Personal CNC PCB routers

[yyrkoon 250]

So, we're considering purchasing a kit, or parts to build an "inexpensive" CNC PCB router. To build PCB prototypes, before we commit to a design which would later be sent off to a board / PCB house to build in higher quantities. I was wondering if anyone here on these forums has already made that leap and may have some insight on this subject.

 

My buddy and another friend have been doing a lot of Linux CNC / MACH3 "research" on various forums. Related to various controller, and hardware packages. But we're all still up in the air as to what would work best for us.

[greeeg 460]

My personal opinion is not worth it. Based on the following points

• Double sided boards are not easy
• No plated through holes
• Most of my designs are fully SMD (0603 or smaller) often with QFNs or TTSOPs
• DIY setups require ALOT of time to tune/setup
• Commercial solutions are VERY expensive (paying for the time to develop a reliable machine)
• Minimum space is size of cutting bit (typically >0.4mm)
• No soldermask
• Prototyped designs are significantly different to Fabbed designs

This might seem like I'm complaining about things that don't matter. But if you compare a milled PCB and a professionally fabbed PCB from a batch Chinese service, they're worlds apart.

 

I've played with Toner transfer, photosensitive ink transfer, and milled PCBs. Out of all photo-sensitive was the best most repeatable, but my lab space is not setup for making PCBs. It just takes me too long to setup and pack down all the equipment. Photo-sensitive has the advantage that the same process repeated will give you a solder mask.

 

We have a LPRF ProMat S63 at uni, it's an amazing machine. But the upfront cost and cost for PCB blanks and operating costs (broken bits mostly) don't make it an attractive offer. I would much rather timeline a 5 day wait for PCBs from china into my projects.

 

Just my thoughts, If your prototypes are primarily single side, with larger components. Or if you use alot of through hole parts. It should be a good fit.

[Fred 453]

I agree with greeeg. I went from CNC milled PCBs to presensitized photoresist boards to DirtyPCBs. CNC is great but for many things not really for PCBs.

[terjeio 134]

I agree with greeg too, I did not even try to mill PCBs even if I own a CNC mill - dismissed out of hand due to poor resolution,  cumbersome setup and involved workflow. However, for single sided designs I am very happy with my laser exposer now that I have mastered the process.

 

 

This PCB took 1h30min to make from plotting (from KiCad) to developed soldermask. It then needs one hour in the reflow oven for "hardening" the soldermask before drilling and milling the edges  (I am using Mach3 for my mill). The soldermask is not perfect - most likely due to it beeing way past it "best before" date. BTW the footprint in the middle is for a 2553.

 

"Inexpensive"? - for me, yes - as I make quite a few one-offs and small runs (typically < 5).

[yyrkoon 250]

I agree with greeeg. I went from CNC milled PCBs to presensitized photoresist boards to DirtyPCBs. CNC is great but for many things not really for PCBs.

Can you elaborate more Fred ? You do not think that having some sort of "in house" way to manufacture one off prototypes is worth having ? As a way to do prototypes without having to send off to an out of house PCB fab ?

[yyrkoon 250]

OK so here are my counter points, which I'm perfectly happy to discuss further.

 

My personal opinion is not worth it. Based on the following points

• Double sided boards are not easy
• No plated through holes
• Most of my designs are fully SMD (0603 or smaller) often with QFNs or TTSOPs
• DIY setups require ALOT of time to tune/setup
• Commercial solutions are VERY expensive (paying for the time to develop a reliable machine)
• Minimum space is size of cutting bit (typically >0.4mm)
• No soldermask
• Prototyped designs are significantly different to Fabbed designs

 

 

• Double sided boards . . . this is why PCBs use the 3 alignment holes right ? I do understand that setup time would increase however.
• Plated through holes . . . I'm not sure is a big deal for a prototype.
• Our designs will also be as many SMD parts as well. We will have a pick and place machine eventually. For now we have tweezers, magnifying fixtures, and a vacuum manual placement device. Plus one of us is near sighted and can pretty much place parts, even small parts by hand and eye. Reliably.
• Setup . . .yeah we knew about that.
• Not sue what you mean about "commercial solutions" boards would be mass produced out of house. Only one or two off in house prototypes would be done in house.
• Minimum space size I do not think would be too much of a problem for one off prototypes.
• Solder mask . . . could be a spray on conformal coating. With chemicals to keep the "mask" from sticking to solder areas. If a solder mask is even needed.
• Prototype indeed can be significantly different to fabbed designs. And in fact I think that can actually play into our favor in many of the above situations.

 

So, I'm not arguing here, at least not really. I'm willing to hear more on the subject. But bit cost is not prohibitively high, we have A LOT of in house double sided copper clad boards currently. While double sided copper clad from ebay is also inexpensive. We too have also played with toner transfer boards, and that is why we're thinking of CNC milled board. Toner transfer in our experience is not reliable. We even own a large PCB chemical sink . . .

 

But, Like I mentioned above I am willing to discuss all of this further. You have the hands on, we do not.

[Fred 453]

I didn't find milling PCBs to be very effective. It was OK for through hole stuff but for anything finer it was too difficult to get good results. The only plus was the fact that the isolation routing and drilling always lined up perfectly.

 

I got on much better with photoresist, with results similar to terjeio's above. It was fun but I realised it would often take me two weeks to find the few free hours I needed for etching, so no real time saving in the end. Do it if you enjoy it and like the challenge, not to save time or money.

 

CNC milling is however great for making enclosures and random stuff like that.

[yyrkoon 250]

I agree with greeg too, I did not even try to mill PCBs even if I own a CNC mill - dismissed out of hand due to poor resolution,  cumbersome setup and involved workflow. However, for single sided designs I am very happy with my laser exposer now that I have mastered the process.

 

IMG_8045.JPG

 

This PCB took 1h30min to make from plotting (from KiCad) to developed soldermask. It then needs one hour in the reflow oven for "hardening" the soldermask before drilling and milling the edges  (I am using Mach3 for my mill). The soldermask is not perfect - most likely due to it beeing way past it "best before" date. BTW the footprint in the middle is for a 2553.

 

"Inexpensive"? - for me, yes - as I make quite a few one-offs and small runs (typically < 5).

 

That board for prototype purposes does not look terrible. For mass production, not so good, but looks fine for a prototype I think.

[yyrkoon 250]

CNC milling is however great for making enclosures and random stuff like that.

 

Yeah I knew that, I used to work in a CNC shop milling various parts for various jobs. Such as key lock key-ways( for house doors ), Plus a lot of experimental stuff for . . . well companies and organizations I really can not talk about. But, the key-ways were for Schlage lock inc. We mass produced those.

 

PCB boards though . . . no hands on there yet,

[greeeg 460]

@@yyrkoon

 

• Double sided alignment - I believe that you can use some form of holes and pins to re-align the PCB. This may have gotten better, but I never had a good workflow. Your CNC probably needs a nice fixture plate to make this reliable.
• Plated Through holes - Fair, enough. (This is a show stopper for me)
• Small SMT parts - I haven't seen a milled PCB that went below 0.65mm pitch TTSOPs. You should be fine for SMT passives.
• Commercial solutions - I was talking about a commercial PCB prototype plotter. My only experience was with this (http://www.lpkf.com/products/rapid-pcb-prototyping/circuit-board-plotter/protomat-s63.htm) (From memory, roughly a $20K machine.)
• Prototype being different from final design increases the total time spent designing, and if you're using high speed signals (USB, LVDS, 50 Ohm transmission lines) Really depend on the design and board geometry.

I feel like I'm in the same boat as @Fred, And my opinion is biased against cheap in-house prototyping. Personally fabricating PCBs is not fun for me, designing / assembling and testing are the parts I find fun. So I'm more than happy to pay for someone else to do it reliably and work on another aspect of the project while I wait.

 

I really like the results from @terjeio's laser plotter, I think that's a much better solution than milling.

[yyrkoon 250]

I feel like I'm in the same boat as @Fred, And my opinion is biased against cheap in-house prototyping. Personally fabricating PCBs is not fun for me, designing / assembling and testing are the parts I find fun. So I'm more than happy to pay for someone else to do it reliably and work on another aspect of the project while I wait.

 

I really like the results from @terjeio's laser plotter, I think that's a much better solution than milling.

I do not think that fabricating in house would be fun for me either. But I do not have to, as I'm the 'code monkey'. However, I am the in house go to Linux guy usually. So if it involved any Linux setup I'd probably have to be involved. One of my buddies claims that he can setup in around 20 minutes and that he uses software that does all the alignment for him. Once he zero's the mill. But he also uses all the fancy Orcad related tools. I'll believe it when i see it though.

 

One of the major issues for us is that it takes 2 weeks to get boards back From China when we go 5 off proto's . . .But if a customer needed  prototype like RIGHT NOW I suppose we could expodite the shipping, but that cost would not be out of house. The customer would pay for it.

[yyrkoon 250]

I actually think that additive process, 3D printing would be the way to go with this. I know people are already doing this, but suspect that one would require a very expensive system from HP/ Adjilent technologies. Somewhere in the range of ten of thousands, to hundreds of thousands in costs.

[jazz 209]

So, we're considering purchasing a kit, or parts to build an "inexpensive" CNC PCB router. To build PCB prototypes, before we commit to a design which would later be sent off to a board / PCB house to build in higher quantities. I was wondering if anyone here on these forums has already made that leap and may have some insight on this subject.

 

My buddy and another friend have been doing a lot of Linux CNC / MACH3 "research" on various forums. Related to various controller, and hardware packages. But we're all still up in the air as to what would work best for us.

 

At the time when price for fabricated PCB's was high, I made complete standalone software for PC / micro side for G files with 2 mill / drill tools.

 

 

At the time when I started building hardware for it, PCB's price go down, and I gave up. Didn't see any reason for it anymore. I agree with greeeg.

 

For prototypes I use p2p.

 

[Apr30 2]

@@jazz,

neat. What's the ? of the wires?

[enl 227]

I have been through a number of generations of in house prototype and hobby scale small volume, and if I can avoid it, I don't do it myself. That said, I don't make a lot of boards anymore, so there is a large grain of salt involved when I say that, with a little care, prototyping on a mill can be viable. It is what I do most of the time these days, as I have the equipment. It isn't as fast as photo, or even toner transfer. There is a mess involved unless dust collection is dead on-- handling the fibreglass dust is a different league than chips and dust from pretty much any other material. What follows is off the top of my head and based on my (probably somewhat outdated) experience.

 

Positives include consistent trace width-- UV is also good, but requires good technique or results can get pretty bad--, no shorts or opens like plague toner transfer and sloppy UV, lower cost than UV if the equipment is already in house, the afore-mentioned alignment positives, no second setup for drilling, and no wet chem. Double sided isn't a big deal with proper use of alignment holes or fixtures, and other in house methods have similar issues.

 

Negatives are dust control, through hole plating (which is the same for most other in house methods), board properties, workholding issues, and leveling.

 

The key to good results is flat and level. A vacuum hold down on a flat bed it pretty much a dead requirement for good results, and accepting that the bed is going to need replacement periodically due to drill damage is a part of it.. If the bed is dead on, then the feature size can be quite good using a 90 degree point tool for the fine work-- depth controls width between close features. I run two tools for clearing: a 90 deg point for outlines and separation of close features (depth controls cut width), and a 0.75mm bullnose for larger area clearing and wide clearance, followed by a drill bit. If the board isn't held dead flat and level, the results will be bad, with nonuniform feature widths and variable substrate thickness between traces. I use a plugin for Eagle to generate the G-code.

 

I would say that the biggest drawback to milling prototypes involving high frequency devices is the change in substrate properties due to the substrate removal, both due to dielectric loss and due to increased moisture pickup. I have never had a major issue, since I have never milled when I anticipated an issue, but I have seen the effects in a few cases and needed to adjust component values to compensate. The key thing is that the prototype board may have characteristics very different from the production board.

 

That said, I don't recommend milling unless there is a compelling reason. For the few boards I do that way, it is ok, and 0.2mm traces on 0.5mm centers is very achievable. I prefer to use a service since I can usually wait. In a pinch, for something simple, I might even use a sharpie and etch, though that is last resort. I can do 0.5mm trace on 1.2 centerlines that way, which is fine for a lot of one-off, since I still use as much 0.1" (2.54mm) lead space devices as I can. I'm old and have poor eyesight. 10 sec with pliers and through hole devices are surface mount.