Home made PCB etching using UV light tubes by using negative dry film photoresis

[EEVaditya]

Hi
I am etching PCB(size:6x4 inches) at home by UV light tubes using negative dry film photorsist.
specifications are as follows:
1) I am using  4 Philips Actinic BL 8W tubes.
     Tube wattage 8W
     Tube length from base to base is 288.3mm
2) I am using negative dry film photoresist(Blue colour film)
3) I am keeping the blue film laminated pcb with OHP sheet printed ckt layout on it in between two glass plates.
4) Then I am keeping the whole thing under UV light tubes for Exposing.
5) I kept height of about  5 to 6 inches between tubes and PCB.
6) Exposing it for about 20 minutes.
7)Then developing it with developer(sodium carbonate) with measurement as 10g developer in 1litre water, by keeping gap of 10 minutes between exposing and development.
Then etching it with HCL and Hydrogen peroxide with measurement of 1/2 unit HCL for 1 unit Hydrogen peroxide.
9) Then Stripping it with stripper/remover(caustic soda) with same measurement as taken in development.
I did above process by seeing various online videos.
But I am not getting perfect result, means after exposing I am getting blue coloured circuit on my PCB which is correct according to videos but  also a thin blue layer on remaining part of PCB which should be copper as per videos.
Can any one guide me as to
1) Exactly how much time do I need to expose the pcb under UV lights?
2) Is the developer and etchant and remover quantity correct?
3) How much time developing be done?

[sleemanj]

Can any one guide me as to
1) Exactly how much time do I need to expose the pcb under UV lights?
2) Is the developer and etchant and remover quantity correct?
3) How much time developing be done?

1) This depends on your UV lights and setup.  You will need to experiment. You want after exposure that you can see the image in the resist, not too strongly, but not too weakly either.  Usually in the area of 2 to 3 minutes is common for people who expose with UV leds (for me, 2m30s, using 8 1 Watt UV leds). You should do a test stepped exposure to determine your best time (ie,split your artwork in sections, expose for 1m the first section, expose for 1m10 the second .... and then develop, the best developed one is the time you should use).

2) I use about 30g/L for developer (Sodium Carbonate or Percarbonate or Peroxyhydrate or even Bicarbonate in a pinch), but the actual ratio is not important as you will be observing the process anyway, making it "to strong" in my experience doesn't really make it faster.  For the stripper, I use the same developer solution (I don't use hydroxide at all), I just leave it to soak for half an hour. Acetone will also work (soak for 20 or 30 seconds and it will come off).

3) Depends on your developer solution and how hard you exposed.  Usually takes about 3 minutes for me.  Rub gently with fingers after about 2 minutes soaking.

See my dry film tips: http://sparks.gogo.co.nz/dry-film-tips.pdf

[poorchava]

I do use dry film from time to time when I have to make several identical boards. I have to admit that while resolution is really good,  it's very hard not to get a speck of dust between the pcb and the dry film.  Laminating the film without having wrinkles or air bubbles trapped underneath is also difficult. What is giving the best results right now is applying the film under water,  which kind of eliminates problems with air bubbles and most of dust,  but getting perfect layer is still not easy.

[kerrsmith]

I follow the steps in the following video by Mads Nielsen:



I make the slight changes as shown in an earlier post I made:

https://www.eevblog.com/forum/chat/diy-pcb-advice/msg635313/#msg635313

The exact times and quantities of chemicals I use are:

Photo Resist on Copper:
Laminate - 5 times

Photo Resist Exposure:
UV exposure - 9 minutes
(this is using and old black light (F15T8/BLB) tube)

Photo Resist Developing:
Sodium carbonate - 5g / 500ml

Copper Etching:
Hydrochloric acid - 25ml
Hydrogen peroxide - 25ml
(you can also add 25ml water as well but I find it etches faster without it and is still just as neat)

Photo Resist Removal:
Sodium hydroxide - 5g / 100ml

This method is giving me really good results and is pretty quick too - I can have a board ready in under an hour.  The only part I time is the UV exposure, the rest I do by carefully looking to make sure all the resist has developed away (the milky colour has gone on all non tracks and pads) and when etching that all the small holes have etched out on pads.

[nctnico]

IMHO you can save yourself a lot of trouble by buying pre-coated boards and pre-made developer. In my experience the temperature of the developer is a critical parameter so the best is to keep it at room temperature.

[kerrsmith]

IMHO you can save yourself a lot of trouble by buying pre-coated boards and pre-made developer. In my experience the temperature of the developer is a critical parameter so the best is to keep it at room temperature.

Yes, I have found it does develop quicker if it is slightly warm - I usually use half cold tap water and half hot water just to raise the temperature slightly.  By the time the chemicals have dissolved and you add the copper board the solution is warmish and seems to work well.

I have not tried the pre-coated boards as I have not had any difficulty in laminating the photo resist on to my copper clad boards but I may give them a go when I run out of resist and see if they are any different.

I use the separate chemicals as they are pretty cheap and last for ages as you are only using 5g at a time or 25ml of the liquid ones.