Author Topic: Optimal Wavelength of laser for pcb  (Read 899 times)

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Offline Geocheats2

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Optimal Wavelength of laser for pcb
« on: May 22, 2018, 06:10:25 pm »
Hello to the community.

I would like to ask if this el-cheapo https://www.ebay.com/itm/Focusable-500mw-808nm-Infrared-IR-Laser-Diode-Dot-Module-12V-TTL-Fan-Cooling/253473468469 UV laser would be able to engrave the traces on a copper clad board. Or should I go with a lower wavelength ??

Keep in mind I just want to skip the film phase

Looking forward to your reply
George
« Last Edit: May 22, 2018, 06:15:24 pm by Geocheats2 »
 

Online Rerouter

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Re: Optimal Wavelength of laser for pcb
« Reply #1 on: May 22, 2018, 06:18:33 pm »
 you need a UV laser if you wanted to expose a UV film,

Actually cutting traces in a PCB with a laser would be hard, because copper is very reflective you would need to coat it in a film anyway.
 

Offline Geocheats2

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Re: Optimal Wavelength of laser for pcb
« Reply #2 on: May 22, 2018, 06:21:21 pm »
As far as I have read, you have to coat the PCB 3-4 times with black spray paint for optimal results, but will this laser be enough to burn through the coating and the copper ??
« Last Edit: May 22, 2018, 06:23:00 pm by Geocheats2 »
 

Online Rerouter

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Re: Optimal Wavelength of laser for pcb
« Reply #3 on: May 22, 2018, 06:24:28 pm »
Why not simply buy UV pre-sensitized boards and draw your traces with a low power UV laser,
 

Offline Geocheats2

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Re: Optimal Wavelength of laser for pcb
« Reply #4 on: May 22, 2018, 06:37:19 pm »
Price-Difference  :-\

 

Offline TurboTom

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Re: Optimal Wavelength of laser for pcb
« Reply #5 on: May 22, 2018, 06:41:02 pm »
In order to remove the copper or to do any type of "real" engaving, you need a pulsed laser since it needs to evaporate the material. CW lasers are just scarring the surface. That may be okay for processing wood or some (coated) plastics but completely unsuitable for ablating metal. The typical way to go would be a high frequency, Q-switched YAG laser, to machine copper preferably frequency doubled to 532nm (since copper reflects IR radiation pretty well). Read: expensive ;-)

With one of these ubiquitious 405nm diode lasers, you could very well slectively expose a photoresist and then chemically process the PCB. But I understood you would like to eliminate the chemicals...

Cheers,
Thomas
 

Offline Geocheats2

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Re: Optimal Wavelength of laser for pcb
« Reply #6 on: May 22, 2018, 06:44:41 pm »
In order to remove the copper or to do any type of "real" engaving, you need a pulsed laser since it needs to evaporate the material. CW lasers are just scarring the surface. That may be okay for processing wood or some (coated) plastics but completely unsuitable for ablating metal. The typical way to go would be a high frequency, Q-switched YAG laser, to machine copper preferably frequency doubled to 532nm (since copper reflects IR radiation pretty well). Read: expensive ;-)

With one of these ubiquitious 405nm diode lasers, you could very well slectively expose a photoresist and then chemically process the PCB. But I understood you would like to eliminate the chemicals...

Cheers,
Thomas

If i just burn the 3-4 layers of black paint will i able after that to etch the board and transfer my sketch?

(i don't care about the chemicals I just want better quality than the toner transfer method i been using)
 

Offline chris_leyson

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Re: Optimal Wavelength of laser for pcb
« Reply #7 on: May 22, 2018, 07:57:16 pm »
And are you going to use an X-Y galvo scanner and flat field optics to project to the pattern onto the board ? Good luck with that then. And you want to use a class IV laser you can't even see  :scared:
« Last Edit: May 22, 2018, 08:07:28 pm by chris_leyson »
 

Offline dmills

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Re: Optimal Wavelength of laser for pcb
« Reply #8 on: May 22, 2018, 08:21:34 pm »
Well big, crude, poor beam quality Q switched 532 is not actually that expensive on the surplus market as there are loads of "KTP" and "800" series Laserscope arc pumped ex medical units kicking around.
Do not take this as a recommendation to go there, the things are massive eye hazards (Especially the KTPs which have the scariest optical bed I have ever worked on).

However it is a different order of magnitude as a project, and a different order of magnitude in terms of eye hazard (And 808nm is not exactly safe). Even the mirrors and lenses for Q switched beams of any real power are a difficult problem, if you have a beam waist at the optic is will probably take catastrophic damage within a faction of a second, even with your standard surgical laser that has very poor beam quality, being in general highly multimode, so not good for fine lithography.

Also that 808nm is near IR, not UV a very different part of the spectrum, so take anyone selling a 808nm diode as UV as being a seller who does not know at all what they are doing. 

On eye safety, any class 4 laser is bad news, class 4 IR is worse news because you cannot even see the leakage, and any Q switched rig is just fucking scary, get the right eyewear, for the right wavelengths, and expect to pay the right money for it, the certifications on the eyewear are there for a reason.
Also, when messing with class 4, for gods sake mount the thing in a machine enclosure, nobody needs a class 4 laser in a hand held package with free space optics, that is just wrong.

Regards, Dan.
 
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Online Hero999

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Re: Optimal Wavelength of laser for pcb
« Reply #9 on: May 22, 2018, 08:47:45 pm »
The seller is correctly stating it's an IR laser. It's the original poster who has made a mistake by mentioning UV.

IR is no good for vaporising copper, which is very reflective in that region. A violet 405nm laser would be far more suitable, as copper is less reflective, at shorter wavelengths.

Of course any laser, powerful enough to vaporise copper on a PCB, whether visible or not, should only be used with adequate eye protection and protective clothing as it can burn the skin too.
 

Online Marco

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Re: Optimal Wavelength of laser for pcb
« Reply #10 on: May 23, 2018, 12:09:14 am »
If i just burn the 3-4 layers of black paint will i able after that to etch the board and transfer my sketch?

(i don't care about the chemicals I just want better quality than the toner transfer method i been using)

This might work, using the unburned paint as a mask for chemical etching. But the question is how good the resolution would be. A quick google shows people have done this before.

I don't think "burning" the copper will ever work without some ungodly expensive fibre pulse laser ... I doubt even microsecond pulses are short enough. If it's not fast enough it will burn the substrate making it conductive and delaminate the remaining copper.
 

Offline dmills

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Re: Optimal Wavelength of laser for pcb
« Reply #11 on: May 23, 2018, 01:48:32 am »
For a Q switched laser, microseconds is forever!

Tens to low hundreds of ns is more like it, being as the pulse is basically defined by the time it takes to dump the excess population inversion into the lower laser level, and in common Q switched laser systems that is basically the time it takes light to round trip the cavity a few dozen times.

Regards, Dan.
 

Offline chris_leyson

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Re: Optimal Wavelength of laser for pcb
« Reply #12 on: May 23, 2018, 02:34:41 am »
LPKF seem to have three laser etching systems, LPKF ProtoLaser R 1030nm pulsed 1ps, ProtoLaser S4 532nm and ProtoLaser U4 355nm. Anyway, the OP want's to remove paint and not copper so a CW laser would work OK. To remove copper you need a pulsed laser and that is a completely different ball game entirely.
 

Online Hero999

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Re: Optimal Wavelength of laser for pcb
« Reply #13 on: May 23, 2018, 03:28:56 am »
In order to remove the copper or to do any type of "real" engaving, you need a pulsed laser since it needs to evaporate the material. CW lasers are just scarring the surface. That may be okay for processing wood or some (coated) plastics but completely unsuitable for ablating metal. The typical way to go would be a high frequency, Q-switched YAG laser, to machine copper preferably frequency doubled to 532nm (since copper reflects IR radiation pretty well). Read: expensive ;-)

With one of these ubiquitious 405nm diode lasers, you could very well slectively expose a photoresist and then chemically process the PCB. But I understood you would like to eliminate the chemicals...

Cheers,
Thomas

If i just burn the 3-4 layers of black paint will i able after that to etch the board and transfer my sketch?

(i don't care about the chemicals I just want better quality than the toner transfer method i been using)
Sorry, I missed you just want to vaporise the paint.

The optimal wavelength is anything which the paint absorbs, which we can assume to be anything in the visible spectrum. An IR laser might not be any good, since there's a possibility the paint may be reflective at that wavelength. A test would need to be done to confirm that the paint doesn't reflect at the laser's IR wavelength. Another problem is the manufacturer might change the formulation of the paint in future, so the next batch might be IR reflective.

In short, just use a visible laser, powerful enough to vaporise the paint. The actual wavelength is unimportant.

Oh another point: are you sure the paint will completely vaporise? Heating to a high temperature will most likely leave char and ash residue, which will still need to be removed. It would have to get very hot to completely vaporise everything. Hopefully the char will oxidise, but the paint would have to be thin enough to allow enough oxygen in and even then there will still be ash.
 

Offline ajb

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Re: Optimal Wavelength of laser for pcb
« Reply #14 on: May 23, 2018, 04:07:55 am »
I've tried this using a 35W CO2 laser engraver (Epilog Helix).  One challenge is that you need to remove the paint as quickly as possible, preferably in one pass, because as soon as you expose the copper its reflectivity and thermal conductivity come into play.  I had a hard time getting the last little bit of paint off as a result, but then I didn't really spend much time experimenting with the process.  Mostly it was just a lark since I had the engraver available and some copper clad board on hand.  I did manage to get one decent board out of the process, though.

I think using sensitized PCBs and a UV laser is probably a much more effective way to go, since the exposure of the mask is not a thermal process you don't need nearly as much power. 
 

Online Marco

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Re: Optimal Wavelength of laser for pcb
« Reply #15 on: May 23, 2018, 04:26:57 am »
Marco Reps on youtube simply scrubbed it with a brush and dish soap to get the remains off. I suspect finding a module with a sufficiently good/small dot will be more important than wavelength.
 

Offline ajb

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Re: Optimal Wavelength of laser for pcb
« Reply #16 on: May 23, 2018, 04:36:29 am »
Marco Reps on youtube simply scrubbed it with a brush and dish soap to get the remains off. I suspect finding a module with a sufficiently good/small dot will be more important than wavelength.

Did he do one with the paint method?  The only videos I remember used photosensitive PCBs.
 

Offline purfield

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Re: Optimal Wavelength of laser for pcb
« Reply #17 on: July 17, 2018, 04:48:05 pm »
I built a system to laser etch PCBs similar to the LPKF Protolaser. I used a 1064nm Q-switched laser, a galvanometer scan head, and an XY stage.  Spent a lot of time and money putting it together (about $10k USD).  It took a lot of parameter tweaking to keep from burning the FR4 substrate under the vaporized copper.  I managed to get it working though, and the system could pattern a square inch of 1oz copper in a little over a minute.  The scan head controller I used had some buggy software that kept me from being able to accurately calibrate the laser positioning and perform field stitching. 
 

Offline Old Printer

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Re: Optimal Wavelength of laser for pcb
« Reply #18 on: July 18, 2018, 10:38:56 am »
My day job is running 50 & 75 watt co2 Epilog lasers. I spent a fair amount of time trying the paint method with a lot of different types of paint. I did not have very good results. I also had problems getting that last fine paint film off and it was enough to keep the enchant from properly reaching the copper. I have been laser engraving for 20 years, but just with co2 lasers. Hard to believe but it can burn through a half inch board but won't touch tin foil.
I used to have the equipment to make litho film negatives and expose pre coated pcb's in a vaccume contact frame. Those were the best results, I was able to make very tiny traces and 2 sided boards. Unfortunately shops that run litho film have pretty much disappeared.
Epson has a proprietary inkjet film process that silkscreen printers use for their negs and positives. If you can find so one running one of those that could be a source for the film. The black is very dense, which is one of the major challenges, along with sharp images, when trying to find a replacement for litho film negs.
Frustrating :(
 

Offline Siwastaja

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Re: Optimal Wavelength of laser for pcb
« Reply #19 on: July 19, 2018, 05:32:03 am »
If you are fine working with etching, just get some dry film photoresist (such as Dupont Riston) and a standard office laminator to apply it on the copper clad. Excellent industry-grade results with great repeatability, and it's not that expensive. You can expose that stuff with a 405nm laser (although 380nm would be optimal, allowing working with a bit less power, but the lasers are more expensive so it makes little sense), easily with just a few dozen mW of power. (Or of course you can use more power, if you can move the laser fast enough.)
 

Online JS

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Re: Optimal Wavelength of laser for pcb
« Reply #20 on: July 19, 2018, 09:31:23 am »
...
(i don't care about the chemicals I just want better quality than the toner transfer method i been using)
  What are your problems? How much better? I've done 0.5mm pitch PCBs with toner transfer, no touch ups needed while being careful. I bought a laminator and that makes transfer so much more controlled, I know I have to take the PCB a certain number of times and get really good results, I knew I would also need it if I intended to use the photoresist way and the expense for it was the same as the next batch of PCBs I needed, so I went for it, never regret. The quality for the toner transfer I make is better than some photoresist I've seen from my friends, proper transfer paper is also a must, mocking around with magazine or glossy paper doesn't cut it.

  Then there is the photoresist film, you will be done with a few UV tubes, much cheaper and faster than the laser to etch the cooper directly, and much easier to run multiples of the same one. Direct carving (laser or cnc mill) are nice to do one offs as quick and clean process but I think the end results of chemicals is better and cheaper to tool up. Also, once you have the UV exposure you could add anti solder mask and print with UV ink giving a pretty nice finish, you would be just plated vias away from manufactured PCBs.

  I'm thinking now in building a double sided UV box but more for the solder mask and UV ink than to replace the toner (but it will probably be replaced having the thing) while it needs to be quite beefy you only need a few seconds of exposure for the etching UV material, then a few minutes to cure the solder mask.

JS
If I don't know how it works, I prefer not to turn it on.
 

Online Marco

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Re: Optimal Wavelength of laser for pcb
« Reply #21 on: July 19, 2018, 09:42:28 pm »
Did he do one with the paint method?  The only videos I remember used photosensitive PCBs.
I meant this one.

Relying on microsteppers for exact position with a 3D printer is always going to be a bit iffy though, they're just not designed for that. Personally I'd try line by line printing with optical feedback for more exact positioning.
« Last Edit: July 19, 2018, 11:54:01 pm by Marco »
 

Offline AE7OO

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Re: Optimal Wavelength of laser for pcb
« Reply #22 on: July 21, 2018, 01:27:48 pm »
Here is my method or PCB creation... >:D

I use the cool method of toner transfer using the following steps.

1. Generate a PCB image that follows the rules for OSH Park
2. Create a PDF mirror file, including traces, vias and drill holes
3. Take it down to FedEx(I don't own a laser), and have them print it on their cheap glossy paper using high quality.
4. Cut a copper clad board to the proper size,
5. use a green scrubbie to make bright and clean with alcohol and acetone.
6. I have a tight container of ~80% alcohol and 20% acetone that I apply to board(make it wet)
WARNING: this is the only major problem area, to little acetone and the toner won't stick to board; to much acetone and you get spreading/blobs.  I use a little glass test tube to measure out the two components and store it in a tightly sealed bottle.
7. Apply image, press to remove air pockets and apply more mixture until the image is visible through the paper.
8. Lightly clamp board between two old PCB boards for about 30 min.  After playing with the method you'll figure out how much pressure to use and how.  I use the two old boards so that I get even pressure.
9. Remove board from clamp and let air dry
10. Soak in water for about 10 min, and then run under running water to remove any bits of paper left while lightly rubbing.
11. Clean with alcohol, you now have a toner transfer board. 
NOTE: If you've screwed up, just clean the board with acetone which will remove the toner. Start over at step 5.
12. Etch (in my backyard) with a mixture of 85-90% hydrogen peroxide(big bottle $3.00) and 10-15% muratic acid(1 gal $9.00).  If I were doing a lot of boards, I would make  Cupric Chloride with a bubbler.  I make a handle from duct tape and just swish the board around until etched and then rinse with water.  I let the mixture evaporate and then rinse out the next time I etch.

Here is a picture of one of my early boards, the chip is a soic-8.

« Last Edit: July 21, 2018, 01:29:42 pm by AE7OO »
 


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