I use mostly single sided SRBF laminate and it is commonly slightly bowed. I attach this to the bed of the CNC mill using double sided tape. Mostly this works OK but if the bow is big enough it can lift part of the board off the tape which messes up the isolation milling.

Is there a sensible way of flattening this laminate at home?

 

I use mostly single sided SRBF laminate and it is commonly slightly bowed. I attach this to the bed of the CNC mill using double sided tape. Mostly this works OK but if the bow is big enough it can lift part of the board off the tape which messes up the isolation milling.

Is there a sensible way of flattening this laminate at home?

Can you do height profile mapping?

 

Can you do height profile mapping?

I do, but if part of the board because of the bow lifts up, even slightly, during the milling then the board will not be acceptable.

 

I do, but if part of the board because of the bow lifts up, even slightly, during the milling then the board will not be acceptable.

Have you considered using a vacuum table?
https://piersonworkholding.com/vacu...MItq2onJaQ-QIVQsLCBB0oHAuwEAAYASAAEgI7rfD_BwE

 

I did try a vacuum table but it wasn't very successful. I was using a vacuum cleaner as the source of the vacuum and I think it needs a much more powerful suck to work well and that gets expensive. Also you need to block off the parts not covered by the PCB which gets to be a bit of a pain.

 

Silicon rubber kitchenware makes excellent inexpensive sealing material for a home-made vacuum table. I have used it very successfully for sealing pogo pin vacuum test fixtures

 

I use mostly single sided SRBF laminate and it is commonly slightly bowed. I attach this to the bed of the CNC mill using double sided tape. Mostly this works OK but if the bow is big enough it can lift part of the board off the tape which messes up the isolation milling.

Is there a sensible way of flattening this laminate at home?

Hi
In general, PCB warp and twist results from un-balanced copper load on both sides of the board (naturally, as the board layup becomes more complicated, the copper balance is more complicated). In your case, with a single sided board - the copper is surely unbalanced, and the copper weight on the printed side will have a great influence on the amount of warping.
The best straightening strategy is placing the board in an oven with some weight on it and heating it as close to the Tg as possible, then cool very slowly. This helps in taking out the residual stresses, but be carefull - heating may cause oxidation of exposed copper, if you have some.
I'll be happy to further assist, if you need.

 

The best straightening strategy is placing the board in an oven with some weight on it and heating it as close to the Tg as possible, then cool very slowly. This helps in taking out the residual stresses, but be carefull - heating may cause oxidation of exposed copper, if you have some.

What is Tg for SRBF or SRBP?
How long should it be held at that temperature?
Would a film of oil (or something else) protect the copper?

 

As far as I understand, SRBF and SRBP represent a large family of materials, so as much as you can tell me the exact material designation, I will be able to give a better estimate. I suppose that the Tg is supposed to be somewhere between 110 to 130, but I am guessing.
Oil will be able to protect the copper from oxidation (as far as the oil's boiling point is well over your heating temperature), and before soldering, you will have to degrease it. Nevertheless, sometimes using simply an active soldering flux will also do the job, even for oxidized copper.

 

For instance: https://www.rapidonline.com/r-tech-copper-clad-fr2-epoxy-paper-printed-circuit-board-583654

A bit puzzled though as a site I found says FR1 is epoxy and FR2 uses pheolic resin.

 

Off the wall thought:
It may be a bit of a kludge, but could you add one or more spring loaded rubber caster wheels to push down on the laminate near where it is being milled?

 

For instance: https://www.rapidonline.com/r-tech-copper-clad-fr2-epoxy-paper-printed-circuit-board-583654

A bit puzzled though as a site I found says FR1 is epoxy and FR2 uses pheolic resin.

It is not possible to get the information from this web site, but after some "digging", I would like to offer you another site, that gives a bit of useful information:
https://www.bestpcbs.com/blog/2016/08/whats-the-difference-for-fr1-fr2-fr3-and-fr4-materials/

 

OK, so I will have a go with 105C and see what happens.

 

I tried this out and it does work though after the board has been left for a couple of weeks the surve does return but only slightly and would not be a problem for me.