Solder Mask

[IconicPCB]

I use liquid photo image-able solder mask . No film, direct laser exposure.
Home made gear.
Expose and develop in calcium hydroxide.

Both solder mask and component overlay.

[sleemanj]

I use liquid photo image-able solder mask . No film, direct laser exposure.
Home made gear.
Expose and develop in calcium hydroxide.

Both solder mask and component overlay.

UV laser? 

I've never heard of calcium hydroxide being used for "developing" liquid mask, I've only heard of (organic) solvents being used (chinese usually say "gasoline", I think the last time I ever tried I was using mineral turps).

[james_s]

In the past I've used Pebeo Vitrea stained glass paint to make a solder mask in the past and it worked reasonably well. I haven't bothered in a long time though, a mask isn't really needed for DIY boards, if I do need it then I send out for the board.

I still etch boards at home fairly frequently though, I've got the toner transfer process dialed in so it's a piece of cake. A while back I wired up a small TFT display then realized I needed a boost converter for the backlight driver. I whipped up a circuit from the datasheet, did a layout, etched and assembled, it was under 2 hours from idea to finished assembled working board. If I had ordered a board and waited the project would have been stalled for weeks, I wanted to get the hardware done and working that day and easily did so. If I want a one-off and it's something reasonably simple then it makes sense to do it myself, it's easy and costs almost nothing.

Also it's kind of fun to etch a board, I mean why build anything myself when I can go out and buy a device ready made from China? It kind of defeats the purpose of a hobby to just go out and buy something. I've noticed there seem to be people who are compelled to project their own needs and interests on everyone else. They don't like doing something therefore it's a waste of time for anybody to do it.

[KL27x]

They don't like doing something therefore it's a waste of time for anybody to do it.

I personally don't get the UV soldermask thing, so I can relate to AR. I am so curious to know why OP wants an improved homespun solder mask to the point he is talking about precision measuring equipment. I suspect this might be a coppercone2 type of thread, but I hold out hope for some actually reasonable reason. OP, it sounds like you want a surface plate and a dial indicator, BTW, to ensure your solder mask is the same thickness all the way around to the nearest thou. Should only set you back a few hundred dollars, unless your boards are insanely large

The stuff on the market is essentially the same stuff the pros use, no? UV cured epoxy based paint? I think the pros apply with a silkscreen, though? Like the way they make high quality T shirts?

Heck, on FPC the soldermask is essentially a piece of kapton tape with holes cut in it.

[IconicPCB]

Liquid phooimageable soldermask is is screen printed on,
I have also tried short nap roller; results are so so .

Screen printer with a bit of time to blend the layer cover gives good results prior to baking it for exposure.

[KL27x]

So using your silkscreen plus laser CNC, I suppose you should get the same results as the professionals, more or less, but without making a custom silkscreen for every board.

edit: I imagine it takes awhile to expose the entire board minus the pads, though. And there's the clean up after the silk screening.

[IconicPCB]

correct. No product specific tooling, only soft tooling

[KL27x]

Well, there ya go. OP asked, and he got some cool answers. Two never before seen-on-TV DIY solder masks. IconicPCB pro-quality with just one re-useable silkscreen and a UV CNC laser cutter, and a quick and dirty solder mask with a Sharpie pen.

If he's Coppercone2's twin brother, he will find theoretical problems with every known method without having tried any one of them, and will (maybe) one day come up with something better just by thinking real hard. 

[PixieDust]

What happened in the coppercone2 thread?

The only reason I've got for doing all this is simple. If something is worth doing, it's worth doing right. So I'm trying to figure out a way to make PCBs at home that have similar quality to a professionally made board. Not trying to re-invent the wheel here. PCBs have been made for a long time now and to make one these days should be easy as cake because everything should be known by now.

I've got a dti, but I'm not sure whether it's up to the task. Was wondering if other people have experience in this regard.

[james_s]

You're not going to achieve the same quality in a home etched PCB as you get from a commercial fab, at least not without a great deal of work and expense. Home etching has uses but I gave up trying to make anything really fancy when the Chinese boards got cheap. Now I just make boards at home when I want something right away or a quick one-off.

[KL27x]

You're not going to achieve the same quality

I imagine you could. Probably for less than $10K in equipment, if your max PCB size is modest. The CNC mill is the most expensive part. But it's a process that requires a fair bit of dedicated space and a good deal of skilled labor.

What happened in the coppercone2 thread?

It's not A thread. Copper is one of our esteemed members. He very enthusiastically comes up with ambitious, exotic solutions that solve problems that are already solved, but his ideas include some theoretical improvement in some regard (which no one else understands/appreciates) but which is usually impractical for other very obvious reasons. He has some objection to every existing solution and every offered suggestion. Then, after going on about it in a way which might give the impression that he has all the parts and equipment and could actually undertake this complex, expensive, and ambitious endeavor at any given moment, he comes to the conclusion that the most efficient solution is duct tape and a garbage bag.

[3roomlab]

VQFN-56 (8mm×8mm) is possible but you may need to remove some of the "hanging chads" using a pair of tweezers.

I could see in the last pic there are copper rivets, but what is the small pins that do not look like rivets? are they also "rivets"  for "via"-ing?

[Fred27]

I assumed they were blobs of solder paste that had been applied with the stencil.

[Mark]

VQFN-56 (8mm×8mm) is possible but you may need to remove some of the "hanging chads" using a pair of tweezers.

I could see in the last pic there are copper rivets, but what is the small pins that do not look like rivets? are they also "rivets"  for "via"-ing?

As Fred27 guessed correctly, they are solder paste from the solder stencil, this was a 160 pin "Low Pin Count" FMC connector for the Zynq Zedboard.  The connector was mounted in the bottom side of the board and reflowed at the same time as the top-side components. 
To make the rivet connections more reliable, I now place an octagonal SMT pad top & bottom so that the rivets get covered with solder paste. 

[james_s]

You're not going to achieve the same quality

I imagine you could. Probably for less than $10K in equipment, if your max PCB size is modest. The CNC mill is the most expensive part. But it's a process that requires a fair bit of dedicated space and a good deal of skilled labor.

I would classify $10k in equipment, dedicated space and a good deal of skilled labor as "a great deal of expense and work".

[PixieDust]

duct tape and a garbage bag.

This will certainly not do .

[IconicPCB]

sample prior to immersion silver

[KL27x]

^Nothing wrong with that.

I would classify $10k in equipment, dedicated space and a good deal of skilled labor as "a great deal of expense and work".

I would, too. PixieDust never complained about the difficulty or cost of any of these methods. He has complained only of the quality and durability of results. I let him decide what is too much work or cost.

[PixieDust]

sample prior to immersion silver

Now there's something to write home about. Just to make sure I got this straght, you used screen printing for the soldermask and the silkscreen white text?

For exposure you used a laser CNC?

[IconicPCB]

Material silkscreened on in both cases.

Laser imaged directly on the PCB.

Copper mechanically milled off.

Holes activated and plated.

Copper electrically testd against gerber net list.

[IconicPCB]

At silver stage .

Surface finish suitable for wire bonding.

[PixieDust]

Copper electrically testd against gerber net list.

I was wondering why netlists existed. Now it makes sense!

[IconicPCB]

Gerber net list is the second best reference.
Your CAD package net list is the real source information.
Gerber files can and do contain errors.
There was a time when a well known CAD package  had issues with generating correct Gerbers.

[james_s]

That's a very serious bug. A PCB package that can't reliably spit out error free gerber files isn't worth having.

[Siwastaja]

That's a very serious bug. A PCB package that can't reliably spit out error free gerber files isn't worth having.

It's easy to say that, but that would exclude many widely appreciated, professional tools, such as Altium Designer, which has had serious gerber export bugs in the past (and probably still has some lurking around when you least expect it).

Mistakes happen. Software always has bugs. That's why you need to double-check. Having a PCB EDA which guarantees correct output files (and actually takes responsibility if not meeting this guarantee) would speed up the workflow and reduce the risk that errors slip through double-checking, but not a single PCB EDA manufacturer claims this feature.