Beginner wanting to learn PCB Milling

[NeoMoses]

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.

[JRoque]

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 but try eBay 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, 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 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

[sendkeys]

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

[JRoque]

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

[NeoMoses]

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

[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 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

[NeoMoses]

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.

[MikeAber]

This is an area I am also interested in.

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

Mike

[ViperTX]

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

Also check out cnconabudget.com

[JRoque]

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

[sendkeys]

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

[NeoMoses]

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?