52832 is 0.4mm, so there's definitely a need to accurately etch that pitch. I seem to recall running into components with even lower lead pitch than that, but offhand I can't remember which components those were.

[NeverDie]

On another thread (https://forum.mysensors.org/topic/10812/the-harvester-ultimate-power-supply-for-the-raybeacon-dk/211?_=1598132652123) we were talking about using a laser to directly etch the copper clad on a PCB, which I think would be hard to do without a fiber laser. Nonetheless, it just now occurred to me that using a regular etching laser might be just the ticket to use for removing black solder mask over solder pads, precisely because it would fail at removing the copper underneath. After all, many people are already using this technique for removing cheap black paint (used as an acid etching mask) from copper PCBs, so I presume it would work equally well for selectively removing black solder mask? At least to me, this sounds extremely promising.

[Mishka]

@NeverDie Yeah, it's a very interesting option! Similar approach might be to use a UV printer. The UV paint is known to be resistant to FeCl3 and hence results in nice and clean edges. But that's subject of paint and a laser engraver could be used over UV paint too.

On the other hand, a fiber laser might be a nice all-in-one solution. It can do the PCB routing, can cut the board edges, and drill everything in one pass. After that, the same device can be used to manufacture solder mask using a kapton tape and also engrave the silk layer on top of it. Finally, it can cut stencils.

The only missing part is the through hole plating. I still have concern that laser drilled the edges will be good enough for metalization, this has to be checked. But a previously drilled and plated board is much easier to etch with laser rather than a milling machine.

[NeverDie]

@Mishka said in CNC PCB milling:

@NeverDie Yeah, it's a very interesting option! Similar approach might be to use a UV printer. The UV paint is known to be resistant to FeCl3 and hence results in nice and clean edges. But that's subject of paint and a laser engraver could be used over UV paint too.

On the other hand, a fiber laser might be a nice all-in-one solution. It can do the PCB routing, can cut the board edges, and drill everything in one pass. After that, the same device can be used to manufacture solder mask using a kapton tape and also engrave the silk layer on top of it. Finally, it can cut stencils.

The only missing part is the through hole plating. I still have concern that laser drilled the edges will be good enough for metalization, this has to be checked. But a previously drilled and plated board is much easier to etch with laser rather than a milling machine.

Somewhere out there is a product (it has a youtube video) where you pull a special paste through the via's under a vacuum and then do regular electroplating to get your vias plated. It's meant for DIY.

I wonder if you could just squeegee fine grained solder paste into the vias and then heat it up to make the connections? I suppose you'd want to do it after the solder mask phase. If the vias are big enough, I don't see why this wouldn't work. In the worst case it might take more than one pass, and it might also have the advantage of "tinning" your regular solder pads.

[Mishka]

Here is a fiber laser machine example: https://mylasermart.com/product/ultra-high-speed-laser-machine/

It uses 50W fiber laser. Minimal track width is 0.05 mm! Space between tracks is 0.025 mm which is limited by the beam size. Precision ±2 µm.

This particular one doesn't look any cheap, but it gives the strong hint what to look for.

[NeverDie]

@Mishka The company best known for direct laser etching of PCBs is called LPKF. If cost is no barrier, they've got great solutions that they can ship you today. Lots of impressive youtube videos about their products. If mylasermart, or anybody else, can do the same or similar for a lot less though, it would certainly be interesting.