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Questions on optic disc lens and possible options for PCB fabrication

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LAN_403

Martin King

Wed Jan 26 2011, 07:13PM

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

They are UV tubes but not particularly "speciality" They are marked :-

SYLVANIA
BLACKLIGHT U.K.
F15W/350 BL

And are widely available on the net. My unit uses 12 tubes (6 top, 6 bottom) and 6 ballasts but TBH I VERY rarely use more than about a quarter of the available area so most people could make do with a much smaller unit than mine.

Martin.

Conundrum

Wed Jan 26 2011, 08:25PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

tried to do this a while back, but ran into problems with the positioning.

Maybe use an HP laserjet mechanism with the diode replaced with 200mW bluray writer diode, add timing using magnetic sensors (shouldn't affect the motor) and an old scanner as the X axis?

-A

Martin King

Wed Jan 26 2011, 11:22PM

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

2Spoons wrote ...

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.

You can get that thin with diy UV but I'll admit it's not easy and TBH if I needed to go that thin (which I never have) I'd probably send the job to the Chinese to do. The main issue I have with toner transfer is time (proper cleaning and prep. of bare board seems to be essential) and consumable cost (for very fine work you appear to need proper transfer paper and preferably a foil layer as well) and the process is destructive to your artwork, I've done runs of 60 or more boards off a single inkjet artwork in the past (although again I would probably send a job that size of to the Chinese these days!). I've seen claims from suppliers of toner transfer suppliers of "make a board in 8 minutes" which I find VERY hard to believe unless they're not including board cleaning/drying etc. time and etching time. It's takes me a MINIMUM of about 15 minutes to UV a board (that's everything from printing the artwork to etched board but not including general faffing around time) :-

30ish seconds to print artwork.
3 min 30s exposure.
30ish seconds develop. (maybe a minute if I need to mix fresh developer)
approx 10 minutes etch (with fresh etchant it can be much quicker, with old etchant it can be much slower), and that's with either 1 or 2 ounce board, some companies supplying board for toner transfer seem to supply 1/2 ounce copper board!

Martin.

2Spoons

Thu Jan 27 2011, 02:39AM

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

I only use toner for prototypes - I too would rather use a chinese fab for bigger runs. I only did all the flex circuits that way because we couldn't wear the 2 week lead time. It also took a while to find someone who could make flex that would flex without cracking the copper!
Like all processes, toner transfer takes some time to perfect. I found getting the heating right to be very important - I built a temp controlled hotplate with a silicone cover that applied pressure to the board using vacuum. Giving the copper a good scrub with a scouring pad was also important. And you do need the proper transfer sheet (I use the blue ones)

8 minutes? Yeah, i'd love to see that! Usually takes me about 30 minutes.

Ken M.

Thu Jan 27 2011, 06:04AM

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

Thanks martin for the info on the tubes, I was asking because there are so many different "UV" tubes for a variety of purposes with different wavelengths, and I was unsure at what to look for if I go with a basic uv box.

If I do go with one (Most likely will due to simplicity...) I looks like I could use bug zapper lights which I could get in a small size.

Electroholic

Thu Jan 27 2011, 08:10AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

rather than focusing the uv using lens, why dont you use an optical fiber?

Ken M.

Thu Jan 27 2011, 04:02PM

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

Because when I think of transmissive fiber I picture the dim light emitted from a fiber optic cable from a solder project I did in college, unlike using a lens that would just focus or disperse the the light.

Martin King

Thu Jan 27 2011, 06:53PM

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

2Spoons wrote ...

I only use toner for prototypes - I too would rather use a chinese fab for bigger runs.

I mainly do prototypes but occasionally I may need to do an urgent large run, so UV is really the only option for me. For non-urgent large runs I use PCB cart. My personal view is that UV done properly is less hassle overall than the toner methods I've seen. but I guess both methods have their advantages/disadvantages.

Martin.

Ken M.

Fri Jan 28 2011, 06:23AM

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

I only wanted some way to make my own boards just because the best bang for the buck place I've seen for small orders is pcbexpress or expresspcb...damn those 2 c ompanies for having an almost identical name, any ways what ever company it is has 3 3.5x2.8inch double sided, with through hole plating for $51, my problem is I only every want or need 1 board be it the prototype or the finished product, however I'd like the prototype look like a finished board all the time just in case I only end up making the prototype and not needing to make any revisions.

Martin King

Sat Jan 29 2011, 05:29PM

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

Just for fun I added some test pieces to a board I needed to do this morning. I can't find my microscope at the moment so the pics are from my SLR and also a backlit one from a slide scanner (this makes the tracks look thinner than they really are) All tracks checked out OK for continuity/shorts. The round pads are 40th with 15th holes and 50th with 25th holes. Track widths are 5th, 8th, 10th, 12th and 15th the DIL pads are 0.1" apart. These measurements are what the PCB CAD software says they SHOULD be I haven't measured them to see what they actually ended up as. Oh and this is 1oz copper board, it would be even easier with 1/2oz board. PHOTOS

Although it looks like some of the tracks are broken, they're not.

NOTE: You CAN NOT achieve this sort of result with out of date or poor quality photoboard or nearly expired etchant (however they are fine for more run of the mill boards) and ideally you need vacuum pulldown to ensure intimate contact of the artwork with the PCB. Etchant was HOT Sodium persulphate.

Martin.

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