making double sided PCB's

[djh82uk]

Hiya

How do you guys go about making double sided pcb's on your mill? I can do single sided with no problems, but when i flip the board, i cannot get it to line up right.

I use mach2 and eagle/pcb-gcode.

i do the bottom first, then drill, then mill, flip, line up the spindle with one of the holes, switches off the steppers controllers and line mach2 up to the same hole.

I then switch on the stepper drives, and move the axis to the origin onscreen, zero all axis

then start the job.

It lines up but is far from perfect.

I know milling is not optimal for pcb's, but i would like to perfect it somewhat.
Any ideas?

DJH

[Oldmanandhistoy]

Originally Posted by djh82uk i do the bottom first, then drill, then mill, flip, line up the spindle with one of the holes, switches off the steppers controllers and line mach2 up to the same hole. I then switch on the stepper drives, and move the axis to the origin onscreen, zero all axis

There could be part of your problem; do you notice the steppers kick when you switch them back on?
Might be worth a try doing the same without switching the stepper off/on.

John

[djh82uk]

I guess i could use the enable line on the drives?

My biggest problem is getting the workpiece flat, i cannot find any spring loaded or floating heads, and im 90% sure that most of the un eveness is dues to the double sided tape as it gets air bubbles that i cannot get rid off.

I need some way of holding the boards, i was thinking what about say 1/2" aluminium with an inverted keyway milled down it that the board fits into, then screw them down tight into the mdf bed?

any thoughts?

DJH

[djh82uk]

I found this in a tutorial, does it make sense to anyone?

"Phase 3 was the one I was dreading the most, flipping the board over and lining it all up ready for the back. This turned out very straight forward. I had made a note of the dimensions of the 3 mounting holes. This can be done in Eagle by clicking the info button then clicking on the holes. Pcb-gcode references the back face dimensions using negative X. So all I had to do was send the mill to the hole offsets with a -ve X, jog down the z to line up with the drilled hole, then clamp the board down."

what that about -ve X?

DJH

[Robin Hewitt]

Have you not found Olimex yet?

I used to make my own pcb's but it really isn't worth the effort any more

1 piece 6.3" x 3.9" DS, pth, 2 resist, 1 legend, gold plated £17 plus shipping from Bulgaria. Okay he only cuts to rectangles but you have CNC.

http://www.olimex.com/pcb/index.html

[djh82uk]

Well I may well use Olimex for semi large runs in the future, but I have 32 various projects at different stages of prototyping that I hope to turn into products withing the next year or so, olimex is ruled out purley by cost, lets say an avergae board costs £10 to prototype, thats £320, and thats only if each board only requires one prototype, I don't have that much faith in my use of Eagle, or even in my electronics design. I could well be looking at over £400.

Wheras If I proto them myself, I find the problems, and I have only wasted a board that cost me less than £1. Plus i get to try and learn & perfect something I could not do before.

I have more time than money at the moment.

plus I have never gotten on with chemical etching etc, I found it very hard to get repeatable results.

DJH

[samco]

I flip the board and use 2 different sets of registration pins (and 2 different coordinate systems.) This is so I am using the same 2 edges on the copper clad as the lineup edges.

http://www.electronicsam.com/images/...ostart/top.JPG

sam

[martinw]

Originally Posted by Robin Hewitt Have you not found Olimex yet? I used to make my own pcb's but it really isn't worth the effort any more 1 piece 6.3" x 3.9" DS, pth, 2 resist, 1 legend, gold plated £17 plus shipping from Bulgaria. Okay he only cuts to rectangles but you have CNC. http://www.olimex.com/pcb/index.html

Dear Robin,

Many thanks for that. I stopped doing prototypes in my ferric chloride tank when the one-off Eurocard price got below £70. £17 plus shipping???? I'm gasping.

Best wishes

Martin

[djh82uk]

I agree that Olimex is very cheap compared to other proto services

Samco

How do you line them up? Thats a very precise looking board

Could you just go through a brief walkthrough of what you do, do you use PCb-Gcode and mach 2/3?

DJH

[kreutz]

I agree that the fastest way to test a design is by making your own PCB prototypes, that way you send only the finished tested design to the fabrication house and can sit for a few days waiting for the boards, knowing that your design is ready to hit the market.

Unfortunately, so far, I have no way to make my own pcbs, so my designs take a couple of weeks breaks between revisions to allow for the time it takes for the revised PCB designs to come back from the fab. That is the main reason I joined the CNCzone, in order to make my own PCB router someday...

Kreutz.

[Robin Hewitt]

Originally Posted by martinw Many thanks for that. I stopped doing prototypes in my ferric chloride tank when the one-off Eurocard price got below £70. £17 plus shipping???? I'm gasping.

It used to be $25 until RoHS and he had to start gold plating. He also tacks on VAT if you're in the union

Can't afford to make quantity anything in the UK but fortunately my main product was picked up by a company in Kowloon. Less fortunately I got cloned in Taiwan but they didn't do it so well.

Not for quantity, Olimex is really one off bargains. OTOH I do use them for a little interface card. I get 40+ from his standard panel plus an extra £1.65 for exceeding his 500 hole limit

You have to jump through all his hoops if you want to shop, this was my last $33 panel...

[martinw]

Dear Robin,

Nice boards.

Thank-you for the information.

Best wishes,

Martin