PCB Isolation Routing

Hi Guys, I have been PCB Isolation routing for quite some time now. I'm looking for some advice with regards to Aluminium backed PCB's. I have probably gone through about 20 150x100 boards generally without success. The problem is that somehow the copper becomes attached to the aluminium when routed.
I don't have this problem when I route small tracks or standard FR4 boards only long tracks on aluminium backed boards.

I originally used V bits but I have switched over to carbide engraving bits desinged for this purpose from preciseBIT. And have routed at 18,000 rpm and 26,000 rpm both at 550mm/minute. I have also run programs where I route the tracks 3 times over to ensure they are clear of any debris and I thoroughly clean them afterwards. I have inspeced the boards with a 200x viewing USB microscope and can see no interconneting bits.

Does anyone have any experience with this? Thanks

If the copper is becoming attached to the aluminium does this mean you are going too deep ?
Sorry for the silly question but I have never seen aluminium backed boards, I have run some tests for customer who wnated to see if the KX mills could engrave circuit boards and we just used off the shelf carbide engraving bits from Arc Euro trade

Well you are correct in some ways although I still go this deep on the smalled tracks and I don't have problems. The big problem is the board consists of 75micron copper, 70 micron ceramic and 160 micron aluminium. So Ideally I would land somwhere in the 70 microns of ceramic all the time but my CNC router (RoutoutCNC) just won't do it. It will start like that but by the time it gets to the other side its either to deep or not even touching the board.

OK this looks like the surface of your bed isn't flat to the same plane as the gantry which is quite usual with these cheaper routers, even my Teckno Isel router varies over the bed.

Trick is to get a sacrificial plate and get the router to mill this flat, don't move it and attach to that.
You can buy some gel mats that are sticky on both sides to hold flat panels securely without bowing, not cheap but they do a good job.

I think I will have to route pocket, I have a vacuum table to hold the PCB's but its on the MDF top. Any tips on removing KRESS collets? I use pliers but the weight and power I have to put in removing the collet after undoing the net I feel would affect the accuracy of the machine every time.

I know, they are a pain in the backside, in fact they no longer sell just the collets, you have to buy then with a nut now.
I support the nut on an old socket and tap the collet thru with an alloy drift.