Woo Hoo! What a great end to the weekend!
It’s not 100% perfect…but it’s definitely my best board yet! The middle bottom has a few small bits of overexposure. And there’s one flaw in my layout which will have to be solved with a bodge wire (I found two ground sections are disconnected - no wonder I still had air wires. They weren’t coming from the ground pads…they were going TO the ground pads nearest the floating sections…but oddly enough the grounds on those sections didn’t have their own air wires.)
Let’s back track just a little to how this went.
Laminating the board was straight forward. I’m now doing this underwater in a shallow tub of cold water. I very gently wipe standing water off the outside of the board/film after removing it but VERY gently because I’m trying to leave a film of water between the UV film and the board right until it goes into the laminator. Since I’ve been using this method I’ve been getting flawless perfect sensitized boards. I use 4 passes through the laminator on it’s 5mil setting - I rotate the board 180 each time so the opposite edge gets fed in first - and then every other time I flip so the opposite face is up. I put the board between two sheets of copier paper while doing this for protection. The film is slightly larger than the board so it gets bonded to the sheet of copier paper. When it’s done I use a sharp knife cut cut the board free leaving the overhanging film bonded to the paper. I’ve been using the same carrier sheet of paper 2-3 times with no ill effects.
Once it was laminated I cut out a copy of my negative artwork and line it up with the board - then place it inside my contact printing frame. This goes under my exposure rig (which I’m still not 100% happy with) and with the new vellum I use a 3 minute exposure:
Note - here’s a shot of the old vellum on the right (staedtler brand I get at Staples) and the new (Strathmore laser translucent) on the left - you can really see the color/density difference:
The Strathmore vellum is much less opaque - but it’s also thicker and heavier and is more even in it’s coloration. But…I’m not sure it’s the best for this. It’s definitely better in my diffusor but I think I may go back to using the Staedtler vellum for the prints since it’s higher opacity seems to result in less leakage in the masked areas. I need to experiment here further still.
Anyway - after a 3 minute exposure the design is visible on the board but it’s VERY light. It goes into the developer (2 heaping 1/4 tsps of sodium carbonate in 1.5 cups of 95-100f water - made fresh so it’s at temp.) where I gently wipe it with a foam brush and the exposed areas darken and get more blue while the unexposed areas wash away. The developer will become milky as the unexposed film is washed away. You can rub it with your fingers and feel the design develop. The film is pretty tough but it’s best to be gentle still.
If you want to do any retouching to the film - now is the time to do it since it’s still somewhat soft.
Next I put it under the UV light again with the diffusor removed for 3 more minutes. This “sets” the remaining film and turns it dark opaque purple and the film gets very hard:
If I hadn’t been in a rush and had looked more closely I would have seen the slight imperfections near the bottom and cleaned them up before hardening the mask. They kind of jump out at me now. Oh well, the board still probed out OK despite them.
Then I took it outside and found I had forgot to cover my etchant yesterday and it was almost fully evaporated already. So I got out a different tray and made up a fresh batch - instead of 1:1 HCL/H2O2 I tried a 1:2 HCL:H2O2 this time. And promptly learned that the new tray had a crack in it.
After cleaning that up (thankfully the counters outside are due for replacement anyway!) I got out another tray and made up a second batch of etchant. This time my bottle my HCL is in broke even worse - but none spilled at least…it’s definitely time to get rid of that bottle and move what’s left into a better container! I put the shallow tray into a bigger tray with water I heated in the microwave for 2 minutes. It was around 100F I’d say but I didn’t actually measure it.
The board went in and I didn’t even bother adding any salt this time. The extra heat and H2O2 made for a much more aggressive etch and after just 2-3 minutes the board was completely etched:
I was REALLY impressed with how much more effective the etchant was with the higher H2O2 concentration and a bit more heat.
Then came the slow part - stripping off the mask. I almost bought some Lye at the store today…but I saw more and more writeups of people saying the only failed boards they’ve had were ones they used lye on. So I skipped it. Instead I re-use the developer but put it in the microwave for 1:30 and add 1 more teaspoon of sodium carbonate - then let it sit for 15-30 minutes. Come back and wipe it gently with the foam brush again and most of the mask will come right off if it didn’t already. If there’s still mask left I heat the solution back up for another minute and let the board sit for another 15-20 minutes.
Really stripping the mask when it’s done takes as long as the rest of the process combined.
And in the end I have a nearly perfect board:
Here’s some microscope shots of the biggest flaws I found:
This is actually a dent in the copper on the board. This board was sesitized, exposed, and cleaned several times and got a little scratched/dented in the process. But will still work.
This little dangler on the central trace shouldn’t be there. It was easily removed with an xacto knife just in case:
This was the worst part of the board. Again - a bit of work with the xacto cleaned up the traces. The lack of a drill hole in the one pad will make drilling it slightly trickier…but not that big of a deal.
I’m really impressed with the detail in the logo from the schematics:
This whole thing is about 10mm tall. The actual logo itself is just 160px x 146px:
And you can see most of the “poor detail” is from the original and the rest is from converting it to B&W loosing the greyscape info.
Ok - out to the drill press. And I may try adding a solder mask tonight - but I’m not going to solder this up until tomorrow. Don’t want to dig in on that this late in the day.
Forgot he had done some PCB fab videos…I’ll have to dig them up.
(which should be getting better soon thanks to another project I started…more on that in a moment.)
