Ultra violet light source for making PCB

[Astrid]

I am thinking about building of Ultra violet exposure unit for making PCB (dry Photoresist or complet screen printing)
I can not decide how to use the UV light source.
- UV LED e.g 10pcs 3W UV LED, distance from PCB less 10cm
- UV fluorescent tube e.g 4 pcs 9W tube, distance from PCB less 10cm
- 120W mercury discharge lamp distance from PCB less 1m

Illuminated area A3, minimum line thickness on PCB 0.25 mm

What source do you think is the best?

 

[betwixt]

Fluorescent tubes will be cheapest and they are easily available. I doubt you will find UV LEDs at the right wavelength to work with PCB resist paint and I'm not sure about the mercury lamps wavelength either. The track thickness isn't directly related to the type of lamp but the glass quality and thickness. All it has to do is support the mask and PCB while letting as much light reach it as possible. Don't forget that the mask is normally used with printed side against the board so there isn't much space for light dispersion between them. My box is 40 years old, uses two fluorescent tubes although it can't do as big as A3 and it easily does 0.2mm tracks.

Brian.

 

[sky_123]

The distance probably doesn't need to be as much as 10cm, less is probably fine. I built mine in a flatbed scanner case years ago, with 2 tubes too.
As a suggestion you could intersperse visible light flurorescent tubes in it too (with a switch). That way, it serves duty as a light table too.

 

[Astrid]

Conventional UV photoresist working with light in the UVA radiation 320 nm - 400 nm
Today is not a problem for this buy LED.
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Mercury vapor discharge lamp have big peak on 375nm see Figure 10 https://www.palagems.com/gem_lighting2.htm

Truth 4x fluorescent cheaper , for example disassemble **broken link removed**

 

[carpenter]

I wonder what the light output power (lm/W) provided by the individual light source sources (UV LED, UL florescent tube, high pressute Hg discharge lamp) in the range interesting for photo resit < 420nm.
I tried to find some relevant data, but not so much as a manufacturer refurbished Narva silent

 

[tpetar]

Some examples of UV LED :

https://yveslebrac.blogspot.com/2010/11/single-led-uv-pcb-exposure-box.html

https://www.instructables.com/id/UV-LED-Exposure-Box/

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