You got it while I was posting the solution as part of my big update 
Yes. I had neglected to re-enable printing holes so they got left off in the “fixed” version. Obviously not the end of the world since they get drilled out anyway. But they really do help with lining up the drill bit. And the ones for jumpers in the poured areas disappear completely without the holes.
For the scaling problem…
Make a grid in PS, the size of a sheet (A4 or letter depending where you live), with a 2.54mm spacing.
Print that on plain paper.
Measure, verify it doesn’t vary along the length and the width.
It does happen with laser printers, especially in the width direction (that’s because the laser is deviated by a rotating mirror and that has to be compensated to get exact scaling along the whole width)
Then compute the scaling factor.
It can be different in both directions, in which case you’ll have to resize in PS and print at 100% (I think that’s the best option even if the scaling is uniform, you can use fractionnal percentages while the printer usually doesn’t allow that).
Did a few tests last night comparing the Print to PDF output from kicad to the Plot to PDF output in Kicad. I had been using Plot but gave Print a try and the scaling issue seemed to go away. But…the output from print isn’t nearly as good. Like the pads on the DIP socket:
See how the center is offset a pixel or two? It’s not if I do a plot output. And if I take this and invert it in photoshop (since you can’t print to PDF inverted) it gets even worse…I wind up with lines through the middle of the pads that only get enhanced when printed in B&W:
But…I went back to using the Plot output and now I’m not getting a scale mismatch. I think the problem was Plotting as SVG instead of PDF was introducing the scaling issue. I’m now getting prints that are the correct scale at least.
Though I’m still experimenting with print settings to find what causes the least distortion. I tried label mode and that reminded me that this printer has a straight through paper path option - and that seems to help quite a bit. (though there’s no much room behind my printer so the sheet can get scrunched when it comes out and then it does get distorted worse.) The less curling mode doesn’t seem to make any difference. But with the paper type set to label and the back open I’m getting much better results that I can layer more accurately.
Though there’s still always one trace (not always the same one) that just doesn’t want to line up right.
Before I went to bed last night I tried one more suggestion and put a few drops of water between the transparencies to hold them together while I lined them up. That one appears to be almost perfect…and this morning it’s still aligned. So I may give that a try tonight.
I also found a number of people suggesting a particular laser printable vellum which is only translucent - but apparently passes UV quite well and holds toner better so they get very good results with just a single layer. I ordered a pack to try.
I also had a few other thoughts about exposing the UV film yesterday.
I have a laser on my CNC and a CO2 UV laser. The laser on my CNC is 445nm - that’s just a little outside the 100-400nm UV range…but may still have enough UV to work. The CO2 laser would definitely work…the big problem there would be getting it it to run low enough power and move fast enough to not just burn away the film. I’ve found a few other people who’ve used both methods…but having to raster trace the whole design it would take way too long on my CNC…the CO2 could probably do it in a reasonable time…but…my CO2 needs some serious TLC before I can use it. I upgraded all of the mirrors a few months ago and trying to re-align them has been frustrating to say the least. (Mostly due to lack of space around the laser which makes it very difficult physically to reach the mirrors let alone make tiny accurate adjustments to them.)
I also found this interesting project: https://hackaday.com/2017/06/15/laser-pcbs-with-ldgraphy/ he uses a fixed laser with a rotating mirror and a 3rd fixed mirror to trace lines. It still takes about 8 minutes to expose a small board but he seems to be able to get very detailed results. Unfortunately the project hasn’t seen an update in 3 years and was still in a state of development when he seems to have moved on to other things. And most of the updates/info were on google+ and are now gone 
Plus for smaller boards like these I still want to experiment with printing UV resin onto the board to act as a mask. But…it’s really only practical for very small boards and I don’t think it will give anywhere near the detail the UV photoresist gives.
Or you can do this :
Well, if you’re already out of real-estate, another printer may not be the smartest move…
Love Marco’s videos…hadn’t seen that one before! I wouldn’t have thought of using acetone vapors to fuse the toner…didn’t realize that was possible. Definitely an interesting approach. I was kind of thinking along the same lines when I saw my printer had the straight through paper path option…started wondering if I could get it to print straight to a board. But…didn’t want to risk damaging the printer printing on something that thick!
I see he has a more recent video where he uses a 405nm laser diode on a 3d printer to expose boards:
And a comment on that first one that he now uses a laser engraver to expose boards:
So my idea of using my CNC isn’t too far off…but I like his idea of using paint as a mask and then burning it off. Which is a lot quicker than doing a raster of the whole board.
His approach towards flexible PCB’s is interesting as well…
Though his most recent PCB video he seems to have gone back to UV resist with a 405nm laser to expose it:
I’d have to swap to a different laser module to do this on my CNC…but I’d probably pick up one of those cheap 2020 rail based engravers if I wanted to go that route since my CNC is setup more for big material rather than ultra high accuracy.
And the big issue is that any of the laser exposing methods aren’t great for big fill areas since you’re having to do it with a tiny dot being traced over the area…
Still…I may fire up my CNC and see if my laser diode has enough UV to expose the resist…
Lots of options…
I have not enough time to keep up with all his videos.
Definitely will have to browse thru his latest ones.
I’ve been a big fan of his for a few years. Lots of great stuff on his channel. I had totally forgot about his laser PCB experiments but remember watching them when some of them came out. I hadn’t seen the modified laser printer though - that was before I found his channel.
Also, I remembered that I have a pad of vellum here from another project. I already ordered the vellum designed for laser printers and which several sources recommend but thought I’d see if the laser can print on the vellum I have.
It can!
Though…even with my printer set to maxium density I’m not sure a single sheet is going to be dense enough for a good exposure. I’ll try it but I’m wary of how well it may or may not work.
But - it also doesn’t deform from the heat like the transparency film is. So stacking two layers is MUCH easier and appears to give better results than most of the stacked transparencies I’ve done (the one with water to hold the layers together is still the best and maybe slightly better than the stacked vellum…and that trick doesn’t work well with the vellum since the fibers get too wet too fast and it starts to warp.)
So tonight I’ll have to try 1 sheet of vellum, stacked vellum, and the stacked transparencies with water to help align them and see which gives the best results. Good thing I got a lot of boards cheap to experiment with 
(And more arriving today…this time in a size that will fit the yusynth boards so I can build some of his designs.)
Ok. Time to get a little serious and stop just playing around. I’m going to try and be a little more careful and control some variables a bit better.
I’m past the bad part of the roll of UV film so that problem solves itself. I was more careful cutting a piece off and this time I put the board in water and put the film on the the board under water. This did seem to help a bit. I was able to slide it around and work out any air bubbles quite nicely. I think I got the most evenly consistently covered board yet. I gave it 4 passes through the laminator - 2 on each side.
I stepped up my exposing game. One of my nicer tripods (inherited from my wife) has a big 3/8-16 threaded screw on the bottom of the center post. So I fired up Fusion 360 and designed a little adapter that would thread onto that (since I didn’t have any 3/8-16 nuts on hand and didn’t want to deal with going to the store just for one stinking nut) and printed it out. The design took about 5 minutes and the print about 35. Man I love having a 3D printer
The threads on the bottom of the tripod shaft:
My quick and dirty adapter:
F360 has a built in tool for making threads now…the hole doesn’t even have to be the right size…just close. So easy. Even on a low quality setting for my printer they printed out well enough to screw onto the threads just fine:
Then grabbed a few bolts washers and nuts…they aren’t the idea size…but 10-24 is what I had on hand and they’ll do:
Extend one section of legs on the tripod and position my UV lamp 12" above the top of my contact printing frame…seems like it should give full and even enough coverage:
So…now I have a way to get consistent exposure!
Let’s do an exposure test with that nicely coated board. I found a nice set of exposure tests here: https://ezcontents.org/pcb-fabrication-part-1-dry-film
Printed them out on my vellum and decided to see how a single piece of vellum would do. There are 10 swatches on the exposure test so I did 10 - 30 second exposures. I started with a piece of cardboard covering all but one then pulled it back to expose the next set of tests every 30 seconds…with a timer. Then developed it.
This was where I made another mistake. I forgot to remove the protective film off the resist before developing it. After 5 minutes in the developer it STILL wasn’t developing and I was starting to really wonder why. Then I noticed the film separating from the board and remembered…oops. I ripped part of the resist removing the film. I’m not sure if that’s because the developer had softened it or if my 4 passes through the laminator weren’t sufficient with the water I used to position the resist. Bummer…that makes this test a bit less helpful. But…still good for judging exposure through one sheet of vellum.
And here it is:
Ok, so right off the bat - 30 seconds won’t cut it with vellum. And the entire second half is no good with the areas that were masked off showing quite a lot of leakage. Let’s take a closer look:
Ok. So about the same. 2 looks a bit underdeveloped, and 5 looks like it’s showing a bit of leakage. So let’s zoom in on 3 and 4 (or 1:30 and 2:00):
These both look pretty darn good. I inspected them under my microscope…and actually took a BUNCH of close up photos I planned to share…but…the scope saved them all with the same timestamp and non-consecutive file numbers. So it’s really hard to tell which is which
but I’m pretty sure this is the center of row 3:
That looks almost perfect. But…if you look at the top of row 3 in the big picture you’ll see some of the tiny text up there isn’t quite right. Here’s a look at the tops of #3 and #4:
So the text at the top of #3 seems slightly under exposed…but the text on #4 looks a little overexposed as its’ starting to block up.
Same with the second set of lines…on #3 they’re well separated and clearly defined…but on #4 we’re starting to get some bleed between them.
So for one sheet of vellum I’m thinking an exposure of 1:45 is looking like it may be the sweet spot. Or at least pretty close to it. And it looks like 1 layer of vellum will resolve 10mil traces.
Note - I think this test pattern actually came from here: https://github.com/sleemanj/pcb-test-pattern
And was reworked based on the text in the blog post where I found it. And I think he shrank it down (inadvertently or not I can’t say) when processing it as it looks smaller to me. Now, I don’t trust my cheap calipers on something this small…but that 8 at the top of #4 measures as 0.025mm wide - which is just about 10mil. So I’m masking things here that are quite a bit smaller than the 10mil traces kicad is configured to generate.
I think it looks like one layer of vellum with an exposure in the 1:30-2:00 will give me a successful mask for a high quality modern board layout.
For the Yusynth layouts…it should be a piece of cake.
So…I think I’m going to make a few final tweaks to mine…print it out once more. And give it a go again now that I have these exposure tests to go by!
Alright…I’d say this is a big step up from my last attempt at this circuit. There are still some fairly serious issues…but if the drilling goes well tomorrow I think I’m going to try and build this one.
I laminated the UV film and then exposed the board for 1:45 with a single layer of vellum. When I went to peel the protective plastic off I ran into my first issue as the film wasn’t completely bonded on two corners. I could have started over at this point…but the two bad areas weren’t in critical spots so I wasn’t overly worried about them. A bigger concern was that I saw some signs of bleed through the toner in a few places. But I was hopeful it may be under exposed enough to wash away in the developer.
A lot of it did. But not all of it. Still I decided to go ahead and etch this board. So while I prepared the etchant I put the board back under the UV to extra harden the mask. Some of the sites I saw with the best looking results suggested this so I figured I’d give it a try. I could definitely tell it darkened the mask considerably so I assumed it was also quite a bit harder. Here it was ready to go into the etchant:
I should have stopped and taken some time to clean up a few spots where there was substantial bleed. I should have actually done that before I hardened the mask. Live and learn.
Still - the mask looks a LOT better than last time and even the artwork I added (copied from MFTM’s original schematic and cleaned up in photoshop then made into a custom footprint) appears to have come out well.
After etching:
Still looking about the same. There were a few areas that didn’t etch as well as I was hoping and the process still took longer than the first time. I think tomorrow I’m going to give the Muratic acid version a try since everything I’ve read says faster etching times have fewer issues.
Removing the mask proved quite difficult. I tried a stronger washing soda mix but it didn’t seem to help. I also tried acetone and it barely touched it…same with a scotch brite. Oh boy. Well, some sites suggested longer time in the washing soda with heat so I put it on the 3d printers heat bed and tossed in an extra teaspoon of soda and left it for 30-40 minutes.
That got almost all of it off:
So the good news. A lot of fine detail really did come out well. And I probably can fix the bad areas and actually make this board usable. The left corners are damaged…but not to a point that ruins anything.
You can see that I used a setting in kicad to give me smaller holes this time which I was told help center the bit better. They don’t come across well in the photo - but they are there.
I think a slightly shorter exposure may have worked better. Now that I know how the film can be re-exposed after development my thought process around exposure is shifting a bit. yes…a denser print would still make this come out better…but I think a 1:30 minute exposure would have worked better and still give me all the detail I needed. I’m also thinking that maybe making a few tweaks to the light source to better collimate the light may help get more even exposure since it’s fairly obvious that the center got more exposure than the edges. Raising my light higher may help as well…it will reduce the intensity but may give me more even light.
I also think improving the exposure with the vellum is more likely to give consistently good results than trying to deal with two layers of either transparency or vellum. And honestly…most of the problems here would be better solved with a change in the design rules I’m using in Kicad to make easier to etch traces. I’ll definitely do that on the next board I attempt but don’t really want to bother on this one.
How about a few microscope shots to finish this update off?
The custom artwork came out better than I expected. Still a few overexposed bits…but more detail than I expected.
These two traces were some of the hardest to separate. Took me 4 tries with an xacto under the scope to get them apart from each other.
Here’s one of the spots where the mask wasn’t well bonded. The ground pad here was damaged…but still has one connection and I can do a few things to repair it still:
Here’s one of the other areas where overexposure resulted in too much leakage:
I’ve cleaned most of these up…will check it again tomorrow after I try drilling it. If drilling goes well and I get these spots cleaned up then I will probably try the solder mask and silkscreen transfer before I try soldering this up…but will likely try soldering it up.
There is an issue with the solder mask. Can you spot it?
There are pads that aren’t masked so they’ll get soldermask over them At first I thought I had screwed up and was using an older soldermask…but then it hit me. Those are the vias for jumper wires. I thought I had the “Do not tent vias” box checked which is supposed to remove mask from the vias but apparently I forgot. Thankfully the version I printed on vellum i did remember to check the box and that’s the version I plan to use anyway.
I suspect if I had done this with one of the Yusynth layouts my exposure from today would have given me a usable board. Most of the problems here are unrealistic design rules for the process - next layout I try I’ll know to set some more forgiving board rules before I start.
Overall though I’m really happy with how much improved this is over my last try. It doesn’t look that different…but it’s far closer to being a usable board!
So…good news…UV film as solder mask appears to work quite well:
Bad news…after drilling I forgot to finish fixing bridged traces BEFORE adding the solder mask. And it’s proving MUCH more difficult to do with the mask in the way…so the mask is going to have to come off. I probably won’t bother putting it back on before soldering up the board because aligning it was kind of a pain and it’s really NOT needed for this board.
But the 1:30 exposure seems to have worked quite nicely for it.
Oh - and the damaged parts of the mask…That was where I taped the board down while applying the silkscreen on the back. Apparently peeling tape off while it’s still hot likes to take the mask wtih it. Should help me remove the mask at least
And the silk? Uh…meh:
It was really hard to get it to stay aligned because the toner transfer paper is so slick you can’t really tape to it. And I should have scuffed up this side of the board first as the toner didn’t want to stick well to it. So…it’s better than nothing…but also not great.
But again - I don’t really need soldermask or silkscreen for this board. I was just curious to see how hard they would be to do. And they’re not that hard…but unless I need them I don’t think I’ll do them again in the future.
So - going to strip the mask. See if I can’t finish cleaning up the bridged traces…and then try building this thing.
Well, I may give the 808 board one more try. Stripped most of the mask and did some work under the scope cleaning up traces…but there are still bridges I just can’t find or can’t eliminate. Feeling like it would be time better spent just chalking this board up as a learning experience and exposing another.
But…while it was stripping I gave a Yusynth board a go.
First…I remembered…I have a full darkroom setup in storage…including a nice exposure timer. So since exposure is where I seem to be having some issues why not step up my game a bit more.
So…Yusynth EMS diode VCF you’re up with a 90 second exposure (15 seconds shorter than I used for the 808 board.)
And…still seems a little overexposed…but not evenly so:
But the traces and clearances are big enough on this board that I’m going to go for it:
Also switched to HCL based etchant this time. Seemed to work quite a bit quicker despite not being as warm. But also not something I’d want to use in the house. And my 3 year old bottle of HCL cracked (not surprising since it’s been sitting outside in the desert heat) so if I want to keep going with that I’ll need to pick up more.
So it seem I’m still having exposure issues with a single layer of tracing paper. I really don’t want to have to double up sheets. Even with the design rules more like Yusynth’s lining up two printouts is just one more place for problems to creep in and something I really want to avoid.
I have some toner reactive foil on order that will be here in a few days. That’s one method that may work to make the negative more dense.
But - it also seems the exposure just isn’t even enough. So I’m back to thinking about modifying my exposure lamp. This morning I started making a quick and dirty solution to get better collimated light. This site has some instructions on building a proffesional style UV exposure setup. I saw that they recommended using 1/2" deep 1/2" square black light grid to collimate the light. I know I can get white grid at the hardware store…but I have a 3D printer and black filament so a few minutes in Fusion 360 and a few hours on the printer:
But…I didn’t read the full instructions before designing and printing that. Whoops.
They say to stack two pieces of the 1/2" grid to get a 1" deep grid. And they say to place it 2.75" away from the lights to avoid moire fringes. And sure enough when I put this in front of my light I get a lot of moire fringes. Grrr. It took 5 hours to print this - printing a taller version is going to take quite a bit longer. For now…I put a piece of tracing paper in above the grid…that seems to have softened things up and eliminated the grid pattern at the expense of cutting out a good bit of light. I’ll give it a try while I wait on the new version to print.
So…looks like I get to do some exposure tests again.
And that yusynth board is probably done stripping the mask so I should go clean and probe that to see if it’s worth drilling. I really want to solder SOMETHIGN today (I think I have all the parts for my gate grinder…but I really really want to solder a board I etched!)
Alright. It’s not perfect…but probing it out there are no broken traces and no bridges so I’m going to build the Yusynth filter tonight (as long as have all the components…I think I do…)
Backlit view:
This is the worst part…this part of the board got a bit more exposure than the rest:
But none of it bridges so I’ll build it.
And…doing an exposure test of my modified light. Here’s the light as I’ve been using it (actually this is raised up a good bit higher than it was to help even things out and show the uneven light better), not sure how well the photo shows it but there’s a cross shaped hot spot - in person it’s really obvious:
Here it is with my attempt at a collimator attached - since the grid is too close to the lights there’s bad moire patterns that are really noticeable in person and the cross hotspot is still somewhat there- but a bit less so in the photo:
But with a piece of tracing paper above the grid I now get this:
MUCH more even light.
But since it’s more than twice as far away and there’s a sheet of paper between the light and what I’m exposing now it will take rather longer exposure times. Which probably isn’t a bad thing given how big of a difference there were between the 30 second exposures. Having a longer exposure time should give me more wiggle room on either side of an optimal exposure.
Just exposed the test pattern…but our pizza just arrived so won’t try developing it until after dinner
Have you tried thick white PVC to columnate by diffusion? I remember this worked in the older lightbox style exposure systems.
I haven’t yet. I do have some 1/4" thick white acrylic…but…acrylic doesn’t pass UV well. That’s why it cuts so well with a UV laser.
And it appears that my two changes so far to even out the light may have gone too far. The last test came out completely unexposed. Just a few spots along the edges that got full exposure for the full 300 seconds / 5 minutes darkened. The combination of the inverse square law and the piece of tracing paper have cut down my UV enough that I need to start with a minimum of a 5 minute exposure with this setup.
So…I’m lowering the lamp back down about halfway and will do another test if it means more even exposure and getting good results with 1 layer of negative I can live with a 5 minute plus exposure. But…I have a feeling that pushing the exposures that long will only make the bleed through the dark parts of my negatives even worse.
Given the sizes of many boards I wonder if a contact exposure method using glass (say an old scanner bed with UV) might simplify matters. I still use magazine and laser printer for simpler things. Take a look at old 1:27 film contact printers for example to get an idea how to simplify your approach. Keep going. I’m bedridden just now and your progress is a great read.
Also your acrylic will let some UV through ; part diffuser and columnator. Sanded/frosted glass works as well.
That’s a common method - using an old scanner and putting strips of UV led’s into it.
If I had some strips of UV led’s on hand I’d give that a try. But I don’t. I can order some…but trying to see what I can do with what I have (I’ve bought too much stuff lately already!) Though even then they still tend to use a grid between the LED’s and the object being exposed.
Apparently just adding the layer of tracing paper as diffusor is REALLY cutting down the UV. I moved the lamp a foot closer to the contact frame and started with a base exposure of 2 minutes - then did 30 second exposures on each strip in the test strip. Lifted it up…and…it still looked like I had no exposure at all. So gave it another 2 minutes…wash, rinse, repeat…up to 8 minutes base exposure before it started to show any signs of having been exposed. I gave it another 2 for a 10 minute base exposure plus 10 30 second tests so 10:30 - 13:00 total exposures. It still looked a bit underexposed overall…but I’m leaning more towards under exposing than over exposing at this point.
The results…are…a little perplexing:
The left most colum is the most exposure this time with 13:30. The right most 5 is the least with 10:00
In general the left side looks better than the right…but confusingly the 1 column that got the most exposure looks worse than the 2 column next to it.
I’m guessing this is due to falloff away from the center of my lights intensity. With a 10 minute base exposure 30 second differences aren’t really big enough. I need to do another with 10 minutes base and 1 minutes columns. But that will have to wait until tomorrow. I need to take a break for a bit tonight!
Another thing I’ve considered is adding a turntable under my frame to help compensate for hot spots. I have a couple microwave turntable motors from when I scrapped a bunch of microwaves to build a welder a few years back. So it wouldn’t be hard to wire one up. I’m just worried it could add more variation if my exposure time is too low. But with 10 minute + exposures that may work well.
And…overall I think any of these would have given an almost perfect result with my 808 board. So while I’m not happy with 10 minute+ exposures it does look like I’m at a point where I can get a good exposure without any pinhole leaks through the black parts of my negative. Honestly on all of these the things that aren’t resolving are smaller than the smallest thing I’m currently looking to resolve.
I’m tempted to try and 14 minute exposure with my 808 negative just to see how it goes.
I’m pretty sure the acrylic would cut down the UV way more than the sheet of tracing paper does. Plus it’s expensive cast acrylic and I don’t really want to cut it down unless I have to. Or even peel off the protective film since it’s kind of earmarked for some projects once my laser cutting is going again. If I had some cheap extruded acrylic that was 1/8" thick I’d probably give it a try. But I don’t have any of that on hand right now and haven’t seen any at any local stores either.
I’m going to give this some more thought and research - but will probably try exposing my 808 board again tomorrow.
And maybe doing another Yusynth board. Turns out I can’t solder up the EMS filter tonight. I got it mixed up with the Steiner filter. I have the parts for the Steiner filter…I don’t have the parts for the EMS filter Maybe I’ll start soldering up that Gate Grinder just to melt some solder on SOMETHING tonight…
Ok - I really don’t know when to quit but I think I’m getting better at this. Decided to try one more board tonight. The Steiner VCF from yusynth since I do have the parts to build that one.
I didn’t stop to take photos during the process. Used the current light setup with a 13 minute exposure. I did have a bit of light damage to the mask along the very bottom of the board. I’m not sure where/how it happened though. I think it may be happening in the laminator since there’s a bit of a “bump” as the boards come out of the rollers and I’ve noticed the edge on a couple of boards isn’t quite right. So I may have to look into modifying the laminator or finding one that’s more suited to this (the path on the Scotch one I’m using is FAR from ideal.)
Also, I re-used the HCL based etchant from earlier since it supposedly gets stronger as it’s used. But I didn’t bother to heat it this time so it worked slower and that may have affected the etch quality in a few places.
But it’s still a usable board and other than the spot on the bottom where the mask was damaged I think it’s my best yet:
Back lit to show some details:
What’s funny is that while most of it came out far better than my previous attempt at this board - which never went past the mask since it was inverted - the logo is probably the worst part. On the inverted mask that was one of the clearest parts:
Too late to drill AND build this tonight, and I don’t really feel like going out to my shop to use the drill press again anyway right now. So…tomorrow’s project.
And…maybe I’ll give my 808 board one more try with a 15 or 16 minute exposure since it has more detail and I don’t see any signs of leaking through the masked areas.
That one damaged spot I’ll probably augment with some leads just to make sure that ground trace doesn’t fail.
So “too late to drill” last night but apparently I decided it wasn’t too late to dig in on re-routing the 808 with new design rules for bigger traces and clearances. Next thing I know it’s 3AM and I’m realizing I should really get some sleep 
But…
Little happier with this now.
Initially I was just going to reroute a few traces that were worryingly close and hard to get a clean etch on. Then I wwitched to wider footprints on the transistors that will be easier to etch. At that point I basically decided to just reroute all of the traces and bump them from 0.25mm up to 0.35mm and increase the clearances similarly. Finally I moved the decoupling caps on the TL074 to be right next to the pins which should be a bit more technically correct and allowed me to clear up some trickier jumpers in that area.
Two ground pads are still shows ratlines…but…the are attached to the GND net so I’m not sure why they’re doing that. And fresh light of day shows me that I missed resizing the vias on one jumper.
And now looking at it I see a few spots that could probably be improved further by rotating a few components. But I think it’s “good enough” and worth trying to etch again. Between my improved exposure setup and the more realistic design rules I think I can get a good etch off this now.
So…tried exposing that with the same 13 minute exposure that worked well on the Yusynth board last night…and. Failure. It’s too underexposed. Even with the new wider traces some just didn’t take. The 808 artwork was almost completely lost. So I think I need to fix the exposure situation.
Thankfully the mailman showed up with some new options today Unfortunately he didn’t show up until about an hour ago so I don’t have a ton of time today to experiment with them.
1st - I got the strathmore laser vellum that a number of people suggest. It’s heavier than the vellum I’ve been using - but considerably more translucent. Seems to take toner well - but when I did two copies of a print out back to back the second one came out horrible with places where the toner just didn’t take. So apparently the printer needs to cool down between prints on the vellum. I let it rest a few minutes and ran another and it was just as good as the first.
So I suspect this will help shorten exposure times since it seems more translucent. Though hard to say how UV translucent it is until I do some tests.
2nd - I got a few sheets of “Toner reactive foil”. Note - this isn’t the special TRF sold specifically for PCBs. It’s the cheapest black foil I could find on Amazon.
So I did a quick test wtih it. I put two old printouts - 1 on my original vellum and one on transparency film through the laminator with this foil. I did two passes through the laminator on the 5mil setting. This…may have been too much as the foil wrinkled and appears to have been overheated. At the same time I didn’t get a perfect transfer.
Here’s a side by side on vellum:
Left is with foil right is straight out of my printer. You can see the foil did make it a lot denser…but it also lost a lot of detail. here’s a closeup that shows both better:
No Foil:
Foil:
But you can also see the foil not only bled over the non-toner parts it also didn’t bond very well to the foil.
But - on the transparency print it bonded to the toner MUCH better…though it still bled too much, foil on the left:
And a set of closeups:
No foil:
With foil
Looking at the “spent” foil you can clearly see how much better it transferred to the print on the transparency (top):
So I’m going to try the foil again at the lower temp 3mil setting and only give it one pass to see if that helps with the bleeding. But I have a feeling the toner would only help with considerably larger traces like on the Yusynth designs.
But - I’m going to replace my diffusion sheet with a piece of this new vellum and do an exposure test of a normal print with this vellum as well. I’m also going to try the foil on a sheet of this vellum since it’s freshly printed and may work better.
