Author Topic: Making high quality home etching easy - 6/6mil PCBs exposed with an SLA printer  (Read 1996 times)

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Offline TmaxElectronics

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Just a note to start with: this is not a full tutorial, only a collection of info about my idea. There is a little guide further down, but I will make a proper tutorial if the interest is there.

I know making PCBs yourself is mostly a thing of the past in the age of cheap express prototype board houses, but from time to time it can still come in handy to make your own.
I've been making mine the good old fashioned way with transparencies and an inkjet printer, but actually getting them right was probably the most annoying part of making the PCBs.

To make live easier I've started using the photomasking LCD from my Elegoo Mars SLA printer as a replacement for the transparency some time ago and I think I've nailed down the process now. I think I've seen a video of somebody trying something similar but he used the resin as a photomask, which didn't give as good a result as my technique, so I thought I'd share it here too.

First off: the results.
My latest PCB goes right down to 6/6mil spacings, and despite using the dry-film style photoresist for the first time and over-exposing it I still managed to etch it first try. Here are two 6mil traces between adjacent soic-8 pads:


I can easily get traces between 0402 and larger SMD components and tested qfn footprints down to 0.5mm pitch.

For double layer boards I also made an alignment jig, with which I consistently get the layer offset small enough for 1mm vias (0.7mm hole) not to short out against the ground plane from offset holes.

How to get the gerbers into the printer:
The Video I watched had the guy basically create a 3d model from them and then used the normal chitubox software. But that's tedious and doesn't easily allow for configuration of base-material parameters.

So I decided to write a little software that allows you to import gerbers, apply scale corrections, adjust layer alignment and some more things and then just gives you back your .cbddlp file for the printer. It support almost the entire gerber standard with the exception of arcs (at least for the moment).

But there's a catch... I'm not the desktop software kind of a guy; I can only program java and my skills aren't the best. That in combination with me getting easily bored by a project lead to me getting it to the point where I can use it, but not really anybody else (unfinished UI, no printer/exposure presets etc.). If there is enough interest in the project I will pick up development again though.
That being said, here's the repo: https://github.com/TMaxElectronics/Gerber2Chitubox

So here's the process:

First you'll need to modify the screen of your printer, this is a little dangerous so do it only if you are sure you can get a replacement screen (CHECK THAT! MARS SUPPORT WAS JUST DROPPED F.E.). By default the printers lcd has a glass pane in front of it for protection and likely flatness too. This however reduces exposure accuracy a lot (more like 0.4mm/15mil process) because of the lamp geometry. To fix this you will have to remove the piece of glass.

First (carefully!) remove the display assembly from the printer. unfortunately it is glued in quite well (at least it was in my printer) which made it impossible to do without damage. (this is where the replacement screen might come in

Once you have the screen out you can start separating the glass pane. The two parts are glued together very well but putting a drop or two of isopropanol in between the actual lcd and the glass almost immediately loosens the glue. Slowly peel it apart. It shouldn't take much force at all, if it does add a bit more IPA.

Then install only the LCD in the printer and put the thinnest non-transparent tape you can find around the outside of it so it looks like this:


I also recommend making some alignment helper. The one I made registers in the space for the resin tank to make using it repeatable. This is less critical for doing single layer exposures, but absolutely essential for double. Something like this (ignore the numbers):


Sidenote:
you can't print 3d without the glass in front of the LCD, if you have used thin enough tape however, you can just lay it back onto the screen. It will stick down a bit again but not enough to make removing it a pain. Make sure to re-level your build platform after that though.

sort-of-guide:
  • Export the gerbers from your PCB-CAD. You will want to tell it not to use arcs (altium has an option right in the last dialog for that)
  • Open them with the software I created. To do that, just run it with the java runtime environment, click the "+" button bottom left, and select all your gerber files. I recommend adding the drill files as well to generate centering holes
  • Export the individual layers. Select each layer in the list on the left and click export. Select your printer (currently only the mars 1 is supported :-[), and type in the parameters for your laminate.
    You also need to mirror the layer if it is on the bottom of the PCB. To make sure you are doing it right I recommend adding some text to each layer, and verifying that is it not mirrored in the layer preview in the export dialog. If desired you can add a centering holes too: select the layer with the holes in the bottom box, and adjust the hole size if you want.
    Then click export and name the file (right now you need to manually add the .cbddlp extension) and Copy the file to your usb stick like any other 3d print
  • Prepare your base material, developer, etchant and what other things you might need once the exposure is completed. Remember that the software adds 2mm clearance from the LCD edge to the print, and the LCD has a bezel too. That is to say: cut your board quite a bit larger than the dimensions you want it to be in the end, and trim it down afterwards
  • Align the base material on the LCD. Non mirrored layers will align on the right side while mirrored once are aligned on the left, this is so you can use only one reference edge for double layer exposures. You can briefly start the print if you aren't sure which side it will align on. If you're making a double layered board make sure to mark which corner was where so you don't forget it. Also make sure to sand any burs off the edges of the board or you might damage your LCD. To improve quality I also recommend putting some weights on the PCB, just make sure the base-plate arm won't hit them once its fully down
  • Expose the board. Select the file on the printer and hit start like with any normal 3d print
  • If you have a second layer to expose, flip the board and align it to the horizontally opposite edge (you can verify you have it the right way around with the corner markings you made on the board)
  • Develop & Etch. This step is the same as with other exposure methods.
  • ?
  • Profit (couldn't resist the joke :P)

I have recorded some video of me explaining it in detail but I'm not that happy with the way I did, but I'll re-record it if people are interested.
So what do you think, is this something that is just useful for me or a project that could help others too? If there's enough interest I'll document everything properly and also get the software up to snuff. I'd love to get your feedback on this :)
« Last Edit: January 21, 2022, 12:58:30 pm by TmaxElectronics »
 
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Online Zucca

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Edit: jeez those pictures are huge, sorry about that. Any way to make them smaller?

Code: [Select]
[img width=XXX]path_to_ing[/img]
XXX is the width of the picture....

example:

Code: [Select]
[img width=400]https://i.imgur.com/MkQ3AEc.jpg[/img]

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Offline TmaxElectronics

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XXX is the width of the picture....
Thank you so much, I've added that to the initial post  :)
 

Offline thm_w

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Nice work. Seems like a lot lower than 6mil is possible.
One thing that isn't clear, is the device still usable as a 3D printer, or has it been modified beyond normal use?


One of the older threads here: https://www.eevblog.com/forum/3d-printing/printing-pcb-with-3d-printer/
 

Offline E-Design

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@TmaxElectronics,

"I know making PCBs yourself is mostly a thing of the past in the age of cheap express prototype board houses,"....

Yes we hear that argument alot. However, the value of doing it yourself is NOT to save money in my opinion.. It is to save TIME prototyping.

With DIY circuit boards, one can go from idea to working prototype in *one afternoon*. and by evening iterate or throw away the idea.
One cannot (for any sane amount of money) purchase a PCB for delivery in a few hours. So I DIY boards to rapidly prototype and save time. The DIY method therefore is justified as a valid approach to this very day.

For that reason, I am very much interested and hearing more about what you have done here. Keep up the great work!

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Offline TmaxElectronics

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Quote
One thing that isn't clear, is the device still usable as a 3D printer, or has it been modified beyond normal use?
In theory it should be easily un-modified. If you keep the glass panel you removed from the screen and used some thin enough tape you should be able to just place it back when you want to 3d print something again. But full disclaimer: I haven't tried this yet. I rarely use my printer for its intended purpose and have a spare lcd on hand so I just swap out the entire assembly everytime I do print something.
I'll just do a benchy run tomorrow with the glass back in place, then we know more :)

Quote
It is to save TIME prototyping.
Totally agree! Even though 1 week is fast, there are some PCBs you simply need NOW :D
I haven't timed a full run with the new dry film resist because I'm still getting used to it, but with the pre-sensitised boards I could get from a gerber file to finished double layer pcb in hand in <1h (if it didn't have too many holes of course :P )

Oh and I forgot to mention in the initial post that I am also kind of working on hardware that will make things even easier. You can buy the LCD screens cheaply from aliexpress and it wouldn't be too hard to build some hardware that takes gerbers from an sd card or the network and throws them onto a display without any need for the chitu hardware at all. The display uses two seperate 4 lane mipi dsi interfaces, so an FPGA would be required.

But nice to hear people are interested, I'll be sure to update you on any progress I make (mainly with the still terrible software lol)
 

Online dunkemhigh

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But nice to hear people are interested

I am interested in the sense of following what you're doing and thining of possibilities. But would I use this? Hmmm.

I went through a phase of etching (still got a tank of etchant int the garage awaiting  some activity) but switched to milling. Apart from not having to mess with chemicals, and have somewhere to mess with them and then dispose of them, it was the holes that got me. Holes with relatively thin annular rings would be prone to the copper lifting when drilled, and getting accurate positioning on very small holes could be a drag. With milling you start with no tracks or pads at all, so making the holes is no problem and then the milled annular ring can be thinner. Perfect registration too. But it can be a lot of dicking about to get a good setup and I wouldn't even dream of trying to get 6mil tracks.

So, I am wondering right now if an answer may be to pre-drill and then use the holes to accurately position the screen. Previous etching setups used printed output which, even on film, could stretch. You seem to have the double-sided issue resolved so maybe that or a similar thing could be used for the drilling and exposing.
 

Offline nctnico

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Oh and I forgot to mention in the initial post that I am also kind of working on hardware that will make things even easier. You can buy the LCD screens cheaply from aliexpress and it wouldn't be too hard to build some hardware that takes gerbers from an sd card or the network and throws them onto a display without any need for the chitu hardware at all. The display uses two seperate 4 lane mipi dsi interfaces, so an FPGA would be required.
No. An NVidia Jetson module suffices; this has Mipi DSI output (depending on the model). But I think a HDMI or display port to DSI adapter is much more convenient. Just hook it up to your PC/laptop as an external monitor. I still have a UV exposure box; maybe an LCD screen is an interesting upgrade. However I have a feeling that the PCB needs to be as close to the glass as possible to get a sharp image. Then again, developing the PCBs has always been a bit iffy but that is probably also due to me using laser printing on tracing paper which stays a bit translucent.
« Last Edit: January 22, 2022, 08:06:19 pm by nctnico »
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Offline E-Design

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I've had good success cutting boards with a low cost desktop CNC (3018), and I am able to turn out a decent smt board with say a few dozen components in a couple of hours from start to finish.
Anything seriously complex or having too small pitch parts etc.. and I will send it to a board house.. but simple stuff is great to mill one out in a morning or afternoon.

With my current setup, I cannot achieve 6 mil trace / space so I keep things to 8 minimum and 10 is comfortable.
I am also interested to see what others are doing -- if it is somehow faster or can get finer geometries.

@dunkemhigh, I have not had any problem with the copper rings lifting on holes.. could be the batch or brand of copper board you are using where the copper bond strength isnt that great.. Ive had a couple of those and when I found them, I purged them out of my stock. Additionally, could be a drill speed (too slow) or plunge rate issue.. or too much runout in the setup. I agree with a lot of dicking about get a good setup.. once its dialed in though, great results!

« Last Edit: January 22, 2022, 09:15:47 pm by E-Design »
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Online dunkemhigh

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The pad lifting didn't always happen, but I figured the problem was too much torque for the width of the ring. Starting off with a narrow ring and then not getting the drill absolutely centered probably wouldn't help! Could have been a board quality issue, although nothing else seemed to be wrong with them.

The switch to dry working wasn't necessarily down to one thing, just a combination of several irritations.
 

Offline nctnico

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Over my life I have etched a large number of boards. Drilling has never been a problem but then again I have been using tungsten drills and a small (precission) drill-press.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Online dunkemhigh

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There is a possibility that I'm just bloody useless at this stuff :)
 

Online Zucca

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XXX is the width of the picture....
Thank you so much, I've added that to the initial post  :)

YRW. Please consider to make them smaller and upload the pic to the EEVBlog.
They will stay there forever, I hope.
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Offline TmaxElectronics

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Holes with relatively thin annular rings would be prone to the copper lifting...
Interesting, never had that issue myself. I usually add a centering hole of 0,4mm to each pad, that way alignment ist pretty easy even when hand-drilling.
The software has direct support for that btw ;)
You can just add you NCDrill file as a gerber layer and select it as a drill guide overlay in the export dialog. Even allows you to modify hole sizes to be the same everywhere.

Quote
So, I am wondering right now if an answer may be to pre-drill and then use the holes to accurately position the screen
Or you could just route out two edges of the PCB and align them to the edge of a metal sheet like the one I have on my printer now :)

Quote
I'll just do a benchy run tomorrow with the glass back in place, then we know more :)
I did run a print just now, and at a glance I don't see anything wrong with using the printer after the mod. It might need a little longer exposure times from the worse optical contact between LCD and glass but for my test the old settings worked fine (though they are quite conservative though).

One more problem though...
I just tried to de-laminate the glass from one of the original chitu replacements for the elegoo mars and it seem like they changed the adhesive. I just wasn't able to seperate the two parts from one another, not to mention completely trashing the display while trying, despite using the same method I was using the three times or so i did it before. So be careful if you try this, if it takes quite a lot of force you're probably best off calling off the experiment.
It might be possible to seperate them with a lot of heat though, gonna have to make a setup to test that soon.
 

Online dunkemhigh

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Quote
One more problem though...

Thanks for the info (and the testing!). I am at the thinking it might be a possible project at the moment, so could be a while before actually trying anything :)
 

Offline dirtcooker

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@TmaxElectronics,
nice project. The latest generation of these MSLA printers like the MARS 3 4k should be able to make very good pcboards. jlcpcb.com and others often have gerber file size limits of 5 or 10MB. This is not a limitation for most boards, but I have one project with detailed artwork, the gerber is 83MB (5MB compressed) and the board houses choke on it. I think it could be made using a 4k screen direct to pcboard exposure. I wrote a python program to generate the artwork as an 8192x8192 bmp and as an svg vector file. inkscape reads both files no problem, but svg2mod, kicad 6, blender 3 all crash. So I am unable to extrude the file for use in the MARS3. kicad's bitmap2component successfully converted it to a kcad_mod file in about 10 min or so, and I was able to produce the gerber.

Thus I would like to avoid all the software conversions. The screens are available cheap, for example https://www.amazon.com/ELEGOO-Inches-Monochrome-Resolution-Printer/dp/B08NTBN8S5

Does anyone know how to hook this up to an HDMI board, so it can be plugged into a PC as a display device? This might work, I dunno: https://www.displaymodule.com/products/display-adapter-for-hdmi-to-mipi-dsi?variant=31902301421666

This appears to be a complete solution: https://www.aliexpress.com/item/1005003493405410.html

There are numerous applications for this: B&W prints, microwave metamaterials and antennas, glass lab-on-a-chip (LOC) devices.
This is what the PC board artwork looks like, with 0.2mm dia holes in an otherwise solid copper layer, over 100k of them on a 100mm dia disk.
« Last Edit: May 03, 2022, 06:36:38 pm by dirtcooker »
 

Offline thm_w

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Does anyone know how to hook this up to an HDMI board, so it can be plugged into a PC as a display device? This might work, I dunno: https://www.displaymodule.com/products/display-adapter-for-hdmi-to-mipi-dsi?variant=31902301421666

PJ089Y2V5 is listed as 8 lane MIPI, this thing says 4 lane.
TM089CFSP01 not sure, probably the same.
Also its listed as 50 vs 60pin in some places, so may not work.

Interesting that these companies are building HDMI boards, I wonder what their end application is. People making DIY resin printers I suppose?
 

Offline eugene

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DIY PCB fab might be relevant today. A benchtop CNC suitable for doing all the drilling could probably be DIY'ed for a few hundred dollars. Plated through holes would be nice, but we're talking about turning something around in a couple of hours. You can shove a piece of wire through the hole before soldering everything. Solder mask might be a luxury I could live without when prototyping. Might be a feature! Multilayer boards? I don't know.

Good quality DIY PCB fabrication with fine pitch copper, well located vias, and not too much artistic hand work might not be an unrealistic goal.
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Online ace1903

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Little bit help please :D
Locally I can find only Creality LD-006 SLA printer with 3840x2400 resolution.
This resolution is probably with x3 interpolation since display is converted to monochromatic mode.
Since I do not own SLA printer I do not know if I can use Gerber2Chitubox program for LD006, and if this program can make this conversion to monochromatic mode?
Before investing in LD006 I would like to know if changes into software are needed and if this printer can make PCB with comparable results with Elegoo?
My Java knowledge is not great but I think I can make small  patches if needed.

 


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