PCB milling - Achievable minimum width of isolation path

[Sandberg]

Dear all,

I have joined this forum a few minutes ago and looked through some of the posts. However, I did not find a real answer to my question.

Some SMD components have a pitch of 0.4 mm, hence the width of the isolation path should be less than 0.1mm and positioned accurately to 0.1 mm also.

Can this be done with DIY milling machines and if so how in terms of tools, milling head and milling machines? I am considering buying a CNC 3040C that is specified to have a positioning accuracy of 0.04 mm and a repositioning accuracy of 0.02 mm. Hence well within the 0.1 mm required on positioning accuracy. The width of the isolation path may the be max 0.15mm. Can that be done with a milling machine of the kind of the CNC 3040C (< $1000)?

Has anyone tried milling PCBs using a vacuum table and calibration of the tool height at several points across the PCB just prior to start of milling?

I am aware of professional machines (>$5000) that can achieve the 0.1 mm width of the isolation path positioned within 0.1 mm, hence professional machines can do it.

I really appreciate a frank reply from people who have experience in milling PCBs for SMD with the tiniest pitch.

Thanks in advance.

Regards,

Sandberg

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[Bubba]

Sandberg,
I am not the best one to respond to this as I am still debugging my setup. I have a homebuilt router and so far in my calibration tries, about the best I can achieve for isolation is about .13mm (~.005") using a 30° V bit on my homebrew vacuum chuck.
My spindle is by Paul Jones Engineering and I don't find any detectible run out. I also use an "autoleveling" software package to take care of the variations in board thickness.

In my estimation, you will need not only an accurate, repeatable platform, but a very stable spindle with no run out and use a finer bit that I am using. V bits are not to a sharp point and depending on supplier, will have differing tip sizes. Even then, you will need to calibrate each bit before using it.

Hope this helps and look forward to other peoples thoughts.

[Sandberg]

Bubba,

I appreciate your input, which confirms my fears that it is not for DIY or <$1000 machines to mill a PCB for SMD. This I have seen other claim as well on the internet, but most of the info I have found is a couple of years old, so maybe someone has had a good idea in the mean time ....

Other inputs are most welcome.

[Mzones]

Instead of trying to mill them, have you thought about etching them?

[Sandberg]

Mzones,

Yes, I have thought of etching the PCBs, but that is a rather complicated process requiring unpleasant chemicals. There is also a photographic process involved. I tried it some years back, but gave up.

I am getting to the conclusion that having the PCBs made by a company offering small series and prototype PCBs is the best for me.

[blinkenlight]

Personally, what I consider reliably achievable is 2mm through-hole or 1.27mm pitch SOIC. I'm not excluding it is physically possible to execute higher density PCBs on a hobby mill, but one has to keep in mind that the thinnest v-tip mill I have seen was 0.1mm at the _tip_, so the milled groove is by definition always thicker than that. There might be non-v-tip special ultra-thin end mills thinner than that, but frankly, I hesitate to even use the 0.1mm-tipped "v" ones because even those break by just looking at them. I was just recently bummed by Atmel's apparent choice to only produce 0.8mm TQFP Atmega328 MCUs instead of any SOIC ones - I had to default back to the DIP version because of that in this case, even though I _might_ produce a usable 0.8mm pitch PCB if I try hard enough: I just can't be bothered to put in that kind of effort.

My $0.02 in short: SMD work - certainly possible. SMD work at current standards - quite iffy if possible at all.

[Sandberg]

blinkenlight,

Thanks a lot. You confirm my fear, that I should not get started on PCB milling using <$1000 milling machines. I agree that SOIC at 1.27 mm pitch should be doable, but 0.8, 0.65, 0.5 and 0.4 that are in use today will require special milling machines costing >$5000 and then I am better off having the PCB made by a professional company offering small series and single prototype PCB at a cost of about €50 each. First I do not have a budget of $5000 and if I had I would prefer to spend it on a quality sampling oscilloscope.

I appreciate this forum. It has saved me from a failed investment of about $1000.