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Questions on optic disc lens and possible options for PCB fabrication

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Ken M.

Tue Jan 25 2011, 07:22PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

With doing a DIY PCB the 2 most common ways are the toner transfer and the UV photo etch, both are some what limited in how small the pads and traces can get, not to mention human error when placing the sheet to transfer the image from the transparency or tts paper to the actual board.

Now there seems to be people painting the copper clad then using a laser to etch of the paint in areas that don't need the copper, the problem with this still seems to be trace and pad size since you have to burn the paint off, which if trying to make a small pad for say a LQFP chip or other small footprint part could result in burning more paint then is needed to be removed also the laser beams diameter.

Then there's the etching the copper right off the board idea, which isn't likely to work without a professional laser etcher/engraver.

So last night I started thinking what about using an optical discs laser or just perhaps its lens with a UV light source and make a DIY mil that might be able to laser etch if using a powerful enough laser, the question then was how much power can one of those lens handle.

The other option like I said was to use a UV light source laser beam, LED, something that has a 400nm wavelength and just use the lens to focus in and out to allow the beam to be (hopefully) anything from 1mil up to 1inch or larger and use the motor assembly to move the head back and forth like a inkjet printer, but this brings up the same question of how much power can the lens handle and a new question of are the lens polarized to specific wavelengths of light or are they just a peice of glass?

Myke

Tue Jan 25 2011, 09:45PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

While reading your post, I thought up the idea of somehow spreading a thin coat of toner on the board and then use a laser to heat and fuse the toner sticking it to the board. This would need a lower laser power and also seems like it could get a fairly high accuracy if the toner were spread evenly enough and not too thinly or thickly.

Just an idea to add that's sort of similar.

Martin King

Tue Jan 25 2011, 10:06PM

Registered Member #3040 Joined: Tue Jul 27 2010, 03:15PM
Location: South of London. UK
Posts: 237

How thin are you looking to go? I can achieve this

without breaking too much of a sweat using a home-brew UV set-up and ink jet masters. I can also do double sided (but not plated (yet)). All the equipment I use is here

. Some of the hair brained schemes I come across on the net such as "toner transfer" mystify me when bog standard UV exposure is dead simple and commercially proven ! The main limit on the UV process is the quality of the masters and if you need to go EXTREMELY fine then you may need to investigate a collimated exposure unit. Laser photo-plotters are used in commercial production but that's just speeding things up by removing the step of making a photo master. For home production I don't really see the need to print a master as being a major issue.

Martin.

Daedronus

Tue Jan 25 2011, 10:22PM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
Location:
Posts: 370

I did some PCBs with a (relatively) cheap Chinese CNC.
I can cut more or less any IC foot print.
Even the ones with 0.5mm pitches.

The nice part is that the same set-up will also do the drills...

Wyatt

Tue Jan 25 2011, 11:48PM

Registered Member #3490 Joined: Wed Dec 08 2010, 11:55PM
Location: The Granite State
Posts: 34

Martin King wrote ...

How thin are you looking to go? I can achieve this

without breaking too much of a sweat using a home-brew UV set-up and ink jet masters. I can also do double sided (but not plated (yet)). All the equipment I use is here

Holy crap!I didnt realize that could be done at that level.Beautiful!

2Spoons

Wed Jan 26 2011, 01:15AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

Using toner transfer I've made double sided pcb (flexible pcb actually) with 5 mil (0.127mm) track and space. From a panel of 24, only 1 circuit failed. If you are going UV laser, use it with UV resist - that way you can use fairly low power. Laser will be far superior to LED for minimum spot size.

Ken M.

Wed Jan 26 2011, 08:27AM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

@myke, the laser to toner is a good idea but I imagine getting a perfect spread would be hard, and the heat transfer of the copper may be an issue.

@martin That's probably about what I need, which I was going to do the exposure thing but I have no light box, I'm horrible at crafting style stuff such as wood working, mostly because I'm impatient, not to mention trying to get the proper distribution of light for an even exposure, not to mention getting a proper master print and having to have clean transparency all the time.

@deadronus yes I looked into the CNC milling of pcbs but those Are somewhat pricey.

@spoons the TTS is something I though about but I don't quiet trust the fact that you are heating and applying pressure to melting plastic powder.

The reason I was thinking of using a UV led or a UV laser was so that I could have the Beam of UV light adjusted as needed for a given trace or space then have the head unit act like a printer head and just expose the photo-resist as needed in the areas needed and it would work with any board from 10mm x 10mm all the way up to say a 12inch by 12inch (sorry for using 2 separate units of measure) or larger and not be wasting any transparency or TTS paper or ink in the process.

The idea of using a LED or Laser with a cd player/burner lens is the fact that the pits on a CD/DVD/Blue-ray are approximately 500nm wide, now there's no way I'd expect to get that good of a resolution with a home brewed idea, but I think maybe a 1,23, or 4 mil beam up to what ever size say for a ground plane or high current trace could be achievable.

Martin King

Wed Jan 26 2011, 10:46AM

Registered Member #3040 Joined: Tue Jul 27 2010, 03:15PM
Location: South of London. UK
Posts: 237

Ken M. wrote ...

....but I have no light box, I'm horrible at crafting style stuff such as wood working, mostly because I'm impatient, not to mention trying to get the proper distribution of light for an even exposure, not to mention getting a proper master print and having to have clean transparency all the time.

Unfortunately, if you're impatient then you are probably going to struggle to get good results whatever method you use and how are you going to build a CNC UV laser if you can't make a simple lightbox?. My lightbox took me all of a day to make and has churned out 100's of boards. If you're not good at woodwork then you can often get the wood cut for you by the supplier (you may have to pay a small charge but it's worth it for the hassle it saves). If I get time I'll try and measure mine up and post a cutting list then it's simply a matter of glueing the bits together. As for cleaning transparencies I tend to just re-print them if I need to do another batch, otherwise I store them in A4 plastic wallets to keep them clean.

Martin.

Ken M.

Wed Jan 26 2011, 06:26PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

Martin, are you using specialty UV bulbs or just standard florescent bulbs?

Pinky's Brain

Wed Jan 26 2011, 07:06PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Plenty of people have used old pen plotters together with blue lasers to directly expose PCBs. Just search youtube.

If you happen to have a plotter and a blue laser diode lying around it's an option ... obviously not going to be as fast as simply having a laser printer print a pattern on a sheet to use as a contact mask in a lightbox.

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