PCBs with a tan...

[The Tone God]

I have an old tanning lamp that I sometimes use for exposing boards. Works quite well. The trick is getting the timing and distance right for the exposure. If you sensitize your own boards try to make the coating as uniform as possible. Something like a foam brush is good for the sensitizer solution.Try to put something like a sheet of glass to hold the transperency to the board for a clearer image.

Andrew

[LinuxMan]

Ok.

Just went and bought myself a small piece of glass (for one PCB). I'll get the
chemicals and photo sensitive boards in two days time.

I'll still try to do the solarium method... We'll all see how well it goes in my
test run.

Cheers
LM

[Hal]

oh man i had a nice post written out and the site went down last night....


anyway, the chem labs in my high school have UV boxes for cleaning the safety googles....if you're in higgh school, or have access to one, check it out....

[gez]

Gez:

Will this photo process work with a halogen lamp?  I have one down in my shop that's the perfect size to expose a board.  I checked the web and couldn't find enough data to conclude whether enough UV was emitted by a halogen bulb or not.

Many moons ago I used to know some 'grass' farmers (yes, that type) and they used to bore me rigid about UV content of various light sources.  That's were I got the idea of using fluorescent lights (glad something positive came out of that period).  According to them Halogen (and they used them too) had a higher UV content, so I'd say yes it should work.  

Again, you might have to have the board right up close to it.

[gez]

I think that the tracing paper might cause more diffusion of the light, but it might be the only way to help keep the density of the image unless you feel like tracing the positive with an opaque pen

I only use one layer of tracing paper and that's all I've ever used.  I mentioned that you might need more just in case the paper in different parts of the world is a little on the thin side (how would I know?!).

The board I buy says that exposure time is between 2 - 2.5 mins and with the paper it takes 2.5 mins (it always seems to be the longest time quoted).  When I've used really thick baking paper (thin white stuff is excellent) or doubled-up the normal paper I use, I get areas that don't etch (blocks too much light).  The paper is necessary though in order to make the image more opaque, you'll get poor results without it (with an inkjet that is).

[guitarhacknoise]

cool, awesome, and excellent!
This topic has taken me back a few years! almost makes me want to get back into lithography!
-matthias

[markr04]

By the way - an old broken scanner you should be able to find for free. All you need to buy are two UV lamps - there's your box!

Neat concept. I have an old SCSI scanner that I would gladly butcher for the sake of this. Can you elaborate on it? Or point me in the right direction? Where to buy UV lights? Will flourescent ones from the hardware store work?

Thanks!

[Mike Burgundy]

Fluorescent UV lights work fine - I have no experience with regular fluorescents or halogen. I do know (after having done a job for a lighting specialist) that halogen *will* probably work, IF you manage to find an old-style, non-UV filtered bulb. Apparently nowadays they're all filtered.
What you do with the scanner is just find a way to get the fluorescent tubes mounted, done.
I know of several of these, they all use fluorescents from tanning machines. Two to three, lengthwise in the scanner, done. The nice thing about this setup is the lid - it shields you from UV, and presses down on the board/design combo so you get good contact.

[markusw]

Maybe I´ve missed something but this is the way I do it at home without any special equipment.
Since I do not have a UV lamp I use a standard 12V/50W halogen bulb writing desk lamp in about 18-20 cm distance from the PCB. With this kind of lamp it takes about 30 min of exposure. This for sure is far longer than with a UV illuminator, but who cares? Important: On my lamp there is a protective glass in front over the bulb. I have to remove it because otherwise exposure times get a little bit too long. It seems to block some UV light.

I place the photo sensitized copper board with the copper side up on my writing desk and overlay it with two layout copies from a laser printer but it should work the same with inject layouts. On top I put a small glass plate I have take from a picture frame and fix it to the table with some tape. This is to be sure that the transparency is in direct contact with the board.

For developing I use 1% sodium hydroxide, for etching ferric chloride.

This it how it looks like:





Maybe the resolution is´nt as good as with a UV lamp and short exposures but it´s pretty sufficient for me.

Markus

[Torchy]

Why two laser layout copies ? better definition ?

Im itching to get a step up from the laser-printer-and-label method (which, incidentally,sucks) but the cost of light boxes and bubble tanks is heavy.

[markusw]

I have not tested it with just one copy but I think it should work the same (depending on how "perfect" the print is).
IMHO you really do not need a special equipment, just a writing desk lamp, some plastic trays and a little more patience than with the UV illuminators and bubble tank. After exposing I just put the PCB in 1% sodium hydroxide (for about 2-3 min), wash it under tap water, and finally put it in another tray with ferric chloride for etching (the concentration does not really matter as long as the solution is dark brown-yellow). If you rock the tray now and then the process is much faster (to really speed it up you have to rock it all the time). Anyway, usually it´s done after 30-45 min. So far I had no problems with my kitchen-made PCBs. When the ferric chloride solution gets green or blue it is time to replace it with a fresh one.

When using inject transparencies it might be even easier to find two copies that really match. I use standard laser printer tranparencies and obviously due to the heat it´s sometimes really hard to find to matching copies. Actually I really ought to check it witch just one.

For getting the right exposure time a just did a series from 15-60 min and 30 min turned out to be fine. It´s just important to put the lamp always in the same distance from the PCB.  

Good luck,

Markus

[gez]

When using inject transparencies it might be even easier to find two copies that really match. I use standard laser printer tranparencies and obviously due to the heat it´s sometimes really hard to find to matching copies. Actually I really ought to check it witch just one

That's why I use tracing paper with a single transparency.  The paper makes the image more opaque but is transluscent so allows enough light through.

[markusw]

That's why I use tracing paper with a single transparency. The paper makes the image more opaque but is transluscent so allows enough light through.

I don´t really get it how the tracing paper is able to correct little imperfections in the print. Let´s assume there is a small blank in one of the traces. Does the tracing paper blur a little bit thereby covering the blank? On the other hand, does one have to increase the exposure time when using tracing paper? :?:  :?:

Anyway, thanks for the tip!

Markus

[gez]

I don´t really get it how the tracing paper is able to correct little imperfections in the print. Let´s assume there is a small blank in one of the traces. Does the tracing paper blur a little bit thereby covering the blank? On the other hand, does one have to increase the exposure time when using tracing paper?

I use an inkjet. The image you get when you print off a transparency is nice and detailed but it lets through too much light and is next to useless. When I've had laser copies done at my local print shop, although much better, it's the same. The tracing paper just blocks out a bit of light so the single transparency seems more opaque than it actually is. However, the paper is translucent enough to let through just enough light to the exposed bits for them to develop properly (though you usually need to use the longest exposure time quoted for the board you use).  Without the paper not enough light is blocked and you end up with a blank board (or as good as).

I've read that with a laser printer, and if you can find the right size stuff, you can print directly onto tracing paper (this is where I got the idea from) which would cut out the middleman.  Don't know how this pans out with an inkjet though.

Another thing you can do is print off your image onto ordinary paper and spray it with WD-40. This makes it transparent enough to be used. I have done this and it does work, but the detail isn't quite as good as using the transparency and tracing paper method (there is no deterioration of the image using this technique).

I tend to use 'grease-proof' paper as it works out cheaper than tracing paper.  The fine white stuff works great, but the thick yellow stuff doesn't (blocks out too much light and patterns within the paper appear on the finished board).

Doing the tracing paper trick works best with a laser printer.  You get very slight 'pitting' with the inkjet, but I'm not complaining (my boards work and that's all that matters, plus if you tin your boards it's even less of a big deal).



The fading is a result of the camera flash, but you can see pitted bits of copper at the top of the board.  Like I said, you get better results with a laser printer.

PS  If your artwork has slight flaws when you print it off you can touch them up with a permenant marker pen.

[markusw]

You´ve convinced me. I am definitely going to check this in my setting.

[guitarhacknoise]

hello again!
hey gez,
after more thought, I'm still not with the tissue paper method.  seem like it is just another light barrier. of course I've seen that it works, but does it work in your favor? i'm not so sure.  the "pitting" you are experiencing is probably due to the larger fibers present in the tissue paper blocking more light than the areas with smaller fibers (also could be pinholes in your master). but like you mentioned there are lots of different papers out there. I guess my aversion is diffusion. diffusion is bad, it's hard to get an even exposure if the light is reaching the board unevenly.
The best kind if image to use would have to be an actual film positive (this is their actual purpose!), you could probably fit 4 to 6 board layouts on a 9 x 12 sheet, check out your local print shops for the cheapest price (make sure they do it in house or the price will skyrocket).
as far as "touching up" an ink-jet or photocopy type of positive, an actual opaque pen from a photography or lithography supply shop will still be the best bet, hands down.
(next time you're bored, try and black out your t.v. screen with a sharpie.)
with all this said I have to agree with all the methods here, because whatever works......................works!
-matthias

[David]

OK, Gez, we're all ears.  Tell us about the sodium hydroxide part.  When do you use that?  Where can Mr. Average DIY buy something like this without a security clearance?  What strength solution do we need to use?
Markusw hit on it in his earlier post, but I need detailed instructions on using a chemical that could be harmful.  I'll worry about ferric when I get to the etching part.  I need to understand the imaging part first.

[gez]

OK, Gez, we're all ears.

And I'm all mouth!  

There's a new generation of developers that are free of Sodium Hydroxide.  Not only are they safer to use but they have a wider safety margin (you can leave a board in for up to 30 X longer than necessary without any adverse effects).

I use a brand called 'Seno'.  I think it's European.  You should be able to find something equivalent in the States.

Once you've exposed your board you just dip it in developer for about 30 - 40 seconds (you'll see the image appear once it's in - gently moving the board with a spoon helps remove any stubborn ink, though I've heard of people using soft toothbrushes) then you rinse under flowing water followed by an etch in ferric.

[markusw]

For sure the imaging (exposure/developing) part is the most tricky part. Actually not tricky, but it needs some more care than the etching.

You could do the layout for a small PCB (e.g. a millenium bypass if you can use it) ideally with traces of different width to check how thin you can go. Then perform several exposures (e.g. starting with 10 min, 20, 30, 45 and 60). You can keep the already exposed PCBs in the dark until you´re done with all exposures. Important: keep the distance between the board constant (light intensity decreases by distance^2).

Then prepare youself the developing solution (any kind will do). The easiest and safest way is to use a ready to use solution like the one Gez mentioned. Put the board into the solution and rock the tray slightly so the solution is in motion. When the image is clear with no spots between the traces take it out and rinse it.

I just use sodium hydroxide because I´ve it available and it´s cheap too. I disolved 15 g in 100 ml of distilled water and keep it as a stock solution in an air tight polypropylene (not glass!) bottle because you can etch glass with it. The stuff gets rather hot when you disolve it, so be sure to ware gloves. For developing I just dilute it 1:15 with water. But once again: take great care with sodium hydroxide!! Always ware gloves and ensure that nothing gets into your eyes because you easily can get blind, especially with concentrated solutions.

The etching is actually the easiest part. Ferric chloride is much less caustic than sodium hydroxide but it stains fingers and even steel. Just dissolve it in distilled (or tap) water, around 20-40 g in 100 ml water will do. You can do this with a kitchen balance (just be sure to keep it clean). Put the board in the solution and...... keep rocking
:wink:

[gez]

The easiest and safest way is to use a ready to use solution like the one Gez mentioned

Actually, Seno do powder too and that's what I prefer to use.  Once the solution is made it has a limited shelf life so I mix it on a need to basis.