Making fine pitch PCB prototypes with fiber laser

24 Comments

There are quite a lot of inexpensive and fairly reliable PCB manufacturers that can produce double-sided PCB’s with solder-mask and silkscreen in a day or two, but what if you need it now? I will not cover expensive prototyping machinery nor messy printer/etching process instead let’s use a 20W Fiber laser. Because‚Ķ who does not like lasers, right?

Goal

The ultimate goal is to have a soldered fine pitch (0.1mm/4mill track and clearance) component as fast as possible (30min) along with a few passive components.
The material of choice is common FR-4 with 0.018 or 0.035mm copper thickness. It would be perfect to have double-sided routing, but via copper plating process complexity and time restriction imposes limits to single-sided design without drilling (though with some drawbacks it can be done).

Design preparation

Gerber files

For this experiment, I used one of the fresh upcoming camera design. Skipping Gerber export step as it varies from software to software. For this test prepare 3 Gerber files:

  • TOP tracks layer
  • TOP Solder-mask layer
  • Contour layer

FlatCam import

FlatCAM lets you take your designs to a CNC router. You can open Gerber, Excellon or G-code, edit it or create from scatch, and output G-Code. Isolation routing is one of many tasks that FlatCAM is perfect for. It’s is open source, written in Python and runs smoothly on most platforms.

http://flatcam.org/

FlatCam is also an ideal tool to prepare DXF/DWG vector files for further processing. Feel free to explore this powerful and open-source tool.

  • File / Open / Open Gerber… and load all prepared files
  • Double click on each Gerber layer and generate Isolation Routing layers
  • Double click on each Geometry layer and Generate CNCJob object

Then export each CNC job layer to an SVG file. Here we go, Gerber files were converted to more usable DWG files that can be used by EZCAD software.

EZCAD import

LIT Laser systems represents the latest in smart fiber laser technology. Our approach has drasticly reduce the price of laser systems. This unprecedented value and versatility has enabled students, technicians, engineers, inventors, makers, and hobbyists a chance to own laser systems that have been out of reach for many.

https://www.litlaser.com/ezcad

EZCAD comes with the vast majority of laser marking machines and is considered a de-facto tool. Unfortunately has some imperfections (actually tons of them). One of the major ones – outdated and buggy vector file importer. So after opening the top layer we will see a broken image (which is easy but tedious to fix)

Make copper traces

First, let’s fix the vector file imported in EZCAD. Here is the workflow that worked:

  • Select all geometry
  • Click Edit / UnGroup
  • Select each jump line and delete. I know this is tedious work, but could not find any quick workarounds
  • Click Edit / Group

This is another nasty EZCAD bug – if you would apply hatching now, geometry will be totally messed up.

  • Quick workaround – Click Modify / Curve Edit / Auto Connect (0.010mm) and geometry hatching looks better (might need grouping / ungrouping step)

For track isolation use hatching and laser parameters like in the screenshot above. Not ideal, but should be good to start experimenting.

It took about 20 cycles to cut through 0.035mm copper foil. Some of these passes were with increased power to 90% to speed up the material removal rate. A good hint when to decrease laser power is to observe copper color – with decreased layer thickness it will heat up more and change color. 50% of power will not greatly damage the substrate, while higher power settings make resin burn.

Prepare soldermask layer

Use PCB UV Curable Solder Repairing Paint (also good choice Dynamask 5000 dry film)

  • Spread the paint evenly on the PCB (use a thick transparent plastic sheet and rubber roller to spread evenly)
  • Make sure there are no bubbles
  • Introduce to 365nm UV light to cure. This should take a few minutes, for exact timing read material specifications, and experiment.
  • The protective sheet should peel off without damaging the freshly cured solder mask

More or less evenly spread and cured solder mask. This forms a pretty resistant layer that can withstand soldering in high temperatures.

Open solder mask

Rinse and repeat importing solder-mask layer into EZCAD software.

Laser settings in screenshot above. Depending on your layer thickness several passes will be required.

Cut PCB contour

The final step is to cut PCB out of stock material. A laser will not warp and skew FR-4 material so this is a very nice way to have PCB made to size. It will burn edges though, but light touch with 400 grit sandpaper will fix edges.

Laser parameters are in the screenshot. To cut through 1.6mm FR-4, wobble parameter is enabled (click Advanced... button)

Same parameters can be used to drill holes.

Will it solder?

Moment of truth – 0402 capacitors soldered with hot air and after Ultrasonic cleaning look charming.

Of course bare copper will oxidize very quickly so proper care should be taken. Other than that usual soldering job.

And for your entertainment and understanding macro video with each step

Final thoughts

Well with all experiments, preparations and writing an article it took half a day. If issues with vector file import are fixed, it should be possible to have simple in 30min.

While making PCBs with 1064nm fiber laser is quick and a clean process it has some drawbacks.

  • FR-4 material burns and smells, also there is a danger of having burnt resin between tracks. Good ventilation is a must!
  • Isolating tracks cam be uneven. Some areas can be burnt through, some will have remaining copper.
  • High energy pulsed laser would work much better, but the price of such a machine is beyond the roof.
  • Stencil from stainless sheet metal can be also cut with laser. Main concern is not to overheat stainles steel. Another issue is uneven edges. This is not an issue for 0402 component pads, but smaller pads will have issues.
  • During import into EZCAD, missed cleaning some geometry so some pads are incorrect. But for proof of concept and laser parameter tuning this is irrelevant.
  • A good UV light source is a must. While the surface of the etched PCB can harden pretty fast, the deeper layer can remain untouched. Soldering with hot air or cleaning can open these defects spreading uncured paint.

Comments ( 24 )

  1. jipe
    Hi, Really good job! I just wonder how powerful is your laser? Is that a CO2 laser? At least more than 50, or even 100W ?
    • saulius
      Thanks! Actually it's 20W fiber laser (1064nm). Powerful CO2 laser will not do better job at removing copper without substantial FR4 material damage.
  2. TheDarkTiger
    Awesome! A clear step by step process, that's very nice. Quick question, you say "Same parameters can be used to drill holes." ; did you try it? I think you need to remove coper beforehand where you "drill"?
    • saulius
      No need to remove copper. Drilling 0.2mm vias with laser looks not so shabby. 0.2mm holed drilled with laser in 1.5mm FR4 PCB Will be updating instructions with more details in a few days, stay tuned.
  3. TheDarkTiger
    Impressive! If only there was a single format for pcb and an other for laser cut, one could create a program to automatically configure everything without always tweaking the parameters until it fits. Thank you for sharing your discoveries!
    • saulius
      That would be perfect! My goal is to fine-tune parameters so it would work as a baseline. Gerber processing works fine already (though more automation would be nice to have) and EZCAM already does not require geometry cleanup.
  4. Matt Hope
    You could finish the end product in a liquid tin bath, it's easier to solder and protect the copper from oxidation. Also, for the via, I don't think there is a quick solution for home-made PCB. I've used in the past via rivets, it does a great job, but it is time consuming and the via need to be quite big (0.6mm drill, 1.5mm pad). I saw some people having success with carbon powder and solder paste, but it required a lot of trial and error to make it work.
    • saulius
      Hi Matt, thank you for reminding about rivets! This could be helpful in some cases. And regarding oxidation - laser does good job cleaning copper from oxides so if PCB is soldered within a few hours (or days if conditions are dry) there is no need to coat fresh made board.
  5. B Thomas
    Are you aware of any open source alternatives to EZCAD which will work with one of the inexpensive fiber lasers ?
    • saulius
      Hi Thomas, not that I am aware of. There is an alternative (also commercial) called Lightburn.
  6. andreas
    Thank you for all the details! I've seen videos of people successfully structuring FR4-PCBs, but up to now unfortunately most times without details on the used parameters. That is exactly the purpose I bought my 30W fiber laser for last year. Unfortunately I did not have any usable success up to now. I managed to remove copper, but always burned (really burned...) the FR4. With reduced power I was not able to remove the copper. I even had trouble to engrave into the backside without copper cladding without burning the FR4. Sometimes it even ignited a flame. I looking forward to read more. Maybe I can adopt something. Thanks a lot so far!
    • saulius
      For Copper/FR4 transition - try reducing power just slightly above threshold where copper is being vaporized. Also keep low pulse per area count (reduce laser freq, increase speed).
  7. cejasmasmas
    Hi, when you export to svg, you can open the svg file in inkscape, and save as .plt (HP Graphics Language Plot File), this way ezcad2 opens the file correctly without anymore processing, you have to install and additional plugin in but after that it just works
    • saulius
      Thank you! Was trying to avoid extra software packages and Inkscape has bugs of it's own. Anyway found better solution - export G-Code from FlatCam and open in EZCAD. Works like a charm!
  8. s-ol
    Really nice! Are you aware of PCB via rivets? I don't have access to a fiber laser, but with a co2 laser and a CNC mill I was able to make double-sided boards using them. They are basically just little copper rivets that you insert on one side and mushroom over on the other. I recommend also soldering them, purely mechanical contact tends to turn intermittent over time IME. http://fabacademy.org/2020/labs/opendot/students/sol-bekic/projects/laser-board/
    • saulius
      Thank you for reminding about rivets... but they are huge and require tedious work to install.
  9. Felipe
    A engraving laser module can do the job too? 40W Laser Module Kit Laser Cutting Engraving Module Blue Light Module Set Laser Engraving Machine Cutting Tool Metal Engravable https://a.aliexpress.com/_mr6HgqH
    • saulius
      Felipe it will not work. You need at least Fber or YAG laser.
  10. cejasmasmas
    Forgot about G-Code export, thats even better, I bought a 50w fiber laser for this purpose, tested a few copper clad boards, got carried away with the power settings and totally destroyed the boards, managed to create a few with fair results, In the end I spray painted them and removed the paint as with a Co2 laser, the good thing is that the fiber laser doesn't leave the transparent mask the Co2 leaves, so after removing the paint you can go directly to the acid, getting really nice reliable results, the one thing I didn't test was to actually cut them, it's good to know it can be done, thank you
    • saulius
      I did many unsuccessful testes earlier. There are many parameters to tinker with. As you probably noted trickiest thing is to remove copper with minimal damage to FR4 material - try removing copper in multiple passes with minimal power settings. Soldermask will fix minor FR4 damages.
  11. joposter
    You have got me looking for machines. The result looks very usable! may i ask what precision you could achive? did you try some stress tests to find minimum trace width and pitch?
    • saulius
      Technically laser spot is 0.02mm (on papers). Have not tested what actually can be achieved, though. 0.1 is looking pretty good. 0.07mm should be also doable. Everything smaller should be not quite reliable.
  12. Shingo
    Within an hour after reading this, I ordered CO2 laser cutter. My idea is to use Kapton adhesive tape/film instead of PCB UV Curable Solder Repairing Paint, Dynam"a"sk (you have typo) and UV cure machine. Mine will be delivered in March so if you're interested in, please try it!
    • saulius
      Thank you for noticing a typo Shingo! Fixed. Kapton tape cut with CO2 laser might actually work. Though thinking about many issues like bunt tape edge and lesser CO2 laser resolution (making an assumption that it has mechanical beam drive instead of galvoscanner).

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