Making Double Sided Prototype PCB using CNC Milling machine

[Anil Gupta]

I am designing Electronics project for industrial & consumer   applications. I generally design using micro controller like 8051 series mcu.

For this often need to make small circuit boards for testing modules (sensor , wifi etc), Option is either use bread board or make small quantity of PCB through PCB fabrication companies

Both method has problem -(1) Bread board become very clumsy, messy wiring  & often chances of  wrong wiring.

(2) Fabrication through PCB fabrication companies - Even fasted service take 5-8 days minimum - 3 days for fabrication + shipping time. In India it is costly also. Even if you go for 30 mm x 30 mm board it cost USD 10 per board ( major cost is setup charges ) if you go for 5 days fabrication . And if some changes is required then again 5-8 days time & additional charges.If you are designing & testing new circuit , you often need to change design after testing result.So developing a small module may take 25-30 days

One option is to make  Prototype PCB using CNC Milling machine at home .PCB can be ready within minutes & in a single days you can have 3-4 test version of module .

I have seen video of this type of  making  Prototype PCB using CNC Milling machine and also series  of post & video  by Mr Esaj on this forum. His series is excellent & has detailed discussed & information on  this subject.

I want to purchase a decent  PCB CNC Milling machine which I almost finalized(CN 6040 type of  CNC Milling/routing  machine)

I found both software flatcam & bCNC good option for using with this machine. I will use Arduino CNC shield with  GRBL program.

I hope I will be able make good quality prototype PCB using CNC Milling machine using auto level option & good milling bits

But my only problem  is with double sided PCB. I have to use four alignment/marker hole option for this .

I wanted to know

(1) Which type of base material good for using as flat bed surface for placing PCB (sacrificial” layer)?

(2) How to hold PCB at bed surface? ( i don't want to use adhesive tape for that)

(3) alignment/marker hole will be drilled for every double sided  PCB. After some time there may be there may be overlapping alignment hole & alignment pins will  be loose ( as current aliment hole is overlapped by previously drilled hole making hole size bigger or distorted )

So often I have to change holding base. I also planning to offer super fast low cost prototype services in India using  PCB  CNC Milling machine and expect to mill around 30-40 pcbs per day

Is there any other method for aligning pcb( when pcb side is changed for bottom layer & vis versa ) is  for double sided PCB milling?