PCB Exposure?

[KH602]

Hi there,

I recently bought some photosensitive copper clad from rapid electronics and using four 9watt UV 365nm bulbs to expose my pcb, however it is not exposing the pcb how I thought it would.

It's been a few years since I used this method so I know what to expect before developing but it doesn't seem to be removing the photoresist around the pcb mask. I am using a clear associate with the pcb mask on.
I also have tried using 2 9watt UVC germicidal blubs which has a shorter wavelength and still no joy.

Really don't quite understand why it isn't exposing the board through the associate. I have noticed that it has removed a tiny bit of the photoresist that the associate isn't covering the pcb,
mainly around the edges which are holding the pcb mask down with clear tape.

Anyone have any ideas why this would be happening? Like I said before I have used this method before but quite some time ago, yet all the websites and tutorials seem to be the same and match what UV lights I am using.

Would appreciate if anyone could help me out trying to get my pcbs to expose and producing a better etch.

I forgot to mention, i have even left the UV lights on for 30mins+ and still no joy, yet websites advise 2-10mins exposure

Cheers guys.

[mattthegamer463]

No offense if this is a stupid remark, but you're bathing the exposed board to remove the exposed resist, right?

[KH602]

No, you expose the photoresist board first then develop it to bring the tracks out,
Then wash it. Then you etch it.

But I can't get the photosensitive pcb to fully expose
Before I even develop the board or even get to any of the other stages.

Which is why I am asking if anyone knows why or how is the board clearly not exposing the
The layout when using what appears to be correct uv exposure etc

[CodeMonk]

Someone gave me this link awhiel back.
Haven't read it recently so I don't know if it will help you.
Be worth a look at least :

http://www.instructables.com/id/How-to-make-a-printed-circuit-board-PCB-using-th/

[Perrow]

I use a 3W UV led, expose for about 4 minutes. After it's exposed I can see the tiniest color shift in the resist if the light is right. Then I develop using common household caustic soda. Rinse, then etch with sodium persulfate. Works perfectly.

[Ice-9]

But I can't get the photosensitive pcb to fully expose
Before I even develop the board or even get to any of the other stages.

Which is why I am asking if anyone knows why or how is the board clearly not exposing the
The layout when using what appears to be correct uv exposure etc

If I understand what your saying above, your expecting to see the exposure before developing ther board ? On most modern photosensive PCB materials you will not see anything on the PCB after exposure, you only see a the traces etc after developing the PCB.

[KH602]

its been that long since i used this method and looking at other tutorials and photos it seemed like you could see
the tracks partially before developing.

anyway i am just trying to develop the board now using this stuff, http://www.rapidonline.com/Tools-Equipment/Seno-4007-Photoresist-Universal-Developer-Crystals-34-0395/?sid=a9708be5-3283-4b71-8f5a-81669913468e
dont know if its any good but so far i can see the faint tracks in the photoresist but its not taking it away, if it is, its stupidly slow

[Mike Burgundy]

but its not taking it away, if it is, its stupidly slow

The developer develops the photoresist - this leaves the unlit photoresist hard, ands the lit bits soft - but it wont remove them. To do that, simply rinse under a running tap. You should be able to just see the tracks now.

[KH602]

but if it doesnt appear to take it all way just leaving the tracks, how is the ferric chloride i have going to etch around the tracks if theres still photoresist around the tracks?

[Mike Burgundy]

If rinsing after developing doesn't take away everything that's supposed to be taken, there's something wrong.
Either the photosensitive layer is old (heat can kill this stuff pretty quick) or contaminated with light (direct sunlight contains UV, taking the protective film off indoors just before youre processing the board is the way to go - even then keep as much light from hitting he board as possible), the developer is contaminated (doubt that), wrong developer, exposure time is off, or the specific color of light is wrong. I'm sure there are other things that can throw a spanner in the works. I don't know that developer, so can't say anything about it, unfortunately, but it looks to be ok.
I think the problem probably lies in the exposure side - either the board caught too much light before exposure, or you're using a material for the artwork that miraculously blocks UV or something. I'd sacrifice a board (or strip of board) to do an exposure test. Tape your artwork medium to the board, and use a thick black card to shield it from UV, move it along exposing more of the board every minute or 30seconds - that should give you increments for exposure time, so you can choose the best one. If you make sure there's also a bit not covered by your artwork medium, you've also confimed wether the medium is transparent to UV or not.

Edit: FWIW I use a facial tanner which is more or less a UV cannon. Don't even use transparencies, just plain paper straight from the printer, toner side down. Everything flat on the floor, sheet of glass over it for stability, tanner on top, fire it up for 1 minute(!!)

[KH602]

yeah i am using a nail curer, however i wasnt sure if the standard uv lights that came with it were working or not,
so i am using 2 standard UV blubs and 2 germacidal blubs. I have been playing around with exposure and i have
got it to devlope some of the pads but its not doing the rest of it and its been in there for like 20-30mins now.

last time i tried it i did it for 10mins but it wasnt enough. i have noticed it goes from a green to a silvery blue
the resist, and under the artwork the pads are yellow, but i cant get the whole mask to come out yellow, which
i assume its been exposed properly ready for development.

[Perrow]

I used a tanner before I got my UV led, exposed the board->transparency->glass sheet for four minutes. The tanner took a while to get to full effect.

[KH602]

The first exposure i got part of the board developed as it left yellow squares for smd pads etc.
that was done for 5 mins.

the second exposure i tried i did if for 10-15 mins and it appears as though the yellow was there, but
had gone after, so maybe exposing for too long?

[Perrow]

The resist can be burned off by too strong developer, I've yet to experience that one but it can happen. Apparently you should be careful using caustic soda as unresolved soda will burn through even unexposed resist in seconds.

Do the exposure test suggested above, it'll help you figuring out your optimal exposure times.