Hi all,
I'm wanting to make a few PCBs for some small projects laying around, but have never really done this before. Can someone point me in the right direction for some good tutorials/background info? I believe my machine would be well suited for this (30K spindle, ballscrews, etc...). I think I'll start out with a single sided board for simplicity.

Right now, my basic understanding of the process is:
- Buy board with copper plated side.
- Layout desired circuit in CAD program/Make toolpaths.
- Cut away everything that you don't want connected, leaving only the desired traces.

My questions are:
1. What type of material is best for milling circuits from?
2. Where to get above material?
3. What size bits/mills to use? I'm assuming carbide is a must for this application.
4. Are there any good CAD/CAM programs that make this really easy?
5. What types of feeds/speeds to use?
6. How deep do you normally cut? Just enough to break the copper surface, or deeper into your substrate?

As you can see, I've got quite a bit to learn. Any help would be greatly appreciated.

Hi there.

1. What type of material is best for milling circuits from?

Copper composite. Not sure this is what you're asking. PCB blanks usually come in 1/2, 1 or 2 oz pours. In my experience, I've found 2 oz easier to work with when milling but other thickness work too and can be cheaper.

2. Where to get above material?

Many places sell these. I buy most of my electronics stuff from Mouser (http://www.mouser.com/index.cfm?handler=displayproduct&lstdispproductid=277240&e_categoryid=112&e_pcodeid=50101) but try eBay (http://search.ebay.com/FR4-PCB_Business-Industrial_W0QQcatrefZC6QQfromZR4QQfsooZ1QQfsopZ1QQsacatZ12576) as well.

3. What size bits/mills to use? I'm assuming carbide is a must for this application.

This depends mostly on your route lines and how close they are together. End-mills for this purpose can be very small. I cut most of my circuits with a .0312" (0.79mm) endmill. I've been buying my mills from different places but HF has good, resharpened (ie: some previously used) USA made tools that are for this purpose.

NOTE: these are normally $12.99 but here's a trick to get then at $6.49. Go here (http://www.harborfreight.com/cpi/taf/Basket.taf), click on "order from printed catalog" and enter item 34640-1RHB. You can't beat qty 50 USA made endmills for $6.49! I have about 500 pieces of these and keep buying more as they are a great deal. All are carbide, top quality, 1/8" shank rated at 60K RPM. You'll see a combination of mills and drills. The last few boxes I've gotten have not had collars on the tools but still is a good deal even if you're not into milling PCBs.


4. Are there any good CAD/CAM programs that make this really easy?

I use Protel for schematic capturing and PCB manufacturing but many use the free version of Eagle (http://www.cadsoft.de/) with good results.


5. What types of feeds/speeds to use?

I've recently been cutting mine at 15 ipm with 6500 RPM on the spindle. Yes, you don't need to be >25K RPM to mill PCBs. I also have a 45K RPM spindle and frankly, can't tell the difference at that feedrate. I guess I could mill faster with a quicker spindle.


6. How deep do you normally cut? Just enough to break the copper surface, or deeper into your substrate?

My best work has been when I barely make it below the copper. For a 2 oz copper clad, that comes out to 0.0028" (0.0711mm) deep.

JR

JRoque Great tip on the endmills deal :)

I ordered 50 of them couple months back when they were onsale. I only got 3 endmills out of that 2 were chipped.
Did i just get a bad lot? or are they 95%+ drillbits most the time?
still a good deal but i am thinking about ordering some more but i dont need anymore drill bits :)

Hi. Yes most of the boxes I've received have had more drills than mills. I picked two, pictured below, and counted them. One had 29 mills and the second had 22 mills. Out of 500 I've only seen 1 chipped, maybe I was lucky. Again, the last 4 boxes I ordered came in with no collars which is a bit disappointing but in reality that doesn't really matter much since most of these, if not all, have been resharpened and shorten anyway.

I remember getting a box of these some time ago and finding only a few endmills with lots of drill bits so they vary greatly on what you get. But even if you get just a few, it might be a good deal still. I think I've seen these going on eBay for $20 per box. One thing I'll say about HF, them guys run on molasses. It takes no less that 3 weeks to get anything from them. Granted, with a dirt cheap shipping charge.

Cheers,
JR

Another question: When milling PCBs, do you create many burrs on the copper layer? If so, how do you de-bur these? Also, has anyone had a problem with the copper de-laminating?


Copper composite. Not sure this is what you're asking. PCB blanks usually come in 1/2, 1 or 2 oz pours. In my experience, I've found 2 oz easier to work with when milling but other thickness work too and can be cheaper.

Basically, I was just wanting to know what trade names to look for when shopping. Now I know, thanks for the great information JRoque

Hey. Yes, I've gotten some burrs if I mill in too deep or feed too fast. Feed speed is probably the real culprit. The few burrs I get I can easily remove with the tip of a small screwdriver or even a fingernail.

"FR4" is probably the most common PCB composition. Search for FR4 to see all the details. I have not had the copper pulled off the fiberglass yet.

Here's (http://www.cnczone.com/forums/showpost.php?p=48540&postcount=22) a sample of a PCB I milled some time ago. You can see a bit of burring in there but it has not affected the operation. That's a weather sensor board that sleeps outside. The "silkscreen" (lettering) was scratched on with a fine bit spinning at 100 RPM. Note that the process used in the posting link is no longer how I do it but instead I use the end mill to drill, mill and cut.

JR

Ok, another question: 2 flute or 4 flute endmills? Is flute clogging a problem? Also, any recommended coatings like TiCN or TiAlN? I've had good luck with TiCN when milling large pieces of dead soft copper, so I might give it a try here, too.

For deburring, would a light touch with sandpaper ~1000 grit work? Seems like a couple quick passes might help knock off some burrs but not remove much base material.

This is an area I am also interested in.

It is nice to see that 30K is not needed.

Mike

Sure, or you could burnish the burrs with a smooth piece of rounded steel like a stainless steel spool.

Also check out cnconabudget.com

Hey Neo, most of the tools I've seen in the above package are 2 flutes. I guess that due to the small size itself. I have never had any clogging issue, fiberglass doesn't tend to stick to anything when dry. The amount of copper is really minimal so no problems with that either. I have no experience with alloys coatings on PCB tools. However, plain carbide tools seem to last forever so that might not be even needed.

Adding a bit of my own 2 cents, I would be concerned with runout on the spindle to be use for this purpose. Not only precision is needed to make accurate cuts, it can also save the tool. I got lucky and my homegrown spindle turned out to have a very low runout. My Porter Cable, on the other hand, has .002" runout - simply unacceptable to work with these tiny tools. The other issue I've had is trying to get the PCB mounted flat on the mill table. Just a small variance in height and it could mean the difference between a great copper cut or no cut at all. I need to find time and make a jig to hold the PCB with 4 adjusting posts for precise leveling.

Give it a shot. Mount a flat-nose, center cut end-mill on your router, take a few minutes adjusting Z if needed and cut in at about .0028" deep

Regards,
JR

Thank you JRoque for that picture :) Looks like you got alot of good stuff much better then my lot. Im going to give it another try right after i move.

Thanks again :)

Many thanks for the great info. As soon as I get back from vacation (July 15) I'll give it a shot!

Another question: Solder Mask - how is this applied, and is it feasible for the do it yourselfer?

You have to mask off where you don't want the solder mask to be applied....I believe there are some hobby spray on options....before long..you'll find it cheaper to prototype the layout then have some make the PCB for you.

Hello. I agree with Viper. The principal benefit from milling your own PCBs is speed and cost of using the already existing CNC machine. However, the benefit curve quickly turns toward outsourcing when you get into more complex areas like having to soldermask, silkscreen or multilayer a PCB. But half the fun is trying to condense your circuit into a single-sided layout and soldering an MLP chip without a mask.

JR