- Single sided boards are straight forward to mill.
- Double sided do tend to be more tricky as the alignment can be difficult when flipping the board
- I did it quickly and tested the circuit.
- I have to make changes so I have not lost a week waiting for the board to come back.
- My machine has manual tool change and I prefer that as I can keep an eye on the machine.
Let's take a serious look at this example ( i will try not to rant and rave... Promise ) ohhh, this is going to be a long one...
1) Single sided boards are indeed 'easy'. Pop in a plate of copperclad and away we go. Setup time is a few minutes. I remember that from my 95S. Drill two registration holes, put the pins in , load the file, let it generate the milling pattern , set home and off we go. Fine
Problems:
- You need to use their board material ( at least with the 95S ) as it has thin copper ( half ounce). They jacked up the prices.
- you need sacrifical material as well , or you drill in the bed of the machine....
- the plates are made for the bed of the machine. Drilling the regholes means you only could use about 3/4 of the available surface to avoid the head running into the registration pins. Everytime you mill a board you have scrap material.
Your particular board has what . 8 mil track and gap ? I can etch that with a spunge in 3 minutes. Faster than the lpkf can mill it. But, granted, no chemicals. The cost of the milling bits though ...
Now, in order to do this particular board : how much extra time did you spend to tweak the layout so it could be made single sided? How much concessions did you have to do in terms of design rules? That also costs money. Answering 'it's a quick proto , the real board will be doublesided' fails you. The goal of a quickturn is to have the real deal fast. If you need to rework it for production you are burning again time and money doing another layout and introducing additional variables in the system. The quickturn needs to be identical to the production.
2) double sided tends to be more tricky. Nah, once you got the registration holes drilled the machine software does the rest. But... Doublesided is one step. Metallisation is the problem. Sure you could tweak the layout so you can use stubs of wire or the component pins if thru-hole, but you still could not place vias under a component. And you fall back to the problem that your proto is not identical to your production. Duplication of work , introducing variables, time, money, yaddayadda... And you have to solder all those bridges which costs again time and money... You can buy their plating system (multicontac II) which i also had. Oh boy now we are golden... Ehhh here is how that stuff works:
-now you need their board material. No escaping. They give you a special substrate , doublesided but each side has two layers of copper. The top layer peels off and acts as a protecting surface for the mill so it doesnt scuff up the layer beneath when drilling and so it wont corrode. You drill regholes , drill all the holes first , and go through the plating process. They use basically the black hole process with a twist. You first go through two nasty chemicals that etch the fiberglass material in the holes. Here is problem 1: there is no agitation. So on small holes air bubbles can get trapped meaning the copper wont stick very well later.... After a quick wash ( darn it now i need running water and a drain and a permit to dump that washwater down the drain....) you get into the black ink. Again no agitation.... That ink has a limited lifespan... And is expensive. You need new chemicals every 6 months, used or not... And getting rid of the old ones is a hassle too. You are not a pcb house that knows what to do. Oh ,but here is -tatadadaaaa- lpkf to the rescue. You can ship it back to us. We send you two big drums , pour everything in there and ship it back. Of course the drums cost you but it makes life easier. You do need a chemical transport though... Good luck finding one. I spent three weeks on the phone with various companies.( this is hazmat)
-what's in it?
-Ehh, dunno. It's from lpkf. Plating solution and some other stuff.
-We need description and chemical names sir for the paperwork.
-Ehh lpkf process is 'secret' they don't release the names of the chemicals.
Eventually the transport company got in touch eith lpkf and it was all sorted out. But still three weeks.... Time, money .. All that stuff you know...
Where was i ? Ah yes. So we now have black ink. Time to dry the board and peel off the extra copper foils so we have clean , unscuffed copper and holes with dry ink in em. Time to pull out the pocket microscope and inspect each and ever hole.. Dont want any air bubbles in there.. Time keeps on ticking ticking ticking.. into the future....
Plating time ! Woohoo. This has agitation. Oh but wait... How much current do i need ? How long ? Do i need to add a bit of glycol to the plating solution ? What all that muck floating at the surface ? Is my solution well balanced? I dunno , let's wing it and see what happens.... Fast forward an hour or so ( as their plater is grossly underpowered )
Pull it out wash and dry ( permits....for the wastewater). Now, they don't use pulseplating so you do have problems with phosphorisation( or is it sulphurisation.. Can't remember. The deposited copper is of lesser quality than the real copper and it has trapped one of the chemicals elements from the plating solution. H2s04.. Ah yes sulphurisation it is. That is what pulse plating is about. It strips the sulphur deposit by temporarily reversing current. ( many times a second )
Anyway. We now hopefully ha a board where there is copper in each and every hole .. If there were no air bubbles, if there was ink in every hole... If if if..
Milling time. Time keeps on ticking ..... Flip the board ... Time keeps on ticking ... Oh no , it broke a milling bit ! Oh no the software crashed ? Oh no it crashed and milled a line to nowhere cutting through half the traces ... Redo from start.. And you have to use a complete new panel because you need the double foil....
In practice: to do this you spend a whole day drilling , washing, inking, drying, inspecting, plating, washing, milling in the hope to have a board. 8 hours.... The shop around the corner, which is a real board shop, can do it in 4... With soldermask silkscreen and flying probe test... Oh wait ! What? Test !!! Darn it, i knew i forgot something. Assuming everything went right and the machine did not mess up , we still need to test our vias! surely we are not going to assemble a board with vias under components without testing it ! So grab your favorite ohmmeter, magnifier and prepare to burn the midnight oil testing each and every via.... Timekeeps on ticking...
Oh boy.. And i'm only at point 2.. Time for point 3
3) i did it quickly and tested the circuit. No you didn't, you spent half a day trying to make a singlesided layout , another half a day futzing around with a machine and assembling a board that was nowhere near the real deal. If you find a mistake you are going to burn another day futzing more with that machine. You self admitted you don't like the toolchanger because then you can keep an eye on the machine. These machines are very addictive. Just like the 3d printers . You assume to shove something in there and let it do its thing while you go off and be productive at something else.. Not! You sit there watching the darn thing. Meanwhile the dollars fly out the window.... And the boss pays ( or if you are a one man shop... You pay.. Through the nose)
Now, your board has what, 20 parts on it ? You could have grabbed a little demoboard from the cpumaker for 20$ , spiderwebbed some thru hole stuff on it and tested your design equally well. The time it costs you to solder the parts on that pcb is equal to the time soldering the spiderweb. You saved the time on the machine and the time doing the special singlesided layout. So i just shorted all that time and money. If it is a one off : build it on perfboard.
4) a week ? Any pcb shop out there offer 8 hour or next day turnaround. Live in a high-tech area and you can get 4 hour. 8 hours doing it yourself or 8 hours where someone else does it while you do something else. You surely are not sitting around waiting for the board are you ? There is other productive things to do meanwhile. And in raw cost ... I'm betting the pcb shop will be cheaper, even on an 8 hour turn. Plus: real board with soldermask, silkscreen , full electrical test and surface finish to your liking (hasl, enig, enepig, osp, tinflash, silverflash : you pick)
If this is for schools: many a boardhouse will strike deals for cheap boards. Students don't waste a day milling their board and they don't need it then and there either, as the day will be over and tomorrow they have a different subject to study. Labtime comes along again next week. So you have 7 days of fabtime (most boardshops run 7 days a week so the chemistry doesn't go off)
Plus no clumsy student fingers drilling in their hands, breaking bits, messing up settings, or otherwise vandalizizing the machine and holding everyone up. Yay! We have a win-win situation.
-i can keep an eye on it. If my boss catches me wasting time staring at that machine he'd first fling it trough the window and then me through the door.
Now draw your conclusion....
Mine says : It may work for that 1% of the boards out there.. The rest ? It takes more time and costs more money and it ain't worth the hassle.