photo resist board

[1878]

Hello Everyone...

I've decided to go the photo resist/transparency/UV light route for making PCB's, but I'm having problems 

Basically, I don't think the first stage is going well. I photocopied the PCB design onto a plastic sheet, peeled the protective paper off the board, positioned the transparency on the copper side and placed it under the UV bulb (4 inches away) for about 20-25 minutes. There was a very faint image of the PCB when I checked. I went to the next stage according to the instructions I got with the copper board, which was,

'Mix together 0.5 litres approximately with one teaspoonful of sodium hydroxide (available from most chemists) and pour into a tray. Gently rock the exposed PCB in the tray until the unwanted photo resist is dissolved away'

but there was nothing left ?!?! Anyone got any ideas where I might be going wrong here ??

Cheers.

[norbizzle2012]

what type of transperency are you using?  Maybe you exposed to the light for too long

[davent]

I'm guessing like the previous poster that the exposure was too long. I expose for 12min. an inch away from a regular fluorescent tube. You need to establish an exposure time by doing a test print. I always make a sandwich out of two transparencies of the circuit to ensure that i've got good light stopping artwork.

Cut yourself a long narrow strip of board say the same length as your transparency artwork.

Make the sandwich of your art and the pcb board and place under the light but leave the light off for now.

Take a piece of cardboard or some other thin opaque material and place it overtop of the pcb board  leaving only say, a ¼ of the board exposed and turn on your light.

Wait 5 minutes then move the cardboard so ½ the board is exposed.

Wait 5 minutes move the cardboard so ¾ of the board is exposed.

Wait 5 minutes and remove the cardboard and expose for another 5 minutes.

Now develop the board in your sodium hydroxide bath. You now have a board with four different exposure strips; 5, 10, 15 or 20 minutes. From this you should be able to make a pretty good guess as to the minimum exposure time needed to get full copper exposure with maximum etchant resist left on the board. Too short an exposure, the resist won't all dissolve in the sodium hydroxide where it's been exposed to light, too long of an exposure and all the resist will dissolve.  With your time now established you should have no problems getting  great etchant ready boards that are as good as your artwork!

You could wait less time between moves, maybe two minutes and create more strips with different times if you want to refine the timing OR do a second test print based around your guesstimation to zero in on the best time. With my light set up and different brands of boards i've found an exposure of 9-12 minutes will get me what i need.

Take care,
dave

[1878]

Thanks for the replies...

I'm gonna try again tomorrow with a shorter exposure time. I didn't realise you could OVER do it

[solderman]

Hello Everyone...

I've decided to go the photo resist/transparency/UV light route for making PCB's, but I'm having problems 

Basically, I don't think the first stage is going well. I photocopied the PCB design onto a plastic sheet, peeled the protective paper off the board, positioned the transparency on the copper side and placed it under the UV bulb (4 inches away) for about 20-25 minutes. There was a very faint image of the PCB when I checked. I went to the next stage according to the instructions I got with the copper board, which was,

'Mix together 0.5 litres approximately with one teaspoonful of sodium hydroxide (available from most chemists) and pour into a tray. Gently rock the exposed PCB in the tray until the unwanted photo resist is dissolved away'

but there was nothing left ?!?! Anyone got any ideas where I might be going wrong here ??

Cheers.

Hi
I think 20 min is too long. I expose mi ne for  9-12 min depending on brand of cupper. A really important thing is to put a glass or plexi on top of your art work to flat it out and prevent light to get under your artwork. I use a laser printer and a transparent OH paper. It works fine for me.

[Ice-9]

Hi 1878,

I expose my photoboard for 2min and 20 seconds , you shouldn't see the the pcb pattern on the board at this stage, only after you develop the board will you see the tracks on the pcb .
What type of UV bulb are you using?

For example with the light i use (1x8watt UV tube) 2.30min is good 3mins is overexposed. Ohh and i also use a laser printer at work to print onto tracing paper (not transparencies) You also want the printed side of your transparency in contact with the pcb as beleive it or not the thickness of the transparency if the other way up can let light bleed through and ruin the job

follow the advice for getting your ideal exposure from Davent,  expose 1/2"  of board every so many minutes and develop to get your perfect expose time.

[captntasty]

I use 3M Ink Jet Transparencies ( product # CG3480) but find when I print in B&W I have to layer two images - 2 copies of the board and tape them together so they do not allow light through the traces.  I use a 15 watt bulb for about 4 or 5 minutes - that might actually be over kill... I also use sodium hydroxide - the actual product is Roebic Heavy Duty Crystal Drain Opener, about a 1/4 and 1/8 teaspoon into a cup of water. Sometimes water temperature can also increase or decrease developing times - I go with sort of luke to slightly warm for about a minute...  it dife3rent each time.  If your mix is to strong it will develop instantly - back to the drawing board! It is tricky to find the right strength when doing it this way - it's a lot of trial and error - keep trying to vary the strength until you find the right measurements.

[robmdall]

I didn't see any mention of developing the board before etching?? I may have missed it 

[1878]

Sodium Hydroxide is the manufacturers preferred developer for the board I bought.

[Ice-9]

The developer crystals that i use is called "Sodium Metasillicate"  should work on all photo board i think.

[1878]

Haven't had a chance to try any of your suggestions yet. I'm going away for the weekend but I'm hoping to have a good go on Monday after work.

Thanks again for the replies.

[1878]

Just a small update...

I've got the developing part down now, but I think the etching solution is a bit weak. I'll pick up more crystals tomorrow and try again. I had my board 2 inches under the light for 3 minutes and it worked a treat.

Thanks for your help.

[robmdall]

Ice-9, I am interested in the tracing paper process you are using. I have issues when using OT films. I have read that tracing paper is a great alternative. Is there a specific type / brand you have had better luck with?

Also, does anyone Tin coat their PCB's? It does not appear to be advantageous to tin a board? When tinning is done, is it for ease of soldering or added life span? Is there a method of coating a completed board after soldering?

Thanks in advance for any direction.

Bob