Laser marking PCBs -- what's needed?

[gwideman]

I'd like to find out what's needed to mark PCBs with a laser, in order to add serial number or barcode, possibly other annotations, that sort of thing.

These would be manufactured PCBs, with solder mask and silk screen.  So really what I'm asking about is probably laser marking of the solder mask (say green, as an example), or silk screen (possibly a dedicated white rectangular area).

At the moment, the use case is to mark the numerous copies of prototype assemblies that are in different states of revision during testing.  (Marking with "permanent" marker works poorly as it doesn't withstand cleaning -- for example with IPA or other flux remover.)  So at this small-quantity stage, manual positioning of the board in a laser cutter/etcher would be fine, I don't need a conveyor driven process.  (But experience from that realm might be informative too.)

I'm most interested in what people have tried, what type and power laser was able to produce what results, notably readability and resolution.

(In case it's not clear, I'm not asking about the much-more-easily google-able laser-curing of resist, or even ablating the copper or cutting of the board for making the PCB in the first place.)

Thanks!

[Mangozac]

An affordable laser serial number/QR coding system for production is something I would be very interested in as well!

[thm_w]

A thermal printed polyester QR/barcode sticker would also work, they withstand IPA.
Maybe someone with a cheap laser machine could test it out for you.

https://jtechphotonics.com/?p=1164
https://www.heatsign.com/pcb-laser-marking-machine-all-that-you-need-to-know/

[tjlusco]

I have done this with a Trotec Speedy 400 and the results were great! Although, that machine is completely overkill for etching solder mask (120W), I had the power set to 10% and the speed quite high. The settings used are similar to that of cutting paper, so just about any laser cutter should work.

You cannot mark FR4 directly, you need solder mask over copper. FR4 burns and creates nasty fumes. I've personally tried green and white solder mask, and they both turned out great. One thing, the text will be "raw copper" so this will oxidize and tarnish over time, but the readability against solder mask is good still.

Resolution fantastic, is as good as your laser cutter can achieve. Ours has 1000 DPI, so better than your average laser printer.

For marking the same thing on a batch of boards, this would be great. You size your artwork to the PCB, fill a "plate" full of the artwork in the software, arrange your PCBs on the plate in the same array, start the job. Individualised serial numbers were a pain with our laser cutter software, we had manually update the artwork SVG and re-setup the job each time.


For examples, the white one was one I've done, the green is from a RPI Zero 2 which has a lasered QR code on the back.

[james_s]

My friends have a Chinese laser marking machine at their shop, I think it uses a 30W fiber coupled laser. I have no idea what it cost but I can find out along with the specifics if it would be helpful. It works well to mark anodized aluminum so I'm fairly sure it would have no trouble marking solder mask.

I'm sure it must be thousands of dollars though so unless you're doing a very large volume the printed labels someone else mentioned might make more sense. Lasers are fun though.

[gwideman]

A thermal printed polyester QR/barcode sticker would also work, they withstand IPA.

...but I would expect that thermally printed labels don't fare well during hot-air rework or nearby soldering?

https://jtechphotonics.com/?p=1164
https://www.heatsign.com/pcb-laser-marking-machine-all-that-you-need-to-know/

Thanks for those links, quite informative!

[ataradov]

...but I would expect that thermally printed labels don't fare well during hot-air rework or nearby soldering?

They don't. Not because of the thermal printing, but because the base material shrinks. All sticky labels I've seen are the first to go in the first sight of heat during rework.

[beanflying]

Typically for engraving or ablating paint/mask you will only need a few Watts of CO2 or even a Diode Laser. In reality on a 40W CO2 Laser with good optics you would be looking at maybe 10-20% power and as fast as you can drive the head to get the job done.

Personally I would AVOID all of the cheap diode Laser kits as they have no cover and fume extraction among their other failings and I would avoid the very bottom of the barrel K40 evilbay CO2 options even though they will likely do your job. While the cover and extraction can be overcome with the Diode offerings they would then be very limited in what else you could use them for in your shop.

So if you are going ahead with this consider if you might want to cut Acrylics or even Laser mark front metal panels (using Laserbond or similar). If this might be where you are heading then 40-60W of 400x600 bed CO2 is worth a think.

[Berni]

I did it using a 50W pulsed fiber laser.

The soldermask seams to be taken off pretty easily on low power settings, leaving clean untouched copper exposed. I found this out while testing if the laser can be used to etch traces into a blank copper board. The results ware a complete failure for the copper cutting part, it did have enough power to cut trough the copper but as soon as it did the FR4 was turned into a burning charred mess. Only way i got it to work was to use a painted board, burn the paint with the laser and etch the copper with chemicals. So i dropped the idea. But it did teach me that these pulsed lasers are great at removing anything on top of the copper when the power is dialed down. Includes cleaning rust.

These galvo steered pulsed lasers are really fast. Something like that QR code literally takes <1 second to engrave start to finish. But they start at about 3 grand for the cheep chinese ones. A better choice might be a CO2 laser or if you don't mind one marking taking up to a minute you can get away with a diode laser. They are much cheaper.

[gwideman]

Typically for engraving or ablating paint/mask you will only need a few Watts of CO2 or even a Diode Laser.  In reality on a 40W CO2 Laser with good optics you would be looking at maybe 10-20% power and as fast as you can drive the head to get the job done.

That's the conclusion I'm coming to, nice to hear it confirmed.

Personally I would AVOID all of the cheap diode Laser kits as they have no cover and fume extraction among their other failings

I'm aware that fume extraction could be an issue. Other than that, I'd be interested to hear reasons to avoid a diode laser, as these seem an OK match, power wise, at least for lowish volume not concerned with super high throughput.

.. and I would avoid the very bottom of the barrel K40 evilbay CO2 options even though they will likely do your job. While the cover and extraction can be overcome with the Diode offerings they would then be very limited in what else you could use them for in your shop.
So if you are going ahead with this consider if you might want to cut Acrylics or even Laser mark front metal panels (using Laserbond or similar). If this might be where you are heading then 40-60W of 400x600 bed CO2 is worth a think.

I have, in the past, used Epilog laser cutter/engravers and also Hurricane brand large Chinese ones, for purposes such as you list. I'm aware that the smaller, much less powerful units are not in the same league.  However, at the moment I'm looking to do some low volume tasks engraving tasks, with some amount of researching, experimentation and gaining experience that might also lead to a higher-volume production setup in future (with upgraded equipment).  I'm not looking for a way to talk myself into this being a down payment on an all-singing all-dancing unit, though thanks for the temptation :-)

[beanflying]

The major anti against Diodes is the speed/acceleration of the head and corresponding engrave speed. I am currently doing some work on my little Laser to shed some weight from the head so I can raise the acceleration and speed a Diode by comparison will be moving maybe 5? times more fixed weight than even a standard CO2 Lens and tube assembly.

Enabling the purchase is part of what I do join the TEA thread to find out

Few threads in Mech Eng you might want to look at

https://www.eevblog.com/forum/mechanical-engineering/laser-exhaust/ Enclosure issues for a Diode Laser

https://www.eevblog.com/forum/mechanical-engineering/40w-300x200mm-laser-cutter-engraver-vollerun/ some of the journey with me little 40W CO2

I have most of the bits in the shack to build a 1200x900 100W Laser when I find some space and time 

[thm_w]

...but I would expect that thermally printed labels don't fare well during hot-air rework or nearby soldering?

They don't. Not because of the thermal printing, but because the base material shrinks. All sticky labels I've seen are the first to go in the first sight of heat during rework.

Sure, though depends on the size of the board. If the label is off in the corner, and you are working on a BGA in the middle 5cm away, its not going to be a problem.
I do smaller parts within 6mm of a label, if you are fast, the label is not affected (~35s hot air).

[gwideman]

As the OP, I received by email a notification of a response to this topic that is quite interesting.  That response appears to have been deleted.  I wonder if that was because the response included the name of the manufacturer providing the advice? If someone knows the reason for deletion perhaps they could comment.

Anyhow, here is the advice from that email:

As a manufacturer [...] recommends the following methods for adding serial numbers, barcodes, and other annotations on PCBs:

1. Laser Type and Power

• CO2 Lasers: Suitable for marking solder mask and silkscreen layers, with a power range of 10W-30W.
• UV Lasers: Ideal for high-precision marking, with a power range of 3W-10W.

2. Marking Methods

• Solder Mask (Green): Use CO2 or UV lasers, adjusting laser parameters to avoid damaging the copper layer.
• Silkscreen (White): Use CO2 lasers to remove ink, or UV lasers for high-precision marking.

3. Readability and Resolution

• UV Lasers: Achieve high resolution, with a line width as fine as 0.01 mm.
• Contrast: Laser etching reveals the underlying color, creating a sharp contrast.

4. Small Batch Production

• Manual Positioning: Use fixtures to hold PCBs in place, ensuring consistency.
• Vision Alignment Systems: Improve efficiency and precision.

Experience Sharing

• Cleanliness: Keep the marked area clean after laser marking, avoiding strong solvents.
• Durability: Laser markings are more durable than traditional markings and are not easily erased.