What is the typical PCB fabrication process in a professional PCB house?

Question

I have been etching my own boards as part of my hobby interest into electronics, and I can't help but wonder how exactly is the typical printed circuit board manufactured? Unfortunately, details on the process are extremely scarce online.
I am aware that a similar question already exists, but it doesn't really explain anything at all and the answer to the question hinges on a youtube video that has since been removed.

I have been trying to piece together the process from information available online and from my own experience, with my current assumption (about single and double sided boards) being the following:

1. Hole drilling for holes, leads and vias on the bare dielectric substrate (e.g. FR4) followed by cleaning.
2. Activation for electroplating (applying a thin conductive layer) and rinsing.
3. Copper electroplating and rinsing.
4. Surface polising and cleaning.
5. Photoresist application, UV exposure and photoresist development (removal of either exposed or unexposed resist, depending on chemicals used).
6. Copper etching, rinsing and photoresist removal.
7. Solder mask application, UV exposure, development (removal of either exposed or unexposed solder mask, depending on chemicals used) and curing.
8. Optional tin and/or gold plating of exposed copper followed by cleaning.
9. Silkscreen printing, ink curing.

Is the order of steps at all correct? What solvents are used for cleaning? What chemicals are used for surface activation for electroplating? Which electrolytes are used for electroplating? Which etching chemicals are employed? Is the solder mask and photoresist applied as a dry film or as an UV curable ink, or is a photolithography technique used at all?

Yeah, I'm curious about everything.

Answer 1

Back when I did board design more actively, typical process was purported to be:

• pre-bonded (not plated-on) copper on board material (from outside suppliers)
• drill
• art onto photo-resist
• etch/clean/remove resiston inner layers.
• stack layers (and pray that they don't spin one on you)
• at some point in here mill the edge of the board to the correct shape.
• electroless (nickel? or copper?) to get some metal in the drilled holes so that plating could work.
• plating to get more copper in the drilled holes and connect the layers/traces at each drilled hole. Plating with tin or tin/lead to reduce tarnish issues.
• Etch the outer layers here, or after next step...
• Possibly masking and additional nickel and gold plating if there were gold contacts. Talk about your hefty upcharges.
• Solder resist.
• Silkscreen.

Actually, it may be that they only drilled the registration holes (which may or may not end up on the final board) before etching and bonding, and drilled all the component holes AFTER etching and bonding.) I do distinctly remember a probelmatic layout (by a fancypants outside contractor with CAD!) where the registration holes for one layer were off by 0.050 inches so the holes were not always catching full copper on that layer.

Never visited a fab house, but I designed a few boards and checked a lot more (including good old 4x photo-reduction art - who-hoo!) as well as making my own single-layer stuff. Multi-layer we sent out.

So, missing from your list would be stacking and bonding layers, and plating the through holes. On your list but I don't think it happens is plating on the copper in the first place - as far as I know it was and is a copper sheet/foil that is bonded to the substrate. In some cases it might be built up by additional plating for a hefty upcharge, but mostly it's not. Cheaper and faster to use 2 oz foil than to plate 1 oz up to 2 oz.

Solder mask was, as far as I know, silkscreened on just like the silkscreen layer - but this is also pre-SMT days so that might well be different now that things have to be more precise. Wave soldering was state of the art and all pins were at least 2.54 mm apart.

Answer 2

There's a pretty in depth analysis of the process in a book called Right the first time, chapter 41. The book's pretty amazing and it's a great general PCB design guide. You can download it free, but it does require you to enter name and email etc. The whole section is only about 12 pages long, it goes into the overall process but perhaps won't meet your desire to know the particular chemicals and technical specifications involved. I suspect that aspect is pretty different for each manufacturer and something they'd only release to their workers.