DIY UV exposure.

[cjb]

Hi,

I have a setup similar to the one you are proposing and have got good results.

My exposure box consists of two parallel short (~15cm) U.V. tubes in wooden box. The box is lined with reflective (silvered) paper and is topped with a thin (3mm) sheet of glass.

One point to note is that soda-lime glass tends to absorb certain parts of the spectrum. However, this has not prooved a problem for the thin glass I used.

The cover is a sheet of wood with a 1cm layer of dense foam attached.

With this, I get very repeatable exposure times of 3 minutes or so, at a good resolution.

Hope this helps,

Chris.

 

[lexter]

Thanx, All!

Now I feel quite confident about this project and ready to start!!! As soon as I will get my microcontrollers delivered, I will start with the timer!

Thanx again!

 

[Hero999]

Monkey.. UV tubes are mercury vapor bulbs, same thing. The only difference between UV tubes and common fluorescent light tubes is the phosphor coating on the inside of the tube which converts the UV into human visible light. UV tubes should therefore actually be cheaper than common fluorescent tubes because they don't have to pay for the phosphor coating. They're even easier to find nowadays because UV tubes are very popular in water purification products because the light spectra inactivates active biological compounds. (virii bacteria)

That's not true at all.

Only germicidal lamps (which is what you're talking about and aren't fluroscent lamps) don't have a phosphor and they're much more expensive because they're made of quatz rather than glass which is much more difficult to form in to the required shape. They emit 237nm radiation which is in the UVC spectrum and is very dangerous, it causes severe burns to both the skin and eyes.

Fluroscent UV lamps are made of glass and have a phosphor coating that converts the UVC radiation to UVA or UVB radiation. The UVA types are commonly known as blacklights and are fairly safe to veiw with the naked eye providing you're not too close.

For a PCB UV exposure, you want black light tubes, insect killer tubes or those used for reading the flurecent markings on bank notes are perfect. Germicidal tubes are no good as the UVC radiation doesn't pass through glass and most plastic films very well. You can buy incandescent UV bulbs which aren't very good as they only last for half as long as visible bulb for the same wattage as the fillament temperature is much higher and they emit most of their spectrum in the visible violet region which isn't very effictive. If you don't want to bother with ballasts and starters then you can buy blacklight compact fluroscent tubes which plug in to a standard light bulb fitting and are perfect for developing PCBs.

Two 8W black light tubes about 70mm away will develop a PCB the size of an A4 piece of paper in under 10 miniutes.

 

[monkeybiter]

thanks for the elaboration.

 

[crusty]

dude, all you gotta do is tape it to a freakin fluorescent bulb for like a week, bam, it's gone, or leave it out in the sun for a day or two. Geez yall get all technical over something so easily done for FREE!!!

 

[Oznog]

Yeah I was gonna point out that UV comes in many different freq.
UV is broken into Vacuum UV (40-190 nm), Far UV (190-220 nm), UVC (220- 290 nm), UVB (290-320), and UVA (320-400 nm). In general, shorter wavelength UVs are capable of more dramatic effects because they've got more energy.
UV LEDs are barely UV, around 395 nm (varies by model). Blacklight fluorescents (bug zapper lights too) 365 nm.

UVB is the big skin burner, but that's far off. Germicidal can potentially cause eye damage, but that's <280 nm.

I liked the blacklight-white tubes that don't have the purple filter glass, generate the same UVs, but let out visible light too so the room and project don't look all funky without additional lighting.

 

[justDIY]

are UV reactive photo resist boards much less expensive than visible light resist boards?

The boards I (used) to use exposed just fine in 8-10 min under a pair of 15w fluorescent tubes (just regular daylight tubes, nothing fancy). The instructions claim a regular incandescent lamp or fluorescent tube lamp is all that is required.

 

[jpanhalt]

are UV reactive photo resist boards much less expensive than visible light resist boards?

I think the popularity of UV resist boards is that they can be handled in a normally lighted room and do not need a dark room. The positive resist also helps a tiny bit in checking the image. Last, the developer for many current UV boards is just diluted lye (NaOH) or a weaker base, such as sodium carbonate. John