LASER cutting and marking. 4

[itsmoked]

I thought a while back there was some discussion between members who had CNC laser systems.

I have several questions about the subject as I need to do occasional/regular stencils for board assembly.

Any knowledge around here?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

For solder paste?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

Yes primarily, but other uses are being contemplated like copyrighting marks, etc.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

Not that I know much about it. We have one company that does that with great sucess. They have some information on their homepage:

http://www.mikroponent.se/en/index.html

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[MikeHalloran]

I have some experience with having stainless sheet cut by CNC laser. The machines are too expensive to buy unless you can keep them very, very busy. The companies who do it as a service are fairly numerous so their pricing has evolved to fairly uniform, affordable levels.

Caveats/facts:

In ~16 gage stainless, a cutting laser leaves a kerf around .007" wide, a little wider for higher power/ greater thickness. For a given laser and thickness, the kerf width is consistent enough to make parts that assemble without trimming.

There is a small HAZ, I'm guessing .005" wide, too small to see but wide enough to interfere with welding the cut edges. You can weld through it, but the weld will be ugly, and the welder may notice that it acts odd. To get a good weld, you have to snag the edges just a little.

Pricing is proportional to the total length of cut, with an adder for the number of separate cuts/penetrations.

Most vendors will accept or even prefer a DXF file, with only the cut details, all on layer 0. Other layers, or drawing objects that are not intended to be cut, will confuse them.

Most vendors assume that the DXF file shows the cut edge you want, not the cutter path. They can work with just the cutter path, but you have to specifically tell them, and remind them with each order.

We tried cutting and marking with the same laser, but it didn't work; the dwell at the corners of characters like 'L' left tiny holes. So we had to pay extra handling to have them mark the sheet with a low power laser, then cut it on a high power laser. You might consider instead a barcode style notch array in an unused edge, or a shaped identifier tab with a narrow attachment that you can tear off when it's no longer useful.

The edges as received are quite sharp but burr-free. Under magnification, the edge looks as if the cut were made as a line of precisely drilled tiny holes, which is sort of how the laser does cutting. You will want to smooth and bevel the edges if the parts will be subject to handling by bare hands.

Both laser cutting and abrasive waterjet cutting can produce holes with edge distances that would tear out with a punch or a shear, e.g. .015" or less in .125" thick material. Great for making parts that resemble tubesheets.

All the lasercut parts I bought arrived clean.
Waterjet parts may arrive with a layer of abrasive dust.
Make that _highly_ abrasive dust. But no HAZ.



Mike Halloran
Pembroke Pines, FL, USA

 

[MacGyverS2000]

Keith,

I have a CO2 laser and I'm expecting a CNC routing table beginning of the month (and lots of bits awaiting something to spin them). If you don't mind plastic stencils (Mylar) rather than stainless, I may be able to help. Mylar lasts for many hundreds, if not thousands of boards, if treated reasonably... stainless is really only needed if you plan on doing 10's of thousands plus.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

Thanks Skogs. I'm not looking to buy really, I'm looking more to implement.

Between a fellow EE and myself we have 3 CNC router tables. We use them constantly for many different jobs including one-offs, prototypes, and even batch jobs. We have all the typical CAD and CAM software and know how to use it, and all of its quirks. We do hot-knifing, acrylic routing, engineering plastics of all kinds, circuit board routing and drilling, and aluminum sheetmetal.

We were just discussing board builds we need to do. One of us just received some solder paste which has a stunningly short shelf life and we always end up with a bunch extra that just dies.

If we could generate our own stencils in minutes we could make much better use of paste when it's available. Having LASER ability would open up more possibilities depending on available cutting power.

So, we're looking to add laser ability to our existing machines. We can buy various LASERs from numerous places, but what should we look for? I'm looking for general information from someone who's done this.

What's a rational power to purchase? What wavelength is best? What safety gear is commonly used. What are frequent complaints?


Mike: Thanks for that really nice summary. I have never ordered LASER'd sheetmetal before. Usually I end up with water jetted stuff, partly because I didn't know much about it. You've brought me up enough to now seriously consider it next time. Down with grit!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

Whoa Dan! Cross post.

That's what I want to make - Mylar stencils.

We only ever do 3 or 4 boards sometimes up to 10. Usually we have some board house do larger quantities. So, heck yeah, we don't need no stink'n SS stencils!

But even Mylar, the job expense, expense of shipping, and urgency makes having someone else do them border on ridiculous. We tend to work weekends. Inevitably we need a stencil made at 8pm on Friday so we can use it Sat, because we got a board back from the fab house Friday, at 5pm. "Going out" for a stencil is just another headache so we end up hand soldering which is its own headache.

Do you mind answering questions about your system or would you rather not?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MacGyverS2000]

Happy to help... LOML has dinner plans for later this evening, but if you give me a call around 4:30 EST I should be home. 410-929-7405

You will need some practice to get it right, but since you're only working with one material you shouldn't have a problem.

To get you started, here are a few answers to the questions above:
What's a rational power to purchase?
If you only intend to use it for prototyping stencils, a 25-35W system will be sufficient ($6-7k for a US system, $4-600 for a Chinese). If you have even the slightest inclination towards using it for other things, consider getting more power.
What wavelength is best?
In general terms, organics (wood, plastic, etc.) work best with CO2 systems (the prices I mentioned above). Metal (disregarding kW-sized system that cost $250k+) is best done with fiber/YAG (double to triple the price, and the Chinese fiber system haven't quite caught up with their CO2 brethren in pricing).
What safety gear is commonly used?
None needed for eyes as long as you keep the lid closed (the better systems use tempered glass, though acrylic works). For ventilation, most exhaust to the outside air... personally, I exhust back into the room after it is scrubbed with a custom built activated charcoal and HEPA filter box.
What are frequent complaints?
Not sure what you're asking here...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[MacGyverS2000]

On a side note, you should get 6+ months of shelf life out of "stencil juice" if you keep it in the fridge...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[zappedagain]

or the freezer is even better...and more than 6 months if you give it a stir to mix the flux back in before you use it. We don't do that with production boards, of course, but I've used solder paste well past the expiration date when I am prototyping.

Keith, On a side note, instead of stinkin' stencils, have you checked out Advanced Assembly (aapcb.com)in Colorado? Their business model is set up around building prototype PCB (i.e. small quantities). I haven't used them yet, but I plan to try their services on my next prototype with tricky SMD parts on it.

John D

 

[MacGyverS2000]

I have yet to find a US-based PCB shop that will etch a board for a reasonable price, which is ironic/amusing considering they often send it to a shop in China anyway (yes, I've checked the board tag from AA, always comes up from some factory in China, often Shenzhen or similar locale). US quotes are typically 4-5 times what I get it for directly from China (actually, I work with a Canadian-based outfit that does all of the legwork, I just pay an extra $15-20 in FedEx charges). I even got them to change houses at my last job, saved 'em a ton...

US-based assembly, however, is surprisingly inexpensive (at least for prototype-level work). $50 for two boards with up to 100 components each, including fine-pitch BGAs. I can't do BGAs, so they are a real boon for me...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

Thanks Dan for the number and the offer! I won't bug you though as I don't think a CO₂ is going to work anyway. (see below)

I've been cruising the CNC forums reading all about the LASER setups. It's looking like everyone is using CO₂. When I first looked at video of a CO₂ laser, they'd cropped it so I could only see the nice little cylindrical thing at the bottom. It had hoses going to it, so I was thinking that's the CO₂ feed... Turns out that was just the lens system with air shielding. DOH!

As I mentioned we use our CNCs like a drill press where we bolt on hot knives, overhang extensions, large routers, zip routers, etc., etc. But these large glass based CO₂ lasers don't look amenable to ON/OFF installations.

I'm really surprised at how limited 25-35W is. When in college I went with a prof to a business to help set up a 5W Argon Ion laser. He placed a spacial filter (pin hole) in the beam path and we triggered the laser. Instantly smoke came boiling off the metal filter because it wasn't aligned yet.

So, to hear '30W would be sufficient' to cut a few mils of Mylar... Dang!

We were thinking solid state lasers. These are like large power resistors, a fist size one. Installing one would be like changing router motors.

Here's some examples:

http://shop.ebay.com/engkerim34/m.html?_nkw=&_armrs=1&_from=&_ipg=&_trksid=p4340

Re:SIDE NOTE

Yes, I have gotten the juice to work for about 30 days of refrigeration. After that it seems to lose something important. Could be because I always use the water cleanable type. It might have water in it that evaporates.

Zapped: Freeze!! Wow, I had no idea. I thought it said; "do not freeze".

I'll check out aapcb!
I insist on building the first unit myself since that's when you discover footprint problems etc.
However I have often wished I could have some hard parts mounted.


I generally use

http://www.pcb4u.com/

They have a 10 boards $100 offer for fab.

Your "$50 dollar two boards place" is really amazing.

Thanks again Dan for the offer.




Keith Cress
kcress -

http://www.flaminsystems.com

 

[MacGyverS2000]

Keith,

I'm not sure what you're trying to accomplish, then. CO2 is the exact laser type you need if you want to cut stencils out of mylar.

Wattage is deceiving as wavelength plays a huge roll. For example, a 25W CO2 laser (at 10um) will make a nice dark burn on a piece of wood. A 25W fiber laser (at 1um), on the other hand, won't make a single mark on the wood... but it'll make a solid black mark on stainless steel. A limited number of plastic can be marked with a fiber system, but a CO2 will cut most plastics. It's not that 25W is limited in what it can cut, it just allows you to cut stuff at 80 inches per second! It's also typically the smallest system you can purchase these days.

Wattage also effects speed. If you insist on going down that eBay laser diode route (it's essentially a CD player read head diode), you'll finish cutting your stencil sometime in 2012 (assuming you started cutting tomorrow). Not only that, but your cut edges will be more like undefined rolls... you'll melt the plastic rather than truly cutting it. Not a good idea for a solderpaste stencil.

You have to trust those "in the know"...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

Thanks again Dan. I'll run this by my compatriot. I haven't seen a single use of a diode laser based router yet. Only 'fun' paper charring etc. All the lasers I've seen so far are indeed CO2.

Our current position is if the 'bolt on' laser diode method will reasonably cut any kind of thin plastic, blue black, red, Mylar, Rubylith, ABS, black paper, or whatever, it will allow us to make usable stencils.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[zappedagain]

Dan,

Are you working with AP Circuits or a different company up in the great white North? Just curious; I've had good luck with AP Circuits for bare boards.

John D

 

[MacGyverS2000]

APC? Bah! Just as overpriced as the rest of them.

Let me give you an example using one of my prior boards and APC's online quote system.

APC:
Outline, 5"x5" square
Board: 0.062 FR4
Soldermask: stock green, both sides
Silkscreen: stock white, both sides
Holes: 100 (APC-limited sizes)

Cost: $2,000+ when shipped by FedEx



My place:
Outline: Complicated (5" diameter circle with tabs)
Board: 0.062 FR4
Soldermask: Multiple colors to choose from (I chose red), both sides
Silkscreen: Multiple colors to choose from (I chose white), both sides
Holes: 100 (no list of drill sizes, just designed with what I needed)

Cost: <$500 when shipped by FedEx.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[btrueblood]

smoked,

Gotta go with Mac on this, a CO2 laser is the way to go for stencils. Just don't cut PVC film - it gives off HCl vapor as it's cut. Acrylic works quite loverly, haven't done mylar yet, but shouldn't be much issue other than smoke.

"what are the drawbacks"

The Chinese lasers are cheap, but they are typically water-cooled lamps, and have a pretty finite life. There are solid state CO2 laser heads used by US-made laser marking/cutting houses, which have much better lifetimes.

We purchased a 35W Epilog laser marker system awhile back for doing in-house nameplate marking (on anodized aluminum, or pretreated stainless), and it works like a champ. Cuts nice stencils in acrylic or cardboard too. We did a batch of paint stencils for our sister company, using 3M blue masking tape, and they worked spiffily. I've looked into acquiring a chinese version for personal/home use, like Mac, but decided against it due to maintenance and performance vs. price reasons, and am saving money to buy a low-end Epilog marker, someday. Ease of use factors into that too (the Epilog prints directly from CAD and/or graphics programs).

Personally, I would vent the exhaust outdoors. We have a HEPA filter system here at work, but it's not 100% effective, and is eventually going to cost a fair bit of money to replace the elements. If we were cutting more organic material, it would definitely clog up faster...but YMMV, and running the machine full time can pull a lot of air from the room.

Good luck!

 

[itsmoked]

Thanks b! We're sort of stalled here for the moment with other projects and are mulling our options.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MacGyverS2000]

running the machine full time can pull a lot of air from the room

Most of the companies specify 5-600 CFM for the blower (what they don't specify is @4" of water, so your countertop cooling fan won't work). That's an 8x8 room evacuated of air every minute. Try heating that during the winter! The bill is lovely. Hence why I filter and evacuate back into the room.

Dan - Owner

http://www.Hi-TecDesigns.com