Author Topic: PCB Isolation Milling Software for a fine feature test project  (Read 6351 times)

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Offline rx8pilotTopic starter

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Re: PCB Isolation Milling Software for a fine feature test project
« Reply #25 on: January 22, 2018, 09:03:42 pm »
Vacuum chuck plus z map seems like it would be the best trick.

I have Renishaw probes on my machine which is technically capable of pulling that off. The reality is that I would have to write custom software on the machine and on my desktop to pull it off. It may be a fun challenge, but the reality is the time necessary would be hard to find.

Regarding the high frequency stuff: I don't know what the surface finish is that milling leaves behind but it might result in higher loss than expected. For projects I am working on (mind you, these are > 100 GHz things so I don't know how this scales to 20 GHz) surface roughness of the materials is a big deal and causes a lot of additional losses. You might find the same happens when the edges are rough due to milling?

I'm curious as to the performance here and would be interested to be able to compare some results.

The edge finish is a combination of the tool, spindle speed, linear feed rate, and total runout at the tool tip. The Chemical process almost certainly has smoother edges but not necessarily consistent. At 20Ghz - things are rather sensitive. At 100Ghz - everything is broken and you just manage various levels of broken. Not sure how you pull that off - you are decades ahead of me.  :-+

I believe I can pull off very clean and consistent edges as far as machining is concerned, but not sure how it would compare to a normal chemical processed PCB. Keep in mind, my goal is to use this process to -
A: Do practical experiments to better understand the engineering and scientific principles as I study them.
B: So sanity checks on specific design elements to avoid a bust on expensive, special impedance controlled, fancy substrate, blind/buried vias, PCB prototypes.
C: Make various 1-off test fixtures

I do not expect to re-invent the wheel on the bleeding edge of RF design - only use it to educate myself on how variations in geometry impact the signals and how simulation varies from reality. Driven by 50% business needs and 50% pure curiosity.

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Online IconicPCB

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Re: PCB Isolation Milling Software for a fine feature test project
« Reply #26 on: January 22, 2018, 10:00:44 pm »
Unnamed,


Milling is not likely to produce much of a problem; is anything depending on the tool it is likely to provide a cleaner edge than the chemically milled boards.

Major problem is the smoothness of copper surface since the surface finish contributes to electrical length variation. We have machined cavity filters and pressed mu;tilayer structures in rogers material.
Major problem was adhesion of layers . Typcally surface texturing is used to improve mechanical anchoring of layers however in case of rogers materials w could not use pumice scrub as that would affect surface quality.

Rogers have an additional step in their multilayer pressing,  a liquid surface treatment whihc improves adhesion of prepreg.
 

Online IconicPCB

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Re: PCB Isolation Milling Software for a fine feature test project
« Reply #27 on: January 22, 2018, 10:08:28 pm »
Jeremy,

A floating head is a mechanism which slides on the surface of  laminate.
There is a depth adjusting mechanism to set the depth of cut.

Once set the head simply follows the surface variation over the contact area.

Z maps are fine over a short period of time and limited range of laminate temperature.
Once the surface of laminate is breached, the stresses inbuilt into the laminate change and laminate bow and twist changes as the product is cut effectively squandering away the beneficial effects of Z mapping.
Sure Z map is better than no Z map.
 

Offline rx8pilotTopic starter

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Re: PCB Isolation Milling Software for a fine feature test project
« Reply #28 on: January 27, 2018, 11:02:37 pm »
The supplies are trickling in......

Harvey tools supplied some rather pricey options that are very high-quality sub micro grain carbide. They specialize in micromachining and have end mills down to .001 inch[.025mm]! You can break these things so easy. The isolation tool is about $25/ea, the .063 compression cutter for routing is $51/ea! Scary.

I also got some bottom of the barrel eBay micro drills - about $6 for a kit of 10 drills delivered.

The test FR4 material is a range. I got .060 2oz, .060 1oz, and .012 1oz. I measured them and they are rather flat - within .0005"/.013mm which is better than I expected. There is a natural bow to the material, so the only way it will ever be that flat is on a precision vacuum chuck. I think with that level of flatness, I should be able to get some very fine features.

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Offline jeremy

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Re: PCB Isolation Milling Software for a fine feature test project
« Reply #29 on: January 28, 2018, 12:37:01 am »
FYI I've seen a number of cnc manufacturers recommend 17.5 um (0.5 oz) copper for feature sizes below 150um (6mil). Also to reduce the cutting forces on the really tiny isolation bits, they cut the 17.5um copper in 2-3 passes.
 


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