Photosensitive PCB manufacturing

[GIGER]

Hello guys!

I'm trying to manufacture a PCB with the UV lamp method.
I have a simple (possibly) question.

Before exposing the pcb to the lamp, is it really needed to warm up the lamp first?
I'm asking because if I have to then i come up with the following scenario:
Outside of the room I turn on the lamp, wait 5-10minutes. Then, I turn off the lamp
wait 5 minutes (for security reasons) and then go inside the room and place my PCB
in the lamp chamber. Afterwards, I go outside the room and turn on the lamp again.

If I really have to do the above stuff, the lamp is it going to still be warmed up?

 

[betwixt]

A normal UV strip tube starts emitting UV almost immediately and stabilizes it's output very quickly. You do not need to warm it up, doing so will only change the exposure time by a few seconds. You will probably do more damage to the tube by repeatedly cycling the power!

Brian.

 

[GIGER]

A normal UV strip tube starts emitting UV almost immediately and stabilizes it's output very quickly. You do not need to warm it up, doing so will only change the exposure time by a few seconds. You will probably do more damage to the tube by repeatedly cycling the power!

Brian.

Thank you very much sir!

An other question that I have is the correspondence of the NaOH in the water, after the PCB exposure to the light. 1L of water corresponds to -?- NaOH?

 

[betwixt]

The concentration is not critical, if it is weak it just takes a little longer before the resist is dissolved. I normally use pre-mixed developer which uses a combination of NaOH and KOH but it is quite expensive. I suggest you make a saturated solution at room temperature (not warmed up) and see how you get on with that. If you look at the PCB in dim or red lighting you can see when the developing has finished. You first see the outline of the tracks then a few minutes later the exposed areas 'drift' away leaving clean copper visible.

Brian.

 

[GIGER]

The concentration is not critical, if it is weak it just takes a little longer before the resist is dissolved. I normally use pre-mixed developer which uses a combination of NaOH and KOH but it is quite expensive. I suggest you make a saturated solution at room temperature (not warmed up) and see how you get on with that. If you look at the PCB in dim or red lighting you can see when the developing has finished. You first see the outline of the tracks then a few minutes later the exposed areas 'drift' away leaving clean copper visible.

Brian.

Thank you very much again. Your answers were very specific and understandable.

Kind regards !

 

[GIGER]

The concentration is not critical, if it is weak it just takes a little longer before the resist is dissolved. I normally use pre-mixed developer which uses a combination of NaOH and KOH but it is quite expensive. I suggest you make a saturated solution at room temperature (not warmed up) and see how you get on with that. If you look at the PCB in dim or red lighting you can see when the developing has finished. You first see the outline of the tracks then a few minutes later the exposed areas 'drift' away leaving clean copper visible.

Brian.

This morning I put 55g in 500mL water(it was not saturated), and when I sank the PCB into the water, the exposed surface turned into purple colour instantly. I am assuming that I should put ~20g NaOH in my mix, in order not to do it so reactive.

Then , I cleared it with water and when I put my PCB in the FeCl3 it etched the whole board, even my schematic...
Do you know why this happened?

If it helps , I exposed the PCB in the UV chamber for about 20mins ( 125W lamp ). Actually, it is a mercury lamp.

I'd greatly appreciate any help!

 

[D.A.(Tony)Stewart]

You might also try a Xenon tube paper scanner with glass removed and replaced with board.panel.

A few power on Calibrations may expose the material faster with stronger intensity at close proximity. In fab shops the board travels over a T5 UV tube at close proximity for fast developing. THis is normally done in an environmentally controlled room.

Etching with a milder acid but with agitation may improve results to circulate the acid and particles. Increasing acid temp also accelerates erosion.

 

[betwixt]

If it helps , I exposed the PCB in the UV chamber for about 20mins ( 125W lamp )

I think that might be the problem - I use two 28cm 8W tubes spaced about 5cm apart for 4 minutes! I suspect the light was so bright it completely penetrated the artwork and made even the black areas over-expose. Try a MUCH shorted period with a 125W lamp, you probably only need 10 - 20 seconds.

The way to test it is to make a test strip. Use a completely black mask that no light can pass though and a narrow stip of PCB material, about 10cm long. Cover all but 1cm and expose the board to UV for 5 seconds, then move the mask so 2cm are uncovered and repeat for another 5 seconds. When you have uncovered all the board, you should have a 'step' of exposures at 5 second intervals, put it in NaOH and see which part takes about 1 minute for the resist paint to dissolve, that corresponds with the best time exposure to use.

Also be careful not to expose the phot-resist paint to too much room light, always work in dim lighting and if possible a red light to minimize further exposure. Remember that the resist paint is still light sensitive even after it has been in the NaOH.

Brian.

 

[GIGER]

I think that might be the problem - I use two 28cm 8W tubes spaced about 5cm apart for 4 minutes! I suspect the light was so bright it completely penetrated the artwork and made even the black areas over-expose. Try a MUCH shorted period with a 125W lamp, you probably only need 10 - 20 seconds.

The way to test it is to make a test strip. Use a completely black mask that no light can pass though and a narrow stip of PCB material, about 10cm long. Cover all but 1cm and expose the board to UV for 5 seconds, then move the mask so 2cm are uncovered and repeat for another 5 seconds. When you have uncovered all the board, you should have a 'step' of exposures at 5 second intervals, put it in NaOH and see which part takes about 1 minute for the resist paint to dissolve, that corresponds with the best time exposure to use.

Also be careful not to expose the phot-resist paint to too much room light, always work in dim lighting and if possible a red light to minimize further exposure. Remember that the resist paint is still light sensitive even after it has been in the NaOH.

Brian.

Today I made some experiments.
My lamp was still the same (125W mercury) at a distance of 40cm from the PCB.
As you said, 20 minutes was WAY too much time and I decreased it at 5 minutes.
I made a few experiments and I tested the quantity of the NaOH in the water.
Also, (i will back with more info and be more specific) I concluded that 2% NaOH needs 3-3.5 minutes to remove the photosensitive surface.
The step that you have proposed is a very good idea and i'll definitely try it.

I'll come back for more info. Thanks for all your kind answers.