Old 04-18-2016, 05:11 PM #1
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Default Direct laser PCB etching (through Cu ablation)

This is an experimental and exploratory thread, not a complete project.

Background:

It is well known to all that there are expensive machines using
super-powerful lasers to cut, drill and etch PCBs in the electronic
industry. It is less known that the new powers provided by extremely
powerful laser diodes accompanied by now accessible high quality lenses,
may provide the some of the same magic to DIY builders.

This project aim to explore the possibility to use laser diodes
to directly etch the copper layer on a PCB.


The main motivation for this project are two videos that appeared a 2
years ago from a user called "Hobby Elektronik". (Who knows, perhaps
he's even a member of LPF?) After those videos there was never any news
or updates about this technology.

(1) PCB Laserprinter (2014-01-04)
(2) PCB Laserprinter Version 2 (2014-02-16)

In the first video it is clear that he only used the laser to etch the
UV mask on the PCB. This is a significant improvement from using regular
UV exposure in terms of speed. Naturally, the next logical step would
be to simply skip the UV and subsequent horrible chemical etching, by
just ablating (etching) the Copper from the PCB directly.

The second video appears to show this, but the comments from the video
maker denies this is the case. However, he has more than a very good
reason to not tell what is really going on. This technology would be a
total game-changer for the hobbyist DIY PCB manufacturer, if viable.

Reading up on the subject, I'm under the impression that this might be
possible. However, I still have not seen any concrete or determinate
results that can confirm or deny this possibility.

I'm hereby reaching out to the LPF community to determine once and for all,
if this is possible using any of our available laser diodes.

No matter what the results, I'd like to find a solution that at least
reproduces or improve upon that solution.


More Video Details:

In the video and accompanying YouTube comments,
we can extract the following info:

Code:
Power Supply/Driver Chipset:

- Linear Tech, LTC-1446  -- Dual 12-Bit Rail-to-Rail Micropower DACs in SO-8 (for LD reference voltage)
- ??,                    -- Dual Op-Amp for current limiter
- Rohm, BU4053BF         -- Triple 2-Channel Analog Muliplexer/Demultiplexer
- ATmega 88 


Laser Head:

Laser(s):               2 x 405 nm (to have 2 lines per sweep!?)
Estimated LD Power:     60 - 100 mW 
Origin:                 Laserdiode from a XBOX Laser unit
Alignment current:      10 mA
Pulse current:          90 mA
PWM Duty Cycle:         50%
PWM frequency:          60 KHz
Lens:                   AixiZ Blue Laser Glass Lens for 405-455nm
CNC paramters:

Code:
Speed:                  255 mm/s        (0.18 s/line @ 27.5 mm x 46 mm)
Width:                  0.0508 mm       (with 2227 pixels per 0.0206 mm)
Total Time:             280 s = 3.2 minutes

Laser Modulation:

start:  50 ms 
stop:   50 ms
data:   75 ms
--------------
Total:  ~175 ms/line 
    =   ~0.18 s/line
So here we go, my humble request to the LPF community:
a) If you are in possession of a high power < 455 nm laser,
please get a one sided PCB and try irradiate it with many different
configurations of:

- LD optical power
- PWM duty cycle
- Lense types
- Focal points
- Cu surface "enhancements" such as heating, abrasion, lacquer,
coloring, and whatever else you can think of...

b)
Please document your findings (with pictures) and post them here.

c) Feel free to experiment, but take all safety precautions since polished Cu is highly reflective.

d) Provide any research articles or other documentation of these methods.
(Cu is one of the most researched elements of the entire Periodic Table!)

e) It might be useful to get an order of magnitude estimate of how much energy it
takes to vaporize a certain area (spot) of Cu of a standard PCB.



Last edited by SIEVA; 04-18-2016 at 05:12 PM.
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Old 04-18-2016, 05:11 PM #2
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Default Cu Ablation Energy Calculation

So I decided to attempt some calculations for Cu ablation.
I'm sure there are several mistakes in here, so please try it for yourself.

First we need to calculate the energy needed to turn a small isolated
PCB spot of Cu into vapor. Then we need to repeat the calculation taking
into account the dissipation due to heat conductivity of the surrounding
Cu.

A) Calculating the phase changes

Thus we need to calculate the following energies (enthalpies):



(We use units of grams [g] and set M=1.)
Code:
ΔE(solid:Tr --> solid:Tm)       = M Hs dT       = Hs (Tm - Tr) = 0.386 [J/g.C] * (1085 - 25)[C] =  409.2 [J/g]
ΔE(solid:Tm --> liquid:Tm)      = M Hf          = 209 [J/g]
ΔE(liquid:Tm --> liquid:Tb)     = M Hl dT       = Hl (Tb - Tm) = 0.572 [J/g.C] * (2562 - 1085)[C] = 844.9 [J/g]
ΔE(liquid:Tb --> vapor:Tb)      = M Hv          = 4730 [J/g]
-----------------------------------------
ΣE = 6193 [J/g]
Where:

Code:
Tr = Room temperature                   =   25 C
Tm = Temperature of Cu melting point     = 1085 C
Tb = Temperature of Cu boiling point     = 2562 C

Hs = Heat capacity (solid)
Hl = Heat capacity (liquid)
Hf = Latent heat of fusion (melting)
Hv = Latent heat of vaporization
Sum these up and the result should be in [J/g].
This is the energy in Joules required to vaporize 1 g of Cu).


B) Next we need calculate how much (in grams) of Cu there is in this "spot".

PCB Cu layers come in various thickness:

Code:
---------------------------------
0.5 oz --> ~17.5 μm (0.7 mils)
1.0 oz -->    35 μm (1.4 mils) *
2.0 oz -->    70 μm (2.8 mils)
---------------------------------
* = most common
Let's assume a spot size diameter as used for the dots in DVD-HD and
DVD-BlueRay media, which are 620 and 480 nm.




Code:
D = (620 + 480)/2 = 550 nm 
A = Pi * R^2 = Pi * (D/2)^2 = 4*Pi/D^2 = 41.54 [μm^2]
V = 35 * 41.54 = 1454 [μm^3] = 1454 * 10^(-18) m^3

Mass (spot)    = V * Cu-density 
        = 1454 * 10^(-18) [m^3] * 8940 [kg/m^3] 
        = 1.300 * 10^(-11) [kg]
        = 1454 [um^3] [1 mm/1000 um]^3 * 8.96 [g/cm^3] [1 cm/ 10mm]^3 = 1.303 * 10^(-11) g.

C) Finally we calculate the total energy required to vaporize the "spot".

ΔE_tot = 6193 [J/g] * 1.303 * 10^(-11) [g] = 8.069 * 10^(-8) [J] = 81 nJ

Remembering that the units of a Joule are:

[J] = [kg.m^2.s^(-2)] = [W.s]

So if we can irradiate the sample with 1 W (of optical output) from an
ideal laser diode with no optical losses. We would have to keep the spot
on the same position for at least, t seconds.

t = ΔE_tot/P_ld = ~ 8 * 10^(-8) seconds = 0.08 μs





Some useful properties for Cu:

Code:
Atomic Weight:                  29
Molecular weight:               63.546
Density:                        8960 [kg/m^3]    8.96 [g/cm^3]

Melting point:                  1085 C
Boiling point:                  2562 C

Heat capacity (solid):          0.386 [J/g.K]    24.5 [J/mol.K]
Heat capacity (liquid):         0.572 [J/g.K]   36.33 [J/mol.K]
Latent Heat of fusion:            209 [J/g]     13.59 [kJ/mol]
Latent Heat of vaporization:     4730 [J/g]       300 [kJ/mol]
Thermal conductivity:             401 [W/m.K]
[please check these, they are not always the same on these websites]

See:
https://en.wikipedia.org/wiki/Copper
copper
Resources: General, Atomic and Crystallographic Properties and Features of Copper
Attached Thumbnails
Direct laser PCB etching (through Cu ablation)-subl2.jpg   Direct laser PCB etching (through Cu ablation)-hd_dvd_laser_chart.gif   Direct laser PCB etching (through Cu ablation)-640px-comparison_cd_dvd_hddvd_bd.svg.png  

Last edited by SIEVA; 04-19-2016 at 12:58 PM. Reason: added pictures
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Old 04-18-2016, 05:27 PM #3
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Default Re: Direct laser PCB etching (through Cu ablation)

I haven't tried to do any such calculation for years, so I find it rather strange that it only takes 81 nano Joules to punch a small hole in 35 um Cu layer...

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Old 04-18-2016, 06:23 PM #4
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Default Re: Direct laser PCB etching (through Cu ablation)

I feel like you may have underestimated what it takes to ablate copper. The industrial lasers that do this are typically big solid state lasers capable of very quick energetic pulses or massive CW wattage. Work pieces are also typically preheated to right before a phase change.

You're missing a few key elements in your calculations. Absorbtivity at wavelength is important, and you need to also factor in the heat loss due to conductivity in copper.

I'll run through your calculations later. Seems like a cool project. I'd expect you'd need a lot more wattage than a normal diode laser though.
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Old 04-18-2016, 10:04 PM #5
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Default Re: Direct laser PCB etching (through Cu ablation)

Quote:
Originally Posted by Rivem View Post
Work pieces are also typically preheated to right before a phase change.
Yeah, I've seen that in some absorption spectra graphs. The absorption increases dramatically by increasing the temperature of the substrate.


Quote:
You're missing a few key elements in your calculations. Absorbtivity at wavelength is important, and you need to also factor in the heat loss due to conductivity in copper.
Yes, I know. I lost the original spectra I had saved, but I just found a few new ones.

[1] Light Absorption by Metals with Porous Surface Layer Formed by Oxidization–Reduction Treatment
[doi:10.2320/matertrans.M2012139] https://www.jim.or.jp/journal/e/pdf3/53/09/1556.pdf

[2] Metallic Reflection - Chemwiki

[3] LASER MARKING: How to choose the best laser for your marking application - Laser Focus World



From [2]:



From [3]:



From [1]:



In conclusion, we see a 60% absolute absorbance @ 405 nm, for a
mirror polished surface, which we rarely have, at 25C.

.
Attached Thumbnails
Direct laser PCB etching (through Cu ablation)-chemwiki.jpg   Direct laser PCB etching (through Cu ablation)-pennwell.web.400.367.gif   Direct laser PCB etching (through Cu ablation)-light_absorption_2.png  

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Old 04-20-2016, 07:13 AM #6
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Default Re: Direct laser PCB etching (through Cu ablation)

Adding some inspirational videos and devices...
(and some basic data.)

OTHER videos related to PCB laser etching:


(a) PCB Etching with Lasers | ProtoLaser S (2012)

https://www.youtube.com/watch?v=mzmjGz0_joM
https://www.youtube.com/user/LPKFGroup/videos
LPKF ProtoLaser Series | Laser Etching Prototyping Systems

Interesting is that the beam diameter in this IR model is far greater
than for a CD writer. Other models have Blue/UV diodes and much smaller
spots.

ProtoLaser S:

LPKF ProtoLaser S | Advanced PCB Laser Etching System

Code:
Laser Freq:             "NIR"
Beam Diameter:          25 um (1 mil)
Accuracy:               2 um
Pulse Frequency:        15-100 kHz
ProtoLaser U3:

LPKF ProtoLaser U3 | Advanced PCB Laser Etching System

Code:
Laser Freq:             355 nm
Beam Diameter:          15 um
Accuracy:               2 um 
Pulse Frequency:        10-100 kHz

ProtoLaser 3D:

ProtoLaser 3D

Code:
Laser Freq:             "IR range"
Beam Diameter:          50 um
Accuracy:               25 um
Pulse Frequency:        10-100 kHz

ProtoLaser LDI:

LPKF ProtoLaser LDI | Laser Direct Imaging - Microfluidics

Code:
Laser Freq:             375 nm
Beam Diameter:          1 um
Accuracy:               1 um
Pulse Frequency:        10-100 kHz
---------------------------------------


(b) Laser Marking - Printed Circuit Board (PCB) Fabrication (2013)

https://www.youtube.com/watch?v=W-UZUwjg6y8
Laser Marking Machines | Laser Engraving Machines | LaserStar

Code:
Laser Type              Pulse Fiber Laser
Wavelength              1062 nm 
Beam Diameter:          <30 um
Pulse Frequency:        1 - 500 kHz
Laser Peak Power:       >10 kW
Output Power:           10-100
And this guy is cutting the PCB with a 2W laser, cycling it 100 times.

(c) 2W Laser Engraver Cutting PCB

https://www.youtube.com/watch?v=y_3o4xc0oFo


(d) PCB Laser Drilling, Etching and Cutting With Single Process (2015)

https://www.youtube.com/watch?v=q-uX4iFbekw
PCB Laser Processing - Software For Laser Machines
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Old 04-20-2016, 05:33 PM #7
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Default Re: Direct laser PCB etching (through Cu ablation)

Seeing all the incredible LPF-peoples signatures of amazing lasers, I'd
love to see someone here, pull out their >3W blue lasers and focus it
on a point onto a Cu-island of a standard FR-4 PCB, and tell me if anything
at all happens? Can you see it with the naked eye? With a magnifying glass?

Remember that the Cu layer of a PCB for most driver are usually twice
(or more) as thick (2 oz) than that for low current electronics.
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Old 04-20-2016, 06:55 PM #8
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Default Re: Direct laser PCB etching (through Cu ablation)

Okay, I got a similarly small number on energy to sublimate the copper in a 1 OZ PCB trace with a small spot size.

Turns out the reason you can't do it with a single emitter diode has to do more with the pulse length. Basically, you've got to dump that amount of energy into the spot within a very, very short amount of time.

With my rough calculation, it came out on the order of a few kW. Likely, absorptivity wouldn't even matter if the pulse was on the order of femtoseconds.

All of the examples you gave which actually ablate copper were pulsed solid state lasers. Maybe you could do it at home with a small q-switched YAG.

You could probably melt the copper with a diode though.
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Old 04-21-2016, 08:59 PM #9
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Default Re: Direct laser PCB etching (through Cu ablation)

Quote:
Originally Posted by Rivem View Post
Okay, I got a similarly small number on energy to sublimate the copper in a 1 OZ PCB trace with a small spot size.
Good

Quote:
Turns out the reason you can't do it with a single emitter diode has to do more with the pulse length. Basically, you've got to dump that amount of energy into the spot within a very, very short amount of time.
That doesn't sound completely correct. Because Power as measure in Watts are in terms of Energy/Second, so yes, the shorter the pulse, the higher the "measured" power, but in order to do work on the Cu we still need to supply enough energy (in Joules). Which is why we need to keep that (pulsed?) energy on the spot.

Quote:
With my rough calculation, it came out on the order of a few kW.
Can you provide a sketch/outline of your calculation?

Quote:
Likely, absorptivity wouldn't even matter if the pulse was on the order of femtoseconds.
That is a good question, but the papers above was not all CW, so I can't answer that. Need more research.

Quote:
You could probably melt the copper with a diode though.
Yes, that would be a good start! Anyone?
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Old 04-21-2016, 09:32 PM #10
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Default Re: Direct laser PCB etching (through Cu ablation)

Tried with 2+w, etching, no melting, will try with 7w in a few days when my diode is back from being decanned
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Old 04-21-2016, 11:23 PM #11
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Default Re: Direct laser PCB etching (through Cu ablation)

Quote:
Originally Posted by SIEVA View Post
Good
That doesn't sound completely correct. Because Power as measure in Watts are in terms of Energy/Second, so yes, the shorter the pulse, the higher the "measured" power, but in order to do work on the Cu we still need to supply enough energy (in Joules). Which is why we need to keep that (pulsed?) energy on the spot.
I don't think you understood my statement. Basically, the energy (in Joules) has to be delivered in a certain period of time since the heated volume of material changes over time as copper conducts through the metal. The energy over the amount of time gives the minimum amount of power requires.

This gives two possible situations:
  1. We could supply enough POWER to sublimate a layer of atoms immediately.
  2. We could supply an amount of energy to sublimate a conical volume of material determined by the speed of heat flow down to the substrate.

I figured scenario 1. I did my rough calculation by finding the heat to sublimation per nm^2 of copper and dividing it by the speed of electron interaction across an atom of copper to get the power per nm^2. This would likely be a fast enough interraction not to worry about reflectance as the electrons might not have the time to leave excitement.
Would have to run through it again as it was quick and rough, but I got around 18.5 Watts/ nm^2, so around 3.7 MW pulse power for ~500nm.

Sounds too high for my tastes, but maybe some of the more practically experienced users can give their input.

There may be a chance that a chemical process is the goal instead of sublimation as you've said though. A lot of industrial lasers will pump oxygen or compressed air out the laser head which could certainly react with hot copper.

Anyway, good luck on your project, but you might want to ask some pulsed SS owners to try it out for more luck.

Edit: I'll try to upload some work later.
Also, it's become clear to me that I likely made some conversion errors which may have made the number too high by a factor of up to 10.
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Old 04-22-2016, 01:10 AM #12
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Default Re: Direct laser PCB etching (through Cu ablation)

Directly ablating copper using blu ray diodes doesnt seem that feasible to me.

Even if you could get the laser power density high enough to do it, the question would be what that would do to the pcb material and where the eveporated copper would end up.

It would be little good if the laser managed to sublimate the copper away but also charred the pcb material and have copper vapour condense straight back onto the workpiece, right?

Using a bluray to expose photoresist seems entirely feasible though and probably a good way to manufacture one-off pcb's. Then again it only makes sense for single prototype boards, if you need a couple having them done comercially is a lot easier - especially if you want to have some through holes and/or vias on there - laser exposure will produce none of those.
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Old 04-22-2016, 03:49 PM #13
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Default Re: Direct laser PCB etching (through Cu ablation)

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Originally Posted by VirtueViolater View Post
Tried with 2+w, etching, no melting, will try with 7w in a few days when my diode is back from being decanned
Hi V, thanks so much for at least trying. Just make sure you're using a good lens, as it seem from our calculations that we need a very small spot. Also look for any other marks. Roughening up and pre-heating the surface might also help.

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Originally Posted by Rivem View Post
I did my rough calculation by finding the heat to sublimation per nm^2 of copper and dividing it by the speed of electron interaction across an atom of copper to get the power per nm^2. This would likely be a fast enough interraction not to worry about reflectance as the electrons might not have the time to leave excitement.

Wow, thanks for that explanation and great calculation. Very interesting. However, the 1 nm^2 does seem extremely small. [1 nm ~ 8 Cu atoms wide] But I believe you.

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Would have to run through it again as it was quick and rough, but I got around 18.5 Watts/ nm^2, so around 3.7 MW pulse power for ~500nm.
Hmm, yeah that is a lot. (How did you get the pulse power?)

Quote:
There may be a chance that a chemical process is the goal instead of sublimation as you've said though. A lot of industrial lasers will pump oxygen or compressed air out the laser head which could certainly react with hot copper.
Yeah, but the problem with that, is that it would also cool it at the same time. Another option maybe a having it in a vacuum and boiling the Cu off using an electrical current in addition...but then we're not talking DIY anymore.

Quote:
Also, it's become clear to me that I likely made some conversion errors which may have made the number too high by a factor of up to 10.
I think I also have a transcript typo of the density somewhere...
Again, thank you so much for helping me look into this!

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Originally Posted by Benm View Post
Even if you could get the laser power density high enough to do it, the question would be what that would do to the pcb material and where the eveporated copper would end up. It would be little good if the laser managed to sublimate the copper away but also charred the pcb material and have copper vapour condense straight back onto the workpiece, right?
I don't think it can happen that way, and the evaporated Cu should obviously not be inhaled. The ablation would be carefully controlled by the PWM'ed optical output, just as it's done in professional machines.
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Old 04-22-2016, 04:06 PM #14
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No problem was using a G2 lens best I've got will try 7 w in a couple of days

What temperature should I preheat it to?

Last edited by VirtueViolater; 04-22-2016 at 04:07 PM.
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Old 04-24-2016, 01:20 PM #15
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Default Re: Direct laser PCB etching (through Cu ablation)

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Originally Posted by VirtueViolater View Post
What temperature should I preheat it to?
As high as possible without making the FR4 smell / smoke, perhaps by starting in kitchen oven temp, around 200+ C ?
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Old 04-24-2016, 01:41 PM #16
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Quote:
Originally Posted by SIEVA View Post
As high as possible without making the FR4 smell / smoke, perhaps by starting in kitchen oven temp, around 200+ C ?
Ok, soon as I install my diode I'll give it a try (unheated then preheated) I'll post results after
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