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

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Adwaittronics

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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.
8) 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?
 

Gorgon

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Normally you need to calibrate the exposure time/develop time by exposing a strip of pcb in steps. You start to expose a part so many minutes, and then move the film a bit and expose all, doing this with timed incrememnts you then develop the strip until one of the sections are perfect. Then you know how long to expose and how long to develop. Or you can set the development time fixed, and find out the exposure time from the best part of the strip.

To get a perfect result every time you also need to keep the development solution mix exactly the same every time.

There could also be some tradeoff between lamp intensity, film thickness and opacity, to get the finest details of your PCB perfect. The film side should be on the side closest to the photoresist.
 

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