All this opens the question to me of how do PCB Manufacturers solve Pooling (cheapest prototype boards are already produced as multiboards) and brings me back to: Ask the Manufacturer what he can do for you (if cost is your Problem as well).
I really see not why you would want to punish yourself with this task.
Really good Post from free_electron BTW
They solve pooling using either Fontline or ucam or the other fab tools.
You literally have to imagine it as a 'higher level' layout tool. just like we place components from a library ( a component is nothing but a collection of lines , pads and holes. . a board is a collection of components with additional lines pads and holes. ) they place boards.
So all the boards that we make are 'components' for them. they drop , rotate and shift these. the tool knows the design rules for the panel , in the sense , it knows how much milling space is required between boards. it knows how much the individual boards need to be kept away from the panel border ( they too need a border for the machines to grab the panel and the ink to run out. that is 'wasted space' but required for the machinery. there are registration holes for the machines and whatnot. in that border they also put impedance control coupons , alignment marks and a whole bunch of other fuff that pcb designer do not need, but they need for the production process quality and process control.
So they manipule whole board designs just like we manipulate components. Want mouse bites ? just like we have a trace router , they have a 'border router'. they draw the border and that tool automatically drops mousebites with the right distance between them so that the panel does not crack too easily , the bites autospace and autocenter on edges. castellations ? same thing. Those tools handle that in a few clicks.
you cannot do this as a pcb designer becasue you need to know the production process. are they going to use liquid ink or dryfilm ? what will be scored, what will be milled, what size router bit are we using. all those 'manufacturing rules' are driven by the in house machinery. pcb designers design a board and can send it into any fab out there. but the 'processed' data becomes fab speciic. you can not take those panel files and go to another fab. it may not work as the machinery is different.
They do even more than that. dpeending on foil thickness they actually oversize the traces we design to end up with the correct trace width. they drill larger than what we specify becasue what we specify is the end size they need ot account for plating thickness.
soldermask openings are adjusted depending on ink viscosity.
none of that matters for the board designer as it is fab specific , but it is not portable between fabs. even if those fabs belong to the same company ! this board ? only for that fab, we can;t run it in the other fab due to machine differences. if we can run it even then the 'fab' data is different. i have seen many times that a board got qualified , they changed fabs and there were issues. even though both fabs are own by the same company !
in the end : you can not do panelisation beyond simple step and repeat. And even then : leav it to the fab house. you may not know the criteria for milling channels . You'd think let's mill these boards out. nope. you need corner retaining or the completely milled boards go flying or shifting during the milling of the rest. if that bit backtracks over an already milled channel it will run straight through an already milled board. ( yes they have vacuum tables , but the risk still exists with small boards that fall between suction nozzles )
dont do it. it is a waste of your time.
if you absolutely must have a 'one panel' like for what they do in cheap audio equipment where they crack the boards post-assembly, then you need to design this entire thing as 1 board. but even then there are rules. Such boards are typically phenolic paper, single sided and smt bottom , thru hole top. it saves a lot of time on the pick and place line. you only need 1 line per whole product ( if a product has 5 sub boards you would need 5 different assembly lines the conveyer needs ot be adjust to the size of each sub board. and if the boards are non rectangular each board needs rails to fir the conveyer. that is waste of material and money. make a panel add rails to the panel. assemble the whole thing on one line then crack the assembly , put the main board in the bottom of the case, the frontpanel board in the front , the amplifier connector board int he back, a piece of the board with no parts gets hand soldered on the transformer , etc etc etc.
but that approach is done be designing the entire thing as 1 schematic place and route on one board. it is not done post layout. it is part of the layout.
There is so much about this stuff that people don't realize.. i had been making boards for 23 years professionally ( using fabs) and 8 years at home before that. Then i switched and became full time entrenched in board design and realized : i don't know jack-shit about this stuff... because i had only made rectangular boards...
Start designing boards that need to fit somewhere constrained. odd shapes , keep space between big electrolytic caps so they can apply hot snot to glue them. leave space for selective soldering or conformal coating ( that liquid needs to be kept away from connectors at it wicks in there due to capillary effects ruining the connectors. ) high currents, heavy copper ( 4 or 6 oz copper foils) . boards that do 300 400 ampere, reinforced busbars. Boards for radar at 76 GHz. Boards that run DDR4 at 3.6Ghz , blind, buried, stacked vias , plugged vias, flex-rigid-flex. And then optimize them for assembly speed and reduction of waste material ...
Soldermask ? that is no longer done the way you think . take a look at this :
or
That mask is DRY when it comes out of the machine. and that video is real-time, not sped-up.
Traditional masking is : paint the board with wet ink. let it dry , expose to a film or to a direct-imager. this hardens the ink. then wash away the uncured ink.
drying, time , wasted ink , ink going where you don't want it ( in the holes )
This inkjet machine ? the ink is liquid when it prints , but the inkhead also has a ultraviolet lamp that hardens the ink instantly. the moment the drop hits the panel it is semi-hard. there is only a post-print full cure step required.
Registration and trace widths are possible that you cannot do optically.
bUt .. do you think your local shop has those ? nope. these machines are so expensive they can only be afforded in mega-fabs in the far east. your local shop is still a paint-based shop.
oh, and they spray 2 colors at a time. Soldermask AND silkscreen in one shot !
You may be aware about optical inspection to find shorts and opens in a board .. but , did you know they are now repaired ? They laser cut shorts, and the laser engrave new copper !
And those machines are wickedly fast !
this thing is eye-watering ...