PCB Exposing

[Adwaittronics]

In PCB exposing method by using ultraviolet tube which is suitable, UV-A  tube or UV-C tube?
If  I have not mistaken Philips has a Actinic BL series of UV-A tubes and another company called Sylvania has BL 350 series of UV-A tube am I  correct?

[jahonen]

UV-A should be sufficient to expose PCB, and better for your health UV-C would be the one to erase EPROMs.

Regards,
Janne

[Zepnat]

Bug zapper tubes worked best for me, the ones with white phosphor and give a pale blue light.
Black phosphor UV tubes didn't work at all.
Don't know about the clear ones they might work but not good for your health if left visible.

 Edit: a quick google suggest BL is the tube to look for around 340-350nm UVA.

[SeanB]

Both will work, but the UV-C tubes will give a finer resolution if the mask and the resist will allow it. Can also be used to erase Eprom as well, and cure some clear epoxies.

[homebrew]

Curiously the best results I had with a cheap 300W halogen floodlight (obviously with the UV-Filter Glass removed). Distance 30cm, exposure time 8min. Worked much better for me as a professional UV-exposure unit.

I assume that my inkjet transparency "films" were simply not opaque enough in the UVC range - hence the disappointing results.

[Kremmen]

My simple exposure box does a perfect job every time with 2 simple "blacklight" fluorescent bulbs. Artwork is regular transparency from the laser printer with minor hand retouching to fix blemishes and hairlines. 10 minutes under the lamp works every time for Bungard pre-coated blanks.

[vortexnl]

I bought this facial tanner on a second hand website for like 15 euro's, put a sheet of glass on top, and I can expose my PCB's in 1,5 minute! Here are some pictures of the results:

www.imgur.com/hKik5iR,8Jw2pqy

[Refrigerator]

People buy those halogen bulbs and crush the outer glass wall and that seems to work surprisingly well.

[homebrew]

I bought this facial tanner on a second hand website for like 15 euro's, put a sheet of glass on top, and I can expose my PCB's in 1,5 minute! Here are some pictures of the results:

www.imgur.com/hKik5iR,8Jw2pqy

Someone really wet to town with the curvy lines ...

[skyline_stu]

I use a 400w UV tube.  PPE is a must. About 30 seconds is enough time!
An old highbay HPS luminare works fine.

[poorchava]

I use a nail varnish curing lamp,  bought on an auction site for 5 euro. From what I can tell,  it contains 4 9W tubes,  not sure about the wavelength.  Exposure time for negative dry film photoresist is between 10 and 20s.

[akis]

I have a flatbed UV exposure box bought on ebay from China, it contains 6 UV tubes, 8 W each, total 48 watts. The tubes are pearly white, and have no markings on them. I tried to replace them by buying Philips, like these:
http://123aquatics.co.uk/products/pond-ultraviolet-clarifiers/phillips-uv-tube-607.aspx

or here

http://www.ebay.co.uk/itm/Philips-TUV-8W-G8-T5-Bulb-Lamp-Tube-Short-Wave-Germicidal-UltraViolet-UV-Filter-/221221519545?pt=UK_Pet_Supplies_Fish&hash=item3381d480b9

but the Philips are no good they have dark gaps at one end not sure why, all 8 tubes I bought do this. Obviously not critical if you are killing bugs, but no good if you are trying to develop a PCB.

By the way, I know UV light is bad for you at great intensities and time (skin cancer) or for your eyes if you look at it for too long - but in the process of exposing a PCB you will have very little if any eye exposure, probably much less than going out on a sunny day without sunglasses. Am I right?

[Tac Eht Xilef]

I have a flatbed UV exposure box bought on ebay from China, it contains 6 UV tubes, 8 W each, total 48 watts. The tubes are pearly white, and have no markings on them. I tried to replace them by buying Philips, like these:
http://123aquatics.co.uk/products/pond-ultraviolet-clarifiers/phillips-uv-tube-607.aspx

or here

http://www.ebay.co.uk/itm/Philips-TUV-8W-G8-T5-Bulb-Lamp-Tube-Short-Wave-Germicidal-UltraViolet-UV-Filter-/221221519545?pt=UK_Pet_Supplies_Fish&hash=item3381d480b9

but the Philips are no good they have dark gaps at one end not sure why, all 8 tubes I bought do this. Obviously not critical if you are killing bugs, but no good if you are trying to develop a PCB.

By the way, I know UV light is bad for you at great intensities and time (skin cancer) or for your eyes if you look at it for too long - but in the process of exposing a PCB you will have very little if any eye exposure, probably much less than going out on a sunny day without sunglasses. Am I right?

You should probably read back over this thread, take notice of what others have said, and then investigate very carefully the differences between UV-A, UV-B, and UV-C, which wavelengths are produced by those germicidal & sterilising lamps, and what wavelength is required for developing your particular PCB photoresist.

Hint: EEPROM eraser / germicidal / sterilising UV lamps are a poor UV source for typical home-exposure photo PCB materials, but are a really good source of 3rd-degree sunburn, corneal burns, retinal damage, skin cancers, & cataracts.

[akis]

Thanks for the warning. Do you disagree with SeanB's post ? He says that UV-C provides better resolution. I suppose it also depends on the actual photo resist - it must have a recommended wave length.

[SeanB]

The black at the ends is the cathode guard, common on Philips tubes. The cheap ones probably do not have any, along with having electrodes close to the end as well, so they will both run unevenly and have a short life with the risk of cracking the end seals.

[IconicPCB]

Check the requirements Your chemistry places on UV source wave length and then decide what is better for Your process.

I use a UV source which is about 50 nanometre off the optimum wavelength.
I get reasonable results .

[Tac Eht Xilef]

Thanks for the warning. Do you disagree with SeanB's post ? He says that UV-C provides better resolution. I suppose it also depends on the actual photo resist - it must have a recommended wave length.

Exactly. Most photoresist boards / sheets / liquids for home use have a peak response to ~360-390nm UV, while UV-C is considered to be 100nm-280nm or so, and most UV germicidal lamps output at ~250-260nm and bugger-all (if any) at the necessary wavelengths.

As for resolution: although it's more complicated than this due to optics, size of the photosensitive molecules, etc., you can probably see that a difference of 100-140nm in wavelength is likely to have little effect on the resolution of tracks measured in multiples of 0.01mm (i.e. 10,000nm).

[poorchava]

In a pinch something like a 500W halogene floodlight with front glass removed works too. Just beware of the amount of heat it generates. You can unwillingly perform a thermo-transfer from 40cm away. It works at least with Bungard presensitized boards and Positiv20 spray. Haven't tried it with dry film.