Is there anything like a kit for UV based PCB fabrication?

photomankc

I've been doing some work lately in making my own PCBs with the toner transfer method (Pulsar FX) and while that has worked pretty well for boards with bigger traces and clearances it seems to be tricky for some of the smaller work I need to do to produce some of my breakouts. Last night I had to run the process 4 times before I got all the artwork to stick to the PCB ***AND*** not smoosh the pads together for the SOT-23 sized ADC package and 12mil traces. I finally got 2 reasonably decent boards out of 4 by skipping the Green TRF application but this seemed to expose the limits of the process for me. The other two boards had significant defects from lack of the TRF sealant over the toner.

I'd like to try the photodevelopment route but I'm not interested in starting another hobby of collecting and building light-boxes and exposure cabinets and such. I have not had much luck in finding a kit where that stuff is gathered up and included ready to go. Does anyone know of a source that provides something like this? Alternatively do you know of a good source for the UV developing light specifically? I'd prefer something that is not a danger to my eyes.

LoopyByteloose

I do photodevelop boards - single and double sided. The light doesn't have to be UV. I just use a flourecent desk lamp. I use boards that are already coated with light sensitive material.

The most important element is how you make the transparency.

For me, I use an HP inkjet to print transparencies as the ink in the HP inkjet is very opague and sticks. I tried a Canon and the results were that the ink you bead up on the clear transparency -- no good. Even with the HP, the ink doesn't dry 100%, but remains sticky for quite awhile, so you have to learn to know which side has the ink and be care to not smudge the image.

Other people you laser printers and print two copies of the image. Then they build a double layer to get a dark enough image. I don't bother with that.

Somebody may sell a kit, but you can just buy the boards, a package of developer, a bottle of etchant (I use ferric chloride), and a plastic tray to develop the board and to etch the board.

I use Eagle CAD to design the boards, then print to the HP printer.

If you use a desk lamp, you will have to do some testing to determine the right timing for exposure. Too long and there are spots that have holes in where your wire is supposed to be, too short and the board has spots that have copper where none should be.

I did get an electronic lab timer that attached to a 120VAC relay so I can get the same exposure every time. You can set the light inside a box so the distance is always the same and there is no outside light. Cover the opening with a piece of black cloth.

If you can visit an electronics store locally that sells all this stuff, the salespeople can be very helpful. Buy over the internet is not so helpful. Try to locate a Ham Radio Club in your city to get advice as well.

garyg

A few thoughts about toner transfer and Light sensitive pattern transfer.

I've made a number of circuit boards using the toner transfer method.
This ends up working out pretty good for me unless I try to do very small traces.
One thing that I've noticed is that there is very much Disinformation out there about Toner transfer.
The best thing I've found is to NOT preheat the circuit board you are trying to transfer toner to.
Run the Iron at about 350 or so degrees F.
Dab the iron onto the cool circuit board long enough to melt the toner and only heat the top of the copper board.
General idea here is that you want to melt the toner to the copper board and have the toner cool to below it's meltng point quickly.
It helps very much to use very thin paper on your printed pattern, less dimensional error.
I would imagine that your experience with Pulsar FX is something like a laminator.
My experience is with my wifes iron and Office Max Laser copier.

My only actual experience with Light Sensitive things has to do with screen printing.
I use something called DIAZO to make up my screens.
This seems to be a very good process.
Not very fussy.
I try to position my lamp (I use a 150 watt incandescent) about 18" above the image I'm attempting to burn into the screen.
I run the light for about 7 minutes.
I've made 10 or so screens without a failure.
I even made a screen and printed my circuit using screen printing ink as the etching mask with pretty good success.

The only reason I've never ventured into the world of photosensitive circuit boards is the shelf life of the light sensitive material.
It's quite expensive to purchase small amounts of light sensitive things for a particular project due to the fact that
the shelf life on these items is apparently only about 6 months or so.

Sometimes, It's a year or two before I want to build another circuit board.

As far as I'm concerned, I think that fabricators like OSH PARK are the way to go.
I'm currently experimenting with Eagle Cad.
Once I've passed the learning curve, I'll more than likely have someone like OSH PARK fabricate my circuit boards.
I do get impatient with the process, but I believe I'll get over it eventually.

Thats just my experience, such as it is.
I hope it helps you in some manner

Garyg

photomankc

I was not aware of the shelf-life issues with pre-sensitized boards? I thought they were delivered in sealed pouches to negate that issue.

My process with Pulsar FX does indeed use the laminator. Normally if I can stick to 15/15mils for the tracks then there is enough clearance for a couple passes to fix the toner and a couple passes to add the TRF foil to seal up without the tracks mushing together. It's just some of the surface mount stuff demands something around 10/10. It's then that the TRF phase seems most likely to merge the tracks. I assume that's because the foil is thin and transmits more pressure to the toner while the transfer paper blunts that a bit and lowers the heat transfer as well.

I'd like to be able to handle these tighter spaced designs at home and a light-sensitive process seems the best way to get that. I won't mind paying OSHPark or SeeedStudio for a finished product but I'd prefer to experiment on my own where the cost of a design bug is not so high.

The main issue I'm looking to eliminate if the guesswork I see with different florescent tubes, fixtures, and heights and times. I was hoping that someone sold a device where I don't have to stack a desk light onto a pile of books and stand over it with a stop-watch. I've seen some UV exposure units on EBay that seem like a nice solution.